Ligand-free Pd-Catalyzed C-N Coupling Under Air: Research Of Amination Reaction Of Aryl Halides

CAr-N bond generally exists in the biological-active materials and drugs, aromaticamines which containing CAr-N bond have been widely used in drugs, dyes, pesticides,electroactive materials and metal-catalysts ligands. Therefore, synthesizing this kind ofchemical compounds with high efficiency and low consumption has aroused wideinterest of researchers. Nitrification-reduction, Ullmann reaction and SNAr synthesisare classical synthesis methods of aromatic amines. However, these methods are poorin universal application, the process of synthesis is complex and difficult, chemicalselectivity is uncertain.Recently, transition metal catalyzed reaction is the main method of forming CAr-Nbond. Research hotspot of this method is the selection of catalyst; the selected catalystmust make sure that the reaction has high conversion efficiency and fast reaction rate,but also is good in universal application and region-selectivity of CAr-N forming.Pd-catalyst amination reaction of aryl halide is a common, reliable and practicalmethod of synthesis aryl amine; this method has advanced rapidly over the past severalyears.Compared with other aryl amine containing CAr-N bond, triphenylamine has thespecial free radical quality, it can be used as a stable free radical source, catalyst ofelectrochemical reaction and mild selective oxidant, etc. Chemical compoundscontaining structure of triphenylamine can be used to prepare charge transport material,electroluminescent material, organic dye-stuffs and medicines.4-nitrotriphenylamineis convenient to synthesis other chemical compounds containing structure oftriphenylamine, it is an important intermediate.However, the reported synthesis reaction of triphenylamine, especially4-nitrotriphenylamine, usually requires addition of expensive phosphine ligands or strong alkaline. These kinds of reactions are not suitable for industrial production,because Pd catalysts and phosphine ligands, one hand, are are sensitive to air, thereaction need inert gas protection; in the other hand, strong alkaline reaction conditionnarrows substrate range. Therefore, seek a mild, convenient synthetic method, whichraw material is cheap and easily available, and is facilitating in industrial production,has a very important value of scientific research and industrial production.Transition metal catalyzed cross-coupling reactions without anhydrous andoxygen-free operation under air is one of the frontiers in the modern organic chemistry;for example, Pd catalysts Suzuki coupling reaction under air, Ir catalyst transfer-hydrogenation under air, etc. Pd catalysts reactions need phosphine ligands, which isair sensitive and expensive, to keep the stability of Pd. Rencently, synthesis methods,such as ligand-free Pd catalyst Suzuki reaction, carbonylation coupling reaction andSonogashira reaction, also have been highly valued and gets rapid development.In the research of C-H activation, a ligand-free Pd catalyst C-N cross-couplingreaction under air of diphenylamine and1-Bromo-4-nitrobenzene, which product is4-nitrotriphenylamine has been incidentally found. The reaction has the samedirection of the frontiers in modern organic chemistry: reaction under air without inertgas protection. The reaction is mild, convenient and able to industrial production; thereaction has great value of research. Research mainly focuses on Pd catalyst couplingreaction of amines with the structure of diphenylamine and aryl halides. Comparedwith traditional synthesis methods, this synthesis mild and convenient reaction has agreat research value of synthesis macromolecules containing structure oftriphenylamine.Firstly, diphenylamine and1-Bromo-4-nitrobenzene have been selected asreaction substrate to optimize reaction conditions. The amount of catalyst, reactiontemperature and atmosphere, the type of base, reaction time, solution has beenresearched. The optimizing condition is:5mmol%Pd(OAc)2as the amount ofcatalyst,120℃as the reaction temperature,24h as the reaction time, K2CO3as thebase, DMSO as the solution, input ratio is amine: aryl halides: catalyst; base=1:1.5:0.05:1.5(mmol).Secondly, the reactions of diphenylamine and substituent aryl halides, thereaction of3various substituent diphenylamine and aryl bromide, and the reaction of2various amines have similar structure of diphenylamine and aryl bromide have beenresearched. Results show that catalytic system used in this paper is fir for arylbromide with electron withdrawing group and aryl iodides; it is also fit for diphenylamine with electron donating group. Therefore, the catalytic system can beused to synthesis compounds containing structure of triphenylamine. The NMR andIR data of products have been listed.Finally, single-crystal of (R)-N-(4-biphenyl)-tert-butanesulfinamide, the productof C-N cross-coupling reaction of (R)-tert-butanesulfinamide and4-biphenyl bromidewas cultured. The single-crystal structure has been determined by X-ray four-circlemonocrystal diffraction. The monocrystal diffraction data has been listed, the dataprovide theoretical foundation and data supported to explain C-N coupling reactionmechanism of (R)-tert-butanesulfinamide and aryl bromide.