Phosphorus-Containing Dendrimers with Ferrocenyl Units at the Core, within the Branches, and on the Periphery

The synthesis of new ferrocene derivatives bearing phenoxy and/or formyl groups allows one to obtain phosphorus-containing dendrimers with ferrocene units at the core, within the branches, and at the periphery. Dendrimers with a ferrocene at the core were built from 1,1‘-ferrocenedicarboxaldehyde up to the fourth generation. A marked dendritic effect is observed for this family of compounds; indeed, the ferrocenyl core is insulated from the outside in the largest dendrimers (32 or 64 CHO end groups), and the molecule is almost electrochemically inactive. The first dendrimers having three consecutive ferrocene layers within the branches are also described; inner layers are oxidized at the same potential, but the outer layer needs a higher potential to be oxidized, owing to the presence of electron-withdrawing formyl groups. Dendrimers bearing ferrocenyl groups at the periphery are synthesized up to the ninth generation. These compounds are the largest redox active dendrimers ever synthesized; all these ferrocenyl units are oxidized at the same potential, showing that they are all equivalent and electrochemically independent. The exhaustive electrolysis furnishes multiferrocenium dendrimers, which deposit onto electrodes as a stable and conducting film. The multiferrocenium dendrimers can be reduced again quantitatively to neutral dendrimers without apparent decomposition.