Terminal Vanadium(III) Oxo Complex Isolated

Terminal vanadium(III) oxo species likely play a key role in a number of vanadium-catalyzed reactions, including cleavage of C–C bonds in glycols and naphthol couplings, but chemists have struggled to isolate such a complex. A team led by Christopher J. Chang and Jeffrey R. Long of the University of California, Berkeley, and Mihail Atanasov and Frank Neese of Germany’s Max Planck Institute for Chemical Energy Conversion has now succeeded. The group prepared a terminal V⁴⁺(O) complex with a pentadentate polypyridyl ligand, then successfully reduced it to V³⁺(O) (Inorg. Chem. 2014, DOI: 10.1021/ic5010177). The V³⁺(O) species is dark blue and has a V–O bond length of 1.621 Å, which is among the longest terminal V–O bonds reported. The V³⁺(O) complex is unreactive to either hydrogen- or oxygen-transfer reagents, but it protonates to form a transient V³⁺(OH) species that could lead to new proton reduction chemistry. Computational analysis indicates that efforts to reduce the V³⁺(O) complex to try to prepare V²⁺(O) would instead result in transfer of one or two electrons from vanadium to the ligand.