Propylene dimerization in the presence of nickel hydride complexes formed in situ

Article abstract of DOI:10.1134/S0965544110030059

We study the influence of nickel hydride complexes formed in situ by reaction nickel(0) complexes having phosphorus-containing ligands with Broensted acids in the presence of various modifiers on a catalyst turnover and selectivity in propylene dimerization. The activating action of boron trifluoride etherate is considered. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0965544110030059

ISSN 0965ꢀ5441, Petroleum Chemistry, 2010, Vol. 50, No. 3, pp. 205–213. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © F.K. Shmidt, Ju.Ju. Titova, L.B. Belykh, M. Gomboogiin, 2010, published in Neftekhimiya, 2010, Vol. 50, No. 3, pp. 217–225.
Propylene Dimerization in the Presence of Nickel Hydride
Complexes Formed in situ
†
F. K. Shmidta, Ju. Ju. Titovaa, L. B. Belykha, and M. Gomboogiinb
a Irkutsk State University, Irkutsk
eꢀmail: lbelykh@chem.isu.ru
b Mongolian National University, Ulan Bator
Received November 17, 2009
Abstract—We study the influence of nickel hydride complexes formed in situ by reaction nickel(0) complexes
having phosphorusꢀcontaining ligands with Brönsted acids in the presence of various modifiers on a catalyst
turnover and selectivity in propylene dimerization. The activating action of boron trifluoride etherate is conꢀ
sidered.
DOI: 10.1134/S0965544110030059
†
Catalysis of С2–С6 alkene oligomerization reacꢀ tions of catalytic lower alkene (ethylene, propylene)
tions with nickel complexes has been the subject of oligomerization Ni(I) species are disproportionate to
numerous investigations for more than four decades both Ni(II) and Ni(0) species; i.e. intermediate Ni(I)
[1–3]; these reactions were the basis of the industrial species participate in the formation and regeneration
of catalytically active species. These data have been
confirmed in other reports [7, 8].
The fundamental possibility of catalyzing an oligoꢀ
merization reaction under the action of Niꢀhydride
complexes prepared by interaction of Ni(0) complexes
of phosphorusꢀcontaining ligands, PPh3, P(OEt)3, and
P(OC6H4CH3ꢀo) , with Brönsted acids, H2SO4,
CF3COOH, and3HBF3(OC2H5), has first been shown
in [9–11].
method for propylene oligomerization [4] and, in the
longꢀrange outlook, can be the basis of a number of
petrochemical processes. In recent years, systems
based on nickel
α
ꢀdiimine and bis(imino)pirydine
complexes combined with organoaluminum comꢀ
pounds, particularly methylalumoxanes, have been
intensively studied [2, 3]. The high activity of these
systems, routinely calculated on the gꢀatom of nickel,
has values on the order of
1
×
106 mol (gꢀat Ni h)–1.
However, when calculated per one gꢀatom of alumiꢀ
num, these quantities drop by two to three orders of
magnitude and are not higher than the activity of conꢀ
ventional Zigler systems of AlEt2Cl–Ni(acac)2 type
(acac is acetylacetonate) [5, 6].
In order to elucidate how the components of nickel
hydride complexes affect both catalyst activity and
selectivity in the propylene dimerization reaction, as
well as the modifying action of BF3 etherate, we studꢀ
ied the catalytic properties of systems based on phosꢀ
phorusꢀcontaining Ni(0) complexes activated with
both Brönsted and Lewis acids in the propylene
dimerization reaction.
