Spin trapping in photochemistry of coordination compounds

Rehorek, Detlef; Hennig, H.

doi:10.1139/v82-504

Cited by 27 publications

(3 citation statements)

References 20 publications

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“…For many years the popular nitroxide spin trapping technique has provided evidence for numerous transient metal centered radicals (1). The ability of quinones to form radical complexes and spin adducts with a variety of organometals was recently emphasized (2,3) and added another dimension to the spin trapping chemistry.…”

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confidence: 99%

Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes

Creber¹,

Ho²,

Depew³

et al. 1982

Can. J. Chem.

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. Can. J. Chem. 60, 1504Chem. 60, (1982.A brief account is presented on the use of substituted quinones as spin traps for organometallic radicals and on the applications of CIDEP and esr-HPLC techniques to the study of quinone -organometallic radical complexes. Many of these radical adducts are thermally very stable and can be isolated by the HPLC technique for detailed spectroscopic and chemical studies. This in turn allows us to present a different approach to the "spin trapping" chemistry of unstable organometallic radicals by generating initially a stable quinone -metal carbonyl radical complex, separating the parent radicals by esr-HPLC and using them to react with other organometals via ligand exchange between the CO group(s) and the organometals. It then follows that if the entering organometal ligand is optically active, the substituted radical complex would also be chiral. This simple concept has led to the isolation of the first pure optically active radical complex with well-defined physical properties, including optical rotation. For many years the popular nitroxide spin trapping technique has provided evidence for numerous transient metal centered radicals (1). The ability of quinones to form radical complexes and spin adducts with a variety of organometals was recently emphasized (2, 3) and added another dimension to the spin trapping chemistry. The quinone -metal radical complexes are interesting generally because both the metal centre and the quinone ligands can be redox active. Since the first major study on quinone-metal complexes was carried out by Eaton (4), many other interesting complexes have been synthesized directly by the reactions of metal carbonyls with quinones (5, 6). The use of quinones in spin trapping photochemistry has yet another advantage. There is a large pool of information available for the photochemical and photophysical properties of carbonyl compounds but the quenching of the excited states of carbonyl compounds by various electron donors, including some of the organometals, has continued to attract attention (7). In this laboratory, the photoreduction of quinones by alcohols and phenols (8,9) and by vitamins such as C and K l (10) have been extensively used as model systems for chemically induced magnetic polarization studies. They in turn provide some valuable information about the relative efficiencies of the triplet quenching reaction, the mechanisms of the secondary radical reactions, and the dynamics of the intersystem crossing processes which are responsible for the difference in the spin populations of the triplet sub-levels. The CIDEP technique was further applied to study the quenching of quinone triplets by organometals (11) and the results indicate the nature of electron transfer between the organotin compounds and the triplet quinone in the photochemical primary process. Unequivocal evidence of the electron transfer mechanism was subsequently obtained by the direct esr characterization of the triplet state of the primary radical ion pair formed and tra...

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mentioning

confidence: 99%

Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes

Creber¹,

Ho²,

Depew³

et al. 1982

Can. J. Chem.

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“…[196][197][198] Many of these catalytic cycles involve radicals with very short lifetimes, which require the use of radical traps for detection, thus adding another layer of complexity to the study. 199 Thorough EPR investigations of these systems is often further complicated by poorly understood reactivities and detection issues. For example, copper (I) based complexes, such as [Cu(dap) 2 ] 1 (dap ¼ 2,9-bis(p-anisyl)-1,10-phenanthroline), have been successfully employed in a wide variety of photoredox reactions.…”

Section: Homogeneous Systems For Small Molecule Activationmentioning

confidence: 99%

Paramagnetic species in catalysis research: a unified approach towards (the role of EPR in) heterogeneous, homogeneous and enzyme catalysis

Bracci¹,

Bruzzese²,

Famulari³

et al. 2020

Electron Paramagnetic Resonance

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Paramagnetic (open-shell) systems, including transition metal ions, radical intermediates and defect centres, are often involved in catalytic transformations. Despite the prevalence of such species in catalysis, there are relatively few studies devoted to their characterisation, compared to their diamagnetic counterparts. Electron Paramagnetic Resonance (EPR) is an ideal technique perfectly suited to characterise such reaction centres, providing valuable insights into the molecular and supramolecular structure, the electronic structure, the dynamics and even the concentration of the paramagnetic systems under investigation. Furthermore, as EPR is such a versatile technique, samples can be measured as liquids, solids (frozen solutions and powders) and single crystals, making it ideal for studies in heterogeneous, homogeneous and enzyme catalysis. Coupled with the higher resolving power of the pulsed, higher frequency and hyperfine techniques, unsurpassed detail on the structure of these catalytic centres can be obtained. In this Chapter, we provide an overview to demonstrate how advanced EPR methods can be successfully exploited in the study of open-shell paramagnetic reaction centres in heterogeneous, homogeneous and enzymatic catalysts, including heme-based enzymes for use in biocatalysts, polymerisation based catalysts, supported microporous heterogeneous catalytic centres to homogeneous metal complexes for small molecule actions.

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“…In this technique, a radical is allowed to react with a spin trap molecule to form a more stable radical product, detectable by ESR, which provides a spectrum characteristic for the particular free radical that is trapped. The spin trapping method to detect short-lived radicals was first pioneered by Janzen et al 209 With the advent of ESR spectroscopy and the spin trapping method, it is now possible to identify free radicals produced at physiological temperatures. Spin trapping methods have proved to be a very useful tool in detecting superoxide radical anion both in vivo and in vitro detection.…”

Section: [110] Detection Of Free Radicalsmentioning

confidence: 99%

Synthesis of Azulenylsilane Nitrones as Diagnostic Tools for Superoxide Detection

Tamrakar¹

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Spin trapping in photochemistry of coordination compounds

Cited by 27 publications

References 20 publications

Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes

Some physical and chemical aspects of spin trapping of organometallic radicals by quinones: optically active radical complexes

Paramagnetic species in catalysis research: a unified approach towards (the role of EPR in) heterogeneous, homogeneous and enzyme catalysis

Synthesis of Azulenylsilane Nitrones as Diagnostic Tools for Superoxide Detection

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