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

Abstract

Six highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) [Rh 2(OOCR F) 4, R F=C 7F 15, CH 2C 6F 13, CH 2CH 2C 6F 13, CH 2CH 2C 8F 17, CH 2CH 2C 10F 21, and CH 2OCH 2CH 2C 10F 21] 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 Rh 2(OOCC 7F 15) 4 and Rh 2(OOCCH 2C 6F 13) 4 are interesting, since they are soluble in perfluoro(methylcyclohexane) and catalyze the CH insertion reaction more effectively than all other catalysts, including Rh 2(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.