Ethylene Polymerization and Copolymerization with Polar Monomers by Benzothiophene-bridged BPMO-Pd Catalysts

Abstract

A series of new bisphosphine-monoxide (BPMO) ligands based on benzothiophene backbone and the corresponding palladium complexes {K2-2-P(O)(Ph)2-3-PR1R2-C8H4S}PdMeCl {2a: R1 = R2 = Ph; 2b: R1 = R2 = 2-OMe-Ph; 2c: R1 = R2 = 2-CF3-Ph; 2d: R1 = Ph, R2 = 2-(2′,6′-(OMe)2C6H3)-C6H4} were synthesized and fully characterized by 1 H-, 13C-, 31P-, and 2D-NMR spectroscopy and single-crystal X-ray diffraction. In the presence of Na+B[3,5-(CF3)2C6H3]4− (NaBArF), these complexes showed very high activities (up to 2.0 × 107 gmo−1·h−1) for ethylene polymerization. More significantly, these catalysts enabled the copolymerization of ethylene with a broad scope of commercially available polar comonomers such as acrylates, acrylic acid, acrylonitrile, vinyltrialkoxysilane, allyl acetate, and long-chain 6-chloro-1-hexene to give functionalized polyethylene with reasonable catalytic activities (up to 106 g·mol−1·h−1) and incorporations (up to 5.3 mol%). This contribution suggests that, besides the modulation of conventionally steric and electronic factors, the connectivity (at different linking positions) of BPMO (P,O) donors to the heteroaryl backbone also greatly influences the catalyst properties in terms of catalytic activity, polymer branching content, comonomer scope, and comonomer incorporation.