Metalation of polyamine dendrimers with ethynylcobalticenium for the construction of mono- and heterobimetallic polycationic metallodendrimers.

The introduction of robust redox groups at the periphery of common amine-terminated dendrimers is of interest in the design of dendritic nanobatteries, sensors, and redox catalysts. Here we are applying the recently discovered uncatalyzed hydroamination of ethynylcobalticenium, a mild "green" reaction that quantitatively yields trans-enamines without the formation of any byproduct, to functionalize dendrimers that are terminated with primary or secondary amino groups. Poly(amido amine) (PAMAM) dendrimers terminated by primary amino groups and arene-centered dendrimers terminated by secondary amino groups yield dendrimers that contain up to 81 trans-enamine-cobalticenium termini using this reaction. The hydroamination reaction was also conducted with dendrimers that contained ferrocenylmethylamino groups, which yielded dendrimers that contained both ferrocenyl and cobalticenium termini. The size of the dendrimers was investigated using both dynamic light scattering and diffusion-ordered spectroscopy (DOSY) (1)H NMR spectroscopy, and the number of electrons involved in heterogeneous multielectron transfers at electrodes was searched by cyclic voltammetry. The latter works well up to the 27-branch dendrimer, whereas the 81-dendrimer yielded a result in an excess amount (110 electrons) owing to adsorption onto the cathode that becomes all the more significant as the metallodendrimer size increases.