Hiroshi Shinokubo

Unambiguous Identification of Möbius Aromaticity for meso-Aryl-Substituted [28]Hexaphyrins(1.1.1.1.1.1)

meso-Aryl-substituted [28]hexaphyrins(1.1.1.1.1.1) have been examined by (1)H, (13)C, and (19)F NMR spectroscopies, UV-vis absorption spectroscopy, magnetic circular dichroism spectroscopy, and single-crystal X-ray diffraction analysis. All of these data consistently indicate that [28]hexaphyrins(1.1.1.1.1.1) in solution at 25 degrees C exist largely as an equilibrium among several rapidly interconverting twisted Möbius conformations with distinct aromaticities, with a small contribution from a planar rectangular conformation with antiaromatic character at slightly higher energy. In the solid state, [28]hexaphyrins(1.1.1.1.1.1) take either planar or Möbius-twisted conformations, depending upon the meso-aryl substituents and crystallization conditions, indicating a small energy difference between the two conformers. Importantly, when the temperature is decreased to -100 degrees C in THF, these rapid interconversions among Möbius conformations are frozen, allowing the detection of a single [28]hexaphyrin(1.1.1.1.1.1) species having a Möbius conformation. Detailed analyses of the solid-state Möbius structures of compounds 2b, 2c, and 2f showed that singly twisted structures are achieved without serious strain and that cyclic pi-conjugation is well-preserved, as needed for exhibiting strong diatropic ring currents. Actually, the harmonic-oscillator model for aromaticity (HOMA) values of these structures are significantly large (0.85, 0.69, and 0.71, respectively), confirming the first demonstration of stable Möbius aromatic systems consisting of free-base expanded porphyrins without the assistance of metal coordination.

Synthesis of directly connected BODIPY oligomers through Suzuki-Miyaura coupling.

Treatment of a meso-arylboron dipyrrin (BODIPY) with NBS provides mono- and dibrominated BODIPYs at the 2- and 6-positions in excellent yields with high regioselectivity. Brominated products can be employed as a nice building block for the synthesis of a variety of BODIPY derivatives through Suzuki-Miyaura coupling. Because of a lack of substituents at the 1,3,5,7-positions, a directly β-β-linked BODIPY dimer exhibits a completely coplanar conformation of BODIPY units, offering effective π-conjugation.

A Porphyrin Nanobarrel That Encapsulates C60

A porphyrin nanobarrel, 1, that can encapsulate C(60) effectively was prepared via a concise coupling route. The structures of both 1 and C(60)@1 were confirmed by single-crystal X-ray diffraction analysis.

Facile Synthesis of Biphenyl-Fused BODIPY and Its Property

A biphenyl-fused BODIPY was synthesized through a facile oxidative cyclization of peripheral aryl-substituents at the β-position of the BODIPY unit. The extended π-system of the fused BODIPY induces near-infrared (NIR) absorption and strong π-π interactions in the solid state. These features are beneficial for the application of the dye as a functional material. The biphenyl-fused BODIPY dye was demonstrated to exhibit photocurrent conversion ability on the basis of its n-type semiconducting property.

Marriage of porphyrin chemistry with metal-catalysed reactions.

The development of porphyrin synthesis by means of transition metal-catalyzed reactions is explored in this feature article. Porphyrins have been receiving much attention in a wide area of chemistry as functional dyes, non-linear optical materials, ligands for a variety of metals, structural motifs in supramolecules, and so forth. However, they have been merely recognized as a reaction substrate in transition metal-catalyzed transformations. Recently, application of such new methodologies to porphyrin synthesis has proven to be very powerful to create new types of porphyrinic compounds, which have their own intriguing structures and properties. New transformations on porphyrins via transition metal catalysis offer us prospects of new designs of architectures, thus facilitating further development of this important class of functional molecules.

Synthesis of Arylated Perylene Bisimides through C−H Bond Cleavage under Ruthenium Catalysis

Treatment of perylene bisimide (PBI) with various arylboronates in the presence of a ruthenium catalyst provides tetraarylated PBIs at 2,5,8,11-positions in good yields with perfect regioselectivity. The electronic nature of the introduced aryl substituents has a significant impact on their optical and electronic properties. This protocol has been applied to the synthesis of a water-soluble emissive PBI derivative.

Regioselective Ru-catalyzed direct 2,5,8,11-alkylation of perylene bisimides.

