Dual Role of Azide as a Quencher and Stimulator of Singlet Oxygen Generation on Some Manganese Oxides

Abstract

Sodium azide is a known singlet oxygen (1O_2) quencher in both homogenous and heterogeneous catalytic transformations. We report a paradoxical trend of a strong enhancement in the 1O_2 production during H2O2 disproportionation seen on some MnOx catalyst, specifically layered δ-MnO2. Studies with 1O_2-specific probes show that this activation is due to N_3^- complexation with lattice MnII of δ-MnO2 that upon rapid air oxidation produces a metastable surface MnIII-azide complex that strongly catalyzes H2O2 disproportionation. In contrast, a bulk MnIII-azide complex does not produce 1O_2. Due to this dual role, the use of NaN3 as diagnostic tool for 1O_2 intermediacy should be carefully reconsidered.