New highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) as catalysts for carbenoid CH insertion reactions

Six highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) [Rh2(OOCRF)4, RF=C7F15, CH2C6F13, CH2CH2C6F13, CH2CH2C8F17, CH2CH2C10F21, and CH2OCH2CH2C10F21] were prepared and characterized. Their suitability as catalysts for intermolecular carbenoid CH insertion was investigated for the reaction of methyl diazoacetate with hexane. In the frame of fluorous synthesis, only Rh2(OOCC7F15)4 and Rh2(OOCCH2C6F13)4 are interesting, since they are soluble in perfluoro(methylcyclohexane) and catalyze the CH insertion reaction more effectively than all other catalysts, including Rh2(OAc)4. The same two catalysts were also used to achieve 1,5-cyclization of an α-diazo-β-keto ester by intramolecular CH insertion. Unfortunately, deterioration of the catalysts occurs to a significant extent during all reactions, and therefore, the possibilities to recover and reuse them are rather limited.