ALKYLIDYNE(CARBABORANE) COMPLEXES OF THE GROUP-6 METALS .5. PROTONATION STUDIES ON [NET4][W(CC6H4OME-2)-(CO)2(ETA-5-C2B9H9ME2)]

Dichloromethane solutions of [NEt4][W( = CR)(CO)2(eta(5)-C2B9H9Me2)] (R = C6H4OMe-2) at -78-degrees-C on treatment with HBF4.Et2O in the presence of the substrates L = CO, PPh3, PHPh2, CNBu(t) and PhC2Ph afford the complexes [W(CO)2L2{eta(5)-C2B9H8(CH2R)(Me2}] (L = CO, PHPh2 or CNBut, [W(CO)3(PPh3){eta(5)-C2B9H8(CH2R)Me2}] and [W(CO)(PhC2Ph)2{eta(5)-C2B9H8(CH2R)Me2}] respectively. The corresponding protonation reaction employing dppm (Ph2PCH2PPh2) as the substrate yields [W(CO)2(dppm){eta(5)-C2B9H8(CH2R)Me2}] as the major product, together with small quantities of [activated W{CH(R)PPh2CH2PPh2}(CO)2(eta(5)-C2B9H9Me2)]. The structure of [W(CO)3(PPh3){eta(5)-C2B9H8-(CH2R)Me2}] has been established by X-ray diffraction. The tungsten atom is eta(5) co-ordinated by the nido-icosahedral fragment C2B9H8(CH2R)Me2. In the latter the exopolyhedral CH2R group is bonded to the boron atom which is in the beta position with respect to the two carbon atoms in the open pentagonal activated CCBBB face of the cage ligating the tungsten. The latter also carries three terminally bound CO groups and the PPh3 ligand. Addition of aqueous HI to CH2Cl2 solutions of [NEt4][W( = CR)(CO)2(eta(5)-C2B9H9Me2)] affords the salt [NEt4][WI(CO)3{eta(5)-C2B9H8(CH2R)Me2}]. In the latter there is a 2,1,8 arrangement for the nonboron vertices of the WC2B9 icosahedron, in contrast with the closo-3,1,2-WC2B9 structures of the other products. The NMR data (H-1, C-13-{H-1}, B-11-{H-1} and P-31-{H-1}) for the new compounds are reported and discussed in relation to the molecular structures.