Benchmark approach to search of cost-effective and accurate density functional for homolytic cleavage of CMg bond of Grignard reagent

摘要

Grignard reactions are of importance in organic chemistry for the synthesis beta-keto esters and diethyl malonate, alcohols, aldehydes or ketones, monocarboxylic acids, and other organometallic compounds. Generally, the heterolytic dissociation of CMg bond in Grignard reagent is the key step in these reactions. Recently, homolytic cleavage of the CMg bond in Grignard reagents has been reported in the preparation of stable radicals. These reactive species react with other compounds, which result in the formation of hydrocarbons and their derivatives. Therefore, the study of homolytic cleavage of CMg bonds is quite vital to better understand the kinetics and thermodynamics of these reactions. In the current study, a benchmark approach is adopted to find a cost-effective and accurate density functional (DF) for bond dissociation energies measurement of the CMg bond of Grignard reagents. Twenty-nine DFs from 13 density functional theory (DFT) classes with three types of basis sets (Pople' 6-31G(d) and 6-311G(d), Dunning's aug-cc-pVDZ, and Karlsruhe' def2-SVP basis sets) are implemented for the measurement of dissociation energies of the CMg bond. Theoretical dissociation energy values are compared with experimental reported values of the CMg bond of selected Grignard reagents. TPSSTPSS of the meta-GGA class with 6-31G (d) basis set gave accurate results, and its Pearson's correlation is 0.95. SD, root mean square deviation, and mean unsigned error of this method are 2.36 kcal mol(-1), 2.33 kcal mol(-1), and -0.46 kcal mol(-1), respectively. TPSSTPSS of the meta-GGA class is a one-electron, self-interaction, error-free Tao-Perdew-Staroverov-Scuseria functional that performed better with the 6-31G(d) basis set.