N-Heterocyclic Carbene/Palladium(Ⅱ) Catalyzed Cross-Coupling Reactions

N-Heterocyclic carbene, whose steric hindrance and electronic effects are easy tocontron, is a strong σ electron donor, and can increase the electron density of the centralmetal atom, while the metal atom has a feedback π bond to carbon atom. N-Heterocycliccarbene metal-complexes were widely used to catalyze the coupling reactions. In this thesis,we synthesize the imidazolium salt, which is the precursor of N-Heterocyclic carbene, as aligands, N-Heterocyclic carbene metal complexes were also synthesized, and weinvestigated the application of N-Heterocyclic carbene metal complexes in couplingreactions.1. Taking the aryl boronic acids, aryl halides and aryl sulfonates as the substrate, weascertain the optimum reaction conditions through changing a series of factors, the catalysts,the reaction solvent and bases included. A novel N-heterocyclic carbene-palladium-(II)–pyridine [IPr*-Pd(II)-Py] has been successfully developed as an effective catalyst for theSuzuki coupling reaction, and the yields were up to75-93%. Compared with theconventional phosphine ligand catalysts, we found that NHC metal complexes didn’t needthe protection of inert gas, and were not easy to produce palladium black under thereactions.2. A NHC Pd-complex, has been successfully employed as a highly efficient andrecyclable catalyst for the Sonogashira reactions of aryl bromides with various terminalacetylenes, and the yields were up to89%. No matter what electron withdrawing group is onthe terminal acetylene benzene ring or aryl halides benzene ring, the target compound had ahigher yield.3. A NHC Pd-complex, has been successfully employed as a highly efficient andrecyclable catalyst for the Sonogashira reactions of aryl bromides with various terminalolefins. We ascertain the optimum reaction conditions through changing a series of factors,the yields were up to85%under the optimum reaction conditions.We have been successfully synthesized a series of coupling compounds under theoptimum reaction conditions, these compounds were characterized by MS,1H NMR andelemental analysis.