A direct amination of isoprene by aniline - Catalyzed by palladium complexes

Article abstract of DOI:10.1002/zaac.200570049

The reaction of isoprene with aniline, catalyzed by Pd (acac) ₂-(RO)₃P-CF₃COOH, (1:4:4) (R = Me, Et, acac = (CH₃CO)₂CH-) in MeCN solution, results in high (up to 89 mol.%) selectivity of N-(3-methyl-2-buten-1-yl) aniline. The presence of telomeric products in the reaction mixture is observed at a P/Pd ratio of 1:2 and 1:1. The use of (1,1,1-trifluoro, 4-perfluorocyclohexyl -2,4-butanedionato) palladium as the catalyst gives rise to 92 mol% mol.selectivity of telomers by the favored tail-to-head and head to head coupling.

Full text of DOI:10.1002/zaac.200570049

A Direct Amination of Isoprene by Aniline ؊ Catalyzed by Palladium
Complexes
E.A. Petrushkina*, N. E. Mysova, and A. V. Orlinkov
Moscow/Russia, A.N. Nesmeyanov Institute of Organo-Element Compounds, Russian Academy of Sciences
Received December 20th, 2004; accepted February 16th, 2005.
Abstract. The reaction of isoprene with aniline, catalyzed by Pd
(acac)2Ϫ(RO)3P-CF3COOH, (1:4:4) (R Me, Et, acac
(CH3CO)2CH-) in MeCN solution, results in high (up to 89 mol.%)
selectivity of NϪ(3-methyl-2-buten-1-yl) aniline. The presence of
telomeric products in the reaction mixture is observed at a P/Pd
ratio of 1:2 and 1:1. The use of (1,1,1-trifluoro, 4-perfluorocyclo-
hexyl -2,4-butanedionato) palladium as the catalyst gives rise to 92
mol% mol.selectivity of telomers by the favored tail-to-head and
head to head coupling.
ϭ
ϭ
Keywords: Palladium; Telomerization; Catalysts.
Introduction
telomers [4, 6]. The assumption that in the presence of
uncoordinating acids, the cationic palladium complexes re-
sponsible for formation of telomers with a head-to-head
skeleton are formed, was confirmed by the use of well-
known cationic palladium complexes as catalysts [7]. In the
presence of coordinating acids, the change in composition
and the ratio of catalytic system, PdX2 -R3P-HX (HX Ϫ
the acid), allows for the formation of telomers with a natu-
ral 2,6-dimethyloctane skeleton, including α-geranyldialkyl-
amines [6, 8]. IR and UV spectra of products of the reaction
with Pd(acac)2ϪBF3 · OEt2ϪC4H6 were investigated [9] and
the structure of cationic hydridpalladium complex,
[(C4H6)nPdH]BF4, is proposed. This complex was active in
the telomerization of 1,3 Ϫ butadiene with dialkylamines.