It has been shown for Ziglerꢀtype catalytic systems
containing Ni(acac)2
alkyl, Ph), and AlR3 – nCln
,
NiX2(PR3)2 (X = Cl, Br, R =
= 0, 1, 2) that interaction
(
n
of components of the catalytic system leads to interꢀ
mediate or final nickel species of various Ni oxidation
states, (Ni(II), Ni(I), and Ni(0)) containing phosꢀ
phine, alkyl, and hydride ligands, in which the species
play an important role in the formation and regeneraꢀ
tion of complexes active in the catalysis of oligomerꢀ
ization reactions [1, 5, 6]. When Ni(II) is alkylated
with organoaluminum compounds, Ni(II)ꢀalkyl comꢀ
plexes form. These complexes, containing a single
coordinated phosphine ligand, initiate the alkene oliꢀ
gomerization process to yield Ni(II)ꢀhydride comꢀ
plexes that are true catalytically active species. It was
first found in [6] that alkylaluminum halides oxidated
Ni(0) complexes to Ni(I) complexes. Under condiꢀ
EXPERIMENTAL
Nickel complexes were synthesized according to
procedures described in the literature: Ni[PPh3]4 [12],
Ni[P(OEt)3]4 [13], Ni[P(OC6H4CH3ꢀo)2]2(C2H4) [14],
Ni(CDT)(P(С6H11)3 (CDT is cyclododecatriene) [15],
Ni(C2H4)[P(С6H11)3]2 [15].
Toluene was purified by treatment with concenꢀ
trated sulfuric acid, washed out with a sodium carbonꢀ
ate aqueous solution, dried over P2O5, and twice disꢀ
tilled over sodium. Chlorobenzene and dichlorobenꢀ
zene were dried over calcium chloride and distilled.
Just prior to the experiment, the solvents were passed
through a column packed with granulated Al2O3 calꢀ
†
Deceased.
cined at 500 С and degassed under vacuum. BF3 etherꢀ
°
205

206
SHMIDT et al.
Table 1. Results on propylene dimerization in the presence of Ni[P(OC6H4CH3ꢀο)]2)(C2H4) – HX catalyst system, cNi = 6.7 ×
10–3 mol/l, v = 10 ml, p
= 1 atm
in
C3H6
Hexene composition, wt %
Turnover
number,
Catalyst
lifetime,
min
HX/Ni,
mol/mol
No.
X
T
,
°
C
Solvent
2ꢀ and 4ꢀ 2ꢀmethꢀ
methylpentꢀ ylpentꢀ1ꢀ nꢀhexenes thylbutꢀ
2,3ꢀdimeꢀ
mol C3H6
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
gꢀat Ni
2ꢀenes
53.3
57
ene
2.1
0.9
1,2ꢀene
0.5
HSO–4
HSO–4
1
2
50
50
10 Toluene
22
15
2300
940
43.0
35.0
10 Chlorobenzene
7.1
3 CF3COO– 40
4 CF3COO– 50
5 CF3COO– 70
6 CF3COO– 160
7 CF3COO– 250
8 CF3COO– 50
9 CF3COO– 50
10 CF3COO– 50
11 CF3COO– 50
10 Toluene
10 Toluene
10 Toluene
10 Toluene
10 Toluene
45
45
40
36
30
50
16
7
1800
2200
2300
3200
3800
1040
540
63.6
58.4
63.7
56.5
56.6
57.1
52.6
47.8
59.4
1.3
2.0
1.8
2.3
1.5
3.0
1.0
2.5
3.7
25.0
26.3
25.7
34.4
36.3
25.6
34.0
36.5
32.8
10.1
13.3
8.8
6.8
5.6
0
Chlorobenzene
14.3
12.4
13.2
4.1
30 Chlorobenzene
50 Chlorobenzene
10 oꢀDichlorobenzene
150
29
1400
ate was distilled in vacuum over calcium hydride
Dimerization products were analyzed by the GLC
using
(
53 C/46 mm Hg) and used as a 0.5 M solution in tolꢀ method on a Khromꢀ4 chromatograph at 50
°
°С
two capillary columns 100 m in length, which have
dinonyl phthalate or vacuum oil as a stationary phase.
uene or chlorobenzene. Brönsted acids were introꢀ
duced into the catalytic system as a solution in toluene
or chlorobenzene, or dosed by means of a micropipet.
NMR spectra were recorded on a WP200SV pulse
spectrometer (Brucker).
