Exceptionally persistent nitrogen-centered free radicals. Syntheses, ESR spectra, isolation, and X-ray crystallographic structures of N-(arylthio)-2-tert-butyl-4,6-diarylphenylaminyl and N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyl radicals

Article abstract of DOI:10.1021/jo960347d

The preparation, ESR spectra, isolation, and X-ray crystallographic structure of N-(arylthio)-2-tert-butyl-4,6-diarylphenylaminyls (1) and N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyls (2) are described. The aminyls are generated by PbO₂ oxidation of N-(arylthio)-2-tert-butyl-4,6-diarylanilines and N-(arylthio)-4-tert-butyl-2,6-diarylanilines. The kinetic ESR study shows that the aminyls are quite persistent, even in the presence of oxygen, and exist in the individual radical forms. Among the seventeen aminyls prepared, N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-diphenylphenylaminyl(1b), N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-bis(4-chlorophenyl)phenylaminyl (1f), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-diphenylphenylaminyl (2b), N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2h), and N-[(3,5-dichlorophenyl)thio]-4-tert-butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2j) are isolated as radical crystals. The crystallographic structures of 1b and 2b are determined by the X-ray crystallographic analyses. Aminyls 1 and 2 give similar ESR spectra consisting of 1:1:1 triplets with the α_N values of 0.921-0.948 mT. Deuteration of the phenyl groups on the anilino benzene ring gives rise to a further splitting of the nitrogen 1:1:1 triplet by the anilino meta (0.126-0.138) and phenylthiyl ortho and para protons (0.077-0.096 mT). Upon recording at high gain, one of the partly deuterated aminyls gives satellite lines due to ³³S isotopes at natural abundance from which α³³_s is determined to be 0.51 mT. The ESR parameters for 1 and 2 are compared with those for structurally close N-(arylthio)-2,4,6-triarylphenylaminyl and N-(arylthio)-2,4,6-tri-tert-butylphenylaminyl.

Full text of DOI:10.1021/jo960347d

4300
J . Org. Chem. 1996, 61, 4300-4308
Excep tion a lly P er sisten t Nitr ogen -Cen ter ed F r ee Ra d ica ls.
Syn th eses, ESR Sp ectr a , Isola tion , a n d X-r a y Cr ysta llogr a p h ic
Str u ctu r es of N-(Ar ylth io)-2-ter t-bu tyl-4,6-d ia r ylp h en yla m in yl a n d
N-(Ar ylth io)-4-ter t-bu tyl-2,6-d ia r ylp h en yla m in yl Ra d ica ls1
Yozo Miura,* Masayoshi Momoki, and Tomohiro Fuchikami
Department of Applied Chemistry, Faculty of Engineering, Osaka City University,
Sumiyoshi-ku, Osaka 558, J apan
Yoshio Teki† and Koichi Itoh
Department of Material Science, Faculty of Science, Osaka City University,
Sumiyoshi-ku, Osaka 558, J apan
Hisashi Mizutani
Department of Chemistry, Faculty of Science, Osaka City University, Sumiyoshi-ku, Osaka 558, J apan
Received February 20, 1996X
The preparation, ESR spectra, isolation, and X-ray crystallographic structure of N-(arylthio)-2-
tert-butyl-4,6-diarylphenylaminyls (1) and N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyls (2) are
described. The aminyls are generated by PbO2 oxidation of N-(arylthio)-2-tert-butyl-4,6-diaryl-
anilines and N-(arylthio)-4-tert-butyl-2,6-diarylanilines. The kinetic ESR study shows that the
aminyls are quite persistent, even in the presence of oxygen, and exist in the individual radical
forms. Among the seventeen aminyls prepared, N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-diphen-
ylphenylaminyl (1b), N-[(4-nitrophenyl)thio]-2-tert-butyl-4,6-bis(4-chlorophenyl)phenylaminyl (1f),
N-[(4-nitrophenyl)thio]-4-tert-butyl-2,6-diphenylphenylaminyl (2b), N-[(4-nitrophenyl)thio]-4-tert-
butyl-2,6-bis(4-chlorophenyl)phenylaminyl (2h ), and N-[(3,5-dichlorophenyl)thio]-4-tert-butyl-2,6-
bis(4-chlorophenyl)phenylaminyl (2j) are isolated as radical crystals. The crystallographic structures
of 1b and 2b are determined by the X-ray crystallographic analyses. Aminyls 1 and 2 give similar
ESR spectra consisting of 1:1:1 triplets with the aN values of 0.921-0.948 mT. Deuteration of the
phenyl groups on the anilino benzene ring gives rise to a further splitting of the nitrogen 1:1:1
triplet by the anilino meta (0.126-0.138) and phenylthiyl ortho and para protons (0.077-0.096
mT). Upon recording at high gain, one of the partly deuterated aminyls gives satellite lines due to
33S isotopes at natural abundance from which a33S is determined to be 0.51 mT. The ESR parameters
for 1 and 2 are compared with those for structurally close N-(arylthio)-2,4,6-triarylphenylaminyl
and N-(arylthio)-2,4,6-tri-tert-butylphenylaminyl.
In tr od u ction
to nitroxides and nitronyl nitroxides which have a
localized electron spin because they can be easily pre-
pared and have an exceptional stability. Therefore, the
quest of a new class of stable free radicals has been
strongly desired for the further advances in chemistry
and physics of purely organic magnetism. Standing on
this background, we have made an effort to search for a
new class of stable free radicals as a part of a program
directed toward the syntheses of high-spin or ferromag-
netic materials.1,4 Our extensive studies on thioaminyls
(R′N˙ SR) (Chart 1) have shown that N-(arylthio)-2,4,6-
triarylphenylaminyls (3) are exceptionally persistent and
can be isolated as pure radical crystals.5 Their magnetic
studies have shown that, although most 3 couples anti-
ferromagnetically in the crystal state, three thioaminyls
couple ferromagnetically with the J 1/k values of 1.8-14.0
K.6,7 As an extension of this study we have investigated
N-(arylthio)-2-tert-butyl-4,6-diarylphenylaminyls (1) and
For recent years the chemistry of stable free radicals
have been largely stimulated by the expectation that
organic free radicals might have ferromagnetic proper-
ties. Many free radical crystals have widely been inves-
tigated from the view points of the purely organic
magnetism.2 Some radical crystals including 2-(p-nitro-
phenyl)nitronyl nitroxide have found to be purely organic
ferromagnets at very low temperatures.3 However, most
of the stable free radicals investigated have been limited
† Adjunct associate professor of the Institute for Molecular Science,
Oakazaki 444.
X Abstract published in Advance ACS Abstracts, J une 1, 1996.
(1) ESR Studies of Nitrogen-Centered Free Radicals. 48. Part 47:
Miura, Y.; Oka, H.; Yamano, E.; Teki, Y.; Takui, T.; Itoh, K. Bull. Chem.
Soc. J pn. 1995, 68, 1187.
(2) Proceedings of the 4th International Conference on Molecule-
Based Magnets, Salt Lake City, 1994 (in Mol. Cryst. Liq. Cryst. 1995,
273, 274.).
(3) Kinoshita, M.; Turek, P.; Tamura, M.; Nozawa, K.; Shiomi, D.;
Nakazawa, Y.; Ishikawa, M.; Takahashi, M.; Awaga, K.; Inabe, T.;
Maruyama, Y. Chem. Lett. 1991, 1225. Chiarelli, R.; Nobak, M. A.;
Rassat, A.; Tholence, J . L. Nature 1993, 363, 147. Nogami, T.; Tomioka,
K.; Ishida, T.; Yoshikawa, H.; Yasui, M.; Iwasaki, F.; Iwamura, H.;
Takeda, N.; Ishikawa, M. Chem. Lett. 1994, 29. Ishida, T.; Tsuboi, H.;
Nogami, T.; Yoshikawa, H.; Yasui, M.; Iwasaki, F.; Iwamura, H.;
Takeda, N.; Ishikawa, M. Chem. Lett. 1994, 919; Sugawara, T.;
Matsushita, M. M.; Izuoka, A.; Wada, N.; Takeda, N.; Ishikawa, M. J .
Chem. Soc., Chem. Commun. 1994, 1723; Mukai, K.; Konishi, K.;
Nedachi, K.; Takeda, K. J . Magn. Mater. 1995, 140-144, 1449.
