Intermediate-spin iron(IV)-oxido species with record reactivity The lecture will start with a short discussion of a range of current projects in the Comba group from various areas of bioinorganic and coordination chemistry and then will concentrate on high-valent nonheme iron chemistry. The iron(IV)-oxido complex trans-N3-[(L)FeIV=O(Cl)]+, with a tetradentate bispidine as supporting ligand (see Figure), has an S = 1 electronic ground state (in contrast to enzymes with an S = 2 ground state), is the most reactive nonheme iron model system known so far, with a reactivity similar to nonheme iron enzymes (C-H abstraction of cyclohexane, -90°C (propionitrile), t1/2 = 3.5 sec), and with 100% selectivity produces cyclohexyl chloride.1-3 In absence of organic substrates, there are various self-decay pathways, one leading to an oxido-bridged diiron(III) species. The reactivity of this “resting state” as well as reasons for the unprecedented reactivity of trans-N3-[(L)FeIV=O(Cl)]+ are discussed on the basis of temperature-dependent kinetics, a thorough spectroscopic analysis of the ferryl complex and the analysis of the electronic ground state involving ligand field and quantum-chemical methods.