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31.
Thomas Kauffmann 《Angewandte Chemie (International ed. in English)》1997,36(12):1258-1275
Hitherto there was no reaction known that permits transformations of R1R2-CO → 0.5 R1R2R3C–CR1R2R3 in one step. This type of additive–reductive carbonyl dimerization is now possible using alkoxy(alkyl)tungsten(v) complexes with aromatic, heteroaromatic or α,β-unsaturated aldehydes and ketones. When a corresponding phenyl complex was employed in a test experiment, it was revealed that an aliphatic ketone could be used as the substrate in this reaction. A second interesting type of reaction is the transformation of CH3 ligands into μ-CH2 ligands, which occurs during the treatment of MeLi or Me3Al with molybdenum or tungsten chlorides (oxidation states VI and V, for Mo additionally IV) at low temperatures with liberation of CH4. Here, the question arises as to whether the intermediate involved has a terminal CH2 ligand (Schrock carbene complex) or a μ-CH3 ligand (CH3 bound by a two-electron three-center bond to two metal atoms). Of all the μ-CH2 complexes obtained, those which were synthesized by the action of MeLi on molybdenum chlorides can be recommended as reagents for carbonylmethylenation of aldehydes and ketones. They display high selectivity, very low basicity, a surprising resistance to protons, they are readily available, can be easily modified and, as regards their selective behavior, they have been investigated more thoroughly than other readily accessible carbonylmethylenation reagents of comparable selectivity. The results of NMR spectroscopic investigations on the structure of the μ-CH2 complexes, and associated reaction mechanisms are discussed. A survey of carbonylmethylenation reagents, which have been reported in the literature, permits comparisons to be made with carbonylmethylenating molybdenum and tungsten complexes. 相似文献
32.
含钼化合物及其配合物的抗癌抗肿瘤活性 总被引:4,自引:0,他引:4
钼是生命体所必需的微量元素。本文介绍了钼在人体中的作用,钼缺乏和钼过量对人体的影响,并介绍了含钼化合物以及配合物的抗癌抗肿瘤研究情况。 相似文献
33.
在以加氢汽油为溶剂,MoCl_3(C_7H_(15)COO)_2(Mo)为主催化剂,(i-Bu)_2AlO〈O〉(Al)为助催化剂合成1,2-聚丁二烯的二元催化体系中,添加BF_3CH3·OEt_2等,对体系的催化活性影响显著。以的混合物为第三组份加入催化体系,较大幅度提高了钼系催化体系的活性。在Mo/Bd=8.0×10~(-5)(摩尔比),聚合5小时,丁二烯转化率可达到70%。初步搞清了钼催化体系合成的1,2-聚丁二烯中产生凝胶的条件,推测了凝胶的生成原因,考察了聚合条件对催化活性、分子量及微观结构含量的影响。 相似文献
34.
This paper reports a new method for preconcentration and separation of trace amounts of molybdenum in seawater samples prior to determination by inductively coupled plasma–atomic emission spectroscopy (ICP–OES). Diethylenetriaminetetraacetic acid-functionalized polysiloxane (DETAP) was synthesized by carboxymethylation of amino groups on triamine immobilized polymer, which was prepared by modification of 3-chloropropylpolysiloxane with diethylenetriamine. The resulting polysiloxane is highly selective and efficient in chelating Mo(VI) at trace levels. It can be used as a column packing material. The polysiloxane column can be reused over ten times without losing its original properties, so it is suitable for preconcentration of molybdenum species in seawater samples before determination. The parameters governing the characteristics of polysiloxane for adsorption of Mo(VI) were investigated. These include the effect of pH, amount of polysiloxane, equilibrium time, adsorption isotherm, maximum adsorption capacity, interfering ions, flow rate, capacity for reuse, and desorption. The precision of the preconcentration method, calculated as the relative standard deviation of seawater samples, was 3%. The preconcentration factor was 100. The detection limit, defined as 3 times the standard deviation of five replicate measurements of the blank sample at pH 3, was 0.17 g L–1. Measurement results for standard reference materials were in good agreement with the certified values [(CRMs), NASS-2 Seawater (Open Ocean) and CASS-2 Seawater (Coastal)]. 相似文献
35.
The hexamolybdenum cluster complex [Mo6(3-Cl)8(O2CMe)6]2–, 1 was isolated as the Bu4N+ salt in 71% yield from the reaction of (Bu4N)2[Mo6(3-Cl)8Cl6] with AgO2CMe in CH2Cl2 solvent. The compound was characterized by single crystal X-ray diffraction analysis. The cluster contains an octahedral arrangement of six molybdenum atoms with eight chloride ligands bridging the eight trianglar faces and six carboxylate ligands terminally coordinated through one oxygen atom to each of the six molybdenum atoms. Crystal data: space group =P21/n,a=10.713(3)Å,b=14.43(1)Å,c=21.919(4)Å, =94.37(2)°,Z=2, 1965 reflections,R=0.036. 相似文献
36.
The crystal structures of molybdocene‐amino acid compounds of the type [Cp2MoIV(κN, κO‐AA)]+Cl—·xH2O with AA = D ‐phenylalaninato (x = 1.5), DL ‐leucinato (x = 2) and DL ‐valinato (x = 1) have been determined (Cp = η5‐C5H5). The compounds feature an almost planar, five‐membered chelate ring of the aminocarboxylate moiety (deprotonated amino acid) with the molybdenum atom. In the phenylalaninato complex π‐stacking between the phenyl rings is found. The complexes were proven kinetically stable at pH < 1 for at least 24 h. 相似文献
37.
Alistair J Usher Nigel T Lucas Simon Petrie Mark G Humphrey Anthony C Willis 《Journal of organometallic chemistry》2004,689(1):50-57
Reaction of WH(CO)3(η-C5Me5) with IrCl(CO)2(4-H2NC6H4Me) affords WIr3(μ-CO)3(CO)8(η-C5Me5) in low yield. A structural study reveals a WIr2-centred plane of bridging carbonyls, in contrast to the crystal structure of WIr3(CO)11(η-C5H5) (all-terminal carbonyl distribution). DFT calculations reveal an increasing proclivity to adopt an all-terminal CO disposition for clusters MIr3(CO)11(η-C5H5) in the gas phase on proceeding from M=Cr to Mo and then W, consistent with structural studies in the solid state for which the tungsten-containing cluster is the only all-terminal example. Increasing electron donation from the ligands in the tungsten system (either from phosphine substitution or cyclopentadienyl permethylation) suffices to impose a plane of bridging carbonyls in the ground state structure. 13C NMR fluxionality studies reveal that CO exchange mechanism(s) for WIr3(CO)11(η-C5H5) and the related tetrahedral cluster W2Ir2(CO)10(η-C5H5)2 are very fast and involve all carbonyls on the clusters. DFT calculations on MIr3(CO)11(η-C5H5) (M=Cr, Mo) substantiate a ‘merry-go-round’ mechanism for carbonyl scrambling in these systems, a result which is consistent with the scrambling behaviour seen in the NMR fluxionality studies on the W-containing congener. 相似文献
38.
F. Sanem Koçak 《Journal of organometallic chemistry》2006,691(23):5030-5037
Thermal substitution reaction of Cr(CO)4(η2:2-1,5-cyclooctadiene), Mo(CO)4(η2:2-norbornadiene), and W(CO)5(η2-bis(trimethylsilyl)ethyne) with N,N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO)4(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO)5(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO)4(bfeda). The electrochemical behavior of the M(CO)4(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH2Cl2 solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO)4(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO)4(bfeda) and W(CO)4(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom. 相似文献
39.
Jörg Fridgen Georg Eickerling Ana M. Santos 《Journal of organometallic chemistry》2004,689(17):2752-2761
Novel chiral 2′-pyridinyl alcohols derived from isopropylidene-protected carbohydrates are reported. They show different characteristics at the hydroxy group, but are all suitable ligands for chiral molybdenum(VI) complexes of the type MoO2L2 (L = chiral 2′-pyridinyl alcoholate). MoO2(acac)2 served as starting material in the complex syntheses. The structure of one ligand and one dioxo complex were exemplary established by X-ray crystallography. For catalytic runs in the enantioselective epoxidation catalysis trans-methylstyrene was used as model substrate, tert-butylhydroperoxide and cumolhydroperoxide, resp., as the oxidant. 相似文献
40.
Harry Adams Sarah A Morris Jeffrey C Motley 《Journal of organometallic chemistry》2004,689(3):522-527
Transfer of dithiolene ligands from [Ni(S2C2Ph2)2] to the dimolybdenum complex [Mo2(μ-C2R2)(CO)4Cp2] (R=CO2Me, Cp=η-C5H5) affords the first example of a dithiolene alkyne complex, [Mo2(μ-C2R2)(μ-S2C2Ph2)2Cp2], together with [Mo2(μ-SCRCR)(μ-SCPhCPh)Cp2] in which sulfur transfer from dithiolene to alkyne has occurred. 相似文献