Giant redox dendrimers were synthesized with pentamethylcobalticinium termini for the fifth, sixth, and seventh generations (in addition to the nine-arm generation 0) up to a theoretical number of 3(9) tethers (seventh generation, G(7)). Therefore, a functional pentamethyl cobalticinium derivative was synthesized with a long arm. This tether-lengthening strategy was used as in the previously reported ferrocenyl and pentamethylferrocenyl series to overcome the bulk constraint at the periphery of short-tethered dendrimers. These polycationic cobalt-sandwich metallodendrimers were characterized by H-1, C-13, and Si-29 NMR, MALDI-TOF mass spectrometry (for generation 0), elemental analysis, UV-vis spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM), and cyclic voltammetry. UV-vis spectroscopy and analytical data are consistent with a moderate amount of defects (G(5) and G(6)) that largely increases for G7 (which contains 14 000 +/- 1000 pentamethylcobalticinium termini). Cyclic voltammetry reveals full chemical and electrochemical reversibility for the cathodic reduction [dendr-(C5H4CoCp)-Cp-III*](+) -> [dendr-(C5H4COCp)-Cp-III*] up to G(7) as in the iron-sandwich series, showing that electron transfer is fast among the flexible peripheral redox sites.
Giant redox dendrimers were synthesized with pentamethylcobalticinium termini for the fifth, sixth, and seventh generations (in addition to the nine-arm generation 0) up to a theoretical number of 3(9) tethers (seventh generation, G(7)). Therefore, a functional pentamethyl cobalticinium derivative was synthesized with a long arm. This tether-lengthening strategy was used as in the previously reported ferrocenyl and pentamethylferrocenyl series to overcome the bulk constraint at the periphery of short-tethered dendrimers. These polycationic cobalt-sandwich metallodendrimers were characterized by H-1, C-13, and Si-29 NMR, MALDI-TOF mass spectrometry (for generation 0), elemental analysis, UV-vis spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM), and cyclic voltammetry. UV-vis spectroscopy and analytical data are consistent with a moderate amount of defects (G(5) and G(6)) that largely increases for G7 (which contains 14 000 +/- 1000 pentamethylcobalticinium termini). Cyclic voltammetry reveals full chemical and electrochemical reversibility for the cathodic reduction [dendr-(C5H4CoCp)-Cp-III*](+) -> [dendr-(C5H4COCp)-Cp-III*] up to G(7) as in the iron-sandwich series, showing that electron transfer is fast among the flexible peripheral redox sites.