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New (κ2-C,N)-palladacyclic complexes with benzimidazol-2-ylidene ligand: Synthesis, crystal structures and characterization
Inorganic Chemistry Communications 12 (2009) 990–993
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
New (j2-C,N)-palladacyclic complexes with benzimidazol-2-ylidene ligand: Synthesis, crystal structures and characterization M. Emin Günay a,*, Rukiye Gümüsßada a, Namık Özdemir b, Muharrem Dinçer b, Bekir Çetinkaya c a
Department of Chemistry, Adnan Menderes University, 09010 Aydın, Turkey Department of Physics, Ondokuz Mayıs University, 55139 Kurupelit-Samsun, Turkey c Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey b
a r t i c l e
i n f o
Article history: Received 14 June 2009 Accepted 1 August 2009 Available online 7 August 2009 Keywords: Palladacycles N-heterocyclic carbene Unsymmetrical benzimidazolium salt Crystal structure
a b s t r a c t Reaction of unsymmetrical benzimidazolium bromides (1) with Ag2O and subsequent transmetallation with chloro-bridged dinuclear palladacycle, [Pd(dmba)(l-Cl)]2 (dmba: N,N-dimethylbenzylamine) afforded benzannulated monocarbene complexes [Pd(dmba)(NHC)Cl], 2. The palladacycles (2a–c) were characterized by elemental analysis; NMR spectroscopy and the molecular structure of 2a and 2c were determined by X-ray crystallography. Ó 2009 Elsevier B.V. All rights reserved.
Palladacycles have been known for over 30 years [1–4]. They are intensively studied classes of organopalladium derivatives, primarily due to their easy synthetic accessibility, structural versatility and intriguing applications in organic synthesis, organometallic catalysis, and new molecular materials. In particular, most of carbon–carbon bond forming reactions such as Heck reaction, Stille reaction, Suzuki reaction and other C–C couplings are palladium catalyzed [5–7]. In the C–C bond formation reactions, the role of palladacycle moiety has been proposed to release Pd(0), through a slow process which helps to suppress the nucleation and growth of inactive palladium metal particles [3]. On the other hand, in recent years, the uses of N-heterocyclic carbene (NHC) ligands over various metals have been applied in organometallic chemistry and catalysis [8–10]. In addition, the combination of a palladacycle framework with an NHC was reported by Herrmann [11–13], and others [14,15]. However, to the best of our knowledge, there have been only a few examples of spectroscopically characterized cyclometalated NHC–Pd(II) complexes reported [16,17]. For the present study, we selected the unsymmetrical alkyl substituted benzimidazol-2-ylidene precursor as N-heterocyclic carbene ligand. This choice was guided by several conditions. An important characteristic of the carbene ligands in active complexes is their strong electron donating effect. As a matter of fact, benzimidazol-2-ylidenes have structures reminiscent of imidazole-2ylidenes, but spectroscopic properties and reactivity which are * Corresponding author. Tel.: +90 256 212 8498; fax: +90 256 213 5379. E-mail address: [email protected] (M. Emin Günay). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.08.001
close to saturated imidazole-2-ylidenes [18–20]. However, modifications and overall synthesis of benzimidazol-2-ylidenes are more facile than imidazol(in)-2-ylidenes. Furthermore, methoxyethyl and methylated benzyl substituents have been reported to display enhanced activity [18]. In this work, we describe a practical approach to NHC-ligated palladacycles by carbene transfer from a silver N-heterocyclic carbene precursor to [Pd(dmba)(l-Cl)]2 in room temperature in dichloromethane. The general route to the target NHC ligand precursors and palladacyclic complexes is shown in Scheme 1. The methylated benzyl bromides were synthesized according to the methods previously known [21]. The introduction of the 2-chloroethyl methyl ether substituent into the benzimidazole was achieved by direct alkylation in DMSO. The resulting 1-alkylbenzimidazole can be alkylated to give 1a–c. These salts were purified by recrystallization from EtOH/Et2O. The IR data for unsymmetrical benzimidazolium salts clearly indicate the presence of the –C@N– group with a mC@N stretching vibration between 1553 and 1563 cm1. These benzimidazolium salts have been characterized by 1H and 13 C NMR spectroscopy. 1H NMR chemical shifts were consistent with the proposed structures; the resonances for C2-hydrogens were observed as sharp singlet between 9.88 and 10.46 ppm. 13C NMR of these salts showed the C2 carbon at 141.9–142.8 ppm. The benzylic protons appeared as singlet between 5.78 and 6.91 ppm. The in situ reaction of the Ag–NHC complexes with the [Pd(dmba)(l-Cl)]2 in dichloromethane resulted in the NHC-ligated palladacyclic compound as a crystalline solid [22,23]. The pallada-
M. Emin Günay et al. / Inorganic Chemistry Communications 12 (2009) 990–993
991
N Ar
Pd
N +
(i)
Br-
N
Cl N
Ar
N O
CH3 O
CH3
1a-c
2a-c
a
b
c
Ar
Scheme 1. Reagents and conditions: (i) DCM, Ag2O, 3 h, RT, then [Pd(dmba)(l-Cl)]2, 24 h, RT.
