Materials and instrumentation
2-hydroxybenzaldehyde, 4-nitrobenzaldehyde, glacial acetic acid, PdCl2(CH3CN)2, phenylboronic acid, styrene, CaCl2, KBr, KOH, NaOH, Na2CO3, K2CO3, KOBut, Cs2CO3, MgSO4, CH3CN, ethyl alcohol, ethyl acetate, toluene, i-propanol, triethylamine, DCM, DMSO, DMF, dioxane, chloroform, acetone, methanol, hexane, water and diethyl ether were used as chemicals/reagents. All reagents and solvent used in study were purchased from Sigma-Aldrich and used without additional drying and purification. All of the synthesis was performed using the standard Schlenk tube technique in an inert gas atmosphere. The elemental analyses were carried out using a Thermos Scientific Flas 2000 CNSO analyzer. FT-IR spectra were recorded in the range 400–4000 cm− 1 on PerkinElmer Spectrum 65. 1H and 13C NMR spectra were performed using a Bruker UPB Avance-III 400 MHz NMR spectrometer. UV–Vis spectra were measurement as DMF solutions using a Shimadzu UV-1800 spectrophotometer. Magnetic susceptibility was performed using the Guoy method with Hg[(Co(SCN)4] as calibrant on the Sherwood Auto Magnetic Susceptibility Balance. The C-C coupling products (recorded in the catalytic reactions) were analyzed used with GC-FID Chromatograph methods. Mass Spectrometer Agilent Technologies 6890N. The melting points were determined using an electro-thermal 9200 melting point apparatus. The conductivity of the PdII complexes was measured with the Jenway 4010 conductivity meter in 10− 3 M DMF.
Synthesis and characterization of ( E )-4-ethyl-2-(2-hydroxybenzylideneamino)-5-methylthiophene-3-carbonitrile (S 1 ) and ( E )-4-ethyl-5-methyl-2-(4-nitrobenzylideneamino)thiophene-3-carbonitrile (S 2 )
The novel ligands S1 and S2 were prepared by reacting 2-amino-5-ethyl-4-methylthiophene-3-carbonitrile and 2-hydroxybenzaldehyde (S1) and 4-nitrobenzaldehyde (S2) in the presence of few drops of glacial acetic acid in 20 mL methanol solution for 3 h (characterization data were given in supplementary material). The resulting crude products were recrystallized in hot methanol. The synthesis scheme of the ligands S1 and S2 are given in Fig. 1.
S 1 : Yield: 85%. Yellow solid. M.p.: 150°C. Anal. Calc. for (C15H14N2OS): C, 66.64; H, 5.22; N, 10.36; S, 11.86. Found: C, 66.70; H, 5.20; N, 10.35; S, 11.84%. UV-Vis λmax, nm, (ε, M− 1 cm− 1): 204 (3614), 208 (3211), 215 (2576), 230 (2734), 290 (1807), 375 (3153), 385 (3284), 395 (3372). FT-IR ν, cm− 1: 3449 (–OH), 3058 (Ar. –CH), 2967, 2933, 2872 (Alip. –CH), 2222 (CN), 1619 (CH = N), 1598, 1566, 1492 (Ar. C = C), 1166 (C–O), 761 (C–S–C). 1H-NMR (400 MHz, CDCl3) δ, ppm: 11.99 (s, 1H, –OH), 8.50 (s, H, CH = N), 7.41–6.95 (m, 4H, Ar. –CH), 2.64, 2.63 (q, 2H, CH2), 2.39 (s, 3H, –CH3), 1.22 (t, 3H, –CH2CH3). 13C-NMR (100 MHz, CDCl3) δ, ppm: 161.23 (C7), 160.99 (C2), 156.59 (C8), 139.58-107.56 (C1-C6, C9-C11, C13), 20.88 (C17), 14.37–13.36 (C16, C18).
S 2 : Yield: 80%. Ocher solid. M.p.: 135°C. Anal. Calc. for (C15H13N3O2S): C, 60.18; H, 4.38; N, 14.04; S, 10.71. Found: C, 60.22; H, 4.40; N, 14.10; S, 10.71%. UV-Vis λmax, nm, (ε, M− 1 cm− 1): 205 (3098), 215 (3326), 230 (3353), 235 (3383), 320 (1113), 375 (1891), 378 (1362). FT-IR ν, cm− 1: 3051 (Ar. –CH), 2968, 2929, 2869 (Alip. –CH), 2220 (CN), 1600 (CH = N), 1590 (Ar. C = C), 1556 − 1474 (NO2)asym, 1357, 1338 (NO2)sym, 734 (C–S–C). 1H-NMR (400 MHz, CDCl3) δ, ppm: 8.64 (s, H, CH = N), 8.39–7.26 (m, 4H, Ar. –CH), 2.67 (q, 2H, CH2), 2.41 (s, 3H, –CH3), 1.23 (t, 3H, –CH2CH3). 13C-NMR (100 MHz, CDCl3) δ, ppm: 157.40 (C7), 155.80 (C8), 148.63-109.64 (C1-C6, C9-C11, C13), 20.81 (C16), 14.37–13.64 (C15, C17).
