A comparison of ruthenium-catalysed arene hydrogenation reactions in water and 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids

The hydrogenation of benzene and other arene substrates under biphasic conditions is evaluated using the catalyst precursor Ru(eta(6)-C10H14)(pta)Cl-2 (pta = 1,3,5-triaza-7-phosphaadamantane) immobilised in water and 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids. The effect that contamination of the 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids with chloride has on the hydrogenation reaction has also been examined. Of the immobilisation solvents tested the optimum solvent was found to be chloride-free 1-butyl-3-methylimidazolium tetrafluoroborate. Catalytic turnovers in this solvent are highest, and in general, turnovers for the hydrogenation reactions follow the trend: chloride-free 1-butyl-3-methylimidazolium tetrafluoroborate > water > chloride-contaminated 1-butyl-3-methylimidazolium tetrafluoroborate.