Relative stabilities of hydridocarbonyl and formyl complexes of Rh and Pd: A theoretical study

Abstract

The energy variations accompanying the migration of the hydrogen atom of the hydridocarbonyl complexes H MCO ( M = Rh, Pd), leading to the formation of the formyl species MCHO, have been theoretically studied by means of effective core potential SCF and configuration interaction calculations. The process studied involves the formation of an activated complex and the height of the corresponding energy barrier is found to be markedly different for the two considered metal atoms. In particular, in the case of the Pd complex the presence of a positive charge substantially lowers the energy barrier and favors the formation of the formyl derivative. On the other hand, the energetics concerning the Rh complex are not appreciably influenced by the presence of a positive charge. The difference in behavior of the two metal atoms is rationalized on the basis of the analysis of the electron distribution. The present results indicate that the apparent difficulty of the insertion process cannot be attributed to the different stabilities of the hydridocarbonyl and metalloformyl complexes.