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

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 ΦPL = 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.