Topological Unraveling the [3+2] Cycloaddition (32CA) Reaction between N-Methylphenylnitrone and Styrene Catalyzed by Chromium Tricarbonyl Complex from Electron Localization Function and Catastrophe Theory.

We have investigated the reaction mechanisms of [3+2] cycloaddition (32CA) between N-methylphenylnitrone and styrene catalyzed by chromium tricarbonyl complex at the MPWB1K/6-311G(d,p) level of approximation. Activation energy analysis reveals that these 32CA reactions take place with high activation barriers due to their non-polar character. However, the coordination of chromium tricarbonyl complex to N-methylphenylnitrone or to styrene allows to decrease the activation barrier by about 2 kcal/mol for endo approach of each reaction pathway. The BET study reveals the non-concerted reaction mechanism with the formation of C-C bond before the O-C one along each ortho/endo pathway while the reverse is observed in the meta/endo pathway. Furthermore, along each reaction pathway, the reaction mechanism involves the depopulation of V(N,C) and V(C,C) basins leading to the formation of V(N) basin in first step, followed by V(C). The two last steps correspond to the emergence of V(C,C) and V(O,C) basins which illustrates the formation of C-C and O-C chemical bonds.