Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: Synthesis, structure, and catalytic properties

Article abstract of DOI:10.3762/bjoc.12.85

A series of copper complexes (3-6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes we

Full text of DOI:10.3762/bjoc.12.85

Bi- and trinuclear copper(I) complexes of
1,2,3-triazole-tethered NHC ligands: synthesis,
structure, and catalytic properties
Shaojin Gu*1, Jiehao Du1, Jingjing Huang1, Huan Xia1,2, Ling Yang1, Weilin Xu1
and Chunxin Lu*2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2016, 12, 863–873.
1School of Materials Science and Engineering, Wuhan Textile
University, Wuhan 430200, People's Republic of China and 2College
of Biological, Chemical Sciences and Engineering, Jiaxing University,
Jiaxing 314001, People's Republic of China
doi:10.3762/bjoc.12.85
Received: 12 January 2016
Accepted: 10 April 2016
Published: 03 May 2016
Email:
Shaojin Gu* - gushaojin@hotmail.com; Chunxin Lu* -
chunxin.lu@mail.zjxu.edu.cn
Associate Editor: I. Marek
© 2016 Gu et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
copper; CuAAC reaction; : N-heterocylic carbene; 1,2,3-triazole
Abstract
A series of copper complexes (3–6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via
simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were
fully characterized by NMR, elemental analysis (EA), and X-ray crystallography. In particular, [Cu2(L2)2](PF6)2 (3) and
[Cu2(L3)2](PF6)2 (4) were dinuclear copper complexes. Complexes [Cu3(L4)2](PF6)3 (5) and [Cu3(L5)2](PF6)3 (6) consist of a
triangular Cu3 core. These structures vary depending on the imidazolium backbone and N substituents. The copper–NHC com-
plexes tested are highly active for the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction in an air atmosphere at room
temperature in a CH3CN solution. Complex 4 is the most efficient catalyst among these polynuclear complexes in an air atmo-
sphere at room temperature.
Introduction
N-Heterocyclic carbene (NHC) have interesting electronic and transformations. Recently, the easy synthesis and versatile coor-
structural properties. This resulted in their use as versatile dination ability of 1,2,3-triazoles have led to an explosion of
ligands in organometallic chemistry and homogeneous cataly- interest in coordination chemistry [21] and homogeneous catal-
sis [1-12]. A number of transition metal complexes of NHCs ysis [22-26]. Although a number of metal complexes contain-
containing pyridine [13], pyrimidine [14], pyrazole [15,16], ing 1,4-disubstituted-1,2,3-triazole ligands were well studied,
naphthyridine [17], pyridazine [18], and phenanthroline [19,20] reports concerning their preparation and use of 1,4-disubsti-
donating groups have been studied in metal-catalyzed organic tuted-1,2,3-triazoles bearing NHC ligands are rare [22,23].
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Beilstein J. Org. Chem. 2016, 12, 863–873.
Elsevier et al. [23] reported several of palladium(II) complexes salts have been characterized by NMR spectroscopy. The
containing a heterobidentate N-heterocyclic carbene-triazolyl 1H NMR spectra of these imidazolium salts show singlet peaks
ligand. These palladium(II) complexes are active precatalysts in between 10.04 and 10.89 ppm in DMSO-d6. As seen in
the transfer semihydrogenation of alkynes to Z-alkenes. Scheme 1, copper–NHC complexes 3–6 can be obtained in
Messerle et al. [26] synthesized a series of new cationic Rh(I), 52–90% yields via directly reacting the corresponding imida-
Rh(III) and Ir(III) complexes containing hybrid bidentate zolium salts with an excess of copper powder in CH3CN at
N-heterocyclic carbene-1,2,3-triazolyl donors. We [27] have 50 °C for 5 h.
synthesized a series of nonsymmetrical pincer palladium and
platinum complexes containing 1,2,3-triazole-tethered NHC As shown in Scheme 1, reactions of the pyrimidine imida-
ligands. The obtained palladium complexes displayed high ac- zolium salt 1a with copper powder in acetonitrile afforded a
tivity in aqueous Suzuki–Miyaura cross-coupling reactions.
light yellow Cu(II) complex. In complex 2, the carbenic carbon
atom was oxidized into carbonyl, which is similar with the re-
We are interested in the synthesis and use of functionalized ported pyrimidyl-imidazole complex [32]. However, a red binu-
NHC ligands [20,28-31]. Herein, the synthesis, structural char- clear Cu(I) complex 3 was obtained in 57% yield when we
acterization, and catalytic properties of a few copper-1,2,3-tri- reacted pyrimidyl benzimidazolium salt 1b with copper powder.
azole-tethered NHC complexes is reported.
