Sterically very bulky aliphatic/aromatic phosphine-sulfonate palladium catalysts for ethylene polymerization and copolymerization with polar monomers

Abstract

A class of sterically very bulky aliphatic/aromatic phosphine-sulfonate ligands L1–L4 and the corresponding neutral palladium complexes 1–4 {[κ²(P,O)-(menthyl)ArP(C₆H₄SO₂O)]PdMe(pyr)} (1: Ar = 2-(2′,6′-(MeO)₂C₆H₃)C₆H₄; 2: Ar = 2-(C₆H₅)C₆H₄; 3: Ar = 2-(2′,6′-F₂C₆H₃)C₆H₄; 4: Ar = (MeO)₃C₆H₂) were synthesized and comprehensively identified by NMR spectroscopy, single-crystal X-ray diffraction, and elemental analysis. All of these palladium catalysts were employed in ethylene polymerization, generating highly linear polyethylenes (methyl branches < 1/1000 C) with a high molecular weight (up to 19.4 × 10⁴ g mol⁻¹) in a high activity of up to 3.3 × 10⁶ g mol⁻¹ h⁻¹. More remarkably, in the copolymerization of ethylene and a variety of challenging polar vinyl monomers such as acrylate, acrylic acid, acrylamide, vinyl ether, vinyl acetate, and acrylonitrile, the preferred catalysts 3 and 4 again showed significantly high activity, affording highly linear functionalized polyethylenes with a clearly enhanced molecular weight. Especially for the copolymerization of acrylates with ethylene, both the catalytic activity and the copolymer molecular weight are close to the same order of magnitude for ethylene homopolymerization, which are up to 10⁶ g mol⁻¹ h⁻¹ and 10⁵ g mol⁻¹, respectively.