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A Well-Defined Terminal Vanadium(III) Oxo Complex

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journal contribution
posted on 17.12.2015, 05:31 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.