Rhenium(VII) Oxide/Aluminum Oxide: More Experimental Evidence for an Oxametallacyclobutane Intermediate and a Pseudo‐Wittig Initiation Step in Olefin Metathesis

Reactivity studies of the rhenium(VII) oxide/aluminum oxide olefin metathesis catalyst with various olefins show that initiation does not require an olefin with an allylic C-H bond, and therefore probably takes place via a pseudo-Wittig reaction. While it does not react with ethene in the absence of propene, Re 2 O 7 /Al 2 O 3 catalyses the self-metathesis of Z-stilbene and its cross-metathesis with ethene. Additionally, reaction of Re 2 O 7 /Al 2 O 3 with Z-2-butene followed by 13 C di-labelled ethene shows that it contains only 2 % of active sites.