Theoretical Insights Into The Reaction Of Methane Activation By Transition Metal Ions And Their Cpmplexes

The methane catalyzed by transition metal complexes as catalysts has allowed the controlledtransfer of carbene units into organic substrates. The activation of C-H and C-C bonds of alkanes bygas-phase atomic transition metal ions has been studied intensely over the past decade because of itsimmense scientific and industrial importance. A number of experimental and theoretical studies ofatomic transition-metal ions with small alkanes have provided a wealth of insight concerning theintrinsic interactions of metal ions with bonds composed of carbon and hydrogen atoms. First-rowand second-row transition-metal cations are found to be much less reactive toward methane thantheir third row counterparts, and activation of methane is rarely observed. The studies demonstratethat methane can be spontaneously activated by the third-row transition metal ions Os⁺, Ir⁺, Pt⁺, etc.,yielding the metallic carbene cations and H2. The addition of a single ligand to the metal center candramatically alter the reactivity, and the kind of reaction have been studied in theoreticalinvestigation at the DFT level, but there is little theoretical report about the mechanism of methanecatalyzed by5d latter transition metal.In this paper, we chose several typical reactions that have been carefully studied using quantummethods, obtained some interesting results. On the basis of the molecular orbital theory, thetradition transition state theory as well as quantum chemistry theory, the systems chose have beeninvestigated using Density Functional Theory （DFT）. The structures of the reagents, the reactionproducts and transition states along the reaction paths have been obtained, then obtained thereaction surfaces, the spectrum datum, thermodynamic datum as well as the information of orbitals.The reaction mechanism has been argued deeply using these data.The whole paper consists of five chapters.Chapter1is mainly about the development and application of quantum chemistry, thecharacteristics of methane catalyzed by ligated transition metal and the content of our work inpaper.Chapter2summarizes the theory and computation methods, which offer the useful and reliablequantum methods for us.In chapter3, we have engaged in a detailed study to elucidate the mechanism of methanecatalyzed by ligated transition metal MH⁺（M=Os, Ir, Pt） using the quantum methods and to give asuitable explanation to the experimental results. Thus, the present calculations can provide comprehensive information on the reactions of MH⁺（M=Os, Ir, Pt） and CH4, so as to shed somelight on optimal design of further related syntheses in future. The results indicate that the reactiontakes place more easily along the low-spin potential energy surface. OsH⁺, IrH⁺and PtH⁺are likelyexcellent mediators for CH4activation. The exothermicities of the reactions are3.99,15.66, and12.14kcal/mol, respectively.In chapter4, the reaction mechanism of Ru⁺and methane has been studied. The reaction of Ru⁺and methane has three alternative reaction paths. There is a spin crossing occurring in the reactionpath Ru⁺+CH₄â†'Ru（CH₂）⁺+H₂. The overall reaction is endothermic by25.2kcal/nol with nobarrier in excess of this. The other two paths are not likely to take place under room temperature.In chapter5, the reaction mechanism of [Pt（H）（OH）]⁺and methane has been studied. Theoverall reaction in the favored doublet state is endothermic by3.0kcal/mol. Compared to Pt⁺,[Pt（H）（OH）]⁺is less reactive with respect to the activation of methane.