Syntheses, crystal structure and spectroscopic characterization of bis(dithiocarbimato)-nickel(II)-complexes: A new class of vulcanization accelerators

Article abstract of DOI:10.1016/j.poly.2010.04.026

The compounds (Ph₄P)₂[Ni(RSO₂NCS ₂)₂] [Ph₄P⁺= tetraphenylphosphonium cation; R = CH₃ (1b), CH₃CH₂ (2b), CH ₃(CH₂)₃

Full text of DOI:10.1016/j.poly.2010.04.026

Polyhedron 29 (2010) 2278–2282
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses, crystal structure and spectroscopic characterization of
bis(dithiocarbimato)-nickel(II)-complexes: A new class of vulcanization accelerators
a,c
a
b
Leandro Marcos Gomes Cunha , Mayura Marques Magalhães Rubinger , José Ricardo Sabino ,
c
a,
*
Leila Léa Yuan Visconte , Marcelo Ribeiro Leite Oliveira
a
Departamento de Química, Universidade Federal de Viçosa, Viçosa MG 36570-000, Brazil
Instituto de Física, Universidade Federal de Goiás, P.O. Box 131, Goiânia GO 74001-970, Brazil
Instituto de Macromoléculas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro, P.O. Box 68525, Rio de Janeiro RJ 21941-598, Brazil
b
c
a r t i c l e i n f o
a b s t r a c t
+
Article history:
The compounds (Ph P) [Ni(RSO N@CS ) ] [Ph P = tetraphenylphosphonium cation; R = CH3 (1b),
4
2
2
2
2
4
Received 25 March 2010
Accepted 28 April 2010
Available online 5 May 2010
CH
CS
3
CH
2
(2b), CH
3
(CH
2
)
3
(3b) and CH
3
(CH
)
2 7
2
(4b)] were synthesized by the reaction of RSO N@
O and Ph PBr. The elemental analyses of C, H, N and Ni were consistent
2 4
with the proposed formula for 1b–4b. The IR data were consistent with the formation of bis(dithiocarbi-
2
K
2
Á2H
2
O (1a-4a) with NiCl
2
Á6H
mato)-nickel(II)-complexes. The NMR spectra showed the expected signals for the cation and the dithio-
Keywords:
carbimate anionic complex in a 2:1 proportion. The compounds 2b and 3b were also characterized by
Dithiocarbimates
Nickel complexes
Crystal structures
Vulcanization accelerators
ꢀ
X-ray diffraction techniques. Compounds 2b and 3b crystallize in the P2
1
/c and P1 space groups, respec-
tively. The nickel(II) ions are positioned in special positions being coordinated by four sulfur atoms of the
+
dithiocarbimate moieties in a square planar environment. The Ph
interstice performing weak C–HÁÁÁO and C–HÁÁÁS intermolecular interactions. The activity of compounds
b–4b in the vulcanization of the natural rubber was evaluated. These studies confirm that the bis(dith-
4
P counter-ions enter the structure
1
iocarbimato)-nickel(II)-complexes are new vulcanization accelerators worth of further investigation.
Ó 2010 Elsevier Ltd. All rights reserved.
1
. Introduction
Several dithiocarbamate and N-substituted dithiocarbamate
cies. The improvement and/or modulation of the vulcanization
activity is an interesting possibility for anionic metal-sulfur com-
pounds, which can be accomplished either by modifying the solu-
bility of the complexes salts with the use of different cations or
different R groups on the dithiocarbimate structures, or by using
active counter ions. Besides, the right choice of R groups and coun-
ter-ions can avoid the formation of nitrosamines.
complexes and salts have been used as agrochemicals mainly due
to their high efficiency in controlling plant fungal diseases, and rel-
atively low toxicity [1–6]. It is interesting to note that many dithio-
carbamato-zinc(II)-complexes are simultaneously fungicides and
vulcanization accelerators. A classical example is the bis(dim-
ethyldithiocarbamato)zinc(II) (Ziran) [2]. Bis(dithiocarbamato)-
zinc(II)-complexes are worldwide used in the rubber vulcanization
process and are known as ultra-accelerators due to their extremely
rapid vulcanization properties [1,2,7–10]. Nevertheless, despite
their widespread application in the rubber industries, these acceler-
ators are frequently criticized due to the potential production of
nitrosamines during the vulcanization processes [11]. Derivatives
of the dithiocarbamate class suitable for industrial application have
been prepared from ‘‘safe” amines in order to avoid the formation of
the carcinogenic nitrosamines [12]. Furthermore, dithiocarbamates
such as bis(dimethyldithiocarbamato)zinc(II) show very low scorch
safety [13], what may represent a processing problem.
