Tether-Directed Remote Functionalization Research Articles

Regio-, Stereo-, and Atropselective Synthesis of C60 Fullerene Bisadducts by Supramolecular-Directed Functionalization.

The regio- and stereocontrolled synthesis of fullerene bisadducts is a topic of increasing interest in fullerene chemistry and a key point for the full exploitation of these derivatives in materials science. In this context, while the tether-directed remote functionalization strategy offers a valid approach to this synthetic challenge, no examples of such control have yet been reported using nontethered species. Presented here is a conceptually novel, supramolecular-directed functionalization approach in which noncovalent interactions between untethered residues have been used, for the first time, to amplify (>2800-fold) the regio-, stereo-, and atropselective formation of a C60 fullerene bisadduct racemate from a complex mixture of 130 bisadducts. Remarkably, both enantiomers, which present a sterically demanding cis-1 C60 addition pattern, represent the first examples of fullerene derivatives which combine central, axial, and helical chirality.

Regioselective preparation of a bis-pyrazolinofullerene by a macrocyclization reaction.

A single isomer of a pyrazolinofullerene bis-adduct was prepared by tether-directed remote functionalization. Specifically, a macrocyclization reaction between C60 and a bis-hydrazone reagent has been carried out to generate a regioisomerically pure fullerene bis-adduct which presents a lower LUMO than pristine C60.

Reducing Regioisomers of Fullerene-Bisadducts by Tether-Directed Remote Functionalization: Investigation of Electronically and Sterically Isomeric Effects on Bulk-Heterojunction Solar Cells

C60 bis-adduct containing a mixture of regio-isomers with different LUMO energy levels and steric geometries could greatly affect the morphological and bulk properties. To investigate the regio-isomer effect on solar cell performance, we have successfully designed and synthesized a regio-selective 4-acetatephenyl-4'-methylphenylmethano C60 bis-adduct (S-APM-CBA) by "tether-directed remote functionalization" strategy and a random 4-acetatephenyl-4'-methylphenylmethano C60 bis-adduct denoted as R-APM-CBA by traditional cyclopropanation. The dramatic reduction in the number of regio-isomers in S-APM-CBA is confirmed by the (1)H NMR and HPLC measurements and theoretical calculation. Compared to the R-APM-CBA-based device with a Jsc of 6.63 mA/cm(2), an FF of 44.3% and a PCE of 2.46%, the device using S-APM-CBA yielded a much lower Jsc of 1.48 mA/cm(2), an FF of 32.2%, and a PCE of 0.38%. Consistently, the electron-only device using S-AMP-CBA exhibited lower electron mobility than the R-AMP-CBA-based device. These results imply that the electronic shallow-trap effect ascribed to the LUMO energy variations turned out to be insignificant in the AMP-CBA system. The lower efficiency and mobility of S-AMP-CBA might due to the assumption that the most probable trans-4-III isomer in S-AMP-CBA prevents the intermolecular facial contact of fullerenes, thereby hindering the electron transporting. Furthermore, the nanomorphology of S-AMP-CBA and R-AMP-CBA active layers could be different because of their different three-dimensional structures. This research demonstrated that steric effect of regio-isomers in a given C60 bis-adduct is more crucial than electronic shallow-trap effect.

Macrocyclic malonates. A new family of tethers for the regio- and diastereoselective functionalization of [60]fullerene

Abstract The tether-directed remote functionalization of C60 has been investigated by using cyclic bis- and trismalonate tethers. The reactive malonate groups are connected with alkyl spacers and their synthesis was performed in one step by the condensation reaction of malonyl dichloride with an appropriate diol. Macrocycles containing identical alkyl spacers afforded bis- and triadducts of C60 with rotational symmetry in a regioselective manner and in remarkable yields. In contrast, macrocycles bearing different alkyl spacers led to the formation of Cs-symmetrical bisadducts. Tuning of the spacer’s length gave access to different addition patterns of C60 while, the synthesis of enantiomerically pure trisadducts of C60 with an e,e,e-addition pattern was achieved via cyclopropanation with chiral D3-symmetrical cyclo-tris-malonate tethers. To cite this article: N. Chronakis et A. Hirsch. C. R. Chimie 8 (2005).

Tether-directed remote functionalization of fullerenes C60 and C70

Abstract The article provides an overview of the work on regio- and, in the occurrence, stereoselective tether-directed remote functionalization of fullerenes in the Diederich group, from the initial stages in 1994 to the present. All bisaddition patterns of C60, except cis-1, have been realized with high selectivities, mainly by Bingel-type macrocyclizations. Particular emphasis is placed on the stereoselective generation of the inherently chiral cis-3, trans-3, and trans-2 addition patterns. Besides, one of the rare examples of direct threefold tether-directed cyclopropanation of C60 is presented and the spacer-controlled derivatization of C70 is reviewed. To cite this article: C. Thilgen, F. Diederich, C. R. Chimie 9 (2006).

