Three preorganized metallomacrocycles (9a-c) have been prepared with an immobilized uranyl cation (UO22 +) as an electrophilic center. The macrocyclization in MeOH was accomplished starting from the dialdehyde 7 and the diamines 11a-c using Ba2 + as template ion. Subsequently the Ba2 + complexes 8a-c were reacted with 1 equiv of UO2(OAc)2 to give the uranyl complexes 9a-c in 70 -80 % yield. The association constants of the complexes 9a-c with ammonia, benzylamine, and n-propylamine, determined by 1H NMR spectroscopy in CDCl3, range from 20 to 990 1· mol-1. The highest selectivity for ammonia was observed for 9b (Kass(NH3):Kass (BnNH2) = 33). Molecular mechanics calculations., performed using Quanta/CHARMm, predict that the substitution of the complexed water molecule in the uranyl complex 9a by ammonia is thermodynamically the most favorable.