Transition Metal–NHC Complexes with Embedded [FeFe]-Hydrogenase Mimics

Metal–NHC complexes featuring bioinspired [Fe2(μ-adt)(CO)6] units as N-substituents on the NHC ligand [adt = (SCH2)2N(C6H4)] have been synthesized and characterized. Starting from a 1,3-bis-[Fe2(μ-(SCH2))2N(C6H4)(CO)6] imidazolium salt precursor, which combines the synthetic potential of an N-heterocyclic carbene with the properties of the [FeFe]-hydrogenase mimics, we prepared RuII, IrIII, and AuI complexes in moderate to good yields. Transmetalation from Ag2O enabled the preparation of cyclometalated RuII and IrIII derivatives, while deprotonation with K2CO3 allows the synthesis of the gold(I) complex. DFT calculations indicate that the metal–NHC and [Fe2(μ-adt)(CO)6] fragments remain electronically independent. Cyclic voltammetry has shown that regardless of the coordinated metal, all complexes maintain the usual redox behavior of the [Fe2(μ-adt)(CO)6] unit. The electrocatalytic studies reveal that the RuII, IrIII, and AuI complexes prepared are stable in the presence of up to four equiv of trifluoroacetic acid and are active in proton reduction, though with relatively low turnover frequencies. These results highlight the potential of modular metal–NHC frameworks to support [Fe2(μ-adt)(CO)6] motifs without compromising their electrochemical identity, providing a platform for the development of tunable hydrogenase mimics.