CHEMPHYSCHEM
ARTICLES
tBu2PhOH-CH2-py quenches the rhenium 3MLCT state even
and the solution was neutralized by addition of an aqueous K2CO3
solution. The product (7) was extracted with CH2Cl2, and the com-
bined organic phases were dried over anhydrous MgSO4 prior to
solvent removal on a rotary evaporator. The raw product was puri-
fied by column chromatography on silica gel with CH2Cl2 as eluent
(Rf ꢀ0.4) affording product 7 (PhOH-CH2-py) as a white solid in
more rapidly ((13.3Æ0.1)ꢂ108 mÀ1
s
À1) and with an H/D KIE of
approximately 2, which suggests that CPET stays kinetically
highly competitive with an ET/PT sequence even in a situation
in which the initial ET step is thermodynamically possible.
1
57% yield. H NMR (300 MHz, CDCl3): d=4.10 (s, 2H), 6.82 (td, J=
7.4, 1.3 Hz, 1H), 6.95–7.02 (m, 1H), 7.13–7.21 (m, 3H), 7.32 (d, J=
7.8 Hz, 1H), 7.69 (td, J=7.7, 1.8 Hz, 1H), 8.46 (ddd, J=5.0, 1.8,
0.8 Hz, 1H), 11.67 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=41.7,
118.5, 119.9, 121.9, 122.8, 126.2, 128.7, 130.2, 138.2, 147.8, 156.7,
161.0 ppm; MS (EI): m/z (%): found: 186.0921 [M+H]+, calcd:
186.0913; elemental analysis calcd (%) for C13H13NO: C 77.81, H
5.99, N 7.56; found: C 77.63, H 5.97, N 7.47.
Experimental Section
A suspension of NaH (60% in mineral oil, 1.20 g, 30 mmol) in anhy-
drous THF (6 mL) was cooled to 08C and a solution of 2-bromo-
phenol (1; 3.44 g, 20 mmol) in anhydrous THF (8 mL) was added
dropwise over 1 h under N2 atmosphere. After stirring for an addi-
tional 10 min, iodomethane (9.2 g, 64.8 mmol) was added and the
mixture was allowed to warm up to room temperature prior to
heating at reflux for 19 h. After cooling to room temperature,
water (160 mL) was added and the product was extracted with
pentane (3ꢂ100 mL). The combined organic phases were dried
over anhydrous MgSO4, and the solvent was removed on a rotary
evaporator. Subsequent purification on silica gel with CH2Cl2 as
eluent (Rf ꢀ0.3) gave 1-bromo-2-methoxybenzene (2) in 97%
yield.[27] 1H NMR (300 MHz, CDCl3): d=3.89 (s, 3H), 6.78–6.95 (m,
2H), 7.27 (td, J=8.2, 6.1 Hz, 1H), 7.54 ppm (dd, J=7.8, 1.6 Hz, 1H).
For the synthesis of molecule 8 from 1-bromo-3,5-di-tert-butyl-2-
methoxybenzene (4) and pyridine 5, the same procedure as that
described above for molecule 6 was employed.[8] The quantities of
reactants used in this case were as follows: Cs2CO3: 22.81 g,
70.0 mmol; palladium trifluoroacetate: 0.97 g, 2.9 mmol; tricyclo-
hexylphosphine: 1.63 g, 5.8 mmol; dry p-xylene: 150 mL; 1-bromo-
3,5-di-tert-butyl-2-methoxybenzene (4): 20.86 g, 70 mmol; pyridine
5: 12.10 g, 58.3 mmol. Under the same chromatography conditions
as described above for molecule 6, the Rf value was approximately
0.3, and molecule 8 was obtained in 69% yield as a yellow oil.
1H NMR (300 MHz, CDCl3): d=1.26 (s, 9H), 1.43 (s, 9H), 3.75 (s, 3H),
4.27 (s, 2H), 6.98–7.17 (m, 3H), 7.26–7.31 (m, 1H), 7.56 (td, J=7.7,
1.9 Hz, 1H), 8.57 ppm (ddd, J=4.9, 1.8, 0.9 Hz, 1H).
The same procedure using identical molar quantities of starting
materials was employed for the synthesis of 1-bromo-3,5-di-tert-
butyl-2-methoxybenzene (4) from 2-bromo-4,6-di-tert-butylphenol
(3). On silica gel with CH2Cl2 as eluent, product 4 had Rf ꢀ0.6 and
1
the yield was 97%. H NMR (300 MHz, CDCl3): d=1.30 (s, 9H), 1.40
On subjecting molecule 8 to the same methoxyl-deprotection reac-
tion with aqueous HBr as described above for molecule 6, not only
the methoxyl group but also the tert-butyl substituents of mole-
cule 8 were cleaved off and the reaction afforded molecule 7. It
was therefore necessary to apply the following procedure to
obtain molecule 9.[10] Ethanethiol (0.69 g, 11.2 mmol) was added
dropwise to a suspension of NaH (60% in mineral oil, 0.31 g,
12.8 mmol) in dry N,N-dimethylformamide under N2 atmosphere.