Selective formation of the head-to-head isomer was also
achieved [10] in the absence of an acid as the co-catalyst or
A one-pot for the synthesis of allylamines is the direct am-
ination of 1,3-dienes, catalyzed by transition metal com-
plexes of the nickel triad (Schema 1). These reactions obvi-
ously have a lack, due to their low selectivity. Therefore,
revealing the true intermediate metallocomplexes, respon-
sible for formation of each product, is a major task for the
decision of a selectivity problem. Untill now, no mechanism
has explained all the features of this reaction. The C10-Pd
complexes, prepared by the reaction of isoprene, are formed
as a mixture of two isomers [Pd (PR3) (η1, η3-Me2C8 H10)],
having the methyl groups in the 2,6- or 2,7-position [1]. In
other words, from the four possible directions of addition
of the two isoprene molecules, only tail-to-tail and tail-to-
head coupling products are observed. In the case of the
palladium system, no evidence was found for the formation
of the head to head isomer, as in the case of nickel. The
stoichiometric reactions of the complex [Pd (PR3) η1, η3-
C8H12)] with acidic nucleophiles, such as alcohols, acetic
acid, and with a variety of active methylene compounds
have been described. Reactions of this kind are impossible
in the case of secondary amines [2]. Notwithstanding iso-
prene reacts with dialkylamines in MeCN or MeOH solu-
tion in the presence of a catalytic system consisting of
Pd(acac)2 or Pd(OAc)2 and trialkylphosphite or phosphines
as a phosphoric ligand; this gives rise to the formation of
telomers at all four possible coupling positions of the iso-
prene units [3Ϫ6]. The addition of an acid as a co-catalyst,
even one as weak as CO2, gave rise to a substantial increase
in activity of the catalyst. Besides using acids with various
pKa, it is possible to control the distribution of isomeric
* Dr.Elena A. Petrushkina
A.N. Nesmeyanov Institute of Organo-Element Compounds
Russian Academy of Sciences
Vavilov Str. 28
119991 Moscow / Russia
fax.: 7(095)135-5085
Fig. 1 The effect of the phosphorus/palladium ratio on the product
distribution in the palladium catalyzed reaction of isoprene and
aniline. Reaction conditions: 0.375 mmol Pd(acac)2, 0 -1.5 mmol
(RO)3P; 1.5 or 3.75 mmol TFA; 9 ml CH3CN; 150 mmol isoprene;
75 mmol aniline; 100 °C; 32 h.
e-mail: petrushkina@rambler.ru
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DOI: 10.1002/zaac.200570049
Z. Anorg. Allg. Chem. 2005, 631, 2232Ϫ2235

A Direct Amination of Isoprene by Aniline
Scheme 1
a cationic complex as a catalyst. The reaction of isoprene
with aromatic amines in the presence of the catalysts,
PdX2 -R3P, results in only tail-to-head and tail-to-tail telo-
mers [11, 12]. The attempt to prepare head-to-head and
head-to-tail telomers by this method were very successful
in the case of mono- and dialkylamines; that is, by the use
of catalytic system, PdX2 -R3P-HX (HX Ϫ acid); it failed
in the case of anilines. It was found that the formation,
mainly, of hydroamination products (adducts) [12, 13] and
the formation of telomers did not exceed 5-6 %.
Results and Discussion
The possibility of managing the ratio of l:l-adducts to 2:l-
telomers for the reaction of isoprene and Et2NH has been
shown earlier [4]. A change in catalyst composition and re-
action conditions proved successful. Therefore, we studied
influence the catalyst composition of Pd(acac)2Ϫ(RO)3P -
TFA (TFA Ϫ trifluoroacetic acid) on distribution of
products of isoprene (I) reaction with aniline (II) in MeCN
solution (Scheme 1). The results are given in Table 1.
