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  • Chemistry  (410,929)
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  • 201
    Electronic Resource
    Electronic Resource
    Changing the Reactivity of Enediynes by Metal-Ion Coordination (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 381-385 
    Details
    ISSN: 1434-193X
    Keywords: Enynes ; Macrocycles ; Coordination chemistry ; Crown compounds ; Radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The complex molecular structure and interesting activation mechanisms of naturally occurring enediynes have inspired the synthesis of a variety of simpler model systems to mimic their properties. While in most model compounds nucleophilic attack, isomerization or bioreduction are used to activate the unsaturated system for diradical cyclization, some attempts have been made to employ metal-ion coordination for this purpose. Significant enhancement of the thermal reactivity has been achieved by metal-ion induced conformational and electronic changes of suitably substituted enediynes, such as 1, 5, 6, 17 and 18. Enediyne activation by stoichiometric or catalytic formation of vinylidene complexes, such as 22, from terminal alkynes has also been investigated. This paper summarizes recent results pursuing the activation of enediyne diradical cyclization by metal ions.
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  • 202
    Electronic Resource
    Electronic Resource
    Synthesis of Enantiomerically Pure (-)-Wine Lactone Based on a Palladium-Catalyzed Enantioselective Allylic Substitution (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 419-423 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The first enantioselective synthesis of enantiomerically pure (-)-wine lactone, (-)-1a, a fragrance constituent of various white wines, and its epimer (+)-1b, was carried out. The key steps are allylic substitution of (±)-2-cyclohexen-1-yl acetate (2) with dimethylmalonate using palladium complexes of phosphanyldihydrooxazol L1 or of the phosphanylcarboxylic acid L2 as catalyst, subsequent decarboxylation, iodolactonization and elimination, furnishing enantiomerically pure bicyclic lactone (+)-7 in 47% overall yield. The diastereoselective introduction of methyl groups by SN2′-type substitution with an organocopper compound and by enolate alkylation gave lactone (-)-1a in 43% overall yield from (+)-7.
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  • 203
    Electronic Resource
    Electronic Resource
    Studies Towards the Synthesis of Aplykurodins - Synthesis of 17,18-Dihydro-3,9-di-epi-aplykurodinone B (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 439-448 
    Details
    ISSN: 1434-193X
    Keywords: Aplykurodins ; Marine steroids ; C-C coupling ; Cyclic peroxides ; Lactonization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An approach to the synthesis of aplykurodins, ichthyotoxic marine lactones, is presented. The carbon framework was derived from vitamin D3 by conversion of the readily accessible allyl alcohol 13 to the protected Grundmann's hydroxy ketone 22 and subsequent introduction of the C2 side chain through a Pd0-promoted coupling. Highly stereoselective hetero Diels-Alder reaction with O21 produced the key intermediate peroxide 25. Functional group transformations, coupled with a series of chemo- and stereoselective reactions, finally resulted in the synthesis of the unnatural analogue 17,18-dihydro-3,9-di-epi-aplykurodinone B (6).
    Additional Material: 2 Ill.
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  • 204
    Electronic Resource
    Electronic Resource
    Enantioselective Synthesis of the Unsymmetrical Bis(lactone) (-)-(3E,6R,9E,12S,14R)-Colletol Induced by Chiral Sulfoxides and an Approach to (+)-Colletodiol by Asymmetric Hydroxylation of an α,β-Hydroxy Lactone (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 357-364 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Sulfoxides ; Asymmetric hydroxylations ; Lactones ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A general synthetic strategy towards the two bis(lactones) (-)-colletol (1) and (+)-colletodiol (2) is described. A common intermediate in this synthesis is the 6-membered hydroxy lactone (+)-(3R,5R)-3-hydroxy-5-hexanolide (6), readily prepared by stereoselective reduction of (+)-(SR)-methyl 3,5-dioxo-6-(p-toluenesulfinyl)hexanoate (7). Stereoselective hydroxylation of this hydroxy lactone has allowed efficient access to (+)-colletodiol (2).
    Type of Medium: Electronic Resource
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  • 205
    Electronic Resource
    Electronic Resource
    Studies on the Mercury-Desilylation of Chiral Cyclopropylmethylsilanes - A Stereocontrolled Access to Carba-Sugars (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 401-418 
    Details
    ISSN: 1434-193X
    Keywords: Cyclopropanation ; Allylsilanes ; Mercury-desilylation ; Carbohydrates ; Dihydroxylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Mercury-desilylation of cyclopropylmethylsilanes affords a stereospecific access to homoallylic mercury intermediates, which can be elaborated further. This strategy is illustrated with a short access to carba-furanoses and carba-C-disaccharides.
    Additional Material: 5 Ill.
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  • 206
    Electronic Resource
    Electronic Resource
    Structure-Property Relationships in Mixed Oligoheterocycles Based on End-Capped Oligothiophenes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 425-437 
    Details
    ISSN: 1434-193X
    Keywords: Cyclic voltammetry ; Fluorescence spectroscopy ; Mixed oligomers ; Structure-property relationships ; Organic light-emitting diodes ; Oligothiophenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Novel mixed oligoheterocycles 1-5, containing thiophene/thiazole, thiophene/1,3,4-thiadiazole, thiophene/oxazole, or thiophene/1,3,4-oxadiazole moieties, were synthesized. The introduction of electronegative heteroatoms such as oxygen and nitrogen into the conjugated π-system leads to a more pronounced acceptor character than that found in the analogous oligothiophenes. Characterization of the redox properties reveals that the reduction of the mixed oligomers is facilitated while oxidation is shifted to higher potentials. For this series, clear structure-property relationships could be found by comparing optical properties, in particular absorptions, emissions and fluorescence quantum yields in solution. The X-ray structural determination of mixed thiophene/1,3,4-oxadiazole heptamer 5 indicates that the replacement of thiophene units by 1,3,4-oxadiazoles has a strong influence on the molecular arrangement and intermolecular interactions in the solid state.
    Additional Material: 5 Ill.
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  • 207
    Electronic Resource
    Electronic Resource
    Catalytic Asymmetric Aziridination of Enol Derivatives in the Presence of Chiral Copper Complexes to give Optically Active α-Amino Ketones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 557-561 
    Details
    ISSN: 1434-193X
    Keywords: Amino ketones ; Homogeneous catalysis ; Aziridination ; Copper ; Enols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of acyclic and cyclic enol derivatives 1 has been transformed into the corresponding α-amino-functionalized ketones 2 by means of enantioselective catalytic aziridination with chiral Cu complexes, prepared in situ from [Cu(MeCN)4]PF6 and the optically active ligands 3, by using (N-tosylimino)iodobenzene (PhINTs) as a nitrogen source. The best enantioselectivities (ee values of up to 52%) have been achieved for the electronically deactivated enol acetate 1aδ, but the incorporation of steric bulk and the substitution pattern at the enol double bond do not improve the ee values. The cyclic substrates react considerably less readily (only up to 45% conversion) compared to their acyclic counterparts (complete consumption). A transition structure is suggested for the asymmetric Cu-catalyzed aziridination of the enol acetate 1aδ in the presence of the chiral ligand 3b that could account for the sense of the (R)-configured product 2a.
    Additional Material: 1 Ill.
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  • 208
    Electronic Resource
    Electronic Resource
    D2-Symmetric Chiroporphyrins Derived from (1R)-cis-Hemicaronaldehydic Acid: Preparation and Spectral Characterization (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 583-589 
    Details
    ISSN: 1434-193X
    Keywords: Porphyrins ; Chiral auxiliaries ; Macrocycles ; Pyrethroids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Esters, N,N-disubstituted amides, and a N-acylurea derived from the enantiopure industrial intermediate (1R)-cis-hemicaronaldehydic acid (or biocartol) are convenient synthons for the preparation of a series of chiroporphyrins by condensation with pyrrole. These chiral meso-tetracyclopropylporphyrins are obtained exclusively as the D2-symmetric α,β,α,β atropisomer, generally in low to moderate yields (2-20%), and in the urea case in excellent yield (60%). Hydrolysis of the urea substituents affords a chiroporphyrin with mono-N-substituted amide groups. 1H-NMR spectroscopy indicates that the ester, amide, and urea stereogenic groups sit on the porphyrin close to the metal binding site and restrict substrate or ligand access along a C2-symmetric groove. This structural feature of chiroporphyrins and of their metal complexes is of high potential interest in asymmetric catalysis and chiral recognition.
    Additional Material: 3 Ill.
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  • 209
    Electronic Resource
    Electronic Resource
    Anthracene-Containing [2]Rotaxanes: Synthesis, Spectroscopic, and Electrochemical Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 591-602 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Molecular recognition ; Molecular shuttles ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two dumbbell-shaped compounds (8 and 11), each composed of two polyether chains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetraarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-dioxyanthracene unit, have been synthesized. Two [2]rotaxanes (9 · 4 PF6 and 12 · 4 PF6) have been prepared by interlocking these dumbbell-shaped compounds (8 and 11) with a bipyridinium-based tetracationic cyclophane (15 · 4 PF6) - namely, cyclobis(paraquat-p-phenylene). A [3]rotaxane (10 · 8 PF6) incorporating two cyclophane components (15 · 4 PF6) was also obtained when the 9,10-dioxyanthracene-containing dumbbell-shaped compound (8) incorporating two 1,4-dioxybenzene recognition sites was employed. The 1H-NMR spectroscopic investigation of the [2]rotaxanes (9 · 4 PF6 and 12 · 4PF6) revealed that the cyclophane component encircles one of the two 1,4-dioxybenzene recognition sites in the 9,10-dioxyanthracene-containing [2]rotaxane (9 · 4 PF6) and the 2,6-dioxyanthracene unit in the other [2]rotaxane (12 · 4 PF6). These structures have been confirmed by UV/Vis and electrochemical experiments. Comparison with the spectroscopic properties of simple model compounds shows the presence of electronic interactions which lead to (i) the occurrence of very efficient energy transfer processes in the dumbbell-shaped components and (ii) perturbations in the absorption spectra with appearance of two charge-transfer absorption bands and complete luminescence quenching in the [2]rotaxanes. For the 2,6-dioxyanthracene-containing [2]rotaxane (12 · 4 PF6), it has been demonstrated that the cyclophane can be displaced from the dioxyanthracene to the 1,4-dioxybenzene station upon electrochemical oxidation.
    Additional Material: 9 Ill.
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  • 210
    Electronic Resource
    Electronic Resource
    A Radical-Based Strategy for the Synthesis of Higher Homologues of Sinefungin (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 627-631 
    Details
    ISSN: 1434-193X
    Keywords: Complex nucleoside ; Antibiotics ; Radicals ; Zn-Cu couple ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Homosinefungin 5, which can be considered as an analogue of S-adenosylmethionine (SAM) and of S-adenosylhomocysteine (SAH), has been synthesized by means of a sequence in which the key step was the addition of a radical, produced by the simple treatment of an iodide precursor with a zinc-copper couple, to suitably activated olefins.
    Additional Material: 1 Ill.
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  • 211
    Electronic Resource
    Electronic Resource
    Replacement of the Cleavable Phosphodiester Bond of a Hammerhead Ribozyme Substrate by an Amide Linkage (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 633-638 
    Details
    ISSN: 1434-193X
    Keywords: Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
    Additional Material: 3 Ill.
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  • 212
    Electronic Resource
    Electronic Resource
    Solid-Phase Synthesis of Dihydropyrans by Eu(fod)3-Catalysed [4+2] Heterocycloaddition of Vinyl Ethers with Benzylidenepyruvic Acid Esters. Comparison with Conventional Homogeneous Liquid Phase Conditions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 639-643 
    Details
    ISSN: 1434-193X
    Keywords: Solid-phase synthesis ; Wang resin ; Hetero Diels-Alder reactions ; Dihydropyrans ; Reductive reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The OH groups of Wang resin were esterified with benzylidenepyruvic acid (1) to give the immobilized 1-oxabutadiene 2. The latter reacted with vinyl ethers 3a-h (dienophiles) in the presence of Eu(fod)3, and the resulting adducts 4a-h underwent reductive cleavage with LiAlH4 to afford the dihydropyrans 5a-h in high (62 to 100%) overall yields. A similar sequence carried out under conventional homogeneous liquid phase conditions led to significantly lower yields. The endo/exo selectivity of the cycloaddition reaction was the same in both cases.
    Additional Material: 2 Tab.
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  • 213
    Electronic Resource
    Electronic Resource
    Synthesis of Pyridinium Amphiphiles Used for Transfection and Some Characteristics of Amphiphile/DNA Complex Formation (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 665-673 
    Details
    ISSN: 1434-193X
    Keywords: Cationic amphiphiles ; Transfection ; Pyridinium salts ; Vesicles ; Lipoplex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/DNA complexes have been determined.
    Additional Material: 2 Ill.
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  • 214
    Electronic Resource
    Electronic Resource
    Evaluation of the Regioselectivity in Pauson-Khand Reactions of Substituted Norbornenes and Diazabicyclo[2.2.1]heptanes with Terminal Alkynes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 681-689 
    Details
    ISSN: 1434-193X
    Keywords: Pauson-Khand reaction ; Cyclopentenones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---1-Methyl-norbornene ester 9 and 1-methyl-2,3-diazabicyclo[2.2.1]heptene ester 10 were employed in intermolecular Pauson-Khand reactions with various terminal alkynes 11a-f to give the dimethyl 1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 12 and 13, and diethyl 2,3-diaza-1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 14 and 15, respectively. Whereas the co-cyclization of norbornene 9 with alkynes 11 bearing small substituents R resulted in the preferred formation of 12 (12:13 ≤ 85:15), regioisomer 13 was obtained as the major product when sterically bulky alkynes were employed (12:13 ≥ 6:94). For 2-methyl-3-butyn-2-ol 11e a strong temperature dependency of the regioselectivity was found. The ratio of regioisomers (12e:13e) changed from 95:5 at -25 °C to 12:88 at 120 °C in toluene. In contrast, reactions with 2,3-diazanorbornene 10 showed only moderate regioselectivities in favour of 14 (14:15 ≤ 69:31), regardless of the temperature and the size of R. The observed regioselectivities support a mechanism for the Pauson-Khand reaction in which the apical rather than the basal anti oriented carbon monoxide ligand of cobalt alkyne complex 1 is replaced by the alkene.
    Additional Material: 1 Ill.
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  • 215
    Electronic Resource
    Electronic Resource
    From Amino Acids to Fused Chiral Pyrrolidines and Piperidines via the INOC Route (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 645-655 
    Details
    ISSN: 1434-193X
    Keywords: INOC ; Pyrrolidines ; Piperidines ; Stereoselective synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular nitrile oxide olefin cycloaddition (INOC) reactions of oximes 1-3 and of 24-27 derived from L-amino acids have been found to proceed stereoselectively, yielding tricyclic fused pyrrolidines and piperidines. Further manipulation led to chiral hydroxymethyl-substituted fused piperidines 33-35 and to 3-amino-4-(1-hydroxypropyl)-2-mercaptomethyl-N-methylpiperidine (36). The structures and stereochemistries of the fused systems, as well as those of the piperidines, have been established by NMR.
