Design,Synthesis And Properties Of The Salen-Type Organic Cages

Porous organic cages（POCs）are growing rapidly as a new type of porous materials.POCs have the advantages of stable structure,large specific surface area and light material,which are widely used in gas storage,gas separation,catalysis,sensing and other fields.Based on this,we synthesized a series of Salen-type porous organic cages with metal coordinated,which were applied in the separation of C₂H₂/C₂H₄ and the ring-opening polymerization of cyclic ester monomers.The main research contents are described as follows:（1）Three Salen-type organic cages,Salen@cage-1,Salen@cage-2,Salen@cage-3,were designed and synthesized by Schiff base condensation,which was simple and high-conversion using trialdehyde and diamine as reaction monomers.Among them,Salen@cage-1 had a high adsorption amount to nitrogen,and its specific surface area(S_BET)could reach 800 m²g^-1.We optimized the reaction conditions and finally golden yellow single crystal of Salen@cage-1was gotten successfully.According to the single crystal X-ray diffraction analysis,the configuration of Salen@cage-1 was just like a three-dimensional fan with three leaves.Each molecular cage owned a large cavity structure,and the distance between benzene rings in the two parallel planes is about 7.191?.（2）By the reactions of various metal acetate with the organic cage Salen@cage-1,four organic cages coordinated by metal ions,Salen-Fe@cage,Salen-Cu@cage,Salen-Zn@cage,Salen-Pd@cage were obtained.These cages also had a high specific surface area,702 m²g^-1,303 m²g^-1,337 m²g^-1 and 780 m²g^-1,respectively.Among them,the copper-based organic cage,Salen-Cu@cage,showed best performance of C₂H₂/C₂H₄ separation in the gas adsorption test.At 273 K and 1 bar,the maximum adsorption capacity of acetylene and ethylene by Salen-Cu@cage was 66.8 cm³g^-1 and 44.1 cm³g^-1,respectively,and the C₂H₂/C₂H₄ separation ratio was 2.50 by ideal adsorbed solution theory（IAST）.（3）By the reactions of rare-earth-metal amido complexes with organic cage Salen@cage-1,four organic cages coordinated by rare-earth-metal ions,Salen-Y1@cage,Salen-Sc@cage,Salen-Lu@cage,Salen-Y2@cage,were obtained.These cages also had high specific surface areas of 686 m²g^-1,526 m²g^-1,429 m²g^-1,and 455 m²g^-1,respectively.We applied these rare-earth-metal coordinated organic cages to the ring-opening polymerization of cyclic ester monomers,which showed relatively high catalytic activity.Salen-Y1@cage catalyzed the ring-opening copolymerization of caprolactone（ε-CL）and valerolactone（δ-VL）,and the molecular weight of copolymer reached up to 133.8 kg/mol with narrow molecular weight distribution（M_w/M_n=1.59）.Compared with conventional metal catalysts in ring-opening polymerization,organic cage based catalysts had the advantage of solvent resistance.For example,for the polymerization ofε-CL catalyzed by Salen-Y1@cage,the conversion of the monomer could be 97%after seven cycles of catalyst.This provided a new idea for the development of new rare-earth-metal catalysts for cyclic ester polymerization.