1,2,3,4,5-Pentamethylcyclopentadiene was prepared following a procedure by Bergman et. al.12 a) Synthesis of 3,4,5-Trimethylhepta-2,5-dien-4-ol
In a 2 L three-neck round-bottomed flask equipped with a dropping funnel and a reflux condenser, lithium granules (14.94 g (2.153 mol, 4.05 equiv.) were suspended in diethyl ether (75 mL). 2-Bromo-2-butene (108.0 mL, 1.062 mol, 2.00 equiv.) was transferred into a dropping funnel and 3 mL were added to the reaction flask to activate the lithium granules. The mixture was diluted by adding diethyl ether (500 mL) and the remaining 2-bromo-2-butene was added dropwise at a rate such that the mixture remained at reflux. Following the addition, the mixture was stirred for one hour at room temperature. Subsequently, freshly distilled ethyl acetate
NaBArF 4 + HCl B F3C CF3 F3C F3C F3C CF3 CF3 CF3 Et2O 0 °C - NaCl O H O Br 4 Li -2 LiBr Li O O 2 2 OH 1) 2) H2O
(53.0 mL, 0.537 mol, 1.01 equiv.) was added dropwise, yielding a yellowish suspension. After stirring for one hour at room temperature, the mixture was carefully poured into a 5L round- bottomed flask containing 1.5 L of a saturated aqueous NH4Cl solution. The phases were
separated and the aqueous phase was brought to a pH of 9 with diluted HCl. The aqueous phase was extracted with 3x100 mL of diethyl ether and the combined organic phases were dried over MgSO4, filtered, and concentrated to about 100 mL.
b) Synthesis of 1,2,3,4,5-Pentamethylcyclopentadiene
In a three-neck round-bottomed flask equipped with a dropping funnel and a reflux condenser,
p-toluenesulfonic acid-monohydrate (9.250 g, 48.63 mmol, 0.09 equiv.) was suspended in
diethyl ether (150 mL). The concentrate from step a) was added dropwise at a rate such that the mixture remained at reflux. After stirring for one hour, 200 mL of a saturated aqueous NaHCO3
solution was added and the phases were separated. The organic phase was washed with 50 mL of the NaHCO3 solution. The combined aqueous phases were subsequently extracted with
diethyl ether (3x100 mL). The combined organic phases were then dried over MgSO4, filtered,
and the solvent removed in vacuo. The resulting orange oil was distilled under reduced pressure (10-1 mbar, 55-65 °C) to yield the product as a light yellow oil.
Yield: 51.35 g (376.9 mmol, 71%).
1H NMR (300.13 MHz, 300 K, CDCl3): δ (ppm) = 1.01 (d, 3JHH = 7.6 Hz, 3H),
1.80 (d, 4JHH = 18.2 Hz, 12H), 2.50 (m, 1H).
8.2.6 Synthesis of 1,3-Bis(1-naphthylmethyl)imidazolium Chloride, [INpMeH]Cl (XXXIX)
XXXIX was synthesized following a procedure by Dyson and co-workers.13
1-(Chloromethyl)naphthalene (31.4 mL, 210 mmol) and N-trimethylsilylimidazole (14.7 mL, 100 mmol) were dissolved in dry THF (50 mL) and stirred at 60 °C overnight. A voluminous, colorless solid formed, which was isolated by filtration, washed with diethyl ether (100 mL), and dried in vacuo. The crude product was dissolved in hot CH2Cl2 (600 mL), cooled in an ice
bath and precipitated by adding diethyl ether (600 mL). After storage at –30 °C overnight, the OH cat. TsOH - H2O H N N SiMe3 + 2 Cl THF 60 °C, 16 h - Me3SiCl N N+ Cl– XXXIX
mixture was filtered, washed with diethyl ether (400 mL), and dried in vacuo, yielding a colorless powder. Yield: 25.0 g (65.0 mmol, 65%). 1H NMR (300.13 MHz, 300 K, CDCl3): δ (ppm) = 6.03 (s, 4H, NCH2Np), 6.89 (d, JHH = 1.6 Hz, 2H, NCHCHN), 7.41-7.61 (m, 8H, CHnaph), 7.85-7.93 (m, 4H, CHnaph), 8.05 (d, JHH = 8.3 Hz, 2H, CHnaph), 11.47 (s, 1H, NCHN).
8.2.7 Synthesis of 1,3-Bis(1-naphthylmethyl)benzimidazolium Chloride, [BNpMeH]Cl (XL)
XL was prepared following modified procedures reported by Komarova and co-workers (a) and
Gök and co-workers (b).14
a) Synthesis of 1-(1-Naphthylmethyl)benzimidazole
Benzimidazole (1.181 g, 10.00 mmol) was dissolved in dimethylsulfoxide (20 mL) and KOH (0.842 g, 15.00 mmol) was added. After stirring at room temperature for 30 minutes, 1-(chloro- methyl)naphthalene (1.766 g, 10.00 mmol) was added and the mixture was stirred for another two hours. The resulting mixture was then poured into water (200 mL). The cloudy suspension was extracted with chloroform (6x25 mL). The chloroform phases were combined and dried with magnesium sulfate. After filtration and removal of the solvent in vacuo, the crude product was purified by column chromatography over silica gel using dichloromethane / methanol (20:1) as the eluent. Yield: 2.352 g (9.110 mmol, 91%). 1H NMR (300.13 MHz, 300 K, CDCl 3): δ (ppm) = 5.70 (s, 2H, NCH2Np), 7.02 (dd, JHH = 7.1 Hz, 1.1 Hz, 1H), 7.22-7.36 (m, 4H, CHAr), 7.51 (m, 2H, CHnaph), 7.80-7.91 (m, 5H, CHnaph and NCHN).