    Additional Material: 3 Ill.
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  • 216
    Electronic Resource
    Electronic Resource
    Structural and Biosynthetic Investigations of the Rubromycins (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 729-735 
    Details
    ISSN: 1434-193X
    Keywords: Rubromycins ; Natural products ; Biosynthesis ; Quinones ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The structure of the known secondary metabolite β-rubromycin was corrected, based on spectroscopic and chemical investigations, from o-quinone 1 to p-quinone 6. By feeding [U-13C3]malonic acid to the rubromycin-producing strain, Streptomyces sp. A1, the polyketide origin of the skeleton was verified, but the identity of the starter unit and the folding mechanism of the polyketide chain are still unclear. From the culture broth of the strain A1, in addition to 6, the co-metabolites γ-rubromycin (3), δ-rubromycin (4) and 3′-hydroxy-β-rubromycin (7) were isolated. Their structures were determined or confirmed by detailed spectroscopic analysis. The rubromycins inhibit HIV-1 reverse transcriptase (RT) and are cytostatically active against different tumor cell lines.
    Additional Material: 1 Ill.
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  • 217
    Electronic Resource
    Electronic Resource
    New Approach to β-Lactam-Fused Enediynes (“Lactenediynes”) by Stereoselective Pinacol Coupling (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 939-946 
    Details
    ISSN: 1434-193X
    Keywords: Enediynes ; Vanadium ; C-C coupling ; Macrocycles ; Lactams ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short synthesis of unfunctionalized lactenediyne 3 by closure of the ten-membered ring at the double bond site is reported. After failure of the known methodologies, this closure was eventually successfully achieved thanks to a highly stereoselective, vanadium(II)-mediated pinacol coupling of bis(alk-2-ynal) 7.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99471_s.pdf or from the author.
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  • 218
    Electronic Resource
    Electronic Resource
    Synthesis of (S)-9-Methylgermacrene-B, the Male-Produced Sex Pheromone of the Sandfly Lutzomyia longipalpis from Lapinha, Brazil, and Its (R)-Isomer (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 955-962 
    Details
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Pheromones ; Pheromones ; Terpenoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Both the enantiomers of 9-methylgermacrene-B (1) were synthesized from the enantiomers of methyl 3-hydroxy-2-methylpropanoate (2). The male-produced sex pheromone of the sandfly Lutzomyia longipalpis (the vector of the protozoan parasite Leishmania chagasi) from Lapinha, Brazil, was identified as (S)-1 by GC comparison.
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  • 219
    Electronic Resource
    Electronic Resource
    Synthesis of New Soluble Annelated Polypyridines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 987-994 
    Details
    ISSN: 1434-193X
    Keywords: Addition reactions ; Octahydroacridine ; Polypyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new octahydroacridine with a tert-butoxypropyl group in the 9-position was prepared and was used in the synthesis of new soluble annelated polypyridines. Quinquepyridine with 11 adjacent rings was prepared in 17-25% yield by condensation of an α-methylene ketone and an enolisable ketone in the presence of ammonium acetate under basic conditions.
    Additional Material: 4 Ill.
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  • 220
    Electronic Resource
    Electronic Resource
    Molecular Dynamics-Based Models Explain the Unexpected Diastereoselectivity of the Sharpless Asymmetric Dihydroxylation of Allyl D-Xylosides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 995-1005 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric hydroxylations ; Allyl ethers ; Carbohydrates ; Molecular modeling ; Molecular dynamics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The catalytic asymmetric dihydroxylation of several allyl 2-O-benzyl-α-D-xylosides with AD-mix β and PYR(DHQD)2 shows almost no diastereofacial selectivity if the 3- and 4-OH groups are unprotected or acetylated. Acetal, benzyl ethers and benzoyl esters enhance the diastereoselectivity, in the opposite sense to that predicted by the “AD mnemonic”, which is completely lost using AD-mix α. In an attempt to understand this behaviour, computational studies of the asymmetric dihydroxylation (AD) of olefins using Sharpless' and Corey's catalysts have been carried out using molecular dynamics. A three-step algorithm was developed taking advantage of the enzyme-like behaviour of catalyst-olefin systems and applied using an ESFF force field. To validate our approach, the first sampling step procedure was then refined and performed using a modified CVFF force field. This led to a U-shaped model in good agreement with that proposed by Corey for the AD of allyl 4-methoxybenzoates, which brings to the fore a role for the methoxy group. This model also accounts for the observed enantioselectivity of styrene dihydroxylation. When applied to the AD of allyl xylosides using AD-mix β, our model accounts well for the observed diastereoselectivity. Both synthetic and modelling results confirmed that aromatic groups on the olefin could be involved in π-π stacking interactions with the aromatic rings of the catalyst and should be important, if not a prerequisite, to achieve high enantio- and diastereoselectivity.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99372_s.pdf or from the author.
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  • 221
    Electronic Resource
    Electronic Resource
    A Facile Solid-Phase Strategy for the Synthesis of Oligonucleotide-Tetraphenylporphyrin Conjugates (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1013-1018 
    Details
    ISSN: 1434-193X
    Keywords: Oligonucleotides ; Conjugation ; Porphyrinoids ; Solid-phase synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A convenient solid-phase synthesis of oligonucleotides conjugated at the 3′-end with a tetraphenylporphyrin residue, by means of a new polymeric support bearing as a linker a lysine derivative, has been developed. A porphyrin linked 17-mer, designed for antisense experiments, has been prepared in good yields, and its hybridization properties with a complementary DNA fragment evaluated by UV thermal analysis.
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    Oxidation of N-Benzyl Aziridine by Molecular Iodine: Competition of Electron Transfer and Heterolytic Pathways (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1037-1043 
    Details
    ISSN: 1434-193X
    Keywords: Electron transfer ; Radical ions ; Oxidations ; N-Dealkylation ; Aziridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Excess N-benzyl aziridine (1) reacts with I2 to afford dimer 2, tetramer 3, benzaldehyde (4), and iodoamine 5. The reaction is interpreted as occurring by both electron transfer (ET) and heterolytic mechanisms. An ET mechanism is substantiated for the oxidation by I2 of dimer 2 and tetramer 3, both being substrates easier to oxidise by electron abstraction than 1. Several auxiliary reactions were performed on 1 in order to firmly establish the boundaries to the competition between the ET and heterolytic mechanisms. For the reaction of 1 with 5 a reaction scheme is proposed; in a particular case, a pseudo-first order kinetic law is followed.
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    Activation of Oximic Nucleophiles by Coordination of Transition Metal Ions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1045-1050 
    Details
    ISSN: 1434-193X
    Keywords: Hydrolysis ; Nucleophilicity ; α-Effect ; Metal ion complexes ; Oximes ; Biomimetic models ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A kinetic study of the reactivity in the cleavage of p-nitrophenyl acetate of a series of 2-pyridineoximes, 1-4, and their complexes with NiII, ZnII and CuII is reported. Complexation of the oximic ligands leads to a remarkable increase in the acidity of the oximic group, following the order CuII 〉 NiII 〉 ZnII. The oximates of free ligands and their metal complexes, being α-nucleophiles, are quite effective in promoting the cleavage of PNPA. However, the reactivity, as defined by the second-order rate constants, is not predictably related to the acidity of the oximic function. The corresponding Brønsted plot shows a linear behaviour up to a pKa value of ca. 8, above which the reactivity of the uncomplexed oximic functions levels off to a limiting value. In the case of the metal ion complexes, a large effect of the ligand structure on the reactivity was observed. As a consequence, complexes of appropriate ligands and metal ions show a reactivity that exceeds the apparent limiting one of the oximates. The origin of such effects and their possible implications in the development of new reactivators of phosphorylated acetylcholinesterase are discussed.
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    Isomerization of Matrix-Isolated Formamide: IR-Spectroscopic Detection of Formimidic Acid (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1061-1063 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Matrix isolation ; Density functional calculations ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ultraviolet irradiation of matrix-isolated formamide (1) in solid argon with light of wavelength 248 nm leads to the formation of formimidic acid (2). Comparison of the experimental IR spectrum of the photoproduct with the calculated IR spectrum of 2 shows clearly that two rotamers 2a and 2b are formed.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99501_s.pdf or from the author.
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    The Cohalogenation of 1-N-Vinylpyrimidinediones: A New Approach to Nucleoside Analogs (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1507-1516 
    Details
    ISSN: 1434-193X
    Keywords: Nucleosides ; Nucleosides ; Radical reactions ; Hydrogen transfer ; CH-π interaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new approach to the synthesis of nucleoside analogs has been developed, which involves initial chemo- and regioselective cohalogenation of 1-N-vinylpyrimidinediones 10a,b using N-bromosuccinimide in the presence of variously substituted propargylic alcohols. Radical carbocyclization of the resulting β-bromo propargylic ethers 17-22 then leads to 3-methylenetetrahydrofurans 23-26. In such cyclizations, different reactivities have been observed for diastereomers 22a,b obtained by cohalogenation with (R)-1-benzyloxybut-3-yn-2-ol; although the expected anti 3-methylenetetrahydrofurans 27a,b were obtained, the syn diastereomers 28a,b were only the minor constituents of a mixture in which bicyclonucleosides 29a,b were the major components. The formation of 29a,b results from a 1,6-hydrogen transfer followed by cyclization, which might be favored by a CH-π interaction in radical intermediate synII.
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    Atypical Regioselectivity in the Electrochemical Reduction-Nucleophilic Substitution of 2-Nitroanisole (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1517-1520 
    Details
    ISSN: 1434-193X
    Keywords: Electrochemistry ; Regioselectivity ; Solvent effects ; o-Quinone imines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The electrochemical reduction-Bamberger substitution of 2-nitroanisole in 1 M H2SO4 yields predominantly 2,5-dimethoxyaniline, not the expected 2,4-isomer. The selectivity was found to be acid- and solvent-dependent, with lower acidity and less polar solvents favoring the formation of 2,4-dimethoxyaniline during galvanostatic electrolysis. A mechanistic working hypothesis involving an ortho-quinone monoimine dication is presented to direct further synthetic studies.
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    Synthesis of 10β,17α-Dimethyl-17β-(1,2-dioxopropyl)estra-5,9-diene-3-ketal (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1521-1525 
    Details
    ISSN: 1434-193X
    Keywords: Ketones ; Steroids ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of a new progestomimetic steroid, analogous to the cetaloxopromegestone precursor of Trimegestone has been carried out in eight steps from 9α-hydroxyandrost-4-ene-3,17-dione. This latter compound can be obtained from the fermentation of γ-sitosterol, a sterol extracted from soya bean oil.
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    Tandem Silylformylation/Wittig Olefination of Terminal Alkynes: Stereoselective Synthesis of 2,4-Dienoic Esters (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1131-1135 
    Details
    ISSN: 1434-193X
    Keywords: Carbonylation ; Wittig reactions ; Rhodium ; Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The rhodium(I)-catalysed sequential silylformylation/Wittig olefination of terminal alkynes with hydrosilanes and carbon monoxide in the presence of stabilised P-ylides leads to substituted 2,4-dienoic esters in a one-pot procedure. The α,β,γ,δ-unsaturated esters are generated with high (2E,4Z) stereoselectivity in good to excellent yields. Conversions of the products in [2+1] cycloaddition reactions are presented.
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    Isolation of Macrocyclic Metacyclophanes From the Attempted Synthesis of [7.0]Metacyclophanes of the Myricanone Series by Thorpe-Ziegler - Intramolecular Cyclization of Diaryls Substituted by ω-Cyanoalkyl Chains (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1527-1533 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Myricanone ; Diaryls ; C-C coupling ; Dinitriles ; Condensation reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The syntheses of the diaryls 14 and 21, substituted by two ω-cyanoalkyl chains (one on each ring), are described. Treatment of the unsymmetrical diaryl 14 with NaN(Me)Ph in a Thorpe-Ziegler reaction failed to give any definite product. Under the same conditions the symmetrical diaryl 21 led to an isomeric mixture of dimeric enaminonitriles 24. Mild acidic hydrolysis of the latter yielded the isomeric β-ketonitriles 25, whereas more drastic hydrolytic conditions led to the macrocyclic diketone 26.
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    A New Preparative Synthesis of 1-D-6-O-(2-Amino-2-Deoxy-D-glycopyranosyl)-chiro-Inositol 1-Phosphate and 1,2-Cyclic Phosphate (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1539-1545 
    Details
    ISSN: 1434-193X
    Keywords: Inositolphosphoglycans ; Oligosaccharide synthesis ; Insulin mediators ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A convenient preparative synthesis of 1-D-6-O-(2-amino-2-deoxy-α-D-glycopyranosyl)-chiro-inositol 1-phosphate (III) and -1,2-cyclic phosphate (IV) using D-chiro-inositol as starting material is reported. Compound III has been previously found to behave as type P inositolphosphoglycans (the putative second messengers of insulin-like growth factor I) in organotypic cultures of chicken embryo. The synthesis of III and IV, now reported, considerably improves previous synthesis of III and permits the effective preparation of these substances for biological investigation.
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    Attempted Synthesis of Type-A Inositolphosphoglycan Mediators - Synthesis of a Pseudohexasaccharide Precursor (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1547-1562 
    Details
    ISSN: 1434-193X
    Keywords: Inositolphosphoglycans ; Oligosaccharide synthesis ; Insulin mediators ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A block synthesis approach to the inositol-containing pseudohexasaccharide 1 is presented. The myo-inositol building block 6 has been prepared using a key regioselective acylation through a boron-tin exchange reaction and the 2-azido-2-deoxy glycosyl donors 15 and 17 have been synthesized from D-glucosamine using a diazo transfer reaction. The anomeric position of the mono- and disaccharide building blocks has been temporarily protected as phenyl thioglycoside and this function was then converted into the different leaving groups to perform the glycosylation reactions. Both trichloroacetimidates and fluorides have been used as glycosyl donors for the construction of the different glycosidic linkages. The protected pseudohexasaccharides 44, 48-50, which are precursors of pseudohexasaccharide 1, have been efficiently prepared and fully characterized. Pseudohexasaccharide 1 contains the fundamental structural features which have been proposed for type A inositolphosphoglycans, which may be involved in the insulin-signaling process.
