Monitoring the Formation and Reactivity of Organometallic Alkane and Fluoroalkane Complexes with Silanes and Xe Using Time-Resolved X-ray Absorption Fine Structure Spectroscopy,Journal of the American Chemical Society

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Monitoring the Formation and Reactivity of Organometallic Alkane and Fluoroalkane Complexes with Silanes and Xe Using Time-Resolved X-ray Absorption Fine Structure Spectroscopy
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-07-15 , DOI: 10.1021/jacs.8b13848
Stuart A. Bartlett _{1,

2,

3} , Nicholas A. Besley ₄ , Andrew J. Dent ₅ , Sofia Diaz-Moreno ₅ , John Evans _{1,

5,

6} , Michelle L. Hamilton _{1,

4} , Magnus W. D. Hanson-Heine ₄ , Raphael Horvath ₄ , Valentina Manici _{1,

4} , Xue-Zhong Sun ₄ , Michael Towrie _{1,

7} , Lingjun Wu ₄ , Xiaoyi Zhang ₈ , Michael W. George _{1,

4,

9}

Affiliation

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO)6, we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding. These results offer a step toward elucidating the structure, bonding, and chemical reactivity of transient species by X-ray absorption spectroscopy, which has sensitivity to small structural changes. The XAFS results indicate that the bond lengths of metal-alkane (W-H-C) bond in W(CO)5(heptane) as 3.07 (±0.06) Å, which is longer than the calculated W-C (2.86 Å) for binding of the primary C-H, but shorter than the calculated W-C (3.12 Å) for the secondary C-H. A statistical average of the calculated W-C alkane bond lengths is 3.02 Å, and comparison of this value indicates that the value derived from the XAFS measurements is averaged over coordination of all C-H bonds consistent with alkane chain walking. Photolysis of W(CO)6 in the presence of HSiBu3 allows the conversion of W(CO)5(heptane) to W(CO)5(HSiBu3) with an estimated W-Si distance of 3.20 (±0.03) Å. Time-resolved TRIR and XAFS experiments following photolysis of W(CO)6 in perfluoromethylcyclohexane (PFMCH) allows the characterization of W(CO)5(PFMCH) with a W-F distance of 2.65 (±0.06) Å, and doping PFMCH with Xe allows the characterization of W(CO)5Xe with a W-Xe bond length of 3.10 (±0.02) Å.

中文翻译：

使用时间分辨 X 射线吸收精细结构光谱法监测有机金属烷烃和氟烷烃与硅烷和 Xe 配合物的形成和反应性

具有弱配位配体的配合物通常在化学反应中形成，并且可以在确定反应性方面发挥关键作用，特别是在催化反应中。使用时间分辨 X 射线吸收精细结构 (XAFS) 光谱结合时间分辨 IR (TRIR) 光谱和六羰基钨 W(CO)6，我们能够从结构上表征有机金属烷烃配合物的形成，确定WC 距离，并监测与硅烷的反应性，以形成有机金属硅烷配合物。在掺有氙的全氟溶剂中进行的实验最初提供了相应的溶剂化配合物，该配合物在 Xe 存在下具有足够的反应性，然后我们可以观察 Xe 与金属中心的配位，提供对金属 - 氙键合的独特见解。这些结果为通过 X 射线吸收光谱阐明瞬态物质的结构、键合和化学反应性迈出了一步，X 射线吸收光谱对微小的结构变化具有敏感性。XAFS 结果表明，W(CO)5(庚烷)中金属-烷烃 (WHC) 键的键长为 3.07 (±0.06) Å，这比计算的 WC (2.86 Å) 长，用于结合初级 CH ，但比计算出的次级 CH 的 WC (3.12 Å) 短。计算出的 WC 烷烃键长的统计平均值为 3.02 Å，该值的比较表明，从 XAFS 测量得出的值是所有 CH 键的平均配位与烷烃链行走一致的。在 HSiBu3 存在下 W(CO)6 的光解允许 W(CO)5(庚烷)转化为 W(CO)5(HSiBu3)，估计 W-Si 距离为 3。20 (±0.03) 埃。W(CO)6 在全氟甲基环己烷 (PFMCH) 中光解后的时间分辨 TRIR 和 XAFS 实验允许表征 W(CO)5(PFMCH)，WF 距离为 2.65 (±0.06) Å，并且用 Xe 掺杂 PFMCH 允许W(CO)5Xe 的表征，W-Xe 键长为 3.10 (±0.02) Å。

更新日期：2019-07-15

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