Iminophosphinite pincer palladium complexes: Synthesis and application

Article abstract of DOI:10.1016/j.ica.2009.12.031

Iminophosphinite pincer palladium complexes were synthesized and evaluated as potential catalysts in the Suzuki coupling reactions of phenylboronic acid and various aryl halides. The iminophosphinite ligands were synthesized through condensation reactions

Full text of DOI:10.1016/j.ica.2009.12.031

Inorganica Chimica Acta 363 (2010) 961–966
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Iminophosphinite pincer palladium complexes: Synthesis and application
Jake Yorke a, Jessica Sanford a, Andreas Decken b, Aibing Xia a,
*
a Department of Chemistry, Mount Saint Vincent University, Halifax, Nova Scotia, Canada B3M 2J6
b Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 October 2009
Received in revised form 7 December 2009
Accepted 11 December 2009
Available online 16 December 2009
Iminophosphinite pincer palladium complexes were synthesized and evaluated as potential catalysts in
the Suzuki coupling reactions of phenylboronic acid and various aryl halides. The iminophosphinite
ligands were synthesized through condensation reactions between 2-bromo-3-hydroxybenzaldehyde
and 2,4,6-trimethylaniline and 2,6-diisopropylaniline, followed by phosphorylation with chlorodiphenyl-
phosphine and chlorodicyclohexylphosphine. Oxidative addition of the pincer ligands to Pd2(dba)3 affor-
ded palladium iminophosphinite complexes [(2-(CH@NR)-6-(OPR02)C6H3)PdBr] (R = 2,6-iPr2C6H3, R0 = Ph
(2a) or Cy (2b); R = 2,4,6-Me3C6H2, R0 = Ph (2c) or Cy (2d)). Reaction of 2b and silver trifluoroacetate gave
the corresponding iminophosphinite palladium trifluoroacetate (3). The solid state structures of 2a, 2d,
and 3 were determined by X-ray single crystal diffraction studies.
Keywords:
Palladium complexes
Pincer types
Unsymmetrical ligands
Iminophosphinites
Cross-coupling reactions
The Suzuki reaction
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Results and discussion
Trident pincer-type transition metal complexes, which contain
a central aryl ring with two ortho-substituted donor groups, have
played an important role in organometallic synthesis and cataly-
sis since Shaw’s pioneering work [1]. Their steric and electronic
features can be modified at the donor sites as well as the metal
sites which may give rise to excellent stability and/or activity.
The chemistry of the pincer complexes has been extensively re-
viewed recently [2–7]. Among the pincer ligands symmetrical
pincer types (Fig. 1, A1 = A2 and/or E1 = E2), which contains two
identical donors at the two ortho-positions, are the most common
such as PCP and NCN types. However, the unsymmetrical (A1 – A2
and/or E1 – E2) type (e.g. PCN) pincer complexes have attracted
increasing attention due to their bonding versatility and catalytic
applications [8–16]. When the unsymmetrical ligands contain
both soft and hard donors, they may exhibit hemilabile properties
which could facilitate substrate interaction with the metal center
and stabilize the intermediate in the catalytic cycles [9,10,17–21].
Herein we wish to describe the synthesis, characterization and
catalytic application of novel PCN type iminophosphinite pincer
palladium complexes.
2.1. Synthesis
The synthetic routes for the palladium complexes were outlined
in Scheme 1. Regioselective bromination of 3-hydroxybenzalde-
hyde in acetic acid gave 2-bromo-3-hydroxybenzaldehyde [22].
Refluxing of 2-bromo-3-hydroxybenzaldehyde with 2,6-diisopro-
pylaniline or 2,4,6-trimethylaniline in ethanol afforded the desired
imines 1a or 1b as pale yellow solids. The imines reacted readily
with chlorodiphenylphosphine or chlorodicyclohexylphosphine at
room temperature in the presence of p-N,N-dimethylaminopyri-
dine (DMAP) in THF to afford the corresponding iminophosphinites.
