Isolation, characterization, and reactivity of the reaction products of the dimeric, Ti–O–Ti bridged anhydride form of the 1,2-di-titanium(IV)-substituted α-Keggin polyoxometalate with aqueous 30% H2O2

The isolation and characterization of the monomeric bis[peroxotitanium(IV)]-substituted α-Keggin polyoxometalate (POM) K7[α-l,2-PW10(TiO2)2O38]·8H2O (1) and the monomeric bis[hydroperoxotitanium(IV)]-substituted α-Keggin POM K5[α-l,2-PW10(TiOOH)2O38]·5H2O (2) are described. The orange solution was prepared by adding an excess amount of aqueous 30% H2O2 to the in situ-generated monomeric Keggin species [α-1,2-PW10Ti2O40]7− in a neutral aqueous solution derived by the hydrolytic cleavage of the dimeric, Ti–O–Ti bridged anhydride form K10[α-l,2-PW10Ti2O39]2·18H2O. Reprecipitation of the orange solution with MeOH gave a thermally stable yellow species containing the peroxo groups (compound 1) whereas reprecipitation with EtOH yielded a relatively unstable orange species that would contain the hydroperoxo groups (compound 2). The characterization of 1 and 2 was accomplished by a complete elemental analysis, TG/DTA, FTIR, UV–vis, solution (31P and 183W) NMR and 31P CPMAS NMR spectroscopy, and (for 1 only) X-ray crystallography. Complex 1 did not show any activity for 2-propanol oxidation in the absence of 30% H2O2 whereas complex 2 showed an effective activity for the oxidation reaction.

Graphical abstractThe isolation and characterization of the monomeric bis[peroxotitanium(IV)]-substituted α-Keggin polyoxometalate (POM) K7[α-1,2-PW10(TiO2)2O38]·8H2O (1) and the monomeric bis[hydroperoxotitanium(IV)]-substituted α-Keggin POM K5[α-1,2-PW10(TiOOH)2O38]·5H2O (2) are described. Complex 1 did not show any activity for 2-propanol oxidation in the absence of 30% H2O2 whereas complex 2 showed an effective activity for the oxidation reaction. Figure optionsDownload full-size imageDownload as PowerPoint slide