Department of Chemistry , University of Kansas , Lawrence , Kansas 66045 , United States.
Inorg Chem. 2018 Jul 2;57(13):7825-7837. doi: 10.1021/acs.inorgchem.8b00917. Epub 2018 Jun 21.
The solution properties of Mn-hydroxo and Mn-methoxy complexes featuring N amide-containing ligands were investigated using H NMR spectroscopy. The H NMR spectrum for one of these complexes, the previously reported Mn(OH)(dpaq) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino- N-quinolin-8-yl-acetamidate) shows hyperfine-shifted signals, as expected for this S = 2 Mn-hydroxo adduct. However, the H NMR spectrum of Mn(OH)(dpaq) also shows a large number of proton resonances in the diamagnetic region, suggesting the presence of multiple species in CDCN solution. The majority of the signals in the diamagnetic region disappear when a small amount of water is added to a CHCN solution of Mn(OH)(dpaq). Electronic absorption and Mn K-edge X-ray absorption experiments support the formulation of this diamagnetic species as the μ-oxodimanganese(III,III) complex [Mn(μ-O)(dpaq))]. On the basis of these observations, we propose that the dissolution of Mn(OH)(dpaq) in CDCN results in the formation of mononuclear Mn-hydroxo and dinuclear μ-oxodimanganese(III,III) species that are in equilibrium. The addition of a small amount of water is sufficient to shift this equilibrium in favor of the Mn-hydroxo adduct. Surprisingly, electronic absorption experiments show that the conversion of [Mn(μ-O)(dpaq))] to [Mn(OH)(dpaq)] by added water is relatively slow. Because this dimer to monomer conversion is slower than TEMPOH oxidation by [Mn(OH)(dpaq)], the previously observed TEMPOH oxidation rates for [Mn(OH)(dpaq)] reflected both processes. Here, we report the bona fide TEMPOH oxidation rate for [Mn(OH)(dpaq)], which is significantly faster than previously reported. H NMR spectra are also reported for the related [Mn(OMe)(dpaq)] and [Mn(OH)(dpaq)] complexes. These spectra only show hyperfine-shifted signals, suggesting the presence of only mononuclear Mn-methoxy and Mn-hydroxo species in solution. Measurements of T relaxation times and proton peak integrations for [Mn(OMe)(dpaq)] provide preliminary assignments for H NMR resonances.
使用 H NMR 光谱研究了具有 N 酰胺基配体的 Mn-羟基金属和 Mn-甲氧基配合物的溶液性质。这些配合物之一的 H NMR 谱，即先前报道的 Mn(OH)(dpaq)（dpaq = 2-[双（吡啶-2-基甲基）]氨基-N-喹啉-8-基-乙酰胺）显示出超精细位移信号，这是预期的 S = 2 Mn-羟基金属加合物的特征。然而，Mn(OH)(dpaq)的 H NMR 谱也显示出在 CDCN 溶液中存在大量抗磁性区域的质子共振，表明存在多种物种。当向 Mn(OH)(dpaq)的 CHCN 溶液中加入少量水时，抗磁性区域中的大多数信号消失。电子吸收和 Mn K 边 X 射线吸收实验支持这种抗磁性物种作为 μ-氧二锰（III,III）配合物[Mn(μ-O)(dpaq))]的配方。基于这些观察结果，我们提出 Mn(OH)(dpaq)在 CDCN 中的溶解导致单核 Mn-羟基金属和双核 μ-氧二锰（III,III）物种的形成达到平衡。加入少量水足以使这种平衡有利于 Mn-羟基金属加合物。令人惊讶的是，电子吸收实验表明，通过添加水将[Mn(μ-O)(dpaq))]转化为[Mn(OH)(dpaq)]的反应相对较慢。由于这种二聚体到单体的转化速度比[Mn(OH)(dpaq)]的 TEMPOH 氧化速度慢，以前观察到的[Mn(OH)(dpaq)]的 TEMPOH 氧化速率反映了这两个过程。在这里，我们报告了 [Mn(OH)(dpaq)]的真实 TEMPOH 氧化速率，明显快于以前报道的速率。还报道了相关的 [Mn(OMe)(dpaq)]和[Mn(OH)(dpaq)]配合物的 H NMR 谱。这些谱线仅显示超精细位移信号，表明在溶液中仅存在单核 Mn-甲氧基和 Mn-羟基金属物种。[Mn(OMe)(dpaq)]的 T 弛豫时间和质子峰积分测量提供了 H NMR 共振的初步分配。
