Cycloaddition mechanisms of CO2 and epoxide catalyzed by salophen – an organocatalyst free from metals and halides

Abstract

The cycloaddition mechanisms of CO₂ and epichlorohydrin catalyzed by salophen as an organocatalyst were investigated using B3LYP density functional theory computations. The kinetically most favored neutral pathway involves a concerted and synergistic mechanism of phenolate as a nucleophile and phenol as a H-bonding donor in epoxide ring opening and CO₂ addition. The computed apparent barrier (33 kcal mol⁻¹) is in line with the reaction conditions (120 °C and 10 bar CO₂). A similar and anionic route with a much lower apparent barrier (17 kcal mol⁻¹) to react under milder conditions has been proposed and this has to be proven experimentally.