Buchwald-Hartwig amination reaction using supported palladium on phosphine-functionalized magnetic nanoparticles

Article abstract of DOI:10.1007/s13738-015-0682-0

The supported palladium on phosphine-functionalized magnetic nanoparticles (Pd-PFMN) was found to be an efficient magnetically separable catalyst for the Buchwald-Hartwig amination reaction (BHAR) under solvent-free conditions. All of the reactions in the presence of Pd-PFMN catalyst afforded the corresponding products in good to excellent yields. The catalyst can be easily separated from the reaction mixture using an external magnetic field, and it can be reused at least five cycles without significant loss in its initial catalytic activity.

Full text of DOI:10.1007/s13738-015-0682-0

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0682-0
ORIGINAL PAPER
Buchwald–Hartwig amination reaction using supported
palladium on phosphine‑functionalized magnetic nanoparticles
Narges Zarnaghash1 · Farhad Panahi1 · Ali Khalafi‑Nezhad1
Received: 24 February 2015 / Accepted: 12 June 2015
© Iranian Chemical Society 2015
Abstract The supported palladium on phosphine-func-
tionalized magnetic nanoparticles (Pd-PFMN) was found
to be an efficient magnetically separable catalyst for the
Buchwald–Hartwig amination reaction (BHAR) under sol-
vent-free conditions. All of the reactions in the presence of
Pd-PFMN catalyst afforded the corresponding products in
good to excellent yields. The catalyst can be easily sepa-
rated from the reaction mixture using an external magnetic
field, and it can be reused at least five cycles without sig-
nificant loss in its initial catalytic activity.
9]. Since the discovery of the BHAR (1995) [10, 11], a
range of modifications for this reaction has been developed
to increase the reaction efficacy [12, 13]. A survey in this
field demonstrated that major advances have been obtained
on developing new and more effective phosphorus ligands.
The chemical structures of some of the used phosphorus
ligands in BHAR are shown in Fig. 1 [14–19]. It should
be mentioned that some of these ligands have been showed
high activity in BHAR.
Despite the high activity of phosphorus ligands in metal-
catalyzed organic reactions, they often suffer from some
disadvantages, such as intrinsic toxicity, foul-smell, easy
oxidization during reaction process, difficulty of extraction,
tedious purification process, and lack of recoverability [20,
21]. Stabilization of these ligands on a recyclable support
is one of the most important approaches to improve their
applicability in organic reactions [22–24]. However, sepa-
ration and recovery of these ligands on solid supports usu-
ally required filtration or centrifugation; therefore, the effi-
ciency of the recovered ligands can be somewhat reduced.
In the recent years, magnetic nanoparticles (MNPs) have
attracted much attention because of their easy preparation,
large surface area ratio, facile separation by use of mag-
netic force, and low toxicity and price [25].
Recently, in our research group, MNPs were function-
alized using chlorodiphenylphosphine (ClPPh2) and phos-
phine-functionalized magnetic nanoparticles (PFMN) as
a recyclable phosphorus ligand were obtained [22]. Also,
palladium (II) complex of PFMN ligand (Pd-PFMN) was
prepared and its catalytic activity evaluated in the Heck
reaction of chloroarenes. The results revealed that, this new
catalyst showed high catalytic activity in the Heck reaction
of chloroarenes [22]. This activity is attributed to the high
reactivity of Pd complex involving phosphorus ligands and
dispersible ability of MNPs in solution as a high surface
Keywords Buchwald–Hartwig amination reaction
(BHAR) · Palladium · Phosphine-functionalized magnetic
nanoparticles (PFMN) · Phosphorus ligands · Arylamines
Introduction
The Buchwald–Hartwig amination reaction (BHAR) is
generally involved in the coupling of aryl halides with
amines mediated by a suitable palladium catalyst to afford
arylamines [1–3]. Arylamines are very important structural
motif in organic synthesis due to their widespread applica-
tions in natural products, pharmaceuticals, agrochemicals,
and advanced materials [4–7]. There are many chemicals
and pharmaceutical intermediates with amine structural
units, which are synthesized using the BHAR in the pres-
ence of a palladium catalyst system, representing the syn-
thetic importance of this method in organic synthesis [8,
* Ali Khalafi-Nezhad
khalafi@chem.susc.ac.ir
1
Department of Chemistry, College of Sciences,
Shiraz University, 71454 Shiraz, Iran
1 3

J IRAN CHEM SOC
Fig. 1 The chemical structure
of some of the used phosphorus
ligands in Pd-catalyzed BHAR
area support. Also, the application of this magnetically
recyclable ligand was evaluated in Ru-catalyzed acceptor-
less dehydrogenative coupling reaction of primary alcohols
and 2-aminophenol for one-pot synthesis of benzoxazoles
[23].
