C-H bond activation of palladium complexes that feature pendant benzamidinate ligands and their catalytic behaviours

Article abstract of DOI:10.1002/ejic.201101125

The pendant benzamidines {Ph-C[=N-(2,6-di-iPr-C₆H ₃)](NH∧E)} [∧E = (CH₂)₂NMe₂, CH₂Py] and their palladium complexes [(Ph-C{=N∧E}{NH-(2,6-di- iPr-C₆H₃)})Pd(OAc)₂] [∧E = (CH ₂)₂NMe₂ (1), CH₂Py (2)] have been prepared. Upon heating, the corresponding palladacyclic complexes, [({η¹-C₆H₄}-C(=N∧E){NH-(2,6-di-iPr- C₆H₃)})PdOAc] [∧E = (CH₂) ₂NMe₂ (3), CH₂Py (4)], were obtained. Due to the substituent groups on the ortho positions of the phenyl ring attached to the nitrogen atom of the amidinate group, the C-H bond activation process was observed on the ortho position of the phenyl ring attached to the carbon atom of the amidinate group. This process can be proved by X-ray structural determination. The molecular structures are reported for compounds 1 and 4. Catalytic application of cyclopalladated derivatives 3 and 4 toward the Suzuki reaction was also investigated. Copyright

Full text of DOI:10.1002/ejic.201101125

FULL PAPER
DOI: 10.1002/ejic.201101125
C–H Bond Activation of Palladium Complexes That Feature Pendant
Benzamidinate Ligands and Their Catalytic Behaviours
Ming-Tsz Chen,[a] Kai-Min Wu,[a] and Chi-Tien Chen*[a]
Keywords: C–H Activation / Palladium / Chelates / Metalation / Benzamidinates
The pendant benzamidines {Ph–C[=N–(2,6-di-iPr-C6H3)]-
(NH E)} [ E = (CH2)2NMe2, CH2Py] and their palladium
the nitrogen atom of the amidinate group, the C–H bond acti-
∧
∧
vation process was observed on the ortho position of the
phenyl ring attached to the carbon atom of the amidinate
group. This process can be proved by X-ray structural deter-
mination. The molecular structures are reported for com-
pounds 1 and 4. Catalytic application of cyclopalladated de-
rivatives 3 and 4 toward the Suzuki reaction was also investi-
gated.
∧
complexes [(Ph–C{=N E}{NH–(2,6-di-iPr-C6H3)})Pd(OAc)2]
∧
[ E = (CH2)2NMe2 (1), CH2Py (2)] have been prepared. Upon
heating, the corresponding palladacyclic complexes, [({η1-
C6H4}–C(=N E){NH–(2,6-di-iPr-C6H3)})PdOAc] [ E = (CH2)2-
NMe2 (3), CH2Py (4)], were obtained. Due to the substituent
groups on the ortho positions of the phenyl ring attached to
∧
∧
Thus the isolation of precursors for the cyclometalation re-
action might be achieved. In this paper, we present benz-
amidinate ligand precursors with bulkier substituents to
study how the cyclometalation steps take place. The appli-
cation of palladacyclic complexes to a Suzuki reaction is
also examined.
Introduction
C–H bond activation is a well-known process by means
of oxidative addition or electrophilic substitution reactions
to afford cyclometalated complexes. Cyclometalated com-
plexes play important roles in modern organometallic
chemistry, such as organic synthesis, asymmetric synthesis
and photochemistry.[1,2] These processes predominantly fo-
cus on the second- and third-row transition metals with N-
donor ligands.[1,2] The mechanistic investigations of these
reactions have been studied with respect to ligand precur-
sors precoordinated to the metal centre followed by ar-
rangement of the ligand precursors to allow for C–H bond
activation.[3] Although cyclometalation reactions on palla-
dium(II) complexes have been thoroughly studied by a
number of research groups, not many of these processes are
known to result in isolation of the corresponding organo-
metallic complexes.[4–7]
Results and Discussion
Synthesis of Benzamidinates Ligand Precursors and Pd
Complexes
The desired N,NЈ-disubstituted benzamidines were pre-
pared according to a method similar to our previous re-
port.[8] Treatment of N-(2,6-diisopropylphenyl)benzimidoyl
chloride[9a] with the corresponding amines (1 molar equiv.)
in the presence of triethylamine affords benzamidines {Ph–
∧
∧
C[=N–(2,6-di-iPr-C6H3)](NH E)} ( E
= (CH2)2NMe2,
In our previous report,[8] we used molecular structures to
demonstrate that the cyclometalation reaction happened at
the ortho position of the phenyl ring attached to the nitro-
gen atom rather than at the ortho position of the phenyl
ring attached to the carbon atom of the amidine function.
