Thiopseudourea ligated palladium complexes: synthesis, characterization and application as catalysts for Suzuki–Miyaura, Sonogashira, Heck and Hiyama reactions

Abstract

A series of new non-phosphine 1-(2-picolyl)-3-benzoylsubstituted-2-benzyl-2-thiopseudourea ligands 2a–2f have been synthesized in two steps from commercially available benzoyl chlorides. Treatment of these ligands with Pd(OAc)₂ in a 1 : 1 molar ratio in dichloromethane (DCM) at room temperature provided convenient access to the corresponding N,N,O-tridentate palladium(II) complexes [Pd(OAc){ArCONHC(N(CH₂Py)}SCH₂C₆H₅] (Ar = C₆H₅ (3a); 4-F-C₆H₄ (3b); 4-Br-C₆H₄ (3c); 4-I-C₆H₄ (3d); 4-Me-C₆H₄ (3e); 3,4,5-(OMe)₃-C₆H₂ (3f)) in almost quantitative yields. The new ligands and their palladium complexes were characterized by NMR, IR, ESIMS, and HRMS analysis. The molecular structure of complex 3c has been determined by X-ray single-crystal diffraction. These Pd(II) complexes have been used as catalysts for the Suzuki–Miyaura, Sonogashira, Heck and Hiyama cross-coupling reactions.