m-Diethynylbenzene Macrocycles:  Syntheses and Self-Association Behavior in Solution

Abstract

m-Diethynylbenzene macrocycles (DBMs), buta-1,3-diyne-bridged [4(n)]metacyclophanes, have been synthesized and their self-association behaviors in solution were investigated. Cyclic tetramers, hexamers, and octamers of DBMs having exo-annular octyl, hexadecyl, and 3,6,9-trioxadecyl ester groups were prepared by intermolecular oxidative coupling of dimer units or intramolecular cyclization of the corresponding open-chain oligomers. The aggregation properties were investigated by two methods, the (1)H NMR spectra and the vapor pressure osmometry (VPO). Although some discrepancies were observed between the association constants obtained from the two methods, the qualitative view was consistent with each other. The analysis of self-aggregation by VPO revealed unique aggregation behavior of DBMs in acetone and toluene, which was not elucidated by the NMR method. Namely, the association constants for infinite association are several times larger than the dimerization constant, suggesting that the aggregation is enhanced by the formation of dimers (a nucleation mechanism). In polar solvents, DBMs aggregate more strongly than in chloroform due to the solvophobic interactions between the macrocyclic framework and the solvents. Moreover, DBMs self-associate in aromatic solvents such as toluene and o-xylene more readily than in chloroform. In particular, the hexameric DBM having a large macrocyclic cavity exhibits extremely large association constants in aromatic solvents. By comparing the aggregation properties of DBMs with the corresponding acyclic oligomers, the effect of the macrocyclic structure on the aggregation propensity was clarified. Finally, it turned out that DBMs tend to aggregate more readily than the corresponding phenylacetylene macrocycles, acetylene-bridged [2(n)]metacyclophanes, owing to the withdrawal of the electron density from the aromatic rings by the butadiyne linkages which facilitates pi-pi stacking interactions.

Synthesis of acetylene-functionalized [2]rotaxane monomers directed toward side chain-type polyrotaxanes

“…32 3-Bromo-5-(triisopropylsilylethynyl)benzoic acid 3 was prepared from 3-bromo-5-iodobenzoic acid by means of Sonogashira coupling, according to literature. 33 Pseudorotaxane 2 was prepared in situ from DB24C8 and hydroxy-terminated sec-ammonium salt 1 in chloroform. To a solution of 2 were added 3, N,N¢-dicyclohexylcarbodiimide and a catalytic amount of tributylphosphane, 30,34 and the mixture was stirred for 1 h at room temperature.…”

Structural Diversity in the Self‐Assembly of Pseudopeptidic Macrocycles

“…[14] Within all the concentration range studied herein, we observed a single set of signals, thus implying a fast exchange regime on the NMR timescale (Figure 4 a) for the self-assembly process as well. The nonlinear fitting of the chemical shift of the NH proton signal to an isodesmic self-aggregation model [15] (see Figure S8 in the Supporting Information) rendered an association constant of K = 35.7 AE 9.8 m À1 . [16] The self-diffusion rate of m-1 a was also measured by DOSY experiments at different overall concentrations.…”

Synthesis of thiophenophanes with ethyne and ethene spacers

“…3,4 The advantage of using acetylene linkage is the linearity of the ethynic bond, which turns the molecule more rigid and creates non-collapsible cavity. 5,6 Further the molecules will possess molecular co-planarity due to the presence of sp hybridised carbon atoms. The cavity size of a macrocycle can be altered by increasing or decreasing the number of acetylene linkages in the molecule.…”