Functional alkoxides

Another potential of functionalized alkoxide ligands was uncovered about ten years earlier. Tailor-made, predominantly multiply functionalized ligands attracted attention as models for binding sites of metallo-enzymes [95]. 

Aspinall, H.C., Bickley, J.F., Gaskell, J.M., Jones, A.C., Labat, G, Chalker, P.R., et al. (2007) Precursors for MOCVD and ALD of rare earth oxides - complexes of the early lanthanides with a donor-functionalized alkoxide ligand. Inorganic Chemistry, 46, 5852-5860. 

This strategy was adopted to alleviate tedious techniques of mixing multicomponent precursors with different properties. In view of their technological demands, tin(II) heterometallic alkoxides are the most studied class of compounds and their properties can be modulated by chelating ligands like /3-diketonates, carboxylates, and functionalized alkoxides for specific purposes. These compounds also facilitate the formation of oxoalkoxides, either by hydrolysis or by some side reactions. 

Scheme 2.12.1 Coordination modes of alkoxides (la) and functionalized alkoxides (lb) where X -NRy and M = the same or different metals ...

In a typical preparation, 50 mg of methyl methacrylate copolymer was dissolved in a mixture of lOcm of titanium butoxide and 2cm of mercaptopropyltriethoxysi-lane. Another synthesis with higher amounts of the thiol-functionalized alkoxide was also performed. To evaluate the role of the thiol sdicon alkoxide on nanoporous hybrid formation, some syntheses were performed using only the methyl metacry-late copolymer and the titanium alkoxide. 

The following mechanism appears reasonable (compare Section VI, 12), It assumes that the function of the aluminium ieri.-butoxide, or other alkoxide. is to provide a source of aluminium ions and that the aluminium salt of the secondary alcohol is the actual reactant. Aluminium with its sextet of electrons has a pronounced tendency to accept a pair of electrons, thus facilitating the initial coordination and the subsequent transfer of a hydride ion ... 

The TT-allylpalladium complexes 241 formed from the ally carbonates 240 bearing an anion-stabilizing EWG are converted into the Pd complexes of TMM (trimethylenemethane) as reactive, dipolar intermediates 242 by intramolecular deprotonation with the alkoxide anion, and undergo [3 + 2] cycloaddition to give five-membered ring compounds 244 by Michael addition to an electron-deficient double bond and subsequent intramolecular allylation of the generated carbanion 243. This cycloaddition proceeds under neutral conditions, yielding the functionalized methylenecyclopentanes 244[148], The syn-... 

Reaction with base brings the alcohol function of the halohydrin into equilibrium with Its corresponding alkoxide... 

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

Transesterification of methyl methacrylate with the appropriate alcohol is often the preferred method of preparing higher alkyl and functional methacrylates. The reaction is driven to completion by the use of excess methyl methacrylate and by removal of the methyl methacrylate—methanol a2eotrope. A variety of catalysts have been used, including acids and bases and transition-metal compounds such as dialkjitin oxides (57), titanium(IV) alkoxides (58), and zirconium acetoacetate (59). The use of the transition-metal catalysts allows reaction under nearly neutral conditions and is therefore more tolerant of sensitive functionality in the ester alcohol moiety. In addition, transition-metal catalysts often exhibit higher selectivities than acidic catalysts, particularly with respect to by-product ether formation. 

Fig. 6. Dependence of stmctural density of alkoxide-derived porous silica gels as a function of sintering temperature held for 12 h for three different...

Reaction of Enolate Anions. In the presence of certain bases, eg, sodium alkoxide, an ester having a hydrogen on the a-carbon atom undergoes a wide variety of characteristic enolate reactions. Mechanistically, the base removes a proton from the a-carbon, giving an enolate that then can react with an electrophile. Depending on the final product, the base may be consumed stoichiometricaHy or may function as a catalyst. Eor example, the sodium alkoxide used in the Claisen condensation is a catalyst ... 

Various inorganic esters have been claimed as coupling agents for reinforced plastics, including aminobenzyl phosphonates, dicetylisopropylborate, alkoxy compounds of aluminum, zirconium and titanium, zircoaluminates, and numerous substituted titanates [1]. These metal alkoxides could function in a similar manner to the orthosilicates by reacting with hydroxylated substrates. Like the simple orthosilicates such as tetraethyl orthosilicate (TEOS), it is less evident how an-... 

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