Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany.
Center for Computational Quantum Chemistry and Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
J Am Chem Soc. 2020 Nov 18;142(46):19457-19461. doi: 10.1021/jacs.0c09317. Epub 2020 Nov 9.
We report the first preparation of the -,- conformer of dihydroxycarbene () by means of pyrolysis of oxalic acid, isolation of the lower-energy -,- () and -,- () product conformers at cryogenic temperatures in a N matrix, and subsequent narrow-band near-infrared (NIR) laser excitation to give . Carbene converts quickly to via quantum-mechanical tunneling with an effective half-life of 22 min at 3 K. The potential energy surface features around were pinpointed by convergent focal point analysis targeting the AE-CCSDT(Q)/CBS level of electronic structure theory. Computations of the tunneling kinetics confirm the time scale of the → rotamerization and suggest that direct → H + CO decomposition may also be a minor pathway. The intriguing latter possibility cannot be confirmed spectroscopically, but hints of it may be present in the measured kinetic profiles.
我们首次通过热解草酸的方法制备了二羟卡宾（）的 -，- 构象异构体，在 N 基质中低温下分离出低能量的 -，-（）和 -，-（）产物构象异构体，然后通过窄带近红外（NIR）激光激发得到。在 3 K 下，通过量子力学隧穿，卡宾快速转化为 ，有效半衰期为 22 分钟。通过针对 AE-CCSDT(Q)/CBS 电子结构理论水平的会聚焦点分析，精确定位了约 处的势能面特征。隧穿动力学的计算证实了 → 构象异构化的时间尺度，并表明直接 → H + CO 分解也可能是一个次要途径。有趣的后一种可能性无法通过光谱学确认，但在测量的动力学曲线中可能存在一些迹象。
