The [FeFe]-hydrogenases are exceptionally efficient enzymes that reduce protons to hydrogen gas under mild conditions. Many model compounds have been synthesized as a means to understand the functionality of the [FeFe]-hydrogenases. These models are also potential catalysts in their own right, with some including photosensitizers that could allow the reduction to be driven by the absorption of light. Model compounds with all CO ligands or CO and PMe3 ligands have been studied using ultrafast UV or visible pump, IR probe spectroscopy in an effort to better understand the interactions of the active site with light. However, models with cyano ligands, which more closely match the biological active site, have been more difficult to study. In this work, three model compounds were studied: [Fe2(μ-S2C3H6)(CO)4(CN)2]2– (1a), b) [Fe2(μ-S2C2H4) (CO)4(CN)2]2– (1b), c) [Fe2(μ-S2C3H6)(CO)5(CN)1]– (2a). These models showed long-lived signals consistent with loss of a CO ligand and possible isomerization of ground electronic state photoproducts, as seen with all-CO and CO/PMe3 models. However, the data does not show evidence of a significant fast (~150 ps) decay seen in the all-CO and CO/PMe3 model compounds. This is apparently due to the absence of the metal-to-metal charge transfer band in the cyano functionalized models. These results show that the incorporation of cyano ligands can significantly alter the photoproducts produced immediately after excitation, which could influence the eventual catalytic activity of a photosensitized catalyst.

Ultrafast dynamics of cyano functionalized [FeFe]-hydrogenase model compounds

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.