メソアリル置換された膨張したポルフィリンが酸化的に割れたときの完全にピ結合ヘリックス
Shohei Saito1, Ko Furukawa, Atsuhiro Osuka
1Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Journal of the American Chemical Society
|January 30, 2010
まとめ
研究者らは,2つの銅イオン周りのpi結合オリゴピロメタンヘリクスを合成した. これらの構造は,独特の近赤外線吸収と銅 (II) イオン間の反鉄磁気相互作用を示しています.
科学分野:
- 超分子化学 超分子化学
- マテリアルサイエンス 材料科学
- 無機化学 無機化学とは
背景:
- 拡張ポルフィリンは,調節可能な電子特性を持つ多用途のマクロサイクル化合物です.
- Pi結合システムは,新しい電子および磁気材料の開発に不可欠です.
- 銅(II) イオンは,分子組立の中で磁気相互作用を媒介することができます.
研究 の 目的:
- 新しいパイ結合オリゴピロメタンヘリクスを合成し,特徴づけること.
- 銅 (II) イオンを巻き込むこれらの螺旋構造の電子および磁気特性を調査する.
- 材料科学の応用におけるこれらのシステムの可能性を探求する.
主な方法:
- 膨張したポルフィリンが酸化的に裂け,オリゴピロメタンヘリクを形成する.
- 電子トランジションを研究するために,光譜分析 (UV-Vis-NIR) を行う.
- 磁気相互作用を調査するための磁気感受性および電子回転共振 (ESR) 測定.
主要な成果:
- 2つのCu (II) イオンをカプセル化した,完全にpi結合したオリゴピロメタンヘリクスを成功裏に合成しました.
- 明確な近赤外線吸収帯が観察され,有効なπ電子移位を示しています.
- 磁気測定で内部Cu (III) イオン間の反鉄磁気結合が実証されました.
結論:
- 合成されたヘリクスは,ピ-電子の有意な移位による円滑に結合した背骨を有している.
- この研究は,螺旋構造内の銅 (II) イオン間の反鉄磁気相互作用の存在を明らかにしています.
- これらの発見は,π結合金属超分子系における磁気相互作用の理解に貢献します.
関連する概念動画
Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
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Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
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