Purification
of a metathesis mixture can give you all sorts of problems (especially
when using high catalyst loadings). Sometimes you need multiple columns
to get a colorless product. Sometimes residual ruthenium can cause the
product to isomerize during distillation or decompose over time.
Numerous methods have been reported for the removal of metathesis
catalysts after a reaction. In general, you need a ligand or adsorbent
that binds ruthenium better than your product, or a reagent that will
react with the residual ruthenium preferentially. Unfortunately the
optimal process tends to vary on a case by case basis.
