Preparation Of Porous Organic Polymers Containing Thiourea Functional Groups And Its Efficient Catalytic Performance

Porous organic polymers?POPs?have high specific surface area,stable chemical properties,and adjustable composition and structure.As a class of novel organic porous materials,POPs have outstanding performance in the fields of heterogeneous organic catalysis,adsorption and separation,optoelectronic devices,and so on.In terms of organocatalysis,small molecular thiourea organocatalysts with double hydrogen-bonding catalysis have attracted much attention due to their high catalytic activity and mild reaction conditions.However,there are still some inevitable problems with high catalyst dosage and difficulty in separation and recovery for such catalysts.To solve these problems,we put forward a research thought of constructing the heterogeneous catalysts of POPs containing thiourea functional groups by combining the thiourea moieties with the framework structure of POPs.Two kinds of new POPs containing thiourea functional groups were designed and synthesized.One was directly used as an unsupported POP catalyst,and the other was used to construct a supported Me-POP catalyst as a carrier for supporting metal Pd.We studied their composition,morphology,structure and catalytic properties,as well as catalytic mechanism.The results laid the foundation for the construction of functionalized POPs materials and highly efficient heterogeneous organic catalysts,which could be expected to provide effective strategies to address the inherent problems of small molecule organic catalysts.The main contents and results of the study are as follows.1.Through the reaction of tris?4-aminophenyl?amine?TAA?and 1,4-phenylene diisothiocyanate?PDT?,a new porous organic polymer TAA-PDT connected with thiourea structure was synthesized under different conditions.The Michael reaction of?-nitrostyrene and diethyl malonate was chosen as the model reaction to investigate the catalytic ability of TAA-PDT,to explore its optimal catalytic conditions and recyclability.The results showed that TAA-PDT synthesized under better reaction conditions had a BET specific surface area of 49m²/g.Moreover,TAA-PDT synthesized in solvents of different polarities exhibited very different surface morphologies.In the Michael reaction,under the reaction conditions of using mesitylene as a solvent,addition of K₂CO₃,and heating at 40?,the dosage of catalyst TAA-PDT could be as low as 0.03 mol%of the substrate,and yield up to 82%,with TON and TOF as high as 2700 and 25 h^-1 respectively.In addition,TAA-PDT had no significant decrease in catalytic performance after 5 catalytic cycles,showing excellent recyclability and reusability.2.The building block with diaminothiourea structures PT was synthesized through PDT and hydrazine hydride.Then the porous organic polymer containing thiourea functional groups connected with imine bonds TFP-PT was successfully prepared by PT and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde?TFP?.At last,Pd-TFP-PT was successfully obtained through the framework of TFP-PT loaded with Pd nanoparticles.The catalytic activity of Pd-TFP-PT for the Michael reaction and reduction of nitrophenol were studied.As the result showed,the BET specific surface areas of TFP-PT and Pd-TFP-PT synthesized under better reaction conditions were 64 m²/g and 61 m²/g,respectively.And the content of Pd nanoparticles in Pd-TFP-PT was 0.31 mmol/g.Furthermore,Pd nanoparticles were evenly distributed on the skeleton,whose particle size were concentrated around 4?5 nm.As a heterogeneous catalyst,Pd-TFP-PT had both hydrogen-bonding catalysis and organometallic catalysis.The yield of the Michael reaction catalyzed by 0.08 mol%Pd-TFP-PT could reach up to 60%.On the other hand,when Pd-TFP-PT catalyzed the reduction of p-nitrophenol?4-NP?,the apparent rate constant k and normalization rate constants k_nor were as high as 0.296 s^-1 and 47.74 mmol^-1 s^-1,respectively.After the catalytic reduction of 4-NP in multiple cycles,PT-TFP-PT still maintained the original catalytic performance,without leakage of Pd nanoparticles.The results of the catalytic experiments on these two heterogeneous POPs catalysts containing thiourea functional groups proved that the special framework structure of POPs could increase the concentration of catalytic active sites,give full play the catalytic effect of active sites,show better catalytic effect than the corresponding homogeneous catalyst,which greatly reduce the amount of catalyst,having excellent recyclability and reusability,in line with the concept of green chemistry.