Two Isomers with an Al4C8 Framework

The co-condensation. by annealing from - 196 degrees C to room temperature, of the high-temperature species AlCl and 3-hexyne (EtC=CEt) with an excess of toluene leads to the formation of the compound (AlCl . EtC=CEt)(4). Characterisation by X-ray analysis revealed the presence of two isomers in the same crystal: a dimeric 1,4-dialumina-2,5-cyclohexadiene and a 1,4,7,10-tetralumina-2,5,8,11-cyclododecatetraene. Both isomers exhibit aluminium-olefin pi-bonding, with the Al-4 entities present in a tetrahedral arrangement. The bonding in both isomers is discussed on the basis of ab initio calculations performed for model compounds.