Dumbbell-shaped compound

Figure 13.30 Cyclic voltammetric patterns (argon-purged MeCN/Et4NPF6 0.05 M, 298 K, glassy carbon electrode, scan rate 200 mV/s) for rotaxane 316+, its dumbbell-shaped component 326+, ring 2, and model compounds 332+, 344+, 352+, and 362+.

Figure 14 shows [2]rotaxane 13 + which contains two recognition sites in its dumbbell-shaped component. In this compound, the stable structure is that with the macrocyclic component surrounding the benzidine recognition site, but shuttling of the macrocycle between the two sites can be controlled electrochemically [43]. The... 

Several macrocyclic compounds have been prepared using Wittig reactions including tetraepoxyannulenes, which utilized the ylide derived from phos-phonium salt (57), and rotaxanes, molecules in which one or more macrocyclic components are trapped around a rod section of a dumbbell-shaped molecule, obtained by treating terephthaldehyde derivatives with dibenzylic bis(triphenyl-phosphonium)-stoppered [2]rotaxane (58). Aromatic triesters have been obtained by the (ethoxycarbonylmethylene)triphenylphosphorane-catalysedcyclo-trimerisation of ethyl propynoate. ... 

In order to achieve photoinduced shuttling, the carefully designed rotaxane shown in the top of Fig. 13 has been recently synthesized [7f]. This compound is made of the electron-donor macrocycle R and a dumbbell-shaped component which contains... 

The structure of the rotaxane was characterized by mass spectrometry and NMR spectroscopy, which also established, along with cyclic voltammetry, that the stable translational isomer is the one in which the R component encircles the Ai unit, in keeping with the fact that this station is a better electron acceptor than the other one. The electrochemical, photophysical, and photochemical (under continuous and pulsed excitation) properties of the [2] rotaxane, its dumbbell-shaped component, and some model compounds containing electro- and photoactive units (Fig. 13) were investigated. In an attempt to obtain the photoinduced abacus-like movement of the R macrocycle between the two stations A, and A2, two strategies were devised one was fully based on processes involving only the rotaxane components (intramolecular mechanism), while the other one required the help of external reactants (sacrificial mechanism). 

Fig. 12. Three mechanisms of rotaxane formation stoppering is the addition of bulky end groups to a suitably functionalized pseudorotaxane clipping is the formation of the macrocyclic component around a preformed dumbbell-shaped compound slipping is the thermodynamically controlled self-assembly of the macrocycle around the dumbbell-shaped component at elevated temperatures...

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