The reaction of benzothiazole sulfenamide with (TMS)3SiH: An example of degenerate-branched chain process

Article abstract of DOI:10.1016/j.jorganchem.2005.01.031

The reaction of sulfenamide 3 with (TMS)₃SiH initiated by the decomposition of AIBN at 76°C has been studied in some detail. The reaction is a rare example of a radical chain-branching process. The two main products are dialkylamine 4 and the thiosilane 5. It is also established that 2-mercaptobenzothiazole (2) is formed in a substantial yield as one of the by-products. The mechanism of this chain autocatalytic reaction is complex due to a mix of different radical chain reactions and some discussion is provided. The amine obtained in a quantitative yield can arise from two independent routes of attack of (TMS)₃Si^. radical on sulfenamide 3. The minor route affords thiol 2 that can act as a catalyst for the major route during the reaction course and then gives a salt with secondary amine, which precipitates upon cooling. The origin of autocatalysis is discussed in some detail.

Full text of DOI:10.1016/j.jorganchem.2005.01.031

Journal of Organometallic Chemistry 690 (2005) 1756–1762
www.elsevier.com/locate/jorganchem
The reaction of benzothiazole sulfenamide with (TMS) SiH:
3
An example of degenerate-branched chain process
a,
Vladimir T. Varlamov , Carla Ferreri , Chryssostomos Chatgilialoglu
b
b,
*
*
a
Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation
b
ISOF, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy
Received 18 November 2004; accepted 20 January 2005
Available online 2 March 2005
Abstract
The reaction of sulfenamide 3 with (TMS)
The reaction is a rare example of a radical chain-branching process. The two main products are dialkylamine 4 and the thiosilane 5.
3
SiH initiated by the decomposition of AIBN at 76 ꢀC has been studied in some detail.
It is also established that 2-mercaptobenzothiazole (2) is formed in a substantial yield as one of the by-products. The mechanism of
this chain autocatalytic reaction is complex due to a mix of different radical chain reactions and some discussion is provided. The
Å
amine obtained in a quantitative yield can arise from two independent routes of attack of (TMS)
minor route affords thiol 2 that can act as a catalyst for the major route during the reaction course and then gives a salt with sec-
3
Si radical on sulfenamide 3. The
ondary amine, which precipitates upon cooling. The origin of autocatalysis is discussed in some detail.
ꢁ
2005 Elsevier B.V. All rights reserved.
Keywords: Tris(trimethylsilyl)silane; Sulfenamide; Free radical; Kinetics; Reaction mechanism
1
. Introduction
Dialkylaminyl radicals (R N ) can be generated by a
superior reactivity of 1 towards Bu Sn radicals was
3
noted. However, in these reactions the presence of small
quantities of (Bu Sn) O significantly improved the reac-
Å
2
3
2
variety of methods [1]. The two main methods that are
also compatible with radical chain reactions for syn-
thetic purposes make use of N-hydroxypyridine-2-thione
carbamates and arenesulfenamides. Newcomb and
coworkers [2,3] measured rate constants for a series of
dialkylaminyl radical reactions, including cyclizations
tion performance by increasing the yield of cyclization
products. The initial suggestion that this additive cata-
lyzes dialkylaminyl radical reaction [4] was found to
be incorrect [3], and later its role was found to be that
of scavenging the thiol 2 [3,5], which is a good hydrogen
donor and may be produced in situ from the reaction of
and hydrogen abstraction from Bu SnH, t-BuSH, PhSH
3
adventitious disulfide and Bu SnH.
3
and PhSeH, using N-hydroxypyridine-2-thione carba-
mates. Tsanaktsidis and coworkers [4,5] reported on
the preparation of arenesulfenamides and their utility
as precursors of dialkylaminyl radical in the presence
N
S
N
S
S NR
SH
2
of Bu SnH. From a variety of arenesulfenamides, the
3
1
2
*
Corresponding authors. Tel.: +39 051 6398309; fax: +39 051
398349 (C. Chatgilialoglu). Fax: +7 096 5249676 (V.T. Varlamov).
