The role of Salen ligands is that they are important auxiliary means in transition metal catalysis, and can regulate the activity and selectivity of catalytic reactions by forming stable coordination complexes with metal ions. Salen ligands play an important role in transition metal catalysis, and can significantly improve the activity, selectivity and stability of catalytic reactions through bidentate coordination, regulating electronic and steric effects. It has a wide range of applications in asymmetric catalysis, redox reactions and CH activation, and has become an important tool in organic synthesis and catalytic research.