Ab initio MO study of the full cycle of olefin hydroformylation catalyzed by a rhodium complex, RhH(CO)(2)(PH3)(2)

The potential energy profile for the full cycle of olefin hydroformylation catalyzed by RhH-(CO)(2)(PH3)(2), consisting of olefin coordination and insertion, CO insertion, H-2 oxidative addition, and aldehyde reductive elimination, as well as ligand coordination and dissociation, is investigated using the ab initio molecular orbital method. Structures of nearly all isomers of intermediates and transition states involved in each step are determined mainly at the Hartree-Fock level, and the potential energy profile is calculated at MP2 and MP4 levels. The site preference for trigonal-bipyramidal intermediates and transition states discriminates possible paths of the catalysis. The coordinatively unsaturated intermediates are strongly coordinated and stabilized by a solvent olefin molecule, while the transition states are not solvated. The energetic and entropic effects of solvation play the critical role in determining the activation free energies. Including the solvent effect, the H-2 oxidative addition step from a solvated intermediate has one of the highest barriers, 'consisting of desolvation energy and the intrinsic activation energy.