[FeFe]-hydrogenase proteins can catalyze the reversible oxidation of hydrogen, H2 ↔ 2H+ + 2e-, under mild conditions and thus are prime candidates for biomimetic efforts in developing hydrogen evolving catalysts of artificial photosynthetic systems. Although significant progress in biomimetic synthesis and computational simulations of hydrogenase active sites have been made, changes in chemical and physical properties of the catalytic active sites under irradiation on minute timescale has not yet been fully characterized. In this work, photochemical processes of [(μ-pdt)Fe2(CO)4(PMe3)2] (pdt = SCH2CH2CH2S; Me = CH3) were investigated by electronic absorption and infrared spectroscopies in THF and MeCN, respectively. Upon irradiation, besides two parent peaks at 1942 and 1900 cm-1, several features were observed at the regions of 2001 and 1868 cm-1. However, the corresponding photoproducts are difficultly characterized by experiments due to couplings of photolysis, solvent adducts, and the fluxional variations of the terminal ligands. To elucidate structural behaviors of [(μ-pdt)Fe2(CO)4(PMe3)2] in photochemical processes, the calibrated density functionals theory (DFT) approaches have been carried out on structures, energies, and IR spectroscopies of the model complex via the thermal fluxional variations of ligands, the low- and high-spin pathways of CO disassociations, and solvent adduct associations. The reproduced time-resolved IR spectroscopies by the DFT calculations are in very good agreement with the experimental ones. On the basis of the calculated energetic properties and simulated vibrational frequencies of all possible photoproducts, the photochemical processes observed by the experiment were unraveled in silico.

Probing photochemical processes of [FeFe]-hydrogenase model compounds by combined spectroscopic/computational study

255th National Meeting (2018)

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