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Structural characterization of the first linearly arranged Ag3 complexes supported by naphthyridine-functionalized N-heterocyclic carbenes
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Inorganic Chemistry Communications 11 (2008) 404–408 www.elsevier.com/locate/inoche
Structural characterization of the first linearly arranged Ag3 complexes supported by naphthyridinefunctionalized N-heterocyclic carbenes Jiansheng Ye a, Shouwen Jin a, Wanzhi Chen a,*, Huayu Qiu b,* b
a Department of Chemistry, Zhejiang University, Xixi campus, Hangzhou 310028, China Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, China
Received 30 November 2007; accepted 7 January 2008 Available online 19 January 2008
Abstract Reactions of the imidazolium salts with Ag2O afforded trinuclear silver complexes [Ag3(L)2(CH3CN)](PF6)3 (L = 2,7-bis(alkylimidazolylidenyl)naphthyridine), which have been characterized by NMR spectroscopy and X-ray diffraction analysis. The complexes consist of ˚ ). The linearly arranged Ag3 cores showing weak silver–silver interactions as evidenced by the short silver–silver contacts (3.10–3.24 A complexes are intensely emissive in their solid states. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Silver; Naphthyridine; N-heterocyclic carbene; Silver–silver interaction; Luminescence
Since Arduengo isolated the first free N-heterocyclic carbene (NHC), numerous transition metal complexes of NHC have been studied since M–NHC complexes have shown enhanced catalytic activities in many organic transformation processes [1]. Silver–NHC complexes are important since such complexes are often used as carbene transfer reagents for the preparation of other metal–imidazolylidene complexes avoiding the use of free carbenes which are not always easily available [2]. Some silver complexes or coordination polymers containing N-heterocyclic carbenes have been found unique physical properties and may be potentially useful in material science [3]. Furthermore, the antibacterial activities of these complexes have also been reported [4]. We are interested in the chemistry of heteroarene-functionalized N-heterocyclic carbene ligands because such bidentate or multidentate ligands containing both strong and weak donating atoms have shown good activities in *
Corresponding authors. Fax: +86 571 88273314 (W. Chen). E-mail address: [email protected] (W. Chen).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.01.010
homogeneous catalysis. For instance, a hemilabile pyrazolyl-functionalized N-heterocyclic carbene complex of palladium(II) is an excellent catalyst for Heck and Suzuki crosscoupling reactions in ionic liquids [5]. Pyridine-functionalized heterocyclic carbene complexes of palladium give rise to highly active and very stable catalysts for Heck, Suzuki, and Sonogashira coupling reactions, with turnover number of up to 1.7 106 being achieved [6]. Nickel complexes of pyridine-functionalized N-heteroccylic carbenes have also been proven to be efficient catalysts for C–C formation reactions under mild conditions [7,8]. In addition, the heteroarene-functionalized N-heterocyclic carbenes are able to construct multinuclear clusters having Ag–Ag interactions, which often show interesting luminescence properties. So far, a few trinuclear [8,9] and tetranuclear [10,11] silver clusters stabilized by functionalized NHCs have been reported. These silver clusters consist of triangular Ag3 or square Ag4 rings. The 1,8-naphthyridine bridge has a similar dimension to those of carboxylate and formamido bridges, and thus can be used as linkers for forming metal–metal-bonded units. Herein we report the preparation
J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
