Synthesis of Multinuclear Copper Complexes Bridged by Diquinolylamidinates and Their Application to Copper-Catalyzed Coupling of Terminal Alkynes and Aryl, Allyl, and Benzyl Halides

Article abstract of DOI:10.1021/om501139f

A dinuclear copper complex containing N,N′-diquinolylformamidinate and a tetranuclear copper complex containing N,N′-diquinolylacetamidinate were synthesized. The structure of complexes was confirmed by X-ray analysis, showing that copper atoms were bridg

Full text of DOI:10.1021/om501139f

Article
pubs.acs.org/Organometallics
Synthesis of Multinuclear Copper Complexes Bridged by
Diquinolylamidinates and Their Application to Copper-Catalyzed
Coupling of Terminal Alkynes and Aryl, Allyl, and Benzyl Halides
Takayuki Nakane,† Yuta Tanioka,† and Naofumi Tsukada*,†,‡
‡
†Department of Chemistry, Graduate School of Science, and Research Institute of Green Science and Technology, Shizuoka
University, Shizuoka 422-8529, Japan
S
* Supporting Information
ABSTRACT: A dinuclear copper complex containing N,N′-
diquinolylformamidinate and a tetranuclear copper complex
containing N,N′-diquinolylacetamidinate were synthesized. The
structure of complexes was confirmed by X-ray analysis, showing
that copper atoms were bridged by amidinates and hydroxo or oxo
ligands. The multinuclear copper complexes were effective for the
coupling reactions of terminal alkynes and aryl, allyl, and benzyl
halides.
In the course of our studies for catalysis using dinuclear
complexes,11 we found that 8-aminoquinoline is a suitable
substructure of chelate-bridging ligands for formation of
dinuclaer complexes including copper.11g We herein report
the synthesis and characterization of multinuclear copper
complexes bridged by N,N′-di-8-quinolylamidinates12 and a
study of their catalytic activity in the cross-coupling of terminal
alkynes and aryl, allyl, and benzyl halides.
INTRODUCTION
■
Chemical transformation of organic compounds catalyzed by
transition metal complexes has been a useful and indispensable
tool for organic synthesis. While most of the catalysis
progresses on a single metal site, catalysis with multinuclear
complexes has been studied because cooperation of metal
centers is expected not only to improve the efficiency and
selectivity of catalysis but also to promote reactions that are not
possible on a single metal site.1 Among them, multinuclear
copper complexes have received much attention as mimics of
active sites in oxidases and oxygenases that contain copper
centers.2,3 Various complexes have been synthesized, and their
catalytic reactivity for oxidation and oxygenation reactions has
been thoroughly studied.3,4 In contrast, nonoxidative reactions
catalyzed by multinuclear copper complexes have been rarely
studied, although mononuclear copper complexes and salts
have been extensively utilized as catalyst for various trans-
formations of organic molecules.5
The palladium−copper cocatalyzed Sonogashira coupling of
aryl or vinyl halides and terminal alkynes is one of the most
convenient methods for preparation of aryl alkynes and related
conjugated enynes.6 Recently, much attention has been
attracted to the palladium-free Sonogashira coupling because
palladium complexes are considerably expensive. Various
catalytic systems for the Sonogashira-type coupling catalyzed
by copper salts and complexes, including dinuclear complexes,
have been reported.7,5i A related copper-catalyzed cross-
coupling of allyl halides with terminal alkynes is also achieved
by using tetraalkylammonium salts as an additive.8,9 In contrast,
however, a related copper-mediated coupling of benzyl halides
is rather limited. The reported procedures require using 1 equiv
of copper iodide.10
RESULTS AND DISCUSSION
■
Synthesis of Di- and Tetranuclear Copper Complexes.
