Pentiptycenyl Substituents in Insertion Polymerization with α-Diimine Nickel and Palladium Species

Motivated by the need for a new generation of α-diimine Ni­(II) and Pd­(II) catalysts for tuning the catalytic activity, polymer molecular weight, comonomer incorporation, and branching density in ethylene polymerization and copolymerization with polar monomers, a family of α-diimine Ni­(II) and Pd­(II) catalysts Ipty-Ni1–4 and Ipty-Pd1–4 derived from sterically demanding and rotationally restricted pentiptycenyl N-aryl substituents were synthesized and fully characterized by NMR, IR, MALDI-TOF, elemental analysis, and X-ray diffraction. Pentiptycenyl-substituted Ni­(II) and Pd­(II) catalysts were further probed in ethylene (co)­polymerization as a comparison with the rotationally free dibenzhydryl substituent reported previously. In the Ni-catalyzed ethylene polymerization (20–80 °C), catalytic activities ((0.64–3.74) × 106 g mol–1 h–1), polymer molecular weights ((1.1–37.7) × 104 g mol–1), branching densities (6–55/1000C), and melting points (94–135 °C) could be tuned over a broad range. In the Pd-catalyzed ethylene polymerization, these catalysts gave varied catalytic activities ((1.4–54.7) × 104 g mol–1 h–1) and polymer molecular weights ((0.8–39.6) × 104 g mol–1), but similar branching densities (62–72/1000C). Furthermore, these palladium catalysts exhibited a high MA incorporation of 1.0–4.1 mol % in the copolymerization of ethylene and methyl acrylate (MA). On the basis of these results, comparisons of the pentiptycenyl-derived and the dibenzhydryl-derived α-diimine Ni­(II) and Pd­(II) catalysts on ethylene (co)­polymerization were made in detail.