Reaction of a {Co(NO)}8 complex with superoxide: Formation of a six coordinated [CoII(NO)(O2–)] species followed by peroxynitrite intermediate

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide–Dioxygen Interconversion

“…Inspired by the high-fidelity NO-to-nitrite conversion during superoxide-mediated transformation of DNIC 1 into the [Fe 3+ ( Me Pyr) x (NO 2 ) y (O) z ] n adduct via formation of DNIC 2-K-crown , DTBP was further utilized to probe the transient formation of • OH/ • NO 2 derived from the potential Fe-bound peroxynitrite intermediate. ,,− Consistent with the reported phenol nitration activity of intermediate [(TMEDA)­Fe­(NO)­(ONOO)] (TMEDA = tetramethylethylene­diamine), reaction of {Fe­(NO) 2 } 10 DNIC [(TMEDA)­Fe­(NO) 2 ] with 1.5 equiv of O 2(g) in the presence of 2 equiv of DTBP resulted in the formation of 2,4-di- tert -butyl-6-nitrophenol (NO 2 -DTBP) and coupled bisphenol 3,3′,5,5′-tetra- tert -butyl-(1,1′-biphenyl)-2,2′-diol (Figure a). In the presence of 4 equiv of DTBP, reactions of DNIC 1 with [K-18-crown-6-ether]­[O 2 ] in a 1:2 or 1:6 molar ratio, in comparison, led to no formation of NO 2 -DTBP or bisphenol (Figure b,c). − In an attempt to identify the potential formation of Fe-superoxide or Fe-peroxynitrite intermediate(s), the reaction between DNIC 1 and [K-18-crown-6-ether]­[O 2 ] in a 1:2 molar ratio was investigated using UV–vis spectroscopy at −80 °C. As shown in Figure S6, a shift of the UV–vis absorption bands from 350 nm (DNIC 1 ) to 370 nm (DNIC 2-K-crown ) without formation of other distinctive features was observed. , Based on the DTBP assay and low-temperature UV–vis experiments, superoxide-mediated monooxygenation of Fe-bound NO in DNIC 1 leads to the sequential assembly of DNIC 2-K-crown and an [Fe 3+ ( Me Pyr)­(NO 2 ) y (O) z ] n adduct without transient formation of peroxynitrite-derived • NO 2 / • OH species.…”

“…As shown in Scheme e and Figure S9a, reaction of {Fe­(NO) 2 } 9 -{Fe­(NO) 2 } 10 DNIC 1-red with 1 equiv of O 2(g) in THF led to the assembly of DNIC 2-K-crown (yield 75% based on Fe). Using DTBP as a trapping reagent for peroxynitrite-derived • NO 2 and • OH species, ,,− no formation of NO 2 -DTBP nor bisphenol products was observed during the oxygenation of DNIC 1-red in the presence of 4 equiv of DTBP (Figure S9b). Moreover, the reaction between DNIC 1-red and O 2(g) was monitored by UV–vis spectroscopy at −80 °C but failed to identify potential Fe-peroxynitrite or Fe–O 2 intermediate(s) (Figure S9c).…”

“…Besides the biological metabolism of O 2 – into O 2 and H 2 O 2 catalyzed by superoxide dismutase (SOD), , heme proteins (i.e., oxyhemoglobin and oxymyoglobin) were reported to promote the dioxygenation of NO into biologically benign NO 3 – . − In lipopolysaccharide (LPS)-activated macrophages, a dinitrosyl iron unit (DNIU) [Fe­(NO) 2 ] was discovered as a metallocofactor assembled under inflammatory conditions based on the formation of a distinctive electron paramagnetic resonance (EPR) signal at g = 2.03. − Inspired by natural utilization of (non)­heme centers for maintaining biological NO/O 2 – homeostasis, biomimetic studies on reactions between (a) [M­(O 2 n – )] complexes ( n = 1 or 2) and NO, − (b) [M­(NO) x ] complexes ( x = 1 or 2) and O 2 , ,− and (c) [M­(NO)] complexes and O 2 – were performed to identify the formation of metal-bound peroxynitrite intermediates, − of which rearrangement into NO 2 – and NO 3 – occurred via formation of transient • NO 2 species. In particular, Nam, Karlin, Kumar, and co-workers pioneered investigations of reactivity of {Co­(NO)} 8 complexes toward O 2 – . , During reaction of O 2 – with complexes [(L)­Co­(NO)] 2+ (L = 12-TMC, 13-TMC, or HMTETA), transient formation of the intermediate [(L)­Co 2+ (OONO)] + followed by O–O bond cleavage was reported to yield complex [(L)­Co­(NO 2 )] + with O 2(g) evolution.…”

Reaction of a nitrosyl complex of Mn(ii)–porphyrinate with superoxide: NOD activity is favoured over SOD activity

“…6 Following this, a number of both heme and non-heme model PN complexes of Fe, Co, Mn, Cr, Cu were reported in the literature. 7–11 These complexes are synthesized mainly using two routes, via the reaction of metal nitrosyls with reactive oxygen species and via the reaction of metal–superoxo/peroxo/hydroperoxo complexes with NO. However, examples of well-characterized discrete PN complexes are very rare.…”

“…10 A few examples of Co and Mn–PN complexes have also been reported from our group. 11 A {Co(NO)} 8 complex in the porphyrin ligand framework reacts with H 2 O 2 to give the Co III –PN intermediate, which then decomposes to Co III –NO 3 − via a Co III –O˙ species. 11 e Similarly, a {Mn(NO)} 6 complex upon reaction with O 2 − yielded a very unstable Mn IV O species via the formation of Mn III –PN.…”