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New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties
Polyhedron 29 (2010) 3036–3045
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New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties Mitra Ghassemzadeh a,⇑, Samira Bahemmat a, Masoomeh Mahmoodabadi a, Babak Rezaii-Rad a, Hassan Hosseini Monfared b, Effat Mottefakeri b, Bernhard Neumüller c a
Chemistry and Chemical Engineering Research Center of Iran, Iran Department of Chemistry, Faculty of Sciences, Zanjan University, Zanjan, Iran c Fachbereich Chemie, Philipps Universität, Marburg, Germany b
a r t i c l e
i n f o
Article history: Received 2 May 2010 Accepted 7 August 2010 Available online 21 August 2010 Keywords: 1,2,4-Triazoles Palladium(II) complexes S,N ligands ‘‘Sandwich” effect
a b s t r a c t The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear PdII-complex [(PPh3)Pd(HL1)Cl]Cl2CH3CN (1). The complex [(PPh3)Pd(HL1)I]Cl1/2H2O (2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH (3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol. All the complexes have been characterized by a combination of FT-IR-, 31P NMR-spectroscopy, elemental analyses and mass spectrometry. The molecular structures of the complexes were determined by X-ray diffraction studies. The unit cell of 2 exhibits two crystallographically independent complexes, while the unit cell of 3 contains three crystallographically independent molecules. While the triazole moiety in 1 and 2 acts as a bidentate chelating ligand, the deprotonated triazole compound in 3 acts as a bridging agent between two metal centers. Single-crystal X-ray diffraction revealed that the packing mode of the heterocycle by the phenyl rings of the PPh3 moiety is responsible for the interesting observed ‘‘sandwich” effect. The X-ray structure of the complex [Pd(py)4]Cl21/2H2O (4) is also reported. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The chemistry of 1,2,4-triazole and its derivatives has received considerable attention because of their effective biological importance and applications. They are known to possess significant antitumor, antibacterial, fungicidal, hypotensive, hypothermic and antiinflammatory activities [1–8]. In addition to these applications, the coordination chemistry of 1,2,4-triazoles as a ligand is widely studied [9] and reviewed [10,11]. Up to 200 single crystal X-ray determinations of metal complexes with 1,2,4-triazoles as ligands well demonstrate the growing interest in the chemistry of this class of ligands. Metal complexes of 1,2,4-triazole and its derivatives often exhibit enhanced biological activities compared to the uncomplexed ligands [12–17]. Among the 1,2,4-triazole derivatives, the mercapto- and thionesubstituted 1,2,4-triazole ring systems have also been studied and reviewed [18–25]. 4-Amino-5-methyl-2H-1,2,4-triazole-3(4H)thione (AMTT, HL1) shows, as a weak monoprotic acid, thione–
⇑ Corresponding author. Tel.: +98 21 44 58 07 20; fax: 98 21 44 58 07 62. E-mail address: [email protected] (M. Ghassemzadeh). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.08.012
thiol tautomerism in solution (forms I and II), as illustrated in Scheme 1. Therefore, such ligands exhibit various coordination modes as thioxo groups and triazoline nitrogen atoms are present on each heterocyclic ring [26–28]. Some of the observed coordination modes of the 1,2,4-triazole ring system to metal centers are presented in Scheme 2. We have previously reported the synthesis and molecular structure of CuI- and AgI-complexes containing AMTT and its Schiffbases, in which the ligand acts either as S-monodentate (form A, Scheme 2) or bidentate N,S-chelating (form B, Scheme 2), and have found that such heterocycles can be used as good stabilization agents for soft metal ions in low oxidation states [29–31]. We have recently reported the synthesis and characterization of the silver(I) complex [{[Ag(AETT)]NO3}2]n (AETT = 4-amino-5-ethyl-2H-1,2, 4-triazole-3(4H)-thione) with new coordination modes between silver(I) ions and the sulfur atoms of the 1,2,4-triazole-3-thione moieties, as shown in Scheme 3. These coordination modes lead to the formation of a 10-membered Ag–S ‘‘mosaic” pattern and cause a two dimensional endless framework [32]. The present work concerns the synthesis and characterization of mono- and binuclear palladium(II) complexes of sulfurated triazole AMTT with triphenylphosphane as a co-ligand.
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H N N S
2. Experimental N N HS
Me N NH2
2.1. Materials
Me N NH2 II
I
Scheme 1. Thione (I) and thiol (II) tautomers of AMTT.
H N N M1 S
H N N S
Me N NH2
M1
A
H N N
M2 S
Me N NH2
M1
B M2 H N N
S M1
Me N NH2 C
H M3 N N
M2 S
Me N NH2
Me N NH2
M1
E
D
Scheme 2. Potential binding modes of AMTT to metal centers.
M1 M2 S M2A
M2
R N NH2
S
M1
M2d
F
2.2. Physical measurements IR spectra were recorded (KBr) on a Perkin–Elmer 883 spectrometer. Melting points were recorded on a Büchi B545 melting point apparatus and are uncorrected. 1H NMR and 31P NMR spectra were recorded on a Bruker-AQS AVANCE 300 MHz using TMS (d = 0.0 ppm) as an internal standard and 85% aqueous H3PO4 as an external standard. Mass spectra were recorded on a Fisons Instruments Trio 1000 spectrometer (EI = 70 eV). Elemental analyses (C, H and N) were performed on a ThermoFinigan Flash EA 1112 series elemental analyzer. 2.3. Synthesis
H N N
H N N
All chemicals except 4-amino-3-methyl-1,2,4-triazol-5-thione [33] were purchased from Merck or Fluka and were used without further purification. Complex 4 is produced by the recrystallization of [PdL2]Cl2 (L = 4-amino-3-hydrazinyl-6-methyl-1,2,4-triazin5(4H)-one) from pyridine as a pale yellow solid mass and is identified as the same complex reported by Drew et al., namely [Pd(Py)4]Cl2.3H2O [34,35].
R N NH2 G
Scheme 3.
2.3.1. Synthesis of [(PPh3)Pd(HL1)Cl]Cl.2CH3CN (1) A solution of HL1 (0.13 g, 1 mmol) in methanol/acetonitrile (20 mL, 1/1) was treated with a solution of palladium(II) chloride (0.17 g, 1 mmol) in the same solvent mixture (20 mL) and stirred for 2 h at room temperature. After completion of the reaction, which was monitored by thin layer chromatography (TLC) using
Table 1 Crystallographic data for 1, 2, 3 and 4.
a b c d
Compound
1
2
3
4
Empirical formula Formula mass Crystal size (mm) Crystal system Space group a [pm] b [pm] c [pm] a [°] b [°] c [°] V [pm3 106] Z Dcalc. [g cm3] Absorption correction l (Mo Ka) [cm1] T [K] 2hmax [°] Index range h k l Reflections collected Unique reflections (Rint) Reflections with Fo > 4r(Fo) Parameters Flack parameter R1 wR2 (all data) Maximum residual electron density [e pm3 106]
C25H27Cl2N6PPdS 651.86 0.42 0.15 0.1 Monoclinic P21/c 1906.4(2) 1326.0(1) 1122.9(1) 90 97.11(1) 90 2816.7(4) 4 1.537 Numerical 10.05 193 52.10
C21H22ClIN4O0.5PPdS 670.21 0.49 0.38 0.32 Triclinic P1
C58H54.67Cl3N4O1.33P3Pd2S 1273.18 0.37 0.32 0.31 Triclinic P1
1146.6(1) 1399.8(2) 1748.1(3) 100.34(2) 106.53(2) 90.01(2) 2642.2(7) 4 1.685 Numerical 21.29 193 52.16
1493.6(1) 2511.6(2) 2594.1(2) 115.56(1) 97.73(1) 99.76(1) 8405(1) 6 1.509 Numerical 9.52 193 51.94
C20H26Cl2N4O3Pd 547.75 0.31 0.21 0.19 Monoclinic Cc 1251.6(1) 1273.5(2) 1524.7(2) 90 107.50(1) 90 2317.8(5) 4 1.57 Numerical 10.59 193 52.32
23 ? 23 16 ? 16 13 ? 13 27 186 5504 (0.0891) 3629 338
13 ? 14 17 ? 17 21 ? 21 25 854 9561 (0.0692) 6394 552
18 ? 18 30 ? 30 31 ? 31 82 940 30493 (0.0414) 19554 1929
0.0356 0.077a 0.495
0.0494 0.1320b 1.826
0.0396 0.0986c 1.157
w ¼ 1=½r2 ðF 2o Þ þ ð0:0384 PÞ2 ; P ¼ ½maxðF 2o ; 0Þ þ 2 F 2c =3. w ¼ 1=½r2 ðF 2o Þ þ ð0:0757 PÞ2 . w ¼ 1=½r2 ðF 2o Þ þ ð0:0579 PÞ2 . w ¼ 1=½r2 ðF 2o Þ þ ð0:0317 PÞ2 .