Table 1 Composition of products of isoprene reaction with PhNH2 in the presence of the catalyst, Pd(acac)2-(RO)3-CF3CO2H in MeCN
solution at 100 °C (0.375 mmol Pd(acac)2, 0 -1.5 mmol (RO)3P; 0.375Ϫ15 mmol TFA; 9 ml CH3CN; 150 mmol isoprene; 75 mmol aniline)
Catalyst
τ (h) Isoprene
conversion, %
selectivity,
mol %
Molar ratio of catalyst components R
dimers adducts telomers (III) (V) (VI)
(VII) (VIII) (IX) (X) (XI) unidentifiable
1:4:4
Me 32
Et 32
Me 32
76
62
39
83
85
70
49
67
1
99
100
66
91
92
57
96
49
9
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
82
65
23
Ϫ
69
23
26
37
11
84
89
57
59 14
47 21
36 10
42 15
15
3.5
16
38 14
51 14
11 10
17 24
23 16
8
5
3
1
2
Ϫ
7
9
3
8
12
0.5
1
4
9
2
7
1
5
5
4
7
12
15
10
31
14
4
5
15
26
8
29
22
31
21
Ϫ
33
8
8
43
4
1:4:10
Et
Et
32
87
1:4:20
Me 32
Et
Et
32
32
1:4:40
1:2:4
51
9
8
1
6
Mea) 168 59
7
6
2
18 35
15 26
Ϫ
Ϫ
1
22
18
3
Eta) 168 73
7(2b)
)
28
Et
Et
Et
Et
32
32
31
82
98
85
82
95
56
80
96
6(0,1b)) 71
6
11
1:2:10
1:1:1
Ϫ
Ϫ
Ϫ
12
9
100
31
77
62
54
84
7
2
2
3
1
18 34
3
1
9
5
4
6
1
5
7
12
12.5 0.5
1:1:4
Me 37
Et
Et
85
32
10
47 15
8
10 17
1
1
1:1:10
5
1
3
5
1:0:10
1:2:4c)
Et
Et
32
7
37
19
Ϫ
Ϫ
100
8
Ϫ
92
50 20 10
21
4
1
2
1
27
2
44
9
10
a) Reaction was carried out at 20 °C
b) Hydrogenized dimers of isoprene Mϩϭ138
c) Reaction carried out in the presence of complex (XV) instead Pd(acac)2
Z. Anorg. Allg. Chem. 2005, 631, 2232Ϫ2235
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E.A. Petrushkina, N. E. Mysova, A. V. Orlinkov
in 1978 [16]. Apparently, anilide-palladium complexes can
catalyze telomerization in the case of anilines too, as in the
absence of an acid co-catalyst, telomers of isoprene and ani-
line are formed with tail to tail skeleton. In the presence of
acid, apparently, the protonation of amide-palladium com-
plexes (XIV) can not give rise to bis- anilines complexes
which can catalyze the telomerization. The bis-aniline com-
plexes can be formed from more acidic bis(β-diketonato)
palladium, for example, such as Pd(hFac)2 [17]. As similar
bis-amine palladium complexes in the case of Et2NH have
proved to be active catalysts for telomerization and result
in the formation of similar bis-aniline complexes in situ, we
used (1,1,1-trifluoro, 4-perfluorocyclohexyl -2,4-butane-
dionato) palladium1) (XV) as a catalyst for telomerization
and found the expected result. The main products of reac-
tion were telomers with tail-to-head and head-to-head skel-
etons. Complex (XV) was prepared by method described
in [18].
Scheme 2
In the case of the diene (I) reaction with amine (II)
(Fig.1), we observed a picture completely distinct from that
of diene (I) reaction with Et2NH. At the TFA/Pd ratio of
10, a maximal selectivity to the formation of adducts was
observed with a at P/Pd ratio of 0 and 2; at the TFA/Pd
ratio of 4, maximal selectivity of adduct formation was
found at P/Pd ratios of 1 and 4; the selectivity was minimal
at P/Pd ϭ 2, in the case of both phosphites. The law of
symmetry was observed for the selectivity of telomers for-
mation; that is, the maximal selectivity of telomers was ob-
served at P/Pd ϭ 2 (65 %).
Experimental Part
Infrared spectra were recorded on a Carl Zeis “Specord M-82”
spectrometer using KBr pellets. 1H NMR spectra were recorded on
Bruker WP-200SY and Bruker AMX-400 instruments at 200 MHz
and 400 MHz, respectively (CDCl3, internal standard Ϫ TMS).
The GC-MS analysis carried out on the Analitical VG 7070E in-
strument at 70 eV and a temperature of 150 °C for the ionic source.
The MS analysis carried out on the Finnigan Polaris Q instrument
at 70 eV and a temperature of 150 °C for ionic source C. The GC
analyses were carried out on a Finnigan 9001 instrument using a
30 m DB 5.625 capillary quartz column (temperature program from
50 up to 200 °C, with a rate of 8°/ min and from 200 up to 310 °C
with a rate of 120°/min); C21H44 was the GC standard. Isomeric
composition of products (VIII-XI) was determined by comparison
of retention rate [12]. The monomers were used with 99 % purity.
