Reactions of the free radical nitrogen monoxide (NO) with metal–oxygen species of metalloproteins are relevant to NO metabolism and detoxification. For example, oxyhemoglobin and oxymyoglobin react with NO to form nitrate. The ferryl state of these globins also reacts with NO to reduce them to the FeIII state, forming nitrite. This has led to the suggestion that the role of NO could be that of an antioxidant of oxoiron(IV) and oxoiron(IV) protein radicals to inhibit oxidative damage. In turn, the ferrylglobin-mediated oxidation of NO to nitrite may play a role in NO scavenging and detoxification. In the case of peroxidase enzymes, NO has been shown to increase the activity of some enzymes by accelerating reduction of compound II to the FeIII state. While synthetic examples do exist for the chemistry of superoxometal complexes and NO, knowledge of the fundamental reactivity between oxometal complexes and NO is limited. To gain insight into the reactivity of synthetic oxoiron(IV) complexes toward NO, the reaction of [FeIVO(tmc)(OAc)]+ with NO, where the Fe center is coordinated by the macrocyclic nitrogen-donor ligand 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc), has been investigated. This reaction caused reduction of the FeIV center to FeII and produced nitrite, which was identified in the form of [FeII(tmc)(ONO)]+. Mechanistic studies have been conducted to distinguish between two possible pathways involving either oxygen atom or oxide(·–) ion transfer from the FeIVO group to NO. As a result of studying the reactivity of a different oxoiron(IV) complex, [FeIVO(N4Py)]2+, toward NO, the formation of FeII and nitrate was observed. Mechanistic studies have revealed a 2:1 stoichiometry between FeIV and NO. From these results, a mechanism can be proposed that includes an initial oxide(·#8211;) ion transfer from FeIVO group to NO to form nitrite, followed by an oxygen atom transfer from a second equivalent of [FeIVO(N4Py)]2+ to the nitrite intermediate to form nitrate. This second step chemistry was confirmed by independently studying the reaction of [FeIVO(N4Py)]2+ with nitrite to form nitrate. There is also a biological inorganic chemistry in which metal nitrosyl species are oxidized to form innocuous nitrite or nitrate. In this context, the oxidation of the synthetic nitrosyl complex [Fe(tmc)(NO)]2+ has been studied, which also produced [FeII(tmc)(ONO)]+. The molecular structure of [FeII(tmc)(ONO)]+ determined by X-ray crystallography indicates a bidentate binding mode of the nitrito ligand via both oxygen atoms. The oxidation results are consistent with a net oxide(·–) ion transfer mechanism forming [FeII(tmc)(NO2)]+, followed by a subsequent linkage isomerization. For comparison purposes, several related, independently synthesized [FeII(tmc)X]+ complexes (X = NO2–, NO3–, AcO–) have been characterized by spectroscopic techniques, X-ray crystallography and differential pulse and cyclic voltammetry. A final investigation involved studying the reactivity of a series of [FeIVO(tmc)X]+ (X = CF3SO3–, CF3CO2–, AcO–) complexes toward organic substrates by oxygen atom transfer and hydrogen atom abstraction to construct a reactivity trend depending on the strength of the axial ligand X.

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Hochvalente Metal-oxo-, -peroxo- und -nitrenzentren später Übergangsmetalle werden als reaktive Intermediate vieler technologisch interessanter und biologischer Transformationsreaktionen wie die Oxidation von Kohlenwasserstoffen, Hydroxylierung, Aminierung, Aziridierung und Sauerstoffreduktion angenommen. Die Isolierung und Charakterisierung solcher Intermediate, wenngleich sie sich schwierig gestaltet, kann wichtige Informationen zum Mechanismus solcher Reaktionen liefern und kann somit zu einer gezielten Optimierung und Herstellung von verbesserten Katalysatoren genutzt werden. In dieser Arbeit wurden drei unterschiedliche Intermediate – Eisenoxo , Kobaltperoxo- und Kupfernitrenkomplexe – näher untersucht. Es konnte in dieser Arbeit gezeigt werden, dass die Reaktivität der hier untersuchten hoch-valenten reaktiven Intermediate maßgeblich abhängig vom Ligandsystem, dem Zentralmetall und dem verwendeten Oxidationsmittel sind. / High-valent metal-oxo, -peroxo and -nitrene cores of late transition metals have been proposed as reactive intermediates in transformations that are both technologically attractive and fundamental for the functioning of biological systems, like the activation of C−H bonds in hydrocarbons and the reduction of dioxygen. The isolation and characterization of such species, despite being challenging, provides valuable information about the mechanisms of the reactions performed and can help in the design of improved catalysts. In this work, three different kinds of intermediates were studied, namely iron-oxo, cobalt-peroxo and copper-nitrenes. Several new reactive species were isolated and spectroscopically characterized, and their reactivity was thoroughly investigated. It was shown that the reactivity patterns of the high-valent reactive intermediates here studied depend greatly on subtle changes in the ligand system, the metal center and the oxidant employed.