A plausible mechanism for this process has been reported
by us. However, the palladium chelate complexes that could
be precursors for cyclometalation reactions cannot be iso-
lated easily due to the quick cyclometalation process. To
prove this plausible mechanism, the ortho-hydrogen atoms
of the phenyl ring attached to the nitrogen atom of the ami-
dine function were substituted with iPr groups to prevent
the ortho-metalation of the palladium chelate complex.
CH2Py) in moderate yield. N-(2,6-Diisopropylphenyl)-NЈ-
(2-dimethylaminoethyl)benzamidine has already been re-
ported.[9b,9c] N-(2,6-Diisopropylphenyl)-NЈ-(2-methylpyrid-
ine)benzamidine was characterized by NMR spectroscopy
as well as elemental analyses. Due to the tautomeric rota-
tion of amidine, complex and broad signals were found in
1
the H NMR spectrum. Therefore high-temperature NMR
spectroscopic data are reported in the Exp. Section for N-
(2,6-diisopropylphenyl)-NЈ-(2-methylpyridine)benzamidine.
Treatment of benzamidines with Pd(OAc)2 (1 molar equiv.)
in dichloromethane afforded palladium chelate complexes 1
or 2. The gradual formation of the corresponding cyclomet-
alated compound 3 was observed upon standing compound
1 in a solution of [D]chloroform at room temperature for a
couple of days with an upfield shift of the NH peak and
[a] Department of Chemistry, National Chung Hsing University,
Taichung 402, Taiwan, Republic of China
1
E-mail: ctchen@dragon.nchu.edu.tw
the loss of one –OAc peak in the H NMR spectrum. The
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C–H Bond Activation of Palladium Complexes
syntheses of palladacyclic complexes 3 and 4 were achieved
In each palladium chelate complex, one NH singlet
by heating 1 in toluene or 2 in THF at 80 °C. Complexes 3 around δ = 10 ppm (δ = 9.99 ppm for 1; 10.20 ppm for 2)
and 4 can also be prepared by an alternative route by means and two peaks that correspond to –OAc groups were found
1
of direct reactions of benzamidines with Pd(OAc)2 in tolu- in the H NMR spectrum. For each palladacyclic complex,
ene at 80 °C. Complexes 1–4 were characterized by NMR the NH singlet moved upfield (δ = 6.67 ppm for 3; 6.83 ppm
spectroscopy as well as elemental analyses. A summary of for 4) and only one peak that corresponded to the –OAc
the syntheses and proposed structures of palladium com- group appeared around δ = 2 ppm (δ = 2.11 ppm for 3;
1
plexes is shown in Scheme 1.
2.21 ppm for 4) in the H NMR spectra, which indicates
that the carbon metalation of the phenyl group might hap-
pen instead of NH deprotonation with the release of one
molar equivalent of HOAc, as shown in Figures 1 and 2.
Suitable crystals of 1 for X-ray refinement were grown
from a solution of dichloromethane/hexane. The molecular
structure is depicted in Figure 3. The bond angles [from
84.02(10) to 96.86(9)°] around the palladium metal centre
can be described as a slightly distorted square planar with
two cis-oriented nitrogen atoms from the benzamidinate li-
gand and two oxygen atoms from two –OAc groups. The
chelate ring of complex 1 is nearly coplanar with the torsion
angle O(1)–O(3)–N(3)–N(2) = 1.3°. The bond lengths of
Pd–Namine [2.042(3) Å] and Pd–Nimine [2.042(3) Å] are
within those [2.044(4)–2.0683(19) Å for Pd–Namine
;
1.991(2)–2.050(2) Å for Pd–Nimine] found in palladium
N,NЈ-chelate complexes.[7b] The bond lengths of Pd–OOAc
[2.021(2) and 2.032(2) Å] are close to those [1.983(4)–
2.029(2) Å] found in palladium acetate complexes.[7b,10f]
The C–N bond lengths of the NCN moiety are not equal
with 1.337(4) and 1.308(4) Å, respectively, thus indicating
Scheme 1. Preparation of palladium complexes 1–4.
