Influence of Cocatalyst on the Stereoselectivity of Unbridged 2-Phenylindenyl Metallocene Catalysts

Abstract

Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium dichloride, in the presence of methylaluminoxane (MAO), are catalyst precursors for the synthesis of elastomeric polypropylene. The nature of the cocatalyst is shown to have a significant influence on the productivity and stereoselectivity of these metallocenes. Propylene polymerizations in liquid propylene in the presence of bis(2-phenylindenyl)zirconium dimethyl (5) activated by three different types of methyaluminoxane, trityl tetrakis(pentafluorophenyl)borate (1), dimethylanilinium tetrakis(pentafluorophenyl)borate (2), or tris(pentafluorophenyl)borane (3), revealed a significant influence of activator on the polymerization behavior of these catalysts: both the productivity and stereoselectivity of the catalyst systems were highest with MAO and lowest with the borane 3 (MAO > 1 ≈ 2 . 3). Catalysts derived from the borane 3 yielded amorphous atactic polypropylenes under conditions where those from cocatalysts MAO, 1, or 2 yielded semicrystalline, low-tacticity polypropylenes. The type of MAO also influences the stereoselectivity: MAOs containing isobutylaluminum groups yielded higher tacticity polypropylenes than those with only methylaluminum groups. Solution polymerizations in solvents of varying polarities revealed that the polarity of the solvent influenced the productivities but had little influence on the stereoselectivity.

Endowing Aspecific, Unbridged‐Metallocene Propylene‐Polymerization Catalysts with Isospecificity: The Unprecedented Role of MAO

“…[25][26][27] In conclusion, we have devised a novel synthetic strategy for the synthesis of isospecific, unbridged-metallocene catalytic systems for propylene polymerization. The class I unbridged metallocene with E = NEt 2 , OMe, SMe, etc.…”

Alkylidenverbrückte, symmetrische, zweikernige Metallocenkomplexe als Katalysatoren für die Propylenpolymerisation

“…So wurden von Spaleck dinukleare Metallocenkatalysatoren zur Darstellung von isotaktischem Polypropylen [32] beschrieben. Umfangreiche Untersuchungen ü ber die Polymerisationseigenschaften unverbrü ckter Metallocenkatalysatoren und den Einfluss des Gegenions auf die Aktivität und Stereoselektivität der Katalysatorsysteme in der Propylenpolymerisation wurden von Waymouth angestellt [33][34][35][36]. Im Folgenden wird ü ber die Synthese und Charakterisierung symmetrischer, alkylidenverbrü ckter, zweikerniger Komplexe berichtet und der Einfluss verschiedener Cokatalysatorsysteme auf die Polymerisationseigenschaften dinuklearer Metallocenkatalysatoren diskutiert.…”

“…Das MAO-Gegenion wechselwirkt offenbar schwächer mit der aktiven Spezies als Borat-Ionen. Brintzinger und Mü lhaupt [60], sowie Ewen [67] und Waymouth [34] fanden ebenso niedrigere Polymerisationsaktiviäten fü r die borataktivierte Propylenpolymerisation. Die Verwendung der starken Lewis-Säure B(C 6 F 5 ) 3 als Aktivator fü hrte zu keiner Polymerisation von Propylen.…”

“…oder nahezu ungeeignet[34]. Es wird allgemein davon ausgegangen, dass die aktive Spezies während der Polymerisation ein kationischer Komplex ist, der durch Abstraktion eines Methylanions entsteht.…”

Propylene Polymerization Using ansa‐Zirconocenes with Water/Pentafluorophenol‐Modified Methylaluminoxane

“…[11][12][13][14][15][16][17][18][19][20] Recently, several research groups have studied the effect of the cocatalyst on the stereoregularity of propylene polymerization. [17,21,22] We have reported the enhancement of productivity, stereoregularity, and regioregularity as well as increased molecular weight of 1-butene polymerization with a 2,2-thiobis(phenoxy)titanium complex (1) [23][24][25][26] by isobutylmethylaluminoxane (MMAO) modification using water [27] or both water and pentafluorophenol. [28] In these studies, we claim that the addition of water and pentafluorophenol induces the structural and electrical changes in the aluminoxane and the reduction of ''free'' trimethylaluminum (TMA).…”