2022 Fiscal Year Research-status Report
反芳香族B,N-カルベンσ配位子の開発と常磁性/アニオン性金錯体の合成と物性解明
| Project/Area Number |
21K05099
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| Research Institution | Hiroshima University |
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Principal Investigator |
SHANG RONG 広島大学, 先進理工系科学研究科(理), 助教 (70754216)
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| Project Period (FY) |
2021-04-01 – 2024-03-31
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| Keywords | main group ligand / electronic tuning / redox active ligand |
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| Outline of Annual Research Achievements |
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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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
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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| Strategy for Future Research Activity |
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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| Causes of Carryover |
The incurring amount will be used for replacement of old or broken instruments and consumables such as cheimcal reagents for experiments needed.
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Research Products
(10 results)
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[Presentation] Bis(borane)-containing ligands: effects on bonding and reactivity2022
Author(s)
Rong Shang*, Souta Saito, Yoshitaka Kimura, Shu Furukawa, Leonardo I. Lugo-Fuentes, Kohei Susukida, Takumi Oishi, J. Oscar C. Jimenez-Halla, Joaquin Barroso-Flores, Yohsuke Yamamoto, Tsutomu Mizuta
Organizer
Singapore International Chemical Conference (SICC-11)
Int'l Joint Research / Invited
