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New Carbaalanes Containing Clusters of Aluminum and Carbon Atoms:  (AlEt)8(CCH2C6H5)5H, (AlMe)8(CCH2C6H5)5(C⋮C-C6H5), and (AlMe)7(CCH2CH3)4H2. Quantum Chemical Characterization

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journal contribution
posted on 28.09.2000, 00:00 by Werner Uhl, Frank Breher, Jörg Grunenberg, Arne Lützen, Wolfgang Saak
The open carbaalane cluster (AlEt)7(CCHC6H5)2(CCH2C6H5)3H (2), which was obtained in our group only recently, reacted with an excess of diethylaluminum hydride with hydroalumination of its CC double bonds and formation of the compound (AlEt)8(CCH2C6H5)5H (4). The central cluster of the product comprises a cube of eight Al atoms, five faces of which are occupied by C-benzyl groups; the sixth face is bridged by a hydrogen atom. The carbaalane (AlMe)8(CCH2C6H5)5(C⋮CC6H5) (5) was obtained by hydroalumination of Me2AlC⋮CC6H5 by Me2AlH at 60 °C. Its structure is similar to that of 3, but the bridging hydrido ligand has been replaced by an ethynyl group, which is coordinated to four Al atoms and shows a quite unusual C⋮C stretching vibration of 1956 cm-1. The first carbaalane possessing only aliphatic substituents, (AlMe)7(CCH2CH3)4H2 (6), was obtained by the reaction of Me2AlC⋮CCH3 with Me2AlH. Its structure contains an Al7C4 cluster, which is quite similar to that of the closo-borate [B11H11]2-. An intense emission of a cluster vibration characteristic for carbaalanes was assigned at about 325 cm-1 in the Raman spectra. The structure and bonding of arachno-type cluster compounds related to 4 were investigated by quantum chemical calculations. A delocalized multicenter bonding situation was verified with only weak direct Al−Al interactions.

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