Intramolecular Csp3‑H Activation at a Platinum(IV) Center Resulting from O2 Activation: The Role of a Proton-Responsive Ligand and Trans Influence

Aerobic oxidation of a dimethylplatinum(II) complex featuring 1,1-di(2-pyridyl)ethanol as a supporting ligand leads to the formation of two unexpected PtIV complexes (in ∼1:1 ratio), neither of which results from direct oxidation typical for PtII centers supported by popular κ2-(N,N) ligands. While one product features an isomerized PtIV center stabilized by the κ3-(N,N,O) ligand coordination mode, surprisingly, the other product results from intramolecular activation of the ligand methyl fragment. Mechanistic studies, reactivity of model complexes, and DFT calculations reveal that the critical proton-responsive nature of the ligand allows formation of intermediates that result in a concerted metalation deprotonation (CMD)-like C–H activation at PtIV. To the best of our knowledge, this is the first mechanistic delineation of Csp3-H activation at PtIV, despite being known for other high-valent platinum group metal centers.

以1,1-二(2-吡啶基)乙醇（1,1-di(2-pyridyl)ethanol）为支撑配体（supporting ligand）的二甲基铂(II)配合物（dimethylplatinum(II) complex）的需氧氧化反应，生成了两种比例约为1:1的非预期铂(IV)（PtIV）配合物，二者均未遵循由常见κ2-(N,N)型配体（κ2-(N,N)）稳定的Pt(II)中心的典型直接氧化路径。其中一种产物的Pt(IV)中心发生异构化，通过κ3-(N,N,O)配位模式的配体实现稳定；而令人意外的是，另一种产物则源于配体甲基片段的分子内活化。机理研究、模型配合物（model complexes）的反应性考察以及密度泛函理论（DFT）计算表明，该配体特有的质子响应特性，可促成关键中间体的生成，进而在Pt(IV)中心发生类协同金属化去质子化（CMD）型C(sp³)-H键活化（Csp3-H activation）。据我们所知，尽管其他高价铂族金属中心的C(sp³)-H键活化已有报道，但本研究首次实现了Pt(IV)中心C(sp³)-H键活化的机理解析。