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Organometallics 2009, 28, 5590–5592 DOI: 10.1021/om900398h
An Arene-Mercury(II) N-Heterocyclic Carbene Complex Yongsheng Liu, Xiangjian Wan, and Fengbo Xu* State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China Received May 15, 2009 Summary: Reaction of a carbene precursor containing an anthracene fluorophore and two N-picolyl moieties with Hg(OAc)2 produces the title complex. X-ray studies and UV-vis and fluorescence spectroscopy confirm that a strong interaction exists between the mercury atom and anthracene.
Since the discovery of the first stable N-heterocyclic carbenes (NHCs),1 increasing attention has been focused on these compounds as ancillary ligands for organometallic chemistry and homogeneous catalysis.2 A large number of transition-metal complexes with these special types of carbene ligands have been synthesized.2,3 Recently, polydentate ligands based on NHCs containing pyridine have attracted great attention.4-6 *To whom correspondence should be addressed. E-mail: xufb@ nankai.edu.cn. (1) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1992, 113, 361–363. (2) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1291–1309. (b) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39–91. (c) Herrmann, W. A.; K€ocher, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2162–2187. (3) (a) Jazzar, R. F. R.; Macgregor, S. A.; Mahon, M. F.; Richards, S. P.; Whittlesey, M. K. J. Am. Chem. Soc. 2002, 124, 4944–4945. (b) Grundemann, S.; Albrecht, M.; Kovacevic, A.; Faller, J. W.; Crabtree, R. H. Dalton Trans. 2002, 2163–2167. (c) Caddick, S.; Cloke, F. G. N.; Hitchcock, P. B.; Leonard, J.; Lewis, A. K. d. K.; McKerrecher, D.; Titcomb, L. R. Organometallics 2002, 21, 4318–4319. (d) Kaur, H.; Zinn, K.; Stevens, E. D.; Nolan, S. P. Organometallics 2004, 23, 1157–1160. (e) Clement, N. D.; Cavell, K. J. Angew. Chem., Int. Ed. 2004, 43, 3845–3847. (4) (a) Lee, K. M.; Chen, J. C. C.; Lin, I. J. B. J. Organomet. Chem. 2001, 617–618. (b) Son, S. U.; Park, K. H.; Lee, Y. S.; Kim, B. Y.; Choi, C. H.; Lah, M. S.; Jang, Y. H.; Jang, D. J.; Chung, Y. K. Inorg. Chem. 2004, 43, 6896–6898. (c) Catalano, V. J.; Malwitz, M. A.; Etogo, A. O. Inorg. Chem. 2004, 43, 5714–5724. (d) Chen, J. C. C.; Lin, J. B. Organometallics 2000, 19, 5113–5121. (e) Loch, J. A.; Albrecht, M.; Peris, E.; Mata, J.; Faller, J. W.; Crabtree, R. H. Organometallics 2002, 21, 700–706. (f) Poyatos, M.; Mata, J. A.; Falomir, E.; Crabtree, R. H.; Peris, E. Organometallics 2003, 22, 1110– 1114. (g) McGuinness, D. S.; Gibson, V. C.; Steed, J. W. Organometallics 2004, 23, 6288–6292. (h) Danopoulos, A. A.; Tsoureas, N.; Wright, J. A.; Light, M. E. Organometallics 2004, 23, 166–168. (i) Danopoulos, A. A.; Wright, J. A.; Motherwell, W. B. Chem. Commun. 2005, 784–786. (5) (a) Garrison, J. C.; Simons, R. S.; Talley, J. M.; Wesdemiotis, C.; Tessier, C. A.; Youngs, W. J. Organometallics 2001, 20, 1276–1278. (b) Baker, M. V.; Skelton, B. W.; White, A. H.; Williams, C. C. Organometallics 2002, 21, 2674–2678. (c) Garrison, J. C.; Simons, R. S.; Tessier, C. A.; Youngs, W. J. J. Organomet. Chem. 2003, 673, 1–4. (d) Baker, M. V.; Brown, D. H.; Haque, R. A.; Skelton, B. W.; White, A. H. Dalton Trans. 