15 ? 15 15 ? 15 18 ? 18 11 260 4528 (0.0368) 3952 272 0.00(3) 0.0282 0.0596d 0.43
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H2N N
Pd(PPh3)Cl S
Cl.2CH3CN
N NH
a
b
1
NH2 N S
H2N N
Pd(PPh3)I S
Cl.1/2H2O
N NH 2
N NH HL1
c H2N N
Pd(PPh3)Cl S
Cl.1/3H2O.MeOH
N N Pd(PPh3)2Cl 3
Scheme 4. (a) PdCl2, PPh3 in MeOH/MeCN; (b) NaI in MeOH/MeCN; and (c) PdCl2, PPh3, NaOAc (2:3:1) in MeOH/MeCN.
ethylacetate/hexane (1/1 v/v) as the eluent, the reaction mixture was treated with triphenylphosphane (0.26 g, 1 mmol) and was stirred for a further 2 h. Completion of the reaction was monitored by TLC using the same eluent as mentioned above. The reaction mixture was filtered, washed with cold acetonitrile and dried at room temperature. Yield: 0.48 g, 84%, mp: 225 °C, Anal. Calc. for C21H21Cl2N4PPdS (569.78): C, 44.27; H, 3.71; N, 9.83. Found: C, 44.20; H, 3.69; N, 9.97%. IR (KBr) [m/cm1]: 3047 s, 3022 s, 2872 s, 2762 s, 1969 w, 1899 w, 1604 m, 1506 s, 1479 s, 1433 s, 1390 m, 1357 m, 1311 w, 1184 m, 1097 s, 1072 w, 997 s, 748 s, 690 s, 534 s, 509 s, 451 w. EI-MS (70 eV): m/z 262 (PPh3), 130 (HL1). 31 P NMR (d/ppm, CDCl3): 29.89 (s). 2.3.2. Synthesis of [(PPh3)Pd(HL1)I]Cl1/2H2O (2) A solution of 1 (0.56 g, 1 mmol) in methanol/acetonitrile (20 mL, 1/1) was treated with sodium iodide (0.15 g, 1 mmol) at room temperature and stirred for 3 h. After completion of the reaction (TLC), the crude product was filtered and washed with water (2 10 mL), dried and characterized as a pure material. Single
Fig. 1. Molecular structure of the ion pair in complex 1 (thermal ellipsoids at the 40% probability level), the hydrogen atoms of the phenyl rings are omitted for clarity. Selected bond lengths [pm] and angles [°]: Pd1–N2 214.6(3), Pd1–P1 225.2(1), Pd1–Cl1 229.9(1), Pd1–S1 230.1(1), S1–C1 172.4(4), C1–N1 133.8(5), N1– N2 141.1(5), N1–C2 138.1(5), C2–N3 130.5(5), N3–N4 137.0(5), N2–Pd1–Cl1 89.6(1), P1–Pd1–Cl1 89.67(4), N2–Pd1–S1 87.1(1), P1–Pd1–S1 93.78(4), C1–S1– Pd1 95.6(1), C2–N1–C1 108.7(3), N1–C1–N4 104.9(3), C1–N4–N3 112.4(4), N4–N3– C2 104.9(3), N3–C2–N1 109.1(4).
Fig. 2. Molecular structures of the cations in complex 2 (thermal ellipsoids at the 40% probability level), the hydrogen atoms of the phenyl rings are omitted for clarity. Selected bond lengths [pm] and angles [°]: Pd1–N1 212.1(5), Pd1–P1 224.4(2), Pd1–S1 231.9(2), Pd1–I1 260.26(9), S1–C1 171.3(7), C1–N2 135.1(9), N2–C2 139.0(9), C2–N3 133(1), N3–N4 135.9(9), N4–C1 133.8(9), N2–N1 142.6(8), N1–Pd1–P1 177.9(2), N1–Pd1–S1 87.8(2), P1–Pd1–S1 94.03(6), N1–Pd1–I1 88.4(2), P1–Pd1–I1 89.80(5), C1–N2–C2 109.0(6), N2–C2–N3 108.2(6), C2–N3–N4 105.6(6), N3–N4–C1 112.6(6), N4–C1–N2 104.5(6); Pd2–N6 212.1(5), Pd2–P2 224.2(2), Pd2– S2 231.2(2), Pd2–I2 259.99(8), S2–C4 171.1(7), C4–N5 136.3(9), N5–C5 139.0(9), C5–N7 128.7(9), N7–N8 139.3(9), N8–C4 132.3(9), N6–Pd2–S2 87.8(1), P2–Pd2–S2 94.23(6), N6–Pd2–I2 88.1(1), P2–Pd2–I2 89.85(5), C1–S1–Pd1 95.1(3), H7–O1–H8 102.7, H9–O2–H10 142.1, C4–N5–C5 108.1(5), N5–C5–N7 110.1(6), C5–N7–N8 104.9(6), N7–N8–C4 112.4(6), N8–C4–N5 104.2(6).
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crystals suitable for X-ray analysis were obtained by recrystallization from a methanol solution of 2. Yield: 0.60 g, 90%, mp: 228 °C, Anal. Calc. for C21H21ClIN4PPdS (677.28): C, 39.01; H, 3.72; N, 8.27. Found: C, 38.94; H, 3.70; N, 8.30%. IR (KBr) [m/cm1]: 3188 w, 2978 w, 2939 m, 2854 m, 2690 m, 2634 m, 2387 m, 2351 m, 2333 m, 1799 w, 1768 w, 1714 s, 1612 s, 1516 m, 1460 w, 1375 w, 1332 s, 1226 m, 1166 w, 1126 vw, 1068 w, 1012 w, 977 w, 918 w, 887 w, 858 w, 715 m, 671 w, 609 vw, 520 m, 490 w, 459 w. EI-MS (70 eV): m/z 130 (HL1), 262 (PPh3). 31P NMR (d/ppm, CDCl3): 35.74 (s). 2.3.3. Synthesis of [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH (3) To a solution of HL1 (0.13 g, 1 mmol) in methanol (20 mL), a solution of sodium acetate (0.08 g, 1 mmol) in water (2 mL) was added. The obtained solution was treated with palladium chloride (0.35 g, 2 mmol) and stirred for 1 h. After completion of the reaction, which was monitored by TLC using ethyl acetate/ petroleum ether (1/2) as the eluent, the orange reaction mixture was treated with a solution of triphenylphosphane (0.78 g, 3 mmol) in same the solvent (10 mL) and was stirred for a further 3 h. After completion of the reaction (TLC test), the solid was filtered and washed with cold methanol (2 5 mL). The filtrate was kept at 4 °C to give bright orange single crystals after a few days. Yield: 1.20 g, 95%,
mp: 245 °C. Anal. Calc. for C58H54Cl3N4OP3Pd2S (1267.26) C, 54.97; H, 4.29; N, 4.42. Found: C, 54.89; H, 4.30; N, 4.45%. IR (KBr), [m/cm1): 3350, 1620, 1471, 1431, 748–696. 1H NMR (d/ ppm, CDCl3): 1.24 (s, 3H, CH3), 7.35–7.72 (m, 45H, 3PPh3). 31P NMR (d/ppm, CDCl3): 23.53, 30.43. MS (70 ev) m/z: 129 (L1), 262 (PPh3). 2.4. Crystal structure analyses of 1, 2, 3 and 4 (Table 1) Table 1 shows the crystallographic data of complexes 1–4. The crystals of 1, 2, 3 and 4 were covered with perfluorinated oil and mounted on the top of a glass capillary under a flow of cold gaseous nitrogen. The orientation matrix and unit cell dimensions were determined from 8000 ( 1–3, Stoe IPDS I) and from 5000 (4, Stoe IPDS II) reflections (graphite-monochromated Mo-Ka NH2 N S N N III Scheme 5. Hückel aromaticity in L1.
