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Structural modulation of silver complexes and their distinctive catalytic properties† 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−
Received 24th September 2013, Accepted 25th October 2013 DOI: 10.1039/c3dt52655k www.rsc.org/dalton
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.
Introduction Coordination polymers are comprised of metal centers and ligands, and their physical/chemical properties depend on not only the nature of the metal center and ligand but also the connection model between them. The connection pattern can be influenced by the reaction temperature, solvent, auxiliary ligand, counterion and so on.1–3 Therefore, it is challenging to synthesize the desired structure for an undeveloped system. So far, not only complexes with fascinating structures but also their potential applications as functional materials in many fields have attracted more and more attention.4,5 Within various metal ions, Ag(I) is of particularly interest due to its versatile coordination patterns and its high catalytic performance.6–8 As for the ligands, the oxazoline-containing compounds are always used in catalysis because of their adjustable structures, easy preparation, high stabilities during hydrolysis and oxidation reactions, and their strong coordination capabilities due to the in-plane N lone pair and their
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China. E-mail: [email protected]; Fax: +86 25 8331 4502 b Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123, China c Department 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
2252 | Dalton Trans., 2014, 43, 2252–2258
moderate chemical hardness.9,10 Although many research groups have developed oxazoline-containing catalysts for a homogeneous system, their use in coordination polymers as heterogeneous catalysts are significantly less developed.11,12 In this paper, a new oxazoline-containing ligand, 4,4′-di(2oxazolinyl)biphenyl (L), was synthesized, and three different complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3) were obtained under different reaction media with and without different crystal nucleation inductors. Complexes 1–3 were applied for cycloaddition reactions between methyl acrylate and methyl 2-(benzylideneamino)acetate. The results indicated that the unique structural features of complex 3 play a vital role in its catalytic properties.
Experimental Materials and methods All commercially available chemicals and solvents were of reagent grade and were used as received without further purification. The ligand L was synthesized according to the reported procedure.13 Elemental analyses for C, H and N were performed on a Perkin-Elmer 240C Elemental Analyzer at the analysis 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
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out on an LCQ System (Finnegan MAT, USA) using a mixed solution of methanol and water (1 : 1) as the mobile phase. Preparation of [Ag2(L)2(OOCCF3)2] (1). AgOOCCF3 (6.6 mg, 0.03 mmol) and L (8.8 mg, 0.03 mmol) in 8 mL of methanol was stirred for about 2 min. After filtration, the filtrate was diffused by diethyl ether at room temperature. After several days, colorless crystals appeared. Yield: 61%. Anal. Calcd for (C40H32Ag2F6N4O8): C, 46.81; H, 3.14; N, 5.46%. Found: C, 46.94; H, 3.26; N, 5.21%. IR (KBr pellet, cm−1): 2979 (w), 1690 (s), 1631 (vs), 1556 (m), 1498 (m), 1431 (s), 1400 (m), 1371 (s), 1328 (m), 1259 (s), 1199 (s), 1139 (s), 1095 (s), 1021 (m), 1005 (m), 941 (s), 836 (s), 793 (m), 725 (s), 681 (m). Preparation of [Ag(L)0.5(OOCCF3)] (2). AgOOCCF3 (6.6 mg, 0.03 mmol), L (8.8 mg, 0.03 mmol) and pyrazine (2.4 mg, 0.03 mmol) in 8 mL of methanol was stirred for about 2 min. After filtration, the filtrate was diffused by diethyl ether at room temperature. After several days, colorless crystals appeared. Yield: 42%. Anal. Calcd for (C11H8AgF3NO3): C, 35.99; H, 2.20; N, 3.82%. Found: C, 35.87; H, 2.31; N, 3.71%. IR (KBr pellet, cm−1): 2982 (w), 2918 (w), 1632 (vs), 1497 (m), 1483 (m), 1431 (m), 1400 (m), 1374 (s), 1337 (m), 1260 (vs), 1183 (vs), 1140 (vs), 1096 (vs), 1023 (m), 941 (s), 837 (s), 792 (s), 725 (s), 681 (m). Preparation of [Ag(L)2](OOCCF3)(H2O)2 (3). Complex 3 was obtained by the same procedure used for the preparation of 2 except that pyrazine was replaced by imidazole (2.0 mg, 0.03 mmol) with a yield of 35%. Anal. Calcd for (C38H36AgF3N4O8): C, 54.23; H, 4.31; N, 6.66%. Found: C, 54.37; H, 4.16; N, 6.54%. IR (KBr pellet, cm−1): 2982 (w), 2918 (w), 1632 (vs), 1497 (m), 1482 (m), 1430 (m), 1400 (m), 1373 (s), 1336 (m), 1260 (s), 1184 (vs), 1139 (vs), 1096 (vs), 1023 (m), 1005 (m), 941 (s), 837 (s), 792 (s), 725 (s), 681 (m), 520 (w), 446 (w). Preparation of methyl 2-(benzylideneamino)acetate (1a). In a 100 mL flask, benzaldehyde (2 mmol, 0.212 g), glycine methyl ester hydrochloride (10 mmol, 1.255 g), and triethylamine (10 mmol, 1.1 mL) were dissolved in 50 mL of dichloromethane. Excess anhydrous MgSO4 was added. The solution was refluxed for 12 hours before filtration. The filtrate was washed with water three times, and the organic layer was dried over anhydrous Na2SO4. After evaporation, the product was obtained as a light yellow oil with a yield of 84%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.80 (s, 3H), 4.45 (s, 2H), 7.43–7.48 (m, 3H), 7.80–7.81 (m, 2H), 8.32 (s, 1H) (Fig. S1, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.01, 61.88, 128.46, 128.58, 131.19, 135.61, 165.36, 170.46 (Fig. S2, ESI†). IR (KBr pellet, cm−1): 3062 (w), 3028 (w), 3002 (w), 2952 (m), 2880 (w), 2851 (w), 1748
Scheme 1
Paper
(vs), 1647 (s), 1602 (w), 1580 (w), 1492 (w), 1435 (m), 1385 (w), 1346 (w), 1310 (m), 1273 (s), 1200 (s), 1176 (s), 1080 (w), 1055 (m), 1023 (m), 961 (w), 851 (w), 759 (s), 694 (s). ESI-MS: calcd for C10H11NO2 (M + 1) 178.08, found: 178.25. Preparation of methyl 2-(4-methoxybenzylideneamino)acetate (1b). Compound 1b was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 4-methoxybenzaldehyde to give a white solid product with a yield of 82%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.80 (s, 3H), 3.87 (s, 3H), 4.41 (s, 2H), 6.96 (d, J = 8.5 Hz, 2H), 7.75 (d, J = 9.0 Hz, 2H), 8.24 (s, 1H) (Fig. S3, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.02, 55.33, 61.92, 114.02, 128.60, 130.12, 162.11, 164.64, 170.76 (Fig. S4, ESI†). IR (KBr pellet, cm−1): 2964 (m), 1745 (m), 1647 (m), 1602 (m), 1508 (w), 1460 (w), 1441 (w), 1417 (w), 1352 (w), 1306 (w), 1255 (m), 1200 (m), 1180 (m), 1159 (w), 1071 (w), 1023 (w), 959 (w), 833 (m), 774 (w), 669 (w). ESI-MS: calcd for C11H13NO3 (M + 1) 208.09, found: 208.42. Preparation of methyl 2-((naphthalen-2-yl)methyleneamino)acetate (1c). Compound 1c was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 2-naphthaldehyde to give a white solid product with a yield of 76%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.83 (s, 3H), 4.51 (s, 2H), 7.29–7.58 (m, 2H), 7.88–7.94 (m, 3H), 8.06 (d, J = 8.5 Hz, 1H), 8.12 (s, 1H), 8.48 (s, 1H) (Fig. S5, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.13, 62.06, 123.91, 126.54, 127.42, 127.89, 128.53, 128.72, 130.60, 133.01, 133.31, 134.98, 165.44, 170.57 (Fig. S6, ESI†). IR (KBr pellet, cm−1): 2998 (w), 2950 (w), 2878 (w), 1721 (vs), 1641 (m), 1420 (m), 1347 (w), 1323 (m), 1264 (s), 1176 (m), 1118 (w), 1066 (m), 1006 (m), 963 (m), 903 (w), 888 (w), 854 (m), 831 (s), 755 (s), 634 (w). ESI-MS: calcd for C14H13NO2 (M + 1) 228.09, found: 228.42. Preparation of methyl 2-((anthracen-9-yl)methyleneamino)acetate (1d). Compound 1d was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 9-anthracenecarboxaldehyde to give a yellow solid product with a yield of 70%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.90 (s, 3H), 4.78 (s, 2H), 7.52 (t, J = 7.8 Hz, 2H), 7.59 (m, 2H), 8.05 (d, J = 8.5 Hz, 2H), 8.55 (s, 1H), 8.62 (d, J = 9.0 Hz, 2H), 9.49 (s, 1H) (Fig. S7, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.27, 63.02, 124.77, 125.32, 126.96, 128.85, 129.95, 131.23, 165.16, 170.60 (Fig. S8, ESI†). IR (KBr pellet, cm−1): 3047 (w), 2952 (w), 2891 (w), 1750 (s), 1644 (m), 1602 (w), 1519 (w), 1443 (m), 1414 (w), 1382 (w), 1349 (m), 1234 (m), 1211 (s), 1185 (s), 1066 (m), 1001 (w), 960 (w), 875 (w), 840 (w), 723 (s), 670 (w). ESI-MS: calcd for C23H25N (M + 1) 278.11, found: 278.42.
