Palladium(II)-catalyzed amination of isoprene with aniline

Article abstract of DOI:10.1007/s11176-005-0344-5

The reaction of isoprene with aniline, catalyzed by the Pd(acac) ₂-(RO)₃P-CF₃CO₂H system, 1 : 4 : 4 [R = Me, Et; acac = (CH₃CO)₂CH], in MeCN provides N-(3-methylbut-2-en-1-yl)aniline with a high selectivity (up to 84%) and a nearly quantitative yield (75%). At 1 : 4 : 20 and 1 : 4 : 40 molar component ratios in the catalytic system, up to 28-31% of N,N-(2,3-dimethylprop-2-en-1-yl)aniline is formed. Telomeric reaction products appear at 1 : 2 : 4 and 1 : 1 : 10 ratios.

Full text of DOI:10.1007/s11176-005-0344-5

Russian Journal of General Chemistry, Vol. 75, No. 6, 2005, pp. 910 914. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005,
pp. 963 968.
Original Russian Text Copyright
2005 by Petrushkina, Mysova, Orlinkov.
Palladium(II)-catalyzed Amination of Isoprene with Aniline
E. A. Petrushkina, N. E. Mysova, and A. V. Orlinkov
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
Received January 22, 2004
Abstract The reaction of isoprene with aniline, catalyzed by the Pd(acac)2 (RO)3P CF3CO2H system,
1: 4: 4 [R = Me, Et; acac = (CH3CO)2CH], in MeCN provides N-(3-methylbut-2-en-1-yl)aniline with a high
selectivity (up to 84%) and a nearly quantitative yield (75%). At 1:4:20 and 1:4:40 molar component ratios
in the catalytic system, up to 28 31% of N,N-(2,3-dimethylprop-2-en-1-yl)aniline is formed. Telomeric
reaction products appear at 1: 2: 4 and 1: 1: 10 ratios.
Allylamines are used in organic chemistry as basic
building blocks for complex organic molecules. The
can serve as starting materials in the synthesis of such
compounds as - and -amino acids, alkaloids, or
carbohydrates. One of the most perspective and con-
venient synthetic approaches to allylamines involves
direct amination of 1,3-dienes, catalyzed by com-
plexes of transition metals of the Ni triad. Depending
of the nature of the catalytic system, hydroamination
of 1,3-dienes is accompanied by their telomerization.
Palladium(II) and palladium(0) complexes frequently
give 2:1 telomerization products. As shown in [1 7],
the [Pd]:[P] molar ratio of 1:4 in the Pd(acac)2
(BuO)3P catalytic system is optimal for telomerization
of isoprene (I) with various amines in MeCN. With
mono- and dialkylamines and with isoprene as 1,3-di-
ene, acid additives in a catalytic system containing
palladium(II) diacetylacetonate (acac) complexes and
P(III) ligands allow one to control the regioselectivity
of telomer formation [1 3]. With strong acids, such as
BF3 OEt2, N-(3,6-dimethylocta-2,7-dien-1-yl)dialkyl-
amines are formed highly selectively [1]. Evidence
for the suggestion that in the presence of noncoordinat-
ing acids cationic Pd(II) complexes are formed, that
are responsible for the formation of telomers like II,
was obtained in [4, 5]; therewith, compounds II
formed with a selectivity of up to 96%. In the
presence of coordinating acids, by varying the com-
position of catalytic system A [PdX2 R3P HX, where
HX is acid] one can prepare telomers with a natural
2,6-dimethyloctane skeleton, specifically, -geranyl-
dialkylamines, with a selectivity of up to 40% [2].
The reactions of isoprene with aromatic amines, un-
like those with aliphatic amines, in the presence of
catalytic system A provide isoprene hydroamination
products (adducts) [6 8]. Components for catalytic
system A were found, that allowed N-(3-methylbut-2-
en-1-yl)aniline (III) and methylaniline (IV) to be
prepared with a selectivity of 78 95% [6 8], and,
therewith, the yield of telomers was no higher than
5 6%. We studied the reaction of isoprene with
aniline, catalyzed by system B [Pd(acac)2 (RO)3
CF3CO2H, where R = Me, Et] in MeCN, aiming at
preparing synthetically useful isomeric adducts
other than amine III, such as N-(1,2-dimethylprop-2-
en-1-yl)aniline (V), N-(1,1-dimethylprop-2-en-1-yl)-
aniline (VI), and N-(2-methylbut-2-en-1-yl)aniline
(VII), as well as exploring the possibility of formation
of telomers VIII XI (the reactions were performed in
sealed glass ampules 25 ml in volume). The resulting
data are presented in the table.
