Learning from Vitamin B12-mediated reactions: Cobalt(III)–carbon bond‐assisted catalytic C–H difluoroacylation of (hetero)arenes by controlled‐potential electrolysis

Md. J. Hossain, Toshikazu Ono, Yoshio Yano, Yoshio Hisaeda

ChemElectroChem, 2019, in press. 

This paper is dedicated to special collections for  “Organic Electrosynthesis”, Guest Editors: Profs.Robert Francke, Dan Little, and Shinsuke Inagi.

有機化合物へのジフルオロアルキル基の導入は、医薬品、農薬、機能性材料等の開発の観点から重要です。本研究では、ビタミンB12酵素反応に学び、電解ジフルオロアルキル化反応を達成しました。以前に報告したビタミンB12を用いた電解トリフルオロメチル化反応、パーフルオロアルキル化反応 (Chem. Commun., 2017, 53, 10878-10881)の続報となります。

The synthesis of difluoromethylated (CF2R) (R = H, alkyl/aryl, CO2R, etc) compounds has received considerable attention in recent years. In this study, the cobalt(III)–carbon bond‐mediated catalytic C–H difluoroacylation of unactivated arenes and heteroarenes using BrCF2CO2Et is reported. This catalytic cycle is based on a valence change of the cobalt catalyst, a naturally derived vitamin B12 derivative, driven by controlled‐potential electrolysis at ‐0.8 V vs. Ag/AgCl under visible‐light irradiation in DMSO. A broad substrate scope is demonstrated and two compounds were characterized by X‐ray crystal structures. Mechanistic studies showed that the reaction proceeds through a radical pathway mediated by homolytic cleavage of the cobalt(III)–carbon bond. Over 100 turnover number was observed due to the inherent stability of vitamin B12 framework. This naturally derived catalytic system has potential applications in medicinal chemistry and materials science.


Flexible-Color Tuning and White-Light Emission in Three-, Four-, and Five-component Host/Guest Co-crystals by Charge–Transfer Emissions as well as Effective Energy Transfers

Toshikazu Ono, Yoshio Hisaeda

J. Mater. Chem. C, in press (Hot Paper)

本研究では、3成分、4成分、5成分結晶の創製を通じて、励起光照射下にて多色・白色発光を示す超分子発光体の開発を行いました。ナフタレンジイミド誘導体(NDI)とトリスペンタフルオロフェニルボラン(TPFB)から形成される超分子ホスト(NDI-TPFB)が、複数種の芳香族ゲストを取り込み、結晶を生成します。得られた多成分結晶は、NDIとゲストの間で発光性電荷移動錯体を形成し、取り込むゲスト分子の種類に依存して青色〜近赤外発光を示します。水色と橙色発光を示すゲスト分子を混合することで、白色発光が得られることを見出しました。本論文は高い評価を受け、J. Mater. Chem. C誌のHot Paperに選出されました。

Three-, four-, and five-component host/guest crystals with multi-color and white light emission is described. Our strategy is based on confinement of aromatic donor guests in supramolecular acceptor hosts. The supramolecular acceptor hosts (NDI–TPFB) were composed of N,N’-dipyrid-3-yl-1,4,5,8-naphthalenediimide (NDI) with two tris(pentafluorophenyl)borane (TPFB) linked by boron–nitrogen dative bonds as Lewis acid–base pairs, which spontaneously formed upon mixing the components. In the first part, a set of three-component crystals with 14 different aromatic guests were characterized to elucidate the structure–property relationships. In the latter part, a series of 17 types of four- and five-component crystals were formed with the use of binary or ternary guest inclusion systems, and their structural and photophysical properties were investigated. Among them, 14 types of crystals were formed effectively without destroying the crystal structure, as determined by X-ray diffraction and fluorescence microscope. Notably, flexible color tuning, including white light emission, was realized by tuning the guest ratio and the combinations. Various intermolecular interactions such as C–H•••F interactions, π-π stacking, charge-transfer interactions, and inclusion phenomena were important to forming the crystals. This approach yields a rational solution of multicomponent crystals could be potentially useful for obtaining novel photofunctional solid-state systems.


Visible Light-driven One-pot Amide Synthesis Catalyzed by the B12 Model Complex under Aerobic Conditions

Hui Tian, Hisashi Shimakoshi, Toshikazu Ono, Yoshio Hisaeda

ChemPlusChem, 2019, in press.

