Search

To develop the biomimetic chemistry of [NiFe]-H2ases, we have synthesized cysteine residue-containing [NiFe]-H2ase mimics (diphosphine)Ni[SCH2CH(CO2Me)NHCOC5H4-η5]2Fe (1, diphosphine = Ph2P(CH2)2PPh2; 2, Ph2PCH＝CHPPh2; 3, 1,2-(Ph2P)2C6H4; 4, (Ph2P)2NCH2C6H4Me-p; 5, (Ph2P)2NCH2CO2Et; and 6, (Ph2P)2N-2-CH2C5H4N) for the first time by a simple and convenient method. The full spectroscopic characterization of 1–6 along with X-ray crystallographic characterization of 1, 2 and 4 has proved that complexes 1–6 consist of two cysteine residue moieties that are bridged to their diphosphine-chelated Ni(II) centers and two η5-cyclopentadienyl-coordinated Fe(II) centers. On the basis of electrochemical and electrocatalytic studies, complexes 1 and 4 have been found to be catalysts for H2 production from HOAc with moderate icat/ip and overpotential values under CV conditions. In addition, a possible 2E2C (E = electrochemical, C = chemical) mechanism is briefly suggested for this type of H2 evolution reaction (HER). [ABSTRACT FROM AUTHOR]

Two types of new [Fe]-H2ase models were synthesized using well-designed synthetic methods. The first type of trisubstituted pyridine ligand-containing models [2-MeOCH2-4-O2P(OPh)2-6-COCH2C5H2N]Fe(CO)2R (1, R = I; 2, R = EtS, 3, R = MeCOS), [2-MeOCH2-4-O2P(OPh)2-6-COCH2C5H2N]Fe(CO)2(MeCN)BF4 (4) and [2-MeOCH2-4-O2P(OPh)2-6-COCH2C5H2N]Fe(CO)(PPh3)I (5) were synthesized on the basis of preparing the new trisubstituted pyridine precursors L1–L6, whereas the second type of pentasubstituted pyridine ligand-containing model [2-MeO-3,5-Me2-4-OP＝O(OPh)O-5′-(N2-iPrCO-2′,3′-O-CMe2-guanosine)-6-COCH2C5N]Fe(CO)2(η2-6-Me-2-SC5H3N) (6) was synthesized via the esterification reaction of a new phosphatoguanosine derivative L7 with the corresponding pentasubstituted pyridine ligand-containing precursor (2-MeO-4-HO-3,5-Me2-6-COCH2C5N)Fe(CO)2(η2-6-Me-2-SCH5H3N) (D) in the presence of the dehydrating agent DCC. While all the new precursors L1–L7 and models 1–6 were fully characterized via elemental analysis and various spectroscopic techniques, the molecular structures of model 5 and precursor D were confirmed via X-ray crystallography. In addition, model 1 has been found to be a catalyst for proton reduction to H2 from TFA under CV conditions. [ABSTRACT FROM AUTHOR]