CH bond activation of methane in aqueous solution: A hybrid quantum mechanical/effective fragment potential study.

CH bond activation of methane in aqueous solution: A hybrid quantum mechanical/effective fragment potential study.

MedLine Citation:	PMID: 21919013 Owner: NLM Status: Publisher
Abstract/OtherAbstract:	In this study, we investigated the CH bond activation of methane catalyzed by the complex [PtCl(4) ](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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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H bond promoted by the [PtCl(4) ](2-) catalyst in aqueous solution occurs through a direct oxidative addition of the C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.

Authors:	Júlio C S Da Silva; Willian R Rocha
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Publication Detail:	Type: JOURNAL ARTICLE Date: 2011-9-15
Journal Detail:	Title: Journal of computational chemistry Volume: - ISSN: 1096-987X ISO Abbreviation: - Publication Date: 2011 Sep
Date Detail:	Created Date: 2011-9-15 Completed Date: - Revised Date: -
Medline Journal Info:	Nlm Unique ID: 9878362 Medline TA: J Comput Chem Country: -
Other Details:	Languages: ENG Pagination: - Citation Subset: -
Copyright Information:	Copyright © 2011 Wiley Periodicals, Inc.
Affiliation:	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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