Substrate Hydroxylation by the Oxido–Iron Intermediate in Aromatic Amino Acid Hydroxylases: A DFT Mechanistic Study

Olsson, Elaine; Martı́nez, Aurora; Teigen, Knut; Jensen, Vidar R.

doi:10.1002/ejic.201001218

Cited by 6 publications

(2 citation statements)

References 62 publications

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“…94 Here we restrict our calculations only to two functionals, one is a plain B3LYP and the other is B3LYP-D functional (also called B3LYP-D2) incorporating dispersion correction of Grimme et al [105][106][107] All the geometry optimizations are performed using the B3LYP and the B3LYP-D functionals. [105][106][107] Both the functionals have proven track-record of predicting the structures and the energetics accurately for such metal mediated catalytic reactions 94,[113][114][115][116][117][118][119][120][121][122][123][124][125][126] and between the two the dispersion corrected functional is found to be superior 126 for spin state energetics. The dispersion corrected functionals tend to favour low-spin complexes over high-spin as the electron density of low-spin complexes are compact, which gives raise to larger r À6 attraction between metal and the ligand.…”

Section: Computational Detailsmentioning

confidence: 99%

ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

Ansari

Rajaraman

2014

Phys. Chem. Chem. Phys.

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There is a growing interest in probing the mechanism of catalytic transformations effected by non-heme iron-oxo complexes as these reactions set a platform for understanding the relevant enzymatic reactions. The ortho-hydroxylation of aromatic compounds is one such reaction catalysed by iron-oxo complexes. Experimentally [Fe(II)(BPMEN)(CH3CN)2](2+) (1) and [Fe(II)(TPA)(CH3CN)2](2+) (2) (where TPA = tris(2-pyridylmethyl)amine and BPMEN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) complexes containing amino pyridine ligands along with H2O2 are employed to carry out these transformations where complex 1 is found to be more reactive than complex 2. Herein, using density functional methods employing B3LYP and dispersion corrected B3LYP (B3LYP-D) functionals, we have explored the mechanism of this reaction to reason out the importance of ligand design in fine-tuning the reactivity of such catalytic transformations. Dispersion corrected B3LYP is found to be superior to B3LYP in predicting the correct ground state of these species and also yields lower barrier heights than the B3LYP functional. Starting the reaction from the Fe(III)–OOH species, both homolytic and heterolytic cleavage of the O···O bond is explored leading to the formation of the transient Fe(IV)=O and Fe(V)=O species. For both the ligand systems, heterolytic cleavage was energetically preferable and our calculations suggest that both the reactions are catalyzed by an elusive high-valent Fe(V)=O species. The Fe(V)=O species undergoes the reaction via an electrophilic attack of the benzene ring to effect the ortho-hydroxylation reaction. The reactivity pattern observed for 1 and 2 are reflected in the computed barrier heights for the ortho-hydroxylation reaction. Electronic structure analysis reveals that the difference in reactivity between the ligand architectures described in complex 1 and 2 arise due to orientation of the pyridine ring(s) parallel or perpendicular to the Fe(V)=O bond. The parallel orientation of the pyridine ring is found to mix with the (πFe(dyz)–O(py))* orbital of the Fe-oxo bond leading to a reduction in the electrophilicity of the ferryl oxygen atom. Our calculations highlight the importance of ligand design in this chemistry and suggest that this concept can be used to (i) stabilize high-valent intermediates which can be trapped and thoroughly characterized (ii) enhance the reactivity and efficiency of the oxidants by increasing the electrophilicity of the ferryl oxygen containing FeVO species. Our computed results are in general agreement with the experimental results.

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Section: Computational Detailsmentioning

confidence: 99%

ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

Ansari

Rajaraman

2014

Phys. Chem. Chem. Phys.

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“…145 Computational studies have also been performed to investigate the mechanism of pterin-dependent aromatic amino acid hydroxylases. 152,153…”

Section: Figurementioning

confidence: 99%

Manganese and Nickel Complexes as Catalysts for Aromatic Oxidation

Rius¹

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The development of selective aromatic oxidation catalysts based on non-noble metals has emerged over the last decades, mainly due to the importance of phenol products as intermediates for the generation of pharmaceuticals or functional polymers. In nature, metalloenzymes can perform a wide variety of oxidative processes using molecular oxygen, including arene oxidations, however, the implementation of such enzymes in the chemical industry remains challenging. In this context, chemists have tried to mimic nature and design synthetic non-noble metal catalysts inspired by these enzymes. This introduction chapter aims at providing a general overview on aromatic oxidation reactions catalyzed by metalloenzymes as well as synthetic first-row transition-metal complexes as homogeneous catalysts. The enzymes and complexes discussed in this chapter have been classified on the basis of the transition-metal ion present in their active site, i.e., iron, copper, nickel, and manganese. The main points of discussion focus on enzyme structure and function, catalyst design, mechanism of operation in terms of oxidant activation and substrate oxidation, and substrate scope. At the end of the chapter, the aim and scope of this thesis is outlined.

