Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr3)2]BF4/BF3OEt 2 catalytic systems

Article abstract of DOI:10.1134/S0965544111030157

Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr₃)₂]BF₄ + BF ₃OEt₂ catalytic systems, where R = C₆H ₅, o-CH₃C₆H₄, p-CH₃C ₆H₄, or o-CH₃OC₆H₄, has been studied. Under the optimal conditions (B/Pd = 8, T = 75°C, R = C ₆H₅), the conversion of styrene to the products exceeds the conversion for the known analogs and reaches 1.5 tons of styrene/g-atom of palladium with amounts of dimers and trimers of 91 and 9%, respectively. The dimers consist of up to 100% 1,3-diphenylbutene-1 with a trans/cis isomer ratio of 95/5.

Full text of DOI:10.1134/S0965544111030157

ISSN 0965ꢀ5441, Petroleum Chemistry, 2011, Vol. 51, No. 3, pp. 157–163. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © D.S. Suslov, V.S. Tkach, M.V. Bykov, M.V. Belova, 2011, published in Neftekhimiya, 2011, Vol. 51, No. 3, pp. 169–175.
Selective Dimerization of Styrene to 1,3ꢀDiphenylbuteneꢀ1
in the Presence of [(acac)Pd(PAr ) ]BF /BF OEt Catalytic Systems
3
2
4
3
2
D. S. Suslov, V. S. Tkach, M. V. Bykov, and M. V. Belova
Irkutsk State University, ul. Karla Marksa 1, Irkutsk, 664003 Russia
eꢀmail: tkach@chem.isu.ru; tkach_vs@bk.ru
Received October 25, 2010
Abstract—Selective dimerization of styrene to 1,3ꢀdiphenylbuteneꢀ1 in the presence of
[
o
(acac)Pd(PAr ) ]BF + BF OEt catalytic systems, where R = C H , oꢀCH C H , pꢀCH C H , or
ꢀCH OC H , has been studied. Under the optimal conditions (B/Pd = 8, T = 75°C, R = C H ), the conꢀ
3 6 4 6 5
3 2 4 3 2 6 5 3 6 4 3 6 4
version of styrene to the products exceeds the conversion for the known analogs and reaches 1.5 tons of
styrene/gꢀatom of palladium with amounts of dimers and trimers of 91 and 9%, respectively. The dimers
consist of up to 100% 1,3ꢀdiphenylbuteneꢀ1 with a trans/cis isomer ratio of 95/5.
DOI: 10.1134/S0965544111030157
Dimerization of alkenes in the presence of metal cesses of conversion of diene hydrocarbons, norꢀ
complex catalysts is an effective method for the proꢀ bornene, and its derivatives.
duction of olefins of a higher molecular weight, which
are used as intermediates in the chemical industry, or
EXPERIMENTAL
directly as the desired products [1, 2]. In particular,
dimers of styrene are in demand as feedstock for
organic synthesis, in the production of synthetic rubꢀ
ber, insulating oil, as solvents for polystyrene and heatꢀ
transfer agents, as well as the trimers [3].
Styrene dimerization reaction was carried out in a
thermostatted glass vessel under argon. After charging
the reactor with styrene and the components of the
catalytic system, the reaction mixture was stirred over
Among a large number of catalysts based on transiꢀ 0.5 h at room temperature to form the catalyst and
tion metal compounds capable of dimerizing styrene then the temperature of the experiment was set up.
[
4–15], the catalysts based on Pd complexes are charꢀ The reaction rate was monitored by measuring the
acterized not only by traditionally high selectivity of consumption of styrene; at the end of the experiment,
styrene conversion to dimers, but also a high converꢀ styrene and the reaction products were distilled off,
sion of styrene into the products.
In a series of efficient palladium catalysts for the
selective dimerization of styrene, catalytic systems
based on palladium bisꢀacetylacetonate and boron triꢀ
fluoride etherate are active also in the processes of diꢀ
and oligomerization of ethylene and propylene [16,
and the yield was determined by weighing the subꢀ
stances. The styrene conversion was monitored by
GLC with a TSVETꢀ100M instrument, a 2.7ꢀm
packed column with the SEꢀ30 stationary phase, a
column oven temperature of 100°С, nitrogen as the
carrier gas, and a pressure at the column inlet of
0
.8 atm.
