Kinetic and mechanistic studies on the disproportionation equilibrium of µ-oxo-bis[bis(isopropyl thioxanthato)oxomolybdenum(V)] and on the decomposition reaction of bis(isopropyl thioxanthato)dioxomolybedenum(VI)

Abstract

µ-Oxo-bis[bis(isopropyl thioxanthato)oxomolybdenum(V)], [Mo^V₂O₃(S₂CSPrⁱ)₄], undergoes a disproportionation reaction in solution to exist as an equilibrium mixture with [Mo^IVO(S₂CSPrⁱ)₂] and [Mo^VIO₂(S₂CSPrⁱ)₂]. This reaction is followed by slow decomposition of the latter to give [Mo^V₂O₄(S₂CSPrⁱ)₂] and [–SC(S)SPrⁱ]₂. Rates of the disproportionation of [Mo^V₂O₃(S₂CSPrⁱ)₄] and of the decomposition of [Mo^VIO₂(S₂CSPrⁱ)₂] have been determined by concentration-jump relaxation and conventional spectrophotometric techniques respectively, in 1,2-dichloroethane. The decomposition reaction is interpreted to proceed via a molybdenum(VI) complex with a unidentate thioxanthato-ligand as an intermediate, which decomposes in a rate-determining step, yielding unstable [Mo^VO₂(S₂CSPrⁱ)] and the ·S₂CSPrⁱ radical, both of which rapidly dimerize to give [Mo^V₂O₄(S₂CSPrⁱ)₂] and [–SC(S)SPrⁱ]₂, respectively.