Synthesis of carbonates from CO₂ and epoxides catalyzed by the system of N‐heterocyclic carbene, hydrogen bond donor, CrCl₂, and tetrabutylammonium bromide

Abstract

Athree-component catalytic system including pyridine-bridged benzimidazolium salts, CrCl 2 , and tetrabutylammonium bromide (TBAB) was developed. Based on the control experiments and spectroscopic measurements, the role of the three components in the catalytic process was clarified, in which benzimidazolium salts were used as N-heterocyclic carbene precursor, a new Cr complex generating from the coordination of CrCl 2 with pyridine nitrogen and pyrazole nitrogen bearing benzimidazolium salts was employed as hydrogen bond donor, TBAB was used as nucleophilic reagent, respectively. Under mild conditions (50 C and 1 bar CO 2 ), the terminal epoxides displayed high reactivity in the three-component catalytic system. The catalytic system showed also high catalytic activity for the internal epoxides by increasing the temperature and CO 2 pressure and/or prolonging the reaction time.

Guanidinium iodide salts as single component catalysts for CO2 to epoxide fixation

“…However, the multistep preparation, meticulous purification, and the elevated price associated with the synthesis of most metal-based catalysts could be the bottlenecks of their largescale production, which make it desirable to develop metal-free catalysts or organocatalysts to perform the cyclic carbonate production. In fact, numerous compounds of this type based on N-heterocyclic carbenes, 46,47 phosphonium, [48][49][50][51] or ammonium salts 49,[52][53][54][55] have reported exceptional results for this process.…”

A highly efficient and reusable amorphous Pd(ii)/crystal Pd(0)-grafted porous polymer framework for catalytic CO2 cycloaddition

“…It is worth mentioning that CO 2 is a thermodynamically inert molecule and utilization of CO 2 as a chemical feedstock is not an easy task. In recent times, several homogeneous catalysts have been reported for the synthesis of cyclic carbonates via CO 2 incorporation into oxiranes, such as organic bases, 1,2 organocatalysts, [3][4][5][6] quaternary phosphonium salts, [7][8][9] quaternary ammonium salts, [10][11][12] alkali metal salts, [13][14][15][16] transition metal complexes, [17][18][19][20][21] N-heterocyclic carbene [22][23][24][25] and ionic liquids. [26][27][28] Most of the reported systems were developed as potential catalysts for the cycloaddition of CO 2 to epoxides, but the main disadvantage is difficulty in separating the desired product from the reaction mixture and relatively inferior thermal stability, and it cannot be regenerated for repeated use.…”

Carboxylation of terminal alkynes with CO2 catalyzed by imidazolium-bridged bis(phenolato) rare-earth metal complexes

“…In the past two decades, various imidazole salt-based catalysts have been widely used in CO 2 conversion, including organic molecule catalysts, such as 1,3-di-tert-butyl-1Himidazol-3-ium chloride 23 and pyridine-bridged benzimidazolium salt, 24 ionic liquid, [25][26][27][28][29] and metal-containing complexes, mainly focused on Zn and Al complexes. [30][31][32][33] In 2017, Yao's group synthesized and characterized the first rare-earth metal adducts containing imidazole salt, and the utilization of the adducts for the conversion of CO 2 to cyclic carbonates was studied under mild conditions, which shows that it is feasible to prepare rare-earth metal catalysts bearing imidazole salts that perform well in CO 2 fixation. 34 In 2015, our group developed a rare-earth metal amide catalyst to realize the direct carboxylation of alkynes with carbon dioxide, and the target carboxylic acids were obtained in 70-99% yields under mild conditions (40 1C, 1 bar CO 2 ).…”