RNNNNNNR: A Tamed High-Energy Compound

Chemicals with high nitrogen content also tend to be highly energetic, so chemists must tread lightly when handling or storing them lest they explode. But for a new hexaazadiene compound, Ryan E. Cowley and Patrick L. Holland at the University of Rochester and coworkers have discovered that tying it up as a ligand in a transition-metal complex renders it fairly stable (J. Am. Chem. Soc., DOI: 10.1021/ja801375g). The researchers had been exploring the chemistry of iron complexes made from 1-adamantyl azide, N₃R, where R is the tricyclic hydrocarbon adamantane. When the team added N₃R to the iron(I) complex LFeNNFeL, where L is a diketiminate ligand bearing diisopropylphenyl groups, two N₃R molecules coupled to form RN₆R^2–. This novel anion coordinated to iron, forming what the researchers believe is the first transition-metal complex with a hexaazadiene ligand (shown). The string of six catenated nitrogen atoms that snakes through the middle of the complex is stabilized by the bulky iron(II) diketiminate units. This stability contrasts greatly with metal-free neutral hexaazadienes, which are known to decompose quickly upon heating or photolysis, Holland notes.