As shown in [7], the reaction of isoprene with
PhNH2 in the presence of the Pd(acac)2 (BuO)3P
CF3CO2H catalytic system (component molar ratio
1:4:10) gives adduct III with a selectivity of 78%.
We found that with less bulky phosphites as com-
ponents of the catalytic system, adduct III is formed
with a higher selectivity (86%), and the total yield of
adducts is 25% (see table). As seen from data in the
table and in [7], at the 1:4:10 component molar ratio
in system B, the major reaction product is adduct III
with any phosphite. Longer heating of the reaction
mixture (87 instead of 32 h) renders the formation of
adduct III less selective. At the 1:4:4 molar com-
ponent ratio in system B, adduct III is formed with a
high selectivity (up to 84%; yield 75%). Increased
fraction of acid in system B (1:4:20 and 1:4:40)
adversely affects the selectivity of adduct III forma-
tion; therewith, more adducts V VII are formed, and
the selectivity of adduct VII formation increases to
28 31%. With less phosphorus ligand, the selectivity
of adduct formation changes and the spectrum of re-
action products widens to include telomers. Telo-
mers appeared in the reaction mixture in the presence
of catalytic system B with the 1:2:4 component ratio
1070-3632/05/7506-0910 2005 Pleiades Publishing, Inc.

PALLADIUM(II)-CATALYZED AMINATION OF ISOPRENE WITH ANILINE
911
Composition of products of the reaction of isoprene with PhNH2 in the presence of the Pd(acac)2 (RO)3 CF3CO2H
catalytic system in MeCN [Pd(acac)2 0.5 mol%, isoprene: PhNH2 = 2: 1, 25 ml of MeCN per 0.2 mol of PhNH2, 100 C]
Yield, %
Composition of adducts, %
Composition of telomers, %
R
, h
III
V
VI VII
VIII IX
X
XI
1: 4: 4
Me
Et
Me
Et
Et
Me
Et
32
32
32 13
32
87
32 30
32
32 16
0.9
75
62
25
59
34
40
33
30
5
84
89
86
9
5
4
1
2
5
4
14 85
91
9
1: 4: 10
10 14 86
13 28 73
17 40 60
17 34 66
31 47 53
28 45 55
42 54 46
19 41 59
22 42 58
26 40 60
43 71 29
26 57 43
37 68 32
35 61 39
57 46 53
42 21 68
25 43 57
21 40 60
6
2
65 15
50 23 10
61 17
44 16
30 17 25
40 12
55 22
53 20
8
1: 4: 20
5
9
2
1: 4: 40
1: 2: 4
Et
Mea 168
2
24
25
31
6
4
5
9
6
9
9
10
7
20 42
23 40
25 47
18
17
17
Eta
Et
168 14(3b)
8
32 13(0.1b)
36
85
5
26
55
40
66
4
4
1: 2: 10
1: 1: 1
Et
Me
Et
Et
Me
Et
Me
Et
Et
32
34
31
82
37
85
37
Traces 51 14
5
46
16
14
13
23 28
34 31
22 31 10
37 26
18 15 10
14 19 11
56 18
7
8
8
26 49
22 48
27 47
26 45
5
3
2
3
13
19
16
15
1: 1: 4
6
7
7
2
11
1: 1: 10
32 24(0.01b)
32
30
28
15
1
13
25 43
8
11
1: 0: 10
50 20 10
a
b
+
The reaction was performed at 20 C.
Hydrogenated isoprene dimers (M 138).
