(2,2'-Bipyridine)bis[3,5-difluoro-2-[5-(trifluoromethyl)-2-pyridinyl-κN][phenyl-κC]iridium(III) Hexafluorophosphate

• Methyl Terephthalaldehydate [T0012]
• Ir[dF(CF₃)ppy]₂(bpy)PF₆ [B6161]
• Piperidine
• Boric Anhydride
• Acetonitrile

To a solution of methyl terephthalaldehydate (2.00 g, 12.2 mmol, 1.0 eq), Ir[dF(CF₃)ppy]₂(bpy)PF₆ (240 mg, 0.240 mmol, 2.0 mol%), B₂O₃ (0.849 g, 12.2 mmol, 1.0 eq) in acetonitrile (60 mL) was added piperidine (3.60 mL, 36.6 mmol, 3.0 eq) at rt under N₂. The mixture was placed at a distance of 2-3 cm from Blue LED lamp. The solution was stirred at rt under visible light irradiation. After 17.5 hours of irradiation, the reaction mixture was filtered through a plug of celite. The resulting solution was concentrated under reduced pressure. 2 mol/L HCl (30 mL) and ethyl acetate (30 mL) were added to the residue and the resultant mixture were separated. 2 mol/L NaOH (30 mL) was added to the water layer and extracted with ethyl acetate (30 mL). The combined organic layer was washed with brine, dried over Na₂SO₄ and concentrated under reduced pressure to give a crude product (1.17 g, brown oil). The crude was purified by column chromatography (hexane:ethyl acetate = 99:1 - 79:21 on silica gel) giving compound 1 as a yellow oil (678 mg, y. 48%).

Acetonitrile was degassed with nitrogen for 1 hour before use.
Irradiated using 40 W blue LED lamps (3 cm away, with cooling fan to keep the reaction at room temperature).
The reaction mixture was monitored by ¹H NMR.

¹H NMR (400 MHz, CDCl₃); δ 7.92 (d, J = 8.2 Hz, 2H), 7.34 (d, J = 8.2 Hz, 2H), 3.84 (s, 3H), 3.44 (s, 2H), 2.30 (brs, 4H), 1.54-1.48 (m, 4H), 1.40-1.37 (m, 2H).

¹³C NMR (101 MHz, CDCl₃); δ 166.8, 144.1, 129.3, 128.7, 128.5, 63.2, 54.3, 51.7, 25.7, 24.1.

• Photoredox-catalyzed Direct Reductive Amination of Aldehydes without an External Hydrogen/Hydride Source
• R. Alam, G. A. Molander, Org. Lett. 2018, 20, 2680.

• Reductive Amination by Photoredox Catalysis and Polarity-Matched Hydrogen Atom Transfer
• X. Guo, O. S. Wenger, Angew. Chem. Int. Ed. 2018, 57, 2469.