Useful Preparation of 6-Phenyl-2,2′-Bipyridine Ligands Bearing Di-n-butylaminophenyl or Gallate Derivatives Substituted in the 3- or 4-Positions

Abstract

A simple protocol for the efficient preparation of substituted 6-phenyl-2,2′-bipyridine derivatives is described. A reverse type of Diels-Alder reaction between a 6-phenyl-2-pyridyl-1,3,4-triazine and 4-N,N-di-n-butylaminophenyl- or gallate-ethynyl derivatives at high temperature provide a mixture of two products easily separable by column chromatography. A variety of ligands suitable for the synthesis of cyclometalated platinum complexes have been produced. Additional substitution of the Pt-Cl by various donor-acceptor ethynyl fragments is feasible by mean of copper(I) catalysis.

Key words

triazine - retro-Diels-Alder - gallate - fluorescence - platinum

References and Notes

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19

3,4-Bis( N , N -dibutyl-4-aminophenyl)-6-phenyl-2,2′-bipyridine(4)
A Schlenk tube was charged with 6-phenyl-2-pyridyl-1,3,4-triazine (1, 125 mg, 0.53 mmol), N,N-dibutyl-4-{2-[4 (dibutylamino)phenyl]ethynyl}benzenamine (230 mg, 0.53 mmol) and o-dichlorobenzene (1 mL). The mixture was argon-degassed via at least three freeze-pump-thaw cycles, heated to 190 °C and finally stirred in the dark for 1-3 d. The solvent was removed under high vacuum. The residue was treated with H₂O and extracted with CH₂Cl₂. The organic extracts were washed with H₂O, then with sat. brine and filtered through cotton wool. The solvent was removed by rotary evaporation, and the residue was purified by chromatography on aluminium oxide eluting with CH₂Cl₂-PE (v/v 0:1 to 50:50) to afford 194 mg (57%) of 4 as a white to light pink powder. ¹H NMR (400 MHz, CDCl₃): δ = 8.59 (d, 1 H, ³ J = 4.5 Hz), 8.11 (d, 2 H, ³ J = 7.0 Hz), 7.80 (s, 1 H), 7.49-7.35 (m, 4 H), 7.19 (d, 1 H, ³ J = 8.0 Hz), 7.09 (ddd, 1 H, J = 7.5, 4.8, 1.3 Hz), 6.78 (ABsys, 4 H, J _AB = 9.0 Hz, ν₀δ = 220.6 Hz), 6.55 (ABsys, 4 H, J _AB = 8.8 Hz, ν₀δ = 144.5 Hz), 3.24 (t, 4 H, ³ J = 7.5 Hz), 3.17 (t, 4 H, ³ J = 7.5 Hz), 1.59-1.44 (m, 8 H), 1.38-1.24 (m, 8 H), 0.95 (t, 6 H, ³ J = 7.3 Hz), 0.92 (t, 6 H, ³ J = 7.5 Hz). ¹³C NMR (100 MHz, CDCl₃): δ = 160.2, 157.7, 155.3, 150.5, 149.0, 147.5, 146.9, 139.9, 135.3, 133.3, 132.2, 130.7, 128.6, 128.5, 127.3, 126.3, 125.2, 124.7, 121.6, 121.5, 111.7, 111.1, 50.8, 50.7, 29.5, 29.4, 20.5, 20.4, 14.2, 14.1. UV/Vis (CH₂Cl₂): λ nm (ε, M^-1 cm^-1) = 355 (sh, 19200), 331 (2860), 263 (30600). IR (KBr): ν = 3039 (w), 2955 (m), 2929 (m), 2870 (m), 1605 (s), 1517 (s), 1463 (m), 1364 (s), 1285 (m), 1198 (s), 1095 (m), 818 (s) cm^-1. MS-FAB⁺: m/z (nature of the peak, relative intensity) = 639.3 (100) [M + H]⁺. Anal. Calcd for C₄₄H₅₄N₄: C, 82.71; H, 8.52; N, 8.77. Found: C, 82.54; H, 8.29; N, 8.47.

20

Crystal data for 4 at 293 K: C₄₄H₅₄N₄, M = 638.91, monoclinic, space group P2₁/c, a = 15.161(5) Å, b = 25.720(5) Å, c = 10.503(5) Å, α = 90.000(5)°, β = 107.245(5)°, γ = 90.000(5)° V = 3911.44(10) ų, Z = 4, λ = 0.71069 Å, D _c = 1.085 g cm^-3, µ = 0.063 mm^-1, 23064 reflections collected with θ £ 18.91°, 3085 unique, R(int) = 0.1214, and 1926 observed reflections [I ³ 2σ(I)], 433 parameters, R1 = 0.0830, wR2 = 0.2397 refined on F ². CCDC 649879.

22

Crystal data for 7 at 293 K: C₃₀H₃₂ClN₃Pt, M = 665.13, triclinic, space group P-1, a = 9.147(1) Å, b = 9.979(1) Å, c = 15.290(2) Å, α = 80.500(3)°, β = 80.922(2)°, γ = 73.057(3)°, V = 1307.8(3) ų, Z = 2, λ = 0.71069 Å, D _c = 1.689 g cm^-3, µ = 5.49 mm^-1, 15122 reflections collected with θ £ 27.61°, 5869 unique, R(int) = 0.0501, and 4993 observed reflections [I ³ 2σ(I)], 354 parameters, R1 = 0.0383, wR2 = 0.0919 refined on F ². CCDC 649883.