Chromium(IV)–Peroxo Complex Formation and Its Nitric Oxide Dioxygenase Reactivity

Abstract

The O2 and NO reactivity of a Cr(II) complex bearing a 12-membered tetraazamacrocyclic TMC ligand, [CrII(12-TMC)(Cl)]+ (1), and the NO reactivity of its peroxo derivative, [CrIV(12-TMC)(O2)(Cl)]+ (2), are described. By contrast to the previously reported Cr(III)-superoxo complex, [CrIII(14-TMC)(O2)(Cl)]+, a Cr(IV)-peroxo complex (2) is formed in the reaction of 1 and O2. Full spectroscopic and X-ray analysis reveals that 2 possesses a side-on η2-peroxo ligation. A quantitative reaction of 2 with NO affords a reduction in Cr oxidation state and production of a Cr(III)-nitrato complex, [CrIII(12-TMC)(NO3)(Cl)]+ (3). The latter is suggested to form via a Cr(III)-peroxynitrite intermediate. A Cr(II)-nitrosyl complex, [CrII(12-TMC)(NO)(Cl)]+ (4), derived from 1 andNO could also be synthesized; however, it does not react with O2.

Mononuclear Manganese–Peroxo and Bis(μ‐oxo)dimanganese Complexes Bearing a Common N‐Methylated Macrocyclic Ligand

“…[8,13] In addition, it is noteworthy that the ring size of the supporting ligands does not affect the MnO 2 core (Table 1) DFT calculations were also carried out on 2, and the calculated structure could be compared to the crystal structure to gauge the reliability of the calculations. These comparisons indicate that the deviation on the Mn À O distance is 0.01 , whereas the OÀO bond difference is slightly larger: 0.03 (Table 1 and Table S2 in the Supporting Information).…”

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. …”

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

“…of NO generates a stable Cr(IV)-oxo species, [Cr IV (14-TMC)(O)(Cl)] + ( 3 ), via the formation of a presumed Cr(III)-peroxynitrite intermediate, [Cr III (14-TMC)(OON=O)(Cl)] + ( 2 ) (Scheme 1, reactions a and b), unlike the NO reaction of a Cr(IV)-peroxo complex bearing the 12-TMC. 12 To the best of our knowledge, this study presents the first strong evidence for the formation of a high-valent metal-oxo complex in the reaction of a metal-superoxo species and NO. Further, 3 does not lead to a nitrate containing product with NO 2 addition, but it does react with NO to give a Cr(III)-nitrito complex, [Cr III (14-TMC)(NO 2 )(Cl)] + ( 4 ) (Scheme 1, reaction c).…”

“…9-12 Especially, in the case of Ni and Cr complexes with the 14-TMC 13 and 12-TMC 13 ligands, the TMC ring size was found to alter the structure of the resulting [M( n -TMC)(O 2 )] n+ complexes; the larger ring size ligand (e.g., 14-TMC) forms metal-superoxo complexes (e.g., Ni(II)-superoxo 10b and Cr(III)-superoxo 11 ), whereas the smaller ring size 12-TMC chelate forms metal-peroxo complexes (e.g., Ni(III)-peroxo 10b and Cr(IV)-peroxo 12 ). In addition, we recently reported the NOD reactivity of the Cr(IV)-peroxo complex; this species reacted with NO to give a Cr(III)-nitrate product, [Cr III (12-TMC)(NO 3 )(Cl)] + , however, without detection of any intermediates such as Cr-PN or Cr-oxo species.…”

“…In addition, we recently reported the NOD reactivity of the Cr(IV)-peroxo complex; this species reacted with NO to give a Cr(III)-nitrate product, [Cr III (12-TMC)(NO 3 )(Cl)] + , however, without detection of any intermediates such as Cr-PN or Cr-oxo species. 12 …”