Spectroscopic Identification of an FeIII Center, not FeIV, in the Crystalline Sc–O–Fe Adduct Derived from [FeIV(O)(TMC)]2+

Prakash, Jai; Rohde, Gregory T.; Meier, Katlyn K.; Jasniewski, Andrew J.; Heuvelen, Katherine M. Van; Münck, Eckard; Que, Lawrence

doi:10.1021/jacs.5b00535

Cited by 62 publications

(82 citation statements)

References 30 publications

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“…In addition to biological oxidations, redox-inactive metal ions are also frequently employed to improve the stability and/or to modulate the reactivity of transition metal catalysts in heterogeneous oxidations. 6 Nam and Fukuzumi reported that Lewis acid like Sc 3+ can substantially accelerate the electron transfer rate from a series of one-electron reductants to a nonheme oxoiron(IV), Fe IV (N4Py)(O), 7 and similar acceleration effect was also observed in oxidative dimerization and Ndemethylation of N,N-dimethylaniline. Different from the complicated biological and heterogeneous systems, homogeneous system can offer simpler models to help understanding how these redox-inactive metal ions participate in the oxidation events and affect the reactivity properties of redox-active metal ions.…”

Section: Introductionmentioning

confidence: 76%

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

Choe

Yang

et al. 2015

Dalton Trans.

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Redox-inactive metal ions can modulate the reactivity of redox-active metal ions in a variety of biological and chemical oxidations. Many synthetic models have been developed to help address the elusive roles of these redox-inactive metal ions. Using a non-heme manganese(II) complex as the model, the influence of redox-inactive metal ions as a Lewis acid on its catalytic efficiency in oxygen atom transfer was investigated. In the absence of redox-inactive metal ions, the manganese(II) catalyst is very sluggish, for example, in cyclooctene epoxidation, providing only 9.9% conversion with 4.1% yield of epoxide. However, addition of 2 equiv. of Al(3+) to the manganese(II) catalyst sharply improves the epoxidation, providing up to 97.8% conversion with 91.4% yield of epoxide. EPR studies of the manganese(II) catalyst in the presence of an oxidant reveal a 16-line hyperfine structure centered at g = 2.0, clearly indicating the formation of a mixed valent di-μ-oxo-bridged diamond core, Mn(III)-(μ-O)2-Mn(IV). The presence of a Lewis acid like Al(3+) causes the dissociation of this diamond Mn(III)-(μ-O)2-Mn(IV) core to form monomeric manganese(iv) species which is responsible for improved epoxidation efficiency. This promotional effect has also been observed in other manganese complexes bearing various non-heme ligands. The findings presented here have provided a promising strategy to explore the catalytic reactivity of some di-μ-oxo-bridged complexes by adding non-redox metal ions to in situ dissociate those dimeric cores and may also provide clues to understand the mechanism of methane monooxygenase which has a similar diiron diamond core as the intermediate.

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Section: Introductionmentioning

confidence: 76%

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

Choe

Yang

et al. 2015

Dalton Trans.

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“…More interestingly, the isomer shift found for 2 is halfway between the values for 1 and 3 . 9 However, the magnitude of the coupling constant J cannot be reliably determined, because Mössbauer measurements at higher temperature (up to 180 K) and high applied fields (up to 7 T) show that the electronic systems of these compounds still exhibit intermediate magnetic relaxation.…”

Section: Resultsmentioning

confidence: 99%

The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe–O–M Complexes Derived from [Fe^IV(O_anti/syn)(TMC)]²⁺ Isomers

et al. 2016

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Tetramethylcyclam (TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) exhibits two faces in supporting an oxoiron(IV) moiety, as exemplified by the prototypical [(TMC)-FeIV(Oanti)(NCCH3)](OTf)2, where anti indicates that the O atom is located on the face opposite all four methyl groups, and the recently reported syn isomer [(TMC)FeIV(Osyn)(OTf)](OTf). The ability to access two isomers of [(TMC)FeIV(Oanti/syn)] raises the fundamental question of how ligand topology can affect the properties of the metal center. Previously, we have reported the formation of [(CH3CN)-(TMC)FeIII−Oanti−CrIII(OTf)4(NCCH3)] (1) by inner-sphere electron transfer between Cr(OTf)2 and [(TMC)FeIV(Oanti)(NCCH3)]-(OTf)2. Herein we demonstrate that a new species 2 is generated from the reaction between Cr(OTf)2 and [(TMC)FeIV(Osyn)(NCCH3)]-(OTf)2, which is formulated as [(TMC)FeIII−Osyn−CrIII(OTf)4(NCCH3)] based on its characterization by UV−vis, resonance Raman, Mössbauer, and X-ray absorption spectroscopic methods, as well as electrospray mass spectrometry. Its pre-edge area (30 units) and Fe−O distance (1.77 Å) determined by X-ray absorption spectroscopy are distinctly different from those of 1 (11-unit pre-edge area and 1.81 Å Fe−O distance) but more closely resemble the values reported for [(TMC)FeIII−Osyn−ScIII(OTf)4(NCCH3)] (3, 32-unit pre-edge area and 1.75 Å Fe−O distance). This comparison suggests that 2 has a square pyramidal iron center like 3, rather than the six-coordinate center deduced for 1. Density functional theory calculations further validate the structures for 1 and 2. The influence of the distinct TMC topologies on the coordination geometries is further confirmed by the crystal structures of [(Cl)(TMC)FeIII−Oanti−FeIIICl3] (4Cl) and [(TMC)FeIII−Osyn−FeIIICl3](OTf) (5). Complexes 1–5 thus constitute a set of complexes that shed light on ligand topology effects on the coordination chemistry of the oxoiron moiety.

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“…Lastly, 3 has an Fe⋯Ce distance of 3.825(5) Å, which is longer than those found for other Fe III –O–M complexes, e.g. ≤ 3.61 Å for M = Fe III , [9b],[14] and 3.64 for M = Sc III , [8] reflecting the larger ionic radius of the Ce IV center.…”

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confidence: 82%

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

et al. 2017

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CAN or CeIV(NH4)2(NO3)6 is often used in artificial water oxidation and generally considered to be an outer-sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)FeIII–O–CeIV(OH2)(NO3)4]+ (3), a complex obtained from the reaction of [(N4Py)FeII(NCMe)]2+ with 2 equiv. CAN or [(N4Py)FeIV=O]2+ (2) with CeIII(NO3)3 in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the FeIV and CeIV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S = 1 FeIV in 2 to S = 5/2 in 3, which is found to be facile despite the formal spin forbidden nature of this process. This observation suggests that FeIV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.

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Spectroscopic Identification of an Fe^III Center, not Fe^IV, in the Crystalline Sc–O–Fe Adduct Derived from [Fe^IV(O)(TMC)]²⁺

Cited by 62 publications

References 30 publications

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe–O–M Complexes Derived from [Fe^IV(O_anti/syn)(TMC)]²⁺ Isomers

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

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Spectroscopic Identification of an FeIII Center, not FeIV, in the Crystalline Sc–O–Fe Adduct Derived from [FeIV(O)(TMC)]2+

Cited by 62 publications

References 30 publications

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer

The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe–O–M Complexes Derived from [FeIV(Oanti/syn)(TMC)]2+ Isomers

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

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Spectroscopic Identification of an Fe^III Center, not Fe^IV, in the Crystalline Sc–O–Fe Adduct Derived from [Fe^IV(O)(TMC)]²⁺

The Two Faces of Tetramethylcyclam in Iron Chemistry: Distinct Fe–O–M Complexes Derived from [Fe^IV(O_anti/syn)(TMC)]²⁺ Isomers