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.