Influence of the nitrogen donors on nonheme iron models of superoxide reductase: high-spin Fe(III)-OOR complexes.
A new five-coordinate, (N(4)S(thiolate))Fe(II) complex, containing tertiary amine donors, [Fe(II)(Me(4)[15]aneN(4))(SPh)]BPh(4) (2), was synthesized and structurally characterized as a model of the reduced active site of superoxide reductase (SOR). Reaction of 2 with tert-butyl hydroperoxide (tBuOOH) at -78 degrees C led to the generation of the alkylperoxo-iron(III) complex [Fe(III)(Me(4)[15]aneN(4))(SPh)(OOtBu)](+) (2a). The nonthiolate-ligated complex, [Fe(II)(Me(4)[15]aneN(4))(OTf)(2)] (3), was also reacted with tBuOOH and yielded the corresponding alkylperoxo complex [Fe(III)(Me(4)[15]aneN(4))(OTf)(OOtBu)](+) (3a) at an elevated temperature of -23 degrees C. These species were characterized by low-temperature UV-vis, EPR, and resonance Raman spectroscopies. Complexes 2a and 3a exhibit distinctly different spectroscopic signatures than the analogous alkylperoxo complexes [Fe(III)([15]aneN(4))(SAr)(OOR)](+), which contain secondary amine donors. Importantly, alkylation at nitrogen leads to a change from low-spin (S = 1/2) to high-spin (S = 5/2) of the iron(III) center. The resonance Raman data reveal that this change in spin state has a large effect on the nu(Fe-O) and nu(O-O) vibrations, and a comparison between 2a and the nonthiolate-ligated complex 3a shows that axial ligation has an additional significant impact on these vibrations. To our knowledge this study is the first in which the influence of a ligand trans to a peroxo moiety has been evaluated for a structurally equivalent pair of high-spin/low-spin peroxo-iron(III) complexes. The implications of spin state and thiolate ligation are discussed with regard to the functioning of SOR.
Namuswe
Frances
F
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Hayashi
Takahiro
T
Jiang
Yunbo
Y
Kasper
Gary D
GD
Sarjeant
Amy A Narducci
AA
Moënne-Loccoz
Pierre
P
Goldberg
David P
DP
D000478:Alkylation; D000588:Amines / Q000737:chemistry; D032701:Biomimetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006418:Heme; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D010545:Peroxides / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature
D000588:Amines; D008024:Ligands; D009942:Organometallic Compounds; D010545:Peroxides; D006418:Heme; D007501:Iron; D010088:Oxidoreductases; C121849:superoxide reductase; D009584:Nitrogen