Oxidizing Functional Groups: Looking for New Types of Extreme Properties in Main-group Compounds

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Oxidizing functional groups, such as nitrogen oxides (-NO, -NO2, -ONO, -ONO2, etc.), polyoxygen (-O3-, -O2-, etc.) or polynitrogen (-N2, -N3, etc.) groups tend to impart unusual properties to molecules that bear them. Compounds that contain these groups are often capable of burning themselves under evolution of hot gases (N2, COx, H2O, etc.) and are therefore most often metastable with respect to decomposition, which can be quite spectacular (explosive). This metastability often places compounds with oxidizing groups at the very edge of existence. Beyond their energetic character, compounds bearing oxidizing groups display a range of other fascinating and useful properties. Nitrogen-oxide-groups are highly electron-withdrawing, and compounds bearing them are often unusually strong Bronsted acids that form weakly-coordinating anions. Dinitrogen-bearing molecules are convenient precursors to highly-reactive intermediates and azo compounds, in particular, are strongly colored compounds produced on an industrial scale as dyes. Nitro and azo-containing compounds display varied interactions with light, with many of them being relevant in non-linear optics, fluorescence, phosphorescence and even light-induced photoisomerization. Nitro groups are also present in many pharmacologically active species and nitric oxide is a very important signaling molecule in biological processes, showing the tremendous relevance of many oxidizing functional groups. Despite their very well-developed organic, metal and transition-metal chemistry, oxidizing groups like nitrogen oxides and -N2 functional groups have a very limited known chemistry with metalloids and non-metals of the third period and below ("heavy" main-group elements, HMG). Part of the problem is arguably due to the possibility of going from the +3 to +5 oxidation state for pnictogens, for example, or to the strong oxophilicity of elements like phosphorus, aluminium and silicon compounds. Such issues are challenges to the exploration of HMG-oxidizing group compounds but in no way make it impossible, particularly when tailored methods can be considered. Based on the fascinating properties displayed by organic oxidizing-group-containing compounds, we expect that their heavy main-group counterparts will also display an array of exotic properties. We will use a unique combination of approaches inspired by energetic material synthesis, fluorine, inorganic, organometallic and main-group chemistry to explore the synthesis of HMG compounds bearing oxidizing groups, focusing on the following research axes in the next five years: Axis I: Formation of main-group species containing nitrogen oxide functional groups that are directly attached to the HMG element (E) (RnE-NO2, RnE-ONO, RnE-ONO2, RnE-NO, etc. E = P, Si); Axis II: Formation of main-group diazo and diazonium derivatives (RnP-N2+ and RnP=N=N); Axis III: Nitration reactions on heavy benzene analogues (phosphabenzenes, arsabenzenes, etc.).