Electronic structure and redox reactions of vanadium(II) polypyridine, isocyanide, and phosphine complexes

Abstract

Electronic absorption spectra and redox reactions are reported for a variety of vanadium(II) complexes of strong-field ligands. The absorption spectra of [V(L–L)₃]²⁺(L–L = polypyridine) are dominated by intense metal-to-ligand charge-transfer (m.l.c.t.) transitions. The m.l.c.t. absorption maxima for [V(L–L)₃]²⁺, and half-wave potentials for reduction of [V(L–L)₃]²⁺, are sensitive to substituents in the polypyridine rings. In contrast, the [V(L–L)₃]^3+/2+ redox process is primarily metal-localized. Cyclic voltammetry performed on [V(CNBu^t)₆]²⁺ shows that the 0, I, II, and III oxidation states are readily accessible; [V(dppe)₃][V(CO)₆]₂[dppe = 1,2-bis(diphenyl-phosphino)ethane] exhibits waves attributable to [V(dppe)₃]^3+/2+, [V(dppe)₃]^2+/+, and [V(CO)₆]^0/–. The lowest-energy spin-allowed electronic transitions in [V(CN Bu^t)₆]²⁺ are primarily d–d in nature, whereas those in [V(dppe)₃]²⁺ contain substantial m.l.c.t. character.