DOI: 10.1002/cplu.201800522

本研究では、可視光を駆動力とし、空気中の酸素を酸素源として、有害なトリクロロメチル化合物からワンポットで、有用なアミド化合物を合成する手法を見出しました。触媒には天然由来のビタミンB12の誘導体を用い、クーリンで高効率な反応システムの開発に成功しました。本論文は、Front coverに採択され、またeditor’s choiceに選出され、とても高い評価を受けました。本研究は、分子システム化学国際コース一期生の田輝さん(博士)の研究成果です。

A visible light responsive catalytic system with the B12 complex as the catalyst and [Ir(dtbbpy)(ppy)2]PF6 as the photosensitizer was developed, which provides a convenient and efficient way for the amide synthesis.  Based on this method, trichlorinated organic compounds were converted to amides in the presence of an amine under aerobic conditions at room temperature in an one-pot procedure.  As this protocol is free from hazardous reagents, extra additives, noble metals, and dangerous gas, the present method provides a novel and efficient approach for the amide synthesis under mild and easily controlled conditions.


Gram-scale synthesis of porophycene derivatives by oxidative macrocyclizations of E/Z-mixed 5,6-diaryldipyrroethenes 

Toshikazu Ono, Ning Xu, Daiki Koga, Toshihiro Ideo, Manabu Sugimoto, Yoshio Hisaeda

RSC Adv. 2018, 8, 39269-39273. (Open Access)

グラムスケールのポルフィセン合成法に関する報告です。5,6-ジアリルジピロロエテンを前駆体とし、酸触媒と酸化剤を最適化することにより、3段階合成で総収率20%を超えるポルフィセン誘導体の合成を達成しました。熊本大学の杉本先生との共同研究の成果です。Open Accessの論文です。

The gram-scale production of porphycene derivatives is reported. This has been achieved by acid-catalyzed ring closure of an E/Z-mixture of 5,6-diaryldipyrroethenes, resulting in the formation of meso-tetraarylporphycenes in yields of up to 80%. E/Z-isomerization of the 5,6-diaryldipyrroethenes under acidic conditions was key to proceed the effective macrocyclization.


Switching of Monomer Fluorescence, Charge‐Transfer Fluorescence, and Room‐Temperature Phosphorescence Induced by Aromatic Guest Inclusion in a Supramolecular Host

Toshikazu Ono, Ai Taema, Aiko Goto, Yoshio Hisaeda

Chem. Eur. J. 2018, 24, 17487-17496. (Cover Picture)

超分子ホストとゲストから構成される有機固体発光材料の創製を行い、ゲスト分子の種類に依存した(i)モノマー蛍光発光、(ii)電荷移動錯体からの蛍光発光、(iii)常温燐光発光材料、となる材料を見出しました。結晶のすりつぶし、ゲスト除去に伴う興味深い発光特性チューニングを達成しました。本研究は高い評価を受け、Chem Eur J誌のHot Paperに選ばれました。Cover Pictureに選ばれました。

Crystal engineering of three‐component crystals with guest‐dependent photoluminescence switching, including (i) crystallization‐induced emission enhancement, (ii) intermolecular charge‐transfer emission, and (iii) room‐temperature phosphorescence under ultraviolet irradiation, was demonstrated. This strategy was based on the confinement of aromatic guests in a supramolecular host (denoted as EBPDI‐TPFB) composed of 5,5′‐(ethyne‐1,2‐diyl)bis(2‐pyridin‐3‐yl‐isoindoline‐1,3‐dione (EBPDI) with two tris(pentafluorophenyl)borane (TPFB) molecules linked by B−N dative bonds that acted as Lewis pairs. The single‐crystal X‐ray structures of complexes with eight different guests were collected, revealing that the size and/or shape of the supramolecular host EBPDI‐TPFB was modulated by the included guest molecules. The excellent guest inclusion ability of EBPDI‐TPFB allowed systematic photoluminescence regulation of the complexes, which exhibited multicolor emissions in the crystalline state. Photoluminescence switching characteristics of the complexes were observed upon removing the guests or mechanical grinding of the crystals. These results indicated that using the host–guest chemistry of multicomponent crystals not only facilitates crystallization, but also can reveal hidden optical functions by combining molecules of interest, which should contribute to the fields of physical chemistry and materials science.


Learning from B12 enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

Keishiro Tahara, Ling Pan, Toshikazu Ono, Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553-2567. 

ビタミンB12触媒に関するレビューがBeilstein Journal of Organic Chemistryに掲載されました。兵庫県立大学の田原先生、東北師範大学の藩先生との共同執筆です。

Cobalamins (B 12) play various important roles in vivo. Most B 12-dependent enzymes are divided into three main subfamilies: adenosylcobalamin-dependent isomerases, methylcobalamin-dependent methyltransferases, and dehalogenases. Mimicking these B 12 enzyme functions under non-enzymatic conditions offers good understanding of their elaborate reaction mechanisms. Furthermore, bio-inspiration offers a new approach to catalytic design for green and eco-friendly molecular transformations. As part of a study based on vitamin B 12 derivatives including heptamethyl cobyrinate perchlorate, we describe biomimetic and bioinspired catalytic reactions with B 12 enzyme functions. The reactions are classified according to the corresponding three B 12 enzyme subfamilies, with a focus on our recent development on electrochemical and photochemical catalytic systems. Other important reactions are also described, with a focus on radical-involved reactions in terms of organic synthesis.


