Ligand-Based Reduction of CO2 to CO Mediated by an Anionic Niobium Nitride Complex

Abstract

The terminal nitride anion complex [Na][N≡Nb(N[tBu]Ar)3] ([Na][1], Ar = 3,5-Me2C6H3) reacts quantitatively with CO2 to give the carbamate complex [Na][O2CN≡Nb(N[tBu]Ar)3] ([Na][O2C-1]). The structure of [Na][O2C-1] as the bis-12-crown-4 solvate, as determined by X-ray crystallography, displays a unique N-bound carbamate ligand without any metal−oxygen interactions. When treated with organic acid anhydrides or acid chlorides, complex [Na][O2C-1] reacts via salt elimination to give the five-coordinate complexes (RC(O)O)(OCN)Nb(N[tBu]Ar)3 (R-2, R = Me, tBu, F3C). We show that complexes R-2 yield the starting complex [Na][1] with concomitant release of CO upon two-electron reduction. This series of reactions constitutes a closed cycle for the conversion of CO2 to CO mediated by a terminal nitride anion complex.