Complexing properties of two benzocrown-ether moieties arranged at a cyclobutane ring system |
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Authors: | Seiichi Inokuma |
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Institution: | Department of Chemistry, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan |
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Abstract: | Biscrown ethers 2a-c and 3a-c arranged at a cyclobutane ring were prepared by intermolecular 2+2] photocycloaddition of vinylated benzocrown ethers. The complexing behavior of 2a-c toward alkali metal cations was evaluated by ESI-MS analysis, liquid-liquid extraction, and the comparison of complexing stability constant. An intramolecular sandwich-type 1:1 (host/guest) complexation was observed by ESI-MS analysis in the competitive system where 2a-Na+, 2b-K+, and 2c-Cs+ were formed selectively. In the liquid-liquid extraction, however, 2a hardly extracted any cation, while both 2b and 2c efficiently extracted larger cations such as K+, Rb+, and Cs+. It was found that the complexing stability constant of 2a-Na+ is lower than that of benzo-15-crown-5-Na+ though extraordinarily high values were obtained for 2b-K+ and 2c-Cs+ complexes compared with those of 18-crown-6-K+ and dibenzo-24-crown-8-Cs+ complexes, respectively. Hence, the excellent complexing ability was achieved by using the cyclobutane ring, which strongly preorganized two benzocrown-ether moieties for the larger alkali metal cations. |
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Keywords: | Bis(crown ether)s Photosynthesis Extraction experiment Complexing ability |
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