A Stable Cyclic (R2 SnAu)3 Anion Having In-Plane σ-Möbius Aromaticity

Abstract

A cyclic (R₂ SnAu)₃ anion (3^- , R₂ 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 KC₈ . 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 Au₃ ^- 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^- .

Keywords: gold complexes; low-valent compounds; stannylenes; σ-Hückel aromaticity; σ-Möbius aromaticity.