Excited state aromaticity in strained 4pi electron ring system: Synthesis and its application to open-shell molecules

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K05073
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 33010:Structural organic chemistry and physical organic chemistry-related
• Research Institution: Hiroshima University
• Principal Investigator: Nakamoto Masaaki 広島大学, 先進理工系科学研究科(理), 准教授 (90334044)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 高歪み結合 / 反芳香族性 / シグマ共役 / シクロブタジエン / 原子価異性化 / ビラジカル

Outline of Final Research Achievements

Experimental studies on molecular conversion induced by light and heat, focusing on tetrahedrane, were carried out. The isomerization of the molecule consisting of highly strained carbon sigma bonds was investigated to form cyclobutadiene, which has a unique pi-electron system known as antiaromaticity. Recently we have expanded a simple and reliable method for synthesizing cyclobutadiene by photoinduced electron transfer of the corresponding tetrahedrane precursors. Based on the Huckel rule, cyclobutadiene shows antiaromatic character because of four pi electrons in single cyclic pi conjugation systems. Therefore the research of a stable compound was quite limited. Up to now, more than 20 stable tetrahedrane derivatives, including boron-substituted and phosphorus substituted and so on, have been successfully synthesized. Furthermore, most of them could be converted into the corresponding isomer of cyclobutadienes.

Free Research Field

有機元素化学

Academic Significance and Societal Importance of the Research Achievements

芳香族分子を平面から歪ませ、球面状にしたフラーレン関連分子やシクロカーボンのようなベルト状芳香族分子に注目が集まっている。また適切に共役系を設計することで、non-ケクレジラジカル構造の分子の合成も報告されている。環状4nパイ電子系の分子は反芳香族性を有するとされているが、このような構造的特徴を有した分子は一般に反応活性であり，その物性は未解明なまま残されている。特徴的なπ電子系では、光エネルギーを利用する化学変換の機構として働くことが挙げられ、π電子系と光エネルギーの相互作用を詳細に理解する上で重要な概念の一つされている。