In the current study, in continuation of our previous
work on heterogeneous palladium catalysts [22, 23, 26,
27], we would like to develop the synthetic practicality of
Pd-PFMN catalyst by synthesis of some arylamines, using
BHAR under heterogeneous and solvent-free conditions.
Experimental
General
Scheme 1 Synthetic route for the preparation of Pd-PFMN catalyst
The Pd-PFMN catalyst has been fully characterized using some dif-
ferent microscopic and spectroscopic techniques [22]. For easier
access a TEM, SEM image and XRD pattern of Pd-PFMN catalyst
are shown in Fig. 2
Chemicals were purchased from Merck to Aldrich chemi-
cal companies. All the chemicals and solvents were used
1 3

J IRAN CHEM SOC
Fig. 2 a A TEM image, b a
SEM image and c a XRD pat-
tern of Pd-PFMN catalyst
as received without purification. Magnetic nanoparticles
were prepared via the co-precipitation of Fe(III) and Fe(II)
ions in the presence of sodium hydroxide based on previ-
ous report [28]. Fe3O4@SiO2 nanoparticles were also pre-
pared based on the literature procedure [28]. Pd-PFMN
catalyst was prepared based on our previous report [22].
(0.06 g, 1.2 mol%) was stirred for 24 h. Afterward, the
mixture was cooled down to room temperature and the cat-
alyst was magnetically separated from the reaction mixture
and washed with diethyl ether (2 × 10 mL) followed by
deionized and oxygen-free water (2 × 10 mL). The reused
catalyst was dried for the next run. The aqueous phase was
extracted with diethyl ether (2 × 10 mL) and the combined
organic phases were dried over Na2SO4. The products were
purified by column chromatography (hexane/ethyl acetate)
to obtain the desired purity.
1
For recording H-NMR and 13C-NMR spectra we used a
Brucker (250 MHz) Avance DRX, and samples were dis-
solved in pure deuterated DMSO-d6 and CDCl3 solvents
with tetramethylsilane (TMS) as internal standard. Mass
spectra were recorded on a FINNIGAN-MAT 8430 mass
spectrometer operating at 70 eV. FT-IR spectroscopy (Shi-
madzu FT-IR 8300 spectrophotometer) was employed for
characterization of the compounds. Melting points were
determined in open capillary tubes in Barnstead Electro-
thermal 9100 BZ circulating oil melting point apparatus.
The reaction monitoring was accomplished by TLC on sil-
ica gel PolyGram SILG/UV254 plates.
4‑Phenylmorpholine (3a)
Yield: 94 %, 152 mg. 1H-NMR (250 MHz, CDCl3/TMS): δ
(ppm) = 3.13–3.16 (m, 4H), 3.83–3.87 (m, 4H), 6.85–6.92
(m, 3H), 7.24–7.29 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/
TMS): δ (ppm) = 49.5, 66.6, 116.2, 119.9, 129.5, 151.0.