(4) Teki, Y.; Miura, Y.; Tanaka, A.; Takui, T.; Itoh, K. Mol. Cryst.
Liq. Cryst. 1993, 233, 119. Miura, Y.; Matsumoto, M.; Ushitani, Y.
Macromolecules 1993, 26, 2628. Miura, Y.; Ushitani, Y.; Inui, K.; Teki,
Y.; Takui, T.; Itoh, K. Macromolecules 1993, 26, 3698. Miura, Y.;
Matsumoto, M.; Ushitani, Y.; Teki, Y.; Takui, T.; Itoh, K. Macromol-
ecules 1993, 26, 6673. Miura, Y.; Ushitani, Y. Macromolecules 1993,
26, 7079.
(5) Miura, Y. Rev. Hetroatom Chem. 1990, 3, 211.
S0022-3263(96)00347-7 CCC: $12.00 © 1996 American Chemical Society

Persistent Nitrogen-Centered Free Radicals
J . Org. Chem., Vol. 61, No. 13, 1996 4301
Ch a r t 1
Sch em e 1
N-(arylthio)-4-tert-butyl-2,6-diarylphenylaminyls (2).8 As
shown by their structures, aminyls 1 and 2 are analogues
of 3: one of three aryl groups at the 2,4,6-positions of
the anilino group is replaced by a tert-butyl group.
Although the tert-butyl group is superior as a protecting
group, it has no ability to stabilize the aminyls electroni-
cally. Nevertheless, our ESR study on 1 and 2 has shown
that they are quite persistent and some can be isolated
as radical crystals. In this paper we report on the
generation, ESR spectra, isolation, and X-ray crystal-
lographic structures of 1 and 2.
Resu lts a n d Discu ssion
Syn th eses of P r ecu r sor s 6 a n d 7. The syntheses
of N-(arylthio)-2-tert-butyl-4,6-diarylanilines (6) and
N-(arylthio)-4-tert-butyl-2,6-diarylanilines (7) were per-
formed according to Scheme 1. Thus, treatment of 2- and
4-tert-butylaniline with benzyltrimethylammnonium tri-
bromide (BTMA Br3) in CH3OH in the presence of CaCO3
gave 2-tert-butyl-4,6-dibromoaniline and 4-tert-butyl-2,6-
dibromoaniline in 97 and 96% yields,9 respectively. The
bromoanilines were then subjected to the palladium-
catalyzed cross-coupling reaction with 2 equiv of phenyl-
boronic acid or 4-chlorophenylboronic acid (Suzuki reac-
tion10) to yield the corresponding 2-tert-butyl-4,6-diaryl-
aniline and 4-tert-butyl-2,6-diarylaniline in 77-86 and
77-94% yields,9 respectively. The reactions of 2-tert-
butyl-4,6-diarylanilines or 4-tert-butyl-2,6-diarylanilines
with arenesulfenyl chlorides in dry ether in the presence
of Et3N gave 6 and 7 in 16-50 and 11-72% yields,
respectively, after chromatographic separation and sub-
sequent crystallization. The crystals of 6 and 7 isolated
often showed a light green or purple color, even after
recrystallization. This was ascribed to the contamination
with 1 or 2 generated during recrystallization.
Gen er a tion a n d ESR Sp ectr a of 1 a n d 2 Ra d ica ls.
Aminyls 1 and 2 were generated by oxidation of 6 and 7
with PbO2 in benzene. When PbO2 was added to a stirred
solution of 6 or 7 in benzene, the solutions turned green,
blue, purple, or wine-red and gave an intense 1:1:1 triplet
ESR spectrum. In most cases the oxidation was fast and
the color change occurred immediately. However, in the
cases of Ar2 ) 2,4-Cl2C6H3 (6c, 6g, 7c, and 7i), it was
slow; in particular, 6c and 6g. Therefore, the color
changes occurred 1-3 min after addition of PbO2. The
reason why the oxidation is slow for such precursors is
not obvious. A typical ESR spectrum of 2c is shown in
Figure 1, and the ESR parameters are summarized in
Table 1.
The ESR spectra of most radicals are a simple 1:1:1
triplet split by the interaction with the 14N nucleus, with
a relatively large peak-to-peak width (∼0.13 mT) due to
the presence of numerous unresolved proton hyperfine
splittings. In the cases of 1g, 2d , and 2f the 1:1:1 triplet
spectra were further split by the interaction with aro-
matic protons, but their hyperfine resolutions were quite
poor. Only two exceptions are 2c and 2i. In their ESR
spectra the 1:1:1 triplet was further split with a relatively
good resolution by the interaction with the two anilino
meta and one arylthiyl ortho protons, as shown in Figure
1. The magnitudes of the proton hfs constants were
determined by computer simulation and assigned on the
basis of the ESR results of partly deuterated thioaminyls
8 and 9 as described below.
1
Furthermore, we tried to detect H ENDOR signals for
some aminyl radicals to ascertain the proton hfc con-
stants for 1 and 2. Among the aminyls examined, only
2b gave an ENDOR spectrum upon the measurements
at -75 °C using toluene, after 400 accumulations. As
shown in Figure 2, three pairs of signals were observed
from which the proton hfc constants of 0.123, 0.0776, and
0.0184 mT were determined. Based on the ESR results
of the partly deuterated aminyls, 0.123, 0.0776, and
0.0184 mT were, respectively, assigned to the anilino
meta, arylthiyl ortho, and arylthiyl meta protons.
(6) Teki, Y.; Itoh, K.; Miura, Y.; Ueno, S.; Kitagishi, Y. Mol. Cryst.
Liq. Cryst. 1995, 272, 23.
(7) Teki, Y.; Tajima, Y.; Itoh, K.; Ueno, S.; Kitagishi, Y.; Miura, Y.
Mol. Cryst. Liq. Cryst. 1996, 278, 301.
(8) Part of this work was reported as a preliminary communica-
tion: Miura, Y.; Fuchikami, T.; Momoki, M. Chem. Lett. 1994, 2127.
(9) Miura, Y.: Oka, H.; Momoki, M. Synyhesis 1995, 1419.
(10) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.

4302 J . Org. Chem., Vol. 61, No. 13, 1996
Miura et al.
F igu r e 2. 1H ENDOR spectrum of 2b recorded at -75 °C
using toluene as solvent.
Sch em e 2
Ch a r t 2
F igu r e 1. Experimental (a) and computer-simulated (b) ESR
spectra of 2c. The experimental ESR spectrum was obtained
at 20 °C using benzene as solvent.
Ta ble 1. ESR P a r a m eter s for 1 a n d 2 in Ben zen e a t 20
°Ca
radical
aN
g
1a
1b
1c
1d
1e
1f
0.932
0.937
0.948
0.936
0.933
0.937
0.953
0.936
0.932
0.936
0.932
0.934
0.933
0.931
0.930
0.936
0.921
2.0054
2.0055
2.0056
2.0054
2.0057
2.0056
2.0058
2.0055
2.0055
2.0056
2.0054
2.0058
2.0060
2.0057
2.0056
2.0057
2.0055
1g
2a
2bb
2cc,d
2d
2e
2f
anilino meta and arylthiyl ortho protons could be deter-
mined, their unequivocal assignments were impossible
unless either the anilino benzene ring or the arylthiyl
group was deuterated. We therefore prepared partly
deuterated thioaminyls, 8 and 9 (Chart 2). The corre-
sponding precursors 10 and 11 were prepared by the
reaction of 2,4-di(phenyl-d5)-6-tert-butylaniline or 2,6-di-
(phenyl-d5)-4-tert-butylaniline with arenesulfenyl chlo-
rides according to the same procedure as for the corre-
sponding nondeuterated compounds. The radicals were
generated by the same procedure as for nondeuterated
radicals. Typical ESR spectra are shown in Figures 3
and 4, and their ESR parameters are summarized in
Table 2.
As found in the Figure 3, the partly deuterated aminyls
gave a well resolved ESR spectra with a small line width.
However, the ESR spectra of 8a and 9a were considerably
broader than those of the other deuterated thioaminyls,
probably due to the presence of the unresolved nitro
group nitrogen hyperfine splitting.
