Latent olefin metathesis

Monsaert S, Lozano Vila A, Drozdzak R, Van Der Voort P, Verpoort F. Latent olefin metathesis catalysts. Chem Soc Ren. 2009 38(12) 3360—3372. 

These complexes showed higher thermal stabihty in toluene at 80 °C than the Hoveyda first-generation catalyst, with half-lives ranging from 3 to 6 h, depending on the nature of the Schiff base-derived hgand. They also showed latent catalyst behavior, as only moderate-to-low olefin metathesis activity was observed at room temperature in CM and RCM [44]. On the other hand, these complexes were active in the ROMP of cyclooctene and cyclopentene. The NHC-containing catalyst was found to be especially efficient, leading to a TOP of 667 min at room temperature [43]. 

Another methodology to achieve latent chelated olefin metathesis catalysts was adopted by Grubbs et al. [28]. They reported that exchange of the anionic ligands from chlorides to iodides caused a decrease in activity of the catalyst. While in most cases this change is detrimental, it opened another pathway to achieve latent ROMP initiators. Thus, iodide bound complexes 41 and 42, more sterically hindered for olefin association [29], were synthesized and studied for... 

The amount of effort invested in the advancement of latent ruthenium olefin metathesis catalysts for ROMP bodes well for the near future. Certainly, more of these developments will afford ever-more useful macromolecules. The most... 

An alternative approach has been formulated by Katz and co-workers (28). They consider the latent cis specificity in reactions of c/ s-olefins with metathesis catalysts to be quite high, based on their results with a catalyst having very low Lewis acidity. They further propose that the frequently observed lack of stereospecificity is mainly the consequence of cationic processes inherent in the metathesis step which mask stereospecificity. 

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