| Abstract
| - Novel heterogeneous compounds of methylrhenium trioxide (MTO) were prepared with poly(4-vinylpyridine) and polystyrene as polymeric supports. The wide-angle X-ray diffraction (WAXS.)analysis, performed by the application of the difference method, showed, in a representative caseof the poly(4-vinylpyridine)/MTO derivatives, a slightly distorted octahedral conformation on themetal's primary coordination sphere. The Re−O and Re−C bond distances were not influenced bythe polymeric nature of the ligand, while the Re−N bond distance was abnormally shorter thanthose previously observed for homogeneous MTO/Ln complexes, showing a strong coordination ofthe rhenium atom to the support. A set of scanning electron microscopy (SEM) photographs showingthe morphology of the surface of particles of poly(4-vinylpyridine)/MTO and polystyrene/MTOsystems are reported. The reticulation grade of the polymer was a crucial factor for the morphologyof the particles surface. Poly(4-vinylpyridine) 2% cross-linked systems were characterized byparticles with very irregular shape and surface. Poly(4-vinylpyridine) 25% cross-linked systemsshowed particles with regular spherical shape, which morphology was similar to microcapsulesobtained with polystyrene. All novel MTO compounds were efficient and selective heterogeneouscatalysts for the epoxidation of olefins using environmentally friendly H2O2 as oxygen atom donor.The catalyst activity was maintained for at least five recycling experiments.
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