Ⅰ Sthesis And Catalysis Reactivity Of [PSiP] Pincer Iron, Cobalt And Nickel Complexes Formed By Si-H Bond Activation Ⅱ The Mechanism Of Synthesis Of Fluorinated Aromatic Compounds And The Reactivity Of Iron Hydride Complexes

Chemical synthesis is bound up with our lives. The activation and functionalization of inert bonds become more and more important in chemical synthesis. In recent years, the Si-H bond activation has become a hot topic. The Si-H bond can be activated either by precious metals or by base metals. The mechanism of Si-H bond activation of the non-auxiliary molecule is relatively simple. The Si-H bond activation of pincer ligand focuses on compounds containing N anchor group and P anchor group. The complexes generated by Si-H bond activations have been widely used. These complexes can be used either as reactants or as catalysts in organic reactions, such as the synthesis of N2 adduct, the capture of CO2 and application in transfer hydrogenation reaction of aldehydes and ketones. So new ligands containing Si-H bond needed to be designed.The main contents of this paper are the Si-H bond activation of [PSiP] type pincer ligands and the applications of these complexes in catalytic reactions. The main research tasks are as follows.1. A new N-heterocyclic silyl pincer ligand 2 was designed. There is a methyl which is an electron-rich group. The backbond formed from metal center to Si is weaker in this case. So the complexes generated by Si-H bond activation perhaps have better reactivity.2. The Si-H activations of compound 2 were carried out by Fe(PMe3)4, Co(PMe3)4, Ni(PMe3)4, CoCl(PMe3)3 and CoMe(PMe3)4. Typical iron hydrido complex 3 was obtained by the reaction of ligand 2 with Fe(PMe3)4. Complex 3 was not a good catalyst for the reduction of aldehydes and ketones. When complex 7 was treated with trimethylsilylacetylene, isomer complexes 10 and 11 were formed. The combination of compound 2 with CoMe(PMe3)4 afforded Co(I) complex 7. Complex 7 was treated with Mel, the Co(II) complex 8, rather than Co(III) complex, was isolated. Co(III) complex 12 was generated by the reaction of compound 2 with CoCl(PMe3)3 or the combination of complex 7 with HC1.3. Complex 12 was a good catalyst for Kumada coupling reactions, especially for the reaction of Grignard reagent with aryl bromide. The reaction conditions (40℃,24 h, and THF as the solvent) were used. The highest yield was 88%. For the coupling reaction of Grignard reagent and aryl halide, catalytic efficiency was relatively lower. The reaction conditions (50℃,48 h, and THF as the solvent) were selected. The highest conversion rate was 90% and the highest yield was 84%. Moreover, complex 12 was a good catalyst for coupling reaction of dualchloro aryl with Grignard reagent.4. The reactions of [PSiP] ligands 14 and 18 with Fe(PMe3)4, Co(PMe3)4, CoCl(PMe3)3 and CoMe(PMe3)4 were explored. The [PSiP] pincer iron and cobalt complexes 15,16,19,20 were obtained. The chemical properties of these complexes need further research.During the study of chemical reaction mechanisms, the organometallic mechanisms are more complicated. The electronic structure of complex is easily affected by ligands structure and coordination strength between ligand and metal. There are different spin and magnetic properties among different complexes. So there are lots of challenges for researchers in capturing intermediates and explaining the experimental phenomena. The theoretical and computational methods make up for the shortage of experimental science. The density functional theory (DFT) can help us understand the mechanism at the molecular level. It gives us a deeper understanding of chemical reactions.The theoretical and computational methods can be found in many explanations of chemical mechanisms. The combinations of experimental chemistry and theoretical chemistry are being gradually accepted by chemists. It can really predict some experimental results and guide the directions of the unknown reactions. Theoretical chemists have made a lot of efforts in these areas.This paper focuses on the mechanisms of several reactions conducted by DFT Methods. The reaction phenomena are explained by potential energy profiles.1. The mechanism of coupling reaction between perfluorinated pyridine and Grignard reagent was explored by density functional theory method. The reaction needs to overcome a barrier of 18.44 kcal/mol. As a contrast, a reported catalyst was added to the reaction. We could find the two kinds of reactions which one was more likely to occur. From the potential energy profiles, it could be found that the coupling reaction without catalyst was more likely to occur. When the catalyst was added to the reaction, the catalyst reacted with the perfluorinated pyridine firstly forming a stable intermediate. Because of high energy barrier (49.43 kcal/mol) of the next step, the reaction halted. It would lead to reduction in the yield of the coupling product. This conclusion was not in accordance with the reaction of the chlorine pyridine with Grignard reagent.2. Two kinds of reactions between hydrido iron complexes and trimethylsilylacetylene were studied by DFT method. The two kinds of hydrido iron complexes both could react with trimethylsilylacetylene. But different products were obtained. The phenomenon of these experiment results need to be explained. So the DFT method was chosen to explain them. The conclusions of reaction between hydrido iron complex 25 with trimethylsilylacetylene were that the product 26 was a thermodynamically stable product. The synthesis process of 26 was like a relay race. So we predicted that the product 30 should be able to be isolated if the reaction condition was controlled. For reaction between complex 27 and trimethylsilylacetylene, the conclusions were that the product 28 was both a thermodynamically stable product and a kinetically stable product. The product 29 could not be isolated under this experiment condition.