Polish chemists have demonstrated the unprecedented catalytic efficiency of olefin metathesis reactions in a water solution.
Karol Grela and his colleagues from the Polish Academy of Sciences, Warsaw University and Warsaw University of Technology studied the performance of commercially available olefin metathesis catalysts in water. Grela explained 'Water is an ideal "green" replacement for conventional organic solvents because of its low cost and lack of organic vapours.'
Initial work found that ultrasonication of water-insoluble reactants floating on water formed an emulsion, in which smooth catalytic metathesis took place in up to quantitative yields after addition of water-insoluble, commercially available catalysts. Next, Grela's team extended their experiments in water to more challenging cross-metathesis reactions with electron-deficient substrates. Grela: 'This transformation is extremely rare in aqueous conditions, usually leading to poor conversions and low selectivities.'
"Such reactions represent the first successful example of the high-yielding aqueous cross metathesis between an alkene and an electron-deficient partner"
Grela's team revealed that cross metathesis of electron-poor substrates was also possible in water, proceeding with very good yields and selectivities. 'To our knowledge, such reactions represent the first successful example of the high-yielding aqueous cross metathesis between an alkene and an electron-deficient partner,' he said. 'We speculate that under such conditions the sensitive ruthenium intermediates are "protected" inside the water-insoluble organic droplets, thus allowing higher turnovers.'
Jason Eames, a synthetic organic chemist at the University of Hull, UK, was impressed. 'Aqueous olefin metathesis has significant environmental and process advantages,' he said. 'Much attention has been focused previously on the use of water-soluble metathesis reagents, but Grela has now demonstrated that water insoluble metathesis reagents can be used successfully through simple sonification.' Further studies leading to improve the ultrasound conditions for metathesis applications are currently underway in Grela's laboratory.