Deconstruction of cyclic and acyclic trithiocarbonates by C–S and CS bond cleavage during oxidative decarbonylation of dimolybdenum alkyne complexes

Abstract

The dimolybdenum alkyne complex [Mo₂(μ-R¹CCR²)(CO)₄Cp₂] 1 (Cp = η-C₅H₅; R¹ = R² = CO₂Me) reacted with the 1,3-dithiole-2-thiones SCS₂C₂R₂ (R = CO₂Me, SMe, or SCOPh) to afford the new compounds [Mo₂(μ-S)(μ-SCR CRSCCR¹CR²)Cp₂] by a complicated process involving cleavage of the CS bond to give a μ-sulfido ligand, ring opening of the heterocycle and coupling with the alkyne to afford a hybrid thiolate-dimetalla-allyl ligand. One of these products (R = R¹ = R² = CO₂Me) has been structurally characterised. The alkyne complexes 2 (R¹ = R² = CO₂Et) and 3 (R¹ = R² = Ph) furnished analogous products on treatment with SCS₂C₂(CO₂Me)₂ whereas 4, the dimolybdenum complex of the unsymmetrical alkyne PhCCCO₂Et, gave two regioisomers, both of which have also been structurally characterised. Related complexes [Mo₂(μ-S){μ-S(CH₂)_nSCC(CO₂Me)C(CO₂Me)}Cp₂] were formed from 1 and ethylene or propylene trithiocarbonate, SCS₂(CH₂)_n (n = 2 or 3). In contrast, the reaction of 1 with acyclic dialkyl trithiocarbonates SC(SR)₂ afforded complexes containing sulfido (μ-S), thiolate (μ-SR) and CSR units, but surprisingly the last of these occupies the central position in the dimetalla-allyl ligand rather than the terminus. The crystal structure of one of these compounds, [Mo₂(μ-S)(μ-SMe){μ-C(CO₂Me)C(SMe)C(CO₂Me)}Cp₂], has been determined. Based on these observations, a possible mechanism for the reaction is suggested.