Article pubs.acs.org/Organometallics
Palladium Complexes with Tetrahydropyrimidin-2-ylidene Ligands: Catalytic Activity for the Direct Arylation of Furan, Thiophene, and Thiazole Derivatives Emine Ö zge Karaca,† Nevin Gürbüz,† Iṡ mail Ö zdemir,† Henri Doucet,‡ Onur Şahin,§ Orhan Büyükgüngör,∥ and Bekir Ç etinkaya*,⊥ †
Catalysis Research and Application Center, Inönü University, 44280, Malatya, Turkey Centre de Catalyse et Chimie Verte, Institut des Sciences Chimiques de Rennes, Université de Rennes 1, 35042 Rennes, France § Scientific and Technological Research Application and Research Center, Sinop University, 57010, Sinop, Turkey ∥ Department of Physics, Ondokuz Mayıs University, 55139, Samsun, Turkey ⊥ Department of Chemistry, Faculty of Science, Ege University, 35040, Bornova-Iż mir, Turkey ‡
S Supporting Information *
ABSTRACT: The synthesis and characterization of novel 1,3benzyl-3,4,5,6-tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbene palladium(II) complexes (1a−d) were described. The crystal structure of trans-dichlorobis[1,3-bis(4methylbenzyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]palladium(II) was presented. Pd(II) complexes 1a−d were tested as catalysts in the direct C5 or C2 arylation of furans, thiophenes, and thiazoles, with various aryl bromides at 150 °C for 1 h. These complexes exhibited moderate to high catalytic activities under the given conditions.
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INTRODUCTION Intensive attention has been paid to the properties and application of N-heterocyclic carbene (NHC) complexes of transition metals, and the pioneering work on the coordination chemistry of NHC ligands was independently reported by Wanzlick1 and Ö fele2 in 1968 and Lappert and co-workers in the early 1970s.3,4 The isolation of free NHC5 and utilization of NHC complexes in catalysis6 stimulated the search further. Among the NHCs reported, five-membered NHCs derived from imidazol-2-lidenes, imidazolin-2-ylidenes, triazolylidenes, and thiazolylidenes (abbreviated as 5-NHC) have been extensively studied. In contrast, the related six-membered NHCs (6-NHC) are relatively less developed.7 Increasing the NHC heterocycle ring size and thus the corresponding N− CNHC−N bond angle affords markedly different steric and electronic properties, in comparison with those of their traditional five-membered counterparts.8 The strong σ-donating property of 6-NHCs makes them attractive ligand candidates especially for the discovery of new catalytic modes and reactions.9 Much attention has been given to the synthesis of arylated heterocycles due to their biological or physical properties.10 In this context, palladium-catalyzed reactions such as Stille, Suzuki, or Negishi couplings allow the efficient synthesis of a wide variety of bi(hetero)aryls.11 However, these couplings require © 2015 American Chemical Society
the preliminary synthesis of organometallic derivatives. In addition, the required organometallic nucleophilic reagents, particularly when being functionalized, are often not commercially available or are relatively expensive. Moreover, these reactions provide a stoichiometric amount of side products. In recent years, the transition-metal-catalyzed socalled direct arylation has undergone rapid development, and it represents a viable alternative to traditional cross-coupling reactions with organometallic reagents.12−14 Direct arylation reactions through cleavage of C−H bonds is considered as an environmentally and economically more attractive strategy.15 Consequently, the procedure provides a valuable and straightforward technique for the synthesis of biaryls. Ohta and co-workers reported the direct 2- or 5-arylation of furans and thiophenes, with aryl halides, in moderate to good yields by using [Pd(PPh3)4] as the catalyst.12 Since then, the palladium-catalyzed direct arylation of heteroaryl derivatives with aryl halides has proved to be a powerful method for the synthesis of a wide variety of arylated heterocycles.16−23 Only a few examples of (NHC)Pd-catalyzed direct arylations of heteroaromatics have been reported to date.24 In this Special Issue: Mike Lappert Memorial Issue Received: November 28, 2014 Published: May 6, 2015 2487
