学 位 記 番 号 理工博 第

氏 名 易

军

所 属 理工学研究科 分子物質化学専攻 学 位 の 種 類 博士（理学）

学 位 記 番 号 理工博 第

号 学位授与の日付 令和元年

月

日

課程・論文の別 学位規則第４条第１項該当

学 位 論 文 題 名

遷移金属錯体触媒の

、

、および反応メカニズムに関す る理論的研究

英文

論 文 審 査 委 員 主査 准教授 中谷 直輝 委員 教授 波田 雅彦 委員 教授 野村 琴広

【論文の内容の要旨】

Transition metal complexes are one of the most important research topics in the areas of inorganic, organometallic, and catalysis chemistry. A great number of transition metal complexes have been synthesized and particularly in catalysis chemistry, they play important role as a catalyst for production of variety of useful compounds from laboratory experiments to industry. However, fundamental understanding of the working mechanism of catalysis is a critical issue for the rational design of a new catalyst with excellent reactivity and selectivity. Moreover, the reactivity of transition metal complexes is basically correlated to kind of ligands, oxidation and/or spin state, and geometry around the metal center. Therefore, the present work aimed to get insight into these molecular properties based on electronic structure calculations and spectrum simulations to interpret the reaction mechanism and the reactivity. This thesis consists of seven chapters; the first two chapters contain general introduction and basic theories of the quantum chemistry that I employed in this thesis, the next four chapters describe practical applications of quantum chemistry calculations to investigate NMR, XANES, and energy changes of transition metal complex catalysts to totally reveal the reaction mechanisms, and the last chapter draws general conclusions of this thesis.

Chapter 1 introduces backgrounds of the present study; introduction to transition

metal NMR, XANES spectroscopy, reactions and experimental findings in vanadium, titanium, and iridium based complexes, as well as the aim of this thesis.

Chapter 2 contains brief introductions to the density functional theory (DFT), the time-dependent DFT (TD-DFT), the transition state theory, and the molecular orbital theory. The details about computational models that I used in this thesis are also described in this chapter, such like functional, basis set, and software which were used to carry out the calculations.

Chapter 3 describes a theoretical study of ⁵¹V-NMR chemical shifts of polymerization catalysts based on the DFT calculations with multiple linear regression analysis (MLRA). The calculated ⁵¹V-NMR chemical shifts well agree with the experimental values. Our results clearly showed that the solution-phase structures are quite different from the crystal structures. According to MLRA, the ⁵¹V-NMR chemical shifts can be well fitted to natural charge of the V center, the HOMO-LUMO energy gap, and Wiberg bond index of the V=N bond. The obtained MLR model showed that the larger ⁵¹V-NMR chemical shift is obtained by the higher Wiberg bond index, the smaller natural charge, and the smaller HOMO-LUMO gap. These indicated that strong electron-donating ligands, a tight V=N bond, and smaller HOMO-LUMO energy gap result in higher ⁵¹V chemical shift. Since the higher ⁵¹V-NMR chemical shift correlates with the lower catalytic activity, the MLR model suggests that the higher catalytic activity can be achieved by a V catalyst which has electron-with-drawing ligands, a weaker V=N bond, and/or larger HOMO-LUMO energy gap.

Chapter 4 describes the TD-DFT study of the X-ray absorption near-edge structure (XANES) of V and Ti complexes. The calculated spectra well reproduced shapes of the experimental K-edge spectra for various V and Ti complexes. From our detailed analysis, the pre-edge feature was characterized to dipole-allowed transition from 1s orbital to 3d-4p hybridized orbital of the metal center. As a result, the intensity of the pre-edge peak increases as the p-hybridization ratio increases. A characteristic shoulder peak which was observed in the chloride complexes was theoretically assigned to be a couple of excitations from the metal 1s orbital to the chloride 4p orbitals. A similar but weak absorption band was also calculated for the methyl complex, which was assigned to be a couple of excitations to the C-H anti-bonding orbitals. Interestingly, the shoulder peak only appears when these vacant orbital interacts with another vacant orbital. However, because methyl rotation weakens this interaction, the shoulder peak would not be observed in solution phase at the room temperature.

Chapter 5 describes a theoretical study on the reaction mechanism of the V catalysts for ethylene polymerizations. Particularly, role of an aluminum co-catalyst for

the ethylene polymerization have been theoretically investigated. The active species obtained from which the pre-catalyst reacts with the co-catalyst was characterized by combination of the experimental and the simulated XANES spectra. According to our assignment of the active species, I further investigated the energy changes along with the catalytic cycle based on DFT calculations. The overall energy barrier of this V-catalyzed ethylene polymerization was estimated to be 22 kcal/mol.

Chapter 6 describes a DFT study of the reaction mechanism of the iridium-catalyzed enamine synthesis via amide reduction. There are five possible catalytically active species formed by the single or double oxidative addition of tetramethyldisiloxane (TMDS) to iridium complex. In this reaction, the hydrosilylation is the key step, and thus, the prevalent Chalk-Harrod (CH) and modified Chalk-Harrod (mCH) reaction paths have been explored. As the activation barrier of the Si-O bond formation is obviously larger than that of the Ir-O bond formation, the CH mechanism involving insertion of the amide C=O bond into the Ir-H bond is supported from our results. The amides insertion step gives the highest energy barrier both in the CH and mCH mechanism. Thus the amides insertion step is the rate-determining step.

Chapter 7 draws general conclusions that the NMR and XANES spectra simulations are to be powerful methods to extract the factors of chemical reactivity and unravel the complicated reaction mechanism of transition metal complex catalysts.

These theoretical methods play an even more important role for the rational design of a new catalyst.