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Highly productive CNN pincer ruthenium catalysts for the asymmetric reduction of alkyl aryl ketones

Baratta, Walter and Chelucci, Giorgio Adolfo and Magnolia, Santo and Siega, Katia and Rigo, Pierluigi (2009) Highly productive CNN pincer ruthenium catalysts for the asymmetric reduction of alkyl aryl ketones. Chemistry: a European Journal, Vol. 15 (3), p. 726-732. eISSN 1521-3765. Article.

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DOI: 10.1002/chem.200802112

Abstract

Chiral pincer ruthenium complexes of formula [RuCl(CNN)(Josiphos)] (2-7; Josiphos=1-[1-(dicyclohexylphosphano)ethyl]-2-(diarylphosphano)ferrocene) have been prepared by treating [RuCl2(PPh3)3] with (S,R)-Josiphos diphosphanes and 1-substituted-1-(6-arylpyridin-2-yl)methanamines (HCNN; substituent=H (1 a), Me (1 b), and tBu (1 c)) with NEt3. By using 1 b and 1 c as a racemic mixture, complexes 4-7 were obtained through a diastereoselective synthesis promoted by acetic acid. These pincer complexes, which display correctly matched chiral PP and CNN ligands, are remarkably active catalysts for the asymmetric reduction of alkyl aryl ketones in basic alcohol media by both transfer hydrogenation (TH) and hydrogenation (HY), achieving enantioselectivities of up to 99 %. In 2-propanol, the enantioselective TH of ketones was accomplished by using a catalyst loading as low as 0.002 mol % and afforded a turnover frequency (TOF) of 105-106 h-1 (60 and 82 °C). In methanol/ethanol mixtures, the CNN pincer complexes catalyzed the asymmetric HY of ketones with H2 (5 atm) at 0.01 mol % relative to the complex with a TOF of ≈104 h-1 at 40 °C.

Item Type:Article
ID Code:1511
Status:Published
Refereed:Yes
Uncontrolled Keywords:Asymmetric catalysis, chiral resolution, hydrogen transfer, hydrogenation, ruthenium
Subjects:Area 03 - Scienze chimiche > CHIM/06 Chimica organica
Divisions:001 Università di Sassari > 01 Dipartimenti > Chimica
Publisher:Wiley
eISSN:1521-3765
Deposited On:18 Aug 2009 10:05

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