摘要:
While outer-sphere electron-transfer reactions come with a firm experimental and theoretical basis, less is known about the redox reactions occurring by atom-transfer. In the present study, relevant reactions occur upon mixing, (F-8)Fe-III(Cl) (F-8 is tetrakis(2,6-difluorophenyl)porphyrinate) with a series of [(L)Cu-I](+) complexes (L are tripodal tetradentate pyridylalkylamine ligands varying in effective chelate ring sizes: TMPA, PMEA, PMAP) to form (F-8)Fe-II and [(L)Cu-II(Cl)](+). The electron-/atom- (Cl-center dot) transfer process is characterized by electrochemical measurements as well as UV-Vis, H-1 NMR, and EPR spectroscopies. Stopped-flow UV-Vis spectroscopy in THF indicate the following relative rates (k(obs)) [Cu-I(pmea)](+) > [Cu-I(pmap)](+) > [Cu-I(tmpa)(thf)](+). However, the redox potentials as related to Delta G degrees for the reaction, [E-1/2(oxidant) - E-1/2(reductant)], predict the trend [Cu-I(tmpa)(CH3CN)](+) > [Cu-I(pmea)](+) > [Cu-I(pmap)](+). A detailed description of Cu-I-to-Cu-II structural changes is provided and these likely influence the observed [(L)Cu-I](+)/(F-8)Fe-III(Cl) reaction rates. Analogous chemistry is described for a heme-copper system utilizing a heterobinucleating ligand (L-6), which is comprised of a TMPA like moiety tethered at the 6-position of one of the pyridyl donors to a F-8-like heme. Kinetic/mechanistic insights were obtained from transient absorption spectroscopic monitoring in CH3CN following photoejection of carbon monoxide from [(L-6)Fe-II(CO) center dot center dot center dot Cu-II(Cl)]. (C) 2007 Elsevier B.V. All rights reserved.