[FeFe]-hydrogenases are efficient enzymes that produce hydrogen gas under mild conditions. Synthetic model compounds containing all CO or mixed CO/PMe3 ligands have been studied with ultrafast ultraviolet (UV) or visible pump-infrared (IR) probe spectroscopy (TRIR) to better understand the function and interactions of the active site with light. Only a few studies of anionic species containing cyano groups, which more closely match the biological active site, have been performed. In this work, two model compounds dissolved in room temperature acetonitrile solution were examined: [Fe2(μ-S2C3H6)(CO)4(CN)2]2 (1) and [Fe2(μ-S2C2H4)(CO)4(CN)2]2 (2). These species exhibit long-lived transient signals consistent with loss of one CO ligand with potential isomerization of newly formed ground electronic state photoproducts, as previously observed with all-CO and CO/PMe3 containing models. We find no evidence for fast (ca. 150 ps) relaxation seen in the all-CO and CO/PMe3 compounds because of the absence of the metal-to-metal charge transfer band in the cyano-functionalized models. These results indicate that incorporation of cyano ligands may significantly alter the electronic properties and photoproducts produced immediately after photoexcitation which may influence the catalytic activity of the enzyme.
Journal of Physical Chemistry A
iron-iron hydrogenase, cyano ligands, isomeric products, transient infrared spectroscopy, ultrafast