PhNH2, [Pd]
+
+
NHPh
NHPh
NHPh
I
III
V
VI
NHPh
7
1
8
6
4
2
+
+
NHPh
3
NHPh
5
6a
2a
VII
VIII
IX
3a
7
8
6
4
+
+
+ Unidentified telomers
1
3
NHPh
5
2
6a
X
XI
at 20 C; therewith, the adduct fraction contained up
to 38% of compounds V + VII; heating of the reac-
tion mixture at 100 C increases the yield of adducts
and telomers with no essential effect on selectivity. It
should be noted that we are the first to obtain telo-
metic products by the reaction of isoprene with aniline
in the presence of a catalytic system like A, and
telomers IX and X are the most abundant. In the latter
fraction, unidentified components with M+ 229 were
found, that, as judged from the GC retention time, are
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 6 2005

912
PETRUSHKINA et al.
likely to be telomers with the main hydrocarbon chain
no shorter than C8. Excess acid (1:2:10 component
molar ratio in catalytic system B) only slightly affects
the selectivity of adduct formation and fully sup-
presses telomer formation.
in the presence of Pd(acac)2 R3P BF3 OEt2. The
higher the [P]:[Pd] molar ratio at an invariable acid
fraction {[Pd]:[BF3 OEt2] = 1:10}, the higher the
yield of adducts, and at [P]:[Pd] = 1:1 under the
same conditions, telomers are already formed with a
selectivity of 95%. As the quantity of acid is de-
creased at [P]:[Pd]:[BF3 OEt3] = 1:1:1(2), the
conversion of isoprene is decreased to 2%, whereas in
our case the same catalytic system in the reaction with
PhNH2 provides a quantitative yield of adducts. Ap-
parently, such a substantial difference in the reactions
of isoprene with Et2NH or PhNH2 in the presence of
similar catalytic systems is associated with different
coordinating powers of the amines and gives indirect
evidence showing that amines take part not only in the
stage involving attack of palladium-coordinated iso-
prene, but also in early stages of the catalytic cycle,
responsible for the mode and selectivity of coordina-
tion of the 1,3-diene. The first evidence for the in-
volvement of -allyl palladium complexes containing
an amide ligand in telomer formation in the reaction
of isoprene with Et2NH has been obtained in [13].
Amide palladium complex XIV formed by the reac-
tion of bis( -allyl)palladium with Et2NH can catalyze
telomerization of butadiene with Et2NH in the pre-
sence of Ph3P. In the absence of butadiene, complex
XIV reacts nether with Et2NH nor with Ph3P.
With catalytic system B with [Pd]:[P] = 1:1, too,
telomers are formed, isomers IX and X being the most
abundant, and the selectivity of adduct V formation is
up to 31%; excess acid (1:1:10 component molar
ratio in system B) does not exclude telomer formation.
Among adducts, adducts V and VII are formed much
more selectively. From the preparative viewpoint,
adduct V that has an asymmetric center is the most
interesting, and, moreover, it has the lowest boiling
point among the adducts formed and is easily isolable
from the reaction mixture by distillation. Isomer VI is
always the minor component, apparently, because of
the steric hindrances associated with the formation of
a quaternary carbon center. If the catalytic system
comprises no phosphorus ligand, i.e. when the reac-
tion is performed in the presence of Pd(acac)2
CF3CO2H, the conversion of isoprene is low, but
adduct III still remains the major product, and telo-
mers are not formed at all.
Previously the effect of protic and aprotic acids on
the regioselectivity of palladium-catalyzed reactions
of isoprene with amines was discussed in [1, 4].
According to [9, 10], cationic nickel complexes XII
with a 3-1,2-dimethylallyl ligand is 5 times thermo-
dynamically more favorable than cationic nickel com-
plexes XIII with a 3-1,1- dimethylallyl ligand. On
this basis, it was suggested [1, 4] that it is the
formation of cationic -allyl palladium complexes that
is responsible for the alteration of regioselectivity in
the presence of acids.