cyclic complexes, which are very stable in the solid state, were characterized by analytical and spectroscopic techniques [24]. The C2 carbons were found to be shifted downfield in the 13C NMR spectra of the complexes. The chemical shifts for the carbene carbon atom (2a–c) fall in the range d 185.8–186.1 ppm. A brief inspection of literature indicates that in the square-planar complexes, [PdCl(dmba)(NHC)] formed between a NHC and [Pd(dmba)(l-Cl)]2, the NHC ligand might be bonded to Pd atom either trans to ortho-carbon or NMe2 of the dmba moiety [25]. The spectroscopic information obtained above did not allow us to distinguish these possibilities. Therefore, X-ray structure determination was required [26] and the structure of the complexes 2a and 2c are shown in Figs. 1 and 2, respectively. Selected bond lengths and angles are listed in the caption of figures. These complexes contain a benzimidazole ligand with a PdII metal centre, an N,N-dimethyl-1-phenylmethanamine ligand and one chlorine ligand. The coordination around the PdII ion is distorted cis-square-planar, and the PdII ion is coordinated by one amine N atom and one aryl C
Fig. 1. A view of the complex (2a), showing 40% probability displacement ellipsoids and the atom-numbering scheme. Pd1–C1 1.968 (4), Pd1–C21 1.979 (4), Pd1–N3 2.136 (3), Pd1–Cl1 2.4417 (9), O1–C9 1.385 (6), O1–C10 1.422 (8), N1–C1 1.352 (4), N1–C2 1.395 (4), N1–C11 1.470 (4), N2–C1 1.359 (4), N2–C7 1.389 (5), N2–C8 1.459 (5), N3–C28 1.470 (6), N3–C29 1.477 (5), N3–C27 1.489 (6), C8–C9 1.526 (7), C11– 0 C12 1.516 (5) Å A, C1–Pd1–C21 92.74 (15), C1–Pd1–N3 175.59 (13), C21–Pd1–N3 82.87 (15), C1–Pd1–Cl1 89.60 (10), C21–Pd1–Cl1 177.02 (11), N3–Pd1–Cl1 94.81 (10), C9–O1–C10 112.0 (6), C1–N1–C2 110.5 (3), C1–N1–C11 125.8 (3), C2–N1–C11 123.3 (3), C10–O1–C9–C8 175.0 (5), C1–N2–C7 110.5 (3), C1–N2–C8 124.0 (3), C7– N2–C8 125.0 (3), C28–N3–C29 108.0 (4), C28–N3–C27 109.4 (4), C29–N3–C27 109.6 (4), N1–C1–N2 106.4 (3), N2–C8–C9 109.1 (3), O1–C9–C8 107.3 (4), N1–C11–C12 114.8 (3), N2–C8–C9–O1 177.4 (4)°.
Fig. 2. A view of the complex (2c), showing 40% probability displacement ellipsoids and the atom-numbering scheme. Pd1–C1 1.965 (4), Pd1–C31 1.986 (5), Pd1–N3 2.141 (4), Pd1–Cl1 2.4508 (10), O1–C10 1.391 (8), O1–C9 1.404 (7), N1–C1 1.361 (5), N1–C2 1.381 (5), N1–C11 1.478 (5), N2–C1 1.359 (5), N2–C7 1.388 (5), N2–C8 1.460 (6), N3–C24 1.473 (6), N3–C25 1.477 (7), N3–C23 1.485 (6), C8–C9 1.501 (8), C11– 0 C12 1.518 (6) Å A, C1–Pd1–C31 92.99 (18), C1–Pd1–N3 175.59 (16), C31–Pd1–N3 82.69 (17), C1–Pd1–Cl1 89.23 (12), C31–Pd1–Cl1 175.75 (12), N3–Pd1–Cl1 95.02 (12), C10–O1–C9 111.8 (5), C1–N1–C2 111.0 (3), C1—N1–C11 124.7 (3), C2–N1–C11 124.0 (3), C10–O1–C9–C8 176.3 (5), C1–N2–C7 110.7 (3), C1–N2–C8 123.8 (4), C7– N2–C8 125.4 (4), C24–N3–C25 109.7 (4), C24–N3–C23 107.9 (4), C25–N3–C23 108.9 (4), N2–C1–N1 105.8 (3), N2–C8–C9 112.9 (4), O1–C9–C8 109.7 (4), N1–C11– C12 114.4 (3), N2–C8–C9–O1 66.3 (5)°.
