Allyl(carbaborane) complexes of Group 6 metals: preparation and reactivity
Abstract
Treatment of thf (tetrahydrofuran) solutions of [MBr(CO)2(NCMe)2(η3-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(η3-C3H5)(η5-7,8-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(η5-7,8-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(η5-7,8-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)(η5-7,8-C2B9H9Me2)]2d. Treatment of the salt 1c with HBF4·Et2O in the presence of buta-1,3-diene afforded the species [Mo(CO)2(η4-C4H6)(η5-7,8-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(η5-7,8-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(η5-7,8-C2B9H9R′2)] generated in situ, MeC≡CMe, and AgBF4. Reaction of the complex 6a with PMe2Ph gives the species [Mo(CO)(PMe2Ph)(MeC2Me)(η5-7,8-C2B9H9Me2)]6e. Treatment of the reagent Tl2[Mo(CO)3(η5-7,8-C2B9H9Me2)] with AgBF4 in the presence of [W(≡CC6H4-Me-4)(CO)2(η-C5H5)] afforded the dimetal complex [MoW(µ-CC6H4Me-4)(CO)3(η-C5H5)(η5-7,8-C2B9H9Me2)]7.