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  • 1995-1999  (40,425)
  • 1870-1879  (7,124)
  • Chemistry  (47,548)
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  • 101
    Electronic Resource
    Electronic Resource
    An Easy Access to Bicyclic Peptides with an Octahydro[2H]pyrazino[1,2-a]pyrazine Skeleton (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1345-1356 
    Details
    ISSN: 1434-193X
    Keywords: Peptidomimetics ; Octahydro[2H]pyrazino[1,2-a]pyrazine ; Diastereoselectivity ; Tripeptides ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new route to octahydrospiro(cyclopropane-1,1′-[2H]-pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones 12-15 has been developed. Michael additions of primary amines onto methyl 2-Me or tert-butyl 2-tBu 2-chloro-2-cyclopropylideneacetates, followed by DCC- or EDC-induced coupling with Boc- or FmocGlyOH, deprotection and cyclization led to α-amino esters 4a-c and chlorohexahydrodiazepinediones 5a-c, or in the case of 2-tBu to the α-amino ester 7 exclusively. This reaction sequence with (S)-BocPheOH and (S)-BocTrpOH diastereoselectively gave (3′R,5′S)-9a,b and (2′S,6′R)-11a,b as the main products. Further peptide coupling, deprotection and cyclization with 4a-c yielded octahydrospiro(cyclopropane-1,1′-[2H]pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones (7′S,9a′S)-12a-d, (6a′S,11a′S)-12e, (7′S,9a′R)-13a-d and (6a′S,11a′R)-13e which were easily separated. The α-amino esters 9a,b yielded (4′S,9a′R)-14a (≡15a) and (4′S,9a′R)-14b (≡15b), (4′S,7′S,9a′R)-14c and (4′R*,7′S*,9a′S*)-15c. The formation of compounds with three stereogenic centers 14c and 15c was accompanied by partial racemization. The versatility of the reported reaction sequence is limited by the steric availability of the secondary amino group in the intermediates 4, 9 and 10, as well as in the Michael adducts formed from primary amines and 2-Me.
    Additional Material: 4 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    Variable Stereocontrol in Cycloadditions of 1,7,9-Decatrien-3-ones by Different Lewis Acidic Promoters - Application to a Short Synthesis of α-Eudesmol (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1385-1393 
    Details
    ISSN: 1434-193X
    Keywords: Intramolecular Diels-Alder reaction ; 1,7,9-Decatrien-3-ones ; α-Eudesmol ; Lewis acids ; Chelates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Trienones 1-3 were subjected to Lewis acid-promoted intramolecular Diels-Alder reactions. It was shown that with monocoordinating Lewis acids the endo selectivity of the cycloaddition was generally high. The preference for either of the two possible endo products cis-a and cis-b, however, was shown to be highly dependent on the nature of the Lewis acid, and on the substitution pattern of the trienone substrates. Lewis acids with two coordination sites furnished predominantly the exo product trans-b via seven-membered ring chelate intermediates. The chelate-controlled intramolecular Diels-Alder reaction was then utilised as the key step in a stereocontrolled synthesis of the sesquiterpene α-eudesmol. This reaction mode, performed on a model trienone, also paved the way for the synthesis of the pharmaceutically important natural product dihydromevinolin.
    Additional Material: 6 Tab.
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  • 103
    Electronic Resource
    Electronic Resource
    Vinyl- and Divinylcyclopentadienes by Rhodium-Catalyzed Condensation of Alkynes with Cross-Conjugated Amino Metallahexatrienes [= (1-Amino-1,3-butadien-2-yl)carbene Complexes] (M = Cr, W) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2545-2561 
    Details
    ISSN: 1434-193X
    Keywords: Carbene complexes ; Catalysis ; Metallahexatrienes ; Vinyl cyclopentadienes ; Transmetallation ; Rhodium ; Tungsten ; Chromium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report on the first example of a transition metal-catalyzed cyclization reaction of a Fischer carbene complex. It comprises the generation of vinyl- and divinyl cyclopentadienes under exceedingly mild conditions at 20 °C by condensation of (1-amino-1,3-butadien-2-yl)carbene complexes (= cross-conjugated metallahexatrienes) (CO)5M=C(OEt)C(=CHNR2)CR1=CHR23 (M = Cr, W) with alkynes R3C≡CH 4 (R3 = Ph, cyclohex-1-enyl, isopropenyl, methoxymethyl, 1-trimethylsiloxycyclohex-1-yl) in the presence of catalytic amounts of [(COD)RhCl]2. The starting compounds 3 are accessible in high yields by addition of enamines (E)-R2NCH=CHR22 to (1-alkynyl)carbene complexes (CO)5M=C(OEt)C≡CR11 (M = Cr, W; R1 = Ph, cyclohex-1-enyl).
    Additional Material: 2 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    Kinetic Resolution of Racemic Cyclic Sulfoxides Using Hydrolytic Enzymes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2573-2578 
    Details
    ISSN: 1434-193X
    Keywords: Enzymes ; Kinetic resolution ; Sulfoxides ; Chiral resolution ; Hydrolyses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selected racemic trans-2-alkoxycarbonyl-3,6-dihydro-2H-thiopyran S-oxides 2a-h have been subjected to enzyme-assisted hydrolysis under conditions of kinetic resolution to give the corresponding acids and recovered esters with moderate to high enantiomeric purities (up to 95%). The enantioselectivity of the reaction was found to be strongly dependent on the structures of the substrates used.
    Additional Material: 3 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    Approach Toward a Generic Treatment of Gram-Negative Infections: Synthesis of Haptens for Catalytic Antibody Mediated Cleavage of the Interglycosidic Bond in Lipid A (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2593-2600 
    Details
    ISSN: 1434-193X
    Keywords: Endotoxin ; Immunotherapy ; Catalytic antibodies ; Glycosidases ; Azasugars ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to develop a generic treatment for infections with Gram-negative bacteria, we developed a synthesis of 2-acylamino-deoxynojirimycin derivatives (17, 18, 19 and 20), which will be used as haptens for raising catalytic antibodies capable of hydrolyzing the interglycosidic bond in the lipid A moiety of endotoxins. A key intermediate in the preparation of compounds 17, 18, 19 and 20 is 3,4,6-tri-O-benzyl-2-[(benzyloxycarbonyl)amino]-2-deoxy-D-glucono-δ-lactam (6), which was prepared from known 3,4,6-tri-O-benzyl-2-[(benzyloxycarbonyl)amino]-2-deoxy-D-glucosamine (1) in four steps in 47% overall yield. Antibodies were generated against 2-[(6-aminohexanoyl)amino]-2-deoxy-D-glucono-δ-lactam (17) coupled to the carrier protein bovine serum albumin.
    Additional Material: 1 Ill.
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  • 106
    Electronic Resource
    Electronic Resource
    Synthesis of Isotopically Labelled L-Phenylalanine and L-Tyrosine (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2609-2621 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Isotopic labelling ; Ethyl benzoate ; Benzonitrile ; Sodium phenylpyruvate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route to stable-isotope-substituted L-phenylalanine is presented, which allows the introduction of 13C, 15N, and deuterium labels at any position or combination of positions. For labelling of the aromatic ring, a synthetic route to ethyl benzoate (or benzonitrile) has been developed, based on the electrocyclic ring-closure of a 1,6-disubstituted hexatriene system, with in situ aromatization by elimination of one (amino) substituent. Several important (highly isotopically enriched) synthons have been prepared, namely benzonitrile, benzaldehyde, ethyl benzoate, and ethyl diphenyloxyacetate. Labelled L-phenylalanines have been synthesized from both aromatic precursors by initial conversion into sodium phenylpyruvate and subsequent transformation of this intermediate into the L-α-amino acid by an enzymatic reductive amination reaction. In this manner, highly enriched phenylalanines are obtained on the 10-gram scale and with high enantiomeric purities (≥ 99% ee). The method has been validated by the synthesis of [1′-13C]-L-Phe and [2-D]-L-Phe. In addition, two methods are described for the introduction of isotopes into L-tyrosine starting from the isotopically enriched precursors benzonitrile and ethyl benzoate.
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  • 107
    Electronic Resource
    Electronic Resource
    Stereoselective Amination of 5-Substituted γ-Lactones and γ-Lactams - A Convenient Route for the Preparation of 5-Substituted (3S,5S)-3-Acetylaminotetrahydrofuran-2-ones and (3S,5S)-3-Acetylaminopyrrolidin-2-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1581-1584 
    Details
    ISSN: 1434-193X
    Keywords: Tetrahydrofuran-2-ones ; Pyrrolidin-2-ones ; Aminations ; Nitrosations ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Substituted (S)-tetrahydrofuran-2-ones (1a,b) and (S)-pyrrolidin-2-ones (1c,d) were transformed in three steps, by treatment with tert-butoxybis(dimethylamino)methane (Bredereck's reagent), followed by nitrosation and stereoselective catalytic hydrogenation, into the corresponding 5-substituted (3S,5S)-3-acetylaminotetrahydrofuran-2-ones (4a,b) and (3S,5S)-3-acetylaminopyrrolidin-2-ones (4c,d).
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  • 108
    Electronic Resource
    Electronic Resource
    The Synthesis of Novel Cyclic β-Amino Acids as Intermediates for the Preparation of Bicyclic β-Lactams (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2433-2441 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Lactams ; Schiff bases ; Nitrogen heterocycles ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several derivatives of homopipecolic acid are prepared by α-amino alkylation of malonic acid with cyclic imines 6 and 7. These are prepared on a large scale and with different substitution patterns. The β-amino acids 8 and 9 were formed in high yield and with remarkable diastereoselectivity if chiral imines are used as starting materials. The diastereoselectivity of the amino alkylation leading to homopipecolic acid analogues is compared to those of thiazolidineacetic acids by epimerisation experiments. A method for resolution of the obtained racemic β-amino acids by diastereomeric salt formation is described. The β-amino acids 9 and 15 were converted into their corresponding carbacepham analogues 14 and isopenam 16. The isopenam endo-16 was selectively epimerised by mild basic treatment of the N/S-acetal to give an exo-configured precursor of isopenicillin G.
    Additional Material: 2 Tab.
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  • 109
    Electronic Resource
    Electronic Resource
    Synthesis of Trifluoromethyl-Porphyrins and -Chlorins (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2471-2473 
    Details
    ISSN: 1434-193X
    Keywords: Trifluoromethylation ; Porphyrin ; Chlorophyll ; Fluorine ; Zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of zinc 5,15-bis(3,5-di-tert-butylphenyl)porphyrin with S-(trifluoromethyl)-3,7-dinitrobenzothiophene trifluoromethanesulfonate in tetrahydrofuran gave the 10-trifluoromethylated compound as the major product and 2-CF3- and 10,20-di-CF3-porphyrins as the minor products. The direct trifluoromethylation is effective for preparation of longer-wavelength absorbing meso-trifluoromethylated porphyrins and chlorins.
    Additional Material: 2 Ill.
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  • 110
    Electronic Resource
    Electronic Resource
    Molecular Recognition of Azobenzene Dicarboxylates by Acridine-Based Receptor Molecules; Crystal Structure of the Supramolecular Inclusion Complex of trans-3,3′-Azobenzene Dicarboxylate with a Cyclo-bis-intercaland Receptor (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2479-2484 
    Details
    ISSN: 1434-193X
    Keywords: Cyclo-bis-intercaland ; Acridine units ; cis/trans-Azobenzene dicarboxylic acids ; Inclusion compounds ; X-ray structure ; Molecular recognition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The water soluble acyclic 1 and macrocyclic 2 receptor molecules, based on acridine units, form 1:1 complexes with the cis- or trans-2,2′ and 3,3′-azobenzene dicarboxylate substrates. The stability constants of these complexes, determined by 1H NMR spectroscopy, cover a wide range from 30 to 105M-1, thus displaying very pronounced structure selectivity with respect to both substitution pattern and cis, transconfiguration. The complexes of the cyclo-bis-intercaland receptor 2 are two or three orders of magnitude more stable than those of 1. The inclusion complex of cyclo-bis-intercaland 2 with trans-3,3′- azobenzene dicarboxylate has been isolated and its structure has been determined by X-ray crystallography using synchrotron radiation, confirming the intercalation of the substrate between the acridine residues in the species formed.
    Additional Material: 3 Ill.
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  • 111
    Electronic Resource
    Electronic Resource
    Addition Chemistry of Rod-Shaped 1,6-Dicyanohexatriyne: Regioselectivity Control by the Remote Cyano Function (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2491-2500 
    Details
    ISSN: 1434-193X
    Keywords: Addition reactions ; Cycloadditions ; Dicyanohexatriyne ; Enediyne ; Regioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of different alcohols, amines, thioalcohols, ethers, cycloalkanes, tin hydride, alkenes or alkadienes to 1,6-dicyano-1,3,5-hexatriyne (1) leads, with a pronounced regioselectivity, to a series of substituted 1-ene-3,5-diynes. The addition of alcohols, amines and thiols proceeds preferentially in a syn mode leading to diastereomers with an E configuration. The reaction with free radicals, on the other hand, proceeds in an anti addition mode. The [4+2] and [2+2] cycloadditions performed with 1 yielded unsaturated six- and four-membered ring adducts, respectively. The cyclobutene derivatives resulting from [2+2] cycloadditions underwent spontanous electrocyclic ring-opening reactions with the formation of butadiene derivatives. Nucleophilic additions to form 1 lead exclusively to products where the donor atom is bound at C-1. All the reactions, except the formation of 19, showed an excellent regioselectivity with respect to the preferred addition to a terminal C≡C triple bond.
    Additional Material: 2 Ill.
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  • 112
    Electronic Resource
    Electronic Resource
    Pd-Catalyzed Asymmetric Allylic Alkylation of 3-Acetoxy-N-(tert-butyloxycarbonyl)-1,2,3,6-tetrahydropyridine - Preparation of Key Intermediates for Natural Product Synthesis (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2515-2521 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Heterocycles ; Palladium ; Alkylations ; Allyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient synthesis of racemic tetrahydropyridine 1 was developed. Pd-catalyzed allylic alkylation of 1 with malonate and dimethylacetoxymalonate as nucleophiles with the phosphanylcarboxylic acid L1 and the dihydrooxazol L2 as ligands, were carried out and gave enantiomeric excesses of up to 98%. Absolute configurations were determined for all compounds described. From the alkylation products (+)- and (-)-2a, and (+)- and (-)-2b a variety of versatile, nonracemic chiral intermediates were prepared.
    Additional Material: 1 Tab.
