Influence of alcohols on the formation of the nickel complexes active in ethene oligomerization in the catalytic system Ni(PPh3) 4/BF3·OEt2

Article abstract of DOI:10.1016/j.molcata.2005.04.036

The influence of ethanol and selected other alcohols on the formation of active nickel complexes for ethylene oligomerization was studied for the Ni(PPh₃)₄/BF₃·OEt₂ system by EPR and ¹H NMR spectroscopy. Both the presence of Ni(I) complexes and Ni(II) hydrides could be established. Coordinatively unsaturated Ni(I) complexes were shown to be the active catalysts for ethylene oligomerization, whereas the Ni(II) hydrides were shown to be inactive. The alcohol act as a promoter for the Ni(PPh₃)₄/BF₃·OEt ₂ by facilitating the formation of the active Ni(I) complexes.

Full text of DOI:10.1016/j.molcata.2005.04.036

Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
Influence of alcohols on the formation of the nickel complexes active in
ethene oligomerization in the catalytic system Ni(PPh3)4/BF3·OEt2
V.V. Saraeva,∗, P.B. Kraikivskiia,b, S.N. Zelinskiya,b, D.A. Matveeva, A.I. Vilmsa,
A.V. Rohina, K. Lammertsmab
a
Department of Chemistry, Irkutsk State University, Irkutsk 664033, Russian Federation
b
Faculty of Sciences, Department of Chemistry, Vrije University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Received 30 September 2004; received in revised form 11 December 2004; accepted 20 April 2005
Available online 25 May 2005
Abstract
The influence of ethanol and selected other alcohols on the formation of active nickel complexes for ethylene oligomerization was studied
for the Ni(PPh3)4/BF3·OEt2 system by EPR and 1H NMR spectroscopy. Both the presence of Ni(I) complexes and Ni(II) hydrides could be
established. Coordinatively unsaturated Ni(I) complexes were shown to be the active catalysts for ethylene oligomerization, whereas the Ni(II)
hydrides were shown to be inactive. The alcohol act as a promoter for the Ni(PPh3)4/BF3·OEt2 by facilitating the formation of the active Ni(I)
complexes.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Ni(II) hydride complexes; Ni(I) cationic complexes; Proton donor; Activity; Ethene oligomerization
1. Introduction
unclear whether Ni(I) converts to Ni(II) as the catalytically
active species.
In recent years nickel compounds, primarily known as low
molecular oligomerization catalysts for unsaturated hydro-
carbons [1–9], have attracted increasing interest as effective
catalysts for low olefin polymerization [10–21]. Despite the
mechanistic progress that is being made the catalytic role
of the nickel complex and particularly the nature of its va-
lence state remains unresolved. The conventional view is that
Ni(II) hydride complexes catalyze the low molecular olefin
oligomerization, which is based on their identification by
NMR in model systems [22–29] and on the enhancement by
proton donors [30–33]. On the other hand, Ni(I) intermedi-
ates have been detected by EPR spectroscopy in Ziegler-type
catalytic systems [34], and consequently the question arises
whetherNi(I)ionsactivelyparticipateinthecatalyticprocess.
Indirect data [35–38] has been reported on the involvement
of Ni(I) complexes in the catalytic oligomerization, but it is
In this paper we explore how proton donors, such as alco-
hols and acids, influence the formation of active complexes
from the Ni(PPh3)4/BF3·OEt2 catalytic system for the ethy-
lene oligomerization.
2. Experimental
All operations were carried out under argon. Precipi-
tates were separated with glass filters using Schlenk tech-
niques. All reagents were kept under argon in sealed
ampoules.
Toluene and benzene (Merck) were distilled prior to use
over sodium in the presence of benzophenone. Boron tri-
fluoride etherate (Merck) was distilled over LiH before use.
Ethanol (99%, Merck) was reacted with sodium (10 g/L) and
diethylphtalate and subsequently distilled prior to use. All
other alcohols were fractionally distilled using a rectification
column.
∗
Corresponding author. Tel.: +7 3952 423452; fax: +7 3952 425935.
