Dienes, metallocene-catalyzed

The latter transformation requires the use of a small amount of an acid or its ammonium salt. By using [Cp2TiMe2] as the catalyst, primary anilines as well as steri-cally hindered tert-alkyl- and sec-alkylamines can be reacted.596 Hydroamination with sterically less hindered amines are very slow. This was explained by a mechanism in which equlibrium between the catalytically active [L1L2Ti=NR] imido complex and ist dimer for sterically hindered amines favors a fast reaction. Lantha-nade metallocenes catalyze the regiospecific addition of primary amines to alkenes, dienes, and alkynes.598 The rates, however, are several orders of magnitude lower than those of the corresponding intramolecular additions. 

Organo-/-element-catalyzed hydroaminations have been extensively investigated for more than 10 years.1034-1038 Lanthanide metallocenes catalyze the regiospecific intermolecular addition of primary amines to acetylenic, olefinic, and diene substrates at rates which are —1/1000 those of the most rapid intramolecular analogs. Kinetic and mechanistic data argue for turnover-limiting C=C/C=C insertion into an Ln-N bond, followed by protonolysis of... 

Parikh, D. R. Edmondson, M. S. Smith, B. W. Winter, J. M. Castille, M. J. Magee, J. M. Patel, R. M. Karajala, T. P. Structure and Properties of Single-site Constrained Geometry Ethylene-Propylene-Diene (EPDM) Elastomers. In Metallocene-catalyzed Polymers -Materials, Properties, Processing Markets, Benedikt, G. M., Goodall, B. L., Eds. Plastics Design Library New York, 1998 p 113. 

Walter Kaminsky and Hansjorg Sinn (Univ. Hamburg) discovered the key beneficial role of moist MAO for a metallocene-catalyzed polymerization of olefins, cyciooiefins, dienes, styrenes, etc. The discovery was followed by numerous patents on the modification/improvements, e.g., L. H. Slaugh and... 

Recently, a metallocene/MAO system has been used for the polymerization of non-conjugated dienes [204, 205]. The cyclopolymerization of 1,5-hexadiene has been catalyzed by Zieger-Natta catalyst systems, but with low activity and incomplete cyclization in the formation 5-membered rings [206]. The cyclopolymerization of 1,5-hexadiene in the presence of ZrMe2Cp2/MAO afforded a polymer (Mw = 2.7 x 107, Mw/Mn = 2.2) whose NMR indicated that almost complete cyclization had taken place. One of the olefin units of 1,5-hexadiene is initially inserted into an M-C bond and then cyclization proceeds by further... 

Among early and group III transition metals, the yttrocene catalysts have been studied in greatest detail. However, related metallocenes show great promise as catalysts for reductive cyclization. Neodymocene-catalyzed cyclization of 1,5- and 1,6-dienes 14a and 15a proceeds readily in the presence of silane to afford cyclopentanes 14b and 15b.37 Lutetocenes and samarocenes also catalyze silane-mediated cyclization of 1,5-diene 14a to cyclopentane 14b.38 39 In the case of the samarium-based metallocenes, the feasibility of borane-mediated cyclization has been established, as demonstrated by the highly diastereoselective conversion of phenyl-substituted diene 16a to cyclopentane 16b (Scheme ll).40... 

Dienes are less reactive toward transition metals than enynes and diynes, and perhaps for this reason, the development of effective catalyst systems for the cyclization/hydrosilylation of dienes lagged behind development of the corresponding procedures for enynes and diynes. The transition metal-catalyzed cyclization/hydrosilylation of dienes was first demonstrated by Tanaka and co-workers in 1994. Reaction of 1,5-hexadiene with phenyl-silane catalyzed by the highly electrophilic neodymium metallocene complex Cp 2NdCH(SiMe2)3 (1 mol%) in benzene at room temperature for 3 h led to 5- ///76 -cyclization and isolation of (cyclopentylmethyl)phenylsilane in 84% yield (Equation (15)). In comparison, neodymium-catalyzed reaction of 1,6-heptadiene with phenylsilane led to 5- X(9-cyclization to form (2-methylcyclopentylmethyl)phenylsilane in 54% yield as an 85 15 mixture of trans. cis isomers (Equation (16)). 

Bercaw has investigated the application of the 6 2-symmetric, enantiomerically pure lanthanide metallocene derivative (i ,A)-BnBpYH 34 as a catalyst for the asymmetric cyclization/hydrosilylation of 1,5- and 1,6-dienes. Although 34 displayed high activity for the reaction of a number of dienes, asymmetric induction was low. In the best case, reaction of 3,3-dimethyl-1,5-hexadiene with phenylsilane catalyzed by 34 gave silylated cyclopentene 35 in 95% yield with 50% ee (Equation (25)). 

Most addition polymerizations involve vinyl or diene monomers. The opening of a double bond can be catalyzed in several ways. Free-radical polymerization is the most common method for styrenic monomers, whereas coordination metal catalysis (Zigler-Natta and metallocene catalysis) is important for olefin polymerizations. The specitic reaction mechanism may generate some catalyst residues, but there are no true coproducts. There are no stoichiometry requirements, and equilibrium limitations are usually unimportant so that quite long chains are formed 7iv > 500 is typical of addition polymers. 

The copolymerization of ethene with a variety of other alkenes or dienes was also studied. The copolymerization of supercritical mixtures of ethene and propene (120-220 °C and 1000-1500 bar) was catalyzed by the silyl-bridged bis-(tetrahydroindenyl)zirconocene catalyst 19 and MAO at a metallocene concentration of 6 X 10 mole fraction and an Al Zr ratio of 22000 [92]. With a 50 50 mixture of SCC2H4 and scCsHg, the resulting polymer had only 8% incorporation of propene. Increasing concentrations of propene resulted in... 

Trivalent lanthanocene complexes that are isoelectronic (14e, (P) to cationic group 4 metallocenes are also active for olefin polymerization, although their activity is much less than that of Ti and Zr [28,29]. Mashima et al. have reported monocyclopentadienyl rf-diene complexes of tantalum and niobium that are isoelectronic to group 4 metallocenes. These complexes catalyze ethylene polymerization, albeit with low activity [30]. 

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