2004, 3756–3764. (e) Durmus, S.; Garrison, J. C.; Panzner, M. J.; Tessier, C. A.; Youngs, W. J. Tetrahedron 2005, 61, 97–101. (6) (a) Tulloch, A. A. D.; Danopoulos, A. A.; Kleinhenz, S.; Light, M. E.; Hursthouse, M. B.; Eastham, G. Organometallics 2001, 20, 2027– 2031. (b) Wang, X.; Liu, S.; Jin, G. X. Organometallics 2004, 23, 6002– 6007. (c) Chianese, A. R.; Kovacevic, A.; Zeglis, B. M.; Faller, J. W.; Crabtree, R. H. Organometallics 2004, 23, 2461–2468. (7) (a) Lang, H.; Kohler, K.; Blau, S. Coord. Chem. Rev. 1995, 143, 113–168. (b) Berger, A.; Djukic, J. P.; Michon, C. Coord. Chem. Rev. 2002, 225, 215–238. (c) Stepien, M.; Latos-Grazynski, L.; Szterenberg, L.; Panek, J.; Latajka, Z. J. Am. Chem. Soc. 2004, 126, 4566–4580. pubs.acs.org/Organometallics
Published on Web 08/26/2009
Although many arene-metal complexes have been reported,7,8 arene-mercury(II) complexes based on NHC ligands whose structures have been determined by singlecrystal X-ray diffraction methods are still very few.9 In 2003, we reported the first Au(I)-arene complex, which is formed by the reaction of the chelated diphosphine ligand 9,10-bis[N-n-propyl-N-(diphenylphosphino)aminomethyl]anthracene with Auþ ion and adopts a η6 coordination mode.10 We recently presented a series of Au(I)-η2-arene complexes using phosphine ligands.11 In order to understand the chemistry of mercury carbene complexes deeply and to gain an insight into the interaction of mercury with arene, herein we present the synthesis and X-ray structure of an arenemercury(II) complex based on an N-heterocyclic carbene ligand containing two N-picolyl moieties.
Results and Discussion The carbene ligand precursor 9,10-bis[3-(2-pyridylmethyl)imidazolium-1-ylmethyl]anthracene bis(hexafluorophosphate) (L) was prepared according to an established procedure.12 Reaction of the precursor L with Hg(OAc)2 in a 1:1 molar ratio in CH3CN gave the complex LHg (Scheme 1). Diffusion of diethyl ether into an acetonitrile and chlorobenzene solution of LHg afforded yellow crystals of LHg, which were stable in the air and easily soluble in acetonitrile and acetone. In the 1H NMR spectrum of LHg, the carbenium proton resonance disappeared. The peak for the Hg-carbene carbon in the 13C NMR spectrum appeared at 171.0 ppm, which is characteristic for a metal carbene signal. The molecular structure of LHg in the solid state is depicted in Figure 1. The crystal data and selected bond angles and distances are given in Tables 1 and 2, respectively. It is interesting that the whole molecule of LHg possesses a butterfly shape. The mercury(II) center is bound to two carbene ligands and two pyridines. The geometry at the Hg atom coordinating with two 2-carbene carbons is nearly linear, with a C-Hg-C bond angle of 176.1(2)°. The distances between the Hg atom and two carbene carbons, (8) (a) Mascal, M.; Kerdelhue, J. L.; Blake, A. J.; Cooke, P. A. Angew. Chem., Int. Ed. 1999, 38, 1968–1970. (b) Xu, F. B.; Weng, L. H.; Sun, L. J.; Zhang, Z. Z. Organometallics 2000, 19, 2658–2660. (c) Masson, E.; Schlosser, M. Org. Lett. 2005, 7, 1923–1925. (9) (a) Atwood, J. L.; Berry, D. E.; Stobart, S. R.; Zaworotko, M. J. Inorg. Chem. 1983, 22, 3480–3482. (b) H€orner, M.; Bortoluzzi, A. J.; Beck, J.; Serafin, M. Z. Anorg. Allg. Chem. 2002, 628, 1104–1107. (10) Xu, F. B.; Li, Q. S.; Wu, L. Z.; Leng, X. B.; Li, Z. C.; Zeng, X. S.; Chow, Y. L.; Zhang, Z. Z. Organometallics 2003, 22, 633–640. (11) Li, Q. S.; Wan, C. Q.; Zou, R. Y.; Xu, F. B.; Song, H. B.; Wan, X. J.; Zhang, Z. Z. Inorg. Chem. 2006, 45, 1888–1890. (12) Liu, Y. S.; Xu, F. B.; Wang, J. W.; Li, Q. S.; Song, H. B.; Zhang, Z. Z. Acta Crystallogr. 2005, E61, o2930–o2931. r 2009 American Chemical Society