E-mail address: saraev@chem.isu.ru (V.V. Saraev).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.04.036

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V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
HBF3OEt was prepared by reaction of BF3·OEt2 with
intensities of the EPR signals were taken and compared to
those of the individual [Ni(PPh3)3]BF4 complex in diethyl
ether. The EPR spectra were simulated with our published
program [43] in which the hyperfine interaction (HFI) is lim-
ited to the second-order term and where the main axes of the
g-tensor and the HFI tensors coincide. The EPR parameters
of all signals shown in Fig. 1 are summarized in Table 2.
ethanol in a ratio of 2:1 using toluene as solvent. Of the two
resulting phases the lower yellow one containing the product
was collected by syringe and used immediately [39]. HBF4
was used as a toluene solution (>48% by chromatography)
in which it forms a complex. The HBF4-toluene complex
(>98%, NMR) was obtained by dropwise addition of acety-
lacetone (0.352 g, 3.52 mmol) within 2 min to a solution of
BF3·OEt2 (1 g, 7.05 mmol) in 10 ml of toluene, followed by
transfer of the lower phase under an Ar atmosphere into a
polyethylene vessel, and used within 2 h [40]. Ni(PPh3)4 [41]
(PPh3)3NiCl [42], and (PPh3)2NiCl [42] were prepared ac-
cording to literature procedures.
3. Results and discussion
Ni(PPh3)4/BF3·OEt2 in toluene is amongst the most active
catalytic systems in low olefin oligomerization [35,38]. The
activity depends on the ratio of its components, reaching a
maximum activity for ethylene oligomerization of ∼30,000
(C2H4 (mol))/(Ni (mol) × h) at a B:Ni ratio of ≈70, giving
dimers (75%) and trimers (22%) as main products. At a B:Ni
ratio of 10 the activity is reduced 100-fold, but when ethanol
is added (ethanol:Ni = 5) the activity of the systems is nearly
restored. Benzyl alcohol behaves similarly, but iso-propanol
and tert-butanol are weaker promoters (see Table 1).
Proton donors added to Lewis acids are known to give
strong Brønsted acids [39,44,45] that are capable of oxida-
tive addition to Ni(0) to give Ni(II) hydrides. These hy-
drides are usually associated with the active species in Ni
based catalytic systems. On the other hand, it has also been
shown that during the formation of the Ni(PPh3)4/BF3·OEt2
catalytic system Ni(0) is oxidized quantitatively to give
a number of Ni(I) cationic complexes of composition
[(PPh3)3−nNi(OEt2)n]BF4 (n = 0, 1, 2) [38,46,47]. To inves-
tigate possible proton donor induced transformations of the
Ni(0) to Ni(I) complexes, we studied by EPR and 1H NMR
spectroscopy their interaction with alcohols and acids.
[Ni(PPh3)3]BF4: 0.23 ml of BF3·OEt2 was added with a sy-
ringe under Ar to a stirred solution of 0.5 g of Ni(PPh3)4 in
10 ml of toluene (B:Ni molar ratio of 4:1). After 10 min
at room temperature the mixture was cooled to −10 ◦C
and filtered 20 min later. [Ni(PPh3)3]BF4 was precipitated
from the solution by adding 5 ml of heptane, filtered, and
washed (hexane–toluene) to give a brown solid. Calc. for
C54H45P3NiBF4: Ni, 6.3; C, 69.5; H, 4.80; P, 9.99. Found:
Ni, 6.6; C, 69.3; H, 4.86; P, 9.78.
(PPh3)3NiOEt: 98.4 mg (2.14 mmol) of ethanol was added
to 1 g (1.07 mmol) of [Ni(PPh3)3]BF4 in 50 ml of toluene.
The reaction mixture was stirred for 2 h and filtered.
(PPh3)3NiOEt was precipitated from the solution by adding
10 ml of hexane, filtered, washed (hexane), and dried in
vacuum to give yellow crystals. M.p. 15 ◦C. Calc. for
C56H50P3ONi: Ni, 6.6; C, 75.7; H, 5.6; P, 10.25. Found:
Ni, 6.9; C, 73.4; H, 5.2; P, 9.77.
