Novel efficient Mn(I) Electrocatalysts for CO2 Reduction based on N-heterocyclic Carbene ligands

The fac-[Mn(CO)3(N^N)X]n complexes (X=Br, n=0 and X=CH3CN, n=+1; N^N= polypyridyl ligands) have been shown to be competent molecular catalysts for selective electrochemical conversion of carbon dioxide to CO. Nevertheless, the development of novel ligand frameworks for Mn-based CO2 reduction electrocatalysts is nowadays mainly restrained to ancillary functionalization of the bipyridyl motif. We report here the first purely organometallic fac-[Mn(CO)3(bis-MeNHC)Br] (1) complex with unprecedented activity for selective electrocatalytic CO2-to-CO reduction. It revealed to highly outperform the corresponding single NHC-containing Mn catalyst, namely [Mn(CO)3(py-MeNHC)I] (2), in terms of selectivity (faradaic yield = 95%), catalytic turnovers (>100) and maximum TOF (~103 s-1) under CO2 in anhydrous CH3CN. Spectroelectrochemistry (SEC) and DFT calculations reveal a strong electron-density accumulation over the metal center upon reduction due to the redox-innocent nature of the C^C ligand, which is ascribed as the origin of the enhanced reactivity towards CO2 reduction in comparison with N^N and N^C systems.