Intramolecular CH Activation and Metallacycle Aromaticity in the Photochemistry of [FeFe]-Hydrogenase Model Compounds in Low-Temperature Frozen Matrices.

The [FeFe]-hydrogenase model complexes [(μ-pdt){Fe(CO)3 }2 ], [(μ-edt){Fe(CO)3 }2 ], and [(μ-mdt){Fe(CO)3 }2 ], where pdt=1,3-propanedithiolate, edt=1,2-ethanedithiolate, and mdt=methanedithiolate, undergo wavelength dependent photodecarbonylation in hydrocarbon matrices at 85 K resulting in multiple decarbonylation isomers. As previously reported in time-resolved solution photolysis experiments, the major photoproduct is attributed to a basal carbonyl-loss species. Apical carbonyl-loss isomers are also generated and may undergo secondary photolysis, resulting in β-hydride activation of the alkyldithiolate bridge, as well as formation of bridging carbonyl isomers. For [(μ-bdt){Fe(CO)3 }2 ], (bdt=1,2-benzenedithiolate), apical photodecarbonylation results in generation of a 10 π-electron aromatic FeS2 C6 H4 metallacycle that coordinates the remaining iron through an η(5) mode.