Palladium-catalysed amination reactions using cobalt-containing bulky phosphane ligands

Article abstract of DOI:10.1002/ejic.200500306

Aminations of aryl bromides by morpholine have been investigated using palladium complexes as catalyst precursors modified by the cobalt-containing phosphane ligand [(μ-PPh₂CH₂PPh₂)Co ₂(CO)₄][μ,η-PhC≡

Full text of DOI:10.1002/ejic.200500306

FULL PAPER
DOI: 10.1002/ejic.200500306
Palladium-Catalysed Amination Reactions Using Cobalt-Containing Bulky
Phosphane Ligands
[a]
[a]
[a]
Jian-Cheng Lee, Ming-Gin Wang, and Fung-E. Hong*
Keywords: Amination / Palladium / Cobalt complexes / Phosphane ligands / Orthometallation
Aminations of aryl bromides by morpholine have been inves-
tigated using palladium complexes as catalyst precursors
modified by the cobalt-containing phosphane ligand [(µ-
PPh
2
CH
2
PPh
2
)Co
2
(CO)
4
2
][µ,η-PhCϵCP(iPr) ] (4) as phos-
phane ligands do not exhibit comparable efficiency. A novel
palladium complex 5, i.e. Pd(OAc) chelated by deprotonated
PPh
2
CH
2
PPh
2
)Co
2
(CO)
4
][µ,η-PhCϵCP(tBu)
2
] (1). Reactions
2
1 was obtained from the reaction of 1 with Pd(OAc) . As re-
were carried out under various conditions with satisfactory
results. The components of the optimised reaction conditions
consist of 1.0 mmol of aryl bromide, 1.2 equiv. of morpholine,
vealed by the crystal structure, an orthometallation process
occurs between the phenyl ring of 1 and the palladium ion.
Presumably, the process is accompanied by release of one
equivalent of acetic acid. The coordinated acetate ligand
binds to the palladium ion in a bidentate chelating mode.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
1
.4 equiv. of NaOtBu, 1 mL of toluene and 1 mol-% of a 1:1
mixture of 1 and Pd(OAc) . In contrast, related aminations
using [(µ-PPh CH PPh )Co (CO) ][µ,η-pyCϵCP(tBu) (2),
(µ-PPh CH PPh )Co (CO) ][{µ,η-PhCϵCP(cy) }] (3) and [(µ-
2
2
2
2
2
4
2
]
[
2
2
2
2
4
2
Introduction
been prepared and their catalytic efficiencies in phosphane
modified, palladium-catalysed reactions have been evalu-
ated. It was also found that in most of the phosphane
assisted cases, the catalytic efficiencies are higher when
using monodentate rather than bidentate phosphanes.
Among the monodentate phosphane ligands possible, a
series of organometallic versions of tris(alkylphosphanes),
The amination of aryl halides by a phosphane-coordi-
nated palladium catalyst is a much more superior method
for the preparation of aromatic amines than the original
methods using tin amides.[ Clearly, it is neither ecologi-
cally friendly nor practical to use stoichiometric amounts of
tin amides in the amination reaction. Recently, momentous
[9]
1]
2
1
1
[
(µ-PPh CH PPh )Co (CO) ][µ,η-R CϵCPR ] (1: R
=
2
2
2
2
2
4
2
[2]
improvements have been achieved by Buchwald and Hart-
1
2
[9a]
1
2
tBu, R = Ph; 2: R = tBu, R = py; 3:
R = Cy, R =
[
3]
wig in the catalytic amination of aryl bromides using free
amines. Based on their extensive investigations into this
subject, a well accepted mechanism has now been pro-
1
2
Ph; 4: R = iPr, R = Ph), were chosen and used in palla-
dium-catalysed amination reactions (Scheme 1). Results of
a careful examination of the amination reactions catalysed
[
4]
posed. Recently, a second-generation of much more ef-
ficient catalysts for aminations was introduced by Buch-
by Pd(OAc) complexes chelated with 1, 2, 3 or 4 are re-
2
ported in this paper. Following this, the efficiencies of these
ligands in the reactions are compared and discussed.
[
5]
[6]
wald and Hartwig. These are palladium complexes che-
lated by biphosphane ligands such as 1,1Ј-bis(diphenylpho-
sphanyl)ferrocene (dppf) or BINAP. As is known for transi-
tion-metal-complex-assisted catalytic reactions, the rate of
the reductive elimination process is normally enhanced by
employing a bulky ligand such as dppf. Lately, because of
their bulky nature, the use of using metal-containing phos-
phanes in transition-metal catalysed reactions has received Scheme 1.
increasing attention.[ In particular, we were interested in
exploiting a new type of metal-containing phosphane li-
gand which would allow us to gain direct access to a family
7]
of phosphanes which would hopefully be electron-rich and Results and Discussion
bulky in character.[
7,8]
As a result, a new family of novel
cobalt-containing (mono- or bidentate) phosphanes has Amination Reactions Using Palladium Complexes Chelated
by the Cobalt-Containing Phosphane Ligands 1, 2, 3 and 4
[
a] Department of Chemistry, National Chung Hsing University,
Amination reactions of bromobenzene by morpholine
were carried out using palladium complexes chelated by the
Taichung 40227, Taiwan
E-mail: fehong@dragon.nchu.edu.tw
Eur. J. Inorg. Chem. 2005, 5011–5017
© 2005 Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim
5011

J.-C. Lee, M.-G. Wang, F.-E. Hong
FULL PAPER
cobalt-containing phosphane ligands 1, 2, 3 or 4 as the cat-
alyst precursors (Scheme 2).