2g
2h
2ic,e
2j
a
b
The hyperfine coupling constants are given in mT. The 1H
ENDOR spectrum of 2b in toluene obtained at -75 °C gave the
proton hfc constants of 0.123 (anilino meta), 0.0776 (arylthiyl
ortho), and 0.0184 mT (arylthiyl meta). c The proton hfc constants
d
were determined by computer simulation. The other hfc con-
stants determined: 0.125 mT (2H) (anilino meta); 0.096 mT (1H)
(arylthiyl ortho). e The other hfc constants determined: 0.123 mT
(2H) (anilino meta); 0.096 mT (1H) (arylthiyl ortho).
As found in Table 1, the aN values for 1 and 2 are
almost constant, regardless of the position of the tert-
butyl group and the electronic characters of the substit-
uent(s) on the 2,4- and 2,6-diphenyl and phenylthiyl
groups. This indicates that the relative importance of the
canonical structures A and B are not changed by the
electronic characters of the substituents and that the
conformation of 1 and 2 are not affected by the position
of the tert-butyl group.
Gen er a tion a n d ESR Sp ectr a of P a r tly Deu ter -
a ted Ra d ica ls 8 a n d 9. It is essential for the evaluation
of the spin density distribution to precisely determine the
proton hfc constants as well as the nitrogen hfc constants.
Although, for 2c and 2i the proton hfc constants for the
Interestingly, in the ESR spectrum of 9c satellite lines
due to 33S at natural abundance (0.75%), together with
satellite lines due to 13C at natural abundance (1.11%),
were observed in the wings where the spectra were
recorded at high gain (Figure 4). The assignments of
these satellites were made by the intensity ratio of the

Persistent Nitrogen-Centered Free Radicals
J . Org. Chem., Vol. 61, No. 13, 1996 4303
of the satellite lines due to 33S and 13C at natural
abundance to the parent spectrum are 0.19 and 0.56%,
respectively. On the other hand, the observed intensity
ratio of the 33S satellites to the parent spectrum was
0.13% and that of the 13C satellites was 0.40%, which
were close to the theoretical values.
Isola tion of 1 a n d 2. Aminyls 1 and 2 were quite
persistent, even in the presence of atmospheric oxygen.
The stabilities of 1 and 2 were evaluated by following
the radical concentrations by double-integration of ESR
spectra as a function of time. Although the measure-
ments were continued for 10 h at 20 °C under atmo-
spheric conditions, no reduction in the radical concen-
trations was observed. Furthermore, the aminyls showed
no tendency to dimerize, upon cooling to low tempera-
tures, exhibiting that the aminyls existed in the indi-
vidual radical form in solution. On the basis of these
observations we decided to try to isolate the aminyls.
Isolation of 1 and 2 was carried out as follows:
precursors 6 and 7 were treated with PbO2 in benzene,
and the solvent was removed by freeze-drying. The
resulting dark brown or green crystalline powder residue
was crystallized from hexane, hexane-ethyl acetate, or
ethanol. Among the 17 radicals prepared, 1b, 1f, 2b, 2h ,
and 2j were successfully isolated as black (dark brown)
needles or prisms in 33-56% yields. In the unsuccessful
cases, on the other hand, the PbO2 oxidation of the
precursors yielded large amounts of unknown polar
byproducts.11 Note that the radicals isolated have one
or more electron-withdrawing substituent on the 2,4,6-
triphenyl and arylthiyl groups. We explain this result
as follows: introduction of one or more π electron-
withdrawing substituent reduce the lone pair-lone pair
repulsion between N and S of the precursors, strengthen-
ing the N-S bond. Therefore, we understand that the
N-S bond cleavage of 6 and 7 upon oxidation leading to
the polar byproducts takes place to a much less extent
and the suppression of the N-S bond cleavage allows us
to isolate 1b, 1f, 2b, 2h , and 2j as pure radical crystals.
The isolated radical crystals were very stable and showed
no decomposition upon storage at 0 °C.
F igu r e 3. Experimental (a) and computer-simulated (b) ESR
spectra of 8b. The experimental spectrum was obtained at 20
°C using benzene as solvent.
X-r a y Cr ysta llogr a p h ic An a lysis. Upon recrystal-
lization from ethanol (1b) or hexane (2b), a sufficiently
large single crystal suitable for X-ray crystallographic
analysis was provided. Figures 5 and 6 show the ORTEP
drawings of the molecular structures of 1b and 2b. The
selected bond lengths, bond angles, and dihedral angles
are summarized in Table 3.
F igu r e 4. Experimental ESR spectrum of 9c recorded at 20
°C using benzene as solvent. Both wings are recorded at high
gain (100 times). Satellite lines due to 33S (a and b, MN ) +1,
MS ) +3/2; e and f, MN ) -1, MS ) -3/2) and 13C isotopes (c,
MN ) +1, MC ) +1/2; d, MN ) -1, MC ) -1/2) are found.
The X-ray crystallographic analysis of 1b shows the
following structural feature: the N and S atoms are
coplanar with the benzene ring A. This planar group
makes a dihedral angle of 21° with the benzene ring D.
The dihedral angle between the benzene rings A and C
is 34°, while that between the benzene rings A and B is
87°, indicating that there are serious steric congestions
around the N-S bond surrounded by a phenyl group and
a tert-butyl group. On the other hand, the X-ray results
of 2b give the following structural features. The N and
S atoms are coplanar with the benzene ring D (not A),
and this planar group makes a dihedral angle of 21° with
the benzene ring A. The benzene ring A makes a
dihedral angles 64° with the benzene ring B and 45° with
the benzene ring C. Therefore, the steric congestions
around the N-S bond surrounded by the two benzene
Ta ble 2. ESR P a r a m eter s for 8 a n d 9 in Ben zen e a t 20
°Ca
radical
aN
aother
g
8a b
8bb
9a b
9b
0.935
0.937
0.933
0.932
0.934
0.127 (2H),c 0.077 (2H)d
0.138 (2H),c 0.078 (3H)d
0.126 (2H),c 0.083 (2H)d
0.130 (2H),c 0.085 (2H)d
2.0055
2.0054
2.0055
2.0060
9c
0.130 (2H),c 0.51 (33S),e 1.01 (113C)f 2.0060
a
b
The hyperfine coupling constants are given in mT. The hfc
constants are determined by computer simulation. c The hfc
d
constants for the anilino meta protons. The hfc constants for the
arylthiyl ortho and para protons. e The value is determined by the
satellite lines due to 33S at natural abundance. f The value is
determined by the satellite lines due to 13C at the natural
abundance.
satellite lines to the parent spectrum. Since the 33S (I )
1
3/2) and 13C (I ) /2) isotope percents are 0.76 and 1.11,
(11) Miura, Y.; Kitagishi, Y.; Ueno, S. Bull. Chem. Soc. J pn. 1994,
67, 3282.
respectively, the theoretical values of the intensity ratios

4304 J . Org. Chem., Vol. 61, No. 13, 1996
Miura et al.
Ta ble 3. Selected Bon d Len gth s a n d An gles a n d
Dih ed r a l An gles for 1b a n d 2b
1b
Bond Lengths (Å)
Bond Angles (deg)
C1-N1
1.382 (5)
1.618 (3)
1.780 (4)
C2-C1-N1
125.9 (4)
114.2 (3)
123.4 (3)
100.3 (2)
N1-S1
C6-C1-N1
C1-N1-S1
N1-S1-C19
S1-C19
Dihedral Angles (deg)
-5.8 (5) N1-S1-C19-C20 -18.0 (4)
173.7 (3) N1-S1-C19-C24 161.5 (3)
S1-N1-C1-C2
S1-N1-C1-C6
C1-N1-S1-C19 -177.7 (3)
2b
Bond Lengths (Å)
Bond Angles (deg)
C1-N1
N1-S1
S1-C19
1.384 (3)
1.616 (2)
1.750 (3)
C2-C1-N1
C6-C1-N1
C1-N1-S1
N1-S1-C19
126.8(2)
115.4(2)
121.7(2)
101.1(1)
Dihedral Angles (deg)
S1-N1-C1-C2
S1-N1-C1-C6
C1-N1-S1-C19
22.4 (3) N1-S1-C19-C20
2.4(3)
-158.1 (2) N1-S1-C19-C24 -178.7(2)
175.3 (2)
F igu r e 5. ORTEP drawing of 1b.
