An electron-deficient Iridium(III) dihydride complex capable of intramolecular C-H activation
An electron-deficient Iridium(III) dihydride complex capable of intramolecular C-H activation
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DOI：
10.1002/anie.200463000
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Nolan, SP
中科院分区：
文献类型：
--
作者：
Scott, NM;Pons, V;Nolan, SP
固态结构具有双重旋转轴，并清楚地显示了叔丁基基团和铱中心之间的双重agostic相互作用，每个agostic相互作用的距离分别为2.653和1.882（Irvine C9和Irvine H9 A）。四配位IrIII配合物采用了假八面体环境，其中两个空位处于顺式排列，卡宾碳原子彼此反式，但顺式两个顺式氢化物配体。此外，两个顺式空位通过与附近的叔丁基的两个agostic相互作用而被空间保护。3的结构提供了一个罕见的例子，“建议”的中间体的分子内CNOH活化过程。ItBu配体显然在配位不饱和铱配合物中提供了独特的稳定作用。[10]3的X-射线结构表明存在双agostic相互作用，但在环境温度下的NMR光谱表明高度对称的结构。在一定温度范围内（175- 300 K）记录的1H NMR光谱显示了有趣的动态行为（图2）。动态过程在低温下冻结，这导致叔丁基和咪唑部分处于两种不同的环境。我们属性的低温光谱的外观，以较低的对称性结构与固态结构一致。叔丁基基团在其自由环境之间的切换和经历agostic相互作用是NMR光谱随温度变化的原因（图2）。线形分析表明，该过程的ΔH= 7.68 kcal molecular ~（-1），ΔS= 1.11 kcal molecular ~（-1）/度，ΔG = 1.11 kcal molecular ~（-1）/度。
The solid-state structure possesses a twofold rotation axis and clearly shows a double agostic interaction between the tbutyl groups and the iridium center with distances of 2.653 and 1.882 for each agostic interaction (IrÀC9 and IrÀH9A, respectively). The four-coordinate IrIII complex adopts a pseudooctahedral environment with two vacant sites in a cis arrangement with the carbenic carbon atoms trans to each other but cis to the two cis hydride ligands. Furthermore, the two cis vacant positions are sterically protected by two agostic interactions with the nearby tbutyl group. The structure of 3 provides a rare example of a “proposed” intermediate for an intramolecular CÀH activation process. The ItBu ligand apparently provides a unique stabilizing effect in coordinatively unsaturated iridium complexes.[10] The X-ray structure of 3 indicates the presence of a double agostic interaction, but the NMR spectrum at ambient temperature indicates a highly symmetrical structure. The 1H NMR spectra that were recorded over a range of temperatures (175–300K) to probe for agostic interactions in solution revealed interesting dynamic behavior (Figure 2).A dynamic process is frozen out at low temperature, which leads to two distinct environments for the tbutyl and imidazole moieties. We attribute the appearance of the lowtemperature spectra to a lower symmetry structure consistent with the solid-state structure. The switching of the tbutyl groups between their free environments and undergoing agostic interactions is responsible for the changes in the NMR spectra with temperature (Figure2). Lineshape analysis reveals that this process has ΔH= 7.68 kcal molÀ1, ΔS= À11 cal molÀ1 per degree, and ΔG