The CF3 Group as a Synthon of the CF+ Unit in Palladium Chemistry

The homoleptic trifluoromethyl‐palladium(II) complex [Pd(CF3)4]2− (1) is shown to be highly active towards amines. Thus, when treated with primary amines RNH2, it readily undergoes aminolysis of one of the CF3 ligands affording the isocyanide complexes [(CF3)3Pd(CNR)]− (R=aryl). In this process the original CF3 group undergoes total defluorination. Interestingly, the reaction of 1 with secondary amines R2NH proceeds with loss of just two F‐substituents, whereby the Fischer‐type fluoroaminocarbene complexes [(CF3)3Pd(CFNR2)]− are formed (R=Et, Ph). The reaction of 1 with diamines affords different [(CF3)3Pd(NHC)]− complexes containing sterically non‐demanding NHC ligands. Representative examples of various topologies are reported based on the common imidazolidin‐2‐ylidene or benzimidazolin‐2‐ylidene rings as well as the expanded‐ring perimidin‐2‐ylidene. This metal‐tailored synthetic route, where a CF3 group acts as a pre‐carbenic unit, is unprecedented in the vast NHC‐chemistry. It takes place under very mild conditions and is envisaged to be extensible to other non‐isolable NHC ligands. The key difluorocarbene intermediate [(CF3)3Pd(CF2)]− is experimentally detected. Pulling fluorine off: The unusually high activity of the C−F bond found in the homoleptic trifluoromethyl‐palladium(II) complex [Pd(CF3)4]2− is correlated to the very low fluoride‐ion affinity of the conjugate difluorocarbene complex [(CF3)3Pd(CF2)]−, which is experimentally detected. Selective single, double or triple defluorination of a CF3 group is achieved under very mild conditions.