Bibliothek

Notizen: The reaction of trimethylarsane in the superacidic systems hydrogen/fluoride antimony pentafluoride and hydrogen fluoride/arsenic pentafluoride leads to trimethylarsonium fluorometallates. These salts are stable up to 60 °C and 5 °C, respectively. Structures were successfully elucidated in the cases of trimethylarsonium undecafluorodiarsenate and trimethylarsonium hexafluoroantimonate. (CH3)3AsH+As2F11- crystallizes in the monoclinic space group P21/n with four formula units per unit cell with the dimensions a = 7.362(1), b = 12.589(1), c = 13.598(1) Å and β = 95.37(1)°. (CH3)3AsH+SbF6- crystallizes in the monoclinic space group P21/m with four formula units per unit cell with the dimensions a = 8.313(1), b = 8.855(1), c = 13.285(1) Å and β = 94.358(1)°.

Notizen: The μ3-boryloxycarbyne complexes [{Fe(CO)3}3{μ3-COBCl{NtBu(SiMe3)}}2] (1) and [{(η5-C5H5)Ni}3{μ3-COBX(NR2)}μ3-CO] (2a: NR2 = NtBu(SiMe3), × = Cl; 2b: NR2 = N(SiMe3)2, × = Cl; 2c: NR2 = NMe2, × = BNMe2Cl) were obtained by reaction of the anionic complexes K2[{Fe(CO)3}3{μ3-CO}2] and K[{(η5-C5H5)Ni(CO)] with the corresponding chloroboranes Cl2BNR2 {NR2 = NtBu(SiMe3), N(SiMe3)2}, or 1,2-dichlorodiboranes(4) B2(NMe2)2Cl2, respectively. The products are formed by a nucleophilic attack of the CO oxygen atom at the boron centres with subsequent salt elimination. All compounds were characterized by IR and multinuclear NMR spectroscopy, and the structures of 1 and 2c in the solid state were determined by single-crystal X-ray diffraction studies.

Notizen: The course of the replacement of ethanol by water molecules in the VOPO4·2C2H5OH intercalate, and of water by ethanol in VOPO4·2H2O has been studied by X-ray diffraction and infrared and Raman spectroscopy. Formation of mixed phase VOPO4·C2H5OH·H2O was not observed. The shape of the kinetics curves indicates a transition of at least one reaction zone through the crystal. A delay in formation of the product in comparison with the decrease in the amount of starting material can be explained by the existence of non-diffracting advancing phase boundary. In a VOPO4/ethanol/water system, VOPO4·2C2H5OH is formed as the only product when the system contained more than 96 vol% of ethanol, whereas in the system with less than 94 vol% of ethanol only VOPO4·2H2O is present.

Notizen: We investigated the degradation of polychlorinated pollutants, such as dichloroanilines and related anilides, catalyzed by iron(III) tetrasulfonatophthalocyanine (FePcS) with potassium monopersulfate or hydrogen peroxide as oxidant. The reaction is influenced by the positions of the two chloro-substituents and by the nature of the oxidant. The FePcS-catalyzed oxidation of 3,5-dichloroaniline with potassium monopersulfate leads to the formation of more biodegradable products (carboxylic acids) and to potentially toxic dimers (azo and azoxy compounds). The oxidation of 3,4-dichloroaniline by FePcS/H2O2 converts this pollutant into coupling products. The formation of dimers in the catalytic oxidation of dichloroanilines can be avoided by acylation of the amine function.

Notizen: Several R3P=N-P(X)R′2 and Fe[C5H4Ph2P=N-P(X)R′2]2 derivatives (X = S, O) are readily obtained from Staudinger reactions between phosphanes and N3-P(X)R′2. The P=N-P=X groups are easily alkylated on the × atom with methyl or isopropyl triflates. The alkylation induces a lengthening of the P-X bond, as shown by X-ray diffraction studies. This corresponds to a weakening of the P-X bond which can be cleaved with P(NMe2)3 to yield [P=N-P:] linkages. The presence of tricoordinated phosphorus atoms opens the way to a versatile reactivity, including the reaction with alkyl iodides and functionalized azides. These molecules are good models for screening which types of reagents and reactions could be used with macromolecules possessing also P=N-P=X linkages, such as dendrimers.

Notizen: The steric and electronic factors responsible for the reactivity differences between CN and Cl complexes of CpCrIII were examined by DFT/B3LYP computational techniques. The energy difference between quadruplet and doublet [CpCr(CN)2(PH3)], ΔED-Q, was calculated to be 21.2 kcal mol-1 with the LanL2DZ basis set. Although the high-spin configuration is still the ground state for the cyanide complex, the energy gap is 8.7 kcal mol-1 less than that found for the corresponding chloride species. The difference between quadruplet [CpCr(CN)2(PH3)] and doublet [CpCr(CN)2(PH3)2] less free PH3, ΔECr-P, is also smaller than for the Cl system. The components of ΔECr-P for CN and Cl were analyzed by calculating energies at fixed geometries in both spin states, which indicated that the influence of the cyanide group on the pairing energy was more important than changes in Cr-PH3 bond strength or steric effects.

Notizen: The reaction of the carbonyl-functionalized phosphaalkenes RC(O)P=C(NMe2)2 [R = tBu (2a), Ph (2b)] with protic acids and alkylating reagents occurred at the two-coordinate phosphorus atom to give the phosphanyl-substituted carbocations 3a,b and 4a,b. In contrast, treatment with Me3SiOSO2CF3 resulted in attack at the oxygen atom by the silyl group, and the formation of [RC(OSiMe3)=PC(NMe2)2]SO3CF3 (5a,b). Similarly, the Lewis acids B(C6F5)3, Al(tBu)2Cl and AlMe3 were ligated to the oxygen atom of the carbonyl group. Two equivalents of GaMe3 were added to the oxygen and phosphorus atom of the phosphaalkene to yield the thermolabile complexes [RC(OGaMe3)=P(GaMe3)C(NMe2)2] (10a,b). In contrast, one molecule of InMe3 was bound to the phosphorus center of the phosphorus compound. Reaction of the phosphaalkenes with [Ni(CO)4], [Fe2(CO)9] or [{(Z)-cyclooctene}Cr(CO)5] also took place at the pnictogen atom, resulting in complexes of the type [RC(O)P{M(CO)n}C(NMe2)2] (R = tBu, Ph; M = Ni, n = 3; Fe, n = 4; Cr, n = 5). The chemical transformations reported here underline the versatile chemistry of phosphaalkenes and emphasize a relationship between carbonyl-functionalized phosphaalkenes and the well-investigated class of phosphorus ylides. X-ray structures of compounds 6b, 7b*, 10a, 11a and 12a are reported.

Notizen: The layered compound Nb3(Se1-xIx)I7 is obtained when the I atoms at the face-capping sites of the layered compound Nb3I8 are replaced by Se atoms. The amount and distribution of the Se atoms in Nb3(Se1-xIx)I7 were examined by scanning tunneling microscopy. The analysis shows that the distribution of the Se atoms is completely random.

Notizen: The syntheses of the zwitterionic (molecular) spirocyclic λ5Si-silicates 5-9 are described. These chiral compounds contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom. The stereochemistry and dynamic behavior of 5-9 were investigated. For this purpose, compounds 5-9 were studied by solution-state NMR spectroscopy (1H, 13C, 29Si; including VT 1H-NMR studies of 9) and solid-state NMR spectroscopy (13C CP/MAS, 29Si CP/MAS). In addition, compounds 5·H2O, 7, 8, 9·H2O, and 9·2CH3CN were structurally characterized by single-crystal X-ray diffraction, and ab initio investigations of the zwitterion 8 and the related anionic model species 10 were carried out.

Notizen: Borane triethylamine reacts with lithium triphenylsilanide or lithium tert-butyldiphenylsilanide with formation of lithium (triphenylsilyl)trihydridoborate or lithium (tert-butyldiphenylsilyl)trihydridoborate. Complexation of the lithium cation with various ligands allows the isolation of compounds 1, 2a, and 2b. Trimethoxyborane reacts with lithium trimethylsilanide to form lithium tetrakis(trimethylsilyl)borate 3 and lithium tris(trimethylsilyl)methylborate 4. Mixed single crystals of 3 and 4 show an unexpected coordination of the lithium cation due to the lack of any supporting donor molecule. All silylborates exhibit short Si-B bond lengths compared to tricoordinated silylboranes.

Notizen: The new compounds EuPdIn2 (1), YbPdIn2 (2), and YbAuIn2 (3) have been synthesized by high-frequency melting of the elements in sealed tantalum tubes and subsequent annealing at about 900 K. Their crystal structures have been determined by single-crystal X-ray diffraction techniques. Compounds 1, 2, and 3 crystallize with the MgCuAl2-type structure (space group Cmcm), a ternary ordered version of the Re3B type. Structural elements in these compounds are transition metal centered trigonal prisms made up of the rare earth and indium atoms. The transition metal (T) and indium atoms form a three-dimensionally infinite [TIn2] polyanionic network in which the large rare earth metal atoms occupy one-dimensional pentagonal tubes. A semiempirical band structure calculation on 1 reveals a non-vanishing density-of-states (DOS) at the Fermi level. The strongest bonding interactions are found for the In-In and Pd-In contacts; the Eu-Pd and Eu-In interactions are much weaker. Magnetic investigations indicate divalent character of the ytterbium atoms in 2, showing negative susceptibilities below room temperature. Compound 1 exhibits Curie-Weiss behavior above 50 K with an experimental magnetic moment of 7.8(1) μB, thus indicating divalent europium. Ferromagnetic ordering was observed at TC = 14.5(5) K, with a saturation moment of 6.8(1) μB/Eu at 5.5 T and 4 K, as determined from magnetization measurements. Compounds 1 and 2 are found to be metallic conductors.

Notizen: The first two Re4 chalcogenide halide clusters (Pr4N)2Re4Q4(CH3CONH)2Cl8 (Q = S, Se) with ionic molecular structures have been synthesized by treatment of neutral molecular clusters Re4Q4Cl8(TeCl2)4 (Q = S, Se) with Pr4NCl in refluxing CH3CN. During the reaction acetonitrile solvent molecules are converted into acetamido ligands, coordinated as dinucleating ligands to Re-Re bonds.

Notizen: The reactions of [N3P3(dobp)2Cl2] and [N3P3(dobp)Cl4] with a mixture of HOC5H4N-4 and K2CO3 in acetone give the cyclotriphosphazenes [N3P3(dobp)2(OC5H4N-4)2] and [N3P3(dobp)(OC5H4N-4)4], respectively. These compounds react with [W(MeOH)(CO)5] in methanol to give mixtures of the polymetallic complexes [N3P3(dobp)2(OC5H4N-4)2{W(CO)5}x] (x = 1, 2) and [N3P3(dobp)(OC5H4N-4)4{W(CO)5}x] (x = 1-4), which are unstable in solution, slowly undergoing loss of the pentacarbonyl moiety. A complete characterization by multinuclear 1H, 15N, 31P, 183W magnetic resonance has revealed that the complexation of the N atom of one 4-oxypyridine ligand by the W(CO)5 fragment has a measurable effect on other parts of the phosphazene molecule very far away from the coordination site. The changes observed in δ183W have been used to identify the components in mixtures of compounds incorporating different numbers of tungsten atoms in the molecule. The characterization of less sensitive nuclei has been accomplished by means of indirect detection methods.

