Tuning the Regiospecificity of Cleavage in FeIII Catecholate Complexes: Tridentate Facial versus Meridional Ligands

Jo, Du-Hwan; Que, Lawrence

doi:10.1002/1521-3757(20001201)112:23<4454::aid-ange4454>3.0.co;2-s

Cited by 10 publications

(2 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These results imply that the O 2 -incorporation into the aryl ring is through a single-oxygen insertion rather than the insertion of both oxygen atoms of the O 2 as proposed earlier [33,55,58,61,62,63,64]. This incorporation of a single oxygen atom from O 2 is analogous to the reaction of oxygenases in biological systems (Scheme 9c), which leads to distinct intradiol or extradiol ring-opening products, respectively, depending on the initial sites of O 2 coordination [66,67,68,69]. It is expected that the activation and insertion of O 2 into aromatic ring in the present case is dependent on its coordination to the Ti–sites on the TiO 2 surface, just as in the active centre of oxygenases.…”

Section: Photocatalytic Cleavage Of Aryl-ring On Tio2 Surfacesupporting

confidence: 63%

Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique

Pang

Chen

et al. 2014

Molecules

View full text Add to dashboard Cite

During the last several decades TiO2 photocatalytic oxidation using the molecular oxygen in air has emerged as a promising method for the degradation of recalcitrant organic pollutants and selective transformations of valuable organic chemicals. Despite extensive studies, the mechanisms of these photocatalytic reactions are still poorly understood due to their complexity. In this review, we will highlight how the oxygen-18 isotope labeling technique can be a powerful tool to elucidate complicated photocatalytic mechanisms taking place on the TiO2 surface. To this end, the application of the oxygen-18 isotopic-labeling method to three representative photocatalytic reactions is discussed: (1) the photocatalytic hydroxylation of aromatics; (2) oxidative cleavage of aryl rings on the TiO2 surface; and (3) photocatalytic decarboxylation of saturated carboxylic acids. The results show that the oxygen atoms of molecular oxygen can incorporate into the corresponding products in aqueous solution in all three of these reactions, but the detailed incorporation pathways are completely different in each case. For the hydroxylation process, the O atom in O2 is shown to be incorporated through activation of O2 by conduction band electrons. In the cleavage of aryl rings, O atoms are inserted into the aryl ring through the site-dependent coordination of reactants on the TiO2 surface. A new pathway for the decarboxylation of saturated carboxylic acids with pyruvic acid as an intermediate is identified, and the O2 is incorporated into the products through the further oxidation of pyruvic acid by active species from the activation of O2 by conduction band electrons.

show abstract

Section: Photocatalytic Cleavage Of Aryl-ring On Tio2 Surfacesupporting

confidence: 63%

Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique

Pang

Chen

et al. 2014

Molecules

View full text Add to dashboard Cite

show abstract

“…Proposals have ranged from first-sphere effects such as the oxidation state of the iron, or the vastly different endogenous ligand sets, to outer sphere effects from second-sphere residues and to the orientation of the alkylperoxy bond with respect to the cleaved C–C bond. Regarding the metal oxidation state, model studies have shown both Fe II and Fe III complexes are capable of both extradiol and intradiol cleavage. − Early mechanistic studies of the intradiol and extradiol dioxygenases using alternative substrates and other chemical probes lead to the idea that the coplanar alignment of the peroxo O–O bond with the scissile C–C bond (inspired by the Criegee rearrangement for alkylperoxides) dictates the cleavage regiospecificity. , Some of the first computational studies supported this proposal. , More recently, significant advances have come from the trapping, spectroscopic and crystallographic characterization of key enzyme intermediates in the reaction cycles. − Of these studies, two crystallographic intermediates are particularly notable. In-crystallo reaction of the EDO, homoprotocatechuate 2,3-dioxygenase (HPCD) with the slow 4-nitrocatechol (4NC) substrate and dioxygen resulted in an Fe-O 2 -4NC intermediate assigned as an Fe II -peroxy-quinone species, which forms after initial O 2 -activation but prior to catechol cleavage .…”

Section: Introductionmentioning

confidence: 99%

Nuclear Resonance Vibrational Spectroscopy Definition of Peroxy Intermediates in Catechol Dioxygenases: Factors that Determine Extra- versus Intradiol Cleavage

et al. 2023

View full text Add to dashboard Cite

The extradiol dioxygenases (EDOs) and intradiol dioxygenases (IDOs) are nonheme iron enzymes that catalyze the oxidative aromatic ring cleavage of catechol substrates, playing an essential role in the carbon cycle. The EDOs and IDOs utilize very different Fe II and Fe III active sites to catalyze the regiospecificity in their catechol ring cleavage products. The factors governing this difference in cleavage have remained undefined. The EDO homoprotocatechuate 2,3-dioxygenase (HPCD) and IDO protocatechuate 3,4-dioxygenase (PCD) provide an opportunity to understand this selectivity, as key O 2 intermediates have been trapped for both enzymes. Nuclear resonance vibrational spectroscopy (in conjunction with density functional theory calculations) is used to define the geometric and electronic structures of these intermediates as Fe II -alkylhydroperoxo (HPCD) and Fe III -alkylperoxo (PCD) species. Critically, in both intermediates, the initial peroxo bond orientation is directed toward extradiol product formation. Reaction coordinate calculations were thus performed to evaluate both the extra-and intradiol O−O cleavage for the simple organic alkylhydroperoxo and for the Fe II and Fe III metal catalyzed reactions. These results show the Fe II -alkylhydroperoxo (EDO) intermediate undergoes facile extradiol O−O bond homolysis due to its extra e − , while for the Fe III -alkylperoxo (IDO) intermediate the extradiol cleavage involves a large barrier and would yield the incorrect extradiol product. This prompted our evaluation of a viable mechanism to rearrange the Fe III -alkylperoxo IDO intermediate for intradiol cleavage, revealing a key role in the rebinding of the displaced Tyr447 ligand in this rearrangement, driven by the proton delivery necessary for O−O bond cleavage.

show abstract

Iron Catalysis in Biological and Biomimetic Reactions

Müller

Bröring

2008

Iron Catalysis in Organic Chemistry

View full text Add to dashboard Cite

Tuning the Regiospecificity of Cleavage in FeIII Catecholate Complexes: Tridentate Facial versus Meridional Ligands

Cited by 10 publications

References 21 publications

Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique

Unraveling the Photocatalytic Mechanisms on TiO2 Surfaces Using the Oxygen-18 Isotopic Label Technique

Nuclear Resonance Vibrational Spectroscopy Definition of Peroxy Intermediates in Catechol Dioxygenases: Factors that Determine Extra- versus Intradiol Cleavage

Iron Catalysis in Biological and Biomimetic Reactions

Contact Info

Product

Resources

About