Journal of the American Chemical Society
Article
chromatography (30% diethyl ether in pentane) to give diamine 8
(131.0 mg, 20%) as sticky dark yellow oil. Rf = 0.30 (30% diethyl
ether/pentane, 3% deactivated TLC). 1H NMR (600 MHz, acetone-d6):
δ = 6.948 (s, 1H), 5.770−5.684 (m, 5H), 5.028−4.979 (m, 8H),
4.143 (br, 2H), 2.490−2.389 (m, 8H), 1.679 (s, 4H), 1.188 (s, 12H).
13C NMR (150 MHz, acetone-d6): δ = 144.38, 137.14, 126.32, 117.46,
117.43, 101.36, 49.83, 46.98, 43.90, 38.67, 31.43. IR (cm−1): 3363,
3072, 2972, 2956, 2922, 2859, 1636, 1620, 1511, 1438, 1381, 1363,
1315, 1285, 1234, 1189, 1176, 996, 910, 824. HR−ESI MS (0.1%
gel with 10% diethyl ether/pentane. The filtrate was evaporated under
reduced pressure and evacuated under a high vacuum overnight. The
crude product was then purified by PTLC (5% diethyl ether/pentane)
to give 4-tert-butylphenyldiamine 11 as a white solid (35.6 mg, 59%).
mp 120−121 °C (under air). Rf = 0.36 (3% diethyl ether/pentane, 3%
deactivated TLC). 1H NMR (400 MHz, acetone-d6): δ = 7.570 (d, J =
8.4 Hz, 2H), 7.125 (d, J = 8.4 Hz, 2H), 6.878 (s, 1H), 3.034 (br, 2H),
1.697−1.567 (m, 8H), 1.664 (s, 4H), 1.367 (s, 9H), 1.310−1.217 (m,
8H), 1.059 (s, 12H), 0.869 (t, J = 7.2 Hz, 12H). 1H NMR (500 MHz,
benzene-d6): δ = 7.433 (d, J = 8.0 Hz, 2H), 7.381 (d, J = 8.5 Hz, 2H),
7.161 (s, 1H), 3. 322 (br, 2H, exch. D2O), 1.865−1.739 (m, 8H),
1.689 (s, 4H), 1.445−1.363 (m, 8H), 1.154 (s, 9H), 1.015 (s, 12H),
HCOOH in MeOH): m/z ion type (%RA for m/z = 400−410):
405.3262 [M + H]+ (100%, −1.9 ppm for
C
28
1H4114N2).
12
Preparation of 9. A clear yellow solution of diamine 8 (26.0 mg,
0.0643 mmol, 1 equiv) in 2 mL of ethanol was transferred into a
Schlenk vessel equipped with a magnetic stirring bar. Pd/C was added
into the Schlenk vessel to produce a suspension. The Schlenk vessel
was evacuated briefly using a diaphragm pump and charged with
hydrogen gas. The reaction was stirred at room temperature until
completion. The crude product was filtered through a Celite plug with
ethyl acetate, evaporated under reduced pressure and subsequently
evacuated on a high vacuum overnight to produce diamine 9 (25.3 mg,
95%) as a light yellow solid. The crude product was washed with a
small portion (3−4 drops) of methanol (3 times) to yield diamine 9 as
a white solid, used for characterization. mp 91−92 °C (under air). Rf =
0.30 (30% diethyl ether/pentane, 3% deactivated TLC). 1H NMR
(400 MHz, acetone-d6): δ = 6.763 (s, 1H), 5.696 (s, 1H), 4.007 (br,
2H), 1.655 (s, 4H), 1.610−1.556 (m, 8H), 1.263−1.202 (m, 8H),
1.176 (s, 12H), 0.847 (t, J = 7.2 Hz, 12H). 13C NMR (100 MHz,
acetone-d6): δ = 144.04, 125.59, 118.84, 101.39, 49.91, 45.62, 44.44,
38.84, 31.52, 18.14, 15.29. IR (ZnSe, cm−1): 3350, 2955, 2931, 2870,
1622, 1510, 1456, 1380, 1362, 1315, 1230, 1190, 822. HR−ESI MS
1
0.944 (t, J = 7.5 Hz, 12H). H−15N HSQC (acetone-d6): δ (15N) =
−287.9 ppm. 13C NMR (150 MHz, acetone-d6, LB = −0.2 Hz, GB =
0.5 Hz): δ = 151.04, 140.80, 140.77, 134.47, 132.02, 132.01, 127.48,
124.75, 119.28, 119.26, 113.67, 50.33, 50.24, 45.40, 45.38, 44.69,
44.66, 39.29, 35.24, 31.79, 31.75, 18.22, 15.29. IR (cm−1): 3379, 3084,
3027, 2953, 2930, 2869, 1605, 1476, 1456, 1380, 1361, 1268, 1228,
1201, 1179. HR−ESI MS (MeOH:H2O, 3:1): m/z ion type (%RA for
1
m/z = 543−548): 544.4769 [M]+ (100%, 2.3 ppm for 12C38 H6014N2).
General Procedure for the Generation of 2. Diamine 11
(0.70−1.32 mg, 1.28−2.42 μmol) was placed in a custom-made
