Structural modulation of silver complexes and their distinctive catalytic properties

Article abstract of DOI:10.1039/c3dt52655k

A family of silver(i) complexes, [Ag₂(L)₂(OOCCF ₃)₂] (1), [Ag(L)_0.5(OOCCF₃)] (2), [Ag(L)₂](OOCCF₃)(H₂O)₂ (3), was obtained by reactions of 4,4′-di(2-oxazolinyl)biphenyl (L) and AgOOCCF₃ in different reaction media. Compound 1 has a 1D chain structure with alternative connections between the Ag(i) and L ligand. When the crystal nucleation inductor, pyrazine, was added into the reaction system, complex 2 was isolated with no pyrazine observed in its structure. In 2, the 1D inorganic chains formed by Ag(i) cations and OOCCF₃^- anions were connected by the L ligand to produce a 2D network. When a different inductor, imidazole, was added into the reaction system, 3 with (4,4) topology was synthesized, and again no imidazole was found in 3. When 1-3 were used as catalysts for cycloaddition reactions between imino esters and methyl acrylate, 3 affords the highest yield, in which the particular size of the channels in 3 led to its selective catalytic performance.

Full text of DOI:10.1039/c3dt52655k

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Structural modulation of silver complexes and
their distinctive catalytic properties†
Cite this: Dalton Trans., 2014, 43,
2252
Yue Zhao,a Kai Chen,a Jian Fan,b Taka-aki Okamura,c Yi Lu,a Li Luoa and
Wei-Yin Sun*a
A family of silver(I) complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3),
was obtained by reactions of 4,4’-di(2-oxazolinyl)biphenyl (L) and AgOOCCF3 in different reaction media.
Compound 1 has a 1D chain structure with alternative connections between the Ag(I) and L ligand. When
the crystal nucleation inductor, pyrazine, was added into the reaction system, complex 2 was isolated with
−
no pyrazine observed in its structure. In 2, the 1D inorganic chains formed by Ag(I) cations and OOCCF3
anions were connected by the L ligand to produce a 2D network. When a different inductor, imidazole,
was added into the reaction system, 3 with (4,4) topology was synthesized, and again no imidazole was
found in 3. When 1–3 were used as catalysts for cycloaddition reactions between imino esters and methyl
acrylate, 3 affords the highest yield, in which the particular size of the channels in 3 led to its selective
catalytic performance.
Received 24th September 2013,
Accepted 25th October 2013
DOI: 10.1039/c3dt52655k
www.rsc.org/dalton
moderate chemical hardness.9,10 Although many research
groups have developed oxazoline-containing catalysts for a
Introduction
Coordination polymers are comprised of metal centers and homogeneous system, their use in coordination polymers as
ligands, and their physical/chemical properties depend on not heterogeneous catalysts are significantly less developed.11,12
only the nature of the metal center and ligand but also the
In this paper, a new oxazoline-containing ligand, 4,4′-di(2-
connection model between them. The connection pattern can oxazolinyl)biphenyl (L), was synthesized, and three different
be influenced by the reaction temperature, solvent, auxiliary complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag-
ligand, counterion and so on.1–3 Therefore, it is challenging to (L)2](OOCCF3)(H2O)2 (3) were obtained under different reaction
synthesize the desired structure for an undeveloped system. So media with and without different crystal nucleation inductors.
far, not only complexes with fascinating structures but also Complexes 1–3 were applied for cycloaddition reactions
their potential applications as functional materials in many between methyl acrylate and methyl 2-(benzylideneamino)-
fields have attracted more and more attention.4,5
acetate. The results indicated that the unique structural
Within various metal ions, Ag(I) is of particularly interest features of complex 3 play a vital role in its catalytic
due to its versatile coordination patterns and its high catalytic properties.