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-dicarboxylate (2a).14 In a 25 mL test tube, methyl acrylate (0.11 mmol, 9.8 μL), 1a (0.1 mmol, 0.0177 g), triethylamine (0.01 mmol, 1 μL), and the catalyst (0.01 mmol) were dissolved in 2 mL of acetonitrile. This solution was stirred at room temperature until a TLC showed that the reaction was completed. After the removal of the solvent, the crude product was purified by column chromatography to give the pure product (Scheme 1). 1 H NMR (CDCl3, 500 MHz, ppm): δ 2.45 (t, J = 7.5 Hz, 2H), 3.24 (s, 3H), 3.34 (m, 1H), 3.85 (s, 3H), 4.02 (t, J = 8.2 Hz, 1H), 4.57 (d, J = 7.5 Hz, 1H), 7.31–7.32 (m, 3H), 7.34 (d, J = 4.5 Hz, 2H) (Fig. S9, ESI†). 13C NMR (CDCl3, 125 MHz): δ 33.26, 49.67, 51.15, 52.20, 59.87, 65.78, 126.74, 127.55, 128.13, 139.12, 172.98, 173.74 (Fig. S10, ESI†). IR (KBr pellet, cm−1): 3369 (m), 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). Preparation of dimethyl 5-(4-methoxyphenyl)pyrrolidine-2,4dicarboxylate (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
Preparation of dimethyl 5-(naphthalen-3-yl)pyrrolidine-2,4dicarboxylate (2c).14 Compound 2c was obtained by the same procedure used for the preparation of compound 2a. Colorless oil, 1H NMR (CDCl3, 500 MHz, ppm): δ 2.51 (t, J = 8.0 Hz, 2H), 3.16 (s, 3H), 3.44 (m, 1H), 3.88 (s, 3H), 4.09 (t, J = 8.2 Hz, 1H), 4.73 (d, J = 7.5 Hz, 1H), 7.44 (d, J = 8.5 Hz, 1H), 7.48–7.49 (m, 2H), 7.81–7.86 (m, 4H) (Fig. S13, ESI†). 13C NMR (CDCl3, 125 MHz): δ 33.38, 49.56, 51.18, 52.23, 59.91, 65.93, 125.13, 125.44, 125.85, 126.07, 127.56, 127.73, 127.98, 132.87, 133.18, 136.61, 173.02, 173.73 (Fig. S14, ESI†). IR (KBr pellet, cm−1): 3359 (m), 3055 (m), 2996 (m), 2951 (m), 2848 (w), 1731 (vs), 1633 (w), 1601 (m), 1507 (m), 1434 (s), 1373 (m), 1248 (s), 1204 (s), 1166 (s), 1128 (m), 1037 (m), 914 (m), 860 (m), 822 (m), 748 (m), 647 (w). X-ray crystallography The crystallographic data collections for 1 and 2 were carried out on a Bruker Smart Apex II CCD area-detector diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 293(2) K using the ω-scan technique. The diffraction 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
Compound
1
2
3
Empirical formula Formula weight T (K) Crystal system Space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z Dc (g cm−3) F(000) θ Range/° Reflections collected Unique reflections Goof R1a [I > 2σ(I)] wR2b [I > 2σ(I)]
C40H32Ag2F6N4O8
C11H8AgF3NO3
C38H36AgF3N4O8
Table 2
1026.44
367.05
841.58
293(2) Monoclinic P21/c 14.7044(15) 15.9797(16) 16.2718(17) 90.00 91.634(2) 90.00 3821.9(7) 4 1.784 2048 1.79–25.50 7085
293(2) Triclinic ˉ P1 5.5736(17) 9.681(3) 10.993(4) 82.393(5) 81.503(5) 84.252(5) 579.5(3) 2 2.103 358 2.67–25.01 2006
200 Monoclinic C2/c 18.055(9) 13.972(8) 14.544(9) 90.00 106.986(18) 90.00 3509(3) 4 1.593 1720 3.18–27.49 4013
[Ag2(L)2(OOCCF3)2] (1)a Ag1–N4 2.129(6) Ag1–O8 2.522(6) Ag2–N1#1 2.154(6) N4–Ag1–N3 153.6(2) N3–Ag1–O8 91.7(2) N2–Ag2–O6 108.3(2)
5358
1969
3456
1.038 0.0711 0.1859
1.104 0.0424 0.1058
1.081 0.0497 0.1327
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.
