Palladium(ii) complexes based on 1,8-naphthyridine functionalized N-heterocyclic carbenes (NHC) and their catalytic activity

Article abstract of DOI:10.1039/c0dt00990c

Palladium complexes containing 2,7-bis(mesitylimidazolylidenyl) naphthyridine (NHC-NP) have been synthesized and characterized. Reaction of [{Ag₃(NHC-NP)₂}(PF₆)₃] with [Pd(PhCN)₂Cl₂] provided an unusual dipalladium complex bridged by two NHC-NP units, forming a 20-membered dinuclear metallacycle [{Pd₂(NHC-NP)₂Cl₂}(PF₆)] (2) in high yield. Treatment of 2 with KI in acetone yielded a neutral species [Pd ₂(NHC-NP)I₄] (3). Meanwhile, the pyridinyl N-heterocyclic carbene (NHC-Py) precursor, 1-(2-pyridinyl)-3-mesitylimidazolium chloride, reacted with Pd₂(dba)₃ directly to form the mononuclear palladium complex [Pd(NHC-Py)Cl₂] (4). These complexes were characterized by elemental analyses as well as NMR spectroscopy, and the structures of 3 and 4 were further identified by X-ray diffraction analysis. The use of these palladium complexes for Suzuki-Miyaura and Kumada-Corriu coupling reactions has been examined. There is no significant difference in catalytic activities between 2 and 4 in Suzuki-Miyaura coupling reactions. However, the catalytic activity of 2 in the Kumada-Corriu coupling of ArBr with cyclohexylmagnesium bromide is quite different from that of 4. Thus complex 2 is active for the cross coupling, but complex 4 is active for the reduction of aryl halides.

Full text of DOI:10.1039/c0dt00990c

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PAPER
Palladium(II) complexes based on 1,8-naphthyridine functionalized
N-heterocyclic carbenes (NHC) and their catalytic activity†
Yung-Hung Chang, Zu-Yin Liu, Yi-Hung Liu, Shei-Ming Peng, Jwu-Ting Chen and Shiuh-Tzung Liu*
Received 10th August 2010, Accepted 12th October 2010
DOI: 10.1039/c0dt00990c
Palladium complexes containing 2,7-bis(mesitylimidazolylidenyl)naphthyridine (NHC-NP) have been
synthesized and characterized. Reaction of [{Ag3(NHC-NP)2}(PF6)3] with [Pd(PhCN)2Cl2] provided an
unusual dipalladium complex bridged by two NHC-NP units, forming a 20-membered dinuclear
metallacycle [{Pd2(NHC-NP)2Cl2}(PF6)] (2) in high yield. Treatment of 2 with KI in acetone yielded a
neutral species [Pd2(NHC-NP)I4] (3). Meanwhile, the pyridinyl N-heterocyclic carbene (NHC-Py)
precursor, 1-(2-pyridinyl)-3-mesitylimidazolium chloride, reacted with Pd2(dba)3 directly to form the
mononuclear palladium complex [Pd(NHC-Py)Cl2] (4). These complexes were characterized by
elemental analyses as well as NMR spectroscopy, and the structures of 3 and 4 were further identified
by X-ray diffraction analysis. The use of these palladium complexes for Suzuki–Miyaura and
Kumada–Corriu coupling reactions has been examined. There is no significant difference in catalytic
activities between 2 and 4 in Suzuki–Miyaura coupling reactions. However, the catalytic activity of 2 in
the Kumada–Corriu coupling of ArBr with cyclohexylmagnesium bromide is quite different from that
of 4. Thus complex 2 is active for the cross coupling, but complex 4 is active for the reduction of aryl
halides.
