ALKYLIDYNE(CARBABORANE) COMPLEXES OF THE GROUP-6 METALS .2. ALKYLIDENE GROUP CAPTURE ON PROTONATION IN THE PRESENCE OF CHELATING PHOSPHINES

In CH2Cl2 solutions at ca. -78-degrees-C the salts [PPh4][W(= CC6H4Me-4)(CO)2(eta(5)-C2B9H9R'2)](R' = Me or H) upon treatment with HBF4.Et2O, in the presence of dppm (PPh2PCH2PPh2) or dope (Ph2PCH2CH2PPh2), afford the complexes [activated W{CH(C6H4Me-4)PPh2(CH2)nPPh2}(CO)2(eta(5)-C2B9H9R'2)] (n = 1 or 2, R' = Me; n = 2, R' = H). The compound [activated W{CH(Me)PPh2CH2CH2PPh2}(CO)2(eta(5)-C2B9H11)] was similarly prepared from [NEt4][W(= CMe)(CO)2(eta(5)-C2B9H11)], dppe and HBF4.Et2O. In contrast, treatment of [Net4][W(= CMe)(CO)2(eta(5)-C2B9H9Me2)] in CH2Cl2 at -78-degrees-C with HBF4.Et2O and dppe or dmpe (Me2PCH2CH2PMe2) gives the complexes [W(CO)2L2{eta(5)-C2B9H8(Et)Me2)] (L2 = dppe or dmpe). The molecular structure of [activated W{CH(C6H4Me-4)PPh2CH2PPh2}(CO)2(eta(5)-C2B9H9Me2)] has been established by a single-crystal X-ray diffraction study. Within the five-membered WCPCP ring the bond distances are W-C 2.342(9), C-P 1.802(9), P-C 1.81(1) and P-W 2.482(3) angstrom. The ligated carbon and phosphorus atoms of the ring, and the two essentially linearly bound CO ligands, form a pyramidal arrangement with the tungsten atom, the other side of which is co-ordinated by the nido-icosahedral C2B9H9Me2 cage in the usual eta(5) manner. The NMR spectra (H-1, C-13-{H-1}, P-31-{H-1} and B-11-{H-1}) of the new compounds are reported and discussed in relation to their structures.