Furtherly, we got a yellow Cu(I)–NHC complex 4 in about
70% yield from pyridine imidazolium salt 1c and copper
powder (Scheme 1). In addition, a triangular Cu(I) complex 6
Results and Discussion
Synthesis and spectroscopic characterization can be obtained when a flexible ligand was used. Complex 6
The imidazolium salts (1a–e) were prepared according to the re- consists of a triangular Cu3 core bridged by three NHCs, which
ported procedure in 61–90% yields [27]. These imidazolium is similar with the published Cu3 complexes containing flexible
Scheme 1: Synthesis of copper complexes 2–6.
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Beilstein J. Org. Chem. 2016, 12, 863–873.
ligands [33]. Interestingly, we can also obtain a similar trian- space group Pnna. The remaining atoms of the cation are
gular Cu3 complex 5 rather than a binuclear copper complex related by a crystallographic 2-fold symmetry. In complex 2,
using a rigid pyridine benzimidazolium salt 1d. These results the copper ion is four-coordinate in a distorted square planar
demonstrated that the structures vary depending on the N sub- ligand environment of two nitrogen atoms and two oxyen
stituents and on the imidazolium backbone. Fine adjustment of atoms. The Cu–O bonds are in trans configuration and Cu–O
the structure of the ligand can lead to different structures.
distances are shorter than Cu–N distances. The two ligands are
arranged in head-to-tail manner. And the Ntriazole did not partic-
All of the prepared copper–NHC complexes are stable in air. ipate in the corrdination.
They were fully characterized by NMR, elemental analysis
(EA), and X-ray crystallography. The generation of these Single crystals of complex 3 suitable for an X-ray diffraction
copper–NHC complexes were confirmed by the absence of the study were grown from acetonitrile solution and diethyl ether.
1H NMR resonance signal of the acidic imidazolium protons The molecular structure of complex 3 is depicted in Figure 2.
between 10.04 and 10.89 ppm. The 1H NMR spectra of all
the complexes display only one set of resonance signals
assignable to the corresponding ligands, indicating two or
three magnetically equivalent ligands. 13C NMR spectra of
the copper(I) complexes showed their carbenic carbon reso-
nances at 177.6–191.2 ppm, which are in the normal range of
157.6–216 ppm [34,35].
Single crystal X-ray diffraction studies
To obtain additional insight into the coordination and supramo-
lecular properties, suitable single crystals of all the copper
complexes were obtained for single-crystal X-ray diffraction
analysis. Crystals were grown by slow diffusion of diethyl ether
into an acetonitrile solution of the copper complex at room
temperature.
Figure 2: ORTEP the cationic section of [Cu2(L2)2](PF6)2 (3). Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms and
anions have been removed for clarity. Selected bond distances (Å) and
angles (°): Cu2-C5 1.896(3), Cu2-N14 1.911(3), Cu2-N1 2.362(3),
Cu2-Cu1 2.7867(7), Cu1-C26 1.898(3), Cu1-N7 1.915(3), Cu1-N8
2.340(3); C5-Cu2-N14 173.37(13), C5-Cu2-N1 77.64(13), N14-Cu2-N1
108.15(12), C5-Cu2-Cu1 69.80(9), N14-Cu2-Cu1 111.70(8), N1-Cu2-
Cu1 98.90(7), C26-Cu1-N7 167.08(15), C26-Cu1-N8 78.22(13),
N7-Cu1-N8 111.77(13), C26-Cu1-Cu2 73.57(9).
Green-yellow single crystals of complex 2 suitable for an X-ray
diffraction study were grown from acetonitrile solution and
diethyl ether. The molecular structure of complex 2 in the solid
state is depicted in Figure 1 along with the principal bond
lengths and angles. Complex 2 crystallizes in the orthorhombic
Figure 1: X-ray diffraction structure of copper(II) complex 2 with thermal ellipsoids drawn at 30% probability. The anion and hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles (°): Cu1-O1 1.931(4), Cu1-N6 2.042(5); O1-Cu1-O1A 180.0(3), O1-Cu1-N6A 90.5(2),
O1-Cu1-N6 89.5(2), N6-Cu1-N6A 180.00(8). Symmetry transformations used to generate equivalent atoms: −X, Y, 0.5−Z.
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Beilstein J. Org. Chem. 2016, 12, 863–873.
Complex 3 crystallizes in the monoclinic space group C2/c. The given in Figure 4. The molecule structure consists of a trian-
Cu(I) complex contains two crystallographically equivalent Cu gular Cu3 core bridged by three NHCs ligands. Each NHC
centers, which are doubly bridged by two L2 ligands. The two forms the 3c-2e bond with two Cu(I) ions with almost equal
ligands are arranged in head-to-tail manner. The copper ions are bond distances (average 2.085 Å), longer than normal Cu–NHC
each tri-coordinated by one carbene carbon atom, one nitrogen bonds and reported triangular Cu3 complexes [33,41]. The Cu3
from pyrimidine, and one nitrogen atom of the triazole rings cores of complex 5 possess nearly equilateral angles close to
from two different L2 ligands. The Cu–carbene bond distances 60°, whereas in complex 6, the core is crystallographically
are 1.896(6) and 1.899(5) Å, which are comparable to the restrained to an equilateral triangle. The Cu–Cu distances are
known Cu(I)–NHC complexes [36-39]. The Cu1–Cu2 separa- around 2.4887 Å and are shorten than that of complexe 6, which
tion is 2.7867(7) Å, showing a weak metal−metal interaction. may be attributed to more rigid ligand.
