Deciphering the origin of million-fold reactivity observed for the open core diiron [HO–FeIII–O–FeIVO]2+species towards C–H bond activation: role of spin-states, spin-coupling, and spin-cooperation

Ansari, Mursaleem; Senthilnathan, Dhurairajan; Rajaraman, Gopalan

doi:10.1039/d0sc02624g

Cited by 18 publications

(16 citation statements)

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“…Both a radical mechanism, based on the oxyl character of the FeO group, or a concerted mechanism seem plausible for the open models. In computational studies of model complexes, it was found that the reactivity of the Fe(IV)O unit is modulated by the ligand to the second iron, 132 similar to what has been discussed for the Raman calculations before. Further examination of these distinct possibilities will be pursued in the future using the here developed QM/MM setup.…”

Section: Resultssupporting

confidence: 74%

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

et al. 2021

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The determination of the diiron core intermediate structures involved in the catalytic cycle of soluble methane monooxygenase (sMMO), the enzyme that selectively catalyzes the conversion of methane to methanol, has been a subject of intense interest within the bioinorganic scientific community. Particularly, the specific geometry and electronic structure of the intermediate that precedes methane binding, known as intermediate Q (or MMOH Q ), has been debated for over 30 years. Some reported studies support a bis-μ-oxo-bridged Fe(IV) 2 O 2 closed-core conformation Fe(IV) 2 O 2 core, whereas others favor an open-core geometry, with a longer Fe–Fe distance. The lack of consensus calls for a thorough re-examination and reinterpretation of the spectroscopic data available on the MMOH Q intermediate. Herein, we report extensive simulations based on a hybrid quantum mechanics/molecular mechanics approach (QM/MM) approach that takes into account the complete enzyme to explore possible conformations for intermediates MMOH ox and MMOH Q of the sMMOH catalytic cycle. High-level quantum chemical approaches are used to correlate specific structural motifs with geometric parameters for comparison with crystallographic and EXAFS data, as well as with spectroscopic data from Mössbauer spectroscopy, Fe K-edge high-energy resolution X-ray absorption spectroscopy (HERFD XAS), and resonance Raman 16 O– 18 O difference spectroscopy. The results provide strong support for an open-core-type configuration in MMOH Q , with the most likely topology involving mono-oxo-bridged Fe ions and alternate terminal Fe-oxo and Fe-hydroxo groups that interact via intramolecular hydrogen bonding. The implications of an open-core intermediate Q on the reaction mechanism of sMMO are discussed.

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Section: Resultssupporting

confidence: 74%

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

et al. 2021

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“…We have tested the D3 dispersion at B3LYP-D3/TZVP(all atoms)//B3LYP-D3/LanL2DZ(Mn),6-31G*(C, H, N, O) level of theory for selected species and only marginal differences are noted (see Table S8 in ESI). Although the chosen methodology is shown to yield a good numerical estimate of spin-state energetics and thermodynamic/kinetic data, ,,− it has been shown in several cases that when two spin states lie very close to each other, the DFT methods fail to predict correct ground state. − A limited benchmarking was undertaken with BP86, TPSSh, PBE0, M06L, and wB97XD functionals to understand the small energy gap computed, which suggests that the B3LYP method chosen is reliable if the gap is sufficiently large (see Table S9 in the ESI). The ab initio DLPNO-CCSD(T) has recently gained popularity because of its high accuracy in predicting the correct ground state relative to experimental observations , and its affordability for larger molecules.…”

Section: Computational Methodologymentioning

confidence: 99%

Mechanistic Insights into the Oxygen Atom Transfer Reactions by Nonheme Manganese Complex: A Computational Case Study on the Comparative Oxidative Ability of Manganese-Hydroperoxo vs High-Valent Mn^IV═O and Mn^IV–OH Intermediates

