A Planar Five‐Membered Aromatic Ring Stabilized by Only Two π‐Electrons. Issue 31 (23rd June 2022)

• Record Type: Journal Article
• Authors: Kysliak, Oleksandr; Schreiner, Simon H. F.; Grabicki, Niklas; Liebing, Phil; Weigend, Florian; Dumele, Oliver; Kretschmer, Robert
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 31(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-23
• Subjects: Aromaticity -- Gallium -- Inorganic Ring Systems -- NICS; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202206963
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Many chemicals known today are partially or fully aromatic, since a ring framework experiences additional stabilization through the delocalization of π‐electrons. While aromatic rings with equal numbers of π‐electrons and ring atoms such as benzene are particularly stable, those with the minimally required two π‐electrons are very rare and yet remain limited to three‐ and four‐membered rings if not stabilized in the coordination sphere of heavy metals. Here we report the facile synthesis of a dipotassium cyclopentagallene, a unique example of a five‐membered aromatic ring stabilized by only two π‐electrons. Single‐crystal X‐ray diffraction revealed a planar Ga5 ring with almost equal gallium–gallium bond lengths, which together with computational and spectroscopic data confirm its aromatic character. Our results prove that aromatic stabilization goes far beyond what has previously been assumed as minimum π‐electron count in a five‐atom ring fragment. Abstract : Although doubted in the past, two π‐electrons are just enough to stabilize five‐membered aromatic compounds that are even stable at room‐temperature, as shown by the facile synthesis of a dipotassium cyclopentagallene. This compound is a unique example of a five‐membered aromatic ring stabilized by only two π‐electrons. Single‐crystal X‐ray diffraction revealed a planar Ga5 ring with almost equal gallium–gallium bond lengths.