F igu r e 7. UV-vis spectra of 1b and 6b in benzene: (s) 1b,
1.49 × 10-4 M; (- - - -) 6b, 1.49 × 10-4 M.
conclusion is in accordance with the ESR results that
show an extensive delocalization of the unpaired electron
spin to the anilino and phenylthiyl benzene rings.
UV-vis Sp ectr a . Aminyls 1 and 2 are characterized
by a green (1a -g), blue (2c, 2e, 2f, 2i), purple (2a , 2b,
2d , 2j), purplish blue (2g), or dark wine-red color (2h ).
The UV-vis spectra of 1b, together with the correspond-
ing precursor 6b are illustrated in Figure 7, and the UV-
vis absorption data for 1 and 2 are summarized in Table
4.
As shown by Figure 7, aminyl 1b shows the absorption
peaks attributable to the characteristic green color at 641
(ꢀ 5750), 512 (5600), and 424 nm (13400). The large ꢀ
values indicate that the absorptions are due to the π-π
transitions. On the other hand, 6b absorbs only at 355
nm (ꢀ 13000) in the UV-vis region. Likewise, the other
aminyls also show the absorption peaks corresponding
to the characteristic color in the visible region from which
their presence can be readily recognized.
Sp in Den sity Distr ibu tion . The spin density dis-
tribution in 2 was elucidated by the Hu¨ ckel and
McLachlan-Huckel molecular orbital (MO) calculations
using the following parameters: RN ) R + 0.6â, RS ) R
+ â, âCN ) 1.1â, âNS ) 0.7â, âCS ) 0.7â, λ ) 0.7. The set
of parameters have been always employed in our calcula-
tions on thioaminyl radicals.12 The Coulomb integrals
between C2-C7 and C6-C13 are changed as follows on
F igu r e 6. ORTEP drawing of 2b.
rings are serious, but less so than in 1b. On the basis of
the above X-ray results it is concluded that both radicals
have an approximately planar π-framework consisting
of the A and D benzene rings and N and S atoms.
However, the ortho-substituted phenyl group(s) are
twisted from the A benzene ring. Accordingly, the
unpaired electron can extensively delocalize from the
nitrogen to the anilino and phenylthiyl groups, but
cannot delocalize to the ortho benzene ring(s). This

Persistent Nitrogen-Centered Free Radicals
J . Org. Chem., Vol. 61, No. 13, 1996 4305
Ta ble 4. UV-Vis Sp ectr a l Da ta for 1 a n d 2 in Ben zen ea
Ta ble 6. Com p a r ison of ESR P a r a m eter s of 1-4a
lmax, nm (e, L mol-1 cm-1
)
radical
aN
aH
a33
g
b
radical
S
1a
1b
632, 521 (sh)
1 (and 8) 0.932-0.953 0.127-0.138
2 (and 9) 0.921-0.936 0.123-0.130
2.0054-2.0058
641 (5750), 512 (5600), 424 (13400),
370 (13600), 338 (sh, 11100)
645, 530 (sh)
633, 528 (sh)
638, 525 (sh)
647 (6440), 503 (sh, 5740),
428 (16100), 375 (16900)
652, 530 (sh)
0.51 2.0055-2.0060
3
4
5
0.890-0.896 0.133 -0.134 0.51 2.0054-2.0059
1c
1d
1e
1f
1.230
0.959
2.0066
2.0059
0.126
a
b
The hyperfine coupling constants are given in mT. The value
for the anilino meta protons.
1g
2a
2b
hand, the delocalization of the unpaired electron spin
onto the 2- and 6-phenyl groups is negligibly small due
to their twisting.
579, 501
583 (6000), 492 (9690),
387 (12500), 309 (11300)
593, 527 (sh)
580, 518 (sh)
594, 520 (sh)
2c
2d
2e
2f
2g
2h
The spin density distribution in 1 was also elucidated.
As shown by the ESR results of the aminyls shown in
Tables 1 and 2, the aN and aH values for 1 and 8 are very
similar to those for 2 and 9. Therefore, it can be
concluded that the spin density distributions in 1 and 2
are very similar to each other, and this was supported
by the McLachlan-Hu¨ckel MO calculations of 1 and the
crystallographic results which show a similar conforma-
tion for 1 and 2.
595, 522 (sh)
583, 502 (sh), 366
594 (5590), 485 (8130),
387 (12000), 306 (10700)
599, 525 (sh), 374
584 (6440), 522 (sh, 3530),
373 (13100)
2i
2j
a
For the isolated radicals, the ꢀ values are given in parentheses.
Com p a r ison of Hyp er fin e Cou p lin g P a r a m eter s.
Aminyls 1 and 2 are structurally close to 3, 4, and 5.
Their ESR parameters are compared in Table 6. It was
previously reported that, although unsubstituted 5 was
quite unstable and its isolation was impossible,13 aminyls
3 and 4 were quite stable and could be isolated as radical
crystals.14,15 Among the isolable aminyls 1, 2, 3, and 4,
only 4 reacts with oxygen to decompose to nonradical
compounds.14 This oxygen-sensitive property of 4 was
ascribed to its twisted conformation clarified by the X-ray
crystallographic analysis showing that the anilino group
make a dihedral angle of 91° for the planar group
consisting the N atom and phenylthiyl group. Therefore,
an electronic stabilization by the anilino group cannot
be expected. On the other hand, 1, 2, and 3 adopt a
nearly planar conformation, as shown by their X-ray
crystallographic analyses. Accordingly, the ESR param-
eters (a and g) for 1, 2, and 3 are very similar to each
other and also similar to those for 5. However, their ESR
parameters are quite different from those of 4 adopting
a twisted conformation.
Con clu sion s. Thioaminyl radicals 1 and 2 were
generated by PbO2 oxidation of the corresponding precur-
sors. The ESR studies showed they are quite persistent
even in the presence of oxygen and exist in the individual
radical form. Isolation of the aminyls was attempted and
five radicals were obtained as pure radical crystals. The
X-ray crystallographic analyses showed that both 1 and
2 adopt a similar planar conformation, in accordance with
the ESR results showing that the unpaired electron is
extensively delocalized from the nitrogen to the anilino
and arylthiyl groups.
Ta ble 5. Exp er im en ta l a n d Ca lcu la ted Hyp er fin e
Cou p lin g Con sta n ts for 2
position obsd hfc consta calcd spin density calcd hfc consta,b
N
S
1
2
3
4
5
6
7
0.932 (N)c
0.51 (33S)d
0.495
0.203
1.09 (N)
0.467 (S)
-0.042
0.119
-0.029
0.111
0.123 (H)c
0.078 (H)
-0.029
0.116
-0.001
0.001
-0.000
0.001
8, 12
9, 11
10
13
-0.003
0.007
-0.002
0.006
14, 18
15, 17
16
19
-0.012
0.024
-0.008
0.022
20, 24
21, 23
22
0.0776 (H)c
0.0184 (H)c
-0.065 (H)
0.022 (H)
a
b
Hyperfine coupling constants are given in mT. Derived using
The magnetic susceptibility measurements for the
isolated thioaminyls are in progress and the results will
be published elsewhere.
equation, aX ) QXFX, where QH ) -2.7, QN ) 2.2, Q33 ) 2.3 mT.12
S
c The values for 2b determined by 1H ENDOR. The value for 9c.
d
Exp er im en ta l Section
the basis of the X-ray results: âC2-C7 ) (cos2 64°)â )
0.192â, âC6-C13 ) (cos2 45°)â ) 0.500â. As found in Table
5, the calculations agree well with the experimental data,
predicting that there is an extensive delocalization of the
unpaired electron spin onto the anilino and phenylthiyl
groups, in accordance with the ESR results. On the other
Melting points were determined on a Yanagimoto micro
melting point apparatus and are uncorrected. The IR, UV-
visible, and 1H NMR spectra were recorded as previously
reported.15
(13) Miura, Y.; Kinoshita, M. Bull. Chem. Soc. J pn. 1977, 50, 1142.
(14) Miura, Y.; Yamamoto, A.; Katsura, Y.; Kinoshita, M.; Sato, S.;
Tamura, C., J . Org. Chem. 1982, 47, 2618.
(12) Miura, Y.; Asada, H.; Kinoshita, M.; Ohta, K. J . Phys. Chem.
1983, 87, 3450.
(15) Miura, Y.; Tanaka, A.; Hirotsu, K. J . Org. Chem. 1991, 56, 6638.

