General procedure for the synthesis of bis(trimethylphenyl)boron fluoride from 2-bromo-1,3,5-trimethylbenzene and boron trifluoride ethyl ether: 1.07 g (44 mmol) of magnesium shavings and 7.96 g (40 mmol) of 2-bromo-1,3,5-trimethylbenzene were added under nitrogen protection to a 100 mL two-necked, round-bottomed flask equipped with a reflux condenser and a nitrogen inlet. With stirring and cooling in an ice bath, 14 mL of anhydrous tetrahydrofuran (THF) was slowly added. The mixture was heated to initiate the reaction, and the reaction temperature was controlled with an ice bath as soon as the reaction began to exotherm. After the exotherm slowed down, another 20 mL of anhydrous THF was added and the mixture was heated under reflux conditions for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature. The prepared Grignard reagent was slowly added dropwise via syringe to a 20 mL solution of anhydrous THF containing 2.3 mL (18.4 mmol) of boron trifluoride ethyl ether (BF3-OEt2) at 0°C. After dropwise addition, the reaction mixture was brought to room temperature and stirred overnight (12 hours). At the end of the reaction, the solvent was removed by evaporation and the residue was extracted with 80 mL of hexane. The resulting suspension was filtered using a Schlenk filter and the supernatant was concentrated under reduced pressure. The crude product was purified by vacuum sublimation (110 °C/0.05 mmHg) to give a white solid product. Yield: 3.9 g (79%). Product characterization data: 1H NMR (300 MHz, CDCl3) δ 2.30 (s, 6H), 2.31 (s, 6H), 2.34 (s, 6H), 6.87 (s, 4H); 13C NMR (75 MHz, CDCl3) δ 21.3, 22.3, 128.5 (CH), 140.6, 142.4; 11B NMR ( 160 MHz, CDCl3) δ 53.2; 19F NMR (282 MHz, CDCl3) δ -14.62; HRMS (ESI) calculated value C18H22BF [M-F]+ 249.1815, measured value: 249.1815.
