PGSE diffusion measurements and overhauser NMR studies on the salts [Rh(1,5-COD){(S,S)-4,4′-dibenzyl-2,2′-bis(2-oxazoline)}](anion) and [Rh(1,5-COD){(S,S)-2,2′-isopropylidene-bis(4-tert-butyl-2-oxazoline)}](anion)

PGSE NMR diffusion measurements and Overhauser studies on the salts [Rh(1,5-COD){(S,S)-4,4'-dibenzyl-2,2'-bis(2-oxazoline)}](X), 1, and [Rh(1,5-COD){(S,S)-2,2'-isopropylidene-bis(4-tert-butyl-2-oxazoline)}](X), 2, X = (a) CF3SO3, (b) PF6, (c) BArF, (d) BF4, are reported. In THF solution, there is Substantial ion pairing for the CF3SO3, PF6, and BF4, salts; however, for the two BArF salts, 1c and 2c, the ion pairing is minimal. Strong differences in ion pairing are observed between the two series of complexes for the same anion. This represents the first example of a dependence of the degree of ion pairing on the chiral auxiliary. The H-1 spectra for the BArF salts reveal a different H-1 spin-spin Coupling pattern for the three oxazoline protons, suggesting a slight change in the conformation of the chelate ring due to the larger anion. On the basis of the intensity of the H-1,F-19 HOESY contacts, it would appear that the anions in the tert-butyl series, 2, come closer to the cation than in the benzyl-substituted series, 1.