Dimers were separated by vacuum distillation and anaꢀ
lyzed by gas chromatography–mass spectrometry (MATꢀ
12 instrument, = 100–200 , length of the capillary colꢀ
umn 20 m, SEꢀ30 phase), GLC (Chromꢀ5 instrument, colꢀ
umn length 3.7 m, SEꢀ30 phase, nitrogen carrier gas,
40 ), IR (a Perkin Elmer device, registration range 200–
000 cm ), and H NMR spectroscopy (a Varianꢀ500S
1
7], telomerization of diene hydrocarbons with secꢀ
ondary amines [18], and additive polymerization of
norbornene and alkylnorbornenes [19, 20].
2
Т
°
C
This paper presents the results of experiments on
the effect of various factors, including the ratio of
components of highly organized catalytic systems of
the [(acac)Pd(PAr ) ]BF /BF OEt composition, the
nature of tertiary phosphines, temperature, and the
conditions for the formation of an activated complex
Т
=
1
4
°
С
3
2
4
3
2
–1
1
instrument, TMS standard).
(
AC) on the conversion of styrene to dimers. The aim
Styrene was purified by shaking it with a 5% alkali
was to increase the efficiency of catalytic systems solution until a portion of alkali became colorless.
formed on the basis of Pd(acac)2 and BF OEt2 in the After that it was washed with distilled water, dried over
3
processes of the selective dimerization of styrene to anhydrous calcium chloride, and distilled in a vacꢀ
1
,3ꢀdiphenylbuteneꢀ1, as well as to obtain additional uum. Argon was treated for the removal of moisture
information on the nature of the catalytic action of and oxygen by successively passing it through columns
such systems, which are potentially active in the proꢀ filled with phosphorus pentoxide, granular alkali,
157

158
SUSLOV et al.
molecular sieves
50°С
before use under argon over calcium hydride.
Synthesis of [(acac)Pd(PPh ) ]BF was conducted Pd(acac)2 and BF OEt2, the Pd(acac) + 2PPh +
5
Å, and copper powder heated to acetylacetonate ligand at Pd, BF OEt2, and an unsatꢀ
3
2
.
Boron trifluoride etherate (Acros) was distilled urated hydrocarbon.
Among the investigated catalysts based on
3
2
4
3
2
3
in an argon atmosphere. Boron trifluoride etherate 7BF OEt2 system is the most efficient in the styrene
3
(
0.41 ml, 3.282 mmol) was added dropwise to a soluꢀ dimerization process. In the presence of the system,
tion of Pd(acac)2 (0.5000 g, 1.641 mmol) and PPh3 the conversion of styrene to the desired products
0.8611 g, 3.282 mmol) in 40 ml of benzene. The reaches 75 000 moles per gꢀatom of palladium with the
(
lemonꢀyellow precipitate was filtered on a Schott funꢀ selectivity for dimers represented by 1,3ꢀdiphenylꢀ
nel, washed with benzene and dried in a vacuum. 91% buteneꢀ1 up to 93% [22]. Using such a system as an
yield. Mp 174–176°C.
