Vanadium complexes acetylene

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

Iron. Industrial hygiene chemists have analyzed iron as the o-phenanthrollne or thiocyanate complexes (6,13). In the AAS analysis at 248.3 nm with air-acetylene atomization, nickel and silica are interferences. If iron in ferro-vanadium must be analyzed, a more oxidative solution than the ntiric acid wet ashing of P CAM 173 is required. Nitric acid-hydrofluoric acid will solubilize refractories containing iron. 

Silylation of Na[V(CO)2(Me2PCH2CH2PMe2)2] affords the vanadium carbyne complex see Carbyne Complexes), V(COSiPh3)(CO)(Me2PCH2CH2PMe2)2, which is supposed to be a precursor complex for the formation of a ] -acetylene... 

The photoreduction of N2 by irradiation of vanadium chloride in aqueous ethanol with u.v. light has been describedAn unstable dinitrogen divanadium complex has been proposed to be the key intermediate and the reaction products include NH3, N2H4, and H2. A model system for N2 reduction involves the photoreduction of acetylene and this can be achieved with a sacrificial bipysRu /Co " system. 

Acetylene is quantitatively reduced by V catecholate to ethylene with cw-di-deuteroethylene formed selectively from C2D2, also similarly to enzymatic reduction of C2D2 by nitrogenase. Distinct from N2 reduction, the pH range for the reduction of acetylene is much broader than for dinitrogen (from ca pH 5 to concentrated alkali solution). Kinetic studies of the oxidation of vanadium(II) catecholate complex by dinitrogen have led to the reaction equation ... 

When the 1 1 cycloadducts, generated in situ by addition of an equimolar amount of a phosphaalkyne R C=P to an imidovanadium(v) complex RN=VCl3, are treated with an excess of an acetylene R C CR, quantitative formation of the corresponding 177-1,2-azaphospholes 5 is observed (Scheme 2). Compounds 5 are isolated pure in 31-71% yields and the reaction is regiospecific. A large number of 177-1,2-azaphospholes have been prepared by this route. The formation of the 1,2-azaphospholes proceeds via an insertion of the acetylene into the P-C bond of the vanadium cyclobutene derivative, followed by a reductive elimination <20008417, 2003ZNB44>. 

In the context of alternative substrates for nitrogenases, in particular alkynes, [Equation (4.27)], model compounds are of interest in which the alkyne is coordinated side-on to vanadium. The side-on or rr coordination implies a weakening of the triple bond by TT-back-donation from vanadium-d into the tt orbitals of the ligand, and hence an activation. The activated siloxyacetylene in the complex [ClVdmpe)2 i7 -(Me3SiOC= COSiMe3)] [dmpe = bis(dimethylphosphino)ethane] is reduced by hydrogen to the respective ethene, [Equation (4.39)]. The precursor acetylene complex is formed by... 

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