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Cyclophane‐Type Fullerene‐dibenzo[18]crown‐6 Conjugates with trans‐1, trans‐2, and trans‐3 Addition Patterns: Regioselective Templated Synthesis, X‐Ray Crystal Structure, Ionophoric Properties, and Cation‐Complexation‐Dependent Redox Behavior

Cyclophane‐Type Fullerene‐dibenzo[18]crown‐6 Conjugates with trans‐1, trans‐2, and trans‐3... The fullerene‐crown ether conjugates (±)‐1 to (±)‐3 with trans‐1 ((±)‐1), trans‐2 ((±)‐2), and trans‐3 ((±)‐3) addition patterns on the C‐sphere were prepared by Bingel macrocyclization. The trans‐1 derivative (±)‐1 was obtained in 30% yield, together with a small amount of (±)‐2 by cyclization of the dibenzo[18]crown‐6(DB18C6)‐tethered bis‐malonate 4 with C60 (Scheme 1). When the crown‐ether tether was further rigidified by K+‐ion complexation, the yield and selectivity were greatly enhanced, and (±)‐1 was obtained as the only regioisomer in 50% yield. The macrocyclization, starting from a mixture of tethered bis‐malonates with anti (4) and syn (10) bisfunctionalized DB18C6 moieties, afforded the trans‐1 ((±)‐1, 15%), trans‐2 ((±)‐2, 1.5%), and trans‐3 ((±)‐3, 20%) isomers (Scheme 2). Variable‐temperature 1H‐NMR (VT‐NMR) studies showed that the DB18C6 moiety in C2‐symmetrical (±)‐1 cannot rotate around the two arms fixing it to the C‐sphere, even at 393 K. The planar chirality of (±)‐1 was confirmed in 1H‐NMR experiments using the potassium salts of (S)‐1,1′‐binaphthalene‐2,2′‐diyl phosphate ((+)‐(S)‐19) or (+)‐(1S)‐camphor‐10‐sulfonic acid ((+)‐20) as chiral shift reagents (Fig. 1). The DB18C6 tether in (±)‐1 is a true covalent template: it is readily removed by hydrolysis or transesterification, which opens up new perspectives for molecular scaffolding using trans‐1 fullerene derivatives. Characterization of the products 11 (Scheme 3) and 18 (Scheme 4) obtained by tether removal unambiguously confirmed the trans‐1 addition pattern and the out‐out geometry of (±)‐1. VT‐NMR Studies established that (±)‐2 is a C2‐symmetrical out‐out trans‐2 and (±)‐3 a C1‐symmetrical in‐out trans‐3 isomer. Upon changing from (±)‐1 to (±)‐3, the distance between the DB18C6 moiety and the fullerene surface increases and, correspondingly, rotation of the ionophore becomes increasingly facile. The ionophoric properties of (±)‐1 were investigated with an ion‐selective electrode membrane (Fig. 2 and Table 2), and K+ was found to form the most stable complex among the alkali‐metal ions. The complex between (±)‐1 and KPF6 was characterized by X‐ray crystal‐structure analysis (Figs. 3 and 4), which confirmed the close tangential orientation of the ionophore atop the fullerene surface. Addition of KPF6 to a solution of (±)‐1 resulted in a large anodic shift (90 mV) of the first fullerene‐centered reduction process, which is attributed to the electrostatic effect of the K+ ion bound in close proximity to the C‐sphere (Fig. 5). Smaller anodic shifts were measured for the KPF6 complexes of (±)‐2 (50 mV) and (±)‐3 (40 mV), in which the distance between ionophore and fullerene surface is increased (Table 3). The effects of different alkali‐ and alkaline‐earth‐metal ion salts on the redox properties of (±)‐1 were investigated (Table 4). These are the first‐ever observed effects of cation complexation on the redox properties of the C‐sphere in fullerene‐crown ether conjugates. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Helvetica Chimica Acta Wiley