1
Figure 1. H NMR spectra in CDCl3 for 1 (bottom) and 3 (top).
Eur. J. Inorg. Chem. 2012, 720–726
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M.-T. Chen, K.-M. Wu, C.-T. Chen
FULL PAPER
1
Figure 2. H NMR spectra in CDCl3 for 2 (bottom) and 4 (top).
the localized nature of the imine C=N and amine C–N alation (Scheme 2) to form a six-membered metallacycle
bonds and the 1,3-shift of a proton from the nitrogen atom and prove the existence of palladacyclic precursors in the
of the amine group to the nitrogen atom of the imine group previously proposed mechanism.[8]
on going from the free ligand to the mononuclear CNN
cyclopalladated compound. On the basis of the molecular
structure of 1, the ortho substituents actually prevent the
palladium chelate complexes from taking part in cyclomet-
Suitable crystals of 4 for X-ray refinement were grown
from concentrated chloroform solution. The molecular
structure is depicted in Figure 4. The bond angles [from
81.54(9) to 99.32(9)°] around the palladium metal centre
indicate a complex that has a slightly distorted square-
planar geometry, in which the palladium metal centre is co-
ordinated with one pyridine nitrogen atom, one imine nitro-
gen atom, one metalated carbon atom, and one acetate oxy-
gen atom to form two five-membered metallacycles. The
bond lengths of Pd–Npy [2.113(2) Å] and Pd–Cmetalated
[1.978(3) Å] are within those [1.964(3)–2.150(3) Å for Pd–
Npy; 1.961(4)–2.078(2) Å for Pd–Cmetalated] found in met-
alated palladacycles.[10,11] The bond length of Pd–OOAc
[2.0545(16) Å] are within those [2.036(2)–2.126(3) Å] found
in palladacycles.[8,10f,10g,11] The bond length of Pd–NC=N
[1.9606(19) Å] is close to those [1.981(3)–2.0321(18) Å]
found in palladacycles.[8,10f,10g,11] The C–N bond lengths of
the NCN moiety in 4 are not equal [1.304(3) Å for imine
C(1)=N(2) and 1.351(3) Å for amine C(1)–N(1)], thereby
indicating the localized nature of the imine C=N and amine
C–N bonds. On the basis of the molecular structure of 4,
the cyclometalation reaction happens on the ortho position
of the phenyl ring attached to the carbon atom of the NCN
part to form a five-membered metallacycle as mononuclear
palladium complex 4 rather than a dinuclear species.[7b] No
aliphatic C–H activation product was obtained in this sys-
tem.[6] Compared with the results reported previously,[8] for-
Figure 3. Molecular structure of 1. Selected bond lengths [Å] and
bond angles [°]: Pd–O(1) 2.032(2), Pd–O(3) 2.021(2), Pd–N(2)
2.042(2), Pd–N(3) 2.042(3), C(1)–N(2) 1.308(4), C(1)–N(1)
1.337(4), N(1)–C(8) 1.439(4); N(2)–Pd–O(1) 96.86(9), N(3)–Pd–
O(3) 92.99(11), N(2)–Pd–N(3) 84.14(11), O(3)–Pd–O(1) 84.02(10),
O(1)–Pd–N(3) 177.00(11), O(3)–Pd–N(2) 176.67(10). Hydrogen
atoms on carbon atoms omitted for clarity.
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C–H Bond Activation of Palladium Complexes
Scheme 2. Bulkier group on the ortho positions prevent the palladium chelate complexes from cyclometalation.
mation of six-membered metallacycle through an aromatic
C–H activation seems to be faster than that of a five-mem-
bered metallacycle. Once the ortho position of the phenyl
ring is blocked from forming a six-membered metallacycle,
an aromatic C–H activation might happen on the ortho po-
sition of the phenyl ring to form a five-membered metall-
acycle in this palladium pendant benzamidinate system.