atom from the bidentate ligand, one carbenic C atom from the monodentate ligand, and one Cl atom. The Pd–Cl and Pd–Ccarbene distances are 2.4417 (9) and 1.968 (4) Å for complex (2a) and 2.4508 (10) and 1.965 (4) for complex (2c), respectively. When these bonds are compared with those observed in the literature, it is seen that the Pd–Ccarbene distance is at the lower end of the reported range 1.966–1.996 Å [14,25b,27]. However, the Pd–Cl bond in the complex is somewhat longer than the range observed in the literature (2.379–2.424 Å) [14]. Similar to the complex 2c, the bonding within the N-heterocyclic carbene (NHC) ring indicates a pattern of delocalization that extends from atom N1 to atom N2 through atom C1, the N1–C1 [1.352 (4) Å] and N2–C1 [1.359 (4) Å] distances being significantly shorter than the N1–C2 [1.395 (4) Å] and N2–C7 [1.389 (5) Å] distances as is in similar NHC transition metal complexes [28–30]. These observations in complex 2a and 2c are possibly indicative of a greater partial double-bond character due to partial electron donation by nitrogen to the carbene C-atom donor [31,32]. Theoretical studies also indicate that the stability of these carbenes is due to electron donation from the N-atom lone pairs into the formally empty p(p) orbital on the carbene C atom (herein C1) [33]. The two coordinated C atoms in both complexes are cis to each other, which is in agreement with the fact that the donor groups with the largest trans influence avoid being mutually trans to one another. The change in geometrical parameters due to the difference of the monodentate NHC ligand, does not seem to significantly affect the coordination to the palladium(II) centre. The single-crystal data and X-ray collection parameters are given in Table 1. We have synthesized and characterized novel air- and moisture-stable palladacyclic complexes containing unsymmetrical benzimidazol-2-ylidene prepared by via Ag–NHC intermediate in situ, using the chloro-bridged palladacycle. The structures of 2a and 2c were determined by X-ray analysis. These complexes show a characteristic distorted cis-square-planar Pd(II) center with the carbene and dimethylamino ligands mutually trans to each other and the plane of the benzimidazole ring and the squareplane involving the palladacycle are close to perpendicular.
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M. Emin Günay et al. / Inorganic Chemistry Communications 12 (2009) 990–993
Table 1 Summary of X-ray crystallographic data for complex 2a and 2c. Parameter
2a
2c
Empirical formula Crystal size (mm) Mr T (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) a (o) b (o) c (o) V (Å3) Z qcalcd (Mg/m3) l (mm1) h Range (°) Index ranges
C29H36ClN3OPd 0.72 0.35 0.15 584.46 296 0.71073 Monoclinic P21/c 8.4623 (3) 15.5152 (7) 21.0184 (7) 90 96.283 (3) 90 2743.0 (2) 4 1.415 0.80 1.6–26.8 10 h 10, 19 k 19, 26 l 26 20,673 5830 322 1.05 1.33, 0.68 0.0450, 0.1334 0.0535, 0.1388
C31H40ClN3OPd 0.32 0.28 0.23 612.51 296 0.71073 Monoclinic P21/c 8.9470 (3) 15.8440 (4) 20.5998 (8) 90 100.945 (3) 90 2867.03 (16) 4 1.419 0.77 1.6–26.8 11 h 11, 20 k 16, 26 l 25 15,970 5990 334 1.06 1.63, 0.71 0.0490, 0.1504 0.0623, 0.1577
Number of measured reflections Number of independent reflections Number of parameters Goodness-of-fit (GOF) on F2 Maximum/minimum Dq (e Å3) R, wR (observed data)a R, wR (all data)a a
Refinement method, full-matrix least squares on F2.
Acknowledgments Funding of our research from the TUBITAK (Project No.: 104T 203), Adnan Menderes University (Project Nos.: FEF-07006, FEF07013 and FBE-08001) and Ondokuz Mayıs University (Project No.: F-461) is gratefully acknowledged.
Appendix A. Supplementary material CCDC 728280 and 728281 contain the supplementary crystallographic data for 2a and 2c. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.08.001.
