Electrochemical Degradation of a Dicationic Rhenium Complex via Hoffman-Type Elimination

Electrocatalytic reduction of carbon dioxide (CO2) by transition-metal catalysts is an attractive means for storing renewably sourced electricity in chemical bonds. Metal coordination compounds represent highly tunable platforms ideal for studying the fundamental stepwise transformations of CO2 into its reduced products. However, metal complexes can decompose upon extended electrolysis and form chemically distinct molecular species or, in some cases, catalytically active electrode deposits. Deciphering the degradative pathways is important for understanding the nature of the active catalyst and designing robust metal complexes for small-molecule activation. Herein, we present a new dicationic rhenium bipyridyl complex capable of multielectron ligand-centered reductions electrochemically. Our in-depth experimental and computational study provides mechanistic insight into an unusual reductively induced Hoffman-type elimination. We identify benzylic tertiary ammonium groups as an electrolytically susceptible moiety and propose key intermediates in the degradative pathway. This investigation highlights the complex interplay between the ligand and metal ion and will guide the future design of metal–organic catalysts.