Electroanalytical and Computational Investigation of Oxoammonium-Mediated Hydride Transfer

Oxoammonium-mediated hydride transfer is an important yet relatively underexplored elementary step in C-H functionalization. In this work, we employed cyclic voltammetry (CV) to measure the rates of hydride transfer between electrochemically generated oxoammonium catalysts and 42 substrates including ethers, carbamates, amides, and sulfonamides. Through quantum mechanical (QM) calculations, we uncovered a new transition-state model for hydride transfer in which the N atom of the catalyst resides near a heteroatom (X = N or O) of the substrate to allow alignment of the oxoammonium's O═N+ motif and the substrate's forming C═X+ bond. Energy decomposition analysis was subsequently performed to elucidate the key factors that govern the kinetics of oxoammonium-mediated hydride transfer. Beyond conventional electronic and steric considerations, we identified substrate distortion, secondary orbital interactions, and noncovalent interactions as critical factors that influence hydride transfer reactivity. We anticipate that these kinetic data along with the mechanistic insights they provide will inform future catalyst development and synthetic applications to broaden the scope of oxoammonium catalysis.