Synthesis and characterization of iron complexes of tris-thiolate phosphine tripod ligands as models of the FeS(3) centers of nitrogenase and the Fe(CO)(CN)2 center of hydrogenase

The goal of this research is to synthesize and study new iron thiolate compounds as models for the active site of nitrogenase and hydrogenase. Nitrogenase and hydrogenase enzymes catalyze the reactions (1) and (2), respectively. It is anticipated that the work of this research will provide insight into the structural, physical and reactivity properties of those enzymes.{dollar}{dollar}eqalignno{lcub}&rm Nsb2{lcub}+{rcub}8Hsp+{lcub}+{rcub}16MgATP{lcub}+{rcub}8esp- longrightarrow 2NHsb3{lcub}+{rcub}Hsb2{lcub}+{rcub}16MgADP{lcub}+{rcub}16P{lcub}it i/{rcub}&(1)cr&rm 2Hsp+ + 2esp- rightleftharpoons Hsb2&(2)cr{rcub}{dollar}{dollar} In this work, we have been able to synthesize a series of iron complexes with tris thiolate tripod ligands (PS3) (tris(2-thiophenyl)phosphine) and its derivatives, (PS3*), (PS3{dollar}spprime{dollar}) and ligands. With these ligands, monomeric trigonal bipyramidal and octahedral compounds are obtained with Fe(II), Fe(III) and ligand including CN{dollar}sp-{dollar}, CO, NO, SR{dollar}sp-{dollar}, {dollar}rm Nsb2Hsb4,{dollar} Im, Py, PPh{dollar}sb3{dollar}. In many cases, these compounds have been structurally characterized by X-ray crystallography and studied by cyclic voltammetry, controlled potential electrolysis, IR, NMR, UV-vis, EPR and magnetic susceptibility. The compounds are potential models for iron-sulfur coordination modes in metalloproteins.; The basic coordination chemistry in this series of compounds is reported in chapter I. The spin state of the iron complexes is a function of the axial ligand. The Fe-ligand bond distances are a function of the oxidation state and the spin state of the Fe center.; In chapter II, we have been developed some models for substrates and inhibitors (CO, NO, {dollar}rm Nsb2Hsb4){dollar} interaction with the FeS{dollar}sb3{dollar} center in the MoFe-cofactor of nitrogenase. (Fe(PS3*)(CO)) {dollar}sp{lcub}1-{rcub}{dollar} is a paramagnetic species. (Fe(PS3*)(NO)) is the first example of a paramagnetic (Fe(NO)) {dollar}sp6{dollar}. The chemistry of these model compounds have provided insights for CO binding in nitrogenase.; In chapter III, we report the synthesis of model compounds for the (Fe(CO)(CN){dollar}sb2{dollar}) structural unit in the active site of (NiFe) -Hydrogenase. The rare CN{dollar}sp-{dollar}and CN{dollar}sp-{dollar}/CO complexes have been synthesized and characterized. The spectroscopic changes have been observed upon the Fe(II)/Fe(III) redox reactions. These studies suggest that the (Fe(CO)(CN){dollar}sb2{dollar}) center does not change its oxidation state during the enzymatic mechanism.