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Mechanistic Insights on the ortho-Hydroxylation of Aromatic Compounds by Non-heme Iron Complex: A Computational Case Study on the Comparative Oxidative Ability of Ferric-Hydroperoxo and High-Valent Fe^IV═O and Fe^V═O Intermediates

2013

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ortho-Hydroxylation of aromatic compounds by non-heme Fe complexes has been extensively studied in recent years by several research groups. The nature of the proposed oxidant varies from Fe(III)-OOH to high-valent Fe(IV)═O and Fe(V)═O species, and no definitive consensus has emerged. In this comprehensive study, we have investigated the ortho-hydroxylation of aromatic compounds by an iron complex using hybrid density functional theory incorporating dispersion effects. Three different oxidants, Fe(III)-OOH, Fe(IV)═O, and Fe(V)═O, and two different pathways, H-abstraction and electrophilic attack, have been considered to test the oxidative ability of different oxidants and to underpin the exact mechanism of this regiospecific reaction. By mapping the potential energy surface of each oxidant, our calculations categorize Fe(III)-OOH as a sluggish oxidant, as both proximal and distal oxygen atoms of this species have prohibitively high barriers to carry out the aromatic hydroxylation. This is in agreement to the experimental observation where Fe(III)-OOH is found not to directly attack the aromatic ring. A novel mechanism for the explicit generation of non-heme Fe(IV)═O and Fe(V)═O from isomeric forms of Fe(III)-OOH has been proposed where the O···O bond is found to cleave via homolytic (Fe(IV)═O) or heterolytic (Fe(V)═O) fashion exclusively. Apart from having favorable formation energies, the Fe(V)═O species also has a lower barrier height compared to the corresponding Fe(IV)═O species for the aromatic ortho-hydroxylation reaction. The transient Fe(V)═O prefers electrophilic attack on the benzene ring rather than the usual aromatic C-H activation step. A large thermodynamic drive for the formation of a radical intermediate is encountered in the mechanistic scene, and this intermediate substantially diminishes the energy barrier required for C-H activation by the Fe(V)═O species. Further spin density distribution and the frontier orbitals of the computed species suggest that the Fe(IV)═O species has a substantial barrier height for this reaction, as the substrate is coordinated to the metal atoms. This coordination restricts the C-H activation step by Fe(IV)═O species to proceed via the π-type pathway, and thus the usual energy lowering due to the low-lying quintet state is not observed here.

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Substrate Hydroxylation by the Oxido–Iron Intermediate in Aromatic Amino Acid Hydroxylases: A DFT Mechanistic Study

Cited by 6 publications

References 62 publications

ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

Manganese and Nickel Complexes as Catalysts for Aromatic Oxidation

Mechanistic Insights on the ortho-Hydroxylation of Aromatic Compounds by Non-heme Iron Complex: A Computational Case Study on the Comparative Oxidative Ability of Ferric-Hydroperoxo and High-Valent Fe^IV═O and Fe^V═O Intermediates

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Substrate Hydroxylation by the Oxido–Iron Intermediate in Aromatic Amino Acid Hydroxylases: A DFT Mechanistic Study

Cited by 6 publications

References 62 publications

ortho-Hydroxylation of aromatic acids by a non-heme FeVO species: how important is the ligand design?

ortho-Hydroxylation of aromatic acids by a non-heme FeVO species: how important is the ligand design?

Manganese and Nickel Complexes as Catalysts for Aromatic Oxidation

Mechanistic Insights on the ortho-Hydroxylation of Aromatic Compounds by Non-heme Iron Complex: A Computational Case Study on the Comparative Oxidative Ability of Ferric-Hydroperoxo and High-Valent FeIV═O and FeV═O Intermediates

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ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

ortho-Hydroxylation of aromatic acids by a non-heme Fe^VO species: how important is the ligand design?

Mechanistic Insights on the ortho-Hydroxylation of Aromatic Compounds by Non-heme Iron Complex: A Computational Case Study on the Comparative Oxidative Ability of Ferric-Hydroperoxo and High-Valent Fe^IV═O and Fe^V═O Intermediates