Theoretical Study On The Reaction Mechanisms Of Coupling Reactions And Cyclization Reactions Catalyzed By Several Metals

In this dissertation, the reaction mechanisms of coupling reactions and cyclization reactions catalyzed by several metals have been investigated by using density functional theory (DFT). The investigations include five typical systems:(1) DFT study of ligand-controlled cross-dimerization and cross-trimerization of diphenylacetylene with trimethylsilylacetylene catalyzed by nickel (0) complex, (2) DFT study of the mechanisms of in Pd (â…¡)-HF-catalyzed cyclization reaction and hydrogen shift of 4-benzofuranyl alkynoates:A hydrogen-transport catalysis strategy in the HF-catalyzed indirect [1,3]-hydrogen shift, (3) The role of Al(OH)3 in Aldol reaction catalyzed by chiral diamine QN of cyclohexanone with 4-nitrobenzaldehyde, (4) DFT study of Fe(OTf)2-catalyzed intramolecular amnations of phenyl azido-acrylates, (5) DFT study of Ni(â…¡)-catalyzed transformations of P-H bond.We hope to understand comprehensively the mechanisms of above metal-catalyzed reactions, to explore the essential of the metal catalysis, ligands, additives, substituent groups, reaction temperature and solvents on total reactions. And we also hope to summarize the reaction rules, to guide the experimental study, to reveal the reaction essential. Main research contents and results are shown below.In chapter 1, we introduce briefly the background of coupling reactions and cyclization reactions catalyzed by several metals.In chapter 2, the computational methods of density functional theory (DFT), the polarizable continuum method (PCM) of self-consistent reaction field (SCRF), atoms in molecules (AIM) theory and natural bond orbital (NBO) theory are introduced briefly.In chapter 3, we investigate the reaction mechanism of ligand-controlled cross-dimerization and cross-trimerization of diphenylacetylene with trimethylsilylacetylene catalyzed by nickel (0) complex. The present study will focus on:1) the mechanisms of cross-dimerization of diphenylacetylene with trimethylsilylacetylene,2) the mechanisms of cross-trimerization of diphenylacetylene with trimethylsilylacetylene,3) the influence law of ligands on the selectivity of reactions,4) the role of ligands with different electron-donating ability in the selectivity of the reaction,5) the effect of solvent on the reaction selectivity,6) the comparison of homo- dimerization and cross-dimerization,7) introduced a simple method to estimate the electron-donating ability of various ligands according to the calculated Mulliken charge distribution of ligand-ligand pair,8) the effect of temperature on the reaction selectivity. The calculations suggest that the cross-dimerization involves hydrogen shift process and carbon-carbon coupling reaction. The hydrogen shift process is the rate-limiting step of the cross-dimerization. The cross-trimerization has experienced four transition states. They are the first hydrogen shift reaction, the first C-C coupling reaction, the second hydrogen shift reaction and the second C-C coupling reaction. The second hydrogen shift reaction is the rate-limiting step of the cross- trimerization. Ligands play the decisive role to affect the selectivity of the cross-coupling reaction. The cross-dimerization product should be selectively synthesized using stronger electron-donating ligand, while the cross-trimerization product should be exclusively formed using weaker electron-donating ability ligand. The electron-donating ability of ligands was reconfirmed by the orbital interaction diagram obtained from the AOMix-CDA calculations and electrostatic potential surface. We predict that the use of ligand pyridine-2, 4-dicarbonitrile with the weakest electron-donating ability will significantly promote the formation of cross-trimer. In addition, solvent and temperature had little effect on the reactions.In chapter 4, we study the reaction mechanism of Pd(â…¡)-HF-catalyzed cyclization reaction and hydrogen shift of 4-benzofuranyl alkynoates with the B3LYP functional. We measure the concentration of HF in the imitation of the reaction by ion chromatography according to China’s environmental standard HJ/T84-2001. The test solution consists of TFA (5mL), CH2Cl2 (5mL), and Pd(OAc)2 (0.05 mmol). The test result shows that the concentration of HF is as high as 0.5105 mol/L and reaches the catalyst content. The cyclization reaction and hydrogen transfer have three possible reaction pathways named as A, B