Efficient catalysts for telomerization of butadiene with amines

Article abstract of DOI:10.1016/j.tetlet.2007.10.076

In situ-generated N-heterocyclic carbene (NHC) palladium catalysts and isolated NHC-palladium complexes have been tested for the telomerization reaction of 1,3-butadiene with primary and secondary amines. Superior catalyst activity (TON up to 400.000) and

Full text of DOI:10.1016/j.tetlet.2007.10.076

Available online at www.sciencedirect.com
Tetrahedron Letters 48 (2007) 9203–9207
Efficient catalysts for telomerization of butadiene with amines
Anne Grotevendt,a Maribel Bartolome,b David J. Nielsen,c Anke Spannenberg,a
Ralf Jackstell,a Kingsley J. Cavell,c Luis A. Orob and Matthias Bellera,*
aLeibniz-Institut fu¨r Katalyse e.V. an der Universita¨t Rostock Albert-Einstein-Strasse 29 A,18059 Rostock, Germany
bDepartamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Zaragoza,
C/PEDRO CERBUNA s/n, 50009 Zaragoza, Spain
cSchool of Chemistry, Cardiff University, Cardiff CF103AT, Wales, UK
Received 24 July 2007; revised 8 October 2007; accepted 16 October 2007
Available online 22 October 2007
Abstract—In situ-generated N-heterocyclic carbene (NHC) palladium catalysts and isolated NHC-palladium complexes have been
tested for the telomerization reaction of 1,3-butadiene with primary and secondary amines. Superior catalyst activity (TON up to
400.000) and selectivity are obtained. Applying optimized conditions a variety of octa-2,7-dienylamines were prepared in high yield
and excellent selectivity.
ꢀ 2007 Elsevier Ltd. All rights reserved.
The palladium-catalyzed telomerization of 1,3-dienes
with nucleophiles which was established independently
by Smutny and Takahashi in 1967 is an ideal example
for an environmentally benign synthetic method. Easily
available starting materials are converted in the presence
of a catalyst in a 100% atom efficient manner to give
functionalized octa-2,7-dienes.1–3 The resulting products
have been used as intermediates in the total synthesis of
several natural products,4 as well as precursors for plas-
ticizer alcohols,5 industrial monomers, solvents, corro-
sion inhibitors, and non-volatile herbicides.6
Unfortunately, to date all known telomerizations of
amines require high catalyst loadings (>0.1 mol %),
which makes these reactions less attractive for the prep-
aration of bulk and fine chemicals. Here, we describe
telomerization reactions of 1,3-butadiene with different
primary and secondary amines with unexpectedly high
catalyst activity. To the best of our knowledge the high-
est catalyst turnover number ever reported for this reac-
tion is achieved.
Initially, molecular-defined (carbene)palladium(0) com-
plexes were tested for the model reaction of piperidine
with 1,3-butadiene (Scheme 1, Table 1).13 In exploratory
experiments we discovered that tetrahydrofuran and
toluene are not suitable solvents for these reactions.
Surprisingly, in the presence of methanol, a potentially
competing nucleophile, as solvent the reaction is faster
and proceeded selectively to give the N- and not the
O-telomer! Therefore, in contrast to previous work high
catalyst substrate ratios (1:100,000–200,000) were used
in our studies.
In 2002, we described for the first time the use of palla-
dium carbene complexes for telomerization reactions.
Since then, we have demonstrated the superior catalyst
productivity of these complexes for the telomerization
of butadiene7 and isoprene8 with alcohols. Recently,
we became also interested in similar reactions of amines.
Many efforts have been made to investigate the telomer-
ization of 1,3-butadiene with ammonia,9 primary,10 and
secondary amines.11 Most notably in 2003 Nolan and
co-workers12 applied cationic N-heterocyclic carbene
(NHC) palladium complexes to convert 1,3-butadiene
and different amines to the corresponding telomers.
All catalysts applied are shown in Figure 1. Even at very
low catalyst concentration conversions up to 91% and
excellent selectivity (99%) are observed with 1,3-di-mesi-
tylimidazolin-2-ylidenepalladiumtetramethyldivinyldi-
siloxane 1 and the saturated 1,3-dimesityl-4,5-dihydro-
imidazolin-2-ylidenepalladiumtetramethyldivinyldisilox-
ane 2. To our delight only the linear telomerization
product is formed.
Keywords: Amines; 1,3-Butadiene; Carbene; Homogeneous catalysis;
Palladium.
*
Corresponding author. Tel.: +49 381 1281 113; fax: +49 381 1281
5000; e-mail: matthias.beller@catalysis.de
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.10.076

