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Catalysts, enantioselectivity Ziegler-Natta

The stereoselective behaviour of heterogeneous Ziegler-Natta catalysts is caused by the chirality of the catalytic active site but not by chiral atoms in the growing chain. The model devised by Corradini et al. [282] can explain the experimental results relative to the first insertion of a chiral a-olefin into an initial Ti-CH3 bond [377,378], i.e. the absence of enantioselectivity (discrimination between re and si insertions) but the presence of diastereoselectivity... [Pg.135]

Miller, S. A. and Waymouth, R. M., Stereo- and Enantioselective Polymerisation of Olefins with Homogeneous Ziegler-Natta catalysts , in Ziegler Catalysts, Springer-Verlag, Berlin, 1995, pp. 441-454. [Pg.237]

Ziegler-Natta Various types of Ziegler-Natta catalysts Polymerization mechanism and applications of molecular mechanics to the study of enantioselectivity of some stereospecific catalytic systems having chiral site stereocontrol Mechanism of enantioselectivity and its relevance to catalytic systems 56... [Pg.260]

The discovery that group IV metallocenes can be activated by methylaluminox-ane (MAO) for olefin polymerization has stimulated a renaissance in Ziegler-Natta catalysis [63]. The subsequent synthesis of well-defined metallocene catalysts has provided the opportunity to study the mechanism of the initiation, propagation, and termination steps of Ziegler-Natta polymerization reactions. Along with the advent of cationic palladium catalysts for the copolymerization of olefins and carbon monoxide [64, 65], these well-defined systems have provided extraordinary opportunities in the field of enantioselective polymerization. [Pg.1263]

Busico et al., on the other hand, came to a conclusion [299] that the stereoregularity of polypropylene produced with C2-symmetric group 4 ansa-metallocene catalysts is a result of the interplay of two competing reactions. These are isotactic monomer polyinsertion and a side process of epimerization of the polymer chain at its active end. That makes this class of homogenous catalysts different from the typical Ziegler-Natta catalyst, because with these catalysts enantioselectivity and stereoselectivity are not necessarily coincidental [96]. [Pg.216]

Chiral Cyclopentadienyl Complexes. Since the discovery of the polymerization activity of cyclopentadienyl complexes, they also play a key role in asymmetric catalysis (Fig. 13). Titanocene complexes of chiral tricyclic monocy-clopentadienyl ligand catalyze the enantioselective hydrogenation of unfunctionalized oleflns (105). A similar reaction has been performed with related catalysts such as chiral Ziegler-Natta systems (106) and organolanthanide systems (107). [Pg.691]

Ammendola, P Tancredi, T. Zambelh, A. Isotactic polymerization of styrene and vinylcyclohexane in the presence of a C-enriched Ziegler-Natta catalyst Regioselectivity and enantioselectivity of the insertion into metal-methyl bonds. Macromolecules 1986,19,307-310. [Pg.396]


See other pages where Catalysts, enantioselectivity Ziegler-Natta is mentioned: [Pg.272]    [Pg.17]    [Pg.15]    [Pg.98]    [Pg.379]    [Pg.173]    [Pg.139]    [Pg.334]    [Pg.83]    [Pg.1019]    [Pg.140]    [Pg.12]    [Pg.178]    [Pg.351]    [Pg.379]    [Pg.380]    [Pg.169]    [Pg.628]    [Pg.504]    [Pg.13]    [Pg.173]    [Pg.2]   
See also in sourсe #XX -- [ Pg.45 , Pg.182 , Pg.278 , Pg.284 ]




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