Theoretical investigation of the elimination and addition reactions of methane and ethane with nickel

Abstract

Contracted CI calculations have been performed to study the mechanisms for the concerted elimination and addition reactions of ethane and methane with nickel. It is found that the /sup 1/A/sub 1/ state of nickel-ethane and the /sup 1/A' state of nickel-methane behave very similarly. The elimination barrier, for example, is computed to be 34 kcal/mol for methane and 37 kcal/mol for ethane. For the addition reaction a somewhat larger difference is obtained, the activation energy of methane being 54 kcal/mol and of ethane (breaking the C-C bond) 42 kcal/mol. This difference in activation energy can be explained by the difference in the bond strength of the C-H bond in methane and the C-C bond in ethane, the C-H bond being 16 kcal/mol stronger. The difference between these two systems on one side and H/sub 2/ on the other is large; H/sub 2/ has a computed addition barrier to nickel of only 3 kcal/mol. The hydrogen atoms can much more easily form bonds in several directions at the same time than methyl groups, and this difference leads to higher activation energies for reactions involving methyl groups. For all three systems the reaction takes place with nickel in a d/sup 9/ statemore » and with a large extent of d involvement in the bonding at the bent equilibrium geometry. 23 references, 3 figures, 5 tables.« less