a
2254 | Dalton Trans., 2014, 43, 2252–2258
Selected bond lengths [Å] and angles [°] for complexes 1–3
[Ag(L)0.5(OOCCF3)] (2)b Ag1–N1 2.252(4) Ag1–O3#3 2.305(4) Ag1–Ag1#3 3.1222(10) N1–Ag1–O2 101.27(16) N1–Ag1–O3#2 109.08(14) O2–Ag1–O3#2 106.19(13) O3#3–Ag1–Ag1#3 72.26(10) O3#2–Ag1–Ag1#3 132.57(9) [Ag(L)2](OOCCF3)(H2O)2 (3)c Ag1–N1 2.388(2) N2#3–Ag1–N2#2 108.32(12) N2#3–Ag1–N1#1 113.64(9)
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)
Ag1–O3#2 Ag1–O2 N1–Ag1–O3#3 O3#3–Ag1–O2 O3#2–Ag1–O3#3 N1–Ag1–Ag1#3 O2–Ag1–Ag1#3
2.540(3) 2.361(4) 127.06(14) 129.43(16) 74.08(13) 117.74(11) 72.61(12)
Ag1–N2#2 N2#2–Ag1–N1#1 N1#1–Ag1–N1
2.349(2) 108.20(9) 104.96(12)
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
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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 lengths and angles with their estimated standard deviations are listed in Table 2.
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Results and discussion Description of the crystal structure of complex 1 Complex 1 was prepared by the slow diffusion of diethyl ether 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 coordinated 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 distances 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 hydrogen bonds to give a three-dimensional (3D) structure (Fig. S15c, ESI†). The hydrogen bonding data are summarized in Table S1 in the ESI.† 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 space group (Table 1) and the asymmetric unit the triclinic P1 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, 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 oxazoline 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 connected by the L ligands to produce a 2D network (Fig. 2b). Moreover, the 2D networks are linked together by C2–H2A⋯F2 hydrogen bonds to form a 3D framework (Fig. S16 and Table S1, 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.
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 coordination 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 observed along the c axis, which are filled with the OOCCF3− anions and water molecules.
Description of the crystal structure of complex 3
Cycloaddition reactions between imino esters and methyl acrylates catalyzed by complexes 1–3
To further understand the induction effect of an ancillary ligand on the crystal structure, imidazole instead of pyrazine was used in the reaction system for the preparation of complex 3. The asymmetric unit of 3 contains one L, one Ag(I) cation,
As shown in Scheme 1, complexes 1–3 were used as catalysts for the cycloaddition reactions between imino esters and methyl acrylates and the results are given in Table 3. Complexes 1 and 2 gave about a 40% yield, while AgOOCCF3
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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 1 2 3
57% 42% 41% 74%
1 2 3 4
Phenyl (1a) 4-Methoxyphenyl (1b) Naphthyl (1c) Anthryl (1d)
10 h 10 h 10 h 10 h
96% (2a) 74% (2b) 72% (2c) Trace
a Methyl 2-(4-methoxybenzylideneamino)acetate (0.1 mmol), methyl acrylate (0.11 mmol, 9.8 μL), triethylamine (0.01 mmol, 1 μL), catalyst (0.01 mmol, 10% mol), room temperature, 10 h. b 1H NMR yields based on methyl 2-(4-methoxybenzylideneamino)acetate using CH2Br2 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 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) is smaller than the channels of 3, and the sizes of 1b (containing 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 Xray 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.
Scheme 2
a Imino ester (0.1 mmol), methyl acrylate (0.11 mmol, 9.8 μL), triethylamine (0.01 mmol, 1 μL), complex 3 (0.01 mmol, 10% mol, 8.4 mg), room temperature. b 1H NMR yields based on the imino ester using CH2Br2 as an internal standard.
Fig. 4 PXRD patterns for 3 under different conditions: (a) simulated; (b) as-synthesized; (c) immersed in CH3CN; (d) after the reaction.
Conclusions 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 oxazoline-containing ligand (L). In 1 and 2, the trifluoroacetate anions are coordinated with the metal centers, which correspond to their poor catalytic performance. When the inductor imidazole, was added, complex 3 is composed of (4,4) 2D networks, where 1D channels accommodate the anions. The channel size in 3 is about 8.2 × 6.8 Å, which leads to its selective catalytic performance.
Different imino esters react with methyl acrylate catalyzed by complex 3 in CH3CN.