As the crude iminophosphinites were often viscous oils and difficult
to handle, they were used directly without isolation to react with
tris(dibenzylideneacetone)dipalladium(0), Pd2(dba)3, to give the
novel palladium iminophosphinite pincer complexes 2a–2d in
quantitative yields. The formation of arylphosphinite complexes
2a and 2c required refluxing, whereas 2b and 2d could be obtained
at room temperature. While washing the crude products with 30%
ethyl acetate/hexane and subsequent recrystallization from
CH2Cl2/hexane gave crystals of pincer complexes 2a–2c, we found
that 2d co-crystallized with one equivalent of dba. This is likely
due to the solubility similarity of the two compounds in the sol-
vents. The approach to the pincer complex formation via aryl bro-
mide oxidative addition proved to be straightforward and
provided higher yields than the alternative approach using C–H
activation of non-halogenated aryl ligands [8,9,23]. The reaction
* Corresponding author.
E-mail address: aibing.xia@msvu.ca (A. Xia).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.12.031

962
J. Yorke et al. / Inorganica Chimica Acta 363 (2010) 961–966
of 2d with silver trifluoroacetate (AgTFA) in THF at room tempera-
ture afforded the palladium iminophosphinite trifluoroacetate
complex (3). The novel iminophosphinite PCN pincer complexes
were air and moisture stable, allowing the complexes to be recrys-
tallized with reagent grade solvents and handled in air. They are
also thermally stable and have fairly high melting points (e.g.
286 °C for 2b). The imines and palladium iminophosphinite com-
plexes were characterized by 1H NMR, 13C NMR, and 31P NMR
(where applicable) and infrared (IR) spectroscopy. The solid state
structures of iminophosphinite PCN pincer complex 2a, 2d, and 3
were determined through X-ray diffraction studies. The elemental
analysis results matched well with the expected values.
of the iminophosphinite complexes showed a red-shift of the imine
C@N stretches to 1584 cmꢀ1. In 2d.dba and 3, strong absorptions
were observed at 1680 and 1692 cmꢀ1 for the carbonyl groups of
dba and trifluoroacetate, respectively.
Suitable crystals of 2a, 2d, and 3 for X-ray analysis were grown
from saturated solutions of dichloromethane and hexane. In the
crystal structure of 2a there are two independent molecules per
asymmetric unit that differ in the orientation of the phenyl groups
of the PPh2 moiety. 2d and dba molecules were co-crystallized in
1:1 ratio. The molecular structures of complex 2a, 2d, and 3 are
shown in Figs. 2–4. Selected bond distances and angles are listed
in Table 1. Crystal data and structure refinement data are listed
in Table 2. The structures are similar and show strongly distorted
square–planar geometry around the palladium ion, which bonded
to the phosphinite P atom, the central C atom in the aryl ring, the
imine N atom, and the Br or O atom. The bond angles of P–Pd–N are
159.0°, suggesting significant strain in the core. The trifluoroace-
tate complex 3 has a C–Pd–O bond angle of 170.8° whereas the
C–Pd–Br bond angles of 176.2° and 179.3° in 2a and 2d are closer
to linearity. The bond lengths for Pd–C (1.94–1.96 Å), Pd–N (2.14–
2.17 Å), Pd–P (2.21–2.22 Å), and Pd–Br (2.48–2.50 Å), and Pd–O
(2.09 Å) are comparable to the reported values in related palladium
complexes [8–10,13,23–26].
2.2. Characterization
The 1H NMR spectra of imines 1a and 1b showed single reso-
nances at 8.45 and 8.55 ppm for the protons of the imine CH@N
groups and 5.86 and 5.89 ppm for the protons of O–H groups.
The IR spectra showed strong absorptions at 1620 and
1630 cmꢀ1, respectively for 1a and 1b, which are typical for the
C@N double bond. The 1H NMR spectra of the iminophosphinite
pincer complexes 2a–2d showed an upfield chemical shifts of the
imine group to 8.03–8.13 range, with newly acquired coupling to
phosphorus (JPH = 4.6 Hz). The methyl groups in the isopropyl moi-
eties in the complexes (2a, 2b, and 3) split to two signals, com-
pared to a single signal in the free imines 1. The 31P NMR signals
of the complexes are in the range of 157–200 ppm. The IR spectra
2.3. Catalytic studies
We evaluated the application of the palladium pincer complexes
in the Suzuki coupling reaction, one of the most important palla-
dium-catalyzed cross-coupling carbon–carbon bond forming reac-
tions in organic synthesis [27–32]. The results were listed in Table
3. For screening purposes, we chose 4-bromoanisole, a rather inert
aryl bromide, as the organic substrate and investigated a few com-
mon solvents and bases. The yields varied dramatically with differ-
ent solvents and bases, with the combination of Cs2CO3 and
dioxane affording the best yield when 2a is used (entry 5). Under
similar conditions, other palladium pincer complexes also gave
excellent yields (entries 6–9). In addition, excellent yields (entries
7 and 8) were obtained when the experiments were carried out in
air using 2c and 2d, suggesting the pincer complexes are rather ro-
bust in air. These results were comparable to the iminophosphinite
A1, A2 = CH2, NH, or O;
E1, E2 = PR2, NR2, or SR;
X = Cl, Br, or CO2CF3;
M = Pd, Ni, Ru, etc.
