Spin trapping in photochemistry of coordination compounds

The application of spin-trapping technique to detect short-lived paramagnetic species formed during photochemical reactions of coordination compounds is reviewed. Interference of radical recombinations by scavenging action of spin traps has been pointed out to be important at high spin-trap concentrations only. Due to only a limited extent of side reactions, nitrosodurene and phenyl N-tert-butyl nitrone were found to be excellent spin traps for the study of photoreactions of metal complexes in nonpolar solutions, whereas 5,5-dimethyl pyrroline-1-oxide is recommended for aqueous solutions. Using these spin traps, both organic and inorganic radicals, e.g. H, Cl, N3, CN, OH, O2−, as well as solvated electrons and metal-centered free radicals have been detected during the photolysis of coordination compounds. The detection of singlet oxygen by reaction with 2,2,6,6-tetramethyl piperidine is briefly discussed.

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Photoredox Reactions of Iodo Iron(III) Complexes Containing Tetradentate Ligands

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20010109 ◽

2001 ◽

Vol 66 (1) ◽

pp. 109-118 ◽

Cited By ~ 4

Author(s):

Jozef Šima ◽

Dáša Lauková ◽

Vlasta Brezová

Keyword(s):

Schiff Bases ◽

Spin Trapping ◽

Molar Ratio ◽

Oh Radicals ◽

Solvated Electrons ◽

Open Chain ◽

Tetradentate Ligands ◽

Visible Irradiation ◽

Epr Spin Trapping ◽

Spin Trapping Technique

Photoredox reactions occurring in irradiated methanolic solutions of trans-[FeIII(R,R'-salen)(CH3OH)I], where R,R'-salen2- are N,N'-ethylenebis(R,R'-salicylideneiminato), tetradentate open-chain N2O2-Schiff bases with R,R' = H, 5-Cl, 5-Br, 3,5-di-Br, 3,5-di-(CH3), 3-OCH3, 5-OCH3, have been investigated and their mechanism proposed. The complexes are redox-stable in the dark. Ultraviolet and/or visible irradiation of methanolic solution of the complexes induces photoreduction of Fe(III) to Fe(II). Depending on the composition of the irradiated solutions, •CH2OH radicals or solvated electrons were identified by the EPR spin trapping technique. The final product of the photooxidation coupled with the photoreduction of Fe(III) is formaldehyde and the molar ratio of Fe(II) and CH2O is close to 2 : 1. The efficiency of the photoredox process is strongly wavelength-dependent and influenced by the peripheral groups R,R' of the tetradentate ligands.

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Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison CoIII—C

Canadian Journal of Chemistry ◽

10.1139/v82-205 ◽

1982 ◽

Vol 60 (12) ◽

pp. 1402-1413 ◽

Cited By ~ 26

Author(s):

Philippe Maillard ◽

Charles Giannotti

Keyword(s):

Free Radicals ◽

Hydrogen Atom ◽

Spin Trap ◽

Spin Trapping ◽

Spin Adduct ◽

Efficient Manner ◽

Solvent Cage ◽

Selective Deuteration ◽

Equatorial Ligand ◽

Spin Trapping Technique

Using the spin trapping technique with 5,5′-dimethyl 1-pyrroline N-oxide (DMPO), phenyl-N-tert-butyl nitrone (PBN), nitrosodurene (ND), and α-4-pyridyl 1-oxide N-tert-butl nitrone (4-POBN), or their mixtures, we have been able to detect two types of radicals, one is a hydrogen atom spin adduct and the other is the corresponding alkyl of the alkylcobaloximes, salens or cobalamines.By the use of selective deuteration and the preparation of the benzyl bis(diphenylglyoximato)-pyridinato cobaloxime, we have shown that the spin trapped hydrogen atom comes from the chelated hydrogen of the dimethylglyoximato anion of the equatorial ligand of CoIII complexes. Using a mixture of two spin traps gives rise to an esr spectrum containing, at the same time, the hydrogen atom and alkyl spin adducts.To explain such an efficient spin trapping reaction while the homolysis is in competition with a β-elimination process, it should be postulated that the photolysis of such compounds proceeds through a solvent cage environment. This hypothesis explains the strong influence of solvents on the nature of the free radicals trapped. Also the spin trap diffuses in the solvent cage, and is able to trap in a very efficient manner any free radicals occurring in the solvent cage. The excited CoIII complexes and the spin trap in the solvent cage behave like an exciplex, which could explain the spin trapping of the hydrogen atom.

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Homolytic Scission of Interunitary Bonds in Lignin Induced by Ultrasonic Irradiation of MWL Dissolved in Dimethylsulfoxide

Holzforschung ◽

10.1515/hf.2000.062 ◽

2000 ◽

Vol 54 (4) ◽

pp. 357-364 ◽

Cited By ~ 15

Author(s):

Aki Yoshioka ◽

Teruyuki Seino ◽

Masayoshi Tabata ◽

Mitsuo Takai

Keyword(s):

Ultrasonic Irradiation ◽

Spin Trap ◽

Spin Trapping ◽

Spin Adduct ◽

Dmso Solution ◽

Picea Jezoensis ◽

Spin Resonance ◽

Spin Trapping Technique ◽

Secondary Carbon ◽

Stable Nitroxide

SummaryAn electron spin resonance (ESR) method combined with a spin trapping technique was applied to trap and characterize unstable radicals which were generated by ultrasonic irradiation of the dimethylsulfoxide (DMSO) solution of a softwood, Yezo Spruce (Picea jezoensiscarr.) lignin. It was found that an unstable secondary carbon radical, ~CH • in the solution was trapped as the stable nitroxide spin adduct when the DMSO solution was subjected to ultrasonic irradiation in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at 50°C for 30 min. This means that the alkyl phenyl ether bonds, ~CH-O-phenyl, known as interunitary bonds in lignins were homolytically cleaved by the ultrasonic irradiation, although the phenoxy radical Ph-O •, called guaiacoxy radical, i.e. the counter radical of the secondary carbon radical, was not trapped by the BNB spin trap. This suggests that the trapping of the guaiacoxy radical, having a methoxy group in anortho-position, by the BNB molecule, carrying two bulky butyl groups in theortho-positions, is sterically hindered.

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From early spin-trapping experiments to acyl nitroxide chemistry: synthesis of and spin trapping with a water-soluble nitrosopyrazole derivative

Canadian Journal of Chemistry ◽

10.1139/v82-507 ◽

1982 ◽

Vol 60 (12) ◽

pp. 1587-1593 ◽

Cited By ~ 1

Author(s):

M John Perkins ◽

Harparkash Kaur

Keyword(s):

Spin Trap ◽

Preliminary Investigation ◽

Spin Trapping ◽

Water Soluble ◽

Nitroso Compounds ◽

Nitroxide Radicals ◽

Personal View ◽

Spin Traps ◽

Subsequent Investigation

A personal view of early experiments which led to the use of C-nitroso-compounds as spin traps is presented, and it is shown how these experiments resulted in the first isolation, and subsequent investigation, of acyl nitroxide radicals: the use of 1-methyl-4-nitroso-3,5-diphenylpyrazole as a spin trap, and the preparation and preliminary investigation of its water-soluble analogue (1) are described.

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