Indyllithium and the Indyl Anion [InL]−: Heavy Analogues of N‐Heterocyclic Carbenes

Reduction of the indate complex In(NONAr)(μ‐Cl)2Li(OEt2)2 (NONAr=[O(SiMe2NAr)2]2−; Ar=2,6‐iPr2C6H3) with sodium generates the InII diindane species [In(NONAr)]2. Further reduction with a mixture of potassium and [2.2.2]crypt affords the InI N‐heterocyclic indyl anion [In(NONAr)]−, which crystallizes with a non‐contacted [K([2.2.2]crypt)]+ cation. The indyl anion can also be isolated as the indyllithium compound In(NONAr)(Li{THF}3), which contains an In−Li bond. Density functional theory calculations show that the HOMO of the indyl anion is a metal‐centred lone pair, and preliminary reactivity studies confirm its nucleophilic behaviour. The reduction of indium(III) complexes supported by a chelating bis(amidodimethyl)disiloxane ligand afforded the corresponding InII diindane and the InI indyl anion. The latter was isolated as a non‐contact ion pair with the [K([2.2.2]crypt)]+ cation and as the indyllithium complex containing an ionic In−Li bond. These compounds represent the heaviest anionic analogues of N‐heterocyclic carbenes reported to date.