b) Synthesis of 1,3-Bis(1-naphthylmethyl)benzimidazolium Chloride (XL)
1-(1-Naphthylmethyl)benzimidazole (2.352 g, 9.110 mmol) and 1-(chloromethyl)naphthalene (1.609 g, 9.110 mmol) were dissolved in N,N-dimethylformamide (5 mL) and stirred at room temperature for four hours and subsequently at 80 °C overnight, whereupon a voluminous, colorless precipitate formed. The product was precipitated quantitatively by adding diethyl
N H N + Cl N N + Cl N N+ Cl- KOH DMSO r.t., 2 h - HCl DMF r.t. to 80 °C 20 h XL
ether (10 mL). The product was isolated by filtration, washed with diethyl ether (20 mL), and dried in vacuo.
Yield: 3.408 g (7.835 mmol, 86%).
1H NMR (300.13 MHz, 300 K, CDCl3): δ (ppm) = 6.38 (s, 4H, NCH2Np), 7.41 (m, 8H, CHAr
and CHnaph), 7.53 (m, 2H, CHnaph), 7.61 (m, 2H, CHnaph), 7.87 (m, 4H, CHnaph), 8.21 (d,
JHH = 8.3 Hz, 2H, CHnaph), 12.24 (s, 1H, NCHN).
8.2.8 Synthesis of 4,5-Dihydro-1,3-bis(1-naphthylmethyl)imidazolium Chloride, [SINpMeH]Cl (XLI), and Tetrafluoroborate, [SINpMeH]BF4 (XLI')
XLI was synthesized following a procedure by Özdemir and co-workers.15 a) Synthesis of N,N'-4-Bis(1-naphthylmethyl) Ethylenediamine
1-Naphthaldehyde (24.968 g, 159.87 mmol, 2.0 equiv.) was dissolved in methanol (120 mL) and cooled in an ice bath. Ethylenediamine (5.338 mL, 79.93 mmol, 1.0 equiv.) was added via an Eppendorf pipette. After stirring for two minutes, a colorless solid precipitated. The reaction was completed by stirring at room temperature for two hours. Subsequently, sodium borohydride (9.0716 g, 239.8 mmol, 3.0 equiv.) was carefully added in small portions to the suspension of the diimine, leading to a substantial gas evolution and the formation of a clear, pale yellow solution. After stirring for one hour at room temperature, excess sodium borohydride was quenched by adding HCl (3 mol L–1, 15 mL). The mixture was neutralized by
adding Na2CO3 in small portions until gas evolution ceased, yielding a colorless precipitate and
a pale yellow solution. The mixture was extracted with CH2Cl2 (3x150 mL). The combined
organic phases were dried over MgSO4. After filtration and removal of all volatiles in vacuo,
the disubstituted diamine was obtained as a yellowish oil which solidified overnight. The product was washed with n-hexane and dried in vacuo.
Yield: 20.862 g (61.274 mmol, 77%). O 2 + H 2N NH2 1) NaBH4 HC(OEt)3 NH4X N N NH HN NH HN Δ, 16 h - 3 EtOH - NH3 N N+ X- MeOH 0 °C - 2 H2O 2) HCl - NaB(OH)4 XLI (X = Cl) XLI’ (X = BF4)
b) Synthesis of 4,5-Dihydro-1,3-bis(1-naphthylmethyl)imidazolium Chloride (XLI)
Triethyl orthoformate (70 mL, 421 mmol, 6.9 equiv.) and finely powdered ammonium chloride (3.2776 g, 61.274 mmol, 1.0 equiv.) were added to the solid bis(1-naphthylmethyl)ethylene- diamine. The mixture was stirred at room temperature for two hours and refluxed overnight. All volatiles were removed in vacuo, yielding a light brown solid, which was purified by dissolving in hot ethanol, cooling in an ice bath and precipitating with diethyl ether. The obtained off-white solid was isolated by filtration, washed with diethyl ether, and dried in
vacuo.
Yield: 19.903 g (51.440 mmol, 84%).