4306 J . Org. Chem., Vol. 61, No. 13, 1996
Miura et al.
4-Chloro-, 4-bromo-, 2,4-dichloro-, 3,5-dichloro-, 3-nitro-, and
4-nitrobenzenesulfenyl chlorides were obtained by the usual
method.16,17 The preparation of 4-bromobenzenesulfenyl-d4
chloride is described in our previous report.15 Phenylboronic-
d5 acid was obtained by the reaction of phenylmagnesium-d5
bromide with trimethoxyboron, followed by hydrolysis, accord-
ing to the procedure for the corresponding nonlabeled com-
pound.
2-tert-Butyl-4,6-diphenylaniline and 4-tert-butyl-2,6-diphen-
ylaniline were obtained by the Pd-catalyzed cross coupling
reaction (Suzuki reaction) of 2-tert-butyl-4,6-dibromoaniline or
4-tert-butyl-2,6-dibromoaniline with phenylboronic acid ac-
cording to our previously reported method.9
4-ter t-Bu tyl-2,6-bis(4-ch lor oph en yl)an ilin e. By the same
procedure as for 4-tert-butyl-2,6-diphenylaniline, 4-tert-butyl-
2,6-dibromoaniline (5.93 g, 19.3 mmol) was treated with 9.05
g (57.9mmol) of 4-chlorophenylboronic acid in the presence of
2.68 g (2.32 mmol) of (PPh3)4Pd and 16.4 g of Na2CO3 in a
benzene (200)-ethanol (40)-water (75 mL) mixed solvent at
the reflux temperature for 24 h under nitrogen. After the
usual workup, the reaction mixture was chromatographed on
silica gel (Wako gel C200) with 1:1 benzene-hexane as eluant.
Crystallization from hexane gave colorless needles with mp
189-191 °C in 77% yield: 1H NMR (CDCl3) δ 1.32 (s, 9 H),
3.66 (s, 2 H), 7.12 (s, 2 H), 7.43 (d, J ) 8.6 Hz, 4 H), 7.45 (d,
J ) 8.6 Hz, 4 H). Anal. Calcd for C22H21Cl2N: C, 71.35; H,
5.72; N, 3.78. Found: C, 71.30; H, 5.70; N, 3.70.
2-ter t-Bu tyl-4,6-bis(4-ch lor oph en yl)an ilin e. By the same
procedure as for 2-tert-butyl-4,6-diphenylaniline, 2-tert-butyl-
4,6-dibromoaniline (5.19 g, 16.9 mmol) was treated with 7.93
g (50.7 mmnol) of 4-chlorophenylboronic acid in the presence
of 2.34 g (2.02 mmol) of (PPh3)4Pd and 14.3 g of Na2CO3 in a
benzene (170)-ethanol (35)-water (70 mL) mixed solvent at
the reflux temperature for 24 h under nitrogen. After the
usual workup, the reaction mixture was chromatograph on
silica gel with 1:1 benzene-hexane as eluant. Crystallization
from hexane-benzene gave colorless needles with mp 145-
146 °C in 77 % yield (4.80 g, 13.0 mmol): 1H NMR (CDCl3) δ
1.50 (s, 9 H), 4.01 (s, 2 H), 7.16-7.48 (m, 10 H). Anal. Calcd
for C22H21Cl2N: C, 71.35; H, 5.72; N, 3.78. Found: C, 71.25;
H, 5.64; N, 3.84.
Gen er a l P r oced u r e for P r ep a r a tion of N-(Ar ylth io)-
2-ter t-bu tyl-4,6-d ia r yla n ilin es (6) a n d N-(Ar ylth io)-4-ter t-
bu tyl-2,6-d ia r yla n ilin es (7). To a stirred solution of 2.00 g
(6.64 mmol) of 2-tert-butyl-4,6-diarylaniline (or 4-tert-butyl-
2,6-diarylaniline) and 1.46 g (14.4 mmol) of triethylamine in
200 mL of dry ether was added dropwise at 0 °C a solution of
10.0 mmol of arenesulfenyl chloride in 50 mL of dry ether.
After the addition was completed, the mixture (sometime
colored) was continued to stir for 2 h at 0 °C. After filtration,
the filtrate was evaporated under reduced pressure, and the
residue was chromatographed on alumina (Merck, aluminium
oxide 90) using 2:1 (6f), 1:1 (6a , 6b, 6e, 7a , 7b, 7g, 7h ), 1:3
(7c, 7d , 7e, 7f), 1:5 (6c, 6d , 6g, 7j), 1:8 benzene-hexane (7i)
as eluant to give a pure solid or a solid containing small
amounts of diaryl disulfide and/or the starting aniline. Crys-
tallization from the appropriate solvent gave pure compounds.
N -[(3-Nit r op h e n yl)t h io]-2-t er t -b u t yl-4,6-d ip h e n yl-
a n ilin e (6a ): yellowish green plates (ethanol); mp 138-139
°C; yield 34% (1.04 g, 2.28 mmol); IR (KBr) 3390 (NH), 2950
cm-1 (t-Bu); 1NMR (CDCl3) δ 1.61 (s, 9 H), 5.46 (s, 1 H), 6.76-
7.83 (m, 16 H). Anal. Calcd for C28H26N2O2S: C, 73.98; H,
5.76; N, 6.16. Found: C, 74.21; H, 5.82; N, 6.44.
18% (0.58 g, 1.21 mmol); IR (KBr) 3380 (NH), 2950 cm-1 (t-
Bu); 1H NMR (CDCl3) δ 1.59 (s, 9 H), 5.28 (s, 1 H), 6.93-7.58
(m, 15 H). Anal. Calcd for C28H25Cl2NS: C, 70.23; H, 5.27;
N, 2.93. Found: C, 70.36; H, 5.39; N, 3.18.
N-[(3,5-Dich lor op h en yl)th io]-2-ter t-bu tyl-4,6-d ip h en yl-
a n ilin e (6d ): light green plates (ethanol); mp 143-145 °C;
yield 26% (0.82 g, 1.71 mmol); IR (KBr) 3400 (NH), 2950 cm-1
1
(t-Bu); H NMR (CDCl3) δ 1.58 (s, 9 H), 5.39 (s, 1 H), 6.74-
7.57 (m, 15 H). Anal. Calcd for C28H25Cl2NS: C, 70.23; H,
5.27; N, 2.93. Found: C, 70.44; H, 5.40; N, 3.22.
N-[(3-Nit r op h en yl)t h io]-2-ter t-b u t yl-4,6-b is(4-ch lor o-
p h en yl)a n ilin e (6e): light green prisms (ethanol); mp 132-
134 °C; yield 23% (0.80 g, 1.53 mmol); IR (KBr) 3380 (NH),
1
2950 cm-1 (t-Bu); H NMR (CDCl3) δ 1.60 (s, 9 H), 5.53 (s, 1
H), 6.84-7.94 (m, 14 H). Anal. Calcd for C28H24Cl2N2O2S: C,
64.24; H, 4.62; N, 5.35. Found: C, 64.37; H, 4.64; N, 5.34.
N-[(4-Nit r op h en yl)t h io]-2-ter t-b u t yl-4,6-b is(4-ch lor o-
p h en yl)a n ilin e (6f): yellow needles (ethanol); mp 171-173
°C; yield 50% (1.74 g, 3.32 mmol); IR (KBr) 3400 (NH), 2950
cm-1
(t-Bu); 1H NMR (CDCl3) δ 1.60 (s, 9 H), 5.47 (s, 1 H),
6.90 (d, J ) 8.5 Hz, 2 H), 7.02 (d, J ) 9.0 Hz, 2 H), 7.14 (d, J
) 9.0 Hz, 2 H), 7.21 (d, J ) 2.2 Hz, 1 H), 7.38 (d, J ) 8.5 Hz,
2 H), 7.48 (d, J ) 8.5 Hz, 2 H), 7.55 (d ) 2.2 Hz, 1 H), 7.98 (d,
J ) 8.5 Hz, 2 H). Anal. Calcd for C28H24Cl2N2O2S: C, 64.24;
H, 4.62; N, 5.35. Found: C, 64.40; H, 4.70; N, 5.36.
