Metallocene alkyl complexes with d⁰ electron configuration and d⁸‐configured square planar α‐diimine late transition metal alkyl complexes show activity in both C−H activation through σ‐bond metathesis and olefin insertion. Herein, we show by analysis of their M−CH₃ ¹³C chemical shift tensors that these reactions involve a π(M−C) interaction in the horizontal plane of the complex for both d⁰ and d⁸ systems. While in the case of d⁰ systems the interaction of an empty metal d‐orbital and a filled carbon p‐orbital causes partial alkylidene character of the M−C bond, the corresponding metal d‐orbital is filled in d⁸ systems, thus generating a filled π*(M−C) orbital that increases the anionic character of the methyl group. This entails fundamentally different reaction mechanisms for d⁰ and d⁸ systems, which are reflected in the structures of the transition states: While d⁰ olefin insertion can be viewed as a [2+2] cycloaddition reaction, d⁸ olefin insertion rather resembles methyl group migration onto a positively polarized olefin, thus explaining the observed differences in regioselectivity. These findings are translated to σ‐bond metathesis, a reaction which is isolobal to olefin insertion for both early and late transition metals.

中文翻译：

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d8和d0配合物中的CH活化和烯烃插入：基本步骤相同，电子不同

具有d ⁰电子构型和d ⁸构型的平面α-二亚胺晚过渡金属烷基配合物的茂金属烷基络合物在通过σ键复分解和烯烃插入的CH活化中均显示出活性。在此，我们通过分析其M C H ₃ ¹³ C化学位移张量表明，对于d ⁰和d ⁸系统，这些反应在复合物的水平面中都涉及π（MC）相互作用。而在d ⁰的情况下系统空的金属d轨道与填充的碳p轨道的相互作用导致M-C键具有部分亚烷基特征，相应的金属d轨道在d ^8个系统中被填充，从而生成填充的π *（M− C）增加甲基的阴离子特性的轨道。对于d ⁰和d ⁸系统，这需要根本不同的反应机理，这反映在过渡态的结构中：虽然d ⁰烯烃插入可以看作是[2 + 2]环加成反应，但d ⁸烯烃插入反而类似于甲基迁移到正极化的烯烃上，因此解释了所观察到的区域选择性的差异。这些发现被转化为σ键复分解，该反应与早期和晚期过渡金属的烯烃插入等距。