Introduction
N-Heterocyclic carbenes (NHCs) have been developed as an
important class of ligand in both coordination chemistry and
transition-metal mediated catalysis. NHCs exhibit strong s-
donating ability and unique steric demands.1 Analogous to
Chart 1 Naphthyridine based HNC ligands.
phosphines, both steric and electronic tuning as well as their
chelating molds may be crucial for the ligand effect. Thus the
design and investigation of poly(NHC)s with other hetero donors
have received much attention because they allow the preparation
of a variety of topological complexes with variation in steric effect,
bite angles and lability of ligands.1–3
excellent precursors for the preparation of various metal carbene
complexes.1h We report herein the preparation of palladium(II)
complexes containing the NHC II ligand via carbene transfer
reaction and their catalytic behavior in Suzuki–Miyaura and
Kumada–Corriu coupling reactions
The 1,8-naphthyridine unit, which has been shown to be
similar to a bridging carboxylate, can coordinate two metal
ions in close proximity.4 Therefore, designed ligands based on
1,8-naphthyridine have been employed to construct polynu-
clear species.4–5 However, metal complexes based on the
1,8-naphthyridine functionalized with NHC donors are rare
(Chart 1). Metal complexes of Pd(II), Ir(I), Rh(I), W(0) and Ag(I)
containing a single NHC such as I, has been prepared,5a–c but
only silver and gold complexes with double NHCs (II) have
been reported.5d It is known that the NHC-Ag complexes are
Results and discussion
Preparation of naphthyridinyl-NHC palladium complexes
Silver NHC complex 1 was prepared according to the reported
procedure.5d Reaction of 1 with [(PhCN)2PdCl2] in 1 : 2 molar
ratio in anhydrous acetonitrile generates the air-stable dipalladium
complex (Scheme 1). Complex 2 was isolated as a light yellow
microcrystalline solid in 70% yield and fully characterized by
NMR spectroscopy and elemental analysis. The ESI-MS exhibits
a molecular ion signal with m/z = 639 that is consistent with
the formula of [C64H60Cl2N12Pd2]22+. This information clearly
eliminates the structure III which is in a coordination mode with
two metal ions toward one ligand.
Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan.
E-mail: stliu@ntu.edu.tw; Fax: +886 2 2363-6359
† Electronic supplementary information (ESI) available: 1H NMR spectra
of 2 and 4. CCDC reference numbers 787631 and 787630 for 3 and 4,
respectively. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c0dt00990c
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◦
˚
Table 1 Selected bond distances (A) and bond angles ( ) for 3
Pd(1)–C(7)
Pd(1)–C(39)
Pd(2)–C(18)
Pd(2)–C(50)
Pd(1)–I(1)
Pd(1)–I(2)
Pd(2)–I(3)
Pd(2)–I(4)
2.028(7)
2.035(7)
2.005(8)
2.052(7)
2.6007(7)
2.6169(6)
2.6155(8)
2.6026(8)
C(7)–Pd(1)–C(39)
I(1)–Pd(1)–I(2)
C(39)–Pd(1)–I(1)
C(7)–Pd(1)–I(1)
C(18)–Pd(2)–C(50)
I(4)–Pd(2)–I(3)
172.2(3)
168.91(3)
87.07(18)
87.60(18)
175.1(3)
164.84(3)
90.7(2)
C(18)–Pd(2)–I(3)
C(50)–Pd(2)–I(3)
87.8(2)
Scheme 1 Preparation of naphthyridinyl-NHC palladium complexes.
(1)
1
The H NMR spectrum of 2 exhibits four doublets of equal
intensity corresponding to naphthyridine protons, indicating the
chemical non-equivalent nature of these hydrogens (Fig. 1a). The
13C NMR spectrum of 2 also shows two different resonances for the
carbene carbons at d 170.8 and 171.6 ppm, which are in the normal
range for Pd-NHC complexes. These observations are evidence of
the unsymmetrical nature of the naphthyridine-NHC ligand in
this palladium complex. Since the cationic part of the molecular
mass from the mass spectrum is composed of two metal ions and
two ligands, the structure of 2 is proposed to show that each
palladium atom has local square-planar geometry being ligated
by trans bridging NHCs, as well as naphthyridine-nitrogen and
chloride, i.e. only one of the naphthyridine nitrogen atoms in each
naphthyridine is bound to a metal center. Unfortunately, we were
not able to obtain X-ray suitable crystals of 2 for analysis. The
dimetallic framework of the complex was confirmed by its iodo
derivative (see below).