example, Tkach et al. [23] also found that trans–cis
rearrangement between the preactivated and activated
complexes precedes the formation of the
1H NMR (acetoneꢀd6),
δ
1.5 (singlet, 6H, –CH3 of
acac), 5.6 (singlet, 1H, –CH of acac), 7.2–7.8 (mulꢀ
+
–
1
3
[H(L)Pd(PAr ) ] BF AC (Eq. 1). With the optimized
tiplet, 30H, –PPh ]; C NMR (acetoneꢀ 6
d
),
δ
27.5
3 2 4
3
parameters of the process, the catalyst conditioning
time determined by the trans–cis rearrangement can
reach more than 120 min [22]
[
⎯
⎯
CH3 of acac), 102.3 (–CH of acac), 128–136
1
9
1
(
PPh ), 188.4 (–C=O); F{ H} NMR (CD C1 )
3
2
2
δ
–153.51 (singlet, 1F), –153.56 (singlet, 4F) (BF4
,
the ratio of integrals of the signals of 1 : 4 corresponds
1
0
11
to the natural abundance of B/ B isotopes =
R3P
H
R3P
H
11
Pd+
Pd+
1
9.4%/80.6%); B NMR (acetoneꢀd6) 3
δ
–0.56 [BF4,
1
1
quintet, 1 : 4 : 6 : 4 : 1, JBꢀF = 1.1 Hz); P{ H} NMR
PR3
R3P
(1)*
Ph
(
d
acetoneꢀ 6
) 36.0 [–PPh3]).
δ
Ph
IR (cm–1) 1523, 1565 (C=C and C=O bonds of
acac group), 1590 (C=C bonds in benzene ring);
–
*
In the equation, BF4 anion is omitted for clarity
.
1
7
5
465, 1478 (CH of acac); 1020–1150 (BF ); 730,
50, 960, 980 (C–H bonds of benzene ring); 511, 522,
43 (bending vibrations of the P–C bonds and benꢀ
3
4
Based on the analysis of the array of data set on the
mechanism of the formation of complexes active in
the conversion of unsaturated hydrocarbons for the
systems in question, we suggest a new strategy for the
zene ring).
Elemental
C H BF O P Pd, %: Pd 13.0; C 60.3; H 4.5; P 7.6;
B 1.35; F 9.3. Found, %: Pd 12.8; C 61.2; H 4.3; P 7.1;
B 1.1; F 8.25.
analysis,
calculated
for
–
+
taskꢀoriented design of the [H(L)Pd(PAr ) ] BF4 actiꢀ
3
2
41
37
4
2 2
vated complex. The solution to this problem is based
on the previous development of an efficient method
for the synthesis of the cationic palladium complexes
Synthesis of [(acac)Pd(P(
o
ꢀCH C H ) ) ]BF ,
3
6
4 3 2
4
[
(acac)Pd(PAr ) ]BF [24]. These complexes are highly
3 2 4
[
(acac)Pd(P(
p
ꢀCH C H ) ) ]BF ,
and
3
6
4 3 2
4
organized structures and, in essence, they imitate the
composition of the preactivated complexes formed at
the first stage of the interaction between the compoꢀ
nents of the Pd(acac) + 2PAr + 7BF OEt system. The
[
(acac)Pd(P(
o
ꢀCH OC H ) ) ]BF was carried out
3
6
4 3 2
4
similarly to [(acac)Pd(PPh ) ]BF .
3
2
4
2
3
3
2
determining difference of the [(acac)Pd(PAr ) ]BF
RESULTS AND DISCUSSION
the Pd(acac) /BF OEt
Pd(acac) /PR /BF OEt (R = Ph,
tems, the concepts of the composition of the activated
complexes (AC) as palladium hydrides of the HPd(L,
3 2
complexes as preactivated ones is that the organoꢀ
phosphorus ligands are in the cisꢀposition to each
other in the squareꢀplanar complex cation [25]. In this
case, the transformation of the complexes to the AC
with the participation of an unsaturated hydrocarbon
and boron trifluoride excludes the preliminary trans–
cis rearrangement
4
For
and
ꢀBu) catalytic sysꢀ
2
3
2
n
2
3
3
2
L'n)BF4 type (L is unsaturated hydrocarbon, L = L' or
PR3,
n = 1, 2) were experimentally substantiated. In
this case, the structural fragment BF4 in the AC may be
+
+
P
P
L
linked to Pd in chargeꢀtransfer complexes: HPd(L2 – nL'n)F ·
O
O
+L
OEt2 –OEt2
P
P
Pd
+
BF3
⋅
Pd
BF (
+
n
= 0, 1), or in the ion pair form [HPd(L,
–
4
3
O⋅ BF
3
L'2 )] BF (L' = PR3) [21]. General principles for the
O
quite sophisticated mechanism of the formation of
such an activated complex suggest two stages. At the
first stage, the formation of the structural fragment
BF4 directly involves the first acetylacetonate ligand at
Pd, BF OEt2, and trace amounts of H O in an aroꢀ
+
(2)*
L
P
P
O ⋅ BF3
+L
Pd
+
L−H
H
3
2
*
For clarity, P = PAr , L = styrene molecule,
3
–
matic solvent. The second stage suggets the formation
of the Pd–H bond with the participation of the second
and the BF4 anion is omitted in the equatio
.