Anal. Calcd. for C10H13NO (163.22): C, 73.59; H, 8.03; N,
8.58. Found: C, 73.52; H, 8.00; N, 8.51.
General procedure for BHAR catalyzed by the
Pd‑PFMN catalyst
4‑(4‑Nitrophenyl)morpholine (3b)
In a conical flask (10 mL) a mixture of aryl halide (1 mmol),
amine (3 mmol), K2CO3 (2 mmol), and Pd-PFMN catalyst
Yield: 95 %, 198 mg. 1H-NMR (250 MHz, CDCl3/TMS): δ
(ppm) = 3.28–3.32 (m, 4H), 3.77–3.81 (m, 4H), 6.71–6.77
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J IRAN CHEM SOC
Table 1 Studies of various conditions for the BHAR between bro-
Table 2 Optimization of catalyst loading for the synthesis of 4-phe-
mobenzene and morpholine using Pd-PFMN catalyst
nylmorpholine using Pd-PFMN catalyst
O
Br
O
O
Br
Pd-PFMN
(? mol%)
Pd-PFMN
(1 mol%)
O
+
N
2CO3 120 0C
+
N
K
,
solvent
base
temperature
N
H
2a
N
H
24h
3a
1a
3a
3 mmol
1 mmol
Entry
Solvent
Base
T (°C)
Yield (%)a
Entry
Pd-PFMN (mol%)
Yield (%)a
1
DMF
DMF
DMF
DMF
DMF
DMSO
DMSO
DMSO
DMSO
Toluene
Toluene
–
t-BuOK
t-BuOK
Cs2CO3
K2CO3
t-BuOK
t-BuOK
KOH
120
120
120
120
130
120
120
120
120
Reflux
Reflux
120
120
120
100
130
120
120
0b
1
2
3
4
1.0
1.2
1.5
0.8
94
96
96
89
2
87
3
75
4
71
5
89
Reaction conditions: bromobenzene (1 mmol), morpholine (3 mmol),
K2CO3 (2 mmol)
6
54
7
61
a
Isolated yield
8
K2CO3
Cs2CO3
t-BuOK
K2CO3
K2CO3
Cs2CO3
t-BuOK
K2CO3
K2CO3
K2CO3
K2CO3
58
9
61
10
11
12
13
14
15
16
17
18
35
4‑Morpholinobenzonitrile (3d)
33
94c
93c
92c
88c
96c
90d
95e
Yield: 91 %, 171 mg. 1H-NMR (250 MHz, CDCl3/TMS): δ
(ppm) = 3.25–3.29 (m, 4H), 3.82–3.86 (m, 4H), 6.82–6.88
(m, 2H), 7.47–7.53 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/
TMS): δ (ppm) = 47.2, 66.4, 100.9, 114.0, 119.8, 133.5,
152.9. Anal. Calcd. for C11H12 N2O (188.2): C,70.19;
H,6.43; N, 14.88. Found: C, 70.12; H, 6.38; N, 14.82.
–
–
–
–
–
–
4‑(4‑(Trifluoromethyl)phenyl)morpholine (3e)
Reaction conditions: bromobenzene (1 mmol), morpholine
(1.2 mmol), solvent (5 mL), base (2 mmol)
1
a
Yield: 92 %, 212 mg. H NMR (250 MHz, CDCl3): δ
Isolated yield
b
(ppm) = 3.22–3.25 (m, 4H), 3.85–3.88 (m, 4H), 8.92
(d, J = 3.5 Hz, 2H), 7.49–7.53 (m, 2H). 13C NMR
(75 MHz, CDCl3): δ (ppm) = 48.3, 66.8, 114.4, 120.59 (q,
J = 32.3 Hz), 123.0, 126.62 (q, J = 3.7 Hz), 153.5. Anal.
Calcd for C11H12F3NO (231.22): C, 57.14; H, 5.23; F,
24.65; N, 6.06. Found: C, 57.06; H, 5.17; N, 5.98.
No catalyst used
c
3 mmol of morpholine was used
d
2 mmol of morpholine was used
e
4 mmol of morpholine was used
(m, 2H), 8.01–8.07 (m, 2H). 13C-NMR (62.5 MHz, CDCl3/
TMS): δ (ppm) = 47.1, 66.3, 112.6, 125.8, 138.9, 155.0.
Anal. Calcd. for C10H12N2O3(208.2): C, 57.69; H, 5.81; N,
13.45. Found: C, 57.61; H, 5.76; N, 13.40.
4‑(p‑Tolyl)morpholine (3f)
Yield: 86 % 150 mg. 1H NMR (250 MHz, CDCl3): δ
(ppm) = 2.27 (s, 3H), 3.10–3.13 (m, 4H), 3.85–3.89 (m, 4H),
6.85 (d, J = 3.7 Hz, 2H), 7.07 (d, J = 4.0 Hz, 2H). 13C NMR
(62.5 MHz, CDCl3): δ (ppm) = 20.3, 49.6, 65.8, 116.0,
129.6, 129.7, 149.0. Anal. Calcd for C11H15NO (177.25): C,
74.54; H, 8.53; N, 7.90. Found: C, 74.45; H, 8.44; N, 7.79.
