Palladacyclic complexes bearing CNN-type ligands as catalysts in the Heck reaction

Abstract

Preparations of novel unsymmetrical, tridentate nitrogen ligand precursors, PhNC(CMe₂)(NPh)CN(CH₂)₂NMe₂ (1) and PhNC(CMe₂)(NPh)CN(CH₂)Py (2), are described. Treatment of 1 with 1 molar equiv. (COD)PdCl₂ in the presence of NEt₃ or with 1 molar equiv. Pd(OAc)₂ affords orthometallated palladium(II) complexes, [PhNC(CMe₂)(N-η¹-Ph)CN(CH₂)₂NMe₂]PdX (X = Cl (3); X = OAc (4)), respectively. Compound 3 can be yielded via the reaction of 4 with an excess of LiCl in methanol. Treatment of 2 with 1 molar equiv. of (COD)PdCl₂, Pd(OAc)₂ or Pd(TFA)₂ affords orthometallated palladium(II) complexes, [PhNC(CMe₂)(N-η¹-Ph)CNCH₂Py]PdX (X = Cl (5); X = OAc (6); X = TFA (7)), respectively. The crystal and molecular structures are reported for compounds 2, 3, 5 and 6. The application of these novel palladacyclic complexes to the Heck reaction with aryl halide substrates was examined.