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Table 1. Crystal Data and Structure Refinement Details for LHg
Figure 1. Perspective view of LHg and anisotropic displacement parameters depicting 30% probability. Hydrogen atoms have been omitted for clarity. Scheme 1
empirical formula C34H28F12HgN6P2 fw 1011.15 temp (K) 294(2) wavelength (A˚) 0.710 73 cryst syst triclinic space group P1 a (A˚) 10.0653(11) b (A˚) 11.0378(12) c (A˚) 17.9109(19) R (deg) 87.198(2) β (deg) 89.665(2) γ (deg) 63.944(2) 3 1785.2(3) V (A˚ ) Z 2 1.881 calcd density (Mg/m3) -1 4.500 abs coeff (mm ) F(000) 984 cryst size (mm) 0.24 0.20 0.16 2.06, 26.45 θmax, θmin (deg) no. of data collected 10 163 no. of unique data 7202 no. of refined params 486 1.057 goodness of fit on F2a b final R indices (I > 2σ(I)) R1 0.0482 wR2 0.1237 R indices (all data) R1 0.0593 wR2 0.1327 P a 1/2 2 2 2 GOF = { [w(Fo - Fc ) /(n - p)] , where n is the number of reflections and P p is the number of parameters refined. b R1 = P (||Fo| - |Fc||)/ |Fo|; wR2 = 1/[σ2(Fo2) þ (0.0842P)2 þ 2.6172P], where P=(Fo2 þ 2Fc2)/3.
Table 2. Selected Bond Distances (A˚) and Angles (deg) for LHg Bond Lengths
Hg(1)-C(18) and Hg(1)-C(28), are 2.102(7) and 2.107(7) A˚, respectively, which are shorter than those of the Hg atom and two pyridine nitrogen with distances Hg(1)-N(1)=2.670(6) A˚ and Hg(1)-C(N6)=2.590(7) A˚. The two pyridine rings tilt from the associating imidazolium rings by angles of 60.9 and 57.8°, respectively. The two pyridine rings are perpendicular to each other, while the two trans imidazolium ring planes are twisted by an angle of 25.3° to each other. The planes through the anthracene ring systems form dihedral angles of 91.2 and 114.3°, respectively, with two imidazolium ring planes. Such a coordination mode leads to a remarkable structural change in the anthracene ring. For the four binding sites coordinating with mercury at the same time, the 9,10-carbon atoms of the anthracene ring are remarkably bent toward the metal core, out of the coplanar configuration, and form dihedral angles of 11.1° between the side benzene rings in the anthracenyl units. The distances of the mercury ion to the six carbon atoms of the middle ring in anthracene are observed as follows: Hg(1)-C(1)=3.255 A˚, Hg(1)-C(2) = 3.572 A˚, Hg(1)-C(7) = 3.521 A˚, Hg(1)C(8) = 3.218 A˚, Hg(1)-C(9) = 3.193 A˚, Hg(1)-C(14) = 3.178 A˚. The distance of the Hg atom to the centroid of the anthracene is 3.129 A˚, which is within the sum of the van der Waals radii of carbon and mercury (3.25 A˚). This distribution of the Hg-C distances shows incipient η6 (13) Lau, W.; Huffman, J. C.; Kochi, J. K. J. Am. Chem. Soc. 1982, 104, 5515–5517. (14) (a) Kamenar, B.; Penavic, M. Inorg. Chim. Acta 1972, 6, 191–194. (b) Canty, A. J.; Chaichit, N.; Gatehouse, B. M. Acta Crystallogr., Sect. B 1980, B36, 786–789. (c) Lampe, P. A.; Moore, P. Inorg. Chim. Acta 1979, 36, 27–30.
