Fraternal twins: B2O2- or B2N2-doped polycyclic π systems and their formation mechanism via regiodivergent Au- versus amine-catalyzed cyclizations

Abstract

BE-doped polycyclic aromatic hydrocarbons (PAHs; E = NR, O) often exhibit superior optoelectronic properties compared to their carbonaceous congeners. Herein, we report an efficient and convenient synthetic route to this compound class, based on the intramolecular addition of aryl(Mes)BE–H bonds to ortho-positioned butadiyne substituents. The reactions can proceed either under Au(I) or NEt₃ catalysis, with the same substrate giving rise to distinct addition patterns. Treatment of o-MesB(OH)-diphenylbutadiyne or o,o′-bis[MesB(OH)]-diphenylbutadiyne with [Au(PPh₃)(NTf₂)] furnishes an ethynyl-substituted BO-naphthalene or a (BO)₂-binaphthyl (B₂O₂; via 2,3-OC-addition), respectively. In contrast, NEt₃-catalyzed double cyclization of o,o′-bis[MesB(OH)]-diphenylbutadiyne affords the corresponding (BO)₂-naphthylbenzofulvene (iso-B₂O₂; via 1,3-OC-addition). Replacement of NEt₃ with ethylenediamine generates the analogous (BN)₂-doped PAH (iso-B₂N₂). Notably, both B₂O₂ and iso-B₂N₂ show high photoluminescence quantum yields of Φ_PL = 80% and 93%, respectively. Using the formation of iso-B₂O₂ as a model reaction, a plausible mechanistic scenario was elucidated through quantum-chemical calculations and systematic probe experiments, providing further novel BE-doped PAHs.