Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 102. Alkylidyne ligand migration from manganese to a rhodacarbaborane cluster; crystal structure of [Rh{σ,η5-CH(C6H4Me-4)-C2B9H10}(CO)(PPh3)]

Abstract

Treatment of CO-saturated CH₂Cl₂ solutions of the salts [X][Rh(CO) L(η⁵-C₂B₉H₉R′₂)][X = NEt₄, L = PPh₃, R′= H; L = CO, R′= Me; X = N(PPh₃)₂, L = CO, R′= H] with the reagents [Mn(CR)-(CO)₂(η-C₅H₄Me)][BCl₄](R = C₆H₄Me-4 or C₆H₃Me₂-2,6) affords the rhodium complexes [Rh{σ,η⁵-CH(R)C₂B₉H₈R′₂}(CO)L](R = C₆H₄Me-4, R′= H, L = PPh₃ or CO; R = C₆H₄Me-4, R′= Me, L = CO; R = C₆H₃Me₂-2,6, R′= H, L = PPh₃). The structure of the compound [Rh{σ,η⁵-CH(C₆H₄Me-4)C₂B₉H₁₀}(CO)(PPh₃)] was established by X-ray diffraction. The rhodium atom is ligated by the CO and PPh₃ groups [Rh–CO 1.854(3), Rh–P 2.302(1)], and by the CH(C₆H₄Me-4)C₂B₉H₁₀ fragment. In the latter the CH(C₆H₄Me-4) moiety forms a bridge between the rhodium [Rh–C 2.374(3)Å] and a boron atom [B–C 1.501 (4)Å] in the pentagonal face of the cage. This boron atom is in the β site ([graphic omitted]) with respect to the carbon atoms, and all the atoms of the ring are bonded to the rhodium, but the connectivities are somewhat asymmetric [Rh–C 2.373(3) and 2.341 (3)Å, Rh–B 2.205(3), 2.165(3), and 2.237(3)Å]. In the molecule the PPh₃ and C₆H₄Me-4 groups are transoid to one another about the Rh–CH(C₆H₄Me-4)σ bond, but n.m.r. studies on solutions reveal the presence of a second isomer with a cisoid configuration for the PPh₃ and C₆H₄Me-4 groups. Reactions of the rhodium compounds with K[BH(CHMeEt)₃] in tetrahydrofuran led to rupture of the Rh–C(H)R σ bonds and formation, in the presence of NEt₄Cl, of the salts [NEt₄][Rh(CO)L{η⁵-C₂B₉H₈(CH₂R)R′₂}](L = PPh₃, R = C₆H₄Me-4 or C₆H₃Me₂-2,6, R′= H; L = CO, R = C₆H₄Me-4, R′= Me). The n.m.r. data (¹H, ¹³C-{¹H}, ³¹P-{¹H}, and ¹¹B-{¹H}) for the new complexes are reported and discussed.