Thesolid-statestructureof3, crystallizedfromdichloromethane
and diethyl ether, was determined by single crystal analysis. The
structure of dipalladium complex 3 is depicted in Fig. 2, while
selected bond distances and angles are presented in Table 1. The
molecular formulation of 3 consists of two trans-PdI2 fragments
bridged by two NHC II ligands to form a dimer. The geometry
about the metal ion is slightly distorted square planar, as evidenced
by diagonal angles ranging from 164.84(3)◦ to 175.1(3)◦. The
structure is similar to that which has been reported for the analo-
gous dppm dipalladium complex [Pd2X4(dppm)2] by Stille and co-
6
˚
workers. The distance between two palladium centers is 8.853 A,
clearly indicating no metal–metal interaction. Both palladium
atoms are four-coordinated, located in a PdC2I2 coordination
sphere. However, the planes defined by two naphthyridine rings
are not parallel to each other with the dihedral angle of 56.4◦
(Fig. 3). The Pd–C(carbene) bond distances are comparable to those
of other palladium NHC complexes.
Fig. 1 1H NMR spectra in the aromatic region for (a) 2 and (b) 3 (ꢀ
naphthyridine-H; imidazole-H).
᭹
Fig. 2 ORTEP plot of 3 (drawn with 30% probability ellipsoids).
In order to prove the coordination of naphthyridine-nitrogen
toward palladium in 2, ligand substitution around the metal center
was further investigated. Treatment of 2 with KI in refluxing
acetone readily yielded the palladium iodide 3 in high yield (eqn
(1)). The FAB mass spectrum of 3 shows the peak corresponding
to M + 1 ([C64H60I4N12Pd2] + H+), which is in accordance with
Preparation of pyridinyl-NHC palladium complexes
For comparison, we also prepared the pyridinyl-based NHC
complex 4. It has been reported by Crabtree and coworkers that
the reaction of bromide salt 5a with Pd2(dba)3 under refluxing
THF provides the biscarbene palladium complex 6.7 However,
for the reaction of the chloride salt 5b with Pd2(dba)3 under
similar conditions, we obtained the chelation palladium complex 4
(Scheme 2). The ESI-MS spectrum exhibits an ion signal at m/z =
404, which is consistent with the formula of [M - Cl]+, suggesting
the monocarbene palladium species. The molecular structure of 4
was also confirmed by X-ray crystallographic analysis as well as
1
the proposed stoichiometry. The H NMR spectrum of 3 (Fig.
1b) shows six sets of signals in the aromatic region (two from
naphthyridine, two from imidazole and two from mesityl group),
which permits us to establish the symmetrical structure in the
molecule and assign the resonance by 1H–1H COSY experiments.
Nevertheless, the detailed structure of 3 was confirmed by X-ray
diffraction.
490 | Dalton Trans., 2011, 40, 489–494
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Table 3 Suzuki–Miyaura coupling reactions catalyzed by 2 and 4a
Entry
Ar–X
Pd complex
Time/h
Yield
1
2
3
4
5
6
7
8
p-CH3COC6H4Br
p-CH3COC6H4Br
p-CH3COC6H4Br
p-CH3COC6H4Br
p-CH3COC6H4I
p-CH3COC6H4Cl
p-CH3COC6H4Cl
p-CH3OC6H4Cl
p-CH3OC6H4Cl
o-CH3C6H4Cl
2 (0.5 mol%)
2 (0.5 mol%)
4 (0.5 mol%)
4 (0.5 mol%)
2 (0.5 mol%)
2 (1 mol%)
4 (1 mol%)
2 (1 mol%)
4 (1 mol%)
2 (1 mol%)
2 (1 mol%)
1 h
0.5 h
1 h
0. 5 h
1 h
24 h
24 h
24 h
24 h
24 h
24 h
100%
80%
100%
91%
100%
Tracec
Tracec
Tracec
Tracec
Tracec
Tracec
9
10
11
PhCld
Fig. 3 Side-view of 2 showing the orientation of two naphthyridine rings
a Reaction conditions: Ar–X (0.2 mmol), C6H5B(OH)2 (0.3 mmol), Pd
complex, K2CO3 (0.4 mmol) in EtOH (0.5 mL) under refluxing tempera-
ture. b Based on NMR integration with an internal standard. c Aryl chloride
was recovered. d In DMF at 120 ◦C.
(mesityl groups are omitted for clarity).
