Olefin Metathesis in Fluorous Media

Examples of using functionalized, fluorinated carboxylates as alternative X-type ligands for the generation of supported catalyst analogs were previously introduced in section The Attachment of Grubbs-Type Catalysts via the X-Type Ligand . However, the introduction of fluorous functionalities within the catalyst architecture can also be employed to aid in product isolation and to effectively recover/recycle a catalyst via fluorous extraction [141]. Although similar to the IL systems that were discussed in the previous section, this approach instead uses 

Yao and coworkers [ 142] were the first to report a fluorous-functionalized olefin metathesis catalyst. A random, bifunctional, fluorous polyacrylate material, containing both a perfluoroalkyl section and a styrenic Hoveyda ligand section in a 10 1 ratio, was prepared. This was then treated with catalyst 4 to generate the heavy fluorous catalyst 156. This catalyst was then effectively used in a variety of RCM reactions at 50 C, employing a solvent mixture of PhCFj/CHjClj (1 19 v/v). This catalyst system was shown to be efficiently recycled a total of 20 times using a fluorous extraction technique. Unfortunately, no results were reported pertaining to any residual Ru contamination within the organic fractions. 

A number of examples investigating alternative strategies for catalyst immobilization were also described. These, too, are important, as they can alleviate the time and cost barriers toward modifying catalyst architectures for attachment onto a solid support. Ideally, these systems should display many of the same benefits attributed to the covalently immobilized systems however, catalyst leaching is a potential concern due to the lack of a covalent interaction between the catalytic moiety and the supporting matrix. This is more problematic when substrates containing polar functional groups are examined, or the use of polar solvents are required for the process. 

While considerable progress has been made in the field of immobilized metathesis catalysts, a supported catalyst system capable of meeting the economic requirements of catalytic activity and lifetime necessary for a viable, industrially-relevant process has yet to be developed. However, the foundation provided by these research programs aimed at sustainability will help guide future efforts in the field, where emphasis can be placed on achieving an ideal recoverable catalyst, or better yet, an ideal catalyst for olefin metathesis processes. 

Anastas, P.T. and Warner, J.C. (eds) (1998) Green Chemistry Theory and Practice, Oxford University Press, New York. 

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