Reactions of a Chromium(III)-Superoxo Complex and Nitric Oxide That Lead to the Formation of Chromium(IV)-Oxo and Chromium(III)-Nitrito Complexes

Abstract

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [CrIII(14-TMC)(O2)(Cl)]+, with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [CrIV(14-TMC)(O)(Cl)]+, via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from EPR spectroscopy, computational chemistry, and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [CrIII(14-TMC)(NO2)(Cl)]+. The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally.

A Peroxynitrite Dicopper Complex: Formation via Cu–NO and Cu–O2 Intermediates and Reactivity via O–O Cleavage Chemistry

“…This seems to also correspond to known aqueous chemistry: peroxynitrite decomposes through various pathways, 3c,21 , including its degradation according to 2 − OON═O → O 2 + 2NO 2 − under basic conditions and relatively high concentration,s 21b,d,e and such reactivity has even been observed in aqueous chemistry with copper ion. 22 Similarly, Nam and co-workers reported formation of macrocyclic ligand-bound metal−PN complexes, for example, LCr III −PN 23 and non-heme-Fe III −PN 24 species, generated from precursor M−O 2 adducts reacting with NO (g) (Scheme 1). A novel case involves reaction of a macrocyclic ligand (L)Co–nitrosyl complex with potassium superoxide (KO 2 ), leading to LCo III −nitrite + ½ O 2(g) products, all proceeding through putative Co–PN intermediates (Scheme 1).…”

Reactions of Co(III)–Nitrosyl Complexes with Superoxide and Their Mechanistic Insights

“…In such biomimetic studies, mononuclear metal-superoxo species have been shown to react with NO to produce metal-PN (M n+ – − OON=O) intermediates, including examples with heme, non-heme Fe, Co or Cu. 12 For example, we reported recently the conversion of a non-heme Cr IV -peroxo complex to a Cr III -nitrate ion upon addition of NO, 13a whereas the reaction of a Cr III -superoxo complex with NO gave a high-valent Cr IV -oxo species and nitrogen dioxide (NO 2 ) via the formation of a presumed Cr III -PN intermediate. 13b Thus, a variety of outcomes can occur when metal complexes in varying oxidation states mediate reactions of NO (or NO + ) with differing reduced O 2 -derivatives (e.g., superoxide or peroxide).…”

“…12 For example, we reported recently the conversion of a non-heme Cr IV -peroxo complex to a Cr III -nitrate ion upon addition of NO, 13a whereas the reaction of a Cr III -superoxo complex with NO gave a high-valent Cr IV -oxo species and nitrogen dioxide (NO 2 ) via the formation of a presumed Cr III -PN intermediate. 13b Thus, a variety of outcomes can occur when metal complexes in varying oxidation states mediate reactions of NO (or NO + ) with differing reduced O 2 -derivatives (e.g., superoxide or peroxide). Included is the capture of a peroxynitrite (or NO 2 ) intermediate via nitration of added phenols, which is analogous to biologically well established tyrosine nitration which effects biomolecule damage or participates in cellular signalling events.…”

An isoelectronic NO dioxygenase reaction using a nonheme iron(iii)-peroxo complex and nitrosonium ion

“…4,5 In biomimetic studies, mononuclear metal-O 2 complexes, best described as metal-superoxo species, are reported to react with NO to give metal-peroxynitrite (M n + –OON=O, PN) 4,6 intermediates. 7–9 To mimic NOD reactivity, we recently reported the conversion of NO and metal-O 2 species to NO 3 − and metal-oxo species, respectively, using peroxide or superoxide complexes of chromium-TMC (TMC = N -tetramethylated cyclam); a Cr(IV)-peroxo complex ([Cr IV- (12-TMC)(O 2 )(Cl)] + ) reacted with NO to form a Cr(III)-nitrato complex ([Cr III (12-TMC)(NO 3 )(Cl)] + )), 10 whereas a Cr(III)-superoxo complex ([Cr III (14-TMC)(O 2 )(Cl)] + ) and NO gave a Cr(IV)-oxo complex ([Cr IV- (14-TMC)(O)(Cl)] + ) and NO 2 via the formation of a presumed Cr(III)-peroxynitrite intermediate ([Cr III (14-TMC)(OON=O)(Cl)] + ) ‡ 11. …”