- Triazolylidene Iridium Complexes for Highly Efficient and Versatile Transfer Hydrogenation of C=O, C=N, and C=C Bonds and for Acceptorless Alcohol Oxidation
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A set of iridium(I) and iridium(III) complexes is reported with triazolylidene ligands that contain pendant benzoxazole, thiazole, and methyl ether groups as potentially chelating donor sites. The bonding mode of these groups was identified by NMR spectroscopy and X-ray structure analysis. The complexes were evaluated as catalyst precursors in transfer hydrogenation and in acceptorless alcohol oxidation. High-valent iridium(III) complexes were identified as the most active precursors for the oxidative alcohol dehydrogenation, while a low-valent iridium(I) complex with a methyl ether functionality was most active in reductive transfer hydrogenation. This catalyst precursor is highly versatile and efficiently hydrogenates ketones, aldehydes, imines, allylic alcohols, and most notably also unpolarized olefins, a notoriously difficult substrate for transfer hydrogenation. Turnover frequencies up to 260 h-1 were recorded for olefin hydrogenation, whereas hydrogen transfer to ketones and aldehydes reached maximum turnover frequencies greater than 2000 h-1. Mechanistic investigations using a combination of isotope labeling experiments, kinetic isotope effect measurements, and Hammett parameter correlations indicate that the turnover-limiting step is hydride transfer from the metal to the substrate in transfer hydrogenation, while in alcohol dehydrogenation, the limiting step is substrate coordination to the metal center.
- Mazloomi, Zahra,Pretorius, René,Pàmies, Oscar,Albrecht, Martin,Diéguez, Montserrat
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p. 11282 - 11298
(2017/09/25)
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- Reduction of benzylic alcohols and α-hydroxycarbonyl compounds by hydriodic acid in a biphasic reaction medium
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The synthetic protocol for the reduction of alcohols to hydrocarbons by using hydriodic acid, first described by Kiliani more than 140 years ago, was improved to be more applicable to organic synthesis. Instead of a strongly acidic, aqueous solution, a biphasic toluene-water reaction medium was used, which allowed the conversion of primary, secondary and tertiary benzylic alcohols, in good yields and short reaction times, into the corresponding hydrocarbons. Red phosphorous was used as the stoichiometric reducing agent. Keto, ester, amide or ether groups are tolerated, and catalytic amounts of hydriodic acid (0.2 equiv) in the presence of 0.6 equiv phosphorous are sufficient to achieve conversion.
- Dobmeier, Michael,Herrmann, Josef M.,Lenoir, Dieter,Koenig, Burkhard
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supporting information; experimental part
p. 330 - 336
(2012/05/20)
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- Method for preparing α-(4-isobutylphenyl)propionic acid or its precursor
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A method for preparing α-(4-isobutylphenyl)propionic acid or its precursor is here disclosed which comprises a step A of forming p-isobutylstyrene from p-isobutylethylbenzene and a step B of forming α-(4-isobutylphenyl)propionaldehyde from p-isobutylstyrene or a step C of forming α-(4-isobutylphenyl)propionic acid or its alkyl ester from p-isobutylstyrene. Furthermore, a method for preparing said p-isobutylethylbenzene is also disclosed which comprises alkylating isobutylbenzene or 4-ethyltoluene with ethylene or propylene.
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- Formylation and Acylation Reactions Catalysed by Trifluoromethanesulphonic Acid
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Regioselective formylation of toluene, m- and p-xylene, and mesitylene has been achieved by carbonylation in trifluoromethanesulphonic acid at CO pressures of 90-125 atm.In the case of cumene, the formylation reaction is in competition with disproportionation to form di- and tri-isopropylbenzenes, leading to a complex product mixture.Slow addition of cyclohexene or cyclopentene to a mixture of benzene and CF3SO3H under a high CO pressure affords 4-cyclohexylbenzaldehyde and 4-cyclopentylbenzaldehyde in 34percent and 33percent yieds, respectively, while 2-methylbut-1-ene gives 2,2,3-trimethylindanone (39percent) under similar conditions.When cyclohexene is mixed with the acid under carbon monoxide (120 atm) before addition of benzene the major products are cyclohexyl phenyl ketone and cyclohexenyl cyclohexyl ketones.
- Booth, Brian L.,El-Fekky, Teymour A.,Noori, Ghazi F. M.
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p. 181 - 186
(2007/10/02)
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