Scheme 2.
The general procedure for the catalytic reactions under
investigation is as follows. A suitable Schlenk tube was first
charged with 1.0 mmol of bromobenzene, 1.2 equiv. of
morpholine, 1.4 equiv. of NaOtBu, 1 mL of toluene and
1
mol-% of 1/Pd(OAc) . The reaction mixture was then
2
stirred at either 40 °C or 60 °C for 2 to 24 h depending on
the reaction under investigation. The results are shown be-
low (Table 1). Excellent yields (Ͼ99%) were obtained when
the reaction was carried out at 60 °C for 20 h or more (en-
tries 2 and 3). As shown, the reactions reach a satisfactory
yield after about 4 h (entry 7). An induction period is obvi-
ously needed before the reaction reaches a reasonable rate
(
entry 8). Similar reactions were carried out employing 2/
Figure 1. Diagram of 2. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and bond angles [°]: Co(1)–C(2) 1.946(2);
Co(1)–C(1) 2.007(2); Co(1)–P(2) 2.2267(8); Co(1)–Co(2) 2.4876(5);
Co(2)–C(2) 1.957(2); Co(2)–C(1) 1.998(3); Co(2)–P(3) 2.2415(8);
P(1)–C(1) 1.809(3); P(2)–C(44) 1.828(3); P(3)–C(44) 1.828(3); N–
C(3) 1.340(3); C(1)–C(2) 1.359(3); C(2)–C(3) 1.470(4); C(2)–Co(1)–
C(1) 40.17(10); C(1)–Co(1)–P(2) 138.98(8); C(1)–Co(1)–Co(2)
51.43(7); C(2)–Co(2)–C(1) 40.17(10); C(1)–Co(2)–P(3) 131.70(8);
C(1)–Co(2)–Co(1) 51.76(7); C(2)–C(1)–P(1) 132.4(2); Co(2)–C(1)–
Co(1) 76.81(9); C(1)–C(2)–C(3) 136.5(2); Co(1)–C(2)–Co(2)
79.18(9); N–C(3)–C(2) 118.2(2); P(3)–C(44)–P(2) 109.79(15).
Pd(OAc) as the catalyst precursor. However, a reduction
in the efficiency of the catalysis was observed using this L/
Pd combination.
2
Table 1. Amination reactions employing 1/Pd(OAc)
2
or 2/Pd-
(OAc) as the catalyst at various temperatures and reaction times.
2
Entry Time (h) Temp. (°C) Yield (%) (L = 1)[a] Yield (%) (L = 2)[b]
1
2
3
4
5
6
7
8
24
24
20
16
12
8
40
60
60
60
60
60
60
60
67
Ͼ99
Ͼ99
93
94
95
–
80
–
–
82
–
For comparison, similar reactions were carried out using
Pd(OAc) complexes chelated with 3 or 4 as catalyst precur-
2
4
2
94
52
72
–
sors. In these cases, higher reaction temperatures of 80 °C
and longer reaction times of 16 h were required for the reac-
[
a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of tions to be reasonably efficient. Generally speaking, amin-
morpholine, 1.4 equiv. of base, 1 mL of solvent and 1 mol-% 1/
Pd(OAc) . Average of two runs. Determined by gas chromatog-
raphy. [b] 1 mol-% 2/Pd(OAc)
ation reactions carried out employing 3- or 4/Pd(OAc) as
the catalytic systems are not as effective as those based on
2
2
2
.
1
/Pd(OAc) (Table 2). These experimental observations are
2
consistent with the commonly accepted idea that a phos-
Compound 2 was synthesised according to the procedure phane ligand with bulky tBu substituents is generally more
shown in the Experimental Section. The identity of 2 was efficient than that with a less bulky Cy or iPr group.[
established by spectroscopic means as well as by X-ray dif-
8a,10]
fraction methods. Two distinct chemical shifts at δ = 3.04
and 4.26 ppm were observed for the methylenic protons of Table 2. Reactions employing 3/Pd(OAc) or 4/Pd(OAc) as a cata-
2
2
1
lyst at various reaction temperatures and times.
