Metal Alkyls with Alkylidynic Metal-Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts.,Angewandte Chemie International Edition

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Metal Alkyls with Alkylidynic Metal-Carbon Bond Character: Key Electronic Structures in Alkane Metathesis Precatalysts.
Angewandte Chemie International Edition ( IF 16.1 ) Pub Date : 2020-03-13 , DOI: 10.1002/anie.201915557
Christopher P Gordon ₁ , Christophe Copéret ₁

Affiliation

The homologation of alkanes via alkane metathesis is catalyzed at low temperatures (150 °C) by the silica-supported species (≡SiO)WMe5 and (≡SiO)TaMe4 , while (≡SiO)TaMe3 Cp* is inactive. The contrasting reactivity is paralleled by differences in the 13 C NMR signature; the former display significantly more deshielded isotropic chemical shifts (δiso ) and almost axially symmetric chemical shift tensors, similar to what is observed in their molecular precursors TaMe5 and WMe6 . Analysis of the chemical shift tensors reveals the presence of a triple-bond character in their metal-carbon (formally single) bond. This electronic structure is reflected in their propensity to generate alkylidynes and to participate in alkane metathesis, further supporting the role of alkylidynes as key reaction intermediates. This study establishes chemical shift as a descriptor to identify potential alkane metathesis catalysts.

中文翻译：

具有烷基金属碳键特征的金属烷基：烷烃复分解前催化剂中的关键电子结构。

二氧化硅负载的物质（≡SiO）WMe5和（≡SiO）TaMe4在低温（150°C）催化通过烷烃复分解的烷烃同系物，而（≡SiO）TaMe3 Cp *没有活性。对比反应性与13 C NMR标记的差异平行。前者显示出更多的非屏蔽各向同性化学位移（δiso）和几乎轴向对称的化学位移张量，与在其分子前驱体TaMe5和WMe6中观察到的相似。化学位移张量的分析表明，在它们的金属-碳键（正式为单键）中存在三键特征。这种电子结构反映了它们产生亚烷基炔烃和参与烷烃复分解的倾向，进一步支持了亚烷基炔烃作为关键反应中间体的作用。

更新日期：2020-04-21

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