Synthesis of PdII complexes (1, 2)
PdCl2(CH3CN)2 and the appropriate ligand (E)-4-ethyl-2-(2-hydroxybenzylideneamino)-5-methylthiophene-3-carbonitrile (S1) and (E)-4-ethyl-5-methyl-2-(4-nitrobenzylideneamino)thiophene-3-carbonitrile (S2) were dissolved in 30 mL of methanol and stirred for 12 hours at room conditions. The resulting precipitates were collected by filtration, washed with many times diethyl ether, and dried in a vacuum over anhydrous CaCl2. The product was purified by recrystallization from a dichloromethane/DMF mixture (3:1). The structure of the complexes was proposed as in Fig. 2.
Complex 1: PdCl2(CH3CN)2 (0.34 g, 1.30 mmol) and S1 (0.70 g, 2.60 mmol) reacted to give the product a black solid (78%). M.p.: 305°C. Anal. Calc. for (C30H29N4O3.5S2Pd): C, 53.61; H, 4.35; N, 8.33; S, 9.54. Found: C, 53.61; H, 5.17; N, 8.36; S, 9.55%. UV-Vis λmax, nm, (ε, M− 1 cm− 1): 223 (4000), 233 (3868), 242 (3684), 256 (4020), 273 (3861), 296 (3094), 307 (3965), 315 (3978), 325 (3466), 370 (1049), 380 (1052), 400 (1218), 425 (960), 480 (510). FT-IR ν, cm− 1: 3430 (OH/H2O), 3055, 3013 (Ar. –CH), 2963, 2925, 2869 (Alip. –CH), 2222 (CN), 1605 (CH = N), 1590, 1560, 1526 (Ar. C = C), 1144 (C–O), 849 (H2O), 753 (C–S–C)br, 576, 558, 520 (M–O), 470, 457 (M–N). 1H-NMR (400 MHz, CDCl3) δ, ppm: 8.83 (s, H, CH = N), 7.90–6.99 (m, 4H, Ar. –CH), 4.30 (H2O), 2.65 (q, 2H, –CH2), 2.44 (s, 3H, –CH3), 1.32 (t, 3H, -CH2CH3). 13C-NMR (100 MHz, CDCl3) δ, ppm: 162.13 (C7), 149.40 (C2), 145.56 (C8), 134.32–96.05 (C1-C6, C9-C11, C13), 20.15 (C17), 15.04–14.14 (C16, C18). MS [ESI+]: m/z 671.14 (Calc.), 671.759 (Found) [M-H]+. µeff (B.M.): Dia. Molar conductivity (10− 3 M, DMF): 12.00 Ω−1 cm2 mol− 1.
Complex 2: PdCl2(CH3CN)2 (0.60 g, 2.33 mmol) and S2 (0.70 g, 2.33 mmol) reacted to give the product a dark chestnut solid (87%). M.p.: >300 oC. Anal. Calc. for (C15H17N3O4SPdCl2): C, 35.11; H, 3.32; N, 8.19; S, 6.24. Found: C, 35.20; H, 3.40; N, 8.21; S, 6.30%. UV–Vis λmax, nm, (ε, M− 1 cm− 1): 218 (3439), 220 (4084), 225 (2923), 280 (3848), 320 (905), 345 (1029), 365 (837), 375 (666), 410 (1424). FT-IR ν, cm− 1: 3529, 3404 (OH/H2O)br, 3187, 3051 (Ar. –CH), 2967, 2933, 2869 (Alip. –CH), 2220 (CN), 1634 (CH = N), 1592 (Ar. C = C), 1560 − 1475 (NO2)asym, 1359, 1340 (NO2)sym, 736 (C–S–C) 830 (H2O), 561, 546, 518, 506 (M–O), 482, 470, 457 (M–N). 1H-NMR (400 MHz, CDCl3) δ, ppm: 8.70 (s, H, CH = N), 8.15–7.72 (m, 4H, Ar. –CH), 2.64 (q, 2H, CH2), 2.48 (s, 3H, –CH3), 1.33, 134 (t, 3H, –CH2CH3). 13C-NMR (100 MHz, CDCl3) δ, ppm: 159.15 (C7), 157.10 (C8), 148.62–113.80 (C1-C6, C9-C11, C13), 20.76 (C16), 14.75–12.23 (C15, C17). MS [ESI+]: m/z 514.69 (Calc.), 514.93 (Found) [M + 2H]+. µeff (B.M.): Dia. Molar conductivity (10− 3 M, DMF): 9.20 Ω−1 cm2 mol− 1.