Preparation ofTröger Base Derivatives by Cross-Coupling Methodologies

Derivatives of the Troger base are finding increasing application in supramolecular chemistry: they are introduced as rigid scaffolds into synthetic receptors and 'molecular torsional balances' to quantify weak intermolecular interactions, and serve as efficient 'covalent templates' in the tether-directed remote functionalization of fullerenes. This paper describes the facile synthesis of symmetrically (Schemes 1 and 2) and unsymmetrically (Schemes 4 and 5) substituted Troger base derivatives starting from the corresponding, readily available dihalo compounds. A variety of metal-catalyzed cross-coupling reactions, including Suzuki couplings, palladium-catalyzed cyanation and boronation, and copper-catalyzed amidations are used to achieve these transformations. © 2005 Verlag Helvetica Chimica Acta AG.

Hexakis-Adducts of [60]Fullerene with Different Addition Patterns: Templated Synthesis, Physical Properties, and Chemical Reactivity

Representatives of two classes of hexakis-adducts of C60 were prepared by templated synthesis strategies. Compound 8 with a dipyridylmethano addend in a pseudo-octahedral addition pattern was obtained by DMA-templated addition (DMA=9,10-dimethylanthracene; Scheme 1) and served as the starting material for the first supramolecular fullerene dimer 2. Hexakis-adduct 12 also possesses a pseudo-octahedral addition pattern and was obtained by a sequence of tether-directed remote functionalization, tether removal, and regioselective bis-functionalization (Scheme 2). With its two diethynylmethano addends in trans-1 position, it is a precursor for fascinating new oligomers and polymers that feature C60 moieties as part of the polymeric backbone (Fig. 1). With the residual fullerene π-electron chromophore reduced to a `cubic cyclophane'-type sub-structure (Fig. 4), and for steric reasons, 8 and 12 no longer display electrophilic reactivity. As a representative of the second class of hexakis-adducts, (±)-1, which features six addends in a distinct helical array along an equatorial belt, was prepared by a route that involved two sequential tether-directed remote functionalization steps (Schemes 3 and 5). In compound (±)-1, π-electron conjugation between the two unsubstituted poles of the carbon sphere is maintained via two (E)-stilbene-like bridges (Fig. 4). As a result, (±)-1 features very different chemical reactivity and physical properties when compared to hexakis-adducts with a pseudo-octahedral addition pattern. Its reduction under cyclic voltammetric conditions is greatly facilitated (by 570 mV), and it readily undergoes additional, electronically favored Bingel additions at the two sterically well-accessible central polar 6-6 bonds under formation of heptakis- and octakis-adducts, (±)-30 and (±)-31, respectively (Scheme 6). The different extent of the residual π-electron delocalization in the fullerene sphere is also reflected in the optical properties of the two types of hexakis-adducts. Whereas 8 and 12 are bright-yellow (end-absorption around 450 nm), compound (±)-1 is shiny-red, with an end-absorption around 600 nm. This study once more demonstrates the power of templated functionalization strategies in fullerene chemistry, providing addition patterns that are not accessible by stepwise synthetic approaches.

Higher Adducts of C60 by Tether-Directed Remote Functionalization: X-Ray Crystal Structure and Reactivity of a Chiral Hexakis-Cyclopropanated Fullerene with all Addends Located along an Equatorial Belt

Ein ungewöhnliches Additionsmuster liegt bei dem neuartigen sechsfach cyclopropanierten Fulleren (±)-1 vor, das durch eine Sequenz aus Spacer-kontrollierten regioselektiven Fernfunktionalisierungen erhalten wurde. Durch eine Kristallstrukturanalyse wurde festgestellt, dass die sechs Addenden in einer helicalen Anordnung entlang des „Fullerenäquators“ positioniert sind.

Higher Adducts of C60 by Tether-Directed Remote Functionalization: X-Ray Crystal Structure and Reactivity of a Chiral Hexakis-Cyclopropanated Fullerene with all Addends Located along an Equatorial Belt.

An unprecedented addition pattern for the novel hexakis-cyclopropanated C60 (±)-1 was prepared by a sequence of tether-directed regioselective remote functionalizations. The X-ray crystal structure revealed the positioning of the six addends in a distinct helical array along an equatorial belt.

Templated Organic Synthesis. Edited by F. Diederich (diederich@org.chem.ethz.ch) and Peter J. Stang (stang@chemistry.chem.utah.edu). Wiley-VCH: Weinheim. 1999. XX+411 pp. 268 DM. ISBN 3-527-29666-2

Physicochemical theoretical development has been dwarfed by the abundant experimental achievements in molecular recognition studies, including the template effects reported in this book [1-3].[...]

Covalent fullerene chemistry

Abstract

Regiospecific templated synthesis of D 2h-symmetrical tetrakis-adduct C64(COOEt)8 by reversible tether-directed remote functionalization of C60

Tether-directed remote functionalization of C60, followed by further addition step and subsequent removal of the tether-reactive group conjugate(template), led to the first D2h-symmetrical tetrakis-adduct n a regiospecific manner.