FULL PAPER DOI: 10.1002/ejoc.200600296 Formation of a Series of [{Methylphenylenebis(terpyridine)} n Ru II n–1 ](n = 2–6) Oligomers in a Single-Pot Reaction Tae Joon Cho, [a] Charles N. Moorefield, [c] Seok-Ho Hwang, [a] Pingshan Wang, [a] Luis A. Godínez, [d] Erika Bustos, [d] and George R. Newkome* [a,b] Keywords: Bis(terpyridine) / Ruthenium complexes / Metallo-oligomers A series of oligomeric [{methylphenylenebis(terpyridine)} n - Ru II n–1 ] complexes, where n = 2–6, possessing metal-free ter- pyridine end groups was formed and isolated from a single- pot reaction. These oligo complexes were analyzed by 1 H NMR spectroscopy and mass spectrometry. Macrocyclization of combinations of these oligomers gave rise to the known hexagonal metallomacrocycle 7. Cyclic voltammetry (CV) Introduction Supramolecular [1] self-assembly is based on a combina- tion of inherent structural information and bonding poten- tial, such as the ligand juxtaposition within the polytopic building blocks and H-bonding ability, respectively. Lehn, [2] Stang, [3,4] Fujita, [5] Atwood, [6] and many others [7–13] have elegantly demonstrated the resultant structural beauty aris- ing from the application of such parameters. This has prompted our investigation of a new series of self-assemb- ling macrocycles through the use of a terpyridine–metal– terpyridine connectivity. Terpyridine-based monomers [14] have been used in the formation of numerous ordered as- semblies, [15] such as in layered polyelectrolyte films, [16] grids, [17,18] racks, [19–21] Ru II -based dendrimers, [22] helicating ligands, [23] photoactive molecular-scale wires, [24,25] lumines- cent complexes, [26–30] photovoltaic devices, [31] conducting polymers, [32] metallocycles, [33–37] metallodendritic spi- ranes, [38] fullerene–terpyridine complexes, [39–41] and com- bined biotin–terpyridine systems [42] as well as the genera- tion of novel metallopolymers. [14,15] More recently, we reported the creation of a series of bis(terpyridine) ligands each possessing a 120° bond angle with respect to the two ligating moieties (1) and their step- [a] Department of Polymer Science, The University of Akron, Akron, OH 44325-4717, USA E-mail: newkome@uakron.edu URL: www.dendrimers.com [b] Department of Chemistry, The University of Akron, Akron, OH 44325-4717, USA [c] Maurice Morton Institute of Polymer Science, The University of Akron, Akron, OH 44325-4717, USA [d] Centro de Investigación y Desarrollo Tecnológico en Electro- química, Querétaro, México Eur. J. Org. Chem. 2006, 4193–4200 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4193 data of these linear oligomers are discussed and compared to that of the corresponding metallomacrocycle 7. Diffusion coefficients were obtained by means of the Randles–Sevcik equation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) wise, as well as one-step, assembly to give hexagonal met- al(II)-based macrocyclic complexes. [43–45] The potential to synthesize such constructs, with little equilibration (i.e., metal/ligand exchange) under mild physicochemical condi- tions, is predicated on the unique strength and stability of the terpyridine–metal coordination. [46] In the stepwise pro- tocol, [43–45] we described the construction of linear bis(ter- pyridine)Ru II complexes, as precursors to the construction of these hexagons; thus, the realization that these linear constructs could, in their own right, provide unique build- ing blocks to afford access to new utilitarian materials has prompted us to devise conditions which would lead to a series of metallo-oligomers. [47,48] Herein, we report the formation and characterization of a linear [{methyl- phenylenebis(terpyridine)} n Ru II n–1 ] oligomeric family pos- sessing metal-free terpyridine end groups. Results In previous reports, [43–45] a key target was the prepara- tion of the bis(Ru II ) oligomer 5, which was intended for use in the stepwise construction of the hexagonal macrocycle 9. During the course of our work, this trimer was obtained as the dominant product from the reaction of bis(terpyridine) ligand 1 with the bis(Ru III ) adduct 2, however, it was later found that oligomeric side products could be generated as major components by adjusting the metal stoichiometry; thus, the metal/bis(terpyridine) ratio could be manipulated to determine the reaction outcome. Also, the formation of dimer 4 is not possible when starting with pure bis(Ru III ) monomer 2, because there is no literature evidence of metal (Ru III ) loss or exchange under typical reaction conditions to generate [bis(terpyridine)Ru II ] complexes. Therefore, in