Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8571, Japan.
Angew Chem Int Ed Engl. 2017 Aug 14;56(34):10183-10187. doi: 10.1002/anie.201705228. Epub 2017 Jul 3.
Tetrakis(trimethylsilyl)cyclobuta-1,3-diene (1) was subjected to a temperature-dependent EPR study to allow the first spectroscopic observation of a triplet diradical state of a cyclobutadiene (2). From the temperature dependent EPR absorption area we derive a singlet→triplet (1→2) energy gap, E , of 13.9 kcal mol , in agreement with calculated values. The zero-field splitting parameters D=0.171 cm , E=0 cm are accurately reproduced by DFT calculations. The triplet diradical 2 is thermally accessible at moderate temperatures. It is not an intermediate in the thermal cycloreversion of cyclobutadiene to two acetylene molecules.
四（三甲基硅基）环丁-1,3-二烯（1）进行了温度依赖的 EPR 研究，从而首次观察到环丁二烯（2）的三重自由基态。从温度依赖的 EPR 吸收面积，我们得出单重态→三重态（1→2）的能隙 E 为 13.9 kcal/mol，与计算值一致。零场分裂参数 D=0.171 cm，E=0 cm 通过 DFT 计算准确再现。三重态自由基 2 在中等温度下可热激活。它不是环丁二烯热环回分解为两个乙炔分子的中间产物。
