Copper(II) complexes of a heterotopic N-heterocyclic carbene ligand: Preparation and catalytic application

Article abstract of DOI:10.1016/j.jorganchem.2018.01.053

Copper complexes containing a N-heterocylic carbene (NHC)/amidate/pyridine tridentate, 3-mesityl-1-(2-oxo-2-[{pyridin-2-ylmethyl}amino]ethyl)-imidazolin-2-ylidene (HL), were synthesized and characterized. By X-ray single crystal analysis, both Cu(L)(OAc) (3a) and Cu(L)Br (3b) show that the metal center is coordinated by a CNN-tridentate and a anionic donor in a slightly distorted square-planar geometry. These copper complexes are active as catalysts for oxidative bromination of dimethoxybenzene and styrene with the use of LiBr as the bromine source and oxygen as the terminal oxidant.

Full text of DOI:10.1016/j.jorganchem.2018.01.053

Journal of Organometallic Chemistry 859 (2018) 52e57
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Copper(II) complexes of a heterotopic N-heterocyclic carbene ligand:
Preparation and catalytic application
Shih-Chieh Aaron Lin, Yi-Hung Liu, Shie-Ming Peng, Shiuh-Tzung Liu*
Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Copper complexes containing a N-heterocylic carbene (NHC)/amidate/pyridine tridentate, 3-mesityl-1-
(2-oxo-2-[{pyridin-2-ylmethyl}amino]ethyl)-imidazolin-2-ylidene (HL), were synthesized and charac-
terized. By X-ray single crystal analysis, both Cu(L)(OAc) (3a) and Cu(L)Br (3b) show that the metal center
is coordinated by a CNN-tridentate and a anionic donor in a slightly distorted square-planar geometry.
These copper complexes are active as catalysts for oxidative bromination of dimethoxybenzene and
styrene with the use of LiBr as the bromine source and oxygen as the terminal oxidant.
© 2018 Elsevier B.V. All rights reserved.
Received 29 October 2017
Received in revised form
26 January 2018
Accepted 29 January 2018
Available online 1 February 2018
Keywords:
N-Heterocyclic carbene
Amidate
Tridentate
Bromination
Copper
1. Introduction
2. Results and discussion
Complexes with a multiple dentate containing a combination of
disparate donor atoms are believed to exhibit unusual properties as
each donor will give variable influence to the metal center. Among
various donors, N-heterocyclic carbenes (NHC) have received
2.1. Preparation and characterization of complexes
The preparation of the desired carbene precursor 2 is quite
straightforward (Scheme 2). Alkylation of N-mesitylimidazole with
considerable attention due to their strong
s
donor ability and sta-
ethyl
subsequently treated with 2-picolylamine to provide the amide-
linkage product 2. Treatment of with Ag2O followed by
a-bromoacetate gave the imidazolium salt 1, which was
bility. Thus, the use of NHC as the primary donor in the heterotopic
multi-dentates is a good ligand design and numerous systems are
reported [1]. On the other hand, amidate ligands, showing a
different donating property from NHC, have been used as a modular
set for early transition-metal complexes [2]. In surveying the
literature, only few heterotopic dentates containing both NHC and
amidate donors have appeared [3e6] and Scheme 1 shows few
known NHC-based tridentates containing an amidate donor [4e6].
Amidate donors in these NHC-based tridentate not only increase
the chemically stability of metal complexes and also provide a good
catalytic activity on the oxidative boron Heck-type reactions of aryl
boronic acids with alkenes [4c]. In this work we aimed to study the
coordination behavior of a heterotopic tridentate HL containing
NHC/amidate/pyridine donors toward Cu(II) ions and their catalytic
activity.
2
Cu(OAc)2 rendered the desired copper complex 3a as purple solids
in 78% yield. Similarly, the bromide analog 3b was obtained by the
reaction of 2 with Ag2O followed by the treatment of CuBr2.
Ligand 2 has been fully characterized by spectroscopic methods.
ESI-MS spectrum of 2 shows m/z at 335.17, which is consistent with
the formula of C20H23N4O [M-Br]. Absorptions at 1689 cmꢀ1 in the
IR spectrum is the characteristic stretching frequency for C¼O of
the amido moiety, whereas the 1H nmr spectrum of 2 in dmso-d6
shows signals at
d
¼ 9.53 (1H), 5.31 (2H) and 4.47 (2H) corre-
sponding to the protons of the C-2 imidazolium, methylene unit
adjacent to carbonyl and methylene unit attached to pyridinyl ring,
respectively. These data are consistent to the structure of 2.
