Li Longfei, Zhang Beijing, Xie Yi, Xiong Qi, Zhong Yuanbo, Jiang Yansong, Wang Yu, Wang Haobing, Jiang Shang-Da, Zhou Shen, Jiang Xing
South China Advanced Institute for Soft Matter Science and Technology, School of Emergent Soft Matter, South China University of Technology Guangzhou 510640 China
Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, Guangdong Basic Research Center of Excellence for Energy and Information Polymer Materials, South China University of Technology Guangzhou 510640 China.
Chem Sci. 2025 Aug 27. doi: 10.1039/d5sc02322j.
Cyclic oligomers with multiple redox centers are ideal models for intramolecular electron transfer processes, as they feature well-defined spatial geometries and degenerate energy states. The design and synthesis of such structures with strongly interacting monomers, however, remains a significant challenge. Here, we report a one-pot synthesis of an acetylene-bridged ferrocene macrocycle (9) using alkyne metathesis, with a remarkable 43% isolated yield. The macrocycle adopts a chiral / conformation in the crystal, reminiscent of the iconic Penrose triangle. Electrochemical studies suggested that redox processes of all three ferrocene units are reversible and highly correlated, despite relatively long Fe-Fe distances. Hydrogenation of acetylene bridges yielded an analogous trimeric ferrocene macrocycle (14), whose redox waves showed less separation due to the lack of conjugation and through-bond charge transfer. Assuming that the through-space interaction energy is the same for both macrocycles, we estimated that conjugation through acetylene bridges accounts for 25-36% of overall interaction. Trication 9 was obtained by chemical oxidation, and it showed EPR signals with weak anisotropy, indicative of fast intramolecular electron transfer. Varied-temperature (VT) EPR studies suggested intramolecular antiferromagnetic interaction and a doublet ground state (Δ = -0.06 kcal mol) for 9.
具有多个氧化还原中心的环状低聚物是分子内电子转移过程的理想模型，因为它们具有明确的空间几何结构和简并能态。然而，设计和合成具有强相互作用单体的此类结构仍然是一项重大挑战。在此，我们报道了一种使用炔烃复分解反应一锅法合成乙炔桥连二茂铁大环化合物（9）的方法，其分离产率高达43%，令人瞩目。该大环化合物在晶体中呈现出手性/构象，让人联想到标志性的彭罗斯三角形。电化学研究表明，尽管铁-铁距离相对较长，但所有三个二茂铁单元的氧化还原过程都是可逆的且高度相关。乙炔桥的氢化反应生成了类似的三聚二茂铁大环化合物（14），由于缺乏共轭和通过键的电荷转移，其氧化还原波的分离程度较小。假设两个大环化合物的空间相互作用能相同，我们估计通过乙炔桥的共轭作用占总相互作用的25 - 36%。通过化学氧化得到了三价阳离子9，它显示出具有弱各向异性的电子顺磁共振（EPR）信号，表明分子内电子转移很快。变温（VT）EPR研究表明9存在分子内反铁磁相互作用和双重基态（Δ = -0.06 kcal mol）。
