Homogeneous electrocatalytic hydrogen evolution by a N2P2Fe(II) complex: Structural characterization of iron-hydride intermediate

• An iron molecular catalyst with a tripodal N 2 P 2 ligand have been synthesized. • Such iron complex is active for hydrogen evolution under mildly acidic condition. • The iron-hydride intermediate is synthesized and structurally characterized. • The catalytic mechanism is further revealed by theoretical calculation. Development of efficient earth-abundant molecular catalysts for hydrogen evolution is an area of active research for replacing platinum as the preeminent catalyst in hydrogen evolution reaction. [FeFe] hydrogenases exhibit remarkable hydrogen evolution performance, which indicates that earth-abundant iron is the most attractive candidate for development of molecular catalysts. Inspired by [FeFe] hydrogenase, considerable progress has been made in the functional and structural modeling of mono-/di-nuclear molecular catalysts. However, the characterization of iron-hydride involved in the catalytic pathways have largely remained elusive. Herein, we report an air-stable mononuclear N 2 P 2 Fe(II) complex as a functional model of the distal iron in [FeFe] hydrogenase active site and the full characterization of iron-hydride intermediate. This N 2 P 2 Fe(II) complex is an active electrocatalyst for hydrogen evolution from mildly acidic solutions. Notably, the possible iron-hydride intermediate is synthesized by chemical hydride transfer strategy and structurally characterized, which provide insights into the catalytic pathway of the electrocatalytic hydrogen production. This work thus presents an example of iron-based molecular catalyst for hydrogen generation from mildly acid, and molecular structure of possible hydride intermediate.