Theoretical Characterizations of the Ring Expansion of a Metallacyclopropane to a Metallacyclopentane

Abstract

The potential energy surfaces for the ring expansion reactions of 16-valence-electron d10 metallacyclopropane species have been studied using density functional theory (B3LYP/LANL2DZ). Three metallacyclopropane species of the form (η2-TCNE)M(η-CNC6H5)2, where M = Ni, Pd, and Pt, have been chosen as model reactants in this work. Also, the isocyanide with the form CNC6H5 has been used to study the ring expansion reactivities of these group 10 transition metal elements. Accordingly, this ring expansion reaction can be considered to proceed from metallacyclopropane to metallacyclopentane via the insertions of two isocyanide molecules. The present theoretical investigations suggest that the relative 16-valence-electron metallacyclopropane species’ reactivity increases in the order nickelacyclopropane (1) < palladcyclopropane (2) ≪ platinacyclopropane (3). That is, a less electronegative as well as a heavier group 10 atom center will lead to a smaller ΔEst and, in turn, will facilitate the ring expansion reactions with isocyanides. Furthermore, the singlet−triplet energy splitting of the 16 valence-electron metallacyclopropane species, as described in the configuration mixing model attributed to the work of Pross and Shaik, can be used as a diagnostic tool to predict their ring expansion reactivities. The results obtained allow a number of predictions to be made.