When metals are bound to polymers, both inner and outer sphere environments may be engineered. As is illustrated by metalloproteins, macromolecular structure and electronic environment can play important roles in modulating properties, including access to and reactivity at the metal core. For example, the protective polymer shell of hemoglobin prevents iron porphyrin dimerization, whereas in other proteins, the polypeptides influence substrate specificity. 1 Analogous features have been incorporated into synthetic systems including molecularly imprinted polymers 2 and catalysts on solid supports. 3 Although the polymer matrix and metal binding sites are not entirely uniform in these cases, site isolation and architectural control have been achieved in metal-centered dendrimers via iterative methods. 4 Another approach to well-defined polymeric metal complexes 5 involves the preparation of linear polymers with tailored binding sites by controlled polymerization, 6 followed by their chelation to metal ions. 7 This metal template-assisted polymer synthesis is highly modular and allows for systematic control over molecular weight, architecture, and metal position. 8 Especially intriguing are block copolymer analogues 9 such as metal-centered heteroarm stars, which are expected to form discrete higher order assemblies with chromophores localized at the microdomain boundaries. Luminescent [Ru(bpy) 3 ] 2+ analogues are of interest as additives for photonic materials and as probes of polymer interfaces. 10 Although heteroleptic metal complexes with nonpolymeric ligands are commonplace, it was not certain that heteroarm stars would also be easily obtained by chelation. Different factors come into play when coordination chemistry is performed with polymeric ligands. Ligand field stabilization is counterbalanced by entropic losses and interchain repulsion upon convergence, the latter of which is particularly pronounced for dissimilar polymers, which often phase-separate when mixed. Moreover, solvation influences polymeric ligand conformation in a significant way.In this study, strategic manipulation of solvent polarity was used to advantage in the assembly of ruthenium tris(bipyridine)-centered polystyrene-poly(methyl methacrylate) heteroarm stars, 1 and 2 (Figure 1). Macroligands for chelation reactions were prepared by copper-catalyzed atom transfer radical polymerization 11 using bpy ligand initiators. Bipyridine end-and centerfunctionalized polystyrenes, bpyPS, 3, and bpyPS 2 , 4, were generated from 4-(chloromethyl)-2,2′-bipyridine 12 and 4,4′-bis-(chloromethyl)-2,2′-bipyridine, 13 respectively. 5c,8 Poly(methyl methacrylate) ligands, bpyPMMA, 5, and bpyPMMA 2 , 6, (Table 1) were synthesized using bromoester bpy initiators made by esterification of the appropriate hydroxymethyl bpy 14 with 2-bromoisobutyryl bromide. Ruthenium-centered heteroarm star block copolymers were prepared by chelation of two bpyPS n macroli-(1) Bertini, I., Gray, H. B., Lippard, S.
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