Structure/activity relationships for the living Ziegler–Natta polymerization of 1-hexene by the series of cationic monocyclopentadienyl zirconium acetamidinate complexes, [(η 5-C 5Me 5)ZrMe{N(CH 2R)C(Me)N(t-Bu)}][B(C 6F 5) 4] (R=Me, i-Pr, t-Bu, Ph, 2-ClC 6H 4, 3-MeC 6H 4 and 2,4,6-Me 3C 6H 2)

• Published in: Inorganica Chimica Acta 2003-03, Vol.345, p.121-129
• Main Authors: Kissounko, Denis A, Fettinger, James C, Sita, Lawrence R
• Format: Article
• Language: English
• Subjects: Amidinate complexes; Living polymerization; Poly(1-hexene); Ziegler–Natta polymerization
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(02)01288-4

Protonation of (η 5-C 5Me 5)ZrMe 2[N(t-Bu)C(Me)N(CH 2R)] ( 1) [R=( a) Me, ( b) i-Pr, ( c) t-Bu, ( d) Ph, ( e) 2-ClC 6H 4, ( f) 3-MeC 6H 4 and ( g) 2,4,6-Me 3C 6H 2] by [PhNMe 2H][B(C 6F 5) 4] in chlorobenzene at −10 °C provides the titled cationic complexes 2a– g. Both 2b and 2d are active initiators for the living polymerization of 1-hexene at −10 °C, however, whereas 2d functions much like 2a in terms of activity and isoselectivity, propagation from 2b is much less active and it produces atactic material. Complexes 2d and 2g are inactive, presumably due to steric reasons, while intramolecular chloride coordination appears responsible for inhibiting 2e. Finally, 2f, while active as an initiator, was found not to provide a living system as a result of CH activation processes that terminate propagation. A structural study of the precatalysts 1b– d sheds additional light on the nature of ligand effects on activity and stereocontrol for the family of initiators represented by 2. The Ziegler–Natta initiators, [(η 5-C 5Me 5)ZrMe{N(CH 2R)C(Me)N(t-Bu)}][B(C 6F 5) 4] (R=Me, i-Pr, t-Bu, Ph, 2-ClC 6H 4, 3-MeC 6H 4 and 2,4,6-Me 3C 6H 2) ( 2a– g), were prepared and evaluated for their ability to effect the stereospecific living polymerization of 1-hexene. Results reveal that small differences in the coordination sphere of these cationic complexes can have profound effects on polymerization activity, degree of stereocontrol, and relative rates of propagation and termination.