The molecular structure of complex 4 is depicted in Figure 3.
Complex 4 consists of the cation unit [Cu2(L3)2]2+ and two
hexafluorophosphate anions. Complex 4 crystallizes in the
triclinic space group P-1. The two ligands are also arranged in
head-to-tail manner. Each copper ion is three-coordinate in a
trigonal planar ligand environment of two nitrogen atoms and
one NHC carbon center. The Cu–carbene bond distances are
1.888(6) and 1.899(5) Å which are similar with reported
copper-carbene complexes (1.85–2.18 Å) [40]. The Cu1–Cu2
separation is 2.6413(12) Å is shorter than in complex 3, and
slightly higher than reported Cu–Cu separations (2.4907 to
2.5150 Å) of the triangular Cu(I)–NHC clusters [33], showing a
weak metal–metal interaction.
Figure 4: ORTEP drawing of [Cu3(L4)3](PF6)3 (5). Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms and anions
have been removed for clarity. Selected bond distances (Å) and angles
(°): Cu2-N17 2.015(5), Cu2-C50 2.074(6), Cu2-N19 2.107(6), Cu2-C72
2.142(6), Cu2-Cu4 2.4899(11), Cu2-Cu3 2.4928(11), Cu3-N11
2.038(5), Cu3-C27 2.069(6), Cu3-C50 2.113(6), Cu3-N13 2.133(5),
Cu3-Cu4 2.4833(10), Cu4-N22 2.043(5), Cu4-C72 2.044(7), Cu4-C27
2.071(6), Cu4-N7 2.086(6); N17-Cu2-C50 94.8(2), N17-Cu2-N19
112.1(2), C50-Cu2-N19 106.8(2), N17-Cu2-C72 93.5(2), C50- Cu2-
C72 165.4(2), N19-Cu2-C72 81.0(2), N17-Cu2-Cu4 125.46(18), C50-
Cu2-Cu4 113.86(16), N19-Cu2-Cu4 102.90(19), C72-Cu2-Cu4
51.72(17), N17-Cu2-Cu3 129.13(16), C50-Cu2-Cu3 54.18(16), N19-
Cu2-Cu3 115.04(17), C72-Cu2-Cu3 111.50(17), Cu4-Cu2-Cu3
59.79(3), N11-Cu3-C27 94.1(2), N11-Cu3-C50 90.9(2), C27-Cu3-C50
Figure 3: ORTEP drawing of [Cu2(L3)2](PF6)2 (4). Thermal ellipsoids
163.7(2), N11-Cu3-N13 112.2(2), C27-Cu3-N13 112.1(2), C50-Cu3-
are drawn at the 30% probability level. Hydrogen atoms and anions
N13 80.1(2), N11-Cu3-Cu4 131.09(16), C27-Cu3-Cu4 53.18(17), C50-
have been removed for clarity. Selected bond distances (Å) and angles
Cu3-Cu4 112.70(16), N13-Cu3-Cu4 113.70(15), N11-Cu3-Cu2
(°): Cu1-C26 1.888(6), Cu1-N5 1.912(5), Cu1-N7 2.289(5), Cu1-Cu2
128.00(15), C27-Cu3-Cu2 112.99(17), C50-Cu3-Cu2 52.76(16), N13-
2.6413(12), Cu2-C8 1.899(5), Cu2-N11 1.922(4), Cu2-N1 2.311(5);
Cu3-Cu2 97.90(16), Cu4-Cu3-Cu2 60.05(3), N22-Cu4-C72 94.4(2),
C26-Cu1-N5 159.2(2), C26-Cu1-N7 79.0(2), N5-Cu1-N7 116.65(19),
N22-Cu4-C27 92.5(2), C72-Cu4-C27 167.8(2), N22 -Cu4-N7 99.9(2),
C26-Cu1-Cu2 72.49(17), N5-Cu1-Cu2 113.20(15), N7-Cu1-Cu2
C72-Cu4-N7 107.5(2), C27-Cu4-N7 81.1(2), N22-Cu4-Cu3 134.20(17),
105.13(12), C8-Cu2-N11 166.1(2), C8-Cu2-N1 78.6(2), N11-Cu2-N1
C72-Cu4-Cu3 115.49(17), C27-Cu4-Cu3 53.10(17), N7-Cu4-Cu3
110.5(2), C8-Cu2-Cu1 70.45(16), N11-Cu2-Cu1-116.14(15), N1- Cu2-
102.67(18), N22-Cu4-Cu2 134.48(17), C72-Cu4-Cu2 55.33(17), C27-
Cu1 102.03(13).
Cu4-Cu2 113.02(17), N7-Cu4 -Cu2 120.11(16), Cu3- Cu4- Cu2
60.16(3).
Complex 5 was also characterized via X-ray diffraction. It's
structure is shown in Figure 4. Complex 5 consists of two inde- Complex 6 has also been characterized by single crystal X-ray
pendent molecules in the unit cell. Here, only one molecule was diffraction (Figure 5). Complex 6 crystallizes in the hexagonal
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Beilstein J. Org. Chem. 2016, 12, 863–873.
P21/c) [33] and to the trinuclear copper(I) complex containing a
symmetric 1,3-bis(triazole)benzimidazolylidene ligand (mono-
clinic, C2/c) [38]. Three copper atoms are bridged by three
NpyridineCNtriazole NHC ligands forming a Cu3 ring with three
Cu–Cu–Cu angles of 60.0. The geometry of the copper center
can be described as distorted trigonal planar. Each copper ion is
coordinated by one pyridine, one triazole, and two benzimida-
zolylidene ligands displaying a distorted tetrahedral geometry.
The Cu–Cu distance is around 2.5145(12) Å showing a weak
metal–metal interaction, which is similar with the reported tri-
angle Cu(I) complexes and is shorter than in complexes 3 and 4.
The Cu–N and Cu–C bond distances fall in the range of
2.092(5)–2.152(5) Å and 2.024(6)–2.092(6) Å, respectively,
which are slightly longer than in dinuclear complexes 3 and 4.
Benzimidazolylidene acts as a bridging ligand in a u2 mode and
bonded equally to two Cu(I) ions, which is only observed in a
few silver(I) and copper(I) complexes.
Catalytic application in CuAAC reactions
Inspired by the catalytic activity of Cu(I) species supported by
NHC ligand in Cu-catalyzed azide–alkyne cycloaddition
(CuAAC) reaction under mild conditions, copper complexes
2–6 were investigated in the CuAAC reaction of azide and
phenylacetylene. Firstly, we compared the catalytic activity of
different complexes with a complex loading of 0.5 mol %. The
reactions were monitored by 1H NMR analysis at different time
points within 4 h (Figure 6). As seen in Figure 6, the yield in-
Figure 5: ORTEP drawing of [Cu3(L5)3](PF6)3 (6). Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms and anions
have been removed for clarity. Selected bond distances (Å) and angles
(°): Cu1-C26 2.092(6), Cu1-N5 2.092(5) , Cu1-C26A 2.024(6), Cu1-
N9A 2. 152(5), Cu1-Cu1A 2.5141(11), Cu1-Cu1B 2.5141(11); C26-
Cu1-N5 101.8(2), C26-Cu1-C26A 163.7(2), N5-Cu1-C26 92.5(2),
C26A-Cu1-N9 92.0(2), Cu1-Cu1A-Cu1B 60.0. Symmetry transformat-
ions used to generate equivalent atoms: 1−x, 1−y, −z.
space group R3c, which is different to the reported trinuclear creased with the extension of reaction time. The results showed
copper(I) complex containing the symmetric 1,3-bis(2- that complex 4 displays the best activities for the CuAAC reac-
pyridinylmethyl)benzimidazolylidene ligand (monoclinic, tion of benzyl azide and phenylacetylene giving a conversion of
Figure 6: Yield vs reaction time of different copper complex. The reaction was carried out in acetonitrile-d3 at 25 °C using 0.5 mol % copper complex,
yields were determined by 1H NMR spectra, hexamethylbenzene was used as internal standard.
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Beilstein J. Org. Chem. 2016, 12, 863–873.
95%. To further examine the catalytic efficiency of complex 4, carbene ligands have been prepared via simple reactions of
a variation of the catalyst loading from 0.1 to 0.25 to 0.5 mol % imidazolium salts with copper powder in good yields. These
within 5 h was performed to give the expected product in yields complexes have been fully characterized by NMR, elemental
of 17%, 48%, and 100%. As expected, the coupling reaction analysis (EA) and X-ray crystallography. Fine adjustment of the
with low catalyst loading results in incomplete conversion.
structure of the ligand can lead to different structures. All the
Cu–NHC complexes showed high catalyst activity in CuAAC
Subsequently the catalytic activity of different solvents was reactions at room temperature. Among these complexes, com-
tested at a Cu loading of 0.5 mol % (Table 1). Moderate catalyt- plex 4 is the most efficient catalyst in an air atmosphere at room
ic activities were obtained for DMSO or without solvent. When temperature.
