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

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.