Two novel [2]rotaxanes, comprised of a dibenzo[24]crown-8 (DB24C8) macroring bound mechanically to a chemical “dumbbell” possessing two different recognition sitesviz., secondary dialkylammonium (NH2 +) and 4,4‘-bipyridinium (Bpym2+) unitshave been synthesized by using the supramolecular assistance to synthesis provided by, inter alia, hydrogen bonding interactions. One of these rotaxanes bears a fluorescent and redox-active anthracene (Anth) stopper unit. NMR spectroscopy and X-ray crystallography have demonstrated that the DB24C8 macroring exhibits complete selectivity for the NH2 + recognition sites, i.e., that the [2]rotaxanes exist as only one of two possible translational isomers. Deprotonation of the rotaxanes' NH2 + centers effects a quantitative displacement of the DB24C8 macroring to the Bpym2+ recognition site, an outcome that can be reversed by acid treatment. The switching processes have been investigated by 1H NMR spectroscopy and, for the Anth-bearing rotaxane, by electrochemical and photophysical measurements. Furthermore, it is possible to drive the DB24C8 macroring from the dumbbell's Bpym2+ unit, in the deprotonated form of the Anth-bearing rotaxane, by destroying the stabilizing DB24C8−Bpym2+ charge-transfer interactions via electrochemical reduction. The photochemical and photophysical properties of this rotaxane (in both its protonated and deprotonated states) have also been investigated.

A series of secondary dialkylammonium ions (RCH2)2NH2 + have been prepared, and their binding properties toward the macrocyclic polyether dibenzo[24]crown-8 (DB24C8) evaluated. By using this information, a route to a kinetically stable rotaxane-like entitystabilized by noncovalent bonding interactions between the DB24C8 macroring and the ammonium centerwas established, in which the crown ether slips over a dialkylammonium ion's stopper groups (R). However, we have found that the kinetic stability of this rotaxane-like entity is extremely dependent on the nature of the solvent in which it is dissolved, suggesting that pseudorotaxanes lie in the fuzzy domain between two sets of extremes, wherein a beadlike macrocycle and a dumbbell-like component may either (1) exist as a rotaxane or (2) be completely disassociated from one another.

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At a polymer concentration of 1 wt % in dimethylacetamide, fluoride-promoted cleavage of ether linkages in Radel-R (an industrially important aromatic poly(ether sulfone) derived from 4,4′biphenol) leads to ring-closing depolymerization. A high molar mass poly(ether sulfone) is thus converted in good yield to a family of macrocycles containing from eight up to at least sixty aromatic rings. Detailed analyses of the reaction products indicate a linear oligomer content of less than 4 wt %. Individual macrocycles containing eight, twelve, sixteen, and twenty aromatic rings have been isolated and characterized as pure, monodisperse oligomers (the first two by single-crystal X-ray analysis). The cyclic dimer and trimer both adopt open, flattened conformations with substantial free pathways through the ring centers, and the cyclic dimer packs to give a continuous-channel structure in the solid state. These macrocyclic oligomers undergo efficient ring-opening polymerization in the presence of phenoxide and especially thiophenoxide initiators to regenerate high-molar-mass polymer, demonstrating for the first time that the chemical recovery and recycling of high-performance aromatic polymers issin principles entirely feasible.

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The reduction of 2,P-dinitrostyrenes (mainly with alkoxy-or benzyloxy-groups in the 4-and 5-positions) with various reagents is described. Catalytic hydrogenation yields indoles. Hydrazine in the presence of Raney nickel affords the azine and hydrazone of either the nitro-or amino-benzaldehyde from which the nitrostyrene was derived. Lithium aluminium hydride gives a mixture of indoles and cinnolines. Sodium borohydride yields 2, P-dinitrophenylethanes.

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Our childhoods may be recalled when a self-complementary cation, endowed with both a dibenzo[24]crown-8 macroring and a secondary dialkylammonium sidearm, self-assembles to form a two-component supramolecular architecture that is reminiscent of a daisy chain (depicted schematically on the right). This daisy-chain-like superarchitecture is stabilized by a combination of [N -H⋅⋅⋅O] hydrogen bonds and aryl-aryl stacking interactions.