Electrochemical Hydroformylation with a Homogeneous Rhodium Catalyst

Abstract Electrochemical hydroformylation is an attractive pathway to synthesize aldehydes at ambient conditions using electrons sourced from renewable energy as a reductant instead of hydrogen gas sourced from energy-intensive steam methane reforming. However, previously reported electrochemical hydroformylation systems have shown limited rates and selectivities using heterogeneous catalysts, motivating continued development. In this work, we report a homogeneously catalyzed system that achieved a maximum partial current density of 1.1 ± 0.1 mA cm–2 and a Faradaic efficiency of 29 ± 1% toward the conversion of styrene to 2-phenylpropanal at 5 bar CO and 25 °C. Infrared and UV-visible spectroscopies suggested that the initial Rh2Cl2(CO)4 precatalyst undergoes pressure-dependent speciation to Rh(I)–CO species in the presence of CO. Kinetic experiments revealed a complex mechanism in which the rate-determining step likely shifts between electron transfer, substrate coordination, and Rh–H bond cleavage in different substrate concentration and overpotential regimes. Looking forward, the insight from this work informs future strategies to improve the rate and selectivity of electrochemical hydroformylation and other electrochemical C–C bond formation reactions.