DOI: 10.1021/om501201r Organometallics 2015, 34, 2487−2493
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1546, 1518, and 1515 cm−1 respectively for 1a−1d. 13C chemical shifts, which provide a useful diagnostic tool for this type of metal carbene complex, exhibited a singlet resonance at 193.7, 183.7, 192.4, and 192.8 ppm ascribed to the carbenic carbon atom. This is consistent with the trans configuration of the complexes and the increased basisity of 6-NHC ligands relative to five-membered counterparts. The increased σdonation shifts the Ccarb signal to higher frequencies. Structural Characterization of 1a. The crystals of 1a suitable for X-ray analysis were obtained from a chloroform solution layered with diethyl ether. The molecular structure of complex 1a has been confirmed by X-ray single-crystal analyses. Details of data collection and crystal structure determinations are given in the Supporting Information. The molecular structure of 1a with the atom labeling is shown in Figure 1. The asymmetric unit contains two
connection, recently we have reported the C−H bond activation by applying complexes of imidazolin-2-ylidene and benzimidazol-2-ylidene and in situ formed metal systems for arylation of arene and heteroaromatic compounds.25 In view of the above information and the growing interest in catalytic activity of palladium complexes to act as an efficient catalyst in direct arylation reactions, in this article, we now report the synthesis of four new (6-NHC)Pd(II) complexes (1) from 1,3dibenzyl-3,4,5,6-tetrahydropyrimidinium salts. All synthesized compounds were characterized by 1H NMR, 13C NMR, IR spectroscopy, and elemental analysis techniques, which support the proposed structures. The molecular and crystal structure of the complex trans-dichlorobis[1,3-bis(4-methylbenzyl)-3,4,5,6tetrahydropyrimidin-2-ylidene]palladium(II) was determined by single-crystal X-ray diffraction. We examined the activity of the synthesized palladium complexes in the direct arylation of various heteroaromatic compounds with bromobenzene derivatives.
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RESULTS AND DISCUSSION Synthesis of Palladium Carbene Complexes. Since the first catalytic applications of palladium/NHC complexes realized in 1995,26 numerous complexes have been synthesized by using various methods. The reaction of Pd(OAc)2 and imidazolium salts is one of the most frequently used reported methods to afford palladium(II) NHC complexes. However, this well-known methodology used to synthesize (5-NHC)Pd(II) complexes failed when applied to the saturated sixmembered tetrahydropyrimidinium salts, probably due to the low acidity of the C2−H.27 The attempt to synthesize (6NHC)AgX, which is a versatile NHC transfer reagent,28 was similarly unsuccessful. Finally, (6-NHC)Pd complexes (1) have been prepared by Lappert’s procedure4 employing the in situ formed enetetraamine, which can replace the coordinated ligands such as Py, PPh3, and P(OMe)3. The (6-NHC)Pd complexes (1) were obtained in 74−78% yield by reaction of the 6-NHC dimer with 0.5 equiv of [PdCl2(PPh3)2] (Scheme 1). The 6-NHC dimer was not isolated, but generated in
Figure 1. Molecular structure of 1a showing the atom-numbering scheme [(i) −x+1, −y+1, −z+1; (ii) −x+2, −y+2, −z+2]. Selected bond lengths [Å] and angles [deg]: C21−Pd2 = 2.0543(17), N1− C1−N2 = 117.53(16), C1−Pd1−Cl1 = 92.96(5), N4−C21−Pd2 = 120.68(13), C21−Pd2−Cl2ii = 89.30(5), C1−Pd1 = 2.0666(17), Cl1−Pd1 = 2.3123(5), Cl2−Pd2 = 2.3241(5), N1−C1−Pd1 = 121.41(13), C1−Pd1−Cl1i = 87.04(5), N3−C21−Pd2 = 121.61(13).
