(687f) Electrifying Hydroformylation Catalysts Exposes Voltage-Driven C–C Bond Formation

Hydroformylation (thermo-HFN) is an industrially important reaction that couples olefins and carbon monoxide (CO) to make aldehydes. If thermo-HFN were electrified to use protons and electrons instead of hydrogen gas, such an electrochemical hydroformylation (electro-HFN) reaction could be useful in the context of electrified chemicals manufacturing for functionalizing abundant olefins to synthetically versatile aldehydes. Additionally, electro-HFN could provide a method for sequentially elongating carbon chains in the context of electrochemical CO₂-to-fuels conversion. However, electro-HFN represents a complex C–C bond-forming reaction that is difficult to achieve at heterogeneous electrocatalysts. In this work, we import Rh-based thermo-HFN catalysts onto electrode surfaces to unlock electro-HFN reactivity. At mild conditions of room temperature and 5 bar CO, we achieve Faradaic efficiencies of up to 15% and turnover frequencies of up to 0.7 hr^-1. This electro-HFN rate is an order of magnitude greater than the corresponding thermo-HFN rate at the same catalyst, temperature, and pressure. Reaction kinetics suggest that in electro-HFN, protons and electrons directly participate in a non-mediated, electrochemical reaction pathway that is distinct from thermo-HFN and proceeds more readily at mild conditions. Operando x-ray absorption spectroscopy shows the catalyst consists pentacoordinate Rh(III) during catalysis. Most generally, this work demonstrates an experimental strategy for electrifying a well-studied thermochemical reaction to expose a new electrocatalyst for a difficult and underexplored electrochemical reaction.