Chemical Switching Between B2N and B2C Homoaromaticity.

In homoaromatic species, the formal replacement of one or more bonds of the σ-framework by saturated fragments (the homo bridge) can lead to geometry distortions that preserve a certain degree of cyclic π-conjugation. While cationic and anionic homoaromatics are well-established, charge-neutral derivatives occur less frequently but move increasingly into focus as potential photoswitches for responsive materials. We herein report the synthesis of homoaromatic 1-aza-2,4-diazadiboretane with a bicyclic four-membered NB2C motif and demonstrate experimentally and theoretically that the homoaromatic delocalization can also be chemically shifted from the B2N to the B2C moiety by deprotonation of the ring carbon atom. Reaction of the anion with carbon-, silicon-, and tin-centered electrophiles, as well as with water as proton source, effectively reinstates the previous electronic situation. Aromaticity analysis confirms the displacement of the 2π homodelocalization and thus the deliberate chemical alteration of the conjugation path, offering substantial potential for the design and synthesis of chemically responsive electronic materials.