Synthesis And Characterization Of NNN/NNNN-palladium Complexes And Their Application In Suzuki-Miyaura Reaction

A series of novel NNN/NNNN-type ligands and their palladium complexes were synthesized and characterized by NMR,single crystal X-ray diffraction as well as other analysis methods.The catalytic properties of the achiral NNN/NNNN-palladium complexes in the Suzuki-Miyaura reaction were also investigated.The details are as follows:1.Synthesis and characterization of the achiral NNN/NNNN-palladium complexes and their application in the Suzuki-Miyaura reaction（1）Synthesis and characterization of the achiral NNN/NNNN-palladium complexesFirst,a series of achiral NNN-type ligands（3a-f）were synthesized in a one-step sequence using 2-picolinic acid and ortho-aminobenzene with different nitrogen heterocycles as the initial raw materials,and the NNN ligands（3a-f）react with palladium chloride to form corresponding NNN-palladium complex（4a-f）.The diamide framework ligands（6a-c）were synthesized by replacing 2-pyridinecarboxylic acid with oxalyl chloride,and then reacted with acetonitrile palladium chloride to form an achiral NNNN-palladium complexex（7a-c）.All new compounds have been characterized by¹H NMR,¹³C NMR and IR spectra.The molecular structures of complexes 4a and 7a have also been confirmed by single crystal X-ray diffraction.（2）The Suzuki-Miyaura reaction catalyzed by achiral NNN/NNNN-palladium complexesThe catalytic performance of the achiral NNN/NNNN-palladium complexes in the Suzuki-Miyaura coupling reaction was investigated.And the optimal reaction conditions were determined by screening the base,solvent,temperature,reaction time and catalyst etc.When the amount of catalyst is 2 mol%,water and ethanol are used as mixed solvent,the biaryl products could been obtained with up to 99%yield.The experimental results show that both aryl bromides and heterocyclic bromides with electron-withdrawing groups or electron-donating groups can react well with arylboronic acid under the above catalyst system.2.Synthesis and characterization of the chiral NNN tridentate ligand and their palladium complexesThe tridentate ligands containing oxazole/imidazole skeleton were synthesized from commercially available 2-pyridylic acid and o-aminophenyl oxazole/imidazole.With the ligands in hand,the corresponding chiral NNN-palladium complexes were formed by the metalization reaction with palladium chloride.The catalytic properties of the complexes are being further explored.