REACTIVITY OF RU(OEP)(ARYL)2 COMPLEXES IN EXTREME OXIDATION-STATES

Cyclic voltammetry has been employed to study the reactivity of Ru(OEP)(p-XC6H4)2 (OEP = octaethylporphyrin dianion; X = H, CH3, OCH3, Cl, F) complexes in extreme oxidation states. As previously demonstrated for Ru(OEP()(C6H5)2, the [Ru(OEP)(aryl)2]+ complexes undergo Ru-to-N migration of an aryl group, while the [Ru(OEP)(aryl)2]2- complexes lose aryl- to form [Ru(OEP)(aryl)]-. The rates of these reactions (i.e., the stability of the highly oxidized or reduced complexes) depend on the nature of the aryl group. The stability of the [Ru(OEP)(p-XC6H4)2]2- complexes lies in the order Cl much greater than F > OCH3 > H > CH3 and is very sensitive to the ionic strength of the solution. This order results in a curved Hammett plot when the combined sigmap parameter is employed but in a roughly linear plot when inductive effects alone (sigma(I)) are considered. The stability of the [Ru(OEP)(p-XC6H4)2]+ complexes lies in the order Cl > F > OCH3 greater than or similar to CH3 greater than or similar to H at room temperature. The enthalpies of activation for the [Ru(OEP)(p-XC6H4)2]+ reactions follow the trend F > H greater than or similar to Cl > CH3 - OCH3, With DELTAH double dagger values in the range 9-14 kcal/mol. The entropies of activation follow the same trend, with DELTAS(double dagger) values in the range -9 to +4.5 cal/(mol.K). Closer inspection of these data reveals that the major difference exists for X = F (DELTAH double dagger = 14 kcal/mol, DELTAS double dagger = 4.5 cal/(mol.K); the remaining four complexes show similar activation parameters (DELTAH double dagger = 9.3-10.8 kcal/mol, DELTAS double dagger = -4 to -9 cal/(mol.K)). A discussion of the mechanisms of these and related redox-induced reactions is provided.