Highly Robust and Antiaromatic Rhenium(I) Rosarin.

, a highly robust and antiaromatic rhenium(I) complex of triarylrosarin, is synthesized. The H NMR spectrum of shows upfield-shifted pyrrole protons and highly downfield-shifted inner protons that confirm its antiaromatic nature, with density functional theory calculations strongly supporting this interpretation. Antiaromatic absorbs from the UV to near-IR region of the optical spectrum; cyclic voltammetry, thin-layer UV-vis spectroelectrochemistry, and spin-density distributions clearly reveal that the rosarin backbone of undergoes redox chemistry. The X-ray structure of shows a fully coordinated and protonated inner cavity that effectively prevents proton-coupled electron transfer when treated with an acid. A remarkably negative NICS(0) value, clockwise anisotropy of the induced current density ring current, and the aromatic shielded inner cavity in the 2D ICSS(0) map reveal that the T state of is aromatic based on Baird's rule.