Dramatic acceleration of the catalytic process of the amination of allyl acetates in the presence of a tetraphosphine/palladium system

Article abstract of DOI:10.1039/b007860n

The cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane/ [PdCl(C₃H₅)]₂ system catalyses allylic amination in good yields with a very high substrate/catalyst ratio; a turnover number of 680 000 and a turnover frequency of 8125 h^-1 can be obtained for the addition of dipropylamine to allyl acetate in the presence of this catalyst.

Full text of DOI:10.1039/b007860n

Dramatic acceleration of the catalytic process of the amination of allyl acetates
in the presence of a tetraphosphine/palladium system
Marie Feuerstein, Dorothée Laurenti, Henri Doucet* and Maurice Santelli*
Laboratoire de Synthèse Organique UMR-CNRS 6009, Faculté des Sciences de Saint Jérôme, Avenue Escadrille
Normandie-Niemen, 13397 Marseille Cedex 20, France. E-mail: henri.doucet@lso.u-3mrs.fr;
m.santelli@lso.u-3mrs.fr
Received (in Cambridge, UK) 27th September 2000, Accepted 14th November 2000
First published as an Advance Article on the web 15th December 2000
The cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)-
cyclopentane/[PdCl(C3H5)]2 system catalyses allylic amina-
tion in good yields with a very high substrate/catalyst ratio;
a turnover number of 680 000 and a turnover frequency of
8125 h21 can be obtained for the addition of dipropylamine
to allyl acetate in the presence of this catalyst.
was slightly decreased for the addition of morpholine 11 to 2. A
conversion of 93% is observed in the presence of 0.01%
Allylamines are fundamental building blocks in organic
synthesis and their preparation is an important industrial goal.1
Allylic amination is an efficient method for the formation of
allyl–nitrogen bonds.2 The classical method to perform this
reaction is to employ palladium complexes associated with
mono-3 or di-phosphine4 ligands. Phosphine-amine5 ligands
have also been used successfully. Even if the catalysts formed
by association of these ligands with palladium complexes are
efficient in terms of yield of adduct, the efficiency in terms of
the ratio of substrate/catalyst is low. In general 1–5% of these
catalysts must be used. With one of the most active catalysts
based on a polystyrene–phosphine–palladium complex the
reaction can be performed with as little as 0.018% catalyst
(TON: 3200).6 Nevertheless, very high values of ratio substrate/
catalyst have not been reported for this reaction.
Our aim was to obtain complexes capable of very high
turnover numbers in catalysis. The nature of the phosphine
ligand on complexes has a tremendous influence on the rate of
catalysed reactions. Recently a tetraphosphine based on a
cyclobutane ring led to the formation of palladium catalysts for
copolymerization that are more efficient than those of dppe by
a factor of ten.7 In order to find more efficient palladium
catalysts we decided to study the influence of the new tetrapodal
phosphine ligand, cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphi-
nomethyl)cyclopentane (Tedicyp 1)8,9 in which the four
Scheme 1
Table 1 Palladium catalyzed allylic amination11
Product
(major
Ratio
substrate/ frequencyi/ Yield
catalyst (%)
h21
Turnover
Allyl
acetate
Ratio
isomer) a/bh
Amine
2
2
2
2
7
8
13
14
15
16
—
—
—
—
—
1000000 8125
5000000 8333
100000 2062j
1000000 7083
100000 2388
1000000 8111k
68c
14ef
99bf
17af
95e
9
73df
93e
11
10000
250
100000 1111
57e
2
2
12
27
17
29a
1000
13
81c
85/15
10000
100000 1229
250
97bf
83cf
78ag
95a
36b
85e
90/10
68/32
94/6
95/5
95/5
86/14
84/16
100/0
100/0
100/0
100/0
100/0
93/7
2
3
28
7
30a
18a
1000
1000
10000
1000
1000
10000
100
1000
1000
100
1000
100
1000
100
1000
100
49
45
160
30
41
183
3
3
9
11
19a
20a
diphenylphosphinoalkyl groups are stereospecifically bound to
the same face of the cyclopentane ring, on the rate of allylic
amination reaction.
