Novel phosphorus-coordinated palladium(II) complexes derived from 3,5-disubstituted-1H-1,2,4-diazaphospholes: Synthesis and catalytic application in Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.1016/j.ica.2017.02.020

Four novel phosphorus-coordinated palladium(II) complexes(I-IV) were easily prepared by the reaction of 3,5-disubstituted-1H-1,2,4-diazaphospholes with Pd(CH₃CN)₂Cl₂at room temperature and characterized. The catalytic activity of palladium(II) complexes was further evaluated in Suzuki-Miyaura reaction of aryl halides with arylboronic acids, giving the biphenyl derivatives in good yields.

Full text of DOI:10.1016/j.ica.2017.02.020

Accepted Manuscript
Research paper
Novel phosphorus-coordinated palladium(II) complexes derived from 3,5-dis-
ubstituted-1H-1,2,4-diazaphospholes: synthesis and catalytic application in Su-
zuki-Miyaura cross-coupling reactions
Xuefeng Jia, Fang Zhao
PII:
S0020-1693(16)30719-8
http://dx.doi.org/10.1016/j.ica.2017.02.020
ICA 17446
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
27 October 2016
16 February 2017
17 February 2017
Please cite this article as: X. Jia, F. Zhao, Novel phosphorus-coordinated palladium(II) complexes derived from 3,5-
disubstituted-1H-1,2,4-diazaphospholes: synthesis and catalytic application in Suzuki-Miyaura cross-coupling
reactions, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.02.020
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Inorganica Chimica Acta
journal homepage: www. elsevier. com/locate/ica
Novel phosphorus-coordinated palladium(II) complexes derived from 3,5-
disubstituted-1H-1,2,4-diazaphospholes: synthesis and catalytic application in
Suzuki-Miyaura cross-coupling reactions
∗
Xuefeng Jia, Fang Zhao
School of Chemical and Material Science, Shanxi Normal University, Linfen, 041004, China
ARTICLE INFO
ABSTRACT
Article history:
Four novel phosphorus-coordinated palladium(II) complexes(I-IV) were easily prepared by the
Received xx
reaction of 3,5-disubstituted-1H-1,2,4-diazaphospholes with Pd(CH
3
CN)
2
Cl
2
at room
Received in revised form xx
Accepted xx
Available online xx
temperature and characterized. The catalytic activity of palladium(II) complexes was further
evaluated in Suzuki-Miyaura reaction of aryl halides with arylboronic acids, giving the biphenyl
derivatives in good yields.
Keywords:
Palladium(II) complexes
2009 Elsevier Ltd. All rights reserved.
1
H-1,2,4-diazaphospholes
Suzuki-Miyaura cross-coupling
Aryl halides
Arylboronic acids
Suzuki-Miyaura reactions [9]. Subsequently, the palladium
1
. Intrduction
complexes with biaryl-like KITPHOS and dihydro-KITPHOS
P
monophosphines ligands were used for these coupling
Palladium-catalyzed Suzuki-Miyaura reactions are one of the
most versatile methods for the formation of C-C bonds in
synthetic organic chemistry [1]. Over the past decades, special
attention has been concentrated on synthesis of different
palladium complexes and their activity in Suzuki-Miyaura
coupling reactions. For example, N-heterocyclic carbene-
based palladium complexes have proved to be excellent
catalysts for C-C coupling reactions of organic halides with
arylboronic acids [2-3]. Various pincer-type palladium
complexes containing tridentate N-donor ligands have also
been synthesized and applied to this reaction [4-5]. Besides
that, many phosphine-based ligands were successfully used
for palladium-catalyzed Suzuki-Miyaura cross-coupling
reactions [6-8]. In 2010, Buchwald and co-worker reported
the synthesis of 2-aminobiphenyl-derived palladium
complexes with XPhos ligands and their application in
reactions by Doherty’s group [10]. In 2012, Fernández and
Lassaletta documented phosphino hydrazones as efficient
ligands in the palladium-catalyzed asymmetric Suzuki-
Miyaura reactions [11]. In addition, the air-stable
t
PdCl
2
{P Bu
2
(p-NMe
2
-Ph)}
2
complexes were also employed in
the cross-coupling reactions of aryl/heteroaryl chlorides with
arylboronic acids [12] or potassium
dioxolanylethyltrifluoroborate [13] as coupling partners.