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General procedure: The benzimidazolium salt (0.50 mmol) was dissolved in 10 mL CH2Cl2 and Ag2O (0.25 mmol) was added. The resulting black suspension was stirred for 3 h at RT, only a voluminous light grey precipitate remained, followed by addition of [Pd(dmba)(l-Cl)]2 (0.25 mmol). The reaction mixture was stirred for 24 h at RT and then was filtered. The CH2Cl2 removed in vacuo, and the residue was washed with Et2O. The crude product was recrystallized from CH2Cl2/Et2O. [23] Compound 2a: Yield: 0.101 g, 69%, m.p.: 229–230 °C. 1H NMR (d, CDCl3): 2.19 [s, 6H, o-(CH3)3C6H2]; 2.24 [s, 3H, p-(CH3)3C6H2]; 2.80 [s, 3H, CH2N(CH3)2]; 2.82 [s, 3H, CH2N(CH3)2]; 3.26 [s, 3H, CH2CH2OCH3]; 3.65 [d, 2H, J = 12 Hz, NCH2C6H2]; 4.02 [t, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.10 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.70 [d, 1H, J = 8.0 Hz, ArCH]; 5.89 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.07 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.69 [td, 1H, J = 8.0 Hz, Ar-CH]; 6.79 [s, 2H, Ar-CH]; 6.91 [m, 1H, Ar-CH]; 7.05 [t, 1H, J = 7.6 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, ArCH]. 13C NMR (d, CDCl3): 20.8, 20.9, 48.9, 49.6, 49.7, 50.6, 58.9, 71.7, 72.0, 110.8, 111.3, 122.1, 122.6, 122.8, 123.7, 125.4, 128.2, 129.3, 134.6, 135.6, 135.8, 137.9, 138.4, 148.1, 148.5, 186.0. Anal. Calc. for C29H36ClN3OPd (584.48): C, 59.59; H, 6.21; N, 7.19. Found: C, 58.41; H, 5.96; N, 6.99%.Compound 2b: Yield: 0.060 g, 40%, m.p.: 201–202 °C. 1H NMR (d, CDCl3): 2.11 [s, 6H, (CH3)3C6H2]; 2.17 [s, 6H, (CH3)3C6H2]; 2.76 [s, 3H, CH2N(CH3)2]; 2.80 [s, 3H, CH2N(CH3)2]; 3.26 [s, 3H, CH2CH2OCH3]; 3.65 [d, 2H, J = 12.0 Hz, NCH2C6H2]; 3.96 [d, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.09 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.79 [d, 1H, J = 8.0 Hz, ArCH]; 5.95 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.10 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.68 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.92 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.97 [s, 1H, Ar-CH]; 7.02 [t, 1H, J = 8.0 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, Ar-CH]. 13C NMR (d, CDCl3): 16.7, 20.7, 49.2, 49.9, 50.7, 59.2, 71.9, 72.2, 111.1, 111.5, 122.3, 122.8, 122.9, 124.0, 125.6, 132.3, 134.3, 135.0, 135.9, 136.0, 148.4, 148.8, 186.1. Anal. Calc. for C30H38ClN3OPd (598.51): C, 60.20; H, 6.40; N, 7.02. Found: C, 59.93; H, 6.22; N, 6.74%.Compound 2c: Yield: 0.098 g, 64%, m.p.: 208–209 °C. 1H NMR (d, CDCl3): 2.14 [s, 6H, (CH3)3C6H2]; 2.16 [s, 6H, (CH3)3C6H2]; 2.23 [s, 3H, (CH3)3C6H2]; 2.75 [s, 3H, CH2N(CH3)2]; 2.78 [s, 3H, CH2N(CH3)2]; 3.27 [s, 3H, CH2CH2OCH3]; 3.63 [d, 2H, J = 12.0 Hz, NCH2C6H2]; 3.89 [d, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.08 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.79 [d, 1H, J = 8.0 Hz, Ar-CH]; 5.94 [d, 1H, J = 8.0 Hz, ArCH]; 6.09 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.68 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.94 [m, 1H, Ar-CH]; 7.03 [t, 1H, J = 8.0 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, Ar-CH]. 13C NMR (d, CDCl3): 16.8, 17.1, 17.5, 49.3, 49.7, 50.4, 50.7, 59.9, 71.6, 71.8, 111.0, 111.2, 122.0, 122.5, 122.7, 123.7, 128.5, 132.8, 134.3, 134.8, 135.4, 135.6, 135.8, 148.1, 148.6, 185.8. Anal. Calc. for C31H40ClN3OPd (612.54): C, 60.78; H, 6.58; N, 6.86. Found: C, 59.76; H, 6.37; N, 6.61%. [24] 1H and 13C NMR measurements were performed using a Varian Mercury 400 spectrometer operating at 400 and 100 MHz, respectively. NMR multiplicities are abbreviated as follows: s, singlet; d, doublet; t, triplet; sept., septet; m, multiplet; br., broad; signal. Coupling constants J are given in Hz. The FT-IR spectra of solid complexes were recorded on a Varian 900 FT-IR spectrometer. The solid sample was measured as a KBr pellet in the 4000–400 cm1 spectral range. Melting points were measured in open capillary tubes with an Electrothermal-9200 melting point apparatus. Elemental analyses were performed by TUBITAK (Ankara, Turkey) Microlab. [25] (a) S. Iyer, A. Jayanthi, Synlett 8 (2003) 1125; (b) A.G. Gökçe, M.E. Günay, M. Aygün, B. Çetinkaya, O. Büyükgüngör, J. Coord. Chem. 60 (2007) 805. [26] Diffraction data for 2a and 2c were collected on a STOE IPDS II 414 diffractometer using graphite-monochromated Mo Ka radiation 415 (k = 0.71073 Å) at 296 K. 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Stoe & Cie, Darmstadt, Germany, 2002]; molecular graphics: ORTEP-3 for Windows [L.J. Farrugia, J. Appl.
