Synthesis and structural characterisation of Palladium(ii) complexes with N,N′,N-tridentate N′-substituted N,N-Di(2-picolyl)amines and their application to methyl methacrylate polymerisation

The reaction of [Pd(CH₃CN)₂Cl₂] with N′-substituted N,N-di(2-picolyl)amine-based ancillary ligands, for example N,N-di(2-picolyl)cyclohexylmethylamine (L1), N,N-di(2-picolyl)benzylamine (L2), N,N-di(2-picolyl)aniline (L3), and 1,4-bis[bis(2-pyridylmethyl)aminomethyl] benzene (L4), in the presence of NaClO₄ in ethanol yields a new series of [(NN′N)PdCl]X (X≤ClO₄, Cl) complexes, i.e. mononuclear [LnPdCl]ClO₄ (Ln≤L₁, L₂, L ₃) and binuclear [L₄Pd₂Cl₂]Cl ₂. X-Ray crystallographic analysis determined that the Pd atom in complexes [(NN′N)PdCl]X showed a slightly distorted square-planar geometry involving three nitrogen atoms and a chlorido ligand. Moreover, the unit cell included a ClO₄-or Cl-anion as the counterion. The complex [L1PdCl]ClO₄ showed the highest catalytic activity for the polymerisation of methyl methacrylate in the presence of modified methylaluminoxane at 60°C among the mononuclear PdII complexes. Specifically, the activity of binuclear [L₄Pd₂Cl ₂]Cl₂ was 2-fold higher than the corresponding mononuclear [L₂PdCl]ClO₄ per active palladium metal centre.