4‑(2,4‑Dinitrophenyl) morpholine (3c)
1
Yield: 98 %, 248 mg. H-NMR (250 MHz, CDCl3/TMS):
δ (ppm) = 3.18–3.21 (m, 4H), 3.78–3.82 (m, 4H), 7.04 (d,
J = 9.2 Hz, 1H), 8.22 (dd, J = 7.3, 2.4 Hz, 1H), 8.64 (d,
J = 2.0 Hz, 1H). 13C-NMR (62.5 MHz, CDCl3/TMS): δ
(ppm) = 50.8, 66.1, 119.1, 124.7, 128.3, 140.1, 149.7 (2C).
Anal. Calcd. for C10H11N3O5 (253.2): C, 47.43; H, 4.38; N,
16.60. Found: C, 47.37; H, 4.31; N, 16.57.
1‑Phenylpiperidine (3g)
1
Yield: 91 %, 146 mg. H NMR (250 MHz, CDCl3): δ
(ppm) = 1.58–1.81 (m, 6H), 3.17–3.19 (4H), 3.83–3.87
1 3

J IRAN CHEM SOC
Scheme 2 Products of BHAR between different aryl halides and amines using Pd-PFMN catalyst. Reaction conditions: aryl halide (1 mmol),
amine (3 mmol), K2CO3 (2 mmol). All yields are isolated yields
(m, 1H), 6.96–6.99 (m, 2H), 7.23–7.31 (m, 2H). 13C NMR
(62.5 MHz, CDCl3): δ (ppm) = 24.3, 25.9, 50.7, 116.6,
119.2, 128.9, 152.2. Anal. Calcd for C11H15N (161.25):
C, 81.94; H, 9.38; N, 8.69. Found: C, 81.85; H, 9.30; N,
8.61.
160.8.Anal.Calcd. for C12H14N2 (186.26): C, 77.38; H,
7.58; N, 15.04. Found: C, 77.31; H, 7.52; N, 14.96.
1‑Phenylpyrrolidine (3j)
1
Yield: 91 %, 133 mg. H NMR (250 MHz, CDCl3): δ
1‑(4‑Nitrophenyl) piperidin (3h)
(ppm) = 2.02–2.07 (m, 4H), 3.32–3.37 (m, 4H), 6.62–6.72
(m, 3H), 7.26–7.31 (m, 2H). 13C NMR (62.5 MHz, CDCl3):
δ (ppm) = 25.3, 47.5, 111.5, 115.2, 129.0, 147.8. Anal.
Calcd for C10H13N (147.22): C, 81.58; H, 8.90; N, 9.51.
Found: C, 81.48; H, 8.80; N, 9.42.
1
Yield: 93 %, 191 mg. H NMR (250 MHz, CDCl3): δ
(ppm) = 1.65–1.69 (m, 4H), 3.41–3.44 (m, 4H), 6.76–6.80
(m, 2H), 8.06–8.11 (m, 2H). 13C NMR (62.5 MHz, CDCl3):
δ (ppm) = 24.2, 25.1, 48.3, 112.1, 126.1, 137.2, 154.9.
Anal.Calcd. for C11H14N2O2 (206.24): C, 64.06; H, 6.84;
N, 13.5. Found: C, 63.99; H, 6.78; N, 13.42.
1‑(4‑Nitro‑phenyl)‑pyrrolidine (3k)
Yield: 93 %, 178 mg. 1H-NMR (250 MHz, CDCl3/TMS) δ
(ppm) = 2.04–2.10 (m, 4H), 3.37–3.42 (m, 4H), 6.46 (dd,
J = 9.32, 1.63 Hz, 2H), 8.11 (dd, J = 9.3, 1.7 Hz, 2H).
13C-NMR (62.5 MHz, CDCl3/TMS): δ (ppm) = 25.4,
47.9, 110.4, 126.3, 138.4, 139.4, 163.0. Anal. Calcd. for
C10H12N2O2 (192.21): C, 62.49; H, 6.29; N, 14.57. Found:
C, 62.41; H, 6.22; N, 14.23.
