Interaction of 1,2,3-benzodithiazolyls (Herz radicals) with dioxygen

Article abstract of DOI:10.1070/MC2005v015n01ABEH001984

The interaction of 4,6-di-tert-butyl-1,2,3-benzodithiazolyl (Herz radical) 1 with O₂in a hydrocarbon solution leads to substituted N,N′-disulfinyl-2,2′-diaminodiphenyl disulfide 2, the radical decay kinetics corresponds to a self-termination re

Full text of DOI:10.1070/MC2005v015n01ABEH001984

, 2005, 15(1), 14–17
Interaction of 1,2,3-benzodithiazolyls (Herz radicals) with dioxygen
Alexander Yu. Makarov,a Stanislav N. Kim,b,c Nina P. Gritsan,*b,d Irina Yu. Bagryanskaya,a Yuri V. Gatilova and
Andrey V. Zibarev*a,d
a N. N. Vorozhtsov Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk,
Russian Federation. Fax: + 7 3832 30 9752; e-mail: zibarev@nioch.nsc.ru
b Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk,
Russian Federation. Fax: + 7 3832 30 7350; e-mail: gritsan@ns.kinetics.nsc.ru
c Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russian Federation
d Department of Physics, Novosibirsk State University, 630090 Novosibirsk, Russian Federation
DOI: 10.1070/MC2005v015n01ABEH001984
The interaction of 4,6-di-tert-butyl-1,2,3-benzodithiazolyl (Herz radical) 1 with O2 in a hydrocarbon solution leads to substituted
N,N'-disulfinyl-2,2'-diaminodiphenyl disulfide 2, the radical decay kinetics corresponds to a self-termination reaction with a rate
constant, which is a linear function of the concentration of dissolved O2.
The isomeric 1,2,3- and 1,3,2-benzodithiazolyl π-radicals are of
interest for contemporary materials science as potential building
blocks in the design and synthesis of molecular magnets or/and
molecular conductors.1,2 However, their instability towards O2,
especially in solution, represents an impediment to their applica-
tion. The inhibition of this process, based on an understanding
of its chemistry, is obviously necessary to achieve further progress
in the field. Although several research groups have observed
transformations of these radicals into diamagnetic species in
solution under contact with air,2–6 no products were identified.
We studied the reaction of 1,2,3-benzodithiazolyls (Herz
radicals) with O2 in order to isolate and identify the reaction
products and to elucidate the reaction mechanism. Sterically
hindered (i.e. kinetically stabilised) 4,6-di-tert-butyl-1,2,3-benzo-
dithiazolyl 1 (Scheme 1), previously characterised by ESR
spectroscopy,2–4 was chosen for the study.
(140–150 °C) of heterocycle 4 (i.e., a new methodology proposed
in refs. 5–8) were employed in the mechanistic studies.‡,§ In all
cases, the formation of 1 and its quantitative yield were assessed
†
Reaction of 4,6-di-tert-butyl-1,2,3-benzodithiazolyl 1 with dioxygen.
N,N'-Disulfinyl-2,2'-diamino-3,3',5,5'-tetra(tert-butyl)diphenyl disulfide
2. A mixture of 0.30 g (1 mmol) of salt 3§ and 0.18 g (0.5 mmol) of
Ph3Sb in 6 ml of benzene, which was degassed by three freeze–pump–
thaw cycles, was stirred under argon for a week at ambient temperature.
According to ESR measurements, conversion of 3 into 1 is quantitative
under these conditions. When the resulting dark brown-red solution was
exposed to dry air, its colour changed to orange-yellow. After pumping
off the solvent, the solid residue (0.50 g), consisted of a 1:1 molar
mixture of 2 and Ph3SbCl2 (1H NMR data), which corresponds to a
quantitative yield of 2. The crude product was recrystallised twice from
hexane. Compound 2 was isolated as orange-yellow crystals, 0.16 g
(60 %), mp 133–134 °C (lit.,12 134 °C). 1H NMR, d: 7.53, 7.39, 1.38,
1.24. 13C NMR, d: 149.8, 140.9, 137.7, 128.3, 128.1, 124.7, 35.7, 34.8,
31.0, 29.6. 15N NMR, d: 330.0. UV-VIS [heptane, lmax/nm (log e)]: 382
(3.56). MS, m/z: 564.1962 (M+; calc. for C28H40N2O2S4 564.1973).
