Tailor-made well-defined copper nitrenes for catalytic asymmetric C-H amination and aziridination

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Nitrenes are open-shell, low valent compounds, which are particularly reactive due to the electron deficiency configuration at the nitrene nitrogen. Nitrenes can be produced, for example, from suitable metal complexes and organic azides or iminoiodinanes, whereby the metal is oxidised and the valency of the nitrene is saturated by metal-nitrene bonds. Such metallonitrenes are considered key species for catalytic direct amination and nitrene transfer to unsaturated organic substrates and heteroatoms. In particular, the occurrence of terminal nitrenes is considered a decisive factor for the reactivity of the reactions addressed. So far, only a few terminal copper nitrenes have been characterised. By specifically manipulating their electronic properties, it is possible to increase the reactivity of metal nitrenes, whereby the special ligand design is decisive here. The valence electrons and bonding ratios of the metal nitrenes are experimentally accessible via XRD, XAS, ESR, Raman and UV/Vis spectroscopic investigations. In addition, the electronic properties can be modelled theoretically for the identification of the species and thus the spectroscopic properties can be simulated. In nitrene-mediated catalysis, mainly transition metals (Cu, Pd, Fe, Ru, Ag, Ir, Rh, Co, Mn) have played a role so far; due to the large availability and low toxicity, copper is superior to many transition metals. The most effective copper catalysts require harsh thermal conditions. However, the heating of metal-containing azide and iminoiodinane solutions must be avoided at all costs due to their explosive nature and will never find industrial application for safety reasons. Furthermore, although there have been catalytic studies on metal nitrenes for many years, there is rarely a congruence between a functional nitrene system and functional catalyst. In previous studies, we were able to show that bis(pyrazolyl)methane-stabilised copper-nitrene complexes exist as singlet, which is very advantageous for the regio- and enantioselectivity of aminations and aziridinations. We now want to develop this concept further by chirally varying the bis(pyrazolyl)methanes and also extending this complex family towards oxazolines. The possibility to tailor the ligands, together with feedback from spectroscopic characterisation and kinetic as well as catalytic studies, allows a targeted design of reactive metal-nitrenes with tunable properties. In addition, new nitrene sources are to be developed. An important focus is also the potential correlation of the respective spin states with the observed reactivity.