Alkylidenation titanium metallacycles

The metallacycle formed according to scheme (11) is in equilibrium with a small (unobservable) amount of titanium alkylidene complex formed by the opening of the titanacycle ring the alkylidene complex is then trapped by norbornene to give a new titanacycle, and thus the polymer chain is propagated [49] ... 

It was found that titanacyclobutanes could be prepared by removing the aluminum from 3 with a strong Lewis base in the presence of an olefin, as shown in Eq. 9. These metallacycles were stable with respect to rearrangement to an olefin via a 3 hydride process, and showed a tendency to generate intermediate alkylidene complexes in situ. They ultimately proved to be useful as catalysts for the ring opening metathesis polymerization of a variety of strained olefins. [47,48] It should be noted that the masked titanium methylene complex 3 (Eq. 

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