CARBONYL INSERTION INTO METAL HYDROGEN AND METAL METHYL BONDS FOR 2ND-ROW TRANSITION-METAL ATOMS

The carbonyl insertion reaction into metal-hydrogen and metal-methyl bonds has been studied for the entire sequence of second-row transition metal atoms. The energetics of this reaction have been calculated including correlation effects of all valence electrons. The carbonyl addition complexes, the transition states for the insertion reaction, and the product formyl and acetyl complexes have been characterized. From gas-phase values the exothermicity of carbonyl insertion into the metal-methyl bond can be estimated to be about 10 kcal/mol. The actually computed exothermicity is 5-7 kcal/mol larger than this value for the atoms to the left, due to eta2-bond formation, and 7-8 kcal/mol smaller than the gas-phase value for the atoms in the middle of the row, due to a repulsive interaction between the oxygen lone pair and occupied 4d-orbitals. Since the metal-hydrogen bond is normally stronger than the metal-methyl bond, the exothermicity is smaller for insertion into a metal-hydrogen bond. On the other hand, the directionality of the methyl group makes the insertion barrier height smaller for insertion into metal-hydrogen bonds. The addition of chloride ligands will significantly enhance the insertion process for complexes of metals to the right. Ligands are also needed to block formation of stable carbonyl complexes.