Norbornene and methyl methacrylate polymerizations catalyzed by palladium(II) complexes bearing aminomethylpyridine and aminomethylquinoline derivatives

A series of Pd(II) complexes, 1–4 bearing N,N-bidentate aminomethylpyridine and aminomethylquinoline derivatives were synthesized and characterized. Single crystal X-ray diffraction analysis demonstrated that tetra-coordinated Pd(II) complexes adopted distorted square planar geometries around the metal center. In the presence of modified methylaluminoxane (MMAO) as a co-catalyst, Pd(II) complexes 1–4 exhibited significant activities (up to 43.2×10⁵ g_PNB mol Pd⁻¹ h⁻¹) towards the addition polymerization of norbornene (NB) at 25 ℃. Insoluble poly(norbornene) (PNB) was obtained by all the tested catalytic systems, i.e., 1–4/MMAO. The catalytic capabilities of synthesized Pd(II) complexes were also tested towards methyl methacrylate (MMA) in the presence of modified methyl aluminoxane MMAO. Complex 3 with quinoline/piperidine functionalities showed the highest catalytic activity of 8.83×10⁴ g_PMMA mol Pd⁻¹ h⁻¹ at 60°C and resulted in high molecular weight PMMA (M_w = 2.16×10⁶ g mol⁻¹). All the complexes yielded syndiotactic poly(methyl methacrylate) (PMMA) (rr = 0.70). Notably, the steric bulk and electronic properties of the ligand framework affect their activities towards NB and MMA polymerizations, whereas, for PMMA, the stereoselectivities remained unaffected.