Building A Bigger Borazine

Using a modular synthesis, chemists have prepared the first example of a macrocyclic borazine (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201203788). Borazine is a six-membered ring compound with alternating electron-accepting boron atoms and electron-donating nitrogen atoms—an inorganic benzene analog. Chemists are interested in borazines for their hydrogen storage capability and their electronic and optical properties such as strong fluorescence. The latter attributes enable the molecules to be used as anion-recognition sensors and as organic electronic materials. Pangkuan Chen, Roger A. Lalancette, and Frieder Jäkle of Rutgers University have now taken borazines to a new level by inserting phenyl groups between the boron and nitrogen atoms to expand the ring size. The researchers built the bigger borazine modularly via coupling reactions involving silylated and stannylated triphenylamines, boron tribromide, and triisopropylphenylcopper. The expanded borazine has “opened doors to a new family of macrocycles whose opto­electronic properties can be tuned by the choice of acceptor-donor building blocks and potentially by ring size,” says Shih-Yuan Liu, whose group at the University of Oregon synthesizes related boron-nitrogen heterocycles.