Density functional theory approach for improving the catalytic activity of a biomimetic model based on the Fe-only hydrogenase active site

A complete catalytic cycle for H2 oxidation on a model emulating the active site of Fe-only hydrogenases, [Fe2(μ-DTMA)(CO)4(CN)2]2− (DTMA = SCH2NHCH2S), has been investigated using density functional theory (DFT). Our calculations show that the bridged CO group in the fully reduced species does not play a significant role on the H2 activation. According to the studied mechanism, the rate-determining step is neither kinetically nor thermodynamically favorable for the second proton transfer. A modified model aiming to improve the catalytic efficiency has been designed and a plausible catalytic mechanism is suggested. In the new model, [Fe2(μ-PDTN)(CO)4(CN)2]2− (PDTN = SCH2CH(NH2)CH2S), a shorter proton transfer path has been obtained by changing the base position and the process is significantly facilitated. In the modified catalytic cycle, the highest barrier for H2 oxidation is only 7.90 kcal mol−1.