Mechanistic Investigations into the Behavior of a Labeled Zirconocene Polymerization Catalyst

• Published in: Organometallics 2012-03, Vol.31 (5), p.2097-2107
• Main Authors: Moscato, Beth M, Zhu, Bolin, Landis, Clark R
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om3000955

Kinetics associated with the [(SBI)Zr(CH2SiMe2(C6H4)NMe2)][MeB(C6F5)3] (1a)-catalyzed polymerization of 1-hexene in a mixed toluene-d 8/chlorobenzene-d 5 solvent at −33 °C were investigated via 1H NMR and compared to the kinetics associated with the (SBI)ZrMe(MeB(C6F5)3) (1c)-catalyzed polymerization of 1-hexene under identical conditions. In the presence of 1-hexene, both catalysts form an identical propagating species, (SBI)Zr(poly-1-hexyl)(MeB(C6F5)3) (1b), but the concentration of 1b during 1a-catalyzed polymerization is only ca. 40% of the anticipated value. Under reaction conditions, 1b reacts reversibly with the model complex p-TMS-C6H4-NMe2 (2) to yield the outer-sphere ion pair tentatively identified as [(SBI)Zr(poly-1-hexyl)(2)][MeB(C6F5)3] (1e), which acts as an essentially dormant site during 1-hexene polymerization. Warming of 1b in the absence of additives generates the well-defined hydridoborate complex (SBI)ZrMe(HB(C6F5)3) (1d), which does not reinitiate in the presence of 1-hexene. β-Hydride elimination of 1b in the presence of additives such as 1,2-dichloroethane and 2 results in catalyst decomposition.