Vanadium–Cobalt O≡VCo3O4 Oxo Cubanes from V/Co Redox Exchange

The synthesis of a novel vanadium-cobalt oxo cubane [O≡VCo3(μ3-OH)(μ3-O)3(OAc)4(t-Bupy)3]+ (OAc = acetate, t-Bupy = 4-tertbutylpyridine) occurs by way of a metal-metal exchange reaction between the Co4(μ3-O)4(OAc)4(t-Bupy)4 cubane and VCl4(THF)2. Mechanistic investigations reveal that the terminal oxo ligand originates from water, and that a proton source is critical for the metal-metal exchange. The solid-state structure of the [O≡VCo3O4]+ cubane is more distorted from an idealized cubane geometry than previously reported [MCo3O4] heterometallic cubanes (M = Ru, Mn). The cluster is readily deprotonated by basic alumina to produce the neutral cluster, O≡VCo3(μ3-O)4(OAc)4(t-Bupy), the solid-state structure of which reveals retention of the oxo-cubane motif. The observed bonding and reactivity are rationalized with density functional theory, which indicates that the vanadium center does not significantly contribute to the occupied fron-tier molecular orbitals. Electrochemical studies support a quasireversible one-electron oxidation event at 0.85 V vs. Fc/Fc+ in acetonitrile but attempts to isolate the oxidized species instead gave the protonated cluster resulting from C–H bond activation of the solvent.