Synthesis of novel benzimidazole salts and microwave-assisted catalytic activity of in situ generated Pd nanoparticles from a catalyst system consisting of benzimidazol salt, Pd(OA

Novel benzimidazolium salts having N-benzyl or N-(4-substitutedbenzyl) groups were synthesized and their microwave-promoted catalytic activity for the Suzuki–Miyaura cross-coupling reaction were determined using in situ formed palladium(0) nanoparticles (PdNPs) from a catalytic system consisting of Pd(OAc) 2 /K2CO3 in DMF/H2 O. PdNPs were characterized by X-ray diffraction (XRD) pattern and particle size of in situ generated PdNPs from the Pd(111) plane was determined to be of diameter 19.6 nm by the Debye–Scherrer equation.

Turkish Journal of Chemistry http://journals.tubitak.gov.tr/chem/ Research Article Turk J Chem (2013) 37: 721 733 ă ITAK c TUB ⃝ doi:10.3906/kim-1207-18 Synthesis of novel benzimidazole salts and microwave-assisted catalytic activity of in situ generated Pd nanoparticles from a catalyst system consisting of benzimidazol salt, Pd(OAc) , and base in a Suzuki-Miyaura reaction 1, ă u YILMAZ,1 Hasan KUC ¨ ¸ UKBAY, ¨ ¨ ˙ C ˙ ˙ Ulkă Sevim TURKTEK IN ELIKES IR, ă ¨ ¨ ¨ Mehmet AKKURT, Orhan BUYUKGUNGOR ˙ on¨ Department of Chemistry, Faculty of Science and Arts, Ină u University, Malatya, Turkey Department of Physics, Faculty of Science, Erciyes University, Kayseri, Turkey Department of Physics, Faculty of Arts and Science, Ondokuz Mayıs University, Kurupelit, Samsun, Turkey Received: 06.07.2012 • • Accepted: 17.03.2013 Published Online: 16.09.2013 • Printed: 21.10.2013 Abstract: Novel benzimidazolium salts having N-benzyl or N-(4-substitutedbenzyl) groups were synthesized and their microwave-promoted catalytic activity for the Suzuki–Miyaura cross-coupling reaction were determined using in situ formed palladium(0) nanoparticles (PdNPs) from a catalytic system consisting of Pd(OAc) /K2CO in DMF/H O PdNPs were characterized by X-ray diffraction (XRD) pattern and particle size of in situ generated PdNPs from the Pd(111) plane was determined to be of diameter 19.6 nm by the Debye–Scherrer equation Moreover, the yield of the Suzuki–Miyaura reactions with aryl iodides and aryl bromides was found to be nearly quantitative The synthesized benzimidazole salts (1–5) were identified by H and 13 C NMR and IR spectroscopic methods, and micro analysis The molecular structure of was also determined by X-ray crystallography Key words: Benzimidazole salt, N-heterocyclic carbenes, palladium nanoparticles, cross-coupling reaction, Suzuki– Miyaura coupling, microwave Introduction The Suzuki–Miyaura reaction is one of the most versatile and utilized reactions for the selective construction of carbon–carbon bonds, in particular for the formation of biaryls 1−8 Because of the excellent physical and chemical properties of biaryls, they can be used in several organic compound syntheses, such as of monomers for constructing polymers, supramolecular compounds, and natural, pharmaceutical, and agrochemical products 9,10 Nowadays, the Suzuki–Miyaura reaction plays an important role in organic synthetic chemistry to obtain new generation organic materials with many important properties such as electronic, optical, or mechanical Therefore, in recent years, much effort has been devoted to develop and improve the reaction conditions For these purposes, various catalysts or catalytic systems including tertiary phosphines and N-heterocyclic carbenes, solvent, base, and reaction conditions such as temperature and time, and conventional or microwave heating systems have been investigated 11−20 Among the catalysts, those having N-heterocyclic