Cyclodextrins as inverse phase transfer catalysts for the biphasic catalytic hydrogenation of aldehydes: a green and easy alternative to conventional mass transfer promoters

The ruthenium-catalyzed hydrogenation of water-insoluble aldehydes in an aqueous/organic two phase system has been investigated in the presence of cosolvents or cyclodextrins. At low content, i.e. a content that enables to recover quantitatively the catalytic system without loss of metal with a cosolvent, β-cyclodextrin and its dimethylated form appear to be more efficient than cosolvents for performing the reaction. The formation of inclusion complexes between cyclodextrin and various components of the reaction medium (aldehyde, alcohol, hydrocarbon of the organic phase) is discussed on the basis of mass spectrometry, NMR and catalytic experiments.