9204
A. Grotevendt et al. / Tetrahedron Letters 48 (2007) 9203–9207
NHC-Pd catalyst
N
2
N
MeOH
H
Scheme 1. Telomerization reaction of 1,3-butadiene with piperidine.
Table 1. Telomerization of 1,3-butadiene with piperidine in the
presence of defined palladium catalysts
Entry Catalyst
[Pd]
(mol %) (%)
Yielda Selectivityb TONc
(%)
1
2
3*
4
5
6
7
8*
1
1
1
2
3
4
0.001
0.0005
0.0005
0.001
0.001
0.001
91
42
98
91
69
42
47
<1
99
99
99
99
99
99
99
—
182,000
168,000
392,000
182,000
138,000
84,000
94,000
—
4 + NaBF4 0.001
—
—
General conditions: 5.5 g butadiene, 10 mL MeOH, 5.6 mL piperidine
(1.12 equiv), T = 90 ꢁC, t = 20 h, pN2 = 30 bar, * +0.005 mol 5.
a Yield of octa-2,7-dienylpiperidine.
b Selectivity toward octa-2,7-dienylpiperidine.
c Catalyst turnover numbers with respect to 1,3-butadiene.
Figure 2. 1,3-Dimesityl-4,5-dihydroimidazol-2-ylidene Pd complex 2.
At 0.0005 mol % catalyst loading the effect of extra
added ligand was studied (Table 1, entries 2 and 3).
Increasing the ligand concentration resulted in a higher
yield, which clearly shows that the added ligand coun-
teracts degradation during the reaction. For 1,3-dimesit-
yl-4,5-dimethylimidazolin-2-ylidenepalladiumtetramethyl-
divinyldisiloxane 3, the bulkier methyl groups in the
backbone led to a reduced yield (Table 1, entry 5). By
addition of ligand without any palladium source no
conversion takes place (Table 1, entry 8).
100
80
60
40
T = 70 °C
20
0
T = 90 °C
T = 110 °C
Compared to the palladium dvds complexes 1–3 the
allylpalladium(II) complex 4 as well as the cationic
derivative showed a lower catalyst activity (Table 1,
entries 6 and 7).
0
5
10
15
20
25
t /h
General conditions: catalyst 1,0.0005mol% Pd,
11g butadiene, 20ml MeOH, 11.2ml piperidine,
10ml isooctane, 40bar N2.
Notably, we were also able to characterize the highly
active catalyst 2 for the first time by X-ray crystallogra-
phy (Fig. 2). The palladium atom adopts a distorted
trigonal-planar coordination geometry (CE1–Pd1–CE2
130.9, C1–Pd1–CE1 114.8, C1–Pd1–CE2 114.2; CE1,
CE2–mid-points of the C@C bonds of the diolefin).
Figure 3. Catalyst activity at different temperatures.
As shown in Figure 3, 1 shows activity at 70 ꢁC; how-
ever, at 110 ꢁC the reaction is finished in 7 h with a yield
of 95% octa-2,7-dienylpiperidine. Being able to take
samples during the reaction these experiments were
performed in a secured 160 mL stainless steel Parr
˚
The bond length of Pd1–C1 is 2.091(3) A and is in the
range found for other complexes of this type.7c
Cl
Si
O
Si
Si
O
Si
Si
O
Si
N
N
N
N
N
N
N
N
Pd
Pd
Pd
Pd
4
1
3
2
Figure 1. Tested catalysts for telomerization of 1,3-butadiene with piperidine.