Since 8-aminoquinoline was a suitable chelating substructure
for copper in our previous study,11g N,N′-di-8-quinolylforma-
midinate (qfam) and N,N′-di-8-quinolylacetamidinate (qaam)
were used for the preparation of dinuclear copper complexes
(Chart 1). Treatment of a protonated form of qfam (qfamH)
with 2 equiv of Cu(OAc)2 in wet acetone at room temperature
generated a dinuclear copper complex, Cu2(OAc)2(μ-OH)(μ-
qfam) (1), in 83% yield as a dark-green powder (Scheme 1).
Crystallization of 1 by vapor diffusion of diethyl ether into a
solution of dichloromethane afforded a black crystal suitable for
Chart 1. N,N′-Di-8-quinolylamidine Ligands
Received: November 11, 2014
© XXXX American Chemical Society
A
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Article
coplanar with the amidinate plane. Each copper center has a
square-planar geometry. The Cu−Cu distance is 3.403 Å,
indicating that there is no significant metal−metal interaction.
Treatment of a protonated form of qaam (qaamH) with 2
equiv of Cu(OAc)2 in wet acetone at room temperature
generated a tetranuclear copper complex, Cu4(μ-OAc)4(μ-
O)(μ-qaam)2 (2), in 86% yield as a dark-green powder
(Scheme 2). Crystallization of 2 by slow diffusion of n-hexane
Scheme 1. Synthesis of Dinuclear Copper Complex 1
Scheme 2. Synthesis of Tetranuclear Copper Complex 2
X-ray analysis. The molecular structure of 1 is shown in Figure
1, and selected bond lengths and angles are presented in Table
into a solution of dichloromethane afforded a black crystal
suitable for X-ray analysis. The molecular structure of 2 is
shown in Figure 2, and selected bond lengths and angles are
Figure 1. Molecular structure of 1, showing 50% thermal ellipsoids.
Hydrogen atoms and solvent molecules are omitted for clarity.
1. Two copper centers are bridged by a hydroxo ligand and the
chelate-bridging ligand, qfam. The μ-OH ligand is positioned
symmetrically relative to the metal centers. The geometries of
both amidinate nitrogens are planar, Σϕ(N2) = 360.1° and
Σϕ(N3) = 360.0°, and C10 is positioned symmetrically relative
to the nitrogen atoms, indicating that the double bond of the
amidinate is delocalized. Two quinolyl rings are almost
Table 1. Selected Bond Lengths (Å), Bond Angles, and
Torsion Angles (deg) for 1
Cu1−O1
Cu1−N3
Cu2−O1
Cu2−N1
1.877(5)
1.991(5)
1.875(0)
1.978(5)
1.320(7)
94.36(19)
88.3(2)
Cu1−O4
Cu1−N4
Cu2−O2
Cu2−N2
1.939(5)
1.985(5)
1.959(5)
1.984(5)
1.317(7)
95.00(17)
83.01(19)
95.63(18)
83.10(19)
130.3(4)
Figure 2. Molecular structure of 2, showing 50% thermal ellipsoids.
Hydrogen atoms and solvent molecules are omitted for clarity
(inversion center is present in molecule).
N2−C10
N3−C10
O1−Cu1−O4
O4−Cu1−N4
O1−Cu2−O2
O2−Cu2−N1
Cu2−N2−C9
C9−N2−C10
Cu1−N3−C10
C10−N3−C11
C10−N2−C9−C8
C10−N3−C11−C12
O1−Cu1−N3
N3−Cu1−N4
O1−Cu2−N2
N1−Cu2−N2
Cu2−N2−C10
presented in Table 2. While two copper centers in 1 are bridged
by a hydroxo ligand and one molecule of qfam, the complex 2
contains two molecules of qaam and four copper atoms that are
bridged by an oxo ligand. Each qaam has a C2-symmetrical
structure and both qaam display a similar structure. In contrast
to the planarity of qfam in 1, the amidinate plane and two
quinolyl rings of qaam in 2 are twisted probably due to steric
repulsion between the methyl group of the amidinate and the
ortho hydrogen of the quinolyl ring. Each copper center has a
91.05(19)
92.7(2)
112.2(4)
117.6(5)
131.7(4)
116.8(5)
1.2(8)
Cu1−N3−C11
111.5(4)
−0.5(8)
B
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Article
2). The catalytic ability of 1 is lower than 2 (entry 1). Although
the reaction catalyzed by 2 proceeded at lower temperature, the
yield of 3a decreased to 49% (entry 4). Multinuclear complexes
generated in situ were less effective than the isolated complex 2
(entry 6), while similar results were obtained in the case of 1
(entries 1 and 5). The reaction was catalyzed by copper acetate
without nitrogen ligands, giving 3a in moderate yield (entry 7).
