Sandwich-type tungstophosphates in the catalytic oxidation of cycloalkanes with hydrogen peroxide

The tetrabutylammonium salts of sandwich-type tungstophosphates of general formula B-alpha-[M-4(H2O)(2)(PW9O34)(2)](n-), M = Co-II, Mu(II) and Fe-III. proved to be catalysts or catalyst precursors for the oxidation of cyclohexane and cyclooctane with hydrogen peroxide, affording the corresponding alcohol, ketone and alkyl hydroperoxide in variable proportions. Depending on the tungstophosphate used, the oxidation of cyclooctane could also give 1,2-epoxycyclooctane or a cyclooctanedione. With the Fe sandwich anion, cycloalkyl hydroperoxide was generally the most abundant product. The conversion of cycloalkanes was always higher than 68% after 12 h of reaction. Oxidation of cyclooctane into cyclooctanone could be obtained with high selectivity (83%) and conversion (92%) using B-alpha-[Co-4(H2O)(2)(PW9O34)(2)](10-). The Fe sandwich complex showed to be the most effective catalyst, with turnover numbers of 1333 for cyclohexane and of 1930 for cyclooctane, after 12 h. (c) 2006 Elsevier B.V. All rights reserved.