X-ray structure data collected for 2 were in full agreement with
published data.12
Radical 1 was obtained by three different techniques (Scheme 1).
The reduction of Herz salt 3 with Ph3Sb was used in preparative
experiments designed to isolate the final products of interaction
between 1 and O2.† Photolysis (313 nm) and mild thermolysis
14 Mendeleev Commun. 2005

, 2005, 15(1), 14–17
by ESR spectroscopy. Experimental hfc constants are very close
to those reported previously2–4 and agree fairly well with the
data calculated at the B3LYP/6-311G** level of theory.‡
S
Ph3Sb
– Ph3SbCl2
S
Cl
Photolysis of (2–10)×10–4 M solutions of 4§ in hexane was performed
‡
N
in a quartz cuvette degassed by bubbling argon, as well as in an ESR
quartz tube fitted with a Teflon valve and degassed by three freeze–pump–
thaw cycles. The 313 nm line of a DRSh-500 high-pressure mercury
lamp equipped with a water filter and a combination of UVS-2 and ZhS-3
glass filters was used. The yields of 1 were quantitative. After photolysis,
solutions were saturated with dioxygen by the extensive bubbling of O2
or air for 3 min. The UV-VIS and ESR spectra were collected.
Thermolysis of a 10–3 M solution of 4 in squalane (2,6,10,15,19,25-
hexamethyltetracosane), degassed as described above, was performed
in the same type of ESR tubes. The sample was heated to 145 °C for
1 h, cooled to 20 °C, whereupon a reference ESR spectrum of 1 was
measured. The yield of 1 was 95 %.
S
3
S
SCl2
N
S
N
1
∆ or hv
S
N
O2
ESR spectra of radical 1 were recorded on a Bruker EMX spectrometer
(MW power of 0.64 mW, modulation frequency of 100 kHz, modulation
amplitude of 0.01 mT). The spectral integrations and simulations were
performed with the Winsim v1.0 program. The g-factor of 1 was measured
using DPPH as a standard. The yields of 1 were determined with an
accuracy of 10% by comparison of the radical spectral integrals with
the integrals of the spectrum of a single crystal of CuCl2·2H2O standard
containing a known amount of paramagnetic species.
4
S
S
N
S
N
S
Experimental (calculated by B3LYP/6-311G**, S2 = 0.767 and S2 =
= 0.750 after annihilation) hfc constants (G) and g-factor of 1: aN3 8.19
(6.26), aH5 0.71 (1.25), aH7 0.98 (1.50); 2.0077.
O
O
2
§
4,6-Di-tert-butyl-1,2,3-benzodithiazolium chloride 3 and 5,7-di-tert-
Scheme 1
butyl-1,3l4d2,2,4-benzodithiadiazine 4. 2,4-Di-tert-butylaniline was
converted under standard conditions13–15 into N-sulfinyl-2,4-di-tert-butyl-
aniline 9: orange oil, 78%, bp 123–125 °C/3 Torr. 1H NMR, d: 8.43,
7.37, 7.20, 1.44, 1.32. MS, m/z: 251 (M+; calc. for C14H21NOS 251).
Compound 9 was transformed into 1-(2,4-di-tert-butylphenyl)-3-tri-
methylsilyl-1,3-diaza-2-thiaallene 10 by reaction with LiN(SiMe3)2
(hexane, –30 °C; for typical protocols, see refs. 13–15). Compound 10:
The preparative experiments showed that, at room tempera-
ture in concentrated (~0.15 M) benzene solution, 1 reacts with
dissolved O2 to give N,N'-disulfinyl-2,2'-diaminodiphenyl di-
sulfide 2 (Scheme 1), whose structure was confirmed by X-ray
diffraction, in quantitative yield.† Thus, the reactivity of Herz
radicals towards O2 seems different from that of the related
4-aryl-1,2,3,5-dithiazolyl radicals, which are known to produce
1,5,2,4,6,8-dithiatetrazocines in contact with air.9
1
red oil, 72%, bp 135–136 °C/3 Torr. H NMR, d: 7.97, 7.41, 7.19, 1.52,
1.41, 0.29. UV-VIS [heptane, lmax/nm (log e)]: 363 (3.97). MS, m/z:
322.1898 (M+; calc. for C17H30N2SSi 322.1899).