2.1. Method
Ethylene oligoimerization was carried out in a ther-
mostated Schlenk vessel under argon at 23 ◦C. To a vigor-
ously shaken solution of 0.2 g (0.181 mmol) of Ni(PPh3)4
in 10 ml of toluene (CNi = 18 mmol/L) was added 0.23 ml of
BF3·OEt2 (molar ratio B:Ni = 10). After 3 min of stirring the
required amount of the alcohol was added and the argon at-
mosphere was replaced for ethylene over a period of 10 s
after which the ethylene consumption was monitored with a
gas burette (Pethylene = 730 mm). Reaction products were an-
alyzed with (GALS 311) GLC using a 50 m capillary column
(KKL 50-08), a programmed temperature mode, and apiezon
as liquid phase. 1H NMR spectra were recorded at 25 ◦C in
sealed ampoules with a Varian VXR-500S spectrometer us-
ing TMS as standard.
EPR studies were carried out using a PS-100X spectrom-
eter with an operating frequency of 9.6 GHz. Mn(II) in MgO
and diphenylpicrylhydrazyl were used as standards. EPR
spectra were recorded for samples frozen in a glass ampoule
at 77 K (liquid nitrogen). These samples were collected with
a syringe from the reaction vessel (23 ◦C) under argon and
frozen in about 15 s. To estimate the concentrations of para-
magnetic Ni(I) complexes in the samples double integrated
3.1. [Ni(PPh3)3]BF4/EtOH
The initial [Ni(PPh3)3]BF4 cationic complex in toluene
has an EPR signal characteristic for a tricoordinated struc-
ture (Fig. 1, signal 1) [48,49]. When absolute ethanol is
added to the complex (EtOH:Ni = 5) this signal disappears
and a composite EPR spectrum results as a superposition
of two new resonances (Fig. 2, signals 2 and 3). With
time signal 3 increases at the expenses of signal 2 and
is the only one observed after 20–25 s. Throughout the
entire process the integrated intensity of the EPR signals
remains constant. The same EPR behavior is seen with
Table 1
Activity of the catalytic system Ni(PPh3)4/BF3·OEt2 promoted with
alcohols in ethene oligomerization (B:Ni = 10; ROH:Ni = 5; T = 23 ◦C;
P = 730 mmHg)
ꢀ
ꢁ
C H (mol)
Ni (mol)×h
2
4
No.
Alcohol
Ethene oligomerization rate
1
2
3
4
C2H5OH
23000
24000
14600
14500
C6H5CH2OH
i-C3H7OH
t-C4H9OH

V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
127
Fig. 1. Experimental (a) and model (b) EPR spectra (in toluene at T = 77 K) for (1) [Ni(PPh3)3]BF4; (2) (PPh3)2NiOEt; (3) (PPh3)3NiOEt; (4) (PPh3)2Ni(␮-
OEt)2BF2; and (5) (PPh3)(OEt2)Ni(␮-OEt)2BF2.
other alcohols, but the time for the full conversion of
signal 2 → 3 differs amongst them as follows: ethanol
(25 s) > propanol-1 > propanol-2 > butanol-1 > butanol-2 > 2-
methylpropanol-1 > 2-methylpropanol-2 (40 min), reflecting
a steric influence. It is noteworthy that the transformation
period reduces as the HOR:Ni molar ratio increases. Res-
onances 2 and 3 were recorded independently for ethoxide
complex (PPh3)nNiOEt with n being 2 and 3, respectively;
these complexes were prepared in situ from the reaction of
(PPh3)nNiCl with EtONa in toluene.
We conclude that the [Ni(PPh3)3]BF4 cationic complex
is transformed by ethanol first to the electroneutral tricoor-
dinate complex (PPh3)2NiOEt and subsequently to the elec-
troneutral tetracoordinate (PPh3)3NiOEt. The oxidation state
of the transition metal does not change during this process;
parameters of the EPR spectra are give in Table 2. Scheme 1
summarizes the possible sequence of events.
−
On addition of HOR to [Ni(PPh3)3]BF4 the BF4 an-
ion is exchanged for an alkoxy group to afford, under re-
lease of a PPh3 ligand, a neutral tricoordinate Ni(I) complex,
(PPh3)2NiOEt, which is responsible for EPR signal 2. The
released PPh3 is likely complexed to HBF4, but liberated with
additional alcohol, to subsequently coordinate to the newly
formed (PPh3)2NiOEt to give (PPh3)3NiOEt, which is re-
sponsible for EPR signal 3. We next explored the behavior of
this complex toward BF3·OEt2.