Catalytic Suzuki–Miyaura coupling reactions
It has been revealed that bimetallic complexes might be suitable for
the coupling reactions of aryl chlorides.8 Thus we investigated the
catalytic activity of 2 toward the cross-coupling reaction. Under
the typical reaction conditions commonly applied for palladium-
catalyzed Suzuki reactions, results of the coupling reaction of
aryl halides with phenylboronic acid are shown in Table 3. First,
complexes 2 and 4 alone were tested as catalysts for the coupling
of 4-bromoacetophenone with phenylboronic acid in the refluxing
ethanol solution under an atmosphere of nitrogen (entries 2 and
3). The results show that both 2 and 4 are effective catalysts for the
C–C coupling, giving the desired product in 100% yield within
1 h. Notably, the catalytic activity of pre-catalyst 4 is slightly
more active than that of 2 (entry 2 versus 4). However, complexes
2 and 4 are totally ineffective for activated or un-activated aryl
chlorides under the same conditions. Presumably, the two metal
centers modified by the chelating pyridinyl-NHC ligand are too
far away, which weakens the cooperative interaction. Of course,
the decomposition of metal complexes leading to coloidal Pd is
also a possible reason for the lower activity.8i
Scheme 2
by the NMR spectroscopic data. Both 1H and 13C NMR spectra
of 4 are in agreement with the proposed structure. It is noted that
the 13C shift of the carbene carbon appears at 158.7 ppm, which is
up-field by about 10 ppm compared to those for 2.
A view of the ORTEP plot of 4 is presented in Fig. 4, while
selected bond distances and angles are given in Table 2. In the
structure, the palladium atom is in a slightly distorted square
planar geometry that is defined by cis-chelation of the pyridinyl-
NHC ligand and two chlorides. The chelating pyridinyl-NHC
ligand has a typical bite angle of 80.7(2)◦ deviated from 90◦ due
to the geometrical constrain. The pyridine and imidazole rings are
almost coplanar as reflected by the dihedral angle of N(1)–C(1)–
N(2)–C(6) (4.0◦), whereas the mesityl ring is almost perpendicular
to the imidazole ring as indicated by the dihedral angle of C(6)–
N(3)–C(9)–C(10) (89.1◦). The Pd–Ccarbene distance is 1.971 (5) A
˚
and does not differ significantly from the Pd–C distance in similar
palladium NHC complexes.
Catalytic Kumada–Corriu coupling reactions
A further elaboration of catalysis is the use of complex 2 as the
pre-catalyst for Kumada–Corriu coupling with alkylmagnesium
reagents. The coupling of simple alkyl species, especially those
containing fi-hydrogens, has been challenging due to the b-H elim-
ination products from the resulting metal alkyl intermediates.9,10
Here, we have studied the difference of catalytic activity between 2
and 4 on the coupling of aryl halides with alkyl Grignard reagents.
The coupling reaction of aryl bromides with C6H11MgBr
catalyzed by pre-catalyst 2 proceeded smoothly, providing the
cross-coupling products predominately (Table 4, entries 1, 3, 6 and
8) with a small amount of dehalogenated products. The reactivity
of Ar–X toward Grignard reagent decreases in the order iodide
~ bromide ꢀ chloride. Thus, reaction of p-ClC6H4Br with the
Grignard reagent provided p-cyclohexylphenyl chloride as the
product, i.e. the chloro functionality remains intact. However,
when complex 4 was used instead of 2 in the catalysis, the
cross-coupling was obtained in very low yield, producing the
Fig. 4 ORTEP plot of 4 (drawn with 30% probability ellipsoids).
