Dataset Information

Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}(7) Complex with Dioxygen.

ABSTRACT: The nonheme iron complex, [Fe(NO)(N3PyS)]BF4, is a rare example of an {FeNO}(7) species that exhibits spin-crossover behavior. The comparison of X-ray crystallographic studies at low and high temperatures and variable-temperature magnetic susceptibility measurements show that a low-spin S = 1/2 ground state is populated at 0-150 K, while both low-spin S = 1/2 and high-spin S = 3/2 states are populated at T > 150 K. These results explain the observation of two N-O vibrational modes at 1737 and 1649 cm(-1) in CD3CN for [Fe(NO)(N3PyS)]BF4 at room temperature. This {FeNO}(7) complex reacts with dioxygen upon photoirradiation with visible light in acetonitrile to generate a thiolate-ligated, nonheme iron(III)-nitro complex, [Fe(III)(NO2)(N3PyS)](+), which was characterized by EPR, FTIR, UV-vis, and CSI-MS. Isotope labeling studies, coupled with FTIR and CSI-MS, show that one O atom from O2 is incorporated in the Fe(III)-NO2 product. The O2 reactivity of [Fe(NO)(N3PyS)]BF4 in methanol is dramatically different from CH3CN, leading exclusively to sulfur-based oxidation, as opposed to NO· oxidation. A mechanism is proposed for the NO· oxidation reaction that involves formation of both Fe(III)-superoxo and Fe(III)-peroxynitrite intermediates and takes into account the experimental observations. The stability of the Fe(III)-nitrite complex is limited, and decay of [Fe(III)(NO2)(N3PyS)](+) leads to {FeNO}(7) species and sulfur oxygenated products. This work demonstrates that a single mononuclear, thiolate-ligated nonheme {FeNO}(7) complex can exhibit reactivity related to both nitric oxide dioxygenase (NOD) and nitrite reductase (NiR) activity. The presence of the thiolate donor is critical to both pathways, and mechanistic insights into these biologically relevant processes are presented.

SUBMITTER: McQuilken AC

PROVIDER: S-EPMC5502531 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Publications

Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}(7) Complex with Dioxygen.

McQuilken Alison C AC Matsumura Hirotoshi H Dürr Maximilian M Confer Alex M AM Sheckelton John P JP Siegler Maxime A MA McQueen Tyrel M TM Ivanović-Burmazović Ivana I Moënne-Loccoz Pierre P Goldberg David P DP

Journal of the American Chemical Society 20160226 9

The nonheme iron complex, [Fe(NO)(N3PyS)]BF4, is a rare example of an {FeNO}(7) species that exhibits spin-crossover behavior. The comparison of X-ray crystallographic studies at low and high temperatures and variable-temperature magnetic susceptibility measurements show that a low-spin S = 1/2 ground state is populated at 0-150 K, while both low-spin S = 1/2 and high-spin S = 3/2 states are populated at T > 150 K. These results explain the observation of two N-O vibrational modes at 1737 and 16 ...[more]

PMID: 26919583

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Project description:The reactivity between a thiolate-ligated five-coordinate complex [FeII(SMe2N4(tren))]+ (1) and dioxygen is examined in order to determine if O2 activation, resembling that of the metalloenzyme cytochrome P450, can be promoted even when O2 binds cis, as opposed to trans, to a thiolate. Previous work in our group showed that [FeII(SMe2N4(tren))]+ (1) reacts readily with superoxide (O2-) in the presence of a proton source to afford H2O2 via an Fe(III)-OOH intermediate, thus providing a biomimetic model for the metalloenzyme superoxide reductase (SOR). Addition of O2 to 1 affords binuclear mu-oxo-bridged [FeIII(SMe2N4(tren))]2(mu2-O)(PF6)2.3MeCN (3). At low temperatures, in protic solvents, an intermediate is detected, the details of which will be the subject of a separate paper. Although the thiolate ligand does not appear to perturb the metrical parameters of the unsupported mu-oxo bridge (Fe-O= 1.807(8) A, and Fe-O-Fe= 155.3(5) degrees fall in the usual range), it decreases the magnetic coupling between the irons (J=-28 cm(-1)) and creates a rather basic oxo site. Protonation of this oxo using strong (HBF4, HCl) or weak (HOAc, NH4PF6, LutNHCl) acids results in bridge cleavage to cleanly afford the corresponding monomeric anion-ligated (OAc- (6), or Cl- (7)) or solvent-ligated (MeCN (4)) derivatives. Addition of OH- converts [FeIII(SMe2N4(tren))(MeCN2+ (4) back to mu-oxo 3. Thus, mu-oxo bridge cleavage is reversible. The protonated mu-hydroxo-bridged intermediate is not observed. In an attempt to prevent mu-oxo dimer formation, and facilitate the observation of O2-bound intermediates, a bulkier tertiary amine ligand, tren-Et4= N-(2-amino-ethyl)-N-(2-diethylamino-ethyl)-N',N'-diethyl-ethane-1,2-diamine, and the corresponding [FeII(SMe2N4(tren-Et4))]+ (5) complex was synthesized and structurally characterized. Steric repulsive interactions create unusually long FeII-N(3,4) amine bonds in 5 (mean distance=2.219(1) A). The [(tren-Et4)N4SMe2]1- ligand is unable to accommodate iron in the +3 oxidation state, and consequently, in contrast to most thiolate-ligated Fe(II) complexes, [FeII(SMe2N4(tren-Et4))]+ (5) does not readily react with O2. Oxidation of 5 is irreversible, and the potential (Epa=+410 mV (vs SCE)) is anodically shifted relative to 1 (E1/2=-100 mV (vs SCE)).

Dataset Information

Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}(7) Complex with Dioxygen.

Publications

Photoinitiated Reactivity of a Thiolate-Ligated, Spin-Crossover Nonheme {FeNO}(7) Complex with Dioxygen.

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