| Abstract
| - The displacement of the MeB(C6F5)3- anion from seven different zirconocene methyl cationsby neutral Lewis bases, such as dimethylaniline, benzyldimethylamine, and dinbutyl ether,was investigated by 1D and 2D NMR spectroscopy. Equilibrium constants for reactions withdinbutyl ether change by factors of less than 5 between the zirconocene contact ion pairsstudied, despite substantial steric differences. Rate constants of this displacement reaction,however, change by a factor of more than 105 between Me2Si(C5H4)2ZrMe+MeB(C6F5)3-, themost “open” complex, and rac-Me2Si(2-Me-BzInd)2ZrMe+MeB(C6F5)3-, the most highlysubstituted species studied. Kinetic and stereochemical data indicate that Lewis base−anionexchange proceeds by way of an associative mechanism, which occurs without side changeof the zirconium-bound methyl group. DFT calculations support an associative substitutionmechanism and propose five-coordinated reaction intermediates with the Lewis basecoordinated to the central coordination site.
- Displacement of MeB(C6F5)3- anions from several zirconocene methyl cations by neutral Lewis bases (Lb) occurs with rates highly sensitive to substituents at the zirconocene framework and was found, by 1D and 2D NMR spectroscopy, to proceed by way of an associative mechanism, for which DFT calculations indicate a five-coordinated reaction intermediate, with the Lewis bases or olefins coordinated to the central coordination site.
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