Here, we describe the syntheses and the rubber vulcanization
activity of related compounds containing dithiocarbimate anions
derived from sulfonamides with the formula (Ph
4
P)
P = tetraphenylphosphonium cation; R = CH
(2b), CH (CH (3b) and CH (CH (4b)]. The presence
2
[Ni(R–SO
2
N@
+
CS
CH
2
)
2
]
[Ph
4
3
(1b),
3
CH
2
3
2
)
3
3
2 7
)
of the R-sulphonyl group linked to the nitrogen atom of the dithio-
carbimate moiety is important and may avoid the production of
nitrosamines. The compounds 1b–4b were characterized by IR,
1
13
H and C NMR spectroscopies, and by C, H, N and Ni elemental
analyses. The compounds 2b and 3b were also characterized by
X-ray diffraction techniques.
2
. Experimental
Metal(II)-dithiocarbamato-complexes are neutral substances
while the analogous dithiocarbimato-complexes are anionic spe-
2.1. Materials and methods
The solvents were purchased from Merck and used without fur-
*
Corresponding author. Tel.: +55 31 3899 3059; fax: +55 31 3899 3065.
E-mail address: marcelor@ufv.br (M.R. Leite Oliveira).
ther purification. Carbon disulfide and potassium hydroxide were
0
277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.04.026

L.M. Gomes Cunha et al. / Polyhedron 29 (2010) 2278–2282
2279
purchased from Vetec. The tetraphenylphosphonium bromide,
2.3.1. Tetraphenylphosphonium
ethanesulfonyl chloride, butanesulfonyl chloride, octanesulfonyl
chloride and methanesulfonamide were purchased from Aldrich.
The other sulfonamides were prepared from the corresponding
alkylsulfonyl chlorides, in reaction with concentrated ammonia
aqueous solution (Vetec), under reflux. The sulfonamides were
isolated after extraction with ethyl acetate and solvent evapora-
tion. Melting points (m.p.) were determined with a Mettler FPS
equipment. Microanalyses for C, H and N were obtained from a Per-
kin Elmer Elemental Analyzer 2400 CHN. Nickel was analyzed by
atomic absorption with a Varian Spectra AA200 Atomic Absorption
bis(methylsulphonyldithiocarbimato)nickelate(II), (1b)
46 2 4 2 6
Found (Calcd for C52H N O P S Ni): C, 57.72 (58.05); H, 4.15
(4.31); N, 2.72 (2.60); Ni, 5.22 (5.45). M.p. (°C): 211.8–213.4. IR
À1
(CsI) (most important bands) (cm ): 1403 (
mCN), 1285 (
m
SO2as),
1
1129 (
anion signals) (d): 3.1 (s, H1). C NMR (dithiocarbimate anion sig-
nals) (d): 40.1 (C1), 210.3 (N@CS ).
mSO2s), 926 (mCS2as), 396 (mNiS). H NMR (dithiocarbimate
1
3
2
2.3.2. Tetraphenylphosphonium bis(4-
ethylsulphonyldithiocarbimato)nickelate(II), (2b)
Found (Calcd for C54H50N O P S Ni): C, 58.62 (58.75); H, 4.54
Spectrophotometer. The IR spectra were recorded with a Perkin El-
2
4 2 6
1
mer 283 B infrared spectrophotometer using CsI pellets. The
H
(4.56); N, 2.84 (2.54); Ni, 5.43 (5.32). M.p. (°C): 192.7–193.9. IR
1
3
À1
and C NMR spectra were recorded with a Bruker Advance DRX-
00 spectrophotometer in D O for the dithiocarbimate potassium
salts and CDCl for the other compounds.