crystallographically independent molecules. Each Pd(II) ion is coordinated to two chlorine atoms and two carbon atoms, thus exhibiting a distorted square-planar arrangement in a mutually trans environment. The Pd−Ccarb distance (2.066 Å) in 1a is longer than the corresponding bond length (2.066 Å) reported for the trans-[PdBr2(benzimidazol-2-ylidene)2] system.24b This longer bond length is presumably due to greater steric interactions of 6-NHC on coordination, and this is also consistent with the larger N−Ccarb−N angle (117.53°) in 1a. Molecules of 1a are linked into sheets by a combination of C− H···π interactions. Atoms C2 and C32 in the molecule at (x, y, z) act as hydrogen-bond donors to the Cg(7) and Cg(6) benzene rings in the molecules at (x, y, z−1) and (2−x, 2−y, 1−z), so forming zigzag chains running parallel to the [111] and [001] directions (Figure 2). These chains are extended into the 3D supramolecular network by C−H···π interactions. Details of C−H···π interactions are given in the Supporting Information. Catalytic Studies: Direct Arylation of Heteroaromatic Compounds via C−H Bond Activation Using 1a−1d as Catalysts. Direct arylation of heterocycles has received considerable interest among synthetic chemists, as it would eliminate the need for establishing a reactive functionality prior to C−C coupling, enabling direct elaboration and expansion of the core motif.31−33 To the best of our knowledge, Pd-carbene
Scheme 1. Synthesis of Palladium−Carbene Complexes
solution by deprotonation of the corresponding tetrahydropyrimidinium salt by KOBut at 25 °C. The ligand precursor 1,3dialkyl-3,4,5,6-tetrahydropyrimidinium halide was obtained according to the literature.29 All complexes were isolated as air-stable, yellow, crystalline solids, and they were soluble in solvents such as dichloromethane, chloroform, toluene, and tetrahydrofuran and insoluble in nonpolar solvents. The new complexes were characterized by 1H and 13C NMR, elemental analysis, FTIR, and X-ray diffraction. The formation of the Pd-NHC complexes was confirmed by the absence of the 1H NMR resonance signal of the tetrahydropyrimidinium C2−H. The palladium complexes exhibit a characteristic ν(NCN) band typically at 1537, 2488
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cases, only the C5-arylated products were formed. We also performed a study on 4,5-dimethythiazole to induce direct arylation at the C2 position using the same substrates (Table 1). In all cases, the presence of 6-NHC ligands on palladium was found to be profitable. The direct coupling reactions of methyl 2-methyl-3-furoate with bromobenzene, 4-bromonitrobenzene, and 4-bromoanisole proceeded smoothly to generate the corresponding 5-arylated methyl 2-methyl-3-furoate in good yields (65−89%, Table 1, entries 1−3). Concerning the electronic properties of the aryl bromide, electron-withdrawing and electron-donating groups were tolerated. For this reaction, complexes 1a and 1b were found to be slightly more effective catalysts (Table 1, entries 1−3). Similar substrates have recently been employed, by Dong et al.,34 in direct arylation with a Pd(OAc)2 catalyst. Following the same trends as reported by Dong, a lower yield was observed with 4-bromonitrobenzene (Table 1, entry 2). The reaction of a strongly deactivated aryl bromide, 4-bromoanisole, with methyl 2-methyl-3-furoate gave the desired product in 85% yield in the presence of 1 mol % of complex 1b (Table 1, entry 3). 2-Methyl-3-furoate has also been arylated in moderate to good yields using bromobenzene (Table 1, entry 1). For bromobenzene, the best results were achieved with complex 1a in 73% yield. It is notable that in the case of methyl 2-methyl-3-furoate decarboxylation products were not detected. Next, we examined the reactivity of 2-n-butylthiophene using the same coupling partners. As with methyl 2-methyl-3-furoate, substituents on aryl bromides display a minor effect on the reaction (Table 1, entries 4−6). The 5-arylated thiophenes were obtained in 70−88% yields. Bromobenzene was successfully coupled with 2-n-butylthiophene in the presence of 1 mol % of catalyst 1a to give 2-n-butyl-5-phenylthiophene in
Figure 2. Crystal structure of 1a, showing the formation of C−H···π interactions.
