Dehydrogenation Reaction Catalyzed By Ruthenium Complex Via C-H Bond Functionalization

Metal catalyzed reaction has been a significant moity of modern organic reactions, and as a part of metal catalyzed reactions, metal-catalyzed dehydrogenation reactions has also attracted more and more attention. In addition, most generally satisfactory catalysts are mainly transition-metal complexes (Rh , Ir , Ni , Ru , Co ,and Pd ). And recently, ruthenium complexes have already found to dehydrogenate a series of imidazoles deravatives. Therefore, investigating other efficient ruthenium complexes as catalysts for dehydrogenation reactions is highly desirable. In this thesis a series of dihydropyrazine derivatives were synthesized with the corresponding aromatic aldehydes as the substrates. And then, we explored the catalytic dehydrogenation efficiency of dihydropyrazines, applying [RuCl₂ (p-cymene)]₂ as catalyst, and optimized some reaction conditions.Initially, starting from a series of aromatic aldehydes, we synthesized various benzions via specific method. And then these benzions were oxidated by different oxidatants to obtain the cor- -responding aromatic benzil derivatives, such as 1,2-di(thiophen-2-yl)ethane -1,2-dione, 1,2-di (furan-2-yl)ethane -1,2-dione, benzil and 1,2-di-p-tolyethane-1,2-dione. Moreover, after purifica- -tion these oxidative products were characterized by IR and detecting melting point. Secondly, aromatic benzils as starting materials reacted with ethylenediamine with high efficacy, and also the reaction products were characterized by IR and detecting melting point. Consequently, we got the substrates dihydropyrazines with above-mentioned way and explored to improve the yiel- -ds of each above procedure. Finally, using the synthetic ruthenium complex [RuCl2 (p-cyene)]2 as catalyst and dihydropyrazines as the reaction substrates, we investigated the reaction efficency of the catalytic system and gained a serious of the target products, characterized by IR, ¹H-NMR, 13C-NMR, detecting melting point and element analysis.In addition, the optimized reaction conditions, such as solvent and base of the reaction, were explored in this thesis to obtain the conclusion: the catalytic reaction could be most efficiently performed by the in situ generated [RuCl₂(p-cymene)]₂/KOAc using NMP as solvent in the presence of base K₂CO₃. In the reported papers about metal-catalyzed dehydrogenation reactions of N-heterocyclic compounds, there always existed N-H bond in the N-position about the substrate N-heterocyclic compounds. However in dehydrogenation reaction of our thesis, catalyzed by [RuCl₂ (p-cymene)]₂, the reaction substrate were dihydropyrazine deratives which had no N-H bond. So this research could provide some experimental evidences for exploring the mechanism of metal-catalyzed dehydrogenation reaction.