Fig. 3. Molecular structures of the cations in complex 3 (thermal ellipsoids at the 40% probability level). Selected bond lengths [pm] and angles [°]: Pd1–N2 216.2(3), Pd1–P1 225.1(1), Pd1–S1 228.7(1), Pd1–Cl1 230.19(11), Pd2–N4 202.7(3), Pd2–Cl2 229.5(1), Pd2–P2 234.1(1), Pd2–P3 234.7(1), S1–C1 171.1(4), C1–N1 135.4(5), N1–C2 138.1(5), C2– N3 131.1(5), N3–N4 138.7(5), N4–C1 131.3(5), N2–Pd1–S1 88.14(9), P1–Pd1–S1 88.30(4), N2–Pd1–Cl1 90.50(9), P1–Pd1–Cl1 93.09(4), N4–Pd2–P2 91.96(9), Cl2–Pd2–P2 88.20(4), N4–Pd2–P3 90.61(9), Cl2–Pd2–P3 90.09(4), C1–N1–C2 107.5(3), N1–C2–N3 108.7(3), C2–N3–N4 106.6(3), N3–N4–C1 109.8(3), N4–C1–N1 107.4(4); Pd3–N6 215.3(3), Pd3–P4 225.2(1), Pd3–S2 229.2(1), Pd3–Cl3 231.9(1), Pd4–N8 202.5(3), Pd4–Cl4 230.4(1), Pd4–P5 233.7(1), Pd4–P6 235.0(1), S2–C4 171.4(4), C4–N5 136.4(5), N5– C5 137.0(5), C5–N7 130.9(5), N7–N8 138.4(5), N8–C4 131.8(5), N6–Pd3–S2 88.09(9), P4–Pd3–S2 92.17(4), N6–Pd3–Cl3 89.04(9), P4–Pd3–Cl3 90.70(4), N8–Pd4–P5 89.81(9), Cl4–Pd4–P5 90.44(4), N8–Pd4–P6 89.94(9), Cl4–Pd4–P6 90.36(4), C4–N5–C5 107.9(3), N5–C5–N7 109.2(4), C5–N7–N8 106.1(3), N7–N8–C4 110.6(3), N8–C4–N5 106.1(3); Pd5–N10 215.9(3), Pd5–P7 225.4(1), Pd5–S3 229.3(1), Pd5–Cl5 232.1(1), Pd6–N12 202.9(3), Pd6–Cl6 230.1(1), Pd6–P8 235.1(1), Pd6–P9 236.8(1), S3–C7 171.9(4), C7–N9 135.8(5), N9–C8 136.9(5), C8–N11 130.7(5), N11–N12 139.0(5), N12–C7 131.5(5), N10–Pd5–S3 87.52(9), P7–Pd5–S3 92.83(4), N10–Pd5–Cl5 89.28(9), P7–Pd5–Cl5 90.46(4), N12–Pd6–P8 90.60(9), Cl6–Pd6–P8 89.92(4), N12–Pd6–P9 90.70(9), Cl6–Pd6–P9 89.71(4), C7–N9–C8 107.4(3), N9–C8–N11 109.2(4), C8–N11–N12 106.5(3), N11–N12–C7 109.4(3), N12–C7–N9 107.4(4).
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radiation, k = 71.073 pm). The intensities were corrected for Lorentz and polarization effects. In addition, absorption corrections were applied numerically. The structures were solved by direct methods (SIR-92 for 1, 2 and 4 and SHELXS-97 for 3) and refined against F2 by full-matrix least-squares using the program SHELXL97. The position of carbon bonded hydrogen atoms were calculated for ideal positions and all hydrogen atoms except H1–H3 (free refinement) in 2 were refined with a common displacement parameter. Programs used were SIR-92 [36], SHELXS-97 [37], SHELXL97 [38], SHELXTL-PLUS [39] and PLATON [40].
3. Results and discussion 3.1. Synthesis and characterization of 1, 2 and 3 As depicted in Scheme 4, complex 1 can be obtained as orange solid mass by the reaction of HL1 with palladium chloride and triphenylphosphane in a 1:1:1 molar ratio in methanol/acetonitrile. The treatment of 1 with sodium iodide in a molar ratio of 1:1 in the same solvent mixture gave complex 2 as a reddish powder, and complex 3 can be prepared by the treatment of a solution of
Fig. 4. A view of the structure of complex 1, showing the hydrogen bonding interactions between the cations and anions. The phenyl rings and methyl groups are omitted for clarity.
Fig. 5. The packing diagram of 1 showing the hydrogen bonding between the cations and anions.
M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
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HL1 containing sodium acetate with palladium(II) chloride and triphenylphosphane in methanol as bright red-orange crystals.
All the complexes are air-stable. The results of the elemental analyses, together with IR and 31P NMR data, allow us to postulate
Fig. 6. Representation of hydrogen bonds involving cations and anions in complex 2.
Fig. 8. Representation of the cation in 4 (thermal ellipsoids at the 40% probability level). Selected bond lengths [pm] and angles [°]:Pd1–N4 201.9(3), Pd1–N1 203.2(3), Pd1–N3 203.8(3), Pd1–N2 203.9(3), N4–Pd1–N1 90.1(1), N4–Pd1–N3 88.5(1), N1–Pd1–N2 89.9(1), N3–Pd1–N2 91.4(1).
Fig. 7. The packing diagram of 2.
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complexes 1, 2 and 3 being obtained. In IR spectra of the complexes, the absorptions at 1479 and 1433 cm1 (1), 1460 and 1430 cm1 (2), and 1471 and 1431 cm1 (3) can be assigned to C@Nring stretching vibrations. The absorptions around 3188– 3350 cm1 can be assigned to NH2 vibrations in 1–3. The P–C vibrations of the PPh3 moiety are found in the range 744– 691 cm1 [41]. The mass spectra of 1, 2 and 3 show only the main peak of the corresponding ligand and co-ligand triphenylphosphane (m/z = 130 (HL1) for 1 and 2, 129 (L1) for 3 and m/z = 262 (PPh3) for all complexes). The 31P NMR spectra of 1 and 2 in CDCl3 showed a sharp single peak at d 29.89 ppm (1) and d 35.74 ppm (2). Consistent with the structure of 3, the solution 31P NMR spectrum in CDCl3 showed two 31P resonances at d 30.43 ppm for the mono phosphane coordinated palladium atom and at d 23.53 ppm for the two-fold phosphane coordinated metal center. The 1H NMR spectrum of complex 3 shows pronounced changes with respect to the free ligand (HL1), which means that the signal assigned to the triazole proton disappears as a consequence of deprotonation.
Fig. 9. View of the hydrogen bonds in 4 involving chloride anions and water molecules.
3.2. Crystal structures of 1, 2 and 3 Complex 1 crystallizes in the monoclinic space group P21/c, Complexes while 2 and 3 crystallize in the triclinic space group P 1. 1 and 2 consists of [(PPh3)Pd(HL1)X]+ cations (X = Cl (1) and X = I (2)) and chloride anions. Cations of both complexes contain the [(PPh3)Pd(HL1)] core, in which the heterocycle HL1 acts as a bidentate chelating ligand and coordinates to the metal center via its hydrazine nitrogen atom and its thione sulfur atom, like form B as shown in Scheme 2 (Figs. 1 and 2). To complete the square planar arrangement around the palladium ion in these complexes, the fourth coordination places in 1 and 2 are occupied by one chlorine atom and one iodine atom. Complex 2 consists of two crystallographically independent molecules, as depicted in Fig. 2. Complex 3 consists of three crystallographically independent molecules (Fig. 3) and can be described as complex 1 with an additional coordination to a [(PPh3)2ClPd]-moiety through its deprotonated endocyclic NH-group. Therefore, the ligands act as a uni- as well as a bidentate chelating ligand and coordinate to the metal centers using one of their endocyclic nitrogen atoms (l1-Ncoordination to Pd2, Pd4 and Pd6) and their thiol sulfur atom and hydrazine nitrogen atom (l2-N,S-coordination to Pd1, Pd3 and Pd5). The other coordination positions around Pd1, Pd3 and Pd5 are occupied by one chlorine atom and one triphenylphosphane molecule, while the positions around Pd2, Pd4 and Pd6 are occupied by one chlorine atom and two triphenylphosphane moieties. In the cations of 3, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]+, the singly deprotonated 1,2,4-triazole heterocycles (L1) act as a bridging agent between two palladium atoms and show Hückel aromaticity as shown in Scheme 5. The Pd–P bond length of 225.2(1) pm in 1, and mean Pd–P bond lengths of 224.3 pm in 2, 225.23 pm by one triphenylphosphane coordinated a metal center and 234.9 pm by the two-fold triphenylphosphane coordinated the palladium atoms in 3 are shorter than the sum of the single bond radii for palladium and phosphorus, i.e.
