A study of trihapto-pentahapto equilibria in heptadienylpalladium(ii) complexes and the possible role of such complexes in metal complex catalysed 1,4-polymerizations of 1,3-butadiene

Hughes, Russell P.; Jack, T.; Powell, John Wesley

doi:10.1016/s0022-328x(73)80058-0

Cited by 28 publications

(6 citation statements)

References 17 publications

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“…The assumption of post-insertion intermediates including a back-biting coordination of the polymeryl group is supported by the analogous structure of several complexes. [30][31][32][33][34][35] In the reaction path from the pre-insertion intermediate toward the post-insertion intermediate the transformation of the η 3 -allyl bond into a (back-bitten) η 2 bond could involve preliminary formation of a η 1 -allyl bond, as observed for the slow insertion of butadiene into a transition metal-allyl bond (by 1 H NMR experiments 37,38 ). This possible preliminary formation of a η 1allyl bond, although not explicitly considered, is, however, compatible with the pathway assumed in the present study of molecular mechanics.…”

Section: Modelsmentioning

confidence: 92%

“…In other words, the anti -η 3 -coordinated allyl group and the cis -η 4 -coordinated diene monomer of the pre-insertion intermediate become, in the post-insertion intermediate, an η 2 -coordinated double bond and an anti -η 3 -coordinated allyl group, respectively. The assumption of post-insertion intermediates including a back-biting coordination of the polymeryl group is supported by the analogous structure of several complexes. − …”

Section: Modelsmentioning

confidence: 94%

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Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

et al. 1997

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In the framework of Porri's mechanism for the 1,2 and cis-1,4 diene polymerizations, a geometrical and nonbonded energy analysis on possible catalytic intermediates, which include a cyclopentadienyl group coordinated to the transition metal, is presented. Besides pre-insertion intermediates, post-insertion intermediates presenting a “back-biting” coordination of the growing chain are considered. The post-insertion minimum energy intermediates are structurally very close to the endo − endo pre-insertion intermediates (presenting endo coordinations for both the allyl group of the growing chain and diene monomer), independently of the kind of insertion (1,2 or cis-1,4) and of the diene (butadiene, 4-methyl-1,3-pentadiene or (Z)-pentadiene). In our hypothesis the energy differences between the considered post-insertion intermediates are close to those present in the transition states, and this assures the isospecificity and the syndiospecificity of the models for the cis-1,4 polymerization (of 4-monosubstituted monomers) and for the 1,2 polymerization, respectively. This is in qualitative agreement with the stereoregularities of the polymers obtained with a catalytic system based on cyclopentadienyltitanium trichloride. Support for a 1,2 insertion mechanism for butadiene involving an endo − endo pre-insertion intermediate is given by comparison between the calculated minimum energy post-insertion intermediate and the crystalline structure of a catalytic cobalt complex.

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Section: Modelsmentioning

confidence: 92%

Section: Modelsmentioning

confidence: 94%

Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

et al. 1997

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“…Finally, it is possible that the highly electron deficient Ti ion is also coordinated to the penultimate unit of R, which has two π electrons to form a dative bond, the so-called back-biting interaction. − This interaction is expected to be strong and can significantly influence all the steps of the polymerization mechanism. Therefore, we have preferred to use a more realistic model for the growing polymer chain, which in the present study has been modeled by two repeating units, rather than adopting a more sophisticated and reliable computational approach on a simplified model.…”

Section: Preliminary Considerationsmentioning

confidence: 99%

Polymerization Mechanism of Conjugated Dienes in the Presence of Ziegler−Natta Type Catalysts: Theoretical Study of Butadiene and Isoprene Polymerization with CpTiCl₃−MAO Initiator

2000

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The mechanism of butadiene and isoprene polymerization in the presence of CpTiCl 3 -MAO has been investigated by means of ab initio computations. According to experimental evidence, the catalytically active species are assumed to be [CpTi-P] + organotitanium cations (P ) growing polymer chain). The results show that (i) in the active species, P is coordinated to Ti both with the π allyl group of its ending unit and with the π bond of the penultimate unit; (ii) the cis η 4 coordination of an incoming monomer to the active species requires the breakage of the latter interaction and the change of the allyl coordination mode from η 3 to η 1 . That significant rearrangement of P is predicted to be the rate-determining step of the whole propagation reaction and is predicted to be much easier when the ending unit of P is butenyl rather than 2-methylbutenyl. That finding accounts both for the large difference observed in the homopolymerization rates of butadiene and isoprene and for the fact that in copolymerizations the two monomers exhibit almost the same reactivity.

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“…Hughes and Powell studied the monomer/dimer equilibria shown below and suggested that a wrap-around complex similar to 7 may be involved in BD polymerization initiated by the nickel dimer, [(allyl)Ni(O 2 CCF 3 )] 2 (Scheme 3) [7]. We report here an investigation of simple Pd(II) wrap-around complexes of type 1, with n = 2.…”

Section: Introductionmentioning

confidence: 89%

Synthesis, characterization, and reactivity of (π-allyl)palladium(II) wrap-around complexes with 1,3-dienes

Urbin

Pintauer

White

et al. 2011

Inorganica Chimica Acta

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A study of trihapto-pentahapto equilibria in heptadienylpalladium(ii) complexes and the possible role of such complexes in metal complex catalysed 1,4-polymerizations of 1,3-butadiene

Cited by 28 publications

References 17 publications

Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

Polymerization Mechanism of Conjugated Dienes in the Presence of Ziegler−Natta Type Catalysts: Theoretical Study of Butadiene and Isoprene Polymerization with CpTiCl₃−MAO Initiator

Synthesis, characterization, and reactivity of (π-allyl)palladium(II) wrap-around complexes with 1,3-dienes

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A study of trihapto-pentahapto equilibria in heptadienylpalladium(ii) complexes and the possible role of such complexes in metal complex catalysed 1,4-polymerizations of 1,3-butadiene

Cited by 28 publications

References 17 publications

Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

Molecular Mechanics and Stereospecificity in Ziegler−Natta 1,2 andCis-1,4 Polymerizations of Conjugated Dienes

Polymerization Mechanism of Conjugated Dienes in the Presence of Ziegler−Natta Type Catalysts: Theoretical Study of Butadiene and Isoprene Polymerization with CpTiCl3−MAO Initiator

Synthesis, characterization, and reactivity of (π-allyl)palladium(II) wrap-around complexes with 1,3-dienes

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Polymerization Mechanism of Conjugated Dienes in the Presence of Ziegler−Natta Type Catalysts: Theoretical Study of Butadiene and Isoprene Polymerization with CpTiCl₃−MAO Initiator