NEt2
(Pd
Pd)
NEt2
XIV
Later on it was found that the Pd(acac)2 BF3 OEt2
catalytic system can catalyze the telomerization of
1,3-butadiene with aliphatic secondary amines, result-
ing in 78 99% yields of telomers; with the same
catalytic system in the absence of amines, no other
products than polymers are formed [14]. The IR and
UV spectra of products of the reaction in the Pd(acac)2
BF3 OEt2 C4H6 system were studied, and the struc-
ture the palladium hydride complex [(C4H6)nPdH]BF4
that is catalytically active in telomerization was
proposed on this basis. It was believed that nucleo-
phile is involved exclusively in the final stage of the
catalytic cycle, namely, in the stage of insertion of
secondary amine into the bond of 1,3-butadiene with
the palladium metal center [14]. However, comparison
of the results of isoprene telomerization with primary
[3] and secondary aliphatic amines [1, 2, 12, 15] led
to a suggestion that the coordination complexes of
Pd(acac)2 with amine and phosphorus ligands, like
complexes XV XVII, are involved in formation of
catalytically active centers [3].
+
+
M Ln
M Ln
XII
XIII
V
VII
III VI
Comparison of our data on reaction of diene I with
PhNH2 with data in [1, 11, 12] on telomerization of
isoprene with Et2NH allows us to reveal a consider-
able effect the nature of the amine exerts on the reac-
tion result. Thus, for example, Keim et al. [1] reported
on a direct relation between the yield of adducts and
the quantity of phosphorus ligand in the catalytic
system in the telomerization of isoprene with Et2NH
Later on this suggestion was confirmed by Cher-
1
nyshev et al. [16] who studied the H and IR spectra
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PALLADIUM(II)-CATALYZED AMINATION OF ISOPRENE WITH ANILINE
913
+
+
NHEt2
Pd
NHEt2
Pd
NHEt2
Pd
O
O
O
O
O
O
BF4
acac
(
(
(
O
HNEt2
HNEt2
O
XV
XVI
XVII
of products of the reaction of Pd(acac)2 BF3 OEt3
with Et2NH, as well as the telomerization of 1,3-
butadiene with secondary amines in the presence of
the Pd(acac)2 BF3 OEt2 catalytic system. Previously
complexes XV and XVI were described in [17, 18].
Chernyshev et al. [19] proposed a scheme for the
formation of complex XVII that as actively catalyzed
telomerization of dienes with secondary amines as
Pd(acac)2 BF3 OEt2, which made the referees to
conclude that complex XVII is a precursor of the
active complex [Lm Pd H]+BF4 formed in situ. It
was also mentioned in [19] that the formation of the
latter complex is complete before telomerization
commences, and its concentration does not vary
throughout the reaction. In the present work we also
showed that diene I can react with PhNH2 in the
absence of phosphorus ligand, i.e. in the presence of
the Pd(acac)2 CF3CO2H catalytic system. Moreover,
we obtained indirect evidence for the involvement of
palladium hydride complexes in the catalytic cycle.
GC-MS analysis of products of the reaction in the
presence of system B with 1:2:4 and 1:1:10 com-
ponents molar ratios revealed hydrogenated isoprene
dimers with M+ 138, along with isoprene dimers with
M+ 136, adducts III and V VII, and telomers
VIII XI. The presence of hydrogenated isomer di-
mers can be explained by the fact that cationic pal-
ladium(II) hydride complexes can catalyze hydrogen
transfer from alcohols and amines to the double bonds
in unsaturated hydrocarbons (see, for example, [20]).
In the presence of acids, the possibility of formation
of cationic -allyl complexes depends on a number of
conditions, acid concentration inclusive. However,
analysis of the isomeric composition of the adducts
and telomers shows that in the presence of a larger
quantity of acid (for example, at the 1:4:20 molar
component ratio insystem B), when formation of
cationic complexes is the most probable, the yields of
adducts formed from cationic complex XII do not
increase (see table). Apparently, in the reaction of
isoprene with PhNH2 in the presence of catalytic
system B, unlike the reaction with aliphatic amines,
intermediate complexes XII and XIII are unlikely to
be formed.
EXPERIMENTAL
Gas chromatography mass spectrometry was per-
formed on an Analytical VG-7070E instrument at
70 eV and an ion source temperature of 150 C. The
1H NMR spectra were on Bruker WR-200SY and
Bruker AMX-400 instruments (CDCl3, internal re-
ference TMS).
Gas chromatography was performed on a Finnigan-
9001 chromatograph with a capillary column (l 30 m,
stationary phase DB 5.625, temperature programming
1
from 50 to 200 C at a rate of 8 deg min and from
1
200 to 310 C at a rate of 12 deg min ); the reference
was C21H44. The isomeric composition of VIII XI
was assessed on the basis of retention times [7].