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
New (j2-C,N)-palladacyclic complexes with benzimidazol-2-ylidene ligand: Synthesis, crystal structures and characterization M. Emin Günay a,*, Rukiye Gümüsßada a, Namık Özdemir b, Muharrem Dinçer b, Bekir Çetinkaya c a
Department of Chemistry, Adnan Menderes University, 09010 Aydın, Turkey Department of Physics, Ondokuz Mayıs University, 55139 Kurupelit-Samsun, Turkey c Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey b
a r t i c l e
i n f o
Article history: Received 14 June 2009 Accepted 1 August 2009 Available online 7 August 2009 Keywords: Palladacycles N-heterocyclic carbene Unsymmetrical benzimidazolium salt Crystal structure
a b s t r a c t Reaction of unsymmetrical benzimidazolium bromides (1) with Ag2O and subsequent transmetallation with chloro-bridged dinuclear palladacycle, [Pd(dmba)(l-Cl)]2 (dmba: N,N-dimethylbenzylamine) afforded benzannulated monocarbene complexes [Pd(dmba)(NHC)Cl], 2. The palladacycles (2a–c) were characterized by elemental analysis; NMR spectroscopy and the molecular structure of 2a and 2c were determined by X-ray crystallography. Ó 2009 Elsevier B.V. All rights reserved.
Palladacycles have been known for over 30 years [1–4]. They are intensively studied classes of organopalladium derivatives, primarily due to their easy synthetic accessibility, structural versatility and intriguing applications in organic synthesis, organometallic catalysis, and new molecular materials. In particular, most of carbon–carbon bond forming reactions such as Heck reaction, Stille reaction, Suzuki reaction and other C–C couplings are palladium catalyzed [5–7]. In the C–C bond formation reactions, the role of palladacycle moiety has been proposed to release Pd(0), through a slow process which helps to suppress the nucleation and growth of inactive palladium metal particles [3]. On the other hand, in recent years, the uses of N-heterocyclic carbene (NHC) ligands over various metals have been applied in organometallic chemistry and catalysis [8–10]. In addition, the combination of a palladacycle framework with an NHC was reported by Herrmann [11–13], and others [14,15]. However, to the best of our knowledge, there have been only a few examples of spectroscopically characterized cyclometalated NHC–Pd(II) complexes reported [16,17]. For the present study, we selected the unsymmetrical alkyl substituted benzimidazol-2-ylidene precursor as N-heterocyclic carbene ligand. This choice was guided by several conditions. An important characteristic of the carbene ligands in active complexes is their strong electron donating effect. As a matter of fact, benzimidazol-2-ylidenes have structures reminiscent of imidazole-2ylidenes, but spectroscopic properties and reactivity which are * Corresponding author. Tel.: +90 256 212 8498; fax: +90 256 213 5379. E-mail address: [email protected] (M. Emin Günay). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.08.001
close to saturated imidazole-2-ylidenes [18–20]. However, modifications and overall synthesis of benzimidazol-2-ylidenes are more facile than imidazol(in)-2-ylidenes. Furthermore, methoxyethyl and methylated benzyl substituents have been reported to display enhanced activity [18]. In this work, we describe a practical approach to NHC-ligated palladacycles by carbene transfer from a silver N-heterocyclic carbene precursor to [Pd(dmba)(l-Cl)]2 in room temperature in dichloromethane. The general route to the target NHC ligand precursors and palladacyclic complexes is shown in Scheme 1. The methylated benzyl bromides were synthesized according to the methods previously known [21]. The introduction of the 2-chloroethyl methyl ether substituent into the benzimidazole was achieved by direct alkylation in DMSO. The resulting 1-alkylbenzimidazole can be alkylated to give 1a–c. These salts were purified by recrystallization from EtOH/Et2O. The IR data for unsymmetrical benzimidazolium salts clearly indicate the presence of the –C@N– group with a mC@N stretching vibration between 1553 and 1563 cm1. These benzimidazolium salts have been characterized by 1H and 13 C NMR spectroscopy. 1H NMR chemical shifts were consistent with the proposed structures; the resonances for C2-hydrogens were observed as sharp singlet between 9.88 and 10.46 ppm. 13C NMR of these salts showed the C2 carbon at 141.9–142.8 ppm. The benzylic protons appeared as singlet between 5.78 and 6.91 ppm. The in situ reaction of the Ag–NHC complexes with the [Pd(dmba)(l-Cl)]2 in dichloromethane resulted in the NHC-ligated palladacyclic compound as a crystalline solid [22,23]. The pallada-
M. Emin Günay et al. / Inorganic Chemistry Communications 12 (2009) 990–993
991
N Ar
Pd
N +
(i)
Br-
N
Cl N
Ar
N O
CH3 O
CH3
1a-c
2a-c
a
b
c
Ar
Scheme 1. Reagents and conditions: (i) DCM, Ag2O, 3 h, RT, then [Pd(dmba)(l-Cl)]2, 24 h, RT.
