Ferric alkoxides

The solid surface of the catalyst causes the transition state to be more compressed. Steric repulsions between the incoming monomer and the ultimate unit are minimized if the incoming monomer molecule is forced to be trans to the methyl group of the previous unit. Such a conformational approach also results in minimum repulsion between the incoming monomer and the bulky growing pol3nner chain. " Also, ferric alkoxides are associated with nonpolar solvents. A dimer may have the following structure ... 

By comparison, intramolecular chelation can be expected to reduce the degree of association of the catalyst. Addition of water results in increased association after hydrolysis of the ferric alkoxide. This may explain the effect of promoting stereoregularity by addition of water. The ferric alkoxide catalyst can also be made highly stereospecific by partial hydrolysis and still remain soluble in ether, the polymerization medium. This led to a suggestion that the catalyst may contain active Fe-O-Fe bonds. Such bonds would be formed from condensation of partially hydrolyzed alkoxide derivative. The monomer insertion between the iron-oxygen bonds can be illustrated as follows ... 

The forces of interaction between the iron atoms and the various oxygen atoms as shown aboye assure a cis opening of the epoxide ring. The mechanism of the reaction of the ferric alkoxide is S//2-type. There is therefore increased restriction on the conformation of the monomer unit as it approaches the reaction center. ... 

Low activity has been reported for several simple iron-based initiators including oxides,827 porphyrins,860 carboxylates861-863 and alkoxides, 64-866 However, the ferric cluster [Feslqs-0)(OEt)13], (284), is a highly active initiator for the polymerization of LA 867 97% conversion of 450 equivalents is achieved in just 21 min at 70 °C in toluene. Polydispersities are typically between 1.15 and 1.30, even at monomer loadings of 1,000 equivalents. 

It seems reasonable to propose that the primary interaction inducing the proposed C-H activation mechanism consists in the interaction of the C-H bond with ferric ions, which are the oxidizing agents, as already proposed for the oxidation of different hydrocarbons at the surface chromate species of oxidized MgCr204 [8]. This mechanism implies that the two electrons of the C-H bond are assumed by the catalyst surface, where two ferric ions can become reduced to ferrous ions. But-3-en-2-oxide decomposes easily by elimination (as most alkoxides do) to the corresponding olefin, 1,3-butadiene in this case, and a surface OH group. Two OH s condense to allow water to desorb and oxygen reoxidizes the reduced iron cations. This is a very reasonable catalytic cycle for 1,3-butadiene production. 

The nature of the complexes formed between water, methanol and ethanol molecules and Co cations was determined [24]. A large anomalous ferric component was observed in the spectra of the water-complexed sources but not with the alcohol-complexed sources. This ferric component arose from the radiolysis of the complexed water molecules in the electron capture decay process of Co. Following the electron capture the water in the first coordination sphere of the MSssbauer atom is subjected to a flux of low energy Auger electrons and X-rays. This water is decomposed into H and OH radicals and it is the H radicals that can oxidize the Fe " to Fe +. Interestingly, no anomalous Fe component was observed when methanol or ethanol was the sorbate. Irradiation of alcohols does not lead to the production of alkoxide radicals. 

The coordination catalysts for these reactions are diverse. They can be compounds of alkaline earth metals, like calcium amide, or calcium amide-alkoxide. They can also be Ziegler-Natta-type catalysts. These can be alkoxides of aluminum, magnesium, or zinc combined with ferric chloride. Others are reaction products of dialkylzinc with water or alcohol. They can also be bimetallic //-oxoalkoxides, such as [(RO)2A102]Zn. Other catalysts are aluminum or zinc metalloporphyrin derivatives (see Fig. 4.1). 

Heterometallic aUcoxide is used for the preparation of high purity multicomponents oxide in good yield. Stoichiometric ratio of anhydrous metal chloride and bimetallic alkoxide was taken in anhydrous dichloromethane. The reaction mixture was refluxed with catalytic amounts of ferric chloride (anhydrous). After completion of... 

The phosphitylation of D-mannose with phosphorous triazolides has afforded primarily the mannofuranose 2,3,6-O-phosphite 12. The complexes formed separately between o-fructose and L-sorbose with 1,10-phenanthroline and Co(III) ions have been characterised, while composites prepared by the reaction of simple sugars with tetraethoxysilane and water have been shown to be capable of resolving racemic cobalt and chromium ion complexes. Sodium alkoxide salts of free sugars have been treated with ferric chloride to give iron-sugar complexes and five-fold deprotonated D-mannose forms dinuclear metalates [X2(P-D-Man-/)2] of trivalent (X = Fe, V, Cr and Al) with O-1,2,3,5 and 6 involved in complexation. ... 

The mechanism of the ferric chloride-propylene oxide complex-initiated polymerization has been considered to be a coordinate anionic polymerization in which monomer, propylene oxide, first coordinates with iron, followed by nucleophilic attack of the alkoxide group on one of the oxirane carbons. 

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