Platinum(II)-Catalyzed Cyclization Sequence of Aryl Alkynes via C(sp3)鈥揌 Activation: A DFT Study
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- 作者：Zhi-Feng Li ; Yanzhong Fan ; Nathan J. DeYonker ; Xiting Zhang ; Cheng-Yong Su ; Huiying Xu ; Xianyan Xu ; Cunyuan Zhao
- 刊名：The Journal of Organic Chemistry
- 出版年：2012
- 出版时间：July 20, 2012
- 年：2012
- 卷：77
- 期：14
- 页码：6076-6086
- 全文大小：687K
- 年卷期：v.77,no.14(July 20, 2012)
- ISSN：1520-6904
文摘
The mechanism and intermediates of hydroalkylation of aryl alkynes via C(sp3)鈥揌 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 sp3 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.