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    Preparation of Free and of Specifically Protected Oligo[β-Malic Acids] for Enzymatic Degradation Studies (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1207-1218 
    Details
    ISSN: 1434-193X
    Keywords: Poly[β-(S)-malic acid] ; Biopolyesters ; Oligomers ; Protecting groups ; Allyl ester ; Hydrolase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The polyanionic poly[β-(S)-malic acids] (β-PMA) occur in slime molds (myxomycetes), black yeasts and other fungi and are involved in DNA replication. In order to be able to study the cleavage mechanism of β-PMA hydrolases, we have synthesized cyclic and linear oligomers of malic acid (β-OMA) consisting of up to eight residues. To this end, fragments with three different protecting groups were prepared, with allyl ester groups on the C-terminus, TBDPS groups at the O-terminus, and benzyl ester groups at the side chains (Schemes 2, 3, 7). Selective deprotection and fragment coupling (COCl2/C5H5N/CH2Cl2/-75 °C) gave dimers, tetramers, and octamers, either fully protected or specifically protected at the O- or C-terminus or at the side chain acid groups, and also fully deprotected oligoacids (Schemes 3-7). The new compounds were fully characterized (Rf, IR, 1H- and 13C-NMR spectroscopy, mass spectrometry and elemental analysis or high-resolution electrospray mass spectrometry). Enzymatic degradation experiments with the previously prepared cyclo-tetramer, the unprotected, and the O- or C-terminally protected samples of linear β-OMAs show that the enzyme from Physarum polycephalum is an exo-hydrolase cleaving the chain from the O-terminus.
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    The Interaction between Amminehalocobalt(III) Cations and Polythionate Anions: Hydrogen-Bonding Patterns and S-S Bond Cleavage Reactions (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 189-193 
    Details
    ISSN: 1434-1948
    Keywords: Cobalt(III) ; Dithionate ; Trithionate ; Sulfato ligand ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystal structures of amminehalocobalt(III) compounds with di- or trithionate anions have been determined in order to know whether they interact to adopt specific molecular packing patterns and whether di- and trithionate anions undergo the S-S bond cleavage reactions as has been found for the S4O62- ion. In the structures of p-[Co(tren)(NH3)Cl]S2O6·H2O (1) and t-[Co(tren)(NH3)Cl]S2O6 (2), the configurational differences in the cations dictate the hydrogen-bonding pattern with the dithionate anion to lead to racemic structures. cis-[Co(en)2(NH3)Br]S3O6 (3) also crystallizes in a racemic space group P21/c in which the ions form a macrocyclic hydrogen-bonded network. Aqueous solutions of S3O62- and p-[Co(tren)(NH3)Cl]2+ produce p-[Co(tren)(NH3)(OSO3)]ClO4 (4) which is believed to be derived from the hydrolytic cleavage of S-S bond in the trithionate anion. These results reinforce our previous observation of the S-S cleavage reactions for the tetrathionate anion.
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    A Two-Step Palladium-Catalyzed Coupling Scheme for the Synthesis of Ferrocene-Labeled Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 323-330 
    Details
    ISSN: 1434-1948
    Keywords: Amino acids ; Alkynes ; Ferrocene ; Palladium ; Catalysis ; Bioorganometallic chemistry ; Biosensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes a Pd-catalyzed coupling of ferrocene alkyne derivatives to iodo amino acids. Ferrocene carboxylic acid propargyl amides were easily obtained in high yield. The crystal structures of the propargyl amine derivative 3 and the 1,1-diethylpropargylamine derivative 4 have been determined by X-ray diffraction. Pd-catalyzed coupling to p-iodoanilide amino acids gave the corresponding ferrocene-labeled amino acid derivatives, which were easily purified by diethyl ether extraction in the case of the 1,1-diethyl derivatives 8. The coupling reaction did not require anhydrous solvents and tolerated a variety of functional groups present in peptides such as alcohols (8a, Ser), thioethers (8d, Met), disulfide bonds (cystine, 12) esters (as in the N-labeled Leu derivative 10) and of course amides. A minor by-product of the coupling reaction, namely the homo-dimer bis(ferrocene carboxylic acid propargylamide) 9, was identified in the crude reaction mixtures by mass spectrometry and independently synthesized by oxidative coupling (Glaser and Eglington) of 3. All new compounds were completely characterized spectroscopically, including 15N- and 2D NMR spectroscopy, Mössbauer spectroscopy and electrochemistry. This work introduces a versatile procedure for a selective functionalization of amino acids with organometallics at the C-terminus which is expected to be of general applicability to peptide chemistry.
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    Compared Reductive Chemistry of Molybdenocene and Indenyl-Substituted Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 331-340 
    Details
    ISSN: 1434-1948
    Keywords: Indenyl complexes ; Cyclopentadienyl complexes ; Molybdenocene ; Ring slippage ; Molybdenum ; DFT calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of [IndCpMo(L)Br]Br (L = 1a, CO; 2, NCMe) with Cp2Co in the presence of two equivalents of the ligand L′ gives the ring-slipped neutral complexes [(η3-Ind)CpMoL′2] (L′ = 5, CO; 6, 1/2 dppe; 7, PMe3; 8, P(OMe)3; 9, CNtBu) in good yield. Products 7, 8, and 9, but not [IndCpMoL′], are also formed in the presence of only 1 equivalent of L′ in modest yields. In the case of the reduction of [IndCpMo(L)Br]Br [L = 2, NCMe; 3a, CNtBu; 4, P(OMe)3] mixtures of the complexes, [(η3-Ind)CpMoL2] (8, 9) and [(η5-Ind)CpMoL] [L = 11, P(OMe)3; 12, CNtBu] were obtained. The only product of formal type [(η5-Ind)CpMoL] that could be prepared by these methods was the alkyne complex [(η5-Ind)CpMo(η2-PhC≡CPh)] (10). These results contrast with the well-known reductions of similar bis-cyclopentadienyl cations [Cp2Mo(L)Br]+, which produce [Cp2MoL] complexes under the same conditions. The reduction of the dications [Cp2MoL2][BF4]2 [L = CO; P(OMe)3] with Cp2Co is now reported to afford the neutral complexes [CpMo(η3-C5H5)(CO)2] (13) and [Cp2Mo(P(OMe)3)] (14), respectively, showing that the stability of the ring-slipped complexes is dependent on the other ligands. From DFT and EHMO calculations used to probe the bonding and the energetics of these ring slippage processes it is concluded that weak π acceptor ligands favour η5-Ind → η3-Ind slippage and disfavour η5-Cp → η3-Cp slippage at the CpMoL2 fragment. Redox-induced ring slippages involve very similar energies for both indenyl and cyclopentadienyl complexes and should be able to produce more examples of the otherwise rare η3-Cp coordination mode.
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    Chiral 4-(Diphenylphosphanyl)-1-(dialkylamino)butane Ligands - Synthesis, Applications in Asymmetric Alkylation and Theoretical Study (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 351-358 
    Details
    ISSN: 1434-1948
    Keywords: Aminophosphanes ; Palladium ; Alkylations ; Enantioselectivity ; Theoretical study ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various 4-(diphenylphosphanyl)-1-(dialkylamino)butane ligands were prepared from commercial (2S,3S)-2,3-O-isopropylidene-D-threitol. These ligands, associated with Pd2(dba)3, gave enantioselectivities of up to 75% in the alkylation of racemic 1,3-diphenylprop-2-enyl acetate with dimethyl malonate anion. A theoretical study shows the important role played by two factors in the alkylation reaction: steric control, leading to the formation of a unique diastereoisomer of the π-allylpalladium complex, and orbital control, which orients the attack of the nucleophile trans to the phosphorus atom.
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    Mono and Dinuclear Tungsten Alkenyl-Carbyne Complexes Bridged by Cyanide and Diisocyanide Ligands: Synthesis, Electrochemical- and 183W-NMR Studies (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 341-350 
    Details
    ISSN: 1434-1948
    Keywords: Alkenylcarbynes ; Dinuclear tungsten complexes ; Electrochemistry ; Tungsten NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neutral trans-cyanide alkenylcarbyne complexes 2a and 2b have been prepared by reaction of the complex 1a and 1b with NaCN or [Bu4N]CN. The reaction of complexes 2a and 2b with an equimolar amount of the acetonitrile complexes 1a and 1b in CH2Cl2 leads to the cationic cyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 3a-d. Diisocyanide-bridged bis(alkenylcarbyne) di-tungsten complexes 4a and 4b have been synthesized by the reaction of complexes 1a and 1b with 0.5 equivalents of the diisocyanide 1,4-(CN)2C6H4. IR as well as 1H-, 31P{1H}-, 13C{1H}-, and 183W-NMR data are reported. The spectroscopic data show that in the dinuclear complexes 3a-d, the bridging CN group and the alkenylcarbyne units are located in trans positions, while in the dinuclear complexes 4a and b, the isocyanide groups of the bridging ligand 1,4-(CN)2C6H4 and the two alkenylcarbyne moieties are cis. The 183W chemical shifts of complexes 2a, 2b, 3a-d, 4a, and 4b were obtained through two-dimensional indirect 31P, 183W NMR recording techniques. A downfield shifting of 183W resonances of the cyanide-bridged dinuclear complexes 3a-d with respect to the mononuclear ones, 2a and 2b, was observed. The δ183W of isocyanide bridging dinuclear complexes 4a and 4b appear at higher field than those of the corresponding mononuclear cyanide 2a and 2b in accordance with the higher π-acceptor electron properties of the isocyanide ligand. The electrochemical behaviour of all the complexes has been investigated by cyclic voltammetry and controlled potential electrolysis in aprotic media and at a Pt (or vitreous C) electrode. Complexes 1, 2, or 3 undergo multi-electron irreversible oxidation processes involving anodically induced proton dissociation from the alkenylcarbyne ligands, and irreversible cathodic processes are also observed for all the complexes. The order of the redox potentials reflects that of the net electron π-acceptor/σ-donor character of the ligands and the ligating alkenylcarbynes are shown to behave as remarkably strong π-electron acceptors (even stronger than CO).
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    On the Electronic Properties of Substituted Phosphanylcarbenes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 369-374 
    Details
    ISSN: 1434-1948
    Keywords: Phosphanylcarbenes ; Substituent effects ; Quantum chemical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A phosphanyl group exerts much less π-conjugation properties than an amino group. On this basis, corresponding carbene structures exhibit much smaller singlet-triplet energy separations. Of the various structures investigated quantum-chemically the largest singlet-triplet energy separations are predicted for cyclic diphosphanylcarbenes, in which the two functional groups are incorporated into a ring system and the phosphorus atoms are substituted by phosphoraniminato groups. Then the singlet-triplet energy separations become essentially larger than for the Bertrand-type (push-pull) carbenes.
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    Pentacoordination at Fluoro-Substituted Silanes by Weak Lewis Donor Addition (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 375-381 
    Details
    ISSN: 1434-1948
    Keywords: Fluorine ; Silicon ; Ab initio calculations ; Donor-acceptor systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum chemical calculations at the ab initio level indicate that Lewis donors such as amine or water form weak donor-acceptor complexes with fluoro-substituted silanes. The strength of the donor-acceptor formation increases with increasing degree of fluorine substitution. Amine and water form strong adducts only for tetrafluorosilane. The higher element homologues of Lewis donors, such as phosphane and sulfur dihydride, do not in essence coordinate. A considerable role in donor-acceptor formation is exerted by chelation effects which impose intramolecular interactions on functionalized ligands. The corresponding structures are explored.
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    Reduction of Metal-Stabilized α-CF3-Carbenium Ion Complexes under Mild Conditions: Synthesis, Structures, and Reactivity (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 359-368 
    Details
    ISSN: 1434-1948
    Keywords: Radicals ; Carbenium ions ; Clusters ; Cobalt ; Molybdenum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexed α-CF3 propargyl alcohols of the general formula [(M2L6){μ-η2,η2-RC≡CCH(CF3)(OH)}] were prepared with M2L6 = Co2(CO)6, R = CH3(CH2)4- (1), R = C6H5- (2); M2L6 = Co2(CO)5P(C6H5)3, R = CH3(CH2)4- (3a,b), R = C6H5- (4a,b); M2L6 = Co2(CO)4dppm, R = C6H5- (5); M2L6 = Co(CO)3MoCp(CO)2, R = CH3(CH2)4- (6a,b), R = C6H5- (7a,b). An X-ray molecular structure of the propargyl-alcohol complex [{Co2(CO)4dppm}{μ-η2,η2-C6H5C≡CCH(CF3)(OH)}] (5) was also determined. The related carbenium ions [(M2L6){μ-η2,η3-RC≡CCH(CF3)}][BF4] (8-12) were obtained from the parent propargyl alcohol complexes by direct protonation with HBF4· Et2O in diethyl ether. These carbenium ions were reduced further by Zn in CH2Cl2 to give the alkyne adducts [(M2L6){μ-η2,η2-RC≡CCH2(CF3)}] (13-17), as confirmed by the X-ray molecular structure of [(Co2(CO)4dppm){μ-η2,η2-C6H5C≡CCH2(CF3)}] (17). Treatment of the carbenium ion complex [{Co(CO)3MoCp(CO)2}{μ-η2,η3-CH3(CH2)4C≡CCH(CF3)}][BF4] (8) with NaSMe unexpectedly afforded the reduced alkyne adduct [{Co(CO)3MoCp(CO)2}{μ-η2,η2-CH3(CH2)4C≡CCH2(CF3)}] (13), along with the alkyne-thioether diastereomers {Co(CO)3MoCp(CO)2}{μ-η2,η2-CH3(CH2)4C≡CCH(CF3)[(SMe)}] (18a,b). Presumably, all the reduction reactions proceed primarily by the formation of the transient radical species, which are subsequently transformed into the reduced alkyne complexes by hydrogen abstraction from the solvent medium. Interestingly, in the case of the complexed alcohols [{Co2(CO)5P(C6H5)3}{μ-η2,η2-RC≡CCH(CF3)(OH)}] (3a,b) and (4a,b), the reduction process occurs in acidic medium in THF/CH2Cl2. An extensive study of the electronic and steric factors that influence the stability and reactivity of the carbenium ions were performed, which allowed us to explain the behavior of the related radical species in solution during the reduction process.
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    NMR Investigations of Restricted Rotations and Metallotropic Shifts in Rhenium(I) Tricarbonyl Halide Complexes of Pyridyl Carboxamide and Thioamide Ligands (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 383-391 
    Details
    ISSN: 1434-1948
    Keywords: Pyridyl carboxamides ; Carbonyl complexes ; Rhenium ; Metallotropic shifts ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of rhenium(I) tricarbonyl halide complexes of pyridyl mono- and di-carboxamides and -thioamides has been studied by dynamic NMR techniques. Oxygen coordination to ReI of the carboxamide ligand reduced the energy barrier to C-N rotation by 2-13 kJ mol-1 whereas sulfur-ReI coordination of the thioamide ligands led to a reduction of 28-33 kJ mol-1. In the pyridyl dicarboxamide and -dithioamide metal chelate complexes metallotropic shifts occur between the three donor atoms, O, N, O or S, N, S, energies [ΔG
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    Substrate-Binding Ligand Approach in Chemical Modeling of Copper-Containing Monooxygenases, 1 Intramolecular Stereoselective Oxygen Atom Insertion into a Non-Activated C-H Bond (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 393-398 
    Details
    ISSN: 1434-1948
    Keywords: Copper ; Oxygenase ; Copper-oxygen radical species ; RPY2 ligand ; Oxygenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the reactivity of new copper AlkylPY2 type complexes which react with dioxygen and thus hydroxylate an aliphatic C-H bond of the ligand in the same manner as copper-containing monooxygenases.
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    Second Coordination Sphere Water Molecules and Relaxivity of Gadolinium(III) Complexes: Implications for MRI Contrast Agents (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 399-407 
    Details
    ISSN: 1434-1948
    Keywords: Relaxivity ; Nuclear magnetic relaxation dispersion ; Imaging agents ; NMR spectroscopy ; MRI contrast agents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipolar interaction between the metal ion and proximate water molecules represents an efficient mechanism for solvent relaxation in Gd3+ complexes currently employed as MRI contrast agents. Besides inner sphere (metal bound) and outer sphere hydration molecules, a well-defined second coordination shell may provide an additional mechanism for paramagnetic relaxation leading to a strong enhancement of the relaxivity of the complexes. Through a careful choice of hydrogen-bond-acceptor groups on the ligand we may: (1) promote the formation of a strong interaction; (2) increase the number of water molecules in the second hydration shell; (3) decrease their average distance from the paramagnetic metal center. These possibilities have been explored by considering complexes bearing phosphinate, phosphonate and carboxoamide pendant arms, by exploiting the formation of ion-pairs with cationic substrates and inclusion compounds of these adducts with -cyclodextrin. Finally, the contribution of this relaxation mechanism to the relaxivity of the commercially available MRI contrast agents is discussed and the NMRD data reevaluated and compared with crystallographic data.β
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    2H-1,2-Azaphosphindoles - Synthesis and Characterization (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 417-421 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus ; Benzynezirconocenes ; Azazirconacyclopentenes ; Exchange reactions ; 1,2-Azaphosphindole ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first 1,2-azaphosphindoles 14a,b, 15a,b were obtained in a straightforward manner upon heating diphenylzirconocene in the presence of a cyanophosphane, which afforded azazirconacyclopentenes 11a,b which can be reacted with various dichlorophosphanes. The use of the tetrachlorodiphosphane Cl2P(CH2)2PCl2 instead of a dichlorophosphane allowed the preparation of the bis(1,2-azaphosphindoles) 19, 19′. The monosulfur adduct of the azaphosphindole 14a, i.e. 16a, was characterized by X-ray structure analysis. Alkylation of 14a or 16a with methyltrifluoromethane sulfonate occurred selectively on the intracyclic phosphorus atom or on the sulfur atom, giving the salts 20 or 21, respectively.
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    Reactions of Functional Groups at the Periphery of Group 4 Metallocene Frameworks: Selective Formation of a Cp-Bonded Azaboretidine Derivative by a Hydroboration Route (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 409-416 
    Details
    ISSN: 1434-1948
    Keywords: Functionalized zirconocenes ; Half-sandwich complexes ; Hydroboration ; Propene polymerization/Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-Amino-6-methylfulvene has been coupled with benzoic acid by treatment with 7-azahydroxybenzotriazole and DCC. Subsequent two-fold deprotonation, at the NH and 6-methyl groups, generated the vinylidene-bridged Cp/benzoylamido ligand 5. Treatment of 5 with ZrCl4(THF)2 gave the spiro-metallocene complex 3a (characterized by X-ray crystal structure analysis), while reaction of 5 with (Et2N)2ZrCl2(THF)2 yielded the bridged half-sandwich complex 3b. Treatment of 3a with two molar equivalents of the strongly electrophilic borane HB(C6F5)2 resulted in hydroboration of the exocyclic C=C double bond with concomitant intramolecular N-B adduct formation to yield the azaboretidine-type systems 7 (three diastereoisomers, one of which has been characterized by X-ray diffraction analysis). Similarly, hydroboration of 3b with HB(C6F5)2 yielded the azaboretidine derivative 9. Activation of the complexes 7 and 9 with methylalumoxane led to active homogeneous Ziegler-type propene polymerization catalysts.
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    Inert and Labile [Ru(L)(‘pyS4’)] Complexes with Rigid [RuNS4] Cores and trans-Thiolate Donors [L = PPh3, PEt3, DMSO, CO, NO+, N2H4; ‘pyS4’2- = 2,6-Bis(2-mercaptophenylthio)dimethylpyridine(2-)] (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 423-429 
    Details
    ISSN: 1434-1948
    Keywords: Ruthenium ; Sulfur ligands ; Exchange reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a quest for ruthenium complexes having [RuNS4] cores, a non-fluxional configuration, trans-thiolate donors, and exchangeable coligands L, [Ru(L)(‘pyS4’)] complexes have been synthesized [‘pyS4’2- = 2,6-bis(2-mercaptophenylthio)dimethylpyridine(2-)]. Treatment of [RuCl2(PPh3)3] with ‘pyS4’2- gave [Ru(PPh3)(‘pyS4’)] (1). Alkylation of 1 with excess MeI yielded [Ru(PPh3)(‘pyS4’-Me2)]I2 (2). [Ru(DMSO)(‘pyS4’)] (3) was obtained from [RuCl2(DMSO)4] and ‘pyS4’2-. The PPh3 or DMSO coligands in 1, 2, and 3 proved to be very inert to substitution. Only the DMSO could be displaced by CO under drastic conditions yielding [Ru(CO)(‘pyS4’)] (4). Treatment of [RuCl2(CH3CN)4] with ‘pyS4’2- yielded [Ru(‘pyS4’)]2 (5); in the presence of PEt3 or N2H4 mononuclear [Ru(PEt3)(‘pyS4’)] (6) and [Ru(N2H4)(‘pyS4’)] (7) were formed. Template alkylation of NBu4[Ru(NO)(S2C6H4)2] with 2,6-bis(tosyloxymethyl)pyridine gave [Ru(NO)(‘pyS4’)]Tos (8). Complex 8 proved to be the best suited precursor for L exchange reactions. Under reducing conditions, 8 releases its NO ligand and the resulting [Ru(‘pyS4’)] fragments can combine either with each other to give 5, or with PEt3 and N2H4 to yield 6 and 7, respectively. All complexes have been characterized by spectroscopic methods and elemental analysis; 1, 2, 3, and 4 have also been submitted to X-ray structure analysis.
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    Methyl(2-phosphanylphenolato[P,O])nickel(II) Complexes - Synthesis, Structure, and Activity as Ethene Oligomerization Catalysts (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 431-440 
    Details
    ISSN: 1434-1948
    Keywords: Methylnickel complexes ; 2-Phosphanylphenolate ; Chelates ; Homogeneous catalysis ; Oligomerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of various substituted 2-phosphanylphenols 1a-f with half-molar amounts of cis-[MeNi(μ-OMe)(PMe3)]2 have been found to yield square-planar methyl(2-phosphanylphenolato)(trimethylphosphane)nickel(II) complexes 2a-f. 2JPP coupling constants of 305-316 Hz at low temperature indicate a trans-configuration for the products, while broad 31P-NMR signals at room temperature can be attributed to rapid dissociation of PMe3. Reaction with excess 1 gave rigid bis(2-phosphanylphenolato)nickel(II) complexes as exemplified by 3e, whereas addition of PMe3 to 2a led to the pentacoordinate methyl(2-phosphanylphenolato)bis(trimethylphosphane)nickel(II) complex 4a. Higher yields of 4a and 4d were obtained by reactions of 1a and 1d with Me2Ni(PMe3)3. Single-crystal X-ray diffraction analyses of 3e and 4a have revealed the structures as square-planar trans-bis- and trigonal-bipyramidal mono(2-phosphanylphenolato)nickel(II) P1O-chelate complexes, respectively. The methylnickel complexes 2 and 4 have been found to be effective one-component catalysts for the oligomerization of ethene. High conversions (〉 96%) were achieved with the P-basic derivatives 2e, 2f, and 4d bearing one or two branched alkyl groups (isopropyl, tert-butyl), whereas the diphenylphosphanyl derivatives were less active; 4d gave shorter oligomers than 2e or 2f.
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    Alcoholysis of Aluminum Alkyls Supported by Bulky Phenoxide Ligands: Synthesis, Characterization, and ε-Caprolactone Polymerization Activity of Two Dimeric Aluminum Isopropoxides (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 441-445 
    Details
    ISSN: 1434-1948
    Keywords: Aluminum ; Alkoxides ; Lactone ; Ring-opening ; Polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of trialkylaluminum Al2R6 (R = Me, Et) with 2,2′-methylenebis(6-tert-butyl-4-methylphenol) (mbmpH2) gives the dimeric mono(alkyl) complex [Al(mbmp)R]2 with bridging oxygen atoms. Reaction of [Al(mbmp)R]2 with one equiv. of 2-propanol results in the formation of the dimeric isopropoxide [Al(mbmp)(μ-OiPr)]2. Single-crystal X-ray analysis shows a C2h-symmetric structure with a planar Al2O2 core. Monomeric methylbis(2,6-di-tert-butyl-4-methylphenolato)aluminum, AlMe(OC6H2-2,6-tBu2-4-Me)2 (MAD), was found to react with one equiv. of 2-propanol to give a dimeric isopropoxide [AlMe(OC6H2-2,6-tBu2-4-Me)(μ-OiPr)]2 in which the bulky phenolate, instead of the methyl group, has been displaced. According to the single-crystal X-ray structure analysis, the molecule contains a similar Al2O2 core, but the two 2,6-di-tert-butyl-4-methylphenolato ligands are cis- and orthogonally arranged to each other. ε-Caprolactone is polymerized at 50 °C in toluene in a controlled manner by [Al(mbmp)(μ-OiPr)]2, to give poly(ε-caprolactone) with high molecular weights and narrow molecular weight distributions (Mw/Mn 〈 1.50). The low efficiency values (number of polymer chains initiated per aluminum atom) imply that [Al(mbmp)(μ-OiPr)]2 exists in a monomer-dimer equilibrium. The polymerization of ε-caprolactone by [AlMe(OC6H2-2,6-tBu2-4-Me)(μ-OiPr)]2 is faster, but somewhat less controlled.
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    Effect of Substitution on the ESR Spectra and Electronic Ground State of ZnTPP Cation Radicals (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 447-454 
    Details
    ISSN: 1434-1948
    Keywords: Zinc ; Metalloporphyrins ; Porphyrins ; Cations ; Radicals ; ESR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinc(II) complexes of substituted tetraphenylporphyrins, Zn[T(X-P)P], where X = H, p-F, p-Cl, m-Cl, p-CH3O, and m-CH3O, have been synthesized and characterized. Peripheral substitution shows marked changes in the chemical shifts of the phenyl proton resonances and E1/2 values of the redox couples in the anodic region while the UV/Vis spectra are unaffected. The monocation radicals of these complexes are generated by chemical oxidation with bromine. The ESR spectra reveal the formation of two types of radical species, Zn[T(X-P)P]+·Br- (species I) and Zn[T(X-P)(Brn-P)]+·Br- (species II): Species I at 298 K shows a spectrum, with well-resolved bromine hyperfine features, characteristic of a 2A2u electronic ground state while species II, except for the complex with X = m-CH3O, shows a featureless, isotropic resonance attributable to a 2A1u state. Zn[T(m-CH3O-P)(Brn-P)]+·Br-, on the other hand, exhibits nine resolved nitrogen hyperfine features corresponding to a 2A2u state. Variable temperature ESR spectra (77-298 K) indicate reduction in the bromine and nitrogen hyperfine coupling constants and an increase in the g value of species I from 2.0049 to 2.0060 with lowering temperature and suggest a labile electronic ground state for species I. The p-CH3O substituted complex exhibits an electronic transformation from 2A2u to 2A1u while the remaining complexes, including m-CH3O, show a transformation from 2A2u to an admixed 2A1u/2A2u state. The effect of substitution on the variable temperature ESR spectra are discussed.
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    Low-Coordinate Arsenic Chemistry: Studies of Amino(iminoarsanes) Using UV Photoelectron Spectroscopy and Density Functional Theory (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 477-483 
    Details
    ISSN: 1434-1948
    Keywords: Arsenic ; UV photoelectron spectroscopy ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, we report the gas-phase characterization of two differently substituted amino(iminoarsanes), TmpAs=NSiMe3 and (SiMe2tBu)2NAs=N(SiMe2tBu), by coupling flash vacuum thermolysis (FVT) with UV photoelectron spectroscopy (PES). Quantum chemical calculations, using the DFT method (B3LYP) with the basis set 6-311G(d,p), have also been carried out on the R1As=NR2 unit with R1 = H, NH2, N(CH3)2, N(SiH3)2 and R2 = H, SiH3, in order to study the effect of substitution on the electronic properties and the thermodynamic stability of the As=N skeleton. Similarities with phosphorus analogues are also discussed.
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    Potentially Tridentate Hydrazonic Ligands in the Synthesis of Methyl and Acetyl Palladium(II) Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 463-475 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; Insertion reactions ; Tridentate ligands ; Hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentially tridentate hydrazonic ligands of the type HNNO have been used in the synthesis of some methyl palladium(II) complexes. Depending on the applied experimental conditions two different kinds of complexes are obtained. Thus, the reactions between HL1-HL5 and (COD)PdMeCl in diethyl ether led to the formation of bidentate methyl complexes of the type Pd(HNN)MeCl (1-5), where the ligands maintain a neutral character. However, in the presence of a base such as Et3N or NaOMe, the ligands are deprotonated with the consequent formation of tridentate methyl complexes of the type Pd(NNO)Me (7-10). In solution, complexes 1-5 tend to lose the hydrazonic proton with elimination of methane and formation of a tridentate chloride complex Pd(NNO)Cl (6); this tendency can be correlated with the acidity of the free ligands, which has been determined. On bubbling carbon monoxide through solutions of 1-5, the corresponding acetyl complexes Pd(HNN)[C(O)Me]Cl (11-15) are formed, in which both the cis and trans isomers are present. Their molar ratio is rationalised from the results of a molecular modelling study on the basis of electronic considerations. A remarkably different reactivity has been found in the carbonylation of the tridentate complexes 7-10: they decompose rapidly and quantitatively to palladium black and an organic product corresponding to the ligand with an acetyl group bonded to the hydrazonic nitrogen. The X-ray structures of a methyl complex (3) and its corresponding acetyl (13) derivative have been determined.
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    On the Nature of Arene η6 Interactions in the Solid State and the Use of Cylindrophanes as Ligands for Sandwich Complexation of Metals with Longer-Range Interactions with the Benzene Ring (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 485-490 
    Details
    ISSN: 1434-1948
    Keywords: Coordination modes ; Cyclophanes ; Macrocycles ; Sandwich complexes ; Solid-state structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel mode of containment for metal ions which participate in longer-range interactions with aryl rings (≥ 2.5 Å) is demonstrated in the preorganized cylindrical host 1. Three equatorial sulfur atoms in 1 hold metals in a trigonal planar ligand field between two apical benzene centroids at an M-Ar distance of about 3 Å. Evidence of an interaction between the π electrons and the metals is gained by 1H NMR spectroscopy of the complexes, and support for the general description of metal-arene contacts in the 2.5-3.5 Å range as ‘‘bonds’’ is derived from a statistical study of η6-coordination in the solid state. Crystal structures of [Ag(1)]BF4 and [Cu(1)]BF4 confirm the first examples of arene AgI and CuI sandwich complexation and indeed the only structurally characterized CuI-aryl centroid interaction. The two isomeric tris-sulfoxides derived from 1 show less tendency to interact with metals ions.