Perylene tetracarboxylic acid bisimides (PBIs) are an important class of dyes and pigments for widespread practical use, which have been extensively investigated for a long time both in academia and industry. Recently, they have also received much attention as n-type semiconducting materials. Furthermore, owing to high fluorescence quantum efficiency and photostability, they have been a popular motif for single-molecule spectroscopy. Chemical modifications of PBIs are quite important to gain desirable photophysical and electronic properties as well as solubility. In spite of their rich material chemistry, functionalization of the perylene core of PBIs relies on halogenation of the bay area (1,6,7,12-positions) and subsequent transformations (Scheme 1). Selective functionalization at 2,5,8,11-positions remains unavailable to date. Here we wish to disclose the first selective synthesis of 2,5,8,11-substituted PBIs. We have envisioned the potential of direct functionalization of PBIs by organometallic and catalytic means: ruthenium-catalyzed C H bond activation and addition strategy, namely, the Murai–Chatani–Kakiuchi protocol (Scheme 2). This reaction can introduce alkyl substituents to the proximal position of the directing groups. Successful installation of alkyl chains at the 2,5,8,11-positions of PBIs would allow greater modification of properties in the solid state or condensed phase. The reaction procedure is quite simple. A mixture of bis(N-ethylpropyl)PBI 1a and trimethylvinylsilane was heated in mesitylene at 165 8C for 60 h in the presence of [a] Prof. Dr. H. Shinokubo Department of Applied Chemistry Graduate School of Engineering, Nagoya University Chikusa-ku, Nagoya 464-8603 (Japan) E-mail : hshino@apchem.nagoya-u.ac.jp [b] S. Nakazono, Y. Imazaki, Prof. Dr. A. Osuka Department of Chemistry, Graduate School of Science Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan) E-mail : osuka@kuchem.kyoto-u.ac.jp [c] H. Yoo, J. Yang, Prof. Dr. D. Kim Department of Chemistry, Yonsei University Seoul 120-749 (Korea) E-mail : dongho@yonsei.ac.kr [d] Dr. T. Sasamori, Prof. Dr. N. Tokitoh Institute for Chemical Research Kyoto University, Kyoto 611-0011 (Japan) [e] T. C dric, Prof. Dr. H. Kageyama Department of Chemistry, Graduate School of Science Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan) E-mail : kage@kuchem.kyoto-u.ac.jp Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/chem.200901318. Scheme 1. Functionalization of perylene bisimides.

Gram‐Scale Synthesis of Nickel(II) Norcorrole: The Smallest Antiaromatic Porphyrinoid

Small is beautiful: A ring-contracted sister of porphyrin, norcorrole, has been synthesized efficiently as a stable molecule by a nickel-templated strategy. The norcorrole complex is stable but exhibits a distinct antiaromatic character according to the Hückel rule. Oxidation of the norcorrole complex provides an aromatic oxacorrole complex.

Intermolecular Oxidative Annulation of 2-Aminoanthracenes to Diazaacenes and Aza[7]helicenes†

Aniline is oxidized into so-called “aniline black”, well-known black pigments that are a mixture of oligomeric materials containing C N double bonds and fused structures. Since such an oxidative fusion reaction of aniline derivatives is usually uncontrollable and provides many isomers and oligomers, it has rarely been recognized as a synthetically useful transformation. However, the selective oxidation of aromatic amines should provide a powerful protocol to combine two aromatic units into one extended p system if the substrates and reaction conditions are carefully designed. Recently, oligoacenes containing pyrazine units have attracted much attention as promising compounds for electron-transporting materials because of their resistance to oxidation relative to the parent oligoacenes. However, the synthetic strategy for this type of azaacenes has mainly been limited to the classic condensation of ortho-quinone derivatives with aromatic ortho-diamines, both of which are often unstable under air. Here we disclose the selective oxidative fusion of 2-aminoanthracenes mediated by 2,3-dichloro-5,6dicyano-1,4-benzoquinone (DDQ) to provide pyrazine-fused bisanthracenes in high yields. Our approach, which makes use of the more-stable monoamino substrates, would be useful for the construction of various pyrazine-fused oligoacenes. Furthermore, we also found that pyrrole-fused bisanthracenes could be formed under slightly modified conditions. The pyrrole-fused dimer can be regarded as an aza[7]helicene with a stable helical conformation that exhibits circular dichroism (CD) and circularly polarized luminescence (CPL) properties. We used 2-aminoanthracene 1a, the two triisopropylsilylethynyl groups of which enhance the solubility of the starting material and products. We found that the oxidation of 1a with DDQ in CHCl3 (Scheme 1) afforded a pyrazine-fused dimer 2a in 43 % yield as a single regioisomer (Table 1, entry 1). The H NMR spectrum of 2 a was indicative of a C2h symmetrical structure, thus indicating a zig-zag-type structure fused by a pyrazine linkage. Furthermore, another product 3a was obtained as a more polar material in 48 % yield. The H NMR spectrum showed 3a was unsymmetrical, with one NH proton signal detected at d = 9.12 ppm. The parent mass ion peaks of 3a at m/z = 1087.6716 (calcd for (C72H97NSi4) + = 1087.6693) suggested a loss of one nitrogen atom from 2a. On the basis of these data, we assigned 3a as a pyrrole-fused dimer. Finally,

Iridium-Catalyzed Direct Tetraborylation of Perylene Bisimides

Treatment of perylene bisimides (PBIs) with bis(pinacolato)diboron in the presence of an iridium catalyst provides tetraborylated PBIs at 2,5,8,11-positions in good yields with perfect regioselectivity. The planar structure of the perylene core has been confirmed by X-ray diffraction analysis. Oxidation of tetraborylated PBI with hydroxylamine hydrochloride affords tetrahydroxy PBI in excellent yield, which exhibits a substantially blue-shifted absorption spectrum due to an intramolecular hydrogenbonding interaction between carbonyl and hydroxy groups.