氨基三氧化铼：阻碍C-H-M相互作用的病例？
Amido Rhenium Trioxides: Cases of Hindered Agostic C-H-M Interactions?
摘要：
以Re 2 O 7、Me 3SiCl和相应的胺（iPr）2NH、（iPr）（Cy）NH和（Cy）2NH为原料，采用一锅法合成了（iPr 2N）ReO 3、（iPrCyN）ReO 3和（Cy 2N）ReO 3（Cy =环己基）三氧化二酰胺。在固态下，所有三种配合物的酰胺基配体不对称地配位到ReO 3核心，允许在每种情况下进行一次短Re-H-C接触，这可能表明存在β-agostic相互作用。然而，电荷密度分布的分析为我们提供了明确的标准，即β-agostic相互作用被氧代基团的反式影响所抑制。与结构上相关的四配位d 0钛酰胺配合物的比较突出了一个系统的概念，如何在这些配合物中的β-agostic相互作用的程度可以通过减少反式影响的共同配体控制。因此，我们建议在共价M-H-C原则上由路易斯酸性金属中心的空配位位点支持但实际上由于电子原因而受阻的情况下使用“受阻的agostic相互作用”。我们进一步指出，电子阻碍起源于transinfluence可能会被推翻，通过改变s/p-供体配体的特性。
英文摘要：
The amido rhenium trioxides of composition (iPr2N)ReO3, (iPrCyN)ReO3 and (Cy2N)ReO3 (Cy = cyclohexyl) were synthesized in a one pot reaction starting from Re2O7, Me3SiCl and the corresponding amines (iPr)2NH, (iPr)(Cy)NH, and (Cy)2NH, respectively. In the solid state the amido ligands of all three complexes are asymmetrically coordinated to the ReO3 core allowing for one short Re-H-C contact in each case which might indicate the presence of beta-agostic interaction. However, analysis of the charge density distribution provided us clear-cut criteria that beta-agostic interactions are suppressed by the trans-influence of the oxo-groups. Comparison with structurally related tetra-coordinated d0 titanium amido complexes highlighted a systematic concept how the extent of beta-agostic interactions in these complexes can be controlled by reducing the trans-influence of the co-ligands. We therefore suggest to employ the expression "hindered agostic interactions" in cases where covalent M-H-C are in principle supported by vacant coordination sites at Lewis-acidic metal centers but are actually hindered for electronic reasons. We further point out that electronic hindrance originating from the transinfluence might be overruled by changing the s/p-donor characteristics of ligands.
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