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  • 113
    Electronic Resource
    Electronic Resource
    EPC Syntheses of Trifluorocitronellol and of Hexafluoropyrenophorin - A Comparison of Their Physiological Properties with the Nonfluorinated Analogs (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2533-2544 
    Details
    ISSN: 1434-193X
    Keywords: (S)-4,4,4-Trifluoro-3-hydroxybutanoic acid ; 2-Trifluoromethyl-3-hydroxypropanoic acid (F3-Roche acid) ; Chiral CF3-containing synthetic building blocks ; Natural products ; Cyclizations ; Olfactory comparison ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural products pyrenophorin (1a) and citronellol (2a), in which CH3 groups are replaced by CF3, were synthesized in enantiomerically pure form from simple four-carbon trifluorohydroxy acids (obtained by resolution). The cyclizations of analogous CH3 and CF3 seco acids (cf. 9) to give pyrenophorin derivatives require different methodologies; the F6 derivative 10a could be obtained in only very poor yield; in contrast to pyrenophorin. Most surprisingly, F6-pyrenophorin (1d) has an extremely poor solubility in common organic solvents, and has essentially no antimicrobial activity (see Table 2). The synthesis of F3-citronellol is the first application of an enantiopure F3-Roche acid (12) as a synthetic builiding block (see its derivatives 17-23). An olfactory comparison of F3-citronellol [(R)-(+)-2b] with citronellol and ent-citronellol (Scheme 6) shows that the fluorine derivative has a “very metallic, aggressive” character and lacks totally the “sweetness” of (R)-(+)- and (S)-(-)-2a. A number of generally useful, CF3-substituted electrophilic (iodides 4, 18, 37, tosylates 19, 33, aldehydes 5, 29, 39) and nucleophilic (Li dithiane precursor of 5, Li compounds 20, 38) reagents are described for the first time.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/1999/99137_s.pdf or from the author.
    Additional Material: 1 Ill.
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  • 114
    Electronic Resource
    Electronic Resource
    Oxidation of o-Methoxyphenols with a Hypervalent Iodine Reagent: Improved Synthesis of Asatone and Demethoxyasatone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2579-2581 
    Details
    ISSN: 1434-193X
    Keywords: Hypervalent iodine ; Phenols ; Oxidation ; Cyclohexa-2,4-dienones ; Dimerization ; Asatone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of the 2-methoxyphenols 1c-f with phenyliodonium(III) diacetate (PIDA) in methanol resulted in the formation of the cyclohexa-2,4-dienones 4c-f, which dimerized spontaneously to a single product (5c-f) in each case. Using this method the synthesis of asatone (5a) and its demethoxy analogue (5b) was also accomplished starting from the readily available phenol derivatives 1a and 1b, respectively.
    Additional Material: 1 Ill.
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  • 115
    Electronic Resource
    Electronic Resource
    A New Synthetic Approach Toward (+)-Ambruticin Analogs: Preparation of a C10-C11 cis-Isomer Fragment (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2885-2892 
    Details
    ISSN: 1434-193X
    Keywords: Ambruticin ; Asymmetric synthesis ; Pyranose ; Carbohydrates ; C-Glycosylation ; Alkylations ; Palladium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new methodology has been applied to synthesize an isomer of the west part of (+)-ambruticin based on an efficient asymmetric de novo access to the A unit and sequential stereospecific reactions catalyzed by Pd0 for the construction of the B unit.
    Additional Material: 1 Ill.
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  • 116
    Electronic Resource
    Electronic Resource
    Solvent Effect on the Protonation of Acetylene and Ethylene - Continuum Solvent Quantum Chemical Calculations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2893-2897 
    Details
    ISSN: 1434-193X
    Keywords: Acetylene ; Ethylene ; Carbocations ; Vinyl cation ; Ethyl cation ; Basicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protonation of acetylene and ethylene (yielding the vinyl and ethyl cation, respectively) was investigated computationally by ab initio calculations [B3LYP/6-31G(d,p)], in the gas phase and in water, as modeled by the IPCM and SCIPCM continuum methods. The structures and NBO atomic charges were thus determined for the neutral bases and their protonated forms, while the comparison of gas-phase and aqueous basicities afforded the hydration energies of the protonated bases. It was found that the aqueous protonation of acetylene is more endothermic than that of ethylene by 5 kcal/mol, owing to the lower intrinsic basicity of the former (by 7.4 kcal/mol), which is only partly compensated for by the more exothermic hydration (by 3.8 kcal/mol) of the vinyl cation.
    Additional Material: 5 Ill.
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  • 117
    Electronic Resource
    Electronic Resource
    Conformation Control in Open-Chain Compounds with up to Six Rotatable Bonds (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2929-2936 
    Details
    ISSN: 1434-193X
    Keywords: Local conformer populations ; syn-Pentane interactions ; Conformational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent patterns on 1,3,5…-polyoxygenated-2,4,6…-polymethylated alkane chains, which preferentially adopt a fully extended backbone conformation, have been identified. This is demonstrated by analysis of the vicinal H,H-coupling constants along the backbones of compounds 19, 23, and 24.
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  • 118
    Electronic Resource
    Electronic Resource
    New Heterocycles from the Reaction between Some Natural α-Amino Acid Hydrazides and Formaldehyde (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2943-2948 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; α-Amino acid phenylhydrazides ; Heterocycles ; Cyclization reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ring forming condensation between some natural α-amino acid phenylhydrazides (1) and aqueous formaldehyde (2) has opened a novel synthetic route to hexahydro-1,2,4-triazin-6-one derivatives (3). Polycyclic systems were obtained from the same reaction carried out with L-aspartic acid 1,4-bis(2-phenylhydrazide) (1d), L-histidine phenylhydrazide (1e) and L-tryptophan phenylhydrazide (1f) which gave perhydro-4,6-dioxo-2,8-diphenyl[1,2,4]triazino[4,5-d][1,2,4]triazepine (5) perhydro-1-oxo-3-phenylimidazo[5,4-d][1,2,4]triazino[4,5-a]pyridine (7) and 1,2,3-H-3-(2-phenylcarbazoyl)-β-carboline (8), respectively. Substrates 1 were conveniently obtained by direct reaction of phenylhydrazine with L-α-amino acid esters retaining the original chirality.
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  • 119
    Electronic Resource
    Electronic Resource
    Stereoselective Synthesis of (E)- and (Z)-Acetals of Pent-2-en-4-yn-1-al and Related Dienynes and Dienediynes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2957-2963 
    Details
    ISSN: 1434-193X
    Keywords: Sonogashira-Linstrumelle cross-coupling ; Stille cross-coupling ; Protected enynals ; Transacetalisation ; Pent-2-en-4-yn-1-al ; Deca-2,8-diene-4,6-diyne-1,10-dial ; Dienediynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (3E)-5,5-Diethoxypent-3-en-1-yne was stereospecifically prepared by Sonogashira-Linstrumelle cross-coupling between (E)-3-iodoacrolein diethylacetal and (trimethylsilyl)acetylene. The (Z) isomer was obtained by Stille cross-coupling between the corresponding (Z)-vinyltin and 1-bromo-2-(trimethylsilyl)acetylene. In the case of the (E) isomer, transacetalisation occurred without isomerization affording a large variety of (E)-enynals protected as acetals. It has also been shown to be possible to obtain the corresponding (E,E)-dienediyne through sp-sp homocoupling under appropriate experimental conditions.
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    Synthesis of Enantiomerically Pure Amino Acids Containing 2,5-Disubstituted THF Rings in the Molecular Backbone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2977-2990 
    Details
    ISSN: 1434-193X
    Keywords: β-Turn mimetic ; Conformational analysis ; Synthesis design ; Tetrahydrofuran ; THF amino acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N- and C-protected derivatives of 2,5-disubstituted trans- and cis-THF amino acids 6 and 7 were prepared in enantiomerically pure form from L-alanine. Felkin-Anh-controlled reduction of the ketone 9 was achieved with a 85:15 diastereoselectivity. Epoxidation of 10 and subsequent intramolecular epoxide opening gave the trans- and cis-THF alcohols 11 and 12, which were further transformed into the corresponding N- and C-protected 2,5-disubstituted trans- and cis-THF amino acids. Conformational studies show that the cis-THF diamide 34 is a β-turn mimetic in the solid state and in CDCl3 solution.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99165_s.pdf or from the author.
    Additional Material: 5 Ill.
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    The Addition Patterns of C60 Trisadducts Involving the Positional Relationships e and trans-n (n = 2-4): Isolation, Properties, and Determination of the Absolute Configuration of Tris(malonates) and Tris[bis(oxazolines)] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3027-3039 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Circular dichroism ; Cycloadditions ; Fullerenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of regioisomeric trisadducts of C60 (5-11, 14-18) having the positional relationships e and trans-n (n = 2-4) resulting from successive additions of malonates or bis(oxazolines) to [6,6]-double bonds of the fullerene framework has been isolated and characterized. The new adducts 8-11 and 15-17 represent examples of unprecedented addition patterns. The addition patterns of the new trisadducts with C2, Cs or C1 symmetry have been assigned on the basis of the known positional relationships of the addends in their precursor bisadducts, and those of the C2- or Cs-symmetric representatives have been verified by analysis of their NMR spectra. The absolute configurations of the adducts with inherently chiral addition patterns could be determined either by comparison of the calculated and experimental CD spectra of the bis(oxazoline) adducts or with knowledge of the absolute configurations of the chiral bisadduct precursors containing bis(oxazoline) addends. The CD spectra of the pairs of diastereomers with an enantiomeric addition pattern fA -15/fC -15, fA -16/fC -16, and fA -18/fC -18 show mirror image behavior and pronounced Cotton effects.
    Additional Material: 6 Ill.
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  • 122
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    The Carbene/Bridgehead-Olefin Rearrangement: DFT Calculations on 1-Bicyclo[2.1.1]hexylcarbene and 1-Bicyclo[3.1.1]heptylcarbene; Rearrangement of (5-Bromobicyclo[3.1.1]heptyl)bromocarbene (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3057-3066 
    Details
    ISSN: 1434-193X
    Keywords: Small ring systems ; Strained molecules ; [3.1.1]Propellane ; Alkene dimerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: B3LYP/6-31G(d) calculations on bicyclo[2.1.1]hexylcarbene 7ashowed a preferred propensity for enlargement of the four-membered ring to give 1-norbornene 8. Only at high temperature does a rearrangement of bridgehead olefin 8 to 2-norbornylidene 11 seem to be possible; the competing rearrangement to afford 2-bicyclo[3.1.1]heptylidene 10has a higher activation barrier by 20.2 kcal/mol. For 1-bicyclo[3.1.1]heptylcarbene 12, the preferred stabilization is again enlargement of the four-membered ring to give bicyclo[3.2.1]oct-1(7)-ene 13. The further rearrangement of this alkene to 7-bicyclo[3.2.1]octylidene 16is endothermic by 32.2 kcal/mol and should not take place under moderate conditions. (5-Bromobicyclo[3.1.1]heptyl)bromocarbene 32, a derivative of 12 generated from the tetrabromide 23 with MeLi, rearranged by enlargement of the four-membered ring to give alkene 31, which reacted to give the head-to-head 2π+2π dimer 26, whose structure was established by X-ray crystallography.
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  • 123
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    Diastereoselective Synthesis of a Precursor of Homocarbocyclic Nucleosides (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3085-3087 
    Details
    ISSN: 1434-193X
    Keywords: Nucleoside analogue ; Nucleosides ; Palladium ; Dihydroxylations ; Catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient diastereoselective synthesis of an immediate precursor for a rapid access to a variety of homo-carbocyclic nucleosides, is described. The synthetic scheme involves a high yielding new type of Pd(0) catalyzed cyclization of a suitable hydrazine derivative together with a stereospecific OsO4 triggered dihydroxylation step.
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  • 124
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    Efficient Biomimetic-Type Synthesis of the Benzo[a]naphthacenequinone Antibiotics G-2A and G-2N (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3099-3103 
    Details
    ISSN: 1434-193X
    Keywords: Antibiotics ; Biomimetic-type synthesis ; Polyketides ; Quinones ; Aldol reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trioxo ester 15 was prepared by attachment of two vicinal C-4 and C-6 ketide side chains on the anthraquinone core (6b). Mild base treatment of 15 initiated successive aldol condensations to produce the benzo[a]naphthacenequinone 16 regioselectively in one operation. Deprotection of 16 afforded the antibiotic G-2A (1) and decarboxylation of 1 lead to G-2N (2).
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  • 125
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    Convenient Syntheses of Novel α- and β-Amino Acids with Spiropentyl Groups (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3105-3115 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Spiro compounds ; Michael addition ; Copper reagents ; Curtius degradation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic spiropentylglycine (8) has been synthesized by sodium borohydride reduction of benzyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Bn), nucleophilic substitution of the chlorine in the product 6 with azide and hydrogenolytic deprotection of the resulting 7 (overall yield 15%). An alternative approach to 8 consisted of the coupling of the higher-order cuprate 10, generated by halogen-metal exchange from bromospiropentane (9), with the electrophilic glycine equivalent 11 followed by deprotection (overall yield 47%). Enantiomerically pure (1′-aminospiropentyl)acetic acid [(R)-16] (overall yield 16% from 5-Me) and 1-aminospiropentanecarboxylic acid [(R)-23] (29% from 5-Me) were obtained from the Michael adduct 14-Me of (4R,5S)-4,5-diphenyloxazolidin-2-one (13) and methyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Me). Racemic 1-aminospiropentanecarboxylic acid (R/S-23) was prepared by rhodium-catalyzed addition of dimethyl diazomalonate to methylenecyclopropane and subsequent Curtius degradation of the halfester 28 via the azide 29 (overall yield 14%). Upon standing in aqueous solution, 23 underwent complete rearrangement to the new 1-amino-2-methylenecyclobutanecarboxylic acid (24). The interesting derivative of azabicyclo[3.1.0]hexane-1-carboxylate 34 with an annelated spiropentane moiety and a β-amino acid fragment was incidentally obtained in a one-step intermolecular domino reaction starting with the addition of lithium benzylamide to methyl 2-chloro-2-cyclopropylideneacetate (32, 41% yield).
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  • 126
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    Studies Directed Toward the Synthesis of Taxanes: Construction of the Tricyclo[5.3.1.01,7]undecane System (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3251-3256 
    Details
    ISSN: 1434-193X
    Keywords: Taxol ; Nitrile oxide ; Cycloaddition reactions ; Isoxazoline ; Cyclopropane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular nucleophilic substitution of an epoxide by the anion of a nitrile was used to construct the bicyclo[3.1.0]hexane system of 9, derived from 8, and of 14, derived from 13. The intramolecular 1,3-dipolar cycloaddition of nitrile oxide 4, obtained from 14, led to isoxazoline 3. However, it was not possible to convert 3 into the corresponding β-hydroxy ketone. Rearrangements of 3 were observed in the presence of dehydrating reagents leading to compounds 19-21, which are structurally related to 11(15→1)abeotaxanes.
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  • 127
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    Synthesis of a Dinuclear ZnII-Calix[4]arene Enzyme Model with Additional General Base Groups - Catalytic Activity in Phosphate Diester Transesterification (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3269-3275 
    Details
    ISSN: 1434-193X
    Keywords: Calixarenes ; Enzyme mimetics ; Phosphatases ; Transesterification ; Zinc ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calix[4]arenes modified at the upper rim with two pairs of functional groups were synthesized and were used as starting materials for the synthesis of an enzyme model 3-Zn2 that has two ZnII centers and two dimethylamino groups. Under neutral conditions, this dinuclear metallo-enzyme model is catalytically active in the cleavage of the phosphate diester bond of the RNA model substrate 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP). The kinetics of 3-Zn2 were compared with a mononuclear complex 1-Zn and a dinuclear complex 2-Zn2 that lack the dimethylamino groups. A catalysis mechanism is proposed where the ZnII centers of 3-Zn2 cooperate in the activation of the phosphoryl group while one of the dimethylamino groups acts as a general base in the deprotonation of the hydroxyl group of HPNP.
