Transmission of Point Chirality to Axial Chirality for Strong Circular Dichroism in Triarylmethylium-o,o-dimers

In memory of Kurt Mislow (1923–2017) and Shô Itô (1924–2018)

Published as part of the Cluster Atropisomerism

Abstract

Triarylmethylium-o,o-dimers adopt a twisted geometry so that two diarylmethyliums are stacked in a slipped manner. Thus, chiral auxiliaries on the aryl groups induce a preference in the axial chirality of the central biphenyl unit. Strong circular dichroism is attained through exciton coupling, which can be used for additional spectral output in their electrochromic behavior. Diastereoselectivity based on π–π stacking exhibits unique solvent effects, thus endowing multifunctional response properties.

Key words

chiral induction - axial chirality - exciton coupling - redox system - electrochromism - flow microreactor - dication - dye

• References and Notes

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• 11 Experimental procedures and characterization data for new compounds are given in the Supporting Information. Selected analytical data are as follows: (R,R,R,R)-5: Mp 83–86 °C (decomp.). IR (KBr): 2928, 2856, 1608, 1574, 1556, 1460, 1434, 1376, 1280, 1197, 1160, 1110, 1030, 917, 849, 598 cm^–1. ¹H NMR (300 MHz, CD₃CN): δ = 6.73–7.84 (24 H, brm), 4.79 (4 H, m), 1.75 (8 H, brm), 1.24–1.57(44 H, brm), 0.83–1.83 (12 H, brm) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 190.85, 190.59, 173.70, 173.68, 171.03, 170.85, 146.18, 144.28, 144.17, 142.69, 142.56, 140.63, 136.64, 136.55, 134.18, 134.14, 133.83, 133.81, 133.21, 132.92, 131.88, 131.85, 128.2259, 119.14, 118.33, 118.25, 79.29, 79.19, 77.72, 77.48, 36.35, 36.27, 36.26, 36.20, 32.10, 32.08, 32.05, 29.43, 25.51, 25.49, 25.44, 22.91, 19.76, 19.57, 19.47, 13.98 ppm. FAB-LR-MS: m/z = 997 ([M – 2SbCl₆]⁺, 15%). UV/Vis (CH₂Cl₂): λ_max = 538 (log ε 5.00), 417 (4.57), 280 (4.63) nm. CD (CH₂Cl₂): λ = 564 (Δε +31), 534 (–19), 406 (+2.9), 281 (–4.6), 267 (+1.5) nm. Anal. Calcd for C₇₀H₉₂Cl₁₂O₄Sb₂: C, 50.45; H, 5.56; Cl, 25.53. Found: C, 50.43; H, 5.31; Cl, 25.45. (R,R,R,R)-5 ²⁺(SbCl₆ ⁻)₂: Mp 83–86 °C (decomp.). IR (KBr) 2928, 2856, 1608, 1574, 1556, 1460, 1434, 1376, 1280, 1197, 1160, 1110, 1030, 917, 849, 598 cm^–1. ¹H NMR (300 MHz, CD₃CN): δ = 6.73–7.84 (24 H, brm), 4.79 (4 H, m), 1.75 (8 H, brm), 1.24–1.57(44 H, brm), 0.83–1.83 (12 H, brm) ppm. ¹³C NMR (75 MHz, CDCl₃):δ = 190.85, 190.59, 173.70, 173.68, 171.03, 170.85, 146.18, 144.28, 144.17, 142.69, 142.56, 140.63, 136.64, 136.55, 134.18, 134.14, 133.83, 133.81, 133.21, 132.92, 131.88, 131.85, 128.2259, 119.14, 118.33, 118.25, 79.29, 79.19, 77.72, 77.48, 36.35, 36.27, 36.26, 36.20, 32.10, 32.08, 32.05, 29.43, 25.51, 25.49, 25.44, 22.91, 19.76, 19.57, 19.47, 13.98 ppm. FAB-LR-MS: m/z = 997 ([M – 2SbCl₆]⁺, 15%). UV/Vis (CH₂Cl₂): λ_max = 538 (log ε 5.00), 417 (4.57), 280 (4.63) nm. CD (CH₂Cl₂): λ = 564 (Δε +31), 534 (–19), 406 (+2.9), 281 (–4.6), 267 (+1.5) nm. Anal. Calcd for C₇₀H₉₂Cl₁₂O₄Sb₂: C, 50.45; H, 5.56; Cl, 25.53. Found: C, 50.43; H, 5.31; Cl, 25.45. (R,R,R,R)-7: IR (neat): 3406, 2930, 2857, 1606, 1505, 1465, 1376, 1291, 1244, 1175, 1114, 829, 756, 665 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 6.99–7.26 (10 H, m), 6.75–6.83 (12 H, m), 6.07 (2 H, d, J = 7.3 Hz), 4.41 (2 H, s), 4.30–4.36 (4 H, m, J = 6.0 Hz), 1.16–1.82 (52 H, brm), 