@article{Mecking1998Mecha-9686,
  year={1998},
  doi={10.1021/ja964144i},
  title={Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and alpha-Olefins with Methyl Acrylate},
  number={5},
  volume={120},
  issn={0002-7863},
  journal={Journal of the American Chemical Society},
  pages={888--899},
  author={Mecking, Stefan and Johnson, Lynda K. and Wang, Lin and Brookhart, Maurice}
}

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    <dc:creator>Wang, Lin</dc:creator>
    <dcterms:issued>1998</dcterms:issued>
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    <dc:contributor>Mecking, Stefan</dc:contributor>
    <dc:creator>Mecking, Stefan</dc:creator>
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    <dcterms:title>Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and alpha-Olefins with Methyl Acrylate</dcterms:title>
    <dc:creator>Johnson, Lynda K.</dc:creator>
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    <dc:contributor>Brookhart, Maurice</dc:contributor>
    <dcterms:abstract xml:lang="eng">Mechanistic aspects of palladium-catalyzed insertion copolymerizations of ethylene and α-olefins with methyl acrylate to give high molar mass polymers are described. Complexes [(N^N)Pd(CH2)3C(O)-OMe]BAr'4 (2) or [(N^N)Pd(CH3)(L)]BAr'4 (1: L = OEt2; 3: L ≡ NCMe; 4: L ≡ NCAr') (N^N ≡ ArN = C(R)-C(R)= NAr, e.g., Ar ≡ 2,6-C6H3(i-Pr)2, R ≡ H (a), Me (b); Ar' ≡ 3,5-C6H3(CF3)2) with bulky substituted α-diimine ligands were used as catalyst precursors. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches as -CH2CH2C(O)OMe groups. The effects of reaction conditions and catalyst structure on the copolymerization reaction are rationalized. Low-temperature NMR studies show that migratory insertion in the η2-methyl acrylate (MA) complex [(N^N)- PdMe{H2C=CHC(O)OMe}]+ (5) occurs to give initially the 2,1-insertion product [(N^N)PdCH(CH2CH3)C-(O)OMe]+ (6), which rearranges stepwise to yield 2 as the final product upon warming to -20 °C. Activation parameters (ΔH  = 12.1 ± 1.4 kcal/mol and ΔS  = -14.1 ± 7.0 eu) were determined for the conversion of 5a to 6a. Rates of ethylene homopolymerization observed in preparative-scale polymerizations (1.2 s-1 at 25°C, ΔG  = 17.4 kcal/mol for 2b) correspond well with low-temperature NMR kinetic data for migratory insertion of ethylene in [(N^N)Pd{(CH2)2nMe}(H2C=CH2)]+. Relative binding affinities of olefins to the metal center were also studied. For [(N^N)PdMe(H2C=CH2)]+ + MA  5a + H2C=CH2, Keq(-95 °C) = (1.0 ± 0.3) X 10-6 was determined. Combination of the above studies provides a mechanistic model that agrees well with acrylate incorporations observed in copolymerization experiments. Data obtained for equilibria 2 + H2C=CHR"  [(N^N)Pd{(CH2)3C(O)OMe}(H2C=CHR")]+ (R"≡ H, Me, nC4H9) shows that chelating coordination of the carbonyl group is favored over olefin coordination at room temperature. Formation of chelates analogous to 2 during the copolymerization is assumed to render the subsequent monomer insertion a turnover-limiting step.</dcterms:abstract>
    <dcterms:bibliographicCitation>First publ. in: Journal of the American Chemical Society ; 120 (1998), 5. - S. 888-899</dcterms:bibliographicCitation>
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    <dc:contributor>Johnson, Lynda K.</dc:contributor>
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