Fig. 10. The packing diagram of 4 showing the hydrogen bonding between cations and anions.
M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
241 pm [42], and fall in the lower range (221–246 pm) of PdII–PPh3 bond reference values (230.2 pm) encountered in 248 entries [43]. The Pd–S bond distances of 230.1(1) pm (1), mean 231.55 pm (2) and mean 229.06 pm (3) are comparable with those reported for strong Pd–S coordination as observed in the complexes [(AMTTO)Pd(PPh)3Br]Br.MeOH (Pd–S: 227.5(2) pm) [44] and [Pd2(l-H3L)2]2DMSO (H3L = two-fold deprotonated 3,5-diacyl1,2,4-triazole-bis(4-methylthiosemicarbazone; Pd–S: 226.3(3) pm) [45]. The Pd–Cl bond distances of 229.9(1) pm in 1 and mean 231.39 pm by Pd1, Pd3 and Pd5 and mean 230 pm by Pd2, Pd4 and Pd6 in 3 are in good agreement with the observed distances in a series of triphenylphosphane-chlorine-palladium complexes, such as [(AMTTO)Pd(PPh3)Cl]ClCH3OH (Pd–Cl: 231.14(6) pm) [46]. The mean Pd–I bond distance of 260.12 pm in 2 is similar to those observed in [(AMTTO)Pd(PPh3)I]2CH3OH (Pd–I: 261.58(9) pm) [44]. Each cation in 1 acts as a bridging agent between its own chloride anion through its NH-group and the anions of two adjacent molecules through the hydrogen atoms of their NH2-moieties via hydrogen bonding (N2–H1 Cl2b: 326.2(4) pm, N2–H2 Cl2a: 333.0(4) pm and N4–H3 Cl2: 308.9(4) pm, Fig. 4). This coordina-
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tion arrangement is responsible for the formation of chains along the [0 0 1] direction (Fig. 5). The chloride anions in 2 act as a bridging agent between the cations (Fig. 6). The Cl1 atoms coordinate to three N–H-moieties (one intramolecular hydrogen bonding to one NH2-group and two intermolecular hydrogen bondings to the NH2- and NH-groups of the adjacent cation, N1–H1 Cl1: 315.6(6) pm, N6–H4 Cl1: 314.5(6) pm and N8–H6 Cl1: 311.3(8) pm). The Cl2 anions are responsible for the connections via hydrogen bonding between two layers (by coordination to the NH2- and NH-groups of the molecules of other layers, N4–H3 Cl2a: 311.4(7) pm, N6–H5 Cl2b: 315.6(6) pm). Each Cl2 anion coordinates to the NH2-moiety of the adjacent molecule via hydrogen bonding, simultaneously (N1–H2 Cl2: 313.4(6) pm). These coordination modes lead to a 2D-layers parallel to (0 0 1) as shown in Fig. 7. It is noteworthy to mention, that in all the complexes, the five-membered heterocycles are planar. A similar interesting chloride–hydrogen bonding composition can be observed in the palladium(II) complex [Pd(Py)4]Cl21/2H2O (4). Complex 4 crystallizes in the monoclinic space group Cc with a Flack-parameter of 0.00(3) and consists of [Pd(Py)4]+-cations
Fig. 11. Molecular structures of three crystallographically independent complexes of 3 showing the hydrogen bonding between the cations and two Cl-ions.
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and chloride anions (Fig. 8). Although the molecules are nearly centrosymmetric, the structure could not be transformed into space group C2/c, which was confirmed by the Flack parameter. This was checked by standard procedures with the program PLATON [40]. In addition, the unit cell of 4 shows that Cc is the correct space group. The palladium center in the square planar cation is surrounded by four pyridine molecules. The chloride anions and the solvent molecules in 4 are responsible for the formation of a network of hydrogen bridges parallel to (0 0 1) as illustrated in Fig. 9 and Fig. 10 (O1–H1 Cl2a: 320.3(5) pm, O1–H2 Cl2a: 320.3(5) pm, O2–H3 Cl1a: 315.9(5) pm, O2–H4 .Cl2b: 311.1(5) pm, O3– H5 Cl2c: 314.5(5) pm, O3–H6 Cl1b: 317.1(5) pm). The dihedral angles between the ‘‘best” planes through the PdN4-plane (A: Pd1 N1 N2 N3 N4) and the planes through pyridine molecules (B: N1 C1 C2 C3 C4 C5, C: N2 C6 C7 C8 C9 C10, D: N3 C11 C12 C13 C14 C15, E: N4 C16 C17 C18 C19 C20) are (A, B) 97, (A, C): 63, (A, D): 94 and (A, E) 74°. Complex 3 contains one water molecule and six methanol molecules per three complex molecules. In each complex, the hydrazine amine moiety of the five-membered heterocycles acts as a bridging agent between two chloride anions using its two hydrogen atoms (Fig. 11). They link the chloride anion of the same complex to the anion of the adjacent one via hydrogen bonding (N2–H1 Cl7a: 324.3(3) pm, N2–H1–Cl7a: 163°; N2–H2 Cl7: 323.8(4) pm, N2–H2–Cl7: 164°; N6–H3 Cl9b: 332.6(5) pm, N6– H3–Cl9b: 159°; N6–H4-Cl8: 313.1(4) pm, N6–H4–Cl8: 175°; N10–H5 Cl8b: 329.6(3) pm, N10–H5–Cl8b: 159°; N10–H6 Cl9: 320.9(4) pm, N10–H6–Cl9: 169°). The chloride ion Cl9 acts as a bridging agent between one methanol molecule and the water molecule via hydrogen bonding (O1–H7 Cl9: 323.5(5) pm, O1– H7–Cl9: 126° and O5–H12 Cl9: 310(2) pm, O5–H12–Cl9: 130°). Fig. 12 represents the unit cell of complex 3. The dihedral angle between the ‘‘best” planes in the non-planar complexes of 3 (A: Pd1 P1 Cl1 N2 S1; B: Pd2 Cl2 P2 P3 N4; C: Pd3 P4 Cl3 N6 S2; D: Pd4 P5 P6 Cl4 N8; E: Pd5 Cl5 P7 S3 N10 and F: Pd6 P8 P9 Cl6 N12) are 101 (A, B), 110 (C, D) and 119° (E, F). The steric
M2 N N S M1
R N NH2 H
Scheme 6.
hindrance induced by the bulky phenyl rings of the three coordinated triphenylphosphane groups in 3 is responsible for the deviation from the planar geometry observed in 1 and 2, since no significant differences are found between the bond distances and bond angles in the corresponding ligands in the complexes. In each cation of 3, the triphenylphosphane ligands of the second palladium ion are trans-positioned. According to this coordination arrangement, the five-membered heterocycle is packed by two phenyl rings of the triphenylphosphane molecule like a sandwich with a p-stacking effect. The shortest distances between the central lying atoms of the heterocycles in the sandwiches from the phenyl rings are N3 C59: 326.0(5) pm, N7 C94: 318.3(5) pm and N11 C144: 313.0(5) pm. 4. Conclusion In conclusion, we have synthesized and characterized two mononuclear and the first binuclear palladium complex containing the well known 4-amino-3-methyl-1,2,4-triazol-5-thione moiety. According to the determined crystal structures, we found that the 1,2,4-triazole moiety acts as a bidentate chelating ligand through its sulfur and nitrogen atoms, while the singly deprotonated triazole moiety acts as a bridging agent between two metal centers. It can simultaneously act as a bidentate chelating agent through its thiole sulfur atom and hydrazine nitrogen atom to one metal center and as a uni-dentate agent via its endocyclic nitrogen atom to the other metal center. Consequently, this new
Fig. 12. The packing diagram of 3.
M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
coordination mode can be described as form H as depicted in Scheme 6. In addition, the binuclear complex [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH shows the formation of an interesting ‘‘sandwich” effect due to the arrangement of the phenyl rings. 5. Supplementary data CCDC 772285, 772286, 699146 and 772287 contain the supplementary crystallographic data for 1, 2, 3 and 4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail: [email protected].