Schlenk-EPR-tube (5 mm OD) and then it was placed under a high
vacuum (10−4 mTorr). The whole EPR sample tube was wrapped with
heating tape and heated at 70 °C overnight. The next day, the heating
tape was removed in the sample area and the remaining part of EPR
tube was heated at 110 °C overnight. THF (∼0.1 mL, ∼10 mm
height) was added to the vessel by vacuum transfer, and then the
solution was stirred for 30 min at −30 °C. n-BuLi (0.14−0.26 M in
hexane, 12−27 μL, 3.08−5.81 μmol, 2.4 equiv) was added to produce
the corresponding dianion. After stirring at −30 °C for 3−5 h, the
orange reaction mixture was evaporated at −45 °C and then immersed
in liquid nitrogen. 2-MeTHF (∼0.1 mL) was added to the reaction
mixture by vacuum transfer, and then the reaction mixture (under a
vacuum) was immersed in liquid nitrogen. Subsequently, iodine was
vacuum transferred to the sample tube wall, just above the reaction
mixture. Iodine was mixed into the reaction mixture at −115 °C, and
then the green solution was stirred at −115 °C for 1 h. The resultant
green solution was stored in liquid nitrogen; EPR spectra were
obtained at 132 K.
(MeOH:H2O, 3:1): m/z ion type (%RA for m/z = 410−420):
413.3888 [M + H]+ (100%, −1.9 ppm for
C
28
1H4914N2).
12
Preparation of 10. NBS (14.3 mg, 0.0805 mmol) in degassed
chloroform (1 mL) was added dropwise to a solution of diamine 9
(30.2 mg, 0.0732 mmol) with NaHCO3 (74.3 mg, 0.878 mmol) and
anhydrous Na2SO4 (124.7 mg, 0.878 mmol) in degassed chloroform
(3 mL) at −40 °C under N2 atmosphere to produce a heterogeneous
orange solution. After stirring at −40 °C for 1 h, an excess of Na2S2O5
was added and then the reaction mixture was allowed to attain room
temperature and was stirred for additional 10 min. After the solids
were filtered off, the filtrate was concentrated in vacuo to yield a brown
oil. The crude product was filtered through a short plug of silica gel
and eluted with 30% diethyl ether/pentane to give a brown film. A
small portion of MeOH (3 drops) was added to the brown film and
evaporated under N2 to give bromodiamine 10 (30.5 mg, 85%) as a
brown semisolid. Rf = 0.67 (4% diethyl ether/pentane, 3% deactivated
General Procedure for the Measurements of χT for
Statistical Analyses for 1 and 2. After obtaining the samples
using the protocol described in the generation of 2, 2-MeTHF was
added by vacuum transfer at liquid N2 temperature, to obtain ∼4−5 cm
height solution in the EPR tube. The resultant solution was mixed
by hand with a stirbar (and external magnet) for additional 15−30 min
at −115 °C, and then EPR spectra at 132 K were taken. Two EPR
spectra for both the sample and the nitroxide reference were obtained
and their double integrations were averaged, separately for the sample
and for the reference. Subsequently, the sample and the reference
were annealed at −115 and 22 °C, respectively. Following the
annealing, the sample and the reference were frozen carefully with
liquid N2 to give a continuous (and bubble-free) block of 2-MeTHF
glass, prior to placing the sample and the reference in the EPR cavity
for another set of spectra. Overall, n = 5−6 of independent sets of
spectra were obtained for each of the three samples of 2 and their
references (Table 3). The EPR spectra for 1 were obtained using the
samples contained in the SQUID tubes; n = 4 sets of spectra were
obtained for each of the two samples (Table 4).