Deprotonation of imidazolium salt 2 with a strong base,
expecting to produce the corresponding free carbene, unfortu-
nately failed presumably due to the interference from the depro-
tonation of the amido proton. Alternatively, the imidazolium salt
was converted into its silver carbene complex via the reaction of 2
* Corresponding author.
E-mail address: stliu@ntu.edu.tw (S.-T. Liu).
https://doi.org/10.1016/j.jorganchem.2018.01.053
0022-328X/© 2018 Elsevier B.V. All rights reserved.

S.-C. Aaron Lin et al. / Journal of Organometallic Chemistry 859 (2018) 52e57
53
Scheme 1. NHC-based tridentate containing an amidate donor.
Scheme 2. Preparation of copper(II) complexes.
with Ag2O in acetonitrile. Without further purification, the silver
Table 1
Selected bond distances (Å) and bond angles (deg) for 3a and 3b.
complex was subjected to undergo the carbene transfer reaction
with Cu(OAc)2. The desired copper carbene complex 3a was ob-
tained as dark purple solid in 78% yield, whereas carbene transfer
reaction with CuBr2 gave 3b as yellowish green solid in 70% yield.
Due to the paramagnetic nature of Cu(II), the 1H nmr spectrum
of 3a shows broaden signals, giving no information about the
structure. Infrared spectra of 3a show distinctive absorptions at
1587 and 1565 cmꢀ1 in solid state as well as 1592 and 1569 cmꢀ1 in
CHCl3, which are assigned to the carbonyl stretching of the amido
moiety and the coordinating acetate ligand, respectively.
Comparing to the free ligand, the carbonyl stretching frequency of
the amido group in 3a appears a dramatic shift, indicating the co-
ordination of amido moiety toward the metal center. Absorption
spectrum of 3a in MeOH exhibits three signals at 220
(ε ¼ 7.2 ꢁ 103), 256 (ε ¼ 4.2 ꢁ 103), 340 (sh, ε ¼ 2.4 ꢁ 102) and 602
(ε ¼ 40) nmꢀ1. The weak broad band around 602 nm is due to d-
d transition of copper(II) complexes in a tetrahedrally square planar
geometry [7]. As for 3b, electronic absorptions at 219, 250, 340 (sh)
and 640 nm and the carbonyl stretching frequency at 1595 cmꢀ1 are
quite similar to those for 3a, indicating a similarity of coordination
environment between two species. The meff values of the bulk solids
of 3a and 3b were found to be 1.43 and 1.71 mB at 295 K, respec-
tively, which are close to the spin value for d9-systems. Neverthe-
less, both structures are confirmed by X-ray crystallography.
Crystals of 3a-b suitable for X-ray diffraction analysis were ob-
tained by slow diffusion of Et2O into a saturated solution of the
complex in N,N-dimethylformamide. Selected key bond distances
and angles are summarized in Table 1, while ORTEP plot for 3a and
3b are illustrated in Figs. 1 and 2, respectively.
Complex
3a, X ¼ O(2)
3b, X ¼ Br(1)
Cu(1)-C(10)
Cu(1)-X
Cu(1)-N(3)
Cu(1)-N(4)
C(14)-O(1)
1.962(3)
1.989(2)
1.947(2)
2.005(3)
1.240(4)
1.330(4)
92.29(12)
82.03(11)
90.28(10)
99.67(11)
162.80(12)
161.14(11)
1.941(4)
2.3874(6)
1.942(3)
2.016(3)
1.244(4)
1.329(5)
92.09(14)
82.3(12)
95.79(9)
97.92(10)
158.88(15)
154.25(11)
C(14)-N(3)
C(10)-Cu(1)-N(3)
N(3)-Cu(1)-N(4)
N(4)-Cu(1)-X
X-Cu(1)-C(10)
C(10)-Cu(1)-N(4)
N(3)-Cu(1)-X
In both complexes, the copper atom displays a distorted square-
planar geometry with the coordination of
a
pyridine-
imidazolinylidene-amidate tridentate and a terminal acetate in 3a
or a bromide in 3b. The bond lengths of the Cu atom and the car-
bene carbon [Cu(1)-C(10)] are 1.962(3) Å in 3a and 1.941(4) Å in 3b,
respectively, which are typical for such bonding. The distance of
Cu(1)-N(3) is slightly shorter than that of Cu(1)-N(4), showing a
stronger donating ability of the amidate ligand versus the pyridinyl
nitrogen donor. The angle of N(3)-Cu(1)-N(4) (around 82ꢂ) devi-
ating from 90ꢂ is presumably due to the geometrical constraint of
Fig. 1. ORTEP plot of 3a (30% probability ellipsoids).