et al. 2021

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Understanding the comparative oxidative abilities of high-valent metal-oxo/hydroxo/hydroperoxo species holds the key to robust biomimic catalysts that perform desired organic transformations with very high selectivity and efficiency. The comparative oxidative abilities of popular high-valent iron-oxo and manganese-oxo species are often counterintuitive, for example, oxygen atom transfer (OAT) reaction by [(Me2EBC)MnIV–OOH]3+, [(Me2EBC)MnIV–OH]3+, and [(Me2EBC)MnIVO]2+ (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane) shows extremely high reactivity for MnIV–OOH species and no reactivity for MnIV–OH and MnIVO species toward alkyl/aromatic sulfides. Using a combination of density functional theory (DFT) and ab initio domain-based local pair natural orbital coupled-cluster with single, double, and perturbative triples excitation (DLPNO-CCSD(T)) and complete-active space self-consistent field/N-electron valence perturbation theory second order (CASSCF/NEVPT2) calculations, here, we have explored the electronic structures and sulfoxidation mechanism of these species. Our calculations unveil that MnIV–OOH reacts through distal oxygen atom with the substrate via electron transfer (ET) mechanism with a very small kinetic barrier (16.5 kJ/mol), placing this species at the top among the best-known catalysts for such transformations. The MnIV–OH and MnIVO species have a much larger barrier. The mechanism has also been found to switch from ET in the former to concerted in the latter, rendering both unreactive under the tested experimental conditions. Intrinsic differences in the electronic structures, such as the presence and absence of the multiconfigurational character coupled with the steric effects, are responsible for such variations observed. This comparative oxidative ability that runs contrary to the popular iron-oxo/hydroperoxo reactivity will have larger mechanistic implications in understanding the reactivity of biomimic catalysts and the underlying mechanisms in PSII.

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“…Dioxygen (O 2 ) occupies a critical position in a great variety of oxidation reactions involved in both chemical reactions and biological processes. [1][2][3][4][5][6] In aerobic biology, O 2 -related oxidation reactions are achieved by a series of evolutionary metalloenzymes such as cytochrome P450 through the interaction with O 2 , resulting in the formation of reactive oxygen species (ROS) such as singlet oxygen ( 1 O 2 ), hydroxyl radical (cOH) and superoxide anion (O 2 À ) or reactive metal-O 2 intermediates including metal superoxo, (hydro)peroxo, and metal-oxo species. [7][8][9][10][11] Among the active species, 1 O 2 with an unoccupied p* orbital has strong electrophilicity and unique reactivity and selectivity to serve as a synthetic reagent, attracting enormous interest from both fundamental studies and practical application elds.…”

Section: Introductionmentioning

confidence: 99%

Highly selective generation of singlet oxygen from dioxygen with atomically dispersed catalysts

Mao

et al. 2022

Chem. Sci.

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Deciphering the origin of million-fold reactivity observed for the open core diiron [HO–Fe^III–O–Fe^IVO]²⁺species towards C–H bond activation: role of spin-states, spin-coupling, and spin-cooperation

Abstract:
Our results unequivocally reveal the importance of spin states, spin coupling and spin cooperation in controlling the reactivity in dinuclear Fe-oxo species.

Cited by 18 publications

References 174 publications

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

Mechanistic Insights into the Oxygen Atom Transfer Reactions by Nonheme Manganese Complex: A Computational Case Study on the Comparative Oxidative Ability of Manganese-Hydroperoxo vs High-Valent Mn^IV═O and Mn^IV–OH Intermediates

Highly selective generation of singlet oxygen from dioxygen with atomically dispersed catalysts

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Deciphering the origin of million-fold reactivity observed for the open core diiron [HO–FeIII–O–FeIVO]2+species towards C–H bond activation: role of spin-states, spin-coupling, and spin-cooperation

Abstract: Our results unequivocally reveal the importance of spin states, spin coupling and spin cooperation in controlling the reactivity in dinuclear Fe-oxo species.

Cited by 18 publications

References 174 publications

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

Structure–Spectroscopy Correlations for Intermediate Q of Soluble Methane Monooxygenase: Insights from QM/MM Calculations

Mechanistic Insights into the Oxygen Atom Transfer Reactions by Nonheme Manganese Complex: A Computational Case Study on the Comparative Oxidative Ability of Manganese-Hydroperoxo vs High-Valent MnIV═O and MnIV–OH Intermediates

Highly selective generation of singlet oxygen from dioxygen with atomically dispersed catalysts

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Deciphering the origin of million-fold reactivity observed for the open core diiron [HO–Fe^III–O–Fe^IVO]²⁺species towards C–H bond activation: role of spin-states, spin-coupling, and spin-cooperation

Abstract:
Our results unequivocally reveal the importance of spin states, spin coupling and spin cooperation in controlling the reactivity in dinuclear Fe-oxo species.

Mechanistic Insights into the Oxygen Atom Transfer Reactions by Nonheme Manganese Complex: A Computational Case Study on the Comparative Oxidative Ability of Manganese-Hydroperoxo vs High-Valent Mn^IV═O and Mn^IV–OH Intermediates