In the recent years, we have reported two kinetic
studies on the reaction of aminyl radicals with
(TMS) SiH. In particular, the hindered 2,2,6,6-tetra-
6
E-mail addresses: varlamov@icp.ac.ru (V.T. Varlamov), chrys@
isof.cnr.it (C. Chatgilialoglu).
3
0
022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.031

V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
1757
methylpiperidinyl radical [6] and a variety of diarylami-
nyl radicals [7] were used in connection with some appli-
cations of silicon hydrides as process stabilizers for
organic polymeric materials subject to oxidative degra-
dation [8]. Since the removal of PhS moiety from a vari-
the compound 6 was formed by the reaction of corre-
sponding amine with thiol. Indeed, this salt could easily
be obtained by the addition of an equimolar or some-
what greater amount of amine 4 to a saturated solution
of 2-mercaptobenzothiazole (2) in toluene. After heating
to 90–100 ꢀC followed by cooling to room temperature,
lustrous crystals of 6 slowly precipitated.
ety of RSPh by (TMS) SiH could be an efficient reaction
3
Å
depending on the stabilization of the forming radical R
[
8], we tested the reaction of sulfenamide 1 with
TMS) SiH in order to verify its potentiality as dialky-
laminyl radical precursor. Based on the available kinetic
(
3
N
S
Me
N
S
7
H
H
S
N
S
Å
CH Ph
2
data for the reaction of R N radicals with group 14 hy-
2
2
drides [9,10], we are expecting (TMS) SiH to be a rela-
3
6
tively good hydrogen donor towards these radicals.
We anticipate that the reaction is indeed an efficient
chain process producing the corresponding dialkylamine
quantitatively and, more importantly, it is a rare exam-
ple of radical chain-branching process.
Since the early sixties, this reaction has been well
known for thiol 2 with a variety of amines, such as
piperidine, triethylamine, cyclohexylamine and methyl-
amine [11]. With methylbenzylamine it was never re-
ported. Recently, the salt with MeNH has been used
2
in studies of solid-state reactions probed with the atomic
force microscope (AFM) [12]. Obtained by us crystals of
2
. Results and discussion
6
In D O, the H NMR spectrum gave an optimal distri-
were soluble in chloroform and less soluble in water.
1
2
.1. Product studies
2
bution of chemical shifts and integrals for the aromatic
protons, whereas in CDCl the integrals for each aro-
Sulfenamide 3 was obtained by the reaction of sulfe-
3
nyl chloride prepared in situ from the disulfide with the
corresponding secondary amine and purified by flash
chromatography [4]. When a toluene solution contain-
ing equimolar amounts (ꢀ0.1 M) of compound 3 and
matic proton were not well resolved. Chemical shifts
of methyl and methylene groups in the salt 6 were distin-
guishable from those in either the amine 4 or the sulfen-
amide 3 (see Section 3).
0
(
TMS) SiH was heated at 76 ꢀC for 6 h, no new prod-
A mixture of 2,2 -dibenzothiazolyl disulfide 7 (as a
suspension, 0.43 g) and (TMS) SiH (0.32 mL) in tolu-
3
ucts were formed and the reactants remained un-
0
3
changed. In the presence of 2,2 -azobisisobutyronitrile
(
ene (7 mL) was heated for ꢀ7 h at 93 ꢀC in an Ar
atmosphere. During this time, the disulfide was com-
pletely dissolved to form a transparent weakly yellow
solution. The chain reaction, initiated by the decom-
position of the disulfide [13], occurred between the
components affording the thiosilane 5 and thiol 2 in
good yields.
AIBN) as radical initiator, the reaction proceeded
smoothly as shown by GC analysis. Scheme 1 shows
the formation of the two main products. The yield of
amine 4 was nearly quantitative. Product 5 is a new
compound, identified by comparison with a sample ob-
tained by an independent synthesis (see below). It is
worth mentioning that the GC runs also showed a few
minor peaks.
One of these by-products was isolated in a pure form.
