Nitrous acid as a source of NO and NO2 in the reaction with a macrocyclic superoxorhodium(III) complex

The title reaction takes place according to the stoichiometry 2L(2)RhOO(2+) + 3HNO(2) + H2O --> 2L(2)Rh(OH2)(3+) + 3NO(3)(-) + H+ (L-2 = meso-Me-6-[14]ane-N-4). The kinetics are second order in HNO2 and independent of the concentration of (LRhOO2+)-Rh-2, rate = (k(1) + k(2)[H+])[HNO2](2), where k(1) = 10.9 M-1 s(-1) and k(2) = 175 M-2 s(-1) at 25 degreesC and 0.10 M ionic strength. The reaction produces two observable intermediates, the nitrato ((LRhONO22+)-Rh-2) and hydroperoxo ((LRhOOH2+)-Rh-2) complexes. The product analysis and kinetics are indicative of the initial rate-controlling formation of NO and NO2, both of which react rapidly with (LRhOO2+)-Rh-2 in subsequent steps. The reaction with NO produces mainly (LRhONO22+)-Rh-2, which hydrolyzes to (LRh)-Rh-2(OH2)(3+) and NO,(-)(3). Another minor pathway generates the hydroperoxo complex, which was detected by its known reaction with Fe-aq(2+). The reaction of NO2 with (LRhOO2+)-Rh-2 requires an additional equivalent of HNO2 and produces (LRh)-Rh-2(OH2)(3+) and NO3- via a proposed peroxynitrato complex (LRhOONO22+)-Rh-2. This work provides strong evidence for the long-debated reaction between HNO2 and H2NO2+ to generate N2O3.