Propylene dimerization was carried out in a temꢀ
peratureꢀcontrolled shaken vessel, using continuꢀ
ous propylene feeding to the reactor under a presꢀ
sure of 1 atm. The reactor, preliminarily blown with
argon, was charged with a solvent and a Ni(0) comꢀ
plex. Then the reaction mixture was saturated with
propylene, and Brönsted acid, or BF3 etherate, and
a proton donor was added. The reactor was intenꢀ
sively shaken, and the rate of propylene absorption
was determined. Because the propylene diꢀ and oliꢀ
gomerization process in the presence of the studied
catalytic systems has a nonsteady character, in order
to compare their catalytic properties, the number of
moles of converted propylene per one gꢀatom of
nickel (the turnover number, TON) for the entire
life of catalyst operation are given. These results and the
data on hexene compositions are given in Tables 1 and
2. The concentrations of the initial Ni(0) complexes
are given as notations to the tables, whereas concenꢀ
trations of other components can be calculated
from the molar ratios between the components
given in Tables 1 and 2.
RESULTS AND DISCUSSION
The dependence of the initial rate of propylene oliꢀ
gomerization in the presence of the Ni[P(OC6H4CH3ꢀ
)2]2(C2H4)–CF3COOH catalytic system on the conꢀ
centration of trifluoroacetic acid is given in Figs. 1a, 1b.
It is likely that the nonlinearity of this dependence
with increasing reaction rate to the limiting value is
caused by the equilibrium protonation reaction of the
Ni(0) complex with trifluoroacetic acid.
o
The PMR spectrum of the Ni[P(OC6H4CH3ꢀ
o
)2]2(C2H4)–CF3COOH catalytic system has a highꢀ
field resonant signal at = –10.5 ppm (doublet of douꢀ
δ
blets, Fig. 2). The location of the resonant signal is charꢀ
acteristic of hydride ligands, and the multiplicity pattern
corresponds to the proton split on two nonequivalent
phosphorus nuclei (Fig. 2a). The PMR spectrum agrees
with the squareꢀplanar structure of the nickel complex,
where phosphite ligands are in the cisꢀposition with
respect to each other:
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

PROPYLENE DIMERIZATION IN THE PRESENCE
207
R,
mol(l min)–1
(а)
1/R
(b)
1.2
1.0
0.8
0.6
0.4
0.2
6
5
4
3
2
1
0
0.5
1.0
1.5
2.0
2.5
cCF COOH
3.0
mol/l
0
1
2
3
4
5
6
1/c
,
l/mol
,
3
Fig. 1. Dependence of (a) propylene dimerization rate in the presence of the Ni[P(OC H CH ꢀo) ] (C H )–CF COOH catalyst
3 2 2 2 4 3
6
×
4
–2
system on CF COOH concentration; (b) reverse rate on reverse concentration,
is toluene.
c
= 1
10 mol/l,
V
= 10 ml,
Т
= 10°С
, solvent
3
Ni
1
R
1
cHX
⎛
⎞
H
C H
(oꢀCH ꢀC H ꢀO) P
Kinetic equation (
1
) is linearized in ꢀꢀ
=
f ꢀꢀꢀꢀꢀꢀ
6
4
4
4
3
3
⎝
⎠
Ni
O
C
O
CF3
C H
(oꢀCH3ꢀC64H4ꢀO)3P
4
coordinates using parametrization over Ni(0) concenꢀ
When a nickel hydride complex interacts with ethꢀ
ylene at = –30 , the spectral pattern varies. The
resonant signal corresponding to a hydride ligand disꢀ
appears, and a new broadened signal appears in the
Т
°
С
(а)
T
= 25°C
PMR spectrum at
caused by resonance of
δ
= 0.1 ppm (Fig. 2b), which is
ꢀalkyl protons of nickel comꢀ
σ
plexes. The hyperfine structure of the signal is not
observed owing to dynamic equilibrium between
nickel hydride and its
σ
ꢀethyl complex. When the
temperature is increased, the linewidths of this signal
decrease and its intensity simultaneously decreases
(Fig. 2c). Similar changes in the PMR spectrum were
(b)
T
=
⎯30°C
observed for an individual
σ
ꢀalkyl complex
(acac)Ni(C2H5)(PPh3)2 [16].
