2020 Fiscal Year Research-status Report
Iron-catalyzed Activation of Unreactive Bonds for Organic Materials Synthesis
| Project/Area Number |
19K15555
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| Research Institution | The University of Tokyo |
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Principal Investigator |
シャン ルイ 東京大学, 大学院理学系研究科(理学部), 特任准教授 (50793212)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | iron catalysis / C-H activation / C-O activation / C-C coupling / thiophene / annulation / polycondensation / narrow-band-gap |
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| Outline of Annual Research Achievements |
This research project successfully achieved using iron catalysis to make a variety of organic electronic materials, through 1) a regioselective thienyl C-H/C-H coupling and 2) a novel iron-catalyzed tandem annulation strategy to 1,4-dihydropentalene framework.
1) We found that an iron(III) salt in combination with tridentate phosphine ligand and AlMe3 as base selectively cleaves thienyl C-H bond at C2 position and allows regioselective thienyl-thienyl coupling of high efficiency using a mild oxalate ester as oxidant for catalyst turnover. The reaction is compatible with various pi-units generally found in optoelectronic materials and is accelerated by ligand optimization to allow C-H/C-H polycondensation to allow synthesis of various small molecular, oligomeric and polymeric semiconductive materials of importance in energy device applications.
2) Carbon-bridge between arylene and vinylene units is an essential strategy to flatten and stabilize the conjugated system in design of organic electronic materials. An iron-catalyzed method using simply FeCl2 and PPh3 as catalyst in the presence of magnesium powder and LiCl, followed by oxidation with 1,2-dichloropropane is achieved for the synthesis of carbon-bridged arylenevinylenes with high efficiency and diversity. The method allows a new four-step modular synthetic route to access indeno[2,1-a]indenes. The method also enables synthesis of a new type of fused thiophene molecules, namely 4,8-dihydropentaleno[1,2-b:4,5-b']dithiophenes, which are of high HOMO level and narrow band gap for developing narrow band gap materials.
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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
We developed two types of new iron catalysis that enable synthesis of a variety of organic electronic materials, including new materials showed promising functions in optoelectronic devices. The research project lead to discoveries of new catalytic reactions, new mechanistic understanding, and new materials of novel properties and functions. These results are beyond our initial exceptions that we believe now iron catalysis will become a new tool in preparation of organic electronic materials with advantages of not only cost and sustainability, but also materials qualities.
We targeted two essential synthetic challenges in synthesis of functional organic semiconductors 1) thienyl C-H/C-H coupling, because thienyl-thienyl coupling with regioselectivity control is arguably one of the most important transformation for organic pi-electronic materials science as evidenced by a diversity of small molecular, oligomeric, and polymeric semi-conductive materials containing thiophene-thiophene linkage. This transformation is ideally achieved through direct C-H/C-H coupling. We achieved iron catalyzed C-H/C-H dimerization and polycondensation for thienyl donor polymers. 2) we developed new annulation strategy for 1,4-dihydropentalene frameworks to enable development of new narrow-band-gap acceptor materials. These transformations are developed using only earth abundant elements such as Fe, Al, and Mg. Notably, these catalytic methods lead to development of new materials which showed promising applications in optoelectronic devices in comparison with the state-of-the-art materials.
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| Strategy for Future Research Activity |
The future research plan will focus on 1) iron-catalyzed C-H/C-H coupling to develop new oligomeric and polymeric conjugated materials. A new type of tridentate phosphine ligand is now developed by us as the key enabler for iron catalysis. We desire to discover other novel iron-catalyzed C-H activation reactions using a library of these ligands. Besides C-H/C-H homocoupling, cross coupling with absolute selectivity control will be explored for future development of C-H coupling method to allow co-polymerization.
For iron-catalyzed tandem annulation strategy, the method will be further optimized to achieve polyannulation to access larger pi-extended conjugation systems for development of new narrow-band-bap materials.
Also, we will examine the photophysical and electrochemical properties of many of materials we prepared by using both the methods mentioned above and will discover their uses in photodetector devices, solar cell devices, and light emitting diodes.
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| Causes of Carryover |
For attending conferences which were postponed because of COVID-19 pandemic
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