Visible Light Promotes PIII/PV-Catalyzed Reductive N-Arylation of Nitroarenes at Room Temperature

Visible light irradiation is found to accelerate the reductive coupling of nitroarenes and arylboronic acids under conditions of P^III/P^V catalysis. Specifically, blue light (λ_exc = 427 nm) illumination of catalytic mixture composed of a redox active main group catalyst (1,2,2,3,4,4-hexamethylphosphetane P-oxide, i.e. P•[O]) and terminal reductant (1,3-diphenyldisiloxane) enables formation of diarylamines from nitroarenes and arylboronic acids at ambient temperature. In situ ³¹P NMR data demonstrate the importance of fast in situ P^V=O→P^III reduction by the hydrosilane reductant to permit productive room temperature reductive coupling. Moreover, the present photochemical method expands the scope of the organophosphorus-catalyzed reductive coupling reaction to accommodate 2,6-disubstituted nitroarenes, which were previously poorly reactive under prior thermal (dark) reaction conditions. Transient absorption experiments are consistent with excitation of the nitroarene to generate a triplet excited state, which is quenched by intermolecular electron transfer from the P^III resting state of the catalyst with rate constants near the diffusion-controlled limit (k _q = 2.93×10⁹ M^-1s^-1). These results establish the successful interface of a P^III/P^V catalytic cycle with photon input, suggesting additional opportunities for photo-driven methods that exploit organophosphorus-based catalytic intermediates.