Notizen: The direct functionalization of C-H bonds by formation of a C-C bond is an interesting and important alternative to coupling reactions involving halide derivatives. These reactions are complex but during the past few years a number of new systems have been developed which display promising scope. This microreview will briefly mention the different mechanisms leading to C-H activation and describe the new systems leading to the catalytic formation of carbon-carbon bonds.

Notizen: Complex 1bshows an unprecedented high activity in the Heck reaction. Kinetic studies show that in this system not the oxidative addition but the alkene coordination/migratory insertion is the rate determining step.

Notizen: The new compounds K4Nb2S10O and Rb4Nb2S10O have been synthesized by the reaction of potassium or rubidium alkaline polychalcogenides with NbO2, Nb2O5, or mixtures of Nb and NbO. Their structures consist of discrete [Nb2Q11]4- anions (Q = O, S) built up of two face-sharing pentagonal bipyramids, which are connected via the alkali metal cations.

Notizen: The transformation of acetylene into vinylidene, as promoted by the metal fragment [(pp3)Co]+ [pp3 = P(CH2CH2PPh2)3], is unimolecular and features the hydride-acetylide species as an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step involving 1,3-H shift. The best computational results are obtained by mimicking the pp3 ligand with actual ethylenic chains rather than with single PH3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride-acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for CoI and RhI derivatives at the MP2 level. For the fragment [(pp3)Co]+, the barrier associated with transformation of the hydride-acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants (28.6 kcal/mol). The situation is reversed for the analogous RhI system, with the initial π-acetylene adduct being slightly more stable. Although higher in energy, the hydride-acetylide species is the experimentally detected product of the reaction of acetylene with the fragment [(pp3)Rh]+. The salient chemical aspects of the 1,3-H shift are discussed in terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride ligand along the substantially linear Co-Cα-Cβ grouping.

Notizen: All three dinuclear complexes [Pd2(donp)2(bpy)2] (1) (H2donp = 1,8-naphthyridin-2,7-dione), [Pd2(H2nonp)2(bpy)2](ClO4)2 (2), and [Pt2(H2nonp)2(bpy)2](PF6)2 (3) (H3nonp = 7-amino-1,8-naphthyridin-2-one) exhibit the μ-1ĸN1:2ĸN8 bridging mode for their head/tail orientated naphthyridine ligands. Whereas 1 and 3 may be prepared by direct reaction of the dinucleating ligand with [MCl2(bpy)], formation of competing tripalladium(II) complexes must be avoided for 2 by employment of the precursor H2acnonp (7-acetamido-1,8-naphthyridin-2-one), which affords [H2nonp]- on cleavage of its original acetyl group. A mixture of the head/tail (4a) and head/head (4b) isomers of [Pd3(Hnonp)2(bpy)3](ClO4)2 is obtained when H3nonp is treated with [PdCl2(bpy)] and LiOH at room temperature for 2 d, followed by precipitation with LiClO4. Contrastingly exclusive formation of 4a is observed upon refluxing this reaction mixture for 3 d in aqueous solution. The [Hnonp]2- ligands exhibit a μ3-1ĸN1:2ĸN8:3ĸN7 bridging mode that leads to short Pd···Pd interactions of 2.781(2) and 2.775(2) Å. Similar metal-metal distances of 2.771(3) and 2.816(3) Å are observed in head/head-[Pt3(acnonp)(Hnonp)(bpy)3]Cl2 (5). An in situ 2e--oxidation (Ag+/Ag) of the [Pt3]6+ core in triplatinum(II) species such as 5 formed by the reaction of [PtCl2(bpy)] with H2acnonp allows the isolation of diamagnetic dark-brown head/head-[Pt3(Hnonp)2(NO3)(bpy)3](ClO4)2(NO3) (6) with an average oxidation state of Pt (2.67+). The Pt-Pt distances of 2.723(2) and 2.670(2) Å are markedly shorter than in 5.

Notizen: New heteroleptic indium compounds have been synthesized starting from indium(III) halides and hexamethyldisilazyllithium to form MeXInN(SiMe3)2 [X = Cl (1), Br (2)], and then subsequent alcoholysis to afford the molecules [ClMeIn(OtBu)]2 (3), [BrMeIn(OtBu)]2 (4), {ClMeIn[O(C6H4)OMe]}2 (5), {[(SiMe3)2N]MeIn(OtBu)}2 (6) and [MeIn(OtBu)2]2 (7). The molecular structures of molecules 3-7 have been obtained by single crystal X-ray diffraction studies. The structures of the compounds 3-7 are almost identical: 3-5 crystallize in the monoclinic crystal system with two dimeric molecules per unit cell in the space group P21/c, 6 crystallizes in the monoclinic space group C2/c with four molecules per unit cell, and compound 7 crystallizes in the triclinic crystal system with one dimeric molecule per unit cell in the space group P-1. The central centrosymmetric In2O2 ring, common to all the compounds, is achieved by two bridging oxygen atoms. Due to the additional coordination by an oxygen atom of the methoxy group, the coordination number of the metal center rises from 4 to “4+1” if the OtBu ligand (compounds 3, 4, 6, and 7) is exchanged for a methoxyphenol ligand (compound 5). In addition to the In2O2 ring the compound 5 possesses two annealed five-membered InO2C2 rings. The common indium methyl group of all compounds, which is transfered by an original route from the silicon to the indium atom, is used to compare structural and spectroscopic properties of the molecules, as there is a correlation between the In-C bond length and the chemical shift of the methyl group which depends on the ligand system used.

Notizen: The X-ray structure of a phenanthroline-(phen-)strapped 1,10-diphenylporphyrin 1 has been resolved. From the structure obtained, it is apparent that in spite of the rigidity of the strap the porphyrin ring is only slightly distorted, and that the substituents on the phen moiety define what would seem to be a hydrophobic pocket. Metallation of the free base 1 with zinc(II) acetate yields a metallic complex (1)Zn with a free axial coordination site. Crystallization of the zinc complex in the presence of a hindered base (N-methylimidazole, denoted N-MeIm) in organic solvents affords single crystals of a porphyrinatozinc(II) species, in which two water molecules are surprisingly present in the encumbered (distal) pocket of the phen site. One water molecule is axially bound to the zinc(II) ion, while the other is doubly hydrogen-bonded, as an H-bond donor to the phenanthroline and as an H-bond acceptor to the axial water ligand.

Notizen: Migration of coordinated PtII from the endocyclic N(1) site to the exocyclic nitrogen atom in 9-methyladenine occurs at high pH values. The resulting N(6)-platinated complex has been characterized by X-ray crystal structure analysis and by 1H- and 195Pt-NMR spectroscopy. The 1H-NMR spectra show that the PtII(dien) unit at N(6) can adopt either a syn or an anti conformation with respect to the N(1) site, and that protonation of the ring nitrogen atoms N(1) and/or N(7) perturbs the syn/anti equilibrium.

Notizen: Two mononuclear six-membered chelate PdCl2 complexes 2a, b of the two different types of tetrameric oligonitriles 1a, b have been synthesized. Both contain square-planar palladium(II) with a cis arrangement of the chloride atoms. In complex 2a of the ω-amino-substituted N-methoxycarbonyl oligonitrile 1a the metal center is coordinated by the nitrogen atoms N1 and N3. Within the chelate ring alternating bond lengths for the C-N bonds are observed, whereas the non-complexed, more flattened part of the oligonitrile chain shows almost equal C-N bond lengths, indicating strong donor-acceptor interactions involving the terminal amino group and the N3-Pd moiety of the molecule. The complex 2b is derived from the thiobenzoyl ligand 1b bearing a terminal (R)-fenchylidene group. In 2b the sulfur atom S1 and the nitrogen atom N2 are involved in complexation. In contrast to 2a, strong bond-length alternation is observed in 2b for the complexed and the non-complexed part of the ligand. From the NMR spectra of both complexes no indication for a migration of the PdCl2 unit along the chain could be derived.

Notizen: The new chiral ligands 2-butyl-8-chloro-1-(4,8-di-tert-butyl-2,10-dimethoxy-5,7-dioxa-6-phosphadibenzo[a,c]cyclohepten-6-yl)-1,2-dihydroquinoline (BIPHENPHOSHQUIN, 3) and 2-butyl-8-chloro-1-(3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yl)-1,2-dihydroquinoline (BINAPHOSHQUIN, 4; 4a: SaRC, 4b: SaSC) have been synthesized starting from the rigid backbone of 8-chloroquinoline. The reactions of 3 and 4 with rhodium(I), palladium(II), and platinum(II) substrates are reported. The reaction of 3 with [Rh(CO)2Cl]2 in a 2:1 molar ratio in hexane afforded a binuclear chloro-bridged rhodium(III) species by intramolecular oxidative addition of the C-Cl bond of ligand 3 across the rhodium(I) centers. The rhodium(III) complex 5, incorporating the enantiomers SaRC-3 and RaSC-3, has been fully characterized by X-ray diffractometry. Reactions of [Pd(PhCN)2Cl2] with the ligands 3 and 4a in 1:2 molar ratio in toluene afforded the products cis-[Pd(3)2Cl2] (9) and cis-[Pd(4a)2Cl2] (10). Similarly, reaction of [Pt(COD)I2] with 4a in a 1:2 molar ratio afforded the complex cis-[Pt(4a)2I2] (11). An X-ray analysis has been carried out to obtain information on the effect of the ligand 4a on the overall structure of 11.

Notizen: The functionalized ligands 1 and 2 bearing hydrogen-bonding recognition groups have been synthesized. Their assembly by metal ions such as CuI and PdII having different coordination geometries generates different receptor architectures for the binding of suitable substrates. Addition of the complementary bis(imide) Janus molecules (4-7) to [1a, 2a, CuTf] or to [1b, 2b, Pd(BF4)2] mixtures leads to a moderate selective increase of the fraction of the [(1a)2Cu]+ or [(1b)2Pd]2+ complex depending on the Janus substrate used. Largest enhancements are observed for those Janus substrates that may be expected to display highest geometrical complementarity with the two complexes. These results represent a process directed by target binding based on dynamic combinatorial chemistry.

Notizen: Chiral racemic rhenium thioaldehyde complexes [CpRe(NO)(PPh3)(η2-S=CHR)]PF6 (2a-g) bearing functionalized aliphatic groups R [R = CH2Ph (a), COOEt (b), CH2COOMe (c), CH2C(O)NHCH2Ph (d), (R)-CH(NC8H4O2)COOMe (e), (S,S)-CH(Me)C(O)NC4H7COOMe (f), C4H3O (g)] have been obtained by hydride abstraction from the corresponding thiolate complexes [CpRe(NO)(PPh3)(SCH2R)] (1a-g). With the exception of 2b, only single stereoisomers with like configurations at rhenium and the thioaldehyde carbon atom were obtained. In some cases, the corresponding sulfinate complexes [CpRe(NO)(PPh3)(SO2CH2R)] (3d-f) were formed as by-products. The analogous toluenesulfinate complex [CpRe(NO)(PPh3){SO2(4-C6H4CH3)}] (3a) has been prepared from [CpRe(NO)(PPh3)(THF)]BF4 (8), and the structure of 3e has been determined by X-ray crystallography. The use of phosphorus ligands other than PPh3 was briefly explored with the synthesis of [CpRe(NO)(PR′3)(η2-S=CHR)]PF6 (5a-d) [R′ = OPh, R = Ph (a), 4-C6H4Cl (b), R′ = iPr, R = Ph (c), H (d)]. Nucleophilic addition of NaSMe to [CpRe(NO)(PPh3){η2-S=CH(4-C6H4OMe)}]PF6 (5e) gave the dithioacetal complex [CpRe(NO)(PPh3){SCH(SMe)(4-C6H4OMe)}] (9) in high yield and with low diastereoselectivity. Diels-Alder additions of 5a, e with 2,3-dimethylbutadiene and 2,3-dimethoxy-butadiene gave complexes of cyclic thioethers (10a-c). From the relative rates of reaction (5a 〉〉 5e) and the low diastereoselectivity, it was concluded that the cycloadditions as well as the nucleophilic addition proceed via the linkage isomers [CpRe(NO)(PR′3)(η1-S=CHR)]PF6.

