Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers

Y. Mitsushige, H. Yasuda, B. P. Carrow, S. Ito, M. Kobayashi, T. Tayano, Y. Watanabe, Y. Okuno, S. Hayashi, J. Kuroda, Y. Okumura, K. Nozaki*
ACS Macro Lett. 2018, 7, 305–311. DOI: 10.1021/acsmacrolett.8b00034

Abstract: A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ2-P,O-(R12P)CH2P(O)R22]PdMe(2,6-lutidine)][BArF4] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. X-ray crystallographic analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd−O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost constant Pd−P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R2 = Me) showed the best catalytic performance in the homo- and copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R1 = t-Bu; R2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymerization of ethylene and allyl acetate (≤12.0 mol %) or methyl methacrylate (≤0.6 mol %). The catalytic system represents one of the first examples of late-transition-metal complexes bearing an alkylene-bridged bidentate ligand that afford high-molecular-weight copolymers from the copolymerization of ethylene and polar monomers.

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