2
by H NMR spectroscopy. Large differences in the shifts
imply that the back-and-forth motion of the bridging dppm
group around the dicobalt fragment is rather slow. The 31
NMR spectrum displays two singlets in a ratio of 2:1 at δ
39.03 ppm (2 P, dppm) and 42.74 ppm (1P), respectively,
Entry Time (h) Temp. (°C) Yield (%) (L = 3)[a]
Yield (%) (L = 4)[b]
P
1
2
3
4
5
6
7
4
6
6
60
60
80
80
80
80
80
20
21
52
53
62
74
85
–
–
=
25
31
47
62
82
8
for three phosphorus atoms. The ORTEP diagram for 2 is
depicted in Figure 1. As revealed from the structure, the
pyridyl ring and the phosphanyl group of the bridged al-
kyne point away from the centre of the molecule to prevent
severe steric hindrance. This situation is also true for the
10
14
16
[
a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of
morpholine, 1.4 equiv. of base, 1 mL of solvent and 1 mol-% 3/
Pd(OAc) . Average of two runs. Determined by gas chromatog-
coordinated dppm ligand and the P(tBu) substituent. All
2
2
four carbonyls are located at the terminal positions.
2
raphy. [b] 1 mol-% 4/Pd(OAc) .
5012
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Eur. J. Inorg. Chem. 2005, 5011–5017

Pd-Catalysed Amination Reactions Using Co-Containing Phosphane Ligand
FULL PAPER
observed in 4 were similar to those observed for 2 except
that the iPr groups are not as bulky.
Amination reactions were carried out with various ratios
of 1/Pd(OAc) or 3/Pd(OAc) under the reaction conditions
2
2
shown below (Table 3). The optimum yield was achieved
when the reaction was conducted with an NaOtBu / toluent
solvent system and a L/Pd(OAc) ratio of 1:1 (Table 3, entry
2
3). The positive role played by the phosphane ligand in the
reaction can be clearly seen. No conversion was observed
without the presence of phosphane (Table 3, entry 6).
Again, better efficiency was obtained by employing 1/
Pd(OAc)2.
2
Table 3. Reactions employing various ratios of Pd(OAc) /L.
Entry
L/Pd(OAc)
2
Yield (%) (L = 1)[a] Yield (%) (L = 3)[b]
1
2
3
4
5
6
2:1
1.5:1
1:1
0.5:1
0.1:1
0:1
36
73
94
88
57
0
54
62
85
71
23
0
Figure 2. Diagram of 4. Hydrogen atoms are omitted for clarity. [a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of
Selected bond lengths [Å] and bond angles [°]: Co(1)–C(1) 1.959(4),
morpholine, 1.4 equiv. of NaOtBu, 1 mL of toluene and 1/Pd-
Co(1)–C(2) 1.978(4), Co(1)–P(2) 2.2427(10), Co(1)–Co(2) (OAc) at 60 °C for 4 h. Average of two runs. Determined by gas
2
2
2
1
4
1
5
.4896(7), Co(2)–C(2) 1.951(3), Co(2)–C(1) 1.984(3), Co(2)–P(3)
.2253(10), P(1)–C(1) 1.795(3), P(2)–C(43) 1.841(3), P(3)–C(43)
.840(4), C(1)–C(2) 1.351(5), C(2)–C(3) 1.478(5), C(1)–Co(1)–C(2)
chromatography. [b] 3/Pd(OAc) at 80 °C for 16 h.
2
As has been established, a well chosen base/solvent sys-
tem is essential for the success of an efficient palladium-
catalysed coupling reaction. As a consequence, amination
0.13(14),
C(1)–Co(1)–P(2)
139.80(11),
C(2)–Co(1)–P(2)
01.18(10), C(1)–Co(1)–Co(2) 51.30(10), C(2)–Co(1)–Co(2)
0.21(10), P(2)–Co(1)–Co(2) 99.21(3), C(2)–Co(2)–C(1) 40.15(14),
C(1)–Co(2)–P(3) 138.94(11), C(2)–Co(2)–Co(1) 51.17(10), C(1)– reactions of bromobenzene by morpholine employing 1- or
Co(2)–Co(1) 50.41(11), C(43)–P(2)–Co(1) 108.62(12), C(43)–P(3)–
3
/Pd(OAc) as the catalyst precursor with various base/sol-
2
Co(2) 110.70(11), C(2)–C(1)–P(1) 137.7(3), C(2)–C(1)–Co(1)
0.7(2), C(2)–C(1)–Co(2) 68.6(2), P(1)–C(1)–Co(2) 142.8(2),
vent systems were carried out at 60 °C for 4 h (Table 4).
As shown, the best base/solvent composition is NaOtBu/
toluene (entry 1). This may be partially due to the reductive
7
Co(1)–C(1)–Co(2) 78.29(12), C(1)–C(2)–C(3) 137.1(3), C(1)–C(2)–
Co(2) 71.2(2), C(1)–C(2)–Co(1) 69.2(2), Co(2)–C(2)–Co(1)
[
11]
7
8.62(13), O(2)–C(15)–Co(1) 176.0(4), P(2)–C(43)–P(3) 110.73(18). capacity of NaOtBu in toluene.
