C-H Activation Catalyzed By Rhenium Hydride Compounds

Rhenium complexes are important transition metal catalysts, being widely used in industrial production and basic research. Different transformations, such as oxygen transfer reaction, reduction and C-H bonds activation, have been catalyzed by rhenium oxides and rhenium carbonyl compounds. However, rhenium hydride complexes have been not attracted much attention yet. There is few instance of rhenium hydride complexes-catalyzed transformations. In this thesis, we focus on the catalytic property of rhenium hydride complexes, and disclose rhenium-catalyzed dehydrogenation coupling of alcohol for construction of C-C double bonds.In addition, we successfully achieve the rhenium hydride complex-catalyzed inter- and intra-molecular sp2 C-H bond alkylation by introducing CO as an elegant ligand that is a new development for rhenium chemistry.This thesis includes two parts:Part 1. Rhenium-catalyzed acceptorless dehydrogenative couplingTransition metal-catalyzed dehydrogenative coupling of alcohol represents an efficient, green and atom-economical method to construct intricate scaffolds. Compared with conventional oxidation of alcohol, the hazardous wastes are not to be worried, and it is not necessary to use excess oxidant. Despite the significant contributions to C-X bonds forming have been made by dehydrogenative functionalization of alcohol, base and hydride acceptors were usually required, which was not environmentally friendly. In this aspect, the development of base-free and acceptorless dehydrogenative coupling for the formation of C-C bonds is highly desirable. To meet the challenge, herein we disclose an unprecedented rhenium-catalyzed acceptorless dehydrogenative coupling for construction of C-C double bonds, which is conducted under neutral condition. Through the mechanistic investigations, it is found that rhenium hetaphydride complex as a versatile catalyst promotes a possible dual activation pathway.Part.2 CO-enabled rhenium hydride catalyst for inter-and intra-molecular directed C(sp2)-H alkylationThe C-H bonds activation is hotspot in organic chemistry recent years. Developing novel C-C coupling via C-H functionalization has been taken more and more attentions. In the past decades, rhenium carbonyl compounds-catalyzed C-H activations made much contribution to C-H alkylation and alkenylation. However, these catalysts are not satisfied in term of stiff price and hard preparation from simple rhenium sources. In this view, the development of inexpensive and accessible catalysts to accomplish these transformations was still a significant requirement. Herein, we successfully achieve the rhenium hydride complex-catalyzed inter-and intra-molecular sp2 C-H bond alkylation under CO atmosphere. Moreover, the intramolecular reactions afford a novel and efficient strategy to construct 3-methylindolone frameworks. In addition, it is found that the mechanism distinguishes with previous work about rhenium carbonyl catalysts, and Re-H species is suggested to be a key intermediate via deuterium labeling experiments.