Isoprene, solvents, ligands and TFA were purified and stored under
argon. Aniline was distilled over KOH pellets and kept under ar-
gon. Palladium acetylacetonate was prepared according to the lit-
erature. All reactions were carried out under argon.
We considered the possible use of other methods for the
enhancement of telomer selectivity. The study of diene (I)
telomerization with monoalkyl amines and the comparison
of these results with those of the isoprene telomerization
with dialkylamines allows us to make assumptions about
the participation of coordination complexes of Pd(acac)2
with phosphoric ligands and amines, like XII and XIII in
the formation of catalytic active centres [14] (Scheme 2).
This assumption was confirmed later by [15], which was
devoted to the study of IR and 1H NMR spectra of reaction
products of mixture Pd(acac)2ϪBF3 · OEt2 with Et2NH.
The structure of the cationic complex containing two amine
ligands was proposed. It catalyzed the telomerization of
butadiene and Et2NH with the same efficiency, as the cata-
lytic system Pd(acac)2-BF3 · OEt2. Thus, the complex
shown in Scheme 2, is the precursor of an active complex
containing amine ligands together with butadiene with the
formula [Lm-Pd-H]ϩ BF4, which is formed in situ. Cer-
tainly, we supposed that in the case of a reaction of isoprene
with aniline, the appropriate coordination palladium com-
plexes explain the unusual results for this reaction. How-
ever, as was shown earlier [16] bis-amine complexes are not
formed from Pd(acac)2 and anilines; in this case, amide
complexes like XIV are mainly formed (Scheme 3).
Reaction of isoprene with aniline in MeCN solution
Pd (acac)2 or complex (XV) (0.375 mmol), (EtO)3P or (MeO)3P
(0.375, 0.75, or 1.5 mmol), MeCN (9 ml), isoprene (150 mmol), ani-
line (75 mmol) and finally CF3CO2H (0.375, 0.75,1.5, 3.75, 7.5 or
1) We accord a thank to Prof. Dr. A.Z. Rubezhov and Dr. A.A.
Bezrukova for provision of a sample of complex (XV).
The complexes containing amide ligands are able to cata-
lyze butadiene telomerization with Et2NH as was shown
Scheme 3
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© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Z. Anorg. Allg. Chem. 2005, 631, 2232Ϫ2235

A Direct Amination of Isoprene by Aniline
composited bands as 462 and 484 cmϪ1 and are tentatively assigned to the cis
15 mmol) was placed in a glass tube in argon. The sealed tube was
heated to or maintained at 20 °C (see the Table). The products
distilated in vacuo with t.b. 40-170 °C (2 mmHg) was analyzed by
GC and GC-MS methods. 1H NMR spectra of isomers (III, V, VII,
VIII, XI) have been published in [12].
isomer. MS (70 eV, 150 °C): m/z ϭ 944 (Mϩ, 11 %), 663 (Mϩ Ϫ C6F11, 5 %),
References
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Adduct (VI): 1H NMR (CDCl3), δ ϭ: 1.16 and 1.21 (s, 6H, 2CH3); 4.69-5.00
(m, 2H, CH2ϭ); 5.17-5.43 (m 1H, CH ϭ); 6.61 (m 3H, Ph); 7.14 (m 2H,
Ph). MS (70 eV, 150 °C): m/z ϭ 161 (Mϩ, 67 %), 146 (Mϩ Ϫ CH3, 92 %),
120 (Mϩ Ϫ C3H5, 96 %), 118 (Mϩ Ϫ C3H7, 16 %), 93 (Mϩ Ϫ C5H8, 40 %),
77 (Mϩ Ϫ C6H5, 25 %).
