Visible light generation of chromium(V)-oxo salen complexes and mechanistic insights into catalytic sulfide oxidation
Visible light generation of chromium(V)-oxo salen complexes and mechanistic insights into catalytic sulfide oxidation
复制标题
DOI：
10.1016/j.ica.2020.119681
复制
发表时间：
2020-09
影响因子：
2.8
通讯作者：
Seth Klaine;Ngo Fung Lee;Angeline Dames;Rui Zhang
中科院分区：
文献类型：
--
作者：
Seth Klaine;Ngo Fung Lee;Angeline Dames;Rui Zhang
在可见光照射下，Salen-铬(III)氯酸盐或溴酸盐前驱体生成了Salen-铬(V)-氧络合物，这些络合物在光谱和动力学上与Phi(OAc)2化学氧化铬(III)形成的络合物没有区别。本工作中观察到的光化学归因于顶端反离子中O-X键的异质裂解，导致金属的两电子氧化形成铬(V)-氧物种。在准一级反应条件下，测定了3与有机底物的氧化反应的二级速率常数，观察到硫化物氧化反应的活性特别低。在本研究中，在少量水存在下，六价铬(III)Salen络合物能有效地催化Phi(OAc)2将芳基硫化物氧化成亚硫醚。竞争产物与Hammett相关图的研究表明，所观察到的铬(V)-氧物种不太可能是铬(III)SALENS与Phi(OAc)2催化的硫化物氧化的主要氧化剂。
Visible light irradiation of the photo-labile salen-chromium(III) chlorate or bromate precursors produced salen-chromium(V)-oxo complexes that were spectroscopically and kinetically indistinguishable from those formed by chemical oxidation of chromium(III) salens with PhI(OAc)2. The photochemistry observed in this work is ascribed to theheterolyticcleavage of the O-X bond in the apical counterion that results in a two-electron oxidation of the metal to form the chromium(V)-oxo species. Second-order rate constants for oxidation reactions of3with organic substrates were determined under pseudo-first order condition, and particularly low level of reactivity for sulfide oxidations was observed. In this study, chromium(III) salen complexes effectively catalyzed the oxidation of aryl sulfides into sulfoxides with PhI(OAc)2in the presence of a small amount of water. The competition product studies with the Hammett correlation plot indicated that the observed chromium(V)-oxo species is not likely to serve as the major oxidant for the sulfide oxidations catalyzed by chromium(III) salens with PhI(OAc)2.