performance.6–8 As for the ligands, the oxazoline-containing
compounds are always used in catalysis because of their adjus-
table structures, easy preparation, high stabilities during
hydrolysis and oxidation reactions, and their strong coordi-
nation capabilities due to the in-plane N lone pair and their
Experimental
Materials and methods
All commercially available chemicals and solvents were of
reagent grade and were used as received without further purifi-
aCoordination Chemistry Institute, State Key Laboratory of Coordination Chemistry,
cation. The ligand L was synthesized according to the reported
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093,
procedure.13 Elemental analyses for C, H and N were per-
China. E-mail: sunwy@nju.edu.cn; Fax: +86 25 8331 4502
bJiangsu Key Laboratory for Carbon-Based Functional Materials and Devices,
Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University,
Suzhou 215123, China
formed on a Perkin-Elmer 240C Elemental Analyzer at the ana-
lysis center of Nanjing University. FT-IR spectra were recorded
in the range of 400–4000 cm−1 on a Bruker Vector22 FT-IR
spectrophotometer using KBr pellets. 1H NMR and 13C NMR
spectra were recorded in CDCl3 at 500 MHz and 125 MHz,
respectively, on a Bruker Avance 500 spectrometer. The
electrospray (ES) mass spectral measurements were carried
cDepartment of Macromolecular Science, Graduate School of Science, Osaka
University, Toyonaka, Osaka 560-0043, Japan
†Electronic supplementary information (ESI) available. CCDC 962763–962765.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt52655k
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out on an LCQ System (Finnegan MAT, USA) using
a
(vs), 1647 (s), 1602 (w), 1580 (w), 1492 (w), 1435 (m), 1385 (w),
mixed solution of methanol and water (1 : 1) as the mobile 1346 (w), 1310 (m), 1273 (s), 1200 (s), 1176 (s), 1080 (w), 1055
phase.
(m), 1023 (m), 961 (w), 851 (w), 759 (s), 694 (s). ESI-MS: calcd
Preparation of [Ag2(L)2(OOCCF3)2] (1). AgOOCCF3 (6.6 mg, for C10H11NO2 (M + 1) 178.08, found: 178.25.
0.03 mmol) and L (8.8 mg, 0.03 mmol) in 8 mL of methanol
Preparation of methyl 2-(4-methoxybenzylideneamino)-
was stirred for about 2 min. After filtration, the filtrate was acetate (1b). Compound 1b was obtained by the same pro-
diffused by diethyl ether at room temperature. After several cedure used for the preparation of compound 1a except that
days, colorless crystals appeared. Yield: 61%. Anal. Calcd for benzaldehyde was replaced by 4-methoxybenzaldehyde to give
(C40H32Ag2F6N4O8): C, 46.81; H, 3.14; N, 5.46%. Found: C, a white solid product with a yield of 82%. 1H NMR (CDCl3,
46.94; H, 3.26; N, 5.21%. IR (KBr pellet, cm−1): 2979 (w), 1690 500 MHz, ppm): δ 3.80 (s, 3H), 3.87 (s, 3H), 4.41 (s, 2H), 6.96
(s), 1631 (vs), 1556 (m), 1498 (m), 1431 (s), 1400 (m), 1371 (s), (d, J = 8.5 Hz, 2H), 7.75 (d, J = 9.0 Hz, 2H), 8.24 (s, 1H) (Fig. S3,
1328 (m), 1259 (s), 1199 (s), 1139 (s), 1095 (s), 1021 (m), 1005 ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.02, 55.33, 61.92,
(m), 941 (s), 836 (s), 793 (m), 725 (s), 681 (m).
114.02, 128.60, 130.12, 162.11, 164.64, 170.76 (Fig. S4, ESI†).
Preparation of [Ag(L)0.5(OOCCF3)] (2). AgOOCCF3 (6.6 mg, IR (KBr pellet, cm−1): 2964 (m), 1745 (m), 1647 (m), 1602 (m),
0.03 mmol), L (8.8 mg, 0.03 mmol) and pyrazine (2.4 mg, 1508 (w), 1460 (w), 1441 (w), 1417 (w), 1352 (w), 1306 (w), 1255
0.03 mmol) in 8 mL of methanol was stirred for about 2 min. (m), 1200 (m), 1180 (m), 1159 (w), 1071 (w), 1023 (w), 959 (w),
After filtration, the filtrate was diffused by diethyl ether at 833 (m), 774 (w), 669 (w). ESI-MS: calcd for C11H13NO3 (M + 1)
room temperature. After several days, colorless crystals 208.09, found: 208.42.
