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

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-ⁱPr₂-Ph)­NCMeCMeN­(2-CONHMe-6-ⁱPr-Ph)}­PdMeCl (1a,a′) and {(2,6-ⁱPr₂-Ph)­NCMeCMeN­(2-CONMe₂-6-ⁱPr-Ph)}­PdMeCl (1b,b′) and the “second-generation” catalysts [{2,6-(CHPh₂)₂-4-Me-Ph}­NCMeCMeN­(2-CONHMe-6-ⁱPr-Ph)]­PdMeCl (1d,d′) and [{2,6-(CHPh₂)₂-4-Me-Ph}­NCMeCMeN­(2-CONMe₂-6-ⁱPr-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 ⁱPr-substituted catalyst [{2,6-(CHPh₂)₂-4-Me-Ph}­NCMeCMeN­(2,6-ⁱPr₂-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.