    Additional Material: 4 Ill.
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  • 128
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    N-(α-Chloroalkyloxycarbonyl)pyrrolidines as a Source of Oxygenated d1-Reagents (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3005-3012 
    Details
    ISSN: 1434-193X
    Keywords: Organolithium compounds ; d1-Reagents ; Lithiation ; Carbamates ; 1,2-Diols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of the N-(α-chloroalkyloxycarbonyl)pyrrolidines 1 with lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol-%) in the presence of different electrophiles [iBuCHO, tBuCHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO, Me3SiCl], in THF at temperatures ranging between -78 and -60°C leads, after hydrolysis with water, to the expected functionalized carbamates 2. Deprotection of compounds 2, derived from carbonyl compounds, with lithium hydroxide in a mixture of ethanol and water at 80°C affords the correponding 1,2-diols 3.
    Additional Material: 2 Tab.
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  • 129
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    Synthesis of Reactive Sulfines by Flash Vacuum Thermolysis: Thioformyl Cyanide S-Oxide and Thioxoethanal S-Oxide (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3041-3045 
    Details
    ISSN: 1434-193X
    Keywords: Thiocarbonyl compounds ; Sulfines ; Flash vacuum thermolysis ; Cyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thioformyl cyanide S-oxide and thioxoethanal S-oxide were synthesized by retro Diels-Alder cleavage of their dimethylanthracene adducts under flash vacuum thermolysis conditions. They were characterized by low-temperature IR and NMR spectroscopy. The formation of thioformyl cyanide S-oxide was also confirmed by mass spectrometry.
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  • 130
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    A Novel Approach to the Synthesis of Precursors of Tricyclic β-Lactam Antibiotics (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3067-3072 
    Details
    ISSN: 1434-193X
    Keywords: Thioester ; Enolate ; Imine ; Lactams ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective synthesis of two precursors of tricyclic β-lactam antibiotics (trinems) has been attempted by a novel approach that involves a highly stereoselective azetidinone ring-forming reaction followed by the reduction of a functionalized aromatic substituent at C-4 of the β-lactam nucleus.
    Additional Material: 2 Ill.
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  • 131
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    Studies Relevant to Ellagitannin Chemistry: Strain-Energy Induced Opening of the D-Glucono-δ-lactone Ring of an Ellagitannin Derivative and the Synthesis of Ellagitannin Natural Products with a D-Gluconic Acid Moiety (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3079-3083 
    Details
    ISSN: 1434-193X
    Keywords: Natural product ; Ellagitannins ; Gluconic acid derivatives ; Atropisomerism ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The opening of the D-glucono-δ-lactone ring of the ellagitannin derivative 8, which contains a hexabenzyloxydiphenoyl moiety, to the corresponding gluconic acid derivative 9 under mild acidic conditions was investigated. This transformation was found to occur quantitatively upon treatment of the D-glucono-δ-lactone derivative 8 with silica gel.
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    The Effect of Lewis Acids on the Pinacol Homocoupling Reaction of Aldehydes Promoted by Samarium Diiodide (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3369-3374 
    Details
    ISSN: 1434-193X
    Keywords: Pinacol reaction ; Lewis acid ; Samarium diiodide ; 1,2-diols ; Carbonyl compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of various Lewis acids on the samarium diiodide promoted pinacol homocoupling of aldehydes was investigated. The reaction of benzaldehyde proceeded with fair to good 1,2-anti-stereoselectivity, while in the case of other aromatic and aliphatic aldehydes syn-stereoselectivity was generally observed. Chiral α-alkylaldehydes allowed for an almost complete stereocontrol favoring syn-1,2-diols.
    Additional Material: 5 Ill.
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    Consequences of the Preeminent Reactivity of 2-OH in Sucrose: Cyclic Acetalation at 2-OH and 3-OH under Basic Conditions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3393-3398 
    Details
    ISSN: 1434-193X
    Keywords: Sucrose ; Acetalation ; Etherification ; Carbohydrate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of unprotected sucrose with tert-butyl chloromethyl ketone in dimethylformamide was investigated as a model for the study of the relative reactivity of the various hydroxy groups of sucrose. Besides the monoethers arising from the substitution of the chlorine atom by 2-OH and 1′-OH of sucrose, the major product is a tert-butyl hydroxymethyl 5-membered ring acetal involving 2-OH and 3-OH. The formation of this product illustrates the preeminent reactivity of 2-OH towards the carbonyl group of the α-chloromethyl ketone, leading to an intermediate hemiacetalic anion, which can enter by intramolecular acetal formation through an intermediate epoxide.
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    Cycloisomerization of 1-Phenyl-1-buten-3-yne to Naphthalene via Cinnamylidene Carbenes - A Complex Reaction Involving 1,2-C Switches and 1,2-Styryl Migrations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3407-3412 
    Details
    ISSN: 1434-193X
    Keywords: Enyne pyrolysis ; 13C,D labelling ; Alkenylidene carbenes ; 1,2-Styryl migration ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal conversion of [4-13C,4-D]- (1) and [4-13C]-1-phenyl-1-buten-3-yne (7) has been studied in a quartz tubular reactor at 650 °C (1, in the presence of N2 and N2/toluene, respectively) and at 600 and 620 °C (mixture of 1 and 7, in N2 only) at a reaction time of approximately 0.3 s. The liquid pyrolyzates were analyzed spectroscopically. By means of a special calculation method reported recently, the naphthalene isotopomers formed by reaction pathways other than those proceeding via cinnamylidene carbenes were arithmetically eliminated and the reaction events proceeding via carbene intermediates were mechanistically analyzed. The result of this analysis undoubtedly suggests a complex reaction in which the rates of the partial reactions may be placed in the following order: 1,2-D(H) 〉〉 1,2-styryl 〉 1,6-C,H.
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    One-Pot and Sequential Asymmetric Hydrogenation of β,δ-Diketoesters into Functionalized 1,3-Diols: From anti- to syn-Stereoselectivity (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3421-3427 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric hydrogenation ; 3,5-Dioxoester ; Diols ; Lactone ; Ruthenium catalyst ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymmetric hydrogenation of methyl 3,5-dioxohexanoate (1) into mixtures of 3,5-dihydroxyesters (2) and 3-hydroxylactones (3) has been reinvestigated with a variety of ruthenium catalysts. Catalysts bearing diphosphanes which possess axial chirality such as (S)-MeO-Biphep give predominantly (3R,5S)-anti-2 in up to 78% de and 95% ee, affording an efficient synthesis of (S)-6-methyl-5,6-dihydro-2-pyrone [(S)-5] in up to 95% enantiomeric excess. On the contrary, some Ru-{amidophosphane-phosphinite} complexes catalyze sluggishly the formation of syn-2 in up to 92% de but with poor enantiomeric excesses. In all cases, methyl (R)-3-hydroxy-5-oxohexanoate [(R)-11] is the exclusive primary hydrogenation product, which can be isolated in high yields and enantiomeric excesses up to 78%. Further hydrogenation of enantiomerically enriched (R)-11 in a separate experiment affords (3R,5R)-syn-2 in high diastereomeric and enantiomeric excesses (up to 80% and 98%, respectively), provided a Ru-(R)-Binap-type catalyst is used.
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    The Highly Selective Oxidation of a Tricarbonyliron Complex (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3455-3458 
    Details
    ISSN: 1434-193X
    Keywords: Stereoselectivity ; Carbonyliron Complex ; Oxidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tricarbonyliron complex 2a underwent selective and diastereoselective oxidation with tert-butyl hydroperoxide at room temperature to provide, after decomplexation, the peroxyether 5 which, on reduction, yielded the corres-ponding secondary alcohol 7.
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    Stereoselective Inter- and Intramolecular Pauson-Khand Reactions of N-(2-Alkynoyl) Derivatives of Chiral Oxazolidin-2-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3459-3478 
    Details
    ISSN: 1434-193X
    Keywords: Alkyne complexes ; Asymmetric synthesis ; Chiral auxiliaries ; Cyclopentenones ; Pauson-Khand reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete account of the intermolecular and intramolecular Pauson-Khand reactions of N-(2-alkynoyl) derivatives of chiral 2-oxazolidinones is presented. The intermolecular Pauson-Khand reactions with norbornene or norbornadiene take place under mild conditions and in high yields. Phenyl- or trimethylsilylpropiolate derivatives lead to the exclusive formation of 1,4-dicarbonyl regioisomers, while mixtures of 1,3- and 1,4-regioisomers are obtained with tetrolate derivatives. The diastereoselectivity of the reaction, determined by the substitution pattern of the oxazolidinone moieties, can be very high (up to 17.5:1 dr) for the formation of 1,4-dicarbonyl regioisomers, and the diastereomeric products can often be separated by column chromatography. Under the appropriate conditions, the intramolecular Pauson-Khand reactions of oxazolidinone-derived enynes can also take place with very good yields, but with low diastereoselectivities. The absolute configurations of several adducts have been determined, and the stereochemical outcome of the reaction has been rationalized.
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    Rearrangement of 2-(4-Hydroxyalkyl)-1,3-dioxolanes to 2-Hydroxyethyl Alkanoic Esters by 1,5-Hydride Shift - An Unprecedented Intramolecular Redox Reaction (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3495-3499 
    Details
    ISSN: 1434-193X
    Keywords: Hydride abstraction ; Carbenium ions ; Rearrangement ; Intramolecular redox reaction ; Deuterium label ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(4-Hydroxyalkyl)-1,3-dioxolanes (3a/3b, 5-7) undergo an acid-catalyzed rearrangement to give 2-hydroxyethyl alkanoic esters 8-11. The postulated mechanism, proceeding via the benzylic carbenium ion B and the 1,3-dioxolan-2-ylium cation C, is supported by the stereochemistry of the reaction and the results of deuterium labeling experiments.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99248_s.pdf or from the author.
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    Configurational Stability and Stannylation of Dipole-Stabilised Cyclic Tertiary Benzylic α-Oxycarbanions, which Occurs with Retention or Inversion of Configuration Depending on R and X of R3SnX Used (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3511-3518 
    Details
    ISSN: 1434-193X
    Keywords: 2,4,6-Triisopropylbenzoates, 1-indanyl, 1,2,3,4-tetrahydro-1-naphthyl ; N,N-Diisopropylcarbamate, 1-indanyl ; Carbanions, configurational sStability ; Stereochemistry, stannylation ; Liquid chromatography, determination of ee ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4,6-Triisopropylbenzoates of 1-indanol and 1-tetralol (ee 98%) are deprotonated at -78 °C in hexane by sBuLi/TMEDA to give partly configurationally labile organolithium intermediates 5a and 5b, which are deuterated by MeOD with retention of configuration. These intermediates are stannylated by trimethyltin chloride with inversion as determined by lithiodestannylation followed by addition of MeOD to produce deuterated esters of low ee. Stannylation of (S)-5b with (-)-menthyldimethyltin bromide affords stannane 7 (de ≥ 95%) with inversion. The carbanion derived from (S)-1-indanyl N,N-diisopropylcarbamate (9) is configurationally stable. It reacts with trimethyltin chloride favouring inversion of configuration (ee up to 17%). Tributyltin chloride and tributyltin triflate yield stannanes 11b of opposite stereochemistry, the latter giving retention of configuration. Tributyltin bromide behaves similarly to the chloride, but the ee of the reaction product is only about 30%.
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    Palladium-Catalyzed Hydrovinylation of Vinyl Triflates with Alkynes An Approach to the Synthesis of 3-Vinylfuran-2(5H)-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3305-3313 
    Details
    ISSN: 1434-193X
    Keywords: Palladium ; Hydrovinylation ; Cyclizations ; Furan-2(5H)-ones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of alkynes with vinyl triflates in the presence of catalytic amounts of Pd(OAc)2 and HCOOK, omitting phosphane ligands, affords hydrovinylation products usually in good to high yields. The reaction has been employed to develop a regioselective synthesis of 3-vinylfuran-2(5H)-ones from methyl 4-hydroxy-2-butynoates.
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  • 141
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    New Chiral Catalysts Containing N,O-Heterocycles Derived from Chiral Amino Alcohols (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3323-3333 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Catalysis ; Amino acids ; Crown ethers ; Heterocyclic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enantioselectivity exerted by a new series of chiral catalysts containing N,O-heterocycles of different sizes has been checked in the addition of diethylzinc to benzaldehyde, which was used as a model reaction. The catalysts were derived from natural amino acids, following a relatively simple procedure, and in several cases excellent ee values were obtained. The results were complementary since ee's ranged from 98% (R) to 94% (S) excesses of the final 1-phenylpropan-1-ol. Molecular mechanics calculations suggested that the production of the R alcohol may be explained by a mechanism similar to that described by Noyori, in which ZnEt2 interacts solely with the N-C-C-OH fragment, whereas the formation of the S enantiomer needed the direct participation of the lateral chain of the parent amino acid and the N,O-heterocycle.
    Additional Material: 3 Ill.
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  • 142
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    Tetraacylethenes as Dienophiles and Hetero Dienes in Two-Step Diels-Alder Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3343-3351 
    Details
    ISSN: 1434-193X
    Keywords: C-C coupling ; Cycloadditions ; Dehydrogenations ; Electron deficiency ; Isomerisations ; Oxidations ; Zwitterionic intermediates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation with barium manganate of the enol of tetraacetylethane (10) affords tetraacetylethylene (7a) in good yield. Treatment of the 1,3-diketones 15a and b with iodosobenzene in the presence of boron trifluoride does not result in oxidative coupling yielding 10 and diacetyldibenzoylethane 17, respectively, as has been reported by Moriarty et al. Instead the known difluoroborylenolates 16 are formed. Oxidative coupling of the sodium enolate of 15b with iodine affords the meso-tetraketone meso-17 and diacetyldibenzoylethylene (E)-7b besides small amounts of rac-17 and the bisenol 19. In the presence of 1,4-diazabicyclo[2.2.2]octane, meso-17 and 19 tautomerise yielding identical equilibrium mixtures of meso-17, rac-17, and 19 (26:29:45). Dehydrogenation with 5,6-dichloro-2,3-dicyanobenzoquinone of meso-17 yields (E)-7b and an isomer (77:23) which was assigned structure (Z)-7b on the basis of spectroscopic evidence. - Tetraacetylethylene (7a) reacts with 1,2-dimethylenecyclohexane to afford two different [4+2]cycloadducts, viz. the spirocyclic dihydropyran 25 (30 %) and the tetraacetyloctalin 27. Whereas the latter is stable, the former isomerises to the latter on heating. Formation of both [4+2]cycloadducts and the isomerisation 25 → 27 are interpreted by invoking the zwitterion 26 as common intermediate. Monoolefines that cannot generate stable carbenium ions don't give [4+2]cycloadducts with 7a. In contrast, α-methylstyrene yields the oxa Diels-Alder product 30. The structures of (E)-7b, 19, 25, and 27 are established by X-ray diffraction analyses.
