Branching the electron-reservoir complex [Fe(eta(5)-C5H5)(eta(6)-C6Me6)][PF6] onto large dendrimers: "click", amide, and ionic bonds.

Several strategies have been used to functionalize 1,3,5-trisubstituted arene-cored dendrimers with the organometallic electron-reservoir moiety [Fe(eta(5)-C(5)H(5))(eta(6)-C(6)Me(6))](+), 1, to provide dendritic multielectron reservoirs. They all start from the carboxylic acid [Fe(eta(5)-C(5)H(4)COOH)(eta(6)-C(6)Me(6))][PF(6)], 2, or its acyl chloride derivative [Fe(eta(5)-C(5)H(4)COCl)(eta(6)-C(6)Me(6))][PF(6)], 3. For this purpose, a series of new polyamine dendrimers from G(0) to G(2) with 1--> 3 C connectivity of the branching to the core have been synthesized. Amide, "click" and ionic ammonium carboxylate linkage successfully provided G(0), G(1), and G(2) metallodendrimers with 9, 27, and 81 cationic terminal organoiron groups respectively. Further construction of large metallodendrimers up to G(7) with approximately 14 000 organoiron termini was only possible by combining amide, "click", and tether lengthening strategies to avoid steric bulk at the dendrimer periphery. Reduction of the 18-electron Fe(II) metallodendrimers, exemplified by a G(4)-DAB-64-Fe(II) complex, was achieved exergonically using the parent electron-reservoir complex [Fe(eta(5)-C(5)H(5))(eta(6)-C(6)Me(6))], 1a, at -30 degrees C in MeCN, which allowed further reduction of 64 equiv of C(60) to C(60)(*-) using the 19-electron Fe(I) metallodendrimer.