The DFT Study On C-C And C-H Bond Activated By Transition Metal

Over the past few decades, the σ-bond is the simplest, strongest, and mostordinary among chemical bonds, many organometallic chemists have been attractedby a variety of selective the C-C and C-H bond activation of alkanes by transitionmetal atoms （M）, ions （M⁺） and theiroxide ions （MO⁺） in the gas phase. Thus, more orless sophisticated mass spectrometric techniques have been applied to providethermochemical data as well as some insights into the reaction mechanisms andperiodic trends of reactivity between transition metal ions and small ligands.Simultaneously, the C-C and C-H bond activated by transition metal have been thesubject of theoretical research due to the crucial role that these most ordinary bondsplay in lots of reactions which provides important mechanistic informations andmodels for analogous reactions. In order to probe the σ-bond activation by transitionmetal in the gas phase, one of our current focuses, therefore, has been on the reactionof Ni⁺with butanone and MO⁺with CH4.In the paper, on the basis of the molecular orbital theory, the tradition transitionstate theory as well as Darrin J. Bellert group、P. B. Armentrout experimental results,the systems choosed have been carefully investigated using Density Functional （DFT）Methods. The structures of the reagents, the reaction products and the transition statesalong the reaction paths have been obtained, and then obtained the reaction surfaces,the spectrum datum, the thermodynamic datum as well as the information of orbitals.The reaction mechanism has been argued deeply using these data, which couldprovide helpful evidence for further experimental studies.The whole paper consists of four chapters. Chapter1mainly reviews theexperimental and theoretical investigations for the C-C and C-H bond activation ofalkanes by transition metal and our main work in this paper. The second chaptersummarizes the theory of quantum chemistry and calculation methods of this paper.The contents of two chapters were the basis and background of our studies and offerus with userful and reliable quantum methods.In chapter3, the reaction of Ni⁺with butanone have been investigated using DensityFunctional. The calculated results show that the processes of activate two different σ-bond of C-C bond coexisted in the reaction system and they are parallel reactions.Elimination of ethylene and acetaldehyde corresponds to the C-C₂H₅bond is activatedwhile elimination of methane correspond to C-CH₃bond is activated. Firstly, theformation and character of the reactant concomplexes had been discussed using theelectronic charge transfer, the NBO analysis and the molecular orbital theory.Secondly, the reaction path channels had been studied on potential energy surfaces（PESs）. Thirdly, the intrinsic reaction coordinate（IRC） was then calculated to probethe reaction path and check if the correct transition state was located. To betterunderstand the competition between the two decomposition processes, we haveanalyzed the crucial activation barriers of the elementary steps using the ActivationStrain Model. Furthermore, the two elimination reactions start with the Ni⁺andbutanone reactants are all exothermic.In chapter4, the gas phase reactions of Mo+with CH4have been investigated. Wediscuss detaily the crossing points between four PESs of different spin multiplicitiesin the reaction pathway to better understand the spin inversion processes involved inthe reaction. A series of crossing points （CPs） involving the structures and energyvalues has been located for the sake of comparison, the mathematical algorithm toMECPs developed by Harvey et al. had also been employed. The energetically morefavorable channel was confirmed according to thermodynamic and dynamic date. Allof our calculated results in this thesis are in agreement with the early experimentalfindings.