(i) Friedel-Craft reaction:
But aniline undergoes salt formation with AlCl3 (Lewis acid used as catalyst). So N acquires positive charge and hence acts as strong deactivating group for further reaction.
(ii) In aromatic diazonium salts, due to resonance their is dispersal of positive charge on benzene ring.
But in aliphatic diazonium salts, resonance is not possible, so aliphatic diazonium salts are less stable than aromatic diazonium salts.