Some Evidence of a Dual Stereodifferentiation Mechanism in the Polymerization of Propene by α-Diimine Nickel Catalysts

Pappalardo, Daniela; Mazzeo, Mina; Antinucci, Simona; Pellecchia, Claudio

doi:10.1021/ma000982s

Cited by 72 publications

(37 citation statements)

References 26 publications

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“…The decreased activity observed with an increase of the steric hindrance in the apical position can be explained by assuming that the C s -symmetric ligand has a smaller productivity than the C 2 -symmetric one, [50] as observed in both CO/styrene copolymerization [14] and polymerization of propylene. [51] It is also reasonable that an increase of the coordinating ability of the counterion reduces the activity of C ssymmetric catalysts more than C 2 -symmetric ones, therefore in ortho-monosubstituted catalysts the counterion exerts a twofold role by decreasing the rate of copolymerization of the individual isomers in a differential way and changing the relative amounts of the four possible isomers.…”

Section: Activitymentioning

confidence: 99%

The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II)–Diimine Catalysts for CO/p‐Methylstyrene Copolymerization

Binotti

Bellachioma

Cardaci

et al. 2007

Chemistry A European J

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The catalytic activity and stereoselectivity of complexes [Pd(eta(1),eta(2)-C(8)H(12)OMe)(Ar--N==C(R')--C(R')==N--Ar)]X in the copolymerization of CO and p-methylstyrene have been correlated with their interionic structure in solution and in the solid state, as determined by (19)F,(1)H-HOESY NMR spectroscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine ligands bearing electron-donating substituents and with the least coordinating counterion. Copolymers with a microstructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical positions and the coordinating ability of the counterion increase. The counterion is located close to the diimine in both solution and the solid state but it moves toward the palladium as the steric hindrance in the apical positions decreases. When the latter is small the counterion competes with the substrate for apical coordination, and consequently it affects the productivity. In the case of ortho-dimethyl-substituted ligands the counterion is confined in the back, above the N==C(R')--C(R')==N moiety, and does not affect the productivity. However, it contributes to increasing the stereoregularity of the copolymer by making the aryl moieties more rigid. With R'=Me and Ar=o-Me(2)C(6)H(3) an ll of 81 % and 72 % was obtained with X(-)=CF(3)SO(3) (-) or BArF(-), respectively. The isotacticity of the copolymers produced by ortho-monosubstituted catalysts depends greatly on the counterion and ranges from 30 % to 59 % with X(-)=BArF(-) and X(-)=CF(3)SO(3) (-), respectively, with Ar=o-EtC(6)H(4) and R'=Me. Based on the interionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of C(s)-symmetric isomers with respect to their C(2)-symmetric counterparts.

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Section: Activitymentioning

confidence: 99%

The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II)–Diimine Catalysts for CO/p‐Methylstyrene Copolymerization

Binotti

Bellachioma

Cardaci

et al. 2007

Chemistry A European J

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“…The other unsymmetrical (-diimine)nickel(II) catalysts were synthesized according to the literatures. 21,30 The ortho substituents on aromatic rings of the unsymmetrical (-diimine)nickel(II) catalysts are composed of isopropyl and methyl groups. The unsymmetrical (-diimine)nickel(II) catalyst 3b and 3e have C 1 symmetry.…”

Section: Resultsmentioning

confidence: 99%

Ethylene Polymerizations with Unsymmetrical (α-Diimine)nickel(II) Catalysts

Jeon

Kim

2008

Polym J

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Four unsymmetrical (-diimine)nickel(II) catalysts were synthesized by sequential stepwise condensation of acenaphthenequinone with the corresponding aniline compounds and subjected to ethylene polymerizations with MAO. Interestingly, when the catalysts have the same composition of the ortho substituents, the catalyst with two ortho isopropyl substitients on one side and two ortho methyl substituents on the other side produced polyethylenes with higher branching densities and lower molecular weights than the catalyst with one ortho isopropyl and one ortho methyl substituent on each side. However, branch distribution was not changed by the position of the ortho substituents. The catalysts have unique characteristic, production of branched polyethylene only from ethylene monomers. A chain walking (-hydride elimination and readdition to the other carbon) followed by ethylene coordination and insertion produces a methyl branch. Repeated chain walkings followed by ethylene coordination and insertion make a longer branch.Control of ortho substituents on aromatic rings of (-diimine)nickel(II) catalysts is important to achieve a proper catalytic activity. 13 The ortho substituents have been reported to locate at axial site of the catalysts, and they retard chain transfer reactions, promote the chain walking, and accelerate the rate of migratory insertion. Therefore, as steric bulkiness of the ortho substituents increases, molecular weights of polyethylenes, branching densities of polyethylenes, and polymerization activities increased.14 Some researchers further modified the ortho substituents of the (-diimine)nickel(II) catalysts to get novel polymerization results. Brookhart et al. reported that electron withdrawing ortho substituents of the (-diimine)-nickel(II) catalyst increased turnover frequency of ethylene polymerization presumably because electron withdrawing ortho substituents made nickel more electrophilic.14 Rieger et al. reported chiral C 2 symmetric (-diimine)nickel(II) catalysts bearing ortho phenyl substituents produced high molecular weight polyethylenes with high activities.15 Guan et al. reported cyclophane-based (-diimine)nickel(II) catalyst which was highly active for ethylene polymerizations even at high temperature ($90 C). 16 Zhu et al. reported that molecular weights of the polyethylenes produced by rac-(-diimine)-nickel(II) catalyst were significantly higher than those produced by meso-(-diimine)nickel(II) catalyst. 17Another way to modify the ortho substituents of the (-diimine)nickel(II) catalysts is making the (-diimine)nickel(II) catalysts as unsymmetric. But there have been few reports on ethylene polymerizations with unsymmetrical (-diimine)-nickel(II) catalysts due to the lack of proper synthetic method for unsymmetrically substituted -diimine ligands. [18][19][20][21][22] In this study, new unsymmetrical (-diimine)nickel(II) catalysts were synthesized by stepwise acid catalyzed condensation reaction followed by condensation with TiCl 4 /DABCO. The catalysts were subjected to ethylene poly...

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“…Room-temperature polymerizations with both Ni and Pd initiators yield atactic polypropene. Low temperature polymerizations proceed by chain end control to yield moderate syndioselectivity, (rr) as high as 0.8, but usually less McCord et al, 2001;Pappalardo et al, 2000;Zambelli et al, 2001].…”

Section: -8b A-diimine Chelates Of Late Transition Metalsmentioning

confidence: 99%

Stereochemistry of Polymerization

Odian

2004

Principles of Polymerization

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Constitutional (formerly: structural) isomerism is encountered when polymers have the same overall chemical composition (i.e., same molecular formula) but differ in connectivitythe order in which the atoms are connected to each other. Polyacetaldehyde, poly(ethylene oxide), and poly(vinyl alcohol) are constitutional isomers. The first two polymers are CH CH 3 O C H 2 CH OH CH 2 CH 2 O n n Polyacetaldehyde Poly(ethylene oxide) Poly(vinyl alcohol) n obtained from isomeric monomers, acetaldehyde and ethylene oxide. The third is obtained by hydrolysis of poly(vinyl acetate) since vinyl alcohol does not exist (it is the enol form of acetaldehyde). Poly(methyl methacrylate) and poly(ethyl acrylate) are isomeric polymers CH 2 C CH 3 CO 2 CH 3 CH 2 CH CO 2 C 2 H 5 n n Poly (methyl methacrylate) Poly (ethyl acrylate) formed from isomeric monomers. Poly(E-caprolactam) and poly(hexamethylene adipamide) are isomeric even though the monomers are not isomeric. Similarly, the 1 : 1 copolymer of Principles of Polymerization, Fourth Edition.

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Some Evidence of a Dual Stereodifferentiation Mechanism in the Polymerization of Propene by α-Diimine Nickel Catalysts

Cited by 72 publications

References 26 publications

The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II)–Diimine Catalysts for CO/p‐Methylstyrene Copolymerization

The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II)–Diimine Catalysts for CO/p‐Methylstyrene Copolymerization

Ethylene Polymerizations with Unsymmetrical (α-Diimine)nickel(II) Catalysts

Stereochemistry of Polymerization

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