CO activation through C-N, C-O and C-C bond formation

• Published in: Physical chemistry chemical physics : PCCP 2020-01, Vol.22 (3), p.136-1312
• Main Authors: Eftaiha, Ala'a F, Qaroush, Abdussalam K, Okashah, Ibrahim K, Alsoubani, Fatima, Futter, Jonas, Troll, Carsten, Rieger, Bernhard, Assaf, Khaleel I
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp05961j

A comparative model for the chemisorption of CO 2 was explored via three representative reaction pathways: carboxylation of cyclohexanone, carbonation of cyclohexanol, and carbamation of cyclohexylamine. The model substrates were activated using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, an amidine superbase). For each of these reactions, the formation of the corresponding CO 2 adducts was confirmed by 13 C nuclear magnetic resonance and Fourier-transform infrared spectroscopy measurements. It was demonstrated that CO 2 fixation occurred through either an enol-CO 2 adduct ( i.e. carboxylation), proton shuttling process ( i.e. carbonation), or self-activation mechanism ( i.e. carbamation). Volumetric adsorption measurements indicated that cyclohexanol was superior in its uptake capacity (11.7 mmol CO 2 g −1 sorbent) in comparison to cyclohexylamine (9.3 mmol CO 2 g −1 sorbent) or cyclohexanone (8.5 mmol CO 2 g −1 sorbent). As supported by density functional theory calculations, this trend was expected given the fact that the carbonation reaction proceeded through a more thermodynamically favorable reaction process. CO 2 fixation reactions have been explored using different organic substrates upon activation with a superbase.