A R T I C L E S
Sviridenko et al.
(0.1 Torr) at 20 °C, the residue was dissolved in benzene, the solution
triethylamine (7 mL) and benzene (15 mL) was stirred at 70-75 °C
was filtered through a layer of Al , and the solvent was distilled off.
The residue was then dissolved in benzene and twice chromatographed
on silica gel. Elution with benzene yielded 40 mg (41%) of compound
2
O
3
for 2.5 h. The yield of compound 18 was 690 mg (77%), mp 156-157
1
°C (benzene). H NMR (CDCl
3
) δ 3.69 (s, 8 H, 4 OCH
); 4.15-4.22 (m, 4 H, 2 ArOCH
(s, 2 H, H (1), H (4)), 7.69 (d, 4 H, 2 H (2′), H (6′), J ) 8.2), 7.89 (d,
2
); 3.86-3.95
(m, 4 H, 2 ArOCH
2
CH
2
2
CH ); 7.08
2
-
1
1
(
6
3c, mp 125-126 °C (hexane-benzene mixture). IR, ν (cm ) 2200
CtC); 2980 (CH ); 2958, 2988 (C-Har). Found (%): C, 67.74; H,
. Calcd (%): C, 67.62; H, 6.52; N, 5.84.
,4,5,5-Tetramethy-2-[3-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-
pentaoxa-benzocyclododecen-15-ylethynyl)phenyl]-2-imidazoline-1-
-
1
3
4 H, 2 H (3′), H (5′), J ) 8.2), 10.05 (c, 2 H, CHO). IR, ν (cm ) 1697
.34; N, 5.66. C27
4
H
N O
31 2 6
28 7
(CdO), 2204 (CtC). Found (%): C, 73.14; H, 5.45. C32H O . Calcd
(%): C, 73.27; H, 5.38.
The structure of the synthesized radicals and the parameters of their
ESR spectra are given in Table 1.
1
9
oxyl (15b). A mixture of iodide 10b (100 mg, 0.25 mmol), alkyne
2 (70 mg, 0.27 mmol), PdCl (PPh (20 mg), and CuI (10 mg) in
1
2
3 2
)
Results and Discussion
piperidine (10 mL) was stirred under argon flow at 20 °C for 3 h. The
solvent was removed in vacuo with an oil pump (0.1 Torr) at 20 °C,
the residue was dissolved in benzene, the solution was filtered through
a layer of Al O , and the solvent was distilled off. The residue was
2 3
dissolved in benzene and twice chromatographed on silica gel. Elution
Thus, a series of 2-imidazoline-1-oxyl derivatives with the
general structure A-Sp-R were synthesized, which have in one
molecule an acceptor of positive or negative charge (A) that
can also be the luminophore, and a stable nitroxyl radical of
the 2-imidazoline series (R) connected with a bridge (Sp).
Having a luminophore in the radical ion pair is necessary to
observe the MFE/MARY/OD ESR effect. Negative charge
acceptor is required in nonpolar and nonviscous alkanes to slow
the “free” electron and extend the lifetime of the pair to at least
several nanoseconds so that magnetic interactions would have
ample time to affect its spin state before recombination. In the
case of solvent 1,4-dioxane that will also be discussed in this
work, where the mobility of the “free” electron is apparently
lower, an electron acceptor can still slow it down even more
and thus improve the signal. A positive charge acceptor can
provide some extra possibilities, e.g. to form a stable radical
cation with long relaxation and decay times or to change the
effective HFI in the cation partner of the pair by capturing it to
an acceptor with a different HFI structure.
Since acceptors have proved to be such a convenient tool to
probe the properties of the spin system, in this work they were
employed to introduce the “third spin” into the pair. In the
synthesized series of spin-labeled acceptors the third spin (a
stable radical R) is present in the precursor of the (bi)radical
ion to be formed. Similarly to conventional acceptors, these
compounds can be used to create a system with desired
properties, while the stable radical thus introduced into one of
the pair partners will be involved in the exchange interaction
with the accepted spin. As expected, the third constituent of
the spin-labeled acceptor, the bridge Sp, can be used to control
the extent of exchange coupling by modifying the structure of
the spacer.
with chloroform yielded 50 mg (41%) of compound 15b, mp 93-95
-
1
°
H
C (benzene). IR, ν (cm ) 2195 (CtC); 2988 (CH
ar). Found (%): C, 68.55; H, 7.58; N, 5.66. C29
C, 68.35; H, 7.32; N, 5.50.
,5-Bis-(4-(4,4,5,5-tetramethyl-2-imidazoline-1-oxyl-3-oxide)-phenyl-
ethynyl)-4-amine-pyridine (13j) and 1,5-Bis-(4-(4,4,5,5-tetramethyl-
-imidazoline-1-oxyl)-phenyl-ethynyl)-4-amine-pyridine (15j). A
3
); 2945, 2988 (C-
H N O . Calcd (%):
37 2 6
1
2
mixture of iodide 10j (200 mg, 0.57 mmol) and compound 11 (300
mg, 1.2 mmol) was stirred in piperidine (3 mL) in the presence of
PdCl (PPh ) (20 mg) and CuI (10 mg) under argon flow at 20 °C for
2 3 2
3
2
h. The solvent was removed in vacuo with an oil pump (0.1 Torr) at
0 °C, the residue was dissolved in benzene, the solution was filtered
through a layer of Al
was dissolved in benzene and twice chromatographed on silica gel.
