[Fe(C5Ar5)(CO)2Br] complexes as hydrogenase mimics for the catalytic hydrogen evolution reaction

A new iron-based hydrogenase mimic, [Fe(C₅(p-C₆H₄Br)₅)(CO)₂Br], was synthesised and characterised using X-ray crystallography. Two analogous catalytic precursors, [Fe(C₅Ar₅)(CO)₂Br] (Ar = C₆H₅; p-C₆H₄Br), were also analysed electrochemically in order to investigate how bulkier and more electron withdrawing C₅Ar₅ ligands affect the catalytic generation of hydrogen from trichloroacetic acid. Compared to previously reported iron-based cyclopentadienyl analogues, these complexes were found to have smaller overpotentials and larger turnover numbers. The [Fe(C₅(p-C₆H₄Br)₅)(CO)₂Br] complex was found to be the most efficient of the two catalytic precursors with a turnover number of 25, an overpotential of around 310 mV and a faster rate of reaction compared to [Fe(C₅Ph₅)(CO)₂Br].