How to Control Inversion vs Retention Transmetalation between PdII–Phenyl and CuI–Alkyl Complexes: Theoretical Insight,Journal of the American Chemical Society

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How to Control Inversion vs Retention Transmetalation between PdII–Phenyl and CuI–Alkyl Complexes: Theoretical Insight
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2017-10-02 00:00:00 , DOI: 10.1021/jacs.7b04383
Hong Zheng ₁ , Kazuhiko Semba ₂ , Yoshiaki Nakao ₂ , Shigeyoshi Sakaki ₁

Affiliation

Transmetalation between Pd(Br)(Ph^A)(PCyp₃)₂ (Ph = phenyl, Cyp = cyclopentyl) and Cu(C^aHMePh^B)(NHC) (NHC = 1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene) is an important elementary step in recently reported catalytic cross-coupling reaction by Pd/Cu cooperative system. DFT study discloses that the transmetalation occurs with inversion of the stereochemistry of the C^aHMePh^B group. In its transition state, the C^aHMePh^B group has almost planar structure around the C^a atom. That planar geometry is stabilized by conjugation between the π* orbital of the Ph^B and the 2p orbital of the C^a. Another important factor is activation entropy (ΔS°^‡); retention transmetalation occurs through Br-bridging transition state, which is less flexible than that of the inversion transmetalation because of the Br-bridging structure, leading to a smaller activation entropy in the retention transition state than in the inversion transition state. For C^aHMeEt group, transmetalation occurs in a retention manner. In the planar C^aHMeEt group of the inversion transition state, the C^a 2p orbital cannot find a conjugation partner because of the absence of π-electron system in the C^aHMeEt. Transmetalation of C^aHMe(CH═CH₂) occurs in a retention manner because the vinyl π* is less effective for the conjugation with the C^a 2p because of its higher orbital energy than the Ph π*. The introduction of electron-withdrawing substituent on the Ph^B is favorable for inversion transmetalation. These results suggest that the stereochemistry of the C^a atom in transmetalation can be controlled by electronic effect of the C^aHMeR (R = phenyl, vinyl, or alkyl) and sizes of the substituent and ligand.

中文翻译：

如何控制Pd ^{II –}苯基与Cu ^{I –}烷基络合物之间的反转与保留重金属转移：理论见解

Pd（Br）（Ph ^A）（PCyp ₃）₂（Ph =苯基，Cyp =环戊基）和Cu（C ^a HMePh ^B）（NHC）（NHC = 1,3-双（2,6-二异丙基苯基） -咪唑烷基-2-亚甲基）是最近报道的Pd / Cu协同体系催化交叉偶联反应中的重要基本步骤。DFT研究表明，随着C ^a HMePh ^B基团立体化学的反转，发生了金属转移。在其过渡态中，C ^a HMePh ^B基团在C ^a原子周围几乎具有平面结构。该平面几何形状通过Ph ^B的π*轨道之间的共轭来稳定和C ^a的2p轨道。另一个重要因素是活化熵（ΔS ° ^‡）。保留的过渡金属化是通过Br桥过渡态发生的，由于Br的桥接结构，其弹性不如反型过渡金属化，因此在保留过渡态下的活化熵比在反型过渡态下要小。对于C^一HMeEt基，转移金属化发生在保留方式。在平面的c-^一个HMeEt组反转过渡态中，C^一2p轨道找不到因为在C缺乏π电子体系中的缀合配偶^一个HMeEt。C ^a的重金属化HMe（CH = CH ₂）以保留的方式出现，因为乙烯基π*的轨道能量高于Phπ *，因此与C ^a 2p的共轭作用较弱。在Ph ^B上引入吸电子取代基有利于反型金属转移。这些结果表明，可通过C ^a HMeR（R =苯基，乙烯基或烷基）的电子效应以及取代基和配体的大小来控制金属转移过程中C ^a原子的立体化学。

更新日期：2017-10-03

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