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Acknowledgements
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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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Structural modulation of silver complexes and their distinctive catalytic properties† 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−
Received 24th September 2013, Accepted 25th October 2013 DOI: 10.1039/c3dt52655k www.rsc.org/dalton
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.
Introduction Coordination polymers are comprised of metal centers and ligands, and their physical/chemical properties depend on not only the nature of the metal center and ligand but also the connection model between them. The connection pattern can be influenced by the reaction temperature, solvent, auxiliary ligand, counterion and so on.1–3 Therefore, it is challenging to synthesize the desired structure for an undeveloped system. So far, not only complexes with fascinating structures but also their potential applications as functional materials in many fields have attracted more and more attention.4,5 Within various metal ions, Ag(I) is of particularly interest due to its versatile coordination patterns and its high catalytic performance.6–8 As for the ligands, the oxazoline-containing compounds are always used in catalysis because of their adjustable structures, easy preparation, high stabilities during hydrolysis and oxidation reactions, and their strong coordination capabilities due to the in-plane N lone pair and their
a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China. E-mail: [email protected]; Fax: +86 25 8331 4502 b Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University, Suzhou 215123, China c Department 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
2252 | Dalton Trans., 2014, 43, 2252–2258
moderate chemical hardness.9,10 Although many research groups have developed oxazoline-containing catalysts for a homogeneous system, their use in coordination polymers as heterogeneous catalysts are significantly less developed.11,12 In this paper, a new oxazoline-containing ligand, 4,4′-di(2oxazolinyl)biphenyl (L), was synthesized, and three different complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3) were obtained under different reaction media with and without different crystal nucleation inductors. Complexes 1–3 were applied for cycloaddition reactions between methyl acrylate and methyl 2-(benzylideneamino)acetate. The results indicated that the unique structural features of complex 3 play a vital role in its catalytic properties.
Experimental Materials and methods All commercially available chemicals and solvents were of reagent grade and were used as received without further purification. The ligand L was synthesized according to the reported procedure.13 Elemental analyses for C, H and N were performed on a Perkin-Elmer 240C Elemental Analyzer at the analysis 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
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out on an LCQ System (Finnegan MAT, USA) using a mixed solution of methanol and water (1 : 1) as the mobile phase. Preparation of [Ag2(L)2(OOCCF3)2] (1). AgOOCCF3 (6.6 mg, 0.03 mmol) and L (8.8 mg, 0.03 mmol) in 8 mL of methanol was stirred for about 2 min. After filtration, the filtrate was diffused by diethyl ether at room temperature. After several days, colorless crystals appeared. Yield: 61%. Anal. Calcd for (C40H32Ag2F6N4O8): C, 46.81; H, 3.14; N, 5.46%. Found: C, 46.94; H, 3.26; N, 5.21%. IR (KBr pellet, cm−1): 2979 (w), 1690 (s), 1631 (vs), 1556 (m), 1498 (m), 1431 (s), 1400 (m), 1371 (s), 1328 (m), 1259 (s), 1199 (s), 1139 (s), 1095 (s), 1021 (m), 1005 (m), 941 (s), 836 (s), 793 (m), 725 (s), 681 (m). Preparation of [Ag(L)0.5(OOCCF3)] (2). AgOOCCF3 (6.6 mg, 0.03 mmol), L (8.8 mg, 0.03 mmol) and pyrazine (2.4 mg, 0.03 mmol) in 8 mL of methanol was stirred for about 2 min. After filtration, the filtrate was diffused by diethyl ether at room temperature. After several days, colorless crystals appeared. Yield: 42%. Anal. Calcd for (C11H8AgF3NO3): C, 35.99; H, 2.20; N, 3.82%. Found: C, 35.87; H, 2.31; N, 3.71%. IR (KBr pellet, cm−1): 2982 (w), 2918 (w), 1632 (vs), 1497 (m), 1483 (m), 1431 (m), 1400 (m), 