A Binaphthyl‐Bridged Salen Zirconium Catalyst Affording Atactic Poly(propylene) and Isotactic Poly(α‐olefins)

Abstract

Summary: A binaphthyl‐bridged salen dichlorozirconium (IV) complex that displays an octahedral structure with a trans‐O, cis‐N, and cis‐Cl arrangement was synthesized and tested as a precatalyst for ethylene and α‐olefin polymerization. While use of methylaluminoxane (MAO) cocatalyst afforded poor catalytic activity, activation by mixtures of aluminium alkyls such as AliBu3 and either MAO or [CPh3][B(C6F5)4] resulted in reasonable polymerization activities for ethylene, propene, and higher α‐olefins. Quite unexpectedly, while the polymerization of propene results in the production of a high‐molecular‐weight stereoirregular polymer, highly isotactic polymers are obtained under similar conditions from polymerization of 1‐butene, 1‐pentene, and 1‐hexene.Polymerization employing the binaphthyl‐bridged salen dichlorozirconium (IV) complex gave unexpected different stereospecificities for the polymerization of propene and higher α‐olefins, to yield ultrahigh‐molecular‐weight atactic poly(propylene) and highly isotactic polymers, respectively.magnified imagePolymerization employing the binaphthyl‐bridged salen dichlorozirconium (IV) complex gave unexpected different stereospecificities for the polymerization of propene and higher α‐olefins, to yield ultrahigh‐molecular‐weight atactic poly(propylene) and highly isotactic polymers, respectively.

Stereospecific and Stereoselective Polymerization of 4‐Methyl‐1‐hexene by Enantiomeric Binaphthyl‐Bridged Salen Dichlorozirconium (IV) Complexes

“…We previously observed [10] that PDI decreases when changing from poly(1-butene) to poly(1-hexene), suggesting that the larger the monomer, the lower the chain transfer rate. It is reasonable to suppose that the larger steric encumbrance of 4MH, due to its C4 substituent, enhances this effect.…”

“…[10] A single crystal X-ray analysis indicated the selective formation of the cis-a isomer, i.e., the octahedral complex with a trans-O-O, cis-N-N and cis-Cl-Cl arrangement. Tetradentate ligands such as rac-H 2 L can afford chiral-at-metal octahedral complexes having a D-or L-configuration (except in the case of the trans isomer).…”

Oscillating Non‐Metallocenes – from Stereoblock‐Isotactic Polypropylene to Isotactic Polypropylene via Zirconium and Hafnium Dithiodiphenolate Catalysts

“…Yet, as has been previously demonstrated for several catalytic systems, it is more challenging to distinguish between the enantiofaces of the "slim" propylene monomer relative to those of bulkier ones by given stereospecific catalysts. [16] A suitable ligand should therefore include bulky enough phenolate substituents so that its complexes would feature more distinct quadrants. [17] …”

A Comparative Study on the Polymerization of α‐Olefins Catalyzed by Salen and Salan Zirconium Complexes

“…[6] The proligand Salan was prepared as described in the literature. [8] Complex 2 was synthesized by dissolving the afforded proligand (1.59 g, 2.62 mmol) in THF (30 mL) and adding the resulting solution dropwise to solid NaH (0.188 g, 7.86 mmol) at room temperature.…”

“…[6] In fact the activation of complex 1 for a-olefin polymerization was achieved by several combinations of aluminium alkyls and methylaluminoxane (MAO) or boron compounds, while MAO alone was not able to generate a catalytically active species. These…”