ALLYL(CARBABORANE) COMPLEXES OF GROUP-6 METALS - PREPARATION AND REACTIVITY

Treatment of thf (tetrahydrofuran) solutions of [MBr(CO)2(NCMe)2(eta3-C3H5)] (M = Mo or W) with Na2[7,8-C2B9H9R'2] (R' = H or Me), followed by addition of [N(PPh3)2]Cl or [NEt4]Cl, afforded the salts [Y][M(CO)2(eta3-C3H5)(eta5-7,8-C2B9H9R'2)] [Y = N(PPh3)2, R' = Me, M = Mo 1a or W 1b; Y = NEt4, R' = H, M = Mo 1c] in high yield. These species may be synthesised, but in lower yield, from allyl bromide and Tl2[M(CO)3(eta5-7,8-C2B9H9R'2)] generated in situ. Protonation of the salts 1a and 1b with HBF4.Et2O in the presence of CO or PPh3 yielded the compounds [M(CO)2L2(eta5-7,8-C2B9H9Me2)] (M = Mo 2a or W 2b, L = CO; M = Mo 2c or W 2e, L = PPh3). The synthesis of 2c was accompanied by formation of the tricarbonyl species [Mo(CO)3(PPh3)(eta5-7,8-C2B9H9Me2)] 2d. Treatment of the salt 1c with HBF4.Et2O in the presence of buta-1,3-diene afforded the species [Mo(CO)2(eta4-C4H6)(eta5-7,8-C2B9H11)] 5. When reactions of 1a-c with HBF4.Et2O were carried out in the presence of alkynes, the bis(alkyne) complexes [M(CO)(RC2R)2(eta5-7,8-C2B9H9R'2)] (M = Mo, R = R' = Me 6a; M = W, R = Ph, R' = Me 6b; M = Mo, R = Me, R' = H 6c) are formed. The compounds 6a and 6c can also be obtained from reactions between Tl2[Mo(CO)3(eta5-7,8-C2B9H9R'2)] generated in situ, MeC=CMe, and AgBF4. Reaction of the complex 6a with PMe2Ph gives the species [Mo(CO)(PMe2Ph)(MeC2Me)(eta5-7,8-C2B9H9Me2)] 6e. Treatment of the reagent Tl2[Mo(CO)3(eta5-7,8-C2B9H9Me2)] with AgBF4 in the presence of [W(=CC6H4Me-4)(CO)2(eta-C5H5)] afforded the dimetal complex [MoW(mu-CC6H4Me-4)(CO)3(eta-C5H5)(eta5-7,8-C2B9H9Me2)] 7.