Method for the preparation of metal carbene complexes

A process for preparing a metal carbene complex of the formula (I)

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• wherein
• M is a transition metal atom selected from the group consisting of ruthenium, rhodium, iron, cobalt, osmium and iridium;
• L denotes neutral electron donor ligands ligated to said metal, such groups being the same or different;
• X is an anionic ligand;
• R1 and R2 are each independently selected from the group consisting of hydrogen, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C2-C20 alkenyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocycloalkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted vinyl,
• a is 2 or 3 and
• b is 1 or 2,
• such process comprising reacting a sulfur ylide of the formula Ar2S═CR1R2 or its precusor, wherein each Ar is independently selected from aryl, substituted aryl, and aryl or substituted aryl bound to a polymeric unit, with an appropriate metal complex comprising a transition metal atom selected from the group consisting of ruthenium, rhodium, iron, cobalt, osmium and iridium, at least two neutral ligands capable of forming donor bonds with said metal and at least one further organic or inorganic anionic group which form a complex with said metal, including dimers of such metal complex, at a temperature between +80° C. and −80° C., in an inert solvent and under inert atmosphere, to give the metal carbene complex of formula (I).