Spectroscopic studies of side-on peroxide-bridged binuclear copper(II) model complexes of relevance to oxyhemocyanin and oxytyrosinase

Baldwin, Michael J.; Root, David E.; Pate, James E.; Fujisawa, Kiyoshi; Kitajima, Nobumasa; Solomon, Edward I.

doi:10.1021/ja00052a043

Cited by 175 publications

(210 citation statements)

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“…Pre-treatment of the dissolved [(Tp R1,R2 )MA C H T U N G T R E N N U N G (Pz Me,tBu )] pre-catalysts with O 2 led to product distributions and TOFs that were very similar to those found in the absence of O 2 , so that it may be argued that tBuOOH and O 2 both lead to the same active species. The results of EPR spectroscopy and ESI-MS suggest that the initial product of the reaction of [(Tp Me,Me )MnA C H T U N G T R E N N U N G (Pz Me,tBu )] with O 2 contains a Mn III (O) 2 Mn IV core. Prolonged exposure to O 2 leads to a different dinuclear complex containing three Obridges and resulting in different TOFs/product distributions.…”

Section: Resultsmentioning

confidence: 99%

“…In the last decade these facially coordinating tripodal N 3 donors have also been increasingly employed for the complexation of metal oxo moieties in the area of bioinorganic chemistry: Tp R1,R2 ligands were, for instance, chosen to model histidinerich coordination environments in certain oxygenating iron and copper enzymes, [2] such as the tyrosinases, the soluble methane monooxygenase, acetylacetone dioxygenase, catechol dioxygenases, and a-ketoglutarate-dependent iron enzymes. [3,4] In recent years, Tp R1,R2 metal oxo research has also been extended to the element manganese, with a focus on dioxygen and peroxide reactivity.…”

Section: Introductionmentioning

confidence: 99%

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Four‐Coordinate Trispyrazolylboratomanganese and ‐iron Complexes with a Pyrazolato Co‐ligand: Syntheses and Properties as Oxidation Catalysts

Tietz¹,

Limberg²,

Stößer³

et al. 2011

Chemistry A European J

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A series of complexes of the type [(Tp(R1,R2))M(X)] (Tp = trispyrazolylborato) with R(1)/R(2) combinations Me/tBu, Ph/Me, iPr/iPr, Me/Me and for M = Mn or Fe coordinating [Pz(Me,tBu)](-) (Pz = pyrazolato) or Cl(-) as co-ligand X has been synthesised. Although the chloride complexes were very unreactive and stable in air, the pyrazolato series was far more reactive in contact with oxidants like O(2) and tBuOOH. The [(Tp(R1,R2))M(Pz(Me,tBu))] complexes proved to be active pre-catalysts for the oxidation of cyclohexene with tBuOOH, reaching turnover frequencies (TOFs) ranging between moderate and good in comparison to other manganese catalysts. Cyclohexene-3-one and cyclohexene-3-ol were always found to represent the main products, with cyclohexene oxide occasionally formed as a side product. The ratios of the different oxidation products varied with the reaction conditions: in the case of a peroxide/alkene ratio of 4:1, considerably more ketone than alcohol was obtained and cyclohexene oxide formation was almost negligible, whereas a ratio of 1:10 led to a significant increase of the alcohol proportion and to the formation of at least small amounts of the epoxide. Pre-treatment of the dissolved [(Tp(R1,R2))M(Pz(Me,tBu))] pre-catalysts with O(2) led to product distributions and TOFs that were very similar to those found in the absence of O(2), so that it may be argued that tBuOOH and O(2) both lead to the same active species. The results of EPR spectroscopy and ESI-MS suggest that the initial product of the reaction of [(Tp(Me,Me))Mn(Pz(Me,tBu))] with O(2) contains a Mn(III)(O)(2)Mn(IV) core. Prolonged exposure to O(2) leads to a different dinuclear complex containing three O-bridges and resulting in different TOFs/product distributions. Analogous findings were made for other complexes and formation of these overoxidised products may explain the deviation of the catalytic performances if the reactions are carried out in an O(2) atmosphere.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Four‐Coordinate Trispyrazolylboratomanganese and ‐iron Complexes with a Pyrazolato Co‐ligand: Syntheses and Properties as Oxidation Catalysts

