Synthesis and redox properties of heterobimetallic Re(bpyCrown-M)(CO)3Cl complexes, where M = Na+, K+, Ca2+, and Ba2+

Abstract

The operational electrochemical potential of a molecular electrocatalyst is typically pinned to the reduction potential of the parent complex. The predominant strategy for minimizing the overpotential is to modify the ligand with electron withdrawing functional groups to anodically shift the reduction potential. However, these changes often result in decreased catalytic rates. Re(bpy)(CO)3Cl is a well-known electrocatalyst for selective CO2 reduction to CO. In this work, the synthesis of Re(bpyCrown-M)(CO)3Cl is described, where bpyCrown-M is a bipyridine ligand containing a cyclic ether cavity, and M is a Na+, K+, Ca2+, or Ba2+ ion encapsulated within that cavity. Addition of these cations results in anodic shifts in reduction potential, and the magnitude of the shifts correlate with overall cationic charge. However, electrolysis under catalytic conditions for CO2 reduction results in precipitation of carbonate salts, diminishing overall catalytic activity.