The air and moisture stable system [bmim][BF4]-[Ru-4(eta(6)C(6)H(6))(4)][BF
4] {[bmim](+) = 1-butyl-3-methylimidazolium cation} presents a novel medium
for conducting hydrogenations of arenes; the environmental problems associ
ated with related aqueous-organic biphasic regimes are eliminated.