The catalytic activity of the arene–ruthenium(II) complexes [RuCl2(η6-C6H5OCH2CH2OH)(L)] (L = P(OMe)3 (1a), P(OEt)3 (1b), P(OiPr)3 (1c), P(OPh)3 (1d), PPh3 (1e)) in the isomerization of eugenol into isoeugenol has been evaluated. Best results in terms of activity and selectivity were observed with those catalysts containing an aliphatic P-donor ligand (1a–c). Under optimized conditions, full conversions in extremely short reaction times (5 min), and with high levels of trans-selectivity (up to 98%), could be achieved. Addition of both NaOH or H2SO4 to the aqueous media resulted in rate enhancements, suggesting two different activation pathways of the pre-catalysts. We have evidenced that sodium hydroxide promotes the release of the η6-coordinated arene ligand, while sulfuric acid favours the Ru–Cl bond dissociation and the formation of aquo-derivatives [RuCl(H2O)(η6-C6H5OCH2CH2OH)(L)][Cl].
