| Hydrogenase enzymes catalyze the reversible production and consumption of hydrogen: {dollar}rm2 Hsp+ + 2 esp- = Hsb2.{dollar} In 1995, the crystal structure of hydrogenase from D. gigas revealed that the active site is composed of a dimeric (Ni-Fe) center, not a monomeric Ni center as predicted. This thesis presents synthetic and physico-chemical studies of a series of Ni, Fe and Co complexes of polythiolate ligands as mimics for the active site of hydrogenase. The protonated form of the ligand is tris (o-thiophenyl) phosphine, (P(o-{dollar}rm Csb6Hsb4SH)rbrack,{dollar} which is abbreviated as (PS3) H{dollar}sb3.{dollar} The synthesis and reactions of the (PS3) H{dollar}sb3{dollar} ligand and analogs of this ligand are presented.; Three topics in the realm of metal-sulfur chemistry will be discussed: (1) Monomeric complexes of the type (M(III)(PS2SH){dollar}sb2{dollar}) -(pendant) (M = Fe and Co), (Fe(III)(PS3){dollar}sb2{dollar}) -("S-S" disulfide) and (Fe(II)(PS3){dollar}sb2{dollar}) -(two "S-S" disulfides) have been prepared and characterized. Most significant are the (M(III)(PS2SH){dollar}sb2{dollar}) -pendant compounds which are six coordinate compounds with two pendant thiol (RSH) groups. The reaction of the (M(III)(PS2SH){dollar}sb2{dollar}) -(pendant) compounds with metal(II) ions cleanly forms mixed-metal dimeric compounds. (2) Dimeric mixed-metal, mixed-valent compounds of the type (M(III)M{dollar}spprime{dollar}(II)(PS3){dollar}sb2rbracksp{lcub}1-{rcub}{dollar} were prepared and studied for the series (Ni-Fe), (Ni-Co), (Fe-Co) and (Fe-Zn). In addition, the chemistry of the homonuclear dimeric compound (FeFe) was studied. These compounds are models for the mixed-metal centers discovered in hydrogenase enzymes. (3) Qualitative hydrogen evolution studies were carried out to evaluate the nature of reactions that generate hydrogen. Substantial hydrogen evolving activity was detected for the reaction of Co(II) and Fe(II) ions with the (PS3) ligands.; Taken together, the chemistry of the (PS3) ligand with Ni, Fe and Co under various conditions lead to structural, spectroscopic and reactivity models for the active site in hydrogenase enzymes. The structural (X-ray), reactivity (hydrogen evolution) and physico-chemical (electrochemistry, magnetic susceptibility, UV-vis, Mossbauer, EPR and NMR) studies of the compounds are provided. |
