Mild P–P Bond Cleavage in the Methyldiphosphenyl Complex [Mo₂Cp₂(μ-PCy₂)(μ‑κ²:κ²‑P₂Me)(CO)₂] To Give Novel Phosphide-Bridged Trinuclear Derivatives

Reactions of the title diphosphenyl complex with [Fe₂(CO)₉] and [W­(CO)₄(THF)₂] gave the trinuclear species [Mo₂FeCp₂(μ₃-P)­(μ-PCy₂)­(μ₃-PMe)­(CO)₅] and [Mo₂WCp₂(μ₃-P)­(μ-PCy₂)­(μ₃-PMe)­(CO)₆] following from formal insertion of the 14-electron fragments Fe­(CO)₃ and W­(CO)₄, respectively, in the P–P bond of the diphosphenyl ligand and formation of a new heterometallic bond [Mo–Fe = 2.9294(6) Å and Mo–W = 3.146(1) Å]. Reactions of the diphosphenyl complex with the tetrahydrofuran adducts [ML_<i>n</i>(THF)] (ML_<i>n</i> = MnCp′(CO)₂, W­(CO)₅) led instead to trinuclear diphosphenyl complexes [Mo₂MCp₂(μ-PCy₂)­(μ₃-κ²:κ²:κ¹-P₂Me)­(CO)₂L_<i>n</i>] following from coordination in each case of the corresponding 16-electron fragment ML_<i>n</i> to the lone-pair-bearing P atom of the P₂Me ligand. However, these diphosphenyl complexes were unstable and decomposed at room temperature or under mild heating by the release of methylphosphinidene (PMe), to give the corresponding derivatives [Mo₂MCp₂(μ₃-P)­(μ-PCy₂)­(CO)₂L_<i>n</i>] displaying trigonal-planar phosphide ligands, giving rise to strongly deshielded ³¹P NMR resonances (δ_P ca. 1100 ppm), while being involved in strong π bonding with the unsaturated Mo₂ center of these molecules [Mo–Mo = 2.749(1) Å and Mo–P = ca. 2.30 Å when M = W]. An isolobal analogy could be established between the P→ML_<i>n</i> fragments in these products and a carbyne ligand (CR), supported by density functional theory calculations on the tungsten compound, which also enabled an easy interpretation and prediction of their chemical behavior. Thus, the manganese complex could be reversibly carbonylated (<i>p</i>_CO = ca. 3 atm, 293 K) to give the corresponding electron-precise pentacarbonyl [MnMo₂Cp₂Cp′(μ₃-P)­(μ-PCy₂)­(CO)₅] [Mo–Mo = 3.1318(7) Å], a process also involving a trans-to-cis rearrangement of the Mo₂Cp₂ subunit. On the other hand, decarbonylation of the tungsten complex was accomplished in a refluxing toluene solution to give the hexacarbonyl [Mo₂WCp₂(μ₃-P)­(μ-PCy₂)­(μ-CO)­(CO)₅], a derivative containing an unsaturated 30-electron dimolybdenum center with an intermetallic triple bond