◦
˚
Table 2 Selected bond distances (A) and bond angles ( ) for 4
Pd(1)–N(1)
Pd(1)–C(6)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
N(2)–C(6)
N(3)–C(6)
2.062(4)
1.971(5)
2.340(1)
2.286(1)
1.389(6)
1.333(6)
N(1)–Pd(1)–C(6)
N(1)–Pd(1)–Cl(2)
Cl(1)– Pd(1)–C(6)
N(1)–Pd(1)–Cl(1)
80.7(2)
175.8(1)
172.5(1)
93.1(1)
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Table 4 Results of coupling reaction of aryl halides with C6H11MgBr
N-alkylation reactions catalysed by the iridium complex 4aa
Productsc,d (yield, %)
Cycloh-
Entry Ar–X
[Pd] Time/h Conv.b Ar-C6H11 exene
Ar-H
1
2
3
4
5
6
7
8
9
4-MeOC6H4-Br 2
4-MeOC6H4-Br 2
4-MeOC6H4-I
4-MeOC6H4-Br 4
4-MeOC6H4-Br 4
7
3
5
7
24
7
24
7
24
24
100% 85
55% 42
100% 80
13
9
14
8
2
20
23
26
22
24
23
16
—
16
22
25
19
22
25f
16f
—
30%
32%
80%
28%
72%
18%
Trace
4
7
58
4
C6H5-Br
C6H5-Br
4-ClC6H4-Br
4-ClC6H4-Br
C6H5-Cl
2
4
2
4
2
49e
Trace
—
10
a Reaction conditions: ArX (0.25 mmol), C6H11MgBr (0.75 mmol), and
Pd complex (1 mol%) in THF (1 mL) at room temperature. b Based on
the amount of ArX. c Determined by GC. Yields are based on the amount
of ArX used. d 1% of C6H11–C6H11 was detected by GC in each reaction.
e 4-ClC6H4-C6H11 as the product. f C6H5Cl as the product.
Scheme 4
Summary
We have successfully prepared and structurally characterized a
few novel dinuclear palladium complexes containing a bis(N-
heterocyclic carbene)naphthyridine ligand. In addition, a pal-
ladium complex 4 with a cis-chelation pyrdinyl-NHC ligand
was synthesized via the direct reaction of imidazolium salt 5b
with Pd2(dba)3. These complexes provided suitable models for
comparison of the catalytic activities in the coupling reaction. Both
complexes of 2 and 4 have similar catalytic activities in the Suzuki–
Miyaura coupling reaction, but different activities in the coupling
reaction of aryl bromides with cyclohexylmagnesium bromide.
The dinuclear palladium complex 2 provides excellent reactivity
for the cross coupling product. On the other hand, complex 4
catalyzes the dehalogenation of aryl bromides predominately.
dehalogenated product (entries, 4, 5, 7 and 9). By comparing the
conversion of aryl halides, the activity of 4 appears to be lower than
that of 2. For example, reaction of 4-MeOC6H4Br with C6H11MgBr
only reaches 32% conversion, yielding cyclohexene and anisole in
a ratio of 1 : 1.
From the results shown in Table 4, it appears that the catalytic
activity of 2 is quite different from that of 4. The proposed pathway
for the couplings catalyzed by complexes 2 and 4 are outlined
in Schemes 3 and 4, respectively. It is known that the carbene
donor is a strong s-donor and not easily dissociated from the
metal center. Thus the coordination interaction of the chelating
carbene groups in 2 prevents the dissociation of these donors
from the metal center, and hence it is not feasible to generate a
vacant site for the b-elimination. Therefore, the reductive process
takes place on the intermediate III to yield the coupling product
(Scheme 3). On the other hand, the nitrogen donor of the
bidentate pyridinyl-carbene is labile.11 The vacant site on the metal
center is generated and hence b-elimination occurs to yield the
intermediate V (Scheme 4). Dissociation of the olefin provides
the metal-hydride species VI, which readily undergoes reductive
elimination to provide the reduction product, which also accounts
for the production of nearly equal amounts of cyclohexene and
Ar–H.
Experimental
General information
Nuclear magnetic resonance spectra were recorded in CDCl3
on either a Bruker AM-300 or a Bruker AVANCE 400 spec-
trometer. Chemical shifts are given in parts per million relative
to Me4Si for 1H and 13C NMR. All reactions, manipulations
and purification steps were performed under a dry nitrogen
atmosphere. Tetrahydrofuran was distilled under nitrogen from
sodium/benzophenone. Dichloromethane and acetonitrile were
dried over CaH2 and distilled under nitrogen. Other chemicals and
solvents were of analytical grade and were used after a degassing
process. Silver carbene complex 15b was prepared according to the
method reported previously.
