Iron Complexes for the Electrocatalytic Oxidation of Hydrogen: Tuning Primary and Secondary Coordination Spheres (original) (raw)

A series of iron hydride complexes featuring P R N R′ P R (P R N R′ P R = R 2 PCH 2 N(R′)CH 2 PR 2 where R = Ph, R′ = Me; R = Et, R′ = Ph, Bn, Me, t Bu) and cyclopentadienide (Cp X = C 5 H 4 X where X = H, C 5 F 4 N) ligands has been synthesized; characterized by NMR spectroscopy, X-ray diffraction, and cyclic voltammetry; and examined by quantum chemistry calculations. Each compound was tested for the electrocatalytic oxidation of H 2 , and the most active complex, (Cp C 5 F 4 N )Fe(P Et N Me P Et )(H), exhibited a turnover frequency of 8.6 s −1 at 1 atm of H 2 with an overpotential of 0.41 V, as measured at the potential at half of the catalytic current and using Nmethylpyrrolidine as the exogenous base to remove protons. Control complexes that do not contain pendant amine groups were also prepared and characterized, but no catalysis was observed. The rate-limiting steps during catalysis are identified through combined experimental and computational studies as the intramolecular deprotonation of the Fe III hydride by the pendant amine and the subsequent deprotonation by an exogenous base.