Catenanes cyclophane-polyether

Chirality may be introduced into catenanes of the cyclophane-polyether type by replacement of the / -phenylene unit in the starting material LI089 with a chiral entity such as LI 139 [279] or LI 140 (Eq. 4.82) [280]. 

The discussion can be restricted to the first and second reduction processes that are of particular interest in this context. The shift of the bipyridinium-based process is in agreement with the catenane coconformation in which the bipyridinium unit is located inside the cavity of the macrocyclic polyether (Fig. 13.33a) because of the CT interactions established with both the electron donor units of the macrocycle, its reduction is more difficult than in the free tetracationic cyclophane. The shift of the trans-1,2-bis(4-pyridinium)ethylene-based reduction indicates that, once the bipyridinium unit is reduced, the CT interaction that stabilize the initial coconformation are destroyed and, thereby, the tetracationic cyclophane circumrotates through the cavity of the macrocyclic polyether moving the tra ,v-bis(pyridinium)ethylene unit inside, as shown by comparison of its reduction potential with that of a catenane model compound.19 The original equilibrium between the two coconformations associated with catenane 384+ is restored upon oxidation of both units back to their dicationic states. 

This [2]catenane is composed of a jt-electron-deficient tetracationic cyclophane interlocked with a Jt-electron-rich macrocyclic polyether. In addition to a mechanical bond, [jt Jt] stacking interactions between the complementary aromatic units, [C-H---0] hydrogen bonds between the a-bipyridinium hydrogen atoms and the poly-ether oxygen atoms, and [C-H---Jt] interactions between the 1,4-dioxybenzene hydrogen atoms and the p-phenylene spacers in the tetracationic cyclophane hold the two macrocyclic components together and control their relative movements in solution. As a result of the asymmetry of the tetracationic cyclophane, two transla-... 

The macrocyclization reaction described above has been used to generate a great number of catenane (12) and rotaxane (13) architectures (Scheme 10.4) using both crown ethers [preformed macrocyclic components 14 (strategy A)] and hydroqui-none-based dumbbell-shaped polyethers [preformed acyclic components 15 ( clipping )] as templates [14b, 15]. These templates are also relatively robust with regard to the substitution of different groups into both the tetracationic cyclophane and the neutral frameworks. 

Figure 3.25. Catenane synthesis from a polyether ring and a C-shaped cyclophane precursor...

In an extension of the previous studies involving 13, it has been demonstrated that a number of other [2]-catenanes can be synthesised using self-assembly procedures in which the donor macrocyclic polyethers incorporate both hydroquinone and 1,5-dioxynaphthalene units, while the acceptor tetracationic cyclophanes contain bipyridinium and/or its extended analogue, bis(pyridinium)ethylene. Although the trans carbon-carbon double bond in the bis(pyridinium)ethylene units are... 

The macrocyclic polyether, tris(l,5-naphtho)-57-crown-15 (Figure 5.12) contains a sufficiently large ring size to permit the simultaneous accommodation of two threaded 4,4 -bipyridinium units, which are then appropriately orientated for further template formation of tetracationic cyclophanes. However, the efficacy of template formation for [3]-catenane formation proved to be less than anticipated. The... 

The consequences of increasing the size of the polyether macrocycle to 68 members (that is, by a factor of two over the small ring system) was investigated. Accordingly, the synthesis of tetrakis-/ -phenylene-68-crown-20 was achieved in dimethylformamide at room temperature in excellent yield and this, in turn, was initially used to produce the [2]-catenane 22 (Figure 5.13). From the temperature dependence of the H NMR spectrum, 22 appears to behave like a molecular train - with the tetracationic cyclophane travelling from station to station around the... 

The [2]catenane 19" + incorporates (Figure 31) a macrocyclic polyether containing two dioxybenzene units, and a tetracationic cyclophane comprising a bipyr-idinium and a ram-bis(pyridinium)ethylene unit [36a, 62]. The H NMR spectrum [(CD3)2C0, 213 K] of 19" + shows the signals for two distinct co-conformations in a ratio of 92 8. In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic polyether and the ra 5-bis(pyridinium)ethylene unit is posi-... 

One of the appealing aspects of catenanes that are based upon the interactions between 7t-electron-rich crown ethers and 7t-electron-deficient tetracationic cyclophanes is the modularity that can be employed (Fig. 25) in their template-directed syntheses. Virtually any 7t-electron-rich crown ether with identical or different recognition sites can be introduced into this class of catenanes. Also, by exploiting the different ways in which cyclophanes can be clipped around the preformed ring of a macrocyclic polyether, it is possible to incorporate [46] different 7r-electron-deficient units into the cyclophanes. 

The proposed mechanism is outlined in Fig. 1.6 co-conformation [A ] corresponds to the switch open state and the metastable, co-conformation [B°] the switch closed state of the device. When the applied bias approaches +2 V, the [2]catenane 4" is oxidized to state [A ] wherein the TTF unit is positively charged and so experiences an electrostatic repulsion inside the tetracationic cyclophane, resulting in circumrotation of the macrocyclic polyether and formation of its co-conformational state [B ]. When the voltage is reduced to near-zero bias, the TTF cation radical is reduced, affording the metastable state [B°] which does not return spontaneously to its stable co-conformation [A ] by further circumrotation of the macrocyclic polyether via state [AB ] until the bipyridinium units in the tetracationic cyclophane are reduced. This electromechanical switching mechanism is consistent with temperature-dependent measurements, which indicate... 

Multi-ring catenanes may also be prepared by the cyclophane approach. The polyether LI 160 (Eq. 4.89), the trinaphtho-analogue of L1094, is a large ring and... 

It is obvious that we can only self-assemble [3]catenanes if we increase the size of both the neutral and tetracationic components. So far, the use of TPP68C20 and the large cyclophane [BBIPYBIBTCY]4+ has met with no success. We attribute this lack of catenation to the large dimensions of the two components, and, in the case of TPP68C20, to its flexibility. The macrocyclic polyether TPP51C15 Scheme 21),... 

Bisfunctionalized [2]catenanes have been also prepared by employing template-directed syntheses that involve the interaction of 7t-donors and Jt-acceptors. Reaction (Fig. 10) of the dibromide 31 with the dicationic salt 32 in the presence of either 33 or 34 as the macrocyclic polyether component afforded [105] the [2]catenanes 35 and 36, respectively, after counterion exchange. The aromatic hydroxymethyl group located within the tetracationic cyclophane portion of the [2]catenane 35 was converted [106] into a chloromethyl group by treatment of 35 with 10 M HClaq. After counterion exchange, the chloromethyl group was... 

---