Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States.
Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon 97239, United States.
J Am Chem Soc. 2023 Feb 1;145(4):2230-2242. doi: 10.1021/jacs.2c09874. Epub 2023 Jan 18.
Transition-metal-mediated reductive coupling of nitric oxide (NO) to nitrous oxide (NO) has significance across the fields of industrial chemistry, biochemistry, medicine, and environmental health. Herein, we elucidate a density functional theory (DFT)-supplemented mechanism of NO reductive coupling at a copper-ion center, [(tmpa)Cu(MeCN)] () {tmpa = tris(2-pyridylmethyl)amine}. At -110 °C in EtOH (<-90 °C in MeOH), exposing to NO leads to a new binuclear hyponitrite intermediate [{(tmpa)Cu}(μ-NO)] (), exhibiting temperature-dependent irreversible isomerization to the previously characterized κ-O,O'--[(tmpa)Cu(μ-NO)] () complex. Complementary stopped-flow kinetic analysis of the reaction in MeOH reveals an initial mononitrosyl species [(tmpa)Cu(NO)] () that binds a second NO molecule, forming a dinitrosyl species [(tmpa)Cu(NO)] (). The decay of requires an available starting complex to form a dicopper-dinitrosyl species hypothesized to be [{(tmpa)Cu}(μ-NO)] () bearing a diamond-core motif, to the formation of hyponitrite intermediate . In contrast, exposing to NO in 2-MeTHF/THF (v/v 4:1) at <-80 °C leads to the newly observed transient metastable dinitrosyl species [(tmpa)Cu(NO)] () prior to its disproportionation-mediated transformation to the nitrite product [(tmpa)Cu(NO)]. Our study furnishes a near-complete profile of NO activation at a reduced Cu site with tripodal tetradentate ligation in two distinctly different solvents, aided by detailed spectroscopic characterization of metastable intermediates, including resonance Raman characterization of the new dinitrosyl and hyponitrite species detected.
过渡金属介导的一氧化氮（NO）还原偶联为一氧化二氮（N2O）在工业化学、生物化学、医学和环境健康等领域具有重要意义。在此，我们阐明了在铜离子中心[(tmpa)Cu(MeCN)]（）{tmpa=三（2-吡啶基甲基）胺}上进行 NO 还原偶联的密度泛函理论（DFT）补充机制。在 -110°C 的乙醇中（-90°C 的甲醇中），将暴露于 NO 会导致新的双核亚硝酸盐中间体[{(tmpa)Cu}(μ-NO)]（），表现出温度依赖性的不可逆异构化为先前表征的κ-O,O'--[(tmpa)Cu(μ-NO)]（）配合物。在 MeOH 中反应的互补停流动力学分析揭示了初始的单亚硝酰物种[(tmpa)Cu(NO)]（），它结合第二个 NO 分子，形成二亚硝酰物种[(tmpa)Cu(NO)]（）。的衰减需要一个可用的起始配合物形成二铜-二亚硝酰物种，假设为[{(tmpa)Cu}(μ-NO)]（），具有金刚石核心结构，形成亚硝酸盐中间体。相比之下，将在 -80°C 的 2-MeTHF/THF（v/v 4:1）中暴露于 NO 导致新观察到的瞬态亚稳态二亚硝酰物种[(tmpa)Cu(NO)]（），然后通过歧化介导转化为亚硝酸盐产物[(tmpa)Cu(NO)]。我们的研究提供了在两种明显不同的溶剂中具有三齿四齿配位的还原 Cu 位点上的 NO 活化的近完整图谱，这得益于对亚稳中间体的详细光谱表征，包括新的二亚硝酰和亚硝酸盐物种的共振拉曼表征。