1374 (s), 1337 (m), 1260 (vs), 1183 (vs), 1140 (vs), 1096 (vs), 1023 (m), 941 (s), 837 (s), 792 (s), 725 (s), 681 (m). Preparation of [Ag(L)2](OOCCF3)(H2O)2 (3). Complex 3 was obtained by the same procedure used for the preparation of 2 except that pyrazine was replaced by imidazole (2.0 mg, 0.03 mmol) with a yield of 35%. Anal. Calcd for (C38H36AgF3N4O8): C, 54.23; H, 4.31; N, 6.66%. Found: C, 54.37; H, 4.16; N, 6.54%. IR (KBr pellet, cm−1): 2982 (w), 2918 (w), 1632 (vs), 1497 (m), 1482 (m), 1430 (m), 1400 (m), 1373 (s), 1336 (m), 1260 (s), 1184 (vs), 1139 (vs), 1096 (vs), 1023 (m), 1005 (m), 941 (s), 837 (s), 792 (s), 725 (s), 681 (m), 520 (w), 446 (w). Preparation of methyl 2-(benzylideneamino)acetate (1a). In a 100 mL flask, benzaldehyde (2 mmol, 0.212 g), glycine methyl ester hydrochloride (10 mmol, 1.255 g), and triethylamine (10 mmol, 1.1 mL) were dissolved in 50 mL of dichloromethane. Excess anhydrous MgSO4 was added. The solution was refluxed for 12 hours before filtration. The filtrate was washed with water three times, and the organic layer was dried over anhydrous Na2SO4. After evaporation, the product was obtained as a light yellow oil with a yield of 84%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.80 (s, 3H), 4.45 (s, 2H), 7.43–7.48 (m, 3H), 7.80–7.81 (m, 2H), 8.32 (s, 1H) (Fig. S1, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.01, 61.88, 128.46, 128.58, 131.19, 135.61, 165.36, 170.46 (Fig. S2, ESI†). IR (KBr pellet, cm−1): 3062 (w), 3028 (w), 3002 (w), 2952 (m), 2880 (w), 2851 (w), 1748
Scheme 1
Paper
(vs), 1647 (s), 1602 (w), 1580 (w), 1492 (w), 1435 (m), 1385 (w), 1346 (w), 1310 (m), 1273 (s), 1200 (s), 1176 (s), 1080 (w), 1055 (m), 1023 (m), 961 (w), 851 (w), 759 (s), 694 (s). ESI-MS: calcd for C10H11NO2 (M + 1) 178.08, found: 178.25. Preparation of methyl 2-(4-methoxybenzylideneamino)acetate (1b). Compound 1b was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 4-methoxybenzaldehyde to give a white solid product with a yield of 82%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.80 (s, 3H), 3.87 (s, 3H), 4.41 (s, 2H), 6.96 (d, J = 8.5 Hz, 2H), 7.75 (d, J = 9.0 Hz, 2H), 8.24 (s, 1H) (Fig. S3, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.02, 55.33, 61.92, 114.02, 128.60, 130.12, 162.11, 164.64, 170.76 (Fig. S4, ESI†). IR (KBr pellet, cm−1): 2964 (m), 1745 (m), 1647 (m), 1602 (m), 1508 (w), 1460 (w), 1441 (w), 1417 (w), 1352 (w), 1306 (w), 1255 (m), 1200 (m), 1180 (m), 1159 (w), 1071 (w), 1023 (w), 959 (w), 833 (m), 774 (w), 669 (w). ESI-MS: calcd for C11H13NO3 (M + 1) 208.09, found: 208.42. Preparation of methyl 2-((naphthalen-2-yl)methyleneamino)acetate (1c). Compound 1c was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 2-naphthaldehyde to give a white solid product with a yield of 76%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.83 (s, 3H), 4.51 (s, 2H), 7.29–7.58 (m, 2H), 7.88–7.94 (m, 3H), 8.06 (d, J = 8.5 Hz, 1H), 8.12 (s, 1H), 8.48 (s, 1H) (Fig. S5, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.13, 62.06, 123.91, 126.54, 127.42, 127.89, 128.53, 128.72, 130.60, 133.01, 133.31, 134.98, 165.44, 170.57 (Fig. S6, ESI†). IR (KBr pellet, cm−1): 2998 (w), 2950 (w), 2878 (w), 1721 (vs), 1641 (m), 1420 (m), 1347 (w), 1323 (m), 1264 (s), 1176 (m), 1118 (w), 1066 (m), 1006 (m), 963 (m), 903 (w), 888 (w), 854 (m), 831 (s), 755 (s), 634 (w). ESI-MS: calcd for C14H13NO2 (M + 1) 228.09, found: 228.42. Preparation of methyl 2-((anthracen-9-yl)methyleneamino)acetate (1d). Compound 1d was obtained by the same procedure used for the preparation of compound 1a except that benzaldehyde was replaced by 9-anthracenecarboxaldehyde to give a yellow solid product with a yield of 70%. 1H NMR (CDCl3, 500 MHz, ppm): δ 3.90 (s, 3H), 4.78 (s, 2H), 7.52 (t, J = 7.8 Hz, 2H), 7.59 (m, 2H), 8.05 (d, J = 8.5 Hz, 2H), 8.55 (s, 1H), 8.62 (d, J = 9.0 Hz, 2H), 9.49 (s, 1H) (Fig. S7, ESI†). 13C NMR (CDCl3, 125 MHz): δ 52.27, 63.02, 124.77, 125.32, 126.96, 128.85, 129.95, 131.23, 165.16, 170.60 (Fig. S8, ESI†). IR (KBr pellet, cm−1): 3047 (w), 2952 (w), 2891 (w), 1750 (s), 1644 (m), 1602 (w), 1519 (w), 1443 (m), 1414 (w), 1382 (w), 1349 (m), 1234 (m), 1211 (s), 1185 (s), 1066 (m), 1001 (w), 960 (w), 875 (w), 840 (w), 723 (s), 670 (w). ESI-MS: calcd for C23H25N (M + 1) 278.11, found: 278.42.
