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

Abstract

As table cyclopenta-fused tetraphenanthrenylene macrocycle, CPTP-M,w as synthesized, and the structure was confirmed by X-rayc rystallographic analysis.I te xhibits al arge radical character (number of unpaired electron, N U = 3.52) and asmall singlet-triplet energy gap (DE S-T = À2.8 kcal mol À1 by SQUID). Its backbone contains 60 ([4n]) conjugated p electrons and is globally antiaromatic.N MR measurements and theoretical calculations revealed that its dication/dianion is globally aromatic owing to the existence of [4nÀ2]/[4n + 2] pconjugated electrons.Remarkably,the ring-current map of the tetraanion shows au nique ring-in-ring structure,w ith ad iamagnetic outer ring and ap aramagnetic inner ring.A ccordingly,both the inner-rim and outer-rim protons are deshielded in its 1 HNMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the knowno ctulene,w hichs hows similar electronic properties.

Fully Conjugated [4]Chrysaorene. Redox-Coupled Anion Binding in a Tetraradicaloid Macrocycle

“…While our work was close to completion, 22 Wu et al reported their concurrent research on 3a, based on an essentially identical synthetic strategy. 23 The present account is therefore focused on the anion-binding capability of 3a and its relationship to the redox chemistry of this open-shell coronoid. DFT optimization of the singlet state, is shown in Figure 1.…”

Synthesis and Studies of Stable Nonaromatic Dithia Pyribenzihexaphyrins

“…It has been reported that for rings consisting of localized single and double bonds, very small and negative HOMA values are obtained, suggesting its nonaromatic nature. 38,39 Thus, the spectral and electrochemical properties predicted by DFT agreed closely with the experimental data. In short, the absence of bond length equalization, low-field 1 H NMR shifts, small NICS values, and nonplanar structure 40 undoubtedly supports the nonaromatic nature of macrocycle 4.…”

“…For the quantitative evaluation of aromaticity, the NICS and harmonic oscillator model of aromaticity (HOMA) values were calculated for macrocycle 4 . The isotropic NICS (NICS(0) iso ) and the zz component of the shielding tensor (NICS(0) zz ) values in the S 0 state for the compound 4 are −0.6220 and +4.5369, respectively, suggesting its nonaromatic nature. − Thus, the molecule lacks both local and ground-state global aromaticity. The HOMA indices were calculated along various π-conjugation paths using the optimized structure for macrocycle 4 .…”

“…The HOMA values of macrocycle 4 range from −0.26 to 0.47 (Figure S19). It has been reported that for rings consisting of localized single and double bonds, very small and negative HOMA values are obtained, suggesting its nonaromatic nature. , …”

Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global Aromaticity

“…Here, one additional double-bond has been broken to have diradical (2 unpaired electrons) to tetraradical (4 unpaired electrons) and reaching up to hexadecaradical (16 unpaired electrons) characters (Figures S29-S32). Although the polyradical characters are comparable with the reported values in the literature (Das et al, 2016;Lu et al, 2018;Liu et al, 2019), to date, radical characters beyond decaradical is not reported for macrocycles. Owing to the symmetric structure of all the macrocycles, higher energy orbitals are found to be degenerate (Figures S33--S35).…”