Mechanistic snapshots of rhodium-catalyzed acylnitrene transfer reactions.

Rhodium acylnitrene complexes are widely implicated in catalytic C-H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral rhodium complex with a bidentate dioxazolone ligand, in which photoinduced metal-to-ligand charge transfer initiates catalytic C-H amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone complex allowed structural elucidation of the targeted Rh-acylnitrenoid and provided firm evidence that the singlet nitrenoid species is primarily responsible for acylamino transfer reactions. We also monitored reaction of a nucleophile with the in situ generated Rh-acylnitrenoid, providing a crystallographically traceable reaction system to capture mechanistic snapshots of nitrenoid transfer.