Synthesis And Application Of P-GeH₂-P Pincer Ligands

There are three coordination groups in the Pincer structure that can regulate the electronic and spatial effects in the skeleton,so it is widely used in transition metalcatalyzed reactions.PXP Pincer ligands with silicon and germanium as central donor atoms show unique advantages in this field.Many reports have been published on the synthesis of PSiP Pincer ligands,with PSiP Pincer ligands with a phenyl skeleton attracting attention due to their stronger stability.These ligands can be categorized into P-SiR(R=Me,Ph)H-P type and P-SiH2-P type.Palladium complexes of P-SiR(R=Me,Ph)H-P ligands show catalytic activity in some reactions,while the P-SiH2-P type ligand is characterized by its ability to form species containing Si=M bonds with transition metals.However,few transition metal catalytic reactions involving P-SiH2-P ligands have been reported.Germanium and silicon belong to the same family,and most studies on PGeP Pincer ligands containing a phenyl skeleton focus on P-GeR(R=Me,Ph)H-P type.To date,P-GeH2-P type ligands containing a phenyl skeleton have not been reported.In this paper,a general method for synthesizing P-GeH2-P type ligands with a phenyl skeleton is presented.Using this method,a series of P-GeH2-P ligands were synthesized.By selecting one of the ligands,the complex formed with the transition metal cobalt was studied through single crystal structure analysis,confirming that these ligands can complex with cobalt in a ’pincer’ manner.In this paper,we utilized a P-GeH2-P type Pincer ligand to participate in the dehydroborylation of olefins under a nickel catalyst system.The reaction displayed remarkable compatibility,with the unexpected ability to accommodate substrates containing amino and hydroxyl substitutions.Although various metals have been employed to achieve dehydroborylation of olefins,no relevant reports exist under a nickel catalytic system.This may be due to the comparatively challenging β-H elimination of nickel compared to other late transition metals such as palladium.We propose that the P-GeH2-P complexation endows the system with two distinct characteristics:1)The presence of the GeH2 center structure facilitates the generation of Ni-H species to participate in the catalytic cycle without requiring a strong reducing agent;2)The nickel can exhibit analogous properties to palladium,enabling smooth βH elimination reactions to occur in the nickel catalytic system presented in this paper.Upon further examination of nickel-catalyzed defluorination y-borylation of αtrifluoromethyl olefins,we have observed that theP-GeH2-P complexation modifies the properties of nickel while maintaining its unique characteristics,ultimately leading to better achievement of nickel-β-F elimination.The development of the P-GeH2-P type Pincer ligand presented in this paper may pave the way for the discovery of new catalytic reactions involving various metals in the future.