The kinetics of decay of 1 was followed by UV-VIS
(Figures 1, 2) and ESR spectroscopy, which showed that the
reaction can be described as a second-order self-termination
reaction dR/dt = –kR2, where the time dependence of radical
concentration R is expressed by the equation R(t) = R0/(1 + kR0t).
The product kR0 in the denominator is equaled to a fitting
parameter a, which depends linearly on the initial radical con-
centration R0 (Figure 3), whilst the rate constant k is propor-
tional to the concentration of dissolved O2 (Figure 2). Solutions
saturated with O2 (concentration of 1.56×10–2 mol dm–3)10 or
air (O2 concentration 4.8 times lower) were used in all of the
experiments.
Under argon, solutions of 1.61 g (5 mmol) of 10 and 0.39 g (3.8 mmol)
of SCl2, each in 30 ml of CH2Cl2, were mixed by adding them to 150 ml
of boiling CH2Cl2 over a period of 1 h. After an additional 1 h, the reaction
mixture was cooled to 20 °C, filtered, the solvent was distilled off, and
the residue was fractionally sublimed in a vacuum and recrystallised
from hexane. Compound 4 was obtained as black crystals, 0.10 g (6%
according to SCl2), mp 64–65 °C. 1H NMR, d: 6.61, 5.61, 1.19, 1.13.
13C NMR, d: 156.1, 141.6, 135.9, 125.0, 120.2, 114.5, 35.1, 34.8, 30.4,
30.1. 15N NMR, d: 270.5, 266.4. UV-VIS [CHCl3, lmax/nm (log e)]: 626
(2.68), 383 (3.34), 302 (4.16), 294 (4.18), 258 (3.81).
At 20 °C, a solution of 0.85 g (3 mmol) of 4 in 10 ml of CH2Cl2 was
added to a solution of 0.31 g (3 mmol) of SCl2 in 10 ml of the specified
solvent. The reaction mixture was stirred overnight, filtered, diluted with
100 ml of CCl4/hexane (1:1) and kept at –20 °C. Salt 3 was obtained as
orange crystals, 0.40 g (44%), mp 248–250 °C (241 °C).16 1H NMR, d:
9.26, 7.96, 1.42, 1.29. 13C NMR, d: 161.8, 161.3, 160.6, 149.3, 127.1,
119.9, 37.0, 36.7, 30.1, 30.0. 15N NMR, d: 402.9. UV-VIS [CHCl3,
The kinetics and products of the decay of radical 1 can be
reproduced by assuming that the reaction begins with reversible
l
max/nm (log e)]: 435 (3.45, sh.), 3.77 (3.84), 353 (3.86), 253 (3.65). MS,
4
0.12
1.2
0.8
0.4
0.0
m/z: 266.1043 (M+ – Cl, calc. for C14H20NS2 266.1037).
X-ray structure data for 4: C14H20N2S2, M = 280.44, triclinic, a =
= 10.234(1), b = 11.597(1) and c = 14.922(1) Å, a = 107.066(9)°, b =
= 105.473(9)°, g = 102.981(9)°, V = 1540.8(3) Å3, space group P1, Z = 4,
dcalc = 1.209 g cm–3, m(MoKα) = 0.331 mm–1. The final indices are
wR2 = 0.1453, S = 1.025 for all 5270 F2, R1 = 0.0505 for 3734 F0 > 4s
(486 parameters).
The data were measured on a Bruker P4 diffractometer with graphite-
monochromated MoKα radiation (0.71073 Å) using q/2q scans (2q < 50°).
A correction for absorption was made by an empirical method based on
y scans (transmission of 0.90–0.96). The structure was solved by direct
methods using the SHELXS-97 program and refined in the full-matrix
anisotropic (isotropic for H atoms) approximation using the SHELXL-97
program. The H atoms positions were located from a difference Fourier map.
Atomic coordinates, bond lengths, bond angles and thermal param-
eters have been deposited at the Cambridge Crystallographic Data Centre
(CCDC). These data can be obtained free of charge via www.ccdc.cam.uk/
conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336 033; or deposit@ccdc.cam.ac.uk).
Any request to the CCDC for data should quote the full literature citation
and CCDC reference number 234303. For details, see ‘Notice to Authors’,
Mendeleev Commun., Issue 1, 2005.
0.08
0.04
0.00
1
1
2
3
4
400
600
l/nm
800
Figure 1 UV-VIS spectrum of (1) compound 4 (c = 0.17×10–3 M) in hexane
and its changes upon 313 nm photolysis for (2) 5, (3) 20 and (4) 40 min.