Complex 2. A mixture of 1 (214 mg, 0.13 mmol) and
[Pd(PhCN)2Cl2] (104 mg, 0.27 mmol) in a flask capped with
a septum was evacuated and flushed with nitrogen. Anhydrous
acetonitrile (5 mL) was syringed into the above flask and the
resulting mixture was stirred at room temperature for 6 h. The
reaction mixture was then filtered through Celite to remove silver
salts. The filtrate was concentrated and dissolved into a small
amount of dichloromethane. Upon addition of ether, the desired
complex was precipitated as a light-yellow solid (143 mg, 70%): 1H
NMR (400 MHz, CDCl3): 1H NMR (CDCl3) d 8.85 (d, J = 8.6 Hz,
2H, naphthyridine-H), 8.71 (d, J = 8.6 Hz, 2H, naphthyridine-H),
8.46 (d, J = 8.6 Hz, 2H, naphthyridine-H), 8.13 (d, J = 8.6 Hz,
Scheme 3
492 | Dalton Trans., 2011, 40, 489–494
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Table 5 Crystal data for 3 and 4
Complex
3
4
Formula
FW
C64H60I4N12Pd2(CH2Cl2)·1.5(C4H10O)
C17H17Cl2N3Pd (CH3CN)
481.69
1913.75
Crystal system
Space group
Monoclinic
C2/c
30.3869(6)
19.3940(4)
28.0844(7)
90
111.310(3)
90
15419.2(6)
1.649
7496
0.20 ¥ 0.15 ¥ 0.10
37 292
Trigonal
P3(1)
8.9076(3)
8.9076(3)
21.4007(10)
90
90
120
1470.55(10)
1.632
726
˚
a, A
˚
b, A
˚
c, A
a, ◦
b, ◦
g , ◦
3
˚
V, A ; Z
d (calc.), Mg/m3
F(0,0,0)
Crystal size, mm3
Rflns collected
Independent rflns
q range, ◦
0.20 ¥ 0.15 ¥ 0.10
5506
3824 [R(int) = 0.0283]
3.89–27.50
17 677 [R(int) = 0.0317]
3.11–27.50
Refined method
Goodness of fit on F2
R indices [I>2s(I)]
R indices (all data)
Full-matrix least-squares on F2
1.131
1.036
R1 = 0.0546, wR2 = 0.1665
R1 = 0.0964, wR2 = 0.1852
R1 = 0.0324, wR2 = 0.0807
R1 = 0.0379, wR2 = 0.0825
2H, naphthyridine-H), 8.09 (d, J = 1.6 Hz, 2H, imidazole-H),
7.16 (d, J = 1.6 Hz, 2H, imidazole-H), 7.03 (d, J = 1.6 Hz, 2H,
imidazole-H), 7.01 (s, 2H, Ar–H), 6.99 (s, 2H, Ar–H), 6.92 (s,
2H, Ar–H), 6.89 (d, J = 1.6 Hz, 2H, imidazole-H), 6.73 (s, 2H,
Ar–H), 2.40 (s, 6H, –CH3), 2.38 (s, 6H, –CH3), 2.33 (s, 6H, –
CH3), 2.09, (s, 6H, –CH3), 2.05 (s, 6H, –CH3), 1.59 (s, 6H, –CH3);
13C NMR (100 MHz, acetone-d6): d 11.8, 18.1, 19.7, 19.9, 21.2,
21.3, 114.5, 119.1, 122.6, 123.3, 123.7, 127.1, 129.1, 129.3, 129.6,
129.9, 130.3, 134.8, 135.1, 135.2, 135.4, 136.1, 137.2, 139.6, 139.7,
the residue was chromatographed on silica gel with the elution
of CH2Cl2/acetone (1 : 1). A yellow band from the column was
collected and concentrated to yield 4 as a light-yellow solid (74
mg, 67%): 1H NMR (400 MHz, acetone-d6): d 2.10 (s, 6H, –CH3),
2.31(s, 6H, –CH3), 6.94 (s, 2H, Ar–H), 7.40 (d, J = 2.3 Hz, 1H,
imidazole-H), 7.68 (m, 1H, py-H), 8.18 (d, J = 8.5 Hz, 1H, py-H),
8.38 (m, 1H, py-H), 8.48 (d, J = 2.3 Hz, 1H, imidazole-H), 9.48
(d, J = 8.5 Hz, 1H, py-H); 13C NMR (100 MHz): d 18.0, 21.1
(CH3), 112.8, 117.7, 123.9, 126.3, 129.3, 135.3, 136.1, 139.6, 143.3,
150.8, 152.8 (Ar–C), 158.7 (Pd C); FAB-MS calcd. for [M - Cl]+
C17H17ClN3Pd+: m/z = 404.01; found m/z = 404.01. Anal. Calcd
for C17H17Cl2N3Pd∑CH3CN: C, 47.37; H, 4.18. Found: C, 47.79;
H, 4.29.
