A stable cyclopenta-fused tetraphenanthrenylene macrocycle, CPTP-M, was synthesized, and the structure was confirmed by X-ray crystallographic analysis. It exhibits a large radical character (number of unpaired electron, N =3.52) and a small singlet-triplet energy gap (ΔE =-2.8 kcal mol by SQUID). Its backbone contains 60 ([4n]) conjugated π electrons and is globally antiaromatic. NMR measurements and theoretical calculations revealed that its dication/dianion is globally aromatic owing to the existence of [4n-2]/[4n+2] π-conjugated electrons. Remarkably, the ring-current map of the tetraanion shows a unique ring-in-ring structure, with a diamagnetic outer ring and a paramagnetic inner ring. Accordingly, both the inner-rim and outer-rim protons are deshielded in its H NMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the known octulene, which shows similar electronic properties.
Since the first isolation of 1,3,5,7-tetra-tert-butyl-s-indacene in 1986, core-expanded s- and as-indacenes have attracted intensive
interest. However, there is no reported synthesis of such type of
molecules due to their high reactivity for over 30 years. Herein,
we report the successful synthesis of two relatively stable, core-expanded
indacene isomers, dicyclopenta[b,g]-naphthalene (5) and dicyclopenta[a,f]naphthalene (6). X-ray crystallographic analyses reveal that the backbone
of 5 adopts a bond-delocalized structure, while that
of 6 exhibits a bond-localized character. Variable-temperature 1H NMR/ESR measurements, electronic absorption spectra, and
theoretical calculations confirm that both molecules are globally
antiaromatic and have an open-shell singlet ground state. However, 6 shows stronger antiaromaticity, a larger diradical character
(y
0 = 48%), and a smaller singlet–triplet
energy gap (ΔE
S‑T = −0.99
kcal mol–1) compared to 5 (y
0 = 30%, ΔE
S‑T = −6.88 kcal mol–1), which can be explained
by their different quinoidal structures.
Solution-phase
synthesis of buckybowls remains a big challenge,
and there are limited reports on the fragments of C70.
Herein, we report a new basic subunit of C70 with C
2v symmetry, the dicyclopenta[4,3,2,1-ghi:4′,3′,2′,1′-pqr]perylene (2CP-Per). Its aryl-substituted derivative 2CP-Per-Ar was synthesized and shows a bowl-shaped geometry
according to X-ray crystallographic analysis. A fast bowl-to-bowl
inversion process was observed above 183 K by variable temperature
nuclear magnetic resonance (NMR), with a small inversion energy barrier. 2CP-Per-Ar displays amphoteric redox behavior with a small
electrochemical energy gap (1.29 eV). Different from many other aromatic
buckybowls, 2CP-Per exhibits global antiaromaticity with
a strong paratropic ring current associated with the 16π-electrons
rim, as revealed by NMR measurements and theoretic calculations. Its
dianion is aromatic, similar to its isoelectronic structure coronene.
Its dication is predicted to be aromatic, with a [6]annulene-within-[14]annulene
structure.
Non‐alternant, non‐benzenoid π‐conjugated polycyclic hydrocarbons (PHs) are expected to exhibit very different electronic properties from all‐benzenoid PHs. Reported herein are the syntheses and physical properties of four derivatives of two azulene‐fused s‐indacene isomers, the diazuleno[2,1‐a:2′,1′‐g]‐s‐indacene (DAI‐1) and diazuleno[2,1‐a:1′,2′‐h]‐s‐indacene (DAI‐2). The backbone of both isomers contains 28π electrons and is a 7‐5‐5‐6‐5‐5‐7 fused ring system. X‐ray crystallographic analysis, NMR spectra, and theoretical calculations (ACID, NICS) reveal a structure with two aromatic azulene units fused with a central anti‐aromatic s‐indacene moiety. All compounds exhibit open‐shell diradical character and are magnetically active, but the derivatives of DAI‐2 show larger radical character than the respective ones of DAI‐1. Their dications were isolated in crystalline form and all experimental and theoretical analyses disclose a shift of local (anti)aromaticity along the backbone, with two aromatic tropylium rings at the termini.
Synthesis of fully conjugated cyclophanes containing large‐size polycyclic aromatics is challenging. Now, three benzidine‐linked, hexa‐peri‐hexabenzocoronene (superbenzene)‐based ortho‐, para‐, and meta‐cyclophanes are synthesized through intermolecular Yamamoto coupling reaction of structurally pre‐organized precursors. Subsequent oxidative dehydrogenation gave the corresponding quinoidal benzidine‐linked cyclophanes. Their geometries were confirmed by X‐ray crystallographic analysis and their electronic properties were investigated by electronic absorption, cyclic voltammetry, and DFT calculations. The quinoidal benzidine‐linked cyclophanes show thermally populated paramagnetic activity with a relatively large singlet‐triplet energy gap. Two enantiomers for the ortho‐cyclophanes (1‐NH and 1‐N) were isolated and their chiral figure‐of‐eight macrocyclic structures were identified. The cage‐like cyclophanes 2‐NH and 3‐NH with concave surface can selectively encapsulate fullerene C70.
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