Ruthenium-catalyzed transfer hydrogenation of imines by propan-2-ol in benzene.
2002 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 8, no 13, 2955-2961 p.Article in journal (Refereed) Published
Transfer hydrogenation of a variety of different imines to the corresponding amines by propan-2-ol in benzene catalyzed by [Ru2(CO)4(ÎŒ-H)(C4Ph4COHOCC4Ph4)] (1) has been studied. The reaction is highly efficient with turnover frequencies of over 800 per h, and the product amines were obtained in excellent yields. A remarkable concn. dependence of propan-2-ol was obsd. when the reaction was run in benzene as cosolvent. An optimum was obtained at 24 equiv of propan-2-ol to imine, and further increase of the propan-2-ol led to a dramatic decrease in rate. Also the use of polar cosolvents with 24 equiv of propan-2-ol gave a low rate. It was found that ketimines react faster than aldimines and that electron-donating substituents on the imine increase the rate of the catalytic transfer hydrogenation. Electron-withdrawing substituents decreased the rate. An isomerization was obsd. with imines having an Î±-hydrogen at the N-alkyl substituent, which is in accordance with a mechanism involving a ruthenium-amine intermediate. It was demonstrated that the ruthenium-amine complex from Î±-methylbenzylamine, corresponding to the postulated intermediate, can replace 1 as catalyst in the transfer hydrogenation of imines. A primary deuterium isotope effect of kCH/CD = 2.7 Â± 0.25 was obsd. when 2-deuterio-propan-2-ol was used in place of propan-2-ol in the transfer hydrogenation of N-phenyl-(1-phenylethylidene)amine. [on SciFinder(R)]
Place, publisher, year, edition, pages
2002. Vol. 8, no 13, 2955-2961 p.
ruthenium catalyzed transfer hydrogenation imine propanol mechanism substituent effect
Medical and Health Sciences Natural Sciences
IdentifiersURN: urn:nbn:se:uu:diva-174625DOI: 10.1002/1521-3765(20020703)8:13<2955::AID-CHEM2955>3.0.CO;2-QOAI: oai:DiVA.org:uu-174625DiVA: diva2:527969
CAPLUS AN 2002:536961(Journal)2012-05-232012-05-232012-05-23