Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents.
Alkene metathesis is a widely and increasingly used reaction in academia and industry because of its efficiency in terms of atom economy and its wide applicability. This reaction is notably responsible for the production of several million tons of propene annually. Such industrial processes rely on inexpensive silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C), in contrast with the mild room temperature reaction conditions typically used with the corresponding molecular alkene metathesis homogeneous catalysts. This large difference in the temperature requirements is generally thought to arise from the difficulty in generating active sites (carbenes or metallacyclobutanes) in the classical metal oxide catalysts and prevents broader applicability, notably with functionalized substrates. We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W). This high activity at low temperature broadens the scope of these catalysts to functionalized substrates. This activation process can also be applied to classical industrial catalysts. We provide evidence for the formation of a metallacyclopentane intermediate and propose how the active species are formed.
Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, 8093 Zürich, Switzerland.
Victor
V
Mougel
Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, 8093 Zürich, Switzerland.
Ka-Wing
KW
Chan
Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, 8093 Zürich, Switzerland.
Georges
G
Siddiqi
Department of Chemistry, Graduate School of Engineering Science, Osaka University , 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
Kento
K
Kawakita
Department of Chemistry, Graduate School of Engineering Science, Osaka University , 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
Haruki
H
Nagae
Department of Chemistry, Graduate School of Engineering Science, Osaka University , 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
Hayato
H
Tsurugi
Department of Chemistry, Graduate School of Engineering Science, Osaka University , 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan.
Kazushi
K
Mashima
Paul Scherrer Institute , CH-5232 Villigen, Switzerland.
Olga
O
Safonova
Department of Chemistry and Applied Biosciences, ETH Zürich , Vladimir Prelog Weg 1-5, 8093 Zürich, Switzerland.
Christophe
C
Copéret