Re(I) NHC Complexes for Electrocatalytic Conversion of CO2

The modular construction of ligands around an N-heterocyclic carbene building block represents a flexible synthetic strategy for tuning the electronic properties of metal complexes. Herein, methylbenzimidazolium-pyridine and methylbenzimidazolium-pyrimidine proligands are constructed in high yield using recently established transition-metal-free techniques. Subsequent chelation to ReCl­(CO)5 furnishes ReCl­(N-methyl-N′-2-pyridylbenzimidazol-2-ylidine)­(CO)3 and ReCl­(N-methyl-N′-2-pyrimidylbenzimidazol-2-ylidine)­(CO)3. These Re­(I) NHC complexes are shown to be capable of mediating the two-electron conversion of CO2 following one-electron reduction; the Faradaic efficiency for CO formation is observed to be >60% with minor H2 and HCO2H production. Data from cyclic voltammetry is presented and compared to well-studied ReCl­(2,2′-bipyridine)­(CO)3 and MnBr­(2,2′-bipyridine)­(CO)3 systems. Results from density functional theory computations, infrared spectroelectrochemistry, and chemical reductions are also discussed.