C[BOND]H bond activation of methane in aqueous solution: A hybrid quantum mechanical/effective fragment potential study

Authors

  • Júlio C. S. Da Silva,

    1. Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais, Campus Universitário Pampulha, 31270-901 Belo Horizonte, Minas Gerias, Brazil
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  • Willian R. Rocha

    Corresponding author
    1. Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais, Campus Universitário Pampulha, 31270-901 Belo Horizonte, Minas Gerias, Brazil
    • Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais, Campus Universitário Pampulha, 31270-901 Belo Horizonte, Minas Gerias, Brazil
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Abstract

In this study, we investigated the C[BOND]H bond activation of methane catalyzed by the complex [PtCl4]2−, using the hybrid quantum mechanical/effective fragment potential (EFP) approach. We analyzed the structures, energetic properties, and reaction mechanism involved in the elementary steps that compose the catalytic cycle of the Shilov reaction. Our B3LYP/SBKJC/cc-pVDZ/EFP results show that the methane activation may proceed through two pathways: (i) electrophilic addition or (ii) direct oxidative addition of the C[BOND]H bond of the alkane. The electrophilic addition pathway proceeds in two steps with formation of a σ-methane complex, with a Gibbs free energy barrier of 24.6 kcal mol−1, followed by the cleavage of the C[BOND]H bond, with an energy barrier of 4.3 kcal mol−1. The activation Gibbs free energy, calculated for the methane uptake step was 24.6 kcal mol−1, which is in good agreement with experimental value of 23.1 kcal mol−1 obtained for a related system. The results shows that the activation of the C[BOND]H bond promoted by the [PtCl4]2− catalyst in aqueous solution occurs through a direct oxidative addition of the C[BOND]H bond, in a single step, with an activation free energy of 25.2 kcal mol−1, as the electrophilic addition pathway leads to the formation of a σ-methane intermediate that rapidly undergoes decomposition. The inclusion of long-range solvent effects with polarizable continuum model does not change the activation energies computed at the B3LYP/SBKJC/cc-pVDZ/EFP level of theory significantly, indicating that the large EFP water cluster used, obtained from Monte Carlo simulations and analysis of the center-of-mass radial pair distribution function, captures the most important solvent effects. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011

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