A1
E1
A2
E2
M
X
Fig. 1. Pincer complexes.
RNH2
R = 2,6-iPr2C6H3 (1a);
2,4,6-Me3C6H2 (1b)
Ethanol
HO
HO
O
Br
N
Br
R
1) PR'2Cl, DMAP
2) Pd2(dba)3
AgTFA
THF
O
O
THF
N
P
Pd
Br
P
Pd
O
N
R'
R'
R
R
R'
R'
O
R = 2,6-iPr2C6H3, R' = Ph (2a); R = 2,6-iPr2C6H3, R' = Cy (2b);
R = 2,4,6-Me3C6H2, R' = Ph (2c); R = 2,4,6-Me3C6H2, R' = Cy (2d);
R = 2,6-iPr2C6H3, R' = Cy (3);
F3C
Scheme 1. Synthesis of iminophosphinite pincer palladium complexes.

J. Yorke et al. / Inorganica Chimica Acta 363 (2010) 961–966
963
Fig. 2. Molecular structure of 2a with 50% probability ellipsoids.
Fig. 3. Molecular structure of 2d with 50% probability ellipsoids.
palladium chloride complexes Song reported very recently [8]. How-
ever, the palladium pincer complexes were not as effective towards
aryl chlorides. Only moderate yields were obtained when 40-chloro-
acetophenone was used (entries 11–12), while 4-chlorotoluene gave
low yields (entries 13, 14). In comparison, recently reported palla-
dium PCN complexes by Song coupled 4-chlorotoluene with moder-
ate yields [10], whereas Dupont’s palladium PCN complexes
effectively coupled both activated and deactivated aryl chlorides
[13]. The higher efficiency in the latter palladium PCN complexes
may be attributed to their hemilabile properties, as they contain
weakly bonded pyrazolyl or dialkylamino groups that may facilitate
substrate interaction with the metal center.
bust. They were found to be very active toward 4-bromoanisole
and moderately active toward aryl chlorides in the Suzuki coupling
reaction. The application of the palladium complexes in other cat-
alytic transformations is underway.
3. Experimental
3.1. General procedures
All manipulations were performed under an argon atmosphere
unless otherwise specified. All anhydrous solvents were purchased
from Sigma–Aldrich Canada Ltd. and stored over 4Å molecular
sieves prior to use. Diphenylchlorophosphine, dicyclohexylchloro-
phosphine, 3-hydroxybenzaldehyde, and 4-N,N-dimethylamino-
pyridine were purchased from Sigma–Aldrich Canada Ltd. and
used as received. 2-Bromo-3-hydroxybenzaldehyde was prepared
according to a literature procedure [22]. 1H, 13C, and 31P NMR spec-
tra were recorded on a Bruker AV-500 spectrometer and referenced
2.4. Conclusion
In summary, we have synthesized and characterized a series of
iminophosphinite pincer palladium complexes. The palladium
complexes were easy to make, stable in air, and also thermally ro-

964
J. Yorke et al. / Inorganica Chimica Acta 363 (2010) 961–966
Fig. 4. Molecular structure of 3 with 50% probability ellipsoids.
Table 1
Table 2
Selected bond lengths (Å) and angles (°) for 2a, 2d, and 3.
Crystal data and structure refinement for 2a, 2d, and 3.