By reducing the amounts of copper acetate, the yield was
improved to 89% (entry 8). However, the yield decreased
significantly at lower temperature (entries 9 and 10). Copper
acetate was much less effective than complex 2 at 80 °C. Active
species in the reaction with 2 and the reaction with copper
acetate may be different. The reactions with copper(I) chloride
were also investigated because copper(I) was generally
accepted to be an active species in the copper-catalyzed
Sonogashira-type reaction. While copper(I) chloride was an
active catalyst as well as copper(II) acetate, the addition of
qfamH decreased the catalytic activity of copper(I) chloride
(entries 11 and 12). The active species in the reaction using the
chelate-bridging ligands, including the reaction with 2, possibly
has a copper(II) center along with a copper(I) center.
Table 2. Selected Bond Lengths (Å), Bond Angles, and
Torsion Angles (deg) for 2
Cu1−O1
Cu1−O4i
Cu1−N2
Cu2−O1
Cu2−O5
Cu2−N4
O2−C23
O4−C25
O1−Cu1−O2
O2−Cu1−O4i
N1−Cu1−N2
O1−Cu2−O5
O3−Cu2−O5
N3−Cu2−N4
C10−N2−C10−C11
C21−N4−C20−C19
1.946(3)
2.214(5)
2.019(5)
1.929(3)
2.018(4)
2.044(4)
1.270(7)
1.247(5)
92.14(17)
89.26(18)
79.6(2)
Cu1−O2
Cu1−N1
1.992(5)
2.052(5)
Cu2−O3
Cu2−N3
2.259(6)
2.016(5)
O3−C23
O5−C25
O1−Cu1−N2
O2−Cu1−N1
1.243(11)
1.267(9)
99.28(19)
87.04(18)
93.40(15)
97.48(17)
80.03(18)
44.8(10)
−49.1(8)
O1−Cu2−N4
O5−Cu2−N3
100.32(16)
84.17(17)
distorted square pyramidal geometry with the oxo ligand, and
the oxygen atom of acetoxy ligand, and two nitrogen atoms of
qaam forming the base plane (τ = 0.075 for Cu1, τ = 0.248 for
Cu2).13 Each acetoxy ligand asymmetrically bridges two copper
centers through two oxygen atoms, one of which coordinates to
copper in a basal position and another in an apical position of
another copper center. The apical Cu−O bond distance is
longer than the basal Cu−O bond.
Table 4 summarizes the results of the coupling reaction of
various aryl iodides and several terminal alkynes in the presence
Table 4. Coupling Reaction of Iodoarenes and Terminal
a
Alkynes in the Presence of 2
Synthesis of multinuclear copper(I) complexes by treatment
of the chelate-bridging ligands and copper(I) salts was also
investigated because copper(I) is an actual active species in a lot
of copper-catalyzed reactions. However, any identified com-
plexes were not obtained.
Coupling Reaction of Terminal Alkynes and Aryl
Halides. The catalytic activity of multinuclear complexes 1 and
2 was studied. First, we investigated the palladium-free
Sonogashira coupling of phenyl iodide and phenylacetylene.