The TD-B3LYP/6-311+G** positions and oscillator strengths (f) of the
absorption bands of the parent 1,2,3-benzodithiazolyl are depicted as solid
bars.
Mendeleev Commun. 2005 15

, 2005, 15(1), 14–17
(a)
S
S
O
O2 (1)
(2)
1.2
S
S
O
N
N
1
0.8
0.4
1
5
2
S
0
50
100 150 200
S
(3)
t/min
N
12
8
(b)
2
N
S
S
S
O
O
S
S
N
N
4
1
O
S
S
O
0
S
0
50
100 150 200
/min
t
N
Figure 2 (a) The kinetics of decay of radical 1 absorption at 344 nm
(points) in hexane at ambient temperature and O2 concentrations (1)
3.28×10–3 and (2) 1.56×10–2 M, and their fitting (solid lines) to the
equation Dt = D¥ + ∆D/(1 + at). (b) Linear plot of ∆D0/∆Dt – 1 vs. time.
2
6
products most likely originate from the recombination of thiyl
radicals. However, intermediate stages of this interesting new
reaction, which obviously requires a hetero ring-opening rear-
rangement of one of its early products, are unclear.
S
S
S
O
N
S
O
N
4
3
2
1
0
8
7
Scheme 2
addition of O2 to 1, giving peroxyl radical 5, whereby the equi-
librium is shifted significantly towards 1. Peroxyl radical 5 may
then add 1 to give peroxide 6 (Scheme 2), which is an isomer of
final product 2.
The value of k can be expressed in terms of the rate constants
of the above elementary reactions (1–3, Scheme 2) by the equa-
tion k = (k1k3/k2)[O2] = k3K12[O2]. From the value of k measured
for two O2 concentrations, the value of k3K12 was deduced to be
(3.5 0.5)×102 dm6 mol–2 s–1. Assuming that the rate constant
of radical recombination k3 is close to the typical value of
~109 dm3 mol–1 s–1, the equilibrium constant K12 can be estimated
to be as low as ~4×10–7 dm3 mol–1. Therefore, reaction (1) is endo-
thermic and its enthalpy can be roughly estimated at ~50 kJ mol–1.
UMP2/6-311G** single point energy calculations at geometries
optimised at the UHF level predict a value of 111 kJ mol–1.
Two possible mechanisms may be considered for the trans-
formation of 6 into 2: (1) peroxide bond splitting to form
O-centered radicals 7, which may subsequently undergo ring-
opening isomerization to give S-centered radicals 8, whose
recombination affords 2, and (2) a [3,3] sigmatropic shift re-
sembling a Cope rearrangement (Scheme 2).
Model B3LYP/6-311G** calculations performed for non-
benzo-fused archetypes of the species presented in Scheme 2
failed to yield a transition state for a concerted Cope-like rear-
rangement of 6 to 2. At the same time, the calculations revealed
that the homolytic cleavage of the peroxide bond followed by
rearrangement and recombination of the resulting radicals is a
thermodynamically favourable process.
0.0
0.1
0.2
M
0.3
R0/m
Figure 3 Concentration dependence of the fitting parameter a = kR0 on
the initial radical concentration R0.
In contrast to R–N=S=O compounds, R–N=Se=O derivatives
are highly unstable,11 which seemingly reflects thermodynamic
non-attractiveness of the –N=Se=O function. On this basis, it
might be possible to suppress, or at least to attenuate, the
instability of Herz radicals towards O2 by going to their 2-Se
counterparts (i.e., 1,2,3-benzothiaselenazolyls), which have so
far received little attention.2
We are grateful to Professor Yuri N. Molin, Dr. Victor A.
Bagryansky and Professor Matthew S. Platz for helpful dis-
cussions. This work was supported by the Russian Foundation
for Basic Research (grant no. 04-03-32259), the Federal Ministry
for Education and Science (project no. UR.05.01.022) and the
Division of Chemistry and Materials Science of the Russian
Academy of Sciences.
References
Thus, the final products of the reaction of Herz radicals with
O2 were identified for the first time as substituted diphenyl
disulfides bearing two –N=S=O groups. The reaction begins
with the reversible formation of peroxyl radicals while its final
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Mendeleev Commun. 2005 17