Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 16, Issue 24, Pages 7256-7264Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201000411
Keywords
aldol reaction; imines; Lewis acids; polyoxometalates
Categories
Funding
- CNRS
- IUF
- UPMC
- le ministere de l'education nationale
- de l'enseignement superieur et de la recherche
- ANR [JC05 41806]
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The preparation of new organosoluble Lewis acidic polyoxometalates (POMs) is reported. These complexes were prepared by the incorporation of Zr, Sc, and Y atoms into the corresponding monolacunary Dawson [P2W17O61](10-) and Keggin [PW11O39](7-) polyoxotungstates. The catalytic activity of these compounds was evaluated for C-C bond formation in the Diels-Alder, Mannich, and Mukaiyama-type reactions. Comparisons with previously described Lewis acidic POMs are reported. Competitive reactions between imines and aldehydes or between various imines demonstrated that fine tuning of the reactivity could be reached by varying the metal atom incorporated into the polyanionic framework. A series of experiments that employed pyridine derivatives allowed us to distinguish between the Lewis and induced Bronsted acidity of the POMs. These catalysts activate imines in a Lewis acidic way, whereas aldehydes are activated by indirect Bronsted catalysis.
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