4‑(Piperidin‑1‑yl)benzonitrile (3i)
1
Yield: 93 %, 172 mg. H NMR (250 MHz, CDCl3): δ
(ppm) = 1.65 (m, 6H), 3.32 (m, 4H), 6.81–6.86 (m, 2H),
7.44–7.48 (m, 2H). 13C NMR (62.5 MHz, CDCl3): δ
(ppm) = 24.2, 25.2, 48.4, 101, 6, 107.9, 114.0, 133.5,
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J IRAN CHEM SOC
Table 3 Comparison of the results of the synthesis of 4-(p-tolyl)Morpholine using BHAR catalyzed by Pd-PFMN and other reported methods
O
O
Cl
N
+
N
H
H
3C
3f
H
3C
Entry Reaction conditions
Time (h) Yield (%)a TONb TOF (h−1 c
)
References
1
2
3
4
5
6
7
Pd-PFMN (1.2 mol% Pd), K2CO3, 120 °C
24
27
19
20
24
1
85
98
92
89
93
97
90
71
98
3.0
3.6
This work
[3]
Pd2(dba)3 (1 mol%), 2 (2 mol%), NaO-t-Bu, toluene, 70 °C
Pd2(dba)3 (0.1 mol%), 2 (2 mol%), NaO-t-Bu, toluene, 100 °C
Pd2(dba)3 (0.5 mol%), 10 (1 mol%), NaO-t-Bu, toluene, 100 °C
Pd(dba)2 (1 mol%), 7 (2 mol%), NaO-t-Bu, DME, 120 °C, under N2
Pd(OAc)2 (0.5 mol%), 12 (1 mol%), NaO-t-Bu, toluene, 80 °C
920
178
93
48.4
8.9
[3]
[14]
3.9
[19]
194
90
194
4.5
[30]
Pd(OAc)2 (1 mol%), Polymer-supported dialkylphosphinobiphenyl ligand
20
[31]
(1.3 mol%), NaO-t-Bu, toluene, 80 °C
8
Pd(OAc)2 (1 mol%), 1 (2 mol%), KOH, toluene, 90 °C
Pd(OAc)2 (1 mol%), 13 (1 mol%), NaO-t-Bu, toluene, 50 °C
Pd(dba)2 (0.5 mol%), 15 (1 mol%), NaO-t-Bu, toluene, 110 °C
PdCl2/3 (0.5 mol%), NaO-t-Bu, DME, 110 °C
20
2
97
89
97
90
97
89
4.8
44.5
9.7
[32]
[33]
[34]
[35]
10
11
12
20
48
194
180
3.7
a
Isolated Yield
b
c
TON = mol product/mol catalyst
TOF = TON/h
4‑(Pyrrolidin‑1‑yl) benzonitrile (3l)
XRD pattern correspond to SiO2, demonstrating the core–
shell structure of material. The peaks are indexed as the
(220), (311), (400), (422), (511), (440), and (533) planes
of the Fe3O4 nanoparticle [22]. The Pd-PFMN catalyst was
applied in the BHAR to evaluate the catalytic performance
in this process. To assess the catalytic reactivity of the Pd-
PFMN catalyst, the BHAR between bromobenzene (1a)
and morpholine (2a) was selected as simple model sub-
strate and optimization study is shown in Table 1.
1
Yield: 91 %, 156 mg. H-NMR (250 MHz, CDCl3/TMS)
δ (ppm) = 2.01–2.06 (m, 4H), 3.29–3.34 (m, 4H), 6.49
(dd, J = 6.9, 2.0 Hz, 2H), 7.43 (dd, J = 6.9, 2.1 Hz, 2H).
13C-NMR (62.5 MHz, CDCl3/TMS): δ (ppm) = 25.4, 47.5,
103.7, 111.4, 119.2, 132.9, 133.4, 147.1. Anal.Calcd. for
C11H12N2 (172.23): C, 76.71; H, 7.02; N, 16.27. Found: C,
76.65; H, 6.97; N, 16.21.
