List of Tables
2.2. Experimental Section
2.2.1. Chemical and Instrumentation
All experiments were carried out under an inert nitrogen atmosphere using standard Schlenk and glove box techniques. Anhydrous grade solvents (Aldrich) were dried over activated molecular sieves (5Å). Spectrophotometric-grade THF (Merck) was used for photophysical measurements. Commercial reagents were used without further purification after purchase.
Deuterated solvents from Cambridge Isotope Laboratories were used. NMR spectra were recorded on a Bruker AM 300 (300.13 MHz for 1H, 75.48 MHz for 13C, 96.29 MHz for 11B) or a Bruker AVANCE III HD 400 (400.13 MHz for 1H, 100.61 MHz for 13C) spectrometer at ambient température. Chemical shifts (in ppm) are referenced against external Me4Si (1H, 13C) and BF3·OEt2 (11B). Elemental analyses were performed on a Flash 2000 elemental analyzer (Thermo Scientific) by the Research Facilities Center at University of Ulsan. Melting points (mp) were measured by Melting Point Apparatus SMP30 (Stuart Equipment). Cyclic voltammetry experiments were carried out using an Autolab/PGSTAT101 system.
2.2.2. ((5-Bromo-2-methylphenyl)ethynyl)trimethylsilane (1a)
4-Bromo-2-iodo-1-methylbenzene (3.0 g, 10.1 mmol), CuI (0.09 g, 0.5 mmol), and Pd(PPh3)4
(0.58 g, 0.5 mmol) were dissolved in anhydrous diisopropylamine (i-Pr2NH) (30 mL). Into the solution was added trimethylsilylacetylene (1.42 mL, 10.1 mmol), and the reaction mixture was stirred at 60 C for 20 h. The resulting solution was evaporated off under reduced pressure and the crude product was extracted with diethyl ether (40 mL 3). After evaporation of solvent, the solid residue was purified by column chromatography on silica gel using hexane as eluent. Drying in vacuo afforded a white powder of 1a (2.33 g, 86%). 1H NMR (CDCl3): δ 7.58 (d, J = 2.1 Hz, 1H), 7.34 (dd, J = 9.0, 3.0 Hz, 1H), 7.07 (d, J = 9.0 Hz, 1H), 2.39 (s, 3H),
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0.28 (s, 9H). 13C NMR (CDCl3): δ 139.6, 134.7, 131.5, 130.9, 125.0, 118.6, 102.5, 100.0, 20.4, 0.0
2.2.3. (3-Ethynyl-4-methylphenyl)dimesitylborane (1b)
To a solution of 1a (0.77 g, 2.89 mmol) in THF (10 mL) was added n-BuLi (2.5 M in hexane, 1.38 mL, 3.4 mmol) at −78 C, and the mixture was stirred for 1 h at this temperature. A solution of dimesitylboron fluoride (FBMes2, 0.852 g, 3.17 mmol) in THF (4 mL) was then added. After stirring for 1 h, the reaction mixture was slowly allowed to reach room temperature and was stirred overnight. Removal of the solvent under reduced pressure produced a sticky residue, which was subjected to column chromatography on silica gel using hexane to afford ((5-(dimesitylboryl)-2-methylphenyl)ethynyl)trimethylsilane as a white powder (0.71 g, 56%). 1H NMR (CDCl3): δ 7.65 (d, J = 1.1 Hz, 1H), 7.37 (dd, J = 7.6, 1.3 Hz, 1H), 7.21 (d, J = 7.6 Hz, 1H), 6.84 (s, 4H), 2.51 (s, 3H), 2.34 (s, 6H), 2.01 (s, 12H), 0.27 (s, 9H). Next, this compound (0.71 g, 1.62 mmol) was dissolved in anhydrous THF (30 mL) and tetra-n-butylammonium fluoride (n-Bu4NF, TBAF) solution (1.0 M in THF, 1.9 mL) was added under nitrogen atmosphere. After stirring at room temperature for 3 h, the resulting solution was evaporated off under reduced pressure. The crude product was extracted with diethyl ether (40 mL 3). After evaporation of solvent, the solid residue was purified by column chromatography on silica gel using hexane as eluent. Drying in vacuo afforded a white powder of 1c (0.54 g, 94%). 1H NMR (CDCl3): δ 7.67 (d, J = 1.2 Hz, 1H), 7.41 (dd, J = 7.6, 1.3 Hz, 1H), 7.22 (d, J = 7.6 Hz, 1H), 6.84 (s, 4H), 3.25 (s, 1H), 2.53 (s, 3H), 2.33 (s, 6H), 2.02 (s, 12H).13C NMR (CDCl3): δ 145.1, 143.2, 141.5, 140.9, 140.6, 138.8, 136.9, 129.4, 128.4, 121.9, 82.8, 81.1, 23.6, 21.4, 21.1.