CH3CN was used, the reaction gave an excellent yield (Table 1,
entry 4). However, only a moderate yield was obtained when a Experimental
CH3CN/H2O solvent mixture was used (Table 1, entry 6). Thus, All the chemicals were obtained from commercial suppliers and
CH3CN was selected as the optimal solvent.
were used without further purification. Elemental analyses were
performed on a Flash EA1112 instrument. 1H and 13C NMR
Having optimized the reaction conditions, we extended the spectra were recorded on a Bruker Avance-400 (400 MHz)
CuAAC reaction to other azides and alkynes at room tempera- spectrometer or a Varian 600 MHz NMR spectrometer. Chemi-
ture in CH3CN. As shown in Table 2 (entries 1–5), (azido- cal shifts (δ) are expressed in ppm downfield to TMS at
methyl)benzene, azidobenzene, (2-azidoethyl)benzene, and δ = 0 ppm and coupling constants (J) are expressed in Hz.
2-(azidomethyl)pyridine could react with phenylacetylene in
more than 83% yield (Table 2, entries 1–4). What is more, Synthesis of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-
methyl 1-benzyl-1H-1,2,3-triazole-4-carboxylate could be (pyrimidin-2-yl)-1H-benzo[d]imidazol-3-ium hexafluoro-
afforded in 85% yield via reacting methyl propiolate with phosphate [(HL2)PF6] (1b): Analogously as described in a
(azidomethyl)benzene. This promising catalytic behavior of published work [27], (azidomethyl)benzene (160 mg,
complex 4 prompted us to extend our studies toward a one-pot 1.2 mmol), copper sulfate pentahydrate (12.5 mg, 0.05 mmol),
synthesis of 1,2,3-triazoles from alkyl halides, sodium azide, sodium ascorbate (20 mg, 0.1 mmol), and 3-(prop-2-yn-1-yl)-1-
and alkynes. The three-component version has already been (pyrimidin-2-yl)-1H-benzo[d]imidazol-3-ium bromide (314 mg,
successfully performed and described in previous work [20]. As 1 mmol) were added to a Schlenk tube containing 2 mL of
displayed in Table 2, the reactions proceeded smoothly to water and tert-butyl alcohol (1:1). After the heterogeneous mix-
completion, and the products were isolated in good to excellent ture was stirred vigorously for 24 h at 50 °C, the reaction mix-
yields (83–95%).
ture was diluted with water (20 mL). The obtained yellow solu-
tion was dropwise added to the aqueous solution of NH4PF6. A
white precipitate was collected by filtration and dried. Yield:
Conclusion
In summary, a series of di-, and trinuclear copper(I) complexes 315 mg, 61%. 1H NMR (400 MHz, DMSO-d6) δ 10.89 (s, 1H),
(3–6) stablized by 1,2,3-triazole-tethered N-heterocyclic 9.14 (d, J = 4.9 Hz, 2H), 8.83 (d, J = 8.1 Hz, 1H), 8.39 (s, 1H),
Table 1: CuAAC reaction with different solventsa.
entry
solvent
cat.
yield %b
1
2
3
4
5
6
neat
H2O
4
4
4
4
4
4
50
22
DMSO
53
CH3CN
95
t-BuOH/H2O (1:1)
CH3CN/H2O (1:1)
trace
59
aReaction carried out using 0.5 mol % of complex 4 with different solvents. bYields were determined by 1H NMR spectra and are reported after 4 h,
hexamethylbenzene was used as internal standard.
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Table 2: CuAAC Reaction using complex 4 as catalyst.
entry
1a
substrate
substrate
product
isolated yield %
94 [42]
2a
3a
95 [43]
95 [44]
4a
5a
6b
83 [42]
85 [44]
90 [42]
7b
8b
84 [45]
85 [44]
aReaction conditions: azide 0.5 mmol, ethynylbenzene 0.6 mmol, catalyst 0.5 mol %, CH3CN 3 mL, rt, 6 h. bReaction conditions: alkyl halide
0.5 mmol, NaN3 0.6 mmol, ethynylbenzene 0.6 mmol, catalyst 0.5 mol %, CH3CN/H2O 1:1 (3 mL), rt, 16 h.
8.17 (d, J = 8.0 Hz, 1H), 7.79 (br, 3H), 7.34–7.30 (m, 5H), 6.06 (d, J = 2.4 Hz, 1H), 8.31–8.17 (m, 1H), 8.03 (q, J = 4.3, 3.5 Hz,
(s, 2H), 5.63 (s, 2H); 13C NMR (101 MHz, DMSO-d6) δ 2H), 7.70–7.61 (m, 1H), 7.36 (qd, J = 7.0, 6.5, 2.5 Hz, 5H),
160.34, 159.78, 143.41, 140.45, 136.12, 132.14, 129.62, 129.26, 5.65 (dd, J = 5.1, 2.4 Hz, 4H), 3.39 (s, 1H); 13C NMR
128.69, 128.49, 127.79, 125.52, 53.47, 42.95.