Synthesis of Trifluoromethylated B12 Derivative and Photolysis of Cobalt(III)–Trifluoromethyl Bond

Toshikazu Ono, Kosuke Wakiya, Md. Jakir Hossain, Hisashi Shimakoshi, Yoshio Hisaeda

Chem. Lett. 2018, 47, 979-981. 

トリフルオロメチル基を軸配位子に持つビタミンB12誘導体とその光分解挙動に関する報告です。以前に報告したビタミンB12を用いた電解トリフルオロメチル化反応、パーフルオロアルキル化反応 (Chem. Commun., 2017, 53, 10878-10881)にて、Co-CF3結合のホモリシス開裂によるトリフルオロメチルラジカルの発生が触媒反応の中間体であることを同定しました。

A vitamin B12 derivative with a trifluoromethyl group as an axial ligand, heptamethyl trifluoromethylaquacobyrinate perchlorate, [[(CF3)(H2O)Cob(III)7C1ester]ClO4], is prepared and characterized by elemental analysis, 1H NMR, 19F NMR, ESI-MS, UV-vis absorption, and cyclic voltammetry. The Co–CF3 complex shows homolysis of the Co(III)–CF3 bond under visible light irradiation, which releases a CF3 radical that can be detected by a radical trapping experiment.


Piezofluorochromism in Charge‐Transfer Inclusion Crystals: The Influence of High Pressure versus Mechanical Grinding

Toshikazu Ono, Yoshifumi Tsukiyama, Ai Taema, Hiroyasu Sato, Hidetoshi Kiyooka, Yuma Yamaguchi, Ayumi Nagahashi, Manami Nishiyama, Yuichi Akahama, Yosiki Ozawa, Masaaki Abe, Yoshio Hisaeda

ChemPhotoChem 2018, 2, 416-420. (Front Cover)


The   distinct   piezochromic   luminescent   responses   of charge-transfer  inclusion  crystals,  which  consist  of  smallaromatic guest molecules with naphthalenediimide derivatives,are reported. Reversible multichromism is observed over theentire visible region in response to high pressure, whereas aweak response to mechanical grinding is evident. High-pressuresingle-crystal X-ray diffraction analysis and TD-DFT calculationsclearly suggest that high compression induces a closer arrange-ment with a short interfacial distance between small aromaticguest molecules and naphthalenediimide derivatives, which isproposed as the origin of the drastic luminescent color change.


First entry into nonmetal-centred porphycenes: synthesis of a phosphorus(V) complex of octaethylporphycene

Masaaki Abe, Hiroto Mukotaka, Taro Fujioka, Toru Okawara, Kei Umegaki, Toshikazu Ono, Yoshio Hisaeda

Dalton Trans. 2018, 47, 2487-2491. (Front Cover)


世界初のリンポルフィセンの合成と物性評価を報告しました。Dalton Transactionの表紙を飾りました!

A phosphorus(V) complex of porphycene [P(OEPc)(OMe)2]PF6 (OEPc = 2,3,6,7,12,13,16,17-octaethylporphycenato dianion) has been synthesized and structurally characterized as the first porphycene derivative incorporating nonmetal elements in the macrocyclic cavity. An extremely low energy level of the LUMO is observed, which is rationalized by the low-lying π* orbital of the porphycene ring coupled with the insertion of the highly-inductive pentavalent phosphorus centre. The compound is luminescent in bright red with a quantum yield of 22.7% in CH2Cl2 at 298 K.



ベータ位水素化ポルフィセンコバルト錯体の電気化学挙動と反応性についての論文がDalton Transactions に掲載されました。


雑誌の Inside cover に採用されました。

Koichi Hashimoto,Taro Koide, Toru Okawara, Hisashi Shimakoshi, Yuta Hori, Yoshihito Shiota, Kazunari Yoshizawa and Yoshio Hisaeda

The dihydrogenated porphycene cobalt(II) complex was synthesized and electrochemical experiments were carried out. The one-electron reduction of the complex proceeded at the central metal to afford the Co(I) species; in contrast, for the non-hydrogenated porphycene cobalt(II) complex, the one-electron reduction gave the ligand reduced radical anion species. The reactivity of the one-electron reduced species with alkyl halides showed clear differences between the complexes. Hydrogenation of the β-position of the porphycene makes it possible to generate a central cobalt reduced species possessing a higher reactivity than the ligand reduced radical anion species.

Dalton Transactions, Dalton Transactions, 2019, 48, 872-881.

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