Highly selective ruthenium metathesis catalysts for ethenolysis.

Journal of the American Chemical Society (2011-04-23)
Renee M Thomas, Benjamin K Keitz, Timothy M Champagne, Robert H Grubbs
ABSTRACT

N-Aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium metathesis catalysts are highly selective toward the ethenolysis of methyl oleate, giving selectivity as high as 95% for the kinetic ethenolysis products over the thermodynamic self-metathesis products. The examples described herein represent some of the most selective NHC-based ruthenium catalysts for ethenolysis reactions to date. Furthermore, many of these catalysts show unusual preference and stability toward propagation as a methylidene species and provide good yields and turnover numbers at relatively low catalyst loading (<500 ppm). A catalyst comparison showed that ruthenium complexes bearing sterically hindered NHC substituents afforded greater selectivity and stability and exhibited longer catalyst lifetime during reactions. Comparative analysis of the catalyst preference for kinetic versus thermodynamic product formation was achieved via evaluation of their steady-state conversion in the cross-metathesis reaction of terminal olefins. These results coincided with the observed ethenolysis selectivities, in which the more selective catalysts reach a steady state characterized by lower conversion to cross-metathesis products compared to less selective catalysts, which show higher conversion to cross-metathesis products.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methyl oleate, 99%
Supelco
Methyl oleate, analytical standard
Sigma-Aldrich
Methyl oleate, technical grade, 70%
Sigma-Aldrich
Methyl elaidate, ≥99% (capillary GC)
Supelco
cis-9-Octadecenoic acid methyl ester, certified reference material, 10 mg/mL in heptane
Supelco
Methyl elaidate, analytical standard