Complexes
2a
2d
3
2a
2dꢁdba
741753
C45H51BrNO2PPd
855.15
3
Pd1–C13
Pd1–N1
Pd1–P1
Pd1–Br1
Pd1–O2
1.960(3)
2.156(2)
2.2099(7)
2.4807(4)
1.961(2)
1.9400(18)
2.1357(15)
2.2189(5)
CCDC Number 741752
741754
C33H43F3NO3PPd
696.05
2.1704(17)
2.2077(6)
2.5012(3)
Formula
Formula
weight
Crystal size
(mm3)
Space group
a (Å)
C31H31BrNOPPd
650.85
2.0930(14)
0.38 ꢂ 0.25 ꢂ 0.20 0.40 ꢂ 0.25 ꢂ 0.20 0.60 ꢂ 0.60 ꢂ 0.55
C13–Pd1–N1
C13–Pd1–P1
N1–Pd1–P1
P1–Pd1–Br1
P1–Pd1–O2
C13–Pd1–Br1
C13–Pd1–O2
N1–Pd1–Br1
N1–Pd1–O2
78.92(9)
79.76(8)
158.64(6)
103.80(2)
78.84(7)
79.91(6)
158.75(5)
100.192(16)
79.41(7)
80.09(6)
159.09(4)
ꢀ
P2(1)/n
19.936(2)
14.5068(16)
20.066(2)
90
106.873(1)
90
5553.3(10)
8
1.557
2.189
2624
1.27–27.50
P2(1)/c
12.8250(9)
16.3444(11)
16.7050(12)
90
110.031(1)
90
3289.8(4)
4
1.405
0.662
1440
1.69–27.50
P1
12.1361(16)
12.1462(16)
13.9274(18)
87.047(2)
89.314(2)
74.170(2)
1972.5(4)
2
1.440
1.562
880
1.46–27.50
b (Å)
c (Å)
108.20(4)
170.83(6)
92.54(6)
176.24(7)
97.55(6)
179.29(6)
101.06(5)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
l
(mmꢀ1
)
to SiMe4 and 85% H3PO4, respectively. Infrared spectra were col-
lected on a Nicolet Avatar 330 FT-IR spectrometer. Elemental anal-
yses were carried out by Guelph Chemical Laboratories in Guelph,
Ontario. Melting points were recorded on a Mel-Temp (Electro-
thermal) Apparatus and were uncorrected.
F(0 0 0)
h For data
collection
(°)
Number of
total
reflections
Number of
unique
37 987
12 447
13 611
8574
22 614
7383
3.2. Synthesis of imines
reflections
R (all data)
Rw (all data)
General procedure: 2-bromo-3-hydroxybenzaldehyde (4.02 g,
20.0 mmol) and 2,6-diisopropylaniline or 2,4,6-trimethylaniline
(20.0 mmol) were dissolved in 30 mL ethanol. Formic acid (6
drops) was added to the solution. The resultant yellow solution
was refluxed with stirring for 24 h. After being cooled to room tem-
perature, the reaction mixture was dried over anhydrous MgSO4
and filtered. The filtrate was concentrated to dryness under re-
duced pressure, affording pale yellow solids of 1a or 1b.
0.0303
0.0809
0.0277
0.0742
0.0282
0.0769
123.93, 120.93, 118.49, 113.76, 28.03, 23.54. IR (KBr, cmꢀ1):
3367(m), 2959(s), 2866(m),1630(s), 1568(s), 1460(s), 1364(m),
1287(s), 1182(m), 1030(m), 779(m), 752(m), 713(w).
