DFT investigation of methane metathesis with L2AnCH3 actinide complexes catalysts (L = Cl, Cp, Cp; An = Ac, Th, Pa, U, Np, Pu)

• Published in: Computational and theoretical chemistry 2018-08, Vol.1138, p.123-134
• Main Authors: Talbi-Ingrachen, Fazia, Talbi, Fatiha, Kias, Farida, Elkechai, Aziz, Boucekkine, Abdou, Daul, Claude
• Format: Article
• Language: English
• Subjects: Actinide complexes; C[sbnd]H bond activation; Chemical Sciences; Cheminformatics; DFT calculations; or physical chemistry; Reaction mechanism; Theoretical and
• ISSN: 2210-271X; 2210-2728
• DOI: 10.1016/j.comptc.2018.06.009

[Display omitted] •Activation of CH/CH4 bond by actinide species viewed as one-proton transfer process.•Computations shows a Transition state characteristic of σ–metathesis reaction.•High ability of uranium and neptunium complexes to activate CH bond of methane.•Crucial role of the 5f actinide orbitals in the lowering of the activation barriers. In order to understand the catalytic activity of the actinide complexes L2AnCH3 (An = Ac, Th, Pa, U, Np and Pu; L = Cl, Cp and Cp∗) towards the activation of the CH bond of methane, relativistic ZORA/DFT investigations have been carried out. The results obtained from Linear Transit (LT) and Intrinsic Reaction Coordinate (IRC) calculations show that the mechanism involved in these reactions starts with a proton transfer from methane to the methyl group of the complex leading to the formation of a four center transition state characteristic of a bond metathesis process. The U(III) and Np(III) complexes exhibit a high ability to activate the methane CH bond, the activation energies being respectively equal to 10.5, 17.1 and 21.0 kcal/mol for Cl2NpCH3, Cp2NpCH3 and Cp∗2UCH3 respectively whereas the Th(III) complexes exhibit the highest activation energy, 34.9 kcal/mol for Cp∗2ThCH3. Since the initial step of the reaction is viewed as a proton transfer, the analysis of the charges evolution and frontier molecular orbitals of the complexes and the transition states, shows that a facile polarization of the bonds involved in the reaction has the effect of reducing the activation energy. The role of the metallic 5f orbitals in the reactivity of the L2AnCH3 compounds towards CH4 is analyzed and discussed. More important the 5f actinide orbital contribution, less important is the activation energy.