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Spin‐Trapping Evidence for the Formation of Alkyl, Alkoxyl, and Alkylperoxyl Radicals in the Reactions of Dialkylzincs with Oxygen
Author(s) -
Maury Julien,
Feray Laurence,
Bazin Samantha,
Clément JeanLouis,
Marque Sylvain R. A.,
Siri Didier,
Bertrand Michèle P.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002616
Subject(s) - chemistry , spin trapping , radical , electron paramagnetic resonance , alkoxy group , oxygen , dissociation (chemistry) , alkyl , adduct , enthalpy , oxygen atom , photochemistry , inorganic chemistry , organic chemistry , molecule , nuclear magnetic resonance , physics , quantum mechanics
Abstract The reactions of dialkylzincs (Me 2 Zn, Et 2 Zn, and n Bu 2 Zn) with oxygen have been investigated by EPR spectroscopy using spin‐trapping techniques. The use of 5‐diethoxyphosphoryl‐5‐methyl‐1‐pyrrroline N ‐oxide (DEPMPO) as a spin‐trap has allowed the involvement of alkyl, alkylperoxyl, and alkoxyl radicals in this process to be probed for the first time. The relative ratio of the corresponding spin‐adducts depends strongly on the nature of the R group, which controls the CZn bond dissociation enthalpy, and on the experimental conditions (excess of spin‐trap compared with R 2 Zn and vice versa). The results have demonstrated that Et 2 Zn and, to a lesser extent, n Bu 2 Zn are much better traps for oxygen‐centered species than Me 2 Zn. When the dialkylzincs were used in excess with respect to the spin‐trap, the concentration of the oxygen‐centered radical adducts of DEPMPO was much lower for Et 2 Zn and n Bu 2 Zn than for Me 2 Zn. A detailed reaction mechanism is discussed and CZn, OZn, and OO bond dissociation enthalpies for the proposed reaction intermediates were calculated at the UB3LYP/6‐311++G(3df,3pd)//UB3LYP/6‐31G(d,p) level of theory to support the rationale.