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

The dimolybdenum alkyne complex [Mo-2(mu -(RC)-C-1=CR2)(CO)(4)Cp-2] 1 (Cp=eta -C5H5; R-1=R-2=CO2Me) reacted with the 1,3-dithiole-2-thiones S=CS2C2R2 (R=CO2Me, SMe, or SCOPh) to afford the new compounds [Mo-2(mu -S)(mu -SCR=CRSCCR1=CR2)Cp-2] by a complicated process involving cleavage of the C=S bond to give a mu -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=R-1=R-2=CO2Me) has been structurally characterised. The alkyne complexes 2 (R-1=R-2= CO2Et) and 3 (R-1=R-2=Ph) furnished analogous products on treatment with S=CS2C2(CO2Me)(2) whereas 4, the dimolybdenum complex of the unsymmetrical alkyne PhC=CCO2Et, gave two regioisomers, both of which have also been structurally characterised. Related complexes [Mo-2(mu -S){mu -S(CH2)(n)SCC(CO2Me)=C(CO2Me)}Cp-2] were formed from 1 and ethylene or propylene trithiocarbonate, S=CS2(CH2)(n) (n=2 or 3). In contrast, the reaction of 1 with acyclic dialkyl trithiocarbonates S=C(SR)(2) afforded complexes containing sulfido (mu -S), thiolate (mu -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, [Mo-2(mu -S)(mu -SMe){mu -C(CO2Me)C(SMe)C(CO2Me)}Cp-2], has been determined. Based on these observations, a possible mechanism for the reaction is suggested.