and structural characterization of the first linearly arranged silver complexes stabilized by naphthyridinelinked N-heterocyclic carbene ligands. Refluxing the solutions of 2,7-dichloronaphthyridine and two equivalent of N-methylimidazole, N-mesitylimidazole or N-benzylimidazole in toluene for 3 days afforded the corresponding imidazolium chlorides [12]. Subsequent treatment of the aqueous solutions of the imidazolium chlorides with an excess of NH4PF6 yielded the required imidazolium hexafluorophosphates in high yields (Scheme 1). In their 1H NMR spectra, the downfield resonance signals at ca. 10.5 ppm are characteristic of the acidic CH protons of the imidazolium salts. Treatment of [H2L1]Cl2 with Ag2O in acetonitrile afforded a white solid, which is insoluble in all solvents tested avoiding further purification and characterization. Reactions of 2,7-bis(imidazoliumyl)naphthyridine hexafluorophosphates, [H2L2](PF6)2 and [H2L3](PF6)2, with Ag2O in CH3CN at room temperature led to the formation of the trinuclear complexes [Ag3(L)2(CH3CN)](PF6)3 (Scheme 2) [13]. The compounds were isolated as colorless crystalline solids which are stable. They are identified by elemental analyses and 1H and 13C NMR spectroscopy. 1 H NMR spectra of [Ag3(L2)2(CH3CN)]3+ (1) and [Ag3(L3)2(CH3CN)]3+ (2) show the absence of the acidic imidazolium CH protons illustrating the formation of Ag–imidazolylidene species. The resonance signals of the imidazolylidene and naphthyridine protons are also observed, and consistent with the proposed structures. In the 1H NMR spectrum of 2, the resonance signals due to naphthyridine and imidazolylidene backbone protons are broad, illustrating that naphthyridine and acetonitrile are dynamically coordinated in solution. In the 13C NMR spectra of 1 and 2, the resonances due to carbenic carbons
+ Cl
N
N
N R
N
Cl
tolulene heat
N N R
405
were not observed. The absence of the carbenic carbon resonances is not unusual, and this phenomenon has been reported for a few silver–carbene complexes [14]. The reason is not yet clear, but the dynamic behavior and the poor relaxation of the carbenic carbon are important factors. The molecular structure of [H2L1]Cl2 was established by X-ray diffraction analysis, which is shown in Fig. 1. The asymmetric unit consists of two independent molecules which are essentially the same and six water molecules. The four rings are nearly co-planar as evidenced by the dihedral angles of ca. 7.5° between the naphthyridine and imidazolium rings. The structures of 1 and 2 are also characterized by single crystal X-ray diffraction analyses. The molecular structures are shown in Figs. 2 and 3, respectively [15]. The complexes contain linearly arranged Ag3 cores. The three silver ions in 1 are bound together through two 2,7-bis(mesitylimidazolylidenyl)naphthyridine ligands which act as tridentate C,N,C-pincer ligands. The second naphthyridine nitrogen atom is not coordinated. Two terminal silver ions are each bicoordinated by two imidazolylidenes with Ag–C dis˚ and C– tances in a narrow range of 2.082(7)–2.094(7) A Ag–C angles of 171°, which are similar to those of silver complexes having linear C–Ag–C structural motif [9,14]. The two imidazolylidene rings coordinated to the same silver ion are nearly perpendicular to each other with a dihedral angle of 86°. The central silver ion is tricoordinated in a T-shaped geometry by two naphthyridine nitrogen atoms and one acetonitrile molecule. The Ag–Nnaphthyridine dis˚ ) are approximately equal to those of tances (av. 2.22 A Ag–N bonds in the Pt–Ag complexes also showing metal–metal interactions [16], which are typical for Ag– pyridine complexes. The Ag–Nacetonitrile distance is nearly ˚ , remarkably longer than normal Ag–N bonds, illus2.5 A
N
N
NH4PF6
N N R
2Cl-
H2O
N
N
N R
N
2PF6
(R = methyl, benzyl, mesityl)
Scheme 1. Synthesis of the imidazolium salts.
N N R
N
N
2PF 6-
R
N N R
N
Ag2 O
N
N
Ag
N Ag
N
N
N R Ag
CH 3CN R N
N
N
N
N
R = mesityl, 1; benzyl, 2. Scheme 2. Synthesis of the silver complexes.
N
R
-
N N R
406
J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
Fig. 1. Molecular structure of the cation of [H2L1]Cl2.
Fig. 2. Perspective view of the molecular structure of [Ag3(L2)2(CH3CN)]3+. Thermal ellipsoids are drawn at 30% probability level. Selected bond ˚ ] and angles [°]: Ag(1)–Ag(2) 3.2695(7), Ag(2)–Ag(3) 3.2404(7), Ag(1)–C(44) 2.082(7), Ag(1)–C(23) 2.089(7), Ag(2)–N(9) 2.208(5), Ag(2)–N(3) distances [A 2.235(5), Ag(2)–N(13) 2.496(7), Ag(3)–C(55) 2.086(7), Ag(3)–C(12) 2.094(7), C(44)–Ag(1)–C(23) 171.0(3), N(9)–Ag(2)–N(3) 166.6(2), N(9)–Ag(2)–N(13) 93.3(2), N(3)–Ag(2)–N(13) 100.0(2), C(55)–Ag(3)–C(12) 171.5(3), Ag(3)–Ag(2)–Ag(1) 147.29(2).
