Selective Activation Of C-F/C-H Bond In Fluoroaryl Compounds:Synthesis Of Iron Hydrides And The Exploration Of Their Catalytic Properties

The selective activation and functionalization of inert bond (such as C-H bond, C-F bond, N-H bond, etc) is an effective method to synthesize new-style complex or compound. The merit of this method is the high efficiency, atom economy and good selectivity. Transition-metal complexes are often utilized in the activation of inert bond due to their high activity. The vacant d orbit of metal atom allows the rich-electronic ligand to coordinate to it. The oxidative addition of inert bond to the metal centre is a common approach to cleave it. Among numerous transition-metal complexes, iron, cobalt and nickel complexes attracted increasing attention, in recent years owing to their low price and eco-friendly property.In this dissertation, the fluoroaryl-imine was chosen as the model substrate. The iron and nickel complexes supported by trimethylphosphine were used to activate the C-H, C-F and N-H bond in fluoroaryl-imines. A series of iron hydrides and binuclear nickel complexes were synthesized and applied as catalysts for different reactions. More specifically, the content of this dissertation comprised four sections.1. The reaction of Fe(PMe3)4 with (2,6-difluorophenyl)arylimine was explored. The selective activation of C-H and C-F bond could be controlled via adjustment of the substituent group on aryl. With the auxiliary of silane, a type of iron hydrides via the activation of C-F bond could be obtained in pretty high yields. The mechanism of this reaction could be confirmed by the in situ 19F NMR spectroscopy. During the research on this topic, the catalytic activity of Fe(PMe3)4 and iron hydrides in defluorohydrogenation reaction of fluoroarylimine was also explored.2. Ten iron hydrides were synthesized through the above method. Subsequently, the property of these iron hydrides was explored. The iron hydrides which could react with CH3I or CH3CH2Br to generate the iron halide complexes with elimination of methane or ethane could also react with Bronsted acid to produce hydrogen. So the formic acid dehydrogenation reaction was catalyzed by these iron hydrides. With the auxiliary of NEt3 and LiBF4 (the Lewis acid), the conversion of FA could be up to 31.2% with the TON of 594. Although the conversion was not desirable, the activity of these complexes still superior to many other complexes. The mechanism of this reaction was researched in detail and the decomposition of catalyst was regarded as the reason why the TON was not high. CO2, an effective C1 feedstock, could react with iron hydrides to afford formate iron(?) complexes. The reaction underwent the insertion of C=O double bond of CO2 into Fe-H bond. The formate iron(?) complexes, which were easy to lose a PMe3 ligand, could be stabilized by CO. CS2 could also react with iron hydrides to generate K2-(S,S) thiocarboxyl iron complexes. What interesting is the three-component reaction of complex 4, CS2 and imine L4, which would generate a special iron(?) complex 30. As for the catalytic reaction, iron hydrides were used to catalyze the hydrosilylation reaction of aldehydes, ketones and ?,?-unsaturated aldehydes. The mechanism was studied via the operando IR spectroscopy and a synergy mechanism was proposed.3. Through the reaction of NiMe2(PMe3)3 with fluoroaryl-imine, a series of imine nitrogen bridged binuclear nickel complexes were obtained. Meanwhile, two special reactions were found. One is the reaction of NiMe2(PMe3)3 with (2,6-difluorophenyl)benzylimine, which could generate a mononuclear nickel complex with a huge amine group. The tautomerism between imine and enamine must be the key point leading to this result. The other is the reaction of NiMe2(PMe3)3 with (2,6-difluorophenyl)2-methylphenylimine or (2,6-difluorophenyl)2,6-dimethylphenylimine. From these reactions, the self-coupling product of fluoroaryl-imine was obtained. Based on this result, the self-coupling reaction of fluoroaryl-imines catalyzed by nickel(O) complexe supported by phosphine ligands was explored. In this reaction, F3CSiMe3 was considered to play a significant role. Furthermore, the binuclear nickel complexes synthesized in this dissertation were able to catalyze the hydrosilylation reaction of aldehydes as well. According to the result of the stoichiometric reaction of binuclear nickel complex with H2SiPh2, it is obvious that the Si-H bond in H2SiPh2 was activated by binuclear nickel complex in some extent.4. At last, a simple and effective method to synthesize the fluroarylketone with amine group was proposed. The products were obtained from the reactions of fluoroaryl-ketone with methylamine, ethylamine and dimethylamine aqueous under mild condition, which was transition-metal-free and extra-base-free. Both of the selectivity and yield of this reaction were good. More than 30 new-style arylketones with fluorine and amine group were synthesized and purified by column chromatography on silica gel.Most of new-style complexes in this dissertation were characterized in detail. The representative complexes were analyzed by X-ray crystal diffraction in order to confirm their exact structures. The mechanisms of most reactions were discussed and proposed based on the result of in situ NMR spectroscopy, operando IR spectroscopy and MS.