Synthesis And Properties Of Chiral Metal-Organic Frameworks Based On Chiral Benzimidazole Ligands

Chirality is a fundamental property of nature and one of the most important properties of living systems,and most of the life phenomena and laws in nature are triggered by chirality.In medical pharmacology,chiral drug molecules of opposite conformations even exhibit very different physiological effects and efficacy.In agriculture,chiral herbicides and insecticides likewise exhibit strong stereospecific recognition.Therefore,obtaining chiral molecules with a single conformation is of great importance for human survival and development.In recent years,Chiral Metal-Organic Zeolites（CMOZs）materials have received much attention for their potential applications in asymmetric catalysis and chiral splitting.How to design and synthesize chiral metal-organic frameworks with excellent stability,porosity,and high activity have been a key issue in this field.Zeolite imidazole framework materials developed based on imidazole ligands have received a lot of attention due to their excellent stability,high porosity,directional synthesis,and pore channel tunability,and the introduction of chiral elements on their framework to realize the construction of chiral ZIFs materials is a simple and easy solution.Based on this consideration,two examples of optically pure chiral benzimidazole ligands were designed and synthesized in this paper:（S）-2-（1-Hydroxyethyl）benzimidazole（S-OH-bim）and S,S-1,2-bis（1H-benzimidazole-2-yl）-1,2-ethanediol（S,S-BED）,taking advantage of the ease of coordination of the imidazole ring and the introduction of carboxylic acid ligands to assist in coordination,four examples of N-class-rich two-dimensional compounds and 14 examples of chiral-like molecular sieve compounds were obtained.In this paper,we provide an overview of the development of CMOZs and discuss the properties and potential applications of these 18 compounds in two parts according to the number of central metal nuclei.（1）Four examples of trimetallic N rich two-dimensional compounds were obtained using chiral OH-bim and terephthalic acid ligated with metal zinc and cadmium salts,with OH-bim as the terminal ligand under the addition of a small amount of base.The nanosheets with a large number of exposed N active sites after exfoliation had good chemical stability,and thanks to this structural feature,we compared the performance of the bulk material and the nanoscale sheet material after ultrasonic exfoliation with carbon dioxide cycloaddition as a model reaction,in which the catalytic efficiency before and after exfoliation was doubled for the epoxibromopropane cycloaddition reaction.（2）Using chiral BED and aminophenyl ring dicarboxylic acids coordinated with metal cadmium salts,14 examples of monometallic three-dimensional compounds with two topological network structures were obtained due to the different angles and substituents of the carboxylic acid ligands.Among them,the chiral helical chain formed by connecting the para-carboxylic acid to the BED ligand,and the metal formed the qzd topological network structure;in addition,the two-dimensional layer formed by connecting the para-carboxylic acid to the BED ligand formed the lon topological network structure.The effects of different ligands on their circular dichroism and fluorescence were explored,respectively.In addition,the CMOZ formed by the involvement of 2-aminoterephthalic acid has CPL properties with an asymmetry factor|glum|of about 2.1×10^-3.