Showing papers by "Vadim G. Kessler published in 2000"

The solution thermolysis approach to molybdenum(V) alkoxides: synthesis, solid state and solution structures of the bimetallic alkoxides of molybdenum(V) and niobium(V), tantalum(V) and tungsten(VI)

Abstract: No complex formation can be observed between molybdenum(VI) oxoalkoxides and the alkoxides of niobium(V) or tantalum(V) at room temperature. The bimetallic derivatives of molybdenum(V), Mo4M2O8(OiPr)14, where M = Nb 1 and Ta 2, were instead isolated on cooling from the solutions of the isopropoxides in toluene subjected to a short-time reflux. The X-ray single crystal study showed both 1 and 2 to be built of (iPrO)3M(μ-OiPr)3MoO(μ-O)2MoO(μ-OiPr)2MoO(μ-O)2MoO(μ-OiPr)3M(OiPr)3 non-linear chain molecules with 2 Mo–Mo bonds (2.5836(8) A) and short but non-bonding Mo–M distances (3.1791(8) A for 1 and 3.1746(8) A for 2). According to NMR and EXAFS data this structure becomes very fluxional or might even be partially broken into homometallic components in hydrocarbon solutions. The oxidation of 2 with traces of oxygen leads to the formation of Mo3Ta2O8(OiPr)103. Compound 3 can be isolated in a pure form from the reaction of MoO(OiPr)4 with Ta(OiPr)4(OMe) 6: the presence of methoxide ligands leads to the formation of additional oxoligands via non-reductive thermolysis leading to the formation of a (CH3)2C(OMe)2 ketal as organic byproduct. The molecules of 3 are 5-member rings with a MoO(μ-O)2MoO fragment in the basis (Mo–Mo 2.5730(13) A), coupled to two (μ-OiPr)2Ta(OiPr)3 fragments that are joined together by an oxomolybdate ligand (μ-O)2MoO2. According to NMR-spectroscopic data the aggregate is preserved and rigid in solution. Mo4Ta4O16(OiPr)124 was found to be one of the products of complete oxidation of 2 (and 3) on prolonged contact with dry oxygen. The thermal treatment of the solutions of MoO(OiPr)4 and WO(OiPr)4 in toluene yields MoV4O8(Mo,W)VI2O2(OiPr)125 with a molecular structure very close to its homometallic analog Mo6O10(OiPr)12. The complete X-ray single crystal study was carried out for the sample of 5 with MoV4O8(Mo0.45W0.55)VI2O2(OiPr)12 composition.

Heterometallic Alkoxide Complexes of Variable Composition—A New Way to Ultrafine Powders of Metal Alloys

Abstract: The anodic oxidation of Re metal in MeOH (Me = CH3) provides a mixture of Re2O3(OMe)6 and Re(V) oxoalkoxides that on storage or on heating give insoluble and air stable Re4O6−y (OMe)12+y (I). I can be also obtained by reaction of Re2O7 with MeOH. In the presence of MoO(OMe)4, a heterometallic complex ReMoO2(OMe)7(II) is formed as intermediate, the final product being Re4−x Mo x O6−y (OMe)12+y (III). The electrosynthesis in the presence of WO(OMe)4 gives Re4−x W x O6−y (OMe)12+y (IV) only at very high Re : W ratios in solutions and the W content varies in one and the same sample. The dissolution of Re2O7 in the solutions of MO(OMe)4, M = Mo,W in toluen on reflux yields Re4−x M x O6−y (OMe)12+y with uniform Re : M distribution. The cocrystallization of MoO(OMe)4 and WO(OMe)4 yields (Mo,W)O(OMe)4 (V) with almost uniform Mo : W distribution. The thermal decomposition of II and III in inert atmosphere gives fine powder of the (Re,Mo)O2 phase. The reduction with hydrogen gas converts II and III into an ultrafine powder of Re–Mo alloy at temperatures below 400°C. The latter can be sintered into compact metal at 800–900°C.

Heterometallic Alkoxides of Molybdenum and Heavy Transition Metals—the Synthesis and Prospects of Application

Abstract: The alkoxides of molybdenum and other heavy transition elements such as Ta or Nb were found to be unreactive towards each other. The bimetallic derivatives could be obtained either via partial hydrolysis that gave Mo2Ta4O8(OMe)16 (I) or via partial thermolysis that provided access to Mo4Ta2O8(OiPr)14 (II), Mo3Ta2O8(OiPr)10 (III), Mo4Ta4O16(OiPr)12 (IV), Mo4Nb2O8(OiPr)14 (V) and Mo4W2−xMoxO10(OiPr)12 (VI). I–VI can be isolated only from hydrocarbon media as the presence of alcohols leads to precipitation of insoluble homometallic derivatives of molybdenum. The cathodic reduction of MoO(OR)4 (R = Me, Et) in the presence of LiCl and M(OR)5 (M = Nb, Ta) leads only to formation of LiMo2O2(OMe)7(MeOH) (VII) or LiMo2O2(OEt)7 (VIII) respectively.

Synthetic Approaches to Mixed-Metal Heteroleptic Derivatives of Late Transition Metals

Abstract: The approach based on isomorphous substitution permitted preparation of (Co, Ni)4(acac)4(μ3–OMe)4(MeOH)4(I) via interaction of individual M4(acac)4(μ3–OMe)4(MeOH)4 in toluene/methanol media. The oxidation of I in air in solution in MeOH in the presence of NaOAc and aminoalcohols as catalysts gives Co2Ni2-(acac)4(μ3–OMe)4(OAc)2(II). The symmetrization reaction between a complex formed by a hard Pearson acid and a soft Pearson base and that formed by a soft acid and a hard base led to CuNi2(OCOC2H5)3(ORN)3-(RNOH)(III) and Ni(Ni0.25Cu0.75)2(μ3–OH)(μ2–OAc)(OAc)2(μ2, η2-ORN)3(η2-RNOH)(IV) RN = CH(CH3)-CH2NMe2 via interaction of Ni(ORN)2 with copper propionate and copper acetate hydrate respectively in hydrocarbon media.