祝贺李鹏举同学的文章“Chloride Oxidation by One- or Two-Photon Excitation of N-Phenylphenothiazine”在线发表于
Journal of the American Chemical Society（JACS）
工作简介：
氯化物氧化在氯介导的 C-H 活化这一新兴领域具有巨大的实用性，但由于单电子还原电位E° (Cl •/– )非常正，因此它仍然是一个具有挑战性的过程。常见的过渡金属光氧化剂。本文介绍了两种光催化氯化物氧化途径，涉及N-苯基吩噻嗪 (PTH) 的单光子或连续双光子激发。单光子途径通过氧化猝灭产生 PTH • +，随后歧化产生 PTH 2+氧化氯化物；该途径也可通过 PTH 的电化学氧化获得。通过自由基阳离子激发态2 PTH • +*进行的双光子途径特别令人感兴趣，因为这种超级光氧化剂能够直接将氯化物氧化成氯原子。激光闪光光解表明，双激发态的光氧化通过静态猝灭机制在亚纳秒时间尺度上进行，离子对平衡常数为 0.36 M –1. PTH 光氧化还原化学在纳秒和更长的时间尺度上进行光谱量化，氯化物氧化化学通过与模型有机底物的反应性研究揭示。PTH 的单光子和双光子激发能够氯化有机化合物（如环己烷）的未活化 C(sp 3 )-H 键，从包含第二个激发波长观察到产率显着提高。这项研究为廉价且可商购的有机光氧化剂催化的氯化物氧化提供了新的机理见解。
文章摘要：
Chloride oxidation has tremendous utility in the burgeoning field of chlorine-mediated C–H activation, yet it remains a challenging process to initiate with light because of the exceedingly positive one-electron reduction potential, E° (Cl•/–), beyond most common transition-metal photooxidants. Herein, two photocatalytic chloride oxidation pathways that involve either one- or consecutive two-photon excitation of N-phenylphenothiazine (PTH) are presented. The one-photon pathway generates PTH•+ by oxidative quenching that subsequently disproportionates to yield PTH2+ that oxidizes chloride; this pathway is also accessed by the electrochemical oxidation of PTH. The two-photon pathway, which proceeded through the radical cation excited state, 2PTH•+*, was of particular interest as this super-photooxidant was capable of directly oxidizing chloride to chlorine atoms. Laser flash photolysis revealed that the photooxidation by the doublet excited state proceeded on a subnanosecond timescale through a static quenching mechanism with an ion-pairing equilibrium constant of 0.36 M–1. The PTH photoredox chemistry was quantified spectroscopically on nanosecond and longer time scales, and chloride oxidation chemistry was revealed by reactivity studies with model organic substrates. One- and two-photon excitation of PTH enabled chlorination of unactivated C(sp3)–H bonds of organic compounds such as cyclohexane with substantial yield enhancement observed from inclusion of the second excitation wavelength. This study provides new mechanistic insights into chloride oxidation catalyzed by an inexpensive and commercially available organic photooxidant. Li,P . et. al. J. Am. Chem. Soc. 2022
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