Yamamoto’s group further developed the coupling reaction of
tetrabutylammonium 2-pyridyltriolborate salts with various
aryl/heteroaryl chlorides under PdCl
dicyclohexylphosphino)propane}
CuI/MeNHCH CH OH combined systems [14]. Very
2
dcpp {dcpp=1,3-bis
(
and
2
2
recently, Schoenebeck and co-worker achieved the air-stable
dinuclear iodine-bridged palladium(I) complex as the catalyst
for Suzuki-Miyaura cross-coupling reactions [15].
—
——
∗
Corresponding author. Tel.: +86-150-3435-8409; fax: +86-357-205-8711;
E-mail: jxfliu@163.com

2
Although significant progress has been achieved in this
field, the exploration of new palladium catalyst in
Suzuki-Miyaura Reactions remains highly desirable.
Herein, we report the synthesis and structural
characterization of several palladium complexes using
solvents. Complex
solvents such as CH
soluble in DMSO. Complex II is well soluble in CH
and complex III IV may dissolve in CH OH. However,
I
is insoluble in common organic
Cl , CHCl and CH CN, but slight
Cl
2
2
3
3
2
2
-
3
attempts to get single crystal of I-III at this stage were
not successful. Fortunately, the single crystal of IV was
obtained by slow evaporation of methanol solution at 4
°C and molecular structure was determined by X-ray
diffraction [18]. X-ray structural analysis displayed that
complex IV crystallized in monoclinic with P2(1)/c space
group. As shown in Fig. 1, the central Pd ions take a
precisely planar geometry with two phosphorus atoms
3,5-disubstituted-1H-1,2,4-diazaphospholes
{H[3,5-
R
2
dp] (R = H, -Pr, Ph, -Bu)} [16] as heteroatom-
i
t
containing monophosphine ligands and their catalytic
performance in Suzuki-Miyaura reactions of aryl halides
with arylboronic acids. To our knowledge, the use of a
heteroatom-substituted phosphine as ligands for
palladium-catalyzed Suzuki-Miyaura couplings is rarely
studied [17]. More importantly, our palladium complexes
are also air-stable and tunable catalyst, which may be
conveniently applied in organic synthesis.
from both H[3,5-
ligand of H[3,5-
coordination mode. The selected bond length(Å) and
angle(°) for IV were listed in Table The
t
-Bu
2
dp] and two chlorine atoms. The
t
-Bu dp] adopts monodentate
2
1.
2
. Results and discussion
Cl(1)−Pd(1)−P(1) angle is 90.28(5)° and the
Cl(1)−Pd(1)−P(1A) angle is 89.72(5)°. The bond angles
of both Cl(1)−Pd(1)−Cl(1A) and P(1A)-Pd(1)-P(1) are
2
.1. Synthesis and characterization of palladium
complexes( I-IV)
1
80.0°. These data demonstrate that Pd ions take a
precisely planar geometry. The distance of Pd−P bond
2.2987 Å) in IV is longer than those in palladium(II
complexes with novel bidentate phosphine ligand (Pd−P
.2308 Å) [8b] or Buchwald-Type secondary phosphine
As described in Scheme 1, phosphorus-coordinated
palladium(II) complexes I-IV were easily prepared by
(
)
the reaction of H[3,5-R
Pd(CH CN) Cl in anhydrous CH
temperature. These complexes were isolated as solid with
good yields (49% for ; 84% for II; 77% for III; 95% for
IV, respectively) and characterized by NMR, IR
2
dp] (R = H,
i
-Pr, Ph,
t-Bu) with
3
2
2
3
CN at room
2
oxide ligands (Pd−P 2.2595 or 2.2735 Å) [8c]. But the
Pd−Cl bond length (2.2877 Å) is shorter than the average
distance of these palladium(II) complexes (Pd−Cl 2.338
Å or 2.376 Å) [8b, 8c] and 3,5-di-tert-butyl-1H-pyrazole-
based palladium(II) complexes (Pd−Cl 2.3158 Å) [19].