(CsI) (most important bands) (cm ): 1429 (
1115 (
m
CN), 1280 (
mSO2as),
1
4
2
2s
mSO ), 936 (mCS2as), 394 (mNiS). H NMR (dithiocarbimate
3
anion signals) (d), J (Hz): 1.21 (t, J = 7.4, 6H, H2); 3.13 (q, J = 7.4,
1
3
4
4
H, H1). C NMR (dithiocarbimate anion signals) (d): 8.4 (C2);
6.7 (C1); 212.0 (N@CS ).
2
2.2. Syntheses of the dithiocarbimate potassium salts
2
.3.3. Tetraphenylphosphonium
bis(butylsulphonyldithiocarbimato)nickelate(II), (3b)
Found (Calcd for C58 Ni): C, 59.45 (60.05); H, 4.86
The syntheses of 1a and 2a are described in literature [14,15].
All the procedure was carried out in ice bath. Carbon disulfide
58 2 4 2 6
H N O P S
(
0.2 mol) and potassium hydroxide (0.1 mol) were added to a
solution of the corresponding sulfonamide (0.2 mol) in DMF
100 mL). The mixture was stirred for 2 h previous to the addition
of a second portion of potassium hydroxide (0.1 mol). After stir-
ring for further 2 h, 30 mL of ice cold ethanol was added. The yel-
lowish solid obtained was separated by filtration, washed with ice
ethanol, ethyl acetate, diethyl ether, and dried under reduced
(
(
5.04); N, 2.56 (2.41); Ni, 4.87 (5.06). M.p. (°C): 184.4–185.9. IR
CsI) (most important bands) (cm ): 1425 (
À1
m
CN), 1267 (
m
SO2as),
(
1
1
109 (
anion signals) (d),
H, H3); 1.75 (m, 4H, H2); 3.16 (t, J = 8.0, 4H, H1). C NMR (dithio-
carbimate anion signals) (d): 13.7 (C4); 21.9 (C3); 25.6 (C2);
2.4 (C1); 211.8 (N@CS ).
m
SO2s), 935 (
m
CS2as), 393 (
mNiS). H NMR (dithiocarbimate
J
(Hz): 0.84 (t, J = 7.3, 6H, H4); 1.33 (m,
13
4
5
2
pressure yielding RSO
sulfonamide).
2 2 2
N@CS K Á2H
2
O (ca. 65% based on the
2.4. X-ray diffraction experiments
Crystallographic and structural refinements data of 2b and 3b
2
.2.1. Potassium N-butylsulfonyldithiocarbimate dihydrate, (3a)
À1
are summarized in Table 1. Compounds 2b and 3b samples of pris-
matic shape were used for data collections performed using a Kap-
paCCD diffractometer [17]. Unit cell refinement and data reduction
were performed with Denzo and Scalepack packages [18]. All data
collections were carried out with Co Ka radiation at room temper-
ature. All data were corrected for absorption effects by the Gauss-
IR (CsI) (most important bands) (cm ): 1283 (
m
CN), 1255
CS2as). H NMR (d), J (Hz): 0.89 (t, J
7.4, 3H, H4); 1.41 (m, 2H, H3); 1.66 (m, 2H, H2); 3.49 (t, J = 8,0,
1
(mSO2as), 1106 (mSO2s), 966 (m
=
2
2
1
3
H, H1). C NMR (d): 13.0(C4); 21.1(C3); 25.0(C2); 50.2(C1);
23.6(N@CS ).
2
ian method using indexed faces [19]. The structures were solved by
2
.2.2. Potassium N-octylsulfonyldithiocarbimate dehydrate, (4a)
À1
IR (CsI) (most important bands) (cm ): 1285 (
mCN), 1255
1
Table 1
(m
SO2as), 1112 (mSO2s), 979 (mCS2as). H NMR (d), J (Hz): 0.73–0.78
Crystal data and structure refinement for compounds 2b and 3b.
