Controlling Olefin Isomerization During Olefin Metathesis with Fatty Acid Derivatives

Olefin metathesis with oleochemicals is a very versatile approach to obtain value added chemical intermediates from renewable raw materials.[1] Moreover, acyclic diene metathesis (ADMET) polymerization has developed into a very versatile technique for the preparation of a variety of macromolecular architectures. Applying this efficient catalytic process to monomers from renewable resources will lead to the development of materials with interesting properties that have the potential to replace existing fossil oil based materials. Despite of this success, it is known from low molecular weight model compounds that especially second generation olefin metathesis catalysts show a temperature dependent double bond isomerization activity.[2,3] The mechanism leading to the formation of the ruthenium-hydride species, which are responsible for these isomerizations, is discussed in detail in the literature.[4] One particular problem of ADMET reactions in this respect is that it is rather difficult to study the occurring side reactions with the resulting polymeric materials.
Within this contribution, the synthesis of novel and degradable monomers from fatty acid derivatives will be described and their subsequent polymerization discussed in detail. We will focus our discussion on the investigation of isomerization side-reactions occurring during ADMET polymerizations. Our approach to study isomerisation side reactions of the prepared polyesters depends on their degradation by transesterification with methanol in order to be able to investigate and quantify isomerization side-reactions that occurred during the polymerizations by GC-MS.[5,6] Furthermore, we will correlate these findings to self- and cross-metathesis reactions of low molecular weight model compounds.[7] Finally, a simple method to suppress these isomerizations during ADMET with second generation ruthenium metathesis catalysts will be described.

Financial support from the German Federal Ministry of Food, Agriculture and Consumer Protection (represented by the Fachagentur Nachwachsende Rohstoffe; FKZ: 22026905) is kindly acknowledged.

[1] A. Rybak, P. A. Fokou, M. A. R. Meier, Eur. J. Lipid Sci. Technol. 2008, 110, 797.
[2] S. E. Lehman, J. E. Schwendeman, P. M. O’Donnell, K. B. Wagener, Inorg. Chim. Acta 2003, 345, 190.
[3] F. C. Courchay, J. C. Sworen, K. B. Wagener, Macromolecules 2003, 36, 8231.
[4] B. Schmidt, Eur. J. Org. Chem. 2004, 1865.
[5] P. A. Fokou, M. A. R. Meier, J. Am. Chem. Soc. 2009, 131, 1664.
[6] P. A. Fokou, M. A. R. Meier, Macromol. Rapid Commun. 2010, DOI:10.1002/marc.200900678.
[7] G. B. Djigoué, M. A. R. Meier, Appl. Catal., A 2009, 368, 158.