The elusive cyclotriphosphazene molecule and its Dewar benzene-type valence isomer (P<sub>3</sub>N<sub>3</sub>).

Zhu, Cheng; Eckhardt, André K; Bergantini, Alexandre; Singh, Santosh K; Schreiner, Peter R; Kaiser, Ralf I · Sci Adv · 2020

basic_science · Level V

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Abstract

Although the chemistry of phosphorus and nitrogen has fascinated chemists for more than 350 years, the Hückel aromatic cyclotriphosphazene (P<sub>3</sub>N<sub>3</sub>, <b>2</b>) molecule-a key molecular building block in phosphorus chemistry-has remained elusive. Here, we report a facile, versatile pathway producing cyclotriphosphazene and its Dewar benzene-type isomer (P<sub>3</sub>N<sub>3</sub>, <b>5</b>) in ammonia-phosphine ices at 5 K exposed to ionizing radiation. Both isomers were detected in the gas phase upon sublimation via photoionization reflectron time-of-flight mass spectrometry and discriminated via isomer-selective photochemistry. Our findings provide a fundamental framework to explore the preparation of inorganic, isovalent species of benzene (C<sub>6</sub>H<sub>6</sub>) by formally replacing the C─H moieties alternatingly through phosphorus and nitrogen atoms, thus advancing our perception of the chemical bonding of phosphorus systems.