54
S.-C. Aaron Lin et al. / Journal of Organometallic Chemistry 859 (2018) 52e57
more attractive method due to the ecologically benign. Among
various oxidant, the use of O2 as the terminal oxidant ought to be
the best choice. Thus, we investigated the catalytic activity of 3a in
bromination of styrene and arenes with the use of LiBr as the
bromine source under molecular oxygen in this work. Bromination
of styrene into 1,2-dibromostyrene was chosen to establish the
optimized catalytic conditions.
A reaction of styrene with LiBr in the presence of CF3COOH in
acetonitrile gave the hydration and hydrobromination products as
the major product, which is typical for the electrophilic addition
(Table 2, entry 1). However, 1,2-dibromo-1-phenylethane,
PhCHBrCH2Br, became as the major product upon the addition of
complex 3a in the presence of oxygen atmosphere (Table 2, entry
2), indicating that the copper complex readily assisted the forma-
tion of the brominating agent, i. e. the oxidation of bromide took
place. By increasing the amount of CF3COOH or different acids, the
hydration pathway always competes with the dibromination (en-
tries 3e8). To our delight, the dibromination product was obtained
exclusively by running the reaction in a nitromethane solution
(entry 10). Other solvents provide the less satisfactory results. Ac-
cording to the reaction mechanism proposed by Stahl's and co-
workers (Scheme 3), disproportionation of CuBr2 would provide
the molecular bromine [9], which is for the electrophilic addition of
C¼C. The Cu(I) intermediate could be then oxidized to regenerate
Cu(II) species under acidic conditions. Therefore, the catalytic
amount of 3a responses for the generation of the brominating agent
for the reaction.
To examine the activity of 3a for monitoring reaction progress in
real time, the bromination of styrene catalyzed by 3a was per-
formed and the amount of products were analyzed by 1H NMR
spectroscopy (Fig. 3). At the beginning of the reaction, styrene was
consumed rapidly to form PhCHBrCH3 majorly with a small amount
of PhCHBrCH2Br. However, as the reaction proceeded, the concen-
tration of PhCHBrCH3 was slowly decreased and converted into
PhCHBrCH2Br and eventually reached 100% yield of dibromination
product in 16 h. In a separated experiment, without the presence of
Cu(II) catalyst, we found that styrene was converted into
PhCHBrCH3 via hydrobromination under this reaction condition.
Thus, the pathway of this reaction is proposed in Scheme 4.
Initially, styrene was hydrobrominated to yield PhCHBrCH3. This
step is a reversible reaction and styrene is able to re-generate via an
E1 elimination. In the meantime, styrene was converted into the
PhCHBrCH2Br as the brominating agent was generated in situ by the
Fig. 2. ORTEP plot of 3b (30% probability ellipsoids).
the chelation. It is noticed that the distance between Cu(1) and O(3)
in complex 3a is 2.574(3) Å, indicating a weak interaction. No sig-
nificant discrepancies in other bond lengths and angles are noticed
in complexes 3a and 3b.
2.2. Catalytic bromination of styrene
Due to the low cost and the diverse redox property of copper
metal ions, the use of copper compounds as catalysts in oxidation
reactions has received much attention. NHC-copper catalysts have
provided good level of activity in oxidation of arenes [8]. On the
other hand, the use of halide ions as a halogen source together with
a suitable oxidant for the halogenation of organic substrates is a
Table 2
Bromination of styrene catalyzed by 3a with LiBr as bromine source.a
entry
LiBr
(mmol)
Acid (mmol)
Solvent
Conv.
