A Stable Antiaromatic 5,20‐Dibenzoyl [28]Hexaphyrin(1.1.1.1.1.1): Core AuIII Metalation and Subsequent Peripheral BIII Metalation

5,20‐Dibenzoyl [28]hexaphyrin(1.1.1.1.1.1) was synthesized as the first hexaphyrin bearing meso‐aroyl substituents. The meso‐dibenzoyl substituents are hydrogen‐bonded with the pyrrolic protons to stabilize an antiaromatic dumbbell conformer. Core metalation of this hexaphyrin with Au^III afforded rectangular and aromatic [26]hexaphyrin bis‐Au^III complexes, the major isomer of which was reduced with NaBH₄ to give its antiaromatic 28π bis‐Au^III complex. This complex allowed facile peripheral metalation with B^III owing to the peripheral benzoyl substituents.     

Benzonorcorrole NiII Complexes: Enhancement of Paratropic Ring Current and Singlet Diradical Character by Benzo‐Fusion

Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. Ni^II benzonorcorroles were synthesized and the effect of benzo‐fusion on the antiaromaticity was elucidated. The benzo‐fusion resulted in significant decrease of the HOMO–LUMO gaps and enhancement of the paratropic ring current effect. Furthermore, the introduction of the benzo groups induced singlet diradical character in the antiaromatic porphyrinoid.     

Isolation of an Antiaromatic 9-Hydroxy Fluorenyl Cation

Fluorenyl cations are textbook examples of 4π electron antiaromatic five-membered ring systems. So far, they were reported only as short-lived intermediates generated under superacidic conditions or by flash photolysis. Attempts to prepare a m-terphenyl acylium cation by fluoride abstraction from a benzoyl fluoride gave rise to an isolable 9-hydroxy fluorenyl cation that formed by an intramolecular electrophilic attack at a flanking mesityl group prior to a 1,2-methyl shift and proton transfer to oxygen.     

Characterization of Benzo[a]naphtho[2,3-f]pentalene: Interrelation between Open-shell and Antiaromatic Characters Governed by Mode of the Quinoidal Subunit and Molecular Symmetry

The singlet open-shell character and antiaromaticity are intriguing features in π-conjugated carbocycles. These two exhibit similar chemical and physical properties. However, they rarely coexist in the same molecule. Understanding the interrelation between the open-shell and antiaromatic characteristics in the same molecule is crucial to control the electronic properties. Herein we describe the synthesis and characterization of a new member of diareno[a,f]pentalene, benzo[a]naphtho[2,3-f]pentalene 6 . Unlike its isomer 5 with a closed-shell ground state, 6 exhibits an appreciable open-shell character and a moderate antiaromatic feature. The behaviors of the open-shell index (y₀) against the difference of the proton chemical signal (Δδ(H¹)) between pentalenide dianions/neutral pentalenes for our reported pentalenes 1 , 4 , 5 , and 6 give a thought-provoking conclusion about the interrelation between open-shell and antiaromatic characteristics in this series. The mode of the incorporated quinoidal moiety and the formal molecular symmetry are critical to balance these two characteristics.     

Inside Cover: Perfluoropentaphenylborole (Angew. Chem. Int. Ed. 16/2009)

Perfluoroaryl boranes are an important class of organometallic Lewis acids. The synthesis of perfluorinated compounds brings special challenges to tried‐and‐true synthetic methodologies. In their Communication on page 2955 ff., W. E. Piers and co‐workers present the synthesis of a new, fully fluorinated heterocyclic borane that is also a member of the rare antiaromatic borole class of compounds. The route relies on normally facile transmetallation reactions made more difficult by the electron‐withdrawing C₆F₅ groups of the target product.

     

Tetraalkoxyphenanthrene‐Fused Dehydroannulenes: Synthesis,Self‐Assembly,and Electronic,Optical, and Electrochemical Properties

Novel tetraalkoxyphenanthrene‐fused dehydro[12]‐, [18]‐, and [24]annulenes 1 – 3 were synthesized by using Cu‐mediated or Pd‐catalyzed oxidative macrocyclization reactions as key steps, and their electronic, optical, and electrochemical properties have been investigated in detail. X‐ray crystallographic analysis of a single crystal of 1 a demonstrated that the molecules were arranged longitudinally in a slipped π‐stacked fashion to form a 1D column. ¹H NMR and UV/Vis spectroscopic and cyclic voltammetric analysis in conjugation with nucleus‐independent chemical shift (NICS) calculations for 1 – 3 support that the annulation at the 9,10‐positions of phenanthrene to the dehydroannulene ring enhances the tropicity and decreases the HOMO–LUMO gaps of the molecules relative to the benzannulation and that 1 possesses an antiaromatic character. Self‐association behavior due to π–π stacking in CDCl₃ was observed for 1 and 2 and was quantified by concentration‐dependent ¹H NMR spectroscopic measurements. The self‐assembly of 1 and 2 into well‐defined 1D superstructures with high aspect ratios were obtained, and the morphology and crystallinity of these compounds were investigated by means of SEM and wide‐angle X‐ray diffraction (WAXD) measurements. Furthermore, it was shown that 1 b and 2 b display liquid‐crystalline phases by means of differential scanning calorimetry, polarizing optical microscopy, and variable‐temperature WAXD measurements.