870559-12-9Relevant articles and documents
Dynamic NMR studies of cationic bis(2-phenylindenyl)zirconium pyridyl complexes: Evidence for syn conformers in solution
Lincoln, Alice L.,Wilmes, Gregg M.,Waymouth, Robert M.
, p. 5828 - 5835 (2008/10/09)
The conformationally dynamic unbridged metallocene (2-PhInd) 2ZrMe2 (1) was activated with trispentafluorophenylborane (B(C6F5)3, B2) or trityl tetrakispentafluorophenylborate ( trityl borate , [Ph 3C-][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 (ΔG83°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 C s-symmetric syn conformation.
