THEORETICAL-STUDY OF THE INTERACTION OF ALUMINUM ATOMS WITH 1,3-BUTADIENE AND BENZENE

Theoretical methods are used to study the complexes formed between a neutral aluminum atom and the hydrocarbons, butadiene and benzene. Aluminocyclopentene is predicted to be formed by the addition of aluminum to cis-1,3-butadiene, while addition to trans-1,3-butadiene is predicted to form aluminomethylallyl. The results agree well with an ESR study at 77 K, in which both complexes are observed. A planar aluminocyclopentene is predicted to be bound by 27.2 kcal/mol and aluminomethylallyl is bound by 17.4 kcal/mol with respect to Al + trans-1,3-butadiene (PMP4/6-31G*) when geometries are optimized at the UHF/3-21G* level. When geometries are reoptimized at the UMP2/3-21G* level, an envelope aluminocyclopentene structure is found which is about 4.0 kcal/mol more stable than the planar five-membered ring. Three addition complexes (1,4, 1,2, and 1,3) were considered for the interaction of Al with benzene. In agreement with experiment, the 1,4-complex is predicted to be lowest in energy, giving a binding energy at the [PMP4/6-31 + G**] level of 7.4 kcal/mol, compared to an experimental binding energy of 11.7 kcal/mol.