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2.2.4. 1-Bromo-3-(2-H-o-carboran-1-yl)-4-methylbenzene (2a)
A toluene solution (20 mL) of decaborane (B10H14, 1.18 g, 9.65 mmol) and diethyl sulfide (Et2S, 4.06 mL, 40.3 mmol) was stirred at room temperature for 0.5 h. Into the solution was added a toluene solution (10 mL) of 4-bromo-2-ethynyl-1-methylbenzene (1.57 g, 8.06 mmol), which was obtained from desilylation of 1a using TBAF in THF. The mixture was refluxed for 4 days under nitrogen atmosphere. Work-up and purification of the crude product by column chromatography on silica gel using hexane as eluent afforded 2a as a white powder (0.61 g, 24%). 1H NMR (CDCl3): δ 7.70 (d, J = 1.8 Hz, 1H), 7.39 (dd, J = 8.1, 1.8 Hz, 1H), 7.02 (d, J
= 8.4 Hz, 1H), 4.55 (s, 1H), 3.4−1.0 (br, 10H, B−H), 2.53 (s, 3H). 13C NMR (CDCl3): δ 135.4, 134.0, 133.9, 133.7, 132.5, 120.5, 76.8, 59.), 22.9. 11B NMR (CDCl3): δ −1.8 (2B), −8.6 (3B),
−10.8 (5B).
2.2.5. 1-Bromo-3-(2-Me-o-carboran-1-yl)-4-methyl benzene (2b)
Sodium hydride (NaH, 60% dispersion in mineral oil, 0.06 g, 1.43 mmol) was suspended in dry DMF (5 mL). After cooling down to 0 C, a solution of 2a (0.30 g, 0.96 mmol) in DMF (5 mL) was added slowly to the suspension. The mixture was stirred at 0 C for 1 h, and then MeI (0.18 mL, 2.08 mmol) was added. After stirring at room temperature overnight, the reaction was quenched by addition of saturated aqueous NH4Cl solution, and the mixture was extracted with diethyl ether (20 mL 3). The organic layer was washed with water (20 mL 3), separated, and dried over MgSO4. The solvent was evaporated under reduced pressure and the residue was purified by column chromatography on silica gel using hexane as eluent. Drying in vacuo afforded a white powder of 2b (0.23 g, 74%). 1H NMR (CDCl3): δ 8.01 (d, J = 1.8 Hz, 1H), 7.47 (dd, J = 8.1, 1.8 Hz, 1H), 7.14 (d, J = 8.1 Hz, 1H), 2.68 (s, 3H), 3.4−1.0 (br, 10H, B−H),
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1.74 (s, 3H). 13C NMR (CDCl3): δ 139.0, 137.4, 135.9, 133.5, 130.6, 120.1, 82.8, 79.5, 23.8, 23.6. 11B NMR (CDCl3): δ −1.8 (1B), −3.4 (1B), −8.5 (2B), −10.9 (6B).
