Increased Lewis acidity in hafnium-substituted polyoxotungstates.
Monolacunary polyoxotungstates [alpha(1)-P(2)W(17)O(61)](10-) and [alpha-PW(11)O(39)](7-) react with HfCl(4) to yield [alpha(1)-HfP(2)W(17)O(61)](6-) and [alpha-Hf(OH)PW(11)O(39)](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)-YbP(2)W(17)O(61)]. 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.
Boglio
Cécile
C
Université Pierre et Marie Curie-Paris 6, Laboratoire de chimie organique (UMR CNRS 7611), Institut de chimie moléculaire (FR 2769), C. 229, 4 place Jussieu, 75005 Paris, France.
Micoine
Kevin
K
Rémy
Pauline
P
Hasenknopf
Bernold
B
Thorimbert
Serge
S
Lacôte
Emmanuel
E
Malacria
Max
M
Afonso
Carlos
C
Tabet
Jean-Claude
JC