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Nitric Oxide Dioxygenation by O2 Adducts of Manganese Porphyrins.

PMID: 33180482 (view PubMed database entry)
DOI: 10.1021/acs.inorgchem.0c02464 (read at publisher's website )

Tigran S Kurtikyan, Vardan A Hayrapetyan, Astghik A Hovhannisyan, Garik G Martirosyan, Gohar Sh Hovhannisyan, Alexei V Iretskii, Peter C Ford,

We describe here nitric oxide dioxygenation (NOD) by the dioxygen manganese porphyrin adducts Mn(Por)(η<sup>2</sup>-O<sub>2</sub>) (Por<sup>2-</sup> = the <i>meso</i>-tetra-phenyl or <i>meso</i>-tetra-<i>p</i>-tolylporphyrinato dianions, TPP<sup>2-</sup> and TTP<sup>2-</sup>). The Mn(Por)(η<sup>2</sup>-O<sub>2</sub>) was assembled by adding O<sub>2</sub> to sublimed layers of Mn<sup>II</sup>(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<sub>2</sub>) band. Isotope labeling experiments with <sup>18</sup>O<sub>2</sub>, <sup>15</sup>NO, and N<sup>18</sup>O combined with DFT calculations provide the basis for identifying the initial intermediates as the six-coordinate peroxynitrito complexes (ON)Mn(Por)(η<sup>1</sup>-OONO). Further warming to room temperature led to formation of the nitrato complexes Mn(Por)(η<sup>1</sup>-ONO<sub>2</sub>), thereby demonstrating the ability of these metal centers to promote NOD. However, comparable quantities of the nitrito complexes Mn(Por)(η<sup>1</sup>-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<sup>1</sup>-ONO<sub>2</sub>) is strongly favored (∼90%). The latter are formed via a 6-coordinate intermediate (L)Mn(Por)(η<sup>1</sup>-ONO<sub>2</sub>) (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.

Inorg Chem (Inorganic chemistry)
[2020, 59(23):17224-17233]

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