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    Stabilization of Carbenium Ions Derived from Ethynylestradiol by Different Adjacent Organometallic Moieties. Implication in the Inactivation of the Estrogen Receptor (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 491-497 
    Details
    ISSN: 1434-1948
    Keywords: Clusters ; Steroids ; Protonation ; Carbocations ; Immunoassay ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stabilization of carbenium ions by an adjacent organotransition metal moiety has been evaluated using the classical Deno's method as well as a new procedure based on DCI-MS spectrometry. The ability of transition metal clusters to enhance the stability of a proximate carbocationic center in 17α-alkynylestradiol-[OM] derivatives {[OM] = Co2(CO)6; Co2(CO)4(dppm); Mo2Cp2(CO)4; M3(CO)10, M = Ru, Os; HRu3(CO)9} has been related to their capacity to inactivate the estrogen receptor (affinity marker properties).
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    How to Predict Activation Barriers - Conformational Transformations of Compounds CH3C(CH2PPh2)3-n[CH2P(oTol)2]nMo(CO)3 (n = 1-3): Force Field Calculations versus NMR Data (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 597-615 
    Details
    ISSN: 1434-1948
    Keywords: Tripod molybdenum tricarbonyl compounds ; Conformational analysis in solution ; Dynamic NMR ; Force field calculations ; Activation barriers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tripod metal entities tripodM are sterically congested systems. The conformations adopted by compounds CH3C(CH2PPh2)3-n[CH2P(oTol)2]nMo(CO)3 (n = 1: 1, n = 2: 2, n = 3: 3) will thus be largely determined by the repulsive forces acting in these molecules. The steric demand of the o-tolyl groups impedes their free rotation and enantiomerization processes referring to the compounds as a whole are sufficiently slow to permit their analysis by NMR techniques. Through a combination of line-shape analysis, EXSY methods, and coalescence experiments, the ΔG
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    Sulfonamide-Functionalized Gadolinium DTPA Complexes as Possible Contrast Agents for MRI: A Relaxometric Investigation (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 625-630 
    Details
    ISSN: 1434-1948
    Keywords: NMRD ; MRI ; Contrast agents ; Carbonic anhydrase ; Sulfonamides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel Gd-DTPA derivative with a built-in sulfonamide (SA) was synthesized as a contrast agent for MRI. The complex was designed to selectively target the enzyme carbonic anhydrase. It is shown that the longitudinal relaxation rates of aqueous solutions of Gd-DTPA-SA in the presence of carbonic anhydrase increase significantly. The binding constant is determined to be 15,000 ± 5,000 M-1. This value ensures substantial formation of the carbonic anhydrase adduct at imaging concentrations of Gd-DTPA-SA. The complex interacts with erythrocytes, presumably due to a high affinity for the carbonic anhydrase present on the outer surface of the latter. This takes place even though the enzyme has a low abundance and is easily saturated by small amounts of Gd-DTPA-SA. The interaction of Gd-DTPA-SA with serum proteins is negligibly small. Therefore, the complex could potentially be tested as a selective contrast agent for compartments outside the blood pool.
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    Selective and Environmentally Benign Aerobic Catalytic Oxidation of Alcohols by a Molybdenum-Copper System (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 655-658 
    Details
    ISSN: 1434-1948
    Keywords: Molybdenum ; Copper ; Oxidation ; Alcohols ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of activated primary and secondary alcohols to the corresponding aldehydes and ketones can be carried out with molecular oxygen, in the presence of the bimetallic molybdenum-copper system MoO2(acac)2-Cu(NO3)2 as catalyst.
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    Pyrazolato Metal Complexes: Synthesis, Characterization and X-ray Crystal Structures of Polynuclear Organometallic Re-Mn Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 181-187 
    Details
    ISSN: 1434-1948
    Keywords: Pyrazolato ligands ; Rhenium ; Manganese ; Crystal structure ; Heterometallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By reacting [Re(CO)3(Hpz)2(pz)] (Hpz = pyrazole) with [Mn(CO)5Br] in toluene in the presence of Et3N, the dinuclear complex [(CO)3Re(pz)3Mn(CO)3](Et3NH) (1) was obtained. The reaction of 1 with molecular oxygen affords the tetranuclear compound [(CO)3Re(pz)3Mn(O)3Mn(pz)3Re(CO)3](Et3NH)2 (3) or the trinuclear compound [(CO)3Re(pz)3Mn(pz)3Re(CO)3](Et3NH)2 (5) depending on the experimental conditions. Complexes 1, 3 and 5 were characterized in the solid state by single crystal X-ray diffraction analysis and were showed to contain Re···Mn interactions linked by and tris-μ2-pyrazolato bridges. In 5, a short [2.397(4) Å] tris(μ2-oxo)bridged MnIV-MnIV contact is found, leading to strong antiferromagnetic coupling of the d3 ions. The homometallic species [(CO)3Mn(pz)3Mn(CO)3](Et3NH) (2) was also prepared and found to be isostructural with 1.
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    Controlled Thiolate Coordination and Redox Chemistry: Synthesis, Structure, Axial-Binding, and Electrochemistry of Dinickel(II) Dithiolate Macrocyclic Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 169-179 
    Details
    ISSN: 1434-1948
    Keywords: Macrocycles ; Nickel ; Redox chemistry ; Schiff bases ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single crystal X-ray analysis of [Ni2L1](ClO4)2· MeCN · 1/4 H2O, 1a [formed directly from a mixture of nickel(II) template ions, 2,6-diformyl-4-methyl-thiophenolate, and 1,4-diaminobutane] reveals that the nickel(II) ions are in square-planar N2S2 environments and that the four “bowed” dinickel macrocycles in the asymmetric unit pack around a single central perchlorate template ion encapsulating it to form “star” clusters of stoichiometry {[Ni2L1]4(ClO4)}7+. These “stars” stack together, via π-π-stacking interactions, to form two-dimensional sheets, which are separated from one another by layers of the remaining perchlorate anions and solvent molecules. Reduction, by NaBH4, of the four imine bonds in [Ni2L2](ClO4)22a (analogous to 1a but formed from 1,3-diaminopropane not 1,4-diaminobutane) or [Ni2L2](CF3SO3)22b to amine bonds produces the corresponding tetra-amine complex, [Ni2L3](ClO4)23. These complexes are shown to contain diamagnetic nickel(II) ions by a combination of magnetic, NMR and UV/Vis spectroscopic results. The 1H NMR spectra of 1-3 run in [D3]MeNO2 and in [D3]MeCN are consistent with increasing axial binding ability in the order: 3 〈 2 〈 1. Thiocyanate ion binding studies reveal that 1 and 2 are able to coordinate two thiocyanate ions, forming [Ni2L1(NCS)2] 4 and [Ni2L2(NCS)2] 5 respectively, whereas 3 does not. Single crystal X-ray analyses of complexes 4· 2 MeCN and 5· MeCN show that adjacent square-planar and octahedral nickel(II) ions result. Two one-electron oxidations and two one-electron reductions are a feature of the electrochemistry of 1-3 in MeCN: curiously, the potentials for the oxidation processes are almost invariant whereas those for the reduction processes vary as anticipated. EPR spectroscopy shows that the first one-electron reduction process and the first one-electron oxidation process are metal centred. Spectroelectrochemical studies and redox titrations indicate that a purplish-coloured complex is produced by one-electron oxidation of 2 (λ = 870 nm, ε = 1320 L mol cm-1). The synthesis of a phenolate analogue, [Ni2L′(MeCN)4](ClO4)2 (6), of the thiophenolate complex 2a is also detailed. Complex 6 undergoes two one-electron oxidations in MeCN, but, in contrast to the thiophenolate complexes 1-3, these occur at much higher potentials. Only a single one-electron reduction process is observed and this occurs at a more negative potential than for any of 1-3.
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    Trinuclear Palladium(II) Complexes with 2-Hydroxy-4-methoxyacetophenone N4-Dimethylthiosemicarbazone: Synthesis, Spectral Studies and Crystal Structure of a Tripalladium Complex (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 727-734 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; S ligands ; One-dimensional extended networks ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and spectral characterization of a new triangular, trinuclear palladium(II) complex with the dianion of 2-hydroxy-4-methoxyacetophenone N4-dimethylthiosemicarbazone, 4MeOAp4Me22- is reported. The X-ray crystal structure determination of [Pd(4MeOAp4Me2)]3·DMSO shows it to contain a chair-type hexagon of alternating Pd and S atoms which form a molecular bowl. The crystal structure of H24MeOAp4Me2 shows that it is the E isomer with respect to the imine bond of the thiosemicarbazone moiety.
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    Adducts of o-Silaborane With Water and Methanol (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 735-739 
    Details
    ISSN: 1434-1948
    Keywords: Silaboranes ; Cluster compounds ; Siloxanes ; Silicon ; Boranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of alkoxide adducts of o-silaborane [(TMPDAH)2][(Me2Si2B10H10)2O] (3) and [TMPDAH][(Me2Si2B10H10)OMe] (4) are presented (TMPDA = tetramethylpropylenediamine). For both silaborate clusters 3 and 4 the results of the NMR spectroscopic investigations together with the X-ray single crystal structure determinations are discussed. The geometries of ab initio calculations (HF and B3LYP methods) on the hydroxide adduct [Si2B10H12(OH)]- are compared with the structures of 3 and 4. The dynamic behaviour of the adducts 3 and 4 in solution is discussed with respect to the calculated energy profile for the rotation of the HSi(OH) group.
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    Bis(terpyridyl)-Ruthenium(II) Units Attached to Polyazacycloalkanes as Sensing Fluorescent Receptors For Transition Metal Ions (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 741-748 
    Details
    ISSN: 1434-1948
    Keywords: Terpyridine ; Copper sensing ; Cyclam ; Fluorescence ; Solution studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic strategy has been devised for the preparation of new compounds in which terpyridyl fragments are linked to 1,4,8,11-tetraazacyclotetradecane (cyclam). Reaction of excess cyclam with 4′-[(4-bromomethyl)phenyl]-2,2′:2″,6′-terpyridine afforded the ligand 1-[4′-p-tolyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L1) in which the tetraaza macrocycle was covalently attached to one benzyl-terpyridyl fragment. Under similar conditions reaction of cyclam with excess 4′-[(4-bromomethyl)phenyl]-2,2′:2″,6′-terpyridine gave the tetra substituted cyclam derivative 1,4,8,11-[4′-p-tolyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L2). The multidentate ligand L2 was crystallographically characterised by single-crystal X-ray diffraction techniques. Reaction of L1 with [Ru(mtpy)Cl3] gave the heteroleptic ruthenium(II) complex [Ru(L1)(mtpy)][PF6]2 (mtpy = 4′-methyl-2,2′:6′2″-terpyridine). The fluorescent intensity of the metallo-receptor [Ru(L1)(mtpy)][PF6]2 was quenched selectively in the presence of copper(II) in an aqueous environment. To gain insight into the nature of this interaction, potentiometric titrations on [Ru(L1)(mtpy)]2+ in the presence of Cu2+ were carried out. The quenching of the emission intensity was associated with the presence of the copper {Cu[Ru(L1)(mtpy)]}4+ complex in solution. The receptor 1-[4′-methyl-(2,2′:6′,2″-terpyridyl)]-1,4,8,11-tetraazacyclotetradecane (L3), in which the cyclam fragment is separated from the terpyriyl by a methylene group, has also been synthesised by reaction of 4′-bromomethyl-2,2′:2″,6′-terpyridine and cyclam. With L3 as starting material, the ruthenium complex [Ru(L3)(mtpy)]2+ was prepared in order to evaluate the effect that the nature of the spacer has on the quenching of the fluorescence upon addition of Cu2+.
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    Non-Luminescent 1,2-Diiminetricarbonylrhenium(I) Chloride Complexes - Synthesis, Electrochemical and Spectroscopic Properties of Re(DIAN)(CO)3Cl with DIAN = p-Substituted Bis(arylimino)acenaphthene (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 749-751 
    Details
    ISSN: 1434-1948
    Keywords: Rhenium ; Diimine ligands ; Charge transfer ; Solvatochromism ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Re(1,2-diimine)(CO)3Cl compounds containing the p-substituted bis(arylimino)acenaphthene derivatives DIAN-R with R = H, Me, OMe, Br, and Cl were prepared and characterized. The diimine ligands of this series provide unoccupied orbitals at rather low energies and display a pronounced π-accepting strength. This feature determines the electrochemical and spectroscopic properties of the Re(DIAN-R)(CO)3Cl complexes. All compounds show rhenium(I) to π*(diimine) metal-to-ligand charge transfer (MLCT) absorptions in the visible spectral region. The maxima of these CT bands systematically shift upon modification of the substituents R and are sensitive to variations of the solvent polarity (negative solvatochromism). Re(DIAN-R)(CO)3Cl complexes are non-luminescent both in fluid solution at 298 K and in solvent glass at 77 K.
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    Rhodium and Iridium β-Diiminate Complexes - Olefin Hydrogenation Step by Step (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 753-769 
    Details
    ISSN: 1434-1948
    Keywords: Hydrogenation ; Isomerization ; Rhodium ; Iridium ; Hydrides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bulky β-diiminate ligands [(2,6-C6H3X2)NC(Me)CHC(Me)N(2,6-C6H3X2)]- (X = Me, LMe; X = Cl, LCl) have been found to be effective in stabilizing low coordination numbers (CN) in Rh and Ir complexes. The 14- complex LMeRh(COE) (COE = cyclooctene) has a three-coordinate T-shaped Rh environment and is nonagostic. Coordinative unsaturation is avoided by incorporation of a small ligand (e.g. N2, MeCN, olefins), by the intramolecular coordination of a chlorine atom in LClRh(COE), or by an agostic interaction in LMeRh(norbornene). In solution at room temperature, LMeRh(COE) undergoes rapid isomerization according to the allyl hydride mechanism; the corresponding 2,3-dimethylbutene complex actually prefers the allyl hydride structure. Rhodium(I) complexes of LMe and LCl catalyze olefin hydrogenation; hydrogenation of 2,3-dimethylbutene has been shown to be preceded by isomerization. The shielding properties of the bulky β-diiminate ligands allow direct observation of a number of reactive intermediates or their iridium analogues, including an olefin-dihydrogen complex (with Rh) and an olefin dihydride (with Ir). These observations, together with calculations on simple model systems, provide us with snapshots of a plausible hydrogenation cycle. Remarkably, hydrogenation according to this cycle appears to follow a 14-e/16-e path, in contrast to the more usual 16-e/18-e paths.