(%)
Yields (%)b
1c
2
3
4
5
6
7
8
9
10
11
12
13
14
4.0
4.0
4.0
4.0
2.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
CF3CO2H (1.6)
CF3CO2H (1.2)
CF3CO2H (1.6)
CF3CO2H (2.0)
CF3CO2H (2.0)
H3PO4 (0.4)
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3NO2
CH3NO2
dioxane
toluene
acetone
DMF
98
96
100
100
100
95
e
36
28
e
60
20
15
12
11
35
38
24
0
47
83
72
60
27
31
42
91
98
40
17
e
13
12
29
25
26
7
H3PO4 (1.2)
H2SO4 (0.4)
97
95
CF3CO2H (1.6)
CF3CO2H (1.2)
CF3CO2H (1.6)
CF3CO2H (1.6)
CF3CO2H (1.6)
CF3CO2H (1.6)
100
100
94
100
86
e
e
e
e
80
75
e
e
71
63
e
a
Reaction conditions: styrene (0.4 mmol), LiBr, 3a (0.02 mmol, 5 mol%) and acid in solvent (1 mL) under O2 (1 atm) at 60 oC for 20 h.
NMR yields.
No catalyst.
b
c

S.-C. Aaron Lin et al. / Journal of Organometallic Chemistry 859 (2018) 52e57
55
catalytic activity on the generation of “Br2”, but not as good as
complexes 3a-b, indicating that the designed ligand does assist the
metal ions in generation of bromine for the addition of C¼C.
2.3. Catalytic bromination of m-dimethoxybenzene
The experimental reaction condition of the bromination of m-
dimethoxybenzene (Scheme 5) was based on the study by Stahl in a
similar reaction [9]. A mixture of m-(MeO)2C6H4, LiBr and 3a (5 mol
%) in acetic acid under atmospheric pressure of O2 was heated at
60 ꢂC for 24 h (Table 4). The mono-brominated product 4 was ob-
tained (Table 4, entries 1e4) in various amount under different
reaction parameters. The condition providing the best yield is car-
rying out the reaction with the use of 4 equiv. molar of LiBr at
100 ꢂC, however, with a small amount of the dibromination product
5 (entry 4).
Despite this optimization, we further examined other optimized
conditions. Instead of using acetic acid as the solvent, acetonitrile
was chosen as the solvent for the further investigation. By manip-
ulating the amount of CF3COOH and LiBr, compound 4 was still
obtained as the major product, but not as good as the above opti-
mized condition (Table 4, entries 5e8). According to the reaction
mechanism for this halogenation proposed by Stahl's work
(Scheme 3), the regeneration of Cu(II) species proceeds under acidic
conditions. Inspired by this hint, we screened various acids for this
catalysis to examine such effect (entries 9e14). To our delight, the
desired mono-bromination product 4 could be obtained almost
quantitatively with the use of sulfuric acid and 1.5 equivmolar of
LiBr (entry 11). Based on this condition, solvent effect was then
examined (entries 15e19) and acetonitrile was the best choice for
this catalysis. After these investigation, the standard reaction con-
ditions were determined to be: 5 mol% of 3a, 1.5 equivalents of LiBr
and 1 equivalent of H2SO4 in acetonitrile at 70 ꢂC under an oxygen
atmosphere for 24 h (Table 4, entry 11).
Scheme 3. Catalytic pathway for bromination of C¼C.
Cu(II) catalyst. However, the bromination of C¼C is an irreversible
process. Thus, PhCHBrCH2Br becomes the final product upon a
prolong treatment. The addition of bromine toward double bond
under this catalytic system was also evidenced by the other sub-
strate. Under the optimized condition, cyclohexene was transferred
into trans-1,2-dibromocyclohexane directly within 4 h. No cyclo-
hexyl bromide was detected during the reaction, i.e. hydro-
bromination does not occur with cyclohexene and the addition of
bromine to C¼C takes place directly.
We also evaluated the activity of various copper complexes for
the bromination of styrene under the optimal conditions (Table 3).
It is noticed that both complexes 3a and 3b have the similar activity,
as expected. Quite a number of Cu(II) complexes do exhibit some
A series of experiments was carried out to evaluate the ability of
various copper complexes for the bromination under the optimized
conditions for comparison (Table 5). Some copper complexes
Table 3
Activity of various Cu(II) complexes in bromination of styrene.a
Entry
Catalyst
1
2
3
4
5
6
7
8
Complex 3a
Complex 3b
CuBr2
(Py)2CuBr2
(Py)4CuBr2
(PMDETA)CuBr2
(bpy)CuBr2
[(bpy)2CuBr]Br
[(phen)2CuBr]Br
[(phen)CuBr]2
(tpy)CuBr2
98%
100%
67%
57%
69%
22%
20%
30%
9%
e
e
e
e
27%
39%
27%
73%
70%
64%
84%
69%
75%
84%
e
e
e
e
e
e
9
e
10
11
12
29%
20%
e
e
e
No Cu complex
11%
Fig. 3. Catalytic bromination of styrene with LiBr [Reaction conditions: styrene
(0.6 mmol), LiBr (6 mmol), TFA (1.8 mmol) and 3a (0.03 mmol) in CH3NO2 (1.5 mL) at
a
Condition: styrene (0.4 mmol), LiBr (4.0 mmol), CF3CO2H (1.2 mmol) and Cu
complex (5 mol%) in CH3NO2 (1 mL) at 60 ꢂC for 20 h, yields of products were
determined by 1H NMR spectroscopy.