3j. Elution with chloroform yielded 40 mg (11.7%) of compound
2 3
O , and the solvent was distilled off. The residue
1
-
1
1
3
1
3j, mp 226-227 °C (benzene). IR, ν (cm ) 2205 (CtC); 2988 (CH
455 (NH ); 2938, 2988 (C-Har). Found (%): C, 69.74; H, 6.34; N,
3.66. C35 . Calcd (%): C, 69.52; H, 6.0; N, 13.9.
5j. Elution with benzene yielded 40 mg (14.1%) of compound 15j,
3
);
2
36 6 4
H N O
1
-
1
mp 226-227 °C (benzene). IR, ν (cm ) 2200 (CtC); 2978 (CH
3
);
); 2938, 2988 (C-Har). Found (%): C, 73.74; H, 6.61; N,
. Calcd (%): C, 73.40; H, 6.34; N, 14.67.
,3-Bis-(4-(4,4,5,5-tetramethyl-2-imidazoline-1-oxyl-3-oxide)phen-
3
1
475 (NH
3.99. C35
2
2
36 6 2
H N O
yl-ethynyl)-6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclodo-
decene (13k) and 2,3-Bis-(4-(4,4,5,5-tetramethyl-2-imidazoline-1-
oxyl)-phenyl-ethynyl)-6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-
pentaoxabenzocyclododecene (15k). A mixture of iodide 10k (500
2
0
mg, 0.96 mmol) and alkyne 11 (620 mg, 2.4 mmol) was stirred in
piperidine (10 mL) in the presence of PdCl (PPh (50 mg) and CuI
25 mg) under argon flow at 20 °C for 5 h. The solvent was removed
in vacuo with an oil pump (0.1 Torr) at 20 °C, the residue was dissolved
in benzene, the solution was filtered through a layer of Al , and the
2
3 2
)
(
2
O
3
First, the characteristic time domain was estimated in which
the third spin can affect spin dynamics of the radical ion pair.
This was done using two luminescing negative charge acceptors
introduced into the solution: p-terphenyl-d14 (PTP-d14) and
hexafluorobenzene (HFB), forming a radical pair with a rather
solvent was distilled off. The residue was dissolved in benzene and
twice chromatographed on silica gel.
1
3k. Elution with chloroform yielded 90 mg (12.6%) of compound
-1
1
2
C
3k, mp 128-130 °C (benzene). IR, ν (cm ) 2207 (CtC); 2978 (CH
8748, 2929 (C-Har). Found (%): C, 67.34; H, 6.51; N, 7.04.
. Calcd (%): C, 67.85; H, 6.47; N, 7.09.
5k. Elution with benzene yielded 80 mg (13.2%) of compound 15k,
3
);
low or a very high HFI in the radical anion: second moment
40
H
N O
50 4 9
2
i
1
/2
of their ESR spectra, σ ) (∑ia Ii(Ii + 1)/3) , is ca. 0.6 and
1
1
21
65 G, respectively. In the first case spin evolution in the pair
-
1
mp 82-84 °C (benzene-hexane 1:3, v/v). IR, ν (cm ) 2215 (CtC);
is mostly driven by moderate (tens of gauss) HFI in the solvent
2
7
965 (CH
.66. C40
,3-Bis-(p-formyl-phenyl-ethynyl)-6,7,9,10,12,13,15,16-octahydro-
,8,11,14,17-pentaoxabenzocyclopentadecene (18). A mixture of
3
); 2948, 2998 (C-Har). Found (%): C, 70.74; H, 6.34; N,
H N O . Calcd (%): C, 70.76; H, 6.75; N, 7.5.
50 4 7
22
hole or acceptor radical cation, which corresponds to a longer
time of MFE/MARY formation, about 10 ns. In the second case
it is strong HFI in the HFB radical anion that drives spin
evolution, and the signal is formed at shorter times, about 1 ns.
Providing a spin-labeled hole acceptor as counterion to these
2
5
iodide 10k (900 mg, 1.7 mmol), 4-ethynyl-benzaldehyde (500 mg, 3.8
mmol), Pd(OAc) (20 mg), CuI (10 mg), and PPh (60 mg) in
2
3
(
19) Hyde, E. M.; Shaw, B. L.; Shepher, I. J. Chem. Soc., Dalton Trans 1978,
696.
20) Klyatskaya, S. V.; Tretyakov, E. V.; Vasilevsky, S. F. Russ. Chem. Bull.
001, 50, 868.
(21) Fischer, H., Ed. Landolt-B o¨ rnstein, Magnetic Properties of Free Radicals;
Springer: New York, 1990: Vol. II/17f, p 185.
(22) Borovkov, V. I.; Bagryansky, V. A.; Yeletskikh, I. V.; Molin, Yu. N. Mol.
Phys. 2002, 100, 1379.
1
(
2
2812 J. AM. CHEM. SOC.
9
VOL. 126, NO. 9, 2004