If we suppose that the scheme of the propylene
dimerization reaction (phosphite ligands were omitted
to simplify the scheme) is as follows,
K
c
(c)
Ni(0) + HX
HNiX,
T
= 25°C
k
ef
HNiX + 2C3H6
HNiX + C6H12,
then, assuming the propylene concentration to be
constant, the kinetic equation will be
kefKc[Ni(0)][HX]
R = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ,
(I)
0
–10 ppm
1 + Kc[HX]
1
Fig. 2.
H NMR spectra of Ni[P(OC H CH ꢀ
6 4 3
) ] (C H )–CF COOH catalyst system (a) prior to
treatment with ethylene and (b, c) after treatment,
0.5 mol/l, [CF COOH]/Ni = 5, solvent is tolueneꢀd .
where
R is the reaction rate and [HX] is the concentraꢀ
tion of trifluoroacetic acid. The concentration of proꢀ
pylene is involved in the effective rate constant kef
o
2 2
2
4
3
c
=
Ni
8
.
3
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

208
SHMIDT et al.
trations:
1
also have highꢀfield resonant signals. The signals
are quintets at = –12.9 ppm (JPH = 33 Hz) and
= –12.8 ppm (JPH = 32 Hz), respectively,
40 . Multiplicity of a signal is caused by
δ
1
1
δ
ꢀꢀ = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ + ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ.
kefKc[Ni(0)][HX] kef[Ni(0)]
(II)
R
at
⎯
°
С
spin–spin interaction of a proton with four equivꢀ
alent phosphorus nuclei.
Processing of the experimental results for the
Ni[P(OC6H4CH3ꢀo)2]2(C2H4)–CF3COOH catalytic
It follows from the data given in Table 1 that a
1
R
1
cHX
⎛
⎞
system in ꢀꢀ
=
f ꢀꢀꢀꢀꢀꢀ coordinates (Fig. 1b) allows us
⎝
⎠
temperature increase within a range of 0–50 С
°
leads to a decrease in both the catalyst turnover
and the lifetime. It is caused by an increase in the
rates of conversion of nickelꢀhydride and nickelꢀ
alkyl complexes, which are intermediates of a catꢀ
alyst cycle, to Ni(II) complexes of Pn – 1NiX2 type,
which are inactive in catalysis, under the action of
to determine the equilibrium constant for a protonaꢀ
tion reaction Kc of 0.55 0.05 l/mol and an effective
rate constant
k
ef of (1.8 0.2)
102 min–1.
×
When Ni(0) phosphite nickel complexes
Ni[P(OEt3)]4 and Ni[P(OPh3)]4 are used as preꢀ
cursors, the PMR spectrum of the reaction mixꢀ
ture containing these complexes and CF3COOH Brönsted acids:
H
+ HX
PnNi
PnNi + HX
PnNiX2 + H2
(Reaction 1)
X
–P
H
X
+ HX
Pn – 1NiX2 + H2
(Reaction 2)
Pn − 1Ni
C6H12
C3H6
catalytically
active complex
C3H7
C6H13
+ HX
+ HX
Pn − 1Ni
C6H14 + Pn – 1NiX2
(Reaction 4)
Pn – 1NiX2 + C3H8
(Reaction 3)
Pn − 1Ni
X
X
C3H6
where
n
= 2–4.
HX (P = PPh3, P(OEt)3) catalyst systems proceeds for
no more than 5–15 min and the turnover has rather
low values (Table 2).
By special experiments for the Ni[P(OEt)3]4–
CF3COOH system, it has been shown that the oxidaꢀ
tion rate of Ni(0) to Ni(II) under conditions of the
The Ni[P(OC6H4CH3ꢀo)2]2(C2H4)–HX catalyst
catalytic process is higher than that in the absence of system is more effective in propylene oligomerizaꢀ
propylene. The reason for this effect is likely the higher tion in comparison with the systems based on
interaction rate of Niꢀalkyl complexes with acid (reacꢀ Ni[P(OEt)3]4 and Ni[PPh3]4 complexes. The turnꢀ
tions 3, 4) in comparison with the Niꢀhydride complex over number of the Ni[P(OC6H4CH3ꢀo)2]2(C2H4)–HX
(reactions 1, 2). Because of the high deactivation rate catalyst system is 8–20 times higher (Table 1, lines 1–7)
of catalytically active complexes, catalysis of the proꢀ than those based on Ni[P(OEt)3]4(Ni[PPh3]4)–HX and
pylene dimerization reaction in the presence of NiP4– Ni(PPh3)4 complexes (Table 2, lines 1–3, 9). Such
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

PROPYLENE DIMERIZATION IN THE PRESENCE
209
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

210
SHMIDT et al.