0.88 (12 H, brm) ppm. ¹³C NMR (75 MHz, CDCl₃): δ = 157.27, 157.07, 144.07, 140.87, 140.58, 138.38, 131.56, 130.24, 129.72, 128.56, 125.84, 125.79, 115.05, 114.89, 83.22, 74.00, 73.82, 36.43, 31.81, 29.28, 25.52, 22.59, 19.73, 14.07 ppm. FD-LR-MS: m/z = 1030 (M⁺, BP). FD-HR-MS: m/z calcd for C₇₀H₉₄O₆: 1030.7050; found: 1030.7045. (R,R)-6: Mp 138–142 °C (decomp.). IR (KBr): 3042, 2929, 2856, 2799, 1608, 1576, 1505, 1480, 1443, 1376, 1353, 1286, 1247, 1213, 1186, 1125, 1062, 1013, 948, 848, 807, 759, 746, 619, 573 cm^–1. ¹H NMR (300 MHz, C₆D₆): δ = 7.68–7.63 (3 H, m), 7.59 (1 H, dd, J = 7.9, 1.4 Hz), 7.45 (4 H, br), 7.38 (4H, br), 7.13–7.02 (4 H, m), 6.64 (4 H, brd, J = 7.9 Hz), 6.31 (4 H, brd, J = 7.9 Hz), 4.03 (2 H, br), 2.42 (12 H, s), 1.68–1.52 (2 H, m), 1.39–1.01 (24 H, m), 0.86 (6 H, t, J = 6.9 Hz) ppm. ¹³C NMR (100 MHz, C₆D₆): δ = 156.73, 148.57, 145.79, 145.34, 136.84, 136.64, 129.17, 129.05, 127.90, 127.00, 126.83, 124.68, 124.54, 112.65, 110.03, 73.11, 63.91, 63.65, 39.94, 36.94, 36.88, 32.10, 29.64, 25.80, 22.94, 19.88, 19.85, 14.30 ppm. FD-LR-MS: m/z = 829 (34), 828 (80), 827 (M⁺, BP). FD-HR-MS: m/z calcd for C₅₈H₇₀N₂O₂: 826.5437; found: 826.5437. UV/Vis (CH₂Cl₂): λ_max = (log ε) 270 (4.61) nm. (R,R)-6 ²⁺(SbCl₆ ⁻)₂: Mp 128–132 °C. IR (KBr): 3061, 2927, 2856, 1618, 1606, 1582, 1485, 1464, 1435, 1362, 1315, 1278, 1159, 1109, 1029, 963, 937, 910, 850, 831, 755, 722, 600 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 6.60–8.00 (24 H, brm), 4.72–4.88 (2 H, brm), 3.25 (12 H, m), 1.66–1.90 (4 H, brm), 1.18–1.56 (22 H, brm), 0.87–1.02 (6 H, brm) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 19.38, 19.45, 19.55, 25.35, 25.47, 29.40, 29.48, 29.49, 32.05, 32.1065, 36.13, 36.18, 36.27, 40.81, 41.36, 41.44, 77.45, 77.61, 78.70, 78.71, 113.92, 114.77, 118.66, 127.24, 127.81, 127.88, 130.70, 130.79, 132.47, 132.52, 132.99, 133.47, 133.64, 133.85, 133.94, 134.17, 136.52, 136.63, 138.98, 140.24, 140.30, 140.38, 140.41, 141.21, 141.26, 142.29, 142.41, 143.08, 143.17, 145.37, 145.39, 157.82, 157.98, 170.95, 172.78, 173.00, 191.52, 191.71 ppm. FD-LR-MS: m/z = 8277 ([M – 2SbCl₆]⁺, BP). FD-HR-MS: m/z calcd for C₅₈H₇₀N₂O₂: 826.5437; found: 826.5420. (R,R)-8: Mp 71.0–74.0 °C. IR (KBr): 3411, 2929, 2856, 2800, 1609, 1505, 1466, 1443, 1376, 1351, 1293, 1243, 1162, 1132, 1062, 1132, 1004, 948, 917, 816, 759, 622, 577, 560 cm^–1. ¹H NMR (300 MHz, CDCl₃): δ = 7.10–6.98 (8 H, m), 6.95 (2 H, d, J = 9.0 Hz), 6.86–6.80 (3 H, m), 6.79–6.73 (5 H, m), 6.63 (4 H, dd, J = 9.0, 1.5 Hz), 6.19 (1 H, d, J = 7.7 Hz), 6.03 (1 H, d, J = 7.7 Hz), 5.17 (1 H, brd, J = 7.9 Hz), 4.39–4.26 (2 H, m), 3.63 (1 H, brd, J = 4.8 Hz), 2.95 (6 H, s), 2.91 (6 H, s) 1.72 (2 H, br), 1.50–1.22 (24 H, m), 0.92–0.83 (6 H, m) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 157.07, 156.82, 149.56, 149.40, 144.50, 144.03, 141.39, 141.17, 140.71, 138.52, 136.86, 134.69, 131.58, 131.41, 130.28, 130.20, 129.67, 129.37, 128.62, 128.11, 125.92, 125.72, 125.44, 125.39, 114.93, 114.83, 111.73, 111.69, 83.86, 82.64, 82.59, 73.97, 73.92, 73.76, 40.62, 40.55, 36.51, 36.47, 36.37, 31.80, 29.28, 29.25, 25.53, 25.48, 22.57, 19.77, 19.67, 14.06 ppm. FD-LR-MS: m/z = 863 (22), 862 (63), 861 (M⁺, BP), 844 (24), 843 (35). FD-HR-MS: m/z calcd for C₅₈H₇₂N₂O₄: 860.5492; found: 860.5485.
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