Study On The Formation Of C-N, C-C Bonds Catalyzed By Pd/Cu In The New System

Transition metal-catalyzed cross coupling reactions is one of the most effective methods for the construction of C–X(X = N, C, O, and S) bonds, which has significantly important applications in drugs, natural products, dyes, and regular chemical products. Thus, research on design, development, and applications of transition metal-catalyzed coupling reactions has become an active hot spot. However, systematic exploration of a more effective green system of catalysis for the construction of C–X bonds is the main objective of the research.Based on the literature reports, P, O bidentate ligands; 2N2 O tetradentate ligands; Salen-copper(Salen-Cu) complexes; and Salen-palladium(Salen-Pd) complexes were synthesized. Further, these ligands and complexes were used for the exploration of the effective and green system of catalysis for the construction of C–X bonds.First, we selected copper(I) chloride/L2(CuCl/L2) as catalyst, sodium hydroxide(NaOH) as base, and dimethyl sulfoxide(DMSO) as solvent. Imidazole/benzimidazole was reacted with aryl iodides at 100 °C for 12 h, which afforded the corresponding products in 20–98% yield. Then, we selected copper acetate monohydrate/L2(Cu(OAc)2·H2O/L2) as catalyst, NaOH as base, dioxane as solvent, and pyrazole was reacted with aryl iodides/bromides at 100 °C for 24 h, which provided the corresponding products in the yield 40–98%. Although the reaction was conducted in organic solvent, the catalysis system was effective, mild, and had good applicability for the substrates. More importantly, the P, O bidentate ligand was found to be stable in the system.Second, Salen-Cu complexes were utilized as catalysts, NaOH as base, and water as solvent. The N-arylation of imidazole/benzimidazole was conducted at 100 °C for 20 h in tetrabutyl ammonium bromide(TBAB), giving the corresponding products in 29–99% yields. This catalytic system was green and exhibited good applicability with low loading of Salen-Cu complex. The reaction of 2-bromopyridine was also successful and it provided the corresponding product in 85% yield.Third, Salen-Pd complexes were selected as catalysts for the catalysis of reaction of aryl bromides with arylboronic acid at 100 °C for 3 h, which afforded the corresponding products in the yields 41–99%. Moreover, the system of catalysis was also found to be suitable for gram-scale reaction and the catalyst was successfully recycled and reused. Notably, the catalytic system overcame the influence of steric hindrance, electronic effect, and heterocyclic compounds. The products were obtained in good to excellent yields and the catalytic system was effective and green.Finally, we selected triethyl amine(NEt3) as base, dimethyl formamide(DMF) as solvent, and Na2PdCl4/CuI/L2 as catalyst for catalyzing the coupling of terminal alkynes, giving symmetric diynes in 47–99% and unsymmetric diynes in 45–80%. These catalytic systems, with less catalyst dosage, could catalyze different types of aromatic, aliphatic, and heterocyclic alkynes in high yield and the operation was simple with the good application value.