[17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
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New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties Mitra Ghassemzadeh a,⇑, Samira Bahemmat a, Masoomeh Mahmoodabadi a, Babak Rezaii-Rad a, Hassan Hosseini Monfared b, Effat Mottefakeri b, Bernhard Neumüller c a
Chemistry and Chemical Engineering Research Center of Iran, Iran Department of Chemistry, Faculty of Sciences, Zanjan University, Zanjan, Iran c Fachbereich Chemie, Philipps Universität, Marburg, Germany b
a r t i c l e
i n f o
Article history: Received 2 May 2010 Accepted 7 August 2010 Available online 21 August 2010 Keywords: 1,2,4-Triazoles Palladium(II) complexes S,N ligands ‘‘Sandwich” effect
a b s t r a c t The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear PdII-complex [(PPh3)Pd(HL1)Cl]Cl2CH3CN (1). The complex [(PPh3)Pd(HL1)I]Cl1/2H2O (2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH (3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol. All the complexes have been characterized by a combination of FT-IR-, 31P NMR-spectroscopy, elemental analyses and mass spectrometry. The molecular structures of the complexes were determined by X-ray diffraction studies. The unit cell of 2 exhibits two crystallographically independent complexes, while the unit cell of 3 contains three crystallographically independent molecules. While the triazole moiety in 1 and 2 acts as a bidentate chelating ligand, the deprotonated triazole compound in 3 acts as a bridging agent between two metal centers. Single-crystal X-ray diffraction revealed that the packing mode of the heterocycle by the phenyl rings of the PPh3 moiety is responsible for the interesting observed ‘‘sandwich” effect. The X-ray structure of the complex [Pd(py)4]Cl21/2H2O (4) is also reported. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The chemistry of 1,2,4-triazole and its derivatives has received considerable attention because of their effective biological importance and applications. They are known to possess significant antitumor, antibacterial, fungicidal, hypotensive, hypothermic and antiinflammatory activities [1–8]. In addition to these applications, the coordination chemistry of 1,2,4-triazoles as a ligand is widely studied [9] and reviewed [10,11]. Up to 200 single crystal X-ray determinations of metal complexes with 1,2,4-triazoles as ligands well demonstrate the growing interest in the chemistry of this class of ligands. Metal complexes of 1,2,4-triazole and its derivatives often exhibit enhanced biological activities compared to the uncomplexed ligands [12–17]. Among the 1,2,4-triazole derivatives, the mercapto- and thionesubstituted 1,2,4-triazole ring systems have also been studied and reviewed [18–25]. 4-Amino-5-methyl-2H-1,2,4-triazole-3(4H)thione (AMTT, HL1) shows, as a weak monoprotic acid, thione–
⇑ Corresponding author. Tel.: +98 21 44 58 07 20; fax: 98 21 44 58 07 62. E-mail address: [email protected] (M. Ghassemzadeh). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.08.012
thiol tautomerism in solution (forms I and II), as illustrated in Scheme 1. Therefore, such ligands exhibit various coordination modes as thioxo groups and triazoline nitrogen atoms are present on each heterocyclic ring [26–28]. Some of the observed coordination modes of the 1,2,4-triazole ring system to metal centers are presented in Scheme 2. We have previously reported the synthesis and molecular structure of CuI- and AgI-complexes containing AMTT and its Schiffbases, in which the ligand acts either as S-monodentate (form A, Scheme 2) or bidentate N,S-chelating (form B, Scheme 2), and have found that such heterocycles can be used as good stabilization agents for soft metal ions in low oxidation states [29–31]. We have recently reported the synthesis and characterization of the silver(I) complex [{[Ag(AETT)]NO3}2]n (AETT = 4-amino-5-ethyl-2H-1,2, 4-triazole-3(4H)-thione) with new coordination modes between silver(I) ions and the sulfur atoms of the 1,2,4-triazole-3-thione moieties, as shown in Scheme 3. These coordination modes lead to the formation of a 10-membered Ag–S ‘‘mosaic” pattern and cause a two dimensional endless framework [32]. The present work concerns the synthesis and characterization of mono- and binuclear palladium(II) complexes of sulfurated triazole AMTT with triphenylphosphane as a co-ligand.
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H N N S
2. Experimental N N HS
Me N NH2
2.1. Materials
Me N NH2 II
I
Scheme 1. Thione (I) and thiol (II) tautomers of AMTT.
H N N M1 S
H N N S
Me N NH2
M1
A
H N N
M2 S
Me N NH2
M1
B M2 H N N
S M1
Me N NH2 C
H M3 N N
M2 S
Me N NH2
Me N NH2
M1
E
D
Scheme 2. Potential binding modes of AMTT to metal centers.
M1 M2 S M2A
M2
R N NH2
S
M1
M2d
F
2.2. Physical measurements IR spectra were recorded (KBr) on a Perkin–Elmer 883 spectrometer. Melting points were recorded on a Büchi B545 melting point apparatus and are uncorrected. 1H NMR and 31P NMR spectra were recorded on a Bruker-AQS AVANCE 300 MHz using TMS (d = 0.0 ppm) as an internal standard and 85% aqueous H3PO4 as an external standard. Mass spectra were recorded on a Fisons Instruments Trio 1000 spectrometer (EI = 70 eV). Elemental analyses (C, H and N) were performed on a ThermoFinigan Flash EA 1112 series elemental analyzer. 2.3. Synthesis
H N N
H N N
All chemicals except 4-amino-3-methyl-1,2,4-triazol-5-thione [33] were purchased from Merck or Fluka and were used without further purification. Complex 4 is produced by the recrystallization of [PdL2]Cl2 (L = 4-amino-3-hydrazinyl-6-methyl-1,2,4-triazin5(4H)-one) from pyridine as a pale yellow solid mass and is identified as the same complex reported by Drew et al., namely [Pd(Py)4]Cl2.3H2O [34,35].
R N NH2 G
Scheme 3.
2.3.1. Synthesis of [(PPh3)Pd(HL1)Cl]Cl.2CH3CN (1) A solution of HL1 (0.13 g, 1 mmol) in methanol/acetonitrile (20 mL, 1/1) was treated with a solution of palladium(II) chloride (0.17 g, 1 mmol) in the same solvent mixture (20 mL) and stirred for 2 h at room temperature. After completion of the reaction, which was monitored by thin layer chromatography (TLC) using
Table 1 Crystallographic data for 1, 2, 3 and 4.
a b c d
Compound
1
2
3
4
Empirical formula Formula mass Crystal size (mm) Crystal system Space group a [pm] b [pm] c [pm] a [°] b [°] c [°] V [pm3 106] Z Dcalc. [g cm3] Absorption correction l (Mo Ka) [cm1] T [K] 2hmax [°] Index range h k l Reflections collected Unique reflections (Rint) Reflections with Fo > 4r(Fo) Parameters Flack parameter R1 wR2 (all data) Maximum residual electron density [e pm3 106]
C25H27Cl2N6PPdS 651.86 0.42 0.15 0.1 Monoclinic P21/c 1906.4(2) 1326.0(1) 1122.9(1) 90 97.11(1) 90 2816.7(4) 4 1.537 Numerical 10.05 193 52.10
C21H22ClIN4O0.5PPdS 670.21 0.49 0.38 0.32 Triclinic P1
C58H54.67Cl3N4O1.33P3Pd2S 1273.18 0.37 0.32 0.31 Triclinic P1
1146.6(1) 1399.8(2) 1748.1(3) 100.34(2) 106.53(2) 90.01(2) 2642.2(7) 4 1.685 Numerical 21.29 193 52.16
1493.6(1) 2511.6(2) 2594.1(2) 115.56(1) 97.73(1) 99.76(1) 8405(1) 6 1.509 Numerical 9.52 193 51.94
C20H26Cl2N4O3Pd 547.75 0.31 0.21 0.19 Monoclinic Cc 1251.6(1) 1273.5(2) 1524.7(2) 90 107.50(1) 90 2317.8(5) 4 1.57 Numerical 10.59 193 52.32
23 ? 23 16 ? 16 13 ? 13 27 186 5504 (0.0891) 3629 338
13 ? 14 17 ? 17 21 ? 21 25 854 9561 (0.0692) 6394 552
18 ? 18 30 ? 30 31 ? 31 82 940 30493 (0.0414) 19554 1929
0.0356 0.077a 0.495
0.0494 0.1320b 1.826
0.0396 0.0986c 1.157
w ¼ 1=½r2 ðF 2o Þ þ ð0:0384 PÞ2 ; P ¼ ½maxðF 2o ; 0Þ þ 2 F 2c =3. w ¼ 1=½r2 ðF 2o Þ þ ð0:0757 PÞ2 . w ¼ 1=½r2 ðF 2o Þ þ ð0:0579 PÞ2 . w ¼ 1=½r2 ðF 2o Þ þ ð0:0317 PÞ2 .
