Can carbene decorated [FeFe]-hydrogenase model complexes catalytically produce dihydrogen? An insight from theory.

Cyclic alkyl amino carbene (CAAC) anchored [FeFe]-hydrogenase model complex featuring rotated conformation at one of the iron centers are found to be promising candidate for effective production of dihydrogen. A stepwise comparison of the complete mechanism using the CAAC stabilized model complex [1]0 has been performed with that of an experimentally isolated one ([2]0). Interestingly, the reduction events involved in the catalytic cycles are found to be more favorable than those previously reported for a similar experimentally known system. Furthermore, the computed ΔpKa values indicate that the distal iron center with a vacant coordination site is more basic compared to the amino nitrogen atom of the azadithiolate bridge. We also made an attempt to determine the oxidation states of the iron centers for the intermediates involved in the catalytic cycles on the basis of the computed Mössbauer isomer shift and Mulliken spin density values.