appeared. Yield: 42%. Anal. Calcd for (C11H8AgF3NO3): C,
Preparation of methyl 2-((naphthalen-2-yl)methyleneamino)-
35.99; H, 2.20; N, 3.82%. Found: C, 35.87; H, 2.31; N, 3.71%. acetate (1c). Compound 1c was obtained by the same pro-
IR (KBr pellet, cm−1): 2982 (w), 2918 (w), 1632 (vs), 1497 (m), cedure used for the preparation of compound 1a except that
1483 (m), 1431 (m), 1400 (m), 1374 (s), 1337 (m), 1260 (vs), benzaldehyde was replaced by 2-naphthaldehyde to give a
1183 (vs), 1140 (vs), 1096 (vs), 1023 (m), 941 (s), 837 (s), 792 (s), white solid product with a yield of 76%. 1H NMR (CDCl3,
725 (s), 681 (m).
500 MHz, ppm): δ 3.83 (s, 3H), 4.51 (s, 2H), 7.29–7.58 (m, 2H),
Preparation of [Ag(L)2](OOCCF3)(H2O)2 (3). Complex 3 was 7.88–7.94 (m, 3H), 8.06 (d, J = 8.5 Hz, 1H), 8.12 (s, 1H), 8.48 (s,
obtained by the same procedure used for the preparation of 2 1H) (Fig. S5, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.13, 62.06,
except that pyrazine was replaced by imidazole (2.0 mg, 123.91, 126.54, 127.42, 127.89, 128.53, 128.72, 130.60, 133.01,
0.03 mmol) with
a
yield of 35%. Anal. Calcd for 133.31, 134.98, 165.44, 170.57 (Fig. S6, ESI†). IR (KBr pellet,
(C38H36AgF3N4O8): C, 54.23; H, 4.31; N, 6.66%. Found: C, cm−1): 2998 (w), 2950 (w), 2878 (w), 1721 (vs), 1641 (m), 1420
54.37; H, 4.16; N, 6.54%. IR (KBr pellet, cm−1): 2982 (w), 2918 (m), 1347 (w), 1323 (m), 1264 (s), 1176 (m), 1118 (w), 1066 (m),
(w), 1632 (vs), 1497 (m), 1482 (m), 1430 (m), 1400 (m), 1373 (s), 1006 (m), 963 (m), 903 (w), 888 (w), 854 (m), 831 (s), 755 (s),
1336 (m), 1260 (s), 1184 (vs), 1139 (vs), 1096 (vs), 1023 (m), 634 (w). ESI-MS: calcd for C14H13NO2 (M + 1) 228.09, found:
1005 (m), 941 (s), 837 (s), 792 (s), 725 (s), 681 (m), 520 (w), 228.42.
446 (w).
Preparation of methyl 2-((anthracen-9-yl)methyleneamino)-
Preparation of methyl 2-(benzylideneamino)acetate (1a). In acetate (1d). Compound 1d was obtained by the same pro-
a 100 mL flask, benzaldehyde (2 mmol, 0.212 g), glycine cedure used for the preparation of compound 1a except that
methyl ester hydrochloride (10 mmol, 1.255 g), and triethyl- benzaldehyde was replaced by 9-anthracenecarboxaldehyde to
amine (10 mmol, 1.1 mL) were dissolved in 50 mL of dichloro- give a yellow solid product with a yield of 70%. 1H NMR
methane. Excess anhydrous MgSO4 was added. The solution (CDCl3, 500 MHz, ppm): δ 3.90 (s, 3H), 4.78 (s, 2H), 7.52 (t, J =
was refluxed for 12 hours before filtration. The filtrate was 7.8 Hz, 2H), 7.59 (m, 2H), 8.05 (d, J = 8.5 Hz, 2H), 8.55 (s, 1H),
washed with water three times, and the organic layer was dried 8.62 (d, J = 9.0 Hz, 2H), 9.49 (s, 1H) (Fig. S7, ESI†). 13C NMR
over anhydrous Na2SO4. After evaporation, the product was (CDCl3, 125 MHz): δ 52.27, 63.02, 124.77, 125.32, 126.96,
obtained as a light yellow oil with a yield of 84%. 1H NMR 128.85, 129.95, 131.23, 165.16, 170.60 (Fig. S8, ESI†). IR (KBr
(CDCl3, 500 MHz, ppm): δ 3.80 (s, 3H), 4.45 (s, 2H), 7.43–7.48 pellet, cm−1): 3047 (w), 2952 (w), 2891 (w), 1750 (s), 1644 (m),
(m, 3H), 7.80–7.81 (m, 2H), 8.32 (s, 1H) (Fig. S1, ESI†). 13C 1602 (w), 1519 (w), 1443 (m), 1414 (w), 1382 (w), 1349 (m),
NMR (CDCl3, 125 MHz): δ 52.01, 61.88, 128.46, 128.58, 131.19, 1234 (m), 1211 (s), 1185 (s), 1066 (m), 1001 (w), 960 (w),
135.61, 165.36, 170.46 (Fig. S2, ESI†). IR (KBr pellet, cm−1): 875 (w), 840 (w), 723 (s), 670 (w). ESI-MS: calcd for C23H25N
3062 (w), 3028 (w), 3002 (w), 2952 (m), 2880 (w), 2851 (w), 1748 (M + 1) 278.11, found: 278.42.
Scheme 1 Cycloaddition of methyl 2-(4-methoxybenzylideneamino)acetate and methyl acrylate catalyzed by the Ag(I) compounds in CH3CN.
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Preparation of dimethyl 5-phenylpyrrolidine-2,4-dicarboxy-
Preparation of dimethyl 5-(naphthalen-3-yl)pyrrolidine-2,4-
late (2a).14 In a 25 mL test tube, methyl acrylate (0.11 mmol, dicarboxylate (2c).14 Compound 2c was obtained by the same
9.8 μL), 1a (0.1 mmol, 0.0177 g), triethylamine (0.01 mmol, procedure used for the preparation of compound 2a. Colorless
1
1 μL), and the catalyst (0.01 mmol) were dissolved in 2 mL of oil, H NMR (CDCl3, 500 MHz, ppm): δ 2.51 (t, J = 8.0 Hz, 2H),
acetonitrile. This solution was stirred at room temperature 3.16 (s, 3H), 3.44 (m, 1H), 3.88 (s, 3H), 4.09 (t, J = 8.2 Hz, 1H),
until a TLC showed that the reaction was completed. After the 4.73 (d, J = 7.5 Hz, 1H), 7.44 (d, J = 8.5 Hz, 1H), 7.48–7.49 (m,
removal of the solvent, the crude product was purified by 2H), 7.81–7.86 (m, 4H) (Fig. S13, ESI†). 13C NMR (CDCl3,
column chromatography to give the pure product (Scheme 1). 125 MHz): δ 33.38, 49.56, 51.18, 52.23, 59.91, 65.93, 125.13,
1H NMR (CDCl3, 500 MHz, ppm): δ 2.45 (t, J = 7.5 Hz, 2H), 3.24 125.44, 125.85, 126.07, 127.56, 127.73, 127.98, 132.87, 133.18,
(s, 3H), 3.34 (m, 1H), 3.85 (s, 3H), 4.02 (t, J = 8.2 Hz, 1H), 4.57 136.61, 173.02, 173.73 (Fig. S14, ESI†). IR (KBr pellet, cm−1):
(d, J = 7.5 Hz, 1H), 7.31–7.32 (m, 3H), 7.34 (d, J = 4.5 Hz, 2H) 3359 (m), 3055 (m), 2996 (m), 2951 (m), 2848 (w), 1731 (vs),
(Fig. S9, ESI†). 13C NMR (CDCl3, 125 MHz): δ 33.26, 49.67, 1633 (w), 1601 (m), 1507 (m), 1434 (s), 1373 (m), 1248 (s), 1204
51.15, 52.20, 59.87, 65.78, 126.74, 127.55, 128.13, 139.12, (s), 1166 (s), 1128 (m), 1037 (m), 914 (m), 860 (m), 822 (m), 748
172.98, 173.74 (Fig. S10, ESI†). IR (KBr pellet, cm−1): 3369 (m), (m), 647 (w).
