Development Of Novel N,N-bidentate Ligands And Their Applications In The Pd-Catalyzed Cross-Coupling Reactions

Transition metal catalyzed bond-forming reaction is the forefront area in organic synthesis chemistry and the cross-coupling reaction is one of the most efficient ways for constructing C-C,C-heteroatom bonds.Suzuki and Heck reaction are two kinds of the most widely used methods in cross-coupling reactions.Catalyst plays a crucial role in cross-coupling reactions,by adjusting the electronic and steric environment of the center metal of the ligands.It can activate the catalytic activity,prolong the catalyst lifetime,and so on.Therefore,the development of new ligands has been the research emphasis in developing efficient catalyst.Commonly,the ligands are organic compounds including O,N,P,S with lone pair electrons.N,N-bidentate ligands can be applied in a variety of metal catalytic reactions,which shows good catalytic activities;but comparing with P ligand catalysts,N,N-bidentate ligands in Pd catalytic cross-coupling reactions exhibit significant differences.Generally,electronic effect and steric effect of the P ligand are easier to be modified,and the p feedback effects are existing between P and metal.However,N,N-bidentate ligands are usually insensitive to water and oxygen,relatively easy to synthesize,these features are still attractive for chemists.In this thesis,the N,N-bidentate complexes and their applications in cross-coupling reactions were briefly summarized,then conducted the research progress into three aspects as follow:1.In terms of electronic effect and steric effect,we synthesized a series of N,N-bidentate palladium(II)complexes by using 6,7-dihydroquinolin-8(5H)-one,amine,palladium chloride as raw materials.The synthetic methods included two-step method and one-pot method.According to the structural characterization of Pd catalysts,especially the single crystal X-ray diffraction,the results showed that the electronic effect and steric effect of aryl group possessing great influence on the structures of the catalysts.2.The novel catalysts Pd1-Pd6 have been applied in the Suzuki cross-coupling reaction.p-bromotoluene and phenylboronic acid were used as the standard substrates to optimize the reaction conditions.The results showed that in toluene with potassium carbonate as base,0.001 mol% Pd6 catalyst,the reaction can be completely transformed.It was also found that the catalytic activities of sterically hindered and electron-donating catalysts Pd5 and Pd6 were significantly higher than Pd1-Pd4,the highest TON value could reach 4.7�10~6.Under optimal conditions,the study of the substrate scope was carried out.The results showed that all kinds of aryl bromide substrates could obtain good yield.3.The catalyst Pd6 has been used in Heck cross-coupling reaction.By screening solvent,temperature,dosage of styrene and catalyst,it was found that DMF,0.001 mol% Pd6,130 oC,1.2 eq styrene was the most suitable condition.Under the optimized condition,the aryl bromide with electron-donating groups in para-position could converse into trans-products well.On increasing the amount of catalyst or elevating temperature,the aryl bromides with electron-withdrawing groups in para-position and heterocyclic bromides could also conduct C-C coupling reaction well.