Novel Palladium Complexes Based On Pyridine-containing Alcohol Ligands: Design, Synthesis, And Catalytic Activity

In this thesis, a series of novel palladacycle complexes based on pyridine-containing alcohol ligands were designed and synthesized. The catalytic activity of these bis(alkoxo)palladium(II) complexes has been investigated through different cross-coupling reactions. The main results obtained are as follows: 1. Considering the steric effect and solubility of these bis(alkoxo)palladium(II) complexes, three pyridine-containing alcohol ligands LI-LIII were synthesized with different functional groups. The corresponding bis(alkoxo)palladium(II) complexes Cat.I-III(Scheme 1) were obtained in high yields via alkoxylation with Pd(OAc)2.2. The catalytic activity of bis(alkoxo)palladium(II) complexes Cat.I-III has been studied. These bis(alkoxo)palladium(II) complexes could be used as simple, efficient and environmentally friendly catalysts in many different types of coupling reactions(such as Suzuki, Cyanation, C-H activation, and dehydrogenative Heck reactions)(Scheme 2). It was found that Cat.I exhibited high catalytic activity in the Suzuki cross-coupling reaction and direct C-H arylation of heterocycles. Cat.II showed high catalytic activity in the cyanation reaction of aryl/heteroaryl halides. In addition, the catalytic activity of Cat.III in the dehydrogenative Heck reaction of thiophenes with various olefins under mildconditions was batter than Cat.I-II. Furthermore, a possible mechanism for bis(alkoxo)palladium(II) complex catalyzed dehydrogenative Heck reaction was investigated for the first time.3. Based on the above results, other four new pyridine-containing alcohol ligands LIV-LVII and their corresponding bis(alkoxo)palladium(II) complexes Cat.IV-VII were synthesized with the standard method(Scheme 3). Generally, the yields of palladacycle complexes were obviously affected by steric and electronic effects of the pyridine-containing alcohol ligands, and reduced with the increasing of their steric effect and electron-donating effect(Cat.I~Cat.II~Cat.III > Cat.IV~Cat.V > Cat.VI > Cat.VII). In addition, the catalytic activity of these bis(alkoxo)palladium(II) complexes was also studied in different coupling reactions. The bis(alkoxo)palladium(II) complexes with the suitable ligands such as Cat.III and Cat.V showed high catalytic activity in the coupling reactions under mild reaction conditons. With the high reaction temperature, the catalyticactivity of these complexes was similar.