PdII Complexes of [44]‐ and [46]Decaphyrins: The Largest Hückel Aromatic and Antiaromatic,and Möbius Aromatic Macrocycles

Reductive metalation of [44]decaphyrin with [Pd₂(dba)₃] provided a Hückel aromatic [46]decaphyrin Pd^II complex, which was readily oxidized upon treatment with DDQ to produce a Hückel antiaromatic [44]decaphyrin Pd^II complex. In CH₂Cl₂ solution the latter complex underwent slow tautomerization to a Möbius aromatic [44]decaphyrin Pd^II complex which exists as a mixture of conformers in dynamic equilibrium. To the best of our knowledge, these three Pd^II complexes represent the largest Hückel aromatic, Hückel antiaromatic, and Möbius aromatic complexes to date.     

Aromaticity of N-heterocyclic carbene and its analogues: Magnetically induced ring current perspective

The N-heterocyclic carbene, imidazole-2-ylidene, and its main group (13-15) analogues contain cyclically conjugated 6π electrons. Experimental ¹H nuclear magnetic resonance (NMR) spectra suggest an increase in aromaticity along a period from left to right. Whereas the order along a group is as follows: period 2 > period 5 > period 4 > period 3 due to change in structure. To understand the order of aromaticity, the magnetically induced ring currents of the molecules are calculated using aromatic ring current shielding, gauge-including magnetically induced currents (GIMIC) method and Stanger's σ-model applying the gauge-including atomic orbitals NMR technique. It is found that GIMIC best describes the order of aromaticity especially along a group where current-profile changes on the bivalent atom down a group due to change in electron density. Moreover, the GIMIC provides the visualization of current by sign modulus and the anisotropy of the induced current density plots.     

A Stable All‐Thiophene‐Based Core‐Modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at Different Oxidation States

A soluble and stable core‐modified [38]octaphyrin, MC‐T8 , containing eight thiophene rings was synthesized by Yamamoto coupling followed by oxidative dehydrogenation. X‐ray crystallographic analysis revealed a nearly planar backbone, and the molecule is globally aromatic with a dominant 38π conjugation pathway. The dication MC‐T8²⁺ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC‐T8⁴⁺ becomes aromatic again, with a shallow‐bowl‐shaped geometry. Both the neutral compound and the dication demonstrated open‐shell diradical character with a small singlet–triplet energy gap (?2.70 kcal mol^?1 for MC‐T8 and ?3.78 kcal mol^?1 for MC‐T8²⁺ ), and they are stable owing to effective spin delocalization.     

Using hydrogen bonds to direct the assembly of crowded aromatics

This Minireview details the design, synthesis, and self-assembly of a new class of crowded aromatics that form columnar superstructures. The assembly of these subunits produces helical and polar stacks, whose assembly can be directed with electric fields. In concentrated solutions, these self-assembled helical rods exhibit superhelical arrangements that reflect circularly polarized light at visible wavelengths. Depending on the side chains employed, spin-cast films yield either polar monolayers or isolated strands of molecules that can be visualized with scanning probe microscopy. Also detailed herein are methods to link these mesogens together to produce monodisperse oligomers that fold into defined secondary conformations.     

Structure,stability, and aromaticity of M?SubPc (MB,Al, and Ga): Computational study

A theoretical investigation on the structure, stability, and aromaticity of M‐subphthalocyanine (M? SubPc; M?B, Al, and Ga) was performed at the B3LYP/6‐31+G*//B3LYP/6‐31G* level. The comparison between M? SubPc and the corresponding M? phthalocyanine (M? Pc) was considered. The geometry optimization of the M? SubPc shows that in the Al? SubPc and Ga? SubPc, the steric repulsions among the three azacoupled isoindole moieties increase, as to their macrocycles tend to be far from planarity. The binding energies of Cl? M … aza‐coupled isoindole corrected by the basis set superposition error (BSSE), and the nucleus‐independent chemical shift (NICS) values at the ring center, which are a simple and effective local aromaticity probe, were calculated. The results show that Al? SubPc is less stable than both B? SubPc and Al? Pc for larger steric repulsion, smaller binding energy, and weaker aromaticity. In the same way, Ga? SubPc is less stable than both B? SubPc and Ga? Pc. In addition, the ring expansion reactivity occurring in B? SubPc was confirmed by the global aromaticity mirrored by the electrophilicity index ω values. Therefore, the Al? SubPc and Ga? SubPc remain unknown, while the corresponding compounds Al? Pc and Ga? Pc are known experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005