Theoretical investigation of the reaction between aluminum and propene. Comparison between calculated and experimental ESR results

Stationary points on the potential energy surface describing the reaction between aluminum and propene have been optimized at the MP2 and DFT (B3LYP, BLYP, BP86, and PWP86) levels using the 6-31G(d,p) basis set, including ZPE and BSSE corrections. All methods are found to give very similar geometrical structures and MP2? MP4, and DFT potential energy surfaces, although some variations exist. An initial addition complex is formed between Al and C3H6, located 6-15 kcal/mol below the free reactants in energy. Passing over a transition state barrier of 15-25 kcal/mol, an asymmetric cyclic trans-pi-allylaluminum hydride product is formed at energies similar to the addition complex. A small barrier separates this product from the energetically most stable conformer, cis-pi-allylaluminum hydride. Hyperfine coupling constants (hfcc's) of Al and the protons were computed at all stable structures, using MP2 and DFT methods and the 6-311G(d,p), 6-311+G(2df,p), and IGLO-III (PWP86 only) bases. The hfcc calculations clearly confirm the cis-pi-allylaluminum hydride as being the structure observed experimentally.