Deboronation of a carborane‐substituted diphosphetane 2 in toluene yielded the first nido‐carboranyldiphosphetane 1. The P−P bond in 1 can be broken via dismutation reactions with diaryl dichalcogenides yielding nido‐carboranyl bis‐phosphanes that were not accessible via established synthetic protocols. Additionally, transition metal complexes of 1 could be isolated including one coordination polymer. Notably, when the deboronation of 2 is carried out in ethanol, unprecedented nido‐carborane‐substituted secondary bis‐phosphane monoxides (3, 4) are obtained. These compounds are interesting starting materials for further reactivity studies due to their P−H bonds. Experimental findings are supported by DFT calculations including the calculation of reaction mechanisms and NMR spectroscopic parameters.
Developments in energetic materials are currently focused on the requirements for safer, yet still powerful materials for uses within mining, munitions and rocket propulsion systems One strategy that can be used to achieve these desirable properties is to synthesise new molecules, but this is both time-consuming and resource-intensive. Instead, another strategy is to crystallise energetic molecules with other molecules to form salts or cocrystals. This approach has been used extensively within the pharmaceutical industry in order to enhance desirable properties, e.g. solubility and bioavailability. To date, however, there has been very little research on the cocrystallisation of energetic materials. Examples include trinitrotoluene (TNT) with pyrene, naphthalene, and CL-20. To start this design process, the relationships between the types and strengths of interactions within a crystal structure and materials properties need to be established. Once these structure-property relationships have been established, the engineering of new and improved energetic materials can be achieved. The main focus of this work is on the energetic material 3-nitro-1,2,4-triazol-5-one (NTO) and the characterisation of a selection of new salts and cocrystals. NTO is an insensitive high explosive that has a similar performance to the more widely used explosive, RDX, yet is more stable, less prone to accidental detonation, and more soluble in water. Its high solubility in water is a major issue, as NTO is biologically active and represents a potential risk to the environment. There are only a few known salts of NTO and no published cocrystals, so the design and preparation of the first NTO cocrystals is a key objective. A selection of crystal structures of salts and cocrystals of NTO with nitrogen-rich aromatic systems has been obtained and the results are presented here. Interesting trends between pKa, functional groups, and intermolecular interactions have been observed.
nido‐Carboranes are valuable backbones for the development of phosphorus‐based ligands. The cover, designed by Dr. Christoph Selg (Leipzig University), shows a highlight of the present study: Cu2I2 units bridged by the first nido‐carborane‐substituted diphosphetane, as symbolised by the crabs, forming a one‐dimensional coordination polymer. The diphosphetane is also suitable for functionalization to unprecedented nido‐carborane‐based P,N ligands. More information can be found in the Full Paper by E. Hey‐Hawkins et al. on page 11456.
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