THEORETICAL-STUDY OF THE ACTIVATION OF THE N-H BOND IN AMMONIA BY 2ND ROW TRANSITION-METAL ATOMS

The oxidative addition reaction between ammonia and the entire sequence of second row transition metal atoms has been studied with methods including electron correlation. Geometries and energies for molecular adducts, transition states, and insertion products have been obtained. The results are compared to previously calculated results for the corresponding methane reaction at the same level of accuracy. It is found that the ammonia reaction is much more exothermic and has lower barriers for the atoms to the left. The origin of this difference is the attractive interaction between the ammonia lone pair and empty 4d-orbitals for these atoms. The differences to the methane reaction for the atoms to the right are rather small. The repulsion between the ammonia lone pair and the filled 4d-orbitals of these atoms is not larger than the corresponding repulsion between the methane bonding electrons and the metal. The lowest barriers for the N-H insertion reaction are found for the atoms to the left with values slightly below zero.