Unexpected chemoselectivity in the rhodium-catalyzed transfer hydrogenation of [small alpha],[small beta]-unsaturated ketones in ionic liquids

• Published in: Green chemistry : an international journal and green chemistry resource : GC Vol. 11; no. 12; pp. 1937 - 1940
• Main Authors: Baan, Zoltan, Finta, Zoltan, Keglevich, Gyorgy, Hermecz, Istvan
• Format: Journal Article
• Language: English
• Published: 01.01.2009
• DOI: 10.1039/B913305D
• ISSN: 1463-9262

Chalcone and some other [small alpha],[small beta]-unsaturated ketones were subjected to transfer hydrogenation catalyzed by the dimer [Rh(cod)Cl]2 and the Wilkinson's catalyst in imidazolium-, ammonium- and phosphonium-based ionic liquids. In certain ionic liquids, the reduction of chalcone gave 1,3-diphenylpropan-1-one chemoselectively, in contrast with molecular solvents, which resulted in the formation of 1,3-diphenylpropan-1-ol. An accelerated reaction rate was observed in [emim][BuSO4] and [emin][HeSO4]. The observed chemoselectivity could be maintained applying a 5 molar equivalent excess of [bmim][BF4] to chalcone in 2-PrOH. This phenomenon suggests that there is an interaction between the chalcone carbonyl group and the ionic liquid which prevents reduction of the carbonyl group. The catalyst [Rh(cod)Cl]2 dissolved in an ionic liquid was successfully recycled at least three times, in contrast with Wilkinson's catalyst, which lost its activity on recycling.