Balzani V, Becher J, Credi A, Nielsen MB, Raymo FM, Stoddart JF, Talarico AM, Venturi M
Dipartimento di Chimica G. Ciamician, Universita di Bologna, Italy.
J Org Chem. 2000 Apr 7;65(7):1947-56. doi: 10.1021/jo991467z.
The tetracationic cyclophane, cyclobis(paraquat-4,4'-biphenylene), binds 1,1'-disubstituted ferrocene-based polyethers as a result of (i) [pi...pi] stacking between the pi-electron-deficient bipyridinium units and the pi-electron-rich cyclopentadienyl rings and (ii) [C-H...O] hydrogen bonds between the alpha-bipyridinium hydrogen atoms and the polyether oxygen atoms. However, even the presence of a bulky tetraarylmethane group--which is too large to thread through the cavity of the cyclophane host--at the end of each of the two polyether substituents of the ferrocene-containing guest does not discourage adduct formation of the inclusion type. Thus, in these adducts, the ferrocene unit of the guest is located inside the cavity of the host with its two polyether chains protruding outward from the same side of the host. The alternative pseudorotaxane geometry is not observed in solutions of these 1:1 adducts. The host-guest adducts display absorption bands in the visible spectral region, characteristic of charge-transfer interactions. In the case of one of these adducts, reversible decomplexation/recomplexation takes place upon electrochemical oxidation/reduction of the ferrocene-based unit or upon reduction/oxidation of the tetracationic cyclophane.
四价环番，即环双（百草枯 - 4,4'-联亚苯基），由于（i）缺π电子的联吡啶鎓单元与富π电子的环戊二烯基环之间的[π...π]堆积，以及（ii）α - 联吡啶鎓氢原子与聚醚氧原子之间的[C - H...O]氢键，能够与1,1'-二取代的二茂铁基聚醚结合。然而，即使在含二茂铁客体的两个聚醚取代基的末端存在庞大的四芳基甲烷基团（其太大而无法穿过环番主体的空腔），也不会阻碍包合型加合物的形成。因此，在这些加合物中，客体的二茂铁单元位于主体的空腔内，其两条聚醚链从主体的同一侧向外突出。在这些1:1加合物的溶液中未观察到交替的准轮烷几何结构。主体 - 客体加合物在可见光谱区域显示出吸收带，这是电荷转移相互作用的特征。对于其中一种加合物，在基于二茂铁的单元进行电化学氧化/还原或四价环番进行还原/氧化时，会发生可逆的解络合/再络合。