I
3
1
spectroscopy, HRMS and elemental analysis. The
P
NMR spectroscopy of I-IV revealed that the chemical
shift of phosphorous atom had a slight changes in
comparison to those of H[3,5-R
Bu), which confirmed the formation of palladium(II)
complexes bearing heteroatom-containing
monophosphine ligands.
2
dp] (R = H, i-Pr, Ph, t-
R
Cl
R
Pd(CH CN) Cl
2
3
2
P
R
R
HN
N
N
NH
2
P
Pd
Cl
P
HN N
CH CN, RT
3
R
R
R = H (I) R = i-Pr (II)
R = Ph (III) R = t-Bu (IV)
Fig. 1 X-ray crystal structure of palladium complex IV
Scheme 1. Synthesis of palladium complexes I-IV
Table 1
Selected bond length(Å) and angle(°) for IV
To further identify the coordination mode of 1H-1, 2,
4
-diazaphosphole with palladium atom, we tried to
Pd(1)-P(1)
Pd(1)-Cl(1)
2.2987(11)
2.2877(16)
P(1)-Pd(1)-P(1A)
180.0
180.0
crystallize four palladium complexes in different
Cl(1)-Pd(1)-Cl(1A)

3
follows: Pd complex IV (8 mol%), Cs
2
CO
3
(2 equiv),
P(1)-C(2)
P(1)-C(1)
N(1)-C(1)
N(1)-N(2)
N(2)-C(2)
1.726(4)
1.728(4)
1.327(5)
1.350(6)
1.336(5)
Cl(1)-Pd(1)-P(1),
Cl(1)-Pd(1)-P(1A)
C(2)-P(1)-C(1)
90.28(5)
89.72(5)
and 1a
/
2a = 1:1.5 in DMF (1 mL) at 110°C for 24h.
91.4(2)
Table 2
Screening for optimal reaction conditions
a
C(2)-P(1)-Pd(1)
C(1)-P(1)-Pd(1)
134.92(16)
133.62(15)
Pd catalyst
H
3
COC
Br
+
B(OH)
2
H COC
3
base, solvent
1a
2a
3aa
2
.2. Catalytic activity of palladium complexes ( I-IV)
b
Yield
T
Once palladium complexes I-IV were synthesized and
characterized, we next investigate the catalytic activity of
these complexes in Suzuki-Miyaura cross-coupling
Entry Pd catalyst
Base
Solvent
o
(
C)
(%)
1
2
3
4
5
6
7
8
9
I
Cs
2
Cs
2
Cs
2
CO
3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
DMSO
DMF
DMF
DMF
110
110
110
110
110
110
110
110
160
160
110
110
71
51
54
99
82
62
34
65
54
71
92
44
II
CO
3
reaction. Initially, 4-bromoacetophenone
(1a
)
and
III
IV
IV
IV
IV
IV
IV
IV
IV
IV
CO
3
phenylboronic acid (2a) was chosen as model substrates
to screen reaction conditions and the results were
summaried in Table 2. When the reaction of 1a with 2a
Cs
2
CO
3
K
2
CO
KOH
Et
3
2 3
were carried out in DMF at 110°C using Cs CO as a
3
N
base in the presence of 8 mol% palladium complexes, we
found that palladium complexes I-IV exhibited different
catalytic activity and the desired product (3aa) were
obtained in moderate to good yields (Table 2, entries 1-
Cs
2
Cs
2
Cs
2
Cs
2
Cs
2
CO
CO
CO
CO
CO
3
3
1
0
3
c
1
1
3
4
). Among them, the activity of complex IV was greatly
superior to other complexes I-III, which indicated that
the substituted group (H, -Pr, Ph, -Bu) on 1H-1, 2, 4-
d
1
2
3
a
Reaction conditions: 1a (0.15 mmol), 2a (0.225 mmol, 1.5 equiv), Pd
catalyst (8 mol %), base (0.3 mmol, 2 equiv) in solvent (1.0 mL) at the
indicated temperature for 24h.
