Tailored Ru-NHC Heterogeneous Catalysts for Alkene Metathesis (original) (raw)
2009, Chemistry: A European Journal
The introduction of N-heterocyclic carbene ligands (NHC) has led to major breakthroughs in homogeneous catalysis. [1, 2] However, such homogeneous catalysts can still suffer from deactivation and problems related to catalyst cost and recovery, as well as metal separation from the organic substrates. In the case of the very challenging and promising reaction of alkene metathesis, [3-6] these drawbacks have probably been delaying the development of economical industrial processes. One possible solution would be the development of an efficient heterogeneous catalysts that is highly active (TON and TOF), stable (minimum recycling and leaching) and tolerant to functional groups. Despite numerous efforts in this area (involving permanent grafting of Ru-NHC complexes on various supports [7-10] or other immobilization strategies [11]), heterogeneous catalysts has not fulfilled the aforementioned requirements. Recently, tailored made organic-inorganic materials have proved to be an alternative and advantageous route towards highly active and well-defined heterogeneous catalysts. [12] In particular, fully characterized well-defined Ir-NHC materials displayed catalytic performances comparable to those of homogeneous homologues. This has been attributed to the careful control of the catalyst preparation: synthesis of materials containing regularly distributed NHC-moieties and subsequent selective functionalization into Ir-NHC species, leading to the "single-site" nature of these catalysts. Here, we describe the preparation of highly active and stable Ru-NHC alkene metathesis catalysts through surface organometallic chemistry [13] on hybrid mesostructured materials [14] (Scheme 1).
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