Reactivity of the Anionic Diphosphorus Complex [Mo2Cp2(μ-PCy2)(μ‑κ2:κ2‑P2)(CO)2]− toward Phosphorus- and Transition Metal-Based Electrophiles

The reactions of the Li+ salt of the title anion with chlorophosphines PR2Cl (R = Cy, Ph, tBu) led in all cases to products of formula [Mo2Cp2(μ-PCy2)­(μ-κ2P,P′:κ2P,P″-P2PR2)­(CO)2], with the PR2 group inserted in one of the Mo–P­(basal) bonds of the anion to give novel tridentate phosphinodiphosphenyl ligands, as confirmed by the solid-state structure of the PCy2 compound. When R was the bulky tBu group, this product was in equilibrium with an isomer of formula [Mo2Cp2(μ-PCy2)­(μ-κ2P,P′:κ2P,P′-P2PtBu2)­(CO)2], in which the diphosphorus ligand of the anion binds the PtBu2 group through the lone pair of electrons at the basal P atom in an “end-on” fashion (computed P–P–PtBu2 = 114.7°); the latter isomer was more stable than the former, according to the NMR data and density functional theory (DFT) calculations. The title anion reacted with halide complexes of the type [MXLn] (MLn = FeCp­(CO)2, MoCp­(CO)3, ZrCpCl, Mn­(CO)5, Re­(CO)5) to give compounds of formula [Mo2MCp2(μ-PCy2)­(μ-κ2:κ2:κ1-P2)­(CO)2Ln] incorporating the organometallic fragment MLn also in an “end-on” position at the basal P atom of the anion, as confirmed by the solid-state structure of the Fe compound (P–P = 2.089(2) Å; P–P–Fe = 124.6(1)°). All these complexes, except the Zr compound, underwent a fluxional process in solution involving a swing of the P2 ligand around the Mo–Mo axis with concomitant exchange of the MLn fragment between the P atoms of the diphosphorus ligand, as revealed by variable-temperature NMR experiments. Thermal decarbonylation of the Mn and Re compounds gave hexanuclear derivatives of formula [Mo4M2Cp4(μ-PCy2)2(μ4-κ1:κ2:κ2:κ1-P2)2(CO)12] (M = Mn, Re) as a mixture of two isomers derived from the different assembly of the asymmetric Mo2P2 subunits, as confirmed through X-ray analyses of both compounds. Each of the P2 ligands in these two complexes bind two Mo and two M atoms (M = Mn, Re), with the latter defining central P4M2 six-membered rings with unusual boat conformations.