i
t
diazaphospholes had obvious effect on catalytic activity
of palladium complexes. Subsequently, the impact of the
base on this model reaction was investigated empolying
b
Isolated yield.
c
Palladium complex IV (5 mol%) was used.
d
Palladium complex IV (1 mol%) was used.
the complexe IV as palladium catalyst. When Cs
was replaced by other base such as K CO , KOH and
Et N, the yield of 3aa sharply reduced ranging from 99%,
2%, 62% to 34% (Table 2, entries 4-7). Thus Cs CO
3
2
CO
3
With an optimized catalyst system in hand, the
substrate scope for palladium-catalyzed Suzuki-Miyaura
coupling reaction was evaluated. As summarized in
Table 3, the reaction of several aryl bromide bearing
different groups with phenylboronic acid were firstly
carried out. The experiment results demonstrated that aryl
bromide with electron-withdrawing groups (4-acetyl, 4-
formyl) exhibited high reactivity than those containing
electron-donating groups (4-OMe, H) in this
transformation (Table 3, entries 1, 2 vs entries 3, 4).
Then a variety of arylboronic acids were employed as
substrate to react with 4-bromoacetophenone (1a).
2
3
3
8
2
was best choice to obtain high yields. When the reaction
was performed in DMSO at 110°C, 3aa was isolated in
65% yield (Table 2, entry 8). So DMF should be better
solvent. Then the effect of temperature on the reaction
was also surveyed. The yield of coupled product
obviously decreased after the reaction of 1a with 2a took
place in DMSO or DMF at 160°C for 24 hours (Table 2
,
entries 9 and 10). Finally, we performed this coupling
reaction at lower catalyst loading (5 mol% and 1 mol%),
affording the desired product (3aa) with 92% and 44%
yields respectively (Table 2, entries 11 and 12). As a
result, the optimal reaction conditions were established as
Substrates with methyl group (2b), tert-butyl group (2c
and methoxy group (2d) at the para-position gave the
corresponding products 3ab 3ae in 76–94% yields
Table entries 5-7). Ortho-methyl-substituted
arylboronic acid (2e) also furnished the desired product
)
-
(
3,

4
3
ae with 86% yield (Table 3, entry 8). The lower yields
6
1a (4-COCH3)
1a (4-COCH3)
1a (4-COCH3)
Br
Br
Br
Br
Br
Br
2c (4-t-Bu)
2d (4-OCH3)
2e (2-CH3)
2f (4-F)
3ac
3ad
3ae
3af
77
94
86
72
72
ND
of the products were obtained when substrates bearing
electron-withdrawing group (4-F, 3-Cl) at the para- or
meta-position were used (Table 3, entries 9-10).
However, meta-nitro-substituted phenylboronic acid
proved to be poor substrate under optimal conditions
7
8
9
1a (4-COCH
1a (4-COCH
1a (4-COCH
3
3
3
)
)
)
10
11
2g (3-Cl)
3ag
3ah
c
2h (3-NO
i(1-Naphthyl
boronic acid)
2
)
2
(
Table 3, entry 11). But to our delight, the reaction of 1-
naphthyl boronic acid (2i) with 4-bromoacetophenone
1a) led to the product 3ai in 55 % yield (Table 3, entry
2). These results revealed that arylboronic acid with
electron-donating substituents (4-OMe, 4- -Bu, 2-Me)
1
2
1a (4-COCH
3
)
Br
3ai
55
13
14
15
16
17
18
19
1b (4-CHO)
1b (4-CHO)
Br
Br
Br
Br
Cl
Cl
2d (4-OCH
3
)
3bd
3bg
3cd
3ce
3ea
3ec
82
95
78
91
51
56
(
2g (3-Cl)
1
1c (4-OCH
3
)
)
2d (4-OCH
3
)
t
1c (4-OCH
3
2e (2-CH
3
)
was favorable to this coupling reaction. Sequently, we
performed the Suzuki−Miyaura reaction of 4-
1e (4-COCH
3
3
)
)
2a (H)
1e (4-COCH
2c (4-t-Bu)
2d (4-OCH
methoxyphenylboronic
acid
(2d
)
with
4-
1e (4-COCH
3
3
)
)
Cl
Cl
3
)
3ed
3ee
71
48
bromobenzaldehye (1b) and 4-bromoanisole (1c) under
standard conditions, providing the product 3bd and 3cd
in good yields (82% for 3bd; 78% for 3cd, respectively)
20
1e (4-COCH
3
2e (2-CH )
a
Reaction conditions: aryl halides
1
(0.15 mmol), arylboronic acid
2
(
0.225 mmol, 1.5 equiv), Pd complex IV(8 mol %), Cs
2
CO (0.3
3
mmol, 2 equiv) in DMF (1.0 mL) at 110°C for 24h.
