Ionic Grubbs-Hoveyda Complexes for Biphasic Ring-Opening Metathesis Polymerization in Ionic Liquids: Access to Low Metal Content Polymers

A novel ionic metathesis catalyst, [Ru(1-CH3-4-CO2Py+)(2)(IMesH(2))(CH-2-{2-PrO}-5-NO2C6H3)][OTf-](2) (3b; IMesH(2)=1,3-dimesitylimidazolin-2-ylidene, Py=pyridine), has been prepared. 3b and the Grubbs-Hoveyda catalysts [Ru(1-CH3-4-CO2Py+)(2)(IMesH(2))(CH-2-{2-PrO}C6H4)][OTf-](2) (3a) and [RuCl(1-CH3-4-CO2Py+)(IMesH(2))(CH-2-{2-PrO}C6H4)][OTf-] (5a) were used for ring-opening metathesis polymerization (ROMP) reactions under both homogeneous and biphasic liquid-liquid conditions by using the ionic liquid 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM+][BF4-]) and toluene. All catalysts were active in the ROMP of norborn-2-ene-based monomers, with cis-cyclooctene and dicyclopentadiene providing good yields under homogeneous conditions and complex 5a the most active catalyst. With all catalysts, the use of a chain transfer agent (CTA) allowed for the synthesis of polymers with low metal contents between 10 and 80ppm, corresponding to a ruthenium removal of 98-99.8% without any additional purification step. In addition, the use of a CTA allowed for recycling experiments under biphasic conditions, in which 3a and 5a were particularly active for several cycles.