    Additional Material: 5 Ill.
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  • 143
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    Regio- and Stereoselective Ene and Tandem “Ene-Cycloaddition” Reactions of 2,4-Dioxopentane-3-thione (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3375-3379 
    Details
    ISSN: 1434-193X
    Keywords: α,α′-Dioxothiones ; Ene reactions ; Cyclo additions ; Sulfur heterocycles ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4-Dioxopentane-3-thione 1a reacts as an enophile with various allyl derivatives affording thiophilic ene adducts as single regioisomers with high (E) stereoselectivity. Using allyl ethers or allenes as ene counterparts, the formation of the thiophilic adduct is followed by a fast cycloaddition reaction in which 1a behaves as a diene or a dienophile, respectively.
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  • 144
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    Transketolase-Mediated Synthesis of 4-Deoxy-D-fructose 6-Phosphate by Epoxide Hydrolase-Catalysed Resolution of 1,1-Diethoxy-3,4-epoxybutane (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3399-3402 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Enzyme catalysis ; Epoxide hydrolase ; Transketolase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Deoxy-D-fructose 6-phosphate is synthesised from nonnatural sources in four steps, including two enzymatic reactions. (3S)-1,1-Diethoxy-3,4-epoxybutane is first obtained by epoxide hydrolase-catalysed resolution. Opening of this epoxide by inorganic phosphate leads to 2-deoxy-D-erythrose 4-phosphate. In the last step, transketolase transfers a hydroxyacetyl group from L-erythrulose onto this aldehyde, controlling the second asymmetric center.
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  • 145
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    Synthesis of Modified Ingenol Esters (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3413-3420 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Diterpenes ; Ingenol ; Antitumor agents ; Isosters ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic protocols for the manipulation of the polyhydroxylated southern region of ingenol (1a) were developed, and a series of isosteres of the anticancer compound ingenol 3,20-dibenzoate (1b) was prepared. The biological evaluation of these compounds showed that cytotoxicity was relatively tolerant to changes at C-20, while PKC activation was markedly affected by these modifications. These data suggest that chemical manipulation can effectively dissect cytotoxicity and tumour-promoting activity (or potential) of ingenoids, affording more optimal candidates for development, like 20-deoxy-20-fluoroingenol 3,20-dibenzoate (5b). In mild acidic medium, an unexpected vinylogous retro-pinacol rearrangement of ingenol to a tigliane derivative was observed.
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  • 146
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    Synthesis of Novel Functionalised Zinc Phthalocyanines Applicable in Photodynamic Therapy (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3441-3453 
    Details
    ISSN: 1434-193X
    Keywords: Zinc phthalocyanines ; Tetra- and octa(carboxyalkyl)phthalocyaninatozinc compounds ; Water soluble ; Photodynamic therapy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of several new phthalonitriles 3, 9, 14, 25, 33, and 36, functionalised with carboxyl groups, including two examples of amino acid derivatives is described. All new phthalonitriles were converted into their corresponding phthalocyaninatozinc compounds. The phthalocyanines, 2,3,9,10,16,17,23,24-octa(1-carboxyethyloxy)phthalocyaninatozinc (5), 2,9,16,23-tetra(2-amino-2-carboxyethyl)phthalocyaninatozinc (11), 2,9,16,23-tetra(1-carboxy-2-hydroxyethylaminocarbonyl)phthalocyaninatozinc (16), 1,8,15,22-tetra(carboxybutyl)phthalocyaninatozinc (27), 2,3,9,10,16,17,23,24-octa(carboxyalkyl)phthalocyaninatozinc (39), and the nonidentically substituted 9,10,16,17,23,24-hexa(carboxyalkyl)-2-[4-(N-succinimidyloxycarbonyl)butyl]phthaloyaninatozinc (41) are all sufficiently soluble in water. The nonidentically-substituted compounds are important due to their selective binding to tumor-selective antibodies. UV/Vis-spectroscopy was used to investigate the effect of more or less sterically-demanding substituents in the periphery of the phthalocyanines towards aggregation. The phototoxicity towards cancer cells of some of the new compounds was investigated in several in-vitro experiments.
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  • 147
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    Regio- and Stereoselective Opening of Oxiranes through Neighbouring Group Participation: Stereocontrolled Synthesis of Enantiopure Hydroxylated Oxazolidin-2-ones (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3483-3488 
    Details
    ISSN: 1434-193X
    Keywords: Epoxides ; Epoxide ring opening ; Neighbouring group assistance ; Oxazolidinones ; Aminodiols ; Pyrrolidinones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regio- and stereo-selective ring opening of (S)-pyroglutaminol derived epoxides provides an effective route to protected syn,syn-aminodiol units. The procedure involves the chemoselective aminolysis or alcoholysis of (3R,4R,5R)-N-(tert-butoxycarbonyl)-3,4-epoxy-5-[(1-ethoxy)ethoxymethyl]pyrrolidin-2-one (10), followed by the formation in quantitative yield of oxazolidinone intermediates, through the mediation of neighbouring N-Boc groups. The practical synthetic interest of this route is illustrated by the example of (3R,4S,5R)-3,4-diacetoxy-5-(acetoxymethyl)pyrrolidin-2-one which should serve as useful building block in further syntheses.
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  • 148
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    The Regiochemistry of the Cycloaddition of 4-R-Phenacylpyridazinium Ylides to Nonsymmetrical Substituted Olefins (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3501-3504 
    Details
    ISSN: 1434-193X
    Keywords: Pyridazine ; Ylides ; Tetrahydropyrrolopyridazine ; Regiospecificity ; Structure ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiochemistry of the [3+2] cycloaddition reactions between 4-R-phenacylpyridazinium ylides and acrylonitrile has been studied. Theoretical and experimental studies have been performed, both of which show that the reaction is regiospecific. Four new tetrahydropyrrolopyridazine heterocycles have been obtained. The structures of the new compounds were established by elemental (C,H,N) and spectral analyses (IR, 1H and 13C NMR, MS).
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  • 149
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    Efficient Stereocontrolled Access to 15- and 16-Hydroxy Steroids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3505-3510 
    Details
    ISSN: 1434-193X
    Keywords: Polyhydroxy steroids ; Marine natural products ; D ring hydroxylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four epimeric 15- and 16-hydroxy steroids have been stereoselectively synthesized from epi-androsterone. The key intermediate is the 3β-[(tert-butyldimethylsilyl)oxy]-5α-23,24-bisnorchol-16-en-22-ol (10), which allows both efficient D-ring functionalization and the possibility of facile side-chain construction. In the course of this synthesis, we have found that the stereochemical outcome of the C-15 carbonyl reduction is strongly dependent on the C-16 and C-17 hybridization.
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  • 150
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    Intramolecular Donor-Assisted Cyclization of Organotin Compounds (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 887-898 
    Details
    ISSN: 1434-1948
    Keywords: Tin ; Phosphorus ; Intramolecular coordination ; O ligands ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New intramolecularly coordinated organotin compounds containing the monoanionic O,C,O-coordinating ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- have been synthesized by substitution reactions starting from organotin halides. In view of the enhanced reactivity of the intramolecularly coordinated compounds {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}SnR2R′ (2, R = Ph, R′ = CH2SiMe3; 3, R = R′ = Ph; 6, R = R′ = Cl), cationic tin species are suggested to occur as intermediates in the formation of the heterocyclic compounds [1(Sn),3(P)-Ph2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (8), [1(Sn), 3(P)-Ph(Me3SiCH2)SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)2]C6H2 (15), and {[1(Sn),3(P)-Cl2SnOP(O)(OEt)-5-tert-Bu-7-P(O)(OEt)]C6H2}2 (16). The latter compounds are formed by intramolecular cyclizations of pentacoordinate cationic tin species under elimination of ethyl halide. Furthermore, the synthesis of [1(Sn),3(P)-Ph2SnOP(O)(OH)-5-tert-Bu-7-P(O)(OH)2]C6H2 (13) is described. Reaction of 8 with an excess of Me3SiBr leads to the unexpected formation of {2-[P(O)(OEt)(OSiMe3)]-4-tert-Bu-6-[P(O)(OEt)2]C6H2}SnPhBr2 (9) as a result of an O-Sn bond cleavage initiated by Me3SiBr and subsequent reaction of the intermediate with further Me3SiBr under Sn-C bond cleavage. The high donor capacity and the rigidity of the new ligand {4-tert-Bu-2,6-[P(O)(OEt)2]2C6H2}- are demonstrated by X-ray diffraction analyses of the tetraorganotin compound 2 and the monoorganotin trichloride 6. Furthermore, the molecular structures of the 2,3,1-oxaphosphastannoles 8 and 16 are discussed.
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  • 151
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    Carbynehydrido- and Vinylidenehydridoosmium Complexes with Os(PCy3)2 as a Molecular Unit (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 951-957 
    Details
    ISSN: 1434-1948
    Keywords: Osmium ; Alkynes ; Carbyne complexes ; Hydrido complexes ; Vinylidene complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of OsCl3·2H2O with PCy3 leads under reducing conditions either to [OsH6(PCy3)2] (1) or [OsH2Cl2(PCy3)2] (2). Treatment of 2 with terminal alkynes HC≡CR (R = Ph, SiMe3) affords the carbynehydrido complexes [OsHCl2(≡CCH2R)(PCy3)2] (4, 5), of which 5 (R = SiMe3) is easily converted with traces of water into [OsHCl2(≡CCH3)(PCy3)2] (6). Compound 4 (R = Ph) reacts with NaOMe to yield the vinylidenehydridoosmium(II) complex [OsHCl(=C=CHPh)(PCy3)2] (7) which upon treatment with HBF4/OEt2 gives the five-coordinate cationic species [OsHCl(≡CCH2Ph)(PCy3)2]-BF4 (8). The reaction of [OsH3Cl(PCy3)2] (9) with HC≡CC(CH3)2Cl affords a mixture of [OsHCl2(≡CCH=CMe2)(PCy3)2] (10) and [OsCl2(H2)(=CHCH=CMe2)(PCy3)2] (11). Compound 11 is quite labile and by elimination of H2 gives 10. The molecular structure of 10 has been determined by X-ray crystallography.
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  • 152
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    Synthesis, Structural Characteristics and Biological Activities of Complexes of ZnII, CdII, HgII, PdII, and PtII with 2-Acetylpyridine 4-Methylthiosemicarbazone (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 965-973 
    Details
    ISSN: 1434-1948
    Keywords: 2-Acetylpyridine 4-methylthiosemicarbazone ; Palladium ; Platinum ; Group-12 metal(II) complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2-acetylpyridine 4-methylthiosemicarbazone (H4ML) with halides of zinc(II), cadmium(II), and mercury(II) afforded complexes of the form [M(H4ML)X2] [M = ZnII (1-3), CdII (4-6) or HgII (7-9); × = Cl, Br, or I]. Reaction of H4ML with K2PdCl4 and K2PtCl4 gave compounds of the form [M(4ML)Cl] [M = PdII (10) or PtII (11)]. In all the new compounds, which were characterized by elemental analyses, conductance measurements, and electronic, IR and 1H- and 13C-NMR spectroscopy, and by 113Cd-, 195Pt-, or 199Hg-NMR spectroscopy when relevant, the ligand is N,N,S-tridentate, coordinating to the metal centre through its pyridine and azomethine nitrogen atoms and its thiocarbonyl sulfur atom, as was confirmed by X-ray diffraction studies in the cases of 4· 2 DMSO, 5· 2 DMSO, 6· 2 DMSO, 7· 2 DMSO, 10, and 11. In in-vitro assays, only [Zn(H4ML)Cl2] and [Zn(H4ML)Br2] showed some sign of antifungal activity against Aspergillus niger or Paecilomyces variotii.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98381_s.pdf or from the author.
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    A Molecular Mechanics Force Field for Alkylcobaloximes, a Model of Vitamin B12 Coenzyme - Implications of Steric and Electronic Factors in the Co-C Bond Cleavage (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 981-992 
    Details
    ISSN: 1434-1948
    Keywords: Cobaloximes ; Vitamin B12 ; Semiempirical calculations ; Force field ; Conformation analysis ; Cone angles ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular mechanics force field constants have been derived for alkylcobaloximes, (alkyl)Co(DH)2L (DH = monoanion of dimethylglyoxime and L = planar N-donor ligand), implementing the AMBER force field. Atomic charges have been calculated by the semiempirical ZINDO/1 method. Stretching and bending constants have been calculated by the Badger and Halgren equations, with the introduction of simple functions for the description of the electronic influence of the axial ligands on the coordination geometry. 26 parameters have been optimized, by the Simplex method, to fit 4523 bond lengths and angles of 52 alkylcobaloxime accurate crystal structures. In spite of the oversimplification of the adopted method for the description of the electronic effects, this approach provides a good description of the metal coordination geometries. The root-mean-square deviations of the calculated bond lengths and angles from the experimental values average to 0.023 Å and 1.4°, respectively. The molecular mechanics results are discussed in terms of the steric properties of the axial ligands and correlated with their calculated cone angles. The force field has been used to analyse some conformational features of these compounds, such as the influence of the rotation of the axial ligands on their coordination geometry. The calculated energy for the Co-N rotational barrier agrees well with the experimetal ones derived from dynamic and saturation 1H-NMR spectroscopy in (alkyl)Co(DH)2(2-NH2-py). In order to have more experimental data for this analysis, the crystal structures of two new cobaloximes, (CH2Cl)Co(DH)2L with L = py, 1, and 1-Me-Im, 2) have been determined. The results of a conformational analysis on ribosyl-imidazole derivatives, taken as a suitable vitamin B12 coenzyme model, suggest that the 1-Me-imidazole-like ligands have a significantly greater rotation freedom with respect to the benzimidazole-like ones, but cause similar stretchings of the Co-C bond, and a significantly less stretching of the Co-N one. Implications for the recent findings on the binding mode of the coenzyme B12 in the enzyme active site are discussed.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98399_s.pdf or from the author.
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    Thermochemical Study of Reduction and Oxidation Reactions of Molybdovanadophosphoric Heteropolyacids in Aqueous Solutions (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1009-1014 
    Details
    ISSN: 1434-1948
    Keywords: Heteropolyacids ; Molybdovanadophosphates ; Hydrazine hydrate ; Reduction ; Oxidations ; Thermochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential enthalpies of reduction, -ΔrH4j, have been found at 343 K for 0.2 m aqueous heteropolyacids H3+xPVxMo12-xO40 (HPA-x, where 1 ≤ x ≤ 6) and their salts by hydrazine hydrate (HH). The -ΔrH4j values depend on x and m, where m = [VIV]/[HPA-x]. At m ≈ 0, the initial -ΔrH4j value is 436 ± 14 kJ mol-1 HH for all HPA-x. For HPA-x with 3 ≤ x ≤ 6, the curves -ΔrH4j = f(mj) have maxima associated with formation and reduction of the outer-sphere cation VVVIVO33+. A similar maximum is observed on reduction of 0.1 M VO2ClO4 in 4 M HClO4. No maxima are observed for the reduction of HPA-1, HPA-2, and salts of HPA-3. For HPA-3 salts, -ΔrH4j = f(mj) depends primarily on the pH of the salt solution, rather than on the nature of the cation. Reduction and oxidation of HPA-x and their salts are reversible reactions. In HPA-x solutions, VO2+ in the outer sphere is reduced first, and VV in the inner coordination sphere of the heteropoly anion is reduced next. Differential enthalpies for the oxidation of the reduced HPA-x by dioxygen (-ΔrH2j) have been calculated. The sequence of the oxidation of different VIV forms in the reduced HmHPA-x solutions is the reverse of that for the reduction of the VV forms in the initial HPA-x solutions.