(b)
20°C
(а)
–3 –4 –5 –6 –7 –8 –9 –10 –11 –12 –13 –14
ppm
1
Fig. 4. H NMR spectrum of Ni(PPh ) –60BF OEt
2
3 4
3
8
–2
reaction system in tolueneꢀ
d
at –20
°
С (
c
= 1 × 10 mol/l,
Ni
–50°C
–2
cH O = 3 × 10 mol/l).
2
selectivity in some cases. In particular, the
Ni[P(OEt)3]4–HX catalytic system (X = CF3COO–,
HSO–4 ) in both toluene and chlorobenzene is characꢀ
–12.0
–12.4
–12.8
–13.2
–13.6
δ
, ppm
terized by a high selectivity in the formation of linear
1
Fig. 3. H NMR spectra of Ni(PPh ) –4EtOH–20BF OEt
3 4
3
2
hexenes (up to 87%). The addition of BF3
⋅
OEt2
8
reaction system in tolueneꢀ
d at (a) ⎯50°С and (b) 20°С
–2
changes selectivity, increasing the methylpentene
yield up to 84%.
(c
= 1 × 10 mol/l).
Ni
Examination of the Ni(PPh3)4–4С2H5OH–
20BF3 · OEt2 catalytic system using H NMR specꢀ
an effect can be caused by the fact that the number
of phosphorusꢀcontaining ligands of the
Ni[P(OC6H4CH3ꢀo)2]2(C2H4) complex is less than
1
troscopy at
highꢀfield resonant signal (
the doublet of triplets with spin–spin interaction
Т
= –50
°
С
has allowed us to register a
those of Ni[P(OEt)3]4 and Ni[PPh3]4 complexes.
δ
= –12.80 ppm) that is
The catalytic properties of the systems under conꢀ
sideration are significantly affected by the nature of
the solvent. Replacement of toluene by chlorobenzene
2
2
constants of JP–H = 61.0 and JP–H = 92.8 Hz
(Fig. 3). Such signal multiplicity is caused by proꢀ
ton interaction with two equivalent phosphorus
nuclei in the nickel coordination sphere with a
and
Within the catalyst systems under consideration, chloꢀ
robenzene and ꢀdichlorobenzene act not only as a
oꢀdichlorobenzene results in a TON decrease.
o
2
solvent, but also a reagent which deactivates the cataꢀ
lyst due to the oxidative addition reaction of chloroꢀ
arenes to Ni(0).
spin–spin interaction constant of JP–H = 61.0 Hz
and one phosphorus nucleus at a larger distance
from the proton with a constant of 2JP–H = 92.8 Hz.
Replacement of trifluoroacetic acid by sulfuric acid
used as a cocatalyst within the NiPn–HX, (Р = P(OEt)3,
PPh3) systems, slightly changes the catalytic properꢀ
ties, whereas BF3 etherate introduced into the cataꢀ
lytic system significantly increases the operating time
of the catalyst system; this is seen as an increase in
TON (Table 2, lines 1, 6 and 3, 8). At first sight, it
would be logical to suppose that the role of BF3 in these
systems can be caused by two factors: the formation of
Brönsted acid in the interaction with proton donor
compounds or binding of phosphorusꢀcontaining
ligands, which leads to an increase in the concentraꢀ
tion of coordinatively unsaturated Niꢀhydride comꢀ
plexes. However, it should be noted that addition of
BF3 etherate not only raises the TON, but also changes
When temperature increases to –10
resolved multiplet structure arises, which is transꢀ
formed to a doublet at 20 , and this is related to
stereochemical nonrigidity of the
°
С, a badly
°
С
[(PPh3)3NiH]+(BF3OEt)– nickelꢀhydride complex.
