Activation of Carbon Dioxide by Bicyclic Amidines

Abstract

Activation of the carbon dioxide molecule was achieved using bicyclic amidines (DBU, PMDBD, and DBN). The solution reaction of CO(2) with amidines yielded the corresponding zwitterionic complexes through the formation of a N-CO(2) bond. (13)C NMR data confirmed the carbamic nature of the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2). However, when these adducts were crystallized, the X-ray analyses of the single crystals were in agreement with bisamidinium bicarbonate salt structures, indicating that structural changes occurred in the crystallization process. The elemental and thermogravimetric analysis data for the carbamic zwitterions, DBU-CO(2) and PMDBD-CO(2), initially obtained by the direct reaction of amidines with CO(2), suggest that these molecules are probably associated with one molecule of water by hydrogen-bond formation (amidinium(+)-COO(-)...H(2)O). A correlation was observed between the thermal stability and the transcarboxylating activity for the amidine-CO(2) complexes. Theoretical calculations of hardness were performed at the B3LYP/cc-pVTZ level of theory and showed concordance with the experimental reactivity of DBU and PMDBD toward CO(2).

Supported Absorption of CO2 by Tetrabutylphosphonium Amino Acid Ionic Liquids

“…In addition, as the resonance of CO 2 À in the amino acid anion of the above three ionic liquids is at approximately d = 157 ppm in the 13 C NMR spectrum (400 MHz, DMSO), a new resonance for CO 2 H does not appear. However, the peak area at d = 157 ppm increases in size after absorption of CO 2 .…”

N‐Heterocyclic Carbenes as Efficient Organocatalysts for CO2 Fixation Reactions

“…[4] Whereas the reverse reaction has been proven to be decisive for delivering a number of NHC complexes, [5] in principle, the zwitterionic CO 2 adduct could be utilized as a convenient CO 2 carrier to accomplish CO 2 fixation through the nucleophilic incorporation of the O=C=O unit as proposed for various Lewis base catalyst systems. [6] During our studies on CO 2 fixation to produce highly valuable chemicals, we reported the carboxylative cyclization of propargylic alcohols catalyzed by nBu 3 P in supercritical CO 2 . [7,8] Although the role of the tertiary phosphane catalyst has not been fully understood, we proposed a reaction mechanism involving a putative zwitterionic phosphane-CO 2 adduct which promotes nucleophilic addition of the CO 2 fragment to the unsaturated alcoholic substrate.…”

Novel High Capacity Oligomers for Low Cost CO2 Capture

“…146 Solutions of fatty amines C n H 2n+1 NH 2 (n = 8 -18) in silicon oil and DMSO react with CO 2 to form stable gels due to formation of ammonium carbamates while solutions in fatty alcohols and nitrobenzene remain liquid. 147 Calixarenes modified with amidoamino groups reversibly react with CO 2 in nonpolar solvents at room temperature to yield gels with a three-dimentional network of hydrogen bonds NH 150 Further study showed that interaction between DBU and CO 2 takes place only in the presence of water while in thoroughly dried solution no visual changes observed. 151 Interestingly, the decomposition temperature of the adduct of DBN with CO 2 is substantially lower than that for the DBU:CO 2 adduct (30 o C vs. 58 o C).…”

“…151 Interestingly, the decomposition temperature of the adduct of DBN with CO 2 is substantially lower than that for the DBU:CO 2 adduct (30 o C vs. 58 o C). 150 …”