Synthesis of a Tetrabenzotetraaza[8]circulene by a “Fold‐In” Oxidative Fusion Reaction

Abstract

Tetrabenzotetraaza[8]circulene (1)has been synthesized in good yield by a"fold-in" oxidative fusion reaction of a1 ,2-phenylene-bridged cyclic tetrapyrrole.X -rayd iffraction analysis of 1 has revealed ap lanar square structure with ac entral cyclooctatetraene (COT) core that shows little alternation of the bond lengths.D espite these structural features, 1 shows aromatic-like character,s uch as sharp absorption bands,h igh fluorescence quantum yields (F F = 0.55 in THF), and as ingle exponential fluorescence decay with t F = 3.8 ns.T hese observations indicate ad ominant contribution of an [8]radialene-like p conjugation and hence aromatic character of the local aromatic segments in 1.

Synthesis of Tetrasilatetrathia[8]circulenes by a Fourfold Intramolecular Dehydrogenative Silylation of C−H Bonds

“…These compounds have been used as structural motifs in carbon-rich materials, [1] and organic chemists have extensively explored synthetic strategies to various [n]circulenes to determine their structures and macrocyclic aromaticity. [2] Recently,aseries of [8]circulenesi ncorporating heteroaromatic rings, that is, hetero[8]circulenes, have attractedc onsiderable attention as organic electronic materials for light-emitting diodes and field-effect transistors on the basis of their highly rigids tructures ande ffectivee lectronic perturbation of the heteroatoms.F or example, tetraoxa[8]circulenes, [3] diazadioxa[8]circulenes, [4] and tetrabenzotetraaza[8]circulene [5] have been successfully prepared as core frameworks incorporating four benzene rings with four heteroaromatic rings (Scheme1). Very recently,W ong'sg roup and we have independently re-portedt he synthesis of tetrathia[8]circulenes [6,7] and tetraselena[8]circulene.…”

Sequential N‐Alkylations of Tetrabenzotetraaza[8]circulene as a Tool To Tune Its Optical Properties

“…1.40 )o ft he optimum D 8h COT,s uggesting contribution of [8]radialene-like structure. [10] This is also the case for AC-Bu 2 and AC-Bu 3 ,w hich showed average CÀCb ond lengths of 1.434 .…”

“…The crystal packing structures of AC core are also different, parallel and orthogonal fort he formera nd latter crystals, respectively The structure of AC-Bu 3 has been also confirmed by X-ray diffraction analysis ( Figure S5-1). The MPD valueso ft he two independentmolecules in the asymmetricunit of AC-Bu 3 are calculated to be 0.164 and 0.142 ,r espectively.T he MPD value of AC-Bu 4 was reported to be 0.155 , [10] and thus it is inferred that the MPD values increase gradually upon an increase in the number of N-butyl groups, probably to relieve increasing congestion. The average CÀCb ond length of the cyclooctatetraene (COT) segmento fAC was 1.435 ,w hich is distinctly longert han that (ca.…”

“…We have recentlyr eported a" fold-in"-type oxidative synthesis of tetrabenzotetraaza[8]circulene AC,w hich displays aq uite planar structure and sharp absorption and emission spectra characteristic of polycyclic aromatic hydrocarbons. [10] Furthermore, the peripheralN Hm oieties were tetrabutylated to improve the solubility andt une the optical properties. Pittelkow et al has reported hybrid oxa/aza[8]circulenes, [8] but their synthetic protocols required the N-moieties to be substituted.…”

“…100 equiv) of n-butyl iodide in the presence of sodium hydride in THF at room temperature to give tetra-Nbutylated [8]circulene AC-Bu 4 in 77 %y ield with at race amount of tri-N-butylated product (AC-Bu 3 )( Scheme 1). [10] In order to isolate the partially N-butylated products,t he reaction was conducted with only 3equivalents of n-butyli odide, which gave di-N-butylated (AC-Bu 2 )a nd tri-N-butylated (AC-Bu 3 )products in 52 %and 33 %yields, respectively,after areaction time of 24 h( Scheme 2). When the reaction was run with 2equivalents of n-butyl iodide, the mono-N-butylated product (AC-Bu 1 )w as obtained as the main product in 55 %y ield, along with small amounts of AC and AC-Bu 2 .I ti sw orth noting that only opp-type isomer waso btained as AC-Bu 2 .…”