Study And Application Of Palladium-catalyzed Heck Reaction Between4-Bromostyrene And Aryl Halides

The palladium-catalyzed Heck coupling reaction is an efficient method for the formation of new carbon-carbon bonds and it is also an important way to realize alkenylation of aromatic compounds. In recent years, there is a great development with the Heck coupling reaction, both in homogeneous and heterogeneous catalytic systems. The stilbene compounds are widely used in many research fields, such as medicine, optical brighteners, dyes, molecular probes and organic photoelectronic materials, due to their special intramolecular conjugated systems. The double functional groups compounds with stilbene structure could be efficiently prepared by the palladium-catalyzed coupling reaction between4-bromostyrene and aryl halides. This kind of Heck coupling reaction has not been systematically investigated yet.In this thesis, there are two parts of research work:(1) Study of Pd-catalyzed Heck coupling reaction of4-bromostyreneFirstly, we studied palladium-catalyzed Heck coupling reaction between4-bromostyrene and aryl bromides. The optimized reaction system for aryl bromides is as follows:aryl bromide (1.0mmol),4-bromostyrene (1.5mmol), Pd (OAc)2(0.05mmol), Bu4NI (1.5mmol), KOAc (1.5mmol), DMF (10.0mL), N2,90℃,24h. There are a few advantages over this reaction system. The Pd-catalyzed Heck coupling reaction was carried out in ligandfree condition. The moderate temperature was utilized and high yield of coupling products were isolated. However, the reaction is only appropriate for the aryl bromides with electron-withdrawing group. It is not suitable for aryl bromides with electron-donating groups or aryl iodides.Next, we studied the palladium-catalyzed Heck coupling reaction between4-bromostyrene and aryl iodides. In the above reaction system, the kinds of aryl bromides are limited. In order to extend the scope of substrate for the Heck coupling reaction, we optimized palladium-catalyzed Heck coupling reaction between4-bromostyrene and aryl iodides. The optimized reaction system for aryl iodides is as follows:aryl iodide (1.0mmol),4-bromostyrene (1.5mmol), Pd (OAc)2(0.05mmol), Bu4NI (1.5mmol), Na2CO3(1.5mmol), DMF (10.0mLl), N2,50℃,24h. There are a few advantages over this reaction system. The Pd-catalyzed Heck coupling reaction was carried out in ligand-free condition. The lower temperature was utilized, high yield of coupling products were isolated, and a wider of aryl iodides were applied. Then the reaction system was applied to some aryl bromides. From the above research, we find that the catalytic system is applicable to all aryl iodides and aryl bromides with electron-withdrawing groups.(2) Based on the above Pd-catalyzed Heck coupling products, we successfully synthesized a series of D-A type molecules with stilbene structure by Pd-catalyzed amination. For the synthesized D-A type molecules (4a-4F), the solvent effects, absorption spectroscopy, fluorescence spectroscopy, and cation effects test of Cu+and Fe3+were carried out. The corresponding fluorescence quantum yield was also calculated. From the results of solvent effects, absorption spectra and fluorescence spectra, we found that increasing the polarity of the solvent, the fluorescence quantum yield of the corresponding compounds decreased and the fluorescence intensity weakened. The result of cation effects test showed that these compounds had obvious fluorescence quenching phenomenon with Cu2+, but Fe3+exhibited less obvious effect to these compounds.