Notizen: The [(η4-diene)(η5-RCp)TaCl2] complexes 6a-e (diene = butadiene, isoprene or 2,3-dimethylbutadiene; RCp = pentamethylcyclopentadienyl, methylcyclopentadienyl or cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li2]) to yield the (η4-diene)(η3-cyclooctatetraene)(η5-RCp)tantalum complexes 7. The η3-cot coordination was confirmed by an X-ray crystal structure analysis of the compound [(supine-s-cis-η4-C4H6)(η3-cot)(η5-Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and proneorientation of the (diene)CpTa subunit] were found for the (η4-butadiene)(η3-cot)CpTa system (7e/7e′ = 95:5). Complex 7e cleanly adds the organometallic Lewis acid B(C6F5)3 to yield the betaine system [(η4-C4H6){C8H8B(C6F5)3}Cp*Ta] 8, which contains a substituted bicyclo[5.1.0]octadienyl ligand.

Notizen: ESI mass spectrometry and 51V-NMR spectroscopy have been used to study the reactions occurring between bisperoxo vanadates and a number of histidine and histidine-like ligands, in aqueous alcoholic solutions. Coordination of one and two molecules of ligand is observed with all the compounds investigated affording [VO5L]- and [VO52L]-, respectively. Characterization of these species has been achieved by MSn experiments, which have allowed specific fragmentations of the peroxidic moiety to be distinguished. In particular, with [VO52L]-, two distinct modes of decomposition were observed, depending on the presence in the ligand of a free carboxylic function. - Possible biochemical implications related to vanadium haloperoxidase enzymes are discussed.

Notizen: A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal-ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine-metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π-π stacking of the bipyridine rings.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99078_s.pdf or from the author.

Notizen: The reactivity of aminodihaloboranes R2NBX2 (R = Me, SiMe3; × = Cl, Br) towards transition metal complexes of the type Na[(η5-C5R′5)M(CO)2)] (M = Fe, Ru; R′ = H, Me) was investigated. In the case of Me2NBBr2 and M = Fe the borylcomplexes [(η5-C5R′5)(CO)2Fe{BBr(NMe2)}] (C5R′5 = C5H59a; C5R′5 = C5H4Me 9b; C5R′5 = C5Me510) were obtained. The compounds 9aand 9bwere formed together with the corresponding bridged borylene complexes [μ-BNMe2(μ-CO){(η5-C5R′5)Fe(CO)}2] (C5R′5 = C5H511a; C5R′5 = C5H4Me 11b) in a 1:1 ratio, the latter, however, could be isolated from these mixtures as pure materials. In addition the novel boryl and borylene ruthenium complexes [(η5-C5H5)(CO)2Ru{BX(NMe2)}] (X = Cl 12a; × = Br 12b), [(η5-C5H5)(CO)2Ru{BCl{NSiMe3{BClN(SiMe3)2}}}] (13) and [μ-BN(SiMe3)2(μ-CO){(η5-C5H5)Ru(CO)}2] (14) were obtained by similar methods. All compounds were characterized by multinuclear NMR and IR spectroscopy. The structure of 13 in the solid state was determined by a single-crystal X-ray diffraction study.

Notizen: The new diiron complex [Fe2(tbpo){O2As(CH3)2}(CH3O)(CH3OH)](ClO4)3 · 5 CH3OH · 2 H2O (1) containing a (μ-alkoxo)(μ-dimethylarsinato)diiron(III) core was synthesized using the heptadentate ligand N,N,N′,N′-Tetrakis(2-benzimidazolylmethyl)-1,3-diamino-2-propanol (Htbpo). The complex was characterized structurally by X-ray crystallography. 1reproduces the coordination mode and the stoichiometry of the proposed purple acid phosphatase-arsenate inhibitor complex. More importantly, 1 is a good functional model for the activation of small molecules, since the solvent molecule in the coordination sphere of each iron ion can be substituted very easily by a small substrate molecule. This is confirmed by the comparatively high pH-dependent catalase-like activity of 1. In order to study the influence of the cacodylate bridge on the formation of the metastable adduct with hydrogen peroxide, the analogous hydroxo-bridged complex [Fe2(tbpo)(OH)(NO3)2](NO3)2 · CH3OH · 2 H2O (2) was employed. The reactions of 1and 2 with H2O2 were studied as a function of [H2O2], pH, temperature, and pressure, and the kinetic results including the activation parameters are reported. In the case of compound 2 the reaction proceeds in one step, and the observed first order rate constant, kobs, shows a linear dependence on the hydrogen peroxide concentration with a zero intercept. For complex 1 the kinetic traces could be fitted to two exponential functions. One of the observed pseudo-first-order rate constants, kobs1, exhibits a linear dependence on the hydrogen peroxide concentration with a zero intercept, whereas the other rate constant, kobs2, was independent of the hydrogen peroxide concentration. A mechanistic interpretation is presented.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99068_s.pdf or from the author.

Notizen: Calixareneglycine ester acetamides 4a-c have been synthesized from calixareneacetyl chlorides 5a-c and glycine ethyl ester (6). Their ion-binding properties have been investigated by liquid-liquid extraction with radiotracer techniques. The experiments reveal a moderate affinity towards silver(I) ions, which increases with calixarene ring size.

Notizen: Reactions of the stannaborate salt [NBu4]2[SnB11H11] (1) with the organometallic electrophiles [CpFe(CO)2Br], [(C7H7)Mo(CO)2I], and [CpNi(PPh3)Cl] resulted in substitution of the halide to give the stannaborate coordination products [NBu4][CpFe(CO)2(SnB11H11)] (2), [NBu4][(C7H7)Mo(CO)2(SnB11H11)] (3), and [NBu4][CpNi(PPh3)(SnB11H11)] (4) in high yields. Single crystals of the air- and moisture-stable products have been characterized by X-ray crystal structure analyses.

Notizen: 2-(Diphenylphosphanyl)thiophenol (HSC6H4PPh2) reacts with the carbonyl clusters [Ru3(CO)12] and [Os3(CO)10(MeCN)2] to give mixtures of products, the composition of which depends upon the reaction conditions and the ratio of the reactants. The derivatives [M3(μ-H)(μ-η2-SC6H4PPh2)(CO)9] (1a: M = Ru; 1b: M = Os), [Ru3(μ3-S)(μ-η2-Ph)(μ-PPh2)(PPh3)(CO)6] (2), and [Ru2(μ-η2-SC6H4PPh2)2(CO)4] (3) have been isolated. The SC6H4PPh2 ligand of compounds 1a and 1b has the sulfur atom spanning the same M-M edge as the hydride ligand and the phosphorus atom attached to one of the bridged metal atoms. Compound 2, which contains sulfide, phenyl, diphenylphosphanyl and triphenylphosphane ligands that arise from HSC6H4PPh2, has the Ru3 triangle capped by the sulfide and two Ru-Ru edges spanned by bridging phenyl and diphenylphosphanyl ligands. In complex 3, the two SC6H4PPh2 ligands have the same coordination behavior as in 1a or 1b; this binuclear complex is more conveniently prepared by treating [Ru2(μ-η2-MeCO2)2(CO)4(MeCN)2] with HSC6H4PPh2.

Notizen: CH3C(CH2PPh2)3CoCl (1) is easily accessible from CH3C(CH2PPh2)3CoCl2 by reduction with activated zinc powder. Upon dehalogenation with TlPF6, 1 reacts with dienes to give [tripodCoI-(η4-diene)]+ (2). The heterodienes acrolein and methyl vinyl ketone produce the analogous η4-heterodiene compounds 3. When crotonaldehyde is used as the potential η4-diene ligand, decarbonylation is observed leading to [tripodCoI-(CO)2]+ (4). Reaction of [tripodCoaq](BF4)2 with allyl mercaptan produces [tripodCoI-(η4-thioacrolein)]+ (3a) through dehydrogenation of the ligand precursor. 1,2-Diketones such as benzil and phenanthrenequinone do not coordinate in a η4 fashion but rather generate η2-coordinate enediolato ligands by an electron-transfer process, resulting in compounds of the type {tripodCoIII-[η2-RC(O)=C(O)R]}+ (5). All the compounds have been characterized by standard analytical and spectroscopic techniques, including X-ray analysis in some cases. Compounds 4 and 5 show trigonal-bipyramidal coordination in the solid state, whereas the coordination polyhedra in compounds 2 and 3 are better described as square-pyramidal. While a minimum of two phosphorus resonances might be expected for each of these coordination geometries, only one time-averaged signal is normally observed. Only with the η4-coordinated heterodienes acrolein, methyl vinyl ketone, and thioacrolein present in 3 is there a resolution of the signals of the three chemically distinct phosphorus nuclei at low temperatures. By 31P-NMR line-shape analysis, the activation barriers for the rotational reorientation of the heterodienes are found to be around ΔH≠ = 47 kJmol-1 for all three compounds 3.

Notizen: New salts of thionated (naphthalene-1,8-diyl)bis(phosphonic) acid monoanhydrides [PPh4+]2[C10H6PS2(μ-S)PS22-] (2) and [K+]2[C10H6PS2(μ-S)POS2-]·H2O (3) both containing the C3P2S ring, were prepared in high yields by the reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (1) with NaHS and PPh4Cl, or KOH, respectively, in water. The derivative 3, containing a P=O terminal bond as well as P-S-P bridge, undergoes, in acid conditions, a rearrangement reaction leading to the O,S-symmetrically substituted derivative [K+]2[C10H6PS2(μ-O)PS22-] (4) containing a C3P2O heterocycle. Dipotassium salt 4 was converted into the bis(tetraphenylphosphonium) salt 5 by the treating with PPh4Cl. Hydrolysis of [PyH+][C10H6P(S)(NHMe)(μ-S)PS22-] (15) led to [CH3NH3+][PyH+][C10H6POS(μ-O)POS2-]·1.5 Py (6). New compounds were characterised by 31P{1H}-, 1H- and 13C{1H}-NMR, FT-IR, ES-MS and in the cases 2-6 by X-ray structure determination. The 31P{1H}-NMR spectra of these mixed O,S-derivatives are briefly discussed.

Notizen: New azaalkyl or azacrown ferrocenyl compounds containing a C5H4COCC- linkage are accessible from mono- or diacetylferrocene upon treatment with the appropriate aldehydes (CHOC6H4-p-R, R = NEt2, N-aza-15-crown-5). Preliminary results concerning the electrochemical behaviour of complexes [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (3a), [Fe(C5H4COCH=CHC6H4NEt2)2] (5a), the novel ferrocenophane [Fe(C5H4COCH2)2CHC6H4NEt2] (6a) and its protonated species [Fe(C5H4COCH2)2CHC6H4NHEt2][BF4] (7a), are reported. The ferrocenyl ligand 5a is a rare example of a molecule which is both electroactive and fluorescent.

