Catalysis at the interface of ruthenium carbene and ruthenium hydride chemistry: Organometallic aspects and applications to organic synthesis

Soon after the introduction of stable and defined ruthenium precatalysts for olefin metathesis it was discovered that double bond migrations May interfere with the metathesis reaction. This undesired side reaction has been attributed to the formation of ruthenium hydride species from metathesis-active ruthenium carbene species in situ, Over the past few years, several studies have indeed revealed the existence of pathways leading from ruthenium carbene to ruthenium hy-dride complexes. Furthermore, a number of examples have been published recently where typical precatalysts for olefin metathesis were found to promote non-metathesis trans-formations efficiently in preparatively useful yields and se-lectivities, presumably via the in situ formation of ruthenium hydride species. These results open up a pathway to the development of novel catalyzed reaction sequences that combine ruthenium carbene- and ruthenium-hydride-mediated steps. This paper provides an overview of the field and covers organometallic aspects as well as synthetic applications. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).