Design, synthesis and properties of orthopalladated complexes: Proheterogeneous catalyst

Abstract

The reaction of multidentate ligand, 34(E)-(24(E)-4-aryldiazenyl)phenylimino)methypbenzene-1,2-diol, H2L (H2L1, 1a; H2L2, 1b and H2L3, 1c) and (E)-2-((2-(aryldiazenyl)phenylamino)methyl)phenol, HA (HA(1), 3a; HA(2), 3b and HA(3), 3c) [where H represents the dissociable protons upon complexation, and aryl groups of H2L and HA are phenyl for H2L1 and HA(1), p-methylphenyl for H2L2 and HA(2), and p-chlorophenyl for H2L3 and HA(3)], with Na2PdCl4 separately afforded orthometallated complexes [(L)Pd], (2a, 2b and 2c) and [(A)PdCl] (4a, 4b and 4c) respectively. In the case of [(L)Pd], the deprotonated L2- ligands bind palladium (II) in a tetradentate (C,N,N,O) fashion whereas in the case of [(A)PdCl], the deprotonated A(-) ligands bind Pd(II) in tridentate (C,N,N) manner. X-ray structures of [(L-1)Pd], (2a) and [(A(1))PdCl] (4a) were determined to confirm the molecular structures. Both the complexes 4a and 5a exhibited catalytic activity toward Suzuki and Heck reactions. Conversion of [(A)PdCl] to its oxidized form upon ligand oxidation is reported. (C) 2016 Elsevier Ltd. All rights reserved.