Porous Polymer-supported Pd As A Heterogeneous Catalyst For C-H Halogenation

Catalytic C-H bonds activation has become a powerful tool in modern organic synthesis.Direct functionalization of specific C-H bond is the most atomic economic strategy for constructing C-C and C-heteroatom bonds.The aryl halides have attracted wisdespread attention in the fields of pharmaceuticals,agricultural chemicals natural products and organic synthesis.Many methods have been used to synthesize aryl halides.One of the most green and selective C-H bond halogenation methods is regioselective transition metals-catalyzed.Homogeneous C-H halogenation reactions have been intensely investigated.However,the difficult separation of homogeneous catalysts and the products has limited the application of homogeneous catalysis.It is easy to separate the catalysts from the products for heterogeneous catalysis and the catalyst can be recycled many times.However,most of the current heterogeneous catalytic systems have the disadvantages of poor catalytic activity,complicated preparation steps,and poor substrate tolerance.Therefore,heterogeneous catalyst with high catalytic activity,facile preparation and wide substrate scope tolerance would be highly desirable for C-H activation/halogenation.The main work of this thesis is to synthesize three different heterogeneous catalysts and apply them to C-H activated halogenations,and to investigate their catalytic activity and substrate scope.The first chapter of this thesis mainly introduces the transition metal-catalyzed aromatic C-H halogenation,and focuses on the development of the homogeneous and heterogeneous catalytic C-H halogenation.In the second and third chapters of this thesis,the bidentate ligand phenanthroline was used as the main monomer,and the two kinds of new porous polymer were synthesized through hypercrosslinking reaction and scholl coupling reaction with benzene,respectively.The poly-Pd catalysts was then characterized and used in the catalytic C-H halogenation of 2-phenylpyridine.It showed that the prepared catalyst have a rich microporous structure and catalyze the C-H halogenation of 2-phenylpyridine up to 90%yield with excellent recyclable performance.In the chapter four of this thesis,a salen tetradentate ligand was synthesized from salicylaldehyde and ethylenediamineas,The salen was then constructed into the microporous organic polymer framework by hypercrosslinking method.Pd(OAc)₂was immobilized in the obtained polymer and denoted as poly-salen-Pd.Various analysis methods were used to characterized the polymer support and the catalyst before and after the reaction.The poly-salen-Pd was applied in the C-H halogenation of 2-phenylpyridine.It showed that the poly-salen-Pd has better catalytic activity than its counterpart Pd(OAc)₂catalyst on the same reaction conditions.It also showed excellent reusability without loss of catalytic activity for ten cycles.A broad substrate scope was explored and moderate to excellect yields were obtained.