LAUSR

Cyclopentadienyl anions ([Cp]−) are pervasive ligands in coordination chemistry. In contrast, heavy-element derivatives of these ligands, particularly those that feature arsenic, are not as well developed. In this work, a new arsenic-based heterocycle with a structure analogous to [Cp]− is presented. Reaction of K3As7 with benzyl azide (BnN3) leads to fragmentation of the [As7]3– core and C–H activation of two [BnN] units to give the five-membered arsenic heterocycle [As(NC(Ph))2]−. This arsenic heterocycle was studied by nuclear magnetic resonance and UV–vis spectroscopy, X-ray diffraction, and its electronic structure was investigated computationally.