An azadithiolate bridged terminal CN- and CO ligand co-ordinated synthetic analogue, [Fe2S2(CO)5CN]-, of the Hred state of iron only hydrogenase is synthesized. FTIR spectroscopy corroborated by geometry optimized DFT calculations indicates that one of the CO ligands in this complex acquires a bridging position. This complex is an excellent H+ reduction catalyst with a kcat of 106-7 M-1s-1 (obtained from foot-of-the-wave analysis) and functions between pH 0.3-3.0 with an onset potential of 0.12 V and shows more than 10 million turnovers. Rotating disc electrochemistry indicates that at -0.8 V a substrate diffusion limited catalytic current is obtained with 420 mV overpotential with a kcat of 1011 M-1s-1 i.e. it works at a diffusion controlled rate. Tafel plot and the dependence of onset potential on pH suggests that the catalyst follows a Volmer mechanism and a proton coupled electron transfer generation of a terminal iron-hydride species is the rate determining step for the reaction. DFT calculations corroborate these results and further suggest that the presence of an anionic CN- ligand and an open terminal co-ordination due to the bridging CO ligand increases the pKa of the reduced complex significantly and the kinetic rate of H+ reduction by three orders of magnitude with respect to a neutral [Fe2S2(CO)6] analogue which does not possess a bridging CO at lower over potential range.

Synthetic functional Fe-Fe hydrogenase mimic with bridged CO and terminal cyanide ligands: H<sub>2</sub> production in aqueous medium and contribution of electronic structure toward reactivity

248th National Meeting (2014)

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Synthetic functional Fe-Fe hydrogenase mimic with bridged CO and terminal cyanide ligands: H2 production in aqueous medium and contribution of electronic structure toward reactivity

Synthetic functional Fe-Fe hydrogenase mimic with bridged CO and terminal cyanide ligands: H₂ production in aqueous medium and contribution of electronic structure toward reactivity