(
m, 3H, H8), 1.1–1.4 (m, 10H, H7 to H3); 1.5–1.7 (m, 2H, H2);
13
Compound
2b
3b
3
2
2
.42 (t, J = 8.1, 2H, H1).
2.8(C6); 27.7(C5); 28.3(C3 and C4); 31.1(C2); 50.4(C1);
23.6(N@CS ).
C NMR (d): 13.5(C8); 22.0(C7);
Empirical formula
M
T (K)
C54 H50 N2 NiO4 P2 S6
1104.01
298(2)
2
4 2 6
C58H58N NiO P S
1160.11
299(2)
2
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
triclinic
P1ꢀ
P2
1
/c
2
.3. Syntheses of the nickel complexes
12.1911(3)
14.2762(3)
16.2390(3)
-
109.887(1)
-
2657.73(10)
2
1.380
0.708
10527
6029
0.0201
1.074
10.1209(3)
10.4710(3)
14.3200(4)
71.275(1)
80.178(2)
86.531(2)
1416.16(7)
1
1.360
0.668
26353
6417
The synthesis of 4b is described in literature. In this work, the
preparation of 4b was confirmed by IR and comparison with the
published data [16]. The compounds 1b–4b were prepared as de-
scribed below.
Nickel(II) chloride hexahydrate (20.0 mmol) and tetraphenyl-
phosphonium bromide (40.0 mmol) were added to a solution of
the appropriate potassium N-R-sulfonyldithiocarbimato (40.0
mmol) in 1:1 (100 mL) methanol:water. The mixture was stirred
at room temperature for 1 h and the green solid obtained was fil-
tered, washed with distilled water and dried under reduced pres-
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
l
À3
c
(g cm
(mm
)
À1
)
Reflections collected
Independent reflections
(R )
int
0.0843
1.050
2
Goodness-of-fit (GOF) on F
Final R indices [I > 2
a
sure for 1 day, yielding (Ph
4
P)
2
[Ni(RSO
2
N@CS
2
2
) ] (ca. 90%, based
r
(I)]
R
1
= 0.0603
R
1
= 0.0685
wR = 0.1553
2
wR = 0.1587
2
on nickel (II) chloride hexahydrate). Compounds 2b and 3b were
obtained as dark green/brown single crystals suitable for X-ray dif-
fraction experiments by slow evaporation of their solutions in
methanol:water (2:1) at room temperature.
R
wR
1
(all data)a
0.1047
0.1965
0.1458
0.2195
a
2
(all data)
a
2
wF 2
]1/2
R
1
=
R
(||F
o
| À |F
c
|)/
R
|F
o
|; wR
2
= [
R
w(|F
o
| À |F
c
|) /
R
o
.

2
280
L.M. Gomes Cunha et al. / Polyhedron 29 (2010) 2278–2282
direct methods and refined by the full matrix least squares meth-
od, both using SHELX package [20]. Non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were placed in calculated
positions and refined with riding constraints to their parent atoms.
the spectra of the compounds 1b–4b to higher field (ca. 210 d) if
compared to the spectra of the ligands 1a–4a (ca. 225 d) due to
the complexation by two sulfur atoms [21].
Compounds 2b and 3b yielded dark green crystals by slow
evaporation of their solutions in methanol:water (2:1) at room
temperature. The crystal structure of the compound 4b is already
published by our group [16]. A number of attempts to recrystallise
2.5. Vulcanization
1
b yielded crystals not suitable for X-ray experiments, but the
Natural rubber was compounded following the addition order
crystal structure of the analogue (Bu N) [Ni(CH SO N@CS ] con-
taining the same anionic dithiocarbimato-nickel(II)-complex of 1b
is already published [22]. The infrared and NMR data for 1b and
4
2
3
2
2 2
)
in which each additive appears in the formulation (in phr): natural
rubber, NR (100), stearic acid (2.5), zinc oxide (3.5), sulfur (2.5),
carbon black (0 or 20), aminox (2.0), accelerator (1.2). Natural rub-
ber, Mooney viscosity ML 1 + 4(100 °C) = 74.8, was supplied by
Sociedade Michelin de Participações, Indústria e Comércio Ltda;
the other ingredients were of grades commonly used in the indus-
try. The mixture was carried out in a roll mill with 1:1.25 friction
rate, at room temperature. Rheometric parameters were deter-
mined in an oscillating disk rheometer from Tecnologia Industrial,
at 150 °C and 1° arc, according to ASTM D 2084.
