- Supramolecular control of biomimetic coordination - ZnII cavity complexes presenting two differentiated labile sites in cis positions
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A supramolecular approach to model the active sites of metalloenzymes is to associate a cavity with a tripodal coordination core. One key feature of many enzymes is the possible binding of two different ligands in cis positions relative to each other, which has not yet been described for cavity complexes. Here, the bowl shape of resorcinarene allows such a coordination environment for ZnII complexes. A detailed NMR study with various carboxylic acids evidences size-, shape-, and, thus, regioselectivity for carboxylate coordination in the endo position, the exo position, or both. The coordination of diketonates unambiguously demonstrates the relative cis position of the two labile sites present in the tris(imidazole)zinc(II) bowl complex. An interesting intramolecular exchange process was also observed. Finally, a comparison with calix[6]arene-based complexes (so-called funnel complexes) further highlights the key role of the cavity in the control of properties of the metal ion. A tris(imidazole) core associated with a resorcinarene provides a biomimetic environment for ZnII complexes. The metal ion is embedded in a five-coordinate environment with two sites open for the coordination of exogenous donors in cis positions relative to each other. Carboxylates, diketonates, and deprotonated amides can selectively bind at the endo and/or exo position.
- Gout, Jér?me,Rat, Stéphanie,Bistri, Olivia,Reinaud, Olivia
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- Nanosized gold-catalyzed selective oxidation of alkyl-substituted benzenes and n-alkanes
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We report the synthesis of nanoporous silica-supported gold nanoparticle catalysts and their selective and efficient catalytic properties toward oxidation reactions of various substituted alkylbenzenes and linear alkanes. The Au nanoparticles were synthesized by reducing Au(III) ions in situ within the nanopores of hemiaminal-functionalized mesoporous silica by using the supported hemiaminal groups as reducing agents. The resulting mesoporous silica-supported gold nanoparticles efficiently catalyzed the oxidation reactions of different alkyl-substituted benzenes and linear alkanes with t-butyl hydroperoxide (TBHP) as an oxidant. The catalytic reactions gave up to ～99% reactant conversion and up to ～100% selectivity toward ketone products in some cases. This high selectivity toward ketone products by the catalysts was unprecedented, especially considering the fact that only mild reaction conditions and no additives were employed during the reactions.
- Biradar, Ankush V.,Asefa, Tewodros
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p. 19 - 26
(2012/10/08)
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- PROCESSES FOR PREPARING β-DIKETONE COMPOUND, METAL COMPLEX THEREOF AND METALLIC COMPOUND
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Disclosed is a process for preparing a β-diketone compound such as 2,6-dimethyl-3,5-heptanedione, which comprises reacting an ester compound such as an alkyl isobutyrate with a ketone compound such as 3-methylbutanone in the presence of an alkali metal alkoxide as a catalyst. The process comprises a step 1 in which an ester compound CR1R2R3COOQ is reacted with a ketone compound CR4R5R6COCH2R7 using an alkali metal alkoxide catalyst to give a β-diketone compound CR1R2R3COCHR4R5R6. (In the formulae, R7 is hydrogen or an alkyl group of 1 to 4 carbon atoms while others are each independently hydrogen or an alkyl group of 1 to 3 carbon atoms, and at least one of R1 to R6 is hydrogen.)
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Page/Page column 26
(2008/06/13)
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- Method for preparing chiral diphosphines
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The invention concerns a method for preparing a compound of formula (1) wherein: A represents naphthyl or phenyl optionally substituted; and Ar1, Ar2independently represent a saturated or aromatic carbocyclic group, optionally substituted.
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- Asymmetric hydrogenation method of a ketonic compound and derivative
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The present invention relates to a process for the asymmetric hydrogenation of a ketonic compound and derivative. The invention relates to the use of optically active metal complexes as catalysts for the asymmetric hydrogenation of a ketonic compound and derivative. The process for the asymmetric hydrogenation of a ketonic compound and derivative is characterized in that the asymmetric hydrogenation of said compound is carried out in the presence of an effective amount of a metal complex comprising as ligand an optically active diphosphine corresponding to one of the following formulae: STR1
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- Regio- and Enantio-selective Reduction of α,γ-Diketones by Fermenting Baker's Yeast
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Reduction of various numbers of 2,4 alkanediones by fermenting baker's yeast has been found to be highly regio- and enantioselective, resulting in the formation of 2-hydroxy-4-alkanones.In some cases, optical purities of the products exceeded over 99percent as determined by HPLC analysis of MTPA esters.The highest yield was obtained when the reaction was carried out at pH 8 with low substrate concentration.As the representative β-hydroxyketones, the absolute configuration of (+)-2-hydroxy-4-octanone (2d) and (+)-3-hydroxy-1-phenyl-1-butanone (2h) was unambiguously determined to be (S) by comparing the specific rotation of diol derivatives with those of authentic specimens.
- Ohta, Hiromichi,Ozaki, Kazuhiko,Tsuchihashi, Gen-ichi
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p. 2499 - 2502
(2007/10/02)
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