Synthesis, characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, C-13 NMR, Si-29 NMR and energy-dispersive X-ray spectroscopies, X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy and Brunauer-Emmett-Teller analysis and compared to its homogeneous counterpart [W(CO)(3)Br-2(ATC)] in the epoxidation of 1-octene, cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3hexen-1-ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)(3)Br-2(ATC)] was slightly higher than for the oligomeric catalyst (POSS-ATC-[W(CO)(3)Br-2]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S)-limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.