Barium alkoxides

Purex process, 6,940 Barium, pentakis(diacetamide)-stereochemistry, 1, 99 Barium alkoxides synthesis, 2,336 Barium complexes cryptands, 3,53 phthalocyanines, 2, 863 porphyrins, 2,820 pyridine oxide, 3,9 urea, 3,9... 

Using a tetradentate ligand, Rees and Moreno have proposed the first example of a monomeric barium bis-alkoxide (26). The proposed solution structure (Fig. 2) was determined based on ciyoscopic and spectroscopic data. One notable characteristic of this monomeric barium alkoxide is that it is an ambient temperature liquid. Although the compound exists as a monomer in the solution state, oligomeric species prevail in the absence of solvent. This phenomenon has been ob-... 

Alkoxides Yttrium and barium alkoxides can be obtained by direct reaction of the metal with alcohols (10X10- They readily... 

Bacteriochlorins, 851 Barbituric acid metal complexes, 798 Barium alkoxides synthesis, 336 Barium complexes phthalocyanines, 863 porphyrins, 820 Becium homblei copper accumulation, 964 Benzaldehyde, 2-amino-self-condensation aza macrocycles from, 900 Benzamide, o-mercapto-metal complexes, 655 Benzamide oximes metal complexes, 274 Benzamidine, /V, V -diphenyl-metal complexes. 275 Benzene, 1,2-diamino-reactions with dicarbonyl compounds aza macrocycles from, 902 Benzene, 4 methylthionitroso-metal complexes, 804 Benzenedithiolates metal complexes, 605... 

Shibasaki et al. also developed a barium complex (BaB-M, 14, Scheme 5) for the aldol reaction of acetophenone (la), making use of the strongly basic characteristic of barium alkoxide. The catalyst was prepared from Ba(0-z-Pr)2 and BINOL monomethyl ether, and the products were obtained in excellent yield with up to 70% ee (Scheme 6) [8], Shibasaki et al. attempted to incorporate a strong Bronsted base into the catalyst and developed a lanthanide heterobime-tallic catalyst (15) possessing lithium alkoxide moieties, which promoted the aldol reaction with up to 74% ee (Scheme 6) [9]. Noyori and Shibasaki et al. reported a calcium alkoxide catalyst (16) that was prepared from Ca[N(SiMe3)2]2,... 

Effects of metal size on the coordination enviromnent are nicely demonstrated in the analogous barium compound, obtained in an effort to circumvent the ether cleavage problem using gentler synthetic methods developed for heavy alkali metals. In this method, barium alkoxides were combined with SiMes substituted diphenylmethane. While the method did lead to desilylation in the desired location, upon concentration of the mother liquors of these compounds. 

Alkoxide and aryloxide complexes are moisture-sensitive, and are usually colorless or white solids with melting points substantially above room temperature. An interesting exception to this generalization is provided by the brown barium alkoxides Ba[0(CH2CH20) CH3]2 ( = 2, 3), formed from the reaction of elemental barium with a stoichiometric quantity of the polyether alcohol in THF. They are soluble in diethylether, THF and aromatic hydrocarbons, and are liquid at room temperature. 

The discovery of high-77 superconductors in the late 1980s led to the need to produce homogeneous and high-purity complex metal oxide species, a need that could be met by the use of sol-gel techniques. The first sol-gel routes to yttrium barium copper oxide (YBCO) involved coprecipitation,222 but latterly, routes based on the hydrolysis and condensation of yttrium and barium alkoxides with copper methoxyethoxide have been developed. It is found that the hydrolysis ratio used in the production of the gel can affect the temperature of the onset of Tc and the sharpness of the transition to superconductivity.223... 

The structurally characterized penta- and hexanuclear aggregates are all oxo or hydroxo clusters. A/4(M4-0)06 cores (Fig. IF) having an adamantanelike structure are found for lead and barium alkoxides. The Af5(p5-0)0y (Fig. IG) core seems to display a special stability for large di- or trivalent metals. Hexanuclear aggregates derive from the pentanuclear by the addition of a sixth... 

Poncelet, O., Hubert-Pfalzgraf, L. G., Toupet, L., and Daran, J. C., Molecular precursors of alkaline earths synthesis and structure of [N(C2H40)(C2H40H)2]2Ba, 2EtOH, the first structurally characterized barium alkoxide. Polyhedron, 10, 2045-2050 (1991). 

Joint decomposition of titanium and barium alkoxides makes it possible to obtain high-purity powders of very fine BaTiOs [187, 188]. For this purpose, Ba and Ti alkoxides are merged at temperature between 50 and 100 °C to obtain mixed precursor. Then the mixture is hydrolyzed at room temperature by adding water with a controlled rate. In general, the flow diagram of the process is shown in Fig. 5.9 and the reaction occurring during hydrolysis of metal alkoxides can be presented [188] in the form of chemical equation ... 

The direct aldol reaction of carboxylic acid derivatives and aldehydes (or ketones) is very difficult. Recently, Kobayashi and co-workers (146) extended the ketones to amides as suitable candidates successfully for the direct aldol reaction. The screening of metal sources revealed that Ba(0-tBu)2 was the better catalyst than Sr(0-iPr)2, Ca(0-iPr)2, or Mg(0-iPr)2, whereas rare earth metals (eg, La(0-iPrls) are catalytically inactive in the presence of p-methoxyphenol. In this aldol reaction, barium enolate formed in situ from barium alkoxide and acylamide and... 