3.2. (PPh3)3NiOEt/BF3·OEt2
On addition of an equimolar amount of boron trifluoride
etherate to a toluene solution of (PPh3)3NiOEt (B:Ni = 1),
its EPR resonance is replaced for a new axially symmetric
signal with a well resolved hyperfine structure (HFS) due
to two equivalent 31P nuclei (Fig. 1, signal 4). Its maximum
intensity is half that of the initial complex (PPh3)3NiOEt. Its
shape resembles that of bimetallic Ni(I)-bridged complexes,
like (PPh3)2Ni(␮-X)2AlR2 [34], and differs distinctly
from [(PPh3)2Ni(OEt2)]BF4 [46]. Therefore, we assign
the new EPR resonance to the di-ethoxy bridged structure
(PPh3)2Ni(␮-OEt)2BF2. Its intensity decreases on further
addition of BF3·OEt2 while a new one emerges with a
resolved HFS for a single 31P nucleus (Fig. 1, signal 5,
Fig. 2. Dependence of the ethylene oligomerization of the Ni(PPh3)4/HBF4
catalytic system on the activation (1) with and (2) without BF3·OEt2 using
varying HBF4:Ni ratios at T = 296 K (CNi = 18 mmol/L, Pethylene = 730 mm).

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V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
Table 2
Parameters of EPR spectra for Ni(I) complexes
Signal
1
Complex
g
g
A
(mT)
A (mT)
⊥
Ref.
[49]
||
⊥
||
[Ni(PPh3)3]BF4
2.38z
2.12y
2.07x
2.16
2.36
2.10
6.1 (1P)z
6.4 (1P)y
8.1 (1P)x
–
2
3
4
(PPh3)2NiOEt
(PPh3)3NiOEt
(PPh3)2Ni(␮-OEt)2BF2
2.42
2.01
2.42
–
–
–
4.6 (2P)
6.1 (2P)
5
(PPh3)(OEt2)Ni(␮-OEt)2BF2
2.29z
2.14y
2.03x
5.6 (1P)z
8.0 (1P)y
6.1 (1P)x
6
[(P(OEt)3)3NiL]BF3X
2.04z
2.10y
2.20x
17.5 (1P)z
7.4 (1Pꢀ)z
7.4 (1Pꢀꢀ)z
7.5 (1P)y
5.6 (1Pꢀ)y
3.3 (1Pꢀꢀ)y
18.5 (1P)x
Scheme 1.
Table 2) that has its maximum intensity at a B:Ni ratio of only
2 and fades after that. We speculate that additional BF3·OEt2
causes loss of another phosphine ligand followed by product
degradation. Scheme 2 summarizes the proposed mechanism.
We believe that the phosphine-OEt2 exchange with the
Lewis acid BF3 induces an equilibrium between (PPh3)3
NiOEt and the coordinatively unsaturated (PPh3)2NiOEt
complex even though the latter is not observed directly dur-
ing the addition of BF3·OEt2. It seems fair to assume that
‘free’ BF3 coordinates than immediately to (PPh3)2NiOEt,
enabling fluoride-alkoxide exchange to give after complex
break-up (PPh3)2NiF as a diamagnetic dimer, which has
been reported previously, and BF2OEt. Coordination of this
BF2OEt with the BF3-induced formation of (PPh3)2NiOEt
than results in the di-alkoxy bridged complex.
Removal of a phosphine ligand from the neutral complex
to obtain the coordinatively unsaturated complex, the first
stepinitiatingthereactionsequence, shouldoccurmoreeasily
than from cationic Ni(I) complexes on which we reported
earlier.
Scheme 2.

V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
129
1
and tetrafluoroborate in deuterobenzene was studied by H
NMR.
