Kenichi Kato

Organic radicals can potentially play important roles in functional materials owing to an unpaired electron, but they are usually highly reactive and difficult to use. Therefore, stabilization of organic radicals is important. Among organic radicals, carbon-centered radicals are promising because of their trivalent nature, which enables structural diversity and elaborate designs, but they are also less stable because of the reactivities towards carbon-carbon bond formation and atmospheric oxygen

Pillar[<i>n</i>]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral invers

Stable helical radicals are promising multi-functional molecules in light of intriguing magnetic and chiroptical properties. Attempts were made to extend diphenylmethyl-fused Ni^II porphyrin radical to helical system as the first air-stable organic neutral helical radicals. Intramolecular Pd-catalyzed twofold C-H arylation of methyl- or methoxy-introduced meso-diphenylmethyl Ni^II porphyrins gave a mixture of the target and rearranged radicals. Oxidative fusion reaction of me

The direct fusion of a diphenylmethane segment to a Ni(II) 5,10,15-triarylporphyrin with three linkages furnished an air- and moisture-stable neutral radical through unexpected and spontaneous oxidation. This radical was demetalated by treatment with H2 SO4 and CF3 CO2 H to provide the corresponding free-base radical. These porphyrin radicals are very stable owing to spin delocalization and have been fully characterized through UV/Vis/NIR absorption spectroscopy, X-ray crystallographic analysis,

Trimethylenemethane (TMM) diradical is the simplest non-Kekulé non-disjoint molecule with the triplet ground state (ΔE_ST =+16.1 kcal mol^-1 ) and is extremely reactive. It is a challenge to design and synthesize a stable TMM diradical with key properties, such as actual aliphatic TMM diradical centers and the triplet ground state with a large positive ΔE_ST value, since such species provide detailed information on the electronic structure of TMM diradical. Herein w

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in t

Abstract Organic radicals can potentially play important roles in functional materials owing to an unpaired electron, but they are usually highly reactive and difficult to use. Therefore, stabilization of organic radicals is important. Among organic radicals, carbon‐centered radicals are promising because of their trivalent nature, which enables structural diversity and elaborate designs, but they are also less stable because of the reactivities towards carbon–carbon bond formation and atmospher

Installation of various substituents is a reliable and versatile way to alter the properties of macrocyclic molecules, but high-yield and controlled methods are not always available especially for multifold reactions. Herein, we report 10- and 12-fold introduction of aryl substituents onto both rims of cylinder-shaped pillar[<i>n</i>]arenes, which usually have alkoxy substituents slanting to the cylinder axes. Although alkoxy pillar[5]arenes exist as <i>D</i>₅-symmetric enantiomeric p

Spatial arrangement of multiple planar chromophores is an emerging strategy for molecule-based chiroptical materials <i>via</i> easy and systematic synthesis. We attached five pyrene planes to a chiral macrocycle, pillar[5]arene, producing a set of chiroptical molecules in which pyrene-derived absorption and emission were endowed with dissymmetry by effective transfer of chiral information. The chiroptical response was dependent on linker structures and substituted patterns because of variable i

Control of symmetry is fundamental in molecular design with aimed properties. Herein we report a set of chiroptical C₅ -symmetric molecules with variable dipolar structures based on a rim-differentiated cylindrical macrocycle, pillar[5]arene. Incorporation of electron-withdrawing ester groups formed an explicit two-sided structure, leading to increase in response wavelength and luminescence efficiency. On the other hand, chiroptical measurement of separated enantiomers revealed that s

Abstract The direct fusion of a diphenylmethane segment to a Ni II 5,10,15‐triarylporphyrin with three linkages furnished an air‐ and moisture‐stable neutral radical through unexpected and spontaneous oxidation. This radical was demetalated by treatment with H 2 SO 4 and CF 3 CO 2 H to provide the corresponding free‐base radical. These porphyrin radicals are very stable owing to spin delocalization and have been fully characterized through UV/Vis/NIR absorption spectroscopy, X‐ray crystallograph

A reaction sequence of 2-(diphenylsilyl)phenylation by Negishi coupling and intramolecular sila-Friedel-Crafts reaction has been explored for the synthesis of mono-triphenylsilane-fused porphyrins 5 M and 6 M (M= Ni, Zn) and bis-triphenylsilane-fused porphyrins 7 M and 8 Ni. A triply linked triphenylsilane-fused Ni(II) porphyrin, 13 Ni, was synthesized in a stepwise manner involving the above reaction sequence and a final Pd-catalyzed C-H activating arylative cyclization. The silicon atom in 13

Abstract One-dimensional (1D) channel structures, have spaces, entrances, and exits of specific sizes, therefore guest molecules can travel through the channel from the entrance to the exit. Such 1D channel structures are therefore ideal platforms for transporting molecules. In this mini-review, we will discuss the preparation of molecular-scale continuous 1D channels from pillar[n]arenes by using non-covalent interactions and covalent bonding. Because of their highly symmetrical structures, pil

The role of protein kinase C activation in a coupling of Ca2+-mobilizing receptors/GTP-binding protein/phospholipase C was examined using Xenopus oocytes before and after microinjection of mRNA purified from rat brains. Under voltage-clamp conditions, although the phorbol ester TPA per se never elicited any changes in ionic conductance, chloride current responses of mRNA-injected cells to 5-hydroxytryptamine and acetylcholine (ACh) were suppressed by an 8-min pretreatment of 12-O-tetradecanoyl-4

meta- and para-Phenylenediamine-fused nickel(II) porphyrin dimers were synthesized by S_N Ar reaction of meso,β,β-trichloro nickel(II) porphyrin with meta- and para-phenylenediamines and subsequent Pd-catalyzed intramolecular C-H arylation. Their tetrachlorinated dication diradicals are very stable, allowing SQUID magnetometry and revealing clear open-shell characters for both meta and para isomers with ferro- and anti-ferromagnetic interactions, respectively. The nitrogen analogue of