Nitric Oxide Dioxygenation by O Adducts of Manganese Porphyrins.

We describe here nitric oxide dioxygenation (NOD) by the dioxygen manganese porphyrin adducts Mn(Por)(η-O) (Por = the -tetra-phenyl or -tetra--tolylporphyrinato dianions, TPP and TTP). The Mn(Por)(η-O) was assembled by adding O to sublimed layers of Mn(Por). When NO was introduced and the temperature was slowly raised from 80 to 120 K, new IR bands with correlated intensities grew concomitant with depletion of the υ(O) band. Isotope labeling experiments with O, NO, and NO combined with DFT calculations provide the basis for identifying the initial intermediates as the six-coordinate peroxynitrito complexes (ON)Mn(Por)(η-OONO). Further warming to room temperature led to formation of the nitrato complexes Mn(Por)(η-ONO), thereby demonstrating the ability of these metal centers to promote NOD. However, comparable quantities of the nitrito complexes Mn(Por)(η-ONO) are also formed. In contrast, when the analogous reactions were initiated with the weak σ-donor ligand tetrahydrofuran or dimethyl sulfide present in the layers, formation of Mn(Por)(η-ONO) is strongly favored (∼90%). The latter are formed via a 6-coordinate intermediate (L)Mn(Por)(η-ONO) (L = THF or DMS) that loses L upon warming. These reaction patterns are compared to those observed previously with analogous iron and cobalt porphyrin complexes.