trating that acetonitrile molecule is loosely bonded. The two naphthyridine rings coordinated to Ag(2) atom are also approximately perpendicular with the dihedral angle of 86°. The naphthyridine ring and its attached imidazolylidene rings are not co-planar with the dihedral angles ranging from 26.77° to 51.09° because of complexation to silver ions. The silver–silver interactions have been found in a few silver complexes containing imidazolylidene ligands [8– 11]. The three silver atoms are linearly arranged with two ˚ ). No intershort Ag–Ag contacts (3.2695(7), 3.2404(7) A molecular silver–silver interaction was observed because of the steric hindrance of the substituents. Although compound [Ag3(L3)2(CH3CN)]3+ (2) crystallizes in different space group from 1, the two compounds have essentially the same structures. As shown in Fig. 2,
the compound also has a Ag3 core with a Ag–Ag–Ag angle of 145.59(4)° similar to 1. The Ag–C bond distances for Ag(1) and Ag(2) atoms do not show significant difference as compared to 1. However, the silver–silver bond dis˚ ) are 0.1 A ˚ shorter than those of tances (av. 3.14 A [Ag3(L2)2(CH3CN)]3+. Another feature of 2 is that the Ag–Nnaphthyridine and Ag–Nacetonitrile distances are also distinctly shorter. Argentophilic interaction is a topic of recent research in the field of coordination and organometallic chemistry [17]. Short Ag–Ag contacts have been found in a few silver clusters stabilized by NHC ligands and the Ag–Ag distances ˚ [14]. The Ag–Ag distances cover a wide range of 2.7–3.3 A in 1 and 2 fall in this range illustrating weak Ag–Ag interactions. However, it is not easy to clearly demonstrate that if the close approach of silver atoms is ascribed to
J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
Fig. 3. Perspective view of the molecular structure of [Ag3(L3)2(CH3CN)]3+. Thermal ellipsoids are drawn at 30% probability level, and ˚ ] and angles phenyl rings are omitted for clarity. Selected bond distances [A [°]: Ag(1)–Ag(2) 3.1902(14), Ag(2)–Ag(3) 3.1063(14), Ag(1)–C(9) 2.098(10), Ag(1)–C(47) 2.117(10), Ag(2)–N(7) 2.255(9), Ag(2)–N(1) 2.262(10), Ag(2)–N(13) 2.598(12), Ag(3)–C(19) 2.081(16), Ag(3)–C(37) 2.093(12), C(9)–Ag(1)–C(47) 168.3(4), N(7)–Ag(2)–N(1) 167.3(3), N(7)– Ag(2)–N(13) 91.6(4), N(1)–Ag(2)–N(13) 101.0(4), C(19)–Ag(3)–C(37) 169.2(6), Ag(3)–Ag(2)–Ag(1) 145.59(4).
407
respectively. These vibronically structured bands with spacing between the local maxima of the emission bands of about 17 nm may indicate the involvement of the naphthyridine rings in the emission processes [18]. The similarities of the emission spectra of 1 and 2 suggest that these emissions originate from the same electronic states assignable to ligand-to-ligand charge transfer and MLCT (d–p) transitions. The silver complexes of NHC often show their emission bands below 500 nm [9–11], thus the low-energy bands around 513 nm for 1 and 523 nm for 2 may be attributed to metal-centered charge transfer processes. The solid state photoluminescent properties of these materials have not been well explored, and more work is needed to elucidate the nature of the emission. In summary, we described structural characterization and luminescent properties of the trinuclear silver complexes [Ag3(L)2(CH3CN)](PF6)3 stabilized by novel naphthyridine-functionalized N-heterocyclic carbenes. Short silver–silver contacts are observed for these two compounds. They represent the first examples of linearly arranged Ag3 clusters containing NHC ligands. We are currently exploring application of these complexes to the synthesis of multinuclear nickel and palladium complexes which are potentially useful catalysts. Acknowledgements The authors thank the National Natural Science Foundation of China (20572096), Natural Science Foundation of Zhejiang Province (R405066), and Qianjiang project (2007R10006) for financial support. Appendix A. Supplementary material CCDC 665444, 664078 and 664079 contains the supplementary crystallographic data for [H2L1]Cl2, 1 and 2. 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.2008.01.010. References
Fig. 4. Solid-state emission spectra of 1 (dashed line) and 2 (solid line) upon excitation at 230 nm.