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-dicarboxylate (2a).14 In a 25 mL test tube, methyl acrylate (0.11 mmol, 9.8 μL), 1a (0.1 mmol, 0.0177 g), triethylamine (0.01 mmol, 1 μL), and the catalyst (0.01 mmol) were dissolved in 2 mL of acetonitrile. This solution was stirred at room temperature until a TLC showed that the reaction was completed. After the removal of the solvent, the crude product was purified by column chromatography to give the pure product (Scheme 1). 1 H NMR (CDCl3, 500 MHz, ppm): δ 2.45 (t, J = 7.5 Hz, 2H), 3.24 (s, 3H), 3.34 (m, 1H), 3.85 (s, 3H), 4.02 (t, J = 8.2 Hz, 1H), 4.57 (d, J = 7.5 Hz, 1H), 7.31–7.32 (m, 3H), 7.34 (d, J = 4.5 Hz, 2H) (Fig. S9, ESI†). 13C NMR (CDCl3, 125 MHz): δ 33.26, 49.67, 51.15, 52.20, 59.87, 65.78, 126.74, 127.55, 128.13, 139.12, 172.98, 173.74 (Fig. S10, ESI†). IR (KBr pellet, cm−1): 3369 (m), 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). Preparation of dimethyl 5-(4-methoxyphenyl)pyrrolidine-2,4dicarboxylate (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
Preparation of dimethyl 5-(naphthalen-3-yl)pyrrolidine-2,4dicarboxylate (2c).14 Compound 2c was obtained by the same procedure used for the preparation of compound 2a. Colorless oil, 1H NMR (CDCl3, 500 MHz, ppm): δ 2.51 (t, J = 8.0 Hz, 2H), 3.16 (s, 3H), 3.44 (m, 1H), 3.88 (s, 3H), 4.09 (t, J = 8.2 Hz, 1H), 4.73 (d, J = 7.5 Hz, 1H), 7.44 (d, J = 8.5 Hz, 1H), 7.48–7.49 (m, 2H), 7.81–7.86 (m, 4H) (Fig. S13, ESI†). 13C NMR (CDCl3, 125 MHz): δ 33.38, 49.56, 51.18, 52.23, 59.91, 65.93, 125.13, 125.44, 125.85, 126.07, 127.56, 127.73, 127.98, 132.87, 133.18, 136.61, 173.02, 173.73 (Fig. S14, ESI†). IR (KBr pellet, cm−1): 3359 (m), 3055 (m), 2996 (m), 2951 (m), 2848 (w), 1731 (vs), 1633 (w), 1601 (m), 1507 (m), 1434 (s), 1373 (m), 1248 (s), 1204 (s), 1166 (s), 1128 (m), 1037 (m), 914 (m), 860 (m), 822 (m), 748 (m), 647 (w). X-ray crystallography The crystallographic data collections for 1 and 2 were carried out on a Bruker Smart Apex II CCD area-detector diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 293(2) K using the ω-scan technique. The diffraction 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
Compound
1
2
3
Empirical formula Formula weight T (K) Crystal system Space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z Dc (g cm−3) F(000) θ Range/° Reflections collected Unique reflections Goof R1a [I > 2σ(I)] wR2b [I > 2σ(I)]
C40H32Ag2F6N4O8
C11H8AgF3NO3
C38H36AgF3N4O8
Table 2
1026.44
367.05
841.58
293(2) Monoclinic P21/c 14.7044(15) 15.9797(16) 16.2718(17) 90.00 91.634(2) 90.00 3821.9(7) 4 1.784 2048 1.79–25.50 7085
293(2) Triclinic ˉ P1 5.5736(17) 9.681(3) 10.993(4) 82.393(5) 81.503(5) 84.252(5) 579.5(3) 2 2.103 358 2.67–25.01 2006
200 Monoclinic C2/c 18.055(9) 13.972(8) 14.544(9) 90.00 106.986(18) 90.00 3509(3) 4 1.593 1720 3.18–27.49 4013
[Ag2(L)2(OOCCF3)2] (1)a Ag1–N4 2.129(6) Ag1–O8 2.522(6) Ag2–N1#1 2.154(6) N4–Ag1–N3 153.6(2) N3–Ag1–O8 91.7(2) N2–Ag2–O6 108.3(2)
5358
1969
3456
1.038 0.0711 0.1859
1.104 0.0424 0.1058
1.081 0.0497 0.1327
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.
