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Journal ArticleDOI

Regioselective one-step synthesis of trans-3,trans-3,trans-3 and e,e,e [60]fullerene tris-adducts directed by a C3-symmetrical cyclotriveratrylene tether

01 Jan 1999-Chemical Communications (The Royal Society of Chemistry)-Iss: 12, pp 1121-1122
TL;DR: The first covalent cyclotriveratrylene (C60) adducts were prepared by the tether-directed Bingel reaction, which gave the two C3-symmetrical trans-3,trans-3 and e,e,e tris-adducts with a high degree of regioselectivity as discussed by the authors.
About: This article is published in Chemical Communications.The article was published on 1999-01-01. It has received 39 citations till now. The article focuses on the topics: Cyclotriveratrylene & Bingel reaction.
Citations
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Journal ArticleDOI
TL;DR: Hemmicryptophanes are revealed to be inherently chiral ditopic host compounds, able to encapsulate various guests, including charged and neutral species, and enter the field of stimuli-responsive supramolecular systems exhibiting controlled functions.
Abstract: In the wide area of host–guest chemistry, hemicryptophanes, combining a cyclotribenzylene (or cyclotriveratrylene CTV) unit with another different C3-symmetrical moiety, appears as a recent family of molecular cages. The synthesis and recognition properties of the first hemicryptophane were reported in 1982 by Collet and Lehn, but the very little attention received by this class of host compounds in the 20 years following this first promising result can account for their apparent novelty. Indeed, in the last 10 years hemicryptophanes have aroused growing interest, and new aspects have been developed. Thanks to the rigid shaping unit of the north part (CTV) and also the variable and easily functionalized south moiety, hemicryptophanes are revealed to be inherently chiral ditopic host compounds, able to encapsulate various guests, including charged and neutral species. They also enter the field of stimuli-responsive supramolecular systems exhibiting controlled functions. Moreover, endohedral functionalizati...

145 citations

Journal ArticleDOI
TL;DR: A model system in which a D–A pair is forced to strongly interact through their p surfaces in a very rigid and closely spaced structure is reported, demonstrating how small alterations in the distance between the two p surfaces, and therefore in the degree of orbital overlap and electronic coupling, influence the groundand excited-state interactions.
Abstract: The operation of many emerging organic/plastic optoelectronic technologies, such as solar-energy conversion devices, relies ultimately on the groundand excited-state electronic interactions between donor (D) and acceptor (A) components. The need to understand and control the primary photophysical events occurring within the active layers, as nature illustrates in the photosynthetic reaction center, has prompted chemists to design and study molecular D–A models. In these, the yields and kinetics of energy and/or electron transfer are related to the nature of the D and A components and their relative distance, orientation, or electronic coupling. Importantly, the knowledge gathered so far has led to discrete molecular systems with improved charge-separation performance in solution. However, most of these D–A models fail to reproduce a major characteristic of solid-state devices: molecules are usually confined by intimate van der Waals contacts, and conformational or orientational motion is restricted. Natural photosynthetic systems already demonstrate the importance of orbital overlap between embedded chromophores. In the so-called special pair, for instance, strong electronic coupling between two chlorophyll molecules held in close p–p contact causes a red shift in the absorption that acts as a sink for all the energy collected. 9] Herein we report a model system in which a D–A pair is forced to strongly interact through their p surfaces in a very rigid and closely spaced structure. We demonstrate how small alterations in the distance between the two p surfaces, and therefore in the degree of orbital overlap and electronic coupling, influence the groundand excited-state interactions. To maximize the contact area, we exploited the complementarity between the concave aromatic surface of subphthalocyanines (SubPcs), versatile chromophores that have shown outstanding, tunable properties in D–A systems, and C60. [13] At the same time, in order to hold the two units in close contact and to limit the flexibility of the system, threefold anchoring of the C3-symmetric macrocycle to C60 by means of a Bingel tris-addition reaction was envisaged. We found that, due to the semirigid nature of the tethers employed, this key reaction proceeded with very high regioselectivity and full diastereoselectivity. The three SubPc–C60 D–A systems prepared (Scheme 1) show only small differences in the connection of the spacer to the SubPc macrocycle: a direct C C bond (C series), an oxygen atom (O series), or a sulfur atom (S series). Analysis of SubPc–C60 products 1C, 1O, and 1S by H NMR spectroscopy and HPLC revealed that the regioselectivity of the final tris-addition process is very sensitive to the length and flexibility of the spacer in C3-symmetric SubPc precursors 2C, 2O, and 2S. For instance, compound 2O, having a phenoxy spacer, meets all the requirements for fully regioselective tris-addition to C60 to yield a single regioisomer with C3 symmetry (1O ; Figure 1 and Figures S6–S9, Supporting Information). In contrast, the reaction of SubPc 2C at 20 8C yielded a 5:95 mixture of two regioisomers (1Ca and 1 Cb ; Figure 1 and Figures S1–S5, Supporting Information) that could be separated by column chromatography. The minor component (1Ca) clearly retains the original C3 symmetry of the precursor SubPc, whereas 1Cb has C1 symmetry. The shorter nature of the biphenyl linker seems to restrict formation of a C3-symmetric tris-addition product, and the tether prefers to anchor in a less symmetric arrangement to release strain. These triple addition reactions are not only highly regioselective, but also totally diastereoselective; each SubPc enantiomer generates only one enantiomeric addition pattern. Such selectivities are lost, however, in the formation of 1S from SubPc 2S. Analyses by NMR and HPLC revealed the presence of a complex mixture of isomers that was difficult to separate (Figure S10, Supporting Information). The slightly higher flexibility and diameter of the tether in 2S must be responsible for this effect. [*] Dr. E. Carbonell, Prof. Dr. D. M. Guldi Department of Chemistry and Pharmacy and Interdisciplinary Center for Molecular Materials (ICMM) Friedrich-Alexander-Universit t Erlangen-N rnberg Egerlandstrasse 3, 91058 Erlangen (Germany) Fax: (+ 49)9131-852-8307 E-mail: dirk.guldi@chemie.uni-erlangen.de