15 ? 15 15 ? 15 18 ? 18 11 260 4528 (0.0368) 3952 272 0.00(3) 0.0282 0.0596d 0.43
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H2N N
Pd(PPh3)Cl S
Cl.2CH3CN
N NH
a
b
1
NH2 N S
H2N N
Pd(PPh3)I S
Cl.1/2H2O
N NH 2
N NH HL1
c H2N N
Pd(PPh3)Cl S
Cl.1/3H2O.MeOH
N N Pd(PPh3)2Cl 3
Scheme 4. (a) PdCl2, PPh3 in MeOH/MeCN; (b) NaI in MeOH/MeCN; and (c) PdCl2, PPh3, NaOAc (2:3:1) in MeOH/MeCN.
ethylacetate/hexane (1/1 v/v) as the eluent, the reaction mixture was treated with triphenylphosphane (0.26 g, 1 mmol) and was stirred for a further 2 h. Completion of the reaction was monitored by TLC using the same eluent as mentioned above. The reaction mixture was filtered, washed with cold acetonitrile and dried at room temperature. Yield: 0.48 g, 84%, mp: 225 °C, Anal. Calc. for C21H21Cl2N4PPdS (569.78): C, 44.27; H, 3.71; N, 9.83. Found: C, 44.20; H, 3.69; N, 9.97%. IR (KBr) [m/cm1]: 3047 s, 3022 s, 2872 s, 2762 s, 1969 w, 1899 w, 1604 m, 1506 s, 1479 s, 1433 s, 1390 m, 1357 m, 1311 w, 1184 m, 1097 s, 1072 w, 997 s, 748 s, 690 s, 534 s, 509 s, 451 w. EI-MS (70 eV): m/z 262 (PPh3), 130 (HL1). 31 P NMR (d/ppm, CDCl3): 29.89 (s). 2.3.2. Synthesis of [(PPh3)Pd(HL1)I]Cl1/2H2O (2) A solution of 1 (0.56 g, 1 mmol) in methanol/acetonitrile (20 mL, 1/1) was treated with sodium iodide (0.15 g, 1 mmol) at room temperature and stirred for 3 h. After completion of the reaction (TLC), the crude product was filtered and washed with water (2 10 mL), dried and characterized as a pure material. Single
Fig. 1. Molecular structure of the ion pair in complex 1 (thermal ellipsoids at the 40% probability level), the hydrogen atoms of the phenyl rings are omitted for clarity. Selected bond lengths [pm] and angles [°]: Pd1–N2 214.6(3), Pd1–P1 225.2(1), Pd1–Cl1 229.9(1), Pd1–S1 230.1(1), S1–C1 172.4(4), C1–N1 133.8(5), N1– N2 141.1(5), N1–C2 138.1(5), C2–N3 130.5(5), N3–N4 137.0(5), N2–Pd1–Cl1 89.6(1), P1–Pd1–Cl1 89.67(4), N2–Pd1–S1 87.1(1), P1–Pd1–S1 93.78(4), C1–S1– Pd1 95.6(1), C2–N1–C1 108.7(3), N1–C1–N4 104.9(3), C1–N4–N3 112.4(4), N4–N3– C2 104.9(3), N3–C2–N1 109.1(4).
Fig. 2. Molecular structures of the cations in complex 2 (thermal ellipsoids at the 40% probability level), the hydrogen atoms of the phenyl rings are omitted for clarity. Selected bond lengths [pm] and angles [°]: Pd1–N1 212.1(5), Pd1–P1 224.4(2), Pd1–S1 231.9(2), Pd1–I1 260.26(9), S1–C1 171.3(7), C1–N2 135.1(9), N2–C2 139.0(9), C2–N3 133(1), N3–N4 135.9(9), N4–C1 133.8(9), N2–N1 142.6(8), N1–Pd1–P1 177.9(2), N1–Pd1–S1 87.8(2), P1–Pd1–S1 94.03(6), N1–Pd1–I1 88.4(2), P1–Pd1–I1 89.80(5), C1–N2–C2 109.0(6), N2–C2–N3 108.2(6), C2–N3–N4 105.6(6), N3–N4–C1 112.6(6), N4–C1–N2 104.5(6); Pd2–N6 212.1(5), Pd2–P2 224.2(2), Pd2– S2 231.2(2), Pd2–I2 259.99(8), S2–C4 171.1(7), C4–N5 136.3(9), N5–C5 139.0(9), C5–N7 128.7(9), N7–N8 139.3(9), N8–C4 132.3(9), N6–Pd2–S2 87.8(1), P2–Pd2–S2 94.23(6), N6–Pd2–I2 88.1(1), P2–Pd2–I2 89.85(5), C1–S1–Pd1 95.1(3), H7–O1–H8 102.7, H9–O2–H10 142.1, C4–N5–C5 108.1(5), N5–C5–N7 110.1(6), C5–N7–N8 104.9(6), N7–N8–C4 112.4(6), N8–C4–N5 104.2(6).
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crystals suitable for X-ray analysis were obtained by recrystallization from a methanol solution of 2. Yield: 0.60 g, 90%, mp: 228 °C, Anal. Calc. for C21H21ClIN4PPdS (677.28): C, 39.01; H, 3.72; N, 8.27. Found: C, 38.94; H, 3.70; N, 8.30%. IR (KBr) [m/cm1]: 3188 w, 2978 w, 2939 m, 2854 m, 2690 m, 2634 m, 2387 m, 2351 m, 2333 m, 1799 w, 1768 w, 1714 s, 1612 s, 1516 m, 1460 w, 1375 w, 1332 s, 1226 m, 1166 w, 1126 vw, 1068 w, 1012 w, 977 w, 918 w, 887 w, 858 w, 715 m, 671 w, 609 vw, 520 m, 490 w, 459 w. EI-MS (70 eV): m/z 130 (HL1), 262 (PPh3). 31P NMR (d/ppm, CDCl3): 35.74 (s). 2.3.3. Synthesis of [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH (3) To a solution of HL1 (0.13 g, 1 mmol) in methanol (20 mL), a solution of sodium acetate (0.08 g, 1 mmol) in water (2 mL) was added. The obtained solution was treated with palladium chloride (0.35 g, 2 mmol) and stirred for 1 h. After completion of the reaction, which was monitored by TLC using ethyl acetate/ petroleum ether (1/2) as the eluent, the orange reaction mixture was treated with a solution of triphenylphosphane (0.78 g, 3 mmol) in same the solvent (10 mL) and was stirred for a further 3 h. After completion of the reaction (TLC test), the solid was filtered and washed with cold methanol (2 5 mL). The filtrate was kept at 4 °C to give bright orange single crystals after a few days. Yield: 1.20 g, 95%,
mp: 245 °C. Anal. Calc. for C58H54Cl3N4OP3Pd2S (1267.26) C, 54.97; H, 4.29; N, 4.42. Found: C, 54.89; H, 4.30; N, 4.45%. IR (KBr), [m/cm1): 3350, 1620, 1471, 1431, 748–696. 1H NMR (d/ ppm, CDCl3): 1.24 (s, 3H, CH3), 7.35–7.72 (m, 45H, 3PPh3). 31P NMR (d/ppm, CDCl3): 23.53, 30.43. MS (70 ev) m/z: 129 (L1), 262 (PPh3). 2.4. Crystal structure analyses of 1, 2, 3 and 4 (Table 1) Table 1 shows the crystallographic data of complexes 1–4. The crystals of 1, 2, 3 and 4 were covered with perfluorinated oil and mounted on the top of a glass capillary under a flow of cold gaseous nitrogen. The orientation matrix and unit cell dimensions were determined from 8000 ( 1–3, Stoe IPDS I) and from 5000 (4, Stoe IPDS II) reflections (graphite-monochromated Mo-Ka NH2 N S N N III Scheme 5. Hückel aromaticity in L1.