m
2-Bromo-3-[(2,4,6-trimethylphenylimino)methyl]phenol
(1b):
2-Bromo-3-[(2,6-diisopropyl-phenylimino)methyl]phenol
(1a):
Yield: 4.762 g (75%). Mp 130–132 °C. Anal. Calc. for C16H16BrNO:
C, 60.39; H, 5.07; N, 4.40. Found: C, 59.86; H, 4.78; N, 4.23%. 1H
(CDCl3, 500.13 MHz, ppm): d 8.55 (s, 1H, CH@N), 7.82 (dd, J = 1.5,
7.7 Hz, 1H, Ar–H), 7.32 (t, J = 7.7 Hz, 1H, Ar–H), 7.14 (dd, J = 1.5,
7.7 Hz, 1H, Ar–H), 6.90 (s, 2H, Ar–H), 5.89 (s, 1H, OH), 2.29 (s, 3H,
m-Ar–CH3), 2.14 (s, 6H, o-Ar–CH3). 13C NVR (CDCl3, 125.77 MHz,
ppm) d 161.90, 152.68, 148.33, 135.21, 133.47, 128.83, 127.00,
Yield: 5.76 g (82%). Mp 133-135 °C. Anal. Calc. for C19H22BrNO: C,
63.34; H, 6.15; N, 3.89. Found: C, 63.21; H, 6.45; N, 3.75%. 1H
NMR (CDCl3, 500.13 MHz, ppm): d 8.45 (s, 1H, CH@N), 7.75 (dd,
1H, J = 1.7, 7.9 Hz, Ar–H), 7.36 (t, 1H, J = 7.9 Hz, Ar–H), 7.10 (m,
4H, Ar–H), 5.86 (s, 1H, OH), 2.90 (sept, J = 6.9 Hz, 2H, CH(CH3)2),
1.12 (d, J = 6.9 Hz, 12H, CH(CH3)2). 13C NVR (CDCl3, 125.77 MHz,
ppm) d 161.66, 152.66, 148.72, 137.57, 135.03, 128.86, 124.51,

J. Yorke et al. / Inorganica Chimica Acta 363 (2010) 961–966
965
Table 3
Suzuki reactions of selected halides.a
Pd complex
R
X
+
B(OH)2
R
Ph
Base
Solvent
Entry
X
R
Base
Solvent
Pd complex
Yieldb (%)
1
2
3
4
5
6
7
8
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
COCH3
COCH3
COCH3
CH3
K2CO3
K2CO3
K2CO3
K3PO4
Toluene
DMF
2a
2a
2a
2a
2a
2b
2c
45
11
53
79
97
90
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
99 (95)c
95 (90)c
82
58
58
56
22
2dꢁdba
9
3
10
11
12
13
14
2b
2dꢁdba
3
2b
2dꢁdba
CH3
29
a
b
c
Aryl halide (1.0 mmol), 1.5 mmol phenylboronic acid, 2.0 mmol base, 0.010 mmol Pd complex, 5 mL solvent, 100 °C, 18 h.
GC yields based on aryl halides.
Experiments carried out in air.
120.69, 118.39, 113.39, 20.88, 18.32. IR (KBr, cmꢀ1):
2774(w), 1637(m), 1567(s), 1462(s), 1359(m), 1235(w), 1202(m),
m
2949(m),
38.42, 38.16, 28.64, 27.61, 26.58, 25.81, 24.26, 23.23. 31P NMR
(CDCl3, 202.47 MHz, ppm) d 201.24. IR (KBr, cmꢀ1):
2959(m),
m
1027(m), 776(s).
2929(s), 2858(m), 1584(m), 1458(m), 1383(w), 1324(m), 1234(s),
1178(m), 1043(w), 875(m), 798(s), 749(m).
2c (R = 2,4,6-Me3C6H2, R0 = Ph): Yield: 0.389 g (64%). Mp: 210–
212 °C. Anal. Calc. for C28H25BrNOPPd: C, 55.24; H, 4.14; N, 2.30.
Found: C, 55.47; H, 4.23; N, 2.26%. 1H NMR (CDCl3, 500.13 MHz,
ppm): d 8.12 (d, JPH = 4.6 Hz, 1H, CH@N), 8.03 (m, 4H, Ar–H), 7.50
(m, 6H, Ar–H), 7.19 (d, J = 4.4 Hz, 2H, Ar–H), 7.07 (m, 1H, Ar–H),
6.93 (s, 2H, Ar–H), 2.31 (s, 3H, m-Ar–CH3), 2.30 (s, 6H, o-Ar–CH3).
13C NMR (CDCl3, 125.77 MHz, ppm) d 177.07, 162.18, 145.60,
144.71, 136.19, 133.32, 132.09, 131.97, 132.34, 129.56, 128.88,
128.78, 126.98, 122.82, 115.86, 21.02, 19.11. 31P NMR (CDCl3,
3.3. Synthesis of palladium pincer complexes, [2-(CH=NR)-6-
(OPR02)C6H3)PdBr]
General procedure: 1a or 1b (0.360 g, 1.00 mmol) and 4-N,N-
dimethylaminopyridine (0.122 g, 1.00 mmol) were dissolved in
THF (10 mL). To the solution was added diphenylchlorophosphine
or dicyclohexylchlorophosphine (1.00 mmol) in THF (5 mL). The
resultant mixture was stirred for 17 h and filtered. To the filtrate
was added Pd2(dba)3 (0.458 g, 0.50 mmol) in THF (10 mL). The
mixture was refluxed for 24 h and cooled to room temperature.