80 citations

Journal ArticleDOI
TL;DR: In this article, the authors synthesized two different fullerene−subphthalocyanine−ferrocene conjugates, which were designed so that the ferrocene unit is linked at the axial position through a phenoxy spacer while the C60 is rigidly held close to the concave face of the macrocycle via a 3-fold C3-symmetrical anchoring.
Abstract: We have synthesized two different fullerene−subphthalocyanine−ferrocene conjugates. The molecules were designed so that the ferrocene unit is linked at the subphthalocyanine axial position through a phenoxy spacer while the C60 is rigidly held close to the concave face of the macrocycle via a 3-fold C3-symmetrical anchoring. The Bingel trisaddition reaction leading to the final products proceeded with very high regioselectivities and full diastereoselectivity. The only difference between both systems is the length of the triple tether employed, which finely regulates the regioselectivity of the trisaddition reaction and the distance between the subphthalocyanine and the C60 complementary π−π surfaces. Thus, when the tether is connected to the subphthalocyanine through a direct C−C bond, a short π−π distance of 3.25−3.30 A was calculated. In contrast, when it is connected through a slightly longer C−O−C bond, the distance increases to 3.5−3.6 A. This π−π distance has a strong influence on the ground-state ...

69 citations

01 Mar 2011
TL;DR: A full account of the synthesis, characterization, and studies of the ground- and excited-state electronic interactions occurring in these conjugates, as well as in their reference C(60)-subphthalocyanine-ferrocene dyads, is presented in this article.

66 citations

References
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Journal ArticleDOI
TL;DR: Cyclopropylation of Fullerenes C60 and C70 is achieved by a tandem process followed by intramolecular substitution of the halogen yields fullerene derivatives with functional groups.
Abstract: Cyclopropylation of Fullerenes Cyclopropylation of fullerenes C60 and C70 is achieved by a tandem process. Michael addition of a stabilized α-halocarbanion to fullerenes followed by intramolecular substitution of the halogen yields fullerene derivatives with functional groups.

