Cocatalysts stoichiometry

The change in stoichiometry depending on the experimental conditions is not limited to this catalytic system. An identical problem is found in another system, still based on palladium, but without any other metal-containing cocatalyst. In this last case, the same type of competing stoichiometries has been found and confirmed by the use of deuterated nitrobenzene (see paragraph 6.3.3). 

Metallacyclobutanes, with topological symmetry, can undergo a horizontal shift giving back the initial olefin or a vertical one metathesis. The new metal-carbene species formed are the catalytically active species of the metathesis reaction they react on the starting olefin in the same way as the initial metal-carbene complex to give olefins ultimately found in the overall metathesis stoichiometry. This mechanism now is universally accepted. In particular, Schrock showed in 19 that metal-carbene complexes are active in the absence of cocatalyst. This finding was made possible by the key discovery by Schrock s group at that time that introduc-... 

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