2.2.6. 1-Bromo-3-(2-i-Pr-o-carboran-1-yl)-4-methyl benzene (3b)
This compound was prepared in a manner analogous to the synthesis of 2b using 2a (0.30 g, 0.96 mmol) and i-PrI (0.26 g, 2,80 mmol) in DMF (5 mL) to give a white powder of 3b (0.29 g, 56%). 1H NMR (CDCl3): δ 7.99 (d, J = 1.9 Hz, 1H), 7.47 (dd, J = 8.3, 2.0 Hz, 1H), 7.13 (d, J = 8.3 Hz, 1H), 2.67 (s, 3H), 3.6−1.4 (br, 10H, B−H), 1.74 (sept, J = 6.9 Hz, 1H), 1.07 (d, J = 6.9 Hz, 6H). 13C NMR (CDCl3): δ 139.0, 137.5, 135.9, 133.5, 130.5, 120.2, 91.1, 86.2, 32.2, 24.0, 23.6. 11B NMR (CDCl3): δ −4.0 (1B), −6.1 (1B), −11.4 (8B).
2.2.7. 1-Iodo-5-(2-H-o-carboran-1-yl)-2,4-dimethylbenzene (4a)
To a THF solution (5 mL) of o-carborane (0.29 g, 2.0 mmol) in a pressure vessel was slowly added i-PrMgCl (2.0 M in THF, 1.2 mL, 2.4 mmol) at 0 C, and the mixture was stirred for 1 h. After evaporation of THF, toluene (5 mL), 1,5-diiodo-2,4-dimethylbenzene (0.78 g, 2.2 mmol), and NiCl2 (5.2 mg, 0.04 mmol) were added and the mixture was heated at 140 C for 36 h. The reaction mixture was then quenched with water (10 mL) and extracted with diethyl ether (20 mL 3). The combined ether layers were concentrated to dryness under reduced pressure. The crude product was purified by flash column chromatography on silica gel using hexane as eluent to give a white powder of 4a (0.38 g, 50%). 1H NMR (CDCl3): δ 7.92 (s, 1H), 7.00 (s, 1H), 4.50 (s, 1H), 2.50 (s, 3H), 2.37 (s, 3H). 13C NMR (CDCl3): δ 143.3, 140.9, 135.0, 134.7, 131.1, 98.3, 76.4, 59.8, 27.2, 22.9. 11B NMR (CDCl3): δ −3.0 (3B), −8.3 (7B).
2.2.8. 1-Iodo-5-(2-Me-o-carboran-1-yl)-2,4-dimethylbenzene (4b)
This compound was prepared in a manner analogous to the synthesis of 2b using 4a (0.25 g, 0.66 mmol) in DMF (5 mL) to give a white powder of 4b (0.20 g, 77%). 1H NMR (CDCl3): δ
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8.23 (s, 1H), 7.11 (s, 1H), 2.63 (s, 3H), 2.40 (s, 3H), 1.73 (s, 3H). 13C NMR (CDCl3): δ 144.6, 144.4, 139.8, 135.3, 128.0, 98.0, 82.6, 79.4, 27.3, 23.7, 23.5. 11B NMR (CDCl3): δ −3.2 (2B),
−9.7 (8B).
2.2.9. 1-(Mes2B)-3-(2-H-o-carboran-1-yl)-4-methylbenzene (closo-1)
A toluene solution (20 mL) of decaborane (B10H14, 0.22 g, 1.80 mmol) and diethyl sulfide (Et2S, 0.87 mL, 8.9 mmol) was stirred at room temperature for 0.5 h and then 1b (0.54 g, 1.48 mmol) in toluene (10 mL) was slowly added to this solution. The mixture was refluxed for 4 days under nitrogen atmosphere. After cooling down to room temperature, the solvent was evaporated off under reduced pressure and the residue was purified by column chromatography on silica gel using hexane as eluent, giving closo-1 as a white powder (0.16 g, 22%). 1H NMR (CDCl3): δ 7.68 (s, 1H), 7.42 (d, J = 7.6 Hz, 1H), 7.15 (d, J = 7.6 Hz, 1H), 6.89 (s, 4H), 4.43 (s, 1H), 2.67 (s, 3H), 2.36 (s, 6H), 2.03 (s, 12H). 13C NMR (CDCl3): δ 144.0, 141.1, 140.8, 139.3, 139.2, 139.1, 137.1, 133.8, 131.6, 128.5, 78.2, 59.9, 23.7, 23.6, 21.4. 11B NMR (CDCl3):
δ 75.9 (br s), 1.1 (1B), −3.3 (2B), −9.0 (7B). mp = 180 C. Anal. Calcd for C27H39B11: C, 67.21;
H, 8.15%. Found: C, 67.20; H, 8.12%.