3062 (w), 3029 (w), 2998 (m), 2952 (m), 2886 (w), 2848 (w),
1719 (vs), 1648 (s), 1604 (w), 1494 (m), 1434 (m), 1378 (w), 1114
(s), 1035 (w), 701 (w).
X-ray crystallography
The crystallographic data collections for 1 and 2 were carried
out on a Bruker Smart Apex II CCD area-detector diffracto-
meter with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) at 293(2) K using the ω-scan technique. The diffrac-
tion data were integrated using the SAINT program,15 which
was also used for the intensity corrections for the Lorentz and
polarization effects. A semi-empirical absorption correction
was applied using the SADABS program.16 The crystallographic
data for 3 were collected on a Rigaku RAXIS-RAPID II imaging
plate area detector with Mo Kα radiation (0.71075 Å) using a
MicroMax-007HF microfocus rotating anode X-ray generator
and VariMax-Mo optics at 200 K. Complexes 1–3 were solved by
direct methods and all the non-hydrogen atoms were refined
anisotropically on F2 by the full-matrix least-squares technique
using the SHELXL-2013 crystallographic software package.17
All the hydrogen atoms were generated geometrically and
Preparation of dimethyl 5-(4-methoxyphenyl)pyrrolidine-2,4-
dicarboxylate (2b).14 Compound 2b was obtained by the same
procedure used for the preparation of compound 2a. White
solid, 1H NMR (CDCl3, 500 MHz, ppm): δ 2.42 (m, 2H), 2.84
(br, 1H), 3.28 (s, 3H), 3.80 (s, 3H), 3.83 (s, 3H), 4.01 (t, J = 8.2
Hz, 1H), 4.51 (d, J = 7.5 Hz, 1H), 6.85 (d, J = 8.5 Hz, 2H), 7.23
(d, J = 8.5 Hz, 2H) (Fig. S11, ESI†). 13C NMR (CDCl3, 125 MHz):
δ 33.26, 49.69, 51.25, 52.20, 55.17, 59.87, 65.33, 113.54, 127.90,
131.25, 158.99, 173.06, 173.81 (Fig. S12, ESI†). IR (KBr pellet,
cm−1): 2998 (w), 2952 (w), 2839 (w), 1737 (vs), 1613 (m), 1585
(w), 1514 (m), 1437 (m), 1379 (w), 1248 (s), 1206 (s), 1175 (s),
1112 (w), 1087 (w), 1034 (m), 938 (w), 836 (m), 785 (w), 552 (w).
Table 1 Crystal data and structure refinements for complexes 1–3
Compound
1
2
3
Table 2 Selected bond lengths [Å] and angles [°] for complexes 1–3
[Ag2(L)2(OOCCF3)2] (1)a
Empirical
formula
Formula
weight
C40H32Ag2F6N4O8 C11H8AgF3NO3 C38H36AgF3N4O8
1026.44
293(2)
367.05
841.58
Ag1–N4
Ag1–O8
Ag2–N1#1
N4–Ag1–N3
N3–Ag1–O8
N2–Ag2–O6
2.129(6)
2.522(6)
2.154(6)
153.6(2)
91.7(2)
Ag1–N3
Ag2–N2
Ag2–O6
N4–Ag1–O8
N2–Ag2–N1#1
N1#1–Ag2–O6
2.166(5)
2.153(5)
2.460(6)
112.8(2)
148.7(2)
101.5(2)
T (K)
293(2)
Triclinic
ˉ
P1
200
Monoclinic
C2/c
Crystal system Monoclinic
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
P21/c
14.7044(15)
15.9797(16)
16.2718(17)
90.00
91.634(2)
90.00
5.5736(17)
9.681(3)
10.993(4)
82.393(5)
81.503(5)
84.252(5)
579.5(3)
2
18.055(9)
13.972(8)
14.544(9)
90.00
106.986(18)
90.00
108.3(2)
[Ag(L)0.5(OOCCF3)] (2)b
Ag1–N1
Ag1–O3#3
2.252(4)
2.305(4)
Ag1–O3#2
Ag1–O2
2.540(3)
2.361(4)
γ (°)
V (Å3)
Z
3821.9(7)
4
3509(3)
4
Ag1–Ag1#3
N1–Ag1–O2
N1–Ag1–O3#2