PETROLEUM CHEMISTRY Vol. 51
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2011

SELECTIVE DIMERIZATION OF STYRENE TO 1,3ꢀDIPHENYLBUTENEꢀ1
00
159
1
115
193 208
91
90
80
70
60
50
40
30
20
10
0
2.8E7
2.5E7
2.2E7
1.9E7
1.6E7
1.2E7
9.4E6
6.2E6
3.1E6
0
178
7
7
1
30
51
165
65
103
152
8
3
9
7
139
202
60
80 100 120 140 160 180 200 220 240 260 280 300
m/z
Fig. 1. Mass spectrum of 1,3ꢀdiphenylbuteneꢀ1.
By IR, NMR, and mass spectrometry, it was shown Signals of other aromatic carbons appear in the range
that the product of styrene dimerization in the presꢀ from 126.65 to 129.23 ppm.
ence of [(acac)Pd(PAr ) ]BF / BF OEt based systems is
At the first stage of the study of the selective dimerꢀ
3
2
4
3
2
exceptionally 1,3ꢀdiphenylbuteneꢀ1. According to the ization of styrene in the presence of twoꢀcomponent
GLC data, the cis/trans ratio of 1,3ꢀdiphenylbuteneꢀ1 catalyst systems of the [(acac)Pd(PAr ) ]BF /BF OEt
3
2
4
3
2
isomers is 5/95. The presence of the transꢀ and cisꢀisoꢀ composition, we separately tested both the palladium
mers is also confirmed by the appearance in the IR complexes and BF OEt2 at 45
С. The palladium comꢀ
°
3
⎯1
spectra of absorption bands at 965 and 910 cm , plexes per sedid not show activity in the conversion of
respectively, assigned to
bond [26]
δ
C
vibrations at the double styrene. In the experiment with BF OEt2 (2.63 mol of
⎯H
3
–3
styrene, 1.25
conversion of styrene to a polymer (
observed. An analysis of the polymer by
×
10 mol of BF OEt2), the complete
3
M
= 31 500) was
η
The molecular weight of 1,3ꢀdiphenylbuteneꢀ1,
which is = 208, was confirmed by mass spectromeꢀ
try (Fig. 1).
1
13
H
and C
М
NMR spectroscopy showed that the product is atactic
polystyrene typical of cationic initiators similar to
1
13
Figure 2 shows the H and C NMR spectra of 1,3ꢀ those described in [27].
1
diphenylbuteneꢀ1. In the H NMR spectrum, the
methyl protons in the 4ꢀposition of 1,3ꢀdiphenylꢀ
buteneꢀ1 appear as a signal at 1.98 ppm. The resoꢀ
nance signal at 4.12 ppm characterizes the methine
proton in the 3ꢀposition. Signals of vinyl protons in
the 1ꢀ and 2ꢀpositions appear in the region of
The data on the effect of the B/Pd ratio on the
selectivity and conversion of styrene to the target
products in the presence of the reference catalyst sysꢀ
tem [(acac)Pd(PPh ) ]BF + nBF OEt2 are presented
3
2
4
3
in Table 1.
Table 1 shows that as the B/Pd ratio increases from
to 8, the selectivity for styrene dimers remains within
9–93% at a yield of trimers of 7 to 11%. At relatively
large B/Pd ratios, processes of cationic polymerizaꢀ
tion of styrene begin to occur along with the main proꢀ
cess of selective oligomerization of styrene to dimers.