This property of nickel hydrides with three phosꢀ
phine ligands is a wellꢀknown fact which is
described, e.g., in [17]. At
Т
≤
–50 С, the chemical
°
shift difference between two types of phosphorus
nuclei is large enough to give a spectrum of А2Х
type;
i.e.,
at
low
temperatures
the
[(PPh3)3NiH]+(BF3OEt)– complex has a static
structure, where the metal complex is of squareꢀplaꢀ
nar geometry with two phosphines at the cisꢀ and
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

PROPYLENE DIMERIZATION IN THE PRESENCE
211
one phosphine at the transꢀposition in relation to has highꢀfield resonant signals characteristic of
the proton:
hydride ions: a doublet of triplets,
δ
= –12.60 ppm,
2JP–H = 61.0 Hz (triplet) and JP–H = 92.8 Hz (douꢀ
2
+
blet) (
1
), doublet of doublets,
δ
= –10.10 ppm,
P
P*
2JP H = 61.0 Hz (doublet) and 2JP–H = 92.8 Hz (douꢀ
⎯
Y–
Y = BF3OEt; P = PPh3.
Ni
blet) (
2
), triplet,
δ
= –7.15 ppm, 2JP–H = 55.0 Hz (
3
),
), and
5). These
H
P
2
doublet,
doublet,
δ
= –4.00 ppm, JP–H = 55.0 Hz (
4
δ
= –4.20 ppm, 2JP–H = –91.0 Hz (
NMR monitoring of the Ni(PPh3)4–BF3 OEt2
⋅
resonant signals can be assigned to the following
Ni(II)ꢀhydride complexes:
reaction system (B/Ni = 60) has shown that nickelꢀ
hydride complexes were also formed in the presence of
water (H2O/Ni = 3) (Fig. 4). The 1H NMR spectrum
+
+
+
P
P*
H
L
P*
P
L
Y–
Y–
Y–
Ni
P
Ni
P
Ni
P
H
H
H
(
1
)
(
2
)
(3)
+
+
P
L
P
L
Y–
Y–
Ni
Ni
H
L
L
(4)
(5)
Y = BF3OH, P = PPh3, L =OEt2, solvent
.
Taking into account small concentrations of the electron oxidative addition of Brönsted acid to Ni[PPh3]4
complexes used in catalysis, and a degree of solvent
drying, the formation of nickelꢀhydride complexes at
the real catalytic system is inevitable. Detailed strucꢀ
ture of these complexes and the mechanism of their
transformation to Ni(I) and Ni(II) complexes will be
a subject of special examination, but the fact of the
formation of hydrides in these systems under condiꢀ
tions of catalysis does not cause doubts.
complex. It has been previously shown that interaction of
Ni[PPh3]4 with BF3 OEt2 leads to the formation of paraꢀ
magnetic Ni(I) complexes of [(PPh3)nNi]+BF4– types
= 1, 2, 3) [18], one of the routes for their formation is
decomposition of Ni(II)ꢀhydrides in reaction:
[PnNiH]+X– = [PnNi]+X– + 1/2H2, where X = BF3OEt
⋅
(n
or BF4
.
The formation of nickelꢀhydride complexes in the
In turn, Ni(I) complexes also can turn into catalytꢀ
system under consideration is possible not only by twoꢀ ically active nickelꢀhydride complexes:
[PnNi(I)](BF4) + HBF4
[PnNi(III)–H](BF4)2
[PnNi(II)](BF4)2 + 1/2H2
[PnNi(I)](BF4) + [PnNi(III)–H](BF4)2
[PnNi(II)–H](BF4) + [PnNi(II)](BF4)2
[PnNi(II)–H](BF4) + HBF4
[PnNi(II)](BF4) + H2
where
n
= 1, 2, 3.
