Reversible P–C Coupling Reactions at the Unsaturated Dimolybdenum Carbyne Complex [Mo<sub>2</sub>(η<sup>5</sup>‑C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>(CPh)(μ-PCy<sub>2</sub>)(μ-SPh)(CO)]<sup>+</sup>
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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.
