Ethylene zirconocene dichloride

Ethylene-bridged bis-indenyl zirconocene dichloride-methylalu-moxane system. 

Chiral C2-symmetric ansa-metallocenes, also referred to as bridged metallocenes, find extensive use as catalysts that effect asymmetric C—C bond-forming transformations [4]. In general, bridged ethylene(bis(tetrahydroindenyl))zirconocene dichloride ((ebthi)ZrCl2) 1 or its derived binaphtholate ((ebthi)Zrbinol) 2 [5] and related derivatives thereof have been extensively utilized in the development of a variety of catalytic asymmetric alkene alkylations. 

Titanocene and zirconocene dichlorides (Cp2MtCl2 with Mt = Ti, Zr) were the first metallocenes studied [Breslow and Newburg, 1957 Natta et al., 1957a], The metallocene initiators, like the traditional Ziegler-Natta initiators, require activation by a Lewis acid coinitiator, sometimes called an activator. AIRCI2 and A1R3 were used initially, but the result was initiator systems with low activity for ethylene polymerization and no activity in a-olefin polymerization. The use of methylaluminoxane (MAO), [A1(CH3)0] , resulted in greatly improved activity for ethylene polymerization [Sinn and Kaminsky, 1980], The properties of MAO are discussed in Sec. 8-5g. MAO has two functions alkylation of a transition metal-chloride bond followed by abstraction of the second chloride to yield a metallocenium... 

Supramolecular catalysis may also involve the combination of a host cavity and a metal active site as in the bis(diphenylphosphino)calix[4]arene nickel(II) complex 12.40 which acts as an efficient catalyst for ethylene and propylene polymerisation, and in tandem with zirconocene dichloride, for the formation of linear low-density polyethylene. In the latter case the complex gives very little branching - a significant advantage. The key to the effectiveness of the catalyst involves calixarene-induced changes in the bite angle at the Ni(II) centre, which is square planar in the active form of the catalyst.29... 

Voegele, J. Dietrich, U. Hackmann, M. Rieger, B. Design of Ethylene-bridged ansa-Zirconocene Dichlorides for a Controlled Propene Polymerization Reaction. In Metallocene-based Polyolefins Preparation, Properties and Technology, Scheirs, J., Kaminsky, W., Eds. Wiley Chichester, 2000 Vol. 1, p485. 

A ternary system that consists of a zirconocene dichloride, a trialkyl aluminum, and Ph3C+B(C6F5)4 has been developed by Chien et al. for ethylene and propylene polymerizations with superb activity. The use of excess of R3AI serves both to alkylate the dichloride precursor as well as to scavenge O2. H2O. and other protic impurities in the system. The entire activation process can be perceived as the initial in-situ alkylation of the zirconocene dichloride by the alkylaluminum, followed by subsequent oxidative cleavage of a Zr—R bond by Ph3C+ (eq 45). This... 

Suzuki and Suga reported the use of clays as solid acids to support and activate metallocene catalysts for olefin polymerization. They were able to use much less alkylaluminmn cocatalyst relative to solution polymerization conditions. The clays were slurried with AlMeg in toluene, then treated with a solution containing zirconocene dichloride, II, and AIMeg. The metallocenium cation was presumed formed via abstraction of chloride and/or methyl ligands by acidic sites on the surface of the clay, and the low basicity of the clay smface was proposed to stabilize the coordinatively unsaturated cation. Propylene was copolymerized with 250 psi ethylene at 70°C. For acid-treated KIO montmorillonite, an activity of 3300 X 10 kg polymer/(g Zr h) was obtained. Catalysts based on vermiculite, kaolin, and synthetic hectorite all showed lower but still appreciable activities. In this brief report, the Al/Zr ratio was not specified, and the clay dispersion was not reported. 

Rieger, B. Repo, T. Jany, G. Ethylene-bridged ansa-zirconocene dichlorides for syndiospecific propene polymerization. Polym. Bull. 1995, 35, 87-94. 

For some leading reviews see (a) Resconi, L. Cavallo, L. Fait, A. Piemontesi, F. Selectivity in propene polymerization with metallocene catalysts. Chem. Rev. 2000,100, 1253-1345. (b) Alt, H. G Koppl, A. Effect of the nature of metallocene complexes of Group IV metals on their performance in catalytic ethylene and propylene polymerization. Chem. Rev. 2000, 100, 1205-1221. (c) Halterman, R. L. Synthesis and applications of chiral cyclopentadienyhnetal complexes. Chem. Rev. 1992, 92, 965-994. (d) Halterman, R. L. Synthesis of chiral titanocene and zirconocene dichlorides. In Metallocenes ... 

Heterodinuclear Zr/Fe complex has been prepared by cross-metathesis of 3-butenyl-Cp-substituted zirconocene dichloride with ferrocenylmethyl acrylate (Scheme 12.26) [29]. This Zr/Fe complex exhibited catalytic activity in ethylene and propylene polymerization similar to those of the starting Zr complex. 

Stork M, Koch M, Klapper M, Mullen K, Gregorius H, Rief U (1999) Ethylene polymerization using crosslinked polystyrene as support for zirconocene dichloride/methylaluminoxane. Macromol Rapid Commun 20 210-213... 

A review article has discussed die zirconocene dichloride catalysed cyclometalation of olefins and alkynes with alkylalanes. A usefiil thesis of zirconocme methylamides has been documoited from the sequential reactimi of magnesium amide and a mediyl Grignand reagent to zirconocene dichloride. Chiral ethylene bridged onsa-zirconocene dichlorides have... 

Kolodka, E., Want, W.-J., Charpenier, P. A., Zhu, S., Hamielec, A. E. Long-chain branching in slurry polymerization of ethylene with zirconocene dichloride/modified methylaluminoxane. Polymer (2000) 41, pp. 3985-3991... 

Under the same conditions, syndiospecihc (Cs-symmetric) metallocenes are more effective in inserting a-olefins into an ethylene copolymer than isospecific (C2-symmetric) metallocenes or unbridged metallocenes. In particular, hafnocenes are more efficient than zirconocenes. An interesting effect is observed for the polymerization with ethylene(bisindenyl)zirconium dichloride and some other metallocenes. The catalytic activity for the homopolymerization of ethylene is very high, and it increases when copolymerization with propylene occurs (114) (Fig. 12). Munoz-Escalona et al. (125) observed similar effects in the copolymerization of ethylene with 1-hexene. 

The catalytic cycle proposed for the enantioselective ethyhnagnesation involves the chiral zirconocene-ethylene complex (121), formed upon reaction of the dichloride with two equivalents of EtMgCl. Coupling of the alkene substrate leads to the formation of the metallacyclopentane intermediate, which gives the zirconate (122) with a... 

The regio- and stereoselective zirconocene-catalyzed addition of alkylmagnesium halides to alkenes, a process which has been described previously (see Section 7.5.2, Scheme 7-79) was investigated with ethylene-l,2-bis( M,5,6,7-tetrahydroind-l-enyl)zirconium dichloride [(EBTHI)ZrCl2l) [118] as chiral zirconocene. Thus, treatment of the latter with alkylmagnesium halides leads to the formation of the derived zirconocene-alkene complex 88, characterized by NMR [119], which reacts with cyclic ethers or amines to lead to the corresponding homoallylic alcohol or amine, respectively, in > 95% ee and good overall yield [120] (Scheme 7-103). 

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