Heteroaryl Backbone Strategy in Bisphosphine Monoxide Palladium-Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

The backbone structure of ligand is of critical importance to modulate the selectivity and the reactivity of catalyst. In this contribution, heteroaryl backbone (benzo)thiophene was for the first time installed on bisphosphine-monoxide (PO) ligands. Corresponding palladium complexes {κ2-2-P(2-OMe-Ph)2-3-P(O)(Ph)2-4–Br-C4HS}PdMeCl (2a) and {κ2-2-PR1R2-3-P(O)(Ph)2-C8H4S}PdMeCl {2b: R1 = R2 = 2-OMe-Ph; 2c: R1 = R2 = Cy; 2d: R1 = Ph, R2 = 2-(2′,6′-(OMe)2C6H3)-C6H4} and the compared phenylene-linked palladium complex {κ2-1-P(2-OMe-Ph)2-2-P(O)(Ph)2-C6H4}PdMeCl (2e) were synthesized and fully characterized by 1H, 13C, 31P, and 2D-NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (2a, 2b, and 2d). In the presence of Na+B[3,5-(CF3)2C6H3]4– (NaBArF4), these complexes showed high activities (up to 10 000 kg mol–1 h–1) for ethylene polymerization that are comparable to the prototype phenylene-linked BPMO-Pd catalysts, producing moderate to high molecular weight (Mn up to 90 kDa) linear polyethylenes. These catalysts also copolymerized ethylene with various commercially available polar monomers, such as acrylates, acrylic acid, and vinyl butyl ether, to give linear functionalized polyethylenes with reasonable catalytic activities and moderate copolymer molecular weights and comonomer incorporations. This work provides new ligand backbones that span donor fragments, and points to new opportunities in catalyst designing for olefin (co)polymerization.