1H and 19F PGSE diffusion studies on iridium PHOX complexes: counterion and solvent dependences.

1H and (19)F pulsed gradient spin-echo (PGSE) diffusion studies on cationic mono- and trinuclear iridium complexes containing the PHOX chiral P,N-auxiliary (S)-4-tert-butyl-2-[2-(di-o-tolylphosphino)phenyl]-4,5-dihydrooxazole with the anions BF(4)(-), PF(6)(-), OTf(-), B(C(6)F(5))(4)(-), and BArF(-) in methanol, chloroform, methylene chloride, and 1,2-dichloroethane are reported. In chloroform, the anion and cation within each salt afford almost the same, relatively small, diffusion constant (D-value) suggesting strong ion-pairing. In methanol, the D-value for the cation is the same in the five mononuclear salts, suggesting that the cation is moving independently of the anion (no ion-pairing). In methylene chloride and 1,2-dichloroethane the diffusion data suggest a mixed picture for the five anions. While the smaller BF(4)(-), PF(6)(-), and OTf(-) anions do not affect the translation of the cations, the larger boron-based anions B(C(6)F(5))(4)(-) and BArF(-) clearly slow the motions of the cations. However, it would seem that for all five anions there is some--but not complete--ion pairing in these two solvents.