Variable-Temperature NMR Determination of the Barriers to Rotation about the Ir−C σ-Bond in a Series of Primary Perfluoroalkyl Iridium Complexes [IrCp*{(CF2)nCF3}(PMe3)2]+X- [n = 1, 2, 3, 5, 7, 9, 11; X = I, OTf]

A series of primary perfluoroalkyl iridium complexes [IrCp*{(CF2)nCF3}(PMe3)2]+X- [n = 1, 2, 3, 5, 7, 9, 11; X = I, OTf] has been prepared. X-ray crystallographic studies of a representative example, [IrCp*{(CF2)9CF3}(PMe3)2]+I-, shows the ground state structure of the cation in the solid to be of C1 symmetry, with the perfluoroalkyl ligand adopting a conformation in which the fluorines on each CF2 group reside in different chemical environments. In solution the 19F NMR spectra of all these compounds indicate that the α-CF2 fluorines are diastereotopic at low temperatures, consistent with the solid state structure. On warming, these resonances coalesce, indicating a rotation or windshield-wiper motion of the perfluoroalkyl ligand that samples a conformation of Cs symmetry; Eyring plots of the rate constant/temperature data provide values of ΔH⧧ of ∼33 ± 2 kJ/mol for each system; the values are independent of the counterion. While there is clearly a difference between ΔS⧧ values for the perfluoroethyl comp...