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.

Graphical abstractSix square planar Pd(II) complexes have been prepared from the reactions between [Pd(PPh3)4] and salicylideneimine based tridentate ligands, and characterized by spectroscopic and single crystal X-ray diffraction methods. The Pd(II) complex which contains 5-methoxy-N-(2-mercaptophenyl)salicylideneimine showed efficient catalytic activity in Suzuki–Miyaura cross coupling reactions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of Pd(II) complexes containing ONS donor tridentate ligand and PPh3. ► 1H–31P HMBC spectra established the coupling of P atom with azomethine proton. ► The structures of three of the complexes were studied by X-ray crystallography. ► Pd(II) complexes showed catalytic activity in Suzuki–Miyaura coupling reactions.