So, at a B/Pd ratio of 12, the amount of heavy prodꢀ
6
.92 ppm. In this case, the value of the constant of
2
8
1
2
2
spin–spin coupling of protons H and H is
J =
1
5/27 Hz. This value is very close to that of spin–spin
1
2
interaction between the H and H protons described
in [9], indicating the trans double bond. The aromatic
protons are characterized by a signal of 7.76 ppm.
1
3
In the C NMR spectrum, there are 6 groups of ucts presented mainly by polymers of styrene reaches
signals in the range from 20 to 150 ppm. The resoꢀ 28%. At a B/Pd ratio of 25, the complete conversion of
nance signal at 21.76 ppm refers to the methyl carbon styrene to polymers was observed in the standard
4
3
(
C ). Methine carbon C shows a signal at 43.00 ppm. experiment.
1
The resonance signal at 135.65 ppm characterizes C2
Note a substantial effect of the B/Pd ratio in the
range from 2 to 8 on the product yield, which, in parꢀ
carbon. The signal of the second vinyl carbon C
appears at 138.10 ppm. The signal at 146.63 ppm is ticular, increases roughly 3.5 times. Consequently, for
3
attributed to the aromatic carbon bonded to C atom. the process of selective dimerization of styrene, the
PETROLEUM CHEMISTRY Vol. 51
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2011

1
60
SUSLOV et al.
H4
C H
6
5
C H
6
5
(а)
1
3
CH 2
CH
4
H + H2 C H
1
CH
CH3
6
5
H3
9
8
7
6
5
4
3
2
1
ppm
C H
6
5
(b)
C H
6
5
CH1
CH3
2
4
С1
С2
CH
C H
6
CH3
5
С3
С3
180
160
140
120
100
80
60
40
20 ppm
Fig. 2. NMR spectra of 1,3ꢀdiphenylbuteneꢀ1 in CDCL : (a) H NMR, and (b) 13C NMR.
1
3
B/Pd ratio of 5–8 can be recommended as optimal for
achieving a high conversion of the reactant to the dimerization
desired products.
[(acac)Pd(PPh ) ]BF /5BF OEt catalyst system in the
The typical shape of kinetic curves for styrene
occurring over the
3
2
4
3
2
range of 50–80
the selective dimerization of styrene in the presence of
Table 1. The effect of the B/Pd ratio on the conversion of styrene to the [(acac)Pd(PPh ) ]BF /5BF OEt system is firstꢀ
°
C is shown in Fig. 3. It was found that
3
2
4
3
2
oligomers (catalytic system, [(acac)Pd(PPh ) ]BF + nBF OEt ; order in catalyst and zeroꢀorder in substrate and is
3
2
4
3
2
T = 70°C; reaction time, 6 h; styrene/Pd = 120000; quantity
described by the general rate equation of the type
W =
of Pd, 3.7 × 10–6 mol)
kobs [Pd] (prior to deactivation). On the basis of the
×
data, it can be concluded that the stationary portions
of the rate curves observed in the first stage within a
certain time (from 50 min to 5 h) are caused by a conꢀ
stant concentration of the AC.
Product composition, wt %
Yield, mol of styꢀ
B/Pd
rene/gꢀat of Pd
dimers
oligomers
2
3
5
8
2
26733
56765
66225
92242
111164
93
93
92
89
72
7
7
8
11
28
At the next step, the experiments were carried out
at 70
°
С as the optimum temperature for the
Pd(acac) /PAr /BF OEt catalysts of the previous
2
3
3
2
1
generation [22].