Hg(1)-C(18) Hg(1)-C(28) Hg(1)-N(6)
2.102(7) 2.107(7) 2.590(7)
Hg(1)-N(1) N(1)-C(24) N(1)-C(20)
2.670(6) 1.339(11) 1.345(10)
Bond Angles C(18)-Hg(1)-C(28) C(18)-Hg(1)-N(6) C(28)-Hg(1)-N(6)
176.1(2) 97.5(2) 83.7(3)
C(18)-Hg(1)-N(1) C(28)-Hg(1)-N(1) N(6)-Hg(1)-N(1)
85.0(3) 98.7(2) 87.6(2)
coordination,8,13,14 which is comparable to that of the reported arene-metal complex.8 The ligand L, as a tetradentate coordinating unit, can easily clutch the mercury(II) ions; that capacity should be credited to its two N-carbene functions to chelate the metal over the space above the anthracene π-face. Thus, a mercury-π interaction, which is enforced by the ligand structure, is observed. UV-vis and fluorescence spectroscopy has been employed to confirm the interaction of arene and mercury(II). The absorption spectrum (Figure 2a) showed that LHg possessed the L type absorption pattern (essentially an anthracene type)10,15,16 with a redshift of 4 nm. The red shift of absorption spectrum of LHg compared to that of L is probably a consequence of the shorter Hg-anthracene centroid distance, which destroys the original rigid anthracene (15) (a) Fages, F.; Desvergne, J. P.; Bouas-Laurent, H.; Marsau, P.; Lehn, J. M.; Kotzyba-Hibert, F.; Albrecht-Gary, A. M.; Al-Joubbeh, M. J. Am. Chem. Soc. 1989, 111, 8672–8680. (b) Desvergne, J. P.; Fages, F.; Bouas-Laurent, H.; Marsau, P. Pure Appl. Chem. 1992, 62, 1231–1238. (c) Ishikawa, J.; Sakamoto, H.; Nakao, S.; Wada, H. J. Org. Chem. 1999, 64, 1913–1921. (16) Fages, F.; Desvergne, J. P.; Bouas-Laurent, H. J. Am. Chem. Soc. 1989, 111, 96–102.
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groups and Hg(OAc)2. There exists a strong interaction between the mercury atom and anthracene, which has been confirmed by X-ray studies and UV-vis and fluorescence emission spectra.
Experimental Section
Figure 2. (a) UV-vis absorption and (b) emission spectra of L and LHg at 298 K in acetone (1.0 10-6 mol/L). Both the absorption and emission spectra data show that the main peak positions of LHg have a red shift of about 4 nm compared to that of L.