(
Bu
4 2 3 2 2 2
N) [Ni(CH SO N@CS ) ] are very similar, except for the cations
signals.
The ortep diagrams [23] for compounds 2b and 3b are shown in
Figs. 1 and 2, respectively.
All nickel(II) ions lie in a special position, the coordination envi-
ronment is perfectly planar. The S–Ni bond lengths are 2.2011(11)
and 2.1940(10) for 2b, and 2.1925(11) and 2.1982(11) for 3b. They
are very similar to the S–Ni bond lengths for 4b and (Bu
Ni(CH SO N@CS ] [16,22]. The S1–C–N1 angle ( ) is larger than
the S2–C–N1 angle (b) in the (Bu N) [Ni(CH SO N@CS ) ]
4 2
N) -
[
3
2
2
)
2
a
3
. Results and discussion
4
2
3
2
2 2
[a
= 127(1)° and b = 124(1)°] (Fig. 3) [22]. This is reversed in the
Scheme 1 illustrates the protocol used in the preparation of the
structures of 2b–4b, where b (131°) is larger than (121°) [16].
a
complexes. The procedure involves the reaction of the appropriate
sulphonamides with carbon disulfide in alkaline medium, followed
by the reaction with a nickel(II) salt.
This fact is consistent with the increase in the size of the alkyl
group and can be interpreted on the basis of repulsive interactions
between S1 and the lone-pair located on N1 versus the repulsive
interactions between S2 and the R group. If the R group is large,
the steric effect between S2 and the R group is more important
than that between S1 and the lone-pair [22].
The S1-C1 and S2-C1 bonds show the same length for 3b
(1.741 Å) and are nearly equal for 2b (1.722 and 1.737 Å). They
are slightly shorter than the typical C–S single bond length (ca.
The potassium dithiocarbimates 1a–4a are soluble in water and
insoluble in most organic solvents. These compounds are not very
stable and a white solid is obtained from their aqueous solutions
after some days at room temperature. When kept in the solid state
at the ambient temperature, these potassium salts were also con-
verted into white solids after several months. On the other hand,
the compounds 1b–4b are stable at the ambient conditions. They
are insoluble in water, and soluble in methanol, ethanol, chloro-
form and dichloromethane.
1.81 Å) due to partial
p-delocalization in the NCS2 groups [24].
The literature reports that the CN bond in potassium dithiocarbi-
mates are approximately equal to 1.35 Å [25,26]. The compounds
2b and 3b show slightly shorter CN bonds (1.299 and 1.290 Å) con-
firming the complexation. These facts can be explained by the in-
creased importance of the canonical form (c) upon complexation
(Scheme 2). This leads not only to shorter CN bond lengths in the
À1
A strong band at 1400–1425 cm observed in the vibrational
spectra of 1b–4b was assigned to the mC@N vibration. The masCS
2
was observed at higher frequency in the spectra of the parent
À1
dithiocarbimate potassium salts (940–970 cm ) than in the spec-
À1
tra of the complexes (939 cm ), confirming the complexation. The
complexes, but also to lower wavenumbers for the
spectra of the complexes when compared with the spectra of the
ligands, the higher wavenumbers for the CN in the spectra of
mCS2 in the
spectra of compounds 1b–4b also show the expected medium
À1
band at ca. 390 cm range, assigned to the Ni–S stretching vibra-
m
tion, indicating a didentade coordination by two sulfur atoms of
the complexes, and the variation on the chemical shift of the
1
13
the dithiocarbimato ligand. The H NMR spectra of the complexes
dithiocarbimate group carbon atom signal in the C NMR spectra
showed all the signals for the hydrogen atoms of the tetraphenyl-
phosphonium cation. The remaining signals could be assigned to
the alkyl groups of the dithiocarbimate moiety. The integration
curves were consistent with a 2:1 proportion between the tetra-
after the complexation (see Section 2).
