Zirconium dichloride

Metallocene Catalysts. Polymerization of cycloolefins with Kaminsky catalysts (combinations of metallocenes and methylaluminoxane) produces polymers with a completely different stmcture. The reactions proceeds via the double-bond opening in cycloolefins and the formation of C—C bonds between adjacent rings (31,32). If the metallocene complexes contain bridged and substituted cyclopentadienyl rings, such as ethylene(hisindenyl)zirconium dichloride, the polymers are stereoregular and have the i j -diisotactic stmcture. 

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Zirconium dichloride, ZrCl2, has been made by a month-long reaction of ZrCl and ZrCl at 650—750°C. The product has a three-layer sheet stmcture of close-packed Cl—Zr—Cl (178). 

Zirconocene dichloride (bis[cyclopentadienyl]zirconium dichloride) [1291-32-3] M 292.3, m 242-245 , 248 . Purified by recrystn from CHCI3 or xylene, and dried in vacuum. H NMR (CDCI3) 8 6.52 from MeaSi. Store in the dark under N2 as it is moisture sensitive. [IR, NMR, MS Aust J Chem 18 173 7965 method of J Am Chem Soc 81 1364 7959 and references in the previous entry.]... 

Polypropylenes produced by metallocene catalysis became available in the late 1990s. One such process adopts a standard gas phase process using a metallocene catalyst such as rac.-dimethylsilyleneto (2-methyl-l-benz(e)indenyl)zirconium dichloride in conjunction with methylaluminoxane (MAO) as cocatalyst. The exact choice of catalyst determines the direction by which the monomer approaches and attaches itself to the growing chain. Thus whereas the isotactic material is normally preferred, it is also possible to select catalysts which yield syndiotactic material. Yet another form is the so-called hemi-isotactic polypropylene in which an isotactic unit alternates with a random configuration. 

MOCVD of Zirconia. Yttria-stabilized zirconia is also deposited by MOCVD.Deposition can be accomplished by the codecomposition of the tetramethyl heptadiones of zirconium and yttrium, Zr(CjjHj902)3 and Y(CjjHj902)3, at 735°C. Deposition is also achieved by the decomposition of the trifluoro-acetylacetonates in a helium atmosphere above 300°C.P 1 Other potential MOCVD precursors are bis(cyclopentadienyl)zirconium dichloride, (C5H5)2ZrCl2, and zirconium (IV) trifluoroacetylacetonate,... 

The isotacticities and activities achieved with nonbridged metallocene catalyst precursors were low. Partially isotactic polypropylene has been obtained by using a catalyst system of unbridged (non-ansa type) metallocenes at low temperatures [65]. A chiral zirconocene complex such as rac-ZrCl2(C5H4 CHMePh)2 (125) is the catalyst component for the isospecific polymerization of propylene (mmmm 0.60, 35% of type 1 and 65% of type 2 in Scheme Y) [161]. More bulky metallocene such as bis(l-methylfluorenyl)zirconium dichloride (126) together with MAO polymerized propylene to isotactic polypropylene in a temperature range between 40 and 70°C [162]. 

Based on Chien s research results, Collins et al. modified the basic structure of the catalysts and also achieved elastic material [8,18,19]. In both cases the elastic properties of the polymers are justified in a block structure with isotactic and atactic sequences. In 1999 Rieger et al. presented a couple of asymmetric, highly active metallocene catalysts, e.g., the dual-side catalyst rac-[l-(9-r 5-fluorenyl)-2-(5,6-cyclo-penta-2-methyl-l-q5-indenyl)ethane]zirconium dichloride (Fig. 3). These catalysts allowed building of isolated stereoerrors in the polymer chain to control the tacticity and therefore the material properties of the polymers [9],... 

