Testing diverse strategies for ruthenium catalyst removal after aqueous homogeneous olefin metathesis

Traditionally, olefin metathesis (OM) is carried out in organic solvents such as dichloromethane or toluene. Due to the development of water-resistant or even water-soluble ruthenium catalysts in the last two decades, considerable progress on OM in aqueous media has been made. However, the removal of ruthenium from the product of OM reactions performed in water remains a substantial challenge. In the present work, selected approaches to purify the reaction mixtures after aqueous homogeneous olefin metathesis (AHOM) reactions have been probed to address this shortcoming. It was found that elimination of a water-soluble Ru catalyst after AHOM conducted in neat water can be achieved via addition of thiocyanate ions (with or without support of charcoal additive). The developed purification method can make the aqueous metathesis methodology more practical, allowing easier separation of a spent water-soluble catalyst from the water-soluble metathesis products. Unfortunately, this methodology did not provide satisfactory results in the case of AHOM reactions performed in water/alcohol mixtures. To allow separation of a Ru catalyst in the latter case, a method utilizing a stimuli-responsive polymer was tested, leading however to limited success.