The crystal packing in 2b and 3b is formed by alternated layers
of the anionic complex and of the counter-ion. Due to the lack of
intermolecular interactions involving the terminal atoms of the
alkyl groups, structural disorder was observed for compound 3b,
caused by static disorder due to the butyl groups’ flexibility and
thermal motion. Weak intermolecular interactions of the type
C–HÁÁÁO and C–HÁÁÁS were observed as detailed in the supplemen-
tary material.
1
3
phenylphosphonium cation and the complexes anions. The
NMR spectra of compounds 1b–4b showed the expected signals
due to the dithiocarbimate moiety. The N@CS signal is shifted in
C
2
2
CS2, 4 KOH, DMF
The compounds 1a–4a were not very active as vulcanization
accelerators, showing very low maximum torque values (ca. 10
dN m), indicating a low number of crosslinks, after t90 of ca.
2
(
RSO2NH2
2 RSO2N=CS2K2.2H2O
a, 2a, 3a, 4a
1
6
0 min. As it was said before, the potassium dithiocarbimates are
soluble in water and insoluble in most organic solvents, thus
presenting low solubility in the natural rubber medium, making
it difficult to achieve a good dispersion of the compounds through-
out the polymer matrix, thus leading to poor vulcanization.
The efficiency of the 1b–4b as accelerators for natural rubber
vulcanization was investigated by rheometry. Table 2 shows the
data obtained from the rheometric curves for 1b–4b. These results
were compared to published data for three commercial accelera-
NiCl2.6H2O, 2 Ph4PBr, MeOH/H2O
2 H2O, -2 KCl, -2 KBr
Ph4P)2[Ni(RSO2N=CS2)2]
b, 2b, 3b, 4b
-
1
1
: R = CH3, 2: R = CH3CH2, 3: R = CH3(CH2)3, 4: R = CH3(CH2)7
Scheme 1. The synthetic route for the preparation of the nickel(II) dithiocarbimate
complexes.
4 2
tors, CBS, MBTS and TMTD, as well as to (Bu N) [Zn(4-

L.M. Gomes Cunha et al. / Polyhedron 29 (2010) 2278–2282
2281
S1
O2
S2
O1
Ni
C1
C3
S3
C2
N1
S2
S1
Fig. 1. Ortep [23] diagram of 2b drawn at 30% of atomic displacement probability and the labelling scheme. Symmetry code: (i) Àx, 2 À x, Àx.
O1
S1
S2
O2
S3
C3
Ni
C2
C1
N1
C4
S2
S1
C5
Fig. 2. Ortep [23] diagram of 3b drawn at 30% of atomic displacement probability and the labelling scheme. The large displacement ellipsoids are caused by static disorder
and thermal motion. Symmetry code: (i) Àx, 1 À x, 2 À x.
1
S
2
S
3 6 4 2 2 2
CH C H SO N@CS ) ], ZNIBU, a bis(dithiocarbimato)-metal(II)-
complex previously described [21,27].
β
SO2R
Ni
1C N1
Trithiocarbamato-zinc(II)-complexes are inferred to be impor-
tant intermediates when dithiocarbamates are used in the rubber
vulcanization. It has been suggested that they are formed when
the zinc complex incorporate extra sulfur atoms from the vulcani-
zation mixture into the dithiocarbamate ring (Scheme 3) [9,10].
From the t90 shown in Table 2 it can be seen that vulcanization
with 1b–4b proceeds at lower rates than with ZNIBU [21]. This fact
is probably due to the higher lability of the zinc(II) complexes
when compared with the nickel(II) complexes in the formation of
sulfur-rich compounds [9]. The vulcanization with 1b–4b also pro-
ceeds at lower rates than the commercial compounds in the tested
conditions.
..
α
S
S
2
1
Fig. 3. Comparison between S2–C1–N1 and S1–C1–N1 angles.
-
-
-
S
S
-
N
S
-
RSO2
N
C
RSO2
RSO2
C
N
c
C
-
S
S
S
a
b
Scorch safety is often a major factor limiting mixing and pro-
cessing rates. The data in Table 1 shows an increment in the scorch
Scheme 2. Three canonical forms for N-R-sulfonyldithiocarbimate anion.
