Heteroditopic Chelating NHC Ligand-Supported Co<sup>III</sup> Complexes: Catalysts for the Reductive Functionalization of Carbon Dioxide under Ambient Conditions
Misba Siddique, Biswaranjan Boity, Arnab Rit
Abstract
Synthesis and characterization of heteroditopic chelating NHC ligand-supported air stable Co III –NHC complexes ( 1a – d ), featuring variable triazole N-substituents and thus, being structurally tunable, are reported. These complexes were observed to be very effective catalysts for the reductive functionalization of CO 2 with aromatic amines using hydrosilane under ambient conditions (1 bar of CO 2 pressure and room temperature) to yield diverse N-formylated amines, and importantly, the catalytic activity of the complexes was found to be reasonably tuned by the triazole N-substituents, which is probably due to some electronic modulations, supported by electrochemical analysis, rather than any considerable steric alterations as indicated by the percent buried volume calculation. Notably, the corresponding Co III –NHC complexes generated in situ were also found to be equally effective. It is worth mentioning that this is the first report on the effective N-formylation of less nucleophilic aromatic primary amines by employing a homogeneous Co complex, to the best of our knowledge. In addition, control experiments suggest that this protocol proceeds via Co hydride and formoxysilane intermediate formation.