Tietz¹,

Limberg²,

Stößer³

et al. 2011

Chemistry A European J

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“…40 The donor strength is given by the amount of metal character in the ligand valence orbital due to bonding, and reciprocally the amount of ligand character mixed into the metal d-orbital. From Equation 12a, c 2 quantitates the amount of electron density donated by the occupied ligand valence orbital to the metal through bonding.…”

Section: Cu(ii) Charge Transfer Transitionsmentioning

confidence: 99%

Inorganic and Bioinorganic Spectroscopy

Solomon

Bell

2010

Physical Inorganic Chemistry

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Spectroscopic methods have played a critical and symbiotic role in the development of our understanding of the electronic structure, physical properties, and reactivity of inorganic compounds and active sites in biological catalysis. 1,2 Ligand field theory 3 developed with our understanding of the photophysical and magnetic properties of transition metal complexes. Ligand-metal (L-M) bonding descriptions evolved through the connection of p-donor interactions with ligand to metal charge transfer (LMCT) transitions and p-backbonding with metal to ligand charge transfer (MLCT) transitions. 4 X-ray absorption (XAS) spectroscopy initially focused on the use of extended X-ray absorption fine structure 5 (EXAFS) to determine the geometric structure of a metal site in solution, but evolved in the analyses of pre-edges and edges to probe the electronic structure and thus covalency of ligand-metal bonds. 6 In bioinorganic chemistry, spectroscopy probes the geometric and electronic structure of a metallobiomolecule active site allowing the correlation of structure with function (Figure 1.1). 7 Spectroscopies are also used to experimentally probe transient species along a reaction coordinate, where often the sample has been rapidly freeze quenched to trap intermediates. An important theme in bioinorganic chemistry is that active sites often exhibit unique spectroscopic features, compared to small model complexes with the same metal ion. 8 These unusual spectroscopic features reflect novel geometric and electronic structures available to the metal ion in the protein environment. These unique spectral features are low-energy intense absorption bands and unusual spin Hamiltonian parameters. We have shown that these reflect highly covalent sites (i.e., where the metal d-orbitals have significant ligand character) that can activate the metal site for reactivity. 9 It is the goal of this chapter to provide an overview of the excited-state spectroscopic methods, including electronic absorption, circular dichroism (CD), magnetic Physical Inorganic Chemistry: Principles, Methods, and Models Edited by Andreja Bakac FIGURE 1.2 (a) The interaction of electromagnetic radiation with a metal center promotes an electron from the ground state (Y g ) to the excited state (Y e ) as dictated by the transition moment operator. This leads to the absorption band shape shown in (b). LIGAND FIELD (d ! d) EXCITED STATES

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“…While Tp complexes have been characterized by many different methods very little is known about their electronic spectra and photochemistry. A few spectral assignments [6][7][8] and photochemical observations [9][10][11][12] have been reported. However, Tp À seems to act as a spectator ligand in these cases.…”

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confidence: 99%

Intraligand fluorescence and phosphorescence of tris(pyrazolyl) hydridoborate complexes

Kunkely

Pawlowski

Strasser

et al. 2008

Inorganic Chemistry Communications

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Spectroscopic studies of side-on peroxide-bridged binuclear copper(II) model complexes of relevance to oxyhemocyanin and oxytyrosinase

Cited by 175 publications

References 0 publications

Four‐Coordinate Trispyrazolylboratomanganese and ‐iron Complexes with a Pyrazolato Co‐ligand: Syntheses and Properties as Oxidation Catalysts

Four‐Coordinate Trispyrazolylboratomanganese and ‐iron Complexes with a Pyrazolato Co‐ligand: Syntheses and Properties as Oxidation Catalysts

Inorganic and Bioinorganic Spectroscopy

Intraligand fluorescence and phosphorescence of tris(pyrazolyl) hydridoborate complexes

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