Carboxylates alkoxides

Aluminum porphyrins with alkoxide, carboxylate, or enolate can also activate CO2, some catalytically. For example, Al(TPP)OMe (prepared from Al(TPP)Et with methanol) can bring about the catalytic formation of cyclic carbonate or polycarbonate from CO2 and epoxide [Eq. (6)], ° - and Al(TPP)OAc catalyzes the formation of carbamic esters from CO2, dialkylamines, and epoxide. Neither of the reactions requires activation by visible light, in contrast to the reactions involving the alkylaluminum precursors. Another key difference is that the ethyl group in Al(TPP)Et remains in the propionate product after CO2 insertion, whereas the methoxide or acetate precursors in the other reactions do not, indicating that quite different mechanisms are possibly operating in these processes. Most of this chemistry has been followed via spectroscopic (IR and H NMR) observation of the aluminum porphyrin species, and by organic product analysis, and relatively little is known about the details of the CO2 activation steps. 

In [1677] complex alkoxides and alkoxide-carboxylates were compared as precursors for preparation ofBST films. In contrast to the introduction of alkaline earth carboxylates in the form of preliminary isolated salts, in this work metal alkoxide solution in methoxyethanol containing titanium and alkaline-earth metal was modified by addition of 2-ethylhexanoic acid with subsequent slow distilling off the solvent and repeated dilutions with fresh portions of methoxyethanol. During the distillation process, part of the alkoxide groups are substituted by the 2-ethylhexanoate ligands. The exchange reaction of Ti(OPr )4 with acid was studied in different solvents, and it was demonstrated that in the course of distillation the titanium oxoisopropoxy-2-ethylhexanoate is formed with elimination of ester ... 

Synthesis of the third-generation catalyst is an intricate process. Two crucial steps are (1) Precipitation of the supported catalyst from a solution of Mg2+ ion in organic solvent by the addition of TiCl4. (2) Catalyst activation by heat treatment with TiCl4 and phthalate esters (third component). The precursors for the support could be magnesium alkoxides, carboxylates, sulhte, or sulfinates. They all give particles of different but well-defined morphologies. 

V NMR spectroscopic studies have been carried out with simple dicarboxylates and simple mixed alkoxide-carboxylate systems.60 The complexes that form are generally stable in the acidic pH range. Recent investigations employ a combination of both solid state124 and solution studies, and provide benchmark data for one of the classes of a-hydroxycarboxylate complexes which form in aqueous solution (VL, VL2. V2L22. and V3L2-).8... 

Cp2LnX compounds with alkoxide, carboxylate, and related ligands... 

The majority of cases (Table 1) involve activation of the diene by complexation to Pd(II) and Pt(II) centers. However, other metal-diene complexes have been examined including Ni(II), Ir(I), and Mn(I) complexes. Cationic or neutral complexes are used in the nucleophilic addition reactions. The most common nucleophiles employed are oxygen or nitrogen bases (hydroxide, alkoxides, carboxylates, amines) or stabilized carbon nucleophiles (malonate, j8-diketonates). The dienes employed include 1,5-cyc-looctadiene, norbomadiene, dicyclopentadiene, 4-vinylcyclohexene, 7-(alkylidene)nor-bornene and endo-4-vinylnorbornene. 

Alkoxides, Carboxylates and Oxo Salts. All four elements of this Group form alkoxides, but those of silicon, e.g., Si(OC2H5)4, are the most important the surface of glass or silica can also be alkoxylated. Alkoxides are normally obtained by the standard method ... 

The following group of reactions are analogous to the Michaelis-Arbuzov reaction with the distinction that rather than a halide, the group displaced in the initial stage is a mercaptide, alkoxide, carboxylate, etc. 

Lithium Halide-catalyzed Reversal via Betaine Lithium Halide Adducts. This is the most common mechanism for loss of stereospecificity under Wittig conditions and often contributes to the stereochemical outcome of bezaldehyde reactions in the presence of lithium ion. The process is most facile for ylides containing anionic (alkoxide, carboxylate, or amido) substituents. 

Aluminum alkoxide Carboxylic acid esters from 2 aldehyde molecules Tishdienko reaction... 

The size and shape of the clusters can be influenced to a certain degree by the reaction parameters. The most important parameter is the metal alkoxide/carboxylic acid ratio. An example is shown in Figure 1 (for a given ratio, the same cluster is reproducibly obtained). 

C 13 Carbonates, Cyanides, Thiocyanates, Alkoxides, Carboxylates Compounds with Silicon... 

There is also one interesting report about Ce + alkoxides being formed via controlled oxidation reaction of cerium(III) alkoxide precursors, e.g., by reactions of ceriiun(III) tris[lri(tert-bufyl)methoxide] with either an organic peroxide or benzoquinone. For example, treatment of Ce(OC Bu3)3 with dibenzoylperoxide according to Scheme 4 afforded a mixed cerium(rv) alkoxide carboxylate, which was, however, stable only in solution and decomposed to cerium(III) species when the reaction was carried out on a preparative scale." ... 

Like in the hydrolytic way, the knowledge of mechanisms is made difficult by the conplicated nature of molecular precursors. First, one has to bear in mind that rapid scrambling of ligands (halide, alkoxide, carboxylate, etc.) takes place around metal and semi-metal centers even at room temperature (Eq. 26.10). For instance, a mixture of metal (or silicon) chloride and metal (or silicon) alkoxide rapidly leads to a mixture of chloroalkoxides, which are the actual precursors (Moedritzer, 1971). 

In our group we used time-resolved SAXS to follow the evolution of hybrid alkoxide-carboxylate sol-gel precursors for BaTiOs [91]. The precursor system was based on Ti(IV) isopropoxide dissolved in 2-methoxyethanol and bariiun acetate dissolved in acetic acid. First, spherical primary particles with a radius of 0.45-0.50 nm were formed. We attributed them to large spherical titaniiun oxo clusters with inorganic cores containing 12-18 Ti atoms. These aggregated into... 

---