Metallocene polymerization catalyst ion-pair aggregation by cryoscopy and pulsed field gradient spin-echo NMR diffusion measurements.
Pulsed field gradient spin-echo (PGSE) NMR and cryoscopic measurements have been performed on a series of homogeneous metallocene polymerization catalyst ion-pairs to determine if aggregation is a significant phenomenon under typical polymerization conditions. Cryoscopic measurements on [(Me5Cp)2ZrMe]+[MeB(C6F5)3]- (1), [rac-Et(Indenyl)2ZrMe]+[MeB(C6F5)3]- (2), [(1,2-Me2Cp)2ZrCHTMS2]+[MeB(C6F5)3]- (3), [Me2Si(Me4Cp)(t-BuN)TiMe]+[MeB(C6F5)3]- (4), [Me2Si(Me4Cp)(t-BuN)ZrMe]+[MeB(C6F5)3]- (5), and [Me2C(Fluorenyl)(Cp)ZrMe]+[MeB(C6F5)3]- (6) were carried out in benzene in the 10-18 millimolal concentration range. PGSE measurements, using (p-tolyl)4Si as an internal standard, were also performed on catalyst ion-pairs 1, 4, 6, [(Me5Cp)2ThMe]+[B(C6F5)4]- (7), [(Me2SiCp2)ZrMe]+[MeB(C6F5)3]- (8), and [Cp2ZrMe]+[MeB(C6F5)3]- (9) in the 0.8-10.0 millimolar range. All results are consistent with a 1:1 ion-pair structural model and show little evidence for ion-quadruples or higher-order aggregates.
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
Nicholas G
NG
Stahl
Cristiano
C
Zuccaccia
Tryg R
TR
Jensen
Tobin J
TJ
Marks