Stereo‐ and Regioselectivity of Chiral, Alkyl‐substituted ansa‐Zirconocene Catalysts in Methylalumoxane‐activated Propene Polymerization

Abstract

Up to 94% yields of isotactic pentads are achieved in the polymerization of propene with the ansa‐zirconocene catalysts 1. It emerges that bulky substituents are decisive for the stereoselectivity, while α‐substituents are decisive for the regioselectivity. Moreover, α‐substituents favor the synthesis of long chains (Mw up to 9190). R1  tBu, iPr; R2  H. Me; μ‐X  Me2CCMe2, Me2Si.

A combined experimental—molecular modeling approach for ethene–propene copolymerization with C2-symmetric metallocenes

“…the Indenyl aryl group for the systems of Fig. 1 [18]. It can consequently be concluded that for the metallocenes investigated here, the predominant termination reaction during E/P copolymerizations involves ␤-hydrogen transfer to the monomer after a propene insertion.…”

“…At least in part, this has been related to a much higher regiospecificity induced by the 2-Me group. As noted by Brintzinger and co-workers, the performance of ␣-methyl substituted catalysts approaches that of heterogeneous Ziegler catalysts, in which regio-irregularities are not observed [18]. Besides this indirect effect, a direct influence of the 2-Me substituent on slowing down the kinetics of chain transfer to propene has been suggested [4,6,17].…”

“…These differences between predicted and observed P n must be ascribed to the contribution of alternative chain termination mechanisms during homopolymerization such as, e.g. transfer to Al and/or differences in regio-selectivity [18], which we assumed to be negligible in copolymerizations. It thus seems that it is possible to learn more about propene homopolymerization by studying E/P copolymerization, i.e.…”

Anion Effects on the Activity and Stereoselectivity in Propene Polymerisations Catalyzed by C2‐Symmetric and “Oscillating” Catalysts

“…[2] Other parameters, most notably catalyst activity, are much less understood, and data reported in the literature are often very difficult to compare. [3][4][5][6][7][8][9][10][11][12][13][14] Polymer molecular weights and isotacticities also differ significantly, even under apparently comparable conditions. As Fink et al have demonstrated, the activity maxima of methylaluminoxane (MAO) activated catalysts depend strongly on the Al:metal ratio.…”

Diastereoselective Insertion of Isocyanide into the Alkyl−Metal Bond of Methylbenz[e]indenyl ansa‐Zirconocene Complexes

“…[9,10] It is well-known that the presence of condensed benzene rings in the indenyl ligands of metallocene-type complexes induces a remarkable increase in their catalytic activity, and the addition of a 2-methyl substituent in their Cp rings reduces the incidence of β-elimination processes, providing a significant increase in the molecular weight of the polymer. In this regard the 2-methylbenz[e]indenyl ligand (MBI) is an excellent choice for this purpose.…”