Electron Donor-Acceptor Chromophore Assembly as an Enabling Process for the Overall Light-Driven Reduction of Phosphine Oxides.

Phosphines make up one of the largest classes of organophosphorus compounds, with applications in academic research and industry. Their preparation from phosphine oxides is mechanistically and thermodynamically highly challenging but opens the possibility for phosphorus recycling. We show that phosphine oxides can be converted into their corresponding phosphonium salts and subsequently reduced in a light-driven reaction to obtain the desired phosphines in 40-80% overall yields in a one-pot procedure. The reported methodology is free of exogenously added photocatalysts and utilizes the in situ formation of a photoactive donor-acceptor complex for light absorption and charge separation. Overall, the presented photochemical approach to reducing phosphonium salts that arise from phosphine oxides represents a valuable alternative to classical thermochemical methods for phosphorus recycling.