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

Abstract

Reactivity studies of the rheniumA C H T U N G T R E N N U N G (VII) oxide/aluminum oxide olefin metathesis catalyst with various olefins show that initiation does not require an olefin with an allylic C À 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.

The Effect of Support Acidity on Olefin Metathesis over Heterogeneous Mo/HBeta Catalyst: A DFT Study

“…So the former reaction was choosed to study here [16]. The formation of Mo-carbene species from Mo-oxo precursor and 2-butylene occurs via an oxametallacyclobutane intermediate structure In1 (Scheme 1i), similarly to that reported on the Re 2 O 7 /Al 2 O 3 catalyst [34]. Two transition states of Ts1 and Ts2 were found during this process, corresponding to In1's formation and decomposition.…”

Rhenium Nanochemistry for Catalyst Preparation

“…The activity of rhenium oxide catalysts is revealed in the starting (activation) step for the internal olefins, implying the formation of cyclic intermediates as a compulsory moment in realization of the reaction mechanism [34] (see Scheme 2). Scheme 2.…”

“…An alternative approach exploits wetting of the alumina with a water solution of ammonium perrhenate or perrhenic acid, HReO 4 [22]. Activation of the nanocomposite is always achieved by short term heat-treatment in oxygen atmosphere [34]. The subsequent application has always been tested in argon atmosphere to avoid the loss of rhenium in the form of volatile Re 2 O 7 .…”

Determination of Number of Activated Sites Present during Olefin Metathesis by Supported ReOx/Al2O3 Catalysts

“…1,2,8 In contrast, ~35% of the total supported rhenia sites have concluded to be activated by olefins at room temperature after 2 hours of evacuation on supported rhenia/Al 2 O 3 catalysts prepared in a hydrochloric acid medium. 3 Adsorption of 13 C 3 = on supported (CH 3 ) 3 ReO 3 /alumina followed by evacuation and titration at room temperature with C 2 = gave ~15% activated rhenia sites.…”

“…[1][2][3][4][5][6][7][8] Some studies reported the number of activated rhenia sites to only be ~1-2% of the total supported Re atoms after activation with olefins at room temperature and evacuation for 1-6…”