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

Abstract

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 [MLn(THF)] (MLn = MnCp'(CO)2, W(CO)5) led instead to trinuclear diphosphenyl complexes [Mo2MCp2(μ-PCy2)(μ3-κ(2):κ(2):κ(1)-P2Me)(CO)2Ln] following from coordination in each case of the corresponding 16-electron fragment MLn 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)2Ln] displaying trigonal-planar phosphide ligands, giving rise to strongly deshielded (31)P NMR resonances (δP 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→MLn 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 (pCO = 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.