N-[(2,4-Dich lor oph en yl)th io]-2-ter t-bu tyl-4,6-bis(4-ch lo-
r op h en yl)a n ilin e (6g): colorless prisms (ethanol); mp 152-
153 °C; yield 16% (0.57 g, 1.04 mmol); IR (KBr) 3420 (NH),
1
2950 cm-1 (t-Bu); H NMR (CDCl3) δ 1.58 (s, 9 H), 5.31 (s, 1
H), 6.94-7.53 (m, 13 H). Anal. Calcd for C28H23Cl4NS: C,
61.44; H, 4.23; N, 2.56. Found: C, 61.73; H, 4.25; N, 2.61.
N -[(3-Nit r op h e n yl)t h io]-4-t er t -b u t yl-2,6-d ip h e n yl-
a n ilin e (7a ): brilliant yellow plates (ethanol); mp 162-163
°C; yield 36% (1.10 g, 2.42 mmol); IR (KBr) 3300 (NH), 2950
cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.32 (s, 9 H), 5.27 (s, 1 H),
7.03-7.81 (m, 16 H). Anal. Calcd for C28H26N2O2S: C, 73.98;
H, 5.77; N, 6.16. Found: C, 73.71; H, 5.73; N, 6.32.
N -[(4-Nit r op h e n yl)t h io]-4-t er t -b u t yl-2,6-d ip h e n yl-
a n ilin e (7b): brilliant yellow plates (ethanol); mp 146-148
°C; yield 43% (1.29 g, 2.84 mmol); IR (KBr) 3300 (NH), 2950
cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.32 (s, 9 H), 5.22 (s, 1 H),
6.85 (d, J ) 8.8 Hz, 2 H), 7.21-7.42 (m, 12 H), 7.85 (d, J ) 8.8
Hz, 2 H). Anal. Calcd for C28H26N2O2S: C, 73.98; H, 5.77; N,
6.16. Found: C, 74.24; H, 5.99; N, 6.26.
N-[(2,4-Dich lor op h en yl)th io]-4-ter t-bu tyl-2,6-d ip h en yl-
a n ilin e (7c): colorless needles (ethanol); mp 131-132 °C; yield
30% (0.96 g, 2.01 mmol); IR (KBr) 3300 (NH), 2950 cm-1 (t-
1
Bu); H NMR (CDCl3) δ 1.32 (s, 9 H), 5.10 (s, 1 H), 6.87 (d, J
) 8.3 Hz, 1 H), 6.92 (dd, J ) 8.3 and 1.9 Hz, 1 H), 7.04 (d, J
) 1.9 Hz, 1 H), 7.18 (s, 2 H), 7.23-7.39 (m, 10 H). Anal. Calcd
for C28H25Cl2NS: C, 70.28; H, 5.27; N, 2.93. Found: C, 70.14;
H, 5.38; N, 2.99.
N-[(3,5-Dich lor op h en yl)th io]-4-ter t-bu tyl-2,6-d ip h en yl-
a n ilin e (7d ): colorless prisms (ethanol); mp 122-123 °C; yield
25% (0.80 g, 1.64 mmol); IR (KBr) 3330 (NH), 2950 cm-1 (t-
1
Bu); H NMR (CDCl3) δ 1.32 (s, 9 H), 5.23 (s, 1 H), 6.61 (d, J
) 1.5 Hz, 2 H), 6.94 (t, J ) 1.5 Hz, 1 H), 7.19 (s, 2 H), 7.25-
7.40 (m, 10 H). Anal. Calcd for C28H25Cl2NS: C, 70.28; H,
5.27; N, 2.93. Found: C, 70.05; H, 5.43; N, 3.16.
N -[(4-Ch lor op h e n yl)t h io]-4-t er t -b u t yl-2,6-d ip h e n yl-
a n ilin e (7e): light green needles (ethanol); mp 103-104 °C;
yield 16% (0.460 g, 1.04 mmol); IR ((KBr) 3280 (NH), 2950
cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.31 (s, 9 H), 5.27 (s, 1 H),
6.69 (d, J ) 8.5 Hz, 2 H), 7.00 (d, J ) 8.5 Hz, 2 H), 7.17 (s, 2
H), 7.25-7.37 (m, 10 H). Anal. Calcd for C28H26ClNS: C,
75.74; H, 5.90; N, 3.16. Found: C, 75.51; H, 6.02; N, 2.92.
N -[(4-Br om op h e n yl)t h io]-4-t er t -b u t yl-2,6-d ip h e n yl-
a n ilin e (7f): light green needles (ethanol); mp 126-127 °C;
yield 11% (0.37 g, 0.76 mmol); IR (KBr) 3280 (NH), 2950 cm-1
N -[(4-Nit r op h e n yl)t h io]-2-t er t -b u t yl-4,6-d ip h e n yl-
a n ilin e (6b): brilliant yellow plates (ethanol); mp 158-160
°C; yield 45% (1.36 g, 2.99 mmol); IR (KBr) 3400 (NH), 2950
cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.60 (s, 9 H), 5.41 (s, 1 H),
7.03 (d, J ) 8.8 Hz, 2 H), 6.84-7.60 (m, 12 H), 7.91 (d, J ) 8.8
Hz, 2H). Anal. Calcd for C28H26N2O2S: C, 73.98; H, 5.76; N,
6.16. Found: C, 74.05; H, 5.87; N, 6.40.
1
(t-Bu); H NMR (CDCl3) δ 1.31 (s, 9 H), 5.27 (s, 1 H), 6.63 (d,
J ) 8.3 Hz, 2 H), 7.14 (d, J ) 8.3 Hz, 2 H), 7.17 (s, 2 H), 7.29-
7.37 (m, 10 H). Anal. Calcd for C28H26BrNS: C, 68.84; H,
5.37; N, 2.87. Found: C, 68.65; H, 5.43; N, 2.78.
N-[(2,4-Dich lor op h en yl)th io]-2-ter t-bu tyl-4,6-d ip h en yl-
a n ilin e (6c): colorless prisms (ethanol); mp 154-156 °C; yield
N-[(3-Nit r op h en yl)t h io]-4-ter t-b u t yl-2,6-b is(4-ch lor o-
p h en yl)a n ilin e (7g): light greenish yellow needles (ethanol);
mp 150-152 °C; yield 35% (1.22 g, 2.33 mmol); IR (KBr) 3320
(16) Miura, Y.; Makita, N.; Kinoshita, M. Bull. Chem. Soc. J pn.
1977, 50, 482.
(17) Ku¨hle, E. Synthesis 1970, 561 and 1971, 617.

Persistent Nitrogen-Centered Free Radicals
J . Org. Chem., Vol. 61, No. 13, 1996 4307
(NH), 2950 cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.31 (s, 9 H), 5.15
24% (0.36 g, 0.77 mmol); IR (KBr) 3350 (NH), 2950 (t-Bu), 2240
cm-1 (CD); 1H NMR (CDCl3) δ 1.60 (s, 9 H), 5.41 (s, 1 H), 7.03
(d, J ) 9.0 Hz, 2 H), 7.30 (d, J ) 2.2 Hz, 1 H), 7.60 (d, J ) 2.2
Hz, 1 H), 7.91 (d, J ) 9.0 Hz, 2 H). Anal. Calcd for
C28H16D10N2O2S: C, 72.38; H, 5.64; N, 6.03. Found: C, 72.60;
H, 5.85; N, 6.04.
N-[(3,5-Dich lor oph en yl)th io]-2-ter t-bu tyl-4,6-di(ph en yl-
d 5)a n ilin e (10b): light green plates; mp 137 -138 °C; yield
34% (0.53 g, 1.08 mmol); IR (KBr) 3420 (NH), 2950 (t-Bu), 2250
cm-1 (CD); 1H NMR (CDCl3) δ 1.58 (s, 9 H), 5.39 (s, 1 H), 6.74
(s, 2 H), 6.95 (s, 1 H), 7.29 (s, 1 H), 7.57 (s, 1 H). Anal. Calcd
for C28H15D10NSCl2: C, 68.84; H, 5.16; N, 2.87. Found: C,
68.66; H, 5.29; N, 2.82.
N-[(4-Nitr op h en yl)th io]-4-ter t-bu tyl-2,6-d i(p h en yl-d 5)-
a n ilin e (11a ): brilliant yellow plates; mp 142-143 °C; yield
75% (1.11 g, 2.40 mmol); IR (KBr) 3300 (NH), 2950 (t-Bu); 2250
cm-1 (CD); 1H NMR (CDCl3) δ 1.32 (s, 9 H), 5.23 (s, 1 H), 6.85
(d, J ) 8.8 Hz, 2 H), 7.21 (s, 2 H), 7.85 (d, J ) 8.8 Hz, 2 H).
