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.