A Density Functional Theory Study Of The Spin-forbidden Reactivity Of The Activation Of C₂H₄by Transition Metal

It is well known that the activation of C-H bonds is a key step in numeroussyntheic reactions and catalytic processes. Ethylene, as one of the most importantchemicals, has been widely used in chemical synthesis, hydrogen production, andenergy production. Over the past several decades, gas-phase transition metalchemistry with hydrocarbons has been the subject of intensive experimental andtheoretical research due to the crucial role that these species play in several fields suchas organic chemistry, biochemistry, and catalytic research, which provides importantmechanistic information and models for analogous reactions. As such, ethyleneactivation has been studied extensively by both experimentalists and theorists. Thetheoretical approaches to these reactions also indicated that the transformations ofspin multiplicities occur frequently in thermal reactions. Namely, the reactions did notobey “spin conservation law”. Usually, more than one state is involved in reactionprocess, which ensures the whole reaction always proceeds on the low-energypotential energy surface （PES）. Such a phenomenon is called “two-state reactivity（TSR）”. Today, TSRs have attracted a great deal of interest in the world for the sake ofexact reaction mechanisms.In the paper, we have examined by using density functional theory （DFT） andCCSD （T） methods with corresponding basis sets to explore the reaction mechanismsof TSR. The Gaussian03, Gamess and Molpro program package were performed inthis thesis. More detailedly, geometries and bonding characteristics for all thestationary points involved are investigated at the B3LYP/6-311++G （3df,3pd） level.Final energies are obtained by means of the B3LYP/6-311++G （3df,3pd） single-pointcalculations. In order to evaluate the general reliability of the levels of theory chosen,a comparison of experimentally known binding energies （BDE） with results from theB3LYP calculations is made for a set of representative relevant species.To gain a deepinsight into the interaction between different functional groups, NBO analysis arecarried out on several key minima at B3LYP/6-311++G （3df,3pd） level.The whole paper consists of four chapters. Chapter1mainly reviews the progressand application of quantum chemistry as well as the development and the presentsituation of two-state reactivity. The second chapter summarizes the theoretical硕士研究生：王翠兰专业：物理化学III导师：王永成教授研究方向：化学动力学 background of this thesis; mianly contained the potential energy surface, the naturalbond orbital and spin-orbit coupling mechanism etc. The contents of two chapterswere the basis and background of our studies and offer us with useful and reliablequantum methods.In chapter3and4, the gas phase reactions of the group5metal atoms（V、Ta、Nb） and Th with C₂H₄have been investigated using Density Functional Theory andthe activation of the C-H bonds of the ethylene have been emphasized. To furtherunderstand the "intersystem crossing" mechanism, the spin-orbit coupling matrixelements are discussed in detail. In the same time, we deeply report the reactionmechanism of the group5metal atoms with C₂H₄, possible spin-flip processes and thekey role of SOC. We also discuss detaily the crossing points between two PESs ofdifferent spin multiplicities in the reaction pathway to better understand the spininversion processes involved in the reaction. Our motivation is to facilitate anunderstanding of the role of electronic structures on mechanistic details at a molecularlevel, to clarify the dominant product channels, and all of our calculated results in thisthesis are in agreement with the early experimental findings.