Abstract
The conformationally dynamic unbridged metallocene (2-PhInd)2ZrMe2 (1) was activated with trispentafluorophenylborane (B(C6F5)3, B2) or trityl tetrakispentafluorophenylborate (“trityl borate”, [Ph3C+][B(C6F5)4-], B4) to generate the ion pair [(2-PhInd)2ZrMe+][MeB(C6F5)3-] (2a) or [(2-PhInd)2ZrMe+][B(C6F5)4-] (2b), respectively. Activation parameters for ion-pair separation were determined by line-shape analysis (2a: ΔH⧧ips = 20 ± 1 kcal/mol, ΔS⧧ips = 17 ± 4 eu; 2b: ΔH⧧ips = 15 ± 2 kcal/mol, ΔS⧧ips = 13 ± 7 eu). For 2a, a much slower B(C6F5)3 dissociation−reassociation process was also observed (ΔG⧧83°C = 18.9 ± 0.1 kcal/mol). Both 2a and 2b were treated with a series of o-substituted pyridines, and the behavior of the resulting zirconocenium-pyridyl complexes (3a−8b) was studied by 1H, 13C, and 19F NMR over the temperature range −100 to 100 °C. Below room temperature, 1H NMR NOESY spectra revealed signals characteristic of a Cs-symmetric syn conformation.
Published Version
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