Oxygen/sulfur substitution reactions of tetraoxometalates effected by electrophilic carbon and silicon reagents

Reactions of MO(4)](2)(-) (M = Mo, W) with certain carbon and silicon electrophiles were investigated in acetonitrile in order to produce species of potential utility in the synthesis of analogues of the sites in the xanthine oxidoreductase enzyme family. Silylation of MoO(4)](2)(-) affords MoO(3)(OSiPh(3))](1)(-), which with Ph(3)SiSH is converted to MoO(2)S(OSiPh(3))](1)(-). Reaction with (Ph(3)C)(PF(6))/HS(-) yields the tetrahedral monosulfido species MO(3)S](2)(-), previously obtained only from the aqueous system MO(4)](2)(-)/H(2)S. Dithiolene chelate rings are readily introduced upon reaction with 1,2-C(6)H(4)(SSiMe(3))(2), leading to the square pyramidal trioxo complexes MO(3)(bdt)](2)(-), a previously unknown dithiolene molecular type. Further ring insertion occurs upon reaction of WO(3)(bdt)](2)(-) with 1,2-C(6)H(4)(SSiMe(3))(2), giving WO(2)(bdt)(2)](2)(-). Related reactions occur with ReO(4)](1)(-). Treatment with 1 equiv of (Me(3)Si)(2)S produces ReO(3)S](1)(-); with 3 equiv of 1,2-C(6)H(4)(SSiMe(3))(2), ReO(bdt)(2)](1)(-) is obtained with concomitant Re(VII) --> Re(V) reduction. X-ray structures are reported for MO(3)S](z)(-) (M = Mo, W, z = 2; M = Re, z = 1), MO(3)(bdt)](2)(-), and WO(2)(OSiPh(3))(bdt)](1)(-), a silylation product of WO(3)(bdt)](2)(-). MoO(3)(bdt)](2)(-) is related to the site of inactive sulfite oxidase, and WO(2)(OSiPh(3))(bdt)](1)(-) should closely approximate the metric features of the (dithiolene)MoO(2)(OH)] site in inactive aldehyde/xanthine oxidoreductase. This work provides convenient syntheses of known and new derivatives of tetraoxometalates, among which is entry to a unique class of oxo-monodithiolene complexes.