1H NMR (300 K, 300.13 MHz, CDCl
3): δ (ppm) = 3.59 (s, 4H, NCH2CH2N), 5.36 (s, 4H,
NCH2Np), 7.40 (dd, J = 7.1 Hz, 8.1 Hz, 2H, CHnaph), 7.49-7.54 (m, 4H, CHnaph), 7.59-7.65 (m,
2H, CHnaph), 7.84 (m, 4H, CHnaph), 8.18 (d, J = 8.4 Hz, 2H, CHnaph), 11.10 (s, 1H, NCHN). 13C{1H} NMR (300 K, 75.47 MHz, CDCl3): δ (ppm) = 47.6 (NCH2CH2N), 50.1 (NCH2Np),
122.9 (CHnaph), 125.3 (CHnaph), 126.5 (aryl-CH), 127.7 (CHnaph), 127.9 (Cquart, naph), 128.6
(CHnaph), 129.0 (CHnaph), 130.2 (CHnaph), 131.2 (Cquart, naph), 133.9 (Cquart, naph), 159.2 (NCHN). c) Synthesis of 4,5-Dihydro-1,3-bis(1-naphthylmethyl)imidazolium Tetrafluoroborate
(XLI')
Triethyl orthoformate (14 mL, 10 equiv.) and ammonium tetrafluoroborate (0.8837 g, 8.430 mmol, 1.0 equiv.) were added to the solid bis(1-naphthylmethyl)ethylenediamine (2.870 g, 8.430 mmol, 1.0 equiv.). The mixture was stirred at 120 °C overnight. All volatiles were removed in vacuo. After washing with n-hexane and diethyl ether, the product was dissolved in hot ethanol and precipitated by layering with diethyl ether.
Yield: 3.294 g (7.516 mmol, 89%).
1H NMR (300 K, 300.13 MHz, CDCl
3): δ (ppm) = 3.59 (s, 4H, NCH2CH2N), 5.36 (s, 4H,
NCH2Np), 7.40 (dd, J = 7.1 Hz, 8.1 Hz, 2H, CHnaph), 7.49-7.54 (m, 4H, CHnaph), 7.59-7.65 (m,
2H, CHnaph), 7.84 (m, 4H, CHnaph), 8.18 (d, J = 8.4 Hz, 2H, CHnaph), 11.10 (s, 1H, NCHN). 13C{1H} NMR (300 K, 75.47 MHz, CDCl3): δ (ppm) = 47.6 (NCH2CH2N), 50.1 (NCH2Np),
122.9 (CHnaph), 125.3 (CHnaph), 126.5 (CHnaph), 127.7 (CHnaph), 127.9 (Cquart, naph), 128.6
8.2.9 Synthesis of (R,R)-4,5-Dihydro-1,3-bis((1-naphthyl)ethyl)imidazolium Tetrafluoroborate, [SINpEtH]BF4 (XLII)
The reaction was performed following a procedure by Glorius and co-workers.16 a) Synthesis of (R,R)-N,N’-Bis(1-(1-naphthyl)ethyl)ethylenediamine
(R)-1-(1-Naphthyl)ethylamine (2.9261 g, 17.091 mmol, 2.0 equiv.) and 1,2-dibromoethane (1.6054 g, 8.5457 mmol, 1.0 equiv.) were added to a round-bottom flask and heated to 100 °C overnight (the mixture was stirred until a glassy solid formed after 20 minutes of heating). After cooling to room temperature, the solid was dissolved in NaOH (1 mol L–1, 25 mL) and CH
2Cl2
(25 mL). The pH was adjusted to 13 with NaOH (1 mol L–1) and the phases were separated.
The aqueous phase was extracted with CH2Cl2 (2x10 mL). The combined organic phases were
dried with Na2SO4, filtered, and the solvent removed by rotary evaporation, yielding an orange-
red oil.
b) Synthesis of R,R-4,5-Dihydro-1,3-bis(-1-(1-naphthyl)ethyl)imidazolium Tetrafluoro- borate (XLII)
The crude diamine (a) (3.0887 g, 8.3816 mmol, 1.0 equiv.) was mixed with triethyl ortho- formate (1.394 mL, 8.382 mmol, 1.0 equiv.) and finely ground ammonium tetrafluoroborate (0.8787 g, 8.382 mmol, 1.0 equiv.). The mixture was stirred at 120 °C overnight in an open flask to allow the evaporation of ethanol and ammonia formed in the reaction. After removal of all volatile components in vacuo, the crude product was dissolved in hot ethanol and precipitated by adding diethyl ether after cooling. After storage at 4 °C overnight, the precipitate was isolated by filtration and washed with diethyl ether.
Yield: 1.8435 g (47%). 1H NMR (300.13 MHz, 300 K, CDCl3): δ (ppm) = 1.94 (d, 3JHH = 6.8 Hz, 6H, Np-CH(CH3)N), 3.49-3.79 (m, 4H, NCH2CH2N), 5.83 (q, 3JHH = 6.8 Hz, 2H, Np-CH(CH3)N), 7.43-7.50 (m, 4H), 7.52-7.64 (m, 4H), 7.82-7.93 (m, 4H), 7.82-7.92 (m, 4H), 8.02 (d, J = 8.4 Hz, 2H), 8.62 (s, 1H, NCHN). NH2 2 + Br Br 100 °C, 16 h - 2 HBr NH HN HC(OEt)3 NH4BF4 N N+ BF4- Δ, 16 h - 3 EtOH - NH3 XLII
8.2.10 Synthesis of Ferrocenium Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate,