Preparation and Characterization of N‐Anisyl‐Substituted Hexaaza[1₆]paracyclophane

Abstract

As opposed to the thoroughly studied carbon-bridged calixarenes, [1] heteroatom-bridged [1 n ]metacyclophanes and their derivatives have recently attracted much attention mainly because of novel structure-property relationships originating from the replacement of methylene bridges with heteroatom bridges. [2] On the other hand, only a few reports are known for [1 n ]paracyclophanes, probably as a result of the difficulty in synthesizing them (Scheme 1). [3,4] Aza[1 n ]paracyclophanes can be viewed as macrocyclic oligomers of polyaniline, which is one of the well-known organic conducting polymers. [5] As is apparent from the simple Hückel MO calculations, the HOMOs for linear and cyclic oligoanilines assume different aspects, as exemplified in Scheme 2. As for the linear hexamer, the large MO coefficients are concentrated on the central para-phenylenediamine (PD) moiety. Owing to the localized HOMO character, the ESR studies on the radical cations of linear oligoanilines showed that the spin was confined to the central PD moiety, and therefore, spin delocalization took place only to a small extent. [6] In contrast, the HOMO coefficients of the cyclic hexamer is mainly distributed equally on six nitrogen nuclei. In fact, according to the DFT calculations, the HOMO coefficients of all-N-phenyl-substituted hexaaza[1 6 ]paracyclophane (1') is delocalized over the macrocyclic molecular backbone, and therefore, the DFT-predicted spin density distribution in the corresponding radical cation discerns the delocalized character (Figure 1). In this respect, it is interesting to examine the spin distribution of the radical cation of cyclic oligoanilines in conjunction with the question: to what extent is an unpaired electron delocalized within the polyaniline backbone?However, the preparation of aza[1 n ]paracyclophanes are hitherto unknown, and the elucidation of their electronic properties is in demand from the viewpoint of materials chemistry. This communication reports the synthesis and characterization of electronic structures of all-N-anisyl-substituted hexaaza[1 6 ]paracyclophane (1) and its oxidized species.The title compound (1) was not obtained by the simple single-step coupling reaction from para-halogenated secondary arylamines. In addition, convergent fragment coupling synthesis [1] from the combinations of simple secondary arylamines and aryl halides was also unsatisfactory to us. For example, an equimolar coupling reaction of N,N'-bis(4-Scheme 2. Schematic views of HOMOs of a) linear and b) cyclic hexamers of polyaniline. Scheme 1. Reported heteroatom-bridged [1 n ]paracyclophanes and hexaaza[1 6 ]paracyclophane 1 and 1'.

Luminescent Quadrupolar Borazine Oligomers: Synthesis, Photophysics, and Two‐Photon Absorption Properties

“…Further oxidation of B1N2 by the addition of two equivalents of the Ag salt resulted in the complete disappearance of the initial absorption band, the appearance of additional 1PA bands at 499 and 793 nm, and an increase in amplitude and slight blueshift of the low energy band in the NIR. Again, the 1PA bands in the visible spectral region coincide with those seen in larger conjugated arylamine systems,35b for which the band at ∼500 nm could be due to double oxidation26a at one of the nitrogen atoms. The increase in absorbance of the IV band would suggest an increase in concentration of the delocalized polarons.…”

Issue Information

“…Numerous conjugated organic cyclic compounds have been explored. More recently, heteroatom‐containing systems have attracted interest because the added functionality can offer unique properties and possibly open the door to new applications 11. 12 As an example, Tanaka’s cyclic hexaanilines A (π=phenylene) provide a platform for studies on the aromaticity and molecular magnetism that results from spin delocalization in the radical cation and dication…”

“…12 As an example, Tanaka’s cyclic hexaanilines A (π=phenylene) provide a platform for studies on the aromaticity and molecular magnetism that results from spin delocalization in the radical cation and dication 11 We have introduced an electron‐deficient charge‐reverse analogue13 to A , the conjugated macrocyclic organoborane B with fluorene as the π‐system 14. Herein, we report the first ambipolar macrocycle, which contains nitrogen as donor and boron as acceptor sites, bridged by π‐conjugated phenylene groups.…”

“…Three oxidation and three reduction waves were observed. A comparison of the electrochemical data with those reported for the azacyclophane A (phenylene π‐system)11 and boracyclophane B (fluorene π‐system)14 provides insights into the mutual electronic effects of the adjacent boron and nitrogen centers in the ambipolar structure of 3 (Table 2). Relative to the azacyclophane A , 3 is oxidized at more positive potentials, because the presence of the electron‐deficient neighboring boron atoms decreases the electron density at nitrogen.…”

Synthesis of Pillar[6]arenes and Their Host–Guest Complexes

“…The cyclohexameric amine, hexaaza [1 6 ]paracyclophane 51b (R = H) is not known, but several derivatives of it, in which some or all of the nitrogen atoms bear substituents, have been reported. [65][66][67] The sixfold cyclic ether 51c [cyclohexa(1,4-phenylene oxide)] was first described in 2006. 68 Applications of the compounds 51a-c in supramolecular chemistry have never been studied.…”