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
journal contributionposted on 28.09.2000, 00:00 by Werner Uhl, Frank Breher, Jörg Grunenberg, Arne Lützen, Wolfgang Saak
The open carbaalane cluster (AlEt)7(CCHC6H5)2(CCH2C6H5)3H (2), which was obtained in our group only recently, reacted with an excess of diethylaluminum hydride with hydroalumination of its CC 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of Me2AlC⋮CC6H5 by Me2AlH at 60 °C. Its structure is similar to that of 3, but the bridging hydrido ligand has been replaced by an ethynyl group, which is coordinated to four Al atoms and shows a quite unusual C⋮C stretching vibration of 1956 cm-1.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.