Research On E-Selective Transfer Semihydrogenation Of Alkynes Catalyzed By A Binuclear Cobalt Complex

Alkenes are significant building blocks in organic synthesis with unique reaction properties,which can be easily transformed into other important derivatives.Selective semihydrogenation of alkynes is a classical chemical conversion process to the synthesis of alkenes,and is widely used in the manufacture of pharmaceuticals and fine chemicals.However,noble metal catalysts are currently preferable for the semihydrogenation of alkynes.Recently,due to the earth abundance,low price and environment-friendly characteristics,base metals such as cobalt have drawn a wide range of interest from chemists.Base metal catalysts tend to undergo single electron redox change instead of double electron redox change,which is one of the obstacles to their replacement of noble metal ones.The best strategy to stabilize the oxidation state of the active catalytic center is combining cobalt with redox-active ligand,which can endow base metals with the electronic properties of noble metals.This thesis mainly focuses on the research on the new binuclear cobalt complex with macrocyclic pyridinediimine tridentate ligands（PDI）and the macrocyclic binuclear cobalt complex catalyzed selective semihydrogenation of alkynes has been realized using ammonia borane as the hydrogen source in isopropyl alcohol.The reaction shows high efficiency,good functional group compatibility and excellent stereoselectivity（E/Z up to>99:1）.Moreover,this catalytic system can also be applied to the selective reduction of the alkyne impurities to alkenes and the synthesis of the trans-resveratrol,further demonstrating great potential synthetic utilities.Preliminary mechanistic studies indicate that Z-alkene is firstly generated in the semihydrogenation of alkynes,followed by the conversion to the E-alkene.Deuterium experiments show that the isopropyl alcohol and the BH₃ part of ammonia borane each provide one hydrogen atom in the formation of double bonds.The poisoning experiments demonstrate that the reaction is a homogeneous process.Our investigation on the di Co-PDI catalysts not only provides an efficient and gentle method for the semihydrogenation of alkynes,but also promotes the exploration and exploitation of cobalt catalysis.