Preparation Of Immobilized Cobalt Salen Chiral Electrode Materials And Their Application In The Asymmetric Electrocarboxylation Of Halides

The greenhouse effect caused by excessive CO₂ emissions is one of the causes of global climate anomalies.On the other side,CO₂ is an important and appealing source of C1 for organic synthesis due to its non-toxic and abundant properties,as well as its accessibility and sustainability.However,as CO₂ is both thermodynamically stable and kinetically inert,conventional methods of CO₂ fixation often require demanding reaction conditions,such as high temperatures and pressures,and strong alkaline environments.The use of electrochemistry allows for the simultaneous fixation of CO₂and the synthesis of high-value-added chiral drugs from organic small molecules under mild reaction conditions,where optically active carboxylic acids have important applications in polymer synthesis and drug synthesis.From the point of view of green and sustainable chemistry,asymmetric electrocarboxylation is essentially an environmentally friendly process,and the electrical energy can be provided by renewable sources.There is no doubt that the combination of CO₂ fixation and asymmetric electrocatalysis is not only effective in reducing CO₂ emissions,but also in providing optically active chemicals with high added value.According to the reaction principle,the introduction of asymmetry into non-chiral substrates by electrochemical methods can be achieved by using suitable chiral catalysts.A number of transition metal complexes consisting of chiral ligands,such as chiral Schiff base salen ligands、binaphthyl diphenylphosphine（BINAP）,and transition metal ions have demonstrated their efficiency in promoting carbon-carbon enantioselective formation.However,the difficulty of separating and reusing chiral catalysts in reaction systems has hindered their industrialization.Encapsulation is one of the most commonly used methods for immobilized chiral catalysts,which does not alter the chemistry of the original chiral catalyst.Hence,the use of encapsulation for the immobilization of chiral metal complex catalysts and their application to electrochemical fixation of CO₂ and asymmetric electroorganic synthesis would be an important research project.In this thesis,FDU-12-C was selected as a porous nanocage for the solidification of the chiral catalyst t-Bu（R,R）Co^Ⅱ（salen）and its application as a cathode material in the asymmetric electrocarboxylation of 1-phenylethyl chloride and CO₂.The effect of different silylation reagents on the preparation of the composite and the asymmetric electrocarboxylation was also investigated.The specific parts of the study are as follows:（1）The composites t-Bu（R,R）Co^Ⅱ（salen）@FDU-12-C（C3-X）with different t-Bu（R,R）Co^Ⅱ（salen）additions were synthesized using n-propyltrimethoxysilane（C3）as the silylation reagent.The composites were characterized by ICP,UV-vis,TEM and N₂adsorption and desorption to demonstrate the successful preparation of the composites,and this series of composites were applied as cathode materials in the asymmetric electrocarboxylation reaction of 1-phenylethyl chloride with CO₂ to obtain optically active 2-phenylpropionic acid with an ee value of 86%and a yield of 39%.The effects of electrolytic potential,the amount of encapsulation t-Bu（R,R）Co^Ⅱ（salen）and temperature on the asymmetric electrocarboxylation reaction were also investigated.Due to its immobilization entirely on the electrode surface and encapsulationby FDU-12-C,t-Bu（R,R）Co^Ⅱ（salen）is easily separated from the electrolyte after electrolysis,and its amount used here is only one percent of that added directly to the solution.In addition,the t-Bu（R,R）Co^Ⅱ（salen）@FDU-12-C（C3-X）composite exhibited remarkable stability and reusability,with the yield and ee values of the product remaining essentially unchanged after repeated electrolysis for multiple recoveries.（2）Based on the requirements of green chemistry,we prepared a series of composites t-Bu（R,R）Co^Ⅱ（salen）@FDU-12-C（TMOS-X）with different t-Bu（R,R）Co^Ⅱ（salen）additions,using pre-hydrolysed tetramethoxysilane（TMOS）as a silylation reagent to replace C3 which requires the use of toxic reagents such as pyridine.A series of characterizations such as ICP,XPS,TEM,N₂ adsorption and desorption etc.were carried out to verify their successful synthesis.The electrocatalytic performance of the composites for the asymmetric electrocarboxylation reaction of 1-phenylethyl chloride with CO₂ was subsequently investigated.The effects of different electrolytic potentials and the amount of t-Bu（R,R）Co^Ⅱ（salen）were investigated on the asymmetric electrocarboxylation reaction.