期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 13, 期 19, 页码 5426-5432出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200700010
关键词
aldol reaction; hafnium; imines; Lewis acids; polyoxometalates
Monolacunary polyoxotungstates [alpha(1)-P2W17O61](10-) and [alpha-PW11O39](7-) react with HfCl4 to yield [alpha(1)-HfP2W17O61](6-) and [alpha-Hf(OH)P-W11O39](4-), isolated as organo-soluble tetrabutylammonium (TBA) salts. Subsequent analyses, including mass spectrometry, show that they are stronger Lewis acids than (TBA)(5)H-2[alpha(1)-YbP2W17O61]. The new polyoxotungstates catalyze Lewis acid mediated organic reactions, such as Mukaiyama aldol and Mannich-type additions. In particular, reactions with aldehydes, which were impossible with lanthanide polyoxotungstates, are made possible. Thus these modifications of the polyoxometalate composition allowed fine tuning of the Lewis acidity. The catalysts could be easily recovered and reused.
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