Description of the Reaction Intermediate Stabilization for the Zimmerman Di-π-methane Rearrangement on the Basis of a Parametric Diabatic Analysis

Abstract

The mechanism of the Zimmerman di-π-methane rearrangement has been studied using a parametric diabatic analysis (PDA) on which the diagonal elements on the effective Hamiltonian defining the energies of the diabatic electronic states have been parametrized and modeled upon the use of the vertex form of a parabolic function. The PDA requires two inputs: the energy local minimum of an optimized structure along the intrinsic reaction coordinate and the maximum gradients associated with the barriers for the transition states. In the present work, the PDA was used to gain novel insights into the mechanism of the triplet di-π-methane rearrangement of substituted dibenzobarrelenes. Our results suggest that, when using an electron-withdrawing group as substituent, the activation energy for the rate-determining step is directly modulated by the stabilization of the biradical intermediate on the triplet surface. This mechanistic feature was thoroughly analyzed and discussed within the conceptual framework provided by the diabatic model of intermediate stabilization (DMIS).