SYNTHESIS, STRUCTURES, AND OXO TRANSFER REACTIVITY OF BIS(DITHIOLENE)TUNGSTEN(IV,VI) COMPLEXES RELATED TO THE ACTIVE-SITES OF THUNGSTOENZYMES

A series of bis(dithiolene) tungsten(TV,VI) complexes derived from ben zene-1,2-dithiolate (bdt) has been prepared as an synthetic approach t o pterin dithiolene-bound active sites of tungstoenzymes, one example of which, a archaeal oxidoreductase, has been established crystallogra phically (Chan et al. Science 1995, 267, 1463). With [(WO)-O-IV(bdt)(2 )](2-) (2) as the starting compound silylation with RR'2SiCl afforded [W-IV(bdt)(2)(OSiRR'(2))](1-) (4), Oxidation of 4 with Me3NO gave [(WO )-O-VI(bdt)(2)(OSiRR'(2))](1-) (5), also accessible by silylation of [ (WO2)-O-VI(bdt)(2)](2-) (3). Reaction of 3 or 5 with Me3SiCl resulted in [(WO)-O-VI(bdt)(2)Cl](1-) (6), from which the unstable species [(WO )-O-VI(bdt)(2)L](1-) (L = (BuO-)-O-t, PhS-) were generated in solution . Reductive oxo transfer of 6 with L' = P(OEt)(3) or (BuNC)-N-t/P(OEt) (3) gave [W-IV(bdt)(2)L'(2)] (8 and 9). Sulfido complex [(WS)-S-VI(bdt )(2)(OSiRR'(2))](1-) (12) was obtained in the reaction systems 4/(PhCH 2S)(2)S and S/(Me3Si)(2)S. Structures of [WO(SPh)(4)](1-) and [W(bdt)( 3)](3-) and eight complexes of types 4-6, SI 9, and 12 were determined by X-ray crystallography. Complexes 4 and 5 are tungsten analogues of the desoxo Mo(IV) and monooxo Mo(VI) states of Rhodobacter sphaeroide s DMSO reductase. Six types of reactivity, including oxygen atom trans fer, are recognized by the synthesis and interconversion of the set of complexes. The potential biological relevance of these complexes to t he structure and function of active sites in two families of tungstoen zymes is considered (RR'(2) = Me-3 (4); (BuMe2)-Me-t (4 and 5), (BuPh2 )-Ph-t (4, 5, and 12)).