Introducing the Perfluorinated Cp* Ligand into Coordination Chemistry

Abstract

The reaction of AgBF₄ and [Rh(COD)Cl]₂ (COD=1,5-cyclooctadiene) in presence of [NEt₄ ][C₅ (CF₃ )₅ ] afforded the fluorocarbon soluble complex [Rh(COD)(C₅ (CF₃ )₅ )] by salt metathesis. This complex represents the first example for a successful coordination of the weakly basic [C₅ (CF₃ )₅ ]^- ligand, since its first synthesis in 1980. In addition to [Rh(COD)(C₅ (CF₃ )₅ )] also the byproduct [Rh(COD)(C₅ (CF₃ )₄ H)] was isolated and fully characterized. Accompanying DFT studies showed that the interaction energy of the [C₅ (CF₃ )₅ ]^- ligand towards the 12-electron fragment [Rh(COD)]⁺ is ≈70 kcal mol^-1 lower in comparison to [C₅ (CH₃ )₅ ]^- due to reduced electrostatic interactions and weaker π-donor properties of the ligand. The quantitative but reversible substitution of the [C₅ (CF₃ )₅ ]^- ligand by toluene, converting it into a weakly coordinating anion, experimentally proved the extraordinary weak bonding interaction.