Abstract
After the asymmetric addition of allyltri-n-butyltin to benzaldehyde, a perfluoroalkylated BINOL-Sn complex was separated from the organic product using fluorous reverse phase silica gel. The lightly fluorinated ligand was then recovered by hydrolysis of the Rf6-BINOL-Sn complex with dilute hydrochloric acid and was reused three times without loss of activity or enantioselectivity.
Highlights
The fluorous biphase system has been applied successfully to a wide range of homogeneous catalyses with excellent catalyst recovery and reuse being reported.[1]
We have 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.[5]
The reactivity and enantioselectivity of (R)-Rf6BINOL (1) was evaluated in the asymmetric addition of diethylzinc to benzaldehyde (Scheme 2) and compared directly with (R)-BINOL using the methodology developed by Chan and co-workers.[8]
Summary
The fluorous biphase system has been applied successfully to a wide range of homogeneous catalyses with excellent catalyst recovery and reuse being reported.[1] 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. 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.[4] We have 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.[5] Here, we demonstrate the efficient separation and recycle of a perfluoroalkylated BINOL ligand using fluorous solid-phase extraction.[6]
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