Visible Light Promotes P<sup>III</sup>/P<sup>V</sup>-Catalyzed Reductive <i>N</i>-Arylation of Nitroarenes at Room Temperature
Bora Kang, Marissa N. Lavagnino, Jesse B. Gordon, Kristopher G. Reynolds, Daniel G. Nocera, Alexander T. Radosevich
Abstract
Visible-light irradiation is found to accelerate the reductive coupling of nitroarenes and arylboronic acids under the conditions of P III /P V catalysis. Specifically, blue-light (λ exc = 427 nm) illumination of a 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 31 P 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 × 10 9 M –1 s –1 ). These results establish the successful interface of a P III /P V catalytic cycle with photon input, suggesting additional opportunities for photodriven methods that exploit organophosphorus-based catalytic intermediates.