argentophilic interaction or simple geometric requirement of the ligands. The trinuclear silver complexes are emissive in their solid states. The emission spectra are shown in Fig. 4. The emission spectra of 1 and 2 display unusual multiple bands (415, 436, 444, 470, 483, 496 and 515 nm for 1 and 432, 445, 471, 487, 496 and 523 nm for 2) with kmax = 470 nm and 471 nm upon excitation at 230 nm,
[1] D. Bourissou, O. Guerret, F.P. Gabbai, G. Bertrand, Chem. Rev. 100 (2000) 39. [2] (a) R.S. Simons, P. Custer, C.A. Tessier, W. Youngs, J. Organomet. Chem. 22 (2003) 1979; (b) Y.A. Wanniarachchi, M.A. Khan, L.M. Slaughter, Organometallics 23 (2004) 5881; (c) X.-Y. Yu, B.O. Patrick, B.R. James, Organometallics 25 (2006) 2359; (d) P.L. Chiu, C.Y. Chen, J.Y. Zeng, C.Y. Lu, H.M. Lee, J. Organomet. Chem. 690 (2005) 1682; (e) A. Flahaut, J.-P. Baltaze, S. Roland, P. Mangeney, J. Organomet. Chem. 691 (2006) 3498. [3] (a) A.J. Boydston, K.A. Williams, C.W. Bielawski, J. Am. Chem. Soc. 127 (2005) 12496; (b) C.K. Lee, K.M. Lee, I.J.B. Lin, Organometallics 21 (2002) 10.
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[14] [15]
[16] [17]
[18]
H, 3.66; N, 10.12.1H NMR (400 MHz, DMSO-d6): 8.32, 8.02 (both d, J = 8.4, naphthyridine, each 4H), 8.22, 7.88 (both s, NCHCHN, each 4H), 7.07 (s, C6H2(CH3)3, 8H), 2.47 (s, C6H2(CH3)3, 12H), 2.07 (s, CH3CN, 6H), 1.96 (s, C6H2(CH3)3, 24H).13C{1H}NMR (100.6 MHz, DMSO-d6): 152.9, 151.4, 141.1, 139.1, 136.0, 134.5, 129.2, 125.0, 121.5, 120.7, 118.4, 116.0, 21.0, 17.8, 1.5. [Ag3(L3)2(CH3CN)] (PF6)3: Yield: 60.6%. Anal. Calcd for C58H47Ag3F18N13P3: C, 41.35; H, 2.81; N, 10.81. Found: C, 41.25; H, 3.01; N, 10.42. 1H NMR (400 MHz, DMSO-d6): 9.22 (br. naphthyridine, 4H), 8.42, 8.36 (both br. imidazolylidene, each 4H), 7.93 (s, naphthyridine, 4H), 7.02–6.79 (m, C6H5, 20H), 5.22 (br., CH2, 8H), 2.05 (s, CH3CN, 3H). 13C{1H}NMR (100.6 MHz, DMSO-d6): 153.4, 150.3, 144.1, 136.3, 128.6, 128.2, 126.1, 118.8, 118.5, 65.2, 55.2, 16.1, 1.5. J.C. Garrison, W.J. Youngs, Chem. Rev. 105 (2005) 3978. Crystallographic data for [H2L1]Cl2: C16H22Cl2N6O3, Mr. = 417.30, ˚ , b = 13.408(3) A ˚ , c = 14.895(4) A ˚, triclinic, P 1, a = 10.485(3) A ˚ 3, a = 95.436(4)°, b = 91.399(4)°, c = 107.918(4)°, V = 1980.3(9) A Z = 4, Dcalc = 1.400 Mg/m3, F(0 0 0) = 872, 10453 reflections, collected, 6894 reflections unique (Rint = 0.0321), goodness-of-fit on F2 = 1.001, R [I > 2rI]: 0.0556, 0.1211. For 1: C68H70Ag3F18N14O2P3, ˚ , b = 14.5039(12) A ˚, Mr. = 1873.90, triclinic, P-1, a = 13.6814(12) A ˚ , a = 84.372(2)°, b = 74.770(2), c = 68.9510(10)°, c = 21.6420(19) A ˚ 3, Z = 2, Dcalc = 1.609 Mg/m3, F(0 0 0) = 1880, 19400 V = 3867.2(6) A reflections, 13353 collected, reflections unique (Rint = 0.0205), goodness-of-fit on F2 = 1.058, R [I > 2rI]: 0.0647, 0.1727. For 2: C58H47Ag3F18N13P3, Mr. = 1684.6, monoclinic, P21/c, a = ˚ , b = 13.1562(19) A ˚ , c = 27.3759(18) A ˚ , b = 122.922(5)°, 22.971(2) A ˚ 3, Z = 4, Dcalc = 1.611 Mg/m3, F(0 0 0) = 3335, V = 6944.7(13) A 21722 reflections collected, 11038 reflections unique (Rint = 0.0609), goodness-of-fit on F2 = 1.052, R [I > 2rI]: 0.0912, 0.2189. F. Liu, W. Chen, D. Wang, Dalton Trans. (2006) 3015. (a) T.C.W. Mak, X. Zhao, Q. Wang, G. Guo, Coord. Chem. Rev. 251 (2007) 2311; (b) C.-M. Che, M.-C. Tse, M.C.W. Chan, K.-K. Cheung, D.L. Phillips, K.-H. Leung, J. Am. Chem. Soc. 122 (2000) 2464; (c) K. Singh, J.R. Long, P. Stavropoulos, J. Am. Chem. Soc. 119 (1997) 2942. (a) A.A. Mohamed, J.M. Lo´pez-de-Luzuriaga, J.P. Fackler Jr., J. Clust. Sci. 14 (2003) 61; (b) Y. Zhou, W. Chen, Dalton Trans. (2007) 5123.