O2–Ag1–O3#2
O3#3–Ag1–Ag1#3
O3#2–Ag1–Ag1#3
3.1222(10)
101.27(16)
109.08(14)
106.19(13)
72.26(10)
132.57(9)
N1–Ag1–O3#3
O3#3–Ag1–O2
O3#2–Ag1–O3#3
N1–Ag1–Ag1#3
O2–Ag1–Ag1#3
127.06(14)
129.43(16)
74.08(13)
117.74(11)
72.61(12)
Dc (g cm−3
F(000)
)
1.784
2048
2.103
358
1.593
1720
θ Range/°
1.79–25.50
7085
2.67–25.01
2006
3.18–27.49
4013
Reflections
collected
Unique
5358
1969
3456
[Ag(L)2](OOCCF3)(H2O)2 (3)c
reflections
Goof
Ag1–N1
N2#3–Ag1–N2#2
N2#3–Ag1–N1#1
2.388(2)
108.32(12)
113.64(9)
Ag1–N2#2
N2#2–Ag1–N1#1
N1#1–Ag1–N1
2.349(2)
108.20(9)
104.96(12)
1.038
0.0711
1.104
0.0424
0.1058
1.081
0.0497
0.1327
R1a [I > 2σ(I)]
wR2b [I > 2σ(I)] 0.1859
a Symmetry codes for 1: #1: 1 + x, y, −1 + z. b Symmetry codes for 2: #2:
−1 + x, y, z; #3: 1 − x, 1 − y, 1 − z. c Symmetry codes for 3: #1: −x, y, 3/2
− z; #2: 1/2 − x, 1/2 + y, 3/2 − z; #3: −1/2 + x, 1/2 + y, z.
a R1 = ∑||Fo| − |Fc||/∑|Fo|. b wR2 = |∑w(|Fo|2 − |Fc|2)|/∑|w(Fo)2|1/2
where w = 1/[σ2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3.
,
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Fig. 1 (a) Coordination environment of Ag(I) in 1 with the ellipsoids drawn at the 30% probability level and the hydrogen atoms are omitted for
clarity. (b) 1D chain structure of 1.
Fig. 2 (a) Coordination environment of Ag(I) in 2 with the ellipsoids drawn at the 30% probability level and the hydrogen atoms are omitted for
clarity. (b) 2D network of 2.
refined isotropically using the riding model. The details of the
crystal parameters, data collection and refinements for the
complexes are summarized in Table 1, and selected bond
Results and discussion
Description of the crystal structure of complex 1
lengths and angles with their estimated standard deviations Complex 1 was prepared by the slow diffusion of diethyl ether
are listed in Table 2.
into
a
methanolic solution of AgOOCCF3 and L. X-ray
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crystallographic analysis revealed that 1 crystallizes in the
monoclinic P21/c space group (Table 1). Each Ag(I) atom is co-
ordinated by two nitrogen atoms from two different L ligands
and one oxygen atom from a trifluoroacetate anion (Fig. 1a) to
form a distorted trigonal planar coordination geometry. The
coordination bond distances around Ag1 vary from 2.129(6) to
2.522(6) Å, and the coordination angles are from 91.7(2) to
153.6(2)°, while the bond distances around Ag2 are from 2.153(5)
to 2.460(6) Å and the bond angles are from 101.5(2) to
148.7(2)° (Table 2). Furthermore, the Ag1–O7 and Ag2–O5 dis-
tances are 2.712(9) and 2.711(7) Å, respectively, which imply
the presence of weak interactions between them. In complex 1,
the dihedral angles between the oxazoline and benzene ring
planes are 7.42°, 6.69° and 20.36°, 21.79°, respectively, while
the dihedral angles between the adjacent benzene ring planes
are 13.57° and 30.71°.