Notizen: Ti6O6(MDEA)6·2CH2Cl2 (MDEA = N-methyldiethoxoamine) was obtained by the controlled hydrolysis of the Ti(MDEA)2 complex and analysed by X-ray diffraction. The compound consists of a ring of six [TiO5N] octahedra, edge bridged by μ2-oxide and a μ2-alkoxide arm of the aminoalkoxide ligand.

Notizen: A tetranuclear mixed-spin nickel(II) complex featuring two urea molecules in an unprecedented μ3-ĸN:ĸN′:ĸO coordination mode has been structurally characterized. The two central high-spin nickel(II) ions exhibit ferromagnetic coupling (J = +3.4 cm-1) mediated by the NH2-C-O linkages of the bridging urea. In solution the temperature dependence of the UV/Vis optical absorption and of the magnetic moment indicate that, upon cooling, additional solvent molecules bind to the terminal low-spin metal ions and a concomitant spin change occurs. In the solid state the coordinated urea ligands can be thermally degraded to cyanate within the grip of the multimetallic nickel(II) site.

Notizen: The first fullerene complex of titanium Cp2Ti(η2-C60) has been synthesized by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene Cp2Ti(η2-Me3SiC2SiMe3) with an equimolar amount of fullerene-60 in toluene at room temperature under argon. An X-ray diffraction study of the complex has shown that it has the structure of a titanacyclopropane derivative.

Notizen: The five-step synthesis of the first transition metal complex with the C5(CH3)4CH2CH2PPh2 ligand [η5:η1-C5(CH3)4CH2CH2PPh2]ZrCl3·THF (11), starting from the known compound [2-(dimethylamino)ethyl]tetramethylcyclopentadiene (4) via 4,5,6,7-tetramethylspiro[2,4]hepta-4,6-diene (7), is reported. Lithium cyclopentadienide LiC5(CH3)4CH2CH2PPh2 (9), silylated cyclopentadiene (CH3)3SiC5(CH3)4CH2CH2PPh2 (10) and cyclopentadiene HC5(CH3)4CH2CH2PPh2 (12) were isolated and characterised as pure substances. The crystal structure of the zirconium complex 11 was established by X-ray diffraction analysis.

Notizen: The 2,6-bis(pyrazolyl)pyrazine ligand 1 forms a 2,2-metallamacrocycle 3, composed of two ligands and two cations, in the presence of the Ag+ cation. In the crystalline phase, the 1,3,5-tris(pyrazolyl)benzene ligand 2 leads to an infinite metallatubular network in the presence of the Ag+ cation, composed of the 2,2-metallamacrocycle 4, which is formed from two molecules of 2 and two cations. This infinite network is formed by double interconnection of consecutive metallamacrocycles through binding of Ag+ centers by the free pyrazolyl moieties.

Notizen: Reactions of pure triflic acid (TfOH) with UH3 at 20 °C and with U or UCl3 at 120 °C afforded U(OTf)3 (1), which was transformed into U(OTf)4 (2) by reaction with TfOH at 180 °C; 2 was also synthesized by treating UCl4 with TfOH at 120 °C. The yields were in excess of 90%. The crystal structure of [U(OTf)2(OPPh3)4][OTf] (3) was determined, which revealed a seven-coordinate uranium(III) centre bound by monodentate and bidentate triflate ligands.

Notizen: The molecular and electronic structure of the planar nickel dithiolene (1c, R = H) and of related complexes derived from nickel dithiolene by replacement of Ni by Pd (palladium dithiolene, 2c, R = H) or by Pt (platinum dithiolene, 3c, R = H), or by replacement of S by NH (nickel diiminolene, 1a, R = H), O (nickel dioxylene, 1b, R = H) or Se (nickel diselenolene, 1d, R = H), were studied by density functional theory using the B3LYP functional and the valence triple-zeta basis set 6-311+G* for all atoms except Pd and Pt. For the latter atoms the quasirelativistic effective core potentials of the Stuttgart group were employed. The molecular structure of nickel dithiolene (1c, R = H) is satisfactorily reproduced by DFT calculations. The geometry of the corresponding platinum complexes 3a-3d is more sensitive to relativistic effects, resulting in the contraction of the X-Pt bonds. As shown with the metal dithiolenes, the two ligands are structurally related to mononegative ions of open shell structure. The C-C bond lengths of the complexes are close to those of aromatic and chain-type polymethine structures (about 1.4 Å). The nickel dithiolene (1c, R = H) and related complexes have D2h symmetry and are 14 π-electron systems with 10 π-electrons at the ligands and 4 π-electrons at the metal center. The natural population analysis has confirmed that metal M++ does accept electrons from the ligands but to a lesser extent than expected. The empty d-orbitals of M++ are only partly occupied in the molecular ground state. The positive charge of the metal decreases in the order Ni 〉 Pd 〉 Pt. The 1H chemical shifts and the nucleus-independent chemical shifts (NICSs) of the ring moieties calculated by GIAO-DFT display a pronounced electron delocalization. In agreement with the calculated C-C bond lengths the 1H chemical shifts and the NICS values show a marked bond delocalization. The NICS values show a change of the aromatic delocalization in the order Ni 〉 Pd 〈 Pt and NH 〉 O 〈 S 〈 Se. The wave numbers of the IR spectra of the complexes calculated by DFT are grouped in separate frequency regions. The very intense absorption of 1c (R = H) in the visible region of the spectrum is surprisingly well reproduced by ab initio single-only configuration interaction calculations. While the color band of the palladium complex is predicted to be red-shifted relative to the nickel complex, a blue shift is calculated on passing from the palladium to the platinum complex. The blue shift is, in part, due to the relativistic contraction of bond lengths in the Pt complexes.

Notizen: Di(tert-butyl)aluminium chloride reacted with dilithium bis(trimethylsilyl)hydrazide with the formation of a novel Al2Li2N4 cage compound 1. Its structure consists of a dimeric iminoalane RAl(μN-SiMe3)2AlR (R = CMe3), which is bridged by a dilithiumhydrazido ligand with an intact N-N bond. A heterocubane-type molecule is formed, in which two vertices are occupied by Al atoms, two by Li atoms and four by N atoms. One face of the cube is strongly distorted due to the short N-N distance of the hydrazido group. A similar compound, 3, was formed with bis(neopentyl)aluminium chloride but it was isolated in very poor yield. The reaction of Li2N2(SiMe3)2 with (Me3C)2AlCl in the presence of THF yielded an adduct 2, in which each Li atom of the cage is additionally coordinated via Li-Cl-Al bridges to the ligand (Me3Al)2Cl·THF. The reaction of dilithium bis(trimethylsilyl)hydrazide with tert-butylaluminium dichloride gave, by complete cleavage of the hydrazido groups, a dimeric iminoalane [Me3C(THF)AlNSiMe3]2 (4), in which each aluminium atom is coordinated to one THF molecule. Its uncoordinated, solvent-free form 5 was obtained by heating solid 4 to 150 °C in vacuo for several hours. It was identified as the tetrameric iminoalane (Me3CAlNSiMe3)4, which does not adopt the expected heterocubane-type structure, but consists of three anellated four-membered Al2N2 heterocycles in a kind of ladder structure. Remarkably, the cage compound 1 could not be obtained by the reaction of an excess of lithium hydrazide with the iminoalanes 4 and 5. All compounds 1-5 were characterized by crystal structure determinations.

Notizen: The bishydrosulfido zirconium metallocene compound [Cptt2Zr(SH)2] (2) containing the bulky η5-1,3-di-tert-butylcyclopentadienyl (Cptt) ligand is readily accessible from [Cptt2Zr(CH3)2] (1) upon treatment with H2S. Reaction of 2 with methyltriflate gives the monohydrosulfido complex [Cptt2Zr(SH)(OSO2CF3)] (3) which exists as two isomers in solution, and has been characterized by X-ray diffraction methods. Complex 2 is an effective metallaligand for the controlled synthesis of new trinuclear early-late heterobimetallic complexes (ELHB) with a ZrRh2 core such as [Cptt2Zr(μ3-S)2{Rh(CO)2}2] (4).

Notizen: The gas-phase acidities ΔGacid(298 K) of the sulfanes H2Sn (n = 1-4) have been calculated by ab initio molecular orbital theory using the G2 and G2(MP2) methods, which were applied to the geometries of lowest energy. The results show that the higher sulfanes are surprisingly strong proton donors. The acidities (in kJ mol-1) are as follows: H2S (1444), H2S2 (1406), H2S3 (1370), H2S4 (1347). The latter three values may be compared to those of other strong Brønsted acids like gaseous HNO2 (1396), HCl (1371), and HBr (1332). The monoanions HSn- exhibit an interesting bond length distribution as a consequence of the charge delocalization by hyperconjugation, which in turn may be responsible for the high acidities of the sulfanes.

Notizen: The molecular structures of 5-methyl-1,3-dithia-5-aziniumcyclohexane iodide, 5-chloroborane-5-methyl-1,3-dithia-5-azacyclohexane, 3,5-bis(borane)-3,5-dimethyl-1-thia-3,5-diazacyclohexane, and 1-borane-1,3,5-trimethyl-1,3,5-triazacyclohexane were determined by X-ray diffraction studies. Interactions between hydridic and protic hydrogen atoms are present when the distances between hydridic and protic hydrogen atoms are shorter than 265 pm and angles for B-N-C bonds are smaller than 107.6(3)°. These interactions explain the conformation of the borane adducts in the solid state.

Notizen: Through a variation in the aryl substituents of the formamidinate ligand, a variety of dirhenium compounds has been synthesized with [XArNC(H)NArX]- where Ar is a substituted C6H5 or C6H4 aryl ring and × is p-MeO (1), H (3), m-MeO (4), p-Cl (5), m-Cl (6), m-CF3 (7), p-CF3 (8), 3,4-Cl2 (9), and 3,5-Cl2 (10a, 10b). UV/Vis and NMR spectroscopy and electrochemical data for 1and 3-10 have been obtained. X-ray crystallographic analysis of Re2Cl2(μ-form)4 with four different diarylformamidinate ligands and one analog with two different interstitial solvents are presented; Re2Cl2[(p-MeOC6H4)NCHN(p-MeOC6H4)]4 (1), Re2Cl2[(m-MeOC6H4)-NCHN(m-MeOC6H4)]4 · 2 CH2Cl2 (4), Re2Cl2[(3,4-Cl2C6H3)NCHN(3,4-Cl2C6H3)]4 · 2 CH2Cl2 (9), Re2Cl2[(3,5-Cl2C6H3)NCHN(3,5-Cl2C6H3)]4 · 4 CH2Cl2 (10a), and Re2Cl2[(3,5-Cl2C6H3)NCHN(3,5-Cl2C6H3)]4 · OC4H8 (10b).

