Use of Singlet Oxygen in the Generation of a Mononuclear Nonheme Iron(IV)-Oxo Complex

Abstract

Nonheme iron(III)-superoxo intermediates are generated in the activation of dioxygen (O2) by nonheme iron(II) complexes and then converted to iron(IV)-oxo species by reacting with hydrogen donor substrates with relatively weak C–H bonds. If singlet oxygen (1O2) with ca. 1 eV higher energy than the ground state triplet oxygen (3O2) is employed, iron(IV)-oxo complexes can be synthesized using hydrogen donor substrates with much stronger C–H bonds. However, 1O2 has never been used in generating iron(IV)-oxo complexes. Herein, we report that a nonheme iron(IV)-oxo species, [FeIV(O)(TMC)]2+ (TMC = tetramethylcyclam), is generated using 1O2, which is produced with boron subphthalocyanine chloride (SubPc) as a photosensitizer, and hydrogen donor substrates with relatively strong C–H bonds, such as toluene (BDE = 89.5 kcal mol–1), via electron transfer from [FeII(TMC)]2+ to 1O2, which is energetically more favorable by 0.98 eV, as compared with electron transfer from [FeII(TMC)]2+ to 3O2. Electron transfer from [FeII(TMC)]2+ to 1O2 produces an iron(III)-superoxo complex, [FeIII(O2)(TMC)]2+, followed by abstracting a hydrogen atom from toluene by [FeIII(O2)(TMC)]2+ to form an iron(III)-hydroperoxo complex, [FeIII(OOH)(TMC)]2+, that is further converted to the [FeIV(O)(TMC)]2+ species. Thus, the present study reports the first example of generating a mononuclear nonheme iron(IV)-oxo complex with the use of singlet oxygen, instead of triplet oxygen, and a hydrogen atom donor with relatively strong C–H bonds. Detailed mechanistic aspects, such as the detection of 1O2 emission, the quenching by [FeII(TMC)]2+, and the quantum yields, have also been discussed to provide valuable mechanistic insights into understanding nonheme iron-oxo chemistry.

Constructing Singlet Oxygen “Slow Release” Platform to Optimize the Performance of Commercial Photosensitizers

“…However, the energy gap between S 1 and T 1 (Δ E S1−T1 ) value of AIC (0.84 eV) was obviously lower than that of PHIC (1.42 eV) (Figure 2b), which was easily for intersystem crossing (ISC) to benefit the ROS generation. In contrast to the Δ E T1−S0 of PHIC (0.69 eV), that of AIC was 1.28 eV, which was higher than 0.98 eV (the energy barrier of 3 O 2 / 1 O 2 ), [ 35 ] facilitating 1 O 2 production via energy transfer process. Subsequently, the charge separation abilities and charge transfer rates of PHIC and AIC were further evaluated through photocurrent and the charge transfer resistance experiment, respectively.…”

Efficient Degradation of Intracellular Antibiotic Resistance Genes by Photosensitized Erythrosine-Produced 1O2

“…Fe(IV) is a powerful oxidant that can be produced by oxidation of intracellular Fe-containing complexes. 61 ROO• and RO• produced by hydroperoxide of lipids and proteins have been reported to cause DNA damage. 62−64 Although the addition of PMSO appeared to have some quenching effect (Figure S20), the concentrations of PMSO and its Fe(IV)specific oxidation product PMSO 2 40 did not change significantly (p < 0.05, Figures S21 and S22), suggesting that Fe(IV) was not detected in the iARG degradation system and the weak quenching effect of PMSO was due to other effects.…”

Controllable and Low-Loss Electrochemiluminescence Waveguide Supported by a Micropipette Electrode

“…The successful detection of 1 O 2 by Singlet Oxygen Sensor Green (SOSG) confirms that the PL quenching indeed follows the above photochemical reactions (see Figure S22a,b). 71,72 Meanwhile, the photogenerated 1 O 2 can also lead to the photobleaching of MCW, resulting in the irreversible decrease of PL intensity. 73 Both TPrA • and MCW − involved in the ECL generation (see eqs 3 and 6, respectively) are strong reductants that can be oxidized by O 2 .…”