Amination reactions of bromobenzene by morpholine
Compound 4 was prepared and characterised by spectro- employing 1 with various Pd sources in a NaOtBu/toluene
scopic means. Its crystal structure was also determined by system were carried out at 60 °C for 4 h (Table 5). As
1
X-ray diffraction methods (see below). In the H NMR shown, excellent yields were obtained using Pd(OAc) or
2
3
spectrum of 4, two distinct chemical shifts at δ = 3.27 and [(η -C H )PdCl] as palladium sources (entries 1 and 6) and
3
5
2
3
.42 ppm were observed for the methylenic protons. In ad- this was true using 1 or 3 as the ligand. However, while the
3
1
3
dition, the P NMR spectrum displays two singlets in the [(η -C H )PdCl] system exhibits good catalytic efficiency,
3
5
2
ratio of 2:1 at δ = 37.89 ppm (2 P, dppm) and 23.48 ppm (1 the complex is not suitable for use because of its air-sensi-
P) for three phosphorus atoms. The ORTEP diagram for tivity. Interestingly, no product was detectable when using
complex 4 is depicted in Figure 2. The structural features PdCl as the palladium source (entry 2).
2
Table 4. Reactions employing Pd(OAc)
2
/L with various bases and solvents.
Base
Entry
Pd/Ligand
L = 1[a]
L = 3[b]
Solvent
Yield (%)
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
NaOtBu
NaOtBu
NaOtBu
NaOtBu
KOtBu
KOH
toluene
THF
DME
–
toluene
toluene
toluene
toluene
toluene
94
67
30
–
3
Ϸ 1
4
toluene
–
85
–
37
23
24
0
13
8
0
DME
DMF
toluene
toluene
toluene
toluene
toluene
NaOH
Cs
K
2
(CO)
PO
3
0
0
3
4
[
(
a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of morpholine, 1.4 equiv. of base, 1 mL of solvent and 1 mol-% 1/Pd-
OAc)
2
at 60 °C for 4 h. Average of two runs. Determined by gas chromatography. [b] 1 mol-% 3/Pd(OAc)
2
at 80 °C for 16 h.
Eur. J. Inorg. Chem. 2005, 5011–5017
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5013

J.-C. Lee, M.-G. Wang, F.-E. Hong
FULL PAPER
Table 5. Reactions employing various Pd sources.
Characterisation of a Novel Deprotonated Palladium
Complex Chelated with 1
Entry
Pd source
Pd(OAc)
PdCl
Pd(COD)Cl
PdCl (CH CN)
Pd (dba)
)PdCl]
Yield (%) (L = 1)[a]
Yield (%) (L = 3)[b]
1
2
3
4
5
6
2
94
0
19
59
2
85
0
75
68
28
90
Interestingly, a novel palladium complex 5, namely
Pd(OAc) chelated by deprotonated 1, was obtained from
2
2
the reaction of 1 with Pd(OAc) in toluene at 25 °C for 1 h
2
2
3
2
(Scheme 3). Compound 5 was characterised by spectro-
2
3
3
[(η -C
3
H
5
2
94
scopic means and its crystal structure was determined by
X-ray diffraction (Table 7). As revealed by its crystal struc-
ture, a process of orthometallation must have occurred
[
a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of
morpholine, 1.4 equiv. of NaOtBu, 1 mL toluene and 1 mol-% 1/
Pd(OAc)
chromatography. [b] 1 mol-% 3/Pd(OAc)
2
at 60 °C for 4 h. Average of two runs. Determined by gas which was presumably accompanied by the release of one
2
at 80 °C for 16 h.
equiv. of acetic acid (Figure 3). The acetate ligand is coordi-
nated to the palladium through a bidentate chelating
[
12]
mode.
The palladium metal centre is in a square planar
It has been commonly observed that a better conversion
may be reached for an aryl halide with an electron-with-
drawing rather than an electron-donating substituent in a
palladium-catalysed coupling reaction.[8c] Amination reac-
environment. Two bulky units, P(tBu) and dppm, are in
2
anti positions. There is one diethyl ether molecule in each
asymmetric unit. As has been established, most acetate pal-
ladium complexes are dimeric with two acetates bridging
two palladium ions. We believe that the formation of this
exceptional monomeric structure of 5 is due to the unique
bulkiness and bonding mode of ligand 1. A rather down-
field 31P NMR shift at δ = 91.6 ppm was observed which
we assigned to the corresponding palladium attached phos-
tions employing 1/Pd(OAc) and aryl bromides, with vari-
2
ous electron-withdrawing/donating capacities in a Na-
OtBu /toluene system were carried out at 60 °C for 4 h
(Table 6). The best yield was obtained for aryl halides with
an electron-withdrawing group which is in agreement with
the common observation for palladium-catalysed coupling
reactions (entry 6). Similar trends were observed when em-
ploying 3/Pd(OAc) or 4/Pd(OAc) as the catalyst precursor
1
phorus site. A triplet signal was observed in the H NMR
spectrum corresponding to the two methylenic protons of
the coordinated dppm. This implies that the coordinated
dppm is in a rapid back-and-forth thermal motion. All
these spectroscopic data are consistent with the data ob-
tained from the solid-state structure. The crystal structure
of 5 also demonstrates that only one molar equivalent of
phosphane ligand is needed for effective coordination to a
2
2
(Table 6). Interestingly, in our previous work using 4/
Pd(OAc) as a catalyst precursor in Suzuki reactions, the
2
catalytic efficiency was rather poor. Nevertheless, the effi-
ciency was comparable with that using 1- or 2/Pd(OAc) as
a precursor in amination reactions.