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  • 155
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    Syntheses and Characterization by NMR Spectroscopy and X-ray Diffraction of Complexes Derived from Metals of Groups 2 and 13 and the Ligand Bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1021-1027 
    Details
    ISSN: 1434-1948
    Keywords: Alkaline earth metals ; Group-13 metals ; Coordination chemistry ; Bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine ligand ; Nonacoordinated strontium compound ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 3,5-di-tert-butylcatechol and aqueous ammonia with boron, aluminum, gallium, or strontium chloride, or with calcium or barium acetate produce, under oxidizing conditions, neutral complexes of stoichiometric formulae ML (M = BCl), ML2, [M = Al (2), Ga (3), Ca (4), and Ba (5)], and ML3H [M = Sr (6)] [L = different oxidation states of bis(3,5-di-tert-butyl-1-hydroxy-2-phenyl)amine]. The structures of 1 and 4-6 were established by 1H- and 13C-NMR spectroscopy and of 2, 3, and 6 by X-ray diffraction. The coordination compound ClBL (1) was obtained by transmetallation of ZnL2 with BCl3. It is a tetracyclic compound with tetracoordinated boron and nitrogen atoms, the ligand being in the reduced form, bis(hydroxyphenyl)amine. The paramagnetic complexes 2 and 3 crystallized in the triclinic system and are hexacoordinated with two orthogonal planar ligands bonded to the metal atoms. The ligands appear in two different oxidation states: one as the monoanion and another as a radical dianion. Based on their X-ray diffraction molecular structures, it is deduced that both ligands have similar structures, confirming electronic delocalization and fast interconversion of their oxidation states. Ca and Ba complexes are diamagnetic and hexacoordinated, both ligands being monoanions The strontium complex crystallized in the monoclinic system, the metal atom is nonacoordinated, having two ligands as monoanions, and a third one is a neutral protonated diquinone. Its structure is a distorted helix with three paddles in a C3 geometry and its unexpected diamagnetic behaviour is due to the presence of a reduced protonated ligand.
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    Synthesis, Structure and Reactivity of 3,4-Dihydro-2H-1,2,4,3-triazaboroles (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1193-1198 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Triazaboroles ; Heterocycles ; Halogens ; Cyanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,4-Dihydro-2,4-diphenyl-2H-1,2,4,3-triazaboroles 3a, 3b, and 4 were synthesized by cyclocondensation of N1,N3-diphenylformamidrazone (1) with dibromophenylborane, dibromomethylborane, and boron trichloride. 3-Chloro-3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (4) was converted into 3,4-dihydro-2,4-diphenyl-2H-1,2,4,3-triazaborole (5) by treatment with LiAlH4. The corresponding 3-cyanato and 3-cyano derivatives 6 and 7 resulted from the reaction of 4 with AgOCN and AgCN, respectively. Compound 7 was transformed into the bis(1,2,4,3-triazaborolyl)oxane 8 by silver oxide. Compounds 1-8 were characterized by elemental analyses and spectroscopic methods (1H, 11B, and 13C NMR; IR; MS). The molecular structure of 8 was established by single-crystal X-ray diffraction analysis.
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    Combined Quantum Chemical and Mass Spectrometry Study of [Ge,C,H]+ and Its Neutral Counterpart (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1203-1210 
    Details
    ISSN: 1434-1948
    Keywords: Organogermanium ions ; Mass spectrometry ; Ab initio theory ; NBO ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cation [Ge,C,H]+ has been generated by the electron ionisation of trichloromethylgermane. Collisional activation experiments were used to establish a Ge-C-H connectivity in this species, for which a significant fraction of the ion population was found to survive neutralisation-reionisation mass spectrometry (NRMS) experiments. Thus, the neutral counterpart [Ge,C,H]0 is stable on a microsecond timescale. Becke's 3 parameter hybrid density functional (B3LYP) was used to map the ion and neutral potential-energy surfaces, in conjunction with double-zeta and triple-zeta basis sets. The computational results obtained using the triple-zeta basis sets suggest that, for the cation, the global minimum is the high spin 3Σ GeCH+, with the first Ge-C-H excited state, 1Σ GeCH+, approximately 39 kcal mol-1 less stable. The lowest energy ion structure with H-Ge-C connectivity is bent (3A′′HGeC+,∠H-Ge-C = 126.3) and 69 kcal mol-1 less stable than the global minimum. For the neutral, a doublet (2π) with Ge-C-H connectivity is predicted to be the global minimum. The classical barrier for the neutral 1,2-hydrogen shift reaction on the doublet surface is negligible (0.1 kcal mol-1), while the smallest barrier for the cation is 13.0 kcal mol-1, corresponding to (3A′′) HGeC+ → (3Σ) GeCH+. Natural bond order analysis has been used to establish the order of the metal-carbon bond for selected states of both the neutral and the ion. Neutral and cationic isomers with Ge-C triple bonds were found to be high-energy excited states, with the metal-carbon bonds in the cation and neutral ground states of order 2.0 and 2.5, respectively. The instability of Ge-C triple bonded species is attributed to the energy required for electronic promotion in the metal in order to achieve a hybrid configuration suitable for the formation of such a bond.
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    Linear Five-Centred Chromium Multiple Bonds Bridged by Four tpda2- Ligands [tpda2- = tripyridyldiamido dianion] - Synthesis and Structural Studies (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1243-1251 
    Details
    ISSN: 1434-1948
    Keywords: Metal string complexes ; Multicentered metal-metal multiple bond ; Quadruple bonds ; Metal-metal interactions ; Chromium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear pentanuclear chromium complexes [CrII5(μ5-tpda)4Cl2] (1), [CrII5(μ5-tpda)4(NCS)2] (2), [CrIIICrII4(μ5-tpda)4F2](BF4) (3), and [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4), with four all-syn tri(α-pyridyl)diamido dianion (tpda2-) ligands, have been prepared and structurally characterized. Compounds 1 and 2 possess a delocalized Cr(II)-Cr(II)-Cr(II)-Cr(II)-Cr(II) five-centred metal-metal bond of order 1.5. In both 1 and 2 two values for CrII-CrII bond lengths are found both; the outer ones connected with axial ligands are 2.284(1) and 2.285(2) Å, and the inner ones are 2.2405(8) and 2.246(1) Å, for 1 and 2, respectively. When compound 1 reacts with 2 equiv. of AgBF4 or Ag(OTf), a oxidation reaction takes place and one of the terminal chromium(II) ions is oxidized to produce [CrIIICrII4(μ5-tpda)4F2]BF4 (3) or [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4). Two short Cr-Cr distances [1.969(2) and 2.138(2) Å for 3, 1.846(1) and 1.922(1) Å for 4] are found, with the presence of two quadruple bonds among four adjacent CrII ions. The fifth CrIII ion, which is separated from the neighboring CrII ion by 2.487(2) Å for 3 and 2.610(1) Å for 4, is simply a square pyramidal unit with no metal-metal bonding interaction.
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    Synthesis and Characterization of the Heterometallic Aggregate Pb2Al5(μ3-O)(μ4-O)(μ-OiPr)9(OiPr)3(μ-OAc)3 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1291-1293 
    Details
    ISSN: 1434-1948
    Keywords: Aluminum ; Lead ; O ligands ; Alkoxy carboxylates ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel heterometallic aggregate Pb2Al5(μ3-O)(μ4-O)(μ-OiPr)9(OiPr)3(μ-OAc)3 obtained from the interaction of Pb(OAc)2 and Al(O-iPr)3 is the first structurally characterized example based on lead and aluminum. This compound has been isolated in high yield and examined by 1H-, 13C-, and 27Al NMR, and in the solid state by X-ray crystallography.
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    Pyrazolato Metal Complexes - Synthesis, Characterization, and X-ray Crystal Structures of Heterotrimetallic Re-M2 Derivatives (M = Cu, Ag, Au) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1301-1307 
    Details
    ISSN: 1434-1948
    Keywords: Pyrazolato ligands ; Rhenium ; Group-11 metals ; Heterometallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By treating [(CO)3Re(Hpz)2(pz)] (Hpz = pyrazole) with [Cu(CH3CN)4]BF4, AgNO3, or [Au(tht)Cl] (tht = tetrahydrothiophene) in acetonitrile in the presence of Et3N, the corresponding trinuclear complexes {(CO)3Re(pz)3[M(CH3CN)]2} (1a-c) have been obtained. Treatment of complexes 1a-c with cyclohexyl isocyanide (c-C6H11NC) afforded the derivatives {(CO)3Re(pz)3[M(c-C6H11NC)]2} (2a-c). Complexes 2a-c have been characterized in solution by 1H-NMR spectroscopy and in the solid state by single-crystal X-ray diffraction analysis.
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    Synthesis and Investigations on Nitrido(phthalocyaninato)rhenium Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1309-1313 
    Details
    ISSN: 1434-1948
    Keywords: Phthalocyanines ; Rhenium ; Nitrido(octa-n-alkylphthalocyaninato)rhenium compounds ; Nucleophilic additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of nitrido(tetra-tert-butylphthalocyaninato)rhenium (1) with boron tribromide leading to (tBu4Pc)ReNBBr3 (4) and with acetone to give the imido complex (tBu4Pc)Re[NC(CH3)2CH2C(O)CH3]OH (2b) and its μ-oxo dimer 3 are reported. Starting from the corresponding 4,5-di-n-alkylphthalonitriles and ammonium perrhenate four soluble nitrido(octa-n-alkylphthalocyaninato)rhenium complexes 5-8 were synthesized. Nitrido(octa-n-pentylphthalocyaninato)rhenium (6) was treated with boron tribromide to afford [(C5H11)8Pc]ReNBBr3 (9).
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    Synthesis, Chemistry, and Characterization of Perfluoroaromatic Selenium Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1359-1366 
    Details
    ISSN: 1434-1948
    Keywords: Selenium ; Fluorine ; Multinuclear NMR ; Raman spectroscopy ; X-ray crystallography ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of perfluoroaryllithium RC6F4Li, where R = F or 4-CF3C6F4O, respectively, with selenium gives the known diselanes (RC6F4Se)2 (1a, 1b). Redox reactions of 1 with hydrogen peroxide result in the formation of the seleninic acids RC6F4SeOOH which crystallize as hydrates (2a, 2b); with mercury give the bis(arylseleno)mercuries (RC6F4Se)2Hg (3a, 3b); with sulfuryl chloride or bromine give the selenenyl chlorides (4a, 4b) or selenenyl bromides (5a, 5b). Selenenyl chlorides (4a, 4b) react with a variety of trimethylsilyl reagents Me3SiX (X = Br, CN, NMe2, NEt2) to form 5a, 5b; selenocyanates RC6F4SeCN (6a, 6b); selenenyl amides RC6F4SeNMe2 (7a, 7b) and RC6F4SeNEt2 (8a, 8b). A new synthetic route to diorgano selanes is developed by reaction of 4a, 4b with perfluoroaryllithium to give the symmetric (RC6F4)2Se (9a, 9b). All derivatives are thoroughly characterized and in addition the molecular structures of 2a, 6a, and 9a are established by X-ray crystallography.
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    Solvates of Sodium Bis(borane)dimethylamide (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1373-1379 
    Details
    ISSN: 1434-1948
    Keywords: Sodium bis(borane)dimethylamide solvates ; X-ray structure ; Reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of sodium metal with dimethylamine-borane in THF yields Na[(H3B)2NMe2] (1) which can be isolated as {Na[(H3B)2NMe2]}5·THF or as Na[(H3B)2NMe2]·15-crown-5 (2) and Na[(H3B)2NMe2]·benzo-15-crown-5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN-BH2-NMe2-BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5·THF crystallizes in an extended three-dimensional lattice, in which the Na atoms are coordinated by 6-9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N-H···H-B interactions.
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    Self-Assembly, Structure, and Physical Properties of Tetranuclear ZnII and CoII Complexes of [2 × 2] Grid-Type (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1421-1428 
    Details
    ISSN: 1434-1948
    Keywords: Grid complexes ; Self-assembly ; Co ; Zn ; Coordination chemistry ; Bis(tridentate) ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tretrametallic [2 × 2] grid-type complexes 1-4 are formed by self-assembly of the bis(tridentate) ligands 5 and 6 with ZnII and CoII cations. They have been characterized by spectroscopic studies in solution as well as by crystal structure determination. The substituents in the central pyrimidine ring play an important role in terms of geometry and physical properties of the complexes. They induce an orthogonal orientation of the ligand in the complexes which is critical for the formation of ordered monolayers and extended self-organized arrays of grids. The physical properties of the complexes such as metal-metal interaction and π-π* stacking between the ligands may be modulated by changing these substituents.
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    New Inorganic Metallacycles and the First Six-Membered Covalent “True” Heterocycle - Oxidation of RC(E)NHPPh2 (E = O or S; R = H2N, Ph, or Py) with O, S, or Se to Give RC(E)NHP(E′)Ph2 (E′ = O, S, Se) and Their Coordination Chemistry (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1445-1452 
    Details
    ISSN: 1434-1948
    Keywords: Metallacycles ; Solid-state structures ; Heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct oxidation of PhC(O)NHPPh2, H2NC(S)NHPPh2, (C5H4N)C(S)NHPPh2 with O2, S8, or Se gives [PhC(O)NHP(O)Ph2] (1), [H2NC(S)NHP(S)Ph2] (2), [H2NC(O)NHP-(S)Ph2] (3), [PhC(O)NHP(S)Ph2] (4), [(C5H4N)C(S)NHP(S)Ph2] (5), and [H2NC(S)NHP(Se)Ph2] (6). Deprotonation of 1, 2, 4-6 with potassium tert-butoxide gives K[PhC(O)NP(O)Ph2] (7), K[H2NC(S)NP(S)Ph2] (8), K[PhC(O)NP(S)Ph2] (9), K[(C5H4N)C(S)NP(S)Ph2] (10), and K[H2NC(S)NP(Se)Ph2] (11). Reaction of 4with KOBu and [Cu(Ph3P)2][NO3] gives [Cu(Ph3P)(PhC(O)NP(S)Ph2)] (12) which is the first crystallographically characterised example of a non-ionic six-membered “true” heterocycle (i.e. a ring in which every heterocatom is different). 9 and 10 were treated with [PdCl2(COD)] to give [Pd{PhC(O)NP(S)Ph2}2] (13) and [Pd{(C5H4N)C(O)NP(S)Ph2}2] (14), respectively The anion of 8 coordinates to zinc forming [Zn{H2NC(S)NP(S)Ph2}2] (15). Treatment of 2 or 8 with [PtCl2(COD)] gives [Pt{H2NC(S)NP(S)Ph2}{H2NC(S)NHP(S)Ph2}]+Cl- (16) and [Pt{H2NC(S)NP(S)Ph2}2] (17), respectively. The X-ray structures of 12, 15-17are reported.
