Redox reactions with metal carbonyls of group V

Abstract

AbstractThe carbonylmetalates of cobalt(‐I), manganese(‐I), chromium(‐I), molybdenum(‐I), tungsten(‐I), and the anionic carbonyl cyclopentadienyl derivatives of the zerovalent Group VI metals ([MCp(CO)3]−, M = Cr, Mo, W) are readily oxidized by hexacarbonylvanadium(0) to give the neutral metal carbonyls. In the case of the V(CO)6/[Mn(CO)5]− system, by 13CO‐labeling of the oxidizing agent V(CO)6 it is shown that the redox reaction occurs via an outer‐sphere mechanism. On the other hand, hexacarbonylvanadium(0) behaves as a reducing agent towards NiCp2 and MnCp2, the reduced products being Ni(CO)4 and MnCp(CO)3, respectively. The hexacarbonylmetalates of niobium(‐I) and tantalum(‐I) are oxidized by a number of oxidizing agents, exclusively by a two‐electron transfer process to niobium(I) and tantalum(I). When the acetylacetonato complexes of nickel(II) and iron(III) are used as oxidizing agents, the M(acac)(CO)4 THF complexes (M = Nb, Ta) were obtained, the oxidation by nickel(II) being the preferred one from a preparative point of view. The crystal and molecular structure of the tantalum complex, Ta(acac)(CO)4 THF, has been solved by X‐ray diffraction methods. Crystals are orthorhombic, space group P212121, a = 15.347(3), b = 12.227(3), c = 8.642(3)Å, V = 1621.6 Å3, Dc = 1.900 g·cm−3, Z = 4. The tantalum atom is heptacoordinated, being surrounded by the bidentate acetylacetonato ligand, by four carbon monoxide groups, and by the oxygen atom of the THF ligand. The THF ligand of the complexes is easily substituted, together with one of the carbonyl groups, by isocyanides, and a bidentate tertiary phosphane, while with the monodentate triphenylphosphane a substitutional equilibrium is established.