Metallocene/polypropylene structural relationships: Implications on polymerization and stereochemical control mechanisms

Abstract

A series of group 4 metallocenes possessing chiral ligand environments have been characterized and their structures are compared with their propylene polymerizations. Isotactic, syndiotactic, hemiisotactic, and atactic polypropylenes are produced selectively with chiral monoalkyl metallocene cations paired with perfluorotetraphenyl borate; analogous to the results obtained using methylaluminoxane as a cocatalyst. The relative catalyst stereospecificities suggest specific π‐face selectivities and nonbonded contacts. Trends with solvents, temperatures, and catalyst structures are consistent with contact ion pairing for iPr[CpFlu]Zr‐P(+) in liquid propylene. The specificities of differently structured metallocenes imply chain‐migratory monomer addition reactions.

Syntheses of multi-stereoblock polybutene-1 using novel monocyclopentadienyltitanium and modified methylaluminoxane catalysts

“…The ideal mMAO used as cocatalyst for butene-1 polymerization contains trimethylaluminum (TMA) approaching to 17.7 wt %. The oxidation states of titanium in different Cp*Ti-(OBz) 3 and mMAO catalytic systems were determined by redox titration method. The results show that three active species may exit in the current system, and Ti(IV) active species is in favour of producing polybutene-1.…”

“…The residual TMA is known to have significant influences on catalytic activity of metallocene catalysts and molecular weight and structure of polyolefins. 18,20,21 The results of butene-1 polymerization with Cp*Ti(OBz) 3 activated by three types of modified methylaluminoxanes (mMAO) are given in Table I. From run1 to run3, the higher the content of TMA in mMAO is, the more Ti(IV) complexes are reduced to Ti(III) and Ti(II) states.…”

“…We reported that propene was polymerized with CpTi(OR) 3 or Cp*Ti(OR) 3 /MAO catalysts at 0 -60°C in toluene. 15,16 It was found that all polymerization products obtained were largely atactic polypropene without crystallization.…”

“…The polymer was washed with ethanol and dried in vacuum to constant weight at 60°C. The oxidation states of titanium in different Cp*Ti(OBz) 3 / mMAO catalytic systems were determined by K 2 Cr 2 O 7 redox titration method as described in letures. 17,18 Sodium diphenylaminesulfonate was used as the indicator.…”

Regioselective formation of [2-(η5-cyclopentadienyl)-2-fluorenylpropane]-titanium complexes: precursors, synthesis, structure and reactivity

“…The [CMe 2 (C 5 H 4 )(C 13 H 8 )] 2 − dianionic ligand has previously been used for the synthesis of Cs-symmetric group 4 ansa-metallocenes ([1]b, [7]), and has been found to form tris(cyclopentadienyl)zirconium compounds with unusual ansa-ligand coordination [5c, 8]. The synthesis of tris(dimethylamido)[2-(p 5 -cyclopentadienyl)-2-fluorenylpropane]zirconium via amine elimination has very recently been reported [9], and several related compounds containing the 2-(p 5 -cyclopentadienyl)-2-indenylpropane ligand have also been described ( [5]b -c, [8,10]).…”