Theoretical Study of the Mechanism of the Abstraction Reactions of Heavy Cyclopropenes by Alcohol

Abstract

The potential energy surfaces for the abstraction reactions of heavy cyclopropenes with alcohol have been characterized in detail using density functional theory (B3LYP/LANL2DZdp), including zero-point corrections. Five heavy cyclopropene species including cyclopropene, cyclotrisilene, cyclotrigermene, cyclotritinene, and cyclotrileadene, have been chosen in this work as model reactants. All the interactions involve a hydrogen shift via a two-center transition state. The activation barriers and enthalpies of the reactions were compared in order to determine the relative reactivity of the heavy cyclopropenes. The present theoretical investigations suggest that the relative heavy cyclopropene reactivity increases in the order cyclopropene < cyclotrisilene < cyclotrigermene < cyclotritinene < cyclotrileadene. That is, for alcohol dehydrogenations there is a very clear trend toward lower activation barriers and less endothermic reactions on going from C to Pb. Besides this, our theoretical findings indicate that the final abstraction-addition products should adopt the anti geometry, rather than the syn geometry, from a thermodynamic viewpoint. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.