Syntheses, Structures, and Properties of Oxovanadium(V) Complexes with Ketone and Ketolate Ligands

Wistuba, Tobias; Limberg, Christian; Pritzkow, Hans

doi:10.1002/1521-3749(200211)628:11<2340::aid-zaac2340>3.0.co;2-p

Cited by 5 publications

(1 citation statement)

References 8 publications

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“…The C46–O1 (1.227(4) Å), C47–O2 (1.394(4) Å), and C46–C47 (1.507(4) Å) distances indicate that HCH coordinates to the iron center in a keto form. The C–C and C–O bond distances of the coordinated α-hydroxy ketone in 2 are found to be very similar to those of the reported metal complexes with α-hydroxy ketone ligands, further confirming the monoanionic binding of HCH without enolization. − While the iron center in [(Tp Ph2 )Fe II (HAP)] adopts a distorted-trigonal-bipyramidal coordination geometry (τ = 0.62), the iron center in 2 adopts a distorted-square-pyramidal coordination geometry (τ = 0.45). In the complex, the cyclohexane ring of HCH adopts a chair conformation where the keto and the alcoholate groups are positioned equatorially, enabling the α-hydroxy ketone to bind to the iron center in a bidentate fashion.…”

Section: Resultssupporting

confidence: 68%

Aliphatic C–C Bond Cleavage of α-Hydroxy Ketones by Non-Heme Iron(II) Complexes: Mechanistic Insight into the Reaction Catalyzed by 2,4′-Dihydroxyacetophenone Dioxygenase

2015

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2,4'-Dihydroxyacetophenone dioxygenase (DAD) is a bacterial non-heme enzyme that carries out oxygenative aliphatic C-C bond cleavage of 2,4'-dihydroxyacetophenone (an α-hydroxy ketone) with the incorporation of both the oxygen atoms of dioxygen into the cleavage products. The crystal structure of the iron enzyme DAD has recently been determined, but very little is known about the mechanism of the C-C bond cleavage reaction. With the objective of gaining insights into the mechanism of the reaction catalyzed by DAD, six new biomimetic iron(II)-α-hydroxy ketone complexes, [(Tp(Ph2))Fe(II)(PHAP)] (1), [(Tp(Ph2))Fe(II)(HCH)] (2), [(Tp(Ph2))Fe(II)(HBME)] (3), [(Tp(Ph2))Fe(II)(CHPE)] (4), [(6-Me3-TPA)Fe(II)(PHAP)](+) (5), and [(6-Me3-TPA)Fe(II)(HCH)](+) (6) (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate, 6-Me3-TPA = tris(6-methyl-2-pyridylmethyl)amine, PHAP-H = 2-phenyl-2-hydroxyacetophenone, HCH-H = 2-hydroxycyclohexanone, HBME-H = 2-hydroxy-1,2-bis(4-methoxyphenyl)ethanone, and CHPE-H = 1-(4-chlorophenyl)-2-hydroxy-2-phenylethanone), have been isolated and characterized. The single-crystal X-ray structure of 2 shows a five-coordinate iron(II) complex with one tridentate facial ligand and a monoanionic bidentate α-hydroxy ketone, resulting in a distorted-square-pyramidal coordination geometry at the iron center. The iron(II) complexes react with dioxygen to oxidatively cleave the aliphatic C-C bonds of the coordinated α-hydroxy ketones to afford 2 equiv of carboxylic acids. Mechanistic studies reveal that the C-C bond cleavage reaction proceeds through an intradiol pathway. Additionally, the coordinated α-hydroxy ketones in all of the complexes, except in complex 4, undergo two-electron oxidation to form the corresponding 1,2-diketones. However, the yields of 1,2-diketones are higher with the iron complexes of the tripodal N4 ligand (6-Me3-TPA) in comparison to the facial N3 ligand (Tp(Ph2)). These results strongly support the natural selection of a facial N3 environment at the active site of the iron enzyme DAD.

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Section: Resultssupporting

confidence: 68%

Aliphatic C–C Bond Cleavage of α-Hydroxy Ketones by Non-Heme Iron(II) Complexes: Mechanistic Insight into the Reaction Catalyzed by 2,4′-Dihydroxyacetophenone Dioxygenase

2015

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Die Rolle von Radikalen bei metallvermittelten Oxygenierungen

Limberg

2003

Angewandte Chemie

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Metallvermittelte Oxofunktionalisierungen organischer Substrate sind von fundamentaler Bedeutung – in der Natur genauso wie in Hochschul‐ und Industrielaboratorien. Ungeachtet dessen sind die Mechanismen dieser Reaktionen rätselhaft geblieben, und nur wenige Prozesse werden im Detail verstanden. Dank intensiver Forschung konnte der Wissensstand in den letzten Jahren aber erheblich verbessert werden: So wurde gezeigt, dass viele Oxygenierungen über Radikalintermediate verlaufen – mitunter auch dann, wenn eine vergleichsweise hohe Selektivität Gegenteiliges vermuten lässt. Das zeigen Beispiele aus den unterschiedlichsten Bereichen: von molekularen Metalloxokomplexen, gasförmigen und matrixisolierten Spezies über das Reaktionsverhalten von Metalloenzymen bis hin zu Prozessen an Festkörperoberflächen. Der vorliegende Aufsatz beleuchtet die Vielfalt dieser Systeme und vermittelt einen Überblick über allgemein gültige Reaktionsmuster und Prinzipien sowie einige noch ungelöste Probleme.

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The Role of Radicals in Metal‐Assisted Oxygenation Reactions

Limberg

2003

Angew Chem Int Ed

188

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The oxo-functionalization of organic substrates with the aid of metal oxo moieties is of fundamental importance not only in nature but also in academic and industrial research. Nevertheless the corresponding reaction mechanisms remain among the most enigmatic in chemistry and few of them are understood in detail. Recent research efforts have resulted in significantly improved information: in the cases of many oxygenation reactions evidence has been provided for the occurrence radical intermediates, even though the high selectivity observed suggests to a different mechanism. Examples stem from various areas of chemistry and include processes involving molecular metal oxo complexes, gas-phase and matrix-isolated species, metalloenzymes, and solid-state oxide surfaces. This review treats this seemingly wide variety of systems with the aim of providing an overview of common reactivity patterns and principles, as well as open problems.

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Syntheses, Structures, and Properties of Oxovanadium(V) Complexes with Ketone and Ketolate Ligands

Cited by 5 publications

References 8 publications

Aliphatic C–C Bond Cleavage of α-Hydroxy Ketones by Non-Heme Iron(II) Complexes: Mechanistic Insight into the Reaction Catalyzed by 2,4′-Dihydroxyacetophenone Dioxygenase

Aliphatic C–C Bond Cleavage of α-Hydroxy Ketones by Non-Heme Iron(II) Complexes: Mechanistic Insight into the Reaction Catalyzed by 2,4′-Dihydroxyacetophenone Dioxygenase

Die Rolle von Radikalen bei metallvermittelten Oxygenierungen

The Role of Radicals in Metal‐Assisted Oxygenation Reactions

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