Notizen: This microreview describes the structure, properties and mechanisms of the purple acid phosphatases (PAP). The enzyme is isolated from mammalian, plant and bacterial sources. X-ray structural information is now available for the enzyme from pig (uteroferrin), rat and kidney beans. Features of the mechanism are the concerted action of a labile MII centre (FeII or ZnII) alongside a more inert FeIII. The latter is effective as a conjugate-base FeOH2+, which initiates hydrolysis at the MII-bound phosphate ester by a process involving OH- replacement of OR- at the PV. Histidine residues near to the active site help bind the phosphate and are involved in the release of OR-. Effects of replacement of the FeII by MnII, CoII, NiII, CuII and ZnII, and of FeIII by GaIII,AlIII and InIII have been studied. The mechanistic role of the ZnIIZnII combination in alkaline phosphatases, and other related dinuclear centres is also considered.

Notizen: The synthesis, properties and X-ray single crystal structure analysis of the intramolecularly adduct-stabilised organogallium bisazide (N3)2Ga[(CH2)3NMe2] (1), the mono azide (N3)Ga[(CH2)3NMe2]2 (2) and the trialkylamine adducts of triazidogallium of the type (N3)3Ga(NR3) (3a-d; R = alkyl) are reported. An unusual isomer 1b of compound 1 is described, which was obtained by slow cooling of the analytically pure neat liquid compound 1 to 0 °C. The new and unusual structure 1b can be regarded as a weak associate of dimers linked together by head-to-tail azide bridges. In contrast, compounds 2 and 3a-b (R = CH3, C2H5) are monomeric in the solid state. The suitability of the volatile compounds 1 and 2 as single source precursors to grow GaN thin films by chemical vapour deposition is compared, showing that preferentially oriented crystalline films can be obtained from compound 2 on sapphire substrates at 600-700 °C in vacuo (0.1 Pa). However the films have a grey rather than a transparent appearance, which is presumably due to N-deficiency owing to the lower N-content of the single molecule precursor 2 relative to 1.

Notizen: The tetrapodal pentaamine ligand 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine (1), which contains four equivalent primary amino groups, can be derivatised partly or completely by Schiff base condensation with suitable carbonyl compounds. The new ligands thus obtained are mononucleating, as shown by the X-ray crystal structures of their respective nickel(II) complexes. Reaction of 1 with 1 equiv. of salicylaldehyde and subsequent reduction allows the selective modification of one of the four sidearms. The resulting ligand 2 is hexadentate and uninegative in its nickel(II) complex {[(2)Ni]PF6} (3) with both the secondary amine and the phenoxide functionalities coordinated to the metal centre. The unreduced Schiff base form of the ligand, 4, does not form a complex with nickel(II) as readily, and only a small quantity of the mixed salt {[(4)Ni][(1)Ni(H2O)](Br)2(PF6)} (5)has been obtained. While the overall coordination of 4 resembles that of 2, there is considerably more strain in the appended chelate ring, due to the presence of the C=N double bond. Modification of one arm in 1 can also be achieved by condensation with 1 equiv. of acetylacetone, to give the new ligand 6 which, likewise, is hexadentate in its NiII complex {[(6)Ni](PF6)2} (7). In this case, however, the N/O-functional sidearm is not deprotonated. Rather, it is coordinated as the keto-imine tautomer, making 7 a rare example of a metal complex containing this structural fragment. Two-fold functionalisation of 1 is observed upon reaction with acetone, regardless of whether the ketone is present in stoichiometric amounts or in excess, to give the pentadentate ligand 8with two diagonally juxtaposed isopropylidene-imine units. The complex isolated with this ligand {[(8)Ni](PF6)2} (9) contains pentacoordinate NiII, the sixth coordination site being blocked by the rigidly positioned isopropylidene groups. When reacted with 4 equiv. of trans-cinnamaldehyde, all the primary amino groups in 1 condense to give the four-fold Schiff base 10, which acts as a pentadentate podand towards nickel(II). In this complex, {[(10)Ni(OH2)]Br2} (11), an aqua ligand completes the coordination octahedron. All ligands are stable towards hydrolysis when coordinated to the metal, despite the presence of alkyl-imine groups in some cases.

Notizen: The neopentane-derived functionalized oxetane O(CH2)2C(CH3)(CH2OMs), 1, reacts with indenyllithium (LiInd) or fluorenyllithium (LiFlu) to produce the derivatives O(CH2)2C(CH3)(CH2R) (R = indenyl, fluorenyl), 2. The oxetane ring of 2 undergoes nucleophilic ring-opening by reaction with LiPR′2 to give the chiral chelate ligands (HOCH2)(CH3)C(CH2R)(CH2PR′2) (R = indenyl, fluorenyl), 5. Nucleophilic ring-opening by LiInd or LiFlu is possible too, resulting in the functionalized ansa-Cp ligands (HOCH2)(CH3)C(CH2R)(CH2R′) (R, R′ = indenyl, fluorenyl), 12. Electrophilic ring-opening of 2 with HBr to give (HOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 3, is also possible. The alcohol function of 3 may be activated directly, whereas activation of this group in 5 is only possible after BH3 protection of the phosphane function. The mesylates (MsOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 4, undergo, under basic conditions, spiro cyclization to produce spirocyclobutane derivatives 9 with the α-carbons of the five-membered cycles acting as the spiro centres. Substitution of the mesylate group of 4 by PR2 nucleophiles is therefore not possible. Ansa-Cp derivative (MsOCH2)(CH3)C(CH2Ind)(CH2Flu), 12c also reacts with LiPPh2 with spiro cyclization to produce 9d, instead of giving the substitution product. Tripodal ligands (CH3)C(CH2R)(CHPPh2)2 (R = indenyl, fluorenyl), 11, are accessible by the reaction of (MsOCH2)(CH3)C(CH2PPh2)2 with LiInd or LiFlu. All compounds are fully characterized by the usual spectroscopic and analytical techniques including single-crystal X-ray analyses in several cases.

Notizen: The crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-anti geometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn-anticis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P21 space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J′/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.

Notizen: Treatment of calcium bis[bis(trimethylsilyl)amide] with two equivalents of tris(trimethylsilylmethyl)alane yields (Me3SiCH2)2Al-N(SiMe3)2 (1) and the dimer [(Me3Si)2N-Ca(μ-CH2SiMe3)2Al(CH2SiMe3)2]2 (2). The five-coordinate bridging carbon atoms show Ca-C bond lengths of 264 and 268 pm. A similar reaction with calcium bis[bis(trimethylsilyl)phosphanide] gives the dimer [(Me3SiCH2)2Al-P(SiMe3)2]2 (3) with crystallographic C2 symmetry. A calcium-containing species is not isolable, however, in the presence of DME - ether cleavage reactions and the formation of the centrosymmetric dimer [(Me3SiCH2)2Al-OCH2CH2OMe]2 (4) are observed. The central moiety is an Al2O2 cycle with fivefold coordinated aluminium centers.

Notizen: The magnesiation of triisopropylsilylphosphane with dibutylmagnesium in toluene yields the octanuclear complex [Mg8(PSiiPr3)6{P(H)SiiPr3}4] (1) which consists of MgPSiiPr3 units forming a hexagonal Mg6P6 prism, with two opposite Mg2P2 moieties capped by additional Mg[P(H)SiiPr3]2 groups. If a small amount of THF is present during the metalation reaction [(THF)4Mg6(PSiiPr3)6] (2) also containing a hexagonal Mg6P6 prism can be isolated. The magnesiation of H2P-SiiPr3 in tetrahydrofuran leads to the formation of the tetrameric complex [(THF)MgPSiiPr3]4(3) with a slightly distorted Mg4P4 cubane-like structure.The structures depend strongly on the steric strain caused by the trialkylsilyl substituents and the neutral coligands at the magnesium center. The highest steric strain, which is induced by coordination to every magnesium atom, leads to the smallest MgnPn polyhedron - the central Mg4P4 heterocubane moiety. In compounds 1 and 2 the hexagonal Mg6P6 prism is formed, however, with reduced steric strain as observed for 2 where the Mg-P bond lengths become more similar.

Notizen: The dilithium salts of N-methyl-N′,N′′-bis(diisopropyl)- and -(trimethylsilyl)-diethylenetriamine 1a,b react with SnCl2 affording the corresponding stannylenes 2a,b in 60 and 80% yield, respectively. Compound 1b also reacts with BiCl3 to give the bismuth chloride 5 (90% yield). Derivatives 2b and 5 have a symmetrical bicyclic structure and are monomeric both in solution and in the solid state. When 2b is treated with BiCl3 or PCl3, an oxidation reaction leads to the hypercoordinated tin(IV) dichloride 3 (58% yield), or a transmetallation gives rise to the oniophosphane 4 (95% yield), respectively. Transmetalation reactions also occurred when 5 was treated with AlCl3, GaCl3 or SnCl2 affording the corresponding aluminum chloride 6 (81% yield), gallium chloride 7 (38% yield) or tin dichloride 3 (38% yield). The observed reactivity for 2 and 5 is compared to that reported for Veith's stannylene or bismuth chloride.

Notizen: The nature of ruthenium-amino alcohol precursors in the catalytic cycle of asymmetric hydrogen transfer reactions was studied using two C2-symmetrical tetradentate ligands (1 and 2) that were synthesised from (nor)ephedrine. The structure of the catalyst precursor was examined through catalysis and NMR experiments. It was shown that the active catalyst contains one ligand per metal, which coordinates in a didentate N,O fashion (9). In addition, a RuIICl2 complex, in which N,N′-bis(2-hydroxy-1-methyl-2-phenylethyl)-1,2-diaminoethane (1) coordinates through two nitrogen atoms, was structurally characterised by X-ray diffraction (8). - Based on the results of this study a series of new amino alcohol ligands was synthesised from easily available starting materials. Optimisation of the amino alcohol ligand structure resulted in the most effective chiral amino alcohol ligand (5) so far that is capable of reducing acetophenone at 0 °C with up to 97% ee in the RuII-catalysed transfer hydrogenation.

Notizen: CuI and CuII complexes of cyclic and open-chain polyaza compounds have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. In general, only small amounts of copper are needed to promote the reaction. The catalytic activity depends on the structure of the ligand, e.g. amine-amides are more efficient than polyamines, and on the oxidation state of copper, CuII being more active than CuI. Given that CuI is the active species, these changes of behavior must be related to the stabilities of the complexes. The nature of the counterion also has a noticeable influence on the catalytic activity, the role of which is discussed. XAS measurements suggest the formation of oligomeric species. Some of the chiral ligands lead to small enantiomeric excesses. Open-chain ligands can easily be supported on organic polymers and their complexes can be used as catalysts. Furthermore, cyclic and acyclic complexes can be supported on clays by cation exchange and the solids obtained tend to promote the reaction with a decrease in the trans/cis ratio.

Notizen: -Dynemicin A is a member of the family of enediyne natural products. It is unique in that it combines a ten-membered enediyne with an anthraquinone substructure. These features stimulated the development of synthetic approaches to the natural product itself and of analogs thereof. This review summarizes the total syntheses of dynemicin A. In addition, an overview of the known analogs is presented. The analogs can be classified according to the designed trigger mechanism. Most of the analogs contain a removable carbamate on the nitrogen atom. Others are quite similar to the natural lead in that they contain a quinone substructure, which upon reduction causes opening of the oxirane ring. In addition, there are analogs that contain an aromatic sector, the enediyne, and the oxirane ring but lack the nitrogen heterocycle. In these compounds the aryl ring assumes a different conformation from that in dynemicin A. Many of the simplified analogs proved to be quite active in vitro as well in vivo against murine tumor models. A highlight is compound 30 which is much more active than dynemicin A itself. However, looking at all analogs there is no clear-cut correlation between the DNA-cleaving ability at neutral pH and the in vitro results. From this one might conclude that there are possibly two mechanisms for antitumor activity. One involves diradical formation whereas the other might be due to a ligand-receptor interaction.