(101 MHz, DMSO-d6) δ 149.69, 146.78, 141.06, 141.02,
135.68, 129.29, 128.76, 128.55, 125.77, 125.23, 124.14, 120.07,
Synthesis of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1- 114.75, 53.49, 44.85.
(pyridin-2-yl)-1H-imidazol-3-ium hexafluorophosphate
[(HL3)PF6] (1c): Similarly as described in a previous proce- Synthesis of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-
dure [27], a mixture of (azidomethyl)benzene (160 mg, (pyridin-2-yl)-1H-benzo[d]imidazol-3-ium hexafluorophos-
1.2 mmol), copper sulfate pentahydrate (12.5 mg, 0.05 mmol) phate [(HL4)PF6] (1d): Similarly as described in a previous
and sodium ascorbate (20 mg, 0.1 mmol), 3-(prop-2-ynyl)-1- procedure [27], the imidazolium salt was prepared similarly as
(pyridin-2-yl)-1H-imidazol-3-ium bromide (265 mg, 1 mmol) for [(HL3)PF6] from (azidomethyl)benzene (160 mg,
was added to 2 mL of water and tert-butyl alcohol (1:1). The 1.2 mmol), copper sulfate pentahydrate (12.5 mg, 0.05 mmol),
heterogeneous mixture was stirred vigorously for 24 h at 50 °C. sodium ascorbate (20 mg, 0.1 mmol), and 3-(prop-2-yn-1-yl)-1-
The reaction mixture was diluted with water (20 mL), and the (pyridin-2-yl)-1H-benzo[d]imidazol-3-ium bromide (314 mg,
yellow solution was dropwise added to the aqueous solution of 1 mmol). Yield: 317 mg, 62%. 1H NMR (400 MHz, DMSO-d6)
NH4PF6. A white precipitate was collected by filtration and δ 10.60 (s, 1H), 8.75 (d, J = 4.7 Hz, 1H), 8.46–8.31 (m, 2H),
dried. Yield: 415 mg, 90%. 1H NMR (400 MHz, DMSO-d6) δ 8.25 (t, J = 8.0 Hz, 1H), 8.19–8.10 (m, 1H), 8.02 (d, J = 8.2 Hz,
10.19 (s, 1H), 8.69–8.63 (m, 1H), 8.54 (t, J = 1.9 Hz, 1H), 8.35 1H), 7.79–7.65 (m, 3H), 7.31 (dt, J = 21.5, 7.4 Hz, 7H), 5.95 (s,
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Beilstein J. Org. Chem. 2016, 12, 863–873.
2H), 5.59 (d, J = 5.1 Hz, 2H); 13C NMR (101 MHz, DMSO-d6) 135.75, 132.61, 129.94, 129.67, 129.17, 126.34, 126.19, 125.58,
δ 149.97, 147.61, 143.07, 141.07, 140.46, 136.13, 131.72, 120.66, 116.95, 112.75, 54.12, 43.41; Anal. calcd for
130.09, 129.27, 128.74, 128.50, 128.30, 127.73, 125.73, 125.50, C42H34Cu2F12N14P2: C, 43.80; H, 2.98; N, 17.02; found: C,
117.68, 116.38, 114.80, 53.42, 42.83.
43.51; H, 2.85; N, 16.95.
Synthesis of 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1- Synthesis of [Cu2(L3)2](PF6)2 (4): The compound was pre-
(pyridin-2-ylmethyl)-1H-benzo[d]imidazol-3-ium hexa- pared similarly as for complex 3 from [HL3](PF6) (90 mg,
fluorophosphate [(HL5)PF6] (1e): Similarly as described in 0.20 mmol) with copper powder (64 mg, 1.0 mmol) at 50 °C for
previous procedure [27], the imidazolium salt was prepared 10 h, orange yellow solid. Yield: 71 mg, 68%. 1H NMR
similarly as for [(HL3)PF6] from (azidomethyl)benzene (600 MHz, acetonitrile-d3) δ 7.96 (s, 1H, triazole), 7.90 (br, 1H,
(160 mg, 1.2 mmol), and 3-(prop-2-yn-1-yl)-1-(pyridin-2- 2-py), 7.83 (br, 1H, imidazole), 7.76 (s, 1H, 4-py), 7.57 (br, 1H,
ylmethyl)-1H-benzo[d]imidazol-3-ium bromide (328 g, imidazole), 7.41 (s, 1H, 5-py), 7.37 (d, J = 7.8 Hz, 3H, phenyl),
1 mmol). Yield: 390 mg, 74%.1H NMR (400 MHz, DMSO-d6) 7.30–7.22 (m, 3H, phenyl + 3-py), 5.47 (s, 2H), 5.38 (s, 2H);
δ 10.04 (s, 1H, NCHN), 8.46 (d, J = 4.8 Hz, 1H, 2-Py), 8.39 (s, 13C NMR (151 MHz, acetonitrile-d3) δ 181.20 (Cu-C), 149.68,
1H, triazole), 8.10 (d, J = 8.0 Hz, 1H, 4-Py), 7.94–7.90 (m, 3H), 147.26, 140.72, 138.41, 134.71, 129.02, 128.89, 128.80, 128.28,
7.73–7.59 (m, 3H), 7.46–7.27 (m, 6H, phenyl+benzene), 5.95 128.04, 123.96, 123.48, 112.13, 54.36, 45.69; Anal. calcd for
(s, 4H, CH2), 5.63 (s, 2H, CH2);13C NMR (101 MHz, DMSO- C36H32Cu2F12N12P2: C, 41.19; H, 3.07; N, 16.01; found: C,
d6) δ 153.34, 150.04, 143.67, 140.07, 138.02, 136.14, 131.80, 41.25; H, 3.31; N, 15.46.
