Unsymmetrical palladium(II) N,N,O,O-Schiff base complexes: Efficient catalysts for Suzuki coupling reactions

Palladium offers various applications in the field of fine chemicals. As one of the most widely used catalytic metals, due to its high activity and selectivity, there are many possibilities for carbon-carbon bond formation in the organic synthesis. This study focused on the condensation reaction between the selected aldehyde or ketone, and 1, 2-Phenylenediamine; as a result, two different Schiff base ligands were prepared. The reaction between palladium(II) acetate and Schiff base ligand, in a molar ratio of 1:1, resulted in the formation of palladium(II) Schiff base complexes PdL1 and PdL2 (L-1 = N-2-hydroxyacetophenon-N'-2, 4-dihydroxbenzaldehyde-1,2 phenylenediimine, and L-2 = N-2-hydroxyacetophenon-N'-2-hydroxynaphthaldehyde-1,2 phenylenediimine), as identified by elemental analysis, FT-IR, UV-Vis and H-1 NMR spectroscopies. The X-ray analysis of PdL2 also showed that the Schiff base acted as a tetradentate ligand which, through both phenolic O and azomethine N atoms, could be coordinated to the Pd atom with the square planar geometry. By using GC, the catalytic activity of the Pd(II) complexes for the Suzuki coupling reaction was studied. After 8 h of reaction time at 70 degrees C in ethanol, it was concluded that both Pd(II) complexes served as good catalysts for this reaction by more than 90% conversion of the starting materials to the biphenyl product. (C) 2018 Elsevier B.V. All rights reserved.