3.4. Ni(PPh3)4/HBF3X
The acidic protons of HBF3OEt and HBF4 in C6D6 have
1
low field H NMR chemical shifts at +9.7 and +12.5 ppm,
respectively. When Ni(PPh3)4 is added in a B:Ni ratio of 3,
these resonances decreases and new ones emerge at −8.0
and −5.0 ppm, respectively, that are indicative of hydrides.
For comparison, the hydride ion of low spin pentacoordinated
complex {[P(OEt)3]4NiH}BF3OEt is observed at −15.1 ppm
[25]. However, the high field resonances are rather broad
(ꢀν = 95 Hz) and extremely sensitive to oxygen, disappear-
ing with even the slightest contact with air. Therefore, they
must be attributed to result from either Ni(I) or high spin
Ni(II) complexes. The EPR spectrum of the HBF3OEt sys-
tem does suggest the presence of a various Ni(I) complexes,
but only in low concentration; the spectrum displays a super-
position of non-interpretable signals. On the other hand, the
EPR spectrum of the HBF4 system indicates the absence of
such Ni(I) complexes. Consequently, the broad NMR reso-
nances must be attributed to the high spin tetrahedral Ni(II)
complex [(PPh3)3NiH]BF3X.
Fig. 3. Dependence of the ethylene oligomerization of the Ni(PPh3)4/
HBF3OEt catalytic system on the activation (1) with and (2) without
BF3·OEt2 using varying HBF4:Ni ratios at T = 296 K (CNi = 18 mmol/L,
Pethylene = 730 mm).
In the next experiments we distinguish between the rel-
ative activities of the Ni(I) cationic and Ni(II) hydride
complexes for the Ni(PPh3)4/BF3·OEt2 catalyzed ethylene
3.3. Ni(PPh3)4/BF3·OEt2/HBF4
In the two component system Ni(PPh3)4/BF3·OEt2
(B:Ni = 4) nickel is monovalent and exists in the form of the
tricoordinate complex [Ni(PPh3)3]BF4 [48,49]. On adding
proton acid HBF4 to the reaction mixture as well as in
the presence of excess of BF3·OEt2 phosphine ligands are
eliminated from the Ni(I) cationic complex to give sequen-
tially [(PPh3)2Ni(OEt2)]BF4 and [(PPh3)Ni(OEt2)2]BF4 for
which the EPR spectra have been reported in reference
[46]. The two approaches differ in that elimination of one
(two) phosphine ligand(s) from cationic [Ni(PPh3)3]BF4
requires a 3- (10-)fold excess of HBF4 and a 50- (80-
)fold excess of BF3·OEt2. The ease of forming the Ni(I)
coordinately unsaturated complexes by the proton acid is
due to capturing of the free phosphine as a poorly sol-
uble phosphonium salt, HPPh3BF4. We note that varying
the excess of the acid within the indicated range results
in modest changes in the concentration of the Ni(I) com-
plexes (∼30%), but when the ratios surpass HBF4:Ni > 10 or
BF3·OEt2:Ni > 80 the Ni(I)complexeslose the last phosphine
ligand and disintegrate to give colloidal nickel. Thus, both
the weaker P Ni bond of the Ni(I) alkoxide complexes and
the insipiently formed Brønsted acids HBF3OEt and HBF4
enable the formation of coordinatively unsaturated Ni(I)
complexes.
¨
oligomerization by adding, respectively, the Bronsted acid
HBF4 to the catalytic system or the Lewis acid to the mixture
of Ni(PPh3)4/HBF4.
3.5. Ni(I) catalysis—the tricomponent
Ni(PPh3)4/BF3·OEt2/HBF4 system
When the addition of BF3·OEt2 to the Ni(0) complex
Ni(PPh3)4 in toluene (B:Ni ratio of 4) is followed by
In the remainder of this paper, we explore the alterna-
tive mechanism for the alcohol promoted Ni-catalyzed ethy-
lene oligomerization, namely the potential of forming Ni(II)
complexes in the presence of Brønsted acids [22–25]. To
this end the reaction of Ni(PPh3)4 with ethoxytrifluoroborate
Fig. 4. Relationship between the activity of the system Ni(PPh3)4/
BF3·OEt2/HBF3OEt and the EPR signal intensity.

