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A Scrutiny on the Reductive Amination of Carbonyl Compounds Catalyzed by Homogeneous Rh(I) Diphosphane Complexes
Author(s) -
Tararov Vitali I.,
Kadyrov Renat,
Riermeier Thomas H.,
Börner Armin
Publication year - 2002
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/1615-4169(200202)344:2<200::aid-adsc200>3.0.co;2-4
Subject(s) - chemistry , reductive amination , amination , catalysis , organic chemistry , alcohol , cationic polymerization , amine gas treating , homogeneous catalysis , homogeneous , medicinal chemistry , physics , thermodynamics
The reductive amination of a series of aldehydes with secondary amines and H 2 in the presence of a homogeneous Rh‐diphosphane catalyst was studied in order to establish a general mechanism of this reaction and to identify conditions for the improvement of the amine/alcohol ratio in the product. Several possible intermediates as constituents of changing equilibria like half‐aminals, N , O ‐acetals and aminals were observed in the reaction mixture by means of 1 H NMR spectroscopy. In individual trials, these compounds could be successfully hydrogenated under the conditions applied for reductive amination (50 bar H 2 pressure, MeOH). Some evidence is accumulated that half‐aminals and N , O ‐acetals might be key intermediates of the reductive amination. Moreover, it was found that the formation of the undesired product alcohol is likely based on the reduction of the starting carbonyl compound. However, due to numerous equilibria consisting of several intermediates, general conclusions are hard to be drawn. Proof will be given that, in several cases, the efficiency of the reductive amination of aliphatic aldehydes can be significantly improved by prehydrogenation of the cationic [Rh(dppb)(COD)] + complex.