The reaction proceeded at 120 °C in the presence of 2.5 mol %
of 2, giving diphenylacetylene 3a in 95% yield (Table 3, entry
b
entry
R1
R2
Ph
product
yield (%)
c
1
2
H
3a
3b
3c
3d
3e
3f
99
c
2-Me
4-Me
2-Br
Ph
82
d
c
3
d
Ph
88
4
Ph
53
95
73
49
78
84
5
3-MeO
4-MeO
3-NO2
4-NO2
4-CN
H
Ph
6
Ph
7
Ph
3g
3h
3i
8
Ph
9
Ph
c
10
11
n-Hex
TIPS
3j
94
Table 3. Copper-Catalyzed Coupling Reaction of
a
H
3k
77
Phenylacetylene and Iodobenzene
a
A mixture of an iodoarene (0.30 mmol), a terminal alkyne (0.30
mmol), and K3PO4 (0.30 mmol) in DMF (1.0 mL) was heated at 120
°C for 18 h in the presence of 2 (7.5 μmol). Isolated yields. GC
b
c
d
yields. 150 °C.
b
entry
catalyst (mol %)
temp (°C)
yield (%)
of 2. After extensive screening of various bases, K3PO4 was
found to be more effective than K2CO3 (entry 1). The reaction
of various aryl iodides bearing electron-donating or electron-
withdrawing substituents afforded corresponding diarylacety-
lenes in moderate to high yields (entries 2−9), although some
reactions needed to be carried out at 150 °C (entries 3 and 4).
The reaction of alkyl- and silyl-acetylenes such as 1-octyne and
triisopropylsilylacetylene also proceeded smoothly in the
presence of 2 to give the corresponding aryl alkynes in high
yields (entries 10 and 11).
Coupling Reaction of Terminal Alkynes and Cinnamyl
Chloride. A coupling reaction of allyl halides and terminal
alkynes is one of the most useful methods for preparation of
1,4-enynes. Multinuclear copper complexes 1 and 2 also
catalyzed the coupling reaction. Several copper-catalyzed
coupling reactions of allyl halides and terminal alkynes have
1
1 (5)
120
120
100
80
43
95
70
49
47
65
58
89
35
7
2
2 (2.5)
2 (2.5)
2 (2.5)
3
4
5
Cu(OAc)2 (10) + qfamH (5)
Cu(OAc)2 (10) + qaamH (5)
Cu(OAc)2 (10)
120
120
120
120
100
80
6
7
8
Cu(OAc)2 (5)
9
Cu(OAc)2 (5)
10
11
12
Cu(OAc)2 (5)
CuCl (5)
120
120
89
26
CuCl (5) + qfamH (2.5)
a
A mixture of iodobenzene (0.30 mmol), phenylacetylene (0.30
mmol), and K2CO3 (0.30 mmol) in DMF (1.0 mL) was heated for 18
h in the presence of catalyst. GC yields.
b
C
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Article
already been reported.8,9 However, an addition of tetraalky-
lammonium salts was necessary in most of the reported
reactions. The coupling reaction of cinnamyl chloride and
phenylacetylene in the presence of 1 or 2 proceeded at 60 °C
without the addition of ammonium salts to give diphenyl-1,4-
pentenyne 4a in good yield (Table 5, entries 1 and 2).
of 2. After optimization of reaction conditions, the yield of 4a
increased to 79% (entry 1). The reaction of alkylacetylenes
such as 1-octyne and 1-hexyne gave the corresponding 1,4-
enynes 4b and 4c in high yields (entries 2 and 3). The yield of
4d was low probably due to the lower boiling point of 3,3-
dimethyl-1-butyne (entry 4). An ester group of propargyl
acetate was tolerated under the reaction conditions (entry 5).
The reaction of a conjugate terminal alkyne activated by an
ester group did not afford any coupling product (entry 6).
Although silylacetylenes could be applied to the coupling
reaction, the yield of products varied depending on the silyl
groups. While the yields of products 4g and 4i obtained from
trimethylsilyl- or triisopropylsilylacetylenes were low (entries 7
and 9), the reaction of triethylsilylacetylene gave 1,4-enyne 4h
in 62% yield (entry 8).