99a
44a
98e
4
6
21a
2.5
Our first objective was to evaluate the difference of
efficiency for allylic amination between a monophosphine
ligand such as triphenylphosphine, a diphosphine ligand such as
1,2-bis(diphenylphosphino)ethane (dppe) and our tetraphos-
phine 1. We observed that the addition of dioctylamine 8 to allyl
acetate 2 in the presence of 0.001% catalyst, led to the addition
product 14 in 1 and 3% conversion when PPh3 and dppe,
respectively, were used as ligand and 99% conversion with
Tedicyp (Scheme 1, Table 1). A similar tendency was observed
for the addition of diallylamine 9 to allyl acetate 2. In the
presence of 0.001% catalyst, only 7% conversion was observed
with dppe. With Tedicyp the conversion was 73% in the
presence of 0.0001% catalyst.
6.6
10.3
3.9
13.3
4.1
20.4
4.1
17.5
0.5
43e
4
4
7
8
22a
23a
92d
95a
84b
98a
49bf
100af
51e
4
4
5
10
11
11
24a
25a
26
94/6
91/9
92/8
—
65ef
Conditions: catalyst, see ref 10, THF, 25 °C, a 24 h. b 48 h. c 72 h. d 90 h.
e 130 h. f 55 °C. g In toluene. h For compounds 18–25, a corresponds to the
linear isomer and b to the branched isomer (Scheme 1). For compounds 29
and 30, a corresponds to the monoaddition product and b to the diaddition
product (Scheme 2). i TOF calculated between initial time and 24 h.
j Calculated after 48 h. k Calculated after 90 h.
Next we tried to evaluate the scope and limitations of
Tedicyp–palladium complex for this reaction. The addition rate
DOI: 10.1039/b007860n
Chem. Commun., 2001, 43–44
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catalyst. A turnover number (TON) of 57 000 and a TOF of
1111 h21 were obtained in the presence of 0.001% catalyst. On
the other hand, a significant steric effect was observed with the
bulky diisopropylamine 12. In the presence of 0.1% catalyst
only 81% conversion was obtained after three days.
The complex formed by association of Tedicyp and
[PdCl(C3H5)]2 seems to be more stable and less sensitive to
temperature and poisoning than the complexes formed with
diphosphines.
These results prompted us to investigate the allylation of
amines with substituted allyl acetates. When we used cinnamyl
acetate 3 in the presence of 0.1% catalyst high yields were
obtained for the addition of dipropylamine 7 and diallylamine 9.
A TON of 4400 has also been observed with morpholine 11. We
noted a good regioselectivity for the amination of cinnamyl
acetate 3 in favour of the linear isomer. Similar selectivities
were observed for the addition of diethylamine 6, dipropyl-
amine 7 and dioctylamine 8 to (E)-hex-2-en-1-yl acetate 4. (E)-
N,N-dialkylhex-2-enylamines 21a–23a were obtained regio-
and stereo-selectively in good yield. The regioselectivity of the
addition of cyclic amines 10 and 11 is slightly lower; 6 and 8%
of the branched products 24b and 25b are obtained with
pyrrolidine 10 and morpholine 11. Much lower TON and TOF
were observed in the course of the amination of hindered
3-acetoxy-1,3-diphenylprop-1-ene 5.
of 100000. These results seems to indicate that the active
palladium catalyst requires one tetraphosphine for one palla-
dium centre.
