Chirality of Catalysts for Stereospecific Polymerizations

Guerra, Gaetano; Cavallo, Luigi; Corradini, Paolo

doi:10.1002/0471471895.ch1

Cited by 20 publications

(10 citation statements)

References 73 publications

(134 reference statements)

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“…Borrowing the language of conventional polymer stereochemistry, 97 we will call these syndiotactic, isotactic, and atactic. In a random distribution of pairwise interactions, we can presume that there will exist lengths related by only the center of symmetry, lengths related by only the long axis diad, and lengths in which there is a stochastic arrangement of dimers with these two pairwise relationships.…”

Section: Resultsmentioning

confidence: 99%

Structural Correspondence of Solution, Liquid Crystal, and Crystalline Phases of the Chromonic Mesogen Sunset Yellow

Xiao

Carter

et al. 2014

Crystal Growth & Design

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The azo dye, sunset yellow, is a prototypical, chromonic liquid crystal in which assembly in aqueous solution at high volume fraction leads to lyotropic mesophases with a "package of properties distinct in almost every aspect" (Lydon, J. Curr. Opin. Colloid Interfac. Sci. 2004, 8, 480). In particular, the isotropic to nematic transition in such phases, the consequence of stacking of dye molecules in chains, is difficult to bring into correspondence with athermal theories for rigid rods as well as modifications that consider chain interactions with one another. Chromonic mesogens, small molecules that stack to form lyotropic liquid crystals, prompt structural questions that have yet to be answered; a full understanding of structure should inform colligative properties. Herein, the single crystal structure of a guanidinium salt of the sunset yellow dianion, a known chromonic mesogen, is reported. The compound crystallizes as a dihydrate, tetrahydrofuran solvate in the orthorhombic space group Pnna, with a = 6.8426 (5) Å, b = 20.048(1) Å, c = 21.466(2) Å. The sunset yellow molecules, point group approximately C s , are disordered about a crystallographic diad axis. The structure is informative because pairwise interactions in the disordered crystal structure show a remarkable correspondence with the stereochemistry of sunset yellow molecules in solution and in the liquid crystal phase. The solution structure is here simulated by the combination of molecular dynamics, metadynamics, and quantum chemical computations. The comparable disorder in the fluid and solid states suggests the possibility that stacked aggregates adhere to growing crystals intact. Computations evaluated proposals that stacking faults and branching pointslower the X-ray correlation lengths while preserving extended structures. Evidence is found for stacking faults but not branches. The solution stereochemistry and stereodynamics has implications for the geometry of long rods, for which understanding is a prerequisite for reckoning properties of vexing chromonic mesophases.

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Section: Resultsmentioning

confidence: 99%

Structural Correspondence of Solution, Liquid Crystal, and Crystalline Phases of the Chromonic Mesogen Sunset Yellow

Xiao

Carter

et al. 2014

Crystal Growth & Design

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“…The structures in Scheme , left to right, correspond to the most favored transition state for propagation (PR in the following) and to the transition states leading to a SM and a RM. They are well accepted in the literature. ,,,− At this point, it is worthy to note that the same propene enantioface is involved in the transition states leading to a SM or a RM. For this reason, we define it the “wrong” enantioface.…”

Section: Introductionmentioning

confidence: 88%

“…They are well accepted in the literature. 3,4,6,[11][12][13] At this point, it is worthy to note that the same propene enantioface is involved in the transition states leading to a SM or a RM. For this reason, we define it the "wrong" enantioface.…”

Section: Introductionmentioning

confidence: 99%

Molecular Modeling of Stereo- and Regioselectivity of Group 4 Heterocenes in the Polymerization of Propene

Guerra¹,

Corradini²,

Cavallo³

2005

Macromolecules

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We report a theoretical analysis on the stereo- and regiochemical behavior of the S- and N-based group 4 heterocenesdeveloped by Ewen, Elder, and Jonesin the polymerization of propene to isotactic polypropylene. Somewhat surprisingly, the polymers produced with the N-based heterocene were shown to present a sensibly smaller amount of regiomistakes and a higher amount of stereomistakes relative to the S-based heterocene. To clarify the different mechanistic behavior of these structurally rather similar catalysts, we compared their stereo- and regioselectivity, and we extended our modeling to the corresponding all-carbon bis(indenyl)-based catalyst. Our analysis supports most of the ideas proposed by Ewen, Elder, and Jones to rationalize the experimental behavior.

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“…3,[6][7][8] In the following, we offer a theoretical explanation for the opposite regioselectivities of the two systems, which stem from an extremely subtle interplay of electronic and steric effects. The origin of the different stereoselectivities, already addressed elsewhere, 9,10 is beyond the scope of this paper.…”

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confidence: 87%

Origin of the Regiochemistry of Propene Insertion at Octahedral Column 4 Polymerization Catalysts: Design or Serendipity?

2003

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The new octahedral column 4 catalysts bearing phenoxy-amine or phenoxy-imine ligands have opposite regioselectivities in propene polymerization. In this Communication, we report on a QM/MM investigation indicating that one of the key factors controlling the regiochemistry of propene insertion is the nature of the N atoms: steric and electronic effects related to the different hybridization synergically favor 1,2 or 2,1 insertion when the said N's are respectively of amine or imine type.

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Chirality of Catalysts for Stereospecific Polymerizations

Cited by 20 publications

References 73 publications

Structural Correspondence of Solution, Liquid Crystal, and Crystalline Phases of the Chromonic Mesogen Sunset Yellow

Structural Correspondence of Solution, Liquid Crystal, and Crystalline Phases of the Chromonic Mesogen Sunset Yellow

Molecular Modeling of Stereo- and Regioselectivity of Group 4 Heterocenes in the Polymerization of Propene

Origin of the Regiochemistry of Propene Insertion at Octahedral Column 4 Polymerization Catalysts: Design or Serendipity?

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