A Ferrocene-Peptide Conjugate as a Hydrogenase Model System

This work introduces a bis(cysteine) ligand to build a small peptidic model system of hydrogenase enzymes. Fe(C5H4CO-Cys-OMe)(2) (LH2) has been employed as a chelate for an iron-carbonyl complex, which mimics two essential structural properties of the hydrogenase class of enzyrnes, namely the coordination of the iron-carbonyl core to peptide ligands and the presence of an electrochemical relay in spatial proximity. The treatment of LH2 with Fe-3(CO)(12) yields LFe2(CO)(6) (3a), which is the first peptide-coordinated iron hydrogenase active-site model complex. Compound 3a was fully characterized spectroscopically (H-1 NMR, C-13 NMR, IR and Mossbauer spectroscopy, mass spectrometry and elemental analysis). A single-crystal X-ray analysis confirms the proposed structure and reveals a staggered conformation of the Fe-2(CO)(6)S-2 core. Fourier transform infrared (FTIR) spectroelectrochemistry reveals an electronic interaction between the peptide backbone and the iron-carbonyl cluster, but not with the ferrocene subsite. The introduction of this peptidic cysteine-based ligand into hydrogenase model chemistry helps to confirm the proposed cofactor biosynthesis and understand the electronic interplay between the metal-carbonyl active site and the protein environment in this important class of enzymes. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)