cyclic complexes, which are very stable in the solid state, were characterized by analytical and spectroscopic techniques [24]. The C2 carbons were found to be shifted downfield in the 13C NMR spectra of the complexes. The chemical shifts for the carbene carbon atom (2a–c) fall in the range d 185.8–186.1 ppm. A brief inspection of literature indicates that in the square-planar complexes, [PdCl(dmba)(NHC)] formed between a NHC and [Pd(dmba)(l-Cl)]2, the NHC ligand might be bonded to Pd atom either trans to ortho-carbon or NMe2 of the dmba moiety [25]. The spectroscopic information obtained above did not allow us to distinguish these possibilities. Therefore, X-ray structure determination was required [26] and the structure of the complexes 2a and 2c are shown in Figs. 1 and 2, respectively. Selected bond lengths and angles are listed in the caption of figures. These complexes contain a benzimidazole ligand with a PdII metal centre, an N,N-dimethyl-1-phenylmethanamine ligand and one chlorine ligand. The coordination around the PdII ion is distorted cis-square-planar, and the PdII ion is coordinated by one amine N atom and one aryl C
Fig. 1. A view of the complex (2a), showing 40% probability displacement ellipsoids and the atom-numbering scheme. Pd1–C1 1.968 (4), Pd1–C21 1.979 (4), Pd1–N3 2.136 (3), Pd1–Cl1 2.4417 (9), O1–C9 1.385 (6), O1–C10 1.422 (8), N1–C1 1.352 (4), N1–C2 1.395 (4), N1–C11 1.470 (4), N2–C1 1.359 (4), N2–C7 1.389 (5), N2–C8 1.459 (5), N3–C28 1.470 (6), N3–C29 1.477 (5), N3–C27 1.489 (6), C8–C9 1.526 (7), C11– 0 C12 1.516 (5) Å A, C1–Pd1–C21 92.74 (15), C1–Pd1–N3 175.59 (13), C21–Pd1–N3 82.87 (15), C1–Pd1–Cl1 89.60 (10), C21–Pd1–Cl1 177.02 (11), N3–Pd1–Cl1 94.81 (10), C9–O1–C10 112.0 (6), C1–N1–C2 110.5 (3), C1–N1–C11 125.8 (3), C2–N1–C11 123.3 (3), C10–O1–C9–C8 175.0 (5), C1–N2–C7 110.5 (3), C1–N2–C8 124.0 (3), C7– N2–C8 125.0 (3), C28–N3–C29 108.0 (4), C28–N3–C27 109.4 (4), C29–N3–C27 109.6 (4), N1–C1–N2 106.4 (3), N2–C8–C9 109.1 (3), O1–C9–C8 107.3 (4), N1–C11–C12 114.8 (3), N2–C8–C9–O1 177.4 (4)°.
Fig. 2. A view of the complex (2c), showing 40% probability displacement ellipsoids and the atom-numbering scheme. Pd1–C1 1.965 (4), Pd1–C31 1.986 (5), Pd1–N3 2.141 (4), Pd1–Cl1 2.4508 (10), O1–C10 1.391 (8), O1–C9 1.404 (7), N1–C1 1.361 (5), N1–C2 1.381 (5), N1–C11 1.478 (5), N2–C1 1.359 (5), N2–C7 1.388 (5), N2–C8 1.460 (6), N3–C24 1.473 (6), N3–C25 1.477 (7), N3–C23 1.485 (6), C8–C9 1.501 (8), C11– 0 C12 1.518 (6) Å A, C1–Pd1–C31 92.99 (18), C1–Pd1–N3 175.59 (16), C31–Pd1–N3 82.69 (17), C1–Pd1–Cl1 89.23 (12), C31–Pd1–Cl1 175.75 (12), N3–Pd1–Cl1 95.02 (12), C10–O1–C9 111.8 (5), C1–N1–C2 111.0 (3), C1—N1–C11 124.7 (3), C2–N1–C11 124.0 (3), C10–O1–C9–C8 176.3 (5), C1–N2–C7 110.7 (3), C1–N2–C8 123.8 (4), C7– N2–C8 125.4 (4), C24–N3–C25 109.7 (4), C24–N3–C23 107.9 (4), C25–N3–C23 108.9 (4), N2–C1–N1 105.8 (3), N2–C8–C9 112.9 (4), O1–C9–C8 109.7 (4), N1–C11– C12 114.4 (3), N2–C8–C9–O1 66.3 (5)°.
atom from the bidentate ligand, one carbenic C atom from the monodentate ligand, and one Cl atom. The Pd–Cl and Pd–Ccarbene distances are 2.4417 (9) and 1.968 (4) Å for complex (2a) and 2.4508 (10) and 1.965 (4) for complex (2c), respectively. When these bonds are compared with those observed in the literature, it is seen that the Pd–Ccarbene distance is at the lower end of the reported range 1.966–1.996 Å [14,25b,27]. However, the Pd–Cl bond in the complex is somewhat longer than the range observed in the literature (2.379–2.424 Å) [14]. Similar to the complex 2c, the bonding within the N-heterocyclic carbene (NHC) ring indicates a pattern of delocalization that extends from atom N1 to atom N2 through atom C1, the N1–C1 [1.352 (4) Å] and N2–C1 [1.359 (4) Å] distances being significantly shorter than the N1–C2 [1.395 (4) Å] and N2–C7 [1.389 (5) Å] distances as is in similar NHC transition metal complexes [28–30]. These observations in complex 2a and 2c are possibly indicative of a greater partial double-bond character due to partial electron donation by nitrogen to the carbene C-atom donor [31,32]. Theoretical studies also indicate that the stability of these carbenes is due to electron donation from the N-atom lone pairs into the formally empty p(p) orbital on the carbene C atom (herein C1) [33]. The two coordinated C atoms in both complexes are cis to each other, which is in agreement with the fact that the donor groups with the largest trans influence avoid being mutually trans to one another. The change in geometrical parameters due to the difference of the monodentate NHC ligand, does not seem to significantly affect the coordination to the palladium(II) centre. The single-crystal data and X-ray collection parameters are given in Table 1. We have synthesized and characterized novel air- and moisture-stable palladacyclic complexes containing unsymmetrical benzimidazol-2-ylidene prepared by via Ag–NHC intermediate in situ, using the chloro-bridged palladacycle. The structures of 2a and 2c were determined by X-ray analysis. These complexes show a characteristic distorted cis-square-planar Pd(II) center with the carbene and dimethylamino ligands mutually trans to each other and the plane of the benzimidazole ring and the squareplane involving the palladacycle are close to perpendicular.
