213403-81-7

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• 1310-73-2 sodium hydroxide 

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• 836674-64-7 Fe(C₂₀H₈N₄(C₆H₃F₂)3(C₆H₄OCH₂C₅H₃NCH₂N(CH₂C₅H₄N)2)) 

Relevant academic research and scientific papers

Low-temperature UV-visible and NMR spectroscopic investigations of O2 binding to (6L)FeII, a ferrous heme bearing covalently tethered axial pyridine ligands

In this report, we describe the reversible dioxygen reactivity of (6L)FeII (1) {6L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine} using a combination of low-temperature UV-vis and multinuclear (1H and 2H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue (6L-d8)FeII (1-d8), exhibits downfield shifted pyrrole resonances (δ 28-60 ppm) in all solvents utilized {CH2Cl2, (CH3)2C(O), CH3CN, THF}, indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, (6L)FeII (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH2Cl2, (CH3)2C(O), and CH3CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, (6L)FeII (1) {UV-vis: λmax = 433 (Soret), 529 (sh), 559 nm} reversibly forms a dioxygen adduct {UV-vis: λmax = 422 (Soret), 542 nm}, formulated as the six-coordinate low-spin {δpyrrole 9.3 ppm, 193 K} heme-superoxo complex (6L)FeIII-(O2-) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of (6L)FeII (1) {UV-vis: λmax = 424 (Soret), 542 nm} also occurs to give a similar adduct (6L)FeIII-(O2-) (2) {UV-vis: λmax = 418 (Soret), 537 nm. 2H NMR: δpyrrole 8.9 ppm, 193 K}. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex (6L)FeIII-OH (3) {UV-vis: λmax = 412-414 (Soret), 566-575 nm; ～δpyrrole 120 ppm at 193 K}. This study on the O2-binding chemistry of the heme-only homonuclear (6L)FeII (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [(6L)FeIICuI]+, which are models for cytochrome c oxidase.

Intermolecular versus intramolecular electron-/atom- (Cl{radical dot}) transfer in heme-iron and copper pyridylalkylamine complexes

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, (F8)FeIII(Cl) (F8 is tetrakis(2,6-difluorophenyl)porphyrinate) with a series of [(L)CuI]+ complexes (L are tripodal tetradentate pyridylalkylamine ligands varying in effective chelate ring sizes: TMPA, PMEA, PMAP) to form (F8)FeII and [(L)CuII(Cl)]+. The electron-/atom- (Cl{radical dot}) transfer process is characterized by electrochemical measurements as well as UV-Vis, 1H NMR, and EPR spectroscopies. Stopped-flow UV-Vis spectroscopy in THF indicate the following relative rates (kobs) [CuI(pmea)]+ > [CuI(pmap)]+ > [CuI(tmpa)(thf)]+. However, the redox potentials as related to ΔG{ring operator} for the reaction, [E1/2(oxidant) - E1/2(reductant)], predict the trend [CuI(tmpa)(CH3CN)]+ > [CuI(pmea)]+ > [CuI(pmap)]+. A detailed description of CuI-to-CuII structural changes is provided and these likely influence the observed [(L)CuI]+/(F8)FeIII(Cl) reaction rates. Analogous chemistry is described for a heme-copper system utilizing a heterobinucleating ligand (6L), which is comprised of a TMPA like moiety tethered at the 6-position of one of the pyridyl donors to a F8-like heme. Kinetic/mechanistic insights were obtained from transient absorption spectroscopic monitoring in CH3CN following photoejection of carbon monoxide from [(6L)FeII(CO)?CuII(Cl)].