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V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
Fig. 5. Experimental (a) and model (b) EPR spectra (in toluene at T = 77 K) for [(P(OEt)3)3NiL]BF3X.
addition of HBF4 (2 < B:Ni ratio < 20) a catalytic system
results with a Ni(I) active catalysts (see above) that has a
high activity in ethylene oligomerization. The dependence of
the system activity ((mol (C2H4)/(mol(Ni) × h)) peaks at a
HBF4:Ni molar ratio of 10 (Fig. 2). We note that the activity
maximum for this tricomponent system requires about 1/6 of
the amount of boride that is needed for the two-component
system Ni(PPh3)4/BF3·OEt2.
foraNi(I)tetragonalcomplex, suchas[(P(OEt)3)3NiL]BF3X
with L and X likely being PPh3 and OEt, respectively (see
Table 2), as it shows three nonequivalent phosphorus lig-
ands in a trigonal arrangement with a pseudo-degenerate
ground state [43]. The individual line is wide (ꢀB > 3 mT),
so that the hyperfine structure from the PPh3 ligand cannot
be defined, which is in line with the spectrum reported for
[(P(OBu)3)2Ni(PPh3)2]BF4 [43].
These data indicate that the catalytic nickel system is
monovalent during the ethylene oligomerization and exists in
the form of diamagnetic dimers, which dissociate and coordi-
nate phosphite ligands to form mononuclear complexes. The
extreme dependence of the catalytic activity on the amount of
Brønsted acid indicates the sensitivity of the active catalyst.
On the one hand, the acid eliminates phosphine ligands to
form the active catalytic species, i.e., the coordinately unsat-
urated Ni(I) cationic complexes with one phosphine ligand,
while on the other hand they are destroyed with excess acid.
3.6. Ni(II) catalysis—the tricomponent
Ni(PPh3)4/HBF4/BF3·OEt2 system
Instead, when BF3·OEt2 is added to a premixed solu-
tion of Ni(PPh3)4 and HBF4 (B:Ni ratio of 3) in toluene
in a ratio of 2 < B:Ni < 80, the resulting system, containing
Ni(II) hydride complexes, shows very low ethylene oligomer-
ization activity, less than 2% of the Ni(I) catalyzed sys-
tem (Ni(PPh3)4/BF3·OEt2/HBF4), irrespective of the B:Ni
ratio. The Ni(PPh3)4/HBF4 system itself shows a simi-
lar low activity (Fig. 2), just like the Ni(PPh3)4/HBF3OEt
system, sharply contrasting that of the three component
Ni(PPh3)4/BF3·OEt2/HBF3OEt (B:Ni = 4) that is driven by
the Ni(I) catalyst (Fig. 3).
Catalytic systems based on Ni(I) cationic complexes have
a distinguishing feature. After the oligomerization of ethy-
lene has started, the EPR signals of Ni(I) disappear. This may
be associated with either a change in the oxidation state of
Ni(I) or formation of Ni(I) dimers. However, if triethylphos-
phite P(OEt)3, a catalytic poison, is added to the system
(P:Ni > 3) when it is shows its highest activity, the oligomer-
ization ceases instantly and new intensive EPR signals of
mononuclear Ni(I) complexes emerge with an intensity that
is proportional to the rate of ethylene oligomerization at the
time of poisoning (Fig. 4). The EPR signal (Fig. 5) is typical
4. Conclusions
The following mechanistic conclusions can be drawn from
this study:
1. Coordinatively unsaturated Ni(I) complexes are
the active ethylene oligomerization catalysts of the
Ni(PPh3)4/BF3·OEt2 system.
2. Proton donors, such as alcohols, promote the
Ni(PPh3)4/BF3·OEt2 catalytic system by facilitating
the formation of the coordinatively unsaturated Ni(I)
complexes.
3. Proton donors, such as alcohols, enable the formation
of Ni(II) hydrides, but these are not the active ethylene

V.V. Saraev et al. / Journal of Molecular Catalysis A: Chemical 236 (2005) 125–131
131
oligomerization catalysts at room temperature and under
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The study was supported by the funds NWO (Netherlands)
and RFBR (Russia) (international grant No. 047.015.014)
and the Ministry of Education of RF (grant N E02-5.0-131,
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