In 1, each L ligand connects two different Ag(I) atoms, and
each Ag(I) links two different L ligands, resulting an infinite
one-dimensional (1D) chain (Fig. 1b). The adjacent 1D chains
are further connected together through C6–H6B⋯O7 and C25–
H25A⋯O8 hydrogen bonds to form a 1D double chain
(Fig. S15a and S15b, ESI†), which are arranged in an ABAB
pattern to form a two-dimensional (2D) network. Moreover,
the 2D networks are further linked by C–H⋯F, C–H⋯O hydro-
gen bonds to give
a three-dimensional (3D) structure
(Fig. S15c, ESI†). The hydrogen bonding data are summarized
in Table S1 in the ESI.†
Fig. 3 (a) Coordination environment of Ag(I) in 3 with the ellipsoids
drawn at the 30% probability level while the hydrogen atoms, anions and
free water molecules are omitted for clarity. (b) 2D network of 3, the
anions and free water molecules are omitted for clarity. (c) 3D structure
of 3 from the c axis with the OOCCF3− filling the channel.
Description of the crystal structure of complex 2
When pyrazine was added into the reaction system, complex 2
was isolated. The X-ray diffraction analysis reveals that 2 is in
ˉ
the triclinic P1 space group (Table 1) and the asymmetric unit
of 2 consists of one Ag(I) atom, half an L ligand, and one
OOCCF3−. Interestingly, the pyrazine was not included in
complex 2, acting as a crystal nucleation inductor. As shown in
Fig. 2a, each Ag(I) atom shows interactions with one nitrogen
atom (N1) from one L ligand, three oxygen atoms (O2, O3B,
−
one OOCCF3 anion, and two water molecules. As shown in
Fig. 3a, each Ag(I) atom is surrounded by four nitrogen atoms
from four different L ligands to generate a tetrahedral coordi-
nation geometry. The bond lengths are from 2.388(2) to
2.349(2) Å and the bond angles are in the range of 108.20(9)–
113.64(9)° (Table 2). Within one ligand, the dihedral
angles between the oxazoline and benzene ring planes are
20.28° and 32.69°, respectively. In 3, the Ag(I) and L ligands
are connected together, resulting in a (4,4) 2D network
(Fig. 3b). As displayed in Fig. S17 in the ESI,† the C29–
H15⋯O2 hydrogen bonds further links the 2D networks to
give a 3D framework. In 3, 1D channels (8.2 × 6.8 Å) are
−
O3C) from three different OOCCF3 anions, and another Ag(I),
with a distorted tetragonal pyramid coordination geometry.
The coordination bond lengths lie between 2.252(4) and
3.1222(10) Å, while the bond angles range from 72.26(10) to
129.43(16)° (Table 2) and the dihedral angle between the oxa-
zoline and benzene ring planes is 9.19°. In complex 2, the
−
Ag(I) cation and the OOCCF3 anion are linked together to
form a 1D chain and the adjacent 1D chains are further con-
nected by the L ligands to produce a 2D network (Fig. 2b).
Moreover, the 2D networks are linked together by
−
observed along the c axis, which are filled with the OOCCF3
anions and water molecules.
C2–H2A⋯F2 hydrogen bonds to form
(Fig. S16 and Table S1, ESI†).
