Catalytic activity of ruthenium-arene complexes bearing a carbonate ligand on the synthesis of enol esters

Ruthenium-arene complexes are versatile and efficient catalyst precursors for various important organic transformations such as olefin metathesis, atom transfer radical reactions, transfer hydrogenation of ketones, and isomerization of allylic alcohols. Ruthenium-arene complexes also catalyse the addition of carboxylic acids to terminal alkynes affording vinyl sters in high yields and excellent selectivities. Particularly, we found that the synthesis of vinyl esters was greatly accelerated when the reaction was performed in water-saturated toluene.
Since 2006, ruthenium-arene complexes bearing a carbonate ligand, [Ru(η2-O2CO)(η6-arene)(PR3)], are known to be easily synthesized. However, their catalytic activity has never been reported. As part of our research program directed toward the synthesis of vinyl esters, we decided to investigate the catalytic activity of complexes [Ru(η2-O2CO)(η6-arene)(PPh3)] and [Ru(η2-O2CO)(η6-arene)(PCy3)] for the title reaction.
Ruthenium-carbonate complexes are found to be excellent catalytic species in enol esters synthesis. Indeed, kinetics and selectivities of the reaction were very good wathever the used acid. Moreover, the reaction could successfully be carried out at 40 °C. Finally, the dilution of those complexes was investigated; while the time required for reaching completion increased significantly, a TON of 1500 could be achieved.