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

Abstract

A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ 2 -(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 (R 1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R 2 = Me) showed the best catalytic performance in the homo-and copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R 1 = t-Bu; R 2 = 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.

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

“…7,8 Recently, phosphine-containing palladium catalysts have emerged as powerful alternatives for ethylene copolymerization with polar comonomers. [9][10][11][12][13][14][15][16][17][18][19][20][21] Some of these catalysts possessed comparably even better properties than α-diimine palladium catalysts in copolymerization reactions. However, the Brookhart-type α-diimine-based precatalysts continue to be of great research interest for the reasons that include: (i) the ease of synthesis for both the ligands and the metal complexes, (ii) the versatility of the ligand structures, (iii) the ability to tune the polymer microstructures such as branching and topologies, etc.…”

Mechanistic Studies for Palladium Catalyzed Copolymerization of Ethylene with Vinyl Ethers

“…In addition, bisphosphine monoxide (BPMO) also produces highly linear copolymer microstructures with a random distribution of polar functional groups throughout the polymer chain [ 18 ]. Further, investigations to improve the reactivity and incorporation by modifying the ligand platform, backbone, or substituting group has provided new routes for the catalyst tuning [ 19 , 20 , 21 , 22 ]. To date, the low incorporation of polar monomers and copolymers with low molecular weight is still a challenge.…”

Ethylene (co)Oligomerization by Phosphine‐Pyridine Based Palladium and Nickel Catalysts

“…These cooligomerization parameters are much worse than those of phosphine‐sulfonate palladium catalysts. However, this does represent one of the few catalyst systems that can enable ethylene copolymerizations/cooligomerizations with a series of industrially relevant polar comonomers . The ethylene oligomer generated by Pd‐CH 2 at 20 °C is highly linear based on 13 C NMR analysis (Figure S48, B=3 per 1000 carbon atoms).…”