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

摘要

The dimolybdenum alkylne complex [Mo_2(#mu#-R~1C(ident toCR~2)(CO)_4Cp_2] 1 (Cp = #eta#-C_5H_5; R~1 = R~2 = Co_2Me) reacted with the 1, 3-dithiole-2-thiones S=CS_2C_2R_2 (R = CO_2Me, SMe, or SCOPh) to afford the new compounds [Mo_2(#mu#-S)(#mu#-SCR = CRSCCR~1 = CR~2)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 = CO_2Me) has been structurally characterised. The alkyne complexes 2 (R~1 = R~2 = CO_2Et) and 3 (R~1 = R~2 = Ph) furnished analogous products on treatment with S=CS_2C_2(CO_2Me)_2 whereas 4, the dimolybdenum complex of the unsymmetrical alkyne Phc(ident to)CCO_2Et, gave two regioisomers, both of which have also been structurally characterised. Related complexes [Mo_2(#mu#-S{#mu#-S(CH_2)_nSCC(CO_2Me)=C(CO_2Me)}Cp_2] were formed from 1 and ethylene or propylene trithiocarbonate, S=CS_2(CH_2)_n (n = 2 or 3). In contrast, the reaction of 1 with acyclic dkalkyl 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(CO_2Me)C(SMe)C(CO_2Me)}Cp_2], has been determined. Based on these observations, a possible mechanism for the reactions is suggested.