Computational predictions on Brønsted acidic ionic liquid-catalyzed carbon dioxide conversion to five-membered heterocyclic carbonyl derivatives

Abstract

Experimentally conducted reactions between CO₂ and various substrates (i.e., ethylenediamine (EDA), ethanolamine (ETA), ethylene glycol (EG), mercaptoethanol (ME), and ethylene dithiol (EDT)) are considered in a computational study. The reactions were previously conducted under harsh conditions utilizing toxic metal catalysts. We computationally utilize Brønsted acidic ionic liquid (IL) [Et₂NH₂]HSO₄ as a catalyst aiming to investigate and propose ‘greener’ pathways for future experimental studies. Computations show that EDA is the best to fixate CO₂ among the tested substrates: the nucleophilic EDA attack on CO₂ is calculated to have a very small energy barrier to overcome (TS1_EDA, ΔG^‡ = 1.4 kcal mol⁻¹) and form I1_EDA (carbamic acid adduct). The formed intermediate is converted to cyclic urea (P_EDA, imidazolidin-2-one) via ring closure and dehydration of the concerted transition state (TS2_EDA, ΔG^‡ = 32.8 kcal mol⁻¹). Solvation model analysis demonstrates that nonpolar solvents (hexane, THF) are better for fixing CO₂ with EDA. Attaching electron-donating and -withdrawing groups to EDA does not reduce the energy barriers. Modifying the IL via changing the anion part (HSO₄⁻) central S atom with 6 A and 5 A group elements (Se, P, and As) shows that a Se-based IL can be utilized for the same purpose. Molecular dynamics (MD) simulations reveal that the IL ion pairs can hold substrates and CO₂ molecules via noncovalent interactions to ease nucleophilic attack on CO₂.