期刊
JOURNAL OF ORGANOMETALLIC CHEMISTRY
卷 845, 期 -, 页码 71-81出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jorganchem.2017.02.040
关键词
Palladacycle; Pincer; Catalysis; DFT
资金
- Royal Thai Government
- University of Sussex
- Tertiary Education Trust Fund of Nigeria
Density functional theory (DFT) is used to determine the mechanism for Pd(0) generation from pincer palladacycle pre-catalysts. The elucidated mechanisms comprise two key steps, transmetallation and reductive elimination. It is found that the presence of a base in the pre-catalyst activation step serves to significantly lower the Gibbs free energy barrier of the transmetallation step and the Gibbs free energy of the overall pre-catalyst activation. The DFT results are used to rationalize the catalytic activity of a number of pincer palladacycles in the Suzuki-Miyaura coupling of sterically demanding and electronically deactivated aryl bromides with 2-tolylboronic acid. A strong correlation exists between the Gibbs free energy barrier of the transmetallation step and/or overall pre-catalyst activation energy and the percentage conversions of the Suzuki-Miyaura coupling in the presence of the novel pre-catalysts. The data presented suggest that the slow, controlled release of the true, active catalyst,Pd(0), from the pincer palladacycle pre-catalysts provides the optimum reaction conditions and may be achieved by a high transmetallation energy barrier or overall pre-catalyst activation energy or both. (C) 2017 Elsevier B.V. All rights reserved.
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