Pliego JR. Theoretical free energy profile and benchmarking of functionals for amino-thiourea organocatalyzed nitro-Michael addition reaction.
Phys Chem Chem Phys 2020;
22:11529-11536. [PMID:
32393952 DOI:
10.1039/d0cp00481b]
[Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Amino-thiourea organocatalysis is an important catalytic process for enantioselective conjugate addition reactions. The interaction of the reactants with the catalyst has a substantial effect of dispersion forces and is a challenge for a reliable description when applying density functional theory. In this report, the classical addition of acetylacetone to β-nitro-styrene catalyzed by Takemoto's catalyst in toluene was studied using the PBE functional for geometry optimization and the DLPNO-CCSD(T) benchmark method for single point energy. The complete free energy profile calculated for the reaction was able to explain all experimental observations, including the fact that the carbon-carbon bond formation step is rate-determining. The overall barrier was calculated to be 22.8 kcal mol-1 (experimental value approximately 20 kcal mol-1), and the enantiomeric excess was calculated to be 88% (experimental value in the range of 84 to 92%). Some functionals were tested for single point energy. The hybrid B3LYP presented a high mean absolute deviation (MAD) from the DLPNO-CCSD(T) benchmark method by approximately 20 kcal mol-1. The inclusion of empirical dispersion correction in the B3LYP method decreased the MAD to 6 kcal mol-1. Even the double-hybrid mPW2-PLYP and B2GP-PLYP methods had MAD values of approximately 5 kcal mol-1. The inclusion of the dispersion correction decreased the MAD to 3.6 kcal mol-1. M06-2X and ωB97X-D3 were the most accurate among the tested functionals, with MADs of 2.5 kcal mol-1 and 1.8 kcal mol-1, respectively. Additivity approximation of the correlation energy was also tested and presented a MAD of only 0.6 kcal mol-1.
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