along with a Brönsted acid causes no doubts (Table 2). The
increasing catalyst lifetime and, consequently, the increasing
TON is likely caused by the fact that the rate of oxidation of
the [P3Ni]+BF–4 cation complex to Ni(II) complexes inacꢀ
The contribution of Ni(II) and Ni(III) hydride comꢀ
plexes to catalysis cannot yet be evaluated. However, an
increase in the lifetime of catalyst systems based on
Ni[P(OEt)3]4 and Ni[PPh3]4 and containing BF3 OEt2 tive in catalysis, for example, [PnNi](BF4)2, sharply
⋅
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

212
SHMIDT et al.
decreases because an acidic proton interacts with the nickel cial examination of the kinetics of the reaction of
anion, which has an effective positive charge that is higher nickel complexes with Brönsted acids.
than that at the neutral hydride complex of
PnNi(H)(X) type [19]. This suggestion demands speꢀ
Lower alkene dimerization under the action of nickel
hydride complexes follows the degenerate polymerization
type. The mechanism of hexene formation can be repreꢀ
sented in a schema (ligands at nickel are omitted):
CH3
CH3
CH2
CH2
CH2
C
CH2 CH2 CH3
CH2
CH2
Ni
CH CH3
C
CH2 CH2 CH3
–Ni–H
CH CH3
CH2
CH2 CH3
CH2
Ni
CH3
+ C3H6
Ni
CH2
CH2 CH3
Ni
CH3 CH
CH CH2 CH2 CH3
2
–Ni–H
CH3 CH2 CH2 CH2 CH CH3
CH CH3
CH2
Ni
H
1
CH CH3
CH
CH2
Ni
C
CH CH3
CH2
CH CH3
CH2
CH3
H3C
–Ni–H
H3C CH3
+ C3H6
CH
Ni
H3C CH3
Ni
CH
CH CH CH3
CH3
CH3 CH
CH3 CH CH2 CH CH3
CH3
H3C
–Ni–H
CH3
Ni
CH3 CH CH CH CH3
CH3
After complexation of alkene with a coordinatively whereas abstraction of hydrogen atom from alkyl βꢀcarꢀ
unsaturated nickelꢀhydride complex, hydrogen transꢀ
fer to an alkene double bond occurs to give nickelꢀ
alkyl derivatives. The mode of hydrogen addition to
propylene (Markovnikov and antiꢀMarkovnikov addiꢀ
tion, routes 1 and 2, respectively) and, as conseꢀ
quence, the yield ratio of linear hexenes and 2ꢀmethꢀ
ylpentꢀ1ꢀene to 2ꢀ and 4ꢀmethylpentꢀ2ꢀenes and 2,3ꢀ
dimethylbutene is determined by the polarity of the
Ni–H bond because charges at carbon atoms of a proꢀ
pylene double bond are not the same owing to the
electropositive effect of methyl group, namely:
bon atom leads to regeneration of nickelꢀhydride comꢀ
plex to give hexene. The second stage of interaction of
a nickelꢀalkyl complex with propylene is advantaꢀ
geously determined by the steric effects of the transiꢀ
tion state [1].
It is obvious that the formation of linear hexenes
and 2ꢀmethylpentꢀ1ꢀene is caused by the partially
negative charge at the hydrogen atom. This mode of
hydrogen addition is characteristic of the
Ni[P(OEt)3]4–НХ system. Preferential formation of 2ꢀ
and 4ꢀmethylpentꢀ2ꢀenes indicates
a reverse
–
δ
+
δ
CH2=CH–CH3. Subsequent insertion of monomer
charge distribution within the Ni–H bond. This is
pronounced for systems where BF3 OEt2 is used in
⋅
molecule into the Ni–C bond leads to chain growth,
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010

PROPYLENE DIMERIZATION IN THE PRESENCE
213
combination with ROH, where R = H–, C2H5, CF3CO
In the case of CF3COOH as the cocatalyst, selectivity of
the process also varies when BF3 OEt2 is added; howꢀ
.
REFERENCES
1. F. K. Shmidt, Catalysis of Hydrogenation and Dimerizaꢀ
tion Reactions by Complexes of FirstꢀRow Transition
Metals (IGU, Irkutsk, 1986) [in Russian].