b
(
Table 3, entry 13 vs entry 15). Surprisely, the reaction
Isolated yield.
c
ND = not detected.
of 3-chlorophenylboronic acid (2g) with 1b afforded the
coupling product 3bg in 95% yield and 4-bromoanisole
3
. Experimental
(
1c) reacted with 2e to give 3ce in 91% yield (Table 3,
3
.1 General information
entry 14 vs entry 16). These data indicated that steric
hindrance of substituents on the aryl rings had obvious
influence on substrate reactivity to a certain extent.
Finally, the reactivity of aryl chloride was further
explored. The reaction of 4-chloroacetophenone (1e) with
All the reactions were performed under argon atmosphere
using standard vacuum line techniques. The solvents were
dried and distilled according to standard method. 3,5-
disubstituted-1H-1,2,4-diazaphospholes were synthesized
3 2 2
according to reported procedure [16c]. Pd(CH CN) Cl was
several arylboronic acid such as 2a, 2c, 2d, 2e proceeded
used immediately after preparation. Preparative thin layer
chromatography was carried out on GF-254 silica gel using
smoothly and offered the corresponding products in
moderate to good yield (Table 3, entries 17-20).
1
31
petroleum ether/ethyl acetate as the eluent. The H, P and
Table 3
1
3
C NMR spectra were obtained on 600 MHz spectrometers.
Palladium-catalyzed Suzuki-Miyaura coupling of aryl
The NMR data were reported as chemical shift (δ ppm) and
coupling constants (J) were recorded in hertz unit (Hz). C, H,
and N analyses were measured on an elemental analyzer.
Infrared (IR) spectra were recorded as KBr pellets on FT-IR
spectrometer. HRMS were measured on a TOF mass analyzer.
The X-ray diffraction data of complex IV were collected with
Oxford diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). The structures were solved by the
a
halides with different arylboronic acids
R
R'
Complex IV (8 mol%)
Cs CO , DMF, 110°C
R
R'
X
+
B(OH)2
2
3
1
2
3
b
Yield
Entry
1(R)
X
2(R’)
3
(
%)
1
2
3
4
5
1a (4-COCH
3
)
)
Br
Br
Br
Br
Br
2a (H)
2a (H)
2a (H)
2a (H)
2b (4-CH
3aa
3ba
3ca
3da
3ab
99
88
83
69
76
1b (4-CHO)
direct method and refined through full-matrix least-squares
1c (4-OCH
1d (H)
1a (4-COCH
3
)
2
techniques method on
F
using the SHELXL 2014
crystallographic software package[20].
3
3
)

5
1
3
3
.2 Syntheses
150 mg, 77%; m.p. 170-172℃; H NMR (600 MHz,
CD OD): δ 7.84 (d, J = 6.6 Hz, 5H), 7.44 (d, J = 7.2 Hz, 7H),
.41-7.37 (m, 5H), 7.31 (dd, J = 1.2, 7.2 Hz, 2H), 7.26 (t, J =
3
2 2 2
.2.1 Synthesis of Pd{H[3,5-H dp]} Cl (I)
7
6
1
In a 100ml Schlenk flask, PdCl
dissolved in 20 ml of anhydrous CH
refluxed for one hour to obtain the yellow solution of
Pd(CH CN) Cl . After cooling to room temperature, a
solution of 1H-1,2,4-diazaphospholes {H[3,5-H dp]} (95 mg,
.1 mmol) in anhydrous CH CN (10 mL) was added. A
2
(89 mg, 0.5 mmol) was
1
3
.6 Hz, 1H); C NMR (150 MHz, CD
3
OD): δ 129.1, 128.7,
3
CN and the mixture was
31
28.6, 126.1, 126.0; P NMR (242 MHz, DMSO-d ): δ 72.9.
