Insertion reaction of propane into Rh-H bond in HRh(CO)(PH3)2(C3H6) compound:: A density functional study

Quantum mechanical calculations at the MP4 (SDQ) level using the BP86-optimized geometries were carried out to investigate the energies and reaction mechanism for the propene (CH3-(CH)-H-1=CH22) insertion reaction into the Rh-H bond, using the cis-HRh(CO)(PH3)(2) compound as a model catalytic species. Since the reaction may occur on the branched carbon 1 or in the normal carbon 2, which leads to branched and normal Rh(alkyl) compounds, respectively, we investigated these two mechanisms. The results show that the insertion in the branched carbon has an activation energy of 16.2 kcal/mol, and the activation energy for the reaction to take place at the normal carbon is 14.3 kcal/mol. These activation energies, together with the calculated relative energy of the metal-alkyl compounds formed after the insertion considering these two pathways, were used to access the regioselectivity on this reaction. We found a ratio of normal- and iso-products, n:iso, of (96:4), which is in excellent agreement with the experimental regioselectity of (95:5). (C) 2000 John Wiley & Sons, Inc.