Highly Robust and Antiaromatic Rhenium(I) Rosarin.

1ReH•Cl , a highly robust and antiaromatic rhenium(I) complex of triarylrosarin, is synthesized. The 1 H NMR spectrum of 1ReH•Cl 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 1ReH•Cl 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 1ReH•Cl undergoes redox chemistry. The X-ray structure of 1ReH•Cl 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 1 state of 1ReH•Cl is aromatic based on Baird's rule.