A series of new ionic sulfonated α-diimine ligands were prepared and employed as supporting ligands for the palladium-catalyzed aerobic alcohol oxidation. The electronic properties, rigidity, and steric hindrance of ligands have remarkable influences upon the catalytic activity of the palladium complexes. The best catalytic result could be achieved using ligand 9 with an electron-withdrawing sulfonyl substituent together with bulky groups (iso-propyl in 2,6-positions). This diimine/palladium-catalyzed system is highly efficient for the oxidation of various benzylic alcohols, and showed moderate yields for the secondary aliphatic alcohols and cyclic alcohols.Key words: α-diimine, palladium, aerobic oxidation, alcohol.
制备了一系列新的离子磺化α-二亚胺配体,并将其用作钯催化有氧醇氧化的支持配体。配体的电子特性、刚性和立体阻碍对钯配合物的催化活性有显著影响。配体 9 具有抽电子的磺酰取代基和大体积基团(2,6-位的异丙基),可以达到最佳催化效果。这种二亚胺/钯催化体系对于各种苄醇的氧化具有很高的效率,而对于仲脂肪醇和环醇的氧化则表现出中等的产率。