Reactions of the Unsaturated Ditungsten Anion [W2Cp2(μ-PCy2)(μ-CO)2]− with C- and P‑Based Electrophiles

The Na+ salt of the title anion reacted with MeI to give a mixture of isomeric methoxycarbyne [W2Cp2(μ-COMe)­(μ-PCy2)­(μ-CO)] (major) and methyl-bridged [W2Cp2(μ-CH3)­(μ-PCy2)­(CO)2] (minor) derivatives, following from competitive methylation at the O atoms or at the ditungsten center, respectively. In contrast, its reaction with ClCH2Ph gave exclusively the benzyl-bridged complex [W2Cp2(μ-CH2Ph)­(μ-PCy2)­(CO)2], which in solution displays a medium-strength agostic W–H–C interaction, as suggested by the reduced C–H coupling of 90 Hz for the atoms involved. This complex could be dehydrogenated photochemically to give the 30-electron benzylidyne derivative [W2Cp2(μ-CPh)­(μ-PCy2)­(μ-CO)] in a selective way. The title anion reacted rapidly with several chlorophosphines ClPR2 (R = tBu, Et, Cy) to give also two types of isomers: the phosphinoxycarbyne complexes [W2Cp2(μ-COPR2)­(μ-PCy2)­(μ-CO)] and the mixed-phosphide derivatives [W2Cp2(μ-PCy2)­(μ-PR2)­(CO)2], with the former being obtained selectively when R was the bulky tBu group, whereas the latter was the major product for the smaller Et group. The phosphinoxycarbyne complexes were quite unstable species that could not be isolated as pure materials, but when R = Et, Cy, they underwent thermal rearrangement to give the corresponding mixed-phosphide isomers, among other processes. In contrast, the reaction with ClP­(O)­(OPh)2 gave a more stable phosphatecarbyne complex, [W2Cp2{μ-COP­(O)­(OPh)2}­(μ-PCy2)­(μ-CO)], which could be isolated and fully characterized (W–W = 2.5034(4) Å). The title anion also reacted with P4 via its ditungsten center to give the Na+ salt of the diphosphorus-bridged anionic complex [W2Cp2(μ-κ2:κ2-P2)­(μ-PCy2)­(CO)2]−, following from a symmetrical cleavage of the P4 molecule. The latter anion reacted rapidly with MeI to give the new methyldiphosphenyl-bridged complex [W2Cp2(μ-κ2:κ2-P2Me)­(μ-PCy2)­(CO)2], which could be isolated in good yield.