Palladium (II) complexes based on bidentate chiral Schiff base and amine ligands derived from (−)-myrtenal: Synthesis, characterization and catalytic activity in Suzuki reaction

Abstract

(−)-Myrtenal 1 was reacted with N,N-dimethylethylenediamine and Na2SO4 in PhH to give Schiff base (HL, 2) in 98% yield. Imin 2 was reduced with NaBH4 in EtOH to give diamine (HL, 3) in 94% yield. Reactions of imine 2 and amine 3 with Li2PdCl4 in a 1:1 ratio in MeOH at room temperature provided the palladium chelates PdHLCl2 (4, 6) in 77 and 98% yields. Cyclopalladation of imine 2 using Pd(OAc)2 in PhH at 60 °C followed by treatment with LiCl furnished the chlorobridged dimeric cyclopalladated complex [μ-ClPdL]2 (5) in 61% yield. The proposed structures of new complexes 4–6 were confirmed by 1H, 13C{1H} and 2D NMR spectra. The X-ray analysis of PdCl2HL (4) also showed that the Schiff base acted as a bidentate ligand which could be coordinated to the Pd atom with the square planar geometry. Three new palladium complexes are used as catalysts for Suzuki cross-coupling reactions and exhibit high catalytic activity in the synthesis of biaryl derivatives.