Collect. Czech. Chem. Commun. 1980, 45, 231-237

Mechanistic aspects of chain initiation in radical addition reactions induced by metal ions

Robert Ponec and Jaroslav Málek

Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, 165 02 Prague 6 - Suchdol


Bersuker's concept of redox charge transfer in catalysis has been adopted to study initiating activity of metal ions in radical addition reactions of model organic addends with alkenes. It was found that the most important factor determining the activity of the metal ions was the magnitude of the redox charge transfer δq. Additionally, the spin-allowedness or spin-forbiddenness of the redox step was essential. Two-valent metal ions with configuration d5-d9 do not exhibit, regardless of the spin-allowedness of the redox step, a significant oxidation activity owing to low values of δq. Three-valent metal ions with configurations d1-d3 are also inactive because of relatively lowest values of δq and spin-forbiddenness of the redox step. A transient position is occupied by the Mn3+ (d4) ion for which the redox step is still spin-forbidden, but the value of δq is high enough to evoke satisfactory oxidation activity. Three-valent ions Fe3+, Ni3+ with configurations d5-d7 as well as four-valent ions Pb4+ and Mn4+ show, according to the magnitude of δq, the highest oxidation activity in chain initiation.