complexes bearing a 3,4,5,6-tetrahydropyrimidin-2-ylidene ligand for direct arylation of heteroaromatic compounds have not been reported so far. For the sake of comparison with previously reported results24c,h we decided to use the following reaction conditions: (6-NHC)Pd complexes (1a−1d) 1 mol %; 1 mmol of aryl bromide, 2 mmol of heteroaryl derivative, 2 mmol of KOAc; solvent, DMAc (N,N-dimethylacetamide); reaction temperature, 150 °C; reaction time, 1 h. Under these reaction conditions, four heterocyclic substrates were allowed to react with aryl bromides bearing electron-donating or electronwithdrawing groups at the para position to furnish the arylated products in moderate to good yields (Table 1). Initially, we focused on the direct arylation at the C5 position using methyl 2-methyl-3-furoate, 2-n-butylthiophene, and 2-n-propylthiazole. The coupling reactions were regioselective, and in almost all
Table 1. Direct Arylation of Heteroaromatic Compounds by Using Aryl Bromidesa
Conditions: Pd-NHC (0.01 mmol), aryl halide (1 mmol), heteroaromatic compound (2 mmol), KOAc (2 mmol), DMAc (3 mL), 150 °C, 1 h, conversion of the aryl halide determined by GC and GC-MS. a
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DOI: 10.1021/om501201r Organometallics 2015, 34, 2487−2493
Organometallics 78% yield (Table 1, entry 4). High yields of 2-n-butyl-5-(4methoxyphenyl)thiophene were obtained for the coupling with 4-bromoanisole using catalysts 1a and 1d (Table 1, entry 6). It is worth noting that the use of Pd(OAc)2 without addition of ligands gave coupling product in only 50% yield at 130 °C.35 When the aryl chloride was used, arylated products were formed after 20 h. For example 2-n-butyl-5-(4-nitrophenyl)thiophene was obtained in the coupling with 4-chloronitrobenzene using catalysts 1a−1d in 84%, 82%, 80%, and 81% conversion, respectively. The palladium-catalyzed direct arylation of 2-n-propylthiazole with aryl bromides in DMF has been described by Miura and Nomura.36 We investigated the direct C5 arylation of 2-npropylthiazole with aryl bromides, and the results of these experiments are summarized in Table 1. Selective C5 arylations were observed using bromobenzene, 4-bromonitrobenzene, and 4-bromoanisole, resulting in 68−89% yields of products (Table 1). The reactivity of 2-n-propylthiazole was similar to 2-nbutylthiophene. The reaction of the electron-rich aryl bromide 4-bromoanisole with methyl 2-n-propylthiazole gave the desired product in 89% yield in the presence of 1 mol % of complex 1b (Table 1, entry 6). Bromobenzene was successfully coupled with 2-n-propylthiazole in the presence of 1 mol % of catalyst 1a to give 5-phenyl-2-n-propylthiazole in 77% yield (Table 1, entry 7). High yields of 5-(4-nitrophenyl)-2-n-propylthiazole were obtained for the coupling with 4-bromonitrobenzene using catalyst 1b (Table 1, entry 5). Generally speaking, the complex 1b seems to be a slightly more effective catalyst for this reaction. In previous works, the reaction time was chosen as 20 h for arylation of methyl 2-methyl-3-furoate, 2-n-propylthiazole, and 2-n-propylthiazole with aryl bromides, whereas in the present work the reaction time was shortened to 1 h and higher yields were obtained as compared to our previous results.24c For example bromoarenes were coupled with 2-n-butylthiophene in the presence of imidazolin-2-ylidene-Pd complexes to give the desired product in 10−56% yields only after 20 h,24c whereas the use of (6-NHC)Pd complexes gave higher yields (Table 1, entry 4). Finally, the scope of the direct arylation reaction was extended to 4,5-dimethylthiazole. It should be noted that no example of direct arylation of 4,5-dimethylthiazole with aryl bromides by using Pd−N-heterocyclic carbene complexes has been reported so far. The reaction performed with p-substituted aryl bromides and the results of these experiments are summarized in Table 1, entries 10−12. Bromobenzene, 4bromonitrobenzene, and 4-bromoanisole gave moderate to high yields of C2 arylation products in the presence of 1 mol % catalysts (Table 1, entry 10). Generally, the reactivity of 4,5dimethylthiazole was similar to 2-n-propylthiazole. The reaction of 4,5-dimethylthiazole with bromobenzene generated the corresponding product in 71% yield in the presence of 1 mol % of complex 1b (Table 1, entry 10). High yields of 4,5dimethyl-2-(4-methoxyphenyl)thiazole were obtained for the coupling with 4-bromoanisole using catalysts 1a−1d (Table 1, entry 12) with little variance between the complexes. To our knowledge, these are the first examples applied to direct arylations of furan, thiophene, or thiazoles by using both electron-deficient and electron-rich aryl bromides as the coupling partners catalyzed by [(6-NHC)PdCl2] complexes.
