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.