Catalytic Studies for the Suzuki Reaction
With the aim of demonstrating the catalytic activities of
palladacycles that contain CNN-type ligands,[8,10f,10g,12]
complexes 3 and 4 were introduced into the Suzuki cou-
pling reaction.[13] To examine the catalytic activity, condi-
tions that employ the coupling of 4-bromoanisole with
phenylboronic acid (1.5 equiv.) catalyzed by 3 or 4 (1 mol-
%) in the presence of base (3 equiv.) at 60 °C within 2 h
were conducted. The optimum solvent/base mixture for the
reaction was found to be toluene/K3PO4 after several trials
with a combination of solvents (dimethylacetamide (DMA),
THF and toluene) and base (KF, K3PO4 and Cs2CO3). Se-
lected results are listed in Table 1. Poor conversion exhib-
Figure 4. Molecular structure of 4. Selected bond lengths [Å] and
bond angles [°]: Pd–C(3) 1.978(3), Pd–O(1) 2.0545(16), Pd–N(2)
1.9606(19), Pd–N(3) 2.113(2), C(1)–N(1) 1.351(3), C(1)–N(2)
1.304(3), C(8)–N(1) 1.442(3); N(2)–Pd–C(3) 81.54(9), N(2)–Pd–
N(3) 81.78(8), N(3)–Pd–O(1) 97.42(7), C(3)–Pd–O(1) 99.32(9),
C(3)–Pd–N(3) 163.24(9), N(2)–Pd–O(1) 172.10(8). Hydrogen atoms
on carbon atoms omitted for clarity.
Table 1. Suzuki coupling reaction catalyzed by palladium complexes (solvent: toluene).[a]
Entry
Catalyst
Aryl halide
Base
[Pd] [mol-%]
T [h]
Conversion [%][b]
Yield [%][c]
1[d]
2[d]
3[e]
4[e]
5[e]
6
7
8
9
10
11
12[e]
13[e]
3
4
3
4
4
3
3
3
3
3
4
5
6
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-chloroacetophone
4-chloroacetophone
4-chloroacetophone
4-chloroacetophone
4-bromoanisole
4-bromoanisole
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
KF
1
1
1
1
1
2
2
2
2
3
17
17
0.5
0.5
1
1
3
74
19
82
35
65
82
58
63
81
87
37
72
84
70
–
79
–
–
10–3
10–5
1
80
53
60
77
84
–
2
2
2
1
65
75
K3PO4
1
3
[a] Reaction conditions: aryl halide (1.0 mmol), phenylboronic acid (1.5 mmol), base (3 mmol), toluene (3 mL), 100 °C. [b] Determined
1
by H NMR spectroscopy. [c] Isolated yield (average of two experiments). [d] T = 60 °C. [e] T = 80 °C.
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M.-T. Chen, K.-M. Wu, C.-T. Chen
FULL PAPER
ited by 4 indicated that the catalytic activity of the complex tion for the formation of a six-membered palladacycle had
with pendant amine functionality is better than that with been blocked, the C–H activation process could take place
pendant pyridine functionality in this system (Table 1, en- on the other ortho position to form a five-membered
tries 1 and 2). A similar trend was observed by using less- palladacycle slowly. On the basis of those results demon-
reactive substrate 4-chloroacetophone with 2 mol-% palla- strated by palladium benzamidinate complexes, formation
dium loading within 1 h at 100 °C (entries 10 and 11). Bet- of the six-membered palladacycle seems to be faster than
ter conversion was observed by running reactions from 60 that of the five-membered palladacycle. Under optimized
to 80 °C (entries 1 and 3). Because of the better activity and conditions, 3 exhibits catalytic activity with lower catalyst
solubility of 3, lower catalyst concentrations were investi- loading (10–5 to 10–7) and with electronically deactivated
gated using catalyst/substrate ratios from 10–5 to 10–7 with aryl bromide in the Suzuki reaction. Complex 3 also
4-bromoanisole as substrate. The reactions gave conversion demonstrates catalytic activity with a less reactive aryl
of 82% within 17 h for the 10–5 ratio, and 58% within 17 h chloride-containing electron-withdrawing group.
for the 10–7 ratio at 100 °C (entries 6 and 7). Catalytic ac-
tivity of 3 was tested by using less-reactive 4-chloroaceto-
phenone as substrate with 1 mol-% palladium loading at
100 °C (entry 8). The reaction gave a conversion of 63%
within 0.5 h. Better conversions were found by increasing
Experimental Section
General: All manipulations were carried out under an atmosphere
of dinitrogen by using standard Schlenk line or drybox techniques.
