Synthesis and supramolecular structures of molecular clips.
The syntheses of the novel dimethylene-bridged clips I (n = 0, R = H, OAc, OH, OMe, OSO2CF3; n = 1, R = OAc) are reported. They selectively bind electron-deficient neutral and cationic arom. substrates comparable to tetramethylene-bridged tweezers. The geometry of the noncovalently bound complexes with I (n = 0; R = OAc, OH, OMe) as receptors, derived from single-crystal structure analyses, is, however, different from that of the tweezer complexes. In clip complexes the plane of the included arom. substrate mol. is oriented almost parallel to the naphthalene side-walls of the clip, whereas in the tweezer complex the substrate is oriented parallel to the central arene spacer-unit. 1,2,4,5-Benzenetetracarbonitrile (II) as substrate is placed inside the cavity of the hydroquinone clip (I; n = 0, R = OH) in soln. as well as in the cocrystal. In contrast, it was found for the cocrystal with the diacetate clip (I; n = 0, R = OAc) that II is placed between the naphthalene side-wall of two different clip mols. whereas in soln. II is included into the cavity of I (n = 0, R = OAc). Finally, II forms a 1:2 complex with dinaphthonorbornadiene in soln. as well as in the cryst. state. The findings reported here are instructive for the understanding of the weak noncovalent binding forces particularly the arene-arene interaction.
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