Cooperative Enhancement of Redox Catalysis by a Binucleated Divanadium Complex for Sustainable Oxidation

Vanadium is a nontoxic, earth-abundant metal promising for sustainable biomass upgrading. But vanadium catalysts remain uneconomical because of limited productivity. Redox cooperativity between vanadium centers has been proposed to boost catalytic activity, but this hypothesis remains challenging to study. We report discrete divanadium complexes of the binucleating ligand 1,8-naphthyridine-2,7-dicarboxylic acid (H2ndc), with the composition V2O2(OiPr)2(DMSO)2(ndc)•DMSO (1) and V2O2(OiPr)2(pyridine)2(ndc), and a tetravanadium complex [V2O3(DMF)2(ndc)]2O•DMF. XRD, modelling, and spin magnetometry substantiate two ferromagnetically coupled, alkoxide-bridged vanadium(IV) centers in 1. Complex 1 shows significantly greater activity in the aerobic cleavage of diols and a lignin model compound than its monometallic analogs. Mechanistic experiments including characterization of a substrate-bound catalytic intermediate, provide insight into cooperativity in vanadium redox catalysis. These results establish binucleating ligands as a strategy toward sustainable aerobic oxidations with earth-abundant metals.