STUDY OF THE REACTIONS OF PALLADIUM(II) MACROCYCLIC TETRAAMINE COMPLEXES WITH HYDROXYL AND METHYL RADICALS

The technique of pulse radiolysis has been used to study in aqueous me dia the reactions of hydroxyl radical with 1,4,8,11-tetraazacyclotetra decanepalladium(II) [Pd(cyclam)](2+) and hyl-1,4,8,11-tetraazacyclotet radecanepalladium(II) [Pd(tmc)](2+) and of methyl radical with the for mer complex. While methyl radical appears to be unreactive on short-ti me scales, hydroxyl radical reacts rapidly with the palladium(II) comp lexes to form transitory products absorbing in the near UV-visible reg ion. The second-order rate constants for the OH-reactions are (5.0 +/- 0.7) x 10(9) M(-1) s(-1) for [Pd(cyclam)](2+) and (2.8 +/- 0.7) x 10( 9) M(-1) s(-1) for [Pd(tmc)](2+). The intermediates are reactive towar ds dioxygen with rate constants of (1.3 +/- 0.4) x 10(8) M(-1) s(-1) f or the cyclam case and of (2.4 +/- 0.8) x 10(7) M(-1) s(-1) for the tm c-system. This high reactivity towards O-2 along with other features i ndicates that the reaction-mode of hydroxyl radical with the palladium (II) complexes involves predominately ligand-attack.