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    Mechanism of the Catalytic Oxidation of Tertiary Alcohols by the Water-Soluble Mn-TMPyP/KHSO5 System: β-Fragmentation versus O-Neophyl Rearrangement (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1467-1477 
    Details
    ISSN: 1434-1948
    Keywords: Oxidations ; Tertiary alcohol ; Porphyrins ; Neophyl rearrangement ; Cleavage reactions ; β-Scission ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of 4-(1-hydroxy-1-phenylethyl)benzoic acid HPEBA with a water-soluble metalloporphyrin as catalyst and KHSO5 as oxygen atom donor gives the major products, acetophenone AC and acetylbenzoic acid ABA, by a Caliph-CAr bond cleavage, but a minor product, benzoyloxybenzoic acid BOBA, requires the insertion of an oxygen atom to form the ester. This compound becomes the main oxidation product on increasing the amount of acetonitrile in the reaction medium, and its formation is oxygen-dependent. The conversion is drastically lowered by using D2O instead of H2O, suggesting that an alkoxyl radical is formed in the rate-determining step. Labeling experiments using 18O2 or H218O under different reaction conditions show that the carbonyl oxygen atoms of AC and ABA originate either from substrate, water or dioxygen. However, the carbonyl oxygen atom in the ester group of BOBA originates from dioxygen while the other oxygen atom of the ester remains unlabeled. These results can be explained by an O-neophyl rearrangement of the initial alkoxyl radical to afford a carbon-based radical which then reacts with dioxygen or MnIV-OH/water. In a competitive reaction pathway, direct β-scission of the alkoxyl radical leads to unlabeled products. The oxidation of other tertiary diaryl alcohols is also discussed.
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    Transition-Metal Complexes of the Optically Active Cyclopentadienyl Ligand PinCp*: Crystal Structure of (SRe)-(η5-PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7] (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1497-1505 
    Details
    ISSN: 1434-1948
    Keywords: Half-sandwich complexes ; Molybdenum ; Optically active complexes ; Rhenium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of (η5-PinCp*)Re(CO)3 [PinCp* = tetramethyl(pinanyl)cyclopentadienyl] is described. Successive substitution of two CO ligands by NO+ and PPh3 generates a 1:1 diastereomeric mixture of chiral-at-metal [(SRe)/(RRe)-(PinCp*)Re(CO)(NO)(PPh3)]BF4. The diastereomers are converted with sodium methoxide into the derivative “esters” (SRe)/(RRe)-(PinCp*)Re(COOCH3)(NO)(PPh3), and then with (+)-(R)-(1-naphthylethyl)amine to the “amides” (SRe)/(RRe)-(PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7] [(SRe)/(RRe) = 1:1]. Fractional crystallisation separates the (SRe) isomer with an optical purity of 〉 98%. The latter compound has been characterized by X-ray structure analysis. By treating the (SRe)-amide with CF3CO2H and NaBF4, (SRe)-(PinCp*)Re(CH3)(NO)(PPh3) can be generated. Protolysis of this compound with HBF4/Et2O in CD2Cl2 at -78 °C leads to the solvent-stabilized complex (SRe)-[(PinCp*)Re(NO)(PPh3)(ClCD2Cl)]+BF4-. The thermal and configurational stability of this chiral Lewis acid is investigated at various temperatures. The syntheses of [PinCp*RhCl2]2, PinCp*TiCl3 and PinCp*M(CO)2(NO) (M = Mo, W) are also described. Starting with PinCp*M(CO)2(NO), the relatively stable 16-VE complexes PinCp*MCl2(NO) and PinCp*W(CH2SiMe3)2(NO) are synthesized.
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    Aldehyde Complexes of Zinc Halides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 129-135 
    Details
    ISSN: 1434-1948
    Keywords: Zinc ; Aldehyde ligands ; Halide ligands ; Structural chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aldehyde complexes of the zinc halides were obtained by treating ZnCl2, ZnBr2, and ZnI2 under anhydrous conditions with large excesses of benzaldehyde and various substituted benzaldehydes. Their constitutions were determined by a total of 12 X-ray structure analyses. Three product types were found: ZnHal2(aldehyde)2 (A), [ZnHal2(aldehyde)]∞ (B), and [Zn(aldehyde)6] [Zn2Hal6] (C). All three dissolve readily in the corresponding aldehyde or in polar nonprotic solvents indicating the presence of solvated zinc species in solution.
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    Main Group Metal Directed Self-Assembly in a Tetrameric Trimethyltin(IV) N-nitroso-N-phenylhydroxylaminato Complex Containing an Unprecedented 20-Membered Inorganic (Carbon-Free) Metallamacrocycle (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1593-1596 
    Details
    ISSN: 1434-1948
    Keywords: Metallamacrocycles ; Structure elucidation ; Supramolecular chemistry ; Tin(IV) compounds ; Vibrational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrakis[trimethyl(N-nitroso-N-phenylhydroxylaminato)tin(IV)] was synthesized by reaction of cupferron ([PhN(O)NO]NH4) with trimethyltin(IV) chloride. The complex was characterized by X-ray diffraction analysis, FT-IR and FT-Raman spectroscopy. An X-ray structural analysis of the title complex [Me3Sn(O2N2Ph)]4 reveals the first example of a bridging coordinated cupferronato ligand. This coordination pattern leads to an unprecedented inorganic 20-membered (carbon-free) metallamacrocycle Sn4O8N8 in which four Me3Sn and four PhN2O2 subunits are self-assembled.
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    Geminal Bis(hypersilyl) Compounds - The Reaction of Tris(trimethylsilyl)silyllithium with Dialkyl(chloromethylene)ammonium Chlorides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 21-26 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Silanes, sterically congested ; Tris(trimethylsilyl)silanes ; (Chloromethylene)ammonium chlorides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tris(trimethylsilyl)silyllithium (1) reacts with dialkyl(chloromethylene)ammonium chlorides (molar ratio 2:1) to give the (dialkylamino)bis(hypersilyl)methanes [(Me3Si)3Si]2CHNR2 (5a-c; a: R = Me, b: R = Et, c: R2 = [CH2]5). Due to the extreme bulkiness of the hemispherical (Me3Si)3Si substituents, the structures of these geminal bis(hypersilyl) derivatives are characterized by tremendous distortions of their molecular skeletons. This was confirmed by X-ray structural analyses of 5a and 5c, which revealed considerable elongations of the central Si-C bonds (5a: 2.01 and 1.95 Å; 5c: 1.99 and 1.97 Å) and an extreme widening of the Si-C-Si angles at the central sp3-carbon atoms (5a: 132.6°; 5c: 128.7°). By concentrated sulfuric acid, 5a is converted to give, after hydrolysis, the silanol (Me3Si)2Si(OH)-CH2Si(SiMe3)3 (13). The formation of 13 is discussed as proceeding through the transient silene (Me3Si)2Si=CHSi(SiMe3)3 (11), generated by a formal (dimethylamino)trimethylsilane elimination from 5a according to an acid-induced sila Peterson mechanism.
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    Steric and Electronic Effects on the 103Rh NMR Chemical Shifts of RhI(cyclooctadiene) Compounds Bearing N-Donor Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 27-33 
    Details
    ISSN: 1434-1948
    Keywords: 103Rh NMR ; Rhodium complexes ; Nitrogen ligands ; Chemical-shift computation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study electronic and steric effects on δ(103Rh), the103Rh-NMR spectra of a series of [Rh(cod)L2] complexes (with L = nitrogen, oxygen, or chloride) have been measured by gradient-enhanced HMQC (1H,103Rh) NMR spectroscopy. Density functional computations of representative examples have been performed at the GIAO-B3LYP level of theory. The obtained experimental values of 103Rh shifts fit the generally observed trend of coordinating ligands in the first coordination sphere of the metal: P 〈 N 〈 O. Calculated 103Rh shifts agreed to within 8 % with experimental values. The computational results indicate that the Rh-N bond distance has a larger influence on the chemical shift than the N-Rh-N angle.
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    A Versatile Fluorescent System for Sensing of H+, Transition Metals, and Aromatic Carboxylates (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 35-39 
    Details
    ISSN: 1434-1948
    Keywords: Fluorescent sensors ; Molecular recognition ; Charge transfer excited states ; Metal complexes ; pH Sensors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fluorescent emission of the N,N-dimethylaniline fragment of the tetramine system 3varies with pH, displaying a maximum of the fluorescent intensity, IF, at pH = 5. Binding of transition metals (CuII, NiII) induces fluorescence quenching and modifies the IF vs. pH profile, giving rise to an OFF-ON-OFF type of sensor. The [ZnII(3)]2+complex recognises carboxylate anions, both aliphatic and aromatic. Recognition is signalled via fluorescence quenching only for aromatic carboxylates.
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    Aromatic Phosphenium Cations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 41-49 
    Details
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Aromaticity ; Phosphenium cations ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aromatic stabilization of cyclic phosphenium cations (general type C2N2P+) was studied by experimental methods (synthesis, multinuclear NMR, single crystal X-ray crystallography) and quantum chemical calculations (ab initio methods). The structures of the 1,3,2-diazaphosphole derivatives [(tBuN-CH=CH-NtBu)P+]Cl- (1), (tBuN-CH2-CH2-NtBu)P-Cl (2), [(tBuN-CH=CH-NtBu)P]+PF6- (3) and [(tBuN-CH2-CH2-NtBu)]P+PF6- (4) were examined by single crystal X-ray diffraction. The chloro phosphane [(tBuN-CH=CH-NtBu)P]+Cl- (1) has an ionic P-Cl bond and contains an aromatically stabilized phosphenium cation [shortest distance P···Cl = 275.9(2) pm], while the CC-saturated compound (tBuN-CH2-CH2-NtBu)P-Cl (2) is covalent. The two chloro-phosphanes 1 and 2 differ sharply in their volatility and solubility in organic solvents. Compound 2 is soluble in hydrocarbons and sublimes readily at 90 °C/0.1 Torr but 1 is insoluble in hexanes and not volatile below 180 °C/0.1 Torr. The degree of aromatic stabilization in the phosphenium cation 1 was investigated by ab initio methods. For the model cations [RN-CH2-CH2-NR]P+ and [(RN-CH=CH-NR)P]+, thermochemical stabilization energies of 25.8 kcal · mol-1 (R = H) and 28.1 kcal · mol-1 (R = Me) were obtained from isodesmic hydrogenation reactions at the RHF/MP2/6-31G*//RHF/6-31G* level.
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  • 174
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    Crystal Structure and Intercalation Properties of γ-Zr(AsO4)(H2AsO4) × 2 H2O (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 61-65 
    Details
    ISSN: 1434-1948
    Keywords: Zirconium arsenate ; Crystal structure ; Amine intercalation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystalline structure of γ-Zr(AsO4)(H2AsO4) × 2 H2O (γ-ZrAs) has been refined by the Rietveld method. It has a monoclinic P21 layered structure built up from AsO4 tetrahedra and ZrO6 octahedra stacked along the 001 direction. The cell parameters are: a = 5.5752(6) Å, b = 6.8290(7) Å, c = 12.110(1) Å, and β = 103.03(1)°. The layered nature of γ-ZrAs is confirmed by the intercalation of n-alkylamines (CH3[CH2]nNH2; n = 0-5) as well as of cyclic amines (benzylamine, cyclohexylamine, piperidine, and pyridine). Among the linear amines, only with methyl-, ethyl-, and hexylamine is the maximum incorporation attained. With the cyclic amines, except in the case of pyridine, pure new phases are obtained, with the highest degree of intercalation being one mol of amine per mol of γ-ZrAs.
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  • 175
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    Synthesis of the Stereoisomers of Methohexital by Palladium-Catalyzed Allylation (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 51-59 
    Details
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Allylic alkylation ; 1-Methyl-5-(1′-methylpent-2′-ynyl)barbituric acid ; Palladium catalysts ; Chiral phosphane imine ligands ; Methohexital ; Anesthetic dose ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Allylation of 1-methyl-5-(1′-methylpent-2′-ynyl)barbituric acid (MBS) with allyl acetate using in situ catalysts of palladium(II) acetylacetonate and chiral phosphane imine ligands resulted in the enantioselective formation of 5-allyl-1-methyl-5-(1′-methylpent-2′-ynyl)barbituric acid (Methohexital), an important anesthetic drug. Both, MBS and Methohexital contain two stereogenic carbon atoms. In MBS, the asymmetric centre in the barbiturate system is labile due to enolization. The asymmetric centre in the hexyne side chain is stable and racemic. The two asymmetric centres of Methohexital are stable and give rise to four stereoisomers, two diastereomeric racemates. An analysis of the isomers of MBS and Methohexital was established on the basis of 1H NMR and, in particular, GC including a base-line separation of the four stereoisomers of Methohexital. The stereoselectivity of the allylation is difficult to control, because the new quaternary asymmetric centre in the barbiturate ring of Methohexital is formed within the nucleophile, attacking the η3-allyl ligand of the catalyst from the side opposite to the palladium atom. Classical optically active ligands, such as diop or norphos, give only 2-6 % ee. Chiral phosphane imine ligands are a successful class of compounds, synthesized by Schiff base condensation of (2-formylphenyl)diphenylphosphane with optically active primary amines. The most efficient ligands have a hydroxymethyl and a bulky alkyl substituent at the asymmetric centre in the imine part, e.g. the L-iso-leucinol and the L-tert-leucinol derivatives 5 and 7. In the Pd-catalyzed allylation of MBS a kinetic resolution and the effect of the enantioselective catalyst interplay, the contributions of which are separated. For MBS the best stereoselectivity factor of the kinetic resolution s = kR/kS was 2.6 and 83 % “ee” were achieved. The corresponding values for Methohexital were s = 3.5 and 80 % ee in the α-dl pair. For 10 mixtures of Methohexital stereoisomers the anesthetic doses for rats were determined. With 9.1 mg/kg body weight of the animal the sample obtained from the catalysis with the D-α-phenylglycinol derivative 8 gave a much lower anesthetic dose than the widely used narcotic Brevimytal®Natrium, the sodium salt of the α-dl racemate of Methohexital, with 13.0 mg/kg body weight.
