Abstract: According to the present invention there is provided a metathesis reaction between at least two olefinic compounds which are the same or different, each olefinic compound comprising a non-cyclic olefin or a compound which includes a non-cyclic olefinic moiety. The metathesis reaction is carried out in the presence of a Grubbs first generation catalyst and is characterised therein that it is carried out in the presence of a phenolic compound in the form of a phenol or a substituted phenol, which substituted phenol includes at least one hydroxyl and at least one further moiety other than H and OH attached to an arene ring.

Abstract: The use of a phosphorus containing Ligand as a Ligand for a metathesis catalyst in a catalysed metathesis reaction wherein the phosphorus containing Ligand is a heterocyclic organic compound with a ligating phosphorus atom as an atom in the heterocyclic ring structure of the heterocyclic organic compound. The invention also relates to a metathesis catalyst such a phosphorus containing Ligand and to a metathesis reaction using the catalyst.