When the reaction mixtures were left overnight at room
temperature after the experiment, lustrous colorless nee-
dle-like crystals precipitated in a 5–7% yield with respect
to the starting sulfenamide 3. Chromatographic behav-
ior, NMR, and mass spectrometry analyses indicated
2.2. Reaction mechanism
The effect of the concentration of the initiator and
each of the two reactants on the amine formation was
investigated one at a time. Fig. 1 shows the influence
of the initiation rate (R
) on the time profile of amine
formation using 0.109 M sulfenamide 3 and 0.149 M
i
(
TMS) SiH. AIBN is decomposed at 76 ꢀC with
3
ꢁ5
ꢁ1
ꢁ5 ꢁ1
s ,
where e = 0.6 is the yield of radical escape to the bulk
N
S
Me
AIBN
76 ˚C
kd = 8.15 · 10
s
and k = 2k e = 9.8 · 10
i
d
S N
+
3
(TMS) SiH
CH Ph
2
[
14]. It can be seen that in all experiments the initial
3
reaction rate (d[4]/dt) is much higher than the initiation
rate and the reaction kinetics has a pronounced autocat-
alytic character. An increase in R increased d[4]/dt, and
Me
N
S
H N
+
S Si(TMS)
3
CH Ph
2
i
4
5
shortened the period of the autocatalytic development of
the reaction. Fig. 2 shows that at constant R and [3]
0
Scheme 1. Product studies showing the quantitative formation of
secondary amine 4.
i
the reaction rate (d[4]/dt) is independent of (TMS) SiH
3

1758
V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
Fig. 1. Influence of the initiation rate (R
formation. Experiments were carried out in Ar-saturated toluene at
6 ꢀC containing 0.109 M 3 and 0.149 M (TMS) SiH; curve labels
· 10 M s ): (1) 0.59, (2) 1.46, (3) 2.94, (4) 4.45, (5) 5.88.
i
) on the time profile of amine
Fig. 3. Influence of the [3] on the time profile of amine formation.
Experiments were carried out in Ar-saturated toluene at 76 ꢀC
7
3
containing 0.149 M (TMS) SiH and an initiation rate
3
i
R =
7
ꢁ1
(
R
i
ꢁ7
ꢁ1
2
.94 · 10 M s ; curve labels: (1) 0.037 M, (2) 0.073 M, (3) 0.109 M.
Initiation steps
•
Production of R at a rate = R
i
•
•
(
1)
R + (TMS)
3
3
SiH → RH + (TMS) Si
Propagation steps
•
•
(
TMS)
3
Si + 3 → 5 + R
2
N
(2)
•
•
R
2
N + (TMS)
3
3
SiH → 4 + (TMS) Si (3)
Termination steps
•
2
(TMS)
3
Si → (TMS)
3
Si—Si(TMS)
3
(4)
Scheme 2. Proposed reaction mechanism for the radical initiated
3
reaction of sulfenamide 3 with (TMS) SiH.
Fig. 2. Influence of the (TMS)
of amine formation. Experiments were carried out in Ar-saturated
toluene at 76 ꢀC containing 0.109 M and an initiation rate
= 1.46 · 10 M s ; curve labels: (1) 0.148 M, (2) 0.745 M, (3)
.25 M.
3
SiH concentration on the time profile
Å
3
amine 4 and (TMS) Si radical, thus completing the cy-
3
ꢁ7
ꢁ1
R
i
cle of this chain reaction.
However, the formation of thiol 2 in a 5–7% yield
1
(assuming that all the thiol is transformed to salt 6) sug-
gests the existence of another path between the reaction
concentration, whereas Fig. 3 shows that at constant Ri
and [(TMS) SiH] the reaction rate (d[4]/dt) increased
Å
of (TMS) Si radical with sulfenamide 3. We speculate
3
3
0
proportionally to the sulfenamide concentration.
The above results suggest that the reaction proceeds
via a radical chain mechanism, and that the limiting step
involves the sulfenamide 3. The simplest reaction mech-
that the attack on the nitrogen atom of benzothiazole
moiety to give radical 8 is the most reasonable one
(Scheme 3). The addition of silyl radicals to compounds
containing C@N bonds is quite extensively described
[8,15]. In particular, there are precedents of silyl radical
attacking the nitrogen of heteroaromatic rings like
substituted pyrimidines and pyrazine, which have been
monitored by EPR [16,17]. Radical 8 is expected to de-
cay by b-cleavage of the S–N bond affording the aminyl
anism that accounts for the two main products is shown
Å
in Scheme 2. That is, (TMS) Si radicals, initially gener-
3
ated by small amounts of AIBN, attack the sulfenamide
to form product 5 and aminyl radicals by an S 2-type
H
3
reaction. Hydrogen abstraction from silane gives the

V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
1759
Si(TMS)3
the propagation step in Scheme 2 will be replaced by the
propagation step shown in Scheme 4.
Based on reaction mechanisms in Scheme 2 or 4 and
assuming that the reaction (2) is the rate-determining
step, the rate of formation of amine is given by Eq. (7).
N
Me
•
(
TMS) Si
+
3
S N
3
S
CH Ph
2
8
(
TMS) SiH
3
d½4ꢂ
dt
k
2
R N•
R NH
1=2
2
2
¼
½3ꢂðRiÞ
:
ð7Þ
1=2
•
ð2k Þ
4
(TMS) Si
3
(
TMS) Si
Si(TMS)3
3
N
N
S
S
To determine d[4]/dt, the kinetic curves of R NH accu-
2
S
mulation were approximated by the empirical relation
[
S
ct
R NH] = a + be , where a, b and c are the parameters
2
1
0
9
found by the iteration methods. The plots of the initial
rates vs. square root of the initiation rate are shown in
Fig. 4. This dependence should be fulfilled when the pro-
posed mechanism corresponds to the experimental data.
(
TMS) SiH
3
N
S
N
It can be seen that at moderate R the experimental
i
S
SH
points fit satisfactorily the common line. The parameter
S
•
1/2
ꢁ2
ꢁ1/2
(
TMS) Si
k /(2k ) = 4.84 · 10
(Ms)
obtained from the
ꢁ1 ꢁ1
s to be calculated at
3
2
4
11
2
3
plot, allows k = 3.4 · 10 M
2
9
ꢁ1 ꢁ1
Scheme 3. Proposed reaction mechanism for the formation of thiol 2.
76 ꢀC by taking 2k = 5 · 10 M
s [8]. Thus, the
reaction proceeds via the chain-radical mechanism,
4
although the chains are not too long. For example, using
[
radical and the intermediate 9. We suggest that this
compound is unstable under our experimental condi-
tions and decomposed to give the silyl radical and the
aromatic aminyl radical 10, which is in resonance with
form 11. Indeed, theoretical and spectroscopic data indi-
cated that the unpaired electron is mainly localized on
the S atom [18]. Like PhS radicals under similar condi-
tions [19,20], radical 11 will abstract the H-atom from
the silane to give the thiol 2.
The formation of thiol 2 in mM level during the reac-
tion course can change the nature of one of the propaga-
tion steps as reported in Scheme 4 and shows that
aminyl radicals abstract hydrogen from the thiol and
the resulting thiyl radicals abstract hydrogen from the
silane. Hydrogen donor abilities of group 14 hydrides
are strongly related to the reaction exothermicities [9].
3] = 0.109, [(TMS) SiH] = 0.149 M and [AIBN] =
0 3 0
ꢁ
3
ꢁ7
ꢁ1
1
.5 · 10 M (R = 1.47 · 10 M s ) the initial reac-
i
ꢁ
6
ꢁ1
tion rate equals only 1.86 · 10 M s , that is, the chain
length is close to 10 units.
Fig. 5 shows how the reaction of 3 with (TMS) SiH is
3
Å
inhibited by oxygen. Comparison of curve 2 (on air)
with curve 1 (under argon) indicates a considerable de-
crease in the rate in the presence of O . The inhibition
2
effect of O is most likely to be related to the formation
2
of silylperoxyl radicals and their subsequent transforma-
tions [21].
Å
Based on the rate constants (at 76 ꢀC) of RCH CH
2
2
6
ꢁ1 ꢁ1
s )
with Bu SnH (6.1 · 10 M
and (TMS) SiH
3
3
6
ꢁ1 ꢁ1
Å
(
(
1.2 · 10 M
s
) and of R N with Bu SnH
2 3
), we estimated a rate constant of
6
ꢁ1 ꢁ1
1.6 · 10 M
s
5
ꢁ1 ꢁ1
Å
ꢀ
3 · 10 M
s
TMS) SiH. On the other hand, the reaction of R N
for the reaction of R N with
Å
2
(
3
2
8
ꢁ1 ꢁ1
with PhSH (2.8 · 10 M ) is 3 orders of magnitude
higher [2] and, therefore, soon after the reaction started,
s
•
•
(
TMS)
3
Si + 3 → 5 + R
2
N
(2)
(5)
•
R
2
N + 2 → 4 + 11
•
1
1 + (TMS)
3
SiH → 2 + (TMS)
3
Si (6)
Fig. 4. Plot of the initial rates vs. square root of the initiation rate.
Scheme 4. Propagation steps for the radical chain reaction of
3
Concentrations of reagents: [3] = 0.109 M and [(TMS) SiH] =
sulfenamide 3 with (TMS) SiH in the presence of thiol 2 (cf. Scheme 2).
3
0.149 M.

1760
V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
Fig. 5. Influence of oxygen on the kinetics of amine accumulation.
ꢁ1
ꢁ7
Fig. 6. Kinetic curves of amine formation (1) without additives, (2) in
the presence of 0.0058 M 6, and (3) in the presence of 0.044 M 4.
Experiments were carried out in Ar-saturated toluene at 76 ꢀC
R
argon, (2) air.
i
= 4.48 · 10 M s , [3] = 0.109 M, and [(TMS)
3
SiH] = 0.149 M. (1)
3
containing 0.054 M 3, 0.163 M (TMS) SiH and an initiation rate
ꢁ7
ꢁ1
R
i
= 2.94 · 10 M s
.
Finally the reaction of disulfide 7 with (TMS) SiH is
3
worth a comment. The reaction is a radical chain pro-
cess auto-initiated by thermal decomposition of disulfide
itself [13]. The propagation steps consist with an S 2 at-
However, we cannot exclude that additional radical
formation occurs by reactions involving other products
of side processes. One of us has recently studied the rad-
ical chain reduction of N,N -diphenyl-1,4-benzoqui-
none-diimine (QDI) by thiol 2 (Eq. (8)) [24].
H
tack on the sulfur by silyl radical to give the thiosilane 5
and thiyl radical 11, and hydrogen abstraction from the
0
Å
silane by radical 11. The reaction of (TMS) Si radical
3
QDI þ 2 2 ! QDIH þ 7
ð8Þ
with disulfide 7 is expected to be faster than with sulfe-
namide 3 and, therefore, the addition to the N of benzo-
thiazole should be less important [22].
2
It was found that in the absence of a radical initiator,
chain initiation (i.e., formation of free radicals) proceeds
via the reaction shown in the following equation.
Å
2
.3. The origin of autocatalysis
QDI þ 2 ! HQDI þ 11
ð9Þ
According to Scheme 3, additional radical formation
These findings suggest that autocatalysis in our sys-
tem can be caused by a similar reaction. Visual observa-
is caused by the decomposition of the side product 9.
However, taking into account that thiol 2 is formed in
a 5–7% yield and that formation of amine 4 proceeds
via chain mechanisms with chain lengths close to 10
units, we can conclude that the highest possible rate of
radical formation by radical decomposition of 9 is close
tions of the reaction of 3 with (TMS) SiH show that the
3
reaction mixtures, colorless in the beginning of experi-
ments, gradually gained a more and more pronounced
brownish-orange color. This suggested that compounds
with conjugated multiple bonds accumulated during the
reaction. We suggest that QDI can be considered as a
model of colored by-products of reaction 3 with
to the initiation rate R caused by AIBN. Then accord-
i
ing to Eq. (7), the rate of the whole process is expected
to increase only by a factor of ꢀ1.5, which is too low to
explain the experimental findings. Some tests also
showed that the main two products 4 and 5 as well as
salt 6, are not responsible for the observed autocatalysis.
Fig. 6 shows the reaction kinetics in the presence of
small amounts of amine 4 (curve 3) and salt 6 (curve
(TMS) SiH. Since the concentrations of thiol 2 and col-
3
ored by-products only increase during the reaction, the
rate of radical formation in the reaction between them
also increases continuously, and this explains the auto-
catalytic character of the reaction of 3 with (TMS) SiH.
3
It is worth also mentioning the observed very strong
accelerating effect of amine 4 on the Reaction (8). For
2
) and indicates that both compounds have an accelerat-
ꢁ
3
ing effect on the initial rate of the reaction. On the other
hand, thiosilane 5 showed high thermal stability that ex-
cludes in situ decomposition. We also tested a possible
auto-acceleration of the reaction by the acidic catalysis
of the radical decomposition of sulfenamide 3 and for-
mation of thiol 2 (as a weak acid), without success [23].
example, 3 · 10 M 4 increases the initial rate by ꢀ15
ꢁ4
and ꢀ30 times for the reaction of 1 · 10 M QDI with
ꢁ4
ꢁ4
ꢁ3
5 · 10 M 2 and 1 · 10 M QDI with 1 · 10 M 2,
respectively. These results indicate possible scenarios
for the observed auto-acceleration in the reaction of
the sulfenamide 3 with (TMS) SiH.
3

V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
1761
3
. Experimental
GC analysis on the crude reaction mixture showed the
formation of thiol and thiosilane. After the starting
disulfide was consumed, the reaction mixture was cooled
so that thiol crystallized from toluene and was separated
by filtration (190 mg; 1.14 mmol; 87%). The filtrate was
evaporated and thiosilane 5 was recovered (0.34 g;
3
.1. Materials
Commercially available chemicals were purchased
from Fluka, Sigma, Aldrich and were used as received.
Solvents were purchased from Merck (HPLC grade)
and used without further purification. Analytical TLC
were carried out on silica gel 60 F254 plates (Merck
0.82 mmol; 63% yield referred to disulfide).
1
H NMR (CDCl ) d 0.27 (s, 27 H, TMS groups), 7.28
3
(t, 1H, J = 8 Hz), 7.36 (d, 1H, J = 8 Hz), 7.69 (d, 1H,
3
1
5
744) and revealed with cerium ammonium sulfate/
J = 8 Hz), 7.79 (d, 1H, J = 8 Hz). C NMR (CDCl ) d
3
ammonium molybdate reagent. Products were isolated
either by fractional crystallization or by flash chroma-
tography on silica gel 60 (Merck, 230–400 mesh). Melt-
ing points were determined on a B u¨ chi 510 capillary
0.9 (CH ), 121.0, 121.1, 124.3, 126.8 (CH), 137.6,
+
3
+
153.6, 166.9 (C). EI MS m/z 412 (M ), 339 (M ꢁ 73),
224, 207, 167, 73 (100), 59.
melting point apparatus and are uncorrected. NMR
1
Varian VXR ( H
3
.4. Synthesis of salt 6
spectra were recorded on
1
a
00 MHz, C 100.6 MHz) spectrometer, using the sol-
3
4
vents indicated in parentheses also as the reference peak.
A solution of thiol 2 (200 mg, 1.20 mmol) in toluene
5 mL) was combined with methylbenzylamine
373 mg; 1.30 mmol) and heated at 90–100 ꢀC for 1 h
(
(
1
CDCl signals were at 7.26 and 77.23 ppm, for H and
3
1
3
C NMR spectra, respectively. GC analysis was per-
formed on a HP6850 (Agilent Technologies, Germany)
with a flame ionization detector and a HP-5 column
under nitrogen atmosphere. Upon cooling the reaction
mixture at room temperature, crystals were formed
and separated by filtration. The salt (288 mg;
(
3
(5% phenyl)-methylpolysiloxane capillary column;
0 m, 0.25 mm i.d., 0.25 lm film thickness). Tempera-
1.20 mmol; 83% yield) was washed with cold toluene
and dried under vacuum. M.p. 127–128 ꢀC.
ture started from 70 ꢀC, held for 5 min, followed by an
increase of 9 ꢀC/min up to 280 ꢀC, held for 10 min. A
constant pressure of 13 psi was maintained and nitrogen
was the carrier gas. GC/MS spectra were recorded on a
HP 5890 (Series II) coupled to a Hewlett–Packard mass
selective detector Model 5971A using similar conditions.