A. Grotevendt et al. / Tetrahedron Letters 48 (2007) 9203–9207
9205
Table 2. Telomerization of 1,3-butadiene with piperidine in the
presence of in situ-generated Pd catalysts
autoclave with further changes in conditions. For this
reason the yield at 90 ꢁC (Table 1, entry 2) differs from
the result shown in Figure 3.
Entry
Ligand
Yield (%)
TONa
1
2
3
4
5
6
7
8
9
5
80
>99
54
61
52
49
56
84
10
3
320,000
400,000
216,000
244,000
208,000
196,000
224,000
336,000
40,000
Next, we compared the behavior of 1 with the corres-
ponding in situ-generated Pd catalyst. Figure 4 clearly
demonstrates the advantage of the in situ-system. Full
conversion and quantitative yield of the desired product
are obtained after 8 h at 90 ꢁC. The lower yield in the
presence of the isolated complex is explained by degra-
dation of the ligand. Due to the improved catalyst
productivity we compared different ligands for the
in situ-generated catalysts in more detail. Table 2 shows
selected results.
6
7
PPh3
PCy3
8
9
10
11
12
10
12,000
General conditions: 5.5 g 1,3-butadiene, 10 mL MeOH, 5.6 mL
piperidine (1.12 equiv), T = 90 ꢁC, t = 20 h, pN2 = 30 bar, Pd/
Ligand = 1/4, [Pd] = 0.0005 mol %, (Pd(acac)2).
a Catalyst turnover numbers based on 1,3-butadiene.
The palladium source and palladium-to-ligand ratio
were chosen in agreement with our previous studies con-
cerning the telomerization of alcohols.7 As shown in
Figure 5 imidazolium salts with different anion or imi-
dazolium cations as well as imidazolin-2-ylidene:CO2
adducts were tested.
the mesylate and chloride (Table 2, entries 1 and 8)
are comparable, a dramatic reduction in activity is seen
for bromide and iodide anions (Table 2, entries 9 and
10). On the one hand, the formation of the ylidene
species out of the 1,3-dimesitylimidazolium bromide
and iodide may be hindered; on the other hand, the
more nucleophilic anions may bind to the metal center
In agreement with the defined complexes 1,3-dimesityl-
imidazolium salts gave better results compared to the
1,3-dimesityl-4,5-dimethylimidazolium and the 1,3-
bis(2,6-diisopropylphenyl)imidazolium salts. Surpris-
ingly the 1,3-dimesitylimidazolin-2-ylidene:CO2 adduct
6 is the best catalyst (Table 2, entry 2). The nature of
the anion can also have a significant influence. While
Table 3. Telomerization of 1,3-butadiene with secondary amines
Entry Catalyst
Amine
Yielda Selectivityb
(%)
(%)
1
2
3
4
5
6
7
8
9
1
Pyrrolidine
96
90
95
92
81
78
85
89
99
99
99
99
99
99
99
99
99
99
99
99
100
80
5/Pd(acac)2
1
Morpholine
Dibenzylamine
Diethylamine
5/Pd(acac)2
1
60
5/Pd(acac)2
1
40
catalyst 1
5/Pd(acac)2
1
20
N-Methylaminoethanol 95
In-situ-system
10
11
12
5/Pd(acac)2
1
93
99
99
0
N-Phenylpiperazine
0
5
10
15
20
25
5/Pd(acac)2
t /h
General conditions: Pd(acac)2, 0.0005mol% Pd,
General conditions: 5.5 g butadiene, 10 mL MeOH, Pd = 0.005 mol %,
Pd(acac)2, 1.12 equiv amine, T = 90 ꢁC, t = 20 h, pN2 = 30 bar.
a Yield of octa-2,7-dienylamine.
b Selectivity toward linear octa-2,7-dienylamine.
11g butadiene, 20ml MeOH, 11.2ml piperidine, 10ml isooctane,
Pd/IMes:CO2 = 1/4, 40bar N2.
Figure 4. Comparison of the in situ versus preformed catalyst at 90 ꢁC.
N
N
N
N
N
N
N
N
N
N
N
N
CO2
Br
CO2
MeSO3
Cl
X
5
9
6
7
8
10 X = Cl
11 X = Br
12 X = I
Figure 5. Ligands tested for the in situ catalysts.

