Vinyl-addition polymerizations of norbornene and methyl methacrylate by the palladium(II) complexes ligated by 2-iminomethylquinoline and 2-iminomethylpyridine derivatives

Novel Pd(II) complexes, namely, [L_nPdCl₂] (L_n = L_A and L_B), where L_A is (E)-3-methoxy-N-(quinolin-2-ylmethylene)propan-1-amine and L_B is (E)-N-(pyridin-2-ylmethylene)hexan-1-amine, were synthesized and characterized. X-ray diffraction studies revealed distorted square planar geometries around the Pd(II) center in [L_nPdCl₂] (L_n = L_A and L_B). The catalytic capabilities of the synthesized complexes were tested in vinyl addition polymerization of norbornene (NB) in the presence of the cocatalyst modified methylaluminoxane (MMAO), displaying high activities with conversions ≥ 94% in chlorobenzene at 25 °C. The complex [L_BPdCl₂] displayed the highest activity of up to 4.40 × 10⁶ g_PNB mol Pd⁻¹ h⁻¹ at 25 °C, generating insoluble polynorbornene (PNB) at an NB/Al/Pd ratio of 8,000:500:1. In addition, preliminary methyl methacrylate (MMA) polymerization studies of the [L_nPdCl₂]/MMAO system demonstrated that the activities toward polar vinyl monomer production were in the range of 8.00 × 10⁴ to 8.20 × 10⁴ g_PMMA mol Pd⁻¹ h⁻¹ at 60 °C, yielding a high-molecular-weight syndiotactic poly(methyl methacrylate) (PMMA, M_w = 1.89 × 10⁶ g mol⁻¹).