α-Hydroxyimine palladium complexes: Synthesis, molecular structure, and their activities towards the Suzuki–Miyaura cross-coupling reaction

An activity-promoting strategy for phosphine-free catalytic systems is presented in this study. The strategy is based on a series of non-conjugated N,O ligands with bulky substituents, [Ar–Ndouble bond; length as m-dashC(R)–(R)C(CH3)OH] (L1, R = Acenaphthyl, Ar = 2,6-diisopropylphenyl; L2, R = Ph, Ar = 2,6-dimethylphenyl; L3, R = Ph, Ar = 2,6-diisopropylphenyl). The reaction of PdCl2 with 1 equiv of the ligand L1–3 in methanol affords the four-coordinate palladium complex with the general formula LPdCl2 (1–3). The molecular structures of L3, as well as the palladium complexes 1 and 3, were established by single-crystal X-ray diffraction studies. The application of these palladium complexes as precatalysts was examined for the Suzuki–Miyaura cross-coupling of a range of aryl bromides with arylboronic acids. 3, which incorporates bulky substituents, was shown to be effective in the cross-coupling reactions at 0.01 mol% palladium loading, affording the corresponding biaryls in high yields.