Cobalt Covalent Organic Framework Catalyzed Visible-Light-Driven C-H Annulation

Covalent Organic Frameworks（COFs）are a class of highly ordered crystalline porous organic materials assembled by small organic units.Among them,photoactive COFs,due to their excellent photoactivity,good stability,and easy adjustability,are becoming novel alternative heterogeneous photocatalysts for visible-light-driven organic transformations.However,the regioselectivity in visible-light-driven C-H bond activation reactions always origins from the successful coordination between the transition-metal center and substrates.Therefore,it is of great significance to immobilize transition-metal center into photoactive COFs.The immobilization could endow photoactive COFs with transition-metal catalytic abilities,giving dual-functional metal-covalent organic framework photocatalysts.In this dissertation,a dualfunctional cobalt covalent organic framework catalyst（Co COF-SYNU-1）was successfully synthesized with the introduction of cobalt center into a photoactive COF.Its structure and potential photo activities were characterized and evaluated respectively.Then it was employed as a dual-functional heterogenous photocatalyst in visible-light-driven C-H annulation for the synthesis of isoquinolin-1（2H）-one derivatives.Furthermore,the recyclement of Co COF-SYNU-1 was realized,and its catalytic mechanism was investigated.All the above results were listed as follows:（1）A dual-functional cobalt covalent organic framework photocatalyst（Co COF-SYNU-1）was successfully synthesized.Firstly,the covalent organic framework（BPy-COF）was synthesized via solvothermal method with coordination sites contained [2,2’-bipyridine]-5,5’-dicarbaldehyde and long π conjugated 4,4’,4’’,4’’’-（1,9-dihydropyrene-1,3,6,8-tetryl）tetraaniline.Based on this,the immobilization of cobalt center was carried out via post-synthetic strategy with cobalt acetate tetrahydrate,leading to a crystalline cobalt covalent organic framework（Co COF-SYNU-1）.With a series of analyses for structural characterization and evaluations on potential photoactivity for it,it was proven to possess large BET surface area,good stability,excellent photoactivity,and atomic-level Co dispersion.It could be suitable to serve as a heterogenous dual-functional photocatalyst for visible-light-driven regioselective C-H activation reactions.（2）CoCOF-SYNU-1 was then used as a heterogeneous catalyst for the visible-light-driven CH annulation of amides with alkynes,and a novel method for the synthesis of isoquinolin-1（2H）-one derivatives via visible-light-driven C-H annulation was developed.In this protocol,benefited from the dual catalytic abilities of cobalt covalent organic framework（Co COF-SYNU-1）,the visible-light-driven regioselective [4+2] C-H annulation with amides and alkynes proceeded smoothly,delivering a wide range of isoquinolin-1（2H）-one derivatives with high efficiency.The method exhibits good functional group tolerance and broad substrate scope.More importantly,based on the inherent heterogeneous nature and good stability of Co COF-SYNU-1,the reaction can be easily scaled-up and exhibits excellent catalyst recyclability.Due to the good stability of Co COF-SYNU-1,the reaction efficiency remained unchanged after several cycles.Preliminary mechanistic studies indicate that Co COF-SYNU-1 may accelerate the catalytic cycle with singlet oxygen-induced by photoexcited COF.