A Dicationic Ruthenium Alkylidene Complex for Continuous Biphasic Metathesis Using Monolith-Supported Ionic Liquids

A dicationic ruthenium-alkylidene complex [Ru(dmf)(3)(IMesH(2)) (= CH-2-(2-PrO)-C6H4)][(BF4)(2)] (1; IMesH(2) = 1,3-dimesitylimidazolin-2-ylidene) has been prepared and used in continuous metathesis reactions by exploiting supported ionic-liquid phase (SILP) technology. For these purposes, ring-opening metathesis polymerization (ROMP)-derived monoliths were prepared from norborn-2-ene, tris(norborn-5-ene-2-ylmethyloxy)methylsilane, and [RuCl2(PCy3)(2)(CHPh)] (Cy = cyclohexyl) in the presence of 2-propanol and toluene and surface grafted with norborn-5-en-2-ylmethyl-N,N,N-trimethylammonium tetrafluoroborate ([NBE-CH2-NMe3][BF4]). Subsequent immobilization of the ionic liquid (IL), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([DMIM][BF4]), containing ionic catalyst 1 created the SILP catalyst. The use of a second liquid transport phase, which contained the substrate and was immiscible with the IL, allowed continuous metathesis reactions to be realized. High turnover numbers (TONs) of up to 3700 obtained in organic solvents for the ringclosing metathesis (RCM) of, for example, N,N-diallyltrifluoroacetamide, diethyl diallylmalonate, diethyl di(methallyl) malonate, tert-butyl-N, N-diallyl-carbamate, N,N-diallylacetamide, diphenyldiallylsilane, and 1,7-octadiene, as well as in the self-metathesis of methyl oleate, could be further increased by using biphasic conditions with [BDMIM][BF4]/heptane. Under continuous SILP conditions, TONs up to 900 were observed. Due to the ionic character of the initiator, catalyst leaching into the transport phase was very low (<0.1%). Finally, the IL can, together with decomposed catalyst, be removed from the monolithic support by flushing with methanol. Upon reloading with [BDMIM][BF4]/1, the recycled support material again qualified for utilization in continuous metathesis reactions.