Telomer (IX): 1H, NMR (CDCl3), δ ϭ 0.97 (d, 3H, 6ACH3, J ϭ 6.54 Hz);
1.35-1.49 (m, 4H, 4CH2, 5CH2); 2.01-2.14 (m, 3H, 6CH); 1.66 (s, 3H, 2ACH3);
3.89 (t, 2H, 3CH, J ϭ 6.03 Hz); 4.84-5.92 (m, 1H, 7CH, Jtrans ϭ 18.06, Jcis ϭ
9.66, Jgem ϭ 1.5 Hz); 4.92 and 4.95 (s and s, 2H, 1CH2); 5.62-5.72 (m, 2H,
8CH2, Jtrans ϭ 18.06, Jcis ϭ 9.66, J7-6 ϭ 7.48 Hz); 6.58-6.77 (m, 3H, C6H5);
7.13-7.23 (m, 2H, C6H5). ). MS (70 eV, 150 °C): m/z ϭ 229 (Mϩ 12 %), 172
(Mϩ Ϫ C4H9, 8 %), 146 (Mϩ Ϫ C6H11, 10 %), 93 (Mϩ Ϫ C10H16, 100 %).
Telomer (X): 1H, NMR (CDCl3), δ ϭ 1.00 (d, 3H, 6ACH3, J ϭ 6.54 Hz);
1.26-1.49 (m, 2H, 5CH2); 1.70 (s, 3H, 3ACH3); 1.93-2.14 (m, 3H, 6CH, 4CH2);
3.71 (d, 2H, 1CH2, J ϭ 6.56 Hz); 4.98-5.01 (m, 1H, 7CH, Jtrans ϭ 17.75,
Jcis ϭ 12.14, Jgem ϭ 0.9 Hz); 5.33 (t, 1H, 2CH, J ϭ 6.56 Hz); 5.65-5.75 (m,
2H, 8CH2, Jtrans ϭ 17.75, Jcis ϭ 12.14, J7-6 ϭ 8.25 Hz); 6.58-6.77 (m, 3H,
C6H5), 7.13-7.23 (m, 2H, C6H5). MS (70 eV, 150 °C): m/z ϭ 229 (Mϩ, 28 %),
172 (Mϩ Ϫ C4H9, 5 %), 146 (Mϩ Ϫ C6H11, 16 %), 93 (Mϩ Ϫ C10H16, 100 %).
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(1,1,1-trifluoro, 4-perfluorocyclohexyl -2,4-
butanedionato) palladium (XV)
Mercury(II) oxide (6.5 g, 30 mmol) was dissolved in a solution
(60 cm3) of perchloric acid (1 mol dmϪ3). The solution of mer-
cury(II) perchlorate thus prepared was added with stirring to a
solution (20 cm3) of Na2[PdCl4] (0.5 mol dmϪ3) kept at 0 °C. A
solution of the Na(CF3COCH2COC6F11) salt which was prepared
by dissolving of CF3COCH2COC6F11 (17 cm3, 50 mmol) in a solu-
tion (20 cm3) of sodium hydroxide (2 mol dmϪ3 ), was added drop-
wise. The precipitate was filtered, washed several times with water,
and dried on vacuo. The brown powder was treated with hexane,
and the insoluble material was filtered off. The solvent was evapo-
rated away under reduced pressure to leave yellow needles (9.44 g)
in a 89 % yield. Recrystallization from benzene gave yellow needles.
Analytical Data: C20H2F28O4Pd: C 26.02 (calc. 25.43); F 55.84
(56.32) %.
IR (KBr, pellet): ν 1531vs, 1596vs, 1617m, 1661m and 808m cmϪ1 are as-
signed to the ν(CϭO) ϩ ν(CϭC) and chelate ring π (CH) vibrations, ν(CϪF)
1125-1207vs, 1243vs, br, 1317 vs,br cmϪ1. The region below 700 cmϪ1 shows
Z. Anorg. Allg. Chem. 2005, 631, 2232Ϫ2235
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