Chemoselective Catalysis with Organosoluble Lewis Acidic Polyoxotungstates

• Published in: Chemistry : a European journal Vol. 16; no. 24; pp. 7256 - 7264
• Main Authors: Dupré, Nathalie, Rémy, Pauline, Micoine, Kévin, Boglio, Cécile, Thorimbert, Serge, Lacôte, Emmanuel, Hasenknopf, Bernold, Malacria, Max
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 25.06.2010; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Acetal resins; Aldehydes; aldol reaction; Bonding; Catalysis; Chemistry; Chemistry, Multidisciplinary; Derivatives; Imines; Lewis acids; Physical Sciences; polyoxometalates; Polyoxometallates; Science & Technology; Tuning; aldol reaction; METAL-OXIDE; Lewis acids; LANTHANIDE COMPLEXES; imines; MONOVACANT WELLS-DAWSON; HIGHLY EFFICIENT; EPOXIDATION; IONIC-RADII; ALLYLIC ALCOHOLS; polyoxometalates; CHIRAL POLYOXOTUNGSTATES; POLYOXOMETALATE; WATER
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201000411

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 Brønsted acidity of the POMs. These catalysts activate imines in a Lewis acidic way, whereas aldehydes are activated by indirect Brønsted catalysis. Forming bonds: It is proposed that organosoluble Lewis acidic polyoxometalates containing Zr, Sc, Y, Hf, or lanthanide atoms catalyze CC bond‐formation reactions, such as the Mannich and Mukaiyama‐type reactions (see scheme; M=metal center). These air‐ and water‐stable catalysts activate imines in a Lewis acidic way, whereas aldehydes are activated by indirect Brønsted catalysis.