THEORETICAL-STUDIES OF INORGANIC AND ORGANOMETALLIC REACTION-MECHANISMS .3. THE ORIGIN OF THE DIFFERENCE IN THE BARRIER FOR THE KINETIC AND THERMODYNAMIC PRODUCTS FOR THE OXIDATIVE ADDITION OF DIHYDROGEN TO A SQUARE-PLANAR IRIDIUM COMPLEX

The stereoselective oxidative addition of H-2 to IrCl(CO)(dppe) was examined with ab initio theoretical techniques. Reaction coordinates for the two pathways to addition which lead to the formation of the two isomers were constructed from geometry optimization calculations and were augmented by significant portions of the potential energy surfaces near the transition states. The analysis of the Laplacian of the total charge densities revealed that as the complexes evolve from four-coordinate to six-coordinate species, the ligands in the plane of addition move past regions of charge concentration around the metal center. Electron-withdrawing ligands in the plane of addition reduce this repulsive interaction by delocalizing a portion of the electronic charge. Electron-donor ligands are unable to function in this capacity and therefore contribute to the repulsive interaction of the five-coordinate transition state to a greater extent. The influence of electron correlation on the reaction coordinates was examined and found not to significantly alter the conclusions based on the single-determinant calculations.