Rhenium sulfide cluster substitution chemistry and structural analogs of the mono(pterin) molybdenum enzymes

Chapter 1 reports the terminal ligand substitution chemistry of hexanuclear rhenium sulfide clusters based on the cluster core [Re6S8 ]2+. Treatment of (Bu4N)3[Re 6S8Br6] with triethyl phosphine under forcing conditions leads to a series of site-differentiated clusters of the general formula [Re6S8(PEt3)nBr 6−n](4− n)− (n = 2–6). With the substitutionally inert phosphines defining the stereochemistry, these clusters form a basis set of building blocks for the aggregation of multicluster units.;Chapter 2 is an introduction to the molybdenum enzymes, including an explanation of the classification system devised by Hille and a discussion of each of the three enzyme families.;Described in Chapter 3 is a general synthetic route to compounds containing the cis-MoVIOS functional group of the type found in the xanthine oxidase family of molybdenum enzymes. Described are the preparation and characterization of neutral compounds of the general formula [MoVIOQ(OSiPh3)2(L2)] (Q = O, S; L2 = Me2bipy, 2 py) obtained by reaction of Ph 3SiCl with [MoO4]2− or [MoO3S] 2− in the presence of L2. The MoVIOS group is found to be free of the intramolecular interaction found in the most relevant literature precedent. The terminal sulfide has proven reversibly labile to treatment with tertiary phosphine or cyanide in a manner analogous to xanthine oxidase enzymes.;As an extension of the chemistry in Chapter 3, the analogous tungsten compounds of the general formula [WVIQ2(OSiPh 3)2(Me4phen)] (Q = O, S) were prepared and are discussed in Chapter 4. The expansion of the tungsten series to include the cis-WVIS2 species has allowed direct formation of biologically relevant dithiolene ligands through reaction of the activated alkynes RC≡CR (R = Ph, CO2Me) with the bound sulfides.;Chapter 5 describes an important structural analog of the mono(pterin) molybdenum enzymes. Using the synthetic method developed in Chapter 3, the first MoVI dioxo mono(dithiolene) compound was prepared and structurally characterized. The compound (Et4N)[MoVIO 2(OSiPh3)(bdt)] was shown to possess the square pyramidal geometry, including an apical oxo ligand and a basal dithiolene ligand, observed at several enzyme molybdenum centers. Efforts toward thiolate or terminal sulfide incorporation relevant to the enzyme sites are discussed.