Markovnikov hydroamination of terminal alkenes by phosphine redox catalysis

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 P^III and P^V phosphorus intermediates can undergo transition-metal-like two-electron chemistry raises the question of whether radical P^IV intermediates can mimic other elementary steps in organometallic chemistry^2,3. 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 P^IV mechanism could offer new opportunities for main-group element catalysis and chemical synthesis.