the palladium loading (entry 9) or extending the reaction
Solvents were heated at reflux over the appropriate drying agent
time (entry 10). To compare the catalytic activity of
and distilled prior to use. Deuterated solvents were dried with mo-
lecular sieves.
palladacycles with similar coordination modes in our
previous report,[8] palladacycles 5 and 6 (as shown in
1H and 13C{1H} NMR spectra were recorded either with Varian
Scheme 3) were examined by the reaction of 4-bromo-
Mercury-400 (400 MHz) or Varian Inova-600 (600 MHz) spec-
anisole with phenylboronic acid catalyzed by 1 mol-%
trometers in [D]chloroform at ambient temperature unless stated
palladium loading under optimized conditions at 80 °C (en-
otherwise and referenced internally to the residual solvent peak and
reported as parts per million relative to tetramethylsilane. Elemen-
tries 3–5, 12 and 13). On the basis of these results, the cata-
lytic activity of the five-membered palladacycle that re-
tal analyses were performed with an Elementar Vario ELIV instru-
sulted from cyclometalation at the ortho position of the
phenyl ring attached to the carbon atom of the NCN amid-
ine function seems to be better than that with the six-mem-
bered metallacycle that results from cyclometalation at the
ortho position of the phenyl ring attached to the nitrogen
atom of the NCN amidine function for the palladacycles
with the NMe2 pendant functionality (entries 3 and 12).
However, a reverse trend was observed for palladium
benzamidine complexes with pendant pyridine functionality
(entries 5 and 13).
ment.
Pd(OAc)2 (Aldrich), 2,6-diisopropylaniline (Alfa), 2-(aminometh-
yl)pyridine (Acros) and N,N-dimethylethyleneamine (Acros) were
used as supplied. NEt3 was dried with CaH2 and distilled before
use. N-(2,6-Diisopropylphenyl)benzanilide and N-(2,6-diisopro-
pylphenyl)benzimidoyl chloride were prepared according to modi-
fied literature procedures.[9a]
Preparations
{Ph–C[=N–(2,6-di-iPr–C6H3)][NH(CH2)2NMe2]}: A solution of N-
(2,6-diisopropylphenyl)benzimidoyl chloride (0.9 g, 3 mmol) and
NEt3 (0.70 mL, 4.6 mmol) in toluene (15 mL) was treated with
N,N-dimethylethyleneamine (0.35 mL, 3.4 mmol) at 0 °C then al-
lowed to warm to room temperature. After 24 h of stirring, the
volatile compounds were removed under reduced pressure and the
residue was extracted with hexane (50 mL). The extract was
pumped to dryness to afford a yellow oily product; yield 0.65 g,
62%. This compound has been reported in the literature.[9b,9c]
Scheme 3. The palladacycles bearing the benzamidinate ligand pre-
cursor.[8]
{Ph–C[=N–(2,6-di-iPr–C6H3)](NHCH2Py)}: The preparation of
{Ph–C[=N–(2,6-di-iPr–C6H3)](NHCH2Py)} was similar to that
used for {Ph–C[=N–(2,6-di-iPr–C6H3)][NH(CH2)2NMe2]} but with
N-(2,6-diisoproyplphenyl)benzimidoyl chloride (1.5 g, 5 mmol),
NEt3 (0.84 mL, 6 mmol) and 2-(aminomethyl)pyridine (0.52 mL,
5 mmol). The volatile compounds were removed under reduced
pressure and the residue was extracted with toluene (50 mL). The
extract was pumped to dryness to afford an orange solid; yield
Conclusion
One new benzamidinate ligand precursor and four palla-
dium complexes were prepared and fully characterized. The
catalytic activity of two palladacycles for the Suzuki reac-
tion has been demonstrated. On the basis of the molecular
structures of palladium chelates and palladacyclic com-
plexes, thet formation of six-membered palladacycles actu-
ally proceeds through a palladium chelate complex as an
intermediate followed by a C–H activation process, which
1
1.62 g, 87.4%. H NMR (600 MHz, 333 K): δ = 0.97 [s, 6 H, iPr–
(CH3)2], 1.10 [s, 6 H, iPr–(CH3)2], 3.03 (s, 2 H, iPr–H), 4.64 (s, 2
H, CH2Py), 5.64 (s, 1 H, NH), 6.91 (s, 1 H), 6.97 (s, 2 H), 7.13 (m,
1 H), 7.26 (br., 4 H), 7.38 (br., 2 H), 7.60 (t, J = 7.2 Hz, 1 H), 8.51
(s, 1 H) ppm. 13C{1H} NMR (150 MHz, 333 K): δ = 22.6 (s, CH3–
iPr), 23.7 (s, CH3–iPr), 28.2 (s, CH–iPr), 47.9 (s, CH–Py), 122.0,
122.3, 122.8, 127.9, 128.2, 129.2, 136.3, 149.2 (CH–Ph and CH–
was proposed in our previous report. Once the ortho posi- Py), 135.7, 138.7, 145.1, 154.4, 158.3 (Cipso–C6H5, Cipso–Py and one
724 Eur. J. Inorg. Chem. 2012, 720–726
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C–H Bond Activation of Palladium Complexes
CNN) ppm. C25H29N3 (371.52): calcd. C 80.82, H 7.87, N 11.31;
found C 80.74, H 7.53, N 11.27.