In conclusion, the Tedicyp–palladium complex obtained by
addition of Tedicyp to [Pd(C3H5)Cl]2 provides a convenient
catalyst for the allylic amination reaction. This catalyst seems to
be more stable and less sensitive to poisoning than the
complexes formed with mono- and di-phosphine ligands. This
stability probably arises from the presence of the four
diphenylphosphinoalkyl groups stereospecifically bound to the
same face of the cyclopentane ring. All four phosphines
probably cannot bind at the same time to the same palladium
centre, but the presence of these four phosphines on the ligand
close to the metal centre, along with steric factors, seems to
increase the coordination of the ligand to the palladium
complex. In the presence of this catalyst the amination reaction
can be performed with as little as 0.0001% catalyst. These
results represent an inexpensive, efficient, and environmentally
friendly synthesis. Further applications of this ligand will be
reported in due course.
We thank F. Berthiol for experimental work and the CNRS
for providing financial support.
Notes and references
With primary amines, we obtained mixtures of monoaddition
and diaddition products (Scheme 2). Benzylamine 27 led to the
monoaddition product 29a in 83% conversion and 90%
selectivity in the presence of 0.001% catalyst with a TOF of
1229 h–1. The addition rate of cyclohexylamine 28 is slower
with a TOF of 49 h21 and a lower selectivity in favour of the
monoaddition product 30a is observed.
1 For a review on allylic amination: see, M. Johannsen and K. Jorgensen,
Chem. Rev., 1998, 98, 1689.
2 For reviews on palladium catalysed allylic substitution reactions see: T.
Hayashi, in Catalytic Asymmetric Synthesis, ed. I. Ojima, VCH, New
York, 1993, p. 325; J. Tsuji, Palladium Reagent and Catalysis,
Innovation in Organic Synthesis, Wiley, New York, 1995; R. F. Heck,
Palladium Reagents in Organic Syntheses, ed A. R. Katritzky, O. Meth-
Cohn and C. W. Rees, Academic Press, London, 1985, p. 2; A. Pfaltz
and M. Lautens, Comprehensive Asymmetric Catalysis II, ed. E. N.
Jacobsen, A. Pfaltz and H. Yamamoto, Springer, Berlin, 1999, p. 833;
J.-L. Malleron, J.-C. Fiaud and J.-Y. Legros, Handbook of palladium
catalyzed organic reaction, Academic Press, London, 1997.
3 N. Riegel, C. Darcel, O. Stéphan and S. Jugé, J. Organomet. Chem.,
1998, 567, 219; O. Kuhn and H. Mayr, Angew. Chem., Int. Ed., 1999, 38,
343; J. P. Genêt, M. Balabane, J. E. Bäckvall and J. E. Nyström,
Tetrahedron Lett., 1983, 24, 2745; C. Thorey, J. Wilken, F. Hénin, J.
Martens, T. Mehler and J. Muzart, Tetrahedron Lett., 1995, 36, 5527;
M. Moreno-Manas, L. Morral and R. Pleixats, J. Org. Chem., 1998, 63,
6160.
Scheme 2
Finally, we tried to gain some information on the structure of
the palladium–Tedicyp complex formed. Addition of 1 equiv. of
Tedicyp to 0.5 equiv. of the dimer [PdCl(C3H5)]2 gave a clean
31P NMR spectrum which shows two broad signals at d 19 and
25 (vs. H3PO4). The characteristic signals of the free phosphine
at d 216.3 and 217.7 were not observed. Addition of 1 equiv.
of Tedicyp to 1 equiv. of [PdCl(C3H5)]2 gave an identical 31P
NMR spectrum. Addition of 2 equiv. of Tedicyp to 0.5 equiv. of
[PdCl(C3H5)]2 led to a more complicated spectrum; mainly four
signals of free phosphines at d 216.9, 218.2 , 219.3 and 220.9
4 B. M. Trost, L. T. Calkins, C. Oerlet and J. Zambrano, Tetrahedron
Lett., 1998, 39, 1713; A. Yamazaki and K. Achiwa, Tetrahedron:
Asymmetry, 1995, 6, 51; N. Sirisoma and P. Woster, Tetrahedron Lett.,
1998, 39, 1489; Y. Uozumi, A. Tanahashi and T. Hayashi, J. Org.
