Synthesis
All glassware was oven-dried, assembled hot, and cooled
under a dry argon stream before use. All reactions were
performed under dry argon.
N,N0-Bis(4-butylphenyl)-1,4-phenylenediamine (1). Bis[(40-butyl-
phenyl-4-aminophenyl]-400-tert-butylphenylamine (2). Diamines 1
and 2 were prepared according to the procedure described in
ref. 12.
Scheme 1 Pulses sequence used for the PEANUT experiments.
order to achieve an optimal resolution of nutation frequencies
in the recorded spectra.
Tetraazacyclophane,
C1.
Tris(dibenzylideneacetone)-
The PEANUT experiment is described in Scheme 1. In a
typical experiment the first pulse used was a selective low
power pulse (B1 B 0.7 G). This pulse was set up to be a true
p/2 pulse for species having nutation frequencies higher that
S = 1/2 species in order to better detect eventual signals of
S = 3/2 or S = 2 species. Two steps phase cycling (+x, ꢁx)
was performed on this first pulse. The high turning angle
pulses (B1 B 8 G) had a constant length of 1536 ns and the
x pulse (ꢁx pulse) was incremented (decremented) by 256 steps
of 2 ns, respectively. At every step, the spin rotatory echo was
integrated using a 76 ns gate centred at its maximum.
The obtained time-domain oscillating signal was treated
with second order polynomial baseline correction, sinebell
transformation and symmetrical zero-filling (256 zeroes
added). Then it was Fourier transformed using a numerical
FFT software to yield the corresponding nutation spectrum.
Two-dimensional maps (Magnetic Field vs. Nutation
spectrum) were obtained by successively performing
PEANUT experiments at 200 magnetic field values spaced
by steps of one Gauss.
dipalladium(0), Pd2(dba)3 45.8 mg (0.05 mmol) and tris-tert-
butylphosphine, (t-Bu3P) 16.2 mg (0.08 mmol) were dissolved
in 3 ml of dry toluene and stirred for 30 min. Then
1,3-dibromobenzene (0.236 g, 1 mmol), diamine 1 (0.372 g,
1 mmol), sodium tert-butoxide (0.282 g, 3 mmol) and 22 ml of
dry toluene were added to the reaction flask. The mixture was
stirred and heated at 110 1C for 12 h under an argon
atmosphere. The reaction mixture was then cooled to room
temperature and washed with 30 ml of distilled water. The
aqueous phase was extracted with three 10 ml portions of
diethyl ether. The organic layers were combined and dried
over MgSO4. Removal of the solvents followed by chromato-
graphy on silica gel (CH2Cl2/hexanes/0.5%v MeOH, 1 : 4)
resulted in a white solid. The resulting solid was recrystallized
from CH2Cl2/hexanes to give 0.195 g (0.218 mmol, 43.7%
1
yield) of C1 as white crystals. H NMR (400 MHz, C6D6) d,
7.29–7.26 (m, 8H), 6.96–6.94 (m, 8H), 6.91 (t, J = 7.6 Hz, 2H),
6.86 (s, 8H), 6.78 (dd, J = 8.0 Hz, 2.4 Hz, 4H), 6.68 (t, J = 2.0 Hz,
2H), 2.42 (t, J = 8.0 Hz, 8H), 1.51–1.44 (m, 8H), 1.29–1.20
(m, 8H), 0.84 (t, J = 7.6 Hz, 12H). 13C NMR (100 MHz,
C6D6) d, 149.8, 145.4, 143.3, 137.8, 129.6, 126.2, 125.5, 115.1,
35.4, 34.1, 22.7, 14.1. IR (cmꢁ1) 3026, 2954, 2925, 2854, 1590,
1505, 1489, 1330, 1297, 1275, 1239, 1114, 830, 768, 695. Anal.
Calcd. for C64H68N4: C, 86.10; H, 7.62; N, 6.28. Found:
C, 85.22; H, 7.52; N, 6.15. m/z = 892.7.
The spin multiplicities of detected species were obtained by
comparing the measured nutation frequency (nnut) to the
nutation frequency previously measured for known S = 1/2
systems (nS = 1/2) and using the following relationship:
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
nnut
¼
SðS þ 1Þ ꢁ mSðmS þ 1Þ ꢂ nS¼1=2
Hexaazacyclophane, C2. The same procedure as for
preparation of cyclophane C1 was used. The crude
product was chromatographed on silica gel eluting with
CH2Cl2/hexanes/1%v Et3N, (1 : 2) and then crystallized in
CHCl3/hexanes to give 0.234 g (0.175 mmol) of C2 as a white
powder. The reaction yield was 35%. 1H NMR (400 MHz,
C6D6) d, 7.32(t, J = 2.4 Hz, 2H), 7.28–7.21 (m, 16H), 6.97
(s, 16H), 6.96–6.95 (m, 8H), 6.87 (t, J = 8.0 Hz, 2H), 6.67
(dd, J = 8.0 Hz, 2.4 Hz, 4H), 2.42 (t, J = 7.6 Hz, 8H),
1.50–1.42 (m, 8H), 1.28 (s, 18H), 1.25–1.20 (m, 8H), 0.84
(t, J = 7.6 Hz, 12H). 13C NMR (100 MHz, C6D6) d, 149.0,
146.3, 145.3, 142.8, 142.3, 138.3, 129.7, 126.6, 126.1, 124.4,
This relationship is valid for low magnetic field excitation
(i.e. B1 { D, D the axial zero field splitting parameter
of the considered species).11 In the described experimental
conditions nS=1/2 B 23 MHz (established by measure-
ments with nitroxide free radicals). Then the preceding
relationship predicts nS=1 B 32 MHz and nS=3/2 B 40 MHz
(for mS = ꢃ1/2 2 ꢃ3/2 transitions).
Reagents
1,4-Phenylenediamine, 1-bromo-4-butylbenzene, 1-bromo-4-
tert-butylbenzene, 1,3-dibromobenzene, palladium acetate,
(Pd(OAc)2), 2,20-bis(diphenylphosphino)-1,10-binaphtyl, (BINAP),
tris-tert-butylphosphine, (t-Bu3P), tris(dibenzylideneacetone)-
dipalladium(0), Pd2(dba)3, sodium tert-butoxide, (t-BuONa),
anhydrous acetonitrile, anhydrous butyronitrile, diphenyl-
amine and 4-butylaniline were purchased from Aldrich.
Diphenylamine was purified by liquid chromatography using
CH2Cl2/ethyl acetate (20 : 1). 4-Butylaniline was distilled
under reduced pressure. N-Bromosuccinimide (NBS) was
crystallized from water.
123.6, 120.5, 115.9, 35.4, 34.4, 34.0, 31.6, 22.7, 14.1. IR (cmꢁ1
)
3031, 2957, 2928, 2858, 1592, 1502, 1467, 1316, 1270, 1110,
830, 773, 698. Anal. Calcd. for C96H102N6: C, 86.10; H, 7.62;
N, 6.28. Found: C, 86.24; H, 7.74; N, 6.19. (MH)+/z = 1339.2.
Oxidation procedure
The chemical oxidation of cyclophanes was carried out in an
argon atmosphere. In a typical procedure 80 mL of 0.01 M
solution of cyclophane in CH2Cl2 was oxidized with an
appropriate amount of 0.04 M oxidant solution in BuCN
ꢀc
This journal is the Owner Societies 2009
Phys. Chem. Chem. Phys., 2009, 11, 1362–1368 | 1363