Chauvin mechanism general

The mechanism of the reaction remained mysterious for many years. Several early papers, the first by Chauvin, suggested the correct solution, but this was not generally accepted until much later. The question was whether the two alkenes bound to the metal and underwent rearrangement (called the pairwise mechanism), or whether the alkenes reacted one at a time (the nonpairwise mechanism). The Chauvin Mechanism, equation (41), is now the accepted pathway, and was a particularly imaginative suggestion at a time when both the required metalacyclobutane formation and fragmentation reactions and nonhetroatom substituted carbenes were unknown. 

A mechanism for olefin metathesis reactions, which is now generally accepted, was first proposed in 1970 by Herisson and Chauvin [4]. It is outlined... 

Scheme 3.5 General mechanism for olefin metathesis, proposed by Chauvin in 1971...

In general, olefin metathesis is an organic reaction that allows redistribution of fragments of alkenes by the scission and regeneration of C=C double bonds (Scheme 2.11). The metallic catalysts needed for this reaction have evolved rapidly over the past few decades. The impact of this topic in organic synthesis was demonstrated by the 2005 Nobel Prize in Chemistry awarded to Yves Chauvin, Robert H. Gmbbs, and Richard R. Schrock for elucidation of the reaction mechanism and discovery of highly efficient and selective metathesis catalysts. 

In order to improve the catalytic performance of ruthenium-based metathesis complexes, extensive theoretical [9,10] and experimental [11,12] studies were conducted. The generally accepted mechanism involves the formation of a highly active and unstable 14-electron complex through the dissociation of one of the phosphine ligands (Scheme 11.1) [13-17]. This actual catalytic species allows the binding of incoming olefin to form the Chauvin metallacyclobutane [18] intermediate and eventually the reaction products. 

In the year 2005, Nobel Prize in Chemistry was awarded to Yves Chauvin, Robert H. Grubbs, and Riehard R. Schrock for the development of the metathesis method in organie synthesis [41-43], It is a general view that, this reaction revolutionized different fields of synthetic chemistry. Chauvin proposed the carbene mechanism to explain this reaction [44] and Schrock prepared the first well-defined highly active metathesis catalysts [45], while, Grubbs developed ruthenium based active and air stable catalysts, which are tolerant to various functional groups in the presence of olefins [46]. 

Herisson and Chauvin in 1971 [44], were the first to propose generally accepted mechanism, widely supported with key experimental evidences by Casey [47], Katz [48] and Grubbs groups [49] as shown in Scheme 9.31. 

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