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Table 1 Summary of X-ray crystallographic data for complex 2a and 2c. Parameter
2a
2c
Empirical formula Crystal size (mm) Mr T (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) a (o) b (o) c (o) V (Å3) Z qcalcd (Mg/m3) l (mm1) h Range (°) Index ranges
C29H36ClN3OPd 0.72 0.35 0.15 584.46 296 0.71073 Monoclinic P21/c 8.4623 (3) 15.5152 (7) 21.0184 (7) 90 96.283 (3) 90 2743.0 (2) 4 1.415 0.80 1.6–26.8 10 h 10, 19 k 19, 26 l 26 20,673 5830 322 1.05 1.33, 0.68 0.0450, 0.1334 0.0535, 0.1388
C31H40ClN3OPd 0.32 0.28 0.23 612.51 296 0.71073 Monoclinic P21/c 8.9470 (3) 15.8440 (4) 20.5998 (8) 90 100.945 (3) 90 2867.03 (16) 4 1.419 0.77 1.6–26.8 11 h 11, 20 k 16, 26 l 25 15,970 5990 334 1.06 1.63, 0.71 0.0490, 0.1504 0.0623, 0.1577
Number of measured reflections Number of independent reflections Number of parameters Goodness-of-fit (GOF) on F2 Maximum/minimum Dq (e Å3) R, wR (observed data)a R, wR (all data)a a
Refinement method, full-matrix least squares on F2.
Acknowledgments Funding of our research from the TUBITAK (Project No.: 104T 203), Adnan Menderes University (Project Nos.: FEF-07006, FEF07013 and FBE-08001) and Ondokuz Mayıs University (Project No.: F-461) is gratefully acknowledged.
Appendix A. Supplementary material CCDC 728280 and 728281 contain the supplementary crystallographic data for 2a and 2c. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.08.001.
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General procedure: The benzimidazolium salt (0.50 mmol) was dissolved in 10 mL CH2Cl2 and Ag2O (0.25 mmol) was added. The resulting black suspension was stirred for 3 h at RT, only a voluminous light grey precipitate remained, followed by addition of [Pd(dmba)(l-Cl)]2 (0.25 mmol). The reaction mixture was stirred for 24 h at RT and then was filtered. The CH2Cl2 removed in vacuo, and the residue was washed with Et2O. The crude product was recrystallized from CH2Cl2/Et2O. [23] Compound 2a: Yield: 0.101 g, 69%, m.p.: 229–230 °C. 1H NMR (d, CDCl3): 2.19 [s, 6H, o-(CH3)3C6H2]; 2.24 [s, 3H, p-(CH3)3C6H2]; 2.80 [s, 3H, CH2N(CH3)2]; 2.82 [s, 3H, CH2N(CH3)2]; 3.26 [s, 3H, CH2CH2OCH3]; 3.65 [d, 2H, J = 12 Hz, NCH2C6H2]; 4.02 [t, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.10 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.70 [d, 1H, J = 8.0 Hz, ArCH]; 5.89 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.07 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.69 [td, 1H, J = 8.0 Hz, Ar-CH]; 6.79 [s, 2H, Ar-CH]; 6.91 [m, 1H, Ar-CH]; 7.05 [t, 1H, J = 7.6 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, ArCH]. 13C NMR (d, CDCl3): 20.8, 20.9, 48.9, 49.6, 49.7, 50.6, 58.9, 71.7, 72.0, 110.8, 111.3, 122.1, 122.6, 122.8, 123.7, 125.4, 128.2, 129.3, 134.6, 135.6, 135.8, 137.9, 138.4, 148.1, 148.5, 186.0. Anal. Calc. for C29H36ClN3OPd (584.48): C, 59.59; H, 6.21; N, 7.19. Found: C, 58.41; H, 5.96; N, 6.99%.Compound 2b: Yield: 0.060 g, 40%, m.p.: 201–202 °C. 1H NMR (d, CDCl3): 2.11 [s, 6H, (CH3)3C6H2]; 2.17 [s, 6H, (CH3)3C6H2]; 2.76 [s, 3H, CH2N(CH3)2]; 2.80 [s, 3H, CH2N(CH3)2]; 3.26 [s, 3H, CH2CH2OCH3]; 3.65 [d, 2H, J = 12.0 Hz, NCH2C6H2]; 3.96 [d, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.09 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.79 [d, 1H, J = 8.0 Hz, ArCH]; 5.95 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.10 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.68 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.92 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.97 [s, 1H, Ar-CH]; 7.02 [t, 1H, J = 8.0 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, Ar-CH]. 