Table 5. Copper-Catalyzed Coupling Reaction of
a
Phenylacetylene and Cinnamyl Chloride
Coupling Reaction of Terminal Alkynes and Benzyl
Bromide. In contrast to the reaction of aryl halides and allyl
halides, a related copper-mediated coupling reaction of benzyl
halides is rather limited.10 The reported procedures require
using 1 equiv of copper iodide. Thus, we next investigated the
application of our catalytic systems to the reaction of benzyl
halides. Benzyl bromide reacted with phenylacetylene in the
presence of 5 mol % of 1 to afford diphenyl-1-propyne 5a in
47% yield (Table 7, entry 1). The reaction proceeded in the
b
entry
catalyst (mol %)
yield (%)
1
2
3
4
5
6
7
8
9
1 (5)
68
59
37
71
41
0
2 (2.5)
Cu(OAc)2 (10) + qfamH (5)
Cu(OAc)2 (10) + qaamH (5)
CuI (10) + qaamH (5)
Cu(OAc)2 (5) + bpy (5)
Cu(OAc)2 (5) + phen (5)
Cu(OAc)2 (5)
14
0
CuI (5)
0
Table 7. Copper-Catalyzed Coupling Reaction of
a
a
A mixture of cinnamyl chloride (0.30 mmol), phenylacetylene (0.30
mmol), and K2CO3 (0.6 mmol) in THF (2.0 mL) was heated at 60 °C
Phenylacetylene and Benzyl Bromide
b
for 18 h in the presence of catalyst. GC yields.
Multinuclear complexes generated in situ from copper acetate
and the chelate-bridging ligands also catalyzed the reaction
(entries 3 and 4). Similarly to the reaction of iodobenzene, the
use of a copper(I) salt decreases the yield of 4a. In contrast to
qfamH and qaamH, bidentate nitrogen ligands such as bipyridyl
and phenanthroline are much less effective (entries 6 and 7).
No reaction occurred without nitrogen ligands (entries 8 and
9).
b
entry
catalyst (mol %)
solvent
yield (%)
1
1 (5)
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
toluene
DMF
DMAc
47
17
35
19
19
10
0
2
2 (2.5)
3
Cu(OAc)2 (10) + qfamH (5)
Cu(OAc)2 (5) + qfamH (5)
CuCl (10) + qfamH (5)
Cu(OAc)2 (10) + qaamH (5)
Cu(OAc)2 (10)
4
5
6
Table 6 summarizes the results of the coupling reaction of
cinnamyl chloride and various terminal alkynes in the presence
7
8
Cu(OAc)2 (10) + bpy (10)
Cu(OAc)2 (10) + phen (10)
Cu(OAc)2 (10) + 8-aminoquinoline (10)
1 (5)
0
9
0
10
11
12
13
13
0
Table 6. Coupling Reaction of Cinnamyl Chloride and
a
Terminal Alkynes in the Presence of 2
1 (5)
32
66
1 (5)
a
A mixture of benzyl bromide (0.30 mmol), phenylacetylene (0.45
mmol), and K2CO3 (0.60 mmol) in THF (2.0 mL) was heated at 60
b
°C for 18 h in the presence of catalyst. GC yields.
b
presence of complexes generated from copper acetate and
qfamH in situ. The addition of 2 equiv of copper acetate for
qfamH was more effective than the addition of 1 equiv (entries
3 and 4). Copper acetate did not serve as a catalyst without
qfamH (entry 7). These results indicate that the active species
has multinuclear structures. Similarly to the reaction of
iodobenzene, the use of copper(I) chloride decreased the
yield of 5a (entry 5). Ordinary bidentate nitrogen ligands such
as bipyridyl and phenanthroline cannot be used instead of
qfamH (entries 8 and 9), whereas the reaction with 8-
aminoquinoline gave 5a in low yield (entry 10). After
optimization of solvents, the yield of 5a was improved to
66% by using N,N-dimethylacetamide as a solvent (entries 11−
13).
entry
R
product
yield (%)
1
2
3
4
5
6
7
8
9
Ph
4a
4b
4c
4d
4e
4f
79
80
100
30
67
0
n-Hex
n-Bu
t-Bu
CH2OAc
CO2Me
TMS
4g
4h
4i
33
62
39
TES
TIPS
a
A mixture of cinnamyl chloride (0.30 mmol), a terminal alkyne (0.30
mmol), and K2CO3 (0.60 mmol) in THF (2.0 mL) was heated at 80
b
°C for 18 h in the presence of 2 (7.5 μmol). NMR yields.