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CONCLUSION
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EXPERIMENTAL SECTION
We report here the synthesis and characterization of four new ring-expanded 6-NHC palladium complexes (1a−1d) by thermal cleavage reaction of the enetetraamines, based on 1,3-dibenzyl-3,4,5,6-tetrahydropyrimidin-2-ylidenes. Complex 1a has been characterized by single-crystal X-ray diffraction studies as a trans isomer. The catalytic activity of these complexes was investigated in C5/C2 direct arylation of furan, thiophene, and thiazole derivatives in the presence of KOAc. Moreover, in the present study the product yield was higher and the reaction time shorter (1 h) as compared to previous results. The higher efficiency may be attributed to the higher σdonating ability of 6-NHC as compared to 5-NHC. It has to be emphasized that this procedure is environmentally more attractive than the classical coupling procedures. Finally, we are currently investigating the scope and application of these complexes as catalysts for other metal-catalyzed C−H bond activation reactions.
General Methods. All reactions for the preparation of tetrahydropyrimidinium salts and palladium-(NHC) complexes (1) were carried out under argon in flame-dried glassware using standard Schlenk techniques. The solvents used were purified by distillation over the drying agents indicated and were transferred under Ar: THF, Et2O (Na/K alloy), CH2Cl2 (P4O10), hexane, toluene (Na). All reagents were purchased from Aldrich Chemical Co. Melting points were determined in glass capillaries under air with an Electrothermal9200 melting point apparatus. FT-IR spectra were recorded as KBr pellets in the range 400−4000 cm−1 on an ATI UNICAM 1000 spectrometer. 1H NMR and 13C NMR spectra were recorded using a Varian AS 400 Merkur spectrometer operating at 400 MHz (1H) and 100 MHz (13C) in CDCl3 and DMSO-d6 with tetramethylsilane as an internal reference. All catalytic reactions were monitored on an Agilent 6890N GC and Schimadzu 2010 Plus GC-MS system by GC-FID with an HP-5 column of 30 m length, 0.32 mm diameter, and 0.25 μm film thickness. Column chromatography was performed using silica gel 60 (70−230 mesh). Elemental analyses were performed by Iṅ önu University Scientific and Technology Center. General Method for the Preparation of Palladium Complexes 1a−d. A suspension of the 1,3-benzyl-3,4,5,6-tetrahydropyrimidinium salt (10 mmol) and potassium tert-butoxide (15 mmol) in THF (20 mL) was stirred for 10 h. After the stirring, hexane (20 mL) was added and the mixture filtered. The filtrate was evaporated to dryness (ca. 4 mmol of enetetraamine formed, and the reaction was monitored by 1H NMR). The residue was dissolved in warm toluene (20 mL), and this was used as stock solution, owing to air and moisture sensitivity of the alkenes formed. In the second step, a mixture of [PdCl2(PPh3)2] (0.60 mmol) in toluene (10 mL) and the corresponding alkene (0.60 mmol) in toluene (2.0 mL) was heated under reflux for 2 h and then cooled to 50 °C, and hexane (10 mL) was added. The precipitate formed was filtered off and washed with hexane (2 × 10 mL). The yellow product was recrystallized from CH2Cl2/Et2O (5:15 mL). 