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Syntheses of cis- and trans-Dibenzo-30-Crown-10 Derivatives via Regioselective Routes and Their Complexations with Paraquat and Diquat

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journal contribution
posted on 01.08.2008 by Chunlin He, Zuming Shi, Qizhong Zhou, Shijun Li, Ning Li, Feihe Huang
cis-Dibenzo-30-crown-10 (cis-DB30C10) diester and trans-dibenzo-30-crown-10 (trans-DB30C10) diester were synthesized regioselectively with reasonable yields. These two isomers were further reduced to cis-dibenzo-30-crown-10 diol (1) and trans-DB30C10 diol (2), respectively. The complexations of cis- and trans-DB30C10 diols with paraquat (3) and diquat (4) were investigated by 1H NMR, mass spectrometry, UV−vis spectroscopy, and single-crystal X-ray analysis. The reversible control of complexations of 1·3 and 2·3 by adding small molecules (KPF6 and dibenzo-18-crown-6) was demonstrated by 1H NMR. The addition of 2 molar equiv of KPF6 is enough to dissociate 2·3 and 1·3 completely while the subsequent addition of 2 molar equiv of DB18C6 allows the two complexes to reform. However, 2 molar equiv of KPF6 cannot dissociate 1·4 and 2·4 completely. Because the DB30C10 cavity has a better geometry fit with paraquat 3 than with diquat 4, 4-based complexes have much higher association constants than the corresponding 3-based complexes. In the crystal structure of 1·4, the two hydroxymethyl groups of the crown ether 1 were joined by a “water bridge” to form a “supramolecular cryptand” while this kind of supramolecular cryptand structure was not observed in the crystal structure of 2·4. This is a possible reason for the increase in association constant from 2·4 (3.3 × 104 M−1) to 1·4 (5.0 × 104 M−1).