Advanced buckyball joints: synthesis, complex formation and computational simulations of centrohexaindane-extended tribenzotriquinacene receptors for C60 fullerene

Abstract

The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and π-π interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host.

Tribenzotriquinacene Receptors for C60 Fullerene Rotors: Towards C3 Symmetrical Chiral Stators for Unidirectionally Operating Nanoratchets

“…Unfortunately, 7 is not soluble in the typical solvents for these kinds of investigations (benzene or toluene), so we used a solvent mixture of CHCl 3 and CS 2 , which we used in previous studies; [12][13][14] this allowed us to compare the results from these studies with the corresponding values from our previous investigations on similar [C 60 &tribenzotriquinacene] complexes.…”

“…The oxidative decarboxylation with lead(IV) acetate and copper(II) acetate in a mixture of dry pyridine and dry toluene [16] to olefin 3 (1.50 g of 2 react to 343 mg of 3) is the limiting factor of the synthetic route, because any attempts to scale up this reaction step led to dramatic losses in yield. The spectra of diketone 5 indicate its C 2 symmetry ( 1 H NMR: 5 signals, Figure 1; 13 C NMR: 10 signals, see the Supporting Information). The oxidation of the diols to the diketone is also proven by the carbonyl signal at d = 184.1 ppm and the carbonyl band (1738 cm À1 ) in the infrared spectrum.…”

“…This was also observed in similar tribenzotriquinacene-based host systems. [12][13][14] A more detailed assignment of the NMR signals is given in the Supporting Information. The molecular mass of receptor 7 (M r = 1358.2 u) was confirmed by MALDI and ESI mass spectrometry.…”

“…For a suitable system the fullerene receptor should form a 1:1 complex of the composition [C 60 &receptor] displaying a sufficiently large complex stability constant under the chosen experimental conditions. [12][13][14] Extending these studies, we here focus our investigations on the design and directed (i.e., stereoselective) synthesis of C 3 -symmetrical (chiral) tribenzotriquinacene stators, which are crucial yet unexplored components of a nanoratchet system featuring unidirectional rotation. We also present the first results on the self-assembly of chiral stator (7) with fullerene-type rotors, in conjunction with molecular dynamics (MD) simulations, demonstrating the asymmetry of the rotational energy profile for a rotor like R. [10] Results and Discussion Synthesis of the chiral receptor (7) We herein report the synthesis of the first chiral and enantiopure tribenzotriquinacene receptor 7 for C 60 fullerene possessing C 3 point group symmetry (Scheme 1).…”

“…Following previous work, [13,14] we investigated the host-guest interaction of the chiral receptor 7 with the dipolar rotor R by means of force-field-based molecular simulations. The first principles derived force field (MOF-FF) [30] has been parameterized for receptor 8 a, 10 and 11, [14] and was easily extended to also describe 7.…”