Monomers of 99% purity were used in the work.
Isoprene and aniline were distilled over KOH before
use.
Reaction of isoprene with aniline in MeCN. A
glass ampule was charged under argon with 1 mmol
of Pd(acac)2, 0, 1, 2, or 4 mmol of (EtO)3P or 1, 2,
or 4 mmol of (MeO)3P, 25 ml of MeCN, 400 mmol
of isoprene, 200 mmol of aniline, and 1, 2, 4, 10, or
20 mmol of CF3CO2H. The ampule was sealed and
left to stand at 20 C (see table). Low-boiling reaction
products were removed in a vacuum, and the residue
was distilled collecting a fraction boiling at 40 170 C
(2 mm Hg), that was analyzed by GC and GC MS.
1
The H NMR spectra of isomers III, V, VII, VIII,
and XI were published in [7].
1
Adduct VI. H NMR spectrum, , ppm: 1.16 s
and 1.21 s (6H, 2CH3), 4.69 5.00 m (2H, CH2=),
5.17 5.43 m (1H, CH=), 6.61 m (3H, Ph), 7.14 m (2H,
Ph). Mass spectrum, m/z (I, %): 161 (M+ 67), 146
(92), 120 (96), 118 (16), 93 (40), 77 (25).
1
Telomer IX. H NMR spectrum, , ppm: 0.97 d
(3H, C6aH3, J 6.54 Hz), 1.35 1.49 m (4H, C4H2,
C5H2), 2.01 2.14 m (3H, C6H), 1.66 s (3H, C2aH3),
3.89 t (2H, C3H, J 6.03 Hz), 4.84 5.92 m (1H, C7H,
Jtrans 18.06, Jcis 9.66, Jgem 1.5 Hz), 4.92 s and 4.95 s
(2H, C1H2), 5.62 5.72 m (Jtrans 18.06, Jcis 9.66, J7 6
7.48 Hz), 6.58 6.77 m (3H, Ph), 7.13 7.23 m (2H,
Ph). Mass spectrum, m/z (I, %): 229 (M+ 12), 172 (8),
146 (10), 93 (100), 81 (15), 77 (14).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 6 2005

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PETRUSHKINA et al.
1
Telomer X. H NMR spectrum, , ppm: 1.00 d
(3H, C6aH3, J 6.54 Hz), 1.26 1.49 m (2H, C5H2),
1.70 s (3H, C3aH3), 1.93 2.14 m (3H, C6H, C4H2),
3.71 d (2H, C1H2, J 6.56 Hz), 4.98 5.01 m (1H, C7H,
Jtrans 17.75, Jcis 12.14, Jgem 0.9 Hz), 5.33 t (1H, C2H,
J 6.56 Hz), 5.65 5.75 m (Jtrans 17.75, Jcis 12.14, J7 6
8.25 Hz), 6.58 6.77 m (3H, Ph), 7.13 7.23 m (2H,
Ph). Mass spectrum, m/z (I, %): 229 (M+ 28), 172 (5),
146 (16), 93 (100), 81 (22), 77 (12).
8. Lober, O., Kawatsura, M., and Hartwig, J.F., J. Am.
Chem. Soc., 2001, vol. 123, no. 18, p. 4366.
9. Tolman, S.A., J. Am. Chem. Soc., 1970, vol. 92,
no. 23, p. 6785.
10. Aspects of Homogeneous Catalysis, Ugo, R., Ed.,
Dordrecht: Reidel, 1981, vol. 4, p. 99.
11. Keim, W. and Roper, M., J. Org. Chem., 1981,
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12. Keim, W., Kurtz, K.-R., and Roper, M., J. Mol. Catal.,
ACKNOWLEDGMENTS
1983, vol. 20, no. 2, p. 129.
13. Lazutkin, A.M., Mastikhin, V.M., and Lazutkina, A.I.,
The work was financially supported by the Presi-
dium of the Russian Academy of Sciences (State
Contract no. 10002-251/P-09/118-125/100603-587
for research work GK no. 01-03).
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skii, G.V., Chernyshev, M.L., and Burlakova, O.I.,
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