PETROLEUM CHEMISTRY Vol. 51
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2011

SELECTIVE DIMERIZATION OF STYRENE TO 1,3ꢀDIPHENYLBUTENEꢀ1
161
Turnover frequency, mol of styrene/gꢀat of Pd
×
h
3
2
2
1
1
0000
5000
0000
[
80
°
С
3
2
4
3
2
75
°
С
5000 70
°
°
°
С
С
С
0000 60
5
000 50
that the decrease in the yield on passing from PPh3 to
P(
by an increase in both the basicity of the organophosꢀ
phorus ligand in the series PPh < P( ꢀCH C H )
pꢀCH C H ) and P(оꢀCH C H ) is caused
3 6 4 3 3 6 4 3
0
50 100 150 200 250 300 350
Time, min
o
≈
3
3
6
4 3
P(
nophosphorus ligands PPh3 and P(
characterized by the same cone angles (
differ in basicity, in contrast to P(
P(
pꢀCH C H4)3and steric effects. In this case, the orgaꢀ
3 6
Fig. 3. The typical shape of styrene dimerization rate
curves; the experiments at different temperatures
([(acac)Pd(PPh ) ]BF + 5BF OEt ; styrene/Pd =
pꢀCH C H ) are
3 6 4 3
θ
= 145°), but
3
2
4
3
2
⎯
6
120000; quantity of Pd, 3.7 × 10 mol).
o
ꢀCH C H ) and
3
6
4 3
pꢀ
CH C H ) , for which the values of the cone
3
6
4 3
angles vary considerably (from
at a relatively close basicity.
θ
= 145° to
θ
= 194°)
the experiments up to 80°С, the yield decreases
sharply to 61150 mol of styrene per gꢀatom of Pd
because of thermal deactivation of the AC.
In a series of the [(асас)Pd(PAr ) ]BF /BF OEt sysꢀ
3
2
4
3
2
tems studied as catalysts for the selective dimerizaꢀ
tion of styrene (Table 2), the composition modified
Under the optimal conditions characterized by the
by P(
inactive. The observed effect is presumably due to the and
fact that P(
ꢀCH OC H4)3, which is a monodentate per gꢀatom of Pd, which exceeds that for all known
organophosphorus ligand in nature, behaves as a analogs. In particular, for the Pd(acac)
bidentate ligand under the experimental conditions 7BF OEt system, which is similar in the nature of
during the formation of the AC and blocks coordinaꢀ action, the maximum yield (75 000 moles of styrene
tion sites free for the coordination of substrate moleꢀ per gꢀatom of Pd) was obtained at 70 . By increasing
cules to Pd. This feature can be effectuated upon the the temperature to 75 , the yield for such a system is
o
ꢀCH OC H ) turned out to be substantially use of the [(acac)Pd(PPh
3
)
2
]BF
4 3 2
+ 8BF OEt system
3
6
4 3
T
= 75 С, the yield reaches 153 000 mol of styrene
°
o
3
6
+ 2PPh +
3
2
3
2
°
С
°
С
coordination to palladium in preactivated complexes substantially reduced to 59 000 moles of styrene per gꢀ
of organophosphorus ligands of this type not only by atom of Pd.
the phosphorus atom, but also by the oxygen atom of
the methoxy group of the aryl substituent.
The
Pd(acac) /PAr /BF OEt
2
and
3
3
2
[
(acac)Pd(PAr ) ]BF / BF OEt systems, which are
active in the processes of converting unsaturated
hydrocarbons, have the same nature of catalytic activꢀ
ity due to the identity of the [H(L)Pd(PAr3)2]+BF4 AC.
3
2
4
3
2
The effect of the temperature on the dimerization
of styrene in the presence of the reference catalyst sysꢀ
tem [(acac)Pd(PPh ) ]BF + 5BF OEt was studied
3
2
4
3
2
–
in the range from 50 to 80°C (Table 3). From the analꢀ
ysis of the data it follows that at the experimental conꢀ A substantial difference in the performance of such
ditions the maximum yield reached a value of systems may be caused by the different AC formation
1
14500 mol of styrene per gꢀatom of Pd with a selecꢀ routes. This conclusion is clearly illustrated by the rate
tivity of 92% at 75 . With increasing temperature of curves for the transformation of styrene in the presꢀ
°
С
Table 2. The effect of the nature of tertiary phosphines on the conversion of styrene to oligomers (catalytic system,
–6
[
(acac)Pd(PAr ) ]BF + 5BF OEt ; T = 70°C; reaction time, 6 h; styrene/Pd = 120 000; quantity of Pd, 3.7 × 10 mol)
3 2 4 3 2
Product composition, wt %
Yield, mol of styꢀ
rene/gꢀat of Pd
B/Pd
ν
, cm–1
θ
, deg
dimers
oligomers
Ph
ꢀCH C H
66225
62690
55670
–
93
93
93
7
7
7
2068.9
2066.7
2066.3
2058.6
145
145
194
194
p
3
6
4
4
o
o
ꢀCH C H
3
6
ꢀCH OC H
4
traces
–
3
6
PETROLEUM CHEMISTRY Vol. 51
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2011

1
62
SUSLOV et al.
