Recycling of a perfluoroalkylated BINOL ligand using fluorous solid-phase extraction{

The fluorous biphase system has been applied successfully to a wide range of homogeneous catalyses with excellent catalyst recovery and reuse being reported. However, it is unlikely to be exploited commercially because of intersolvent leaching problems, the prohibitive expense of the perfluorocarbon solvents and concerns about their environmental persistence. An alternative approach, designed by Curran for high throughput organic synthesis, uses fluorous reverse phase (FRP) silica gel as a solid support for the separation of fluorous-tagged products from non-fluorinated reagents, as well as the removal of perfluoroalkylated reagents from organic products. The major advantages of fluorous solidphase extraction are that fewer and shorter fluorous ponytails are required (,40% fluorine content by molecular weight) compared to liquid–liquid extraction using the FBS (.60% fluorine content by molecular weight) and perfluorocarbon solvents are no longer required for either the reaction or separation step. Recently, we reported the first example of separation, recovery and recycle of a perfluoroalkylated Lewis acid catalyst, [Ni{C6F13C(O)CHC(O)C6F13}2], using FRP silica gel after catalyzing the reaction between 2,4-pentanedione and ethylcyanoformate in dichloromethane. We have also extended the applications of this novel separation technique in order to recover and recycle lightly fluorinated BINAP ligands after the ruthenium-catalysed asymmetric hydrogenation of methyl acetoacetate. Here, we demonstrate the efficient separation and recycle of a perfluoroalkylated BINOL ligand using fluorous solid-phase extraction.