Oxo- and hydroxo-bridged heme-copper assemblies formed from acid-base or metal-dioxygen chemistry
Kopf, MA; Neuhold, YM; Zuberbuhler, AD; Karlin, KD
| HERO ID | 5410573 |
|---|---|
| In Press | No |
| Year | 1999 |
| Title | Oxo- and hydroxo-bridged heme-copper assemblies formed from acid-base or metal-dioxygen chemistry |
| Authors | Kopf, MA; Neuhold, YM; Zuberbuhler, AD; Karlin, KD |
| Journal | Inorganic Chemistry |
| Volume | 38 |
| Issue | 13 |
| Page Numbers | 3093-3102 |
| Abstract | The iron-copper dinuclear active site in heme-copper oxidases (e.g., cyctochrome c oxidase) has spurred the development of the inorganic: chemistry of bridged heme-copper complexes, including species possessing (porphyrinate)Fe(III)-O(H)-Cu(II)-L moieties. We describe here the synthesis, by two routes, of [(F(8)TPP)Fe(III)-O-Cu(II)(MePY2)](+) (5) {F(8)TPP = tetrakis(2,6-difluorophenyl)porphyrinate; MePY2 = N,N-bis[2-(2-pyridyl)ethyl] methylamine). First, 5-(CF(3)SO(3)) was generated by reaction of [(MePY2)Cu(II)](CF(3)SO(3))(2) (3-(CF(3)SO(3))(2)) and [(F(8)TPP)Fe(III)-OH] (4) with triethylamine in THF or CH(3)CN in 65-70% yield. The complex was also prepared by reduction of O(2) by a 1:1 mixture of copper(I) and iron(II) complexes, [(MePY2)Cu(I)(CH(3)CN)](BArF) (1-(BArF)) (BArF = tetrakis(3,5-bis-trifluoromethylphenyl)borate) and (F(8)TPP)Fe(II) (2) in O(2)-saturated THF or acetone, at -80 degrees C with subsequent warming to room temperature. Preliminary stopped-flow kinetics on the O(2) reaction with the 1:1 mixture show the formation of at least two intermediates (i.e., a superoxo species (F(8)TPP)Fe-O(2) first, and then a presumed peroxo-bridged Fe-O(2)-Cu species) prior to the formation of the final mu-oxo complex [(F(8)TPP)Fe(III)-O-Cu(II)(MePY2)](+) (5-(BArF)). The (1)H NMR spectrum of 5-(CF(3)SO(3)) in CD(2)Cl(2) exhibits a pyrrole peak at 67.7 ppm (corroborated by (2)H NMR), while downfield (23.4 and 18.9 ppm) and dramatically upfield-shifted resonances (-87.7, -155.4 and -189.4) have been assigned to hydrogens of the MePY2 moiety, by specific deuteration. The mu-hydroxo complex [(F(8)TPP)Fe-(OH)-Cu(MePY2)](OTf)(2) (6-(CF(3)SO(3))(2)) was synthesized by addition of 3-(CF(3)SO(3))(2) to 4 in CH(3)CN, or by protonation of 5-(CF(3)SO(3)) with CF(3)SO(3)H. In a (1)H. NMR-spectroscopic protonation titration (CF(3)SO(3)H)(2) the pyrrole 67.7 ppm resonance for 5-(CF(3)SO(3)) progressively converts to 70.3 ppm, diagnostic of 6-(CF(3)SO(3))(2). The protonation is slow on the NMR time scale. The (1)H NMR spectral properties are consistent with antiferromagnetically coupled high-spin iron(III) and Cu(II) ions (S = 2 spin state), and the interaction is weaker in 6-(CF(3)SO(3))(2) (5-(CF3SO3), mu(eff) = 5.05 mu(B); 6-(CF(3)SO(3))(2), mu(eff) = 5.60 mu(B); Evans NMR method). By titration using a series of organic acids, the pK(a) for 6-(CF3S03)2 has been estimated to be 16.7 < pK(a) < 17.6 (CH(3)CN solvent), or 9.6 +/- 2 (aqueous). Plots of delta vs 1/T for both mu-oxo and mu-hydroxo complexes 5-(CF(3)SO(3)) and 6-(CF(3)SO(3))(2) have been obtained, showing linear Curie (for downfield resonances) or anti-Curie (for upfield peaks) behavior. |
| Doi | 10.1021/ic981431+ |
| Wosid | WOS:000081189300014 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |