| 研究課題/領域番号 |
21K05099
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| 研究種目 |
基盤研究(C)
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| 配分区分 | 基金 |
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| 応募区分 | 一般 |
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| 審査区分 |
小区分34010:無機・錯体化学関連
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| 研究機関 | 広島大学 |
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研究代表者 |
SHANG RONG 広島大学, 先進理工系科学研究科(理), 助教 (70754216)
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| 研究期間 (年度) |
2021-04-01 – 2024-03-31
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| 研究課題ステータス |
交付 (2022年度)
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| 配分額 *注記 |
4,290千円 (直接経費: 3,300千円、間接経費: 990千円)
2023年度: 1,170千円 (直接経費: 900千円、間接経費: 270千円)
2022年度: 1,560千円 (直接経費: 1,200千円、間接経費: 360千円)
2021年度: 1,560千円 (直接経費: 1,200千円、間接経費: 360千円)
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| キーワード | main group ligand / electronic tuning / redox active ligand / Aurate / Carbene / boron / 反芳香族σ配位子 / 有機遷移金属化学 / 機能性材料 |
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| 研究開始時の研究の概要 |
本課題で研究対象とする分子群では，ホウ素と窒素からなる新規カルベン配位子のBNCを 鍵化合物として，反芳香族配位子による電子的、立体的なチューニング効果と，そこから導 かれる酸化還元特性との相関関係を明らかにする。近年，重原子であるがゆえの 特徴的な酸化還元挙動を示す金錯体に備わった触媒機能に注目が集まっており，光や熱によって誘起された電子移動過程の本質を解き明かすことは，また同時に錯体化学において普遍的一 般原理へと導くと期待される。未解明の金錯体を合成単離し， その物理的・化学的特性評価によって触媒能の向上や機能性材料としての基盤構築に貢献する。
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| 研究実績の概要 |
The interplay of aromaticity and antiaromaticity of conjugated π systems is a crucial design strategy for tuning light-initiated electron-transfer properties in designing functional molecules. For transition metal (TM) photocatalysts, while heterocyclic aromatic ligands are widely used for modulation of their (photo)redox behaviors, the effect of antiaromatic ligands remains poorly understood due to a lack of synthetic methodologies. This project proposed a design and synthesis to isolate radical and anionic gold complexes bearing a 4π B, N-heterocyclic Carbene (BNC). The expected antiaromaticity and the inclusion of boron atoms in BNC results in its super π-accepting and σ-donating abilities which are ideal to stabilize and tune unusual oxidation states and radical behaviors of the metal.
The synthesis of several derivatives of BNC Au(I) complexes were established. A 2e reduction of the (BNC-Cl)AuL complex by lithium allowed isolation of a bright orange lithium aurate complex Li[(BNC)AuL]. Computational analysis indicated that, despite of the 4π electron counting, the neutral BNC ligand on Au(I) is mostly non-aromatic in character, due to the localized BN π bonds. After reduction, the gold center remained as +I, whereas the BNC moiety became a 6π aromatic system. In particular, the occupied p orbital at the ligating carbon center was shown to interact strongly with the Au(I) 6p orbital with an interaction energy between 15.5 kcal/mol. This result showed that the gold(I) can form multiple bonds with ligand through its 6p orbital ligands instead of 5d orbitals.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
In addition to the highly π-withdrawing BNC ligand, we developed two more main-group containing heterocyclic ligand systems: 1) a highly π-donating B,N-containing heterocyclic Phosphide (BNP, 6π) and 2) a LX2 CCC-type pincer based on a π rich dipyridal-annulated N-heterocyclic carbene (26π). Firstly, the 6π BNP ligand is expected to be π-donating system. Depending on the metal fragment, it can be a 1e-donating anionic phosphido ligand or a 2e-donating cationic phosphenium ligand. Its complexation on Au(I) will allow direct structural comparison to BNC-Au(I) complexes to reveal bonding characteristics between ligand and metal. As a direct contrast to the π-withdrawing NBC ligand, the synthesis (BNP)Au(L) complexes have been achieved. The redox behaviour of this new class of complexes is being investigated.
Meanwhile, the π-rich (26π) CCC-pincer ligand is expected as a precursor for stable metallacycles. Metal-ligand coplanar metallacycles are expected to have effective orbital interactions between metal d orbitals and ligand π orbitals. The electronic states and bonding then can be investigated by changing the number of π electrons. Metallation to Ir(I) via facile deprotonation/C-H activation led to a homoleptic octahedral Ir(III) bispincer metallacycle with an overall anionic charge. A step-wise 4e oxidation allowed isolation of a racemic mixture of chiral tricationic Ir(III) complex as a black solid. Computational analysis of this complex and experimental data suggested a triplet ground state.
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| 今後の研究の推進方策 |
With establishment of the synthesis of three planar heterocyclic ligands with π-donating and π-withdrawing properties, we have preliminary success on complexation to late transition metals. Regarding the BNC and BNP ligands, the synthesis of homoleptic complexes ([AuL2]+ and [AuX2]-) as well as heteroleptic push-pull systems [e.g. (BNC)Au(BNP)] are being pursued. If successful, their redox chemistry and photophysical properties will be investigated. For the homoleptic CCC-pincer ligand, different ligand derivative are being developed to fine-tune the electronic state of the tricationic complex. In addition to the 5d late transition metals, synthetic methods that allow complexation to earlier transition metal groups and 3d metals will be also targeted.
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