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Zinc dialkoxide

The diethylzinc-alcohol (1 2) system was also extensively studied by Tsuruta and his co workers (85,86). Amorphous zinc dialkoxide was concluded to be an active species, because crystalline zinc alkoxide prepared from zinc chloride and lithium alkoxide proved to have only a very small catalytic activity. Based on kinetic studies of the polymerization of propylene oxide with the ZnEt2-CH3OH (1 2) catalyst system, the catalytically active species was concluded to be the complex formed by coordination of one molecule of monomer to the catalyst. In the polymerization of propylene oxide with the catalyst system, it was concluded that the monomer was polymerized by ring opening brought about by cleaving the CH2-0 bond (87). [Pg.97]

The mechanism of stereoregulation in the stereoselective polymerisation of propylene oxide with zinc dialkoxide and related zinc dialkoxide-ethylzinc alkoxide complexes has been satisfactorily explained by the enantiomorphic catalyst sites model prepared by Tsuruta et al. [52,75], According to this model, the presence of chiral sites with a central octahedral zinc atom, bearing the polymer chain and coordinating the monomer, was assumed to be the origin of the stereoregulation mechanism. [Pg.442]

Goel, S. C., Chang, M. Y., and Buhro, W. E., Preparation of soluble and volatile zinc dialkoxides. X-ray crystal structures of an (amido)zinc alkoxide and a ho-moleptic zinc enolate Inorg. Chem., 29, 4646 (1990). [Pg.52]

Tsuruta et al. (1963) prepared optically active poly (propylene oxide) from one mole of diethylzinc and two moles of (- -)-bomeol or (—)-menthol. They interpreted the catalyst activity as due to monomeric or dimeric zinc dialkoxide and that anionic coordinated polymerization took place by a four-membered ring intermediate similar to (LXV). The proximity of the optically active alkoxide to the point of reaction was thought to cause the asymmetric synthesis. [Pg.241]

The high reactivity of certain metal alkyls is well known. The autoxidation of dialkyIzinc was investigated as early as 1864 by several workers and they showed that dialkylzinc is oxidized rapidly to zinc dialkoxides" ... [Pg.49]

Abraham studied the oxidation of dialkylzinc and observed that rapid oxidation leads to the formation of bis(alkylperoxy)zmc, Zn(OOR)2. However, when the oxidation was carried ont slowly for several days under controlled conditions, zinc dialkoxide was the final prodnct, which on hydrolysis gave alcohol. The reduction of bis(alkylperoxy)zinc with excess of dialkylzinc also afforded zinc dialkoxides ... [Pg.49]

Similar to beryllium n-diaUcoxides, zinc dialkoxides are also insoluble and nonvolatile compounds. " " The alkylzinc alkoxides are, however, less polymeric and exhibit higher volatility. For example, the cryoscopic molecular weight determination in benzene indicates that methylzinc methoxide and terf-butoxide as well as ethylzinc tert-butoxide are tetrameric" with sublimation temperatures of 60, 95, and 105°C, respectively under 0.0001 mm pressure. ... [Pg.60]

The second class of catalysts are zinc(II) mono- or dialkoxides obtained from polyhydric phenols and dialkylzinc with partly polymeric stmctures. This system, extensively studied by Kuran [84], is an optimization of the water/diethylzinc and polyphenol/diethylzinc systems developed by Inoue [85]. The use of soluble zinc phenoxides and their analogous cadmium complexes as catalyst for the copolymerization of CO2 and epoxide was studied extensively by the Darensbourg group [86]. This work focused on the use of mononuclear phenoxide derivatives with bulky substituents, e. g., phenyl- and fe/t-butyl groups, on the aromatic ring to a homogeneous catalytic system and thus enhance the activity of the Zn phenoxides. The catalysts developed are stabilized through ancillary neutral... [Pg.1206]


See other pages where Zinc dialkoxide is mentioned: [Pg.1174]    [Pg.569]    [Pg.57]    [Pg.75]    [Pg.1174]    [Pg.569]    [Pg.57]    [Pg.75]    [Pg.1028]   
See also in sourсe #XX -- [ Pg.442 ]




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