Iminium salts hydrolyse to give the corresponding ketone or aldehyde:
Iminium cations are reduced to the amines, e.g. by sodium cyanoborohydride.  Iminium cations are intermediates in the reductive amination of ketones and aldehydes.
Unsymmetrical iminium cations undergo cis-trans isomerization.  The isomerization is catalyzed by nucleophiles, which add to the unsaturated carbon, breaking the C=N double bond.