Ultralong C(sp³)–C(sp³) Single Bonds Shortened and Stabilized by London Dispersion

Abstract

A carbon–carbon (C–C) single bond longer than 1.7 Å shows unique bond flexibility, even though a C–C single bond is typically rigid and robust. We report here that the bond length of flexible C–C single bonds surrounded by bulky alkyl groups in novel hexaphenylethane-type hydrocarbons might be affected by weak noncovalent interactions, such as London dispersion. Thanks to London dispersion, an ultralong and flexible C–C single bond exhibits an obvious bond contraction. X-ray analyses and Raman spectroscopy provided direct information regarding the bond length and strength, whereas density functional theory calculations explained the bond contraction driven by London dispersion. The change in bond length of an extremely elongated flexible C–C bond would be a good probe for quantifying weak interactions that are usually difficult to detect.

Key words

strained molecules - hydrocarbons - C–C bond length - X-ray analysis - London dispersion

Publication History

Received: 27 July 2022

Accepted after revision: 30 August 2022

Accepted Manuscript online:
30 August 2022

Article published online:
11 October 2022

• References and Notes

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• 24 Diol 4 A 1.56 M solution of BuLi in hexane (1.35 mL, 2.11 mmol) was added to a suspension of 5,6-dibromo-1,2-dihydroacenaphthylene (3; 312 mg, 1.00 mmol) in dry Et₂O (20 mL) at 24 °C, and the mixture was stirred at 24 °C for 1 h. 2,8-Di-tert-butyldibenzosuberenone (669 mg, 2.10 mmol) was added, and the resulting mixture was refluxed for 4.5 h then cooled to 24 °C and diluted with H₂O. The mixture was extracted with EtOAc (×3), and the combined organic layers were washed with H₂O and brine then dried (Na₂SO₄), filtered, and concentrated under reduced pressure. The crude product was purified by washing with MeOH (3 × 20 mL) to give a white solid; yield: 451 mg (57%); mp 193.3–203.1 °C (dec). IR (ATR): 3566, 2960, 2903, 2867, 1596, 1559, 1507, 1490, 1458, 1387, 1362, 1313, 1271, 1215, 1179, 1164, 1145, 1093, 1077, 1044, 1022, 946, 938, 891, 828, 814, 803, 783, 755, 731, 691, 677, 662, 650, 627, 549, 507, 491, 455, 428 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.88 (d, J = 8.3 Hz, 2 H), 7.84 (d, J = 8.5 Hz, 2 H), 7.68 (dd, J = 2.0, 8.3 Hz, 2 H), 7.25 (dd, J = 2.1, 8.4 Hz, 2 H), 6.97 (d, J = 2.0 Hz, 2 H), 6.72 (d, J = 2.0 Hz, 2 H), 6.69 (d, J = 7.3 Hz, 2 H), 6.58 (d, J = 7.3 Hz, 2 H), 5.63 (d, J = 11.4 Hz, 2 H), 5.55 (d, J = 11.4 Hz, 2 H), 3.29–3.12 (m, 4 H), 1.41 (s, 18 H), 1.18 (s, 18 H), 0.94 (s, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 149.16, 147.61, 147.41, 145.21, 138.27, 137.52, 136.41, 134.68, 133.90, 131.68, 131.54, 130.61, 129.33, 126.19, 125.01, 124.41, 124.30, 123.78, 121.38, 116.65, 78.56, 34.54, 34.08, 31.37, 31.34, 29.83. LR-MS (FD): m/z (%): 793.49 (6), 792.49 (23), 791.48 (67), 790.48 (M⁺, bp), 772.46 (5), 500.24 (6). HRMS (FD): m/z calcd for C₅₈H₆₂O₂: 790.47498; found: 790.47359. Diol 6
  A 1.57 M solution of BuLi in hexane (1.35 mL, 2.11 mmol) was added to a suspension of 5,6-dibromoacenaphthylene (5; 310 mg, 1.00 mmol) in dry Et₂O (20 mL) at 22 °C, and the mixture was stirred at 22 °C for 1 h. 2,8-di-tert-butyldibenzosuberenone (668 mg, 2.10 mmol) was added, and the resulting mixture was refluxed for 6 h, allowed to cool to 24 °C, diluted with H₂O, and extracted with CHCl₃ (×3). The combined organic layers were washed with water and brine, dried (Na₂SO₄), filtered, and concentrated under reduced pressure. The crude product was purified by column chromatography [silica gel CH₂Cl₂–hexane (1:3)] to give a pale-orange solid; yield: 283 mg (36%); mp 229.5–261.3 ℃ (dec); R_f = 0.42 (silica gel CH₂Cl₂–hexane, 1:3). IR (ATR): 3560, 2956, 2866, 2362, 1602, 1559, 1507, 1490, 1384, 1361, 1313, 1264, 1206, 1093, 1045, 888, 825, 805, 741, 715, 691, 668, 651, 624, 555, 506 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.86 (d, J = 8.4 Hz, 2 H), 7.82 (d, J = 8.4 Hz, 2 H), 7.69 (dd, J = 2.2, 8.4 Hz, 2 H), 7.27 (dd, J = 2.2, 8.6 Hz, 2 H), 7.00 (d, J = 1.6 Hz, 2 H), 6.98 (d, J = 7.2 Hz, 2 H), 6.75 (d, J = 2.0 Hz, 2 H), 6.70 (s, 2 H), 6.62 (d, J = 7.2 Hz, 2 H), 5.68 (d, J = 11.2 Hz, 2 H), 5.64 (d, J = 11.6 Hz, 2 H), 1.42 (s, 18 H), 1.18 (s, 18 H), 0.97 (s, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 149.50, 147.73, 147.10, 143.23, 138.93, 137.44, 134.41, 134.05, 131.70, 131.03, 130.54, 129.81, 128.70, 127.98, 125.97, 125.07, 124.52, 124.47, 123.80, 121.54, 121.11, 78.62, 34.58, 34.12, 31.35, 31.32. LR-MS (FD): m/z (%): 791.44 (6), 790.44 (25), 789.44 (M⁺, 65), 788.43 (bp), 773.88 (5), 772.87 (9), 772.43 (10), 771.43 (30), 770.42 (45), 499.24 (8), 498.24 (21), 356.14 (16), 301.09 (7), 300.08 (25), 152.05 (5). HRMS (FD): m/z [M⁺] calcd for C₅₈H₆₀O₂: 788.45933; found: 788.46151.
• 25 Polycyclic Hydrocarbon 1- ^t Bu TfOH (110 μL, 1.24 mmol) was added to a suspension of 4 (100 mg, 126 μmol) in anhyd CH₂Cl₂ (1 mL) at 0 °C. HFIP (1 mL) was added and the mixture was stirred at 0 °C for 30 min. Anhyd MeCN (2 mL) and activated Zn powder (1.24 g, 18.8 mmol) were added at 0 °C, and the resulting mixture was stirred at 0 °C for 5 min then warmed to 24 °C and stirred at 24 °C for 10 min. The resulting mixture was diluted with water at 0 °C and extracted with CH₂Cl₂ (×3). The combined organic layer was washed successively with water, sat. aq NaHCO₃, and brine then dried (MgSO₄), filtered through a silica pad, and concentrated under reduced pressure to give a white solid; yield: 95.4 mg (quant); mp 266.4–279.8 °C (dec). IR (ATR): 3028, 2951, 2864, 1603, 1559, 1500, 1476, 1458, 1440, 1429, 1382, 1359, 1290, 1264, 1230, 1206, 1147, 1065, 1023, 948, 902, 886, 841, 804, 792, 765, 752, 719, 703, 689, 654, 600, 511, 467, 447, 434, 430, 424, 420 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.42 (d, J = 6.9 Hz, 2 H), 7.15 (d, J = 7.0 Hz, 2 H), 6.77 (d, J = 2.1 Hz, 4 H), 6.46 (dd, J = 2.2, 8.7 Hz, 4 H), 6.33 (s, 4 H), 6.23 (d, J = 8.7 Hz, 4 H), 3.62 (s, 4 H), 1.12 (s, 36 H). ¹³C NMR (100 MHz, CDCl₃): δ = 148.10, 147.37, 141.98, 138.42, 137.81, 137.58, 135.75, 133.49, 132.46, 127.47, 127.38, 123.05, 121.26, 84.88, 33.73, 31.95, 31.21. LR-MS (FD): m/z (%): 759.40 (8), 758.39 (25), 757.39 (66), 756.38 (M⁺, bp). HRMS (FD): m/z calcd for C₅₈H₆₀: 756.46950; found: 756.47015. Polycyclic Hydrocarbon 2- ^t Bu A 0.79 M solution TMSClO₄ in dry toluene (1.05 mL, 830 μmol) was added to a suspension of 6 (99.7 mg, 126 μmol) in HFIP (3 mL) at 0 °C, and the solution was stirred at 0 °C for 30 min. Anhyd MeCN (7 mL) and activated Zn powder (1.24 g, 190 mmol) were added and the resulting mixture was stirred at 0 °C for 5 min, then warmed to 22 °C and stirred at 22 °C for 5 min. The mixture was then diluted with water at 0 °C and extracted with EtOAc (×3). The combined organic layers were washed with water, sat. aq NaHCO₃, and brine then dried (Na₂SO₄), filtered through a silica pad, and concentrated under reduced pressure. The crude product was purified by column chromatography to give an orange solid; yield: 89.3 mg (93%); mp 208.2–248.6 ℃ (dec.); R_f = 0.30 (silica gel, CH₂Cl₂–hexane, 1:5). IR (ATR): 3031, 2952, 2865, 2361, 1734, 1700, 1684, 1653, 1603, 1559, 1506, 1458, 1419, 1382, 1360, 1290, 1264, 1206, 1148, 1078, 949, 908, 887, 841, 832, 802, 793, 736, 684, 668, 652, 502 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.94 (d, J = 6.8 Hz, 2 H), 7.33 (d, J = 7.2 Hz, 2 H), 7.30 (s, 2 H), 6.79 (d, J = 2.0 Hz, 4 H), 6.44 (dd, J = 2.4, 8.8 Hz, 4 H), 6.36 (s, 4 H), 6.12 (d, J = 8.8 Hz, 4 H), 1.12 (s, 36 H). ¹³C NMR (100 MHz, CDCl₃): δ = 153.62, 148.34, 138.16, 135.99, 135.66, 133.38, 132.45, 129.23, 127.47, 127.26, 126.91, 123.15, 85.85, 33.72, 31.13. LR-MS (FD): m/z (%): 757.44 (8), 756.44 (25), 755.44 (M⁺, 67), 754.43 (M⁺, bp). HR-MS (FD): m/z [M⁺] calcd for C₅₈H₅₈: 754.45385; found: 754.45572.
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