Chem., 1993, 58, 6826.
5 P. von Matt, O. Loiseleur, G. Koch, A. Pfaltz, C. Lefeber, T. Feucht and
G. Helmchen, Tetrahedron: Asymmetry, 1994, 5, 573.
6 B. M. Trost and E. Keinan, J. Am. Chem. Soc., 1978, 100, 7779.
7 C. Bianchini, H. M. Lee, A. Meli, W. Oberhauser, F. Vizza, P.
Brüggeller, R. Haid and C. Langes, Chem. Commun., 2000, 777.
8 D. Laurenti, M. Feuerstein, G. Pèpe, H. Doucet and M. Santelli,
unpublished results.
and some broad peaks between d 40 and 10 were observed in 31
P
NMR. In the first case, addition of 1 equiv. of Tedicyp to 0.5
equiv. of the Pd complex, produced broad signals at d 19 and 25
suggesting that this complex is involved in a succession of
equilibria due to a fast coordination–dissociation process of the
four phosphines of the ligand. The absence of peaks of free
phosphines probably arises from the equilibrium rate which
seems to be of the order of the NMR time scale. Similar results
have already been described; for example, Pd(PPh3)3 is largely
dissociated and the equilibrium rate is of the order of the NMR
time scale even at low temperature.12 Addition of 10 equiv. of
allyl acetate or addition of 10 equiv. of allyl acetate with 10
equiv. of dipropylamine to this Pd–Tedicyp complex (ratio Pd-
dimer/Tedicyp = 0.5) has no influence on the 31P NMR
spectrum; the two broad signals observed at d 19 and 25 are
unchanged.
We have also examined the importance of the ratio
palladium/Tedicyp for the catalysis. We observed that if the
reaction is performed with Pd-dimer/Tedicyp ratios of 0.5, 1
and 2, the rate of the reaction decreases. The TONs after 40 min
were, respectively, 8100, 4000 and 1300 for the addition of
dipropylamine 7 to allylacetate 2 with a ratio substrate/catalyst
9 cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane
Tedicyp 1 was prepared from cis,cis,cis-1,2,3,4-tetrakis{[(tolyl-4-
sulfonyl)oxy]methyl}cyclopentane 3113 by addition of Ph2PLi. 31P
NMR of 1 (162 MHz, THF-d8) d 216.3, 217.7.
10 The
cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopen-
tane/[PdCl(C3H5)]2 complex was prepared by stirring under argon the
tetraphosphine 1 (140 mg, 162 mmol) with [PdCl(C3H5)]2 (30 mg, 81
mmol) in THF (10 ml) for 10 min at room temperature. This complex is
not air stable and must be prepared just before use. dP(162 MHz, CDCl3)
25 (w = 80 Hz), 19.4 (w = 110 Hz).
11 In a typical experiment, the reaction of cinnamyl acetate 3 (1.30 g, 7.4
mmol) and dipropylamine 7 (2.07 g, 14.8 mmol) at 50 °C for 90 h in
distilled THF (20 mL) in the presence of the Tedicyp–palladium
complex (7.4 3 1023 mmol) under argon affords the corresponding
addition product 18 after evaporation and filtration on silica gel (diethyl
ether–pentane: 3/7) in 95% (1.52 g) isolated yield.
12 C. Amatore, A. Jutand, F. Khalil, M. M’Barki and L. Mottier,
Organometallics, 1993, 12, 3168; C. Amatore, G. Broeker, A. Jutand
and F. Khalil, J. Am. Chem. Soc., 1997, 119, 5176.
13 K. Somekawa, M. Nomura, S. Aoki, S. Noma and T. Shimo, Org. Prep.
Proc. Int., 1993, 25, 449.
44
Chem. Commun., 2001, 43–44