Pyridine- and Quinoline-Derived Imines as N,N-Bidentate Directing Groups in Palladium versus Platinum C–H Bond Activation Reactions,Organometallics

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Pyridine- and Quinoline-Derived Imines as N,N-Bidentate Directing Groups in Palladium versus Platinum C–H Bond Activation Reactions
Organometallics ( IF 2.5 ) Pub Date : 2021-01-12 , DOI: 10.1021/acs.organomet.0c00703
Héctor Torralvo ₁ , Joan Albert ₂ , Xavier Ariza _{1,

3} , Mercè Font-Bardia _{4,

5} , Jordi Garcia _{1,

3} , Jaume Granell ₂ , Manuel Martinez _{2,

6}

Affiliation

The C–H activation by Pd(II) and Pt(II) compounds of a wide range of imines related to 2-pyridinecarboxaldehyde, ArCH═NCH₂(CH₂)_nPh (Ar = 2-pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1), which can be useful for bond functionalization assisted by bidentate directing groups, has been studied. The results indicate that the presence of two methyl groups at the α-carbon, relative to the imine nitrogen atom, facilitates the metalation. The heterocyclic fragment of the chelating ligand also shows a relevant influence on the full process, the cyclometalated compounds being more easily formed for the 2-picolinyl than for the 2-quinolinyl derivatives, while for the 2-pyridinyl derivatives the reaction is less favored. These effects have been found to be determinant for both palladium and platinum compounds. The preparative results can be explained by a steric enhancement of the metalation process, the reaction being strongly favored when bulky substituents are located in the proximity (α-carbon) of the coordinating nitrogen atoms (with both palladium and platinum). Furthermore, surprisingly the formation of six-membered platinacycles is especially favored. The kinetico-mechanistic studies of the C–H activation reaction, on some equivalent Pd(II) and Pt(II) coordination complexes of the family, have shown that the nature of the d⁸ metal center plays a determinant role in the reactivity observed. In this respect, the Pt(II) square-planar center has been found to be much more involved in the energetics of the reaction than the Pd(II) equivalent. The full process can be seen as a mechanistic continuum that goes from an electrophilic substitution (Pd(II) centers) to an oxidative addition/reductive elimination sequence (Pt(II) centers). The observation is directly associated with the fact that the Pt(II) center is prone to the existence of oxidatively added Pt(IV) hydrido complexes.

中文翻译：

吡啶和喹啉衍生的亚胺作为钯中的N，N-双齿定向基团与铂C–H键活化反应

Pd（II）和Pt（II）化合物对与2-吡啶甲醛，ArCH toNCH ₂（CH ₂）_n Ph（Ar = 2-吡啶基，2-吡啶啉基，2 -喹啉基，n= 0，1），这对由双齿导向基团辅助的键官能化很有用。结果表明，相对于亚胺氮原子，在α-碳上存在两个甲基有助于金属化。螯合配体的杂环片段也对整个过程显示出相关的影响，与2-喹啉基衍生物相比，对于2-吡啶啉基而言，环金属化的化合物更容易形成，而对于2-吡啶基衍生物而言，反应则较不受欢迎。已经发现这些效应对于钯和铂化合物都是决定性的。制备结果可以通过金属化过程的空间增强来解释，当大量的取代基位于配位氮原子（与钯和铂）的附近（α-碳）时，强烈推荐该反应。此外，出人意料地特别优选六元铂环的形成。在该家族的一些等效Pd（II）和Pt（II）配位络合物上的CH活化反应的动力学机理研究表明，d的性质⁸金属中心在观察到的反应性中起决定性作用。在这方面，已发现Pt（II）方平面中心比Pd（II）等效物更多地参与反应的能量学。整个过程可以看作是从亲电取代（Pd（II）中心）到氧化加成/还原消除序列（Pt（II）中心）的机械连续体。该观察结果与以下事实直接相关：Pt（II）中心易于存在氧化添加的Pt（IV）氢化物络合物。

更新日期：2021-01-25

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