CH₃ReO₃ on γ‐Al₂O₃: Understanding Its Structure, Initiation, and Reactivity in Olefin Metathesis

Abstract

International audienc

Surface and Interfacial Chemistry

“…[15] In a different way CH 3 ReO 3 is activated upon adsorption on γ-alumina, through the C-H bond activation of the methyl ligand, which generate a µ 2 -methylene species, which corresponds to the resting state of a highly active alkene metathesis catalyst (Scheme 1b). [16,17] These examples clearly illustrate our approach, and the critical need to understand surface structures of metal oxides as a first step towards the generation and the design of highly active catalysts. Therefore, our group invests major research efforts towards the molecular understanding of metal oxides, thus allowing design of well-defined metal sites.…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…[478,[488][489][490][491][492][493][494][495][496][497] Thes tructures of the surface sites of MeReO 3 /Al 2 O 3 were investigated in detail by using acombination of IR and solid-state NMR spectroscopy,EXAFS,and DFT calculations using aperiodic model of g-alumina. [498][499][500] Tw oo ft he oxo ligands in the oxo species are bound to adjacent Al sites.T he m-methylene species is formed through C À Hbond activation of the methyl ligand in MeReO 3 on an Al À Osite;inthis species,one of the Re = Og roups is coordinated to an adjacent Al site.T he reaction of 13 C-enriched MeReO 3 /Al 2 O 3 with natural abundance ethylene results in the disappearance of the 13 CNMR signal corresponding to the m-methylene species,thus indicating that this site is responsible for the catalytic activity. [498][499][500] Tw oo ft he oxo ligands in the oxo species are bound to adjacent Al sites.T he m-methylene species is formed through C À Hbond activation of the methyl ligand in MeReO 3 on an Al À Osite;inthis species,one of the Re = Og roups is coordinated to an adjacent Al site.T he reaction of 13 C-enriched MeReO 3 /Al 2 O 3 with natural abundance ethylene results in the disappearance of the 13 CNMR signal corresponding to the m-methylene species,thus indicating that this site is responsible for the catalytic activity.…”

Eine Brücke zwischen industriellen und wohldefinierten Trägerkatalysatoren

“…Die Struktur der Oberflächenzentren von MeReO 3 /Al 2 O 3 wurde mit einer Kombination aus IR‐ und Festkörper‐NMR‐Spektroskopie, EXAFS und DFT‐Berechnungen mit einem periodischen Modell von γ‐Aluminiumoxid ausführlich untersucht. Diese Untersuchungen zeigen, dass MeReO 3 auf die Oberfläche chemisorbiert und dort ein Oxo‐gebundenes Zentrum (85–90 %) und eine μ‐Methylen‐Spezies (10–15 %) bildet (Schema a) . In der Oxo‐Spezies sind zwei der Oxo‐Liganden an benachbarte Al‐Zentren gebunden.…”