Copolymerization of Ethylene with Acrylate Monomers by Amide-Functionalized α-Diimine Pd Catalysts

Abstract

We report the ethylene homopolymerization and ethylene/methyl-acrylate (MA) and ethylene/acrylic-acid (AA) copolymerization behavior of a series of (N,N′-diaryl-α-diimine)­Pd catalysts that contain secondary amide (−CONHMe) or tertiary amide (−CONMe2) substituents on the N-aryl rings, including the “first-generation” catalysts {(2,6- i Pr2-Ph)­NCMeCMeN­(2-CONHMe-6- i Pr-Ph)}­PdMeCl (1a,a′) and {(2,6- i Pr2-Ph)­NCMeCMeN­(2-CONMe2-6- i Pr-Ph)}­PdMeCl (1b,b′) and the “second-generation” catalysts [{2,6-(CHPh2)2-4-Me-Ph}­NCMeCMeN­(2-CONHMe-6- i Pr-Ph)]­PdMeCl (1d,d′) and [{2,6-(CHPh2)2-4-Me-Ph}­NCMeCMeN­(2-CONMe2-6- i Pr-Ph)]­PdMeCl (1e,e′). Activation of 1d,d′ and 1e,e′ by NaB­{3,5-(CF3)2C6H3}4 generates active ethylene polymerization catalysts that produce highly branched (77–81 br/1000 C) polyethylenes with number-average molecular weights (M ns) in the range 26–60 kDa. The replacement of two isopropyl units in 1a,a′ and 1b,b′ with benzhydryl groups in 1d,d′ and 1e,e′ leads to a significant improvement in ethylene homopolymerization performance. The secondary amide-functionalized catalyst 1d,d′ incorporates ca. twice as much MA and ca. three times as much AA as the i Pr-substituted catalyst [{2,6-(CHPh2)2-4-Me-Ph}­NCMeCMeN­(2,6- i Pr2-Ph)]­PdMeCl (1f,f′) in copolymerization with ethylene. The reactions of 1a,a′ and 1b,b′ with metal salts that contain weakly coordinating anions lead to extrusion of CH4 and the formation of [{(μ-κ2-N,N′,κ-O-α-diimine)­Pd}2(μ-CH2)]2+ complexes, in which the amide carbonyl O atoms coordinate to Pd centers.

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

“…23) containing -CONHMe or -CONMe 2 groups on the N-phenyl rings. 153 In ethylene polymerization, i Pr-substituted C45c and C45d showed a higher activity of 10 7 g PE (mol Ni h) −1 than C45a and C45b with ortho-dibenzhydryl groups, and yielded branched (77-81 branches/1000 C) PEs with M n values in the range of 2.6-60 × 10 4 g mol −1 . In ethylene copolymerization, the incorporated levels of MA (Scheme 5) and acrylic acid (AA) using C45a were higher than 45b and i Pr-substituted C8a.…”

“…23 Amide-functionalized α-diimine Pd catalysts. 153 Only recently, Chen and co-workers have studied the ethylene copolymerizations with a family of polar functionalized norbornene type comonomers or nitrogen-containing monomers (NB-NP, NB-OAc and NP, Scheme 5) using paramethoxy substituted α-diimine palladium catalyst C13a. 156 Branched high molecular weight copolymers (55-89/1000 C; M n up to 125 000) with good comonomer incorporations (1.1-9.1%) were obtained.…”

Crystal structure of 3-[(2-acetamidophenyl)imino]butan-2-one

“…Our group is interested in N,N-diaryl -diimine ligands that contain hydrogen-bonding units for transition-metal-catalyzed copolymerization of polar vinyl monomers with ethylene (Zhai & Jordan, 2014;Zhai et al, 2017). We obtained the title compound during the attempted synthesis of an -diimine compound containing an ortho-acetamido group and report its crystal structure in the present work.…”

Tailored Strength Neighboring Group Interactions Switch Polymerization to Dimerization Catalysis

“…Notably, also for other late transition metal catalyst structures the role of substituents' attractive 'secondary' interactions with substrates and the active site is being revealed. [16][17][18] This recently gained understanding provokes the question how stronger such neighbouring group interactions affect catalysis, that is promote certain pathways strongly without shutting down activity due to blocking of the active site. We now show that appropriately placed additional O-donors hit this spot.…”