In this paper, we report the synthesis of a Ti-substituted phosphotungstate, TBA6[(ﾎｳ-PW10O36)2Ti4(ﾎｼ-O)2(ﾎｼ-OH)4] (I, TBA = tetra-n-butylammonium), and its application to H2O2-based oxidn. Firstly, an org. solvent-sol. dilacunary phosphotungstate precursor, TBA3[ﾎｳ-PW10O34(H2O)2] (PW10), has been synthesized. By the reaction of PW10 and TiO(acac)2 (acac = acetylacetonate) in an org. medium (acetonitrile), I can be obtained. Compd. I possesses a tetranuclear Ti core which can effectively activate H2O2 and shows high catalytic performance for several oxidn. reactions, such as epoxidn. of alkenes, oxygenation of sulfides, oxidative bromination of unsatd. compds., and hydroxylation of anisole, giving the corresponding oxidn. products with high efficiencies and selectivities. The catalytic performance of I is much superior to those of previously reported Ti-substituted polyoxometalates. In addn., I is highly durable during catalysis and can be reused several times while keeping its high catalytic performance. Furthermore, we have successfully isolated the truly catalytically active species for the present I-catalyzed oxidn., TBA6[(ﾎｳ-PW10O36)2Ti4(ﾎｼ-ﾎｷ2:ﾎｷ2-O2)4] (II), and its anion structure has been detd. by X-ray crystallog. anal. All of the four Ti2-ﾎｼ-ﾎｷ2:ﾎｷ2-peroxo species in II are active for stoichiometric oxidn. (without H2O2), and II is included in the catalytic cycle for I-catalyzed oxidn. [on SciFinder(R)]
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