General Procedure for Decay Kinetics Measurements for 1
and 2. After obtaining the samples using the protocol described in the
generation of 2, 2-MeTHF was added by vacuum transfer to obtain a
∼3.5−5 cm height solution in EPR tube. EPR spectra of the diluted
samples were taken at 132 K. Then, the samples were annealed at
−78 °C, −27 °C, and 22 °C. For reference, EPR spectra of
TEMPONE or TEMPOL (1 mM in 2-MeTHF) were taken at 132 K.
A similar protocol was implemented for the sample of 1.
1
TLC). H NMR (600 MHz, acetone-d6): δ = 6.868 (s, 1H), 4.186
(br, 1H), 1.727 (s, 4H), 1.621 (m, 8H), 1.292−1.187 (m, 8H), 1.261
(s, 12H), 0.850 (t, J = 7.2 Hz, 12H); unidentified impurities: δ =
7.627, 6.950, 5.611, 4.698, and 4.644 ppm with a relative integration
approximately 3 mol %. 13C NMR (100 MHz, acetone-d6): δ = 140.28,
124.71, 119.52, 98.38, 50.62, 45.24, 43.98, 39.55, 31.88, 18.13, 15.22.
IR (ZnSe, cm−1): 3384, 2955, 2931, 2870, 1612, 1483, 1466, 1425,
1382, 1363, 1290, 1230, 1200, 1182, 1108, 743. HR−ESI MS
(MeOH:H2O, 3:1): m/z ion type (%RA for m/z = 488−497):
490.2903 [M]+ (100%, −4.0 ppm for
C
1H4714N279Br1), 492.2922
28
12
[M]+ (80%, 4.0 ppm for
C
1H4714N281Br1).
12
28
Preparation of 11. Bromodiamine 10 (54.3 mg, 110 μmol) and
4-tert-butylphenylboronic acid (29.5 mg, 165 μmol, 1.5 equiv)
were placed into a Schlenk vessel under N2 atmosphere. Pd(PPh3)4
(25.4 mg, 22.0 μmol, 10 mol %) was added to the vessel in a glovebag
under N2 atmosphere. Benzene (2 mL), ethanol (0.6 mL), and
aqueous Na2CO3 (1 M, 0.6 mL) were bubbled with N2 for 10 min, and
then added to the reaction vessel. The reaction mixture was stirred at
90 °C for 72 h, then poured into distilled water and subsequently
extracted with benzene. The combined organic layers were washed
with 2 M NaOH solution (5 × 4 mL) and brine (3 × 4 mL). The
combined organic phase was dried over anhydrous Na2SO4, and then
concentrated in vacuo to provide the crude product as a colorless film.
The crude mixture was filtered through a short plug of Celite and silica
J
dx.doi.org/10.1021/ja508119d | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX