Alkyl Triarylstannanecarbodithioates: Synthesis, Crystal Structures, and Efficiency in RAFT Polymerization

Article abstract of DOI:10.1002/chem.201703412

Eight alkyl triarylstannanecarbodithioates were synthesized starting from the corresponding triarylstannyl chlorides. They were fully characterized by IR and ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy and mass spectrometry. Their

Full text of DOI:10.1002/chem.201703412

A Journal of
Accepted Article
Title: Alkyl Triarylstannanecarbodithioates: Synthesis, Crystal
Structures and Efficiency in RAFT Polymerization
Authors: Ihor Kulai, Nathalie Saffon-Merceron, Zoia Voitenko,
Stéphane Mazières, and Mathias Albin Destarac
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Alkyl Triarylstannanecarbodithioates: Synthesis, Crystal
Structures and Efficiency in RAFT Polymerization
Ihor Kulai,[a] Nathalie Saffon-Merceron,[b] Zoia Voitenko,[c] Stéphane Mazières,*[a] Mathias Destarac*[a]
Abstract:
Eight
alkyl
triarylstannanecarbodithioates
were
temperature thermolysis, to prepare colorless, odorless and
stable polymers.[9,13–15]
synthesised starting from the corresponding triarylstannyl chlorides.
They were fully characterised by IR and 1H, 13C and 119Sn NMR
spectroscopies, and by mass spectrometry. Their solid-state
structures and geometric parameters were determined and compared
to those of other classes of thiocarbonylthio compounds. These new
organotin derivatives are efficient reversible chain transfer agents for
RAFT agents are categorized according to the structure of
their Z group, including commonly used dithioesters, xanthates,
trithiocarbonates, and dithiocarbamates.[6,16] Each of these
classes is suited to a specific, and often limited, class of
monomers. However, there are some examples of “uncommon”
RAFT agents based on such heteroelements as fluorine,[17]
phosphorus,[18–20] selenium[21–23] or silicon.[24] These elements
bring characteristic properties which allow further tuning of the
RAFT agents’ reactivities, and expand the field of their application,
for example in the use of NMR techniques to monitor the
polymerization process.[19–21,24,25] This addresses the limitations of
1H or 13C NMR for the analysis of polymers due to overlapping
signals and low signal intensities.[26] Heteronuclear NMR with 19F,
31P, 77Se or 119Sn nuclei provide a separate NMR channel for the
quantification of RAFT agent transformations. This approach can
be used to study the RAFT agent consumption, its stability, the
stability of the polymer ω-chain end, as well as to monitor post-
polymerization transformations. Despite the 100% natural
abundance of 19F and high NMR sensitivity, 19F NMR monitoring
of RAFT processes has only been reported in one study.[27] Our
team has used 31P NMR and 119Sn NMR to study the reactivity of
RAFT agent, the nature of the chain end and the efficiency of
block copolymerization with organophosphorus[19,20] and
organotin[25] RAFT agents.
reversible
addition-fragmentation
chain
transfer
(RAFT)
polymerization of styrene (St) and n-butyl acrylate (BA), with
controlled number-average molecular weights (Mn) and narrow
dispersities (Ð < 1.3). In some cases, a loss of control of the
polymerization was evidenced and supported by the observation of
side products by 119Sn NMR. This phenomenon was attributed to the
thermal instability of the Sn-RAFT terminal group.
Introduction
Reversible Addition-Fragmentation chain Transfer (RAFT)
polymerization[1] has been greatly improved since its invention in
the mid-1990s.[2–5] Nowadays, it is one of the most versatile
reversible deactivation radical polymerization (RDRP) techniques
as it tolerates a diverse range of functional groups and reaction
process conditions. RAFT technology allows low dispersity
(co)polymers with controlled molecular weight to be obtained from
a wide range of vinyl monomers through the use of different
classes of RAFT agents of general formula Z(C=S)SR.[6]
The RAFT polymerization process can be summarized as an
insertion of monomer units along the C-S bond of the RAFT agent
as depicted in Scheme 1. Each molecule of RAFT agent gives rise
to a polymer chain that possesses both α- and ω- chain ends
derived from the initial agent. As a result, the obtained polymer is
a RAFT agent itself and can be used for block copolymerization
with other monomers[7] or post-polymerization chain-end
transformations such as hetero-Diels-Alder coupling[8] or
transformation into a thiol.[9–11] This latter process gives access to
further coupling reactions, such as the thiol-ene click reaction.[12]
The chain end can also be removed by radical-induced oxidation,
reduction, or nucleophilic substitution reactions, as well as high
Scheme 1. Simplified representation of RAFT polymerization.
There is a rich literature on the radical chemistry of organotin
reagents, and the first synthesis of a stannanecarbodithioate was
reported in 1980.[28] Originally, they were studied as chelate
ligands for transition metal complexes[29] and there are only a few
reports
on
the
preparation
and
properties
of
stannanedithiocarbonates.[29–38] In a recent communication,
we reported the first use of triphenylstannanecarbodithioates
in RAFT polymerization,[25] and studied their chain transfer
activity using 119Sn NMR. This technique also revealed the
presence of side reactions at the -chain end.
In this study, we report the synthesis, characterization and
crystal structures of a series of triarylstannanecarbodithioates
(Scheme 2), and evaluate their efficiency in RAFT
polymerization with simultaneous 1H, 19F and 119Sn NMR
monitoring.
[a]
Dr. I. Kulai, Dr. S. Mazières, Prof. Dr. M. Destarac
Laboratoire des IMRCP, Université Paul Sabatier, CNRS UMR 5623
118 route de Narbonne 31062 Toulouse Cedex 9, France
E-mail: destarac@chimie.ups-tlse.fr, mazieres@chimie.ups-tlse.fr
Dr. N. Saffon-Merceron
Institut de Chimie de Toulouse, CNRS FR 2599, Université Paul Sabatier
118 route de Narbonne 31062 Toulouse Cedex 9, France
Prof. Dr.Sci. Z. Voitenko
[b]
[c]
Department of Chemistry, Taras Shevchenko National University of Kyiv
12, Lva Tolstoho Street, 01033, Kyiv, Ukraine
Supporting information for this article is given via a link at the end of the
document.
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10.1002/chem.201703412
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Results and Discussion
violet solids. All synthesized compounds are soluble in organic
solvents such as THF, toluene, dichloromethane and 1,4-dioxane.
They are not air-sensitive in the solid state or in solution, which is
an advantage for storage and handling. However, compounds 5
and 6 have poor thermal stability at room temperature that
prevents their use in free-radical polymerization.
As compound 5 is unstable even at -20°C, the only adequate
proofs of its structure are low temperature X-ray diffraction and
NMR spectroscopy analyses (Figures S14 to S16, and Table S1).
Satisfactory spectroscopic and analytical data were collected for
all other compounds of the study. Chemical ionization high
resolution mass spectrometry (CI-HRMS/CH4) of RAFT agents 1-
4 and 6-8 revealed protonated molecular ion [M+H]+ peaks with
m/z that match the theoretical values. The 1H NMR spectra
(Figures S1, S4, S7, S10, S14, S17, S20 and S23) contain
characteristic deshielded signals of the CH and CH2 groups
connected to sulfur with chemical shifts in the range from δ = 5.85
to 4.18 ppm. Their multiplicities confirm coupling of these protons
with tin (4JSn,H = 2.3–7.3 Hz).
The efficiency of RAFT agents is determined by the structure
of their R and Z groups. For the current study, two triarylstannyl
groups, triphenylstannyl (RAFT agents 1-6, Scheme 2) and tri-p-
tolylstannyl (RAFT agents 7 and 8), were synthesized from the
corresponding commercially available triarylstannyl chlorides. In
addition to the original benzyl (RAFT agents 1 and 7) and 1-
phenylethyl R groups (RAFT agents 2 and 8), we studied the
effect of substituting a strongly electron-withdrawing nitro group
(RAFT agent 3) or a weakly electron-withdrawing fluorine (RAFT
agent 4) in the para position of the benzyl group. The fluorine
substituent enables the use of 19F NMR to monitor the
transformations of RAFT agent 4 in the early stages of
polymerization. Finally, the widely used cyanomethyl and 1-
(methoxycarbonyl)ethyl R groups were selected (RAFT agents 5
and 6).
Synthesis and characterization
The 13C NMR spectra (Figures S2, S5, S8, S11, S15, S18,
S21 and S24) exhibit unusual resonances for the carbon atom of
the CS2 group in extremely weak field. Literature data on the 13C
NMR spectra of selected RAFT agents with benzyl or 1-
phenylethyl R-group and variation of Z-groups (Figure S26)
allowed the chemical shifts to be classified according to the
central atom of the Z-group (Figure 1).[17,18,20,40–48] They range
from 195.5 ppm for dithiocarbamates[42] to 242.6 ppm for
phosphorylmethanedithioates,[20] whereas the chemical shifts of
triarylstannanecarbodithioates range from 262.6 ppm to 266.3
ppm.
These chemical shifts are connected to the electrophilic
character of the thiocarbonyl carbon, and are explained by the
covalent radius of the central atom of the Z-group associated with
the electronic effects it produces. In the cases of xanthates and
dithiocarbamates, ᴨ-donation by the oxygen or nitrogen atoms
explains most of the increase of electron density of the
thiocarbonyl carbon and the resulting strong shielding of the
chemical shifts, while with carbon, sulphur and phosphorus in the
Z-group, the electron density decreases. For the electropositive
tin, the electron donating effect is reduced by the size of the tin
atom and the comparatively long Sn-C bond (Table 1).
Triarylstannanecarbodithioates 1-8 were prepared according
to a slightly modified literature method (Scheme 2).[30,35,38]
Originally, lithium metal was used to reduce the starting
triarylstannyl chlorides to triarylstannyl anions. However, due to
the negligible solubility of alkaline metals in THF, reaction takes
place only on the lithium surface and overall conversion of the
starting material lasts up to 72 hours even at elevated
temperatures. The final products are frequently contaminated by
hexaaryldistannanes. To avoid these drawbacks, sodium
naphthalenide[39] was used as a reducing reagent. Due to its
solubility in THF and extremely high reactivity, nearly quantitative
reduction of triarylstannyl chlorides takes place in a few minutes
in a highly exothermic reaction.
Subsequent treatment of the triarylstannyl anions with an
excess of carbon disulfide leads to the formation of
triarylstannanecarbodithioate salts that are detected immediately
by the appearance of a characteristic red color. These salts are
stable and can be isolated. However, they were used directly in
solution without further purification. After alkylation and work up,
the title triarylstannanecarbodithioates were isolated as pink or
Scheme 2. Synthesis and structures of compounds 1-8. Numbers in parentheses represent overall yields after purification.
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moderate level of control over the polymerization of such MAMs
as acrylamides and acrylates.
Typical less activated RAFT agents—xanthates and
dithiocarbamates—demonstrate the lowest chemical shifts of
thiocarbonyl group in 13C NMR due to the conjugation of lone pairs
of oxygen or nitrogen with thiocarbonyl group. More activated
RAFT agents, namely trithiocarbonates, dithioesters and
phosporyl(thio)methanedithioates have much higher chemical
shifts. These factors suggest that the chemical shift of the
thiocarbonyl carbon can be used for the rough evaluation of
activity of RAFT agents. According to this hypothesis, benzyl
chloro- and fluorodithioformates[17] should be efficient in the
polymerization of LAMs (Figure 1). Following the same reasoning,
triarylstannanecarbodithioates should be efficient in the
polymerization of MAMs.
Figure 1. 13C NMR chemical shifts of thiocarbonyl groups of selected
thiocarbonylthio compounds and title triarylstannanecarbodithioates.[17,18,20,40–48]
The 119Sn NMR chemical shift values (Figures S3, S6, S9,
S12, S16, S19, S22 and S25) obtained for RAFT agents 1-8 fall
in a narrow range between δ = -179.5 (5) and -192.7 ppm (3) and
show slight differences in chemical shift depending on the nature
of the S-alkyl substituent. Tri-p-tolylstannanecarbodithioates 7
and 8 have about 10 ppm higher chemical shift values than
corresponding triphenylstannanecarbodithioates 1 and 2 due to
electron-donating effect of p-tolyl groups.[32] Finally, the 19F NMR
spectrum of 4 (Figure S13) consists of a singlet with chemical shift
of -115.6 ppm. The IR spectra exhibit characteristic stretching
bands for the thiocarbonyl bonds in the range of expected values
for C=S bonds involved in a free CS2 group[19,20,30,35,36,38] with
wavenumbers of 1040.5–1050.0 cm-1.
According to the RAFT polymerization mechanism (Scheme
3), the efficiency of RAFT agents is affected by R and Z
substituents.[49] The R group must be a good homolytic leaving
group that is able to reinitiate the polymerization at a similar rate
to that of propagation.[50] The Z group determines the stability of
the intermediate radical and the reactivity of the C=S bond
towards radical addition.[45]
Crystal structures
There are limited data on the crystal structures of
triarylstannanecarbodithioates.[30,36,38] Up to this time only
structures of four compounds, namely benzyl, methyl and
triphenylstannyl triphenylstannanecarbodithioate 1,[36] 9[30] and
10,[38] respectively, and tri-p-tolylstannyl tri-p-tolylstannane-
carbodithioate 11,[38] were reported. However, the Cambridge
Structural Database[52] entries of compounds 1 and 9 contain
some inaccuracies. Based on these facts it was decided to repeat
these two analyses in parallel with determination of crystal
structures of compounds 2-8. For this purpose, methyl
triphenylstannanecarbodithioate 9 was prepared in good yield
according to our synthetic procedure. Its NMR spectra (Figures
S27-S29) and other physical properties are in good agreement
with previously published data.[30]
While attempts to crystallize compound 6 were unsuccessful,
pink crystals of the other eight products allowed us to obtain good
quality X-Ray structures. The molecular structures of 1-5 and 7-9
are very similar (Figures 2, S30-S37). They all crystallize in the
̅
P1 space group except compound 7 which crystalizes in P21
space group with 4 molecules in the asymmetric unit and
̅
compound 9 (space group P 4 21c with ¼ molecule in the
asymmetric unit) (Table S1). Crystals of the compound 9 have a
structure similar to that of tetraphenylstannane[53] (tetragonal with
̅
4 symmetry) in which the carbodithioate group and the phenyl ring
Scheme 3. Main equilibrium of RAFT polymerization.
are disordered over the same sites by symmetry with occupancies
0.25:0.75. Depending on the constraints or restraints used to
refine the structure, the bond lengths and angles might be slightly
different and only one command was used (ISOR) to model the
structure.
The geometric parameters of their crystal structures are listed
in Tables S2-S17, while selected bond lengths (Å) and angles (°)
of planar SnCS2 fragment for compounds 1-5, 7,9 and
compounds 10 ,11[38] are collected in Table 1. Most of the bond
lengths and angles are similar, although the Sn-C and C=S bonds
of compound 3 are unusually short, while the C-S single bond is
elongated. These observations can be explained by the effect of
the strongly electron withdrawing nitro group. At the same time,
the weakly electron withdrawing fluorine in compound 4 has no
visible effect on bond lengths.
Monomers can be divided into two groups: “more activated
monomers” (MAMs) which give propagating radicals with
relatively low reactivity in radical addition due to the enhanced
electronic stabilization and steric factors; and “less activated
monomers”
(LAMs)
which
generate
more
reactive
macroradicals.[51] MAMs are well controlled by active RAFT
agents such as dithioesters or trithiocarbonates whereas LAMs
require less active RAFT agents such as xanthates or
dithiocarbamates.[6] Attempts to use activated RAFT agents to
control the polymerization of LAMs generally result in complete
inhibition of polymerization, as poly(LAM) macroradicals are
relatively poor leaving groups, which disables the fragmentation
process. By contrast, less active RAFT agents provide a
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Figure 2. Simplified molecular views of compounds 1-5,7-9. Thermal ellipsoids represent 50% probability; hydrogens and disordered atoms are omitted for clarity.
Table 2 summarizes selected bond lengths and angles for the
central fragment of selected thiocarbonylthio compounds 12-21
with variation of Z-group structure.[20,54–60] Key bond lengths and
angles are similar for the listed compounds, but more active RAFT
phosphorylmethanedithioates. The phosphorylmethanedithioate
20 has the smallest Z-C=S angle (120.2°) of RAFT agents that
falls in the range of the values observed for
triarylstannanecarbodithioates 1-5, 7-9 (117.5-123.7°).
But the main finding is the correlation between the Z-C bond
(Table 2) and the chemical shift of the carbon of the thiocarbonyl
(Figure 1). The compounds fall into three distinct groups: first N,
Cl, F and O, then S, C and P, and finally tin. The longer the bond,
the higher the chemical shift. This decrease of electron density
reflects the polarity of the bond which has a direct influence on
radical addition to the RAFT agent during polymerization
(Scheme 3).
agents,
namely
trithiocarbonates,
dithioesters
and
phosphorylmethanedithioates have shorter C=S double bonds
(between 1.614 Å for trithiocarbonate 18 and 1.649 Å for
dithioester 17) that are similar to those of the
triarylstannanecarbodithioates 1-5 and 7-9 (1.60-1.64 Å). Less
active RAFT agents such as dithiocarbamates 14 and 15 have
longer C=S bond (1.68-1.70 Å). Moreover, the C-S bond length is
shorter for more active RAFT agents, particularly for
Table 1. Selected bond lengths (Å) and angles (°) for the SnCS2 fragment for the compounds 1-5 and 7-11.
compound
Sn-C
1
2
3
4
5
7[a]
8
9
10[38]
11[38]
2.189
1.629
1.709
122.37
111.96
125.66
2.191
1.626
1.681
117.77
114.52
127.71
2.155
1.608
1.767
123.76
110.92
125.26
2.181
1.626
1.719
118.27
114.35
127.38
2.185
1.624
1.718
118.43
116.54
125.02
2.193
1.619
1.694
119.01
113.75
127.03
2.204
1.622
1.703
120.78
110.22
128.95
2.165
1.641
1.670
122.0
114.3
123.1
2.161
1.632
1.714
119.3
117.4
123.3
2.187
1.619
1.656
117.5
116.1
126.4
C=S
C-S
Sn-C=S
Sn-C-S
S=C1-S
[a]average values for four molecules in the asymmetric unit
Table 2. Selected bond lengths (Å) and angles (°) for the central fragment of common thiocarbonylthio compounds according to the literature data.[20,54–60]
compound
Z-group
Z-C
1
12[54]
13[55]
14[56]
15[56]
16[57]
17[58]
18[59]
19[60]
20[20]
21[20]
SnPh3
2.189
1.629
1.709
122.37
111.96
125.66
OEt
OEt
NEt2
Morpholine
1.318
Ph
Ph
S(CH2)2CO2H
1.746
SCMe2CO2H
1.746
P(O)Ph2
1.848
P(O)(NiPr2)2
1.868
1.313
1.642
1.756
127.89
105.65
126.46
1.332
1.636
1.759
127.40
106.41
126.19
1.288
1.68
1.481
1.632
1.745
123.62
113.50
122.88
1.487
1.649
1.732
123.48
113.01
123.51
C=S
1.702
1.614
1.630
1.635
1.634
C-S
1.788
125.09
113.75
121.15
1.743
1.742
1.748
1.710
1.720
Z-C=S
Z-C-S
S=C-S
122.58
118.11
121.30
126.14
106.51
127.34
126.75
106.90
126.32
120.25
109.55
130.17
124.97
108.49
126.51
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RAFT polymerizations
Table 3. Results of Sn-RAFT mediated polymerizations.
[c]
[d]
Entry
RAFT
agent
1
M[a]
Time
h
M
Mn th
Mn
Ɖ[e]
conv[b]
1.17%
3.93%
38.17%
70.93%
84.57%
93.81%
1.7%
kg mol-1
kg mol-1
ND[f]
1.44
To evaluate the structure-reactivity relationships for the alkyl
triarylstannanecarbodithioates, the RAFT polymerization of n-
butyl acrylate (BA) was performed in the presence of RAFT
agents 1-4, 6 and 7 at 60°C with AIBN as thermal initiator
(Scheme 4). Additionally, compounds 1 and 7 were studied in the
polymerization of styrene (St). The initial reactant ratios
[BA]:[CTA]:[AIBN] = 170:1:0.2 and [St]:[CTA]:[AIBN] = 200:1:0.2
were chosen so that the theoretical number-average molar
masses (Mn th) of the polymers at full conversion were around 20
kg mol-1. Selected conversion-time data, number-average
molecular weights and dispersities of obtained polymers are
summarized in Table 3.
1
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
BA
St
0.5
1
0.77
ND
2
1
1.37
1.23
1.07
1.06
1.08
1.10
ND
3
1
2
8.83
9.73
4
1
3.5
5
15.97
18.94
20.96
0.89
18.11
22.28
24.84
ND
5
1
6
1
8
7
2
0.5
1
8
2
2.7%
1.12
ND
ND
9
2
2
17.3%
51.4%
72.4%
89.5%
1.2%
4.31
4.78
1.16
1.07
1.07
1.10
ND
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
2
3.5
5
11.73
16.31
20.04
0.82
14.30
20.31
24.59
ND
2
2
8
3
0.5
1
3
2.0%
0.99
ND
ND
3
2
13.1%
35.7%
51.0%
67.3%
0.9%
3.41
3.48
1.14
1.07
1.06
1.08
ND
3
3.5
5
8.35
9.29
3
11.67
15.22
0.73
13.59
18.01
ND
3
8
Scheme 4. Sn-RAFT polymerization.
4
0.5
1
4
5.7%
1.78
1.56
1.18
1.06
1.06
1.09
1.13
ND
4
2
52.5%
78.9%
88.0%
93.7%
1.0%
11.96
17.72
19.70
20.95
0.77
13.28
19.97
22.65
24.79
ND
In the case of BA polymerization, a 1 hour inhibition period
was observed for all RAFT agents (Figure 3). This phenomenon
is related to the very high reactivity of Sn-RAFT agents with slow
initialization.[26] The structure of the R-group has a clear effect on
the rate of polymerization, whereas the substitution of Z-group
does not have a significant effect. Hence, 1,4 and 7 with benzyl
or 4-fluorobenzyl R-groups provide the highest rates of
polymerization, consistent with the stability of the benzyl radical,
which is scarcely affected by a para-fluoro substituent. In case of
more stabilized secondary 1-phenylethyl radical (2 and 8) the
polymerization is slightly slower. Finally, significant resonance
stabilization of the 4-nitrobenzyl radical in the case of 3 slows
down the reinitiation and the polymerization in general.
For all the RAFT agents tested, Mn values (Figure 3) increase
linearly during the polymerization in agreement with theoretical
predictions. However, a slight upward curvature can be observed
at higher conversions due to chain termination via recombination.
Dispersities (Figure 3) decrease continuously over the course of
the polymerization, reaching a minimum of 1.06 before slightly
increasing (up to 1.13 in the worst case with RAFT agent 4) after
about 75% conversion due to irreversible deactivation of a small
fraction of growing chains. These features are illustrated by the
evolution of the SEC chromatograms of PBA samples (Figures 3,
S38-S42). Slight shouldering can be observed at high reaction
times due to formation of dead chains with doubled molecular
weight.
4
3.5
5
4
4
8
7
0.5
1
7
7.5%
2.20
2.13
1.25
1.07
1.06
1.08
1.09
ND
7
2
44.3%
76.8%
86.1%
94.1%
1.5%
10.21
17.29
19.33
21.05
0.91
10.15
18.13
21.02
23.50
ND
7
3.5
5
7
7
8
8
0.5
1
8
4.2%
1.50
1.12
1.18
1.09
1.06
1.06
1.07
1.18
1.24
1.31
1.28
1.36
1.42
1.18
1.24
1.33
1.32
1.34
1.44
8
2
22.5%
47.0%
65.0%
84.8%
2.2%
5.46
5.67
8
3.5
5
10.82
14.74
19.05
0.98
11.56
16.20
21.05
1.16
8
8
8
1
2
1
St
4
5.1%
1.59
1.68
1
St
8
10.3%
28.9%
46.4%
55.8%
0.9%
2.67
2.82
1
St
24
48
72
2
6.54
9.07
1
St
10.18
12.15
0.75
18.46
25.36
1.21
1
St
7
St
7
St
4
1.5%
0.86
1.48
7
St
8
4.4%
1.47
2.18
7
St
24
48
72
19.5%
36.0%
43.7%
4.61
8.01
7
St
8.05
16.51
20.08
RAFT agents 1 and 7 showed similar levels of control over the
polymerization of styrene, as well as quite similar polymerization
kinetics (Figure S43), though the reaction was slightly faster in the
presence of 1. Mn values (Figure S44) agreed with theory only at
the initial stage of the polymerization, with strong deviations at
higher reaction times, while Đ increased from 1.18 to 1.44. SEC
analysis (Figures S45 and S46) showed the formation of
multimodal molecular weight distributions. Such behavior may be
7
St
9.66
[a]Monomer. [b]Monomer conversion determined by 1H NMR.
[c]
M
n th
= Mw(RAFT agent) + ([M]0/[RAFT agent]0)×(conv.)×Mw(M).
[d]Determined by SEC. [e]Ɖ = Mw/Mn. [f]Not determined.
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due to thermal degradation of triarylstannanecarbodithioates,
which becomes significant over the long reaction times required
for St polymerization.
The chemical structure of RAFT agent 4 allows both 19F and
119Sn NMR to be used as separate analytical channels to study
the transformations of α- and ω-functionalities respectively over
the course of polymerization.
For this purpose, polymerizations of BA and St were
performed directly in NMR tubes[25] with C6D6 as a solvent and
trifluorotoluene as an internal standard for 19F NMR quantification
of RAFT agent transformations. It should be noted that 19F NMR
is quantitative, whereas 119Sn NMR taken with proton decoupling
can be used only for qualitative evaluation due to the
heteronuclear Overhauser effect.
For each monomer, 6 parallel experiments were performed
(Table 4). The concentration of RAFT agent was increased to
enhance the quality of 119Sn NMR spectra. The initial
concentration ratio of reagents was [Monomer]:[RAFT agent
4]:[AIBN] = 60:1:0.1 corresponding to maximum Mn th values of
8.22 kg mol-1 for BA and 6.79 kg mol-1 for St. To guarantee
uniformity of initial composition, all tubes in the series were
prepared in a glovebox from the same degassed stock solution.
After heating for the requisite times, reaction mixtures were
1
quenched by freezing in liquid nitrogen, then H, 19F and 119Sn
NMR spectra were collected (Figures S47-S58), and, finally, the
contents of each tube were analyzed by SEC.
Table 4. Results of the polymerizations using 4 as CTA with NMR
monitoring.
[d]
[e]
Entry Time
h
M[a]
M
RAFT
conv[c]
18.1
Mn th
Mn
Đ[f]
conv[b]
1.5%
2.8%
6.8%
37.7%
55.3%
75.7%
1.1%
3.4%
6.2%
9.7%
16.5%
29.4%
kg mol-1
0.65
0.75
1.06
3.44
4.79
6.35
0.61
0.75
0.92
1.14
1.57
2.37
kg mol-1
ND[g]
ND
1
0.5
1
BA
BA
BA
BA
BA
BA
St
ND
2
33.0
ND
3
2
56.1%
93.7%
98.3%
99.9%
5.9%
ND
ND
4
4
3.49
4.46
6.61
ND
1.19
1.17
1.12
ND
5
5
6
6
7
1
8
2
St
32.6%
46.2%
58.3%
74.0%
87.9%
ND
ND
9
6
St
ND
ND
10
11
12
12
24
48
St
ND
ND
St
1.18
2.23
1.29
1.33
St
[a]Monomer. [b]Monomer conversion determined by 1H NMR.
[c]RAFT agent conversion determined by 19F NMR.
[d]
M
n th
= Mw(RAFT agent) + ([M]0/[RAFT agent]0)×(conv.)×Mw(M).
[e]Determined by SEC. [f]Ɖ = Mw/Mn. [g]Not determined.
The combination of 1H and 19F NMR allowed precise
quantification of the conversions of monomers and RAFT agent.
The corresponding kinetic plots are shown in Figures S59 and
S60. In BA polymerization, the retardation period lasts only up to
about 50 % RAFT agent conversion (Figure S59). Then
polymerization continues with gradual consumption of RAFT
agent, indicating non-selective initialization. No induction period
was observed in St polymerization (Figure S60). These data
allowed determination of apparent Ctr values of 12.3 for BA and
Figure 3. Results of Sn-RAFT polymerizations of BA. (a) semi-logarithmic
kinetic plot, (b) evolution of Mn and Ð, (c) overlay of SEC chromatograms for
CTA 4.
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8.5 for St (95% confidence intervals 9.6<Ctr<15.0 for BA and
6.4<Ctr<10.8 for St) using non-linear least squares fitting[61]
(Figure 4).
During the polymerization process, no signals outside of
the -120 to -115 ppm region were observed in 19F NMR spectra
(Figures S47-S56). In the case of BA polymerization (Figures 5,
S47), in parallel with decrease of initial RAFT agent peak at -115.9
ppm, two other peaks arise with chemical shifts of -118.2 ppm and
about -118.7 ppm. The first peak can be attributed to the
monoadduct as it arises only at the initial step of the
polymerization and subsequently disappears completely,
reaching a maximum concentration of 13.2 % after 2 hours.
Additionally, its appearance as well-defined peak confirms that
this signal belongs to a small molecule. The broad peak at -118.7
ppm belongs to the polymer’s α-chain end. However, 19F NMR
spectroscopy with proton decoupling reveals a set of separate
peaks which can be attributed to oligomers. Two of them with
chemical shifts of -118.5 and -118.6 ppm are particularly
interesting as they appear only in parallel with the peak of
monoadduct and can be very likely attributed to bis- and triadduct.
Observation of all these peaks confirms the non-selective
RAFT agent initialization. Finally, the intensity of polymer peak
after 8 hours confirms the complete transformation of RAFT agent
into polymer.
Figure 4. Determination of Ctr for the polymerization of BA and St mediated by
RAFT agent 4 based on 1H and 19F NMR data.
