Kinetics of dissociation of molecular oxygen from a superoxorhodium(III) complex and reactivity of a macrocyclic rhodium(II) ion.
The kinetics of disappearance of the superoxorhodium complex L2(H2O)RhOO2+ (L2 = meso-hexamethylcyclam) were determined in the presence of several oxidants (H2O2, (NH3)5CoBr2+, and IrCl62-) in both air-free and air-saturated aqueous solutions. Under air-free conditions, the reaction obeyed first-order kinetics. After the correction for the appropriate stoichiometric factors, the value of the rate constant kh was the same irrespective of the oxidant, kh = 2.18 (+/-0.37) x 10(-4) s(-1) at 25.0 degrees C in acidic solutions. The disappearance of L2(H2O)RhOO2+ was slower in the presence of O2. All the data suggest a sequence of reactions beginning with homolytic dissociation of O2 from L2(H2O)RhOO2+, followed by capture of the newly generated L2(H2O)Rh2+ by added oxidants in competition with O2. The equilibrium constant for O2 binding by L2(H2O)Rh2+ is 109-fold greater than that for the cobalt analogue. This difference is attributed to the lower reduction potential of the rhodium complex.
Ames Laboratory, Iowa State University, Ames, IA 50011, USA.
Magdalena
M
Furczon
Oleg
O
Pestovsky
Andreja
A
Bakac