Synthesis and unexpected reactivity of iron tris(bipyridine) complexes with poly(ethylene glycol) macroligands.
High molecular weight poly(ethylene glycol) (PEG) derivatized iron tris(bipyridine) complexes, presenting hydroxyl end groups for further modification as bioconjugates, copolymers, or cross-linking agents, were synthesized via ring-opening anionic polymerization of ethylene oxide from hydroxyl-functionalized bipyridine (bpy) initiators and subsequent chelation to iron(II). Bpy-centered PEG macroligands (bpyPEG(2)) with molecular weights ranging from 4,000 to 17,000 and low polydispersity indices (<1.1) were obtained. Chelation of the bpyPEG(2) macroligands to iron(II) sulfate was studied in aqueous solution by titration and kinetics experiments, which revealed unexpected air sensitivity compared to nonpolymeric iron tris(bipyridine) complexes. Red-violet aqueous solutions of [Fe(bpyPEG(2))(3)](2+) begin to bleach within hours when exposed to air. Enhanced polymer degradation and gel formation of acrylate-modified bpyPEG(2) in the presence of Fe(2+) suggest that radicals may be involved. Under argon, the chromophores are stable. Polymeric iron complexes are slower to form and faster to degrade in air with increasing bpyPEG(2) molecular weight. These studies demonstrate the influence of molecular weight in polymeric iron tris(bipyridine) complex coordination chemistry and reactivity.
Department of Chemistry, University of Virginia, McCormick Road, Post Office Box 400319, Charlottesville, 22904-4319, USA.
Anne
A
Pfister
Cassandra L
CL
Fraser
D015082:2,2'-Dipyridyl / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry*; D013997:Time Factors; D017186:Titrimetry
D005296:Ferrous Compounds; D008024:Ligands; D009942:Organometallic Compounds; D011092:Polyethylene Glycols; D015082:2,2'-Dipyridyl