Thioxoethenylidene (CCS) as a bridging ligand

The reaction of [Mo(≡CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with [Fe2(μ-SLi)2(CO)6] affords, inter alia, the unsymmetrical binuclear thioxoethenylidene complex [Mo2(μ,σ(C):η2(C′S)-CCS)(CO)4(Tp*)2], which may be more directly obtained from [Mo(≡CBr)(CO)2(Tp*)] and Li2S. The reaction presumably proceeds via the intermediacy of the bis(alkylidynyl)thioether complex S{C≡Mo(CO)2(Tp*)}2, which was, however, not directly observed but explored computationally and found to lie 78.6 kJ mol–1 higher in energy than the final thioxoethenylidene product. Computational interrogation of the molecules [M2(μ-C2S)(CO)2(Tp*)2] (M = Mo, W, Re, Os) reveals three plausible coordination modes for a thioxoethenylidene bridge which involve a progressive strengthening of the C–C bond and weakening of the M–C and M–S bonds, as might be expected from simple effective atomic number considerations.