Metal complexes with polymeric ligands: Chelation and metalloinitiation approaches to metal tris(bipyridine)containing materials

Synthetic approaches to metal complexes with polymeric ligands are describe d. The development of efficient methods for preparing simple bipyridine (bp y) derivatives and their corresponding metal complexes has facilitated thei r use as initiators and coupling agents in polymer syntheses. Ligand reagen ts were utilized as initiators in controlled polymerization reactions to fo rm poly(2-R-2-oxazolines) (R = methyl, ethyl, phenyl, undecyl), polystyrene s, poly(methyl methacrylates) (PMMA)s, poly(epsilon -caprolactone)s, and po ly(lactic acid)s with bipyridine chelates at the end or centers of the chai ns. Poly(ethylene glycol) macroligands were formed by a chain-coupling meth od. Detailed studies of reaction kinetics were performed to determine the s cope and limitations of each reaction type with different catalysts and rea ction conditions. These results are illustrated for bpyPMMA(n) (n = 1 or 2) , which was prepared by atom transfer radical polymerization with a CuBr/1, 4,4,7,7,10-hexamethyltriethylenetetraamine catalyst system. Results of the kinetics investigations performed with other ligands and metalloinitiators are summarized. Macroligands thus prepared were coordinated to a labile met al ion, Fe(II), with standard protocols. Ultraviolet-Visible spectral data for selected Fe-centered polymers are provided that cofirm the production o f the targeted polymeric iron complex products. An inert metal, Ru(II), was used as a template for generating architectural diversity; polymeric compl exes with one to six chains emanating from the central core, as well as dif ferent heteroarm star products, were prepared. (C) 2000 John Wiley & Sons, Inc.