Extending the motif of the [FeFe]-hydrogenase active site models: Protonation of Fe2(NR)2(CO)6−xLx species

Studies on diiron dithiolato complexes have proven fruitful for modeling the active site of the [FeFe]-hydrogenases. Here we present a departure from the classical Fe2S2 motif by examining the viability of Fe2N2 butterfly compounds as functional models for the diiron active site of [FeFe]-hydrogenases. Derivatization of Fe2(BC)(CO)6 (1, BC = benzo-[c]-cinnoline) with PMe3 affords Fe2(BC)(CO)4(PMe3)2, which subsequently undergoes protonation at the Fe–Fe bond. The hydride [(μ-H)Fe2(BC)(CO)4(PMe3)2]PF6 was characterized crystallographically as the C2v isomer. It represents a rare example of a hydrido diiron complex that exists as observable isomers, depending on the location of the phosphine ligands – diapical and apical–basal. This hydride catalyzes the electrochemical reduction of protons.