Table 2
Rheometric parameters for NR mixes compounded with 1b–4b, ZNIBU, CBS, MBTS or TMTD as the accelerator at 1.2 phr (1.2 g accelerator/100 g NR).
Accelerator
Carbon black (phr)
0
t
90 (min)
ts
1
(min)
Ml (dN m)
Mh (dN m)
(Mh À Ml) (dN m)
1b
2b
3b
4b
44.4
32.4
46.2
36.0
34.2
25.2
36.6
25.8
30. 0
21.0
8.73
8.27
7.59
10.18
3.61
3.81
6.0
4.2
6.0
5.4
3.0
2.4
3.0
1.8
2.4
1.8
4.6
4.4
4.0
3.3
1.5
1.9
2.03
2.94
2.14
2.60
1.47
2.94
3.39
4.40
5.53
5.31
2.93
6.21
6.10
6.32
4.63
6.55
21.56
28.11
21.90
26.76
20.89
29.01
22.80
27.77
25.06
32.06
27.09
34.00
23.03
27.54
27.55
34.40
19.53
25.18
19.76
24.16
19.42
26.08
19.42
23.37
19.53
26.75
24.16
27.79
17.03
21.22
22.92
27.85
20
0
20
0
20
0
20
0
20
0
20
0
20
0
20
ZNIBUa
CBSa
MBTSa
TMTDa
1
phr: parts per hundred parts of the resin; t90: optimim vulcanization time; ts : scorch time; Ml: minimum torque; Mh: maximum torque; CBS (N-cyclohexylbenzothiazole
sulfenamide), MBTS (dibenzothiazole disulfide), TMTD (tetramethylthiuram disulfide).
a
Ref. [21].

2
282
L.M. Gomes Cunha et al. / Polyhedron 29 (2010) 2278–2282
S
S
S
S
SS
S
S
complexes lead to similar degrees of crosslinking and showed
higher ts than the compositions with the zinc-analog or with
the commercial accelerators.
S8
R2N
C
Zn
C
NR2
R2N
C
Zn
C
NR2
1
SS
In the light of the aforementioned results it might be concluded
that the new nickel-complexes are active and have facilitated
processing by increasing the scorch time. These compounds are
the first examples of active nickel-dithiocarbimates, being part of
a promising novel class of rubber vulcanization accelerators.
Analogous compounds are being prepared to extend the studies
on their vulcanization activities and on the rubber properties thus
obtained.
Scheme 3. Trithiocarbamato-zinc(II) formation.
time with the nickel compounds when compared to the zinc ana-
log. This is possibly due to the same reason influencing the opti-
mum vulcanization time: the less labile Ni–S bond. The ts values
1
observed for 1b–2b are even higher than those presented by the
commercial accelerators tested, the four new compounds present-
ing better scorch safety than TMTD. These results indicate that the
new accelerators shall enhance the processing safety of industrial
formulations.
5. Supplementary material
The values of (Mh–Ml) are of the same magnitude as those ob-
tained with the commercial accelerators. This indicates that the
obtained vulcanizates show similar degrees of crosslinking. Fur-
thermore, the lower minimum torques (Ml) observed suggest that
the use of the new nickel complexes shall improve the processibil-
ity of the formulations.
CCDC 763755 and 763756 contain the supplementary crystal-
lographic data for 2b and 3b, respectively. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk.
Carbon black is commonly used in the rubber industry as a pig-
ment and a reinforcing filler, especially for tires. As expected, the
use of carbon black increases the (Mh À Ml) values of the mixes
vulcanized with the Ni-derivatives in similar proportions as it does
to the compositions obtained from the commercial accelerators.
The increase in Ml is related to the well known effect on the viscos-
ity caused by carbon black reinforcing character and the increase in
Acknowledgements
This work has been supported by the Brazilian agencies FAP-
EMIG, CAPES and CNPq. JRS is grateful to IFSC-USP (KappaCCD)
for providing access to the X-ray facilities.
D
M to the total crosslink density. Carbon black usually has an
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