6
IR (KBr): υ 3450, 3140, 2958, 2858, 1627, 1490, 1454, 1271,
3
2
2
-1
1
007, 752, 688 cm . HRMS (ESI): m/z calcd for
2
+
C
28
H
22Cl
2
N
4
P
2
PdNa: 674.9630 [M+Na] ; found 674.9635.
1
3
Anal. Calcd for C28
22 4 2 2
H N P PdCl : C, 51.44; H, 3.39; N, 8.57;
yellow-green precipitate appeared immediately and the
reaction mixture was stirred for 12 hours at room temperature.
found: C, 51.18; H, 3.52; N, 8.47.
3
2 2 2
.2.4 Synthesis of Pd{H[3, 5-tBu dp]} Cl (IV).
The resulting precipitate was filtered off, washed with CH
3
CN
As described for I, palladium complexe IV was prepared by
(
5 mL×3) and dried under vacuum. The product was afforded
1
13
the same procedure with PdCl (67 mg, 0.38 mmol) and 3,5-
2
as yellow-green solid. No H and C NMR data are available
2
di-tert-butyl-1H-1,2,4-diazaphospholes {H[3,5-tBu dp]} (150
due to the low solubility of complex I in common organic
3
1
mg, 0.76 mmol). The product was afforded as orange-yellow
solid. Suitable single crystal for X-ray diffraction was
obtained by the slow evaporation of the methanol solution of
solvents, but P NMR data was obtained. Yield: 85 mg, 49%;
31
m.p. 208-210℃; P NMR (242 MHz, DMSO-d
6
): δ 82.1. IR
-
1
(
KBr): υ 3453, 3167, 3095, 2941, 1631, 1179, 1048, 655 cm .
1
IV at 4 °C. Yield: 207 mg, 95%; m.p. 177-179℃; H NMR
HRMS (ESI): m/z calcd for
C H
4 6
Cl
2
N
4
P
2
PdNa: 370.8378
PdCl : C,
1
3
+
3
(600 MHz, CD OD): δ 1.59 (s, 18H), 1.38 (s, 18H); C NMR
[
M+Na] ; found 370.8382. Anal. Calcd for C
4
H
6
N
4
P
2
2
31
(
150 MHz, CD
3 3
OD): δ 30.71; P NMR (242 MHz, CD OD):
1
3.75; H, 1.73; N, 16.04; found: C, 14.03; H, 1.68; N, 15.96.
.2.2 Synthesis of Pd{H[3,5-iPr dp]} Cl (II)
δ 64.0. IR (KBr): υ 3429, 3177, 2958, 2866, 1627, 1472,
3
2
2
2
-1
1
363, 1253, 1099, 1016, 807 cm . HRMS (ESI): m/z calcd
As described for I, palladium complexe II was prepared by
the same procedure with PdCl (53 mg, 0.3 mmol) and 3,5-di-
iso-propyl-1H-1,2,4-diazaphospholes {H[3,5-iPr dp]} (102
+
for
C
20
H
38Cl
2
N
4
P
2
PdNa: 595.0882 [M+Na] ; found
2
5
6
95.0885. Anal. Calcd for C20
38 4 2 2
H N P PdCl : C, 41.86; H,
2
.67; N, 9.76; found: C, 41.72; H, 6.54; N, 9.95.
mg, 0.6 mmol). The product was afforded as pale-yellow solid.
