Ⅰ. DFT Study On The Mechanism Of Selective C-F Bond Activation Of Perfluorotoluene And Octafluoronaphthalene Promoted By Electren-rich Iron,Cobalt And Nickel ComplevesⅡ. Appliaction Of Electron-rich Iron And Nickel Compleves In Chemical Bends (C-O,N-H

Fluorinated compounds are extensively applied in chemistry, chemical industry, materials, pesticide, pharmaceuticals, and so on, especially fluorinated aromatic compounds. Additionally, C-F bond is so strong that fluorocarbons persistence in atmosphere which causes global warming and ozone depletion. In this sense, there is an urgent demand to develop effective routes to convert detrimental fluorocarbons into environmentally benign derivatives. In recent years, selective C-F bond activation has attracted considerable attention because it offers potential opportunities both in synthesis and disposal of polyfluorinated compounds. Different mechanisms of C-F bond activation have been proposed, including oxidative addition, electron transfer, nucleophilic attack, phosphine-assisted pathway and so on.Our group has also obtained much progress in C-F bond activation. However, most of the mechanistic details shown in have not been demonstrated directly via a molecular level theoretical study using the well-established tools of quantum chemistry. To better understand the selective C-F bond activation via low-valent transition metal complexes and to rationalize the earlier experimental findings from our group, quantum chemistry calculation has been performed.Based on the facts aforementioned, the mechanistic details of selective C-F bond activation promoted by low-valent Fe(PMe3)4、Co(PMe3)4and Ni(PMe3)4were investigated by performing density functional theory calculations.The main innovative conclusions obtained in this thesis are shown as follows:(1) While the selective C-F bond activation of perfluorinated toluene (CF3C6F5) by a trimethylphosphinesupported cobalt(O) complex Co(PMe3)4has been achieved in our previous work (Organometallics,2009,28,5771-5776), the proposed mechanism has not been demonstrated directly through quantum chemistry calculations. The present work provides a supplementary theoretical study on a detailed mechanism to better understand the synergistic effect of cobalt center and free PMea ligand on the selective C-F bond activation of CF3C6F5. The calculated results indicate two C-F bonds in CF3C6F5are activated successively via a similar mechanism:the initial oxidative addition of C-F bond to cobalt(O) center, followed by F atom abstraction by a free PMe3ligand. However, it is found that the F atom abstraction with a barrier of34.92kcal mol-1is the bottle-neck step of the first C-F bond activation, while the oxidative addition of C-F bond is the rate-determining step of the second C-F bond activation with a barrier of30.85kcal mol-1. The theoretical results confirm the C-F activation mechanism proposed in our early work, i.e., the Co complex and free PMe3ligands cooperatively promote the C-F bond activation.(2) Our prior investigation indicated that zero-valent Fe, Co and Ni complexes exhibited different reactivity in promoting the activation of C-F bond of octafluoronaphthalene. Co(PMe3)4was found successfully achieving the activation of C-F bond, while Fe(PMe3)4and Ni(PMe3)4come to nothing. To better understand these interesting phenomena, a DFT calculation has been carried out to investigate the mechanistic details of the corresponding reactions. The calculated results demonstrate1) Co(PMe3)4promotes the C-F bond activation via two elementary steps:the initial oxidative addition of C-F bond to cobalt(O) center, followed by F atom abstraction by a free PMe3ligand and forming the highly active·PMe3F radical. F2PMe3is immediately formed through the disproportionation reaction of·PMe3F radical.2) For Fe(PMe3)4, the calculated results suggest the reaction may be feasible. However, the experimental findings indicate Fe(PMe3)4is easy to destroyed via heating.3) As for Ni(PMe3)4, the DFT results show2-C-F bond can be successfully activated via one elementary step and the activation energy is only24.11kcal mol-1. Moreover, the product obtained via calculation is thermodynamically stable. These exciting results encourage us to reexperimentalize the reaction. Surprisingly, the activation of C-F bond of octafluoronaphthalene via Ni(PMe3)4is realized after we increasing the temperature to80℃. These facts repeatedly confirm the important role of computation chemistry played for experimental chemistry. Recently, Concerns about environmental pollution, made the academic research toward to develop the method to use cheap, readily available and environmentally friendly raw materials to synthesize the desired product. The widely existed phenols and alcohols, which are environmentally friendly and easy to get, as an alternative to halides have the basic advantage and will be the future synthesis trend. Currently, direct transformation carbon-oxygen of alcohol is rare. While the carbon-oxygen bond activation of ether is dominated by nickel, report about iron-catalyzed carbon-oxygen bond activation is scarce mainly focus on Kumada Cross-Coupling Reactions, so we decided to explore the carbon-oxygen bond activation by PMe3supported iron complexes.Activation of the N-H/O-H bond of amines or phenols by a transition-metal center may play an important role in developing new catalytic processes based on these abundant compounds.Based on the facts aforementioned, electron rich iron complexes applied in C-O bond activation were studied; N-H/O-H bonds activation mediated by Fe and Ni complexes were also stdudied.The main innovative conclusions obtained in this thesis are shown as follows:(1) We synthesis a series of esters based on8-hydroxyquinoline (subsrates1-4), and explored their reactions with Fe(PMe3)4、Co(PMe3)4and Ni(PMe3)4. And only the reactions of8-quinolinyl esters with iron(O) complex can afford hexa-coordinate chelate-[C,N] iron(Ⅱ) carbonyl complexes via Cacyl-O bond activation and subsequent decarbonylation. The products obtained after the Cacyl-O bond activation were characterized through IR,1H NMR,31P NMR and elemental analysis. And their crystal structures were determined by X-ray diffraction.To our knowledge, this could be the first example of iron(0)-promoted C-O bond activation.(2) Embodied on8-hydroxyquinoline, we synthesized ether substrates17-22. The reaction of substrate18with Fe(PMe3)4afford complexes23. Complexes23was isolated and characterized. From the crystal structures determined by X-ray diffraction, complexes23was found have a distorted tetrahedral configuration. The possible mechanism of the formation process of23was also proposed. As for substrate21, its reaction with Fe(PMe3)4affords an complex including Fe-H bond, which has been confirmed by infrared absorption peaks, and further study is also needed.(3) Using cheap and easy to obtain metals, such as iron or nickel to achieve N-H bond activation and develop a new catalytic reaction system based on nitrogen-containing compounds is of great significance.we synthesized a series of amide and thioamide compounds (25-28). Compound25react with Ni(PMe3)4leading to the formation of complexes29, which has a square planar geometry and Ni η2coordinated to the C=S double bond. Both26and28can react with NiMe2(PMe)3or Fe(PMe3)4, to activate the N-H bond, however the reaction mechanism is much different. Carboxamide reacted with Fe(PMe3)4leads to an S-H bond activation product. Because of the substrate’s imino isomerization reaction, carboxamide is peffered alcohol configuration in the presence of Fe(PMe3)4. The reaction of NiMe2(PMe3)3with the amide only affords a N-H bond activation product through the elimination of a molecular CH4.(4) Complexes36,38were obtained in O-H bond activation of8-Hydroxyquinoline promoted by NiMe2(PMe3)3and Fe(PMe3)4. Iron hydride complexes38can react with Mel, CO, Phenylacetylene.