13C NMR (d, CDCl3): 16.7, 20.7, 49.2, 49.9, 50.7, 59.2, 71.9, 72.2, 111.1, 111.5, 122.3, 122.8, 122.9, 124.0, 125.6, 132.3, 134.3, 135.0, 135.9, 136.0, 148.4, 148.8, 186.1. Anal. Calc. for C30H38ClN3OPd (598.51): C, 60.20; H, 6.40; N, 7.02. Found: C, 59.93; H, 6.22; N, 6.74%.Compound 2c: Yield: 0.098 g, 64%, m.p.: 208–209 °C. 1H NMR (d, CDCl3): 2.14 [s, 6H, (CH3)3C6H2]; 2.16 [s, 6H, (CH3)3C6H2]; 2.23 [s, 3H, (CH3)3C6H2]; 2.75 [s, 3H, CH2N(CH3)2]; 2.78 [s, 3H, CH2N(CH3)2]; 3.27 [s, 3H, CH2CH2OCH3]; 3.63 [d, 2H, J = 12.0 Hz, NCH2C6H2]; 3.89 [d, 2H, J = 12.0 Hz, NCH2N(CH3)2]; 4.08 [m, 2H, NCH2CH2OCH3]; 4.95 [m, 2H, NCH2CH2OCH3]; 5.79 [d, 1H, J = 8.0 Hz, Ar-CH]; 5.94 [d, 1H, J = 8.0 Hz, ArCH]; 6.09 [d, 1H, J = 8.0 Hz, Ar-CH]; 6.68 [t, 1H, J = 8.0 Hz, Ar-CH]; 6.94 [m, 1H, Ar-CH]; 7.03 [t, 1H, J = 8.0 Hz, Ar-CH]; 7. 21 [t, 1H, J = 8.0 Hz, Ar-CH]; 7.54 [d, 1H, J = 8.0 Hz, Ar-CH]. 13C NMR (d, CDCl3): 16.8, 17.1, 17.5, 49.3, 49.7, 50.4, 50.7, 59.9, 71.6, 71.8, 111.0, 111.2, 122.0, 122.5, 122.7, 123.7, 128.5, 132.8, 134.3, 134.8, 135.4, 135.6, 135.8, 148.1, 148.6, 185.8. Anal. Calc. for C31H40ClN3OPd (612.54): C, 60.78; H, 6.58; N, 6.86. Found: C, 59.76; H, 6.37; N, 6.61%. [24] 1H and 13C NMR measurements were performed using a Varian Mercury 400 spectrometer operating at 400 and 100 MHz, respectively. NMR multiplicities are abbreviated as follows: s, singlet; d, doublet; t, triplet; sept., septet; m, multiplet; br., broad; signal. Coupling constants J are given in Hz. The FT-IR spectra of solid complexes were recorded on a Varian 900 FT-IR spectrometer. The solid sample was measured as a KBr pellet in the 4000–400 cm1 spectral range. Melting points were measured in open capillary tubes with an Electrothermal-9200 melting point apparatus. Elemental analyses were performed by TUBITAK (Ankara, Turkey) Microlab. [25] (a) S. Iyer, A. Jayanthi, Synlett 8 (2003) 1125; (b) A.G. Gökçe, M.E. Günay, M. Aygün, B. Çetinkaya, O. Büyükgüngör, J. Coord. Chem. 60 (2007) 805. [26] Diffraction data for 2a and 2c were collected on a STOE IPDS II 414 diffractometer using graphite-monochromated Mo Ka radiation 415 (k = 0.71073 Å) at 296 K. The structures were solved by direct-methods using program SHELXS-97 [G.M. Sheldrick, SHELXS-97: Program for the Solution of Crystal Structure, University of Göttingen, Göttingen, Germany, 1997]. All nonhydrogen atoms were refined anisotropically by full-matrix least-squares methods using program SHELXL-97 [G.M. Sheldrick, SHELXL-97: Program for the Refinement of Crystal Structure, University of Göttingen, Göttingen, Germany, 1997]. All hydrogen atoms were positioned geometrically and treated using a riding model, fixing the bond lengths at 0.96, 0.97 and 0.93 Å for CH3, CH2 and aromatic CH, respectively. The displacement parameters of the H atoms were constrained as Uiso(H) = 1.2Ueq (1.5Ueq for methyl) of the carrier atom. Data collection: X-AREA [G.M. Sheldrick, SHELXS-97: Program for the Solution of Crystal Structure, University of Göttingen, Göttingen, Germany, 1997]; cell refinement: X-AREA; data reduction: X-RED32 [Stoe & Cie. X-AREA (Version 1.18) and X-RED32 (Version 1.04). Stoe & Cie, Darmstadt, Germany, 2002]; molecular graphics: ORTEP-3 for Windows [L.J. Farrugia, J. Appl.
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