119Sn NMR spectra (Figures 6, S51, S52) demonstrate similar
tendencies as were previously observed for methyl acrylate.[25]
A
characteristic drift of the chemical shift towards weaker field was
observed, whereas the chemical shift of the polyacrylate
macroRAFT agent is close to that of RAFT agent 6 with acrylate-
like R-group. Additionally, a sharp peak with a chemical shift of -
186.1 ppm was observed at the initial step of the polymerization.
Its disappearance after 2 hours suggests that it is due to a
monoadduct. After 8 hours, a new peak was observed around -52
ppm. In our previous study[25] this was identified as
The evolution of Mn and Ð (Figures S61-S64) follows the
same trends as in the case of RAFT polymerization under
classical conditions. However, there is a small improvement in the
control that is mostly explained by increased concentration of
RAFT agent.
Detailed examination of 19F and 119Sn NMR spectra (Figures
5 and 6) reveals some intriguing details of RAFT agent
transformations.
Figure 5. 19F NMR spectra of reaction mixtures of: St with Sn-RAFT 4 after 48 h (A) and 2 h (B); Sn-RAFT 4 (C); reaction mixtures of BA with Sn-RAFT 4 after 2 h
(D) and 6 h (E). Each spectrum is fitted to highest intensity. Numbers next to each peak describe the percent fraction of each species in solution.
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Figure 6. 119Sn{1H} NMR spectra of: Sn-RAFT 2 (A); reaction mixtures of St with Sn-RAFT 4 after 48 h (B) and 2 h (C); Sn-RAFT 4 (D); reaction mixtures of BA with
Sn-RAFT 4 after 2 h (E) and 6 h (F); Sn-RAFT 6 (G). Each spectrum is fitted to highest intensity.
bis(triphenylstannyl)sulfide, a product of thermal decomposition of
the polymer’s ω-chain ends. We believe that such loss of polymer
chains is the main driving force for the observed deviations of the
control over molecular weight and shouldering in SEC
chromatograms at higher reaction times.
while the compound with a chemical shift of -54.1 ppm remains
unidentified. The kinetics and mechanism of this thermal
degradation is currently under investigation.
In case of St polymerization, 19F NMR spectra (Figures S53-
S56) demonstrate the same trends as in the case of BA.
Incorporation of St units between 4-fluorobenzyl group and
triphenylstannanecarbodithioate moiety leads to the gradual drift
of the fluorine signal to higher field, while differences in the
chemical shifts allow identification of the monoadduct at -118.5
and higher adducts between -118.96 and -119.03 ppm. However,
the most remarkable point is the formation of two new peaks at -
117.2 and -114.9 ppm after 6 hours of the polymerization. Based
on their appearance, they belong to small molecules and,
hypothetically, should belong to the products of thermal
decomposition of initial RAFT agent which was not yet
transformed into polymer as 19F NMR shows only the evolution of
R-group. At the same time, 119Sn NMR spectra (Figures 6, S57,
S58) allow detection of the decomposition of both initial RAFT
agent and polymer’s ω-chain end. After 48 hours of the
polymerization, the NMR spectrum reveals three new species in
Conclusions
New alkyl triarylstannanecarbodithioates (Sn-RAFT agents) were
synthesized using
chlorides. Their complete characterization using spectroscopic
and spectrometric methods, including X-ray analyses, was
described. The structures obtained were very similar and most of
a simple procedure from triarylstannyl
̅
the compounds crystallize in the P1 space group. For the first time,
the chemical shift in 13C NMR and the bond length of C=S for the
main classes of thiocarbonylthio RAFT agents were discussed
and compared to those of Sn-RAFT agents. The very high
chemical shift (262-266 ppm) of C=S compared to other types of
RAFT agents and bond lengths similar to those of highly reactive
dithioesters and trithiocarbonates indicated a high reactivity of
alkyl triarylstannanecarbodithioates in RAFT polymerization.
Indeed, they were found to control efficiently the RAFT
polymerization of St and BA. The effect of R and Z groups of Sn-
RAFT agents on the kinetics of polymerization of St has been
discussed. In most cases, Mn increases with monomer conversion
addition to the signals of unreacted
4 and polystyrene
macroRAFT agent. Two of them were identified as
bis(triphenylstannyl) sulfide and bis(triphenylstannyl) oxide,[25]
with
a strong upward deviation over the course of the
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(Aldrich, 99%), tin(IV)chloride (Aldrich, 98%) and triphenylstannyl chloride
(Fluka, 95%) were used as received. Tri-p-tolylstannyl chloride was
prepared in two steps according to the literature methods.[63,64] Butyl
acrylate (BA, Aldrich, 99%) and styrene (St, Aldrich, 99%) were passed
through a column filled with neutral aluminium oxide (Brockmann I) prior
to use. 2,2’-Azobis(2-methylpropionitrile) (AIBN, Acros, 98%) was purified
by double recrystallization from methanol.
polymerization, with final dispersities around 1.4. The
polymerization of BA proceeds with a much better control over Mn
values and lower dispersities (Ð < 1.15). High Ctr values of 8.5
and 12.3 have been determined for St and BA, respectively, using
1H and 19F NMR spectroscopy. 119Sn and 19F NMR revealed the
presence of an initialization period during BA (but not St)
polymerization. It also allowed the identification of
di(triphenylstannyl) oxide and di(triphenylstannyl) sulfide among
the by-products, which may explain the deviations from a well-
controlled polymerization. The Sn-RAFT chain end appears to be
thermally unstable, and degrades over prolonged reaction times.
Nevertheless, Sn-RAFT polymerization is one of the few
examples of a RDRP process where heteronuclear NMR allows
observation of an initialization step, determination of chain
transfer constants and the revelation and identification of RAFT
agent decomposition products.
General method for the synthesis of compounds 1-9. A solution of
naphthalene (2.56 g, 20 mmol) in dry THF (50 mL) was stirred with Na
metal (0.46 g, 20 mmol) at ambient temperature for 4 h. Obtained dark
green solution was slowly added at ambient temperature (Caution!
Reaction is highly exothermic) to the corresponding triarylstannyl chloride
(10 mmol) with vigorous stirring and stirred for additional 1 h. Then CS2 (2
mL, 33 mmol) was added dropwise to the orange solution of
(triarylstannyl)sodium at 0-5 °C and stirred for 1 h. Final solution of crude
sodium triarylstannanecarbodithioate was adjusted to 100 mL with dry
THF (0.1 M concentration) and used for the next synthetic steps as it is.
Sodium triarylstannanecarbodithioate solution (50 mL, 5 mmol) was added
dropwise to the corresponding alkyl halide (6 mmol) at 0-5 °C with vigorous
stirring and stirred additionally for 2 h. Then it was concentrated under a
reduced pressure and washed twice with 20 mL of cold hexane to remove
naphthalene and most of impurities. Red oily residue was subjected to
chromatography, eluting with a petroleum ether – ethyl acetate gradient to
collect the pink fraction. After the concentration under a reduced pressure,
the pink oil was crystalized from corresponding solvent (hexane for 1,2,5,6
acetone for 3,4 or pentane for 7,8).
Experimental Section
General: All the reactions were performed using standard Schlenk
techniques involving flame-dried glassware, oven-dried Teflon coated stir
bars and sleeve stopper septa under a dry argon atmosphere. Terumo
single use plastic syringes were used for the measurements of all liquid
reagents and solvents. Air and moisture-sensitive solids were weighed in
a glovebox under a dry argon atmosphere. Products were purified with
flash chromatography on 35–70 mesh silica gel (porosity 90 Å) using
degassed eluents and positive pressure of argon.