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    Cooperative Binding of Nitrile Moieties Within a Bimetallic Pocket: Enforcing Side-On π-Interaction With a High-Spin Nickel(II) Site (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 771-781 
    Details
    ISSN: 1434-1948
    Keywords: Cooperative effects ; Coordination modes ; Nickel ; Bimetallic complexes ; π interactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different cooperative binding modes of nitriles within the bimetallic pocket of a pyrazolate-based compartmental dinickel(II) site have been studied. The H3O2-bridged dinuclear complex 1 reacts with cyanamide to yield 4, in which a secondary hydrogencyanamido(1-) bridge spans the two metal centers at an unusually short metal-metal distance imposed by the primary ligand matrix. In 5, a single 2-cyanoguanidine (cnge) molecule is N-bound to one nickel(II) ion through its nitrile part and is coordinated to the adjacent metal site through an amido nitrogen. The characteristics of the coordination spheres of the metal centers suggest an additional side-on π-bonding interaction of the nitrile moiety with the second high-spin nickel(II) ion. This unusual interaction is corroborated by comparing the IR bands for the ν(C≡N) stretching vibration of 5 with those of complex 6, which has two end-on bound cnge molecules, and those of the related mononuclear complex 7, which lacks a second nickel(II) ion. The nature of the π-bonding interaction in 5 is further analyzed by DFT calculations on relevant model systems. Even though the π-bonding is found to be very weak, it does include some backbonding from occupied 3d MOs at the second high-spin nickel(II) ion to the π* MOs of the nitrile. Such an unconventional π-interaction is suggested to be enforced by the constrained fixation of the nitrile unit within the highly organized coordination pocket of the bimetallic framework. In contrast, the bifunctional 2-hydroxybenzonitrile is accommodated by the distinct binding of the nitrile and phenolate functions to the different metal centers in 8, which confirms that the simultaneous binding of both an OR-function and an end-on bound nitrile is indeed feasible within the active site pocket. Such a situation is reminiscent of the bimetallic effect that has been assumed to enable the cooperative hydration of nitriles at the dinickel(II) site of 1. Complexes 4·(ClO4)2, 5·(ClO4)2, 6·(ClO4)3, 7·(ClO4)(BPh4), and 8·(ClO4)2 have been characterized structurally by X-ray crystallography.
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    Reductive Degradation of Tetracobalt Cluster Complexes with a Facial C8H8 Ligand - Synthesis of [Co3(CO)3(μ3-CO)3(μ3-C8H8)]- and [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)] (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 783-788 
    Details
    ISSN: 1434-1948
    Keywords: Carbocycles ; Clusters ; Cobalt ; Electrochemistry ; Facial ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical reduction of the cluster complexes [Co4(CO)3(μ3-CO)3(μ3-C8H8)L2] 3 (L2 = C8H8), 4 (L = CO), 5 (L2 = C6H8) and 6 (L2 = 6,6-Ph2C6H4) gives the trinuclear anion [Co3(CO)3(μ2-CO)3(μ3-C8H8)]- (7) in high yield. It is proposed that formation of 7 occurs via degradation of the radical anions [3]- - [6]-, which can be generated reversibly via cyclic voltammetry. The anion 7 is stabilised by the facial C8H8 ligand and does not degrade further. Reaction of 7 with [(C5Me5)Ru(NCMe)3][BF4] results in the formation of [Ru(C5Me5)Co3(CO)3(μ3-CO)3(μ3-C8H8)] (8). The crystal structures of [NEt4]+-7, [(C5H5)2Co]+-7, and 8 were determined. In 7 and 8, the cyclooctatetraene ligand is coordinated to the Co3 face of the cluster in the facial mode.
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    Chiral Dilithiomethane Derivatives: Structure Determination and Application in Stereoselective Reactions (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 789-799 
    Details
    ISSN: 1434-1948
    Keywords: Asymmetric synthesis ; Chirality ; Computer chemistry ; Lithium ; Dilithiomethane ; Sulfoximines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and X-ray analysis of chiral dilithiomethane analogues derived from sulfoximines are presented. The structures of the sulfoximine-stabilised mono- and dilithio salts have been compared and allow a rationalization of the second lithiation. Organophosphorus-based dilithiomethane derivatives are also structurally described. The gas-phase structures of N,S,S-trimethylsulfoximine 19 and of its mono- and dilithiated isomers 20-21 were calculated by ab initio methods employing different levels of theory. For an application in asymmetric synthesis, the dilithiation of (N-methyl)-S-ethyl-S-phenylsulfoximine (11) afforded a chiral dinucleophile that undergoes highly regio- and stereoselective alkylation reactions with electrophiles. The transmetallation of a chiral dilithiomethane reagent such as 14 with ClTi(OiPr)3 followed by addition of an aldehyde, constitutes a simple one-pot process for the formation of (E)-alkenylsulfoximines with excellent diastereoselectivity.
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    Microporous Titanosilicates and other Novel Mixed Octahedral-Tetrahedral Framework Oxides (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 801-818 
    Details
    ISSN: 1434-1948
    Keywords: Zeolites ; Microporous zeolites ; Titanosilicates ; Transition metal ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.
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    Temperature-Dependent Photophysical, Photochemical and Redox Properties of Novel Complexes (CO)2CpRu-Ru(Ln)-RuCp(CO)2 and (CO)2CpRu-Ru(Ln)-SnPh3 [Ln = (CO)2(N,N′-diisopropyl-1,4-diaza-1,3-butadiene)] (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 847-855 
    Details
    ISSN: 1434-1948
    Keywords: Photochemistry ; Electrochemistry ; Ruthenium compounds ; α-Diimine complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photophysical, photochemical and redox properties of the title complexes were investigated. Resonance Raman measurements revealed the lowest-energy electronic transition to possess σ→π* character. At low temperatures, long-lived near-IR emission was observed. Irradiation in solution results in homolytic splitting of a Ru-Ru bond as the primary step, followed by secondary reactions of the radical fragments depending on the experimental conditions. (Spectro)electrochemical investigations of the title species proved that the axial [RuCp(CO)2] groups exert a stabilising influence on the corresponding radical cations, while destabilising the corresponding radical anions, compared to the redox behaviour of other ruthenium complexes of this type.
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    How to Find Correlations Between Molecular Shape and Packing in a Molecular Crystal: Application of a Novel Strategy to Recognize n-Point Polyhedra in Three-Dimensional Space (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 857-877 
    Details
    ISSN: 1434-1948
    Keywords: Crystal packing ; Neural networks ; Pattern recognition ; Organometallic compounds ; Close packing ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of hundreds of thousands of molecular compounds have now been determined with the quantitative information being stored in large databases. Chemists are generally interested in that specific part of this information which refers to individual molecules. The packing of molecules and their spatial relation to each other is not the focus of interest, even though the material properties of a molecular crystal are determined by both the packing arrangement of the molecules and their specific properties. The lack of interest in packing has at least one obvious reason. It is difficult for the non-expert to find the appropriate packing categories when looking at a principally infinite lattice. A tool performing this search for individual categories of packing in an automatic manner would therefore be of general importance. The development and application of such a tool is described in this paper. Novel strategies to extract a set of n points forming a specific n-point polyhedron from a set of p points (p 〉 n) is at its basis. Neural networks and second moment analysis are used as the methods of pattern recognition. In order to correlate packing and shape, second moment analysis of molecular shape is also used. This novel method is applied to three classes of organometallic compounds to determine whether the crystals formed by these compounds belong to any of the three classes fcc, bcc, or hcp in an idealized sense. A strong correlation is found between molecular shape and the membership or nonmembership of these classes. The corresponding program, including appropriate tools for visual representation, is available from the authors.
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    In situ NMR Detection of Dihydrides in the Systems [RhH(SnCl3)5]3-/Tertiary Phosphanes/Parahydrogen (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 889-894 
    Details
    ISSN: 1434-1948
    Keywords: Rhodium hydride complexes ; Parahydrogen ; Tin ligands ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidative addition of dihydrogen to the [RhH(SnCl3)5]3-/PR3 system (PR3 = PPh3, PEtPh2, PEt3) leads to the formation of previously unknown dihydride complexes, the 1H-NMR spectra of which have been studied by means of the ParaHydrogen Induced Polarization (PHIP) method. The composition of the resulting complexes crucially depends on the type of the added phosphane. With PEt3 as the phosphane and acetonitrile as the solvent, a complex with a SnCl2L ligand (L = CD3CN) can be detected. All systems examined catalyze the hydrogenation of phenylacetylene. During these reactions, both the 1H-NMR resonances of the dihydride complexes and those of styrene, the hydrogenation product of phenylacetylene, can be detected simultaneously. In the case of SnBr3 ligands, hydrogen addition in the presence of phosphanes leads to similar dihydride complexes, which were also identified via 1H-NMR spectroscopy. Furthermore, a mixed complex of the structure [Rh(SnBr3)nBr6-n]3- has been isolated.
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    Synthesis of the Germanium(I) Compounds [Ge2Hal4]2- and Their Reductive Condensation to Octahedral [Ge6]2- Clusters in an Organometallic Environment (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 879-887 
    Details
    ISSN: 1434-1948
    Keywords: Germanium(I) ; Tetrahalgenodigermanate(2-) ; Octahedral [Ge6]2- clusters ; Organometallic derivatives ; Carbonyl complexes ; Chromium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GeI2 reacts with [M2(CO)10]2- (M = Cr, W) leading to reductive coupling of two GeI2 units to produce the [Ge2I4]2- ligands of [{(OC)5M}I2Ge-GeI2{M(CO)5}]2- (1a and 2a). The [Ph4P] salts of these anions have been characterised by X-ray structure analyses as have the [Ph4P] salts of [{(OC)5M}Cl2Ge-GeCl2{M(CO)5}]2- (1b and 2b) obtained from the iodo derivatives 1a and 2a by halide metathesis with [Ph4P]Cl. Treatment of GeI2 with [W2(CO)10]2- in the presence of 2,2′-bipyridine leads to [{(OC)5W}I2Ge-Ge(bipy){W(CO)5}] (3). The digermanium ligands in 1-3 contain germanium in the unconventional formal oxidation state +I. Reductive condensation of [{(OC)5Cr}I2Ge-GeI2{Cr(CO)5}]2- (1a) by addition of [Cr2(CO)10]2- leads to the octahedral cluster [{(OC)5Cr}6Ge6]2- (4) in a yield of 40%. The sequence of reactions as reported describes the first systematic approach to the synthesis of [E6]2- clusters.
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    Preparation and Properties of Carbonyliron Complexes of 1-Aza-4-oxa-1,3-butadiene (α-Imino Ketone) - X-ray Crystal Structures of Fe(CO)3[MeN=C(Ph)C(Ph)=O] and Fe2(CO)4[tBuN=C(H)(Me)C(O)(O)C(Me)C(H)=NtBu] (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 907-919 
    Details
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; α-Imino ketones ; CO complexes ; Iron complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of Fe2(CO)9 at room temperature in THF or toluene with the α-imino ketones R1N=C(R2)-C(R3)=O (L) (R1 = alkyl, R2 = H, Me, Ph, R3 = Me, Ph) (a-k), initially results in the formation of the mononuclear chelate Fe(CO)3(α-imino ketone) complexes 6 which can be isolated in moderate (6h) to high (6e-g) yield. Under these reaction conditions, complexes 6 subsequently react with [Fe(CO)4] fragments or dimerise, to form the dinuclear complexes Fe2(CO)6(α-imino ketone) (7a-j) or Fe2(CO)4(L-L) (8a,b,k), respectively. The complexes 8 contain two α-imino ketone ligands C-C coupled at the ketone carbon atoms. Complexes 8a,b react with CO at elevated temperatures to quantitatively yield Fe(CO)3(α-imino ketone) (6a,b). This reaction can be reversed photochemically. Irradiation of a solution of 6a,b in the low-energy band results in the reformation of 8a,b in almost quantitative yield. The extremely air-sensitive complexes 6 and the dinuclear complexes 7 and 8 have been characterised spectroscopically (IR, UV/Vis, 1H and 13C NMR) and by elemental analysis. The solid state structures of complexes 6g and 8a have been determined by single-crystal X-ray diffraction. The molecular structure of 6g confirms the flat σ-O,σ-N chelate coordination of the α-imino ketone. The structure of 8a consists of two metal-metal-bonded Fe(CO)2 units, bridged by a formally 10e-donating dianionic C-C coupled (tBu-ADO) ligand. A mechanism for the formation of complexes 8 is discussed.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99351_s.pdf or from the author.
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    Cationic ansa-(η5-Cyclopentadienyl)(η6-arene) Complexes of Titanium (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 929-932 
    Details
    ISSN: 1434-1948
    Keywords: Titanium ; Cyclopentadienes ; Arene complexes ; Cations ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The half-sandwich titanium trimethyl complex (η5-C5H4CMe2Ar)TiMe3 (Ar = 3,5-Me2C6H3) reacts with the Lewis acid B(C6F5)3 to give the ionic TiIV ansa-cyclopentadienyl-arene complex [(η5,η6-C5H4CMe2Ar)TiMe2][MeB(C6F5)3]. In bromobenzene solvent, addition of more B(C6F5)3 leads to C6F5/Me exchange and, subsequently, to formation of an unusual dimeric TiIII dicationic species, {[(η5,η6-C5H4CMe2Ar)Ti(μ-Br)]2}[B(C6F5)4]2, which was structurally characterized. Its formation involves reduction of the transition-metal center, solvent C-Br cleavage and perfluoroaryl-group scrambling.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99383_s.pdf or from the author.
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    Reaction of the Tetrachalcogenides [ME4(dppe)] (M = Pd, E = S; M = Pt, E = S, Se) with Activated Alkynes to Form Dithiolenes and Diselenolenes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 933-938 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; Platinum ; Dithiolenes ; Diselenolenes ; Sulfur ; Selenium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrachalcogenides [ME4(dppe)] (M = Pd, E = S; M = Pt, E = S, Se) react with the activated alkynes RO2CC≡CCO2R (R = Me, Et) to form the dithiolenes and diselenolenes [M{E2C2(CO2R)2}(dppe)]; the structures of the compounds with E = S, R = Et have been determined by X-ray crystallography; [PdS4(dppe)] also reacts with the carbene complex [W(CO)5{C(OEt)C≡CPh}] to yield the bimetallic dithiolene [Pd{S2C2[C(OEt)W(CO)5]Ph}(dppe)].
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    On the Hydrolysis of tBu2Ge(OEt)2: Supramolecular Self Assembly in the Solid State of 2 tBu2Ge(OH)2, (tBu2GeOH)2O, and H2O (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 939-941 
    Details
    ISSN: 1434-1948
    Keywords: Germanium ; Germanol ; Hydrogen bonds ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrolysis of tBu2Ge(OEt)2 is described. Depending on the amount of water used either tBu2Ge(OH)2 (1) or a mixture of the latter and (tBu2GeOH)2O (2) were obtained. A cocrystallate consisting of 2tBu2Ge(OH)2, (tBu2GeOH)2O and water was the subject of a single crystal X-ray diffraction study. In the solid state the individual molecules are connected by hydrogen bonds giving rise to the formation of a polymeric double chain ribbon.