131.29, 129.27, 128.74, 128.48, 127.33, 127.16, 125.33, 124.19,
123.20, 114.48, 114.41, 53.5, 51.4, 42.3.
Synthesis of [Cu3(L4)3](PF6)3 (5): The compound was pre-
pared similarly as for complex 3 from [HL4](PF6) (106 mg,
General procedure for the preparation of Cu(I)–NHC com- 0.20 mmol) with copper powder (64 mg, 1.0 mmol) at 50 °C for
plexes and Cu(II) complex: Analogously as described in [39], 10 h, light yellow solid. Yield: 93 mg, 52%. 1H NMR
all the copper complexes were prepared by the following route: (600 MHz, acetone-d6) δ 8.77 (d, J = 8.1 Hz, 1H, 2-py), 8.46
imidazolium salt (0.2 mmol) and an excess of copper powder (td, J = 8.0, 1.8 Hz, 1H, 4-py), 8.33 (s, 1H, triazole), 8.23–8.20
(64 mg, 1.0 mmol) were placed in 3 mL of MeCN to form a (m, 1H), 7.90 (dd, J = 5.1, 1.5 Hz, 1H, benzimidazole),
heterogeneous mixture solution. After the mixture was stirred at 7.84–7.81 (m, 1H, benzimidazole), 7.68–7.60 (m, 2H, benz-
50 °C for 10 h under air, the solution was filtered through imidazole), 7.44 (dd, J = 7.6, 5.0 Hz, 1H, 5-py), 7.33–7.31 (m,
Celite. Single crystals suitable for X-ray diffraction analysis 3H, phenyl), 6.94–6.92 (m, 2H, phenyl), 5.84 (d, J = 15.8 Hz,
were grown from acetonitrile solution and diethyl ether.
1H), 5.37 (d, J = 15.8 Hz, 1H), 5.18 (s, 2H); 13C NMR
(151 MHz, DMSO-d6) δ 178.99 (Cu-C), 149.61, 148.44,
Synthesis of [Cu-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-3- 142.25, 140.55, 136.19, 134.91, 133.34, 129.31, 128.93, 128.09,
( p y r i m i d i n - 2 - y l ) - 1 , 3 - d i h y d r o - 2 H - i m i d a z o l - 2 - 126.05, 125.82, 124.48, 124.27, 119.09, 118.51 (CH3CN),
one)2](PF6)2 (2): This complex was synthesized by the reac- 112.74, 111.59, 54.13, 41.17, 1.56(CH3CN); Anal. calcd for
tion of [H(L1)](PF6) (1a; 93 mg, 0.2 mmol) with copper powder C132H108Cu6F36N36P6. 3CH3CN: C, 46.39; H, 3.30; N, 15.29;
(64 mg, 1.0 mmol) at 50 °C for 10 h. Yield: 79 mg (75%), light found: C, 45.87; H, 3.40; N, 15.30.
green crystals. Anal. calcd for C34H30CuF12N14O2P2. 0.5
CH3CN: C, 40.39; H, 3.05; N, 19.52; found: C, 40.73; H, 2.95; Synthesis of [Cu3(L5)3](PF6)3 (6): The compound was pre-
N, 19.15.