2
palladium ion. For a conventional PR (R: alkyl or aryl),
3
two or even three ligands are required to sustain a stable
palladium complex.
2
Table 6. Reactions of various aryl bromides employing L/Pd(OAc) .
Scheme 3.
Table 7. Amination reactions employing 5 as catalyst.[a]
Entry
5/Substrate (mol-%)
Yield (%)
1
2
3
0.5
1
1.5
40
78
Ͼ99
[
a] Reaction conditions: 1.0 equiv. of aryl halide, 1.2 equiv. of
morpholine, 1.4 equiv. of NaOtBu, 1 mL of toluene at 60 °C for
4
h. Average of two runs. Determined by gas chromatography.
Buchwald has proposed a phosphane ligand coordinated
palladium complex 6 as an active species in one of the pal-
[
13]
ladium-catalysed amination reactions. However, nothing
further was stated about the bonding mode of the acetate
ligand in 6 probably because its crystal structure was not
established. By comparing 5 and 6, the structural similari-
ties for these two compounds are clear (Scheme 4). The
[
a] Reaction conditions: 1.0 equiv. of bromobenzene, 1.2 equiv. of
morpholine, 1.4 equiv. of NaOtBu, 1 mL of toluene and 1 mol-%
/Pd(OAc) at 60 °C for 4 h. Average of two runs. Isolated yield.
b] 1 mol-% 3/Pd(OAc) at 80 °C for 16 h. [c] 1 mol-% 4/Pd(OAc)
at 80 °C for 16 h.
1
[
2
2
2
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Eur. J. Inorg. Chem. 2005, 5011–5017

Pd-Catalysed Amination Reactions Using Co-Containing Phosphane Ligand
FULL PAPER
substituents, with morpholine, employing 5 in a NaOtBu/
toluene system, were carried out at 60 °C for 4 h (Table 8).
Generally speaking, the efficiencies are lower for 5 than for
1
/Pd(OAc) (Table 6 vs. Table 8). The best yield was found
2
in the case of the aryl bromide with an electron-with-
drawing group (entry 6).
Table 8. Reactions of various aryl bromides employing 5.[a]
Figure 3. Diagram of 5. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Pd–C(4) 2.001(4), Pd–O(5)
2
.163(3), Pd–O(6) 2.171(3), Pd–P(1) 2.2182(11), Pd–C(46) 2.509(5),
Co(2)–C(1) 1.970(4), Co(2)–P(3) 2.2241(11), Co(2)–Co(1)
2
1
1
1
.4764(8), Co(1)–C(2) 1.969(4), Co(1)–C(1) 1.968(4), P(1)–C(1)
.778(3), O(6)–C(46) 1.240(6), O(5)–C(46) 1.266(7), C(46)–C(47)
.495(8), C(3)–C(4) 1.405(6), C(3)–C(2) 1.460(5), C(5)–C(4)
.396(6), C(1)–C(2) 1.362(5), C(4)–Pd–O(5) 161.12(15), C(4)–Pd–
O(6) 101.56(15), O(5)–Pd–O(6) 59.92(14), C(4)–Pd–P(1) 92.04(12),
O(5)–Pd–P(1) 106.48(11), O(6)–Pd–P(1) 166.39(10), C(2)–Co(2)–
C(1) 40.76(15), C(2)–Co(1)–C(1) 40.48(15), C(1)–P(1)–Pd
[
a] Reaction conditions: 1.0 equiv. of aryl halide, 1.2 equiv. of
morpholine, 1.4 equiv. of base and 1 mL of solvent. Average of two
runs. Isolated yield.
1
08.10(13), C(46)–O(6)–Pd 90.5(3), C(46)–O(5)–Pd 90.2(3), O(5)–
C(46)–O(6) 119.4(4), C(47)–C(46)–Pd 177.4(6), C(4)–C(3)–C(2)
19.5(3), C(2)–C(1)–P(1) 121.8(3), C(1)–C(2)–C(3) 130.6(3), C(5)–
1
C(4)–C(3) 117.8(4), C(5)–C(4)–Pd 111.1(3), C(3)–C(4)–Pd 131.1(3).
Concluding Remarks
newly characterised compound 5 can be regarded as a more
complicated, metal-containing version of 6.
We have demonstrated that the amination reactions of
aryl bromides by morpholine can be carried out catalyti-
cally with palladium complexes modified with a novel co-
balt-containing phosphane ligand 1. The catalytic perform-
ance is best with a 1/Pd(OAc) ratio of 1:1. The same reac-
2
tions may also be carried out using palladium complexes
modified with 2, 3 or 4 but with reduced efficiency.
A novel palladium complex 5 was obtained from the re-
Scheme 4.
action of 1 with Pd(OAc) . As revealed by the crystal struc-
2
Complex 5 was employed as the Pd source for the amina-
tions of bromobenzene by morpholine. Reactions were car-
ried out in an NaOtBu/toluene phase at 60 °C for 4 h
ture, a process of orthometallation occurs presumably ac-
companied by the release of one equiv. of acetic acid. We
propose that 5 could be the precursor to the true catalyti-
(
Table 7). The catalytic efficiency of the reaction employing
complex 5 is clearly not as good as that carried out in situ
Table 1, entry 7 vs. Table 7, entry 2). It indicates that com-
0
cally active Pd species.
