Application Of Two-dimensional Nano-materials Afforded Noble Metal Catalyst In C-C Bond Formation

In synthetic chemistry at present, many products could be synthesized by C-C bond formation reactions catalyzed by palladium, either for the first time, or in a more efficient way than before. With the development of modern technology, the need of noble metals continues to rise. How to make the use of noble metals more effectively becomes an important issue. The complanate structure of two-dimensional nano-materials ensures them considerable specific surface area. The surface area and thermal stability make them potential supporters for catalyst. To improve the shortcomings the homogeneous noble metal catalysts, including the poor atom economy, high cost, harsh operating conditions, difficulty in post-treatment, we tried to use two-dimensional nano-materials as a support for noble metals to prepare heterogeneous catalysts. Reduced graphene oxide and MoS2 can be modified in chemical ways. After modification, they can combine with metal ion efficiently, and exhibited good performance and stability in reactions. According to this, we paid our attention to two fields as below.To simplify the procedure of preparation in palladium nano-catalyst for C-C coupling reactions, we tried to use palladium ion to instead the metal. After exfoliated by chemical way, graphene oxide was treated with N-propylethane-1,2-diamine, followed by reduction using hydrazine to afford functional reduced graphene oxide. By means of capacity of amino group in immobilization of palladium ion, we use the FRGO dispersed in DMF to produce the complex catalyst. When the solution of palladium chloride in DMF was added into FRGO, the new catalyst was generated. This catalyst can be widely used in Suzuki-Miyaura reaction. In all the examples we have tried, the reactions are carried out mildly at room temperature with a lower catalyst amount compared to traditional catalysts, and in high yield, moreover, unaffected in the presence of air. Meanwhile, Mizoroki-Heck reaction, C-H bond functionalization reactions of thiophenes and indoles, as well as terminal alkyne C-H activation leading to Glaser coupling under nitrogen can also be catalyzed. The catalyst shows excellent heat resistance.The preparation of single-layer MoS2 nanosheets could be realized by using n-butyl lithium as the intercalation agent to insert lithium ions into the layered structures, followed by exfoliation in water with ultrasonication. Because of the violent nature of chemical exfoliation reaction, the crystal structure of MoS2 became deformed, and the defects could be visible. The MoS2 nanosheets had been proved to contain negative charge after chemical exfoliation. This made the MoS2 nanosheets be able to combine with palladium ion. After dried through cryodesiccation, the two-dimensional MoS2 was dispersed in DMF under ultrasonication, which could be used as catalyst carrier by a straightforward mixing with PdCl2 solution. This catalyst could be widely used in alkenylation of heteroaromatics by direct C-H bond activation. In all the examples we had tried, the reactions were carried out with a lower catalyst amount compared to traditional catalysts, and in high yield. Meanwhile, Mizoroki-Heck reactions, Suzuki-Miyaura reactions and functionalization reactions of thiophene could also be catalyzed by this complex.