Benzyl triphenylstannanecarbodithioate 1[25] (1.89 g, 73%). Pink crystals,
1
m.p.: 94–96 °C (lit. 96 °C[35]). H NMR (300.13 МHz, toluene-d8, 298 K):
4.43 (pt, 4JSn,H = 4.2 Hz, 2H; CH2C6H5), 6.93 (m, 5H, CH2C6H5), 7.09–7.19
3
(m, 9H; 3-H, 4-H, (C6H5)3Sn), 7.57–7.81 (m, JSn,H = 50.7 Hz, 6H; 2-H,
(C6H5)3Sn); 13C{1H} NMR (75.47 МHz, toluene-d8, 298 K): 38.8 (pt, 3JSn,C
= 12.4 Hz; CH2C6H5), 127.5 (s; 3-C, CH2C6H5), 128.7 (s; 4-C, CH2C6H5),
129.1 (pt, 2JSn,C = 55.9 Hz; 2-C, (C6H5)3Sn), 129.5 (s; 2-C, CH2C6H5), 129.8
(pt, 4JSn,C = 12.1 Hz; 4-C, (C6H5)3Sn), 135.7 (s; 1-C, CH2C6H5), 137.4 (pt,
Melting points were measured with a sealed capillary by using the Stuart
automatic melting point SMP40 apparatus. NMR spectra were recorded
using a Bruker Avance AMX 300 spectrometer (strength of the magnetic
field is 7.049 T, operating frequencies are 300.13 МHz for 1H, 282.40 МHz
for 19F, 98.20 МHz for 119Sn and 75.47 МHz for 13C) at 298 K. Chemical
shifts are expressed in parts per million with residual solvent signals as
internal reference (1H and 13C{1H} NMR). The external chemical shift
reference is Me4Sn (0 ppm) for 119Sn NMR and trifluorotoluene (-
63.72 ppm) for 19F NMR. IR spectra were recorded using a Thermo
Fischer Nexus 6700 FTIR spectrometer in ATR mode, values of νmax (in
cm-1) are given for the major absorption bands. High resolution mass
spectrometry (HRMS) was performed on Waters GCT Premier CAB109
TOF mass spectrometer in the chemical ionisation mode (CH4).
1
3JSn,C = 38.6 Hz; 3-C, (C6H5)3Sn), 137.8 (pt, JSn,C = 548 Hz; 1-C,
(C6H5)3Sn), 264.7 (s; CS2); 119Sn{1H} NMR (98.20 МHz, toluene-d8, 298
K): −191.0. IR: 1046.6 (C=S). HRMS (CI, CH4, m/z of [MH+]): found —
515.0245, calculated for C26H23S2Sn — 515.0259.
1-Phenylethyl triphenylstannanecarbodithioate 2.[25] (1.49 g, 56%). Pink
1
crystals, m.p.: 93–95 °C. H NMR (300.13 МHz, toluene-d8, 298 K): 1.44
(m, 3JH,H = 7.1 Hz, 5JSn,H = 3.5 Hz, 3H; CH(CH3)C6H5), 5.84 (m, 3JH,H = 7.1
Hz, 4JSn,H = 7.3 Hz, 1H; CH(CH3)C6H5), 6.90–7.08 (m, 5H; CH(CH3)C6H5),
3
7.09–7.19 (m, 9H; 3-H, 4-H, (C6H5)3Sn), 7.57–7.81 (m, JSn,H = 51.9 Hz,
6H; 2-H, (C6H5)3Sn); 13C{1H} NMR (75.47 МHz, toluene-d8, 298 K): 20.0
(s; CH(CH3)C6H5), 46.3 (pt, 3JSn,C = 13.3 Hz; CH(CH3)C6H5), 127.6 (s; 4-C,
CH(CH3)C6H5), 128.0 (s; 2-C, CH(CH3)C6H5), 128.8 (s; 3-C,
The monomer conversions were determined by 1H NMR spectroscopy.
Number-average molar mass (Mn) and dispersity (Ɖ) values of the polymer
samples were determined by SEC. The SEC analyses were conducted on
a system composed of Waters 515 HPLC pump, Agilent 1260 Autosampler,
Varian ProStar 500 column valve module, set of three Waters columns
(Styragel Guard Column, 20 µm, 4.6 mm × 30 mm, Styragel HR3, 5 µm,
7.8 mm × 300 mm and Styragel HR4E, 5 µm, 7.8 mm × 300 mm), Varian
ProStar 325 UV-Vis detector set at 290 nm and Wyatt Optilab rEX
differential refractive index detector using tetrahydrofuran (THF) as an
eluent at a flow rate of 1.0 mL min-1 (35 °C). The column system was
calibrated with PSt standards (ranging from 860 to 483400 g mol-1) for PSt
and PMMA standards (ranging from 1120 to 138600 g mol-1) for PBA using
the Landau-Kuhn-Mark-Houwink-Sakurada equation.[62] Prior to injection,
samples were diluted to a concentration about 5 mg mL-1 and filtered
through 0.45 µm Nylon syringe filters.
2
CH(CH3)C6H5), 129.1 (pt, JSn,C = 54.3 Hz; 2-C, (C6H5)3Sn), 129.8 (pt,
3
4JSn,C = 12.1 Hz; 4-C, (C6H5)3Sn), 137.4 (pt, JSn,C = 38.6 Hz; 3-C,
1
(C6H5)3Sn), 138.0 (pt, JSn,C = 546 Hz; 1-C, (C6H5)3Sn), 141.3 (s; 1-C,
CH(CH3)C6H5), 264.0 (s, CS2); 119Sn{1H} NMR (98.20 МHz, toluene-d8,
298 K): −192.7. IR: 1040.5 (C=S). HRMS (CI, CH4, m/z of [MH+]): found —
533.0482, calculated for C27H25S2Sn — 533.0420.
4-Nitrobenzyl triphenylstannanecarbodithioate 3 (2.70 g, 80%). Red
crystals, m.p.: 141–143 °C. 1H NMR (300.13 МHz, toluene-d8, 298 K): 4.18
3
6
(s, 2H; C6H4CH2), 6.58 (m, JH,H = 8.8 Hz, JSn,H = 4.5 Hz, 2H; 2-H,
C6H4CH2), 7.13–7.22 (m, 9H; 3-H, 4-H, (C6H5)3Sn), 7.57 (m, 3JH,H = 8.8 Hz,
7JSn,H = 4.5 Hz, 2H; 3-H, C6H4CH2), 7.60–7.82 (m, 3JSn,H = 51.6 Hz, 6H; 2-
H, (C6H5)3Sn); 13C{1H} NMR (75.47 МHz, toluene-d8, 298 K): 37.2 (pt,
2
3JSn,C = 12.4 Hz; C6H4CH2), 123.6 (s; 2-C, C6H4CH2), 129.3 (pt, JSn,C
=
Materials: Solvents were received from Sigma-Aldrich, Alfa Aesar or SDS
and dried, if necessary, by passing through a column packed with activated
molecular sieves 4 Å under a positive pressure of dry nitrogen. Benzyl
bromide (Acros, 98%), bromoacetonitrile (Aldrich, 97%), (1-
bromoethyl)benzene (Aldrich, 97%), 4-bromotoluene (Aldrich, 98%), 4-
fluorobenzyl bromide (Aldrich, 97%), iodomethane (Aldrich, ≥99%),
magnesium (Aldrich, 98%), Na metal (Aldrich), methyl 2-bromopropionate
(Alfa Aesar, 97%) naphtalene (Aldrich, ≥99%), 4-nitrobenzyl bromide
54.8 Hz; 2-C, (C6H5)3Sn), 129.8 (s; 3-C, C6H4CH2), 130.1 (pt, 4JSn,C = 12.2
Hz; 4-C, (C6H5)3Sn), 137.4 (pt, 3JSn,C = 38.8 Hz; 3-C, (C6H5)3Sn), 137.5 (pt,
1JSn,C = 547 Hz; 1-C, (C6H5)3Sn), 142.8 (s; 1-C, C6H4CH2), 147.3 (s; 4-C,
C6H4CH2), 264.8 (s; CS2); 119Sn{1H} NMR (98.20 МHz, toluene-d8, 298 K):
−187.2. IR: 1044.0 (C=S). HRMS (CI, CH4, m/z of [MH+]): found —
564.0101, calculated for C26H22NO2S2Sn — 564.0114.
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4-Fluorobenzyl triphenylstannanecarbodithioate 4 (2.06 g, 77%). Pink
crystals, m.p.: 141–143 °C. 1H NMR (300.13 МHz, toluene-d8, 298 K): 4.29
(s, 2H; FC6H4CH2), 6.48–6.62 (m, 2H; 2-H, FC6H4CH2), 6.65–6.75 (m, 2H;
3-H, FC6H4CH2), 7.11–7.24 (m, 9H; 3-H, 4-H, (C6H5)3Sn), 7.56–7.85 (m,
3JSn,H = 51.0 Hz, 6H; 2-H, (C6H5)3Sn); 13C{1H} NMR (75.47 МHz, toluene-
d8, 298 K): 37.8 (pt, 3JSn,C = 12.4 Hz; C6H4CH2), 115.5 (d, 2JF,C = 21.5 Hz;
Methyl triphenylstannanecarbodithioate 9 (1.85 g, 84%). Pink crystals,
1
m.p.: 127-129 °C (lit. 128-129 °C[30]). H NMR (300.13 МHz, CDCl3, 298
4
K): 2.77 (pt, JSn,H = 2.4 Hz, 3H; CH3), 7.38–7.52 (m, 9H; 3-H, 4-H,
3
(C6H5)3Sn), 7.58–7.82 (m, JSn,H = 51.8 Hz, 6H; 2-H, (C6H5)3Sn); 13C{1H}
3
NMR (75.47 МHz, CDCl3, 298 K): 18.6 (pt, JSn,C = 13.7 Hz; CH3), 128.9
2
4
(pt, JSn,C = 55.4 Hz; 2-C, (C6H5)3Sn), 129.8 (pt, JSn,C = 12.1 Hz; 4-C,
(C6H5)3Sn), 137.2 (pt, 3JSn,C = 38.5 Hz; 3-C, (C6H5)3Sn), 137.6 (pt, 1JSn,C
2
3-C, FC6H4CH2), 129.1 (pt, JSn,C = 55.8 Hz; 2-C, (C6H5)3Sn), 129.9 (pt,
=
4JSn,C = 12.2 Hz; 4-C, (C6H5)3Sn), 131.1 (d, 3JF,C = 8.1 Hz; 2-C, FC6H4CH2),
131.4 (d, 4JF,C = 3.3 Hz; 1-C, FC6H4CH2), 137.4 (pt, 3JSn,C = 38.7 Hz; 3-C,
548.9 Hz; 1-C, (C6H5)3Sn), 266.6 (s; CS2); 119Sn{1H} NMR (98.20 MHz,
CDCl3, 298 K): −192.4. IR: 1045.1 (C=S). HRMS (CI, CH4, m/z of [MH+]):
found — 442.9872, calculated for C20H19S2Sn — 442.9872.
1
1
(C6H5)3Sn), 137.7 (pt, JSn,C = 548 Hz; 1-C, (C6H5)3Sn), 162.4 (d, JF,C
=
246 Hz; 4-C, FC6H4CH2), 265.0 (s; CS2); 119Sn{1H} NMR (98.20 МHz,
toluene-d8, 298 K): −190.4; 19F{1H} NMR (282.40 MHz, toluene-d8, 298 K):
−115.9. IR: 1050.0 (C=S). HRMS (CI, CH4, m/z of [MH+]):found —
537.0179, calculated for C26H22FS2Sn — 537.0169.
Crystallographic data collection and structure determination: Single
crystals of compounds 1-5, 7-9 were selected for X-ray diffraction studies
and were mounted on a microloop (MiTegen) at low temperature (193K).
X-ray diffraction intensity data were measured on a Bruker-AXS SMART
APEX II (1-4, 8), Bruker-AXS Kappa APEX II Quazar (5, 7) diffractometers,
equipped with a 30W air-cooled microfocus source, or on a Bruker-AXS
D8-Venture equipped with a CMOS Area detector (9) by using MoKα
radiation (λ = 0.71073 Å). Phi- and omega- scans were used. The data
were integrated with SAINT, and an empirical absorption correction with
SADABS was applied.[65] The structures were solved by direct methods
(SHELXS-97) and refined using the least-squares method on F2.[66]
Mercury[67] was used was used for molecular graphics. All non-H atoms
were refined with anisotropic displacement parameters. The Hydrogen
atoms were refined isotropically at calculated positions using a riding
model. CCDC 1546707 (1), CCDC 1546708 (2), CCDC 1546709 (3),
CCDC 1546710 (4), CCDC 1546711 (5), CCDC 1546712 (7), CCDC
1546713 (8) and CCDC1557159 (9) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre.[52]
Cyanomethyl triphenylstannanecarbodithioate 5 (1.60 g, 69%). Pink
1
crystals (unstable), m.p.: ~65 °C (decomposition). H NMR (300.13 МHz,
CDCl3, 298 K): 4.23 (pt, 4JSn,H = 2.3 Hz, 2H; CH2CN), 7.46–7.62 (m, 9H; 3-
3
H, 4-H, (C6H5)3Sn), 7.64–7.85 (m, JSn,H = 53.5 Hz, 6H; 2-H, (C6H5)3Sn);
3
13C{1H} NMR (75.47 МHz, CDCl3, 298 K): 17.9 (pt, JSn,C = 12.6 Hz;
2
CH2CN), 114.4 (s; CH2CN), 129.2 (pt, JSn,C = 57.1 Hz; 2-C, (C6H5)3Sn),
4
130.2 (pt, JSn,C = 12.3 Hz; 4-C, (C6H5)3Sn), 136.4 (s; 1-C, (C6H5)3Sn),
137.1 (pt, 3JSn,C = 38.6 Hz; 3-C, (C6H5)3Sn), 262.6 (s; CS2); 119Sn{1H} NMR
(98.20 MHz, CDCl3, 298 K): −179.5.
Methyl 2-(((triphenylstannyl)carbonothioyl)thio)propanoate 6 (1.88 g, 74%).
Pink solid, mp 68–70 °C (decomposition). 1H NMR (300.13 МHz, toluene-
d8, 298 K): 1.26 (m, 3JH,H = 7.1 Hz, 5JSn,H = 3.8 Hz, 3H; CH(CH3)CO2CH3),
3
4
3.19 (s, 3H; CO2CH3), 5.29 (m, JH,H = 7.3 Hz, JSn,H = 5.9 Hz, 1H;
CH(CH3)CO2CH3), 7.12–7.17 (m, 9H; 3-H, 4-H, (C6H5)3Sn), 7.54–7.78 (m,
3JSn,H = 52.5 Hz, 6H; 2-H, (C6H5)3Sn); 13C{1H} NMR (75.47 МHz, toluene-
3
d8, 298 K): 16.0 (s; CH(CH3)CO2CH3), 43.9 (pt, JSn,C = 13.2 Hz;
General polymerization procedure under common conditions: A
solutions (5 mL) that contained the monomers, Sn-RAFT 1-4,7,8, AIBN,
and 1,4-dioxane in the following concentrations: [BA]0=5.10 mol L-1,
[St]0=6.00 mol L-1, [RAFT]0=30.0 mmol L-1, [AIBN]0=6.0 mmol L-1 were
prepared in 15 mL vials, sealed with rubber septa, degassed by bubbling
argon for 30 min and heated at 60 °C in a thermostated heating block.
