On the photochemistry of Fe2(edt)(CO)4(PMe3)2, a [FeFe]-hydrogenase model: A DFT/TDDFT investigation

The photochemistry of the [FeFe] hydrogenases model [Fe-2(edt)(CO)(4)(PMe3)(2)] (edt=1-2 ethane-dithiolate, (1) is investigated at Time-Dependent Density Functional Theory (TDDFT) level, focusing on the effect of the phosphine ligands on the early stages of the photodynamic of the system compared to that of the all CO model Fe-2(pdt)(CO)(6) (2) (pdt=1-3 propanedithiolate). We observed a role of the FeS charge transfer for the lower energy singlet transitions, unveiling a photoisomerization pathway between the lowest energy forms while the higher energy excitations are likely involved in the CO dissociation pathways. TDDFT shows that the average Fe-CO bond elongation in 1 is shorter than that observed in 2, providing the electronic structure rationale on the observation that diiron dithiolates are more photo-stable with respect to the CO photolysis than the all CO model. This is relevant for catalyst photo-stability and is an advantageous and thus desirable feature for practical applications of photo-hydrogen evolution.