TY - JOUR
T1 - Characterization of the Fleeting Hydroxoiron(III) Complex of the Pentadentate TMC-py Ligand
AU - Ching, Wei Min
AU - Zhou, Ang
AU - Klein, Johannes E.M.N.
AU - Fan, Ruixi
AU - Knizia, Gerald
AU - Cramer, Christopher J.
AU - Guo, Yisong
AU - Que, Lawrence
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/9/18
Y1 - 2017/9/18
N2 - Nonheme mononuclear hydroxoiron(III) species are important intermediates in biological oxidations, but well-characterized examples of synthetic complexes are scarce due to their instability or tendency to form μ-oxodiiron(III) complexes, which are the thermodynamic sink for such chemistry. Herein, we report the successful stabilization and characterization of a mononuclear hydroxoiron(III) complex, [FeIII(OH)(TMC-py)]2+ (3; TMC-py = 1-(pyridyl-2′-methyl)-4,8,11-trimethyl-1,4,8,11-tetrazacyclotetradecane), which is directly generated from the reaction of [FeIV(O)(TMC-py)]2+ (2) with 1,4-cyclohexadiene at 40 °C by H-atom abstraction. Complex 3 exhibits a UV spectrum with a λmax at 335 nm (ϵ ≈ 3500 M-1 cm-1) and a molecular ion in its electrospray ionization mass spectrum at m/z 555 with an isotope distribution pattern consistent with its formulation. Electron paramagnetic resonance and Mössbauer spectroscopy show 3 to be a high-spin Fe(III) center that is formed in 85% yield. Extended X-ray absorption fine structure analysis reveals an Fe-OH bond distance of 1.84 Å, which is also found in [(TMC-py)FeIII-O-CrIII(OTf)3]+ (4) obtained from the reaction of 2 with Cr(OTf)2. The S = 5/2 spin ground state and the 1.84 Å Fe-OH bond distance are supported computationally. Complex 3 reacts with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) at 40 °C with a second-order rate constant of 7.1 M-1 s-1 and an OH/OD kinetic isotope effect value of 6. On the basis of density functional theory calculations, the reaction between 3 and TEMPOH is classified as a proton-coupled electron transfer as opposed to a hydrogen-atom transfer.
AB - Nonheme mononuclear hydroxoiron(III) species are important intermediates in biological oxidations, but well-characterized examples of synthetic complexes are scarce due to their instability or tendency to form μ-oxodiiron(III) complexes, which are the thermodynamic sink for such chemistry. Herein, we report the successful stabilization and characterization of a mononuclear hydroxoiron(III) complex, [FeIII(OH)(TMC-py)]2+ (3; TMC-py = 1-(pyridyl-2′-methyl)-4,8,11-trimethyl-1,4,8,11-tetrazacyclotetradecane), which is directly generated from the reaction of [FeIV(O)(TMC-py)]2+ (2) with 1,4-cyclohexadiene at 40 °C by H-atom abstraction. Complex 3 exhibits a UV spectrum with a λmax at 335 nm (ϵ ≈ 3500 M-1 cm-1) and a molecular ion in its electrospray ionization mass spectrum at m/z 555 with an isotope distribution pattern consistent with its formulation. Electron paramagnetic resonance and Mössbauer spectroscopy show 3 to be a high-spin Fe(III) center that is formed in 85% yield. Extended X-ray absorption fine structure analysis reveals an Fe-OH bond distance of 1.84 Å, which is also found in [(TMC-py)FeIII-O-CrIII(OTf)3]+ (4) obtained from the reaction of 2 with Cr(OTf)2. The S = 5/2 spin ground state and the 1.84 Å Fe-OH bond distance are supported computationally. Complex 3 reacts with 1-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOH) at 40 °C with a second-order rate constant of 7.1 M-1 s-1 and an OH/OD kinetic isotope effect value of 6. On the basis of density functional theory calculations, the reaction between 3 and TEMPOH is classified as a proton-coupled electron transfer as opposed to a hydrogen-atom transfer.
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U2 - 10.1021/acs.inorgchem.7b01459
DO - 10.1021/acs.inorgchem.7b01459
M3 - Article
C2 - 28858496
AN - SCOPUS:85029647088
SN - 0020-1669
VL - 56
SP - 11129
EP - 11140
JO - Inorganic chemistry
JF - Inorganic chemistry
IS - 18
ER -