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    Synthesis and Structure of the First [1]Boratitanocenophanes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 69-73 
    Details
    ISSN: 1434-1948
    Keywords: Boron ; Titanium ; Metallocenophanes ; [1]Boratitanocenophanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents two methods for the synthesis of the first [1]boratitanocenophanes. The novel biscyclopentadienylborane [(Me3Si)2NB(C5H5)2], the dilithio salt Li2[(Me3Si)2NB(C5H4)2] (1) of which was characterized by multinuclear NMR methods, was prepared in situ, and served as starting material for several [1]boratitanocenophanes. [Cl2Ti{(C5H4)2BN(SiMe3)2}] (2) was obtained in high yield by a convenient one-pot synthesis starting from 1 and [TiCl3(thf)3], followed by oxidation with PbCl2. The highly reactive [(Me2N)2Ti{(C5H4)2BN(SiMe3)2}] (3) was obtained by the reaction of [(Me3Si)2NB(C5H5)2], prepared in situ, with Ti(NMe2)4and converted into the chloro derivatives [(Me2N)ClTi{(C5H4)2BN(SiMe3)2}] (4) and [Cl2Ti{(C5H4)2BN(SiMe3)2}] (2) by treatment with one or two equivalents of a suitable diaminochloroborane. All [1]boratitanocenophanes were characterized in solution by multinuclear NMR spectroscopy, and in addition the structure of 2 in the crystalline state was determined by a single-crystal X-ray study.
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    [(Trichlorosilyl)dichloroboryl]ethane: Synthesis and Characterisation by Means of Experiment and Theory (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 75-81 
    Details
    ISSN: 1434-1948
    Keywords: TSDE ; Ceramics ; Theoretical IR-spectroscopy ; RI-MP2 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new compound for the molecular synthesis route to high-demand Si/B/N/C ceramics has been found and is described in this work. We report on an elegant “one-pot” synthesis of [(trichlorosilyl)dichloroboryl]ethane (TSDE, Cl3Si-CH[(CH3)(BCl2)]) and its structural characterisation by means of nuclear magnetic resonance and (theoretical and experimental) infra-red spectroscopy. Density functional and Hartree-Fock calculations combined with a perturbational treatment of the electron correlation have been performed. Both methods yield good agreement of theoretical and experimental spectra, with the perturbational approach being slightly superior. In a similar way to the amino compound [(trichlorosilyl)amino]dichloroborane (TADB), TSDE exhibits a planar coordination of the dichloroboryl terminus but tetrahedral neighbourhoods for both carbon and silicon. The electronic structure has been investigated and a σ - n order of the frontier orbitals shall be discussed.
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    Substituted Tungsten Fluorides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 95-99 
    Details
    ISSN: 1434-1948
    Keywords: Tungsten ; Fluorine ; 2,2,2-Trifluoroethoxy ; Bis(2,2,2-trifluoroethyl)amino ; Aza-tungsta-cyclopropane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: WF6 reacts with HOCH2CF3 to form F5W-OCH2CF3 and cis-WF4(OCH2CF3)2. CsF is added to F5WOCH2CF3, yielding the heptacoordinated anion [F6WOCH2CF3]-, which has a capped octahedral structure with the oxygen ligand in an equatorial position. The first step of the reaction of WF6 with HN(CH2CF3)2 results in F5WN(CH2CF3)2. Excess HN(CH2CF3)2 causes deprotonation, yielding the heptacoordinated [F5W(η2CF3-CHN-CH2CF3)]- anion. This can be described as a tungstaazacyclopropane derivative or a π complex between F5W- and CF3-CHN-CH2CF3. The only case in which MoF6 reacts similarly is the formation of F5Mo-OCH2CF3.
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  • 179
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    Ta11Si2Se8 - Condensed Tetrakaidecahedral Ta9Si Clusters Arranged to an Open Network Structure (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 87-93 
    Details
    ISSN: 1434-1948
    Keywords: Selenium ; Silicon ; Silicides ; Tantalum ; Condensed cluster compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ta11Si2Se8 was synthesized from a pre-reacted mixture of the elements in a sealed tantalum tube at 1570 K. Mo-doped crystals were obtained in a welded molybdenum crucible by a chemical transport reaction using TeI4 as a transport agent. The structure of Mo0.11Ta10.89(2)Si2Se8 has been determined by single crystal X-ray means [Pnnm, Z = 2, a = 1184.4(1) pm, b = 1939.4(1) pm, c = 346.48(2) pm, wR2 = 0.069]. The structure of the ternary phase was verified by means of a Rietveld profile fit of a powder X-ray diffractogram. The silicide is isotypic with Ta11Ni2Se8. The structure is composed of Si-centred, tricapped trigonal prismatic Ta9Si clusters. The tetrakaidecahedral Ta9Si clusters are fused into twin chains by sharing the Tapr atoms of facing triangulated prism faces and one out of three capping atoms Tac. Intercluster linkage of the remaining Tac atoms generates a microporous ∞3[SiTa2cTa1/2cTa6/2pr] substructure. The channels of the metal network are sheathed by three-, four-, five-, and sixfold coordinated Se atoms. Four-probe dc resistivity measurements revealed the Mo-doped phase to be a moderate metallic conductor. The bonding interactions contributing to the stability of Ta11Si2Se8 and distinctions in bonding for Ta11Si2Se8 and Ta11Ni2Se8 are analysed on the basis of semi-empirical extended Hückel calculations.
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    Preparation, Structure, and Properties of a Mixed-Valent NiIINiIII Amine-Selenolate Complex (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 189-193 
    Details
    ISSN: 1434-1948
    Keywords: Mixed-valent compounds ; Nickel ; N2Se ligand ; Cyclic voltammetry ; EPR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two dinuclear nickel amine-selenolate complexes of the tridentate amine-selenolate ligand, 4-tert-butyl-2,6-di(aminomethyl)selenophenol (1b), have been synthesized and their properties characterized. The green complex [NiII2(1b)3]Cl (4a) is readily prepared from 1b, NiCl2 · 6 H2O, and NaOMe in methanol or by reaction of coordinatively unsaturated [NiII2(1b)2][BPh4]2 (2b) with another one equivalent of 1b in the presence of triethylamine. The face-sharing, bioctahedral structure of 4a is derived from UV/Vis spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction of its oxidation product, [NiIINiIII(1b)3]2+. The dication was prepared by air-oxidation of 4a in MeOH and isolated as the dark-brown BPh4- salt, [NiIINiIII(1b)3][BPh4]2 · CH3OH (4b). Mixed-valent complex 4b consists of a dinuclear, face-sharing bioctahedral dication with a central N3NiII(μ2-SeR)3NiIIIN3 core and well-separated tetraphenylborate anions. Distortions from D3h symmetry suggest that 4b is a trapped-valence compound in the solid-state. On the CV time scale complex 4a undergoes two reversible one-electron oxidations at E11/2 = -0.15 and at E21/2 = +0.29 V vs SCE, affording 4b and the thermally not stable trication [NiIII2(1b)3]3+, respectively. The EPR spectrum of a powdered sample of 4b reveals an S = 3/2 ground state of the mixed-valent NiIINiIII complex.
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    A Unique Fourfold Intramolecular Hydrogen Bonding Stabilises the Structure of trans-Bis(2-amino-5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine-N3)aquatrichlororuthenium(III) Monohydrate (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 213-215 
    Details
    ISSN: 1434-1948
    Keywords: Ruthenium ; Nitrogen heterocycles ; Hydrogen bonds ; Antitumor agents ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structure of the potential antitumour complex trans-[RuCl3(H2O)(admtp)2] · H2O (admtp = 2-amino-5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine) shows unique and very interesting intramolecular hydrogen-bonding properties with the non-bridgehead pyrimidinic nitrogen atom of admtp acting as hydrogen acceptor and the amino group acting as hydrogen donor.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98348_s.pdf or from the author.
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    A μ-η1-Azavinylidene Complex: Intramolecular Condensation of Two Acetonitrile Ligands at a Dinuclear Molybdenum(III) Site (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 221-223 
    Details
    ISSN: 1434-1948
    Keywords: Dimolybdenum(III) complexes ; Azavinylidene ; C-C coupling ; Acetonitrile ligands ; X-ray crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Removal of a proton from one of the two coordinated acetonitrile ligands in [Mo2Cp2(μ-SMe)3(CH3CN)2](BF4) (1) initiates its intramolecular condensation with the second of the acetonitrile ligands attached to the bimetallic [Mo2Cp2(μ-SMe)3] core, thereby giving rise to the novel μ-η1-azavinylidene complex {Mo2Cp2(μ-SMe)3[μ-η1-N=C(CH3)-CH2CN]} (2). Complex 2 has been characterized by NMR and X-ray methods.
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    Synthesis, Electrochemistry, and Oxygen-Atom Transfer Reactions of Dioxotungsten(VI) and -molybdenum(VI) Complexes with N2O2 and N2S2 Tetradentate Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 313-321 
    Details
    ISSN: 1434-1948
    Keywords: Tungsten complexes ; Molybdenum complexes ; Tetradentate ligands ; Oxygen-atom transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of N2O2 tetradentate ligands with a range of substituents attached to the nitrogen atoms have been prepared (H2Ln) (n = 1-9). Treatment of these ligands and the N2S2 tetradentate ligand H2L10 with [WO2Cl2(DME)] (DME = 1,2-dimethoxyethane) in the presence of triethylamine leads to the formation of cis-dioxotungsten(VI) complexes [WO2(Ln)] (n = 1-10). Reaction of the N2O2 tetradentate ligands H2Ln (n = 1, 3-7) with ammonium molybdate tetrahydrate and dilute hydrochloric acid gives the corresponding molybdenum(VI) analogs [MoO2(Ln)] (n = 1, 3-7). These compounds have been spectroscopically characterized and the molecular structures of [WO2(Ln)] (n = 1, 2, 9) and [MoO2(L5)] have been established by X-ray diffraction analysis. These high-valent compounds participate in oxygen-atom transfer reactions and can catalyze the oxidation of benzoin with dimethyl sulfoxide. The complex [WO2(L10)], which contains an S-donor ligand, has lower reduction potential and higher reactivity toward oxo-transfer reactions than analogous tungsten complexes having N2O2 ligands. The kinetics of these catalytic processes along with the structure and electrochemistry of these dioxotungsten and -molybdenum complexes are described and compared.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/98246_s.pdf or from the author.
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    Synthesis of the Tetradentate Thioether Amine and Thioether Thiolate Ligands ′tpS2(NH2)2′ and ′tpS4′-H2 and Some Representative Six-Coordinate Ruthenium and Osmium Complexes [′tpS2(NH2)2′ =1,2-Bis(2-aminophenylthio)phenylene; ′tpS4′2- = 1,2-Bis(2-mercaptophenylthio)phenylene(2-)] (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 333-339 
    Details
    ISSN: 1434-1948
    Keywords: Cleavage reactions ; C-S cleavage ; Ligand synthesis ; Osmium ; Ruthenium ; S ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search of a tetradentate thioether thiolate ligand that is more stable toward reductive C-S bond cleavage than the parent ligand ′S4′-H2 [′S4′-H2 = 1,2-bis(2-mercaptophenylthio)ethane], the novel tris-phenylene ligand ′tpS4′-H2 (3) [′tpS4′-H2 = 1,2-bis(2-mercaptophenylthio)phenylene] was synthesized via the nitro and amine compounds ′tpS2(NO2)2′ (1) and ′tpS2(NH2)2′ (2). The coordination of ′tpS4′2- to ruthenium centers resulted in the formation of six-coordinate [Ru(L)(PR3)(′tpS4′)] complexes (R = Et, L = PEt34; R = Ph, L = PPh35, CO 6, DMSO 7). The X-ray structure analyses of 4 and 6 revealed that the thiolate donors occupy trans positions; consequently the ′tpS4′2- ligand coordinates in the same way as the ′S4′2- ligand. The stability of the ′tpS4′2- ligand toward reductive C-S cleavage reactions was shown by the synthesis of [Os(PEt3)2(′tpS4′)] (8). In contrast to [Os(PEt3)2(′S4′)], 8 is stable for unlimited periods of time. The X-ray structure analysis of [Ru(Cl)2(PPh3)(′tpS2(NH2)2′)] (9) demonstrates that the potentially tetradentate ligand ′tpS2(NH2)2′ coordinates in 9 through three donors leaving one NH2 donor dangling.
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    Interactions Between Cyclodextrins and TmIII Chelates of Polyazamacrocycles as Studied by NMR in Aqueous Solution (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 287-293 
    Details
    ISSN: 1434-1948
    Keywords: MRI contrast agents ; Macrocyclic ligands ; Cyclodextrins ; Host-guest chemistry ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interactions between α-, β-, and γ-CD and the TmIII chelates of the macrocyclic polyaminopolycarboxylates DOTA and NOTA were studied with the use of 1H- and 13C-NMR shift and relaxation rate measurements. Interactions were only observed between Tm(DOTA)- and γ-CD. The structure and the stability of the concerning supramolecular structures was elucidated by fitting of the NMR titration curves to a theoretical model. It appears that an inclusion compound is formed, where the hydrophobic macrocyclic part of the chelate sits in the γ-CD cavity. This inclusion compound binds a second Tm(DOTA)- molecule at the outside lower rim of the CD cone. The binding occurs probably via hydrogen bonds between non-chelated carboxylate oxygen atoms of the concerning Tm(DOTA)- and CH2OH groups of the γ-CD molecule, which are in a favorable position due to opening of the γ-CD cone angle as a result of the inclusion of the first γ-CD.
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    Some Silicon, Germanium, Tin, and Lead Analogues of Carbenes, Alkenes, and Dienes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 373-381 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Germanium ; Tin ; Lead ; Carbene analogues ; Multiple bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isolation and characterization of thermally stable diaminocarbenes and diaminosilylenes has reawakened interest in the low-coordinated compounds of group-14 elements. The existence of these species is presumably due to interactions between the free electron pairs on the nitrogen atoms and the carbene carbon atom or the silicon atom. The present review is mainly concerned with the heavier analogues R2Ge:, R2Sn:, and R2Pb:, systems without intramolecular donor stabilization that owe their existence principally to steric shielding by the voluminous alkyl or aryl groups R. Dimerizations of these electron-sextet molecules give rise to the double-bond systems of the digermenes, distannenes, and diplumbenes; the latter species have for a long time been considered as being incapable of existence. The properties of these molecules are compared with the results of quantum chemical calculations. A separate section is devoted to the isomers of Si4R6, which include novel tetrasilacyclobutenes and the diene analogues, the tetrasilabuta-1,3-dienes.
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    The Interpretation of the Terminal ν(CO) Spectra of Some Tetranuclear Carbonyl Clusters (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1957-1963 
    Details
    ISSN: 1434-1948
    Keywords: Cluster compounds ; Vibrational spectroscopy ; Spherical harmonics ; Carbonyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The recently suggested spherical (SHM) and tensor (THM) harmonic models are applied to the interpretation of the terminal ν(CO) spectra of twenty six tetrahedral transition metal clusters containing between four and twelve terminal carbonyl groups. Although the SHM is perhaps the more generally relevant, there are species for which the THM is appropriate as a first approximation. The distinction between the two appears to be associated with a disruption of the band structure of the cluster either by the introduction of heterometal atoms or by the presence of a group - acetate ester, halide or hydride - presumably acting as an electronegative substituent.
