Von Benzoborirenen zu Benzoborol‐basierenden 1,2‐Diiminen und antiaromatischen Boroldiiden

Abstract

The reaction of benzoborirene with one equivalent of isocyanides leads to benzene‐fused boretes bearing one imine function, while the reaction with two equivalents of isocyanide affords 2,3‐dihydro‐2,3‐diiminoboroles with perfect regioselectivity. The isocyanide double insertion products represent a novel type of 1,2‐diimine with a benzoborole backbone. The reduction chemistry of the benzoborole‐supported 1,2‐diimine was investigated. Single‐ and two‐electron reduction allow for the isolation and full characterization of a radical anion and a dianion, respectively. In stark contrast to the ordinary boroles, which should turn aromatic by accepting two electrons, the antiaromatic character of the benzoborole backbone is highlighted upon reduction, thus presenting a rare example of antiaromatic borole dianion. Detailed quantum chemical calculations provide a rationale for the observed regioselectivity and the electronic structure of the reduced borole diimine species.