60 ꢂ
PhCHBrCH2Br.
C
under O2 atmosphere (1 atm).
(
)
A
PhCH ¼ CH2, (-) PhCHBrCH3, (:)
Scheme 4. Pathway of catalytic bromination of styrene.

56
S.-C. Aaron Lin et al. / Journal of Organometallic Chemistry 859 (2018) 52e57
Scheme 5. Bromination of arene catalyzed by 3a.
exhibited good activity for this electrophilic aromatic bromination
(Table 5, entries 3e6). By shortening the reaction to 12 h, both
complex 3a and 3b prove to be superior to other copper complexes
(Table 5, entries 12e17), indicating a ligand effect on the catalysis.
The turnover number for 3a is about 20 mol(product)/mol(cata-
lyst), which is higher than other reported works [9].
instrument operating at a magnetic field of 0.1 T between 2 and
300 K.
4.2. Synthesis and catalysis
4.2.1. Preparation of 3-(2-ethoxy-2-oxoethyl)-1-mesityl-1H-
imidazole-3-ium bromide (1)
A mixture of 1-mesitylimidazole (3.2 g, 17 mmol) and ethyl
bromoacetate (3.5 g, 20 mmol) in anhydrous acetonitrile (40 mL)
3. Summary
In this work, we have synthesized and characterized Cu(II)
complexes with a tridentate with NHC/amidate/pyridine donors.
Coordination geometry of both copper complexes 3a and 3b is in a
slightly distorted square-planar geometry as demonstrated by
single crystal and spectroscopic analyses. These copper complexes
are active catalysts for bromination of styrene and dimethox-
ybenzene with the use of LiBr as the bromine source and the oxygen
as the final oxidant. The study proves that the designed ligand does
assist the copper center in generating the brominating agent for
organic substrates. Compared to the literature work, the copper
complexes 3a and 3b appear to be excellent catalysts, which makes
this process potentially useful for synthetic application.
Table 5
Comparison of activity of various Cu(II) complexes.a
entry
Catalystb
Conv.
Yieldc of 4
Yieldc of 5
1
2
3
4
5
6
7
8
3a
3b
CuBr2
100%
100%
87%
94%
100%
86%
74%
60%
35%
51%
62%
99%
100%
65%
80%
79%
73%
95%
80%
85%
90%
95%
84%
72%
58%
34%
49%
62%
98%
100%
64%
78%
79%
73%
4%
18%
e
(Py)2CuBr2
(Py)4CuBr2
(PMDETA)CuBr2
(bpy)CuBr2
[(bpy)2CuBr]Br
[(phen)2CuBr]Br
[(phen)CuBr]2
(tpy)CuBr2
3a
3b
CuBr2
(Py)2CuBr2
(Py)4CuBr2
(PMDETA)CuBr2
e
e
e
e
e
9
e
10
11
12d
13d
14d
15d
16d
17d
e
e
4. Experimental section
e
e
4.1. Methods and materials
e
e
e
General information. Chemicals and solvents were of analytical
grade and used without further purification. Nuclear magnetic
resonance spectra were recorded on a 400 MHz spectrometer.
Chemical shifts are given in parts per million relative to Me4Si for
1H and 13C NMR. N-mesitylimidazole was prepared according to the
literature method [10]. Magnetic measurements were carried out
on polycrystalline samples with a Quantum Design MPMS-3 SQUID
e
a
Conditions: m-C6H4(OMe)2 (0.3 mmol), LiBr (0.45 mmol), Cu complex (5 mol%)
and H2SO4 (0.3 mmol) in CH3CN (0.5 mL) at 70 oC for 24 h.
b
PMDETA¼ N,N,N0,N00,N00-pentamethyldiethylenetriamine; bpy ¼ bipyridine;
phen ¼ 1,10-phenanthroline.
c
NMR yields.