Then molecule 8 (0.50 g, 1.6 mmol) was added and the reaction
mixture was stirred at 1008C overnight. After cooling to room tem-
perature, H2O (4 mL), 1m aqueous HCl (13 mL), and phosphate
buffer (0.5m, pH 7) were added, and the mixture was extracted
with diethyl ether (3ꢂ50 mL). The combined organic phases were
dried over anhydrous MgSO4, and the solvent was removed on
a rotary evaporator. Purification by three successive chromatogra-
phy columns on silica gel using a 7:3 (v/v) pentane/dichlorome-
thane mixture (Rf ꢀ0.5) gave product 9 (tBu2PhOH-CH2-py) in 65%
yield as a white solid. 1H NMR (300 MHz, CDCl3): d=1.31 (s, 9H),
1.47 (s, 9H), 4.10 (s, 2H), 7.06 (d, J=2.5 Hz, 1H), 7.17 (ddd, J=7.6,
5.0, 1.1 Hz, 1H), 7.24 (d, J=2.4 Hz, 1H), 7.34 (d, J=7.8 Hz, 1H), 7.67
(td, J=7.7, 1.8 Hz, 1H), 8.45 (ddd, J=5.0, 1.7, 0.9 Hz, 1H),
11.40 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=28.8, 30.7, 33.2,
34.1, 41.2, 120.7, 121.7, 122.0, 123.9, 125.3, 136.9, 137.0, 140.4,
146.6, 151.8, 160.5 ppm; MS (EI): m/z (%): found: 298.2168 [M+H]+,
(s, 9H), 3.91 (s, 3H), 7.28 (d, J=2.4 Hz, 1H), 7.41 ppm (d, J=2.4 Hz,
1H).
For the synthesis of molecule 5 a solution of 2-picoline (200 mmol)
in anhydrous THF (200 mL) was cooled to À308C and 1.6m n-bu-
tyllithium in hexane (200 mmol) was added slowly. After stirring at
this temperature for 30 min, diisopropyl ketone was added slowly
and the reaction mixture was stirred for another 2 h at room tem-
perature. Subsequently water (300 mL) was added and the result-
ing mixture was extracted with ethyl acetate (3ꢂ200 mL). The
combined organic phases were dried over anhydrous MgSO4, and
the solvent was removed with a rotary evaporator. The raw prod-
uct was purified by column chromatography on silica gel using
a 3:1 (v/v) mixture of pentane and ethyl acetate as eluent (Rf ꢀ0.6).
This procedure afforded pure 5 in 83% yield.[8] 1H NMR (300 MHz,
CDCl3): d=0.88 (dd, J=6.9, 4.9 Hz, 12H), 1.90 (m, 2H), 2.98 (s, 2H),
6.29 (s, 1H), 7.08–7.13 (m, 1H), 7.15 (d, J=7.8 Hz, 1H), 7.58 (td, J=
7.7, 1.9 Hz, 1H), 8.43 ppm (ddd, J=4.9, 1.8, 0.9 Hz, 1H).
Using a heat gun Cs2CO3 (27.90 g, 85.6 mmol) was dried under
vacuum. Subsequently, palladium trifluoroacetate (1.18 g,
3.6 mmol), tricyclohexylphosphine (2.00 g, 7.1 mmol), dry p-xylene
(150 mL), 1-bromo-2-methoxybenzene (2; 16.00 g, 85.6 mmol), and
pyridine 5 (14.70 g, 71.3 mmol) were added under nitrogen. The re-
action mixture was heated at reflux under N2 overnight. After cool-
ing to room temperature the mixture was filtered, and the solvent
was evaporated under reduced pressure. Column chromatography
on silica gel using a 5:1 (v/v) mixture of pentane and ethyl acetate
(Rf ꢀ0.1) afforded the coupling product 6 as a yellow liquid in 73%
yield.[8] 1H NMR (300 MHz, CDCl3): d=3.80 (s, 3H), 4.17 (s, 2H), 6.90
(ddd, J=8.1, 6.3, 2.6 Hz, 2H), 7.03–7.14 (m, 2H), 7.14–7.26 (m, 2H),
7.54 (td, J=7.7, 1.9 Hz, 1H), 8.49–8.58 ppm (m, 1H).
calcd:
298.2165;
elemental
analysis
calcd
(%)
for
C20H27NO·0.1C3H7NO·0.5C5H12: C 80.35, H 9.97, N 4.52; found: C
80.29, H 10.02, N 4.63.
Deuteration of the phenolic functions occurred by dissolving the
individual phenol molecules in a 1:1 mixture of CH3CN and D2O
(99.9%) followed by solvent removal on a rotary evaporator; this
procedure was accomplished twice to ensure high isotope purity.
Luminescence quenching experiments in CH2Cl2 occurred in the
presence of 100 mm CD3OD (99.99%) to avoid significant D/H ex-
change through contact of the phenols with glassware and cuv-
Molecule 6 (0.15 g, 0.78 mmol) was dissolved in aqueous HBr
(47%, 4 mL) and the mixture was heated at reflux for 19 h.[9] After
evaporation of excess acid, water was added to the solid residue,
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ChemPhysChem 2013, 14, 1168 – 1176 1174