Force-Induced Dissolution of Imaginary Mode in Mechanochemical Reaction: Dibenzophenazine Synthesis

Abstract : Dibenzophenazine was recently synthesized mechanochemically at a high yield. On the basis of experimental kinetics and theoretical vibronic coupling density analysis, this efficient synthesis has been expected to involve two types of reaction mechanisms. In this study, the reaction pathways, including the catalytic effect of water, are determined using density functional theory. The lowest-energy path involves stepwise formation of two C–N bonds, and a concerted path with a higher barrier is also found. The highest-energy point along the latter path is not a transition state but a higher-order saddle point. Therefore, the concerted path is not generally accepted as a reaction path. However, even a small mechanical force dissolves imaginary frequencies so that the higher-order saddle point is changed to a transition state. This mechanical dissolution of imaginary frequencies is a new feature of theoretical mechanochemistry.