Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO₂

Abstract

Organocatalysts promote a range of C−N bond forming reactions of amines with CO2. Herein, we review these reactions and attempt to identify the unifying features of the catalysts that allows them to promote a multitude of seemingly unrelated reactions. Analysis of the literature shows that these reactions predominantly proceed by carbamate salt formation in the form [BaseH][RR′NCOO]. The anion of the carbamate salt acts as a nucleophile in hydrosilane reductions of CO2, internal cyclization reactions or after dehydration as an electrophile in the synthesis of urea derivatives. The reactions are enhanced by polar aprotic solvents and can be either promoted or hindered by H‐bonding interactions. The predominant role of all types of organic and salt catalysts (including ionic liquids, ILs) is the stabilization of the carbamate salt, mostly by acting as a base. Catalytic enhancement depends on the combination of the amine, the base strength, the solvent, steric factors, ion pairing and H‐bonding. A linear relationship between the base strength and the reaction yield has been demonstrated with IL catalysts in the synthesis of formamides and quinazoline‐2,4‐diones. The role of organocatalysts in the reactions indicates that all bases of sufficient strength should be able to catalyze the reactions. However, a physical limit to the extent of a purely base catalyzed reaction mechanism should exist, which needs to be identified, understood and overcome by synergistic or alternative methods.

Study of the Cycloaddition of CO2 with Styrene Oxide Over Six‐Connected spn Topology MOFs (Zr, Hf) at Room Temperature

“…In the Gaussian 09 software, we use the B3LYP method, for metal (Zr, Cu) atoms we use basis sets of LANL2DZ, [42] and for non-metal atoms (C, O, N, H), we use basis sets of 6-31G (d). To simplify the calculation, we first perform geometric optimization on Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 (HCOO) 6 (H 2 O) 6 (OH) 6 . By substituting a single carboxylate with different organic ligands, geometric optimization was performed again to obtain ZrÀ BTC, ZrÀ TATB, and ZrÀ PyC(Cu).…”

“…As a complementary technology, carbon capture and utilization (CCU) have the potential to commercialize CO 2 to offset the capture cost and bring economic benefits, [1,2] and are widely favored by researchers. At present, there have been reports on the utilization of CO 2 to prepare carbonate, [3,4] urea derivatives, [5,6] methanol, [7,8] formic acid [9,10] and other chemical products.…”

“…[18] It is not common for triangle connectors to construct ZrÀ MOFs. The use of triangle connectors can synthesize (3,6) and (3,8) connect topologys. [23] The 6-connected topology reported in the literature includes spn topology and kgd topology.…”

N-Heterocyclic Carbene Moiety in Highly Porous Organic Hollow Nanofibers for Efficient CO2 Conversions: A Comparative Experimental and Theoretical Study

“…1,2 Several catalytic pathways have been developed over the past few decades that employ CO 2 as a carbon source to produce valuable chemicals, which are promising for both the industry and academia. These conversions of CO 2 include the synthesis of formic acid, 3 methanol, 4 polycarbonates, 5 carbamates, 6 N-formamide, 7 urea, 8 polyethercarbonate polyols, 9 poly(hydroxy urethane)s, 10 oxazolidinone, 11 and so on. Among these chemicals, methanol is an important CO 2 -based renewable product 12 that has a significant commercial and environmental impact.…”

“…Considering the high levels of CO 2 accumulation in the atmosphere caused by the combustion of fossil fuels and its harmful environmental impact, successful utilization of CO 2 as a C1 chemical feedstock is gaining momentum today in the context of waste to best. , Several catalytic pathways have been developed over the past few decades that employ CO 2 as a carbon source to produce valuable chemicals, which are promising for both the industry and academia. These conversions of CO 2 include the synthesis of formic acid, methanol, polycarbonates, carbamates, N -formamide, urea, polyethercarbonate polyols, poly­(hydroxy urethane)­s, oxazolidinone, and so on. Among these chemicals, methanol is an important CO 2 -based renewable product that has a significant commercial and environmental impact.…”