Directly Arylation Promoted By [N, O] Palladium Complexes

Compounds containing biaromatic or heterocyclic biaryl moities have been widely applied in medicine, pesticides and functional materials. Therefore, the arylation reaction has received much attention, especially in the traditional arylation such as palladium-catalyzed Suzuki, Still, Kumada, and Negishi cross-couplings, which are conveniently achived for the construction of CAr-CAr bonds. However, one main drawback of these methods is the requirement of the prefunetionalization of the substrates, causing operation cumbersome, high cost and environment pollution. Hence, the C-H direct arylation which can converting C-H to C-C bonds has become one of the hot research topic in the chemical industry. On account of the high bond strength of C-H bond, catalyst choice of this C-H activation is essential in the direct arylation reaction.In this thesis, we focused to design the efficient and stable phosphine-free catalytic system for promoting the direct arylation reaction. Herein, a series of bulky and electron-rich [N, O] palladium complex have been synthesized, characterized and used for direct arylation.1. The synthesis of [N, O] palladium complexesFirst, commercially available biacetyl was reacted with anilines to obtain theα-ketoimines. Then treatment of α-ketoimines with trimethylaluminum or phenyl Grignard reagent and subsequent hydrolysis provided the ligands L1-L8. Finally, the [N, O]palladium complex was synthesized by treatment of the ligands with Pd Cl2 in high yields.2. [N, O] palladium-complex-catalyzed C-H directly arylationThe efficiency of these eight [N, O] palladium complexes were successfully applied for the direct arylation between benzo[b]thiophene with aryl bromides under aerobic condition at a temperature of 130 oC. The precatalyst and reaction conditions were subsequently evaluated. The results suggested that the catalytic activities were benefit by the bulky steric phosphine ligands, where the triphenyl backbone, especially the precatalytst C6 showed the most efficiency. Besides, the optimal reaction condition were carried out by the K2CO3 as base, Piv OH as additive and DMAc as solvent. Under the optimal conditions, the aryl bromides, regardless of electron-rich and electron-withdrawing substrates as well as the sterically hindered substrates, did not have a substantial effect on the overall performance of the reaction. Then, a survey of heteroarenes, such as2-methylthiophene, 2-chlorothiophene, thiophene-2-carbaldehyde, furan-2-carbaldehyde,thiazole, imidazo[1,2-a]pyridine, and 1,2,3-triazole, were employed for coupling with aryl bromides, resulting in a versatile, regioselective direct arylation. This easy manipulation is highlighted by the low palladium loading(0.5 mol%) and aerobic conditions. In addition,the study of the mechanism was proposed to proceed via a Pd(0)/Pd(II) CMD pathway in the direct arylation.3. The ligands, palladium complexes and the arylation products were confirmed by1 H and13CNMR. The Crystal structure of the ligand L5, L6, complexes C1, C2 have examination by X-ray.