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A Well-Defined Terminal Vanadium(III) Oxo Complex

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posted on 17.12.2015 by Amanda E. King, Michael Nippe, Mihail Atanasov, Teera Chantarojsiri, Curtis A. Wray, Eckhard Bill, Frank Neese, Jeffrey R. Long, Christopher J. Chang
The ubiquity of vanadium oxo complexes in the V+ and IV+ oxidation states has contributed to a comprehensive understanding of their electronic structure and reactivity. However, despite being predicted to be stable by ligand-field theory, the isolation and characterization of a well-defined terminal mononuclear vanadium­(III) oxo complex has remained elusive. We present the synthesis and characterization of a unique terminal mononuclear vanadium­(III) oxo species supported by the pentadentate polypyridyl ligand 2,6-bis­[1,1-bis­(2-pyridyl)­ethyl]­pyridine (PY5Me2). Exposure of [VII(NCCH3)­(PY5Me2)]2+ (1) to either dioxygen or selected O-atom-transfer reagents yields [VIV(O)­(PY5Me2)]2+ (2). The metal-centered one-electron reduction of this vanadium­(IV) oxo complex furnishes a stable, diamagnetic [VIII(O)­(PY5Me2)]+ (3) species. The vanadium­(III) oxo species is unreactive toward H- and O-atom transfer but readily reacts with protons to form a putative vanadium hydroxo complex. Computational results predict that further one-electron reduction of the vanadium­(III) oxo species will result in ligand-based reduction, even though pyridine is generally considered to be a poor π-accepting ligand. These results have implications for future efforts toward low-valent vanadyl chemistry, particularly with regard to the isolation and study of formal vanadium­(II) oxo species.