1
Yield: 130 mg, 84%; m.p. 180-182℃; H NMR (600 MHz,
3.3 General procedure for palladium-catalyzed Suzuki-
Miyaura coupling reactions
2 2
CD Cl ): δ 12.87 (s, 2H, NH), 4.58-4.53 (m, 2H), 2.95-2.89
(
m, 2H), 1.55 (d, J = 7.2 Hz, 12H), 0.93 (d, J = 6.6 Hz, 12H);
A 25 mL Schlenk tube was charged with aryl halides
0.15 mmol), arylboronic acids (0.225 mmol, 1.5
equiv), Cs CO (0.3 mmol, 2 equiv), Pd catalyst (8
1
1
3
2 2
C NMR (150 MHz, CD Cl ): δ 33.87, 33.77, 29.55, 29.46,
(
2
31
2
7
1
5.05, 24.99, 24.33, 24.28; P NMR (242 MHz, CD
2 2
Cl ): δ
2
3
8.0. IR (KBr): υ 3441, 3122, 2967, 2930, 2866, 1627, 1463,
mol%) and DMF (1.0 mL). Then the tube was sealed and
heated to 110°C in oil bath. After stirring for 24h, the
reaction mixture was cooled and extracted with ethyl
acetate. The combined organic phase was concentrated
and purification of the residue by preparative thin layer
-1
390, 1043, 721 cm . HRMS (ESI): m/z
calcd for
+
C
16
H30Cl
2
N
4
P
2
PdNa: 539.0256 [M+Na] ; found 539.0252.
Anal. Calcd for C16
30 4 2 2
H N P PdCl : C, 37.12; H, 5.84; N, 10.82;
found: C, 37.45; H, 5.62; N, 11.05.
3
.2.3 Synthesis of Pd{H[3,5-Ph
2
dp]}
2
Cl
2
(III)
chromatography furnished the corresponding product 3.
As described for I, palladium complexe III was prepared by
the same procedure with PdCl (53 mg, 0.3 mmol) and 3,5-
diphenyl-1H-1,2,4-diazaphospholes {H[3,5-Ph dp]} (143 mg,
.6 mmol). The product was afforded as dark-red solid. Yield:
4. Conclusion
2
2
In summary, we have reported on synthesis,
characterization and catalytic studies of four novel
0

6
palladium(II) complexes(I-IV) ligated with phosphorus
atom of both 3,5-disubstituted-1H-1,2,4-diazaphospholes
heterocycles and two chlorine atoms. The crystal
structure of complex IV was confirmed by X-ray
diffraction. The palladium complexes IV proved to be
better catalyst for Suzuki-Miyaura cross-coupling
reactions, which could tolerate many functional groups
(d) S.C. Sau, S. Santra, T.K. Sen, S.K. Mandal, D. Koley,
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López-Mardomingo,
E.
Jesús,
Acknowledgements
This project is financially supported by Scientific and
Technological Innovation Programs of Higher Education
Institutions in Shanxi (STIP 2015157). Undergraduate
Training Programs for Innovation and Entrepreneurship
of Shanxi Province (2013156) and Teaching Reform
Project of Shanxi Normal University (SD2014JGKT-52)
are also acknowledged.
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8
Graphical
Abstract
Novel phosphorus-coordinated palladium(II)
complexes derived from 3,5-disubstituted-1H-
Leave this area blank for abstract info.
1
,2,4-diazaphospholes: synthesis and catalytic
application in Suzuki-Miyaura cross-coupling
reactions
Xuefeng Jia, * Fang Zhao
R'
Pd catalyst (8 mol%)
R
R'
X
+
B(OH)2
2 3
Cs CO , DMF, 110°C
20 examples
up to 99% yield
R = 4-Acetyl, 4-Formyl, 4-OMe
R' = 4-Me, 4-OMe, 4-t-Bu, 4-F, 3-Cl, 2-Me
tBu
tBu
Cl
Pd catalyst : HN
N
N
P
Pd
Cl
P
NH
tBu
tBu
Highlights of this manuscript are listed as
follows:
1
. Employing 3,5-disubstituted-1H-1,2,4-
diazaphospholes as heteroatom-
containing monophosphine ligands
. The formation of novel phosphorus-
coordinated palladium(II) complexes
. Good catalytic activity and wide
substrate scope
2
3