The first organometallic dendrimers: Design and redox functions

This review summarizes our original organometallic route to stars, dendrime rs, metallostars and metallodendrimers and the redox functions of these mac romolecules in catalysis and anionic recognition. The synthesis of metal-sa ndwich stars and dendritic cores was achieved using the CpM+ induced polyal lylation and polybenzylation of polymethylbenzenes (M = Fe or Ru) and penta methylcyclopentadienyl ligands (M = Co or Rh). Subsequent functionalization of the polyallyl dendritic cores yielded polyols which are precursors of p olyiodo, polymesylates, polynitriles, polyamines and polybenzaldehaldehyde cores. The synthesis of dendrimers up to 144-nitrile and 243-allyl was subs equently achieved starting from mesitylene. Functionalization of the polybe nzyl. dendritic cores was achieved by regiospecific Friedel-Crafts reaction s (acetylation, chlorocarbonylation) in the para position. Various metallod endrimers were synthesized with amidoferrocene, amidocobaltocenium and FeCp *(eta(6)-N-alkylaniline)(+) termini in which the redox centers show a rever sible behavior and are all independent as observed by cyclic voltammetry. T he 9-, 18- and 24-amidometallocene dendrimers were used for the recognition of the oxo anions H2PO4- and HSO4- by cyclic voltammetry,whereas a 24-iron -alkylaniline dendrimer was efficient to recognize Cl- and Br- anions by H- 1 NMR with sharp dendritic effects. Differences between the responses to th e different anions were large and the largest effects were found for the 18 -Fc dendrimer (dendritic effect). A water-soluble star-shaped hexa-iron red ox catalyst was as efficient as the mononuclear species for the cathodic re duction of NO3- and NO2- in water. In conclusion, metallostars are suitable for catalysis, and metallodendrimers present optimal topologies for molecu lar recognition. These specific functions related to the topologies cannot be interchanged between the metallostars and the metallodendrimers with opt imized efficiency in the present examples.