Title
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Tribenzotriquinacene receptors for fullerene rotors : towards symmetrical chiral stators for unidirectionally operating nanoratchets
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Author
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Abstract
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The synthesis of a stereochemically pure concave tribenzotriquinacene receptor (7) for C-60 fullerene, possessing C-3 point group symmetry, by threefold condensation of C-2-symmetric 1,2-diketone synthons (5) and a hexaaminotribenzotriquinacene core (6) is described. The chiral diketone was synthesized in a five-step reaction sequence starting from C-2h-symmetric 2,6-di-tert-butylanthracene. The highly diastereo-discriminating Diels-Alder reaction of 2,6-di-tertbutylanthracene with fumaric acid di(-)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by H-1 and C-13 NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7% ee, based on the ee (99.9%) of the chiral synthon (1). The absolute configuration of 7 could thus be established as all-S [(2S,7S,16S,21S,30S,35S)-(7)]. Spectroscopic titration experiments reveal that the host forms 1: 1 complexes with either pure fullerene (C-60) or fullerene derivatives, such as rotor 1'-(4-nitrophenyl)-3'-(4-N,N-dimethylaminophenyl)-pyrazolino[4',5':1,2][60]fullerene (R). The complex stability constants of the complexes dissolved in CHCl3/CS2 (1:1 vol.%) are K([C-60 subset of 7])= 319(+/- 156) M-1 and K([R subset of 7])= 110(+/- 50) M-1. With molecular dynamics simulations using a first-principles parameterized force field the asymmetry of the rotational potential for [R subset of 7] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet. |
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Language
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English
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Source (journal)
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Chemistry: a European journal. - Weinheim
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Publication
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Weinheim
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2014
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ISSN
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0947-6539
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DOI
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10.1002/CHEM.201304980
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Volume/pages
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20
:29
(2014)
, p. 9100-9110
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ISI
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000339386700041
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Full text (Publisher's DOI)
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Full text (publisher's version - intranet only)
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