Catenane spacers

Increasing the length of the alkyl spacer in such a way as to yield 1,4-bis(tetrazol-l-yl)butane (abbreviated as btzb) (Fig. 16), changes the dimensionality of the Fe(II) spin crossover material [89]. In fact, [Fe(btzb)3] (C104)2 is the first highly thermochromic Fe(II) spin crossover material with a supramolecular catenane structure consisting of three interlocked 3-D networks [89]. Unfortunately, only a tentative model of the 3-D structure of [Fe(btzb)3](Cl04)2 could be determined based on the x-ray data collected at 150 K (Fig. 20). 

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-... 

A representative selection of [2]catenanes synthesized by this route is given in Table 10.1[14b, 15a, 16]. It is remarkable to note that the first [2]catenane synthesized (entry 2, Table 10.1) could be isolated in 74% yield [14,16], The final entry in the table is an example of an expanded version of the tetracationic macrocycle which incorporates a biphenylene spacer between the paraquat residues and can accommodate two n-stacked aryl rings within its cavity. The reaction results in the isolation of the [3]catenane product in 25% yield with very little (2%) [2]catenane isolated [16p]. A spectacular demonstration of the power of this approach by Stoddart and coworkers was the iterative synthesis of a [5] catenane which the authors dubbed Olympiadane after its resemblance to the Olympic rings [17]. 

Derivative 178 containing a dibenzo-34-crown-10 ring interlocked with macrocycles incorporating two 4,4 -dipyr-idyl moieties tethered by different aryl spacers acts as bistable [2]catenane <20060L2119>. Variable-temperature (VT) NMR studies were used to determine the activation energy required for the conformational interconversions and to demonstrate that, by appropriate incorporation of bulky groups on one or both of the aryl linkers, it was possible to block one or both of the two circumrotation pathways. 

Treatment of Z>fr(butylaminomethyl)biphenyl, other spacers were also used, with CS2 and base generated the Z>fr(dithiocarbamate) ligand (dtc), which with Cu(OAc)2 generated the binuclear copper(ll) dtc macrocycle, then subsequent reaction with NaAuCU gave the novel heteropolymetallic Cu(ll)-Au(lll) catenane <05CC2214>. 

The systems studied by Schuster and Guldi are reported in Fig. 22 56 and 57" are analogous to rotaxanes 33 and 40 with two zinc(II) porphyrins as stoppers, a Cu(I)(dpp)2 as the spacer and a C6o as the electron acceptor are appended to the macrocycle or included in it. SS is a catenane derived from 56 upon axial binding by a bidentate ligand to the zinc ions of the porphyrin stoppers. Rotaxanes 59" and 60 differ from 56 and 57" in having two 50 electron acceptors as stoppers and a zinc porphyrin electron donor appended to the macrocycle and differ from each other in the distance between the electron donor and the copper complex, which has been increased by insertion of a phenylamido group. 

Scheme 17.3 Synthetic routes for linear main-chain poly[2]catenanes. Functional group A reacts with group B to produce Z linkages, while functional group X reacts with the spacer with two Y functional groups to produce V linkages.

Whereas Hunter did not obtain the catenane 16 directly from 14 and 17, but only after preparation of the intermediate 15, we independently succeeded in the same year in a one-step synthesis of a substituted representative of the same catenane type 16 (R = OCH3) starting from the simple components 17 and 18 [31], In connection with earlier syntheses of basket-shaped host molecules [32], we had applied the cyclohexylidene-substituted diamine 17 [33] instead of unsubstituted diphenylmethane, p-phenylene and naphthalene units in order to increase the solubility of macropolycyclic lactams of type 19. The OCH3-substituents introduced via 18 are intended to be cleaved to OH-groups after the cyclization process. This should be useful for further bridging and, in particular, for attaching the bottom of the basket (spacer in 20). 

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