A special case of the chain back skip polymerization mechanism and therefore an entirely different polymerization behavior was observed for differently substituted asymmetric complexes (for example catalyst 3). Although asymmetric in structure, these catalysts follow the trend observed for C2-symmetric metallocenes [20], Chien et al. [23] reported a similar behavior for rac-[l-(9-r 5-fluorenyl)-2-(2,4,7-trimethyl-l-ri5-indenyl)ethane]zirconium dichloride and attributed this difference in the stereoerror formation to the fact that both sides of the catalyst are stereoselective thus isotactic polypropylene is obtained in the same manner as in the case of C2-symmetric metallocene catalysts. 

Negishi reported the zirconium-catalyzed enantioselective carboalumination of alkenes, which consisted of a hydroalumination/alkylalumination tandem process.133-135 This permits the asymmetric syntheses of methyl-substituted alkanols and other derivatives, typically with >90% ee, which represents an increase in ee value by 15% from the previously obtained 70-80%.136-138 The hydroalumination/zirconium-catalyzed enantioselective carboalumination of alkenes was carried out using (—)-bis(neomenthylindenyl)zirconium dichloride as the catalyst (Table 15).133... 

Synthesis of 8,8-Bis(cyclopentadienyl)-7,9-bis(trimethylstannyl)-8-zirconabicyclo[4.3.0]nona-1 (9),6(7)-diene 109 (Scheme 7.31) [172] To a solution of bis(cyclopentadienyl)zirconium dichloride (585 mg, 2.0 mmol) in THF (10 mL) at — 78 °C was added dropwise a solution of w-butyllithium in hexane (2.4 mL, 4.0 mmol). After the reaction mixture had been stirred at — 78 °C for 1 h, a solution of l,8-bis(trimethylstannyl)-l,7-octadiyne (863 mg, 2.0 mmol) in THF (2 mL) was added at the same temperature. The temperature was then allowed to rise to ambient, and the mixture was stirred for a further 3 h. The solvent was then removed under reduced pressure and the product was extracted with toluene. The extracts were filtered and the filtrate was concentrated and kept at 0°C to afford the product 109 (723 mg, 55% yield). 

In the 1980s, researchers introduced bis-cyclopentadienyl zirconium dichloride, catalysts that maintained their high level of activity for long periods of time. These catalysts became the favorites for copolymerizing ethylene with alpha olefms to produce LLDPE. 

Recent advances in the development of well-defined homogeneous metallocene-type catalysts have facilitated mechanistic studies of the processes involved in initiation, propagation, and chain transfer reactions occurring in olefins coordi-native polyaddition. As a result, end-functional polyolefin chains have been made available [103].For instance, Waymouth et al.have reported about the formation of hydroxy-terminated poly(methylene-l,3-cyclopentane) (PMCP-OH) via selective chain transfer to the aluminum atoms of methylaluminoxane (MAO) in the cyclopolymerization of 1,5-hexadiene catalyzed by di(pentameth-ylcyclopentadienyl) zirconium dichloride (Scheme 37). Subsequent equimolar reaction of the hydroxyl extremity with AlEt3 afforded an aluminum alkoxide macroinitiator for the coordinative ROP of sCL and consecutively a novel po-ly(MCP-b-CL) block copolymer [104]. The diblock structure of the copolymer... 

A C2-symmetric ansa metallocene is a racemic mixture of an enantiomeric pair—an example is rac-(dimethylsilyl)bis(l-indenyl)zirconium dichloride (XXXIV), abbreviated as rac-(CH3)2SiInd2ZrCl2. The enantiomers are designated as (R, R) and (S, S) to describe the two coordination sites in each enantiomer. Actually, the synthesis of a C2 ansa metallocene usually produces a mixture of the racemic pair plus the meso compound (R, S). The meso compound, which is a diastereomer of the racemic pair, can be separated from the racemic mixture by physical techniques such as recrystallization. The meso stereoisomer possesses Cs symmetry, and its stereoselectivity is very different from that of the enantiomeric pair (Sec. 8-5a-3). 