2.2.10. 1-(Mes2B)-3-(2-Me-o-carboran-1-yl)-4-methylbenzene (closo-2)
To a solution of 2b (0.20 g, 0.61 mmol) in THF (10 mL) was added a hexane solution of n- BuLi (2.5 M, 0.26 mL, 0.67 mmol) at −78 C, and the mixture was stirred for 1 h at this temperature. A solution of dimesitylboron fluoride (0.18 g, 0.67 mmol) in THF (4 mL) was then added. After stirring for 1 h, the reaction mixture was slowly allowed to warm to room temperature and was stirred overnight. Work-up and purification of the crude product by column chromatography afforded a white powder of closo-2 (0.18 g, 61%). 1H NMR (CDCl3):
δ 7.98 (s, 1H), 7.46 (d, J = 7.6 Hz, 1H), 7.24 (d, J = 7.6 Hz, 1H), 6.86 (s, 4H), 2.78 (s, 3H),
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2.35 (s, 6H), 2.00 (s, 12H), 1.65 (s, 3H). 13C NMR (CDCl3) δ 144.0, 143.2, 141.9, 141.2, 140.7, 139.2, 137.8, 134.3, 128.5, 128.4, 84.3, 79.2, 24.5, 23.5, 23.4, 21.4. 11B NMR (CDCl3): δ 77.3 (br s), 1.5 (2B), −3.4 (2B), −8.9 (6B). mp = 172 C. Anal. Calcd for C28H41B11: C, 67.73; H, 8.32%. Found: C, 67.69; H, 8.27%.
2.2.11. 1-(Mes2B)-3-(2-i-Pr-o-carboran-1-yl)-4-methylbenzene (closo-3)
This compound was prepared in a manner analogous to the synthesis of closo-2 using 3b (0.18 g, 0.51 mmol) to give a white powder of closo-3 (0.15 g, 55%).1H NMR (CDCl3): δ 7.95 (s, 1H), 7.45 (d, J = 7.6 Hz, 1H), 7.23 (d, J = 7.6 Hz, 1H), 6.85 (s, 4H), 2.76 (s, 3H), 2.35 (s, 6H), 1.99 (s, 12H), 1.67 (sept, J = 6.9 Hz, 1H, −CHCH3), 1.00 (d, J = 6.9 Hz, 6H, −CHCH3). 13C NMR (CDCl3): δ 144.6, 143.9, 143.0, 141.2, 140.7, 139.3, 137.6, 134.3, 128.5, 128.2, 90.9, 88.0, 31.9, 24.3, 23.8, 23.5, 21.4. 11B NMR (CDCl3): δ 77.9 (br s), −3.2 (1B), −4.5 (2B), −10.0 (7B). mp = 154 C. Anal. Calcd for C30H45B11: C, 68.68; H, 8.65%. Found: C, 68.65; H, 8.63%.
2.2.12. 1-(Mes2B)-5-(2-Me-o-carboran-1-yl)-2,4-dimethylbenzene (closo-4)
This compound was prepared in a manner analogous to the synthesis of closo-2 using 4b (0.19 g, 0.49 mmol) to give a white powder of closo-4 (0.14 g, 56%). 1H NMR (CDCl3): δ 7.65 (s, 1H), 7.01 (s, 1H), 6.81 (s, 4H), 2.70 (s, 3H), 2.32 (s, 6H), 2.05 (s, 3H), 1.98 (s, 12H), 1.57 (s, 3H). 13C NMR (CDCl3): δ 146.1, 144.8, 142.6, 142.3, 141.9, 140.2, 139.4, 135.9, 128.6, 125.8, 84.4, 79.2, 23.9, 23.2, 23.1, 21.5, 21.4. 11B NMR (CDCl3): δ 78.0 (br s), −2.1 (1B), −4.4 (1B),
−8.9 (3B), −10.9 (4B), −12.6 (1B). mp = 187 C. Anal. Calcd for C29H43B11: C, 68.22; H, 8.49%. Found: C, 68.42; H, 8.25%.
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