Novel imidazolium ion-tagged Ru-carbene complexes: synthesis and applications for olefin metathesis in ionic liquid

Novel Hoveyda-type Ru-carbene complexes 7a,b and 8a,b tethering imidazolium tags at chelating isopropoxy group have been synthesized, and investigated their catalytic activities and recyclabilities in ring-closing metathesis (RCM) and cross metathesis (CM) in ionic liquids. They showed excellent catalytic activities for RCM of various dienes in [bmim][PF₆]/CH₂Cl₂ (1/1, v/v). The recyclability of these catalysts is largely dependent on the tether length and the structures of imidazolium tag and ionic liquid, as well as the composition of the ionic solvent system. A combination of the 2-methylated imidazolium ion-tagged Ru-complex 7b with a mixture of [bdmim][PF₆]/toluene (1/3, v/v) allowed several times recycling without significant loss of catalytic activity in RCM, however low recyclabilities were observed in CMs.