Ruthenium-centered heteroarm stars by a modular coordination approach: Effect of polymer composition on rates of chelation

Bipyridine end- and center-functionalized polymer chains, bpyA and bpyA(2), respectively, were chelated to Ru(II) centers to form Ru(bpyA(n))(2)Cl-2 complexes 1-6 where A = polystyrene (PS), n = 1 (1), n = 2 (2); A = poly(methyl methacrylate) (PMMA), n = 1 (3), n = 2 (4); A = poly(c-caprolactone) (PCL), n = 2 (5); and A = poly(ethylene glycol) PEG, n = 2 (6). Intermediates 1 and 5 were subsequently reacted with a second type of bpy macroligand to generate [Ru(bpyA(n))(2)(bpyB(2))](2+) heteroarm star copolymers for the following combinations: A(n),B = PCL2,PS (7), PCL2,PEG (8), PS,PLA (9), where PLA = poly(lactic acid), and PS,PEG (10). Rates of chelation were affected by macroligand composition, molecular weight, and architecture and paralleled the solubility parameter series for PCL, PLA, PMMA, PS, and PEG in dimethoxyethane (DME). Rates decreased with increasing M-n and were lower for bpyA(2) relative to end-functionalized bpyA of comparable molecular weights within each compositional class.