Synthesis, Structures, and Oxo Transfer Reactivity of Bis(dithiolene)tungsten(IV,VI) Complexes Related to the Active Sites of Tungstoenzymes

Abstract

A series of bis(dithiolene)tungsten(IV,VI) complexes derived from benzene-1,2-dithiolate (bdt) has been prepared as an synthetic approach to pterin dithiolene-bound active sites of tungstoenzymes, one example of which, a archaeal oxidoreductase, has been established crystallographically (Chan et al. Science 1995, 267, 1463). With [W IV O(bdt) 2 ] 2 - ( 2 ) as the starting compound, silylation with RR‘ 2 SiCl afforded [W IV (bdt) 2 (OSiRR‘ 2 )] 1 - ( 4 ). Oxidation of 4 with Me 3 NO gave [W VI O(bdt) 2 (OSiRR‘ 2 )] 1 - ( 5 ), also accessible by silylation of [W VI O 2 (bdt) 2 ] 2 - ( 3 ). Reaction of 3 or 5 with Me 3 SiCl resulted in [W VI O(bdt) 2 Cl] 1 - ( 6 ), from which the unstable species [W VI O(bdt) 2 L] 1 - (L = Bu t O -, PhS - ) were generated in solution. Reductive oxo transfer of 6 with L‘ = P(OEt) 3 or Bu t NC/P(OEt) 3 gave [W IV (bdt) 2 L‘ 2 ] ( 8 and 9 ). Sulfido complex [W VI S(bdt) 2 (OSiRR‘ 2 )] 1 - ( 12 ) was obtained in the reaction systems 4 /(PhCH 2 S) 2 S and 5 /(Me 3 Si) 2 S. Structures of [WO(SPh) 4 ] 1 - and [W(bdt) 3 ] 2 - and eight complexes of types 4 − 6, 8, 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 sphaeroides DMSO reductase. Six types of reactivity, including oxygen atom transfer, are recognized by the synthesis and interconversion of the set of complexes. The potential biological relevance of these complexes to the structure and function of active sites in two families of tungstoenzymes is considered (RR‘ 2 = Me 3 ( 4 ); Bu t Me 2 ( 4 and 5 ), Bu t Ph 2 ( 4, 5, and 12 )).