Halogens vanadium complexes

VO(acac)2 < VO(Et-acac)2 VO(Me-acac)2 BMOV. Conversion rates for all hydrolysis products were faster than for the original species. Both EPR and visible spectroscopic studies of solutions prepared for administration to diabetic rats ocumented both a salt effect on the species formed and formation of a new halogen-containing complex. The authors concluded that vanadium compound efficacy with respect to long-term lowering of plasma glucose levels in diabetic rats traced the concentration of the hydrolysis product in the administration solution. 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

Complexes [VL3]X2 (L = en, 1,2-diaminopropane, 1,3-diaminopropane X = C1, Br, I) and [V(dien)2]X2 were prepared by mixing ethanolic solutions of amine and of vanadium(II) halide. The magnetic moments (3.66-3.91 BM) and electronic spectra were typical of octahedral vanadium(II) and there was no halogen coordination.65... 

Hala, J. Halides, Oxyhalides and Salts of Halogen Complexes of Titanium, Zirconium, Hafnium, Vanadium, Niobium and Tantalum, Vol, 40, Elsevier Science, New York, NY, 1989. 

Coordination compounds of vanadium(V) also catalyze peroxidative halogenation reactions where the reactive oxidant is a monoperoxo complex of a mononuclear vanadium compound (Figure 6) [11,22,92-95,99]. 

Figure 3.166 shows the reactivity and potential of these early transition metal pincer carbene complexes taking vanadium as an example. The broad range of compounds becomes possible owing to the rich redox chemistry of vanadium that makes different oxidation states easily accessible. Here, examples for vanadium(ll), vanadium(III) and vanadium(IV) are shown. Abstraction of halogen is facile making the introduction of different TT-donor ligands possible, even weak ones like acetonitrile. 

Few redox studies with cubic mesoporous materials have been reported [52]. The large, complex, three-dimensional pore system offers a unique environment. Ti- and Cr-substituted MCM-48 have been studied for the selective oxidation of methyl methacrylate and styrene to methyl pyruvate and benzaldehyde, respectively, using peroxides as oxidants and were found to outperform TS-1. Ti-MCM-48 has also been found to be better than Ti-MCM-41, TS-1 and Ti02 for the photocatalytic reduction of CO2 and H2O to methane and methanol. Ti-grafted MCM-48 has also been reported as the first functional biomimic of vanadium bromoperoxidase, active at neutral pH and used in the peroxidative halogenation of bulky organic dyes. 

Shaver and coworkers [319] investigated the mechanism of bis(imino)pyridine ligand framework for transition metal systems-mediated polymerization of vinyl acetate. Initiation using azobisisobu-tyronitrile at 120°C results in excellent control over poly(vinyl acetate) molecular weights and polymer dispersities. The reaction yields vanadium-terminated polymer chains which can be readily converted to both proton-terminated poly(vinyl acetate) or poly(vinyl alcohol). Irreversible halogen transfer from the parent complex to a radical derived from azobisisobutyronitrile generates the active species. 

Trivalent vanadium exists only as a (hexahydrated) ion, V(H20)8, m an aqueous solution. The most readily formed complexes are the halogens and halogenoids. The following complexes are formed with fluoride ions VfI , VFi -H20, VF4-2H20 [6]. Chloride ion forms the VC1 -H20 complex. The cyanide complex [7] has been isolated but is unstable in aqueous solution. However, several thiocyanate complexes have been reported [7,8]. Only the V(SCN) and the V(SCN) appear to be stable in water, the latter only at high concentrations of thiocyanate. 

The vanadium group element homoleptic compounds with uM —C bonds are relatively thermally unstable and very sensitive to oxidizing agents and water. They also have the tendency to expand the coordination number as a result of R" or Lewis base (amine, phosphine, etc.) addition. Heteroleptic complexes possessing cyclopentadienyl, halogen, 0x0, acetylacetonate, etc., ligands are usually more thermally stable than homoleptic complexes such as MR4. 

Various other solvate complexes can be obtained, when transition, metals are reacted with the free halogens in acetonitrile . In this way TiCl4(AN)2, TiBr4(AN)2 and a polyhalide [Ti(AN)6] [Isis are produced. Chlorine, bromine and iodine oxidize vanadium to trivalent compounds, namely VCl3(AN)3AN, [VBr2(AN)4]Br and the polyiodide [V(AN)6][Is]s- With chromium CrCls(AN)3AN, a bromide of variable (composition and [Crl2(AN)4]I are obtaincd. ... 

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