Tertiary Phosphine and Arsine Complexes of Phosphorus Pentafluoride: Synthesis, Properties, and Electronic Structures.

The reaction of PMe or PPh with PF in anhydrous CHCl or hexane forms the white, moisture-sensitive complexes [PF(PR)] (R = Me, Ph). Similar reactions involving the diphosphines -CH(PR) afford the complexes [PF{-CH(PR)}][PF]. The X-ray structures of [PF(PR)] and [PF{-CH(PMe)}][PF] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra (H, F{H}, P{H}) show that in solution in CHCl/CDCl the structures determined crystallographically are the only species present for [PF(PMe)] and [PF{-CH(PMe)}][PF] but that [PF(PPh)] and [PF{-CH(PPh)}][PF] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex F{H} and P{H} NMR spectra have been analyzed, including those of the cation [PF{-CH(PMe)}], which is a second-order AA'XX'BM spin system. The unstable [PF(AsMe)], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh nor SbEt forms similar complexes. The electronic structures of the PF complexes have been explored by DFT calculations. The DFT optimized geometries for [PF(PMe)], [PF(PPh)], and [PF{-CH(PMe)}] are in good agreement with their respective crystal structure geometries. DFT calculations on the PF-L complexes reveal the P-L bond strength falls with L in the order PMe > PPh > AsMe, consistent with the experimentally observed stabilities, and in the PF-L complexes, electron transfer from L to PF on forming these complexes also follows the order PMe > PPh ≈ AsMe.