Metathesis side exchange

Olefin metathesis can also be used in intermolecular reactions.299 For example, a variety of functionally substituted side chains were introduced by exchange with the terminal double bond in 5.300 These reactions gave E Z mixtures. 

With the general mechanism of olefin metathesis established by experimental work, early theoretical studies focused on the details of several of the steps outlined above. Ligand exchange to form the initial olefin complex could occur by either an associative or dissociative mechanism. Experimental evidence from Grubbs and coworkers [2] pointed to a dissociative process. The structure of the active olefin complex was also a matter of uncertainty, as both bottom-bound (trans to L) and side-bound (cis to L) complexes have been reported (Chapter 8). Finally, the detailed structure and reactivity of the metallacyclobutane have been the focus of several theoretical investigations, as this intermediate was not initially experimentally observed (Chapter 8). 

Although the metathesis of terminal alkynes also proceeds rapidly, polymerization of the terminal alkynes displaces the carbyne exchange reactions towards the wrong side towards the starting terminal alkyne that polymerizes except if suitable parameters are ad usted such as temperature, solvent diethyl ether and especially the presence of the potential ligand quinuclidine together with the... 

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