Anal. Calcd for C28H16D10N2O2S: C, 72.38; H, 5.64; N, 6.03.
Found: C, 72.20; H, 5.78; N, 5.96.
(s, 1 H), 7.06-7.92 (m, 14 H). Anal. Calcd for C28H24
-
Cl2N2O2S: C, 64.24; H, 4.62; N, 5.35. Found: C, 64.30; H, 4.67;
N, 5.40.
N-[(4-Nit r op h en yl)t h io]-4-ter t-b u t yl-2,6-b is(4-ch lor o-
p h en yl)a n ilin e (7h ): light yellow plates (ethanol-benzene);
mp 189-191 °C; yield 72% (2.50 g, 4.78 mmol); IR (KBr) 3330
(NH), 2950 cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.32 (s, 9 H), 5.10
(s, 1 H), 6.89 (d, J ) 8.8 Hz, 2 H), 7.17 (s, 2 H), 7.26 (d, J )
8.3 Hz, 4 H), 7.30 (d, J ) 8.3 Hz, 4 H), 7.93 (d, J ) 8.8 Hz, 2
H). Anal. Calcd for C28H24Cl2N2O2S: C, 64.24; H, 4.62; N,
5.35. Found: C, 64.33; H, 4.62; N, 5.37.
N-[(2,4-Dich lor oph en yl)th io]-4-ter t-bu tyl-2,6-bis(4-ch lo-
r op h en yl)a n ilin e (7i): colorless needles (ethanol-benzene);
mp 173-175 °C; yield 15% (0.53 g, 0.97 mmol); IR (KBr) 3320
1
(NH), 2950 cm-1 (t-Bu); H NMR (CDCl3) δ 1.31(s, 9 H), 4.95
(s, 1 H), 6.88 (d, J ) 8.5 Hz, 1 H), 6.98 (dd, J ) 8.5 and 2.2
Hz, 1 H), 7.12 (d, J ) 2.2 Hz, 1 H), 7.14 (s, 2 H), 7.27 (s, 8 H).
Anal. Calcd for C28H23Cl4NS: C, 61.44; H, 4.24; N, 2.56.
Found: 61.69; H, 4.29; N, 2.63.
N-[(4-Br om op h en yl)t h io]-4-ter t-b u t yl-2,6-d i(p h en yl-
d 5)a n ilin e (11b): light green needles; mp 118-121 °C; yield
23% (0.37 g, 0.73 mmol); IR (KBr) 3270 (NH), 2950 (t-Bu), 2250
cm-1 (CD); 1H NMR (CDCl3) δ 1.31 (s, 9 H), 5.27 (s, 1 H), 6.62
(d, J ) 8.3 Hz, 2 H), 7.14 (d, J ) 8.3 Hz, 2 H), 7.17 (s, 2 H).
Anal. Calcd for C28H16BrD10NS: C, 67.46; H, 5.26; N, 2.81.
Found: C, 67.79; H, 5.17; N, 2.74.
N-[(4-Br om op h en yl-d 5)th io]-4-ter t-bu tyl-2,6-d i(p h en yl-
d 5)a n ilin e (11c): light green needles; mp 119-122 °C; yield
16% (0.26 g, 0.51 mmol); IR (KBr) 3300 (NH), 2950 (t-Bu), 2280
cm-1 (CD); 1H NMR (CDCl3) δ 1.31 (s, 9 H), 5.26 (s, 1 H), 7.17
(s, 2 H). Anal. Calcd for C28H12BrD14NS: C, 66.92; H, 5.22;
N, 2.79. Found: C, 66.91; H, 5.31; N, 2.72.
Isola tion of Am in yl Ra d ica ls. Precursor 5 or 6 (100 mg)
was dissolved in 20 mL of benzene with stirring. After 1.0 g
of K2CO3 was added, PbO2 (1.0 g) was added to the vigorously
stirred benzene solution in some portions during 2 min. After
completion of the addition, stirring was continued for an
additional 0.5 min, and the strongly colored mixture was
filtered. The solvent was removed by freeze-drying, and the
resulting strongly colored crystalline residue was recrystallized
from hexane (2b, 2j), ethanol (1b, 1f), or hexane-ethyl acetate
(2h ).
N-[(3,5-Dich lor oph en yl)th io]-4-ter t-bu tyl-2,6-bis(4-ch lo-
r op h en yl)a n ilin e (7j): light green needles (ethanol); mp
169-172 °C; yield 50% (1.81 g, 3.31 mmol); IR (KBr) 3280
(NH), 2950 cm-1 (t-Bu); 1H NMR (CDCl3) δ 1.31 (s, 9 H), 5.08
(s, 1 H), 6.64 (s, 1 H), 7.03 (s, 2 H), 7.15 (s, 2 H), 7.30 (d, J )
8.8 Hz, 4 H), 7.31 (d, J ) 8.8 Hz, 4 H). Anal. Calcd for C28H23
-
Cl4NS: C, 61.44; H, 4.24; N, 2.56. Found: 61.61; H, 4.25; N,
2.69.
2-ter t-Bu tyl-4,6-d i(p h en yl-d 5)a n ilin e. By the same pro-
cedure as for 2-tert-butyl-4,6-diphenylaniline, 6.05 g (19.7
mmol) of 2-tert-butyl-4,6-dibromoaniline was treated with 7.50
g (59.1 mmol) of phenylboronic-d5 acid in the presence of 2.73
g (2.36 mmol) of (PPh3)4Pd and 16.7 g of Na2CO3 in a mixed
solvent of 200 mL of benzene, 40 mL of ethanol, and 79 mL of
water at the reflux temperature for 24 h under nitrogen. After
the usual workup, the reaction mixture was chromatographed
on silica gel with 5:1 benzene-hexane as eluant. Crystalliza-
tion from hexane gave colorless needles with mp 98-100 °C
in 80% yield (4.88 g, 15.7 mmol): IR (KBr) 3460 and 3360
1
(NH2), 2950 (t-Bu), 2250 cm-1 (CD); H NMR (CDCl3) δ 1.52
(s, 9 H), 4.02 (s, 2 H), 7.26 (d, J ) 2.2 Hz, 1H), 7.53 (d, J ) 2.2
Hz, 1 H). Anal. Calcd for C22H13D10N: C, 84.84; H, 7.44; N,
4.50. Found: C, 84.75; H, 7.68; N, 4.53.
N-[(4-Nitr op h en yl)th io]-2-ter t-bu tyl-4,6-d ip h en ylp h en -
yla m in yl (1b): black needles; mp 139-141 °C; yield 56% (56.1
mg, 0.12 mmol); IR (KBr) 2950, 1590, 1570, 1510, 1440, 1330,
1260, 1215, 1180, 1110, 1070, 1050, 1020, 890, 870, 860, 820,
. Anal. Calcd for
C28H25N2O2S: C, 74.14; H, 5.56; N, 6.18. Found: C, 74.20; H,
5.81; N, 6.12.
4-ter t-Bu tyl-2,6-d i(p h en yl-d 5)a n ilin e. By the same pro-
cedure as for 4-tert-butyl-2,6-diphenylaniline, 4.61 g (15.0
mmol) of 4-tert-butyl-2,6-dibromoaniline was treated with 5.08
g (45 mmol) of phenylboronic-d5 acid in the presence of 2.73 g
(1.80 mmol) of (PPh3)4Pd and 12.7 g of Na2CO3 in a benzene
(150)-ethanol (30)-water (60 mL) mixed solvent at the reflux
temperature for 24 h under nitrogen. After the usual workup,
the reaction mixture was chromatographed on silica gel with
5:1 benzene-hexane as eluant. Crystallization from hexane
gave colorless needles with mp 90-93 °C in 83% yield (3.88 g,
12.5 mmol): IR (KBr) 3410 and 3310 (NH2), 2950 (t-Bu), 2250
790, 760, 740, 710, 700, 680, 650 cm-1
N-[(4-Nit r op h en yl)t h io]-2-ter t-b u t yl-4,6-b is(4-ch lor o-
p h en yl)p h en yla m in yl (1f): black needles; mp 161-163 °C;
yield 48% (48 mg, 0.091 mmol); IR (KBr) 2950, 1590, 1580,
1510, 1485, 1330, 1170, 1090, 1070, 1010, 850, 840, 820, 740
cm-1
1
cm-1 (CD); H NMR (CDCl3) δ 1.33 (s, 9 H), 3.7 (br s, 2 H),
. Anal. Calcd for C28H23Cl2N2O2S: C, 64.37; H, 4.44; N,
5.36. Found: C, 64.40 ; H, 4.43; N, 5.33.
7.16 (s, 2 H). Anal. Calcd for C22H13D10N: C, 84.84; H, 7.44;
N, 4.50. Found: C, 84.70; H, 7.57; N, 4.78.
