Synthesis, crystal structures, and application of two new pincer type palladium(II)-Schiff base complexes in C-C cross-coupling reactions

Two new pincer type Pd(II)-Schiff base complexes of the general formula [PdL1(PPh3)] 1 and [PdL2(PPh3)] 2, (where L-1 = 2-(2,3-Dihydroxybenzylideneamino) phenolate and L-2 = 2-(2,3-dihydroxybenzylidene) hydrazinecarbothioamidate) were synthesised by the reaction of the palladium acetate with the corresponding ligand in methanol as yellow crystalline solids in high yields. Both complexes were fully characterized by FT-IR, H-1 NMR, C-13 NMR, P-31 NMR, elemental analysis and single crystal X-ray diffraction studies. The crystal structures confirmed the tridentate nature of the pincer type Schiff base ligands and the distorted square planar geometry around the metal centre in both cases. The triphenylphosphine acted as an auxiliary ligand and occupied the fourth coordination site at palladium. The complexes were found to be efficient homogenous catalysts for a series of Suzuki-Miyaura, Heck-Mizoroki and Sonogashira reactions at a low catalyst loading (0.08 mol%), and without the use of any additives. All organic products were fully characterized by H-1 and C-13 NMR studies. (C) 2017 Elsevier B.V. All rights reserved.