Closely related yet different: a borylene and its dimer are non-interconvertible but connected through reactivity

Abstract

The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)]₄ (<b>I</b>, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B[double bond, length as m-dash]B(CN)(cAAC)] (<b>II</b>), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Furthermore, reactions of <b>I</b> or <b>II</b> with elemental sulfur and selenium in various stoichiometries provided access to a variety of cAAC-stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena-2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addition reactions and solution stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity observed between <b>I</b> and <b>II</b>.