Visible-light-driven C-H Bond Functionalization Catalyzed By Covalent Organic Frameworks

Covalent organic frameworks(COFs),as a new type of organic crystalline porous polymer which are connected by covalent bonds,exhibit great potential for applications in adsorption,sensing,energy storage,and catalysis recently.Among of them,two-dimensional covalent organic frameworks(2D-COFs),possess extended ?-conjugated frameworks,relatively good stability and excellent photoactivities.And distinguished from inorganic photocatalysts,they offer an enticing alternative because of easy recyclbility and expediently adjustable photoelectric properties.Therefore,it is of great importance to develop heterogeneous visible-light-driven C-H functionalization reactions catalyzed by photoactive two-dimensional covalent organic framework materials.In this thesis,we have developed a serial of sustainable and practical protocols for applying photoactive 2D-COFs into the visible-light-driven C-H functionalization reactions.Then we investigated their stability and catalytic mechanisms.The details are as follows:(1)A new method for visible-light-accelerated arylation and alkylation of quinoxalin-2(1H)-ones hydrazines catalyzed by COFs was developed.In this protocol,a variety of C3 substituted quinoxalin-2(1H)-ones were successfully synthesized via radical addition with a hydrazone-based two-dimensional covalent organic framework(2D-COF-1)as the heterogeneous photocatalyst,substituted hydrazines as radical precursors and oxygen in air as the oxidant.The present method exhibits high efficiency,good functional group tolerance,easy scalability and remarkable catalyst reusability.It provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin-2(1H)-ones in an external oxidant-free and greener manner.Besides,photocatalyst recycling experiments and gram-scale experiments demonstrated that the present protocol displayed the broad prospect in industrial applications.(2)A new method for photocatalytic alkylations of N-heterocycles catalyzed by an ultrastable two-dimensional covalent organic framework was developed.In this protocol,heterocycles were selectively and efficiently alkylated with different N-hydroxyphthalimide(NHPI)esters via photocatalytic decarboxylative alkylations in the presence of an olefin-linked two-dimensional covalent organic framework(2D-COF-2).The present method is eligible for a wide range of Nheterocyclics such as quinolines,isoquinolines,quinoxalin-2(1H)-ones,phenanthridines and quinoxalines.Under simple and mild reaction conditions,the reaction efficiency is consistent with diverse alkyl radical precursors.More importantly,relying on the ultrastability of olefin linkage,2D-COF-2 maintained its photoactivity and recyclability under highly acidic conditions.It offers an attractive solution to make 2D-COFs compatible with complex organic reaction conditions,especially with highly organic acidic conditions.It further expands the boundaries of these heterogeneous visible-light-driven organic processes with 2D-COFs.