Biimidazol‐2‐yl–BF2 complexes

Nonfluorescent 4,4′,5,5′‐tetramethyl‐ and 4,5,4′,5′‐bistetramethylene biimidazol‐2‐yls 5 and 6 combined with boron trifluoride to give the tetramethyl and bistetramethylenebiimidazol‐2‐yl–BF2 complexes 9 and 10 isolated as strongly fluorescent BF3 salts, λf (dichloromethane): 377 nm Φ 0.93 and 386 nm Φ 0.90. Similarly, fluorescent bibenzimidazol‐2‐yl 7, λf (ethanol), 370 nm Φ 0.14, gave a BF2 complex 11 isolated as a BF3 salt λf (ethanol), 417 nm Φ 0.68.