1994
DOI: 10.1016/s0167-2991(08)63037-2
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21. The Role of Ion-Pair Equilibria on the Activity and Stereoregularity of Soluble Metallocene Ziegler-Natta Catalysts

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Cited by 14 publications
(19 citation statements)
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“…Analysis of the solvation effects reveals (Table ), not surprisingly, that charged species are stabilized most . Since (CH 3 ) 2 Si[(CH 3 ) 4 C 5 ]( t BuN)Zr(CH 3 ) + B(C 6 F 5 ) 4 - forms an isolable η n -toluene complex,3b calculations were next carried out including Ti−η n -C 6 H 6 complexation ( n = 3 was of lowest energy; eq 3) In this case, the computed ion pair dissociation enthalpy is reduced to +23 kcal/mol.…”
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confidence: 98%
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“…Analysis of the solvation effects reveals (Table ), not surprisingly, that charged species are stabilized most . Since (CH 3 ) 2 Si[(CH 3 ) 4 C 5 ]( t BuN)Zr(CH 3 ) + B(C 6 F 5 ) 4 - forms an isolable η n -toluene complex,3b calculations were next carried out including Ti−η n -C 6 H 6 complexation ( n = 3 was of lowest energy; eq 3) In this case, the computed ion pair dissociation enthalpy is reduced to +23 kcal/mol.…”
mentioning
confidence: 98%
“…I ) currently attract attention as highly efficient and selective agents for producing polyolefins having unprecedented/useful architectures and processing characteristics. , The active species are thought to consist of cation−anion pairs (e.g. II ), and growing experimental evidence indicates that the nature of such ion pairing, as modulated by cocatalyst/counteranion (X - ) and solvent, has significant consequences for catalyst activity, chain transfer characteristics, and possibly stereoselectivity. In contrast to experimental efforts, theoretical studies of such catalysts, while greatly expanding our understanding, have focused almost exclusively on naked group 4 cations. We communicate here preliminary results of the first ab initio computational investigation, including counteranion and solvation, of catalyst generation, catalyst−cocatalyst structural energetics, and the olefin activation/insertion reaction coordinate for a CGC-based ion pair; it is seen that counteranion and solvation effects are substantial.…”
mentioning
confidence: 99%
“…A growing database implicates metallocene ancillary ligation (L, L‘), metal identity (M), and the nature of the abstractor/cocatalyst (A; eq 1) as key factors governing the thermodynamics and kinetics of single-site metallocenium catalyst activation as well as the stereochemical dynamics of the tight ion pairing. , The interplay of these variables influences catalyst activity, thermodynamic stability, chain transfer characteristics, and regio- and stereochemical aspects of monomer enchainment in ways that are not yet entirely understood. In actual polymerization catalytic systems, the identity of alkyls R and R‘ can be quite variable, and little is known quantitatively about how alkyl group steric and electronic characteristics affect metallocenium ion pair thermodynamic stability with respect to the neutral precursors, solution phase structure, and stereochemical dynamics.…”
mentioning
confidence: 99%
“…Using the well-characterized and spectroscopically informative bis(1,2-dimethylcyclopentadienyl)zirconocene framework and B(C 6 F 5 ) 3 as a prototypical abstractor/cocatalyst, ,, a series of metallocenium alkyl methylborate ion pairs ( 2 ) was synthesized from the corresponding methylalkyls ( 1) (eq 2) and characterized by standard spectroscopic and analytical techniques . The abstraction process is, within NMR detection limits, completely selective for the methyl anion .…”
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confidence: 99%
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