A few structures of complex barium alkoxides have been determined. With the bulky triphenylsiloxide ligand the trimer [Ba3(ft3-OSiPh3)2(At-OSiPh3)3(OSiPh3)(thf)] was... 

Heterometallic oxo-alkoxides may also be formed by conversion from heterometallic alkoxides. Thus the insoluble [Pb(OPr)2]j reacted with Ti(OPr% to form [Pb4Ti403PPr g] and [Pb2Ti2(Ai4-0)(/u,3-0Pr )2(/Li-0Pr )4(0Pr )4] presumably by ether elimination. Similarly, from reactions of barium alkoxides and titanium alkoxides the heterometallic oxo-alkoxides [Ba4Ti404(OPr )i6(Pr OH)4][Ba4Ti404(OPr )io(Pr OH)3] and [Ba2Ti40(0Me)ig(Me0H)7]2° were obtained as a result of ether elimination, although similar complexes are readily prepared when the barium alkoxide solution is aerobically oxidized. ... 

Our recent studies have also confirmed such a phenomenon. For example, the barium-hafnium complex [Ba4Hf2 (/ttg-0)(/ 3,r/ -0CH2CH20CH3)g(rj-0CH2CH20CH3)2(ji-H0CH2CH20CH3)4Cl4] was obtained fl-om the reaction of Cp2HfCl2 and an appropriate group 2 barium alkoxide [18]. The key factor was to choose the appropriate thermolysis... 

Some of the recent work in the authors laboratory has shown that catalyst compositions of barium alkoxide salts combined with BuLi as well as with complexes of Mg-Al alkyls also result in low-vinyl solution SBRs (LVSBRs) in hydrocarbon solvent. " Such elastomers have a butadiene portion of ran5-l,4-content as high as 90% and a vinyl content as low as 2%. The comonomer placement in the copolymers is predominantly random. The development and properties of these rubbers will be described more fully in Sections 3 and 4, respectively. 

Random copolymers are commercially produced by both emulsion and solution polymerizations. It was discovered in the author s laboratory that the use of barium alkoxides in combination with organometalhc compounds is yet another method to prepare random styrene/butadiene solution rubbers. With Ba/Mg/Al catalyst systems, random SBRs are obtained with no more than 4% vinyl unsaturation. The principal effect of lower vinyl content is a lower glass transition temperature than that of a corresponding, conventional solution SBR. 

A major development in solution SBRs was first disclosed at the International Rubber Conference in Kiev by R. A. Livigni et and in subsequent publications. " As described in Section 3 of this chapter, these solution SBRs have a butadiene portion of trans-1,4-content 80-90%, vinyl content 2-4%, and a random comonomer sequence distribution. Additionally, the polymerization process, which uses a new catalyst of Mg-Al alkyls complexed with barium alkoxide salts, has all the distinguishing characteristics of organoUthium-initiated polymerization (Tables 13 and 14). 

Bidell W., Shklover V.A., Berke H. Synthesis and structural characterization of new copper complexes and the copper-barium-alkoxide complex BaCu4(0C(R)C(H)C(R)0)4(0R )2(H0R )4 (R = C(CH3)3,R = CH2CH20CH3). Inorg. Chem. 1992 31 5561 Bindal S.R., Kapoor P.N., Mehrotra R.C. Reactions of gallium alkoxides with acyl halides. Inorg. 

Drake S.R., Streib W.E., Chisholm M.H., Caulton K.G. Pacile synthesis and structural principles of the strontium phenoxide Sr4(OPh)g(PhOH)2(THF)6. Inorg. Chem. 1990 29 2707 Drake S.R., Streib W.E., Foiling K., Chisholm M.H., Caulton K.G. Dinuclear barium alkoxides and siloxides displaying variable coordination numbers and asymmetric dispositions ofligands. Inorg. Chem. 1992 31 3205... 

Shibasaki et al. first reported a chiral barium catalyst prepared from BINOL monomethyl ether and barium alkoxide, which was a good catalyst for asymmetric direct-type aldol reactions (Table 1) [21]. In the presence of a barium catalyst, several aliphatic aldehydes were tested, and the desired cross aldol products were obtained in good yields with moderate to good enantioselectivities. For the substrate BnOC(CH3)2CHO, the best enantioselectivity was observed (Table 1, entry 6). Although there is no definitive experimented proof, the barium catalyst was assumed to be monometallic and could be stored for several months under argon atmosphere. 

Shibasaki et al. also developed chiral barium catalysts prepared from barium alkoxide and optically active BINOL 3 or aryloxide 4 derivatives. These catalysts were applied to asymmetric Mannich reactions of p,y-unsaturated esters (Table 27) [101]. In this reaction, the initially formed Mannich adducts isomerized to afford aza-Morita-Baylis-Hillman-type products in moderate to good yields with good enantioselectivities. For four substrate examples, ayloxide 4 ligand worked well (entries 2—4). 

Shifrina, R.R. (1993) Barium alkoxides. Russ. J. Inorg. Chem., 38,1055-1059. 

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