δ = 1.14 [d, J = 6.6 Hz, 6 H, CH–(CH3)2], 1.26 [d, J = 6.6 Hz, 6
H, CH–(CH3)2], 2.21 [s, 3 H, O–C(=O)CH3], 3.25 [sept, J = 6.6 Hz,
2 H, CH–(CH3)2], 4.52 (br., 2 H, CH2Py), 6.83 (s, 1 H, NH), 6.87
(br., 1 H, CH–Ar), 7.12 (br., 1 H, CH–Ar), 7.17 (m, 2 H, CH–Ar),
7.24 (m, 3 H, CH–Ar), 7.42 (t, J = 7.8 Hz, 1 H, CH–Ar), 7.59 (t,
J = 7.2 Hz, 1 H, CH–Ar), 8.35 (d, J = 5.4 Hz, 1 H, CH–Ar) ppm.
13C{1H} NMR (150 MHz): δ = 22.9 [br., CH–(CH3)2], 24.1 [br.,
CH–(CH3)2], 24.4 [s, O–C(=O)CH3], 28.6 [s, CH–(CH3)2], 55.7 (s,
CH2–Py), 120.9, 122.7, 123.2, 123.9, 124.4, 129.5, 130.7, 133.7,
137.8, 149.0 (CH–Ar), 132.0, 145.1, 147.0, 148.8, 152.9, 162.0 [three
Cipso–Ar, one metalated C–Ph, one C–CH–(CH3)2 and one NCN],
177.8 [s, O–C(=O)CH3] ppm. C27H39N3O4Pd (576.02): calcd. C
60.50, H 5.83, N 7.84; found C 60.55, H 6.19, N 7.37.
Complex 1: CH2Cl2 (15 mL) was added at room temperature to a
flask that contained {Ph–C[=N–(2,6-di-iPr–C6H3)][NH(CH2)2-
NMe2]} (0.35 g, 1 mmol) and Pd(OAc)2(0.22 g, 1 mmol). After 1 h
of stirring, the volatile compounds were removed under reduced
pressure to afford a brown solid. The resulting solid was purified
by THF/hexane solution to afford a pale yellow solid; yield 0.44 g,
76%. 1H NMR (600 MHz): δ = 1.12 [d, J = 6.6 Hz, 6 H, CH–
(CH3)2], 1.18 [d, J = 6.6 Hz, 6 H, CH–(CH3)2], 1.82 [s, 3 H, O–
C(=O)CH3], 1.99 [s, 3 H, O–C(=O)CH3], 2.34 (t, J = 6.0 Hz, 2 H,
CH2), 2.71 [s, 6 H, N(CH3)2], 3.07 (t, J = 6.0 Hz, 2 H, CH2), 3.24
[sept, J = 6.6 Hz, 2 H, CH–(CH3)2], 6.91 (d, J = 7.8 Hz, 2 H, CH–
Ar), 6.94 (m, 2 H, CH–Ar), 7.07 (t, J = 7.2 Hz, 1 H, CH–Ar), 7.19–
7.26 (m, 3 H, CH–Ar), 9.99 (s, 1 H, NH) ppm. 13C{1H} NMR
(150 MHz): δ = 21.7 [s, CH–(CH3)2], 23.5 [s, O–C(=O)CH3], 23.6
[s, O–C(=O)CH3], 25.6 [s, CH–(CH3)2], 28.6 [s, CH–(CH3)2], 50.7
[s, N(CH3)2], 53.0 (s, CH2), 65.8 (s, CH2), 123.0, 127.0, 128.3, 128.4,
130.1 (CH–Ar), 129.9, 131.8, 146.6, 168.6 [two Cipso–Ar, one CNN
and one C–CH–(CH3)2], 178.1 [s, O–C(=O)CH3] ppm.
