Palladium(II) complexes with salicylideneimine based tridentate ligand and triphenylphosphine: Synthesis, structure and catalytic activity in Suzuki–Miyaura cross coupling reactions

Square planar palladium(II) complexes of the type [Pd(L)(PPh3)] (1–6) (where L is the dianion of N-(2-mercaptophenyl)salicylideneimine or 5-substituted-N-(2-mercaptophenyl)salicylideneimine or N-(2-mercaptophenyl)naphthylideneimine) have been synthesised from the reactions between [Pd(PPh3)4] and H2L in dichloromethane–ethanol mixture. The new complexes have been characterized by analytical and spectral (electronic, IR, 1H, 13C{1H} and 31P{1H} NMR spectroscopy) techniques. The structures of three complexes (1, 2 and 6) have been solved by single-crystal X-ray diffraction experiments which indicate square planar coordination geometries around palladium(II) by O, N, S and P donor atoms. The palladium(II) complexes (1–6) exhibited good catalytic activity in Suzuki–Miyaura cross-coupling reaction between phenylboronic acid and 4-bromotoluene in N,N-dimethylacetamide at 100 °C. Complex 3 (1 mol%) was found to be the most active and hence was used for probing the scope of possible substrates. Heterocyclic boronic acid and heterocyclic aryl bromides have also been used as substrates to provide heterocyclic biaryls.