Main-group catalysts that mimic transition metal reactivity can expand substrate tolerance and enable transformations not possible at present with metal catalysis1. The discovery that PIII and PV phosphorus intermediates can undergo transition-metal-like two-electron chemistry raises the question of whether radical PIV intermediates can mimic other elementary steps in organometallic chemistry2,3. Here we describe a phosphine–photoredox catalyst system that promotes intermolecular Markovnikov hydroamination of unactivated terminal alkenes with numerous classes of N–H azoles, a reaction that is not possible with late transition metal catalysis. Experimental and computational mechanistic studies support a new elementary step for main-group catalysis, in which a phosphine radical cation activates the alkene to nucleophilic amination by the azole, a step otherwise associated with transition metals. Given the broad value of nucleophilic alkene functionalization in transition metal catalysis, this PIV mechanism could offer new opportunities for main-group element catalysis and chemical synthesis.
