Synthesis Of Carboxylic Acid And Its Derivatives From Carbon Dioxide Catalyzed By Cu

The surge of atmospheric CO₂ concentration has adversely affected the ecological environment.At the same time,as a cheap and readily available,non-toxic and abundant C1 resource,CO₂could be transformed into high value-added chemicals through chemical methods.Carboxylation reaction is of great significance among the many reactions in which CO₂participates.Carboxylic acid compounds are the key intermediates commonly used in the chemical industry,especially in fine chemical production,and the basic skeleton of many natural products,pesticides,and medicines.In previous reports,the carboxylation of CO₂usually required high-energy organometallic reagents,hyperstoichiometric reductants and harsh reaction conditions.In this study,CO₂and aryl boric acid were successfully converted into carboxylic acid and carboxylic ester compounds using cheap and efficient copper as the catalyst.The main research work is as follows:（1）Six multi-dentate N-heterocyclic carbene ligands were synthesized by C-C coupling reaction starting from imidazole,including a tridentate ligand 1,3-bis（2-pyridine）imidazole complex and two tetradentate ligands bis[3-（2-pyridine imidazole）]methane and bis[3-（2-pyridinimidazole）]ethane,which were characterized by NMR spectroscopy.（2）Using phenylboronic acid and CO₂ as the reaction template,through a series of copper source,N-heterocyclic carbene ligands and multi-dentate nitrogen-containing ligands,solvents and other reaction conditions screening,it was found that the carboxylation of CO₂and arylboric acid compounds could occur smoothly under atmospheric pressure with Cu Cl as the catalyst,1,10-phenanthroline ligand,CH₃OK as the base.Under the optimization conditions,the results of the universal study of the functional groups of the substrate showed that the compounds containing electron-donating groups and electron withdrawing groups could be transformed into the corresponding carboxylic acid products,and some sensitive groups（carbonyl,ester and amide groups,etc.）,naphthalene ring derivatives and hetero-atom containing thiophene could also be carboxylated smoothly in the catalytic system.29 carboxylic acid compounds were obtained with yields ranging from 10%to 90%,all of which were characterized by melting point,IR spectroscopy and NMR spectroscopy.（3）After successfully obtained the Cu catalytic system that could activate CO₂under the mild condition,we tried to use the Cu catalytic system to activate CO₂to synthesize biologically active carboxylate compounds to explore the applicability of the catalyst in series reactions,avoiding the use of toxic compounds such as CO and thiocarbonate commonly used in the synthesis of such compounds.We used CO₂as the COO^-source and methyl iodide as the esterification agent.We obtained the optimal reaction conditions for the synthesis of carboxylic acid esters from CO₂and aryl boronic acid compounds by screening the reaction conditions such as copper source,alkali and solvent.The study of the universality of substrate functional groups shew that although the yield was affected by the carboxylation efficiency,after the series reaction,a total of 29 kinds of aryl boronic acid esters with different functional groups were obtained,and the yields ranged from 9%to 77%,and was identified as the target product by IR spectroscopy,NMR resonance and MS spectrometry.（4）Finally,by designing controlled variable experiments and intermediate capture,combined with literature,the mechanism of Cu-catalyzed CO₂participation in carboxylic acids and carboxylate compounds was preliminarily speculated,including catalyst preactivation,transmetallation,CO₂insertion and four steps of transmetallation again.