Carbene Complex Syntheses with Group 4 Metallocene Reagents

Abstract

Since their discovery in the early sixties, transition metal carbene complexes have developed into reagents of rapidly increasing importance for the transformation of organic substrates (Dotz 1983). Examples of this class of compounds serve as the reactive intermediates in olefin disproportionation (“olefin metathesis”) and alkylidene transfer reactions. They may also play an important role in many alkene and alkyne oligomerizations. In addition, transition metal carbene complexes have turned out to be interesting stoichiometric reagents in organic synthesis. Nucleophilic “Schrock-type” carbene complexes of the early transition elements have found specific uses as selective alkylidene donors in “Wittig-type” carbonyl olefination reactions. However, the most remarkable synthetic developments have been achieved with heteroatom stabilized electrophilic “Fischer-type” carbene complexes as reagents in organic synthesis (Brown 1980).