Structural and functional biomimetics of [Fe]-hydrogenase featuring a mono-, di- or tetrasubstituted pyridine ligand with a fac-C, N, and S ligation

Abstract

The combined structural and functional modeling study of [Fe]-H₂ase has remained a great challenge, to date. Now, we report a series of new structural and functional [Fe]-H₂ase models (1–6) that contain a mono-, di- or tetrasubstituted pyridine ligand with a biomimetic fac-C, N, and S ligation. While models 1–3, 5 and 6 are conveniently prepared by a novel flexible pyridine ligand (FPL)-based method, model 4 is prepared simply by an intramolecular CO replacement reaction of model 3. More interestingly, the structural study by spectroscopy and X-ray crystallography proves that these new models include a biomimetic fac-acyl (or methylene) C, pyridyl N, and thioether S ligation to an Fe(II) center and the C–Fe(II) σ bond is trans to an iodo ligand. In addition, the chemical reactivity study proves that they all have the enzyme-like H₂ activation and hydride transfer functions in the presence of imidazolium Im⁺, AgBF₄ and Et₃N. Particularly interesting is that a possible pathway for such H₂ activation and hydride transfer reactions catalyzed by a representative model 4 is proposed and the existence of the highly unstable 5-coordinate intermediate M₄ and Fe–H species M₅ is supported by the isolation and characterization of their MeCN-coordinated derivative 7 and chloro-substituted derivative 8, respectively.