Esters chelation

Partial hydrolysis of TYZOR DC or the monoethylacetoacetate ester chelate, followed by removal of the isopropyl alcohol by-product, gives a dimeric )J.-oxo chelate (8), which also has improved cold-temperature-storage stabiUty (98). 

Several important classes of polar monomers have so far eluded copolymerization by the Pd(II) system. Vinyl chloride insertion, for example, leads to catalyst deactivation following P-halide elimination to form inert chloride species such as 1.32, as shown by Jordan [90], Similarly, attempted vinyl acetate copolymerization results in deactivation by an analogous acetate elimination process, although the ester chelate intermediate that forms after insertion also effectively shuts down the reaction [90], Therefore, -elimination of polar groups represents a significant and unresolved problem for late transition metal polymerization systems unless access of the metal to it is restricted. 

Typical syntheses of Co(III)-amino acid, amino acid ester, and dipeptide ester chelates are described below. The NMR spectra of the isolated products were in accord with expectation. The procedures given here are generally applicable, except for that given for [Co(en)2((iS)-GluOBzl)]I2. If this method is used to coordinate amino acids that are only partially soluble in Me2SO, more forcing conditions (extended reaction times, 1-5 h, 50-60°C) may be required. Dipeptide ester complexes are not always as amenable as [Co(en)2 (Val-GlyOEt)]I3 to crystallization from water. 

Other borate ester chelates containing tetrahedral boron, shown in Fig. 16a, have been prepared as precursors to solvent-supported borate cations (Fig. 16b) that show catalytic activity toward olefin polymerization [54]. 

Fig. 16. Borate ester chelate complex (a) serves as precursor to catalytically active borate ester cation (b). R = alkyl, X = H, Cl, Br...

To prepare hexaaluminates for ceramic applications a slightly different sol-gel process was proposed by Debsikbar.19 Ba-hexaaluminates were prepared via hydrolysis of Al di(isopropoxide) acetoacetic ester chelate and anhydrous Ba acetate obtained by reaction between BaC03 and glacial acetic acid. The substitution of Al(i-OC3H7)3 with the alkoxy ester was intended to control the chemical polymerization during gel formation. The reaction was performed in 1-butanol. The formation of the gel slowly occurred at room temperature in about 10 h. To obtain the final phase the gel precursor was dried at 70 °C for about 2 weeks, ground and calcined at 1200°C for 2 h. However no data on the morphology of the final materials were reported by the author. 

Rather than use a conventional phosphorus reactant, Schmutz et 81. relied on the polymeric reaction product of P2O5 + ethanol. Schmutz et al. also used Li00CCH3-2H20, Ti(OC2H5)4, and aluminum di-sec butoxide acetoacetic ester chelate to synthesize a precursor sol. The researchers used spin-coating techniques with the precursor sol to produce Lij 3 Alg Tij 7(P04)3 thin films on glass substrates at 650°C. The 300°C ionic conductivity was determined to be 4 x 10 S/cm. 

A combination of TMEDA and MCjSiCl makes benzylic copper reagents more stable and permits their applications to conjugate addition to a,P-unsaturated esters. Chelation control is manifested in the cuprate addition to conjugate esters by a trivalent phosphorus atom 8 bonds away. ... 

The extent of PHP adsorption is too low to be measured by loss from bulk solution. The catalysis of PHP hydrolysis by various metal oxides must come from their ability to chelate the ester and polarize the carbonyl C-O bond. Apparently Ti oxides and Fe oxides are capable of doing this, while Al oxides are not. Ionic strength effects on PHP surface-catalyzed hydrolysis are small electrostatics apparently have a minor role in ester chelation and subsequent attack by OH (Torrents and Stone, 1991). 

Amorphous calcium aluminate powders have been synthesized chemically by Uberoi and Risbud [35] by sol-gel methods. These materials were made from calcium nitrate (Ca(N03)2) and by using aluminum di-sec-butoxide acetoacetic ester chelate (A1(0C4H9)2(C6H903)) as the source of alumina. 

Unfunctionalized amines here implies the exclusion of substrates requiring functional groups that are intimately involved in the transition state for production formation, e.g., ester chelation to a metal center. 

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