Barium complex

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... 

Figure 69 The structure of the barium complex [ry5-PhCH(C5H4N-2)]2Ba(diglyme)(THF) 136.

Figure 70 The structure of the barium complex Ba[Ph2P(4-MeC6H5CH)]2 1...

Reaction of the bis-chelate complex 149 and various bis(arylalkyl)barium complexes generates heteroleptic barium complexes with one chelate and one reactive arylalkyl ligand 164. The homoleptic and heteroleptic barium complexes both induce living polymerization of styrene to atactic polystyrene in cyclohexane solution. The fact that no stereocontrol is observed during polymerization despite the presence of the chiral carbanionic ligands is... 

In conclusion, the bis-barium complex of 17 catalyzes the ethanolysis of anilide and ester substrates endowed with a distal carboxylate anchoring group (Table 5.7). The catalyst shows recognition ofthe substrate, induces fairly high reaction rates with catalytic turnover, and is subjected to competitive inhibition by carboxylate anions, as... 

Trans-23 displays photoisomerization behavior typical of an azobenzene (Figure 5.8). Irradiation of the bis-barium complex at 370 nm in EtOH/MeCN (65/35, v/v) leads after 40 s to a stationary state - quasi-cis-28-Ba2 - in which the cis/trans ratio is as high as 95 5. In turn, irradiation ofthe quasi-cis mixture leads to a... 

The bis-barium complex of pure trans-28 (0.10 mM) increases the rate of ethano-lysisof29 (65/35 EtOH/MeCN, 1 mM Me4NOEt, 25 °C) by 230-fold. The corresponding figures for quasi-trans-28-Ba2 and quasi-cis-28-Ba2 are 420- and 1280-fold, respectively. Thus, the behavior of trans and ds isomeric catalysts based on azobenzene closely parallels the behavior of the corresponding stilbene derivatives 26 and 27, in that in both cases the ds form is a superior catalyst in the cleavage of anilide 29. 

These log k values compare well with log k values for respective barium complexes. 

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,... 

In order to accommodate the small, highly charged calcium ion, the cryptand adopts an unsymmetrical conformation in which two of the chains are pushed apart to allow coordination of a water molecule and the N N distance is reduced to 5.44 A (42). In the corresponding barium complex, the structural unit consists of two cryptates, two water molecules, and four thiocyanate anions, two of which (9) are bound through nitrogen to the metal, (43). 

The non-reducing trisaccharide planteose was first isolated22 by Wattiez and Hans from seeds of Plantago major and P. ovata. Extraction of de-fatted seeds of P. ovata with 70% alcohol, conversion of the sugars in the extract to their barium complexes, removal of the barium with sulfuric acid, and extraction of the evaporated sirup with 85% alcohol, gave solutions from which planteose dihydrate gradually crystallized it has m.p. 123-4°, [ ]d + 125.5° (in water). 

In 1940, Murakami published a study21 of the constitution of verbascose. To prepare this sugar, Murakami extracted the finely ground roots with 95% alcohol, clarified the extract with lead acetate, and precipitated the verbascose with barium hydroxide and alcohol. After processing the barium complex in the usual way, and precipitating the saccharide several times from an aqueous solution by alcohol, Murakami obtained verbascose in 0.5-mm. spherocrystals composed of fine needles these had m.p. 253°, [a]20D + 170.2° (in water). The elementary analysis and the cryoscopic molecular-weight values were appropriate for a pentasaccharide. 

These compounds are less thermally and kinetically stable than either their unsubstituted or their decaphenylmetallocene analogues they decompose near 200°C in the solid state (cf. 350°C for the decaphenylmetallocene derivatives [M(C5Ph5)2] M = Ge, Sn, Pb47) and in minutes in THF at room temperature.46 A yellow barium complex has been prepared by the reaction of two equivalents of C5Ph4H2 with the soluble barium amide [Ba N(SiMe3)2 2(thf)2] in THF or toluene [Eq. (3)].41... 

The compound [Ca(hfac)2(H20)2]2153 (Fig. 38) is a centrosymmetric dimer in the solid state, while the analogous barium complex, [Ba(hfac)2 (H20)]x,153 exists as a polymer. Both compounds have M-F interactions similar to those described for [Ba2(hfac)4(Et20)L The smaller size of calcium is probably responsible for the structural differences between these two water adducts. The volatility of these fluorinated complexes is certainly decreased by the M-F interactions, as well as by the overall oligomeric structure of the compounds. What relationship metal ligand interactions of this type play in the incorporation of BaF2 in films prepared from these compounds has not yet been elucidated. Interestingly, no base-free fluorinated /3-diketonate compounds have been structurally characterized. 

As Scheme 13 shows, reaction of the tertiary aldehyde 68 with methyl-phenyl ketone 69 under catalysis by the barium complex 70 gave compound 71 in a smooth reaction and in quantitative yield [23], Only 5 mol % of catalyst and 2.0 eq. of the ketone are needed. However, the ee value of 70 % is only moderate. 

Scheme 14 gives a mechanistic rationale for the role of the barium complex 70. After substitution... 

Purdy efa/. reported the synthesis of the calcium, barium, and strontium complexes of hexafluoroacetylacetone (Hhfac) (4) and trifluoroacetylacetone (Htfac) (5). CVD experiments were performed with the group 2 hfac complexes, and with Ca(tfac)2 to give metal fluoride films, while Ba(hfac)2 has been used to prepare films of YBa2Cu307 s. As with the tmhd derivative, the tfac and hfac barium complexes decompose at, or slightly above, their sublimation temperatures, resulting in significant premature thermolysis of the precursors during deposition. 

Table 15 Selected physical data for barium complexes ...

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