2,11-Dibromo-13,14-dimesityl-5,8-dioxapentaphene: A Stable and Twisted Polycyclic System Containing the o-Quinodimethane Skeleton

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.

Thermodynamically Stable o-Quinodimethane: Synthesis, Structure, and Reactivity

Thermal isomerization of cyclobutaphenanthrene to o-quinodimethane was investigated. Sterically congested substituents or electron-donating substituents on the four-membered ring promoted the ring-opening, affording o-quinodimethane in a relatively stable form. Isolation of the newly prepared o-quinodimethane allowed its structural elucidation and investigation of its potential reactivities. Dual [4+2] cycloaddition of an aryne and o-quinodimethane afforded tetrabenzopentacene, demonstrating the synthetic application of the isolated compound.

Stable N,N'-Diarylated Dihydrodiazaacene Radical Cations

Three stable N,N’‐diarylated dihydroazaacene radical cations were prepared by oxidation of neutral N,N’‐diarylated dihydroazaacenes synthesized via palladium‐catalyzed Buchwald‐Hartwig aminations of aryl iodides with N,N’‐dihydroazaacenes. Both neutral as well as oxidized species were investigated via UV‐vis spectroscopy, single crystal analysis, and DFT calculations. All the radical cations are surprisingly stable—their absorption spectra in dichloromethane remain unchanged in ambient conditions for at least 24 hours.

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

We present the synthesis and the spin switching efficiencies of Ni(II)-porphyrins substituted with azopyridines as covalently attached photoswitchable ligands. The molecules are designed in such a way that the azopyridines coordinate to the Ni ion if the azo unit is in cis configuration. For steric reasons no intramolecular coordination is possible if the azopyridine unit adopts the trans configuration. Photoisomerization of the azo unit between cis and trans is achieved upon irradiation with 505 nm (trans→cis) and 435 nm (cis→trans). Concurrently with the isomerization and coordination/decoordination, the spin state of the Ni ion switches between singlet (low-spin) and triplet (high-spin). Previous studies have shown that the spin switching efficiency is strongly dependent on the solvent and on the substituent at the 4-position of the pyridine unit. We now introduced thiol, disulfide, thioethers, nitrile and carboxylic acid groups and investigated their spin switching efficiency.

An air-persistent oxyallyl radical cation with simple di(methyl)amino substituents

We report an experimental and theoretical study of the 1,1,3,3-tetrakis-di(methylamino)oxyallyl radical cation. Despite simple substituents with minimal steric hindrance, this radical was found to be stable under an inert atmosphere and persistent for several hours in well-aerated solutions.

Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles

Chemical or electrochemical one-electron oxidation of 5-N-arylaminothiazoles was found to afford stable radical cations. For chemical oxidation, 1 equivalent of [(4-BrC6H4)3N][SbCl6] (Magic Blue, MB) was added to CH2Cl2 solutions of the thiazoles, and the thus-obtained radicals showed light absorption in the near-infrared region. Electrochemical oxidation also led to bathochromic shifts in the absorption bands, and the obtained spectra were similar to those derived from the chemically oxidized species. These radicals afforded electron paramagnetic resonance (EPR) spectra that are consistent with the notion of stable nitrogen radicals (half-life≤385 h). The EPR spectrum of a thiazole containing 4-dimethylaminophenyl groups on the nitrogen atom at the 5-position changed significantly upon adding >3 equivalents of MB. Details of the electronic structures of the experimentally obtained radical cations were generated from theoretical calculations.