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

<i>cis</i>-Dibenzo-30-crown-10 (<i>cis</i>-DB30C10) diester and <i>trans</i>-dibenzo-30-crown-10 (<i>trans</i>-DB30C10) diester were synthesized regioselectively with reasonable yields. These two isomers were further reduced to <i>cis</i>-dibenzo-30-crown-10 diol (<b>1</b>) and <i>trans</i>-DB30C10 diol (<b>2</b>), respectively. The complexations of <i>cis</i>- and <i>trans</i>-DB30C10 diols with paraquat (<b>3</b>) and diquat (<b>4</b>) were investigated by <sup>1</sup>H NMR, mass spectrometry, UV−vis spectroscopy, and single-crystal X-ray analysis. The reversible control of complexations of <b>1</b>·<b>3</b> and <b>2</b>·<b>3</b> by adding small molecules (KPF<sub>6</sub> and dibenzo-18-crown-6) was demonstrated by <sup>1</sup>H NMR. The addition of 2 molar equiv of KPF<sub>6</sub> is enough to dissociate <b>2</b>·<b>3</b> and <b>1</b>·<b>3</b> completely while the subsequent addition of 2 molar equiv of DB18C6 allows the two complexes to reform. However, 2 molar equiv of KPF<sub>6</sub> cannot dissociate <b>1</b>·<b>4</b> and <b>2</b>·<b>4</b> completely. Because the DB30C10 cavity has a better geometry fit with paraquat <b>3</b> than with diquat <b>4</b>, <b>4</b>-based complexes have much higher association constants than the corresponding <b>3</b>-based complexes. In the crystal structure of <b>1</b>·<b>4</b>, the two hydroxymethyl groups of the crown ether <b>1</b> 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 <b>2</b>·<b>4</b>. This is a possible reason for the increase in association constant from <b>2</b>·<b>4</b> (3.3 × 10<sup>4</sup> M<sup>−1</sup>) to <b>1</b>·<b>4</b> (5.0 × 10<sup>4</sup> M<sup>−1</sup>).