MOSSBAUER AND SOLID-STATE NMR SPECTROSCOPIC STUDIES OF TIN-MODIFIED RHENIUM-BASED METATHESIS CATALYSTS

Mossbauer and solid-state NMR spectroscopic studies have been carried out on Re2O7/SiO2-Al2O3/SnR(4) metathesis catalysts (R = Me, Et or n-B u). The effects of both the rhenium loading and the SnR(4) alkyl group are presented. The amounts of gas released upon the interaction betwe en Re2O7/SiO2-Al2O3 and SnR(4) do not correspond to a simple stoichiom etry while chemical reactivity suggests the presence of minor amounts of a rhenium-alkylidene species. Mossbauer and NMR data suggest two ki nds of tin sites, with the tin atom linked to the surface by one or tw o Sn-O bonds. The effects of exposure to air and catalyst regeneration on the tin environment have also been investigated. The nature of the tin-containing surface species is discussed.