Thiophene based imino-pyridyl palladium(II) complexes: Synthesis, molecular structures and Heck coupling reactions

The new compounds (5-methyl-2-thiophene-2-pyridyl(R))imine [R = methyl (L1); R = ethyl (L2)] and (5-bromo-2-thiophene-2-pyridyl(R)imine [R = methyl (L3); R = ethyl (L4)] were successfully synthesized via Schiff base condensation reaction and obtained in good yields. These potential ligands were reacted with [PdCl₂(COD)] and [PdClMe(COD)] to give the corresponding complexes [PdCl₂(L)] (L = L1-L4; 1–4) and [PdClMe(L)] (L = L1-L4; 5–8). All compounds were characterized by IR, ¹H and ¹³C NMR spectroscopy, elemental analysis and mass spectrometry. The molecular structures of 1, 2, 6 and 8 were confirmed by X-ray crystallography. The complexes were evaluated as catalyst precursors for standard Heck coupling reactions and showed significant catalytic activities that could be correlated with steric and electronic influences.