Chemoselective catalysis with organosoluble Lewis acidic polyoxotungstates.
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 [P(2)W(17)O(61)](10-) and Keggin [PW(11)O(39)](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 Brønsted acidity of the POMs. These catalysts activate imines in a Lewis acidic way, whereas aldehydes are activated by indirect Brønsted catalysis.
Dupré
Nathalie
N
UPMC Univ Paris 06, Institut Parisien de Chimie Moléculaire (UMR 7201), C. 229, 4 place Jussieu, 75005 Paris, France.
Rémy
Pauline
P
Micoine
Kévin
K
Boglio
Cécile
C
Thorimbert
Serge
S
Lacôte
Emmanuel
E
Hasenknopf
Bernold
B
Malacria
Max
M