May 28, 2012
These metathesis catalysts tolerate functional groups. Olefin metathesis is receiving a lot of attention as a way to interconvert olefins. For example, because of the rapid growth of polypropylene and other key propylene derivatives, propylene supplies are sometimes limited, leading to high propylene prices. The method most frequently used by the petrochemical industry to make so called “on-purpose” propylene is the metathesis of ethylene and straight-chain butenes.
One limitation of olefin metathesis reactions is catalysts that are notoriously sensitive to polar functional groups. If active, robust olefin metathesis catalysts were developed, the scope of metathesis could potentially be broadened to create new production pathways to a variety of functionalized products. It could also allow functionalized materials, such as unsaturated natural oils, to be used as feedstocks for “petrochemical” products.
W. A. Herrmann, W. Schattenmann, and T. Weskamp are developing active olefin metathesis catalysts that resist deactivation by polar groups. The catalysts are based on ruthenium–carbene complexes with various N-heterocyclic ligands. To demonstrate the ability of these catalysts to metathesize unsaturated oils, the inventors allowed methyl oleate to self-metathesize.
In an example, a solution of 3.6 mg catalyst [benzylidenedichlorobis(1,3-diisopropylimidazoline-2-ylidene)ruthenium] in 0.5 mL (CH2Cl)2 was mixed with 1.06 mL methyl oleate at 60 °C for 15 h. Analysis of the reaction mixture showed the presence of 21% 9-octadecene and 21% dimethyl 9-octadecenedioate.
The inventors also cross-metathesized methyl oleate with 1-octene under similar conditions to give 7-tetradecene as the main product. Other isomers also were produced from the reaction of 2-octene (from the isomerization of 1-octene) with methyl oleate. (Evonik Degussa GmbH [Essen, Germany]. US Patent 8,153,810, April 10, 2012; Jeffrey S. Plotkin)