Palladium-Catalyzed Meta-Selective C–H Bond Activation with a Nitrile-Containing Template: Computational Study on Mechanism and Origins of Selectivity

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• 作者：Yun-Fang Yang ; Gui-Juan Cheng ; Peng Liu ; Dasheng Leow ; Tian-Yu Sun ; Ping Chen ; Xinhao Zhang ; Jin-Quan Yu ; Yun-Dong Wu ; K. N. Houk
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 8, 2014
• 年：2014
• 卷：136
• 期：1
• 页码：344-355
• 全文大小：747K
• ISSN：1520-5126

文摘

Density functional theory investigations have elucidated the mechanism and origins of meta-regioselectivity of Pd(II)-catalyzed C鈥揌 olefinations of toluene derivatives that employ a nitrile-containing template. The reaction proceeds through four major steps: C鈥揌 activation, alkene insertion, 尾-hydride elimination, and reductive elimination. The C鈥揌 activation step, which proceeds via a concerted metalation鈥揹eprotonation (CMD) pathway, is found to be the rate- and regioselectivity-determining step. For the crucial C鈥揌 activation, four possible active catalytic species鈥攎onomeric Pd(OAc)₂, dimeric Pd₂(OAc)₄, heterodimeric PdAg(OAc)₃, and trimeric Pd₃(OAc)₆鈥攈ave been investigated. The computations indicated that the C鈥揌 activation with the nitrile-containing template occurs via a Pd鈥揂g heterodimeric transition state. The nitrile directing group coordinates with Ag while the Pd is placed adjacent to the meta-C鈥揌 bond in the transition state, leading to the observed high meta-selectivity. The Pd₂(OAc)₄ dimeric mechanism also leads to the meta-C鈥揌 activation product but with higher activation energies than the Pd鈥揂g heterodimeric mechanism. The Pd monomeric and trimeric mechanisms require much higher activation free energies and are predicted to give ortho products. Structural and distortion energy analysis of the transition states revealed significant effects of distortions of the template on mechanism and regioselectivity, which provided hints for further developments of new templates.