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A Study of Intramolecular Electron Exchange in Copper-Radical Complexes Involved in Catalysis Using ESR Spectroscopy
Korean Journal of Chemical Engineering, September 1997, 14(5), 394-398(5), 10.1007/BF02707058
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Abstract
ESR simulation and experimental results have been presented to show that transition metal-radical complexes can engage in intra molecular electron exchange and that the exchange gives rise to ESR asymmetric line broadening effect. Depending on the relative concentration of the redox-exchange pair, metal or radical-like spectrum can be obtained. Simulation results show that a metal-radical complex can be masked by its redox counterpart upto a relative concentration of 1:2 at a modest exchange rate of 3×108/s. Asymmetric line broadening was predicted to occur upon such metal-radical complexation. Experimentally, a pronounced ESR asymmetric line broadening was observed for Cu(Ⅱ) complexes of various redox-active ligands. Cu(Ⅱ) complex with redox-inert ammonia, however, showed no such evidence. Ligand displacement experiments established the reversibility of metal-radical complexation and the associated ESR line broadening.
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References
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Hanaya M, Iwaizumi M, J. Org. Chem., 435, 337 (1992)
Halpem J, Pure Appl. Chem., 58, 575 (1986)
Halpem J, "The Role of Free Radicals in Organometallic Catalysis," in Paramagnetic Organometallic Species in Activation/Selectivity Catalysis, ed. by Chanon, M., Julliard, M. and Poite, J.C., Kluwer Academic Press, Boston, 423 (1989)
More JK, More KM, Eaton GR, Eaton SS, J. Am. Chem. Soc., 106, 5397 (1984)
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Tkac A, Vesely K, Omelka L, J. Phys. Chem., 75, 2575 (1971)