Notizen: -Reaction of (Z)-1,2-bis(methoxycarbonyloxy)but-2-ene (2) with various N,N-bis(arylsulfonyl)-o-phenylenediamines 1 was catalyzed by a palladium complex associated with chiral ligands to give optically active 1,4-bis(arylsulfonyl)-1,2,3,4-tetrahydro-2-vinylquinoxalines 3 with up to 62% ee. The use of (S)-MeOBIPHEP as the chiral ligand and N,N-bis(p-tolylsulfonyl)-o-phenylenediamine (1i) as the nucleophile led to the highest ee at 25 °C, regardless of the solvent used. The enantioselectivity of the cyclization is strongly affected by the nature of the substituents at the nitrogen atom.

Notizen: -A sea cucumber ganglioside analogue 7 (NGNAα2→ 6Glcβ1→1Cer), which contains a phytosphingosine as a long-chain base and an α-hydroxy fatty acid, has been synthesized. Coupling of the methyl 2-thioglycoside derivative 5 of N-glycolylneuraminic acid with a cerebroside derivative 3, prepared from acanthacerebroside A (1), afforded protected ganglioside analogue 6, which was deprotected to give the corresponding ganglioside 7.

Notizen: -A 1:1 adduct produced in the reaction of nitrosobenzene (2) with 1,3,5-tris(4-methoxyphenyl)-1,3,5-triazinane (3) has been shown by X-ray diffraction structure analysis to be the N′-(4-methoxyphenyl)-N-phenyl-N-oxyformamidinium species 5.

Notizen: -As part of an ongoing project concerning the synthesis of enantiomerically pure α-hydroxy β-amino acids, we have now developed a general strategy allowing the synthesis of anti-α-alkyl α-hydroxy β-amino acids. Our procedure involves the intermediate formation of trans-oxazolines, which are alkylated at C-5 with good to high diastereoselectivity and then hydrolysed under mildly acidic conditions, affording in quantitative yield the corresponding hydroxy amides. The starting (R)-3-amino-3-phenylpropanoic acid and (S)-3-aminobutanoic acid were obtained in enantiomerically pure form by selective enzymatic hydrolysis of the corresponding phenylacetylamides with penicillin G acylase.

Notizen: -Palladium-catalyzed reaction of acidic anilines with (Z)-2-butene-1,4-diyl dicarbonate affords N-aryl-4-vinyloxazolidin-2-ones. The success of the reaction depends on the acidity of the aniline and requires in situ conversion of the dicarbonate into carbamate carbonate by nucleophilic attack of the aniline conjugate base followed by palladium-catalyzed intramolecular cyclization.

Notizen: -The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane-cyclopentene rearrangement was calculated by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the two radical substructures. Thus, the transition structures may be considered, in good approximation, as structures consisting of two weakly interacting radicals.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98349_s.pdf or from the author.

Notizen: -The direct cyclization of 2-amino-4-chloro-3,3-dimethylbutanenitrile with potassium tert-butoxide in THF afforded 1-amino-2,2-dimethylcyclopropane-1-carbonitrile and a dimerization product. Various new cis- and trans-1-(tert-butylamino)-2-benzyl-2-methylcyclopropane-carbonitriles and© the corresponding cyclopropanecarboxamides have been synthesized, with focus on the isolation of the pure stereoisomeric cyclopropanecarboxamides. The relative configuration of the stereoisomers was established by X-ray crystallographic analysis of one of the model compounds. A new route to the latter functionalized cyclopropanes was developed by reaction of 1-methoxycyclopropylamines with potassium cyanide. Some remarkable rearrangements of 1-aminocyclopropane-1-carbonitriles into azetidine and oxazine derivatives via Favorskii-derived intermediates are reported. Various aspects of the chemistry of geminally functionalized cyclopropanes are discussed.

Notizen: -Enyne acetates 2, 4, 6, and 8, as well as enyne oxiranes 10, with different substitution patterns react with organocuprates regioselectively under 1,5-(SN2′′)-substitution to provide vinylallenes 11 and 12. With lithium dimethylcuprate, reduced vinylallenes originating from a (formal) transfer of a hydride ion to the substrate are formed in some cases. The products are usually obtained as mixtures of (E/Z)isomers; however, pure (E)-vinylallenes are formed occasionally. The 1,5-substitutions can also be carried out with catalytic amounts of copper reagents. The reaction of chiral enyne acetate (S)-2a with tBu2CuLi · LiCN proceeds enantioselectively, so that this transformation constitutes a new case of remote stereocontrol.

Notizen: -The reaction of the hydrofluoroborate salt of an open-chain analogue of a Reissert compound with some α,β-ethylenic esters does not give a [4 + 2] cycloadduct, as previously described in the case of ethyl acrylate. The reaction starts with a 1,3-dipolar cycloaddition of a münchnone imine 5c, d. The [3 + 2] cycloadducts 13 evolve via a rearrangement-condensation sequence to give a substituted 2-pyridone derivative 18 or 19. The proposed mechanism has been verified by the isolation and structural X-ray analysis of some compounds of the reaction sequence.

Notizen: -Racemic and enantiopure 2-tert-butyltetrahydropyrimidinones (from pivalaldehyde and 3-aminocarboxylic acids) are converted to Alloc-, Boc-, and Z-protected cyclic imino esters (7-10, Schemes 2-4). These are deprotonated to Li enaminates (K, L). Reactions with electrophiles (prim., sec. alkyl, allyl, benzyl, propargyl halides, aldehydes, imines, enoates) give good yields and are highly diastereoselective (products 11-42, Schemes 5-10). A two-step cleavage (removal of protecting group and hydrolysis) under very mild conditions converts the heterocyclic products to α-branched β-amino acid methyl esters (43-61, Schemes 11-13). The structure of the products is determined by NMR spectroscopy (Figure 1), by chemical correlation (Scheme 14), and by X-ray analysis (Figure 2, 3, 7, Table 1). A structure of the Li enaminates is proposed (Figure 4). Mechanistic models are derived for the reactions occurring with formation of two stereogenic centers with relative topicity like (Figures 5, 6).

Notizen: -The solid-phase synthesis and characterization of a series of peptides (4-15) containing reverse-turn mimetic bicyclic lactams is reported. The bicyclic lactams (1a, 1b) possess high structural similarity to the two central residues of a β-turn. Amino acid conjugates of these bicyclic lactams were synthesized on solid supports following a 9-fluorenylmethoxycarbonyl (FMOC) protection strategy on Wang-Merrifield resin. Coupling between amino acids was accomplished by means of diisopropylcarbodiimide (DIC)/hydroxyazabenzotriazole (HOAt). Coupling between amino acids and the mimics was performed with the potent Carpino's reagent O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU). The final compounds were cleaved from the resin and obtained as N-acetylated methyl esters or benzyl amides.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98399_s.pdf or from the author.

Notizen: -Antarafacial 1,3-sigmatropic shifts in carbonyl derivatives of ketenes, isocyanates, thioketenes and thioisocyanates have been studied by means of ab initio MO calculations. Energy barriers in 20 different systems have been uniformly determined at the MP4SDTQ/6-31G(d,p) level, based on MP2/6-31G(d,p) geometries and corrected for zero-point energies. For formylketene, higher-level calculations using the QCISD(T) method and larger basis sets [up to 6-311++G(2df,2p)] have also been carried out. In carbonylketenes, the migratory aptitude of the substituents R is established as follows: Cl 〉 SH 〉 NF2 〉 NH2 〉 BH2 〉 PH2 〉 F 〉 OCH3 〉 OH 〉 SiH3 〉 H 〉 C6H5 〉 CH3. The barrier heights range from 10 kcal/mol for Cl migration to 35 kcal/mol for phenyl migration. Several factors influencing the energy barriers including the existence of an n-electron pair at the migrating atom, its size, electronegativity and ability to adapt to a hypervalent state, as well as the strengths of the breaking and forming bonds have been examined in detail. Generally speaking, 1,3-sigmatropic rearrangements are feasible thermal unimolecular reactions even under mild experimental conditions.

Notizen: -Five new steroidal alkaloids, plakinamines C (1) and D (2), and the related compounds 3-5 have been isolated from the Vanuatu sponge Corticium sp. Their structures have been elucidated by a detailed spectroscopic analysis, including 2D-HMBC and ROESY correlation experiments. The new compounds show significant in vitro cytotoxicity against human bronchopulmonary non-small-cell lung carcinoma cells (NSCLC-N6) with IC50 values of 〈 3.3-5.7 μg/mL. When tested against T leukemia virus type one (HTLV-I), compounds 1, 4 and 5 were found to exhibit slight anti-HIV activity.

Notizen: -The asymmetric synthesis of (+)-streptenol A was carried out in ten steps and with high enantioselectivity (ee ≥ 96%). The key steps are the α-alkylation of 2,2-dimethyl-1,3-dioxan-5-one RAMP hydrazone A (1), subsequent deoxygenation and elaboration of the side chain via aldehyde B to furnish (+)-streptenol A in 23% overall yield. In analogy, the enantiomer (-)-streptenol A was synthesized using the corresponding SAMP hydrazone in 18% overall yield.

Notizen: -Organolithium and Grignard reagents add to the oxo group of (benzocyclobutenone)tricarbonylchromium(0) (1) diastereoselectively from the exo face of the organic ligand. If acyl anion equivalents are used as nucleophiles, deprotection of the carbonyl functions of the adducts causes ring expansion reactions to occur. Among these a rare example of an anion-accelerated 1-vinylcyclobutenol-cyclohexadienol rearrangement is reported which results, after isomerization, in a naphthol complex. Other ring expansion reactions gave coordinated substituted indanone derivatives. The facial differentiation by the tricarbonylchromium moiety allows for the first time the determination of the distereoselectivity of these reactions. The 1-oxoindan-2-ol derivatives obtained can undergo an α-ketol rearrangement with formation of the corresponding 2-oxoindan-1-ol complexes. Some of these reactions were performed with nonracemic starting material in order to determine how far chirality transfer from the planar chiral starting material to C-2 in the indanone system was possible. The ring expansion was also feasible with the benzocyclobutenedione complex as a starting compound, the reaction giving substituted 1,3-indandione complexes. Crystal structure analyses of three of the complexes prepared are reported.

Notizen: -The oxidation of 3,6-dehydrohomoadamantane (1) was achieved under chemical (NO+BF4-/EtOAc, NO+OAc-/Ac2O, and NO+BF4-/CH3CN), photochemical (photoexcited 1,2,4,5-tetracyanobenzene), and electrochemical (Pt anode, CH3CN, NH4BF4) conditions. Supporting ab initio [density functional theory (BLYP) and Møller-Plesset perturbation theory (MP2)] computations utilizing standard basis sets, 6-31G* (optimizations) and 6-311+G* (single-point energy evaluations), agree with the experimental results implicating the involvement of the same radical cation intermediates in the activation processes. Isomeric radical cations formed from different precursors can equilibrate with low barriers (2.0-11.7 kcal mol-1) and lead to common products. The computed and experimental adiabatic ionization potential of adamantane shows that activation with NO+BF4- is also likely to occur through the adamantyl radical cation. Hence, the bonds need not be attacked directly by the electrophile in the C-H or C-C activation of alkanes with relatively low ionization potentials.

