Re(I) NHC Complexes for Electrocatalytic Conversion of CO2
journal contributionposted on 07.03.2016, 00:00 by Charles J. Stanton, Charles W. Machan, Jonathon E. Vandezande, Tong Jin, George F. Majetich, Henry F. Schaefer, Clifford P. Kubiak, Gonghu Li, Jay Agarwal
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.