carbene ligands have gained enormous popularity due to their potential advantages over tertiary phosphines such as better σ -donor ability, low toxicity, and ∗ Correspondence: hkucukbay@inonu.edu.tr In memory of Prof Dr Ayhan S Demir 721 YILMAZ et al./Turk J Chem thermal stability 8,21−24 In particular, Pd(II)-NHC complexes are more attractive as pre-catalysts because of their stability to air, moisture, and heating and they also have excellent long-term storage profiles Pd(OAc) /benzimidazole or imidazole ligands could be very effective catalytic systems in these reactions 17,25 In recent years, microwave-assisted organic synthesis has been considered a green technology owing to its high reaction rates, purity of products, increased yield, decreased electricity cost, and simplified course of reactions 26−34 The use of metal catalysis in conjunction with microwave heating may also have significant advantages over traditional heating methods, since the inverted temperature gradients under microwave conditions may provide an increased lifetime of the catalyst through elimination of wall effects 35 There are extensive studies about the Suzuki-type C–C cross-coupling reaction incorporating microwave irradiation with high yield in a short time using various ligands other than benzimidazole moiety 27,29−32,34−36 Recently, we have also investigated the catalytic activity of some in situ prepared N-heterocyclic carbene-Pd complexes for Suzuki–Miyaura cross coupling reactions under microwave heating 37,38 Since the nature, size, and electronic properties of the substituent on the nitrogen atom(s) of the benzimidazole may play a crucial role in tuning the catalytic activity, to find more efficient palladium catalysts we have synthesized a series of new benzimidazolium halides, 1–5 (Scheme), containing benzyl, substituted benzyl, and 3-phenylpropyl moieties, and we aimed to investigate the activity of in situ Pd-carbene based catalytic systems for Suzuki cross-coupling reactions Reetz and co-workers were the first to report the use of Pd and Pd/Ni nanoparticles for the Suzuki coupling of aryl bromides and chlorides with phenylboronic acid 39,40 PdNPs are effective catalysts for chemical transformations due to their large surface area and many research groups have used them as an active catalyst for Suzuki–Miyaura cross-coupling reactions 16,41−49 Herein, we report on the microwave-assisted catalytic activity of Pd(OAc) /benzyl and 3-phenylpropyl substituted benzimidazolium salts and base catalytic system through in situ formed PdNPs in Suzuki crosscoupling reactions The X-ray structural analysis of compound was also determined to clarify whether there is crystal water in the benzimidazolium compounds, as in our previous work 50 Experimental All preparations were carried out in an atmosphere of purified argon using standard Schlenk techniques The starting materials and reagents used in the reactions were supplied commercially by Aldrich or Merck The solvents were dried by standard methods and freshly distilled prior to use All catalytic activity experiments were carried out in a microwave oven system manufactured by Milestone (Milestone Start S Microwave Labstation for Synthesis) under aerobic conditions H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded using a Bruker DPX-300 high performance digital FT NMR spectrometer Infrared spectra were recorded as KBr pellets in the range 4000–400 cm −1 on a PerkinElmer FT-IR spectrophotometer The structural characterization of the samples fabricated was investigated by X-ray diffraction (XRD) An automated Rigaku RadB Dmax X-ray diffractometer having CuK α radiation