D
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and dried under reduced pressure. Yield: 98 mg, 86%. Complex 2 was
paramagnetic. This procedure gave a hydrated complex. Water was not
removed under reduced pressure even at 40 °C. Anal. Calcd for
C48H42Cu4N8O9·3H2O: C, 48.73; H, 4.09; N, 9.47. Found: C, 48.11;
H, 4.53; N, 9.19.14
Table 8 summarizes the results of the coupling reactions of
benzyl bromide and various terminal alkynes. The reaction of
Table 8. Coupling Reaction of Benzyl Bromide and
a
Terminal Alkynes in the Presence of 1
Crystallographic Structural Determination. Recrystallization of
1 by vapor diffusion of diethyl ether into a solution of dichloro-
methane afforded a black block. Data collection was carried out with a
monochromatic Mo Kα radiation source (λ = 0.71070 Å) at room
temperature. Eighteen preliminary data frames were measured at 0.5°
increments of ω, to assess the crystal quality and preliminary unit cell
parameters. The intensity images were also measured at 0.5° intervals
of ω. The intensity images were integrated using the Crystal Clear
program package. The structure was solved by direct methods
(SIR92). All non-hydrogen atoms were refined anisotropically by full-
matrix least-squares techniques. All hydrogen atoms were placed in
idealized positions and were included but not refined. Crystal data and
refinement details are summarized in Table S1 (Supporting
Information).
Recrystallization of 2 by layer diffusion of n-hexane into a solution
of dichloromethane afforded a black block. Data collection was carried
out with a monochromatic Mo Kα radiation source (λ = 0.71070 Å) at
room temperature. Eighteen preliminary data frames were measured at
0.5° increments of ω, to assess the crystal quality and preliminary unit
cell parameters. The intensity images were also measured at 0.5°
intervals of ω. The intensity images were integrated using the Crystal
Clear program package. The structure was solved by direct methods
(SIR92). All non-hydrogen atoms were refined anisotropically by full-
matrix least-squares techniques. All hydrogen atoms were placed in
idealized positions and were included but not refined. Crystal data and
refinement details are summarized in Table S1 (Supporting
Information).
Coupling Reaction of Iodoarenes and Terminal Alkynes. To
a mixture of 2 (8.5 mg, 7.5 μmol) and K3PO4 (64 mg, 0.30 mmol)
were added DMF (1.0 mL) and then an iodoarene (0.30 mmol) and a
terminal alkyne (0.30 mmol) in a pressure vial. After stirring at 120 °C
for 18 h, the mixture was cooled to room temperature and filtered
through a short plug of silica gel using ethyl acetate as an eluent. The
yield was determined by a GC analysis of the filtrate, or isolation by
silica gel column chromatography (hexane/ethyl acetate).
Coupling Reaction of Cinnamyl Chloride and Terminal
Alkynes. To a mixture of 2 (8.5 mg, 7.5 μmol) and K2CO3 (83
mg, 0.60 mmol) were added THF (2.0 mL) and then cinnamyl
chloride (0.30 mmol) and a terminal alkyne (0.30 mmol) in a pressure
vial. After stirring at 80 °C for 18 h, the mixture was cooled to room
temperature and filtered through a short plug of silica gel using ethyl
acetate as an eluent. The yield was determined by a GC analysis of the
filtrate, or isolation by silica gel column chromatography (hexane/ethyl
acetate).
