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Synthesis of "meso"-and "racemic"-like diastereomers of Me2Si(3-MeInd)(Ind)ZrCl2 (5 and 6, respectively) was achieved through either metathetical reactions between the dianion of Me2(3-MeIndH)-(IndH) (4) with ZrCl4 or via amine elimination reactions, followed by fractional crystallization. Propylene polymerizations using meso-5 in the presence of methyl aluminoxane under a variety of conditions leads to the formation of low molecular weight, semicrystalline, low tacticity, poly(propylene) (PP). The dominant chain transfer mechanism in this case is shown to involve -H transfer to monomer. In contrast, rac-6 provides higher molecular weight, semicrystalline, elastomeric poly(propylene) (elPP) under a variety of conditions; chain transfer in this case involves, predominantly, -H transfer to Zr. The properties of elPP produced using catalyst 6 show a gradual change from a lightly, cross-linked elastomer to a poorly crystalline thermoplastic, depending on both polymer molecular weight and crystallinity as revealed by differential scanning calorimetry and tensile testing. In particular, more crystalline material exhibits a higher initial modulus, yielding behavior and lower strain to break than less crystalline material of equivalent molecular weight. These findings further define polymer properties for the synthesis of flexible elastomers using this class of catalysts.

Mono- and disubstituted bis(ketenimine) complexes of zirconium (1 and 2, respectively) can be readily prepared by reaction of these ligands (3) with Zr(NMe)4 or, in some cases, the homoleptic tetrabenzyl derivative ZrBn4. Treatment of 1 (Ar = Ph, p-CF3Ph; X = NMe2) with Me2NH·HCl and of 2 (Ar = Ph, X = NMe2) with either Me2NH·HCl or TMSCl provides the corresponding chloro derivatives in high yield. Alkyl derivatives of 2 (X = Me, Bn) can be readily prepared by reaction of the corresponding chloro derivatives with Grignard or organolithium reagents. Monocyclopentadienyl bis(ketenimine) complexes 4 (Ar = Ph, p-CF3Ph; Cp = η5-C5H5, η5-C9H7; X = Cl) were prepared from 1 (Ar = Ph, p-CF3Ph; X = Cl) by reaction with CpLi or IndLi in high yield, and methyl derivatives 4 (Ar = Ph, p-CF3Ph; Cp = η5-C5H5, η5-C9H7; X = Me) were accessible by treatment of the chloro precursors with methyllithium. The X-ray structure of 2 (Ar = Ph; X = NMe2) reveals a distorted-octahedral geometry in which the bis(ketenimine) ligands are σ-bound to the metal and the dimethylamido groups are cis to one another, and the corresponding dichloro derivative also adopts a similar structure in the solid state, whereas the bis(ketenimine) ligands adopt a distorted, η5 binding mode in the monoindenyl derivative 4 (Ar = Ph; Cp = η5-C9H7; X = Cl). Enantiomers of 2 (Ar = Ph, X = Cl) readily interconvert in solution via a Bailar-twist mechanism, as revealed by variable-temperature 1H NMR spectroscopic studies; activation parameters for this process were determined (ΔH ‡ = 9.0 ± 0.45 kcal mol-1; ΔS ‡ = −9.9 ± 1.0 cal mol-1 K-1).

The chnal ansa-metallocenes 1,2-ethylenebis(q6-l-indenyl)-and 1,2-ethylenebis(q5-l-tetrahydroindeny1)zirconium dichloride (1 and 2, respectively) can be supported on partially dehydroxylated SiOz and A l 2 0 3 , and these supported systems can be used to polymerize propylene in the presence of methylaluminoxane. The most active supported systems were derived from partially dehydroxylated Si02 or Alz03 that had been pretreated with excess trimethylaluminum. The properties of the polypropylene produced are essentially indistinguishable from that produced under homogeneous conditions using these same catalysts. IntroductionThe discovery of homogeneous Ziegler-Natta catalysts, derived from metallocene compounds and methylaluminoxane cocatalyst, that combine high activity with excellent stereoregularity in the isotactic polymerization of a-olefins has led to a resurgence of interest in this field.2 Metallocene catalysts that provide access to isotactic,2gpi-k isotactic-stereoblock,2' syndiotactic,2h and isotactic-atactic block2d polymers of propylene have been developed. A significant impediment to the commercialization of such catalytic systems is the cost reflected in the requirement that a verylarge excess of methylaluminoxane (MAO) must be employed to obtain high catalytic activity and catalyst stability., One approach to overcome this problem that has met with some success, at least for ethylene polymerization, involves the preparation of cationic, do, 14 e-, metallocene compounds which do not require a cocatalyst for p~lymerization.~ Another approach, the results of which have been mainly disclosed in the patent literature,, has involved adsorbing an appropriate metallocene compound, with or without an aluminum alkyl, on silica, alumina, or other high surface area support5 and using such systems for ethylene polymerization. In several cases, it is claimed that additional MA0 is not required during polymerization if it is initially deposited or prepared on the surface.As far as we are aware, these studies have been concerned with ethylene polymerization; there appear to have been few reports on propylene polymerization using supported versions of the well-studied ethylenebis(s5-indenyl)-and ethylenebis(~5-tetrahydroindenyl)zirconiwn dichloride catalysts (1 and 2, respectively).6 In this paper, we describe the preparation of supported versions of these catalysts and their use in the polymerization of propylene.

Electrospray-ionization mass spectrometric studies of poly(methylaluminoxane) (MAO) in the presence of [Cp2 ZrMe2 ], [Cp2 ZrMe(Cl)], and [Cp2 ZrCl2 ] in fluorobenzene (PhF) solution are reported. The results demonstrate that alkylation and ionization are separate events that occur at competitive rates in a polar solvent. Furthermore, there are significant differences in ion-pair speciation that result from the use of metallocene dichloride complexes in comparison to alkylated precursors at otherwise identical Al/Zr ratios. Finally, the counter anions that form are dependent on the choice of precursor and Al/Zr ratio; halogenated aluminoxane anions [(MeAlO)x (Me3 Al)y-z (Me2 AlCl)z Me](-) (z=1, 2, 3…︁) are observed using metal chloride complexes and under some conditions may predominate over their non-halogenated precursors [(MeAlO)x (Me3 Al)y Me](-) . Specifically, this halogenation process appears selective for the anions that form in comparison to the neutral components of MAO. Only at very high Al/Zr ratios is the same "native" anion distribution observed when using [Cp2 ZrCl2 ] when compared with [Cp2 ZrMe2 ]. Together, the results suggest that the need for a large excess of MAO when using metallocene dichloride complexes is a reflection of competitive alkylation vs. ionization, the persistence of unreactive, homodinuclear ion pairs in the case of [Cp2 ZrCl2 ], as well as a change in ion pairing resulting from modification of the anions formed at lower Al/Zr ratios. Models for neutral precursors and anions are examined computationally.