805 citations

Journal ArticleDOI
TL;DR: In this article, a bis-functionalization method for the double Bingel reaction with optically active bis-malonate derivatives was proposed, which allowed the diastereoselective preparation of optically-active fullerene derivatives and, ultimately, the enanti-lective extraction of higher cyclopropanated adducts.
Abstract: The macrocyclization between buckminsterfullerene, C60, and bis-malonate derivatives in double Bingel reaction provides a versatile and simple method for the preparation of covalent bis-adducts of C60 with high regio- and diastereoselectivity. A combination of spectral analysis, stereochemical considerations, and X-ray crystallography (Fig. 2) revealed that out of the possible in-in, in-out, and out-out stereoisomers, the reaction of bis-malonates linked by o-, m-, or p-xylylene tethers afforded only the out-out ones (Scheme 1). In contrast, the use of larger tethers derived from 1,10-phenanthroline also provided a first example, (±)-19 (Scheme 2), of an in-out product. Starting from optically pure bis-malonate derivatives, the new bis-functionalization method permitted the diastereoselective preparation of optically active fullerene derivatives (Schemes 4 and 5) and, ultimately, the enantioselective preparation (enantiomeric excess ee > 97%) of optically active cis-3 bis-adducts whose chirality results exclusively from the addition pattern (Fig. 6). The macrocyclic fixation of a bis-malonate with an optically active, 9,9′-spirobi[9H-fluorene]-derived tether to C60 under generation of 24 and ent-24 with an achiral addition pattern (Scheme 4) was found to induce dramatic changes in the chiroptical properties of the tether chromophore such as strong enhancement and reversal of sign of the Cotton effects in the circular dichroism (CD) spectra (Figs. 4 and 5). By the same method, the functionafized bis-adducts 50 and 51 (Schemes 10 and 11) were prepared as initiator cores for the synthesis of the fullerene dendrimers 62, 63, and 66 (Schemes 12 and 13) by convergent growth. Finally, the new methodology was extended, to the regio- and diastereoselective construction of higher cyclopropanated adducts. Starting from mono-adduct 71, a clipping reaction provided exclusively the all-cis-2 tris-adduct (±)-72 (Scheme 14), whereas the similar reaction of bis-adduct 76 afforded the all-cis-2 tetrakis-adduct 77 (Scheme 15). Electrochemical investigations by steady-state voltammetry (Table 2) in CH2Cl2 (+0.1M Bu4NPF6) showed that all macroeyciic bis(methano)fullerenes underwent multiple reduction steps, and that regioisomerism was not much influencing the redox potentials, All cis-2 bis-adducts gave an instable dianion which decomposed during the electrochemical reduction. In CH2Cl2, the redox potential of the fullerene core in dendrimers 62, 63, and 66 is not affected by differences in size and density of the surrounding poly(ether-amide) dendrons. The all-cis-2 tris- and tetrakis(meihano)fullercnes (±)-72 and 77, respectively, are reduced at more negative potential than previously reported all-e tris- and tetrakis-adducts with methane bridges that are also located along an equatorial belt. This indicates a larger perturbation of the original fullerene π-chromophore and a larger raise in LUMO energy in the former derivatives.

169 citations

Journal ArticleDOI
TL;DR: In this paper, a cyclophane-type molecular dyads was synthesized by Bingel macrocyclization of porphyrin-tethered bis-malonates 5 or 5.
Abstract: The synthesis of the cyclophane-type molecular dyads 1 and 1 . Zn was accomplished by Bingel macrocyclization of porphyrin-tethered bis-malonates 5 or 5 . Zn, respectively, with C60 (Scheme). In these macrocycles, the doubly bridged porphyrin adopts a close, tangential orientation relative to the surface of the C-sphere. The porphyrin derivatives 6 and 6 . Zn with two appended, singly-linked C60 moieties were also formed as side products in the Bingel macrocyclizations. The trans-1 addition pattern of the fullerene moiety in 1 and 1 . Zn was unambiguously established by 1H- and 13C-NMR spectroscopy. Due to the close spatial relationship between the fullerene and porphyrin components in 1 and 6 and the corresponding ZnII complexes, the porphyrin fluorescence is efficiently quenched as compared to the luminescence emitted by 5 and 5 . Zn, respectively (Fig. 2). Cyclic-voltammetry studies show that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa in 1 and 1 . Zn are relatively small despite the close proximity between the porphyrin donor and the fullerene acceptor (Fig. 3).

104 citations