Bis(2-arylindene)zirconium dichlorides have been studied for the purpose of synthesizing isotactic-atactic stereoblock polymers [Busico et al., 2001 Lin et al., 2000 Lin and Way-mouth, 2002 Nele et al., 2000], Without the phenyl substituents, bisindenylzirconium dichloride yields atactic polypropene because there is rapid rotation of the r 5-ligands. The 2-phenyl substituents in bis(2-arylindene)zirconium dichloride interfere with each other suf-ficently that rotation is slowed to produce isotactic-atactic stereoblock polypropene. Three conformational isomers (conformers) are possible in this metallocene (Eq. 8-54). There is... 

The (m) fraction is in the range 0.6-0.7 for polymerization at high monomer concentration in the temperature range —25 to 25°C [Resconi et al., 2000]. Substituents on the phenyl groups of the 2-phenylindene ligands, especially meta substituents, slow down the conformational interconversion, and this increases the isotacticity of the polymerization. Both steric and electronic factors operate to affect the interconversion of conformers. Bis(2-phenylin-dene)zirconium dichloride/MAO yields polypropene with (mmmm) = 0.33 for polymerization of liquid propene at 20°C. 3,5-Di-f-butyl and 3,5-difluoromethyl substituents increase (mmmm) above 0.70 [Lin and Waymouth, 2002 Wilmes et al., 2002a,b]. 

Bis(p-fluorenyl) zirconium dichloride, 13 9 Bis(l,10-phenanthroline)copper, DNA cleavage and, 45 260-263... 

Bisphosphanorhodium acetylacetonates, reaction with hexafluoroacetone, 30 289 Bis(p-indenyl) zirconium dichloride, 13 9 Bis (polfluoroalkyl) mercurials, 3 340 properties of, 3 343-344 Bis(polyazamacrocycles), production, 45 100 Bis(pyrazoiyl)borato ligands, 42 292... 

These catalysts were used in combination with methylaluminoxane (MAO) for ethylene-norbornene co-polymerization and compared with isopropylidene[9-fluorenylcyclopentadienyl]zirconium dichloride catalyst activity under identical conditions. 

Semicrystalline polypropylene composition was prepared by Suhm et al. (4) using racdimethylsilanediylbis(2-methyl-4-phenylindenyl)zirconium dichloride and racdimethylsilanediylbis(2-methylindenyl)zirconium dichloride. 

A 20-liter reactor was charged with 3.11 liters of triisobutylaluminum isododecane solution (110g/l) and 800 ml of 30 wt% methylalumoxane toluene solution and then stirred at 50°C for 1 hour. This mixture was then treated with dimethylsilyl (2-methyl-l-indenyl)-7-(2,5-dimethylcyclopenta[l,2-b 4,3-b-,]-dithiophene) zirconium dichloride (13.1 mmol) suspended in isododecane (500 g) and stirred 1 hour at 50°C. The reaction mixture was then diluted with 520 ml of isododecane so that the final concentration of the catalyst mixture was 100 g/1. The catalyst was then used immediately. 

For example, ethylene bis(indenyl) zirconium dichloride can be prepared by the reaction of zirconium tetrachloride with bis(inden-yl)ethane lithium salt in tetrahydrofuran (4). 

Methylene-bis(3-ferf-butyl-l-indenyl) zirconium dichloride (25)... 

An example of such a catalyst system is racemic isopropylene bis(l-indenyl) zirconium dichloride in combination with an alumi-noxane (21). The reaction is carried out in hydrocarbon solvents, e.g., toluene. A solution of norbornene in toluene with the catalyst is degassed and then pressurized with ethene. The polymerization is carried out while stirring at 70°C under constant ethylene pressure at 18 bar. After completion, the polymer is precipitated in acetone and filtered (21). The cycloolefin copolymers obtained in this way have a high thermal shape stability and it is possible to use the polymers as thermoplastic molding compositions. 

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