C27H39N3O4Pd (576.02): calcd. C 56.30, H 6.82, N 7.29; found C
56.36, H 6.71, N 7.25.
General Procedure for the Suzuki-Type Coupling Reaction: Pre-
scribed amounts of catalyst, aryl halide (1.0 equiv.), phenylboronic
acid (1.5 equiv.), base (3.0 equiv.) and a magnetic stir bar were
placed in a Schlenk tube under nitrogen. Toluene (3 mL) was added
by syringe, and the reaction mixture was heated in an oil bath at
the prescribed temperature for the prescribed time. After removal
of the volatile compounds, the residue was diluted with ethyl acet-
ate, then filtered through a pad of silica gel. A sample in [D]chloro-
form was taken for determination of conversion. The crude mate-
rial was further purified by flash chromatography on silica gel.
Complex 2: The procedure for preparation of 2 was similar to that
used for 1 but with {Ph–C(NHCH2Py)[=NH–(2,6-di-iPr–C6H3)]}
(0.37 g, 1 mmol) and Pd(OAc)2 (0.25 g, 1.1 mmol). A yellow solid
was obtained; yield 0.57 g, 96%. 1H NMR (600 MHz): δ = 1.10 [d,
J = 7.2 Hz, 6 H, CH–(CH3)2], 1.20 [d, J = 6.6 Hz, 6 H, CH–
(CH3)2], 1.91 [s, 3 H, O–C(=O)CH3], 2.09 [s, 3 H, O–C(=O)CH3],
3.25 [sept, J = 6.6 Hz, 2 H, CH–(CH3)2], 4.53 (s, 2 H, CH2Py), 6.93
(d, J = 7.8 Hz, 2 H, CH–Ar), 7.00 (m, 2 H, CH–Ar), 7.06–7.10
(overlap, 2 H, CH–Ar), 7.25–7.32 (overlap, 4 H, CH–Ar), 7.78 (m,
1 H, CH–Ar), 8.19 (d, J = 6 Hz, 1 H, CH–Ar), 10.20 (s, 1 H, NH)
ppm. 13C{1H} NMR (150 MHz): δ = 21.6 [s, CH–(CH3)2], 23.4 [s,
O–C(=O)CH3], 25.6 [s, CH–(CH3)2], 28.5 [s, CH–(CH3)2], 62.6 (s,
CH2Py), 119.6, 123.06, 123.12, 127.1, 128.46, 128.54, 130.4, 138.8,
148.9 (CH–Ar), 129.1, 131.5, 146.6, 162.1, 168.9 [three Cipso–Ar,
one NCN and one C–CH–(CH3)2], 178.2, 178.9 [O–C(=O)CH3]
ppm. C27H39N3O4Pd (576.02): calcd. C 58.44, H 5.92, N 7.05;
found C 58.59, H 5.49, N 6.99.
Crystal Structure Data: The crystals were grown from a solution of
1 in dichloromethane/hexane or a solution of 4 in concentrated
chloroform, then isolated by filtration. Suitable crystals of 1 were
sealed in thin-walled glass capillaries under a nitrogen atmosphere
at 293 K and mounted on a Bruker AXS SMART 1000 dif-
fractometer. A crystal of 4 was mounted onto a glass fibre by using
a perfluoropolyether oil “oil-drop” method and cooled rapidly in
a stream of cold nitrogen gas with an Oxford Cryosystems Cryos-
tream unit. Diffraction data were collected at 100 K with an Oxford
Gemini S diffractometer. The absorption correction was carried out
on the basis of symmetry-equivalent reflections by using SADABS
for 1, and semiempirical absorption correction was based on the
spherical harmonics implemented in the SCALE3 ABSPACK scal-
ing algorithm from Crysalis RED, Oxford Diffraction Ltd for 4.[14]
Table 2. Summary of crystal data for compounds 1 and 4.