142.9, 146.3, 151.8, 156.0, 157.4, 170.8 (Pd–C), 171.6 (Pd–C); 31
P
(161.9 MHz): d -143.8 (septet, JP–F = 707.5 Hz); ESI-MS calcd. for
[M]2+ C64H60Cl2N12Pd22+: m/z = 639.12; found 639.16. Anal. Calcd
for C64H60Cl2F12N12P2Pd2: C, 48.93; H, 3.85; N, 10.70. Found: C,
48.54; H, 4.09; N, 10.56.
General procedures for Suzuki–Miyaura coupling reaction.
A
Complex 3. A mixture of 2 (40 mg, 0.025 mmol) and KI (33.2
mg, 0.2 mmol) in acetone (5 mL) was heated to reflux for 12 h.
After removal of solvents, the residue was chromatographed on
silica gel with elution of dichloromethane. A brown fraction was
collected and concentrated to give 3 as a brown solid (43 mg,
mixture of Ar–X (0.2 mmol), C6H5B(OH)2 (0.3 mmol), Pd complex
(2 ¥ 10-3 mmol), K2CO3 (0.4 mmol) in EtOH (0.5 mL) was heated
under refluxing conditions. After reaction for a certain period, the
reaction mixture was filtered through celite to remove the metal
1
species. The filtrate was concentrated and analyzed by H NMR
1
74%): H NMR (400 MHz, CDCl3) d 8.75 (d, J = 8.4 Hz, 4H,
spectroscopy.
naphthyridine-H), 8.61 (d, J = 8.4 Hz, 4H, naphthyridine-H), 7.60
(d, J = 1.9 Hz, 4H, imidazole-H), 6.79 (s, 4H, Ar–H), 6.73 (d, J =
1.9 Hz, 4H, imidazole-H), 6.72 (s, 4H, Ar–H), 2.41 (s, 12H, –CH3),
2.16 (s, 12H, –CH3), 2.15 (s, 12H, –CH3); 13C NMR (100 MHz,
d6-acetone) d 21.1, 21.6, 21.7 (CH3), 121.8, 122.2, 123.6, 126.1,
129.8, 130.0, 136.4, 136.5, 136.6, 139.0, 141.2, 154.7, 156.0 (Ar–
C), 168.2 (Pd C). Anal. Calcd for C64H60I4N12Pd2: C, 44.75; H,
3.52; N, 9.79. Found: C, 44.45; H, 3.47; N, 9.66.
General procedures for Kumada coupling reaction. A mixture
of Ar–X, mesitylene (30 mg, for GC internal standard) and Pd
complex (2.5 ¥ 10-3mmol) in anhydrous THF (1 mL) was placed
in a flask (5 mL). Flash prepared cyclohexylmagnesium bromide
(1.05 M, 0.3 mL) was syringed into the above solution. The
reaction mixture was stirred at room temperature for a certain
period and then quenched with ethanol. The reaction mixture was
analyzed by GC.
Complex 4. A mixture of 5b (100 mg, 0.33 mmol) and
Pd2(dba)3(160 mg, 0.165 mmol) was placed in a flask equipped
with a reflux condenser. The system was flushed with nitrogen
for 20 min. Anhydrous THF (10 mL) was then added to the
above mixture through a flux-needle. The mixture was heated
to reflux for 3 h. The color of the solution changed from red
to deep brown. Potassium chloride (52 mg) was added and
stirred overnight. The mixture was filtered through Celite and
Crystallography. Crystals suitable for X-ray determination
were obtained for 3 [C64H60I4N12Pd2(CH2Cl2)·1.5(C4H10O)] and
4.(CH3CN) by recrystallization at room temperature. Cell param-
eters were determined by a Siemens SMART CCD diffractometer.
Crystal data of these complexes are summarized in Table 5. The
structure was solved using the SHELXS-97 program12 and refined
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494 | Dalton Trans., 2011, 40, 489–494
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