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-alpha-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-Pr-i(2)-Ph)N-CMeCMe-N(2-CONHMe-6-Pr-i-Ph)}PdMeCl (1a,a') and {(2,6-Pr-i(2)-Ph)N-CMeCMe-N(2-CONMe2-6-Pr-i-Ph)}PdMeCl (1b,b') and the second-generation catalysts [{2,6-(CHPh2)(2)-4-Me-Ph}N-CMeCMe-N(2-CONHMe-6-Pr-i-Ph)]PdMeCl (1d,d') and [{2,6-(CHPh2)(2)-4-Me-Ph}N-CMeCMe-N(2-CONMe2-6-Pr-i-Ph)]PdMeCl (1e,e'). Activation of 1d,d' and 1e,e' by NaB{3,5-(CF3)(2)C6H3}(4) generates active ethylene polymerization catalysts that produce highly branched (77-81 br/1000 C) polyethylenes with number-average molecular weights (M(n)s) in the range 2660 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-Pr-i(2)-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 [{(mu-k(2)-N,N',k-O-a-diimine)Pd}2(mu-CH2)](2+) complexes, in which the amide carbonyl O atoms coordinate to Pd centers.