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Zn Catalysts (zn + catalyst)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Recent data on the number of active centers and propagation rate constants in olefin polymerization with supported ZN catalysts

MACROMOLECULAR SYMPOSIA, Issue 1 2004
V.A. Zakharov
Abstract Data on the number of active centers (Cp) and propagation rate constants (Kp) have been obtained by means of polymerization quenching with 14CO of propylene and ethylene polymerization with supported titanium-magnesium catalysts (TMC) with different composition. In the case of propylene polymerization the Cp and Kp values have been measured separately for isospecific, aspecific and low stereospecific centers. Effects of MgCl2 support, internal and external donors are discussed on the basis of data obtained. Data on the strong effect of diffusion limitation at ethylene polymerization with number of TMC have been obtained and a set of methods have been used to exclude this effect. Data on Cp and Kp values at ethylene polymerization with low stereospecific and highly stereospecific catalysts are presented. [source]

ChemInform Abstract: Highly Enantioselective 1,4-Addition of Diethyl Phosphite to Enones Using a Dinuclear Zn Catalyst.

CHEMINFORM, Issue 28 2009
Depeng Zhao
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Self and nonself recognition of chiral catalysts: The origin of nonlinear effects in the amino-alcohol catalyzed asymmetric addition of diorganozincs to aldehydes

THE CHEMICAL RECORD, Issue 2 2001
Ryoji Noyori
Abstract Asymmetric addition of dialkylzincs to aldehydes in the presence of (2S)-3- exo -(dimethylamino)isoborneol [(S)-DAIB] exhibits various nonclassical phenomena. The enantiomeric excess (ee) of the alkylation product, obtained with partially resolved DAIB, is much higher than that of the chiral amino alcohol, while the rate decreases considerably as the ee of DAIB is lowered. The asymmetric amplification effects reflect the relative turnover numbers of two enantiomorphic catalytic cycles, where an essential feature is the reversible homochiral and heterochiral dimerization of the coexisting enantiomeric DAIB-based Zn catalysts. The interplay between the thermodynamics of the monomer/dimer equilibration and the kinetics of alkylation reaction strongly affect the overall profile of asymmetric catalysis. The self and nonself recognition of the chiral Zn catalysts is a general phenomenon when (S)-DAIB is mixed with its enantiomer, diastereomer, or even an achiral ,-amino alcohol. The degree of nonlinearity is highly affected not only by the structures and purity of catalysts but also by various reaction parameters. The salient features have been clarified on the basis of molecular weight measurements, NMR and X-ray crystallographic studies of organozinc complexes, and kinetic experiments, as well as computer-aided quantitative analysis. © 2001 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:85,100, 2001 [source]