First synthesis of unusual arsenic reagent reveals that it breaks periodic trend

An elusive nitrene-like arsenic intermediate has been isolated and characterised for the first time. Analysis has confirmed many of the properties predicted for arsinidenes, but the unusual reactivity suggests heavier main group elements may have more unique chemistry than previously thought.

Carbenes and nitrenes are powerful synthetic intermediates, each containing a neutral centre with two unpaired valence electrons. Although highly reactive and unstable, the versatility of these reagents has made them a cornerstone of synthetic chemistry and both their fundamental nature and their wider reactivity have been extensively studied. However, far less is known about heavier related compounds like arsinidenes, which are too short-lived to characterise. ‘With electron deficient species you need to have substituents to stabilise the system,’ explains Artur Mardyukov, a physical organic chemist at Justus Liebig University in Germany. ‘In the case of carbenes and nitrenes, the orbital overlaps are efficient. But for arsenic the orbitals are more diffuse and the overlap is poor so they’re difficult to stabilise.’