Secondary phosphines from the light-driven reduction of phthalimidophosphines

The preparation of secondary phosphines in an easily implemented and safe way is a challenging task. Herein, we report on the suitability of phthalimide-substituted phosphines as starting materials for the photo-catalytic production of such secondary phosphines in the presence of an IrIII photocatalyst and sacrificial electron donors. While diarylphosphines could be prepared, dialiphatic phthalimide derivatives showed a fundamentally different reactivity. They were found to undergo rearrangement of the phthalimide group, followed by cleavage, to give oxides of the secondary phosphines. Although achieving high-yielding transformations remained a challenge, unexpected mechanistic insights into the fate of the one-electron-reduced phthalimidophosphines formed as intermediates could be obtained. This knowledge is valuable for developing future benign routes to secondary phosphines.