Structure and solution dynamics of [(Ph3P)2Pd(Ph) (FHF)]

The bifluoride complex trans-[(Ph3P)(2)Pd(Ph)(FHF)] (1) was studied by single-crystal X-ray diffraction, IR, and variable-temperature H-1, F-19, and P-31 NMR spectroscopy. Like other transition-metal bifluorides, 1 exhibits fluxional behavior (NMR) in solution at room temperature. When exchange processes are frozen (-60 degreesC), the solution structure of 1 is consistent with the solid-state X-ray data. Although all structural and spectroscopic data point to MF...HF rather than M...FHF character for 1, F-19 NMR magnetization transfer experiments demonstrated a minor contribution of HF dissociation to the exchange. The main process that governs F/F exchange in 1 is intramolecular (DeltaH(double dagger) = 33.7 +/- 2.1 kJ mol(-1); DeltaS(double dagger) = -56.1 +/- 9.6 J mol(-1) K-1), likely occurring via pentacoordinate [(Ph3P)(2)Pd(Ph)(eta (2)-FHF)], in which both fluorines are coordinated to Pd. DFT calculations for two model Pd bifluoride complexes [(R3P)(2)Pd(Me)(FHF)] (R = H, Me) indicated virtually unrestricted rotation around the Pd-FHF bond.