Light Alters the NH 3 vs N 2 H 4 Product Profile in Iron-catalyzed Nitrogen Reduction via Dual Reactivity from an Iron Hydrazido (Fe=NNH 2 ) Intermediate.

Whereas synthetically catalyzed nitrogen reduction (N R) to produce ammonia is widely studied, catalysis to instead produce hydrazine (N H ) has received less attention despite its considerable mechanistic interest. Herein, we disclose that irradiation of a tris(phosphine)borane (P ) Fe catalyst, P Fe , significantly alters its product profile to increase N H versus NH ; P Fe is otherwise known to be highly selective for NH . We posit a key terminal hydrazido intermediate, P Fe=NNH , as selectivity-determining. Whereas its singlet ground state undergoes protonation to liberate NH , a low-lying triplet excited state leads to reactivity at N and formation of N H . Associated electrochemical and spectroscopic studies establish that N H lies along a unique product pathway; NH is not produced from N H . Our findings are distinct from the canonical mechanism for hydrazine formation, which proceeds via a diazene (HN=NH) intermediate and showcase light as a tool to tailor selectivity.