Complex 3: A solution of 1 (0.58 g, 1 mmol) in toluene (15 mL)
was heated at 80 °C for 48 h. The volatile compounds were re-
moved under reduced pressure and the residue was purified by
THF/hexane solution to obtain a white precipitate. The crude prod-
uct was washed hexane (30 mL three times) to afford white solid;
1·CH2Cl2
4·CHCl3·H2O
Formula
Mr
C28H39Cl2N3O4Pd
658.92
C28H34Cl3N3O3Pd
673.33
T [K]
297(2)
100(2)
1
Crystal system
Space group
monoclinic
P21/n
monoclinic
P21/n
yield 0.46 g, 90%. H NMR (600 MHz): δ = 1.16 [d, J = 6.6 Hz, 6
H, CH–(CH3)2], 1.27 [d, J = 6.6 Hz, 6 H, CH–(CH3)2], 2.11 [s, 3
H, O–C(=O)CH3], 2.56 [overlap, 8 H, CH2 and N(CH3)2], 2.84 (br.,
2 H, CH2), 3.21 [sept, J = 6.6 Hz, 2 H, CH–(CH3)2], 6.67 (br., 1
H, NH), 6.80 (br., 1 H, CH–Ar), 6.96 (br., 1 H, CH–Ar), 7.12 (t,
J = 7.2 Hz, 1 H, CH–Ar), 7.20 (d, J = 7.8 Hz, 2 H, CH–Ar), 7.21
(t, J = 8.4 Hz, 1 H, CH–Ar), 7.38 (t, J = 7.8 Hz, 1 H, CH–Ar)
ppm. 13C{1H} NMR (150 MHz): δ = 22.6 [s, CH–(CH3)2], 24.15
[s, O–C(=O)CH3], 24.24 [s, CH–(CH3)2], 28.6 [s, CH–(CH3)2], 46.6
(s, CH2), 47.4 [s, N(CH3)2], 63.6 (s, CH2), 123.3, 123.8, 129.4, 130.4,
a [Å]
b [Å]
c [Å]
a [°]
10.3443(14)
22.158(3)
14.4909(18)
90
9.9600(3)
18.5872(5)
16.5409(5)
90
β [°]
107.768(2)
90
3163.0(7)
4
1.384
0.791
17578
356
6182 (0.0269)
0.0408, 0.1139
0.0517, 0.1215
1.041
101.862(2)
90
2996.80(15)
4
1.492
0.920
28387
363
7152 (0.0385)
0.0356, 0.0889
0.0505, 0.0927
1.019
γ [°]
V [Å3]
Z
ρcalcd. [Mgm–3]
μ(Mo-Kα) [mm–1]
Reflections collected
Parameters
Indep. reflections (Rint
133.9 (CH–Ar), 122.7, 132.2, 144.9, 146.8, 152.5, 161.8 [two Cipso
–
Ar, one NCN, two C–CH–(CH3)2 and one metalated C–Ph], 177.5
[s, O–C(=O)CH3] ppm. C25H35N3O2Pd (515.97): calcd. C 58.19, H
6.84, N 8.14; found C 57.69, H 6.25, N 8.04.
)
Final R indices R1[a], wR2
R indices (all data)
GoF[b]
[a]
Complex 4: A solution of 2 (0.57 g, 0.96 mmol) in THF (3 mL) was
heated at 80 °C for 3 h. The brown suspension was cooled to room
temperature and filtered. The brown residue was washed with THF
[a] R1 = [(Σ|Fo| – |Fc|)/Σ|Fo|], wR2 = [Σw(F2o – Fc2)2/Σw(F2o)2]1/2, w =
to afford a pale grey solid; yield 0.57 g, 59%. 1H NMR (600 MHz): 0.10. [b] GoF = [Σw(F2o – Fc2)2/(Nrflns – Nparams)]1/2
.
Eur. J. Inorg. Chem. 2012, 720–726
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
725

M.-T. Chen, K.-M. Wu, C.-T. Chen
FULL PAPER
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used for all non-hydrogen atoms, and fixed isotropic parameters
were used for hydrogen atoms. Some details of the data collection
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[10]
CCDC-840682 (for 1) and -840683 (for 4) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
We would like to thank the National Science Council of the Repub-
lic of China for financial support (grant number NSC 98-2113-M-
005-002-MY3).
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Received: October 15, 2011
Published Online: December 15, 2011
726
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 720–726