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    New Di- and Trinuclear Complexes with Pyrazolato Bridges. Crystal Structures of [{(C6F5)2Pd(μ-pz)(μ-Cl)}2Pd]2- and [(C6F5)2Pd(μ-pz)2Pd(η3-C4H7)] (pz = pyrazolate) (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 943-949 
    Details
    ISSN: 1434-1948
    Keywords: Pyrazolate complexes ; Palladium ; Platinum ; N ligands ; Bridging ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trinuclear complexes containing pyrazolate bridging ligands of the type [NBu4]2[{(C6F5)2 M(μ-pz)(μ-X)}2M′] (M, M′= Pd or Pt; X = Cl, OH, or pz) (Hpz = pyrazole) have been prepared using [NBu4][M(C6F5)2(acac)] (acac = acetylacetonate) or [NBu4]2[M2(C6F5)4(μ-OH)2] and [M′Cl2(Hpz)2] or [M′(Hpz)4]2+ as starting materials. Asymmetric homo- and heterobimetallic complexes of the types [NBu4][R2M(μ-pz)2Pd(η3-allyl)] and [R2M(μ-pz)2M′L2] (allyl = C3H5 or C4H7; L2 = 2 PEt3 or bipy; R = C6F5 or C6Cl5; M, M′ = Pd or Pt) have been obtained starting from [NBu4][MR2(pzHpz)] and [Pd(η3-allyl)(acac)] or [M′L2Cl2], respectively. The identity of the new complexes has been established by NMR (1H, 19F and 31P) spectroscopy. The crystal structure of [{(C6F5)2Pd(μ-pz)(μ-Cl)}2Pd]2- has an inversion centre, with a bent appearance of the Pd3(μ-pz)2(μ-Cl)2 moiety. The crystal structure of [(C6F5)2Pd(μ-pz)2Pd(η3-C4H7)] has also been determined by single-crystal X-ray diffraction, where a boat conformation of the central “Pd2N4” six-membered rings is observed.
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    Inclusion of Copper(I) into a Novel Bipyridine-Containing Tetraphosphadiplatinacyclophane (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 959-969 
    Details
    ISSN: 1434-1948
    Keywords: Bipyridyldiphosphane ligands ; Macrocycles ; Metallacyclophanes ; Platinum ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5,5′-bis(hydroxyalkyl)-2,2′-bipyridines 4a-c (Scheme 1) were prepared either in one step (4b, 4c) or in four steps (4a) starting with 5,5′-dimethyl-2,2′-bipyridine in each case. Reaction of 4a-c with mesyl chloride afforded the bis(mesylates) [-C5H3N-(CH2)n-CH2-OSO2Me]2 5a-c [n = 1 (a), 2 (b), 3 (c)], which could easily be transformed into the diphosphanes 6a-c by reaction with LiPPh2. Treatment of 6c, 6b with Cl2Pt(NCPh)2 and (RC6H4)2Pt(COD) according to the high-dilution method resulted in the formation of the tetraphosphadiplatinacyclophanes [-C5H3N-(CH2)4-PPh2PtCl2PPh2-(CH2)4-C5H3N-]2 (7c) and [-C5H3N-(CH2)3-PPh2Pt(C6H4R)2PPh2-(CH2)3-C5H3N-]2 (8b, 9b) (8b: R = H, 9b: R = tBu), respectively (Scheme 2). The molecular structures of 8b and 9b were elucidated by X-ray structural analyses. The noncoordinated bipyridine moieties in 8b were employed to encapsulate copper(I) to give the host/guest complex 10b (Scheme 3), which was investigated by FAB-MS, NMR spectroscopy, and cyclovoltammetry. 10b exhibited a quasi-reversible oxidation at E1/2 = -0.31 V and an electrodeposition-redissolution redox system at E1/2 = -0.79 V, owing to the formation of copper at the surface of the working electrode.
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    Rational Design of Homo and Hetero Hexanuclear Coordination Compounds: Syntheses and Magnetic Properties of [Cu2IIM4II] (M = Cu, Ni) Species and the Crystal Structure of {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 · 2 H2O (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 951-957 
    Details
    ISSN: 1434-1948
    Keywords: Copper ; Nickel ; Amides ; Polynuclear complexes ; Magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New homo- and heterometallic hexanuclear complexes of formula {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}(ClO4)4 ·2 H2O [Cu6-tmen] {[Cu(pmdien)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu6-pmdien] and {[Ni(cyclam)]4[Cu2L]}(ClO4)4 · 4 H2O [Cu2Ni4-cyclam] [H8L = tetrakis(aminomethylene)methanetetrakis(oxamic acid), tmen = N,N,N′,N′-tetramethylethylenediamine, pmdien = N,N,N′,N′,N″-pentamethyldiethylenetriamine, and cyclam = 1,4,8,11-tetraazacyclotetradecane] have been synthesized. The crystal structure of [Cu6-tmen] has been determined by single-crystal X-ray diffraction. The structure consists of cationic {[Cu(tmen)(H2O)]2[Cu(tmen)]2[Cu2L](H2O)}4+ hexanuclear units. The hexanuclear cation is made up of two symmetry-related oxamato-bridged trinuclear units connected through the central carbon atom C(6) of the L8- ligand. Variable-temperature magnetic susceptibility measurements (1.8-300 K) have been performed for these series of complexes including the dinuclear precursors of formula Na4[Cu2L] · 10.5 H2O [Cu2-Na], (NMe4)4[Cu2L] · 4 H2O [Cu2-NMe4] and (PPh4)4[Cu2L] · 6 H2O [Cu2-PPh4]. The magnetic data have been interpreted. Evidence of a weak intramolecular ferromagnetic interaction between the two CuII ions in [Cu2L]4- has been observed. For the hexanuclear species, the interaction through the oxamato bridge was found to be equal to -6790, -2650, and -1643 yJ (-342, -133, and -82 cm-1) for [Cu6-tmen], [Cu6-pmdien], and [Cu2Ni4-cyclam], respectively. In these complexes, the weak intramolecular ferromagnetic coupling between the two CuII ions within the dinuclear synthon was masked by intermolecular interactions or local anisotropy.
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    Experimental Evidence for a Second Coordination Sphere Water Molecule in the Hydration Structure of YbDTPA - Insights for a Re-Assessment of the Relaxivity Data of GdDTPA (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 971-977 
    Details
    ISSN: 1434-1948
    Keywords: Lanthanides ; Ytterbium ; MRI contrast agents ; Solid-state structures ; Hydration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low temperature (-100 °C) X-ray structure of the complex K2[Yb(DTPA)(H2O)] has been determined. The metal ion is at the center of a tricapped trigonal prism and is nine-coordinate, binding to the three nitrogens and five oxygens of the ligand and one water molecule. From the structure obtained, three well-defined hydration shells can be observed consisting of: i) one coordinated water molecule; ii) several water molecules in the outer coordination sphere of the YbIII ion and iii) one water molecule surprisingly close to the metal center and hydrogen-bonded to proximate carboxylate groups. A variable-field and temperature NMRD study of the corresponding Gd complex has been performed and the data interpreted by taking into account the presence of second-sphere water molecule(s). The results of the analysis are in excellent agreement with the X-ray structural data.
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    Enantiomerically Pure Complexes of Manganese, Iron, and Zirconium with Pinene-Fused Boratabenzene Ligands - Structures ofexo-FeCp*(C13H17BNMe2) and exo,exo-ZrCl2(C13H17BNMe2)2 (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 979-986 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Transition metals ; Sandwich complexes ; Boratabenzene ; Pinene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of pinene-fused boratabenzene ligands [(1R,9R)6,10,10-trimethyl-4-boratatricyclo[7.1.1.02,7]undeca-2,4,6trienes] C13H17BX (with a: X = NMe2; b: X = OMe; c: X = Me) are described. The lithium salt Li(C13H17BNMe2) [Li(1a)] reacts with [Cp*Fe(NCMe)3]PF6 and with Mn(CO)3Br(py)2 to give diastereomeric mixtures FeCp*(C13H17BNMe2) (4a) and Mn(CO)3(C13H17BNMe2) (7). The mixture 4a undergoes solvolysis in methanol to produce methoxy compounds 4b, which in turn react with LiMe in Et2O to give methyl derivatives 4c. The lithium salts Li(C13H17BX) [Li(1a-c)] react with ZrCl4 in toluene or Et2O to give exo,exo-ZrCl2(C13H17BX)2 complexes (8a-c). The dimethyl derivative exo,exo-ZrMe2(C13H17BNMe2)2 (9) can also be prepared from 8a/LiMe in Et2O. NOE difference spectra have been analyzed to determine the configurations of the diastereomers and to establish a chemical shift criterion for assessing the configuration of the metal-ligand coordination. An independent confirmation of the product stereochemistries has been obtained by single-crystal X-ray structure determinations of exo-4a and 8a.
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    Standard Molar Enthalpies of Formation of Mg and Ca Alkoxides (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 987-991 
    Details
    ISSN: 1434-1948
    Keywords: Thermochemistry ; Alkaline-Earth Alkoxides ; Enthalpy of Formation ; Calcium ; Magnesium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enthalpies of formation of some alkaline-earth alkoxides were determined by reaction-solution calorimetry (ΔfHo[Mg(OMe)2] = -792.6±1.2 kJ/mol; ΔfHo[Mg(OEt)2] = -847.9±2.7 kJ/mol; ΔfHo[Ca(OMe)2] = -890.8±6.4 kJ/mol; ΔfHo[Ca(OEt)2] = -924.5±2.6 kJ/mol; ΔfHo[Ca(OBu)2] =-989.8±5.4 kJ/mol) and allowed us to extend a previously developed model for predicting the enthalpies of formation of Be, Sr and Ba alkoxides.
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    Protonation of [tpmRu(PPh3)2H]BF4 [tpm = Tris(pyrazolyl)methane] - Formation of Unusual Hydrogen-Bonded Species (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 993-1000 
    Details
    ISSN: 1434-1948
    Keywords: Ruthenium ; Dihydrogen complexes ; Dihydrogen bonding ; Hydride protonation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: in CD2Cl2 yielded, in a straightforward manner, the dicationic η2-dihydrogen complex [tpmRu(PPh3)2(H2)](BF4)2, which, as expected, is more acidic than its monocationic Tp [Tp = hydrotris(pyrazolyl)borate] analog [TpRu(PPh3)2(H2)]BF4 (pKa: 2.8 vs. 7.6). The complex [tpmRu(PPh3)2(H2)](BF4)2 is unstable towards H2 loss at ambient temperature. However, acidification of [tpmRu(PPh3)2H]BF4 with excess aqueous HBF4 or aqueous triflic acid in [D8]THF gave very interesting results. Variable-temperature 1H- and 31P-NMR studies revealed that the aqueous acid did not fully protonate the metal hydride to form the dihydrogen complex, but a hydrogen-bonded species was obtained. The feature of this species is that the strength of its Ru-H···H-(H2O)m interaction decreases with temperature; this phenomenon is unusual because other complexes containing dihydrogen bonds show enhanced M-H···H-X interaction as the temperature is lowered. Decrease of the dihydrogen-bond strength with temperature in the present case can be attributed to the decline of acidity that results from the formation of larger H+(H2O)n (n 〉 m) clusters at lower temperatures; steric hindrance of these large clusters also contribute to the weakening of the dihydrogen bonding interactions. At higher temperatures, facile H/H exchange occurs in Ru-H···H-(H2O)m via the intermediacy of a “hydrogen-bonded dihydrogen complex” Ru-(H2)···(H2O)m. To investigate the effect of the H+(H2O)m cluster size on the strength of the dihydrogen bonding in [tpmRu(PPh3)2H]+, molecular orbital calculations at the B3LYP level have been performed on model systems, [tpmRu(PH3)2H]+ + H+(H2O) and [tpmRu(PH3)2H]+ + H+(H2O)2. The results provide further support to the notion that the formation of larger H+(H2O)n clusters weakens the Ru-H····H(H2O)n dihydrogen bonding interaction.
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    Linkage Isomerization in PtII-9-Methyladenine Complexes (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1007-1013 
    Details
    ISSN: 1434-1948
    Keywords: Linkage isomerization ; NMR spectroscopy ; Nucleobases ; Platinum ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(9-methyladenine) complexes of cis-PtII(NH3)2 undergo slow linkage isomerization from the N7 to the N1 site in aqueous solution at elevated temperatures. The ratio of the isomeric complexes during the isomerization process indicates that whilst PtII prefers the N(7) site in the adenine moiety kinetically, it is the N(1) coordination mode which is thermodynamically more stable. The crystal structures of the isomers do not reveal any unusual features; the few apparently structurally significant differences in the bond angles in the N(1)-bound bis(complex) merely reflect the poor quality of the crystal and/or crystal packing effects rather than a direct result emanating from the coordination mode of the ligand.
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    Synthesis and Ring Opening of Methyl 2-Alkyl-3-(alkyl/aryl)-1-benzoylaziridine-2-carboxylates: Synthesis of Polysubstituted Amino Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1569-1576 
    Details
    ISSN: 1434-193X
    Keywords: Aziridines ; Oxazolines ; Ring expansion reactions ; Amino acids ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new method for the preparation of 2,2,3-trisubstituted methyl 1-benzoylaziridine-2-carboxylates is reported. These compounds have been obtained starting from α-alkyl β-amino acids by formation of the lithium dianion and reaction with iodine. The aziridines undergo ring expansion or ring opening, depending on the substituents of the aziridine ring and on the reaction conditions. Following these methods, both α-substituted α-hydroxy β-amino acids and α-substituted β-hydroxy α-amino acids have been synthesised.
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    The Effect of the Carbon Ligand on the Reaction of Organozinc Reagents in the Synthesis of Substituted 2,5-Dihydrofurans: A Rare Example of An Uncatalysed Allylic-Substitution Reaction Involving Alkyl Zinc Halides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1711-1718 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Zinc ; Palladium ; Catalysts ; Sulfur ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Organozinc halides derived from Grignard reagents behave differently in their reaction with ethyl (±±)-(2RS,3SR)-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate (3) according to the hybridisation of the carbon ligand. During the development of short multi-component reactions for the synthesis of diverse functionalized ethyl 2,5-dihydrofuran-3-carboxylates it was discovered that aryl and vinyl zinc halides undergo clean reaction with 3 in the presence of Pd(PPh3)4. In contrast, when alkyl zinc halides are reacted with 3 in the presence of Pd(PPh3)4, reductive desulfonation of 3 is observed. Remarkably, in the absence of a transition metal catalyst, the allylic substitution of 3 with alkyl zinc halides proceeds cleanly and in moderate to good yield.
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    A Simple Stereoselective Synthesis of Enantiopure 2-Substituted Pyrrolidines and Piperidines from Chiral (R)-Phenylglycinol-Derived Bicyclic 1,3-Oxazolidines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1719-1726 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Nitrogen heterocycles ; Heterocycles ; Pyrrolidines ; Piperidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Chiral, nonracemic 2-substituted pyrrolidines and piperidines were prepared in high ee and moderate to good chemical yields in three steps from (R)-phenylglycinol and γ- or δ-chloroketones. The key step of the synthesis was the stereoselective reductive ring-opening of chiral bicyclic 1,3-oxazolidines prepared by condensation of (R)-phenylglycinol and the corresponding ketones.
