A very simple procedure was described recently by David Knight and coworkers for the removal of ruthenium after metathesis reactions. The process involves simply stirring the crude metathesis reaction solution with excess 15% hydrogen peroxide for 1h at room temperature as a biphasic mixture. At low catalyst loadings (0.37 mol%) a single peroxide wash was needed to get the Ru levels down to 2 ppm. At higher catalyst loadings (1.37 mol%) two washes were necessary to reach the same level of Ru. The fact that the process is biphasic and brief make this method in theory compatible with many common organic functional groups. Typically, no peroxides are present in the product after treatment.
The ruthenium dioxide formed can be recovered and reused. One disadvantage of the method is that a large excess of peroxide has to be used, because it decomposes rapidly in the presence of ruthenium oxide. But hydrogen peroxide is cheap.
The reactions were run on relatively small scale, but it sure looks promising. No chromatography required!
Typical procedure: After the completion of the metathesis reaction in DCM, water and 37% aq hydrogen peroxide were added and the mixture was stirred for 1h. The mixture started to effervesce and a black precipitate was formed. The layers were separated and the aqueous was extracted with DCM. The peroxide test for the organic phase is usually negative; if positive, a single sulfite wash was sufficient. After filtering through a silica plug the solvent was removed to yield the product as colorless oil.