Perfluoroalkylated bipyridine

A similar reaction has been conducted under fluorous biphasic conditions, using a perfluoroalkylated bipyridine as ligand to ensure that the copper species resides in the fluorous phase [22], The oxidation of a range of primary alcohols to the corresponding aldehydes was found to be possible, an example of which is shown in Scheme 9.11. The catalyst could be successfully recycled by phase separation, with analytically pure products being isolated even after... 

Recently, Betzemeier et al. showed that the scope of the copper-catalyzed oxidation reaction could be improved by using Cu Br Me2S instead of Cu Cl 97). The coordination of a perfluoroalkylated bipyridine to the metal centre produced a catalyst which could be used under biphasic fluorous conditions. Typically, 40)imol of perfluoroalkylated bipyridine was dissolved in 2mL of perfluorooctane. Next, 40 pmol of Cu Br Me2S was added, followed by a solution of 2 mmol alcohol and 64 imol TEMPO in 2mL chlorobenzene. The resulting biphasic reaction mixture was heated to 90°C under dioxygen (Fig. 27). 

The use of Cu in combination with TEMPO also affords an attractive catalyst [200, 201]. The original system however operates in DMF as solvent and is only active for activated alcohols. Knochel et al. [202] showed that CuBr.Me2S with perfluoroalkyl substituted bipyridine as the ligand and TEMPO as cocatalyst was capable of oxidizing a large variety of primary and secondary alcohols in a fluorous biphasic system of chlorobenzene and perfluorooctane (see Fig. 4.69). In the second example Ansari and Gree [203] showed that the combination of CuCl and TEMPO can be used as a catalyst in l-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid, as the solvent. However in this case turnover frequencies were still rather low even for benzylic alcohol (around 1.3 h 1). 

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