Table 3. The effect of the temperature on the conversion of styꢀ complexes) by charging a reactor with the components
rene to oligomers (catalytic system, [(acac)Pd(PPh ) ]BF
+
3
2
4
of the Pd(acac) /PPh /BF OEt catalytic system in
2 3 3 2
strict proportion and sequence. In the experiment, the
5
BF OEt ; reaction time, 7 h; styrene/Pd = 120000; quantity
3 2
–
6
of Pd, 3.7 × 10 mol)
cationic complex [(acac)Pd(PPh ) ]BF was obtained
3
2
4
directly in the styrene medium at room temperature by
the reaction: Pd(acac) + 2PPh + 2BF OEt
Product composition, wt %
Yield, mol
ofstyrene/gꢀat
of Pd
→
T
,
°
C
2
3
3
2
[
(acac)Pd(PPh ) ]BF + acacBF + 2OEt2. Then,
dimers
oligomers
3 2 4 2
5
BF OEt2 was added to the mixture and the temperaꢀ
3
ture was raised to 70 С. In the case of this experimental
procedure, the rate curve was identical to that for the
system directly using the palladium complex
°
5
0
18100
48250
71100
114530
153000
61150
95
93
93
92
91
88
5
7
6
7
7
7
8
0
[
(acac)Pd(PPh ) ]BF (Fig. 5, curves 1, 2). A distinctive
3 2 4
0
7
feature of the experiments on the in situ formation of
active catalysts is a low reproducibility of results under
optimized conditions; the feature is associated not
5
8
5*
0
9
only with an increase in the temperature to 75 С and
°
the B/Pd ratio up to 8, but, above all, with a high styꢀ
rene/Pd ratio, up to 160 000. The data presented are a
clear illustration of the conclusion that the potentially
high efficiency of the AC generated by the interaction
of components of the Pd(acac) /PPh /BF OEt system
12
*
In the experiment, B/Pd = 8; styrene/Pd = 160000.
2
3
3
2
at high styrene/Pd ratios substantially decreases as
ence of the [(acac)Pd(PPh ) ]BF + 8BF OEt and
3
2
4
3
2
compared with the [(acac)Pd(PAr ) ]BF /BF OEt sysꢀ
3
2
4
3
2
Pd(acac) + 2PPh + 7BF OEt systems (Fig. 4). Figꢀ
2
3
3
2
tem. This may be due to the relative increase in the
amount of uncontrolled impurities in the substrate
and, consequently, to the development of side proꢀ
cesses at the stage preceding the formation of the AC
as an ionic entity. Thus, to obtain high yields of styrene
ure 4 shows that a substantial increase in the converꢀ
sion of styrene to dimers for the
(acac)Pd(PAr ) ]BF /BF OEt system (curve ) even at
) is caused primarily by the
absence of the catalyst formation period, which is typꢀ
ical of the Pd(acac) /2PAr /
[
1
3
2
4
3
2
the same temperature (70 С
°
n
BF OEt catalysts of the dimers, the direct use of palladium complexes of the
2
3
3 2
preceding generation (curve
2).