a 3D framework
Cycloaddition reactions between imino esters and methyl
Description of the crystal structure of complex 3
acrylates catalyzed by complexes 1–3
To further understand the induction effect of an ancillary As shown in Scheme 1, complexes 1–3 were used as catalysts
ligand on the crystal structure, imidazole instead of pyrazine for the cycloaddition reactions between imino esters and
was used in the reaction system for the preparation of complex methyl acrylates and the results are given in Table 3. Com-
3. The asymmetric unit of 3 contains one L, one Ag(I) cation, plexes 1 and 2 gave about a 40% yield, while AgOOCCF3
2256 | Dalton Trans., 2014, 43, 2252–2258
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Table 3 Cycloaddition of methyl 2-(4-methoxybenzylideneamino)-
acetate and methyl acrylate catalyzed by the Ag(I) complexes in CH3CNa
Table 4 Cycloaddition of imino esters and methyl acrylate catalyzed by
complex 3 in CH3CNa
Entry
Ag(I) compound
Yieldb (%) Entry
R
Time
Yieldb (%)
1
2
3
4
AgOOCCF3
57%
42%
41%
74%
1
2
3
4
Phenyl (1a)
10 h
10 h
10 h
10 h
96% (2a)
74% (2b)
72% (2c)
Trace
1
2
3
4-Methoxyphenyl (1b)
Naphthyl (1c)
Anthryl (1d)
a Methyl 2-(4-methoxybenzylideneamino)acetate (0.1 mmol), methyl a Imino ester (0.1 mmol), methyl acrylate (0.11 mmol, 9.8 μL),
acrylate (0.11 mmol, 9.8 μL), triethylamine (0.01 mmol, 1 μL), catalyst triethylamine (0.01 mmol, 1 μL), complex 3 (0.01 mmol, 10% mol,
(0.01 mmol, 10% mol), room temperature, 10 h. b 1H NMR yields 8.4 mg), room temperature. b 1H NMR yields based on the imino ester
based on methyl 2-(4-methoxybenzylideneamino)acetate using CH2Br2 using CH2Br2 as an internal standard.
as an internal standard.
generated the product with a 57% yield. However, complex 3
raised the yield up to 74%. It has been reported that anions
are of vital importance in the cycloaddition reactions between
imino esters and methyl acrylates.18 In 1 and 2, the OOCCF3
−
anions coordinate directly to the Ag(I) atoms, while in 3 the
−
OOCCF3 is free and locates in the channels. In the catalytic
reaction system, the anions in 3 leave the structure easily.
−
However, in 1 and 2, the OOCCF3 directly coordinates with
the Ag(I) atoms, which hardly leave the structure. Thus, the
yields of the products catalyzed by 1 and 2 are lower. In
−
addition, when the OOCCF3 anions leave the structure, they
will leave channels.
To provide insight into the catalytic performance of
complex 3, other imino esters, 1a, 1b, 1c and 1d, were used
and their cycloaddition reactions were tested (Scheme 2). As
shown in Table 4, substance 1a gave the highest yield of 96%
while 1b and 1c were slightly lower (around 70%). Compound
Fig. 4 PXRD patterns for 3 under different conditions: (a) simulated; (b)
as-synthesized; (c) immersed in CH3CN; (d) after the reaction.
1d showed the lowest yield, and the formation of the product
can be confirmed by electrospray mass spectral measurements.
DFT calculations show that the size of 1a (containing phenyl)
Conclusions
is smaller than the channels of 3, and the sizes of 1b (contain-
ing methoxyphenyl) and 1c (containing naphthyl) are similar
to the channels. However, the size of 1d (containing anthryl) is
larger than that of the channels of 3. Therefore, as the size of
the substrate increases, the yield of the reaction decreases.
These results suggest that the channel size in complex 3 plays
an important role in the selective catalysis reaction. As for the
stability of the complex in the solvent, we prove it by powder X-
ray diffraction (PXRD). As shown in Fig. 4, the pattern of the
as-synthesized sample 3, immersed in CH3CN and after the
reaction, is consistent with the simulated one, which confirms
the complex is stable in the reaction.
The effect of the crystal nucleation inductor on the structures
of complexes 1–3 was investigated. Complex 1 is a 1D flexible
chain without the addition of an inductor. After the addition
of the inductor pyrazine, complex 2 is a 2D network, where the
1D AgOOCCF3 chains are linked together by the rigid oxazo-
line-containing ligand (L). In 1 and 2, the trifluoroacetate
anions are coordinated with the metal centers, which corres-
pond to their poor catalytic performance. When the inductor
imidazole, was added, complex 3 is composed of (4,4) 2D net-
works, where 1D channels accommodate the anions. The
channel size in 3 is about 8.2 × 6.8 Å, which leads to its selec-
tive catalytic performance.
Scheme 2 Different imino esters react with methyl acrylate catalyzed by complex 3 in CH3CN.
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Dalton Transactions
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (grant no. 21331002, 91122001
and 21201100) and the National Basic Research Program of
China (grant no. 2010CB923303).
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