Autori: Stasch, A, Ferbinteanu, M, Prust, J, Zheng, WJ, Cimpoesu, F, Roesky, HW, Magull, J, Schmidt, HG, Noltemeyer, M,

Editorial: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 124 (19), p.5441-5448, 2002.

Rezumat:

The reaction of the acetylene RCtCH (R ) Ph, CH2SiMe3) with an excess of AlH3‚NMe3 in
boiling toluene leads to the carbaalane [(AlH)6(AlNMe3)2(CCH2R)6] (R ) Ph 1, CH2SiMe3 2) in good yield. Treatment of 2 with BCl3 under varying conditions gives the chlorinated products [(AlCl)6(AlNMe3)2(CCH2-CH2SiMe3)6] 3 and [(AlCl)6(AlNMe3)2(CCH2CH2SiMe2Cl)6] 4, respectively. The latter clearly demonstrates that the cluster can be stepwise functionalized within the inner and outer sphere. The X-ray single-crystal structures of 1, 2, and 4 have been determined. All compounds have in common that the central core consists of a cluster having eight aluminum and six carbon atoms. The bonding properties in this cluster are described as a new manifestation of three-dimensional surface aromaticity. Each Al4C fragment of the cube is formed by four bonds with three electron pairs, thus leading to a strong delocalization of the electrons. A phenomenological modeling using a three-dimensional Hu¨ckel scheme with fitted parameters to reproduce the energies from ab initio calculations revealed that the orbital scheme localized at one Al4C fragment possesses an orbital sextet with a large HOMO-LUMO gap. This is in line with the criteria of aromaticity. The idea of aromaticity was sustained also by qualitative valence bond reasons enumerating the different resonance structures by means of graph theoretical methods.

Cuvinte cheie: Carbaalane; Clusters; 3D-aromaticity; Ab-initio calculations