3,4,7,8-Tetramethyl-1,10-phenanthroline

• 4-Biphenylboronic Acid (contains varying amounts of Anhydride) [B2294]
• Nickel(II) Bromide Ethylene Glycol Dimethyl Ether Complex (=NiBr₂(glyme)) [N1050]
• 3,4,7,8-Tetramethyl-1,10-phenanthroline (= tmphen) [T0847]
• Bis(sulfur Dioxide)-1,4-diazabicyclo[2.2.2]octane Adduct (= DABSO) [B3960]
• Lithium tert-Butoxide (= LiOtBu)
• tert-Butyl Bromoacetate [B1473]
• 1,3-Dimethyl-2-imidazolidinone (= DMI) [D1477]

Under nitrogen atmosphere, a degassed DMI (20 mL) solution of 4-biphenylboronic acid (792 mg, 4.00 mmol), DABSO (577 mg, 2.40 mmol), tmphen (95 mg, 0.40 mmol), lithium tert-butoxide (320 mg, 4.00 mmol) and NiBr₂(glyme) (123 mg, 0.40 mmol) was stirred at 100 °C for 14 hours. The mixture was cooled to room temperature and tert-butyl bromoacetate (1.17 mL, 8.00 mmol) was added and the reaction mixture stirred for 1 hour. Water (20 mL) was poured into the reaction mixture and the mixture was extracted with diethyl ether (50 mL x 3). The combined organic phase was washed with water (50 mL) and brine (40 mL), dried over sodium sulfate and filtered. The solvent was removed under reduced pressure and the residue was purified by medium pressure preparative chromatography (ethyl acetate:hexane = 5:95 - 15:85 on silica gel) to give compound 1 as a white solid (1.01 g, 76%).

NiBr₂(glyme) and LiOtBu were weighed into a sample tube in a glove box because these reagents are moisture sensitive. If these were used in air, it should be weighted quickly and used up the reagents as soon as possible after opening.
Since the ligand of NiBr₂(glyme) may be desorbed under reduced pressure, depressurization operations is desirable to be finished as soon as possible.
The reaction mixture was monitored by TLC (ethyl acetate:hexane = 2:1, Rf = 0.38) and UPLC-MS.

Compound 1

¹H NMR (400 MHz, CDCl₃); δ 8.00 (d, 2H, J = 8.9 Hz), 7.78 (m, 2H), 7.58–7.66 (m, 2H), 7.42-7.54 (m, 3H), 4.08 (s, 2H), 1.58 (s, 2H), 1.39 (s, 9H).

• Nickel(II)-Catalyzed Synthesis of Sulfinates from Aryl and Heteroaryl Boronic Acids and the Sulfur Dioxide Surrogate DABSO
• P. K. T. Lo, Y. Chen, M. C. Willis, ACS Catal. 2019, 9, 10668.