Syntheses and Structural Characterizations of Benzoxazolyl N-Heterocyclic Carbene-Palladium Complexes and Their Applications
Six seven-membered benzoxazolyl N-heterocyclic carbene(Benzoxa^NHC)palladium complexes with flexible linear alkyl or benzyl linkers were synthesized.Their structures were characterized by NMR,HRMS,and FTIR spectroscopies.The structures of three complexes were further confirmed by X-ray single crystal diffraction.Palladium center adopted slight distorted square planer geometry,and the benzoxazole and NHC planes in its ligand formed a certain angle with each other,not coplanar.The first methylene group connected to a nitrogen-containing heterocyclic carbene fragment exhibited magnetic anisotropy in the complex.The shift difference in the methylene group(Δδg)changed with the increase of the length of the side chain.When the side chain was a linear chain alkyl group of four carbons,Δδg reched maximum.Furthermore,these complexes showed excellent catalytic performance in Suzuki-Miyaura coupling,and could be used to synthesize biphenyl gem-difluoroethenes in the manner of two steps in one pot.
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