A mononuclear iron carbonyl complex [Fe(μ-bdt)(CO)2(PTA)2] with bulky phosphine ligands: a model for the [FeFe] hydrogenase enzyme active site with an inverted redox potentialElectronic supplementary information (ESI) available: FTIR and NMR spectra, X-ray data, coulometry data and computational details. CCDC 933626 for 1. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7dt01994g

A mononuclear hexa-coordinated iron carbonyl complex [Fe(μ-bdt)(CO) 2 (PTA) 2 ] 1 (bdt = 1,2-benzenedithiolate; PTA = 1,3,5-triaza-7-phosphaadamantane) with two bulky phosphine ligands in the trans position was synthesized and characterized by X-ray structural analysis coulometry data, FTIR, electrochemistry and electronic structure calculations. The complex undergoes a facilitated two-electron reduction 1 / 1 2− and shows an inverted one-electron reduction for 1 / 1 − at higher potentials. Electrochemical investigations of 1 are compared to the closely related [Fe(bdt)(CO) 2 (PMe 3 ) 2 ] compound. A mechanistic suggestion for the hydrogen evolution reaction upon proton reduction from acid media is derived. The stability of 1 in both weak and strong acids is monitored by cyclic voltammetry. This mononuclear iron complex displays an inverted redox potential and catalyzes hydrogen evolution in acidic solution.