Liu Meng-Kai, Li Jian, Li Quan-Song, Li Ze-Sheng
Key Laboratory of Cluster Science of Ministry of Education, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China.
Phys Chem Chem Phys. 2022 Mar 9;24(10):6266-6273. doi: 10.1039/d1cp05331k.
Sulfinyl radicals (R-SO˙) play important roles in lots of reactions, while the isomer oxathiyl radicals (R-OS˙) and the isomerization between them are rarely observed due to the poor stability of R-OS˙. In this work, the complete active space self-consistent field (CASSCF) and its multi-state second order perturbation (MS-CASPT2) methods were employed to study the photo-induced reaction mechanisms of phenylsulfinyl radical PhSO˙ 1 and its isomer phenoxathiyl radical PhOS˙ 2. Our results show that 1 and 2 have similar singly occupied molecular orbitals in the ground state but different properties in the excited state, which determine their diverse behaviors after irradiation. Radical 1 can generate 2 by light irradiation, but 2 produces isomerization product 3 (2-hydroxyphenylthiyl radical) and ring-opening product 4 (acyclic thioketoketene radical) in two paths S atom migration intermediate Int1 (2-carbonylcyclohexadienthiyl radical). The former path involves consequent hydrogen shift reactions with a strongly exothermic process while the latter path involves both ring-expansion and ring-opening processes with a high barrier, resulting in a structural and energetic preference for the former path. Moreover, we revealed several conical intersections that participate in the reactions and facilitate the photochemical processes. Our calculations not only remain consistent with and clarify the experimental observations (X. Zeng, , , 2018, (31), 9972-9978) but also enrich the knowledge of sulfinyl radicals and isomer oxathiyl radicals.
亚磺酰基自由基（R-SO˙）在许多反应中起着重要作用，而异构体氧硫基自由基（R-OS˙）及其异构化由于R-OS˙稳定性较差而很少被观察到。在这项工作中，采用完全活性空间自洽场（CASSCF）及其多态二阶微扰（MS-CASPT2）方法研究了苯基亚磺酰基自由基PhSO˙ 1及其异构体苯并氧硫基自由基PhOS˙ 2的光诱导反应机理。我们的结果表明，1和2在基态具有相似的单占据分子轨道，但在激发态具有不同的性质，这决定了它们在光照后的不同行为。自由基1通过光照可生成2，但2通过两条路径生成异构化产物3（2-羟基苯硫基自由基）和开环产物4（无环硫代酮烯自由基），其中一条路径经过S原子迁移中间体Int1（2-羰基环己二烯硫基自由基）。前一条路径涉及随后的氢迁移反应，过程强烈放热，而后一条路径涉及扩环和开环过程，势垒较高，导致前一条路径在结构和能量上更具优势。此外，我们还揭示了几个参与反应并促进光化学过程的锥形交叉点。我们的计算不仅与实验观察结果（X. Zeng, , , 2018, (31), 9972-9978）一致并对其进行了阐释，还丰富了亚磺酰基自由基和异构体氧硫基自由基的知识。
