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

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.