Ligand Effects on Rates and Regioselectivities of Rh(I)-Catalyzed (5 + 2) Cycloadditions: A Computational Study of Cyclooctadiene and Dinaphthocyclooctatetraene as Ligands,Journal of the American Chemical Society

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Ligand Effects on Rates and Regioselectivities of Rh(I)-Catalyzed (5 + 2) Cycloadditions: A Computational Study of Cyclooctadiene and Dinaphthocyclooctatetraene as Ligands
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2012-06-21 , DOI: 10.1021/ja3041724
Xiufang Xu _{1,

2} , Peng Liu ₂ , Adam Lesser ₃ , Lauren E. Sirois ₃ , Paul A. Wender ₃ , K. N. Houk ₂

Affiliation

The first theoretical study on the effects of ligands on the mechanism, reactivities, and regioselectivities of Rh(I)-catalyzed (5 + 2) cycloadditions of vinylcyclopropanes (VCPs) and alkynes has been performed using density functional theory (DFT) calculations. Highly efficient and selective intermolecular (5 + 2) cycloadditions of VCPs and alkynes have been achieved recently using two novel rhodium catalysts, [Rh(dnCOT)](+)SbF(6)(-) and [Rh(COD)](+)SbF(6)(-), which provide superior reactivities and regioselectivities relative to that of the previously reported [Rh(CO)(2)Cl](2) catalyst. Computationally, the high reactivities of the dnCOT and COD ligands are attributed to the steric repulsions that destabilize the Rh-product complex, the catalyst resting state in the catalytic cycle. The regioselectivities of reactions with various alkynes and different Rh catalysts are investigated, and a predictive model is provided that describes substrate-substrate and ligand-substrate steric repulsions, electronic effects, and noncovalent π/π and C-H/π interactions. In the reactions with dnCOT or COD ligands, the first new C-C bond is formed proximal to the bulky substituent on the alkyne to avoid ligand-substrate steric repulsions. This regioselectivity is reversed either by employing the smaller [Rh(CO)(2)Cl](2) catalyst to diminish the ligand-substrate repulsions or by using aryl alkynes, for which the ligand-substrate interactions become stabilizing due to π/π and C-H/π dispersion interactions. Electron-withdrawing groups on the alkyne prefer to be proximal to the first new C-C bond to maximize metal-substrate back-bonding interactions. These steric, electronic, and dispersion effects can all be utilized in designing new ligands to provide regiochemical control over product formation with high selectivities. The computational studies reveal the potential of employing the dnCOT family of ligands to achieve unique regiochemical control due to the steric influences and dispersion interactions associated with the rigid aryl substituents on the ligand.

中文翻译：

配体对 Rh(I)-催化 (5 + 2) 环加成反应速率和区域选择性的影响：环辛二烯和二萘环辛四烯作为配体的计算研究

使用密度泛函理论 (DFT) 计算，首次对配体对 Rh(I) 催化 (5 + 2) 乙烯基环丙烷 (VCP) 和炔烃的环加成反应的机制、反应性和区域选择性的影响进行了理论研究。最近使用两种新型铑催化剂 [Rh(dnCOT)](+)SbF(6)(-) 和 [Rh(COD)](+ )SbF(6)(-)，与之前报道的 [Rh(CO)(2)Cl](2) 催化剂相比，它提供了更好的反应性和区域选择性。在计算上，dnCOT 和 COD 配体的高反应性归因于空间排斥使 Rh 产物复合物不稳定，催化剂在催化循环中处于静止状态。研究了与各种炔烃和不同 Rh 催化剂反应的区域选择性，并提供了一个预测模型，该模型描述了底物-底物和配体-底物的空间排斥、电子效应以及非共价 π/π 和 CH/π 相互作用。在与 dnCOT 或 COD 配体的反应中，第一个新的 CC 键在炔烃上的庞大取代基附近形成，以避免配体-底物空间排斥。这种区域选择性可以通过使用较小的 [Rh(CO)(2)Cl](2) 催化剂来减少配体 - 底物排斥或使用芳基炔烃来逆转，因为 π/π 配体 - 底物相互作用变得稳定和 CH/π 色散相互作用。炔烃上的吸电子基团更倾向于靠近第一个新的 CC 键，以最大限度地提高金属-基材的反键相互作用。这些空间、电子和分散效应都可以用于设计新的配体，以提供对产物形成的区域化学控制，具有高选择性。由于与配体上的刚性芳基取代基相关的空间影响和分散相互作用，计算研究揭示了使用 dnCOT 配体家族实现独特区域化学控制的潜力。

更新日期：2012-06-21

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