After filtration, the volatiles were removed under reduced pressure
to afford orange solids in quantitative yields, which were washed
with 30% ethyl acetate/hexane (3 ꢂ 10 mL) to remove dba and then
recrystallized from CH2Cl2/hexane.
202.47 MHz, ppm) d 157.40. IR (KBr, cmꢀ1):
m 3051(w), 2967(w),
2913(w), 1586(m), 1433(s), 1422(m), 1226(s), 1157(m), 1107(s),
866(s), 754(m), 698(s).
2d (R = 2,4,6-Me3C6H2, R0 = Cy): Recrystallization from CH2Cl2/
hexane gave yellow crystals which contained a 1:1 mixture of
the pincer complex and dba. Anal. Calc. for C45H51BrNO2PPd
(2dꢁdba): C, 63.20; H, 6.01; N, 1.64. Found: C, 63.04; H, 6.24; N,
1.64%. 1H NMR (CDCl3, 500.13 MHz, ppm): d 8.07 (d, JPH = 4.6 Hz,
1H, CH@N), 7.76 (d, J = 16.1 Hz, 2H, CH@CHCO of dba), 7.65 (m,
4H, Ar–H of dba), 7.43 (m, 6H, Ar–H of dba), 7.12–7.09 (m, 5H,
CH=CHCO of dba and Ar–H of 2d), 6.91 (s, 2H, Ar–H), 2.30 (s, 3H,
m-Ar–CH3), 1.28 (s, 6H, o-Ar–CH3), 2.10–1.31 (m, 22H, Cy). 31P
2a (R = 2,6-iPr2C6H3, R0 = Ph): Yield: 0.472 g (73%). Mp 225 °C
(dec). Anal. Calc. for C31H31BrNOPPd: C, 57.20; H, 4.80; N, 2.15.
Found: C, 57.34; H, 4.71; N, 1.99%. 1H NMR (CDCl3, 500.13 MHz,
ppm): d 8.13 (d, JPH = 5.2 Hz, 1H, CH@N), 8.06 (m, 4H, Ar–H), 7.50
(m, 6H, Ar-H), 7.25–7.19 (m, 5H, Ar–H), 7.08 (m, 1H, Ar–H), 3.24
(sept, J = 6.9 Hz, 2H, CH(CH3)2), 1.35 (d, J = 6.9 Hz, 6H,
CH(CH3)0(CH3)00), 1.17 (d, J = 6.9 Hz, 6H, CH(CH3)0(CH3)00). 13C NVR
NMR (CDCl3, 202.47 MHz, ppm) d 200.37. IR (KBr, cmꢀ1):
m
(CDCl3, 125.77 MHz, ppm)
d 176.35, 161.68, 156.79, 145.47,
3043(w), 2928(s), 1680(s), 1648 (w), 1608(s), 1574(m), 1481(m),
1446(s), 1367(m), 1228(m), 1143(m), 1069(m), 1069(m), 866(s),
773(s), 698(s).
144.44, 140.32, 133.17, 132.73, 132.18, 132.06, 128.88, 127.27,
126.99, 123.05, 115.62, 28.55, 24.27, 22.98. 31P NMR (CDCl3,
202.47 MHz, ppm) d 157.67. IR (KBr, cmꢀ1):
m 2959(m), 1585(m),
1437(m), 1233(s), 1177(w), 1107(s), 1024(w), 746(m), 693(m),
525(m).
3.4. Synthesis of palladium trifluoroacetate complex (3)
2b (R = 2,6-iPr2C6H3, R0 = Cy): Yield: 0.513 g (77%). Mp: 286–
287 °C. Anal. Calc. for C31H43BrNOPPd: C, 56.16; H, 6.54; N, 2.11.
