Reversible P–C Coupling Reactions at the Unsaturated Dimolybdenum Carbyne Complex [Mo2(η5‑C5H5)2(CPh)(μ-PCy2)(μ-SPh)(CO)]+

The title complex was formed instantaneously by reacting [Mo2Cp2(μ-CPh)­(μ-PCy2)­(μ-CO)] with [FeCp2]­BF4 in the presence of diphenyl disulfide, but it could not be isolated as a pure material. It most likely displays bridging phosphide and thiolate ligands and essentially terminal carbonyl (Mo–C = 1.987 Å) and carbyne (Mo–C = 1.820 Å) ligands, according to density functional theory calculations. In solution this complex released CO spontaneously to yield the 30-electron complex [Mo2Cp2(μ-CPh)­(μ-PCy2)­(μ-SPh)]­BF4 (Mo–Mo = 2.4772(6) Å), and attempts to crystallize it at low temperature yielded instead the electron-precise aquo derivative [Mo2Cp2(μ-CPh)­(μ-PCy2)­(μ-SPh)­(CO)­(OH2)]­BF4 (Mo–Mo = 2.7820(4) Å). The addition of CO induced the coupling between the carbyne and phosphide ligands, to yield the tricarbonyl phosphinocarbene complex [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)­(μ-SPh)­(CO)3]­BF4 (Mo–Mo = 2.928(1) Å). This coupling process was reversible, since the latter complex could be decarbonylated stepwise by thermal methods, to give first the 32-electron phosphinocarbene derivative [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)­(μ-SPh)­(CO)2]­BF4 (Mo–Mo = 2.7863(4) Å) and eventually yielding [Mo2Cp2(μ-CPh)­(μ-PCy2)­(μ-SPh)]­BF4 via the title complex. In contrast to this behavior, the reaction of the title complex with CNtBu did not induce a P–C coupling process, but eventually led to the displacement of the thiolate ligand to give the dication trans-[Mo2Cp2(μ-CPh)­(μ-PCy2)­(CNtBu)4]2+ via the bis­(isocyanide) complex cis-[Mo2Cp2(μ-CPh)­(μ-PCy2)­(μ-SPh)­(CNtBu)2]­BF4, with these differences being probably steric in origin.