(
plex 5 is not a genuinely catalytically active species. Rather, Experimental Section
complex 5 could be regarded as the precursor to a genuine
Synthesis of (µ-PPh
Dicobalt octacarbonyl Co
(
capacity round flask charged with a magnetic stirrer. The solution
was stirred at 65 °C for 6 h and a yellow coloured compound,
2
CH
2
PPh
(CO)
1.00 mmol, 0.38 g) and toluene (10 mL) were placed in a 100 mL
2
)Co
2
(CO)
4 2
[µ,η-PyCϵCP(tBu) ] (2):
0
catalytically active Pd species. It still requires a reduction
II
0
[14]
2
8
(1.00 mmol, 0.34 g), dppm
process to convert the Pd to the more active Pd species.
Furthermore, the catalytic efficiency could be greatly im-
proved by increasing the molar ratio of 5 (Table 7, entry 3).
For comparison, amination reactions of aryl bromides Co (CO) (µ-P,P-dppm), was produced. Without further separation,
2
6
bearing various electron-withdrawing/electron-donating the reaction flask was then charged with one equiv. of
Eur. J. Inorg. Chem. 2005, 5011–5017
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5015

J.-C. Lee, M.-G. Wang, F.-E. Hong
FULL PAPER
1
PyCϵCP(tBu)
2
(0.25 g) in toluene (5 mL). Subsequently, the solu-
was 80% (0.82 g, 0.80 mmol). H NMR (CDCl
H, arene), 3.30 (t, JPH = 10.2 Hz, 2 H, CH ), 1.53 ppm (d, JPH
): δ = 137.16–124.92 (30 C,
), 38.93 [d, 2 C, -C(CH ], 30.55 [d, 6 C,
]. P NMR (CDCl ):
): δ = δ = 38.8 (s, 2 P, dppm), 91.6 ppm [s, 1 P, P(tBu) ]. MS (ESI): m/z
Pd: calcd. C 55.07, H 4.62; found: C
3
): δ = 7.54–6.92 (24
tion was stirred at 80 °C for 16 h before the solvent was removed
under reduced pressure. The residue was further separated by
CTLC. A dark green coloured band was eluted using a mixed sol-
2
=
1
3
7 Hz, 18 H, tBu). C NMR (CDCl
arene), 41.32 (t, 1 C, CH
-C(CH ], 67.97 ppm [s, 1 C, PhCϵCP(tBu)
3
2
3 3
)
3
1
vent mobile phase (CH
2
Cl
2
/hexane, 1:3) and was identified as 2.
3
)
3
2
3
1
The yield was 72% (0.62 g, 0.72 mmol). H NMR (CDCl
3
2
+
6.90–8.50 (m, 24 H, arene), 3.04 (q, 1 H, dppm), 4.26 (q, 1 H, = 1024 [M] . C51
H
57Co
2
O
7
P
3
31
dppm), 1.23 ppm [d, 18 H, P(tBu)
2
]. P NMR (CDCl
3
): δ = 39.03 53.85, H 4.63.
(
=
C
s, 2 P, dppm), 42.74 ppm [s, 1 P, P(tBu)
2
]. 13C NMR (CDCl
3
): δ
127.86–133.07 (29 C, arene), 30.43 ppm (1 C, dppm).
NO : calcd. C 60.91, H 5.11; found C 61.34, H 5.15.
Amination of Aryl Bromides
44
H44Co
2
4 3
P
Method: An oven-dried Schlenk tube was charged with 1 (8.60 mg,
.01 mmol), Pd(OAc) (2.24 mg, 0.01 mmol) and base (1.4 mmol).
] 4: The tube was evacuated, filled with nitrogen and then the aryl bro-
(1.00 mmol, 0.34 g), dppm
mide (1.00 mmol), toluene (1 mL) and morpholine (1.20 mmol)
1.00 mmol, 0.39 g) and toluene (10 mL) were placed in a 100 mL were added. The tube was sealed with a Teflon screw cap and the
+
MS (EI): m/z = 862 [M]
Synthesis of (µ-PPh CH
Dicobalt octacarbonyl, Co
0
2
2
2
PPh
2 2 4 2
)Co (CO) [µ,η-PyCϵCP(iPr)
2
(CO)
8
(
capacity round flask containing a magnetic stirrer. The solution
was stirred at 65 °C for 6 h during which time a yellow coloured
mixture was stirred at 60 °C for 4 h. After all the starting materials
had been consumed, the mixture was cooled to room temperature
and was then diluted with diethyl ether (40 mL). The resultant sus-
pension was transferred to a separating funnel and washed with
water (10 mL). The organic layer was separated, dried with anhy-
compound, Co
separation, the reaction flask was charged with one equiv. of
PyCϵCP(iPr) (0.22 g) in toluene (5 mL) and the solution was then
2 6
(CO) (µ-P,P-dppm), was formed. Without further
2
stirred at 80 °C for 16 h. The solvent was removed under reduced
pressure and the resultant dark red coloured residue was separated
by CTLC. A dark red band was eluted out using mixed solvent
drous MgSO and concentrated in vacuo. The crude residue was
purified by CTLC with a mixture of hexane/ethyl acetate as the
mobile phase.
