Rotaxanes threading* procedure

The ability of cyclodextrins to bind acyclic guests with pseudorotaxane geometries has been employed (Figure 30) by Harada et al. [46, 47] to self-assemble [2]rotaxanes after the threading procedure depicted schematically in Figure la. The diamine 92 is bound by the methylated a-cyclodextrins 93 and 94 with 1 1 stoichiometries in H20. Reaction of the terminal amine groups of the guest with... 

The diacid dichlorides used so far in rotaxane synthesis all have arene building blocks in common. Nevertheless, the initial amide bond formed between the dichloride and one stopper molecule (cf. 54) is thought to be responsible for successful molecular recognition of the semi-axle and the macromonocycle. Consequently olefinic and aliphatic diacid dichlorides 59a-g were subjected to the threading procedure to test the need for arene units (Figure 25). 

When the homologs of isophthaloyl dichloride 59 f and 59g are subjected to the threading procedure the situation is similar. 59 f leads to the corresponding rotaxane in 7% yield, whereas the homologous rotaxane 60g was only detectable by mass spectrometry [38]. 

For the preparation of rotaxanes, three different routes can be followed (Scheme 6.2A). In the threading procedure, the macrocycle will first encircle the thread to form a so-called pseudorotaxane. By end-capping the thread with bulky groups that prevent de-threading, a [2]rotaxane is formed. The clipping method that is used for the preparation of catenanes can also be applied for the synthesis of rotaxanes hence the macrocycle is assembled in the presence of the end-capped... 

The most obvious way to prepare a rotaxane from a pseudorotaxane is to attach a bulky substituent group to the open end of the threaded molecule. The overall procedure is termed threading (Figure 10.56). For example, reaction of the [2] pseudorotaxanes formed from di-ols 10.68 and 10.69 and bis(bipyridinium) receptor 6.81 with tri-/so-propylsilyl trifluoromethanesulfonate (triflate) in the presence of lutidine gives the corresponding tri-/so-propylsilylated [2]rotaxanes (10.71) in about... 

Preparation of the first rotaxanes was also accomplished by means of statistical threading of a chain through a cycle with following attaching of bulky substituents to the loose ends of the threaded chain [5], Statistical means of molecular threading were pushed out by much more efficient covalent templation procedures developed by Schill etal. [6,7],... 

In these cases 14 and 22 act as beads, threaded on stoppered polyether chains containing the Tr-electron-rich or 7r-electron-deficient stations. This noncovalent interaction simplifies the synthetic procedures necessary, as the unstoppered thread and its bead will self-assemble, and the resulting charge transfer complex can be stoppered with bulky terminal groups to give the functional rotaxane. Other sue-... 

The general procedure of delivering additives in the form of their CD-rotaxanes appears to offer improved solutions to a wide-range of polymer-additive and textilefinishing problems, because of two factors. First, CD-rotaxanation of an additive permits control of its solubility and offers protection (UV and chemical) to the threaded additive. Second, chemical modification of the hydroxyl groups on the... 

The precursors and the reaction steps leading to the Cu(l)-complexed [2]-rotaxane (142) are represented in Figures 48 and 49. Threading of macrocycle (89) onto the dialdehyde derivative of dpp (139) afforded prerotaxane (140) quantitatively. The two porph5nin stoppers, identical in this case, were therefore constructed in a one-pot procedure, by reacting prerotaxane (140) (1 equiv.) with dipyrrylmethane (141) (10 equiv.) and 3,5-di-tert-butylbenzaldehyde (132) (8 equiv.) in dichloromethane... 

The synthesis of the target rotaxane 24+ was achieved in 20% yield by the procedure shown in Scheme 3 [7], The JH-NMR spectrum at room temperature of 24+ (400 MHz, CD3CN) was severely broadened by the fast sliding motion of the bead along the thread. At -40 °C bead sliding was sufficiently slow to allow the observation of the two interconverting translational conformers shown in Scheme 4. In agreement with our previously obtained... 

Display 14 shows a [2]rotaxane being made to order by a clipping procedure. Note that the yield of 32% is much higher than that recorded earlier in Display 5. The reason for the increased efficiency of the self-assembly process is undoubtedly the presence of two hydroquinol rings in the thread component of the [2]rotaxane. See reference [12]. 

The CuAAC click reaction has been widely used for the preparation of interlocked molecules, such as catenanes and rotaxanes [88]. In the case of rotaxanes, the CuAAC reaction has been used mainly for the synthesis of the axle subsequent threading, clipping, or slipping procedures were utilized to produce the mechanically interlocked product. 

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