“Cinderella” elements: Strategies to increase the stability of group 1 complexes by tailoring crown macrocycles

•Receptors L1–L7 form stable complexes with Na+.•Coordination of the pendant arms contributes to the overall stability of the complexes.•Benzimidazole pendants led to more stable complexes, even more than cryptands.•Aniline pendants led to stabilities close to those of the parent crown-ether complexes.

The synthesis and structural characterization of six sodium complexes with bibracchial lariat ethers containing aniline or benzimidazole side arms, and derived from 1,7-diaza-12-crown-4, 1,10-diaza-15-crown-5 or 4,13-diaza-18-crown-6, are reported. The X-ray structures of four of these compounds have been obtained. Additionally, the X-ray structures of a sodium macrobicyclic complex derived from 1,10-diaza-15-crown-5, and a potassium complex with a bibracchial lariat ether containing aniline side arms are also reported. Bonding distances as well as the stability constants in acetonitrile solution confirm that the coordination of the pendant arms provides an important contribution to the overall stability of the complexes, particularly when benzimidazole pendants are present rending more stable complexes, even more than cryptand complexes of the same size. Compared with the parent crown ethers, the stability increases when the side arms contain benzimidazole moieties but remains about the same order when aniline side arms are present.

Graphical abstractThe synthesis of group 1 metal ion complexes with bibracchial lariat ethers containing aniline or benzimidazole side arms, are reported together with a sodium macrobicyclic complex. The coordination of the pendant arms provides an important contribution to the overall stability of the complexes, particularly when benzimidazole pendants are present.Figure optionsDownload full-size imageDownload as PowerPoint slide