In olefin metathesis, olefin isomerization can significantly alter the product distribution and decrease the yield of the desired product, especially with ill-defined catalyst systems.  Additionally, the side products resulting from this unwanted isomerization are frequently difficult to separate via standard techniques.  Well-defined ruthenium-based olefin metathesis catalysts are generally highly selective for olefin metathesis; however, there have been some reports of olefin isomerization occurring with these catalysts as well.

     Recently, we have shown that ruthenium hydride species formed from decomposition of catalysts could be responsible for the isomerization reaction.  This information has allowed us to develop a way to block the unwanted isomerization reaction by scavenging metal hydrides from decomposed ruthenium catalysts.  Isomerizations of allylic ethers and various long-chain aliphatic alkenes have been effectively blocked via the incorporation of additives to the reaction mixture.  These inexpensive additives can be readily separated from the desired products via standard techniques.  This mild and effective method to block olefin isomerization increases the synthetic utility of olefin metathesis via improving product yield and purity.