Inorganic Chemistry Communications 11 (2008) 404–408 www.elsevier.com/locate/inoche
Structural characterization of the first linearly arranged Ag3 complexes supported by naphthyridinefunctionalized N-heterocyclic carbenes Jiansheng Ye a, Shouwen Jin a, Wanzhi Chen a,*, Huayu Qiu b,* b
a Department of Chemistry, Zhejiang University, Xixi campus, Hangzhou 310028, China Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, China
Received 30 November 2007; accepted 7 January 2008 Available online 19 January 2008
Abstract Reactions of the imidazolium salts with Ag2O afforded trinuclear silver complexes [Ag3(L)2(CH3CN)](PF6)3 (L = 2,7-bis(alkylimidazolylidenyl)naphthyridine), which have been characterized by NMR spectroscopy and X-ray diffraction analysis. The complexes consist of ˚ ). The linearly arranged Ag3 cores showing weak silver–silver interactions as evidenced by the short silver–silver contacts (3.10–3.24 A complexes are intensely emissive in their solid states. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Silver; Naphthyridine; N-heterocyclic carbene; Silver–silver interaction; Luminescence
Since Arduengo isolated the first free N-heterocyclic carbene (NHC), numerous transition metal complexes of NHC have been studied since M–NHC complexes have shown enhanced catalytic activities in many organic transformation processes [1]. Silver–NHC complexes are important since such complexes are often used as carbene transfer reagents for the preparation of other metal–imidazolylidene complexes avoiding the use of free carbenes which are not always easily available [2]. Some silver complexes or coordination polymers containing N-heterocyclic carbenes have been found unique physical properties and may be potentially useful in material science [3]. Furthermore, the antibacterial activities of these complexes have also been reported [4]. We are interested in the chemistry of heteroarene-functionalized N-heterocyclic carbene ligands because such bidentate or multidentate ligands containing both strong and weak donating atoms have shown good activities in *
Corresponding authors. Fax: +86 571 88273314 (W. Chen). E-mail address: [email protected] (W. Chen).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.01.010
homogeneous catalysis. For instance, a hemilabile pyrazolyl-functionalized N-heterocyclic carbene complex of palladium(II) is an excellent catalyst for Heck and Suzuki crosscoupling reactions in ionic liquids [5]. Pyridine-functionalized heterocyclic carbene complexes of palladium give rise to highly active and very stable catalysts for Heck, Suzuki, and Sonogashira coupling reactions, with turnover number of up to 1.7 106 being achieved [6]. Nickel complexes of pyridine-functionalized N-heteroccylic carbenes have also been proven to be efficient catalysts for C–C formation reactions under mild conditions [7,8]. In addition, the heteroarene-functionalized N-heterocyclic carbenes are able to construct multinuclear clusters having Ag–Ag interactions, which often show interesting luminescence properties. So far, a few trinuclear [8,9] and tetranuclear [10,11] silver clusters stabilized by functionalized NHCs have been reported. These silver clusters consist of triangular Ag3 or square Ag4 rings. The 1,8-naphthyridine bridge has a similar dimension to those of carboxylate and formamido bridges, and thus can be used as linkers for forming metal–metal-bonded units. Herein we report the preparation
J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