Running the reaction for 12 h.
d
Table 4
a
Optimization for the bromination of m-C6H4(OMe)2.
entry
LiBr (mmol)
Acid
solvent
T
Conv.
(%)
Yield (%)b
4
(oC)
5
1
2
3
4
5
6
7
8
0.6
1.2
1.2
1.2
1.2
0.6
0.45
0.3
1.2
0.6
0.45
0.3
1.2
1.2
0.45
0.45
0.45
0.45
0.45
CH3COOH
CH3COOH
CH3COOH
CH3COOH
CH3CO2H (1 mL)
CH3CO2H (1 mL)
CH3CO2H (1 mL)
CH3CO2H (1 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3CN (0.5 mL)
CH3NO2 (0.5 mL)
dioxane (0.5 mL)
toluene (0.5 mL)
DMF (0.5 mL)
60
60
80
100
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
47
63
68
46
62
66
92
67
87
84
83
60
85
95
71
81
17
70
82
27
30
53
e
e
e
100
100
100
100
83
100
100
100
72
83
18
100
100
33
6
CF3CO2H (1.5 mmol)
CF3CO2H (1.5 mmol)
CF3CO2H (1.5 mmol)
CF3CO2H (1.5 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H3PO4 (0.6 mmol)
CH3CO2H (1.5 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
H2SO4 (0.3 mmol)
30
11
13
e
9
35
14
4
10
11
12
13
14
15
16
17
18
19
e
e
e
8
e
e
38
56
e
CH3OH (0.5 mL)
e
a
Reaction conditions: m-C6H4(OMe)2 (0.3 mmol), LiBr, 3a (5 mol%) and acid in solvent under O2 (1 atm) for 24 h.
NMR yields.
b

S.-C. Aaron Lin et al. / Journal of Organometallic Chemistry 859 (2018) 52e57
57
was heated to reflux for 40 h. After removal of solvents, the residue
4.3. X-ray crystallographic analysis
was re-precipitated from methanol/ether 3 times. The desired
compound 1 was obtained as light-yellow solids (5.33 g, 89%): 1H
Crystals suitable for X-ray determination were obtained for 3a-b
by slow diffusion of ether into a DMF solution at room temperature.
Cell parameters were determined by a Siemens SMART CCD
NMR (400 MHz, DMSO‑d6):
d 9.47 (s, 1H), 8.05 (s, 1H), 7.96 (s, 1H),
7.16 (s, 2H), 5.38 (s, 2H), 4.26 (q, J ¼ 8.0 Hz, 2H), 2.33 (s, 3H), 2.02 (s,
6H), 1.25 (t, J ¼ 6 Hz, 3H); 13C NMR (100 MHz):
d
167.34, 141.03,
diffractometer. Crystal data 3a:
C
22H24CuN4O3, Fw ¼ 455.99,
139.61, 134.91, 131.73, 129.98, 125.17, 124.10, 62.70, 50.65, 21.30,
Triclinic, P-1, a ¼ 8.9332(6) Å, b ¼ 9.1999(3) Å, c ¼ 13.6399(5) Å,
17.54, 14.64. IR (CDCl3) y(C¼O) 1750 cmꢀ1
.
