Comparison of olefin metathesis by rhenium-containing γ-alumina or silica–aluminas and by some mesoporous analogues

Oxide materials with rhenium(V) oxochloro complexes highly dispersed on the surface were prepared by grafting Re(V) alkoxochloro complexes onto γ-Al2O3, chlorinated alumina, 25 and 75 wt% SiO2 silica–aluminas, mesoporous alumina with high specific surface area (685 m2 g−1) and mesoporous silica–alumina (950 m2 g−1). The activities of these catalysts for 1-octene metathesis at room temperature are compared in the presence of a promoter: Bu4Sn or Ph2SiH2. Systems consisting of pure alumina and chlorinated alumina supports with rhenium species and Bu4Sn lead to selective formation of 7-tetradecene and ethylene at 90–100% conversion. There is a dramatic change of selectivities with Bu4Sn and silica–alumina or with Ph2SiH2 and aluminas. The difference is attributed to the formation of hydrido and carbene rhenium surface species which promote at the same time isomerization, self- and cross-metathesis. Mesostructured oxides do not show any clear advantage over commercial supports. Interestingly, modifying γ-alumina with hydrogen chloride increases the catalytic activity even at low rhenium loading (ca. 0.7 wt%).