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    Stable Heterotopic Noncovalent Resorcin[4]arene Assemblies (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1727-1734 
    Details
    ISSN: 1434-193X
    Keywords: Self-assembly ; Vapor-pressure osmometry ; Resorcin[4]arenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Resorcin[4]arene tetracarboxylic acids 5,6 (A) and resorcin[4]arene tetrapyridines 2,3 (P) self-assemble in chloroform solution to form stable heterotopic AP dimers. Data from NMR titration and dilution experiments, as well as from vapor-pressure osmometry (VPO), indicate that the AP dimer is formed with an association constant greater than 107 M-1. Solid-solution extraction experiments are indicative of the formation of a 2:1 trimer (A2P), while self-associated homotopic species (A2 and A3) can be detected by NMR and VPO. Analysis of the heterotopic noncovalent assembly process over a range of compositions shows that these other species are much less stable than the AP heterodimer, which is the exclusive species at an A/P concentration ratio of 1:1 (〉 99.7% of the total at 10 mM).
    Additional Material: 6 Ill.
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    The LiClO4-Mediated Synthesis of β-(Dialkylamino) Sulfoxides and β-(Dialkylamino) Sulfones by Addition of α-Lithiated Salts of Sulfoxides and Sulfones to Aldehydes and (Trimethylsilyl)dialkylamines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1735-1739 
    Details
    ISSN: 1434-193X
    Keywords: Sulfoxides ; β-Amino sulfones ; Mannich type reaction ; Lithium perchlorate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The LiClO4-mediated one-pot reaction of aldehydes with (trimethylsilyl)dialkyl amines and the lithium salt of sulfoxides or sulfones, affords the corresponding β-(dialkylamino) sulfoxides and β-(dialkylamino) sulfones in high yields. The aminosulfoxidation reaction of aliphatic or aromatic aldehydes lacks diastereoselectivity, but the diastereomeric sulfoxides can be separated by HPLC or column chromatography for further use.
    Additional Material: 1 Ill.
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  • 289
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    Electronic Resource
    Hydrohalogenation Reaction of 1,2-Allenic Sulfoxides with AlX3 and H2O: Efficient Synthesis of 2-Haloallyl Sulfoxides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1939-1943 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur ; Halogens ; Hydrohalogenation ; Lewis acids ; Sulfoxides ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrohalogenation reaction of 1,2-allenic sulfoxides 1 afforded 2-haloallyl sulfoxides 2 with yields ranging from 56 to 89%. The influence of the ratio of AlCl3 and H2O on this reaction is discussed and the optimized ratio of allenic sulfoxides, AlCl3 and H2O is 1:0.55:1. For the hydroiodination reaction, a combination of excess NaI, AlCl3, and H2O was used. The reaction is probably mediated by the species formed from the reaction of AlX3 with H2O. Because of the steric hindrance of the substrates, the hydrohalogenation of 1-methyl-1-(methylsulfinyl)-1,2-propadiene (1e), (1-methyl-1,2-propadienylsulfinyl)benzene (1f), and (3-methyl-1,2-butadienylsulfinyl)benzene (1g) did not proceed under the same reaction conditions.
    Additional Material: 2 Ill.
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  • 290
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    Near-Infrared and Visible Luminescence from Terphenyl-Based Lanthanide(III) Complexes Bearing Amido and Sulfonamido Pendant Arms (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1923-1931 
    Details
    ISSN: 1434-193X
    Keywords: Lanthanides ; Polydentate ligands ; Luminescence spectroscopy ; Near-infrared luminescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of m-terphenyl-based ligands bearing three coordinating oxyacetate and two amido or two sulfonamido groups, (1a-b)H3 and (2)H3, respectively, have been synthesized and characterized. The structures of the corresponding neutral complexes have been studied using 1H-NMR spectroscopy and luminescence experiments. The photophysical properties of the (1a-b)Eu, (2)Eu, (1a)Tb, and (2)Tb complexes have been studied to determine the structure of the first coordination sphere in methanol. The first coordination sphere consists of eight donor atoms provided by the ligand (three chelating oxyacetate groups and two amide or sulfonamide oxygens), and one methanol molecule. The (1a)Dy and (1a)Sm complexes exhibited sensitized luminescence in the visible spectral region, but the luminescence intensity was very sensitive to quenching by C-H groups. The near-infrared emitting (1a)Ln and (2)Ln complexes exhibited sensitized luminescence at wavelengths (at 880, 1060, and 1330 nm for Nd3+, at 980 nm for Yb3+, and at 1550 nm for Er3+) of interest for applications in optical telecommunication devices. The luminescence lifetimes of these complexes in DMSO and [D6]DMSO are in the range of microseconds. The luminescent state of the NIR emitting lanthanide ions is very efficiently quenched by high frequency oscillators (such as C-H groups) in the solvent and the ligand.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99457_s.pdf or from the author.
    Additional Material: 8 Ill.
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  • 291
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    Electronic Resource
    The Conformational Behaviour of Non-Hydrolizable Lactose Analogues: The Thioglycoside, Carbaglycoside, and Carba-Iminoglycoside Cases (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1945-1952 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycosides ; Conformation analysis ; Molecular modeling ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The conformational behaviours of several nonhydrolizable lactose analogues, namely methyl α-thiolactoside (1), methyl β-carbalactoside (2) and methyl β-carbaiminolactoside (3) have been studied using a combination of NMR spectroscopy (J and NOE data) and molecular mechanics calculations. Analogies and differences with the natural compounds have been found.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99592_s.pdf or from the author.
    Additional Material: 3 Ill.
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  • 292
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    Synthesis of Benzotri(benzonorbornadienes) (BTBNDs): Rigid, Cup-Shaped Molecules with High Electron Density within the Cavity (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1965-1971 
    Details
    ISSN: 1434-193X
    Keywords: Cup-shaped PAHs ; Host-guest compounds ; Host-guest chemistry ; Cyclizations ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Cyclotrimerisation of benzo-polycyclic bromostannylalkenes 8a-d with Cu(NO3)2·3H2O in THF affords benzotri(benzonorbornadienes) 3a-d as a mixture of the syn and anti isomers. The ratio of syn to anti is close to the 1:3 statistical value in most cases (i.e. in cyclotrimers 3a,b,d), but highly in favour of the anti isomer in 3c, where steric hindrance by the methoxy groups plays an important role in the stereochemistry of the cyclotrimerisation. The substrates for the cyclotrimerisation, i.e. the bromostannyl alkenes 8a-d, were prepared from bromoalkenes 7a-d by treatment with base (LDA) and quenching with trimethyltin chloride. In turn, bromoalkenes 7a-d were prepared from alkenes 5a-d by radical bromination-elimination. The reaction conditions used were designed to minimise Wagner-Meerwein rearrangements that would lead to unwanted bromo isomers. The cup-shaped syn cyclotrimers 3a-d exhibit high electron density within the cavity as determined by AM1 semiempirical calculations of their electrostatic potential surfaces and are valuable substrates for supramolecular chemistry. As an example, it is shown that fullerene C60 is drawn into solution in acetonitrile by complexation with both the syn and anti trimer of benzonorbornadiene 3a.
    Additional Material: 1 Tab.
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  • 293
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    Thermochemistry of 7,7-Difluoro-2,7-toluenediyl (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1983-1986 
    Details
    ISSN: 1434-193X
    Keywords: Radicals ; Dioxygen trapping ; Radical reactions ; Singlet-triplet splitting ; Thermochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---From the oxygen and temperature dependence of the trapping rate of 7,7-difluorobenzocyclopropene (1) in the range 180-240 °C, the energy profile of the equilibrium 1 →←2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (ΔHof = +3.8 kcal·mol-1), as a result of which the heat of formation of the singlet state of the diradical 2 is estimated as 25.7 kcal·mol-1. Whereas the trapping experiments demonstrate unambiguously a triplet ground state for 2, only a lower limit for the singlet-triplet splitting (〉 6 kcal·mol-1) can be given.
    Additional Material: 4 Ill.
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  • 294
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    Synthesis of Biaryl Compounds by Vinylogous Michael Reactions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1977-1982 
    Details
    ISSN: 1434-193X
    Keywords: Biaryls ; Homogeneous catalysis ; Iron ; Addition reactions ; Quinones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Acceptor-substituted cycloalkenones 1 undergo an iron(III)-catalyzed vinylogous Michael reaction - a sequence of enone-dienol tautomerism, [4+2]-cycloaddition, and retro-aldol reaction - with quinone derivatives 3. A variety of products is obtained ranging from meta-terphenyl precursors 5 to dihydronaphthobenzofurans 7. Reaction of 1,2-naphthoquinone (3e) with vinylogous donors 1 yields cross-coupled products 12, which can be further converted into highly functionalized biaryl compounds 13 and 14.
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  • 295
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    Unusual C=C Bond Migration in 3-Ylidene-2,5-piperazinediones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1993-1999 
    Details
    ISSN: 1434-193X
    Keywords: Ketones ; Tautomerism ; Double bond migration ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Treatment of 3-alkylidene or 3-benzylidene-2,5-piperazinediones 6 with catalytic amounts of acid gives rise to the formation of isomers 7 by migration of the C=C bond into the alkyl substituent at position 6, or results in mixtures of racemic 7 and E isomers 8. The existence of tautomeric equilibria is discussed.
    Additional Material: 2 Tab.
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  • 296
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    Hydrolytic Reactions of the cis-Methyl Ester of 3′-Deoxy-3′-thiothymidine 3′,5′-Cyclic(phosphorothiolate) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1987-1991 
    Details
    ISSN: 1434-193X
    Keywords: Nucleotides ; Thiophosphates ; Hydrolyses ; Reaction mechanisms ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of the cis-methyl ester of 3′-deoxy-3′-thiothymidine 3′-S,5′-O-cyclic(phosphorothiolate) (1a) has been followed by HPLC and MS. At pH 〈 2 hydrolysis of the thiophosphate triester moiety is acid-catalyzed (first order), while between pH = 2 and 5 the reaction is pH-independent and at pH 〉 5 first order in hydroxide ion. The uncatalyzed and acid-catalyzed reactions yield two thiophosphate diesters, the 3′-S,5′-O-cyclic phosphorothiolate 2 and 3′-S-phosphorothiolate methyl ester 3, in a 9:1 and 1:3 molar ratio, respectively. The hydroxide ion catalyzed reaction gives the endocyclic P-O and P-S bond-cleavage products (3 and 4, respectively) in a 1:2 molar ratio. The pH-independent reaction is suggested to take place by attack of a water molecule on the carbon atom and concomitant C-O bond rupture, whereas the alkaline and acidic reactions involve attack of the nucleophile on the phosphorus atom and formation of a pseudorotating thiophosphorane intermediate. Under acidic conditions, cleavage of the N-glycosidic linkage competes with the phosphoester hydrolysis, corresponding to 20% of the hydrolysis products at pH 〈 1.
    Additional Material: 2 Tab.
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  • 297
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    Condensation of Glyoxal with Triethylenetetraamine; Isomerization and Cyclization (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 33-35 
    Details
    ISSN: 1434-193X
    Keywords: Glyoxal ; Triethylenetetraamine ; Diethyl Oxalate ; Cyclen ; Ring closure ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The condensation of triethylenetetraamine with glyoxal leads to the formation of four stereoisomers A, B, C, D. A is the thermodynamic product and D the kinetic one. These four compounds exhibit equilibrium and isomerization phenomena which are the key-feature of this cyclen synthesis.
    Additional Material: 1 Ill.
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  • 298
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    Stereodivergent Synthesis of Highly Substituted Tetrahydropyrans (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 73-82 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Oxa-conjugate addition ; Rearrangement ; Tetrahydropyrans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Intramolecular oxa-conjugate addition has been employed in a stereoselective synthesis of enantiopure polyalkyl-substituted tetrahydropyrans, which are frequently found as substructures in many natural products. The requisite cyclization precursors, 7-hydroxy-2-enimides 3 and 7-hydroxy-2-enoates 6 were easily accessible by silyloxy Cope rearrangements of the appropriate chiral syn-aldols. It was found that the stereoselectivity of the cyclization could be controlled by judicious choice of the carboxylic acid derivative, resulting in a kinetically controlled reaction for the imides and a thermodynamically controlled process for the esters. Mechanistic considerations that could account for the stereocontrol of the process are outlined.
    Additional Material: 3 Ill.
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  • 299
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    Syntheses and X-ray Crystal Structures of Functionalised 9,10-Bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 51-60 
    Details
    ISSN: 1434-193X
    Keywords: Dithioles ; Anthracenes ; Lithiation ; Electron donors ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of new derivatives of 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene has been achieved by two different routes. Deprotonation of 8 using LDA in THF at -78 °C, followed by in situ quenching of the lithiated intermediate 9 with N,N-dimethylformamide, N-methyl isothiocyanate and methyl chloroformate gave aldehyde, thioamide and methyl ester derivatives 10-12, respectively. Sulfur insertion into the lithiated species 9 followed by reaction of the transient thiolate anion with benzoyl chloride gave the thioester derivative 13 which served as a convenient shelf-stable precursor of other mono-functionalised derivatives of 8. Debenzoylation of 13 and trapping of the transient thiolate anion with iodomethane and 6-bromohexan-1-ol yielded 14 and 15, respectively. Reaction of cation salt 17 with the anion of anthrone 18 gave compound 20, the thiolate anion of which reacted with 6-bromohexan-1-ol to afford the alcohol derivative 21. Subsequent reactions gave alcohol derivative 25 of the title system. The unexpected product 29 was obtained from reaction of 28 with triethyl phosphite. The X-ray crystal structures of compounds 12, 14, 28, and 29 are reported. The molecules adopt a saddle-like conformation; the bis(1,3-dithiole)benzoquinone system is U-shaped through an ‘accumulating bend’ comprising the boat conformation of the central (quinonoid) ring, folding of both 1,3-dithiole rings along S···S vectors, and out-of-plane tilting of the exocyclic C=C bonds, all in the same (inward) direction.
    Additional Material: 3 Ill.
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  • 300
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    Flash Vacuum Pyrolysis and Photolysis of 3,3,5,5-Tetramethylpyrazolin-4-one - A Matrix Isolation Study (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 91-98 
    Details
    ISSN: 1434-193X
    Keywords: Cyclopropanone ; Allene oxide ; Matrix isolation ; Photochemistry ; Flash vacuum thermolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The flash vacuum pyrolysis of 3,3,5,5-tetramethylpyrazolin-4-one (4) with subsequent trapping of the products in argon at 10 K results in the formation of a complex product mixture with tetramethylcyclopropanone (5) as one of the minor constituents. The 193 nm photochemistry of matrix-isolated 4 is much cleaner, yielding cyclopropanone 5 and allene oxide 9 as the major products. The reaction of tetramethylallene 13 with oxygen atoms yields the same product mixture of 5 and 9 and thus provides an independent route to these species. The experimental IR spectra of 5 and 9 are in good agreement with the results from DFT calculations.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99377_s.pdf or from the author.
    Additional Material: 3 Ill.
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