pared similarly as for complex 3 from [HL5](PF6) (106 mg,
0.20 mmol) with copper powder (64 mg, 1.0 mmol) at 50 °C for
Synthesis of [Cu2(L2)2](PF6)2 (3): This complex was synthe- 10 h, light yellow solid. Yield: 106 mg, 90%. 1H NMR
sized by the reaction of [HL2](PF6) (1b; 102 mg, 0.2 mmol) (600 MHz, nitromethane-d3) δ 8.13 (s, 1H, triazole), 7.92 (td,
with copper powder (64 mg, 1.0 mmol) at 50 oC for 10 h. Yield: J = 7.8, 1.8 Hz, 1H, pyridine), 7.77 (d, J = 7.8 Hz, 1H,
66 mg (57%), red crystals. 1H NMR (600 MHz, acetonitrile-d3) pyridine), 7.59 (d, J = 7.8, 1H, pyridine), 7.61–7.36 (m, 6H,
δ 8.75 (d, J = 8.1 Hz, 2H, benzimidazole), 8.70 (d, J = 4.9 Hz, phenyl + benzimidazole), 7.14–7.08 (m, 2H, benzimidazole),
4H, pyrimidine), 7.88 (s, 2H, triazole), 7.79 (d, J = 7.8 Hz, 2H, 6.95 (ddd, J = 7.5, 5.2, 1.1 Hz, 1H, pyridine), 6.49–6.45 (d,
benzimidazole), 7.59–7.54 (m, 2H, benzimidazole), 7.52 (t, J = 4.8 Hz,1H, benzimidazole), 5.40 (d, J = 15.0 Hz, 1H, -CH2-
J = 7.2 Hz, 2H, benzimidazole), 7.36 (t, J = 4.9 Hz, 2H, pyrimi- ), 5.30 (d, J = 15.0 Hz, 1H, -CH2-), 5.27 (d, J = 15.0 Hz, 1H,
dine), 7.31–7.29 (m, 6H, phenyl), 7.19–7.18 (m, 4H, phenyl), -CH2-), 5.26 (d, J = 15.6 Hz, 1H, -CH2-), 5.21 (d, J = 15.0 Hz,
5.61 (s, 4H, -CH2-), 5.38 (s, 4H, -CH2-); 13C NMR (151 MHz, 1H, -CH2-), 4.98 (d, J = 15.6 Hz, 1H, -CH2-); 13C NMR
acetonitrile-d3) δ 191.23 (Cu-C), 158.73, 157.33 142.39, 136.17 (150 MHz, nitromethane-d3) 177.57 (Cu-C), 151.99, 148.85,
870

Beilstein J. Org. Chem. 2016, 12, 863–873.
141.78, 139.93, 135.15, 134.68, 133.85, 129.16, 128.98, 128.81, gen atom positions for all of the structures were calculated and
128.12, 125.04, 124.62, 124.35, 123.79, 110.58, 110.26, 54.49, allowed to ride on their respective C atoms with the C–H dis-
51.29, 40.72; Anal. calcd for C69H60Cu3F18N18P3: C, 46.90; H, tances of 0.93–0.97 Å and Uiso(H) = 1.2 − 1.5Ueq(C). Disor-
3.42; Cu, 10.79; N, 14.27; found: C, 46.35; H, 3.31; N, 13.95.
dered solvent molecules that could not be modeled successfully
were removed with SQUEEZE [48]. Further details of the struc-
General procedure for the copper-catalyzed CuAAC reac- tural analysis are summarized in Table 3.
tion: Analogously as described in [31], in a 10 mL Schlenk
tube, azide (0.5 mmol), alkyne (0.6 mmol), and 0.5 mol %
Supporting Information
copper complex were dissolved in 3.0 mL of CH3CN. After the
mixture was stirred at rt under air for a desired time, the reac-
Supporting Information File 1
tion was stopped by the addition of H2O (2 mL) to the resultant
mixture. Then the mixture was extracted with CH2Cl2. The
organic layer was separated from the aqueous phase. After the
organic phase was dried over MgSO4, the solution was filtered
and concentrated under vacuum. The residue was purified by
flash chromatography (silica gel, petroleum ether/ethyl acetate,
3:1) to give the desired product
X-ray crystallographic data in cif format CCDC
1424013–1424017.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-12-85-S1.cif]
Acknowledgements
The authors thank the National Natural Science Foundation of
China (21202127), and the Educational Commission of the
Hubei Province (Q20151606) for financial support. Shaojin Gu
gratefully acknowledges financial support from the China
Scholarship Council (201308420278).
X-ray diffraction analysis
Analogously as described in [27], single-crystal X-ray diffrac-
tion data were collected at 298(2) K on a Siemens Smart/CCD
area-detector or Oxford Diffraction Gemini A Ultra diffrac-
tometer with a Mo Kα radiation (λ = 0.71073 Å) by using an
ω-2θ scan mode. Unit-cell dimensions were obtained with least-
squares refinement. Data collection and reduction were per-
formed using the SMART and SAINT software [46]. The struc-
tures were solved by direct methods, and the non-hydrogen
atoms were subjected to anisotropic refinement by full-matrix
least squares on F2 using the SHELXTXL package [47]. Hydro-
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2
3
4
5
6
CCDC number
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1424013
1424014
1424015
1424016
1424017
C70H63Cu2F24N29 C42H34Cu2F12N14P2 C36H32Cu2F12N12P2 C278H237Cu12F72 C69H60Cu3F18N18P3
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