Found: C, 5.74; H, 6.86; N, 2.12%. 1H NMR (CDCl3, 500.13 MHz,
ppm): d 8.09 (d, JPH = 4.6 Hz, 1H, CH@N), 7.22–6.92 (m, 6H, Ar–
H), 3.21 (sept, J = 6.9 Hz, 1H, CH(CH3)2), 2.25–1.60 (m, 20H, Cy),
1.35–1.25 (m, 8H, iPr and Cy), 1.17 (d, J = 6.9 Hz, 6H,
CH(CH3)0(CH3)00). 13C NMR (CDCl3, 125.77 MHz, ppm) d 175.57,
155.76, 145.98, 144.95, 140.32, 127.19, 126.68, 123.33, 122.56,
To a solution of 2b (0.133 g, 0.200 mmol) in THF (10 mL) was
added a solution of AgTFA (0.044 g, 0.20 mmol) in THF (5 mL).
The mixture was stirred at room temperature for 2 h and filtered
through a 2-cm bed of celite. The volatiles were removed under
vacuum to afford pale yellow solids. Yield: 0.220 g (79%). Mp:
194–196 °C. Anal. Calc. for C33H43F3NO3PPd: C, 56.94; H, 6.23; N,
2.01. Found: C, 56.99; H, 6.48; N, 1.99%. 1H NMR (CDCl3,

966
J. Yorke et al. / Inorganica Chimica Acta 363 (2010) 961–966
500.13 MHz, ppm): d 8.05 (d, JPH = 4.6 Hz, 1H, CH@N), 7.25–7.10
(m, 5H, Ar–H), 6.88 (d, J = 7.9 Hz, 1H, Ar–H), 3.19 (sept, J = 6.8 Hz,
2H, CH(CH3)2), 2.56–1.37 (m, 22H, Cy), 1.25 (d, J = 6.8 Hz, 6H,
CH(CH3)0(CH3)00), 1.18 (d, J = 6.8 Hz, 6H, CH(CH3)0(CH3)00). 31P NMR
Acknowledgements
We thank Natural Science and Engineering Research Council of
Canada (NSERC) and Canada Foundation for Innovation (CFI) for
financial support.
(CDCl3, 202.47 MHz, ppm) d 198.99. IR (KBr, cmꢀ1):
m 2959(m),
2928(s), 2851(m), 1692(s), 1595(m), 1460(m), 1423(m), 1324(w),
1236(m), 1199(s), 1027(w), 875(w), 799(m), 707(w).
References
[1] C.J. Moulton, B.L. Shaw, J. Chem. Soc., Dalton Trans. (1976) 1020.
[2] D. Morales-Morales, C.M. Jensen (Eds.), The Chemistry of Pincer Compounds,
Elsevier, Amsterdam, 2007.
3.5. X-ray structures
[3] D. Benito-Garagorri, K. Kirchner, Acc. Chem. Res. 41 (2008) 201.
[4] W. Leis, H.A. Mayer, W.C. Kaska, Coord. Chem. Rev. 252 (2008) 1787.
[5] D. Pugh, A.A. Danopoulos, Coord. Chem. Rev. 251 (2007) 610.
[6] J. Dupont, C.S. Consorti, J. Spencer, Chem. Rev. 105 (2005) 2527.
[7] M.Q. Slagt, D.A.P. van Zwieten, A.J.C.M. Moerkerk, R.J.M.K. Gebbink, G. van
Koten, Coord. Chem. Rev. 248 (2004) 2275.
[8] B. Zhang, C. Wang, J. Gong, M. Song, J. Organomet. Chem. 694 (2009) 2555.
[9] B. Ines, I. Moreno, R. SanMartin, E. Dominguez, J. Org. Chem. 73 (2008)
8448.
[10] J. Gong, Y. Zhang, M. Song, C. Xu, Organometallics 26 (2007) 6487.
[11] Y. Motoyama, K. Shimozono, H. Nishiyama, Inorg. Chim. Acta 359 (2006)
1725.
[12] F.S. Mancilha, B.A. Da Silveira Neto, A.S. Lopes, P.F. Moreira Jr., F.H. Quina, R.S.
Goncalves, J. Dupont, Eur. J. Org. Chem. (2006) 4924.
[13] G.R. Rosa, C.H. Rosa, F. Rominger, J. Dupont, A.L. Monteiro, Inorg. Chim. Acta
359 (2006) 1947.
[14] B.A. Da Silveira Neto, A. Sant’Ana Lopes, G. Ebeling, R.S. Goncalves, V.E.U. Costa,
F.H. Quina, J. Dupont, Tetrahedron 61 (2005) 10975.