Notizen: -The flash vacuum thermolysis (FVT) of cycloalkenyl allyl (or propargyl) sulfides 8, 9, 12, and 13 led, as the main thermal pathway, to the conjugated cycloalkenethiones 1, 3, and 5, resulting from a retro-ene reaction. These reactive thioketones, thus obtained in ca. 70% yield, have been characterized in the gas phase by mass spectrometry, and at low temperature by IR, UV/Vis and NMR spectroscopy. The polymerization of 1, 3, and 5 upon warming is generally more rapid than the other attempted reactions and only the [2 + 3] dipolar cycloaddition with diazomethane led in low yield, besides polymeric materials, to isomeric 1,3-dithiolanes 20 from cyclopentenethione 1. The obtention of the nonconjugated cycloalkenethiones 2 and 4, expected in the FVT of sulfides 10 and 11, has been confirmed only by UV/Vis spectroscopy at -196 °C, due to their rapid enethiolization. In the case of the large-ring sulfide 14, the (E) geometry of the double bond favoured the competitive retro-ene reaction yielding cyclododecene and propynethial; on the other hand, the FVT of the tricyclic gem-dithiol 15, a possible precursor of cyclobutenethione (7), led to vinyl thioketene (18), obtained by thermal ring opening of 7.

Notizen: -Electrochemically generated tetraethylammonium peroxydicarbonate (TEAPC) and tetraethylammonium carbonate (TEAC) react under very mild conditions with pyrroles affording, after addition of a suitable alkylating agent, the corresponding N-alkylated pyrroles in high yields. C-Alkylated pyrroles have not been isolated in any case reported.

Notizen: -The racemic myxobacterial pheromone (±)-1 (stigmolone), which induces the formation of the fruiting body of Stigmatellaaurantiaca, was synthesized from methyl isobutyl ketone (2) in 48% overall yield in four steps

Notizen: -The photochemistry of 4-methyl-9,10-diazoanthrone (7a) and 1,4-dimethyl-9,10-diazoanthrone (7b) was investigated in argon matrices at 10 K. Visible-light irradiation results in the formation of the anthronylidenes 5a and b, respectively, which were identified by oxygen trapping, by comparison of the IR and UV/Vis spectra with that of the parent anthronylidene 6, and by comparison of the IR spectrum with that calculated by DFT methods. The carbenes 5 are thermally stable under the conditions of matrix isolation; however, irradiation with visible or UV light results in the rearrangement to the quinone methides 10a and b.

Notizen: -2-Cyclopentenyl- and 2-cyclohexenylmethyl sulfoximines can be converted into angular carbon-functionalised, highly substituted, isomerically pure (ds ≥ 98%) 2-oxabicyclo[3.3.0]octanes and 2-oxabicyclo[3.4.0]nonanes in high yields by a convenient one-pot sequence. Molecular frameworks such as these can be found in many biologically active natural products. In addition to the methodological work, we report on studies towards the total synthesis of the euglobals G1 and G2 and arenaran A.

Notizen: -Phosphaalkynes 2 and electron-deficient alkynes 11 readily react in a [4 + 2] cycloaddition process with 5,8-bis(trimethylsilyl)cycloocta-1,3,6-triene (8) in its bicyclic form 10 to furnish regioselectively the tricyclodecadienes 12 and 13, respectively. The phosphorus-containing compounds 12 exhibit structural features which make them suitable for homo-Diels-Alder reactions with electron-deficient acetylenes. A single crystal structure analysis of the homo-Diels-Alder adduct 14b confirmed the structure and relative configuration of the phophatricyclodecadienes 12. In solution the tricyclodecadienes 13 are prone to facile cycloreversion yielding the phthalic esters 15 and the cyclobutene 16. The latter is rapidly converted into the corresponding 1,3-butadiene 18, which can be trapped in a Diels-Alder/phospha-ene/Diels-Alder tandem reaction sequence by phosphaalkyne 2a. The phosphatricyclodecadiene 12 is thermally more stable; loss of cyclobutene 16 only occurs under FVP conditions to afford the λ3-phosphinine 22.

Notizen: -Intermolecular addition of radicals to the 1,3-dioxin-4-ones 1a,b and 2a,b with (-)-menthone incorporated as chiral auxiliary in 2-position were investigated. Photochemically generated radicals from 1,3-dioxolane, oxolane, and 2-propanol were added with high facial selectivity from the more exposed a-side. Intramolecular addition of 1,3-dioxolan-2-yl radicals to chiral dioxinones proceeded less efficiently and with lower selectivity also from the a-side. Nevertheless, it was possible to form the new spirocyclic compounds 22-27. The 1,3-dioxin-4-ones 32a,b possessing an unsaturated side chain were attacked by radicals at the terminal double bond. In the case of irradiation of 32b in 1,3-dioxolane a cyclization followed the intermolecular addition of a 1,3-dioxolan-2-yl radical and the dispiro compound 36 was formed. However, the formation of dispiro compound 40 required two reaction steps starting with irradiation of 32b and bromotrichloromethane. The achiral 1,3-dioxin-4-one 44 possessing an unsaturated side chain at C-2 was attacked by 1,3-dioxolan-2-yl radicals preferentially at C-6.

Notizen: -Several new approaches for the enantioselective synthesis of the chromane moiety of vitamin E are described. Sonogashira coupling of 3a with the alkyne 4 and subsequent elimination gave 6, which was bis(hydroxylated) in 93% yield and with 85% ee. Recrystallization gave enantiopure 7a, which was hydrogenated and transformed into the vitamin E precursor 11. The bis(hydroxylation) of 18 and 21 to give 9 and 22, respectively, was less than satisfactory, proceeding with ee values of 28% and 18%. In contrast, stereoselective allylation of ketone 15 followed by removal of the protecting group or ozonolysis of the allyl moiety furnished the allyl alcohol 26 and the aldehyde 27, respectively, in almost enantiopure form, which again could be used as precursors for vitamin E. Partial hydrogenation of 5a gave the alkene 32a and that of 28 the alkene 30b, both of which show interesting atropisomerism.

Notizen: -A series of new clathrate host molecules (1-10) containing two diarylhydroxymethyl groups attached to different positions (1,5 or 1,8) of a basic anthracene construction unit have been synthesized. Their clathrate formation properties with a variety of organic guests, including amines, alcohols, ketones, and other dipolar aprotic compounds or aromatic hydrocarbons are reported (143 examples of clathrates). The inclusion properties and the clathrate stoichiometries depend in a systematic manner on the structure of the host molecules. The crystal structures of six selected clathrates of different classes of compound have been determined by X-ray diffraction.

Notizen: -Michael addition of serine and threonine derivatives 4a-4c to 3,4,6-tri-O-benzyl-2-nitro-D-galactal (1) afforded the corresponding 2-deoxy-2-nitro-α-D-galactopyranosides 5a-5c in good yield and stereoselectivity. 2-deoxy-2-nitroglycosides 5a and 5b were reduced to the 2-acetamido compounds by platinized Raney nickel T4. Manipulation of the protecting groups afforded known N-Fmoc-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-galactopyranosyl)-L-serine (8a) and -threonine (8b), valuable building blocks for O-glycopeptide synthesis.

Notizen: -Batzellines A and B (1a, b) and isobatzellines A and B (2a, b) are 1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline-containing marine alkaloids characterized by the presence of a methylthio substituent at C-2 of the tricyclic system. We describe here the total synthesis of these natural compounds following the synthetic strategy that we have used previously for the synthesis of damirones A and B, batzelline C, isobatzelline C, discorhabdin C, and makaluvamines A, B, C, and D. The introduction of the methylthio group by electrophilic substitution of a pyrrolo[4,3,2-de]quinoline, appropriately substituted and in a suitable oxidation state, is the key step in the success of these syntheses.

Notizen: The effect that additional groups flanking the hydrogen bond donor/acceptor arrays have on the association constants (Ka) of complexes of chloroform-soluble thymine and adenine derivatives has been investigated by NMR shift titration. Constants for thymine and 2,6-diaminoacyl pyridine derivatives, in which the acyl group bears either (CH2)nR or some other substituent, vary greatly. The peak value of Ka = 1130 M-1 occurs for n = 2 and R = phenyl. Computer modeling with CHARMm suggests that this is due to a weak additional stabilization by a C-H-π interaction; in line with this the complex shows small upfield NMR shifts for the terminal methyl groups. Four other receptors were prepared which could, in principle, form hydrogen bonds with all donor/acceptor sites of adenine; NMR titrations, however, showed very low complexation energies, probably due to deviations from the ideal hydrogen bond geometry necessary to form stronger complexes.

Notizen: 3-(Fluoroalkyl)isoxazolidines 6 and -2,3-dihydroisoxazoles 8 have been obtained in enantiomerically pure form with good diastereoselectivity by 1,3-dipolar cycloaddition of diethyl fumarate and dimethylacetylene dicarboxylate, respectively, to the chiral fluorinated nitrone (R)-5. The latter has been prepared from the β-fluoromethyl-β-oxo sulfoxide (RS)-1, by a synthetic sequence where the chiral and enantiomerically pure sulfinyl function acts as a removable source of chirality. Reductive opening of isoxazolidines 6 then afforded amino fluoromethyl diols 7 in good yields.

Notizen: Phosphonate compounds mimic the first transition state occurring during enzymatic carboxyester hydrolysis of natural substrates by forming a covalent bond with the catalytic serine. However, until now the organophosphorus compounds used in the inhibition studies more or less resembled a natural triglyceride substrate. In order to elucidate the interfacial activation and the mechanism of action of lipases, specific inhibitors need to be prepared. To achieve this goal, enantiomerically pure sn-1,2- and sn-2,3-O-didecanoylglycerol compounds were prepared - starting from a C-4 chiral synthon, 3-buten-1,2-diol - and treated with n-pentylphosphonic dichloride and p-nitrophenol to afford the corresponding diastereomeric phosphonates, which were acylglycerol analogs. Subsequent separation of each of the phosphonate diastereomers A/B or ent-A/ent-B, performed by HPLC, led to four enantiopure stereoisomers that will be investigated as inhibitors of Human Pancreatic Lipase (HPL) and Human Gastric Lipase (HGL) using the monomolecular film technique.