Fig. 3. Molecular structures of the cations in complex 3 (thermal ellipsoids at the 40% probability level). Selected bond lengths [pm] and angles [°]: Pd1–N2 216.2(3), Pd1–P1 225.1(1), Pd1–S1 228.7(1), Pd1–Cl1 230.19(11), Pd2–N4 202.7(3), Pd2–Cl2 229.5(1), Pd2–P2 234.1(1), Pd2–P3 234.7(1), S1–C1 171.1(4), C1–N1 135.4(5), N1–C2 138.1(5), C2– N3 131.1(5), N3–N4 138.7(5), N4–C1 131.3(5), N2–Pd1–S1 88.14(9), P1–Pd1–S1 88.30(4), N2–Pd1–Cl1 90.50(9), P1–Pd1–Cl1 93.09(4), N4–Pd2–P2 91.96(9), Cl2–Pd2–P2 88.20(4), N4–Pd2–P3 90.61(9), Cl2–Pd2–P3 90.09(4), C1–N1–C2 107.5(3), N1–C2–N3 108.7(3), C2–N3–N4 106.6(3), N3–N4–C1 109.8(3), N4–C1–N1 107.4(4); Pd3–N6 215.3(3), Pd3–P4 225.2(1), Pd3–S2 229.2(1), Pd3–Cl3 231.9(1), Pd4–N8 202.5(3), Pd4–Cl4 230.4(1), Pd4–P5 233.7(1), Pd4–P6 235.0(1), S2–C4 171.4(4), C4–N5 136.4(5), N5– C5 137.0(5), C5–N7 130.9(5), N7–N8 138.4(5), N8–C4 131.8(5), N6–Pd3–S2 88.09(9), P4–Pd3–S2 92.17(4), N6–Pd3–Cl3 89.04(9), P4–Pd3–Cl3 90.70(4), N8–Pd4–P5 89.81(9), Cl4–Pd4–P5 90.44(4), N8–Pd4–P6 89.94(9), Cl4–Pd4–P6 90.36(4), C4–N5–C5 107.9(3), N5–C5–N7 109.2(4), C5–N7–N8 106.1(3), N7–N8–C4 110.6(3), N8–C4–N5 106.1(3); Pd5–N10 215.9(3), Pd5–P7 225.4(1), Pd5–S3 229.3(1), Pd5–Cl5 232.1(1), Pd6–N12 202.9(3), Pd6–Cl6 230.1(1), Pd6–P8 235.1(1), Pd6–P9 236.8(1), S3–C7 171.9(4), C7–N9 135.8(5), N9–C8 136.9(5), C8–N11 130.7(5), N11–N12 139.0(5), N12–C7 131.5(5), N10–Pd5–S3 87.52(9), P7–Pd5–S3 92.83(4), N10–Pd5–Cl5 89.28(9), P7–Pd5–Cl5 90.46(4), N12–Pd6–P8 90.60(9), Cl6–Pd6–P8 89.92(4), N12–Pd6–P9 90.70(9), Cl6–Pd6–P9 89.71(4), C7–N9–C8 107.4(3), N9–C8–N11 109.2(4), C8–N11–N12 106.5(3), N11–N12–C7 109.4(3), N12–C7–N9 107.4(4).
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radiation, k = 71.073 pm). The intensities were corrected for Lorentz and polarization effects. In addition, absorption corrections were applied numerically. The structures were solved by direct methods (SIR-92 for 1, 2 and 4 and SHELXS-97 for 3) and refined against F2 by full-matrix least-squares using the program SHELXL97. The position of carbon bonded hydrogen atoms were calculated for ideal positions and all hydrogen atoms except H1–H3 (free refinement) in 2 were refined with a common displacement parameter. Programs used were SIR-92 [36], SHELXS-97 [37], SHELXL97 [38], SHELXTL-PLUS [39] and PLATON [40].
3. Results and discussion 3.1. Synthesis and characterization of 1, 2 and 3 As depicted in Scheme 4, complex 1 can be obtained as orange solid mass by the reaction of HL1 with palladium chloride and triphenylphosphane in a 1:1:1 molar ratio in methanol/acetonitrile. The treatment of 1 with sodium iodide in a molar ratio of 1:1 in the same solvent mixture gave complex 2 as a reddish powder, and complex 3 can be prepared by the treatment of a solution of
Fig. 4. A view of the structure of complex 1, showing the hydrogen bonding interactions between the cations and anions. The phenyl rings and methyl groups are omitted for clarity.
Fig. 5. The packing diagram of 1 showing the hydrogen bonding between the cations and anions.
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HL1 containing sodium acetate with palladium(II) chloride and triphenylphosphane in methanol as bright red-orange crystals.
All the complexes are air-stable. The results of the elemental analyses, together with IR and 31P NMR data, allow us to postulate
Fig. 6. Representation of hydrogen bonds involving cations and anions in complex 2.
Fig. 8. Representation of the cation in 4 (thermal ellipsoids at the 40% probability level). Selected bond lengths [pm] and angles [°]:Pd1–N4 201.9(3), Pd1–N1 203.2(3), Pd1–N3 203.8(3), Pd1–N2 203.9(3), N4–Pd1–N1 90.1(1), N4–Pd1–N3 88.5(1), N1–Pd1–N2 89.9(1), N3–Pd1–N2 91.4(1).
Fig. 7. The packing diagram of 2.
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complexes 1, 2 and 3 being obtained. In IR spectra of the complexes, the absorptions at 1479 and 1433 cm1 (1), 1460 and 1430 cm1 (2), and 1471 and 1431 cm1 (3) can be assigned to C@Nring stretching vibrations. The absorptions around 3188– 3350 cm1 can be assigned to NH2 vibrations in 1–3. The P–C vibrations of the PPh3 moiety are found in the range 744– 691 cm1 [41]. The mass spectra of 1, 2 and 3 show only the main peak of the corresponding ligand and co-ligand triphenylphosphane (m/z = 130 (HL1) for 1 and 2, 129 (L1) for 3 and m/z = 262 (PPh3) for all complexes). The 31P NMR spectra of 1 and 2 in CDCl3 showed a sharp single peak at d 29.89 ppm (1) and d 35.74 ppm (2). Consistent with the structure of 3, the solution 31P NMR spectrum in CDCl3 showed two 31P resonances at d 30.43 ppm for the mono phosphane coordinated palladium atom and at d 23.53 ppm for the two-fold phosphane coordinated metal center. The 1H NMR spectrum of complex 3 shows pronounced changes with respect to the free ligand (HL1), which means that the signal assigned to the triazole proton disappears as a consequence of deprotonation.
Fig. 9. View of the hydrogen bonds in 4 involving chloride anions and water molecules.
3.2. Crystal structures of 1, 2 and 3 Complex 1 crystallizes in the monoclinic space group P21/c, Complexes while 2 and 3 crystallize in the triclinic space group P 1. 1 and 2 consists of [(PPh3)Pd(HL1)X]+ cations (X = Cl (1) and X = I (2)) and chloride anions. Cations of both complexes contain the [(PPh3)Pd(HL1)] core, in which the heterocycle HL1 acts as a bidentate chelating ligand and coordinates to the metal center via its hydrazine nitrogen atom and its thione sulfur atom, like form B as shown in Scheme 2 (Figs. 1 and 2). To complete the square planar arrangement around the palladium ion in these complexes, the fourth coordination places in 1 and 2 are occupied by one chlorine atom and one iodine atom. Complex 2 consists of two crystallographically independent molecules, as depicted in Fig. 2. Complex 3 consists of three crystallographically independent molecules (Fig. 3) and can be described as complex 1 with an additional coordination to a [(PPh3)2ClPd]-moiety through its deprotonated endocyclic NH-group. Therefore, the ligands act as a uni- as well as a bidentate chelating ligand and coordinate to the metal centers using one of their endocyclic nitrogen atoms (l1-Ncoordination to Pd2, Pd4 and Pd6) and their thiol sulfur atom and hydrazine nitrogen atom (l2-N,S-coordination to Pd1, Pd3 and Pd5). The other coordination positions around Pd1, Pd3 and Pd5 are occupied by one chlorine atom and one triphenylphosphane molecule, while the positions around Pd2, Pd4 and Pd6 are occupied by one chlorine atom and two triphenylphosphane moieties. In the cations of 3, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]+, the singly deprotonated 1,2,4-triazole heterocycles (L1) act as a bridging agent between two palladium atoms and show Hückel aromaticity as shown in Scheme 5. The Pd–P bond length of 225.2(1) pm in 1, and mean Pd–P bond lengths of 224.3 pm in 2, 225.23 pm by one triphenylphosphane coordinated a metal center and 234.9 pm by the two-fold triphenylphosphane coordinated the palladium atoms in 3 are shorter than the sum of the single bond radii for palladium and phosphorus, i.e.
