Cation–anion association in iminium salts. Use of europium complexes as 1H n.m.r. auxiliary compounds
The cations of the iminium salts (1)–(3) show characteristic 1H n.m.r. shifts induced by Eu(fod)3; (+)-Eu(hfbc)3 generates unequal shifts for enantiotopic groups in the cations of (3) and (5).