was used Scan speed was selected as ◦ −1 in the range of θ = 3–80 ◦ Elemental analyses were performed by LECO CHNS-932 elemental analyzer Melting points were recorded using an Electrothermal-9200 melting point apparatus, and are uncorrected 1-(3-Phenylpropyl)benzimidazole (I), used in this work as a starting compound, was prepared by treating benzimidazole and 3-bromopropylbenzene similar to the literature procedure 51 722 YILMAZ et al./Turk J Chem X-CH2-C6H4-R N N + N DMF N X R= H, X= Cl R= CH3, X= Br R= NO2, X= Cl R= Cl, X= Cl R= Br, X= Br - I R Scheme Synthesis pathways of the benzimidazole derivatives 2.1 GC-MS analysis GC-MS spectra were recorded on an Agilient 6890 N GC and 5973 Mass Selective Detector using an HPINNOWAX column of 60-m length, 0.25-mm diameter, and 0.25-µ m film thicknesses GC-MS parameters for both Suzuki and Heck coupling reactions were as follows: initial temperature 60 ◦ C; initial time, min; temperature ramp 1, 30 ◦ C/min; final temperature, 200 ◦ C; ramp 2, 20 ◦ C/min; final temperature 250 ◦ C; run time 30.17 min; injector port temperature 250 ◦ C; detector temperature 250 ◦ C, injection volume, 1.0 µ L; carrier gas, helium; mass range between m/z 50 and 550 2.2 Synthesis of benzimidazole salts Synthesis of 1-benzyl-3-(3-phenylpropyl)benzimidazolium chloride, A mixture of 1-(3-phenylpropyl)benzimidazole (I) (1.00 g, 4.23 mmol) and benzyl chloride (0.50 mL, 4.34 mmol) in dimethylformamide (5 mL) was refluxed for h The mixture was then cooled and the volatiles were removed under vacuum The solid was crystallized from ethanol/diethyl ether (1:1) White crystals of the title compound (1.16 g, 75%) were obtained, mp 96–98 ◦ C; υmax /cm −1 = 1564 (CN) Anal found: C 75.37, H 6.30, N 7.20 Calculated for C 23 H 23 N Cl (362.90): C 76.12, H 6.39, N 7.72 H NMR ( δ , DMSO- d ): 10.26 (s, 1H, NCHN), 8.13–7.20 (m, 14H, C H , C H , CH C H ), 5.81 (s, 2H, CH C H ) , 4.59 (t, 2H, CH CH CH C H , J = 7.2 Hz), 2.73 (t, 2H, CH CH CH C H , J = 7.8 Hz), 2.29 (quint, 2H, CH CH CH C H , J = 7.5 Hz) 13 C NMR ( δ , DMSO-d ) : 143.1 (NCHN), 141.0, 134.6, 131.8, 131.3, 129.4, 129.2, 129.1, 128.8, 128.7, 127.1, 127.0, 126.5, 114.4, and 114.3 (C H , C H , CH C H ), 50.3 (CH C H ), 47.1 (CH CH CH C H ), 32.4 (CH CH CH C H ) , 30.4 (CH CH CH C H ) 2.3 General method for the synthesis of compounds 2–5 Equivalent amount of the 1-(3-phenylpropyl)benzimidazole and the appropriate alkyl halide were refluxed in dimethylformamide (5 mL) for h Then the mixture was cooled to room temperature and the volatiles were removed under reduced pressure The residue was crystallized from ethanol/diethyl ether (1:1) 1-(4-Methylbenzyl)-3-(3-phenylpropyl)benzimidazolium bromide, Yield, 1.64 g (white crystals), 92%; mp 207–208 ◦ C; υmax /cm −1 = 1565 (CN) Anal found: C 68.27, H 6.09, N 6.49 Calculated for C 24 H 25 N Br (421.37): C 68.41, H 5.98, N 6.65 H NMR ( δ , DMSO-d ): 723 YILMAZ et al./Turk J Chem 10.06 (s, 1H, NCHN), 8.14–7.16 (m, 13H, C H , C H , CH C H CH ) , 5.73 (s, 2H, CH C H CH ), 4.58 (t, 2H, CH CH CH C H , J = 7.2 Hz), 2.73 (t, 2H, CH CH CH C H , J = 7.8 Hz), 2.31 (quint, 2H, CH CH CH C H , J = 7.5 Hz), 2.29 (s, 3H, CH C H CH ) 13 C NMR (δ , DMSO-d ): 142.8 (NCHN), 141.0, 138.6, 131.8, 131.5, 131.3, 129.9, 128.8, 128.7, 127.1, 127.0, 126.5, and 114.4 (C H , C H , CH C H CH ) , 50.2 (CH C H CH ), 47.1 (CH CH CH C H ), 32.4 (CH CH CH C H ) , 30.5 (CH CH CH C H ), 21.2 (CH C H CH ) 1-(4-Nitrobenzyl)-3-(3-phenylpropyl)benzimidazolium chloride, Yield, 1.53 g (yellow crystals), 88%; mp 154–156 ◦ C; υmax /cm −1 = 1557 (CN) Anal found: C 67.12, H 5.57, N 10.01 Calculated for C 23 H 22 N O Cl (407.89): C 67.73, H 