Rationalization of the mechanism of in situ Pd(0) formation for cross-coupling reactions from novel unsymmetrical pincer palladacycles using DFT calculations

Boonseng, Sarote, Roffe, Gavin W, Targema, Msugh, Spencer, John and Cox, Hazel (2017) Rationalization of the mechanism of in situ Pd(0) formation for cross-coupling reactions from novel unsymmetrical pincer palladacycles using DFT calculations. Journal of Organometallic Chemistry, 845. pp. 71-81. ISSN 0022-328X

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Abstract

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-tolyboronic 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.

Item Type: Article
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0146 Inorganic chemistry
Q Science > QD Chemistry > QD0241 Organic chemistry
Depositing User: John Spencer
Date Deposited: 13 Mar 2017 10:06
Last Modified: 11 Sep 2017 05:26
URI: http://sro.sussex.ac.uk/id/eprint/67061

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