Helium was the carrier gas. ESI MS spectra were re-
corded on an Esquire 3000 plus Bruker instrument.
1
H NMR (D O) d 2.56 (s, 3H, NMe), 4.05 (s, 2H,
2
CH ), 7.10 (t, J = 6.8 Hz, 1H), 7.22 (t, 1H, J = 7.2 Hz),
7.30–7.36 (m, 5H), 7.40 (d, 1H, J = 8 Hz), 7.52 (d, 1H,
J = 8.4 Hz). H NMR (CDCl ) d 2.52 (s, 3H, NMe),
2
1
3
3
(
.95 (s, 2H, CH ) 6.59 (broad s, 2H, NH ), 7.17–7.33
2 2
13
m, 8H), 7.47 (d, J = 7.6 Hz, aromatic H). C NMR
(CDCl ) d –34.1 (CH ), 54.7 (CH ), 114.5, 121.1,
3
3
2
1
1
1
5
9
23.9, 126.6, 128.2, 129.0, 129.2 (each CH), 132.9,
+
36.3, 145.5, 189.3 (each C). ESI MS m/z 288.6 (M ),
3
.2. Synthesis of sulfenamide 3
22. C H N S (288.08): Anal. Calc. C, 62.46; H,
1
5
16
2 2
.59; N, 9.71; S, 22.23. Found. C, 62.27; H, 5.57; N,
.70; S, 22.14%.
The preparation was made according to the literature
starting from disulfide (1.3 g; 4 mmol) for the in situ syn-
thesis of sulfenyl chloride and subsequent coupling with
N-benzylmethyl amine (1 g; 8.2 mmol) [4]. The product
was isolated by flash chromatography on silica gel (elu-
ent: n-hexane:ethyl acetate 80:20) and in the first frac-
4. Summary
tions it was obtained as a pure product (750 mg;
1
The reaction of sulfenamide 3 with (TMS) SiH initi-
3
2
NMe), 4.33 (s, 2H, benzyl CH ), 7.25–7.48 (m, 7H),
.3 mmol; 57% yield). H NMR (CDCl ) d 2.96 (s, 3H,
ated by radicals is an efficient chain process producing
the corresponding dialkylamine quantitatively. The
reaction mechanism is complex, being also an example
of a degenerate-branched chain process. Two parallel
reaction mechanisms based on the initial attack of silyl
radical on sulfenamide 3 were suggested, one of which
affords thiol 2 in a substantial amount. Evidence that
additional radical formation in the system derived from
the reaction of thiol 2 with the substances containing
conjugated multiple bonds formed as by-products,
which is also accelerated by main reaction product
amine 4, were also obtained. We believe that these find-
ings can be extended to the reactions of 2-merca-
3
2
1
3
7
.84 (d, 1H, J = 7.9 Hz), 7.87 (d, 1H, J = 7.9 Hz).
C
NMR (CDCl ) d 176.0, 155.1, 137.5, 135.3 (C), 129.1,
3
1
(
28.7, 128.1, 126.1, 123.9, 121.9, 121.2 (CH), 65.2
+
CH ), 45.7 (CH ). EI MS m/z 286 (M ), 165 (100),
2
3
1
22, 77.
3
.3. Synthesis of thiosilane 5
0
A suspension of 2,2 -dithiobis(benzothiazole) (0.43 g;
.30 mmol) in toluene (7 mL) was combined with
1
(
TMS) SiH (0.26 g; 1.03 mmol) and magnetically stirred
3
at 93 ꢀC for 7 h. The reaction was clear after 10 min and
ptobenzothiazole sulfenamides with Bu SnH and
3

1762
V.T. Varlamov et al. / Journal of Organometallic Chemistry 690 (2005) 1756–1762
nicely explain the observed results described in the
introduction.
