Topological unraveling of the [3+2] cycloaddition (32CA) reaction between N-methylphenylnitrone and styrene catalyzed by the chromium tricarbonyl complex using electron localization function and catastrophe theory

Abstract

We have investigated the reaction mechanisms of [3+2] cycloaddition (32CA) between N-methylphenylnitrone and styrene catalyzed by the 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 the chromium tricarbonyl complex to N-methylphenylnitrone or to styrene allows decreasing the activation barrier by about 2 kcal mol⁻¹ for the endo approach of each reaction pathway. BET study reveals the non-concerted reaction mechanism with the formation of the 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 the V(N) basin in the 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 the C–C and O–C chemical bonds.