b
entry
R
product
yield (%)
1
2
3
4
5
6
7
Ph
5a
5b
5c
5d
5e
5f
66
38
48
0
n-Hex
CH2OAc
CO2Me
TMS
63
70
50
TES
TIPS
5g
a
A mixture of benzyl bromide (0.30 mmol), a terminal alkyne (0.45
mmol), and K2CO3 (0.60 mmol) in DMAc (2.0 mL) was heated at 60
b
°C for 18 h in the presence of 1 (15 μmol). Isolated yields.
an alkyl acetylene such as 1-octyne gave the corresponding
product 5b in moderate yield (entry 2). While a conjugate ester
oligomerized or polymerized, a propargyl ester was tolerated
under the reaction conditions (entries 3 and 4). The reaction of
silylacetylenes afforded the products 5e−g in good yields
(entries 5−7).
CONCLUSION
■
We synthesized multinuclear copper complexes bridged by
diquinolylamidinates in order to search a catalyst exhibiting a
new reactivity for organic synthesis. The multinuclear
complexes catalyzed the coupling reaction of terminal alkynes
and organic halides. Although further studies are necessary to
understand how copper centers work cooperatively, the
multinuclear catalysts bridged by diquinolylamidinates showed
reactivity different from mononuclear copper catalysts
supported by ordinary chelate nitrogen ligands. By using the
multinuclear copper complexes, the coupling reaction with
cinnamyl chloride proceeded without the addition of
tetraalkylammonium salts. The multinuclear complexes cata-
lyzed the coupling reaction with benzyl bromide, whereas
mononuclear catalysts were not effective.
Coupling Reaction of Benzyl Bromide and Terminal
Alkynes. To a mixture of 1 (8.4 mg, 15 mmol) and K2CO3 (83
mg, 0.60 mmol) were added DMAc (2.0 mL) and then benzyl
bromide (0.30 mmol) and a terminal alkyne (0.45 mmol) in a pressure
vial. After stirring at 60 °C for 18 h, the mixture was cooled to room
temperature and filtered through a short plug of silica gel using ethyl
acetate as an eluent. The yield was determined by a GC analysis of the
filtrate, or isolation by silica gel column chromatography (hexane/ethyl
acetate).
EXPERIMENTAL SECTION
■
All reactions were carried out using the standard Schlenk technique
under a nitrogen atmosphere. Dry solvents were purchased and used
directly as received. The chelate-bridging ligands, qfamH and qaamH,
were prepared according to literature methods.12
Synthesis of Cu2(OAc)2(μ-OH)(μ-qfam) (1). To a solution of
qfamH (60 mg, 0.20 mmol) in acetone (8.0 mL) and water (0.40 mL)
was added Cu(OAc)2 (73 mg, 0.40 mmol). The mixture was stirred at
room temperature overnight to give a dark-green precipitate, which
was collected by filtration, washed with a small amount of acetone, and
dried under reduced pressure. Yield: 93 mg, 83%. Complex 1 was
paramagnetic. This procedure gave a hydrated complex. Water was not
removed under reduced pressure even at 40 °C. Anal. Calcd for
C23H20Cu2N4O5·H2O: C, 47.83; H, 3.84; N, 9.70. Found: C, 47.43; H,
3.92; N, 8.75.14
Synthesis of Cu4(OAc)4(μ-O)(μ-qaam)2 (2). To a solution of
qaamH (62 mg, 0.2 mmol) in acetone (8.0 mL) and water (0.40
mmol) was added Cu(OAc)2 (73 mg, 0.40 mmol). The mixture was
stirred at room temperature overnight. The addition of diethyl ether
(30 mL) to the solution gave a dark-green precipitate, which was
collected by filtration, washed with a small amount of diethyl ether,
ASSOCIATED CONTENT
* Supporting Information
Crystallographic data (CIF) for 1 and 2, H NMR spectra for
■
S
1
3−5, and characterization data for new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tsukada.naofumi@shizuoka.ac.jp.
■
E
DOI: 10.1021/om501139f
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge Prof. M. Kondo and K. Yamanishi
for X-ray crystal analysis.
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DOI: 10.1021/om501139f
Organometallics XXXX, XXX, XXX−XXX