Metallacyclobutane Substitution and Its Effect on Alkene Metathesis for Propylene Production over W–H/Al₂O₃: Case of Isobutene/2-Butene Cross-Metathesis

Cross metathesis between 2-butenes and isobutene yielding the valuable products propylene and 2-methyl-2-butene has been investigated at low pressure and temperature using <b>WH</b>_<b>3</b><b>/Al</b>_<b>2</b><b>O</b>_<b>3</b>, a highly active and selective catalyst. Two parallel catalytic cycles for this reaction have been proposed where the cycle involving the less sterically hindered tungstacyclobutane intermediates is most likely favored. Moreover, it has been found that the arrangement of substituents on the least thermodynamically favored tungstacyclobutane governs the conversion rate of the cross metathesis reaction for propylene production from butenes and/or ethylene