configuration and results in the bending of the two side benzene rings out of coplanarity (Figure 1). The absorption spectrum is obviously dominated by a ligand-to-metal charge transfer process.17,18 The fluorescence emission spectrum of LHg is shown in Figure 2b. In acetone, LHg shows an anthracene-type fluorescence emission at 370-550 nm similar to but weaker than that of the corresponding precursor L and a red shift of 4 nm was observed. This can be attributed to the ligand-to-metal charge transfer process.19
Conclusion We have prepared one butterfly-shaped molecule by reaction of a bis-carbene precursor containing two N-picolyl (17) Fages, F.; Desvergne, J. P.; Bouas-Laurent, H.; Marsau, P.; Lehn, J. M.; Kotzyba-Hibert, F.; Albrecht-Gary, A. M.; Al-Joubbeh, M. J. Am. Chem. Soc. 1989, 111, 8672–8680. (18) Xu, H.; Xu, F. B.; Li, Q. S.; Duo, W. G.; Song, H. B.; Zhang, Z. Z. Eur. J. Inorg. Chem. 2005, 2869–2874. (19) S€ ußner, M.; Plenio, H. Chem. Commun. 2005, 5417–5419.
General Procedure. The ligand L was prepared as reported in the literature by our group.12 All reactions were carried out under a dry nitrogen atmosphere using standard Schlenk techniques, unless stated otherwise. The solvents were purified by standard methods.20 The melting point was determined with an X-4 digital display micromelting point apparatus. 1H and 13C NMR spectra were recorded at 400 and 100 MHz, respectively, on a Varian Mercury Plus 400 spectrometer. Chemical shifts, δ, are reported in ppm relative to the internal standard TMS. J values are given in Hz. Elemental analyses were measured using a Yanaco MT-3 elemental analyzer. UV-vis spectra were obtained using a JASCO-V570 spectrometer. The fluorescence spectra were measured with a Cary Eclipse fluorescence spectrophotometer. {9,10-Bis[3-(2-pyridylmethyl)imidazolium-1-ylmethyl]anthracene}mercury(II) Bis(hexafluorophosphate) (LHg). A CH3CN solution (60 mL) of L(PF6) (500 mg, 0.62 mmol) and Hg(OAc)2 (196 mg, 0.62 mmol) was refluxed under N2 for 48 h. The solution was evaporated to dryness, and the residue was washed with water and diethyl ether. Recrystallization from CH3CN and diethyl ether (1:6, v/v) produced a yellow solid, which was filtered and dried under vacuum. Yield: 514 mg (82%). Mp: 256-259 °C. Anal. Calcd for C34H28F12HgN6P2: C, 40.39; H, 2.79; N, 8.31. Found: C, 40.11; H, 2.77; N, 8.25. 1H NMR (400 MHz, d6-DMSO): δ 5.09 (s, 4H, CH2), 6.85 (s, 4H, CH2), 7.10 (t, J= 12.1 Hz, 2H, CH), 7.22 (d, J=7.5 Hz, 2H, CH), 7.61 (t, J = 11.3 Hz, 8H, CH), 7.87 (s, 2H, CH), 8.10 (s, 2H, CH), 8.50-8.52 (m, 4H, CH). 13C NMR (100 MHz, d6-DMSO): δ 48.4, 55.1, 123.9, 124.6, 125.1, 125.4, 126.5, 126.7, 128.9, 132.2, 139.1, 149.0, 153.2, 171.0. X-ray Crystallography. A suitable crystal of LHg was mounted on a glass fiber in a random orientation. The structures were solved by direct methods, and all non-hydrogen atoms were subjected to anisotropic refinement by full-matrix least squares on F2 using the SHELXTL package. Data collection was performed at room temperature on a Bruker SMART 1000 CCD diffractometer operating at 50 kV and 20 mA using Mo KR radiation (0.710 73 A˚). An empirical absorption correction was applied using the SADABS program. All hydrogen atoms were generated geometrically (C-H bond lengths fixed at 0.96 A˚), assigned appropriate isotropic thermal parameters, and included in structure factor calculations. More details on data collection and structure calculation are summarized in Table 1.
Acknowledgment. We gratefully acknowledge the financial assistance provided by the National Natural Science Foundation of China (Project No. 20672055). Supporting Information Available: CIF file giving X-ray data for the complex LHg. This material is available free of charge via the Internet at http://pubs.acs.org. (20) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Elsevier Science: Burlington, 2003.