Notizen: The structures of the norbornenyl and norbornyl sulfones exo-5, endo-5 and endo-6 have been determined experimentally, by X-ray analysis, and theoretically by ab initio calculations (HF/6-31+G*). X-ray crystal structure analyses of the lithiated allylic norbornenyl and norbornyl sulfones endo-3/ent-endo-3·2diglyme and endo-4/ent-endo-4·2diglyme revealed dimeric O-Li contact ion pairs devoid of C-Li bonds. The anions of endo-3/ent-endo-3·2diglyme and endo-4/ent-endo-4·2diglyme adopt both the endo conformation (C2-S) and are characterized by in the exo direction pyramidalized anionic C atoms. The degree of pyramidalization of the C2 atom of 3 is higher than that of 4. Ab initio optimizations (HF/6-31+G*) of the structures of the anions of methylenenorbornene I and methylenenorbornane II resulted in local minima featuring non-planar C2 atoms which are pyramidalized in the exo direction in both cases, but to different degrees. In both cases cryoscopy of 3 and 4 in THF at -108.5 °C revealed approximately 1:1 mixtures of monomers and dimers. The sulfones exo-5, endo-5, exo-6 and endo-6 as well as the lithiosulfones 3 and 4 were studied by NMR spectroscopy. 1H-NMR (400 MHz), 13C-NMR (100 MHz) and 6Li-NMR (44 MHz) spectroscopy of 3 and 4 at -100 °C in [D]8THF revealed in each case only one set of signals, independent of the configuration of the starting sulfones. This indicates in both cases that attainment of both the monomer-dimer and the endo/exo equilibria of 3 and 4 is fast on the NMR time scale. According to 6Li{1H}- and 1H{1H}-NOE experiments of 3 and 4 the monomeric and dimeric species endo-3 and endo-4, having endo anions, seem to be preferred in THF solution. Ab initio calculations of the anions of 3 and 4 resulted in structures endo-3(-Li+), exo-3(-Li+), endo-4(-Li+) and exo-4(-Li+) (HF/6-31+G*), whose atomic point charges were calculated by the method of Kollman et al. The C2 atoms of endo-3(-Li+) and endo-4(-Li+) are pyramidalized in the exo direction whereas the C2 atoms of exo-3(-Li+) and exo-4(-Li+) are pyramidalized in the endo direction. According to the calculations, the endo anions are more stable than the exo anions. There is good agreement between the optimized structures of the free anions and the experimentally determined structures of the anions of the contact ion pairs in the crystal. Reactions of 3 and 4 with DX, MeI, EtI, nPrI and nHeI occurred at the C2 atom under the selective formation of the corresponding endosulfones endo-8a-e and endo-9a-e, respectively, in all cases. Thus, an earlier report on the selective formation of the exosulfone exo-9b in the reaction of 4 with MeI has to be revised. Product ratios were independent of the configuration of the starting sulfones and varied with the nature of the electrophile. Selectivities were highest in the case of the norbornyl species 4. Reaction of 3 with PhCHO occurred at the α position (C2) to afford the alcohols endo-8f and exo-8f (88:12) as single diastereomers and at higher temperatures at the γ position (C8), whereas reaction of 4 with PhCHO took place at the γ position even at low temperatures. Methylation of endo-5 and exo-5 at -105 °C by both the stepwise method and by the in situ method gave different ratios of exo- and endo-methylation products. The selectivities of reaction of 3 and 4 with electrophiles have been rationalized by the Curtin-Hammett/Winstein-Holness concepts. It is proposed that endo-3 (endo-4) and exo-3 (exo-4) are conformationally labile on the time scale defined by the rate of their reactions with electrophiles, and are attacked by electrophiles with high selectivities from the exo and the endo face, respectively, because of the shielding by the phenyl group and the direction of the pyramidalization of the anionic C atom. Preferential formation of the endosulfones is thus ascribed to exo attack of electrophiles on endo-3 (endo-4) being faster than endo attack on exo-3 (exo-4) because of Houk's staggering effect. Methylation of 3 and 4 by the in situ method showed 3, whose C2 atom is stronger pyramidalized, to be more reactive than 4. The base-catalyzed H/D exchange of sulfones endo-5, exo-5, endo-6 and exo-6 with NaOCD3 in CD3OD proceeded in all cases with a high degree of retention of configuration.

Notizen: The syntheses of the new pentahelicenes 5, 11, 17, 21, and 28 with various substituents are described. In the case of 2,13-dicyano-[5]helicene (11) optical resolution was achieved by HPLC using a column packed with γ-cyclodextrin. However, the enantiomers racemized within a few hours. On the other hand, the enantiomers of 28 turned out to be stable after separation on triacetylcellulose using MPLC. The crystal structures of 11, 17, and 21 were solved and indicated the typical distortions which are expected for helicenes. The model of the sum of free valence numbers was applied in order to rationalize the reactivity pattern of the photochemical phenanthrene cyclization.

Notizen: The photosensitised oxidation of benzyl ethyl sulfides in aprotic solvents (benzene or acetonitrile) gives the corresponding aldehydes under mild conditions. This is a general reaction which applies to benzyl derivatives containing either electron-donating or electron-withdrawing substituents and furthermore to hetero analogues such as 2-pyridinylmethyl sulfide (not to the 3-indolylmethyl sulfide, since reaction at the heterocycle moiety competes) as well as to allyl sulfides. In a protic solvent (methanol) these sulfides give the sulfoxides instead (except for the nitrobenzyl derivatives, where the aldehyde remains the major product). Among the α-substituted sulfides tested, the α-phenylbenzyl and the 3-cyclohexenyl sulfide give the corresponding ketone (the latter in a low yield), but the α-methylbenzyl sulfide gives the sulfoxide as the main product. The rate for singlet oxygen quenching and for chemical reaction have been measured for representative benzyl sulfides. The reaction is discussed in the frame of the currently accepted mechanism for sulfide photooxygenation. The key step for oxidative C-S bond cleavage appears to be hydrogen transfer from the activated α position in the first formed intermediate, the persulfoxide. This reaction is inhibited in methanol where the persulfoxide is hydrogen-bonded.

Notizen: γ-Butyrolactones were obtained in good yields and high regioselectivity by a Baeyer-Villiger oxidation with H2O2 catalysed by methyltrioxorhenium. The lactonization was chemoselective in the presence of double bonds, aromatic rings, and chlorine substituents. A trimethylsiloxy-substituted ketone was converted directly into a hydroxylated lactone in good yield and regioselectively.

Notizen: We report the first instance of the levelling of oximate reactivity in a deprotonation process, which is shown to have as origin the desolvation of the oximate ion prior to actual proton transfer, in accord with the large predominance of the work term (wr) far exceeding the intrinsic barrier term in the Marcus formulation.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/1999/99076_s.pdf or from the author.

Notizen: 2,4-Dioxoesters 1a-c are selectively converted into optically active 2-hydroxy-4-oxoesters 2a-c by hydrogenation with chiral rhodium-aminophosphane-phosphinite catalysts (82-88% ee) or ruthenium-bisphosphane catalysts (52-67% ee). Direct one-pot hydrogenation of 2,4-dioxoesters 1a-c to 2-hydroxy-4-butyrolactones 4a-c proceeds in high yields; catalytic activities, chemo-, dia-, and enantioselectivities are strongly dependant upon the nature of the substrate and the catalyst.

Notizen: -The interaction of poly(maleic acid-co-alkyl vinyl ether)s and poly(sulfonylethyl maleic acid monoamide-co-alkyl vinyl ether)s with and without (cyanobiphenylyl)oxy chromophores with N-[ω-(substituted azobenzoxy)alkyl]-N,N-dimethyl-N-hydroxyethylammonium bromide surfactants has been studied by UV spectroscopy. The azobenzene unit is functionalized at the 4′-position with a cyano or fluoro substituent and is connected to the surfactant headgroup via a decyl or dodecyl spacer. Upon addition of surfactants to poly(maleic acid-co-butyl vinyl ether) the absorption maxima (λmax) of the azobenzene chromophores immediately show their maximum blue shift. This indicates cooperative binding of surfactant to this polymer, and the formation of micelle-like aggregates surrounded by polyelectrolyte is assumed. Upon addition of the surfactants to the other polyelectrolytes λmax values of the azobenzoxy chromophores gradually shift to lower values indicating a lower cooperativity of surfactant binding. This is attributed to the formation of microdomains by the polyelectrolytes themselves. For these systems the formation of mixed micelles is assumed. The compactness of the microdomains of the maleic acid copolymers is influenced by the pH and binding with surfactants is also influenced by pH. The sulfonylethyl maleic acid monoamide copolymers show no pH dependence in binding above neutral pH. For these polyelectrolytes the cooperativity also becomes less with a longer spacer between backbone and chromophore. Upon elongation of the surfactant spacer or changing the end group from a cyano to the more hydrophobic fluoro substituent a lower λmaxis observed for the chromophores upon initial binding to the polyelectrolytes indicating more cooperative binding. When surfactants and polyelectrolytes are both labelled with chromophores, binding proceeds noncooperatively and the formation of mixed micelles is assumed.

Notizen: -Recently, we reported on cycloadditions between electron-deficient heterodienes and tributyl(ethynyl)tin, which provide a new pathway to stannylated pyridazines and, in one special case, pyridines. In order to broaden the synthetic scope of these reactions, we have developed hetero [4+2] cycloaddition reactions between a number of tailor-made 1,2,4-triazines 5-9 (acting as heterodienes), and tributyl(ethynyl)tin (acting as dienophile). The desired 1,2,4-triazines are readily available, in moderate to very good yields, by the condensation reactions of appropiate carbamidrazones and glyoxals. These cycloadditions open up a novel route to regiospecifically stannylated 2,2′-bi- and 2,2′,6′,2′′-terpyridines 1-4, 11 in good yields. The stannanes 1-4, 11 are versatile synthetic intermediates, and with this strategy various substituents can be incorporated directly by substitution of the stannyl group, as was shown for halogens and carbon electrophiles under Stille conditions.

Notizen: -The name of an additional author (T. W.) should be added as shown above.The elemental analysis data of several compounds were inadvertently omitted and should be added as follows: 3c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.43, H 9.16. 4c: C26H44O8 (484.3): calcd. C 64.44, H 9.15; found C 64.68, H 9.33. 5c: C18H28O4 (308.2): calcd. C 70.10, H 9.15; found C 69.95, H 9.28.

Notizen: N-formylation of a secondary aliphatic amine has been achieved through the in situ reaction of potassium o-nitrophenolate, generated from o-nitrophenol, K2CO3, KOH, and bis(2-chloroethyl)amine hydrochloride in hot DMF. The initial product, N,N-bis[2-(2-nitrophenoxy)ethyl]formamide has been reduced to provide N,N-bis[2-(2-aminophenoxy)ethyl]formamide which after an MnII-templated cyclocondensation reaction with 2,6-diformylpyridine followed by reductive demetallation with NaBH4 gives an N,N′-diformylated 36-membered N8O4 oxaazamacrocycle.

Notizen: Reaction of the ylide (cyclopropyl)3P=CH2 with Michler's thioketone S=C(C6H4NMe2)2 in [D5]pyridine gave the thio Wittig intermediate [(cyclopropyl)3P+-CH2-CAr2-S-] (11; 31P NMR: δ = +27.7). Compound 11 was characterized by X-ray diffraction and shown to exhibit a gauche-betaine-type structure with an S-C-C-P dihedral angle of 52.9(3)° and a P···S separation of 3.312(2) Å. The characteristic averaged 1JPCipso(aryl) coupling constant was used to elucidate the characteristic structural properties of Wittig and thio Wittig intermediates derived by treatment of the series Ph3P=CH2 (2a), Ph2MeP=CH2 (2b), and PhMe2P=CH2 (2c) with bis(p-methoxyphenyl) ketone to give 3 or benzophenone (to give 3′) or bis(p-methoxyphenyl) thioketone (to give 5), respectively. The oxaphosphetane series 3′a-3′c shows a strong response of the 1JPCipso(aryl) values (3a: 94 Hz; 3′b: 74 Hz; 3′c: 47 Hz) to this substituent perturbation, as it is expected for a dynamic trigonal-bipyramidal situation at the phosphorus atom, whereas the thio Wittig intermediate is only very little affected [1JPCipso(aryl) of 5a: 92 Hz; 5b: 86 Hz; 5c: 82 Hz]. Thus, the thio Wittig intermediates 5 seem to exhibit a pronounced phosphonium character in polar solvents and may be regarded as thiabetaine-type intermediates in solution.