N-[(4-Nitr op h en yl)th io]-4-ter t-bu tyl-2,6-d ip h en ylp h en -
yla m in yl (2b): black prisms; mp 140-142 °C; yield 43% (43
mg, 0.094 mmol); IR (KBr) 2950, 1570, 1510, 1330, 1240, 1105,
1075, 890, 855, 785, 775, 755, 740, 705 cm-1. Anal. Calcd for
C28H25N2O2S: C, 74.14; H, 5.56; N, 6.18. Found: C, 73.87; H,
5.41; N, 6.23.
Gen er a l P r oced u r e for P r ep a r a tion of N-(Ar ylth io)-
2-ter t-bu t yl-4,6-d i(p h en yl-d 5)a n ilin es (10) a n d N-(Ar yl-
th io)-4-ter t-bu tyl-2,6-d i(p h en yl-d 5)a n ilin es (11). Precur-
sors 10 and 11 were prepared by the same procedure as for 6
and 7. Thus, a solution of 4.82 mmol of arenesulfenyl chloride
in 30 mL of dry ether was added to a stirred solution of 1.00
g (3.21 mmol) of 2-tert-butyl-4,6-di(phenyl-d5)aniline [or 4-tert-
butyl-2,6-di(phenyl-d5)aniline] and 0.73 g (7.2 mmol) of tri-
ethylamine in 100 mL of dry ether at 0 °C. After the addition
was completed, the mixture (sometime colored) was continued
to stir for 2 h at 0 °C. After filtration, the filtrate was
evaporated under reduced pressure, and the residue was
chromatographed on alumina using 1:1 (10a , 11a ), 1:3 (11b,
11c), or 1:5 benzene-hexane (10b) as eluant to give a pure
solid or a solid containing small amounts of diaryl disulfide
and/or the starting aniline. Crystallization from ethanol gave
pure compounds.
N-[(4-Nit r op h en yl)t h io]-4-ter t-b u t yl-2,6-b is(4-ch lor o-
p h en yl)p h en yla m in yl (2h ): black prisms; mp 123-125 °C;
yield 47% (47 mg, 0.091 mmol); IR (KBr): 2950, 1590, 1570,
1520, 1490, 1340, 1250, 1110, 1090, 1020, 860, 830, 740 cm-1
.
Anal. Calcd for C28H23Cl2N2O2S: C, 64.37; H, 4.44; N, 5.36.
Found: C, 64.62; H, 4.53; N, 5.46.
N-[(3,5-Dich lor oph en yl)th io]-4-ter t-bu tyl-2,6-bis(4-ch lo-
r op h en yl)p h en yla m in yl (2j): dark brown needles; mp 138-
139 °C; yield 33% (33 mg, 0.060 mmol); IR (KBr) 2950, 1560,
1490, 1460, 1400, 1240, 1135, 1095, 1000, 830, 800, 735, 720,
660 cm-1
. Anal. Calcd for C28H22Cl4NS: C, 61.55; H, 4.06;
N, 2.56. Found: C, 61.80; H, 4.06; N, 2.88.
N-[(4-Nitr op h en yl)th io]-2-ter t-bu tyl-4,6-d i(p h en yl-d 5)-
a n ilin e (10a ): brilliant yellow plates; mp 158-160 °C; yield
ESR Mea su r em en ts. ESR spectra were measured on a
J EOL J ES-ME-3X or Bruker ESP300 spectrometer operating

4308 J . Org. Chem., Vol. 61, No. 13, 1996
Miura et al.
at X-band with 100 kHz field modulation. Hyperfine splitting
constants and g values were determined by the simulutaneous
measurements with a dilute Fremy's salt in a dilute K2CO3
aqueous solution (aN ) 1.309 mT, g ) 2.0057) as reference.
Estimated accuracies: (0.01 mT for aN and aH, (0.02 mT for
a33S and a13C, and (0.0001 for g.
397 variable parameters and converged with the unweighted
and weighted agreement factors of R ) 0.035 and Rw ) 0.034.
X-r a y Cr ysta llogr a p h ic An a lysis of 2b.21 A black pris-
matic crystal of C28H25N2O2S (M ) 453.58) having approximate
dimensions of 0.50 × 0.80 × 0.80 mm was mounted on a glass
fiber. All measurements were made on a Rigaku AFC7R
diffractometer with graphite monochromated Cu KR radiation
(λ ) 1.54178 Å). Monoclinic, space group P21/n, a ) 11.434-
(2), b ) 13.453(2), c ) 15.860(2), â ) 101.46(1)°, V ) 2390.9-
1H ENDOR Mea su r em en ts. 1H ENDOR measurements
were carried out at -75 °C on a Bruker (300/350) ENDOR
spectrometer equipped with a TM011 mode microwave cavity
operating at X-band using toluene as solvent.
(6) Å, Z ) 4, Dc ) 1.260 g cm-3
.
The data were collected at a temperature of 20 ( 1 °C using
the ω - 2θ scan technique to a 2θ value of 120.2°. The linear
absorption coefficient, µ, for Cu KR radiation is 14.2 cm-1. An
empirical absorption correction using the program DIFABS18
was applied which resulted in transmission factors ranging
from 0.82 to 1.26.
X-r a y Cr ysta llogr a p h ic An a lysis of 1b.21 A black needle
crystal of C28H25N2O2S (M ) 453.58) having approximate
dimensions of 0.20 × 0.20 × 0.20 mm was mounted on a glass
fiber. All measurements were made on a Rigaku AFC7R
diffractometer with graphite monochromated Cu KR radiation
(λ ) 1.54178 Å). Monoclinic, space group P21, a ) 14.095(5),
b ) 5.855(4), c ) 14.124(3) Å, â ) 90.92(2)°, V ) 1165.5(8) Å3,
The structure was solved by direct methods19 and expanded
using Fourier techniques.20 The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined isotro-
pically. Of the 3951 reflections collected, 3217 reflections with
I > 3.00σ(I) were observed. The final cycle of full-matrix least-
squares refinement was based on the observed reflections and
398 variable parameters and converged with the unweighted
and weighted agreement factors of R ) 0.054 and Rw ) 0.085.
Z ) 2, Dc ) 1.29 g cm-3
.
The data were collected at a temperature of 23 ( 1°C using
the ω - 2θ scan technique to a 2θ value of 113.6°. The linear
absorption coefficient, µ, for Cu KR radiation is 14.5 cm-1. An
empirical absorption correction using the program DIFABS18
was applied which resulted in transmission factors ranging
from 0.90 to 1.10.
The structure was solved by direct methods19 and expanded
using Fourier techniques.20 The non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined isotro-
pically. Of the 1838 reflections collected, 1658 reflections with
I > 3.00σ(I) were observed. The final cycle of full-matrix least-
squares refinement was based on the observed reflections and
Ack n ow led gm en t. We thank Prof. K. Hirotsu,
Osaka City University, for the variable suggestions on
the X-ray crystallographic analyses. This work was
financially supported (in part) by a Grant-in-Aid for
Scientific Research on Priority Area “Molecular Mag-
netism” (Area No. 228/06218226, 04242105) and Gen-
eral Scientific Research (No. 07454191) from the Min-
istry of Education, Science, Sports, and Culture, J apan.
(18) Crystal Structure Analysis Package, Molecular Structure
Corporation: 1985 and 1992.
(19) Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick,
G. M.; Kruger, C.; Goddard, R., Eds.; Oxford University Press: Cary,
NC, 1985, pp 175-189.
(20) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Boaman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system, Technical Report of the Crystallography
Laboratory, University of Nijmegen: 1992.
J O960347D
(21) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.