Syntheses of cis- and trans-dibenzo-30-crown-10 derivatives via regioselective routes and their complexations with paraquat and diquat

cis-Dibenzo-30-crown-10 (cis-DB30CIO) 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 H-1 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 H-1 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 I - 4, the two hydroxymethyl groups of the crown ether I 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 x 10(4) M-1) to 1.4 (5.0 x 10(4) M-1).