[11] M.O. Kolosowa, V.J. Stavrovskaja, J. Gen. Chem. USSR (Engl.
Transl.) 33 (1963) 944–946.
[
12] G. Kaupp, J. Schmeyers, M. Haak, T. Marquardt, A. Herrmann,
Mol. Cryst. Liq. Cryst. 276 (1996) 315–337.
ꢁ6
ꢁ1
[
13] A rate constant of dissociation of 8.3 · 10
s
at 100 ꢀC has
been reported for disulfide 7, see: R.E. Davis, C. Perrin, J. Am.
References
Chem. Soc. 82 (1960) 1590–1594.
14] J.P. Van Hook, A.V. Tobolsky, J. Am. Chem. Soc. 80 (1958) 779–
782.
[
[
[
[
[
[
[
[
[
[
1] B.J. Maxwell, J. Tsanaktsidis, in: Z.B. Alfassi (Ed.), N-Centered
Radicals, Wiley, Chichester, 1998, pp. 663–684.
[15] C. Chatgilialoglu, Chem. Rev. 95 (1995) 1229–1251.
[16] A. Alberti, G.F. Pedulli, Res. Chem. Intermediat. 8 (1987) 207–
246.
2] O.M. Musa, J.H. Horner, H. Shahin, M. Newcomb, J. Am.
Chem. Soc. 118 (1996) 3862–3868.
3] M. Newcomb, O.M. Musa, F.N. Martinez, J.H. Horner, J. Am.
Chem. Soc. 119 (1997) 4569–4577.
4] B.J. Maxwell, J. Tsanaktsidis, J. Am. Chem. Soc. 118 (1996)
[17] C. Chatgilialoglu, C. Ferreri, D. Vecchi, M. Lucarini, G.F.
Pedulli, J. Organomet. Chem. 545/546 (1997) 475–481.
[18] M.M. Alam, H. Konami, A. Watanabe, O. Ito, J. Chem. Soc.,
Perkin Trans. 2 (1996) 263–268.
4276–4283.
5] B.J. Maxwell, B.J. Smith, J. Tsanaktsidis, J. Chem. Soc., Perkin
Trans. 2 (2000) 425–431.
[19] C. Chatgilialoglu, M. Ballestri, D. Vecchi, D.P. Curran, Tetrahe-
dron Lett. 37 (1996) 6383–8386.
6] M. Lucarini, E. Marchesi, G.F. Pedulli, C. Chatgilialoglu, J. Org.
Chem. 63 (1998) 1687–1693.
7] V.T. Varlamov, E.T. Denisov, C. Chatgilialoglu, J. Org. Chem.
[20] B.P. Roberts, Chem. Soc. Rev. 28 (1999) 25–35.
[21] A.B. Zaborovskiy, D.S. Lutsyk, R.E. Prystansky, V.I. Kopylets,
V.I. Timokhin, C. Chatgilialoglu, J. Organomet. Chem. 689
(2004) 2912–2918.
66 (2001) 6317–6322.
8] C. Chatgilialoglu, Organosilanes in Radical Chemistry, Wiley,
Chichester, 2004.
9] C. Chatgilialoglu, M. Newcomb, Adv. Organomet. Chem. 44
3
[22] For comparison, the rate constants for the reaction of Et Si
7
radical with BuSBu and BuSSBu are 1.1 · 10
3.4 · 10 M
and
s , respectively, see: N. Soundararajan, J.E. Jack-
8
ꢁ1 ꢁ1
(
1999) 67–112.
10] M. Newcomb, M.T. Burchill, T.M. Deeb, J. Am. Chem. Soc. 110
1988) 6528–6535.
son, M.S. Platz, J. Phys. Org. Chem. 1 (1988) 39–46.
[23] V.T. Varlamov, Mendeleev Commun. (2003) 33–35.
[24] V.T. Varlamov, manuscript in preparation.
[
(