5.44, N 10.30 H NMR ( δ , CDCl ): 12.20 (s, 1H, NCHN), 8.25–7.19 (m, 13H, C H , C H , CH C H NO ) , 6.16 (s, 2H, CH C H NO ), 4.59 (t, 2H, CH CH CH C H , J = 7.5 Hz), 2.86 (t, 2H, CH CH CH C H , J = 7.2 Hz), 2.51 (quint, 2H, CH CH CH C H , J = 7.5 Hz) 13 C NMR ( δ , CDCl ): 148.3 (NCHN), 144.2, 139.8, 139.3, 131.3 131.0, 129.5, 128.7, 128.4, 127.5, 127.4, 126.6, 124.5, 113.3, and 113.2 (C H , C H , CH C H NO ), 50.2 (CH C H NO ), 47.2 (CH CH CH C H ), 32.6 (CH CH CH C H ) , 30.2 (CH CH CH C H ) 1-(4-Chlorobenzyl-3-(3-phenylpropyl)benzimidazolium chloride, Yield, 1.41 g (white crystals), 84%; mp 142–143 ◦ C; υmax /cm −1 = 1559 (CN) Anal found: C 68.93, H 5.73, N 6.80 Calculated for C 23 H 22 N Cl (397.34): C 69.52, H 5.58, N 7.05 H NMR ( δ , CDCl ): 12.00 (s, 1H, NCHN), 7.54–7.16 (m, 13H, C H , C H , CH C H Cl), 5.91 (s, 2H, CH C H Cl), 4.59 (t, 2H, CH CH CH C H , J = 7.5 Hz), 2.82 (t, 2H, CH CH CH C H , J = 7.2 Hz), 2.46 (quint, 2H, CH CH CH C H , J = 7.5 Hz) 13 C NMR (δ , CDCl ): 143.8 (NCHN), 139.5, 135.2, 131.5, 131.3, 131.0, 129.9, 129.5, 128.6, 128.4, 127.2, 127.1, 126.5, 113.7, and 113.0 (C H , C H , CH C H Cl), 50.6 (CH C H Cl), 47.0 (CH CH CH C H ), 32.5 (CH CH CH C H ) , 30.3 (CH CH CH C H ) 1-(4-Bromobenzyl)-3-(3-phenylpropyl)benzimidazolium bromide, Yield, 1.42 g (white crystals), 69%; mp 196–197 ◦ C; υmax /cm −1 = 1563 (CN) Anal found: C 56.27, H 4.40, N 5.67 Calculated for C 23 H 22 N Br (486.24): C 56.81, H 4.56, N 5.76 H NMR ( δ , DMSO-d ): 10.08 (s, 1H, NCHN), 8.14–7.16 (m, 13H, C H , C H , CH C H Br), 5.78 (s, 2H, CH C H Br), 4.58 (t, 2H, CH CH CH C H , J = 7.2 Hz), 2.74 (t, 2H, CH CH CH C H , J = 7.8 Hz), 2.29 (quint, 2H, CH CH CH C H , J = 7.5 Hz) 13 C NMR (δ , DMSO-d ): 143.1 (NCHN), 141.0, 133.9, 132.3, 131.8, 131.2, 131.1, 128.8, 128.7, 127.2, 127.1, 126.5, 122.5, 114.4, and 114.3 (C H , C H , CH C H Br), 49.6 (CH C H Br), 47.1 (CH CH CH C H ), 32.4 (CH CH CH C H ), 30.4 (CH CH CH C H ) 2.4 Single-crystal X-ray diffraction analysis of 1-(4-bromobenzyl)-3-(3-phenylpropyl)benzimidazolium bromide (5) The X-ray data were collected at 296(2) K on a STOE IPDS II diffractometer with MoK α radiation Data collection, cell refinement, and data reduction were performed with X-AREA and XRED32 52 Crystal structures were solved by direct methods using the SIR97 structure solution program and refined on F by full matrix least-square methods on F using the SHELXL97 program 53,54 All H atoms were positioned geometrically with C—H = 0.93-0.97 ˚ A, and refined using a riding model with Uiso (H) = 1.2 Ueq (C) A summary of the crystal data, experimental details, and refinement results for 724 YILMAZ et al./Turk J Chem is given in Table The molecular structure of in Figure was drawn with ORTEP-3 55 The relevant bond lengths and bond angles are listed in Table Table The crystal data, data collection, and refinement values of compound Crystal data C23 H22 BrN2 Br Mr = 486.23 Triclinic, P -1 a = 8.6978 (5) ˚ A b = 9.0916 (5) ˚ A c = 14.5678 (9) ˚ A Mo Kα radiation T = 296 (2) K Data collection STOE IPDS diffractometer ω scans Absorption correction:integration Tmin = 0.106, Tmax = 0.196 14,941 measured reflections 4337 independent reflections 3690 reflection with I > 2σ(I) Refinement Refinement on F R[F > 2σ(F )] = 0.048 wR(F ) = 0.094 S = 1.09 4337 reflections 244 parameters H atoms constrained to parent site Z=2 Dx = 1.542 Mg m−3 α = 103.098 (5)◦ β = 99.602 (5)◦ γ = 105.739 (5)◦ V = 1047.43 (12) ˚ A3 µ = 3.88 mm−1 Crystal shape and color: block, colorless Rint = 0.118 θmax = 26.5◦ h = –10→ 10 k = –11 → 11 l = –18 →18 Calculated weights w = 1/[σ (Fo2 )+ (0.0414P )2 + 0.5155P ] P = (Fo2 + 2Fc2 )/3 (∆/σ)max