and C. In pathway A, the reaction begins with coordination of Pd(OCOCF3)2 to 4-benzofuranyl alkynoates. The first two steps are continuous cyclization reaction and ring-expansion reaction. The two subsequent [1,2]-hydrogen shift reactions are two-step reactions, and the former [1,2]-hydrogen shift is the rate-limiting step. Calculations indicate that the cyclization reaction in pathway B is similar to that in pathway A. The difference lies in that a HF molecule is introduced in the reaction, and HF plays an important role in the transfer of hydrogen in the reaction. This changes the mechanism of hydrogen transfer, so as to reduce the activation energy of the reaction. This indicates that the rate-limiting step of the entire reaction cycle is no longer the hydrogen shift reaction, but the ring-expansion reaction with lower activation energy. Pathway C is a secondary reaction channel. The reaction begins with coordination of Pd(OCOCF3)2 to the carbonyl oxygen atom. Although the coordination process releases energy more than the path of A and B, but the following ring-expansion reaction and hydrogen transfer reaction have high energy barriers. So the pathway B is the optimal mechanism, and the ring expansion reaction is the rate-limiting step of the tandem reaction.In chapter 5, we study the role of Al(OH)3 in Aldol reaction catalyzed by chiral diamine QN of cyclohexanone with 4-nitrobenzaldehyde by the B3LYP functional. The effect of Al(OH)3 on the reaction mechanism and yield are the key content of the research. Generally, enamine will attack 4-nitrobenzaldehyde in four different ways. Here we mainly study the effect of promoter Al(OH)3 on the aldol reaction, so only the reaction mechanism of the dominant conformation, i.e. the stnti-E conformation, is discussed in detail. With or without Al(OH)3, the three transition states in the process of enamine formation have higher activation energies than those several transition states in the process of formation of C-C bond, that is, the rate-limiting step is in the process of forming enamine, especially the formation of imine with highest energy barrier. As the medium in transferring proton process, Al(OH)3 can not only greatly reduce the energies of various intermediates and transition states, but also can significantly reduce the activation energy of each transition state, which indicate that the co-catalyst Al(OH)3 can accelerate the reaction process. The yields of 2-(hydroxyl (4-nitro phenyl) methyl) cyclohexanone are 30% and 98% catalyzed by QN and QN-Al(OH)3 respectively. Theoretical calculation can better match with experimental results.In chapter 6, using the theoretical level UB3LYP/6-311G (LANL2DZ basis set for Fe), we study the intramolecular amination reaction catalyzed by Fe(OTf)2 of phenyl azido-acrylates to synthesize indole-2-carboxylic acid methyl ester. According to different coordination sites on phenyl azido-acrylates, we designed two possible reaction mechanisms, that is, A and B. In the mechanism A, the catalyst coordinates with the nitrogen and oxygen atoms in phenyl azido-acrylates. In mechanism B, the catalyst coordinates with the carbonyl oxygen atom to start the reaction cycle. The calculated results show that the energies and the energy barriers of mechanism A are very low. In phenyl azido-acrylates, the substituent on the benzene ring impacts seriously the yield of the reaction.In chapter 7, using the theoretical level B3LYP/6-311G (LANL2DZ basis set for Ni and Pd), we study the NiCl2-catalyzed transformations of P-H compounds. The calculated results show that the complexes la and 2b are the most stable intermediates. When starts the reaction from la, it is found that the H(2) or H(3) hydrogen transfer reaction is difficult to occur, whereas it is easy if the hydrogen transfer reaction is started from 2b. In the next step, the P(1)-C(9) coupling reaction is easier to occur because of its low energy barrier. In the P-H transformation of hypophosphorous acid ethyl ester with 4-octyne catalyzed by NiCl2, the main reaction channel is 2bâ†'TS2b4aâ†'4aâ†'TS4a5aâ†'5a. The H(2) shift process is the rate-limiting step with activation energy of 82.1 kJ/mol. PdCl2 catalyzed reaction has higher activation energy because it changes the structures of intermediates and transition states, although its catalyzed mechanism is the same with that of NiCl2. Therefore, compared with PdCl2, NiCl2 is a better catalyst for P-H transformation of hypophosphorous acid ethyl ester with 4-octyne.