MOE Key Laboratory of Bioinorganic and Synthetic Chemistry/KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China.
J Org Chem. 2012 Jul 20;77(14):6076-86. doi: 10.1021/jo300849t. Epub 2012 Jul 11.
The mechanism and intermediates of hydroalkylation of aryl alkynes via C(sp(3))-H activation through a platinum(II)-centered catalyst are investigated with density functional theory at the B3LYP/[6-31G(d) for H, O, C; 6-31+G(d,p) for F, Cl; SDD for Pt] level of theory. Solvent effects on reactions were explored using calculations that included a polarizable continuum model for the solvent (THF). Free energy diagrams for three suggested mechanisms were computed: (a) one that leads to formation of a Pt(II) vinyl carbenoid (Mechanism A), (b) another where the transition state implies a directed 1,4-hydrogen shift (Mechanism B), and (c) one with a Pt-aided 1,4-hydrogen migration (Mechanism C). Results suggest that the insertion reaction pathway of Mechanism A is reasonable. Through 4,5-hydrogen transfer, the Pt(II) vinyl carbenoid is formed. Thus, the stepwise insertion mechanism is favored while the electrocyclization mechanism is implausible. Electron-withdrawing/electron-donating groups substituted at the phenyl and benzyl sp(3) C atoms slightly change the thermodynamic properties of the first half of Mechanism A, but electronic effects cause a substantial shift in relative energies for the second half of Mechanism A. The rate-limiting step can be varied between the 4,5-hydrogen shift process and the 1,5-hydrogen shift step by altering electron-withdrawing/electron-donating groups on the benzyl C atom. Additionally, NBO and AIM analyses are applied to further investigate electronic structure changes during the mechanism.
通过密度泛函理论（B3LYP/[6-31G(d) 用于 H、O、C；6-31+G(d,p) 用于 F、Cl；SDD 用于 Pt]），研究了通过铂(II)中心催化剂通过 C(sp(3))-H 活化芳基炔烃的水合烷基化反应的机制和中间体。使用包括溶剂（THF）的极化连续模型的计算来探索溶剂对反应的影响。计算了三种建议机制的自由能图：（a）导致 Pt(II)乙烯型卡宾形成的一种机制（机制 A），（b）其中过渡态意味着定向 1,4-氢迁移的另一种机制（机制 B），以及（c）一种具有 Pt 辅助的 1,4-氢迁移的机制（机制 C）。结果表明，机制 A 的插入反应途径是合理的。通过 4,5-氢转移，形成 Pt(II)乙烯型卡宾。因此，逐步插入机制是有利的，而电环化机制是不可信的。取代芳基和苄基 sp(3) C 原子的吸电子/给电子基团略微改变了机制 A 前半部分的热力学性质，但电子效应导致机制 A 后半部分的相对能量发生了实质性变化。通过改变苄基 C 原子上的吸电子/给电子基团，可以在 4,5-氢转移过程和 1,5-氢转移步骤之间改变限速步骤。此外，还应用 NBO 和 AIM 分析进一步研究了机制过程中电子结构的变化。
