Radical ions, 41. Durosemiquinone and its BF Analogue – Detection of 1,4‐Diborine as an Unexpected Elimination Product

The photoelectron spectra and the one electron‐reduction behaviour of 1,4‐difluoro‐2,3,5,6‐tetra‐methyl‐1,4‐dibora‐2,5‐cyclohexadiene ( 1 ) and of the isoelectronic duroquinone ( 2 ) are compared. While duroquinone forms a very stable anion radical, durosemiquinone, the radical anion of the BF analogue was observed only as a short‐lived intermediate. In the presence of potassium metal a secondary anion radical is formed, which can be stabilized considerably by complexation of the K + cation with dicyclohexyl‐18‐crown‐6. ESR analysis demonstrates that the latter species is the radical anion of 2,3,5,6‐tetramethyl‐1,4‐diborine ( 3 ˙ ⊖ ), a hitherto unknown benzenoid heterocycle.