Fig. 10. The packing diagram of 4 showing the hydrogen bonding between cations and anions.
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241 pm [42], and fall in the lower range (221–246 pm) of PdII–PPh3 bond reference values (230.2 pm) encountered in 248 entries [43]. The Pd–S bond distances of 230.1(1) pm (1), mean 231.55 pm (2) and mean 229.06 pm (3) are comparable with those reported for strong Pd–S coordination as observed in the complexes [(AMTTO)Pd(PPh)3Br]Br.MeOH (Pd–S: 227.5(2) pm) [44] and [Pd2(l-H3L)2]2DMSO (H3L = two-fold deprotonated 3,5-diacyl1,2,4-triazole-bis(4-methylthiosemicarbazone; Pd–S: 226.3(3) pm) [45]. The Pd–Cl bond distances of 229.9(1) pm in 1 and mean 231.39 pm by Pd1, Pd3 and Pd5 and mean 230 pm by Pd2, Pd4 and Pd6 in 3 are in good agreement with the observed distances in a series of triphenylphosphane-chlorine-palladium complexes, such as [(AMTTO)Pd(PPh3)Cl]ClCH3OH (Pd–Cl: 231.14(6) pm) [46]. The mean Pd–I bond distance of 260.12 pm in 2 is similar to those observed in [(AMTTO)Pd(PPh3)I]2CH3OH (Pd–I: 261.58(9) pm) [44]. Each cation in 1 acts as a bridging agent between its own chloride anion through its NH-group and the anions of two adjacent molecules through the hydrogen atoms of their NH2-moieties via hydrogen bonding (N2–H1 Cl2b: 326.2(4) pm, N2–H2 Cl2a: 333.0(4) pm and N4–H3 Cl2: 308.9(4) pm, Fig. 4). This coordina-
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tion arrangement is responsible for the formation of chains along the [0 0 1] direction (Fig. 5). The chloride anions in 2 act as a bridging agent between the cations (Fig. 6). The Cl1 atoms coordinate to three N–H-moieties (one intramolecular hydrogen bonding to one NH2-group and two intermolecular hydrogen bondings to the NH2- and NH-groups of the adjacent cation, N1–H1 Cl1: 315.6(6) pm, N6–H4 Cl1: 314.5(6) pm and N8–H6 Cl1: 311.3(8) pm). The Cl2 anions are responsible for the connections via hydrogen bonding between two layers (by coordination to the NH2- and NH-groups of the molecules of other layers, N4–H3 Cl2a: 311.4(7) pm, N6–H5 Cl2b: 315.6(6) pm). Each Cl2 anion coordinates to the NH2-moiety of the adjacent molecule via hydrogen bonding, simultaneously (N1–H2 Cl2: 313.4(6) pm). These coordination modes lead to a 2D-layers parallel to (0 0 1) as shown in Fig. 7. It is noteworthy to mention, that in all the complexes, the five-membered heterocycles are planar. A similar interesting chloride–hydrogen bonding composition can be observed in the palladium(II) complex [Pd(Py)4]Cl21/2H2O (4). Complex 4 crystallizes in the monoclinic space group Cc with a Flack-parameter of 0.00(3) and consists of [Pd(Py)4]+-cations
Fig. 11. Molecular structures of three crystallographically independent complexes of 3 showing the hydrogen bonding between the cations and two Cl-ions.
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and chloride anions (Fig. 8). Although the molecules are nearly centrosymmetric, the structure could not be transformed into space group C2/c, which was confirmed by the Flack parameter. This was checked by standard procedures with the program PLATON [40]. In addition, the unit cell of 4 shows that Cc is the correct space group. The palladium center in the square planar cation is surrounded by four pyridine molecules. The chloride anions and the solvent molecules in 4 are responsible for the formation of a network of hydrogen bridges parallel to (0 0 1) as illustrated in Fig. 9 and Fig. 10 (O1–H1 Cl2a: 320.3(5) pm, O1–H2 Cl2a: 320.3(5) pm, O2–H3 Cl1a: 315.9(5) pm, O2–H4 .Cl2b: 311.1(5) pm, O3– H5 Cl2c: 314.5(5) pm, O3–H6 Cl1b: 317.1(5) pm). The dihedral angles between the ‘‘best” planes through the PdN4-plane (A: Pd1 N1 N2 N3 N4) and the planes through pyridine molecules (B: N1 C1 C2 C3 C4 C5, C: N2 C6 C7 C8 C9 C10, D: N3 C11 C12 C13 C14 C15, E: N4 C16 C17 C18 C19 C20) are (A, B) 97, (A, C): 63, (A, D): 94 and (A, E) 74°. Complex 3 contains one water molecule and six methanol molecules per three complex molecules. In each complex, the hydrazine amine moiety of the five-membered heterocycles acts as a bridging agent between two chloride anions using its two hydrogen atoms (Fig. 11). They link the chloride anion of the same complex to the anion of the adjacent one via hydrogen bonding (N2–H1 Cl7a: 324.3(3) pm, N2–H1–Cl7a: 163°; N2–H2 Cl7: 323.8(4) pm, N2–H2–Cl7: 164°; N6–H3 Cl9b: 332.6(5) pm, N6– H3–Cl9b: 159°; N6–H4-Cl8: 313.1(4) pm, N6–H4–Cl8: 175°; N10–H5 Cl8b: 329.6(3) pm, N10–H5–Cl8b: 159°; N10–H6 Cl9: 320.9(4) pm, N10–H6–Cl9: 169°). The chloride ion Cl9 acts as a bridging agent between one methanol molecule and the water molecule via hydrogen bonding (O1–H7 Cl9: 323.5(5) pm, O1– H7–Cl9: 126° and O5–H12 Cl9: 310(2) pm, O5–H12–Cl9: 130°). Fig. 12 represents the unit cell of complex 3. The dihedral angle between the ‘‘best” planes in the non-planar complexes of 3 (A: Pd1 P1 Cl1 N2 S1; B: Pd2 Cl2 P2 P3 N4; C: Pd3 P4 Cl3 N6 S2; D: Pd4 P5 P6 Cl4 N8; E: Pd5 Cl5 P7 S3 N10 and F: Pd6 P8 P9 Cl6 N12) are 101 (A, B), 110 (C, D) and 119° (E, F). The steric
M2 N N S M1
R N NH2 H
Scheme 6.
hindrance induced by the bulky phenyl rings of the three coordinated triphenylphosphane groups in 3 is responsible for the deviation from the planar geometry observed in 1 and 2, since no significant differences are found between the bond distances and bond angles in the corresponding ligands in the complexes. In each cation of 3, the triphenylphosphane ligands of the second palladium ion are trans-positioned. According to this coordination arrangement, the five-membered heterocycle is packed by two phenyl rings of the triphenylphosphane molecule like a sandwich with a p-stacking effect. The shortest distances between the central lying atoms of the heterocycles in the sandwiches from the phenyl rings are N3 C59: 326.0(5) pm, N7 C94: 318.3(5) pm and N11 C144: 313.0(5) pm. 4. Conclusion In conclusion, we have synthesized and characterized two mononuclear and the first binuclear palladium complex containing the well known 4-amino-3-methyl-1,2,4-triazol-5-thione moiety. According to the determined crystal structures, we found that the 1,2,4-triazole moiety acts as a bidentate chelating ligand through its sulfur and nitrogen atoms, while the singly deprotonated triazole moiety acts as a bridging agent between two metal centers. It can simultaneously act as a bidentate chelating agent through its thiole sulfur atom and hydrazine nitrogen atom to one metal center and as a uni-dentate agent via its endocyclic nitrogen atom to the other metal center. Consequently, this new
Fig. 12. The packing diagram of 3.
M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
coordination mode can be described as form H as depicted in Scheme 6. In addition, the binuclear complex [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Cl1/3H2OCH3OH shows the formation of an interesting ‘‘sandwich” effect due to the arrangement of the phenyl rings. 5. Supplementary data CCDC 772285, 772286, 699146 and 772287 contain the supplementary crystallographic data for 1, 2, 3 and 4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail: [email protected].
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