Fast carbon dioxide–epoxide cycloaddition catalyzed by metal and metal-free ionic liquids for designing non-isocyanate polyurethanes

Abstract

The recycling of industrially produced greenhouse gases, such as CO₂, into high-value-added chemicals is one of the most relevant strategies for reaching climate targets. Herein, we present a two-step strategy for how to efficiently convert renewable carbon dioxide (CO₂) into β-hydroxyurethanes using imidazolium ionic liquids (ILs) bearing metal ([ZnCl₄]²⁻ and [CoCl₄]²⁻) or Cl⁻ IL-anions as all-in-one catalysts. The first step involves the rapid (1 h) conversion of phenyl glycidyl ether using ILs and supercritical carbon dioxide (7.7 MPa, 80 °C) to cyclic carbonates in high yield (98%). The DFT calculations suggested a comprehensive mechanistic pathway for the IL-catalyzed CO₂-epoxy reaction showing a rate-determining step of the initial epoxide ring opening and the direct participation of IL-anions. Moreover, the applied ILs are also able to catalyze the subsequent reaction of the formed cyclic carbonates with butylamine resulting in fast formation of β-hydroxyurethanes. Thus, the present concept seems to be a promising strategy for designing non-isocyanate polyurethanes (NIPUs).