[15] C.S. Consorti, G. Ebeling, F.R. Flores, F. Rominger, J. Dupont, Adv. Synth. Catal.
346 (2004) 617.
Crystals of 2a and 2d were grown by recrystallization method
using dichloromethane and hexanes at ꢀ10 °C. Complex 3 was
grown by slow evaporation of a dichloromethane/hexane solution
under argon. Single crystals were coated with Paratone-N oil,
mounted using a polyimide MicroMount and frozen in the cold
nitrogen stream of the goniometer. A hemisphere of data was col-
lected on a Bruker AXS P4/SMART 1000 diffractometer using
x and
h scans with a scan width of 0.3° and 10 s exposure times. The
detector distance was 5 cm. The data were reduced (SAINT) [33]
and corrected for absorption (SADABS) [34]. The structure was solved
by direct methods and refined by full-matrix least squares on F2
(SHELXTL) [35]. All non-hydrogen atoms were refined using aniso-
tropic displacement parameters. Hydrogen atoms were included
in calculated positions and refined using a riding model.
[16] G.R. Rosa, G. Ebeling, J. Dupont, A.L. Monteiro, Synthesis (2003) 2894.
[17] D. Vuzman, E. Poverenov, L.J.W. Shimon, Y. Diskin-Posner, D. Milstein,
Organometallics 27 (2008) 2627.
3.6. General procedures for the Suzuki reactions
[18] S.E. Angell, C.W. Rogers, Y. Zhang, M.O. Wolf, W.E. Jones, Coord. Chem. Rev. 250
(2006) 1829.
[19] E. Poverenov, M. Gandelman, L.J.W. Shimon, H. Rozenberg, Y. Ben-David, D.
Milstein, Organometallics 24 (2005) 1082.
[20] P. Braunstein, F. Naud, Angew. Chem., Int. Ed. 40 (2001) 680.
[21] C.S. Slone, D.A. Weinberger, C.A. Mirkin, Prog. Inorg. Chem. 48 (1999) 233.
[22] W.A.L. Van Otterlo, J.P. Michael, M.A. Fernandes, C.B. De Koning, Tetrahedron
Lett. 45 (2004) 5091.
[23] K. Takenaka, M. Minakawa, Y. Uozumi, J. Am. Chem. Soc. 127 (2005) 12273.
[24] M.C. Lipke, R.A. Woloszynek, L. Ma, J.D. Protasiewicz, Organometallics 28
(2009) 188.
A
20 mL reaction tube was charged with an aryl halide
(1.0 mmol), phenylboronic acid (1.5 mmol), palladium pincer com-
plex (0.01 mmol), and a base (2.0 mmol) in 5 mL of solvent under
argon and heated to 100 °C for 18 h. The mixture was then cooled
to room temperature. The volatiles were removed under a reduced
pressure. The organic product was extracted with ether and ana-
lyzed on an Agilent 6890 GC-FID instrument. The GC yields were
calculated based on unreacted aryl halides and calibrated relative
to standards containing authentic samples of aryl halides and their
biphenyl products.
[25] R. Johansson, M. Jarenmark, O.F. Wendt, Organometallics 24 (2005) 4500.
[26] R.B. Bedford, S.M. Draper, P. Noelle Scully, S.L. Welch, New J. Chem. 24 (2000)
745.
[27] S. Wuertz, F. Glorius, Acc. Chem. Res. 41 (2008) 1523.
[28] N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440.
[29] K.C. Nicolaou, P.G. Bulger, D. Sarlah, Angew. Chem., Int. Ed. 44 (2005) 4442.
[30] A. Suzuki, Chem. Commun. (2005) 4759.
Supplementary material
[31] R.B. Bedford, C.S.J. Cazin, D. Holder, Coord. Chem. Rev. 248 (2004) 2283.
[32] A.F. Littke, G.C. Fu, Angew. Chem., Int. Ed. 41 (2002) 4176.
[33] SAINT 7.23A, Bruker AXS, Inc., Madison, Wisconsin, USA, 2006.
[34] G. Sheldrick, SADABS 2004, Bruker AXS, Inc., Madison, Wisconsin, USA, 2004.
[35] G.M. Sheldrick, Crystallography A64 (2008) 112.
CCDC 741752, 741753 and 741754 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via http://www.ccdc.cam.ac.uk/data_request/cif.