4 - Related Reactions

Abstract

This chapter analyzes the chemistry of metal carbene and carbyne complexes in a wide context. It has undergone very rapid development since the sixties and olefin metathesis reactions now form part of a much larger family of metathesis reactions between multiply bonded compounds. Some examples illustrate the use of stoichiometric metathesis reactions of such complexes in organic synthesis. Olefin metathesis reactions are sometimes accompanied by side reactions and the question then arises as to whether the two types of reaction are related and proceed through the same intermediates, or are completely independent. A situation exists when metal alkyl intermediates, capable of propagating Ziegler–Natta type polymerization, are in equilibrium with metal alkylidene hydride intermediates capable of propagating ring-opening metathesis polymerization (ROMP). This can lead to polymer chains containing units formed both by addition to the double bond and by cleavage of the double bond. In living ROMP, the metal carbene intermediate can be transformed by suitable reaction into another type of chain carrier, which can then propagate the polymerization of a different type of monomer.