a
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Selected bond lengths [Å] and angles [°] for complexes 1–3
[Ag(L)0.5(OOCCF3)] (2)b Ag1–N1 2.252(4) Ag1–O3#3 2.305(4) Ag1–Ag1#3 3.1222(10) N1–Ag1–O2 101.27(16) N1–Ag1–O3#2 109.08(14) O2–Ag1–O3#2 106.19(13) O3#3–Ag1–Ag1#3 72.26(10) O3#2–Ag1–Ag1#3 132.57(9) [Ag(L)2](OOCCF3)(H2O)2 (3)c Ag1–N1 2.388(2) N2#3–Ag1–N2#2 108.32(12) N2#3–Ag1–N1#1 113.64(9)
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)
Ag1–O3#2 Ag1–O2 N1–Ag1–O3#3 O3#3–Ag1–O2 O3#2–Ag1–O3#3 N1–Ag1–Ag1#3 O2–Ag1–Ag1#3
2.540(3) 2.361(4) 127.06(14) 129.43(16) 74.08(13) 117.74(11) 72.61(12)
Ag1–N2#2 N2#2–Ag1–N1#1 N1#1–Ag1–N1
2.349(2) 108.20(9) 104.96(12)
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
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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 lengths and angles with their estimated standard deviations are listed in Table 2.
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Results and discussion Description of the crystal structure of complex 1 Complex 1 was prepared by the slow diffusion of diethyl ether 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 coordinated 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 distances 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 hydrogen bonds to give a three-dimensional (3D) structure (Fig. S15c, ESI†). The hydrogen bonding data are summarized in Table S1 in the ESI.† 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 space group (Table 1) and the asymmetric unit the triclinic P1 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, 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 oxazoline 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 connected by the L ligands to produce a 2D network (Fig. 2b). Moreover, the 2D networks are linked together by C2–H2A⋯F2 hydrogen bonds to form a 3D framework (Fig. S16 and Table S1, 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.
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 coordination 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 observed along the c axis, which are filled with the OOCCF3− anions and water molecules.
Description of the crystal structure of complex 3
Cycloaddition reactions between imino esters and methyl acrylates catalyzed by complexes 1–3
To further understand the induction effect of an ancillary ligand on the crystal structure, imidazole instead of pyrazine was used in the reaction system for the preparation of complex 3. The asymmetric unit of 3 contains one L, one Ag(I) cation,
As shown in Scheme 1, complexes 1–3 were used as catalysts for the cycloaddition reactions between imino esters and methyl acrylates and the results are given in Table 3. Complexes 1 and 2 gave about a 40% yield, while AgOOCCF3
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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 1 2 3
57% 42% 41% 74%
1 2 3 4
Phenyl (1a) 4-Methoxyphenyl (1b) Naphthyl (1c) Anthryl (1d)
10 h 10 h 10 h 10 h
96% (2a) 74% (2b) 72% (2c) Trace
a Methyl 2-(4-methoxybenzylideneamino)acetate (0.1 mmol), methyl acrylate (0.11 mmol, 9.8 μL), triethylamine (0.01 mmol, 1 μL), catalyst (0.01 mmol, 10% mol), room temperature, 10 h. b 1H NMR yields based on methyl 2-(4-methoxybenzylideneamino)acetate using CH2Br2 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 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) is smaller than the channels of 3, and the sizes of 1b (containing 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 Xray 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.
Scheme 2
a Imino ester (0.1 mmol), methyl acrylate (0.11 mmol, 9.8 μL), triethylamine (0.01 mmol, 1 μL), complex 3 (0.01 mmol, 10% mol, 8.4 mg), room temperature. b 1H NMR yields based on the imino ester using CH2Br2 as an internal standard.
Fig. 4 PXRD patterns for 3 under different conditions: (a) simulated; (b) as-synthesized; (c) immersed in CH3CN; (d) after the reaction.
Conclusions 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 oxazoline-containing ligand (L). In 1 and 2, the trifluoroacetate anions are coordinated with the metal centers, which correspond to their poor catalytic performance. When the inductor imidazole, was added, complex 3 is composed of (4,4) 2D networks, where 1D channels accommodate the anions. The channel size in 3 is about 8.2 × 6.8 Å, which leads to its selective catalytic performance.
Different imino esters react with methyl acrylate catalyzed by complex 3 in CH3CN.
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Acknowledgements
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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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