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)

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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)A] and a boron atom [B–C 1.501 (4)A] 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)A, Rh–B 2.205(3), 2.165(3), and 2.237(3)A]. 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.