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    Synthesis, Characterization and Dynamic Behavior of Mono- and Dinuclear Palladium(II) Carbene Complexes Derived From 1,1′-Methylenebis(4-alkyl-1,2,4-triazolium) Diiodides (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1965-1971 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; Carbenes ; Metallacycles ; 1,2,4-Triazole ; Coordination modes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mononuclear palladium carbene complexes 2a-c and 3 derived from 1,1′-methylenebis(4-alkyl-4,5-dihydro-1H-1,2,4-triazole-5-ylidene) have been obtained by the reaction of 1,1′-methylenebis(4-alkyl-1,2,4-triazolium) diiodides 1a-d with palladium acetate under mild conditions. The mononuclear complexes 2a-c have been transformed into their corresponding trans-binuclear complexes 4a-c. All compounds were characterized by spectroscopic techniques and the dynamic behavior of 2a-cand 4a-c has been studied. The X-ray structures of 2a and 4c are reported.
    Additional Material: 3 Ill.
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  • 189
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    Electronic Resource
    Hexakis(alcohol)zinc Complexes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2009-2012 
    Details
    ISSN: 1434-1948
    Keywords: Zinc complexes ; Alcohol ligands ; Structure and bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hexakis(methanol) and hexakis(ethanol) complexes of zinc were prepared under strictly anhydrous conditions and crystallized as perchlorate or hexafluorosilicate salts in space groups of high symmetry. All their OH functions are engaged in hydrogen-bonded cation-anion networks. Their Zn-O distances correspond to those in [Zn(H2O)6]2+. Their water sensitivity can be explained by a gain in entropy and by a gain in polar interactions upon replacement of alcohol by water ligands.
    Additional Material: 5 Ill.
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  • 190
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, Electrochemistry and Reactivity of the Bis(μ-σ-stannanediyl)dinickel Butterfly Cluster [{{(SiMe3)2CH}2Sn-Ni(η5-Cp)}2](Ni2-Sn2) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1987-1993 
    Details
    ISSN: 1434-1948
    Keywords: Cluster ; Nickel ; Tin ; Bimetallic complexes ; Electrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of stannylene [{(SiMe3)2CH}2Sn:] (2) to the unbridged homobimetallic Ni-Ni bond of [{PEt3Ni(η5-Cp)}2] (1) gives the heterobimetallic, tetranuclear compound [{{(SiMe3)2CH}2Sn-Ni(η5-Cp)}2] (3) with a butterfly arrangement and leaves the Ni-Ni bond of 1 intact. Elimination of both PEt3 ligands from the starting material 1 is observed, probably due to steric restraints. Compound 3 is formally related to the hypothetical closo-borane B4H42-. The Ni-Ni bond in 3 is only slightly elongated [2.454(3) Å] when compared to the starting material 1 [2.41(1) Å]. Compound 3 displays a butterfly arrangement with a hinge angle of 62.5°. An alternative route to 3 is by a direct reaction between nickelocene (5) and Lappert's stannylene [{(SiMe3)2CH}2Sn:] in 63% yield. Treating 3 with water results in the cleavage of an Ni-Sn bond and subsequent opening of the cluster cage of 3 to form the trinuclear compound [(η5-Cp)Ni{Sn(CH(SiMe3)2}2OH] (6) having an Sn-OH-Sn bridge. The hydroxy proton in 6 can be exchanged by deuterium within a few minutes, as determined by 1H-NMR spectroscopy, giving the monodeuterio product, [D1]-6. Compound 6 is reactive towards acetonitrile, leading to cleavage of one Ni-Sn bond, elimination of one [{(SiMe3)2CH}2Sn:] unit, and formation of the organotin hydroxo complex [{(SiMe3)2CH}2(OH)Sn-Ni(η5-Cp)(CH3CN)] (7). In this complex, acetonitrile is coordinated to Ni via its σ lone pair, bearing the OH ligand in a terminal bonding mode to tin.
    Additional Material: 6 Ill.
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  • 191
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    Electronic Resource
    Difluorosilanethione F2Si=S by Flash Vacuum Thermolysis of (F3Si)2S and by Reaction of SiS with F2 - Matrix Studies and Ab initio Calculations (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2013-2019 
    Details
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Flash pyrolysis ; Matrix isolation ; Silicon ; Multiple bonds ; IR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Difluorosilanethione F2Si=S (1) has been synthesized by Flash Vacuum Pyrolysis of (F3Si)2S at ≥ 500 °C and trapped in an Ar matrix. Furthermore, 1 has been obtained by co-deposition of SiS and F2/Ar and by pyrolysis of a matrix-isolated SiS2-XeF2 complex under cryogenic conditions. All six vibrational fundamentals of 1 have been observed in the matrix IR spectrum. Ab initio calculations at the MP2 and CCSD(T) levels using large basis sets have been performed. These calculations have guided the detection of 1 and the vibrational assignment. The best estimate of the structure of 1 with C2v symmetry is: r(Si=S) 191.1(1) pm, r(SiF) 156.1(1) pm, ki(FSiF) 103.3(2)°.
    Additional Material: 2 Ill.
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  • 192
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    Electronic Resource
    Photochemical Synthesis and Reactivity of New Chloro-Bridged Complexes with Tungstenocene (η5-C5H5)(η5-C5H4PPh2)WClX (X = H, Cl) and Tetracarbonylmetal (Cr, W) Units (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2029-2035 
    Details
    ISSN: 1434-1948
    Keywords: Tungsten ; Sandwich complexes ; Bimetallic compounds ; Carbonyl complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloro-bridged bimetallic complexes (η5-C5H5)[η5-C5H4PPh2M′(CO)4]W(μ-Cl)X [X = Cl (3), × = H (4); M′ = Cr, W] were prepared by photochemical irradiation of (η5-C5H5)[η5-C5H4PPh2M′(CO)5]WClX [X = Cl (1), × = H (2); M′ = Cr, W]. The reactivity of the chloro-bridged complexes towards Lewis bases was studied; by exposure to CO or phosphanes, a facile cleavage of the chloro bridge accompanied by regio- and stereospecific coordination at M′ occurs. The X-ray structure of complex 3 (M′ = W) is reported.
    Additional Material: 1 Ill.
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  • 193
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    Electronic Resource
    The Lewis Basicity of Diaminocarbene - A Theoretical Study of Donor-Acceptor Complexes of C(NH2)2, NH3 and CO with the Lewis Acids EF3, ECl3 (E = B, Al, Ga, In), TiF4 and TiCl4 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2037-2045 
    Details
    ISSN: 1434-1948
    Keywords: Diaminocarbenes ; Lewis basicity ; Ab initio calculations ; Donor-acceptor complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum chemical calculations at the MP2 level using large valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the title compounds. The nature of the donor-acceptor bond has also been investigated. The calculations show clearly that diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)2, which has a theoretically predicted Al-C bond energy Do = 59.1 kcal/mol. In all the complexes, the strength of the Lewis bases is C(NH2)2 〉 NH3 〉 CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, but the titanium tetrahalides may bind one or two donor molecules with almost the same bond strength. The investigated donor-acceptor bonds have a high degree of ionic character. The largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
    Additional Material: 6 Ill.
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  • 194
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    Electronic Resource
    Clusters on Clusters: closo-Dodecaborate as a Ligand for Au55 Clusters (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2051-2055 
    Details
    ISSN: 1434-1948
    Keywords: Gold clusters ; closo-Dodecaborate ; Conductivity ; Charging energy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The exchange of PPh3 in Au55(PPh3)12Cl6 by Na2[B12H11SH] using a phase-transfer reaction from CH2Cl2 to water needs 6 weeks for reaction, but finally results in the quantitative formation of Au55[(B12H11SH)Na2]12Cl6 (2). Cluster 2, which is of considerable stability in aqueous solution, has been characterized by 1H-NMR, 11B-NMR, and IR spectroscopy as well as by transmission electron microscopy (TEM). The Na+ cations can be exchanged by (octyl)4N+ making the resulting cluster 4 soluble in polar organic solvents. The electrical properties of 2 and 4 are compared with those of Au55[Ph2PC6H4SO3N(octyl)4]12Cl6 (3), the ammonium derivative of the sodium salt. Cluster 3 shows the expected increase of activation energy in the temperature range of 130-250 K owing to the increase of cluster spacing compared with the sodium derivative. However, clusters 2 and 4, show electromigration in the electric field, caused by the huge amount of ionic charges in the ligand shell.
    Additional Material: 4 Ill.
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  • 195
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    Electronic Resource
    Structural Analyses of Borane and Chloroborane Adducts of 1,3,5-Dithiaza-, -Dioxaza-, -Thiadiaza-, and -Triazacyclohexanes and Their Rearrangement Products, Boracyclohexanes (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2063-2068 
    Details
    ISSN: 1434-1948
    Keywords: Borane adducts ; Triazacyclohexanes ; Thiadiazacyclohexanes ; Dioxazacyclohexanes ; Boracyclohexanes ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structural and conformational studies performed by 1H-, 11B-, 13C-, two-dimensional, and variable-temperature NMR spectroscopy of borane and chloroborane adducts of 1,3,5-heterocyclohexanes and their rearrangement products, boracyclohexanes, are reported. N-Methyl derivatives gave equatorial N-borane adducts whereas the N-isopropyl derivatives produced the axial borane compounds. Rearrangement reactions of the adducts gave the first examples of chloroboracyclohexanes bearing boron and nitrogen atoms as stable stereogenic centers. BClH2 and BCl2H adducts were found to be more stable towards ring rearrangement than the corresponding N-BH3 analogs.
    Additional Material: 10 Ill.
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  • 196
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    Electronic Resource
    Crystal Structure and Dynamic Behavior of a New Class of Monocationic Organometallic PdII Compounds with Two Molecules of Bidentate Ligands: [Pd(L-L)(N-N)(CH2NO2)][PF6] (L-L = N-N, dppp) (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2085-2093 
    Details
    ISSN: 1434-1948
    Keywords: Palladium ; N ligand ; P ligand ; Copolymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new classes of organometallic palladium(II) compounds, namely [Pd(N-N)(CH2NO2)2] and [Pd(L-L)(N-N)(CH2NO2)][PF6] [N-N = 2,2′-bipyridine, 1,10-phenanthroline and their substituted derivatives; L-L = 1,3-bis(diphenylphosphino)propane or N-N] have been synthesized and fully characterized both in the solid state and in solution. The crystal structures of [Pd(phen)2(CH2NO2)][PF6] and of [Pd(dppp)(tmphen)(CH2NO2)][PF6] show a square-planar coordination geometry for the palladium atom and an unexpected monodentate coordination for the N-N ligand. The behavior in solution, investigated by NMR spectroscopy, shows the presence of dynamic processes involving only the N-N molecules. This fluxional behavior is different for [Pd(N-N)2(CH2NO2)][PF6] and [Pd(dppp)(N-N)(CH2NO2)][PF6]: in the former it most likely involves the substitution of the nitrogen atom trans to the CH2NO2 moiety by the uncoordinated nitrogen atom of the other N-N ligand; in the latter it may involve the exchange of the two nitrogen atoms at the same coordination site (flipping).
    Additional Material: 5 Ill.
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  • 197
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    Electronic Resource
    First Evidence of a Photoinduced Spin Change in an FeIII Complex Using Visible Light at Room Temperature (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2117-2119 
    Details
    ISSN: 1434-1948
    Keywords: Spin crossover ; Light-induced spin change ; cis-trans Isomerization ; Visible light irradiation ; Iron(III) ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An iron(III) complex [Fe(salten)(Mepepy)]BPh4 containing only one photoisomerizable ligand (Mepepy) has been synthesized, it exhibits a thermally-induced spin crossover in the solid state and in solution {H2salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate); Mepepy = 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene}. The photoisomerizations of both the free and coordinated Mepepy ligand have been observed at room temperature with visible-light irradiation and monitored by UV/Vis and 1H NMR spectrometries. trans-to-cis isomerization of only one photosensitive ligand in the iron(III) complex is sufficient to detect a partial spin change of the iron(III) ion. This photoinduced spin change is seen for the first time from a high-spin state to a low-spin state.
    Additional Material: 3 Ill.
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  • 198
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    Electronic Resource
    Activity of Peroxo and Hydroperoxo Complexes of TiIV in Olefin Epoxidation: A Density Functional Model Study of Energetics and Mechanism (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2135-2145 
    Details
    ISSN: 1434-1948
    Keywords: Density functional calculations ; Epoxidation ; Peroxo complexes ; Titanium ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.
    Additional Material: 9 Ill.
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  • 199
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    Electronic Resource
    Novel Synthesis of Macrocyclic Amine-Thiophenolate Ligands: X-ray Crystal Structure of a Ni4 Complex of an N8S4 Ligand (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2167-2172 
    Details
    ISSN: 1434-1948
    Keywords: Macrocyclic compounds ; Amine-Thiolate Donors ; Polynuclear Complexes ; Nickel ; Condensation reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel route to macrocyclic amine-thiophenolate ligands is described. The new, air-stable thiophenolate precursor 1,2-bis(4-tert-butyl-2,6-diformyl-phenylsulfanyl)ethane (4) is readily condensed with two equivalents of 1,2-ethanediamine or 1,3-propanediamine under medium to high dilution conditions to give 2 × 4 condensation products. The smaller 1 × 2 macrocyclic compounds are not produced under these conditions. Subsequent reduction with NaBH4 (reduction of imine groups) and Na/NH3 (reductive cleavage of aryl-alkylsulfides) provides the 36- and 40-membered amine-thiophenolate ligands H46a and H46b. The macrocyclic compounds are versatile ligands for the preparation of polynuclear transition metal complexes. With divalent nickel H46a forms the di- and tetranuclear complexes [Ni2(6a)] (7) and [Ni4(6a)][ClO4]4 (8). Reaction of 8 with four equivalents of NH4SCN yields the novel isothiocyanate complex [Ni4II(6a)(NCS)4]·10MeCN (9). The structure consists of well-separated molecules of the tetranuclear complex [NiII4(6a)(NCS)4] (Ci symmetry). Two symmetry-related binuclear [N2Ni(μ2-SR)2NiN4] fragments composed of thiolate-bridged distorted planar {N2S2Ni}- and distorted cis-octahedral {(SCN)2N2S2Ni} units reside within the cavity of the macrocycle. The intramolecular distance between the two binuclear units is 6.144(1) Å.
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  • 200
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    Borane Insertion into Group-4 Metal-to-Carbon Bonds: The Reaction of HB(C6F5)2 with (η2-Formaldehyde)zirconocene Dimer and with (Butadiene)zirconocene (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2243-2247 
    Details
    ISSN: 1434-1948
    Keywords: Metallaoxirane ; HBR2 addition ; (Formaldehyde)zirconocene ; (Butadiene)zirconocene ; Heterocycles ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (η2-Formaldehyde)zirconocene dimer (8) cleanly adds one or two molar equivalents of the borane HB(C6F5)2 by insertion of the H-[B] unit into the zirconium-carbon bond of the metallaoxirane moieties to form the mono- and bis-insertion products 16 and 17, respectively. These systems contain five-membered heterocyclic rings that are built up by connecting five different elements, namely H, B, C, O, and Zr. The bis(borane) insertion product 17 was characterized by an X-ray crystal structure analysis. (Butadiene)zirconocene reacts with HB(C6F5)2 in a similar way by insertion of the H-[B] unit into the (butadiene)C4-Zr linkage to form the metallacycle 18.
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