Study On The Synthesis Of Nitrogenous Phosphine-free Bidentate Palladium Complexes And Their Applications In Suzuki Cross-Coupling Reaction

As an important method to form carbon-carbon bond, Suzuki cross-coupling reaction is widely applied for synthesis of natural products, pharmaceuticals, and functional polymer materials. The development of highly efficient and stable catalysts is one of the important tasks to apply Suzuki reaction on practical production. Although electon-rich and bulky phosphine ligands are commonly employed in Suzuki reactions, these catalysts still have shortcomings such as easily sensitive to air oxidation, highly toxic and environmental pollution. Therefore the development of phosphine-free ligands has been intensely investigated recently, where [N,O] ligands and [N,N] ligands have recently been used as ancillary ligands for Suzuki reaction with great success.Learning of other excellent catalysts’ advantages, we have synthetized4types of [N,O]-bidente carboxylc imine ligands and12types of [N,N]-bidente α-diimine palladium(Ⅱ) complexes and studied on their applications in Suzuki reaction. The combination of carboxylc imine L3and PdCl2, also the [N,N]-bidente α-diimine palladium(Ⅱ) C4and C12, are excellent for the Suzuki cross-coupling of various aryl bromides with arylboronic acids.1. A series of [N,O]-bidente carboxylc imine ligands were synthesized according to the reactions between bulky anilines and glyoxylic acid, then we study on their activities in Suzuki reaction. We found that L1-L4can promote the Suzuki reaction catalyzed by PdCl2, where L2is the best. The results also show that the combination of0.002mol% L2and0.001%PdCl2is the excellent catalyst for the coupling of activated aryl bromides, weak electron-donating ability of aryl bromides and ortho-substitued aryl bromides with arylboronic acid.2. According to the reactions between bulky anilines and oxalaldehyde, acenaphthenequinone, dibenzoyl, a series of a-diimine ligands were synthesized, then [N,N]-bidente a-diimine palladium(Ⅱ) complexes were synthesized from the reaction between the ligand and PdCl2in anhydrous methanol. To investigate the activities of these complexes, the reaction between1-bromine naphthalene and phenylboronic acid was chosen as a model. We found that using C4or C12(0.1mol%) can catalyze the Suzuki coupling of various aryl bromides with arylboronic acid in good yields.Most of ligands, palladium complexes and biphenyls were confirmed by1HNMR and13CNMR. The Crystal structure of [N,N]-bidente a-diimine palladium(Ⅱ) complexes C3、 C5、C6、C8、C9and C11have been examined by X-ray.