Mössbauer and solid-state NMR spectroscopic studies of tin-modified rhenium-based metathesis catalysts

Abstract

Mössbauer and solid-state NMR spectroscopic studies have been carried out on Re₂O₇/SiO₂–Al₂O₃/SnR₄ metathesis catalysts (R = Me, Et or n-Bu). The effects of both the rhenium loading and the SnR₄ alkyl group are presented. The amounts of gas released upon the interaction between Re₂O₇/SiO₂–Al₂O₃ and SnR₄ do not correspond to a simple stoichiometry while chemical reactivity suggests the presence of minor amounts of a rhenium–alkylidene species. Mössbauer and NMR data suggest two kinds of tin sites, with the tin atom linked to the surface by one or two 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.