| Abstract
| - The active sites of the xanthine oxidase and sulfite oxidase enzyme families contain one pterin−dithiolene cofactor ligand bound to a molybdenum atom. Consequently, monodithiolene molybdenum complexeshave been sought by exploratory synthesis for structural and reactivity studies. Reaction of [MoO(S2C2Me2)2]1-or [MoO(bdt)2]1- with PhSeCl results in removal of one dithiolate ligand and formation of [MoOCl2(S2C2Me2)]1-(1) or [MoOCl2(bdt)]1- (2), which undergoes ligand substitution reactions to form other monodithiolenecomplexes [MoO(2-AdS)2(S2C2Me2)]1- (3), [MoO(SR)2(bdt)]1- (R = 2-Ad (4), 2,4,6-Pri3C6H2 (5)), and[MoOCl(SC6H2-2,4,6-Pri3)(bdt)]1- (6) (Ad = 2-adamantyl, bdt = benzene-1,2-dithiolate). These complexeshave square pyramidal structures with apical oxo ligands, exhibit rhombic EPR spectra, and 3−5 areelectrochemically reducible to MoIVO species. Complexes 1−6 constitute the first examples of five-coordinatemonodithiolene MoVO complexes; 6 approaches the proposed structure of the high-pH form of sulfite oxidase.Treatment of [MoO2(OSiPh3)2] with Li2(bdt) in THF affords [MoO2(OSiPh3)(bdt)]1- (8). Reaction of 8 with2,4,6-Pri3C6H2SH in acetonitrile gives [MoO2(SC6H2-2,4,6-Pri3)(bdt)]1- (9, 55%). Complexes 8 and 9 are squarepyramidal with apical and basal oxo ligands. With one dithiolene and one thiolate ligand of a square pyramidalMoVIO2S3 coordination unit, 9 closely resembles the oxidized sites in sulfite oxidase and assimilatory nitratereductase as deduced from crystallography (sulfite oxidase) and Mo EXAFS. The complex is the first structuralanalogue of the active sites in fully oxidized members of the sulfite oxidase family. This work provides astarting point for the development of both structural and reactivity analogues of members of this family.
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