4
mobile phase (CH
tified as 4. The yield was 82.0% (0.69 g, 0.82 mmol). H NMR
CDCl ): δ = 7.77–7.00 (m, 25 H, arene), 3.27–3.42 (d, 2 H, CH
.23–2.25 (m, 2 H), 1.23–1.43 ppm [m,12 H, P(iPr)
CDCl ): δ = 37.89 (s, 2 P, dppm), 23.48 ppm [s, 1 P, P(iPr)
: calcd. C 61.95, H 4.90; found: C 62.03, H 4.96.
2 2
Cl : hexane = 1:3) and the compound was iden-
1
The couplings of morpholine with bromobenzene, 4-bromotoluene,
), 3-bromoanisole or 3-chloronitrobenzene were examined using the
2
(
2
(
C
3
31
]. P NMR method. The isolated yields of the corresponding products, N-
2
].
phenylmorpholine, N-(4-methyl)phenylmorpholine, N-(3-meth-
oxyphenyl)morpholine and N-(3-nitrophenyl)morpholine were
3
2
43 2 4 3
H41Co O P
94% (0.153 g), 68% (0.120 g), 80% (0.155 g) and 99% (0.206 g),
Synthesis of [(µ-PPh
2
CH PPh )Co (CO) {µ,η-PhCϵCP(tBu) }]-
PdOAc (5): The two reactants, Pd(OAc) (1.00 mmol, 0.22 g) and
(µ-PPh CH PPh )Co (CO) {µ,η-PhCϵCP(tBu) }] 1 (1.00 mmol,
.86 g) were placed in a 100-mL round-bottomed flask charged
2
2
2
4
2
respectively.
2
[
2
2
2
2
4
2
1
N-Phenylmorpholine: H NMR (CDCl
3
): δ = 6.88–6.93, 7.25–7.30
0
(
m, 5 H), 3.87 (t, 4 H, J = 2.4 Hz), 3.16 ppm (t, 4 H, J = 2.6 Hz).
with a magnetic stirrer and toluene (5 mL). The solution was
stirred at 25 °C for 1 h before the solvent was removed in vacuo.
The crude material was further purified by CTLC. A red-brown
N-(4-Methylphenyl)morpholine: 1H NMR (CDCl
): δ = 3.10 (t, 4
3
H, J = 5 Hz), 3.86 (t, 4 H, J = 4.6 Hz), 6.83 (d, 2 H, J = 8.6 Hz),
7.10 ppm (d, 2 H, J = 8.4 Hz).
2 2
band was eluted with CH Cl and was identified as 5. The yield
Table 9. Crystal data for 2, 4 and 5.
Compound
2
4
5
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
44
H
44Co
2
NO
4
P
3
C
43
H
41Co
2
O
4
P
3
C
51 2 7 3
H57Co O P Pd
861.57
monoclinic
P2 /c
13.8627(12)
14.1883(12)
21.8278(19)
90
832.53
monoclinic
P2 /c
16.0552(12)
11.6582(9)
23.1912(18)
90
1099.14
monoclinic
P2 /c
13.6654(17)
17.291(2)
22.379(3)
90
1
1
1
α (°)
β (°)
96.748(2)
90
4263.5(6)
4
109.574(2)
90
4089.9(5)
4
102.903(2)
90
4858.2(14)
4
γ (°) 3
V (Å )
Z
D
–3
c
(Mgm )
1.342
1.352
1.416
λ (Mo-K ) [Å]
µ (mm )
α
0.71073
0.932
0.71073
0.968
0.71073
1.122
–1
θ range [°]
2.06 to 26.01
8354
495
0.0373
0.0852
0.947
1.86 to 26.02
8001
469
0.0469
0.1649
1.618
1.87 to 26.11
10219
577
0.0429
0.1494
1.035
Observed reflections [F Ͼ 4σ(F)]
No. of refined parameters
R
wR
1
for significant reflections[a]
[
b]
2
fco] r significant reflections
[
GoF
a] R
[Σw(F
= {Σ[w(F 2
– F 2
)]2/Σ[w(F
2 2
) ]}1/2; w = 0.0497, 0.0731 and 0.1277 for 2, 4 and 5, respectively. [c] GoF
[
1
= |Σ(|F
o
o
– F
| – |F
c
c
|)/|ΣF
) /(number of reflections – number of parameters)]
o
||. [b] wR
2
o
c
o
2
2 2
1/2
=
.
5016
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 5011–5017

Pd-Catalysed Amination Reactions Using Co-Containing Phosphane Ligand
FULL PAPER
1
N-(3-Methoxyphenyl)morpholine: H NMR (CDCl
3
): δ = 3.15 (t, 4
[4] a) J. F. Hartwig, in: Modern Amination Methods (Ed.: A.
