Construction And Photocatalytic Application Of S-Tetrazine-and Benzofuran-based Porous Polymers

Porous organic polymers have various structures,tunable band gap structures and porous properties,and have important application prospects in the field of photocatalysis.As heterogeneous photocatalysts,porous organic polymers are easy to recycle and reuse,avoiding the main problems faced by homogeneous photocatalysts(such as difficult separation of products,difficult recovery,and reuse,etc.),have great potential for industrial applications.Nevertheless,the construction of green and efficient organic porous photocatalysts still faces great challenges.In this paper,we embedded functional catalytic units(s-tetrazine)or photoactive building blocks(benzofuran)into porous organic polymers through a bottom-up fabrication strategy,which were then used as photocatalysts.The transformation of organic matter under visible light irradiation has realized the synthesis of a series of high value-added organic molecules.The main work is divided into the following two parts:(1)Synthesis,Characterization and Photocatalytic Application of Tetrazine Hyper Cross-linked Polymers(TZ-HCPs):Two Hyper Cross-linked Polymers(TZ-HCP1 D and TZ-HCP2)were synthesized in one step using Fe Cl3 as catalyst to embed functional s-tetrazine units into Hyper Cross-linked Polymers networks through Friedel-Crafts alkylation.The above-mentioned synthetic method is simple,and the raw materials are cheap and easy to obtain.Experiments show that TZ-HCPs possess large surface area(up to 754 m2 g-1 and 718 m2 g-1,respectively)and excellent photocatalytic activity.Under white light,using ethanol and air as the solvent and oxygen source,TZHCPs can effectively promote the green synthesis of benzimidazole-based products(0.5-4.0 h,28 examples)with yields as high as 99%.In addition,the above method also provides a convenient route for the gram-scale preparation of the diazo ligand 2-(2-pyridine)-benzimidazole(1.87 g,96% yield,0.8 h).Notably,the TZ-HCPs exhibited excellent catalytic stability,maintaining a catalytic yield of 96-99% after 21 cycles.(2)Synthesis,Characterization and Photocatalytic Applications of Benzofurantype covalent organic frameworks(BF-COFs):The photoactive unit benzofuran was successfully implanted into the network structure of covalent organic frameworks,then the heterogeneous photocatalysts BF-COF1 and BF-COF2 were constructed.BFCOFs all have AA-stacked crystal structure,regular pores,and large specific surface areas(422 m2 g-1 and 400 m2 g-1),which are beneficial to the adsorption of substances,host-guest interactions and mass transfer processes.The experimental results show that BF-COFs can not only rapidly catalyze the Cross Dehydrogenation Coupling reaction involving N-phenyltetrahydroisoquinoline(up to 95% yield),but also catalyze β-ketoester and its analogs under illumination.It also showed excellent catalytic effect in the reaction of NH4 SCN to synthesize polysubstituted olefins(28 cases,up to 98%yield).In addition,BF-COFs can also efficiently promote the synthesis of L-prolinederived multi-substituted chiral alkenes(up to 94% yield,≥99% ee),and then ring closure can further achieve optically pure aminothiazoles The preparation of(up to 99%yield,≥99% ee).