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A. Grotevendt et al. / Tetrahedron Letters 48 (2007) 9203–9207
Table 4. Telomerization of 1,3-butadiene with different primary amines in the presence of Pd carbene catalysts
Entry
Catalyst
amine
[Pd] (mol %)
mono-N-telomera (%)
Di-N-telomerb (%)
O-telomerc (%)
1
2
3
4*
5
6
7
8
1
Adamantylamine
tert-Butylamine
Cyclohexylamine
n-Hexylamine
0.005
0.05
0.005
0.05
0.005
0.05
0.005
0.05
22
63
17
40
9
70
17
55
<1
<1
1
12
<1
15
11
25
7
5/Pd(acac)2
1
37
79
0
<1
15
3
5/Pd(acac)2
2
6/Pd(acac)2
1
5/Pd(acac)2
4
General conditions: 5.5 g butadiene, 10 mL MeOH, * 10 ml MeCN, 1.12 equiv amine, Pd(acac)2, T = 90 ꢁC, t = 20 h, pN2 = 30 bar.
a Yield of octa-2,7-dienylamine.
b Yield of bis(octa-2,7-dienyl)amine.
c Yield of methoxyocta-2,7-diene.
N
H
NHC-Pd catalyst
N
NH2
MeOH
OMe
Scheme 2. Telomerization of tert-butylamine with 1,3-butadiene.
and thus produce poorly active catalysts. Notably, tri-
phenylphosphine and tricyclohexylphosphine led to
significant product yields in the range of 50–60 % (Table
2, entries 4 and 5). It should be mentioned that further
reduction of the palladium amount is conceivable by
using ligand 6 with a higher palladium/ligand ratio.
bis(octa-2,7-dienyl)amines, which are formed for the less
sterically hindered amines.
However, increasing the catalyst amount to 0.05 mol %
led to sufficient yields. Adamantylamine, for example,
gave 63% of the corresponding octadienylamine (Table
3, entry 1). Similar yields were obtained for cyclohexyl
and n-hexylamine, while tert-butylamine gave a some-
what lower yield (Table 3, entries 4, 6, 8).
To determine the scope and limitation of the optimized
catalyst system various secondary amines were reacted
with 1,3-butadiene. As shown in Table 3 all educts are
converted in high yield and excellent selectivity. There
is no general trend whether the in situ or the preformed
complex is more reactive. For example, complex 1 gave
a 6% higher yield of the corresponding telomer with
pyrrolidine, whereas the telomer of diethylamine is
obtained in higher yield by the in situ catalyst. By testing
different aliphatic, alicyclic, and benzylic amines we
found that diethylamine and dibenzylamine are less
reactive than the further tested amines. Notably, the
reaction of N-methyl-2-aminoethanol gave selectively
the N-telomer.
In conclusion, we have developed the first time highly
efficient telomerizations of 1,3-butadiene and amines.
By applying defined monocarbenepalladium(0)dvds
complexes as well as in situ-generated catalysts unprec-
edented catalyst activity was obtained. The catalysts
also show remarkable selectivity for a number of amine
telomerization reactions. Further studies on amine telo-
merizations are currently underway in our laboratory.
Acknowledgments
Finally, we applied different primary amines in the telo-
merization reaction (Table 4). It is well known that the
reactivity of the telomerization of amines with 1,3-buta-
diene decreases in order secondary amine > primary
amine > ammonia. In addition, double telomerization
products can be formed in these reactions (Scheme 2).
This work was supported by the state of Mecklenburg-
Vorpommern, the Federal Ministery BMBF, and the
Deutsche Forschungsgemeinschaft (Leibniz-price). We
also wish to gratefully acknowledge support from the
EPSRC/Crystal Faraday Green Chemistry initiative.
Excellent analytic service was provided by Dr. C.
Fischer, Dr. W. Baumann and Dr. D. Michalik (all
LIKAT). We thank Dr. F. Nierlich and Dr. T. Masch-
meyer (Degussa AG; Oxeno Olefinchemie GmbH) for
general discussions.
At 0.005 mol % catalyst loading conversion of the pri-
mary amines to the corresponding telomers is low. Here,
the major byproducts are the methoxytelomer and the

A. Grotevendt et al. / Tetrahedron Letters 48 (2007) 9203–9207
9207
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liter of a stock solution containing 1.24 mg of palladium
acetylacetonate (5.1 · 10À7 mol) in 8 mL MeOH and 9 mL
of
a stock solution containing 1.42 mg of ligand6
(2.0 · 10À6 mol) in 18 mL MeOH were added in a dried
and sealed vessel under argon. Afterwards 5.6 mL piper-
idine (5.7 · 10À2 mol) was added. The mixture was trans-
ferred under argon into a secured 100 mL stainless steel
Parr autoclave. The autoclave was cooled with dry ice and
5.5 g (1.01 · 10À1 mol) of 1,3-butadiene was condensed in
a separate 75 mL pressure cylinder (mass control). The
defined amount of 1,3-butadiene was condensed into the
cooled autoclave and the vessel was heated to the desired
reaction temperature. After 20 h the autoclave was cooled
to room temperature and 5 mL of isooctane as internal
standard was added. In general, the yield of telomers was
determined by GC using HP 6869A gas chromatograph.
The main products were isolated from the reaction
mixture via distillation.
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