First, the model reaction was checked in the absence
of the catalyst in dimethylformamide (DMF) in the pres-
ence of potassium tert-butoxide (t-BuOK), and no product
was detected after 24 h (Table 1, entry 1). The Pd-PFMN
catalyst was used in DMF for the reaction between bro-
mobenzene and morpholine, as 4-phenylmorpholine (3a)
was obtained with 87 % isolated yield (Table 1, entry 2).
The reaction was also checked in the presence of carbon-
ate bases, but no significant difference in activity was
observed (Table 1, entries 3 and 4). When temperature
increased to 130 °C, compound 3a was obtained with 89 %
isolated yield (Table 1, entry 5). Also, in the DMSO sol-
vent, the reaction was not improved (Table 1, entries 6–9).
The reaction was checked in toluene, but less than 40 %
yield of product was obtained (Table 1, entries 10 and
11). A remarkable yield of product was obtained under
Results and discussion
The heterogeneous Pd-PFMN catalyst was prepared based
on our previous procedure in three-step process as shown in
Scheme 1 [22].
According to TEM image (Fig. 2a), the average diam-
eter of the catalyst particles based on the proposed proce-
dure is estimated to be about 10 nm. The SEM image of
Pd-PFMN catalyst (Fig. 2b), show that the catalyst particles
are regular in shape and possess near spherical morphology
with relatively good monodispersity. This image also estab-
lished the point that the Pd-PFMN were created with near
sphere-shaped morphology. According to the XRD patterns
of Pd-PFMN catalyst (Fig. 2c), the strongest peaks of the
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J IRAN CHEM SOC
Table 4 Reusability of Pd-PFMN catalyst in the BHAR
catalyst could be reused for at least five times without any
treatment (Table 4).
The ICP analysis of the catalyst after five cycles of reus-
ability showed that only a very small amount of the Pd
metal (about 1.8 % of Pd) was removed from the substrate.
The results confirmed that the supported Pd on the PFMN
substrate provides the high catalytic activity without leach-
ing of a significant quantity of Pd.
Conclusions
Entry
Yield of product (%)
Recovery of catalyst (%)
The catalytic activity of the supported palladium on phos-
phine-functionalized magnetic nanoparticles (Pd-PFMN) as
a magnetic recyclable palladium catalyst was investigated
in Buchwald–Hartwig amination reaction. This catalyst
system has some advantages with the respect to yield, sol-
vent, and wastes generated when compared to the currently
in use BHAR methods. Reusability (five times) and easy
workup (catalyst can be separated from reaction mixture
using an external magnetic field) were two other advan-
tages of this catalyst system. Using Pd-PFMN catalyst, a
range of arylamines was synthesized in good to excellent
yields.
1
2
3
4
5
94
93
91
90
88
>99
98
>97
97
96
Reaction conditions: bromobenzene (1 mmol), morpholine (3 mmol),
Pd-PFMN (1.2 mol%), K2CO3 (2 mmol) and 120 °C
solvent-free conditions (Table 1, entries 12–16). Thus,
solvent-free as the best condition was recognized for the
BHAR in the presence of Pd-PFMN catalyst. Afterwards,
the catalyst quantity was optimized and 1.2 mol% (0.06 g)
[22] of catalyst selected as optimum amount (Table 2).
Accordingly, the BHAR was properly carried out under
solvent-free condition in the presence of 1.2 mol% Pd-
PFMN catalyst.
It is noteworthy that the Pd-PFMN is a magnetic recy-
clable catalyst and can easily be separated from the reac-
tion mixture by simple external field attraction. In view
of the fact that the Pd-PFMN catalyst was an efficient and
reusable catalyst for the BHAR, its catalytic activity was
evaluated with other substrates (Scheme 2).
Acknowledgments The financial supports of research councils of
Shiraz University are gratefully acknowledged.
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halides proceeded smoothly to furnish the desired products
with good to excellent yields. The generality of this pro-
tocol was observed by the application of a wide range of
aryl halides under the same reaction conditions. The struc-
tural diversity of this reaction was investigated using dif-
ferent cyclic aliphatic amines, leading to the formation of
arylamines.
In order to demonstrate the applicability of Pd-PFMN
catalyst in BHAR, a comparison with some other reported
homogeneous and heterogeneous palladium catalysts is
presented in Table 3. As shown in Table 3, our catalyst sys-
tem is comparable with the reported homogeneous and het-
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