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

The reaction of PMe 3 or PPh 3 with PF 5 in anhydrous CH 2 Cl 2 or hexane forms the white, moisture-sensitive complexes [PF 5 (PR 3 )] (R = Me, Ph). Similar reactions involving the diphosphines o -C 6 H 4 (PR 2 ) 2 afford the complexes [PF 4 { o -C 6 H 4 (PR 2 ) 2 }][PF 6 ]. The X-ray structures of [PF 5 (PR 3 )] and [PF 4 { o -C 6 H 4 (PMe 2 ) 2 }][PF 6 ] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra ( 1 H, 19 F{ 1 H}, 31 P{ 1 H}) show that in solution in CH 2 Cl 2 /CD 2 Cl 2 he structures determined crystallographically are the only species present for [PF 5 (PMe 3 )] and [PF 4 { o -C 6 H 4 (PMe 2 ) 2 }][PF 6 ] but that [PF 5 (PPh 3 )] and [PF 4 { o -C 6 H 4 (PPh 2 ) 2 }][PF 6 ] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex 19 F{ 1 H} and 31 P{ 1 H} NMR spectra have been analyzed, including those of the cation [PF 4 { o -C 6 H 4 (PMe 2 ) 2 }] + , which is a second-order AA'XX'B 2 M spin system. The unstable [PF 5 (AsMe 3 )], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh 3 nor SbE 3 forms similar complexes. The electronic structures of the PF 5 complexes have been explored by DFT calculations. The DFT optimized geometries for [PF 5 (PMe 3 )], [PF 5 (PPh 3 )], and [PF 4 { o -C 6 H 4 (PMe 2 ) 2 }] + are in good agreement with their respective crystal structure geometries. DFT calculations on the PF 5 -L complexes reveal the P-L bond strength falls with L in the order PMe 3 > PPh 3 > AsMe 3 , consistent with the experimentally observed stabilities, and in the PF 5 -L complexes, electron transfer from L to PF 5 on forming these complexes also follows the order PMe 3 > PPh 3 ≈ AsMe 3 .