Polyfluorinated Cyclopentadienones as Lewis Acids

Abstract

The ability of 2,3,4,5-tetrakis(trifluoromethyl)cyclopenta-2,4-dien-1-one and 2,3,4,5-tetrakis(pentafluorophenyl)cyclopenta-2,4-dien-1-one to act as organic Lewis acids in the field of frustrated Lewis pair (FLP) chemistry was evaluated. Whereas the former ketone formed zwitterionic adducts with all phosphines studied, the latter did not react with bulky phosphines and, instead, gave completely organic FLPs. Unfortunately, these did not activate dihydrogen, even under high pressures.

Key words

Lewis acids - frustrated Lewis pairs - steric hindrance - ketones - fluorine - phosphines

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• 16 In a typical reaction, the appropriate phosphine was added in one portion to a solution of ketone 9 in toluene at r.t., and the resulting slurry was stirred at r.t. overnight. The solvent was then removed under vacuum and the crude product washed with pentane. 12: yellow solid; yield: 66 mg (86%); mp 235 °C (decomp.); IR (neat): 742, 856, 926, 991, 1053, 1093, 1104, 1347, 1402, 1494, 1504, 1523, 1978 cm^–1; ¹H NMR (400 MHz, CD₂Cl₂): δ = 1.40 (d, J = 14.7 Hz, 27 H); ¹³C NMR (151 MHz, CD₂Cl₂): δ = 29.2, 42.1 (d, J = 33.9 Hz), 77.9, 96.1, 104.2, 113.6 (m), 114.0 (m), 137.2 (dm, J = 250.4 Hz), 137.9 (dm, J = 251.8 Hz), 139.6 (dm, J = 249.0 Hz), 139.9 (dm, J = 249.0 Hz), 144.7 (dm, J = 246.2 Hz), 145.5 (dm, J = 243.4 Hz); ³¹P NMR (162 MHz, CD₂Cl₂): δ = 106.7; ¹⁹F NMR (282 MHz, CDCl₃): δ = –(165.21–165.02) (m, 4 F), –(164.00–163.80) (m, 4 F), –(158.86–158.52) (m, 4 F), –(140.25–140.14) (m, 4 F), –(139.00–138.85) (m, 4 F); HRMS: m/z [M + Na]⁺ calcd for C₄₁H₂₇OF₂₀PNa: 969.137244; found: 969.137923. 14: yellow solid; yield: 50 mg (93%); mp 229 °C (decomp.); IR (neat): 790, 852, 864, 894, 924, 969, 991, 1060, 1094, 1106, 1287, 1358, 1403, 1475, 1490, 1501, 1522, 1535, 2862, 2933; ¹H NMR (400 MHz, CD₂Cl₂): δ = 0.83–1.00 (m, 4 H), 1.07–1.27 (m, 6 H), 1.38–1.72 (m, 10 H), 2.01–2.12 (m, 2 H), 7.26–7.29 (m, 1 H), 7.32–7.38 (m, 3 H), 7.44–7.48 (m, 1 H), 7.55–7.57 (m, 3 H), 7.70–7.74 (m, 1 H); ¹³C NMR (101 MHz, CD₂Cl₂) (partial): δ = 25.7 (d, J = 1.4 Hz), 26.3 (d, J = 3.8 Hz), 26.9 (d, J = 13.3 Hz), 37.2 (d, J = 51.9 Hz), 83.2, 95.5, 103.5, 113.0, 114.0, 127.7 (d, J = 11.4 Hz), 129.2, 129.7, 130.3, 131.9 (d, J = 10.0 Hz), 134.6 (d, J = 14.3 Hz), 134.7, 137.5 (dm, J = 242.7 Hz), 137.9 (dm, J = 247.0 Hz), 139.5 (d, J = 2.4 Hz), 144.7 (dm, J = 242.7 Hz), 145.5 (dm, J = 240.3 Hz), 148.5 (d, J = 8.6 Hz); ³¹P NMR (162 MHz, CD₂Cl₂): δ = 80.5; ¹⁹F NMR (282 MHz, CDCl₃): δ = –(165.21–165.09) (m, 4 F), –(163.99–163.84) (m, 4 F), –159.68 (t, J = 21.1 Hz, 2 F), –159.36 (t, J = 21.0 Hz, 2 F), –(140.52–140.34) (m, 4 F), –139.77 (dt, J = 25.0, 8.7 Hz, 4 F); HRMS: m/z [M + Na]⁺ calcd for C₅₃H₃₁OF₂₀PNa: 1117.168543; found: 1117.169092.