Aliquots of the reaction mixture (100 µL) were taken at given intervals,
diluted with CDCl3 and analyzed with 1H NMR. Then the excess amount of
monomer and solvent were removed by evaporation at ambient
temperature under vacuum and the residues were analyzed by using SEC.
CH(CH3)CO2CH3), 52.0 (s; CH(CH3)CO2CH3), 129.2 (pt, 2JSn,C = 55.0 Hz;
4
2-C, (C6H5)3Sn), 129.9 (pt, JSn,C = 12.2 Hz; 4-C, (C6H5)3Sn), 137.4 (pt,
1
3JSn,C = 39.5 Hz; 3-C, (C6H5)3Sn), 137.6 (pt, JSn,C = 541 Hz; 1-C,
(C6H5)3Sn), 170.7 (s; CO2CH3), 263.3 (s; CS2); 119Sn{1H} NMR (98.20 МHz,
toluene-d8, 298 K): −186.6. IR: 1743.4 (C=O), 1046.4 (C=S). HRMS (CI,
CH4, m/z of [MH+]): found — 511.0178, calculated for C23H23O2S2Sn —
511.0157.
Benzyl tri-p-tolylstannanecarbodithioate 7 (1.58 g, 57%). Violet crystals,
m.p.: 77–79 °C. 1H NMR (300.13 МHz, toluene-d8, 298 K): 2.09 (s, 9H;
(CH3C6H4)3Sn), 4.46 (pt, 4JSn,H = 4.3 Hz, 2H; CH2C6H5), 6.91–6.96 (m, 5H;
CH2C6H5), 7.02 (d, 3JH,H = 7.3 Hz, 6H, 3-H, (CH3C6H4)3Sn), 7.69 (m, 3JSn,H
General polymerization procedure in NMR tubes: A solutions (5 mL)
that contained the monomers, Sn-RAFT 4, AIBN, and 1,4-dioxane in the
following concentrations: [BA]0=4.94 mol L-1, [St]0=5.59 mol L-1,
[RAFT]0=93.0 mmol L-1, [AIBN]0=9.0 mmol L-1 were prepared in 15 mL
Schlenk tube with PTFE needle valve and degassed by three freeze-
pump-thaw cycles. Then solutions were transferred into 6 NMR tubes in
the glovebox under argon atmosphere and sealed with rubber septa.
Tubes were heated at 60 °C in a thermostated heating block for the
requisite times, frozen in liquid nitrogen and analyzed with NMR. Then the
excess amount of monomer and solvent were removed by evaporation at
ambient temperature under vacuum and the residues were analyzed by
using SEC.
3
= 43.4 Hz, JH,H = 7.9 Hz, 6H; 2-H, (CH3C6H4)3Sn); 13C{1H} NMR (75.47
МHz, toluene-d8, 298 K): 21.4 (pt, 5JSn,C = 6.1 Hz; (CH3C6H4)3Sn), 38.9 (pt,
3JSn,C = 12.2 Hz; CH2C6H5), 127.4 (s; 4-C, CH2C6H5), 128.7 (s; 2-C,
2
CH2C6H5), 129.5 (s; 3-C, CH2C6H5), 130.0 (pt, JSn,C = 57.4 Hz; 2-C,
(CH3C6H4)3Sn), 134.4 (s; 1-C, (CH3C6H4)3Sn), 135.9 (s; 1-C, CH2C6H5),
137.4 (pt, 3JSn,C = 40.7 Hz; 3-C, (CH3C6H4)3Sn), 139.5 (pt, 4JSn,C = 12.1 Hz;
4-C, (CH3C6H4)3Sn), 266.3 (s; CS2); 119Sn{1H} NMR (98.20 МHz, toluene-
d8, 298 K): −181.3. IR: 1040.1 (C=S). HRMS (CI, CH4, m/z of [MH+]): found
— 559.0730, calculated for C29H29S2Sn — 559.0727.
1-Phenylethyl tri-p-tolylstannanecarbodithioate 8 (1.25 g, 44%). Violet
crystals, m.p.: 110–112 °C. 1H NMR (300.13 МHz, toluene-d8, 298 K): 1.47
(d, 3JH,H = 7.1 Hz, 3H; CH(CH3)C6H5), 2.08 (s, 9H; (CH3C6H4)3Sn), 5.86 (m,
4
3JH,H = 7.1 Hz, JSn,H = 7.0 Hz, 1H; CH(CH3)C6H5), 6.91–6.98 (m, 5H;
Acknowledgements
CH(CH3)C6H5), 7.01 (d, 3JH,H = 7.4 Hz, 6H; 3-H, (CH3C6H4)3Sn), 7.67 (m,
3
3JSn,H = 51.0 Hz, JH,H = 7.9 Hz, 6H; 2-H, (CH3C6H4)3Sn); 13C{1H} NMR
The MESR (Ministère de l’Enseignement Supérieur et de la
Recherche), the “Groupement Franco-Ukrainien en Chimie
Moléculaire” GDRI and the Embassy of France in Kiev are
gratefully acknowledged for financial support. The authors thank
Dr. Simon Harrisson for fruitful discussions and his kind help for
data treatment for the calculation of chain transfer constants,
Caroline Toppan for her support during NMR measurements, Dr.
Sonia Ladeira for her help during X-ray diffraction measurements
(75.47 МHz, toluene-d8, 298 K): 20.1 (s; CH(CH3)C6H5), 21.4 (pt, 5JSn,C
=
6.0 Hz; (CH3C6H4)3Sn), 46.3 (pt, 3JSn,C = 13.2 Hz; CH(CH3)C6H5), 127.5 (s;
4-C, CH(CH3)C6H5), 128.1 (s; 2-C, CH(CH3)C6H5), 128.8 (s; 3-C,
CH(CH3)C6H5), 130.0 (pt, 2JSn,C = 56.1 Hz; 2-C, (CH3C6H4)3Sn), 134.5 (s;
1-C, (CH3C6H4)3Sn), 137.4 (pt, 3JSn,C = 40.3 Hz; 3-C, (CH3C6H4)3Sn), 139.4
4
(pt, JSn,C = 12.3 Hz; 4-C, (CH3C6H4)3Sn), 141.4 (s; 1-C, CH(CH3)C6H5),
265.5 (s; CS2); 119Sn{1H} NMR (98.20 МHz, toluene-d8, 298 K): −182.9. IR:
1044.1 (C=S). HRMS (CI, CH4, m/z of [MH+]): found — 571.0887,
calculated for C30H31S2Sn — 571.0885.
This article is protected by copyright. All rights reserved.

10.1002/chem.201703412
Chemistry - A European Journal
FULL PAPER
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This article is protected by copyright. All rights reserved.

10.1002/chem.201703412
Chemistry - A European Journal
FULL PAPER
FULL PAPER
A
series
of
triarylstannane-
Ihor Kulai, Nathalie Saffon-Merceron,
Zoia Voitenko, Stéphane Mazières and
Mathias Destarac
carbodithioates was synthesized.
Introduction of bulky and strongly
electron-positive tin makes them highly
Page No. – Page No.
reactive
reversible
addition-
fragmentation chain transfer agents in
the free-radical polymerization of
Alkyl Triarylstannanecarbodithioates:
Synthesis, Crystal Structures and
Efficiency in RAFT Polymerization
styrene
119Sn NMR allows the monitoring of
their transformations during
polymerization.
and
n-butyl
acrylate.
This article is protected by copyright. All rights reserved.