NMR Studies of the Reaction Path of the o-H2/p-H2 Spin Conversion Catalyzed by Vaska’s Complex in the Solid State
NMR Studies of the Reaction Path of the o-H2/p-H2 Spin Conversion Catalyzed by Vaska’s Complex in the Solid State
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Vaska配合物固态催化o-H2/p-H2自旋转化反应路径的NMR研究
DOI：
10.1007/s00723-012-0395-9
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发表时间：
2013
影响因子：
1
通讯作者：
H.-H. Limbach
中科院分区：
文献类型：
--
作者：
J. Matthes;S. Gründemann;G. Buntkowsky;B. Chaudret;H.-H. Limbach
本文研究了在77 K下，Vaska配合物Ir（CO）Cl（PPh_3）_2（1）在C_6D_6中的冷冻溶液和多晶1与H_2接触时，H_2的o/p自旋转换。本研究的主要目的是阐明以前偶然发现的这类反应的机理（Eisenschmid等JACS 109：8089-8091，1987和Eisenberg ACS 24：110-116，1991）。在298 K下，通过1H核磁共振（NMR）光谱分析，在样品解冻后，p-H2的形成被跟踪，其中发生了二氢与1的氧化加成，导致Vaska的二氢化物Ir（CO）ClH 2（PPh 3）2（2），已知其抑制了仲氢诱导极化（PHIP）。PHIP信号与p-H_2浓度成正比，这是由溶解的-H_2信号的减少所阐明的。发现与多晶粉末相比，冷冻溶液的反应更快。光学显微镜显示，在冷冻过程中，1的小颗粒从溶液中分离出来，与多晶粉末相比，表现出更大的表面积。当H2和D2的混合物暴露于冷冻溶液或暴露于多晶粉末时，通过1H NMR观察到HD的形成。这一发现表明存在涉及两个二氢分子的化学自旋转换。另外，在110 K下冷冻C6 D 6中氢的1H NMR实验表明，在苯分子之间的间隙位点中形成含有气态H2的较大孔以及氢位点。此外，在1的存在下，在-4.5 ppm处观察到信号，这归因于与Ir紧密接触的二氢。
We have studied theo/pspin conversion of dihydrogen in contact with frozen solutions of Vaska’s complex Ir(CO)Cl(PPh3)2(1) in C6D6and with polycrystalline1at 77 K. The main purpose of this study was to elucidate the mechanism of this type of reactions found accidentally previously (Eisenschmid et al JACS 109:8089–8091, 1987 and Eisenberg ACS 24:110–116, 1991). The formation ofp-H2was followed after thawing of the samples by1H nuclear magnetic resonance (NMR) spectroscopy at 298 K, where the oxidative addition of dihydrogen to1occurs leading to Vaska’s dihydride Ir(CO)ClH2(PPh3)2(2) which is known to exhibitpara-hydrogen-induced polarization (PHIP). The PHIP signal was shown to be proportional to the concentration ofp-H2as elucidated from the decrease of the signal of dissolvedo-H2. The reaction was found to be faster for the frozen solution as compared to the polycrystalline powder. Optical microscopy showed that small particles of1are separated from the solution during the freezing process, exhibiting a larger surface area as compared to the polycrystalline powder. When a mixture of H2and D2was exposed to the frozen solutions or to the polycrystalline powder, the formation of HD was observed by1H NMR. This finding indicates the presence of a chemical spin conversion involving two dihydrogen molecules. Additional1H NMR experiments of dihydrogen in frozen C6D6at 110 K indicated the formation of larger pores containing gaseous H2as well as dihydrogen sites in interstitial sites between benzene molecules. Moreover, in the presence of1, a signal at −4.5 ppm was observed which was attributed to a dihydrogen in close contact with Ir.
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影响因子：
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