Construction Of Novel N-heterocyclic Carbene Iron Catalytic System And Study Of Application In Kumada Coupling Reaction

N-heterocyclic carbene (NHCs)/transition-metal catalytic system has shown excellentcatalytic activity towards numerous organic reactions. In this thesis, eight N-heterocycliccarbene azolium salts were synthesized, and the further investigation of their catalyticbehavior in iron-catalyzed Kumada coupling reaction was given."One step" method was taken to get two kinds of mono-imidazolium salts, while sixtypes of bridged-bis-imidazolium or benzimidazolium salts bearing different substituents weresynthesized by “two step” method. All the above-mentioned eight azolium salts werepre-characterized by elemental analysis and1H NMR.In this paper, the catalytic application can be divided into three parts: optimization ofreaction conditions of mono-, bis-azolium salts system; comparison of catalytic activity ofother azolium salts; inspection of the substrate applicability.We took the reaction of p-tolyl magnesium bromide with cyclohexyl bromide as a model,the optimum conditions for mono-azolium1and bis-azolium3catalytic system wereinvestigated, including temperature, time, iron source, catalyst ratio, amonts of catalystloading and substrate ratio. Among which, best results were obtained while using FeCl2asiron source. We observed that the catalyst ratio of azolium salt1with FeCl2is2:1, and1:1forazolium salt3. When other conditions being equal, in addition, higher yield can be obtainedwith2.5mol%catalyst loading in bis-azolium salt3system.The results of other mono-and bis-azolium salts/FeCl2system for model reactionshowed that bis-azolium salt5with moderate steric repulsion obtained the highest yield of91%, while the lower yield for mono-azolium salts, indicating that the bridged bis-azoliumsalt system has greater activation and stabilization on the metal center.Satisfactory outcomes were achieved while substrates with different steric and electronicproperties were tested in bis-azolium salt5system. Similar with the reported essay, thecoupling reaction would be hindered if the substrates has too large or too small stericrepulsion, but there is appreciable improvement while changing to the appropriate conditions.