Crystal structures of three novel dioxotetraperoxodi(molybdenum) heteropolyanions in [PPh4]2[R2SiO2{Mo2O2(μ-O2)2(O2)2}] (R2 = (CH3)2, (i-C4H9)2 or (CH3)(CH2Cl)) and characterization of their tungsten analogues

The reaction of MoO3 [or “WO3 · H2O”], aqueous H2O2 (30 wt%) with R2Si(OR′)2R2Si(OR′)2 in alkaline hydrogen peroxide–ethanol mixtures followed by treatment with PPh4+Cl− affords the corresponding salts of the previously unknown dioxotetraperoxodi(molybdenum or tungsten) heteropolyanion, [PPh4]2[R2SiO2{M2O2(μ-O2)2(O2)2}] in 75–80% isolated yields (R2 = (CH3)2, (i-C4H9)2 or (CH3)(CH2Cl); R′=CH3R′=CH3 or C2H5; M = Mo(VI) or W(VI)). These results are unequivocally established by a combination of elemental analysis, IR, 1H and 13C NMR spectroscopy and complete X-ray crystal structure analysis of the three molybdenum complexes.There is good evidence that the tungsten analogues are isostructural compounds.The O–O bonds are in the 1.464–1.483 Å range, typical of peroxo complexes with η2-O22− and μ2-η2:η1-O22− groups.These complexes represent a type of silicon-based polyoxoperoxo species which are models of moieties that are obtained by grafting on silica surfaces and also in the preparation of organic inorganic mesophases to synthesize MOx–SiO2–MCM-41 or MOx–SiO2–SBA-15.These materials, after calcination, have a highly dispersed MoOx/SiO2 structure and lead to leach-resistant catalysts.

The reaction of MoO3 [or “WO3 · H2O”], 30 wt% aqueous H2O2 with R2Si(OR′)2R2Si(OR′)2 in alkaline hydrogen peroxide–ethanol affords the dimeric title complexes.These compounds represent a type of silicon-based polyoxoperoxo species which are also obtained by grafting on silica surfaces and in the synthesis of organic/inorganic mesophases to prepare MOx–SiO2–MCM-41 or MOx–SiO2–SBA-15.Figure optionsDownload as PowerPoint slide