Determination of the Photolysis Products of [FeFe]Hydrogenase Enzyme Model Systems using Ultrafast Multidimensional Infrared Spectroscopy

Ultrafast transient 2D-IR (T-2D-IR) spectroscopy has been used to study the photolysis products of the [FeFe]hydrogenase enzyme model compound (mu-propanedithiolate)Fe-2(CO)(6) in heptane solution following irradiation at ultraviolet wavelengths. Observation of coupling patterns between the vibrational modes of the photoproduct species formed alongside examination of the appearance time scales of these signals has uniquely enabled assignment of the photoproduct spectrum to a single pentacarbonyl species. Comparison of the vibrational relaxation rate of the photoproduct with that of the parent is consistent with the formation of a solvent adduct at the vacant coordination site, while anisotropy data in conjunction with density functional theory simulations indicates substitution in an axial rather than equatorial position. No firm evidence of additional short-lived intermediates is seen, indicating that the subsequent chemistry of these species is likely to be strongly defined by the nature of the first solvation shell.