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

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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 (TS1EDA, ΔG‡ = 1.4 kcal mol-1) and form I1EDA (carbamic acid adduct). The formed intermediate is converted to cyclic urea (PEDA, imidazolidin-2-one) via ring closure and dehydration of the concerted transition state (TS2EDA, 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.