Metathesis

AbstractIn organic synthesis and polymer science, the metathesis reaction consists of a unique metal‐catalyzed carbon skeleton redistribution in which a mutual exchange of unsaturated carbon–carbon bonds takes place. The reaction is generally reversible and limited to an equilibrium. In its most common embodiment, alkenes serve as reagents. Hence, olefin metathesis constitutes a powerful catalytic method for both cleaving and forming CC double bonds. Alkyne metathesis and ene–yne metathesis are also important synthetic pathways. All three types of metathesis occur intra‐ or intermolecularly and numerous combinations thereof are possible (ring‐closing metathesis, ring‐opening metathesis polymerization, cross‐metathesis, etc).Metathesis has opened up new routes to important petrochemicals, oleochemicals, polymers, and specialty chemicals. The transformation often gives access with remarkable atom economy to structures that are not available by any other means, or only via multistep painstaking procedures. Major industrial processes rely on metathesis for the production of olefins. They are usually based on inexpensive, ill‐defined, multicomponent catalytic systems derived from tungsten, molybdenum, rhenium, or ruthenium salts. Research laboratory applications take advantage of well‐defined metal‐alkylidene complexes of molybdenum and ruthenium that combine high activities and ease of set‐up under reproducible conditions, albeit at the price of a higher cost.