1a. Yield: 0.28 g, 74%; mp 295−296 °C. IR: ν(CN) = 1537 cm−1. 1H NMR (CDCl3): δ 1.74 (p, J = 6 Hz, 4H, NCH2CH2CH2N), 2.31 (s, 12H, CH2C6H4(CH3)-4), 2.90 (t, J = 6 Hz, 8H, NCH2CH2CH2N), 5.36 (s, 8H, CH2C6H4(CH3)-4), 7.05 and 7.33 (d, J = 7.8 Hz, 16H, CH2C6H4(CH3)-4). 13C{H} NMR (CDCl3): δ 20.6 (NCH2CH2CH2N), 21.2 (CH2C6H2(CH3)-4), 43.4 (NCH2CH2CH2N), 60.9 (CH2C6H4(CH3)-4), 128.3, 129.0, 133.3, 136.8 (CH2C6H4(CH3)-4), 193.7 (Pd-Ccarb). Anal. Calcd for C40H48N4Cl2Pd: C, 63.03; H, 6.35; N, 7.35. Found: C, 62.98; H, 6.18; N, 7.33. 1b. Yield: 0.32 g, 78%; mp 2772−273 °C. IR: ν(CN) = 1546 cm−1. 1 H NMR (CDCl3): δ 1.23 (t, J = 5.4 Hz, 12H, CH2C6H4(CH2CH3)4), 1.76 (p, J = 5.7 Hz, 4H, NCH2CH2CH2N), 2.61 (q, J = 7.8 Hz, 8H, 2490
DOI: 10.1021/om501201r Organometallics 2015, 34, 2487−2493
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Organometallics CH2C6H4(CH2CH3)-4), 2.91 (t, J = 5.7 Hz, 8H, NCH2CH2CH2N), 5.55 (s, 8H, CH2C6H4(CH2CH3)-4), 7.08 and 7.36 (d, J = 8.3 Hz, 16H, CH2C6H4(CH2CH3)-4). 13C{H} NMR (CDCl3): δ 15.5 (CH 2 C 6 H 2 (CH 2 CH 3 )-4), 20.6 (NCH 2 CH 2 CH 2 N), 28.5 (CH 2 C 6 H 2 (CH 2 C H 3 )-4), 43.4 (N CH 2 CH 2 CH 2 N), 61.0 (CH2C6H4(CH2CH3)-4), 128.6, 128.8, 133.6, 143.2 (CH 2 C 6 H 4 (CH 2 CH 3 )-4), 183.7 (Pd-C carb ). Anal. Calcd for C44H56N4Cl2Pd: C, 64.58; H, 6.90; N, 6.85. Found: C, 64.59; H, 6.62; N, 6.81. 1c. Yield: 0.30 g, 76%; mp 280−281 °C. IR ν(CN) = 1518 cm−1. 1H NMR (CDCl3): δ 1.15 (t, J = 6.9 Hz, 24H, CH2C6H4N(CH2CH3)-4)2, 1.70 (p, J = 6 Hz, 4H, NCH2CH2CH2N), 2.89 (t, J = 6 Hz, 8H, NCH2CH2CH2N), 3.32 (q, J = 6.9 Hz, 16H, CH2C6H4N(CH2CH3)24), 5.63 (s, 8H, CH2C6H4N(CH2CH3)2-4), 6.85 and 7.38 (d, J = 8.7 Hz, 16H, CH2C6H4N(CH2CH3)2-4). 13C{H} NMR (CDCl3): δ 12.6 (CH 2 C 6 H 2 N(CH 2 CH 3 ) 2 -4), 22.7 (NCH 2 CH 2 CH 2 N), 43.1 (NCH 2 CH 2 CH 2 N), 44.3 (CH 2 C 6 H 2 N(CH 2 CH 3 ) 2 -4), 60.7 (CH2C6H4N(CH2CH3)2-4), 111.6, 123.3, 130.1, 147.1 (CH2C6H4N(CH2CH3)2-4), 192.4 (Pd-Ccarb). Anal. Calcd for C52H76N8Cl2Pd: C, 63.05; H, 7.73; N, 11.31. Found: C, 63.05; H, 7.80; N, 11.29. 1d. Yield: 0.25 g, 70%; mp 252−253 °C. IR: ν(CN) = 1515 cm−1. 1H NMR (CDCl3): δ 1.68 (m, 4H, NCH2CH2CH2N), 2.94 (t, J = 5.4 Hz, 8H, NCH2CH2CH2N), 3.86 (s, 12H, CH2C6H4(OCH3)2-3), 3.87 (s, 12H, CH2C6H4(OCH3)2-4), 5.52 (s, 8H, CH2C6H3(OCH3)2-3,4), 6.72 and 6.81 (d, J = 8.1 Hz, 8H) and 7.32 (s, 4H, CH2C6H3(OCH3)23,4). 