Synthesis and complexation of new molecular clips based on benzoaza-15-crown-5 and diphenylglycoluril with alkali and alkaline earth metal cations

New molecular clips, containing benzoaza-15-crown-5 moieties and diphenylglycoluril core have been synthetized. For the synthesis a previously developed method based on heating 2.1 equivalents of crown ether with one equivalent of diphenylglycoluryl bis-ether in polyphosphoric acid was used. In the case of using benzoaza-15-crown-5 derivatives, complete conversion of the reagents was observed at a higher temperature and required a longer reaction time (yields - 27-42%). Complexing properties towards to alkali and alkaline earth metal cations were evaluated through spectrophotometric titration. The clip with N-methyl groups is similar to the previously studied clip with benzo-15-crown-5 fragments, which suggests the formation of intramolecular sandwich complexes in the case of potassium and rubidium ions. However the observed stability constants are much lower - up to 3 orders of logarithmic units for potassium and rubidium. The molecular clip with unsubstituted nitrogen atoms interacts with alkali metal cations very weakly. Much stronger interactions with alkaline earth metal cations are observed. With large strontium and barium cations, very stable complexes of composition 2:1 (L:M) are formed (logK₂₁>7 for Ba²⁺). A clip with an ester group on nitrogen atoms forms the most stable complexes with the sodium ion among alkaline cations. The stability constant values ​​of this complex are an order of magnitude higher than for the other two clips, which may indicate the participation of oxygen atoms of the ester group in complex formation. In the series of alkaline earth cations, the stability of the complexes increases with increasing cation size.