Carbon-carbon bond formation and cleavage at redox active bis(pyridylimino)isoindole (BPI) germylene compounds

Redox-active ligands provide alternative reaction pathways by facilitating redox events. Among these, tridentate bis(piridylimino)isoindole (BPI) fragments offer great potential, though their redox-active behaviour remains largely underdeveloped. We describe herein a family of BPI germanium(II) complexes and the study of their redox properties. Amido complexes (^RBPI)Ge[N(SiMe₃)₂] 1-R (R = H, Me, Et) showing a κ²-N_py,N_iso coordination to the germanium(II) centre were prepared. In contrast, chloride derivatives (^RBPI)GeCl, 2-R, display dynamic κ³-N_py,N_iso,N_py coordination to the metal centre. The addition of silver bis(trifluoromethane)sulfonimide to compound 1-H generates a dinuclear complex, 3, where the silver atoms are bound to the germanium and one of the imine nitrogen atoms of another BPI fragment. The reduction of 2-R with KC₈ generates dinuclear complexes (4-R) characterized by the formation of new C-C bonds between the isoindoline five-membered rings of two different BPI ligands via a radical mechanism, a transformation that does not take place in the absence of germanium. Interestingly, computational and spectroscopic studies support that the reduction takes place exclusively over the ^RBPI ligand. Strikingly, the newly formed C-C bond is also readily cleaved. Thus, subsequent reduction of 4-R (R = H, Me) using additional KC₈ affords dinuclear species 5-R, with polymeric structures between potassium atoms and the corresponding dinuclear Ge₂(^RBPI₂) fragments.