Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, Bhopal Bypass Road, Bhauri Bhopal 462 066, Madhya Pradesh, India.
MIT School of Engineering, MIT Art, Design and Technology University Pune, Loni Kalbhor, Maharashtra 412201, India.
Inorg Chem. 2022 Jun 13;61(23):8729-8745. doi: 10.1021/acs.inorgchem.2c00651. Epub 2022 May 31.
Chalcogen-bonding interactions have recently gained considerable attention in the field of synthetic chemistry, structure, and bonding. Here, three organo-spiroselenuranes, having a Se(IV) center with a strong intramolecular Se···N chalcogen-bonded interaction, have been isolated by the oxidation of the respective (2-benzamide) selenides derived from an 8-aminoquinoline ligand. Further, the synthesized spiroselenuranes, when assayed for their antioxidant activity, show disproportionation of hydrogen peroxide into HO and O with first-order kinetics with respect to HO for the first time by any organoselenium molecules as monitored by H NMR spectroscopy. Electron-donating 5-methylthio-benzamide ring-substituted spiroselenurane disproportionates hydrogen peroxide at a high rate of 15.6 ± 0.4 × 10 μM min with a rate constant of 8.57 ± 0.50 × 10 s, whereas 5-methoxy and unsubstituted-benzamide spiroselenuranes catalyzed the disproportionation of HO at rates of 7.9 ± 0.3 × 10 and 2.9 ± 0.3 × 10 μM min with rate constants of 1.16 ± 0.02 × 10 and 0.325 ± 0.025 × 10 s, respectively. The evolved oxygen gas from the spiroselenurane-catalyzed disproportion of HO has also been confirmed by a gas chromatograph-thermal conductivity detector (GCTCD) and a portable digital polarographic dissolved O probe. Additionally, the synthesized spiroselenuranes exhibit thiol peroxidase antioxidant activities for the reduction of HO by a benzenethiol co-reductant monitored by UV-visible spectroscopy. Next, the Se···N bonded spiroselenuranes have been explored as catalysts in synthetic oxidation iodolactonization and bromination of arenes. The synthesized spiroselenurane has activated I toward the iodolactonization of alkenoic acids under base-free conditions. Similarly, efficient chemo- and regioselective monobromination of various arenes with NBS catalyzed by chalcogen-bonded synthesized spiroselenuranes has been achieved. Mechanistic insight into the spiroselenuranes in oxidation reactions has been gained by Se NMR, mass spectrometry, UV-visible spectroscopy, single-crystal X-ray structure, and theoretical (DFT, NBO, and AIM) studies. It seems that the highly electrophilic nature of the selenium center is attributed to the presence of an intramolecular Se···N interaction and a vacant coordination site in spiroselenuranes is crucial for the activation of HO, I, and NBS. The reaction of HO, I, and NBS with tetravalent spiroselenurane would lead to an octahedral-Se(VI) intermediate, which is reduced back to Se(IV) due to thermodynamic instability of selenium in its highest oxidation state and the presence of a strong intramolecular -donor atom.
近年来，硫属元素键相互作用在合成化学、结构和键合领域引起了相当大的关注。在这里，通过氧化各自的（2-苯甲酰胺）硒化物，从 8-氨基喹啉配体衍生出三个具有 Se(IV)中心和强分子内 Se···N 硫属元素键相互作用的有机螺硒烷被分离出来。此外，合成的螺硒烷在抗氧化活性测试中，首次通过任何有机硒分子以一阶动力学显示出过氧化氢向 HO 和 O 的歧化，通过 H NMR 光谱监测。具有供电子 5-甲基硫代苯甲酰胺环取代的螺硒烷以 15.6 ± 0.4 × 10 μM min 的高速率分解过氧化氢，速率常数为 8.57 ± 0.50 × 10 s，而 5-甲氧基和未取代的苯甲酰胺螺硒烷以 7.9 ± 0.3 × 10 和 2.9 ± 0.3 × 10 μM min 的速率催化 HO 的歧化，速率常数分别为 1.16 ± 0.02 × 10 和 0.325 ± 0.025 × 10 s。通过气相色谱-热导率检测器（GCTCD）和便携式数字极谱溶解 O 探头也证实了从螺硒烷催化的 HO 歧化中产生的氧气。此外，合成的螺硒烷通过 UV-可见光谱监测苯硫醇共还原剂对 HO 的还原表现出硫醇过氧化物抗氧化活性。接下来，合成的螺硒烷被探索作为合成氧化碘化内酯化和芳基溴化的催化剂。在无碱条件下，合成的螺硒烷激活 I 进行烯酸的碘化内酯化。同样，在合成的硫属元素键合螺硒烷的催化下，通过 NBS 实现了各种芳基的高效化学和区域选择性单溴化。通过硒 NMR、质谱、UV-可见光谱、单晶 X 射线结构和理论（DFT、NBO 和 AIM）研究获得了氧化反应中螺硒烷的机制见解。似乎硒中心的高亲电性归因于分子内 Se···N 相互作用的存在，并且螺硒烷中 vacant 配位位点对于 HO、I 和 NBS 的活化至关重要。HO、I 和 NBS 与四价螺硒烷的反应将导致八面体-Se(VI)中间体，由于硒在其最高氧化态下的热力学不稳定性和强分子内供体原子的存在，该中间体还原回 Se(IV)。
