TDDFT modelling of the CO-photolysis of Fe2(S2C3H6)(CO)6, a model of the [FeFe]-Hydrogenase catalytic site

Upon irradiation with ultraviolet wavelengths, Fe2(S 2C3H6)(CO)6, a simple model of the [FeFe]-hydrogenase active site, undergoes CO dissociation to form the unsaturated Fe2(S2C3H6)(CO) 5 species and successively a solvent adduct at the vacant coordination site. In the present work, the CO-photolysis of Fe 2(S2C3H6)(CO)6 was investigated by density functional theory (DFT) and time-dependent DFT (TDDFT). Trans Fe2(S2C3H6)(CO)5 form and the corresponding trans heptane or acetonitrile solvent adducts are the lowest energy ground state forms. CO dissociation barriers computed for the lowest triplet state are roughly halved with respect to those for the ground state suggesting that some low-lying excited potential energy surface (PES) could be loosely bound with respect to Fe-C bond cleavage. The TDDFT excited state PESs and geometry optimizations for the excited states likely involved in the CO-photolysis suggest that the Fe-S bond elongation and the partial isomerization toward the rotated form could take place simultaneously, favoring the trans CO photodissociation. © 2014 Wiley Periodicals, Inc.