Theoretical Insights Into The Mechanism Of The Small Molecular Alkane Activation By PtX~+(X=F,Cl,Br,I) And [Ir(H)(OH)]~+

Organic small molecular alkane, such as methane and ethane has been studied intensely over the past decade because of its plays an important role in the organic synthesis and industrial production. A great number of experimental and theoretical studies of atomic transition-metal ions with small alkanes have provided a good insight concerning the interactions of metal ions with bonds composed of carbon and hydrogen atoms. The studies illustrate that the first and second-row transition-metal cations are found to be much less reactive toward small alkane, and activation of alkane is rarely observed. However, the small alkane could be spontaneously activated by the 5-d transition metal ions Os⁺, Ir⁺, Pt⁺, etc. Through the method of adding ligands to the metal center can dramatically change the reactivity of metal with alkane, and the kind of reaction have been studied in theoretical investigation at the DFT level, but there is little theoretical report about the mechanism of ethane catalyzed by 5d halide transition metal ions.In this paper, we using（DFT） methods to study the small molecular alkanes activated by Pt X⁺（X= F, Cl, Br, I） and [Ir（H）（OH）]⁺ and gained some interesting results. On the basis of the molecular orbital theory, the tradition transition state theory as well as quantum chemistry theory, the systems chose have been investigated using density functional theory（DFT）, The structures of the reagents, transition states and products along the reaction paths and the detail reaction surfaces have been obtained, then obtained the thermodynamic datum, spectrum datum, as well as the information of orbitals. The reaction mechanism has been discussed deeply using these data.The whole paper consists of four chapters. Chapter 1 mainly introduced about the development and application of quantum chemistry, evolution of small alkane catalyzed by ligated transition metal. Chapter 2 summarizes the theory of quantum chemistry and calculation methods of this paper, which provide us with reliable and userful quantum methods.Chapter 3 The theoretical calculations for the mechanism of ethane catalyzed by ligated transition metal Pt X⁺（X= F, Cl, Br, I） have been carried out at the DFT（B3LYP） level. Both high-spin and low-spin potential energy surfaces have been characterized in detail. For Pt F⁺/C₂H₆ couple, the whole reaction proceeds on the ground-states potential energy surfaces with a spin-allowed manner. For Pt Cl⁺/C₂H₆, Pt Br⁺/C₂H₆ and Pt I⁺/C₂H₆ systems, the crossing point between the different PESs is required. With the difference of the platinum halide cations, the catalytic reactivity in the elimination of H₂ and expulsions of HX has been changed greatly. For Pt F⁺/C₂H₆ and Pt Cl⁺/C₂H₆ systems, the main catalytic products are HF ⁺ HPt（C₂H₄）⁺ and HCl ⁺ HPt（C2H4）⁺,respectively. For the Pt Br⁺/C2H6 system, the products is a mixture of HBr ⁺ HPt（C₂H₄）⁺ and H₂ ⁺ BrPt（C₂H₄）⁺. For the PtI⁺/C₂H₆ system, the main catalytic product is H₂⁺ IPt（C₂H₄）⁺. Our calculations indicate that the reactions take place more easily along the low-spin potential energy surface and the energy barriers are all located energetically below the entrance and exit channels, thus these complexes are good mediators for the activity of ethane.Chapter 4 In this paper we have carried out a theoretical investigation at the DFT（B3LYP） level of the mechanism of methane catalyzed by ligated transition metal [Ir（H）（OH）]⁺, and the comparison with [Pt（H）（OH）]⁺ and IrH⁺ system has been performed. The results indicate that the activation of methane by [Ir（H）（OH）]⁺ complex is undergoes the two step C-H bond activation to complete. A crossing between high-spin and low-spin potential energy surface takes place at the entrance channel of the reaction, so a pathway is opened up that bypasses an energetically rather unfavorable transition structure with a spin-inversion on the low-spin singlet surface. The energy barriers of reaction are all located energetically below the entrance and exit channels, thus, the complex [Ir（H）（OH）]⁺ is a good mediator for the activity of methane.