Zirconocenes with butenes

When zirconocene(l-butene) [5] was reacted in situ with p-tolylchloroacetylenes, the first zircono-zirconacydopropenes were obtained in high chemical yields [237]. 

A valuable route to metallocene complexes is through a cyclometalla-tion reaction with removal of a p-proton from the substrate and elimination of an alkane or arene. Typical of this approach is the formation of zirconocene 1-butene 4 (Scheme 5.3). The C-H activation method avoids the problem of dimerisation of the ir-component since there is none of this initially free of the metal. The method also facilitates the formation of complexes of components which are unstable in the free state, such as ben-zyne, cycloalkynes, and thioaldehydes. It is normally successful for crosscouplings when the component generated on the metal is strongly bound. If this is not the case, exchange with the second ir-component may take place, as described for zirconocene 1-butene (Scheme 5.3), giving the unwanted dimer or mixtures (see Section 5). 

Cyclisations initiated by zirconocene 1-butene are incompatible with ester functionality, a limitation which has been overcome by the use of a diethyl titanocene reagent which gives titanocycles exemplified by 23 (Scheme 5.8). 

The intramolecular coupling of alkenes (and alkynes) with cyanides or hydra-zones induced by zirconocene 1-butene has been reported, - and the intramolecular coupling between alkenes (and alkynes) and ketones or aldehydes induced by Cp2Ti(PMe3)2 is also known. ... 

Kagan et al. were the first to report the corresponding enantioselective catalytic hydrogenation using chiral metallocene derivatives [94, 95]. By using menthyl- and neomenthyl-substituted cyclopentadienyl titanium derivatives in the presence of activators (Scheme 6.5) [96], these authors observed low ee-values (7-14.9%) for the catalytic hydrogenation of 2-phenyl-l-butene into 2-phenylbutane. In contrast, no enantiomeric excess was obtained with the corresponding zirconocene derivatives. 

Butenes, with propylene co-polymers, 4, 1075 -Butene zirconocenes, preparation, 4, 889 Butenyl polystyrene, as solid support, 12, 739 / r/-Butylallene, dichalcogenide additions, 10, 758 />-/ r/-Butylcalix[4]arenes... 

PP-b-PMMA (Mn = 22220, Mw/Mn = 1.14) was produced by CRP via another route. Terminally vinyl PP (Mn = 3100, Mw/Mn = 1.45, isotactic-ity = 32%) prepared using a zirconocene catalyst was converted to terminally brominated PP via PP-SiH prepared by hydrosilylation [70]. The resulting PP-b-PMMA was purified by extraction of unreacted PP with diethyl ether. Poly(ethylene-co-butene)-bZocfc-poly(methyl methacrylate) (EBR-b-PMMA) was synthesized through the bromination of terminally hydroxy-lated EBR (Mw = 3600 g/mol, Mw/Mn = 1.05), which was commercially available [71]. An atactic PP/PMMA had been synthesized by a combination of metallocene catalyses, Cp2ZrCl2 and Me2Si(CpMe4)(.W-f-Bu)TiCl2, and ATRP [72]. 

Kaminsky W, Kulper K, Brintzinger HH, FRWP Wild, Polymerization of Propene and Butene with a Chiral Zirconocene and Methyl Aluminoxane as Cocatalyst, Angew Chem Int Ed Engl, 24,507 (1985)... 

Elimination reactions are typically found in transition metal chemistry. The conversion of allylic ethers into allylzirconocenes [18] is a well-known zirconium-mediated process of this type. In contrast, the y-elimination reactions are less frequently encountered, and only a few examples of y-elimination involving zirconocenes have been reported. When studying isonitrile insertion into zirconacycles, Whitby and coworkers observed an interesting reaction leading to a cyclopropane derivative [19]. The overall transformation is depicted in Scheme 12. Treatment of the diene 18 with preformed butene-zirconocene gave... 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

Compound (CsH4SiMe2NBut)TiCl2 has been synthesized and used as pre-catalyst for ethylene polymerization. The activities and the properties of the polymers have been compared to similar zirconium and hafnium derivatives.720 The consequences of anion-cation interactions on the activity of GGG group 4 metal complexes in olefin polymerizations have been explored for a series of zirconocene derivatives as well as the cationic species [(C5Me4SiMe2NBut)TiMe]+ with the sterically congested tris(perfluorobiphenyl)fluoroaluminate as the counteranion.721 The co-polymerization of ethylene and 1-butene by (CsMe iMe Bu TiC in the presence of... 

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