[(acac)Pd(PAr ) ]BF type is preferred; the synthesis of
3 2 4
the complexes is relatively simple and is characterized
In the next stage of the study, we examined the feaꢀ
sibility of the in situ formation of the AC with a preꢀ by high yields (90% or more).
scribed composition and structure in the substrate
Thus, it was found that the catalytic systems of the
medium (without prior synthesis of cationic palladium
[
(acac)Pd(PAr ) ]BF /BF OEt
composition are
3
2
4
3
2
highly efficient catalysts for the selective dimerization
of styrene to 1,3ꢀdiphenylbuteneꢀ1. Under the optiꢀ
Turnover frequency, mol of styrene/gꢀat of Pd
×
h
mum conditions (B/Pd = 8,
T
= 75 C, Ar = Ph), the
°
20000
18000
16000
14000
12000
10000
1
conversion of styrene to products reaches 1.5 t per gꢀ
atom of Pd, giving dimers 91 and 9% trimers; with the
dimers containing up to 100% of transꢀ and cisꢀ1,3ꢀ
diphenylbuteneꢀ1 in the 95/5 ratio. It was shown that
the decrease in the activity and conversion of styrene
into the target products on the [(acac)Pd(PAr ) ]BF /
3
2
4
8000
6000
4000
2000
2
BF OEt2 catalyst system when changing the nature of
3
the organophosphorus ligands in the series PPh < P(oꢀ
3
CH C H )
≈
P(pꢀCH C H ) is caused by both an
3
6
4 3
3 6 4 3
increase in their basicity and steric properties. The
possibility of obtaining activated complexes of a given
composition and structure in the substrate medium in
situ (without prior synthesis of the cationic Pd comꢀ
plexes) by charging the reactor with the components of
the Pd(acac) /PPh /BF OEt catalytic system was
0
50 100 150 200 250 300
Time, min
Fig. 4. The dependence of the activity on the reaction time
for catalyst systems: ( [(acac)Pd(PPh ) ]BF +8BF OEt2;
styrene/Pd
Pd(acac) +2PPh +7BF OEt (styrene/Pd = 105000,
2
3
3
2
1
)
3
=
2
4
3
studied. It was shown that the direct use of complexes
=
120000,
T
70°C);
(2)
of the [(acac)Pd(PAr ) ]BF4 type is preferred to obtain
T
=
3 2
2
3
3
2
70°C).
high yields of styrene dimers.
PETROLEUM CHEMISTRY Vol. 51
No. 3
2011

SELECTIVE DIMERIZATION OF STYRENE TO 1,3ꢀDIPHENYLBUTENEꢀ1
163
Turnover frequency, mol of styrene/gꢀat of Pd ×
h
1
1
1
4
2
0
8
6
4
2
1
2
1
Pd(acac)
+ PPh + 2BF OEt
3 3 2
2
[(acac)Pd(PPh
+
) ]BF
3 2 4
5BF OEt
3
2
dimerization
[(acac)Pd(PPh
)
]BF
+ 5BF OEt
3 2
dimerization
2
3
2
4
0
50
100
Time, min
150
200
250
Fig. 5. Comparison of systems, in which complex [(acac)Pd(PPh ) ]BF is formed in situ by the interaction of
3
2
4
Pd(acac) +2PPh +2BF OEt2, with the ([(acac)Pd(PPh ) ]BF +5BF OEt system (T = 70°C, styrene/Pd = 50 000).
2
3
3
3 2
4
3
2
ACKNOWLEDGMENTS
13. Z. Jiang and A. Sen, Organometallics 12, 1406 (1993).
1
4. W. P. Kretschmer, S. I. Troyanov, A. Meetsma, et al.,
This work was supported by the Ministry of Educaꢀ
tion and Science of the Russian Federation as a part of
Organometallics 17, 284 (1988).
the 2009–2013 Federal Task Program “Scientific 15. T. Kondo, D. Tagaki, H. Tsujita, et al., Angew. Chem.,
Research and Academic Personnel for Innovative
Russia,” state contract no. 14.740.11.0486.
Int. Ed. Engl. 46, 5958 (2007).
1
6. G. Myagmarsuren, V. S. Tkach, D. S. Suslov, and
F. K. Shmidt, React. Kinet. Catal., Lett. 85, 197
(2005).
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PETROLEUM CHEMISTRY Vol. 51
No. 3
2011