Octulene: A Hyperbolic Molecular Belt that Binds Chloride Anions

Abstract

Octulene,t he higher homologue of kekulene and septulene,was synthesized using the fold-in method. This new hydrocarbon macrocycle contains al arge 24-membered inner circuit, which is peripherally fused to 24 benzenerings.Such an arrangement produces considerable hyperbolic distortion of the p-conjugated surface.T he consequences of distortion in octulene were explored using photophysical methods,w hich revealed ar educed electronic band gap and greater flexibility of the p system. Octulene contains af unctional cavity with ad iameter larger than 5.5 that is capable of efficiently binding the chloride anion in an onpolar solvent (K a = 2.2(4) 10 4 m À1 ,1 %d ichloromethane (DCM) in benzene). The octulene-chloride interaction is stabilized by eight weak C(sp 2 )H···Cl bonds,p roviding the first example of ah ydrocarbon-based anion receptor.

Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species

“…Both the dianion and radical trianion exhibited an intense absorption band in the NIR region (l max = 1474 and 1671 nm, respectively,F igure 3d). These characteristics are very similar to the absorption spectrum of an octulene derivative, [13] thus indicating that indeed, the tetraanion of CPTP can be regarded as an isoelectronic structure of octulene.T he pure dication, dianion, and tetraanion of CPTP-M were isolated and all showed sharp 1 HNMR spectra at room temperature (Figure 4), thus indicating that all these charged species possess ac losed-shell singlet ground state. These characteristics are very similar to the absorption spectrum of an octulene derivative, [13] thus indicating that indeed, the tetraanion of CPTP can be regarded as an isoelectronic structure of octulene.T he pure dication, dianion, and tetraanion of CPTP-M were isolated and all showed sharp 1 HNMR spectra at room temperature (Figure 4), thus indicating that all these charged species possess ac losed-shell singlet ground state.…”

“…[6] Some good examples are the kekulene [7] and hexa-peri-hexabenzocoronene structures, [8] which contain six and seven localized aromatic sextet rings, respectively.However, recent studies demonstrated that large PA Hs with two or four zigzag edges, [9] cyclopenta-fused polycyclic hydrocarbons, [10] and some rigid macrocyclic polyradicaloids [11] could also show global (anti)aromaticity.O ur particular interest herein is am acrocyclic cyclopenta-fused tetraphenanthrenylene (CPTP;F igure 1a). In particularly,the tetraanion can be regarded as an isoelectronic structure of the known structure octulene, [13] which has al ocally aromatic character.T herefore,t he electronic structure,g lobal (anti)aromaticity,a nd polyradical character of CPTP and its charged species are of great interest. Molecule CPTP can be regarded as an expanded version of ap reviously reported tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene (TCPTP), which turned out to be diradicaloid with as mall diradical character.…”

“…Palladiumcatalyzed Suzuki-Miyaura borylation of the phenanthrene dibromide 1 [14] gave the pinacol borate 2,a nd as ubsequent Suzuki coupling reaction between equimolar amounts of 2 and 3 [13] afforded the tetraaldehyde macrocycle 4 in 8% yield after separation by recycling preparative GPC.T reatment of 4 with 2-mesitylmagnesium bromide gave the corresponding tetra-alcohol, and then intramolecular Friedel-Crafts alkylation mediated by BF 3 ·Et 2 Oprovided the tetrahydro precursor 5.O xidative dehydrogenation of 5 with 2,3-dichloro-5,6dicyano-p-benzoquinone (DDQ) in toluene gave the final product CPTP-M,w hich was purified by normal silica-gel column chromatography. Palladiumcatalyzed Suzuki-Miyaura borylation of the phenanthrene dibromide 1 [14] gave the pinacol borate 2,a nd as ubsequent Suzuki coupling reaction between equimolar amounts of 2 and 3 [13] afforded the tetraaldehyde macrocycle 4 in 8% yield after separation by recycling preparative GPC.T reatment of 4 with 2-mesitylmagnesium bromide gave the corresponding tetra-alcohol, and then intramolecular Friedel-Crafts alkylation mediated by BF 3 ·Et 2 Oprovided the tetrahydro precursor 5.O xidative dehydrogenation of 5 with 2,3-dichloro-5,6dicyano-p-benzoquinone (DDQ) in toluene gave the final product CPTP-M,w hich was purified by normal silica-gel column chromatography.…”

Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species

“…[12] Theg ain of one/two aromatic phenanthrene units rather than benzene rings in the open-shell resonance forms C/D of CPTP implies ap ossible larger diradical and teraradical character than that of TCPTP.Furthermore,CPTP has total 60 p-conjugated electrons with arigid structure,and thus it is possible to show global antiaromaticity.Its dication/ dianion has at otal of 58/62 p electrons and thus is possibly globally aromatic,w hereas its tetracation/tetraanion would contain 56/64 p electrons and is possibly globally antiaromatic ( Figure 1b). In particularly,the tetraanion can be regarded as an isoelectronic structure of the known structure octulene, [13] which has al ocally aromatic character.T herefore,t he electronic structure,g lobal (anti)aromaticity,a nd polyradical character of CPTP and its charged species are of great interest.…”

“…Ab ulky mesityl group was attached at the most reactive site of each cyclopenta ring, and as table CPTP derivative CPTP-M was synthesized according to Scheme 1. Palladiumcatalyzed Suzuki-Miyaura borylation of the phenanthrene dibromide 1 [14] gave the pinacol borate 2,a nd as ubsequent Suzuki coupling reaction between equimolar amounts of 2 and 3 [13] afforded the tetraaldehyde macrocycle 4 in 8% yield after separation by recycling preparative GPC.T reatment of 4 with 2-mesitylmagnesium bromide gave the corresponding tetra-alcohol, and then intramolecular Friedel-Crafts alkylation mediated by BF 3 ·Et 2 Oprovided the tetrahydro precursor 5.O xidative dehydrogenation of 5 with 2,3-dichloro-5,6dicyano-p-benzoquinone (DDQ) in toluene gave the final product CPTP-M,w hich was purified by normal silica-gel column chromatography.…”