13C{H} NMR (CDCl3): δ 20.7 (NCH2CH2CH2N), 43.2 (NCH2CH2CH2N), 55.8 (CH2C6H2(OCH3)2-3), 56.3 (CH2C6H2(OCH3)2-4), 61.0 (CH2C6H4(OCH3)2-3,4), 110.3, 111.1, 120.6, 128.9, 148.3, 149.2 (CH2C6H4(OCH3)2-3,4), 192.8 (Pd−Ccarb). Anal. Calcd for C44H56N4O8Cl2Pd: C, 55.85; H, 5.97; N, 5.92. Found: C, 55.87; H, 5.97; N, 5.90. Typical Procedure for Direct Arylations. As described in refs 24c and 24h, in a typical experiment, the aryl bromide (1 mmol), heteroarene derivative (2 mmol) (see Table 1), and KOAc (2 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. The Pd complex (0.01 mmol) and DMAc (3 mL) were added, and the Schlenk tube was purged several times with argon. The Schlenk tube was placed in a preheated oil bath at 150 °C, and the reaction mixture was stirred for 1 h. Then, the reaction mixture was analyzed by gas chromatography to determine the conversion of the aryl bromide and the yield of product. The solvent was removed under vacuum, and the residue was charged directly onto a silica gel column. The products were eluted by using an appropriate ratio of diethyl ether and pentane.24c,34,37 Crystal Structure Analysis. A suitable crystal of 1a was selected for data collection, which was performed on a STOE IPDS II diffractometer equipped with graphite-monochromatic Mo Kα radiation at 296 K. The structures were solved by direct methods using SHELXS-9738 and refined by full-matrix least-squares methods on F2 using SHELXL-9739 from within the WINGX39 suite of software. All non-hydrogen atoms were refined with anisotropic parameters. The H atoms were located from difference maps and then treated as riding atoms with C−H distances of 0.93−0.97 Å. The large SD values and displacement parameters of the C23 atom were caused by the disorder. This disorder was modeled as two different orientations, with occupancy factors of 0.629(10) and 0.371(10), respectively. Molecular diagrams were created using MERCURY.40 Details of data collection and crystal structure determinations are given in Table 1. Figure 1 shows the molecular structure of 1a.
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tion is available free of charge on the ACS Publications website at DOI: 10.1021/om501201r.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the Technological and ̇ AK-BOSPHOScientific Research Council of Turkey TUBIT RUS (France) [109T605], TUBA, and Iṅ önü University Research Fund (I.̇ Ü . B.A.P: 2013/51).
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DEDICATION This article is dedicated to the memory of Professor Michael Franz Lappert.
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REFERENCES
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ASSOCIATED CONTENT
S Supporting Information *
Crystallographic data for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Center: CCDC-1019867 contains the supplementary crystallographic data for this paper. This data can be obtained free of charge from the Cambridge Crystallographic Data Centre, www.ccdc.cam.ac.uk/datarequest/cif. The Supporting Informa2491
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