⋅
ever, this cannot be explained by complexation of BF3
2. V. Gibson and S. Spitzmesser, Chem. Rev. 103, 283
with CF3COO– because BF3 does not form molecular
complexes with CF3COOН [20]. Apparently, within the
catalytic system, there is an exchange of residue of trifluꢀ
oroacetic acid for fluorine to give HF: CF3COOH +
(2007).
3. S. S. Ivanichev, Usp. Khim. 76 (7), 669 (2007).
4. Y. Chauvin, Angew. Chem. Ed 45, 3741 (2006).
5. V. S. Tkach, F. K. Shmidt, V. V. Saraev, and A. V. Kalaꢀ
BF3
BF2(CF3COO) + HF.
bina, Kinet. Katal. 15, 617 (1974).
6. F. K. Shmidt, L. V. Mironova, V. V. Saraev, et al., Kinet.
A similar exchange is observed, e.g., in the interacꢀ
tion of nickel bis(acetylacetonate) with BF3. This is
caused by the fact that the Ni–F binding energy is
higher than that of Ni–O, and the B–O binding
energy is higher than that of B–F. The presence of
BF3X– – anion (X = OH, OEt, and F) within a coorꢀ
dination sphere of nickel, as it was mentioned above,
results in the preferential formation of branched
hexenes. A more detailed analysis of the influence of
hydride complexes on selectivity of dimerization proꢀ
cesses demands further studies of catalytic systems by
physicochemical methods.
Katal. 20, 622 (1979).
7. A. D. Pomogailo, PolymerꢀImmobilized Metal Complex
Catalysts (Nauka, Moscow, 1988) [in Russian].
8. D. Meihard, P. Reuter, and B. Rieger, Organometallics
26 (2007).
9. A. N. Nesmeyanov, F. K. Shmidt, L. V. Mironova, et al.,
Dokl. Akad. Nauk SSSR 233, 379 (1977).
10. F. K. Shmidt, L. V. Mironova, A. G. Proidakov, et al.,
Kinet. Katal. 19, 150 (1978).
11. F. K. Shmidt, L. V. Mironova, A. G. Proidakov, and
A. V. Kalabin, Koord. Khim. 4, 1608 (1978).
12. G. Wilke, E. W. Muller, and M. Kroner, Angew. Chem.
73, 33 (1961).
13. W. Drinkard, D. K. Eaton, J. V. Jessen, and R. V. Lindꢀ
CONCLUSIONS
seg, Inorg. Chem.
14. W. C. Seidel and S. A. Tolman, Inorg. Chem.
(1973).
9, 392 (1970).
9, 23
(1) The formation of nickelꢀhydride complexes in
the interaction of Ni(0) complexes of phosphorusꢀ
containing ligands with Brönsted acids—CF3COOH,
HBF3(OEt), HBF3(OH)—was discovered by 1H NMR
spectroscopy.
15. P. W. Jolly, J. Tkatchenko, and G. Wilke, Angew. Chem.
83, 328 (1971).
16. A. Yamamoto and T. Yamamoto, J. Am. Chem. Soc. 95
,
4073 (1973).
17. A. R. Siedle and R. A. Newmark, Inorg. Chem. 30
,
(2) Both the equilibrium constant for protonation
of the (C2H4)Ni[P(OC4H6CH3ꢀo)]2 complex with trifꢀ
luoroacetic acid and the effective rate constant for
propylene dimerization were determined.
2005 (1991).
18. V. S. Tkach, V. A. Grusnykh, and F. K. Shmidt, React.
Kinet. Catal. Lett. 43, 431 (1991).
19. F. K. Shmidt, V. S. Tkach, L. B. Belykh, and M. Gomꢀ
(3) Selectivity of the propylene dimerization proꢀ
cess was discussed in the context of the nickelꢀhydride
mechanism.
boogiin, Vestn. Irk. Gos. Tehh. Univ. 33, 112 (2008).
20. A. V. Topchiev, Selected Works: Book 2. Alkylation
(Nauka, Moscow, 1965) [in Russian].
PETROLEUM CHEMISTRY Vol. 50
No. 3
2010