Synthesis Of Sulfonated β-Ketoimine And β-Diimine Ligands And Their Catalytic Applications In Carbon-Carbon Cross-Coupling Reaction

The construction of carbon-carbon bond is the one of the most important methods in modern organic synthesis,among which the cross-coupling reaction between electrophilic unsaturated carbon(sp or sp² hybridization)and nucleophilic carbon atom is an important tool.Therefore,since its invention and establishment,it has attracted extensive attention because of its high-efficiency,application to wide range of substrates,and few side reactions.In addition,the product could be easily separated. Up to now,carbon-carbon cross-coupling has been widely used in the synthesis of medicines,agricultural chemicals,natural products and fine chemicals.In recent years, with the development of green chemistry,establishment of environment-friendly catalytic systems has become an important part of catalysis.Phosphine-free catalysts and green solvents have been widely used in carbon-carbon cross-coupling reactions.In this dissertation,the reactions of sulfonated 2,6-diakyl aniline with acetylacetone,2-formylcyclohexanone and 2-phenyl-2-benzoylacetaldehyde afforded a series of sulfonatedβ-ketoimine andβ-diimine ligands under different reaction conditions.The combinations of these ligands with Pd(PhCN)₂Cl₂ or PdCl₂ and Ni(DME)Cl₂ were employed as catalysts in the Heck and Suzuki cross-coupling reactions in organic solvents,aqueous phase/neat water and ionic liquids. Experimental results indicated that these catalysts displayed high catalytic performance.1.Synthesis and characterization of sulfonatedβ-ketoimine andβ-diimine ligandsFirst,aniline compounds with different 2,6-dialkyl groups were sulfonated with concentrated sulfuric acid,subsequently these sulfonated 2,6-diakyl anilines reacted with acetylacetone,2-formylcyclohexanone and 2-phenyl-2-benzoyl-acetaldehyde in methanol and in the presence of formic acid or concentrated hydrochloric acid as catalyst to afford a series of sulfonatedβ-ketomine andβ-diimine ligands.The crude products were recrystallized from methanol/ether.These ligands were characterized by IR,¹H NMR,¹³C NMR,UV,ESI-MS and Elemental Analyses.The structure of L6 ligand was further studied by single-crystal X-ray diffraction.The molecular was found as a "triple" internal salt with three positive charge centers and three negative charge centers.The sodium atom has tetrahedral coordination geometry.2.Investigation on the Heck and Suzuki cross-coupling reactions catalyzed by sulfonatedβ-ketoimine/Pd andβ-diimine/Pd complexes in organic solventsThe effects of reaction medium,temperature,catalyst amount,TBAB amount, ligands and substrates on Heck and Suzuki cross-coupling reactions were investigated. Experimental results indicated that all catalysts have moderate to good catalytic activity.The yields with neutral and active aryl bromides as well as active aryl chlorides were very high even though using extremely small amount of catalyst under catalytic conditions,and certain substrates could be converted to products even within a short period.However,the yields of non-active aryl halides were moderate.It was also found that the steric hindrance had significant influence on the yields.The catalytic reaction conditions for Suzuki reaction were milder than that of Heck reaction.The reaction temperature was lower and reaction time was shorter.3.Investigation on Heck cross-coupling reactions catalyzed by sulfonatedβ-ketoimine/Pd andβ-diimine/Pd complexes in ionic liquidsHeck cross-coupling reactions catalyzed byβ-ketoimine/Pd andβ-diimine/Pd complexes in such ionic liquids as[BMIM]PF₆,[BMIM]BF₄,[EMIM]PF₆ and [EMIM]BF₄ were studied.Under the reaction conditions,140℃/2.0mol%L3/Pd/ 3.0 eq of triethylamine/24h,the highest yield of 90%was obtained in model reaction of bromobenzene with butyl acrylate.The effects of different ligands and different substrates on Heck reaction were investigated.The above moderate yields were obtained for different ligands.The yield of 99%was achieved for p-bromo-acetophenone. The experiment of catalytic recycling indicated that every catalytic system in the four ionic liquids could be used up to six times,but the descending trends were found for the four ionic liquids.The reason for descended catalytic performance was tested and analyzed.Experiment results indicated that gradually enhanced ionic strength,which was generated during the catalytic reaction,may be the main factor.This is the first time thatβ-ketoimine/Pd andβ-diimine/Pd catalysts were applied to catalyze Heck cross-coupling reaction.4.Application of sulfonatedβ-ketoimine/Pd andβ-diimine/Pd complexes as catalysts in Heck and Suzuki catalytic cross-coupling reaction in aqueous phase/neat waterA large difference was found between Heck and Suzuki cross-coupling reactions catalyzed by sulfonatedβ-ketoimine/Pd andβ-diimine/Pd complexes.Under the reaction condition,0.2 mol%L3/Pd/TBAB/100℃/KOH/24h,a yield of 56% was obtained for bromobenzene in Heck model reaction.However,under the reaction condition,0.03 mol%L3/Pd/100℃/KOH/3h,a yield of 96%was observed for bromobenzene in Suzuki model reaction.The effects of different ligands and different substrates on Heck and Suzuki cross-coupling reaction were also investigated.Under the reaction conditions mentioned above,the yields corresponding to the Heck reaction using different ligands and different substrates were moderate,and the catalytic performance was unsatifactory for low-active phenyl halides.But under the same reaction conditions,the yields corresponding to the Suzuki reaction using different ligands and different substrates were satisfactory,and the yield was more than 80%even for low-active substrates.Some substrates could be completely transformed into product rapidly.At the same time,the effects of pressure and temperature on Heck reaction in an autoclave were investigated.It was found that pressure had little influence on the Heck reaction.However,temperature had significant influence on the Heck reaction.The yield for the Heck reaction was greatly enhanced at high temperatures.This is the first time thatβ-ketoimine/Pd andβ-diimine/Pd complexes were used as catalyst in Heck and Suzuki cross-coupling reaction in neat water.5.Investigation of Heck cross-coupling reactions catalyzed by sulfonatedβ-ketoimine/Ni andβ-diimine/Ni complexesThe effects of reaction temperature,base,catalyst amount on the Heck cross-coupling reaction were investigated,and optimized reaction conditions were selected.The yield for bromobenzene was only 53%under selected reaction conditions of 3.0mol%L3/Ni/140℃/2.0 eq NaOAc/24h in the model reaction. Experimental results indicated that the yields of different ligands were low to moderate.The yields of 85%and 74%were obtained for p-bromoacetophenone and m-bromonitrobenzene,respectively.Thus,a conclusion can be drawn that the catalytic performance of Heck reaction catalyzed by Ni complexes was less satisfactory than that of Heck reaction catalyzed by Pd complexes.