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(mu-COMe)(mu-PCy2)(mu-CO)] (major) and methyl-bridged [W2Cp2(mu-CH3)(mu-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(mu-CH2Ph)(mu-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(mu-CPh)(mu-PCy2)(mu-CO)] in a selective way. The title anion reacted rapidly with several chlorophosphines ClPR2 (R = Bu-t, Et, Cy) to give also two types of isomers: the phosphinoxycarbyne complexes [W2Cp2(mu-COPR2)(mu-PCy2)(mu-CO)] and the mixed-phosphide derivatives [W2Cp2(mu-PCy2)(mu-PR2)(CO)(2)], with the former being obtained selectively when R was the bulky Bu-t 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{mu-COP(O)(OPh)(2)}(mu-PCy2)(mu-CO)], which could be isolated and fully characterized (W-W = 2.5034(4) angstrom). The title anion also reacted with P-4 via its ditungsten center to give the Na+ salt of the diphosphorus-bridged anionic complex [W2Cp2(mu-kappa(2):kappa(2)-P-2)(mu-PCy2)(CO)(2)]-, following from a symmetrical cleavage of the P-4 molecule. The latter anion reacted rapidly with MeI to give the new methyldiphosphenyl-bridged complex [W2Cp2(mu-kappa(2):kappa(2)-P2Me)(mu-PCy2)(CO)(2)], which could be isolated in good yield.