Cyclophane‐Type Fullerene‐dibenzo[18]crown‐6 Conjugates with trans‐1, trans‐2, and trans‐3 Addition Patterns: Regioselective Templated Synthesis, X‐Ray Crystal Structure, Ionophoric Properties, and Cation‐Complexation‐Dependent Redox Behavior

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Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services
ISSN
0018-019X
eISSN
1522-2675
DOI
10.1002/(SICI)1522-2675(19991006)82:10<1572::AID-HLCA1572>3.0.CO;2-B
Publisher site
See Article on Publisher Site

Abstract

The fullerene‐crown ether conjugates (±)‐1 to (±)‐3 with trans‐1 ((±)‐1), trans‐2 ((±)‐2), and trans‐3 ((±)‐3) addition patterns on the C‐sphere were prepared by Bingel macrocyclization. The trans‐1 derivative (±)‐1 was obtained in 30% yield, together with a small amount of (±)‐2 by cyclization of the dibenzo[18]crown‐6(DB18C6)‐tethered bis‐malonate 4 with C60 (Scheme 1). When the crown‐ether tether was further rigidified by K+‐ion complexation, the yield and selectivity were greatly enhanced, and (±)‐1 was obtained as the only regioisomer in 50% yield. The macrocyclization, starting from a mixture of tethered bis‐malonates with anti (4) and syn (10) bisfunctionalized DB18C6 moieties, afforded the trans‐1 ((±)‐1, 15%), trans‐2 ((±)‐2, 1.5%), and trans‐3 ((±)‐3, 20%) isomers (Scheme 2). Variable‐temperature 1H‐NMR (VT‐NMR) studies showed that the DB18C6 moiety in C2‐symmetrical (±)‐1 cannot rotate around the two arms fixing it to the C‐sphere, even at 393 K. The planar chirality of (±)‐1 was confirmed in 1H‐NMR experiments using the potassium salts of (S)‐1,1′‐binaphthalene‐2,2′‐diyl phosphate ((+)‐(S)‐19) or (+)‐(1S)‐camphor‐10‐sulfonic acid ((+)‐20) as chiral shift reagents (Fig. 1). The DB18C6 tether in (±)‐1 is a true covalent template: it is readily removed by hydrolysis or transesterification, which opens up new perspectives for molecular scaffolding using trans‐1 fullerene derivatives. Characterization of the products 11 (Scheme 3) and 18 (Scheme 4) obtained by tether removal unambiguously confirmed the trans‐1 addition pattern and the out‐out geometry of (±)‐1. VT‐NMR Studies established that (±)‐2 is a C2‐symmetrical out‐out trans‐2 and (±)‐3 a C1‐symmetrical in‐out trans‐3 isomer. Upon changing from (±)‐1 to (±)‐3, the distance between the DB18C6 moiety and the fullerene surface increases and, correspondingly, rotation of the ionophore becomes increasingly facile. The ionophoric properties of (±)‐1 were investigated with an ion‐selective electrode membrane (Fig. 2 and Table 2), and K+ was found to form the most stable complex among the alkali‐metal ions. The complex between (±)‐1 and KPF6 was characterized by X‐ray crystal‐structure analysis (Figs. 3 and 4), which confirmed the close tangential orientation of the ionophore atop the fullerene surface. Addition of KPF6 to a solution of (±)‐1 resulted in a large anodic shift (90 mV) of the first fullerene‐centered reduction process, which is attributed to the electrostatic effect of the K+ ion bound in close proximity to the C‐sphere (Fig. 5). Smaller anodic shifts were measured for the KPF6 complexes of (±)‐2 (50 mV) and (±)‐3 (40 mV), in which the distance between ionophore and fullerene surface is increased (Table 3). The effects of different alkali‐ and alkaline‐earth‐metal ion salts on the redox properties of (±)‐1 were investigated (Table 4). These are the first‐ever observed effects of cation complexation on the redox properties of the C‐sphere in fullerene‐crown ether conjugates.

Journal

Helvetica Chimica Acta – Wiley

Published: Jan 6, 1999

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