An investigation in ruthenium-based metathesis catalysts has looked at the effects of the catalysts on olefinic substrates with various allylic substituents.

A team of scientists claim that the steric bulk of N-heterocyclic carbene (NHC) ligands of ruthenium-based catalysts significantly affects the efficiency of olefin cross-metathesis (CM) reactions.

IC Stewart, DJ Douglas and RH Grubbs from Caltech believe that NHC ligands establish a general model for selectivity in CM along with steric congestion at the site of the reactive olefin moiety which is a limiting condition.

Three types of ruthenium catalyst were tested according to Noteworthy Chemistry and the third produced the desired CM product with an 87 per cent yield.

The researchers concluded that by reducing the steric bulk of the NHC ligand there was increased efficiency in forming sterically hindered disubstituted olefins.

Producing trisubstituted olefins by CM was surprisingly more efficiency when bulkier NHC ligands that contained N-2, 6-diisopropylphenyl substitutes were used.

Source:

Cross-metathesis reactions show increased efficiency for sterically hindered olefins, 03/03/08

http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=840&content_id=WPCP_008328&use_sec=true&sec_url_var=region1

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