a
¼ 100.225(3)o,
b
¼ 107.748(5)ꢂ,
g
¼ 93.324(4)ꢂ, V ¼ 1043.14(9) Å3,
Z ¼ 2,
Dcalcd ¼ 1.452 Mg/m3,
F(000) ¼ 474,
crystal
size:
0.20 ꢁ 0.15 ꢁ 0.10 mm3, 3.30 to 25.00ꢂ, 6176 reflections collected,
3646 reflections [R(int) ¼ 0.0311], Final R indices [I > 2sigma(I)]:
R1 ¼0.0445, wR2 ¼ 0.1105, for all data R1 ¼0.0527, wR2 ¼ 0.1198,
Goodness-of-fit on F2 ¼ 1.078. Crystal data 3b: C20H21BrCu-
N4O.0.5(C4H10O), Fw ¼ 513.92, Monoclinic, P2(1)/n, a ¼ 8.1841(4) Å,
4.2.2. Preparation of ligand (2)
A mixture of 1 (2 g, 5.7 mmol) and 2-picolylamine (0.9 g,
8.5 mmol) in ethanol (40 mL) was stirred at 60 ꢂC for 65 h. After
removal of ethanol, the residue was re-precipitated from methanol/
ether 3 times to yield yellow solids (2.13 g, 90%): 1H NMR (400 MHz,
b ¼ 21.3054(7) Å, c ¼ 12.8818(4) Å,
a
¼ 90ꢂ,
b
¼ 91.838(3)ꢂ,
g
¼ 90ꢂ,
DMSO‑d6):
d
¼ 9.53 (s, 1H), 9.28 (t, J ¼ 4 Hz, 1H), 8.52 (d, J ¼ 4 Hz,
V ¼ 2244.99(15) Å3, Z ¼ 4, Dcalcd ¼ 1.521 Mg/m3, F(000) ¼ 1048,
1H), 8.09 (s, 1H), 7.94 (s, 1H), 7.78 (t, J ¼ 8 Hz, 1H), 7.43 (d, J ¼ 8 Hz,
crystal size: 0.20 ꢁ 0.15 ꢁ 0.10 mm3, 3.14 to 25.00ꢂ, 8012 reflections
1H), 7.30 (t, J ¼ 6 Hz, 1H), 7.14 (s, 2H), 5.31 (s, 2H), 4.47 (d, J ¼ 4 Hz,
collected, 3933 reflections [R(int) ¼ 0.0370], Final
R indices
2H), 2.32 (s, 3H), 2.03 (s, 6H); 13C NMR (100 MHz):
d
¼ 165.8, 158.3,
[I > 2sigma(I)]: R1 ¼0.0416, wR2 ¼ 0.0873, for all data R1 ¼0.0629,
wR2 ¼ 0.0990, Goodness-of-fit on F2 ¼ 1.028. The structure was
solved using the SHELXS-97 program [11] and refined using the
SHELXL-97 program [12] by full-matrix least-squares on F2 values.
149.6, 140.9, 139.6, 137.5, 135.0, 131.8, 129.9, 125.3, 123.8, 123.1,
122.0, 51.7, 45.2, 21.3, 17.6. IR (CDCl3) y(N-H) 3214 and y(C¼O)
1689 cmꢀ1. ESI-MS: m/z [M-Br] Calcd. for C20H23N4O: 335.18,
Found: 335.17.
5. Supplementary data
4.2.3. Preparation of complex 3a
CCDC 1579378 and 1579379 contain the supplementary crys-
tallographic data for complexes 3a and 3b, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
A mixture of 2 (0.3 g, 0.72 mmol) and Ag2O (0.1 g, 0.43 mmol) in a
50 mL flask was flashed with nitrogen gas. Anhydrous acetonitrile
(10 mL) was syringed intothe flask. The resulting solutionwas stirred
at 65 ꢂC for 20 h. Cu(OAc)2$H2O (0.15 g, 0.72 mmol) was added to the
above solution and stirred for another 20 h. The reaction mixture was
filtered through Celite and ether was added to the filtrate to yield the
desired complex 3a as purple solids (256 mg, 78%). IR (KBr) y(C¼O)
1587 and 1565 cmꢀ1; IR (CHCl3) y(C¼O) 1592 and 1569 cmꢀ1. UVeVis
(MeOH) lmax (ε): 220 (ε ¼ 7.2 ꢁ 103), 256 (ε ¼ 4.2 ꢁ 103), 340 (sh,
Acknowledgment
ε ¼ 2.4 ꢁ 102) and 602 (ε ¼ 40) nmꢀ1
meff ¼ 1.43 mB (295 K); HRMS
;
We thank the National Science Council, Taiwan for the financial
support (NSC100-2113-M-002-001-MY3).
(ESI): m/z 396.1007 [M-OAc]þ, calcd. 396.1017.
References
4.2.4. Preparation of copper complex 3b
A mixture of 2 (55 mg, 0.13 mmol) and Ag2O (18.5 mg, 0.08 mmol)
in a 5 mL flask was flashed with nitrogen. Anhydrous acetonitrile
(1.5 mL) was added and the resulting mixture was heated at 65 ꢂC for
20 h. CuBr2 (29.5 mg, 0.13 3 mmol) and K2CO3 (18.3 mg, 0.13 mmol)
was added to the above solution. After stirring for another 20 h, the
mixture was filtered through Celite. The filtrate was concentrated
and the residue was re-precipitated from acetonitrile/ether to give
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€
€
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