2021 Fiscal Year Annual Research Report
Synthesis of Mid- and Late-Transition Metal Hydride Complexes for N2 Activation and Functionalization
| Project/Area Number |
21F20037
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
侯 召民 国立研究開発法人理化学研究所, 開拓研究本部, 主任研究員 (10261158)
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| Co-Investigator(Kenkyū-buntansha) |
ZHOU XIAOXI 国立研究開発法人理化学研究所, 開拓研究本部, 外国人特別研究員
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| Project Period (FY) |
2021-04-28 – 2023-03-31
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| Keywords | titanium hydrides / N2 activation / carbon dioxide / pyridine |
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| Outline of Annual Research Achievements |
Studies on small molecule activation and transformation by transition metal hydride complexes are of particular interest and importance, but well-defined transition metal complexes that enable activation of small inert molecules such as N2 are still limited. Previously, we reported that hydrogenation of a titanium alkyl complex bearing the rigid acridane-based pincer ligands in the presence of N2 provided a dinitrogen complex via the reduction of N2 by a titanium hydride species, but the reaction process is unclear due to the lack of information of the key reaction intermediates.
In the FY2021, this key intermediate was successfully isolated and structurally characterized as a dinuclear titanium tetrahydride complex. It could readily react with N2, yielding the dinitrogen complex. Notably, further reaction of the dinitrogen complex with carbon dioxide (CO2) gave an isocyanate (-N=C=O) unit via N-N and C=O bonds cleavage and new N=C bond formation. In addition to the N2 activation, the dititanium tetrahydride complex also reacted with pyridine to afford a cyclopentadienyl titanium nitrido complexes through the N-C bond cleavage and the C-C bond formation. These results will lead to developing new reaction processes for activation and transformation of inert molecules via breaking inactive bonds and making new chemical bonds as key steps.
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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
The objective of this research is to design molecular systems for N2 activation and find new transformation reactions. So far, we have structurally characterized a new titanium hydride complex bearing an acridane-based pincer ligand, which enable N2 activation to afford the dinitrogen complex. We found that the dinitrogen unit reacted with CO2, affording isocyanate (-N=C=O) via N-C bond formation and N-N, C-O bonds cleavage. Moreover, the titanium hydride can convert pyridines into cyclopentadienyl and nitrido units. The unique reactivity of the hydride complex is due to the influence of the rigid pincer ligands, demonstrating the importance of ligand environment for activation of the small molecules.
Based on these findings, we concluded the research has been more proceeded than expected.
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| Strategy for Future Research Activity |
With the above mentioned results in hand, we further investigate the new transformation reactions of the hydride complex by using heteroaromatic molecule such as thiophene. In addition, we will explore activation reactions of both N2 and hydrocarbon sources to afford nitrogen-containing organic compounds mediated by metal hydride complexes. The high reactivity of the metal hydrides towards both N2 and carbon-based reagents suggests that these species may serve as a promising platform for N2 functionalization.
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