Ricci), Wiley-VCH: Weinheim, Germany, 2000.; b) R. A. Wied-
enhoefer, H. A. Zhong, S. L. Buchwald, Organometallics 1996,
H, J = 2.4 Hz), 3.85 (t, 4 H, J = 2.4 Hz), 6.45 (d, 1 H, J = 3.6 Hz),
.54 (d, 1 H, J = 4.0 Hz), 7.20 ppm (t, 2 H, J = 4.0 Hz).
6
15, 2745–2754; c) J. Louie, F. Paul, J. F. Hartwig, Organometal-
1
lics 1996, 15, 2794–2805; d) L. M. Aleazar-Roman, J. F. Hart-
wig, J. Am. Chem. Soc. 2001, 123, 12905–12906; e) U.
Christmann, R. Vilar, Angew. Chem. Int. Ed. 2005, 44, 366–
N-(3-Nitrophenyl)morpholine: H NMR (CDCl
J = 2.4 Hz), 3.87 (t, 4 H, J = 2.4 Hz), 7.10–7.14 (m, 3 H), 7.34 ppm
t, 1 H, J = 3.8 Hz).
3
): δ = 3.18 (t, 4 H,
(
3
74.
[5] J. P. Wolfe, S. Wagaw, S. L. Buchwald, J. Am. Chem. Soc. 1996,
18, 7215–7216.
6] M. S. Driver, J. F. Hartwig, J. Am. Chem. Soc. 1996, 118, 7217–
218.
1
4
-Methoxyphenylmorpholine: H NMR (CDCl
H), 3.76 (s, 3 H), 3.78–3.87 (m, 4 H), 3.05–3.07 ppm (m, 4 H).
3
): δ = 6.84–6.91 (m,
1
4
[
[
7
X-ray Crystallographic Studies: Suitable crystals of 2, 4 and 5 were
sealed in thin-walled glass capillaries under nitrogen and mounted
on a Bruker AXS SMART 1000 diffractometer. Intensity data were
collected from 1350 frames with increasing ω (width of 0.3° per
frame). The absorption correction was based on the symmetry
equivalent reflections using the SADABS program. The space
group determination was based on a check of the Laue symmetry
and systematic absences and was confirmed using the structure
solution. The structure was solved by direct methods using the
SHELXTL package. All non-hydrogen atoms were located from
successive Fourier maps and the hydrogen atoms were refined using
a riding model. Anisotropic thermal parameters were used for all
non-hydrogen atoms and fixed isotropic parameters were used for
7] General reviews, see: a) O. Delacroix, J. A. Gladysz, Chem.
Commun. 2003, 665–675; b) A. Salzer, Coord. Chem. Rev. 2003,
2
42, 59–72.
[
8] a) A. F. Littke, C. Dai, G. C. Fu, J. Am. Chem. Soc. 2000, 122,
4
1
020–4028; b) G. Mann, J. F. Hartwig, J. Am. Chem. Soc. 1996,
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Planas, J. A. Gladysz, Inorg. Chem. 2002, 41, 6947–6949; e) Q.-
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[
15]
[9] a) F.-E. Hong, Y.-J. Ho, Y.-C. Chang, Y.-C. Lai, Tetrahedron
2
004, 60, 2639–2645; b) F.-E. Hong, Y.-C. Chang, C.-P. Chang,
[
16]
H atoms. The crystallographic data of 2, 4 and 5 are summarised
Y.-L. Huang, Dalton Trans. 2004, 157–165; c) F.-E. Hong, Y.-
C. Lai, Y.-J. Ho, Y.-C. Chang, J. Organomet. Chem. 2003, 688,
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1
61–167; d) F.-E. Hong, C.-P. Chang, Y.-C. Chang, Dalton
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Chang, S.-C. Chen, B.-T. Ko, Organometallics 2002, 21, 961–
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-261778 and -261779 for compounds 2, 4 and 5, respectively, contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgments
1
[
13] D. Zim, S. L. Buchwald, Org. Lett. 2003, 5, 2413–2415.
We are grateful to the National Science Council of the R. O. C.
[14] R. B. Bedford, C. S. J. Cazin, Chem. Commun. 2001, 1540–
(Grant NSC 93-2113-M-005-020) for financially supporting.
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[
15] G. M. Sheldrick, SHELXTL PLUS User’s Manual. Revision
.1 Nicolet XRD Corporation, Madison, Wisconsin, USA,
1991.
4
[
[
1] M. Josugi, M. Kameyama, T. Migita, Chem. Lett. 1983, 927–
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9
[16] The hydrogen atoms were allowed to ride on carbon atoms or
oxygen atoms in their idealised positions and were held fixed
with C–H distances of 0.96 Å.
2] a) A. S. Guram, R. A. Rennels, S. L. Buchwald, Angew. Chem.
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Received: April 14, 2005
Published Online: November 2, 2005
[
3] J. Louie, J. F. Hartwig, Tetrahedron Lett. 1995, 36, 3609–3612.
Eur. J. Inorg. Chem. 2005, 5011–5017
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5017