A Stable Cyclic (R 2 SnAu) 3 Anion Having In‐Plane σ‐Möbius Aromaticity

A cyclic (R 2 SnAu) 3 anion ( 3 − , R 2 Sn=2,2,5,5‐tetrakis(trimethylsilyl)‐1‐stannacyclopentane‐1,1‐diyl) has been synthesized as a stable blue salt with K + (THF) 6 through the reaction of stable dialkylstannylene 1 with R′ 3 PAuCl (R′=Et, Ph) followed by the reduction with KC 8 . Crystallographic and NMR analysis shows that the six‐membered (SnAu) 3 ring of 3 − is planar and highly symmetric with an equal distance of six Au−Sn bonds. A UV/Vis spectrum of 3 − in hexane reveals an intense absorption maximum at 598 nm. While cyclic Au 3 − with four valence electrons is known as unstable anti‐aromatic anion, 3 − with three divalent tin ligands is stable σ aromatic anion with an unprecedented Möbius orbital array as predicted by the perturbation MO and CCSD analysis of 3 − .