Ligand-Based Reduction of CO2to CO Mediated by an Anionic Niobium Nitride Complex
Jared S. Silvia and Christopher C. Cummins
J. Amer. Chem. Soc. Published online Feb. 1, 2010.

The Cummins group has discovered a new method for performing CO2 to CO conversion that uses an anionic niobium nitride complex as the mediating platform. The important paradigm shift in the discovery is that the CO2 activation and transformation is performed on the ligand scaffold rather than at the metal center directly. The cycle involves three simple steps: activation of CO2 through nucleophilic attack by the terminal nitride ligand of niobium, deoxygenation of the CO2 moiety using simple organic acid anhydrides, and reduction of the substrate by two electrons to release CO and regenerate the starting anionic niobium nitride complex. This ligand-based approach allows for the use of variable, external oxygen acceptors and avoids the pitfall of forming strong metal-oxygen bonds, thus overcoming two major obstacles in the pursuit of efficient CO2 reduction.