and structural characterization of the first linearly arranged silver complexes stabilized by naphthyridinelinked N-heterocyclic carbene ligands. Refluxing the solutions of 2,7-dichloronaphthyridine and two equivalent of N-methylimidazole, N-mesitylimidazole or N-benzylimidazole in toluene for 3 days afforded the corresponding imidazolium chlorides [12]. Subsequent treatment of the aqueous solutions of the imidazolium chlorides with an excess of NH4PF6 yielded the required imidazolium hexafluorophosphates in high yields (Scheme 1). In their 1H NMR spectra, the downfield resonance signals at ca. 10.5 ppm are characteristic of the acidic CH protons of the imidazolium salts. Treatment of [H2L1]Cl2 with Ag2O in acetonitrile afforded a white solid, which is insoluble in all solvents tested avoiding further purification and characterization. Reactions of 2,7-bis(imidazoliumyl)naphthyridine hexafluorophosphates, [H2L2](PF6)2 and [H2L3](PF6)2, with Ag2O in CH3CN at room temperature led to the formation of the trinuclear complexes [Ag3(L)2(CH3CN)](PF6)3 (Scheme 2) [13]. The compounds were isolated as colorless crystalline solids which are stable. They are identified by elemental analyses and 1H and 13C NMR spectroscopy. 1 H NMR spectra of [Ag3(L2)2(CH3CN)]3+ (1) and [Ag3(L3)2(CH3CN)]3+ (2) show the absence of the acidic imidazolium CH protons illustrating the formation of Ag–imidazolylidene species. The resonance signals of the imidazolylidene and naphthyridine protons are also observed, and consistent with the proposed structures. In the 1H NMR spectrum of 2, the resonance signals due to naphthyridine and imidazolylidene backbone protons are broad, illustrating that naphthyridine and acetonitrile are dynamically coordinated in solution. In the 13C NMR spectra of 1 and 2, the resonances due to carbenic carbons
+ Cl
N
N
N R
N
Cl
tolulene heat
N N R
405
were not observed. The absence of the carbenic carbon resonances is not unusual, and this phenomenon has been reported for a few silver–carbene complexes [14]. The reason is not yet clear, but the dynamic behavior and the poor relaxation of the carbenic carbon are important factors. The molecular structure of [H2L1]Cl2 was established by X-ray diffraction analysis, which is shown in Fig. 1. The asymmetric unit consists of two independent molecules which are essentially the same and six water molecules. The four rings are nearly co-planar as evidenced by the dihedral angles of ca. 7.5° between the naphthyridine and imidazolium rings. The structures of 1 and 2 are also characterized by single crystal X-ray diffraction analyses. The molecular structures are shown in Figs. 2 and 3, respectively [15]. The complexes contain linearly arranged Ag3 cores. The three silver ions in 1 are bound together through two 2,7-bis(mesitylimidazolylidenyl)naphthyridine ligands which act as tridentate C,N,C-pincer ligands. The second naphthyridine nitrogen atom is not coordinated. Two terminal silver ions are each bicoordinated by two imidazolylidenes with Ag–C dis˚ and C– tances in a narrow range of 2.082(7)–2.094(7) A Ag–C angles of 171°, which are similar to those of silver complexes having linear C–Ag–C structural motif [9,14]. The two imidazolylidene rings coordinated to the same silver ion are nearly perpendicular to each other with a dihedral angle of 86°. The central silver ion is tricoordinated in a T-shaped geometry by two naphthyridine nitrogen atoms and one acetonitrile molecule. The Ag–Nnaphthyridine dis˚ ) are approximately equal to those of tances (av. 2.22 A Ag–N bonds in the Pt–Ag complexes also showing metal–metal interactions [16], which are typical for Ag– pyridine complexes. The Ag–Nacetonitrile distance is nearly ˚ , remarkably longer than normal Ag–N bonds, illus2.5 A
N
N
NH4PF6
N N R
2Cl-
H2O
N
N
N R
N
2PF6
(R = methyl, benzyl, mesityl)
Scheme 1. Synthesis of the imidazolium salts.
N N R
N
N
2PF 6-
R
N N R
N
Ag2 O
N
N
Ag
N Ag
N
N
N R Ag
CH 3CN R N
N
N
N
N
R = mesityl, 1; benzyl, 2. Scheme 2. Synthesis of the silver complexes.
N
R
-
N N R
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J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
Fig. 1. Molecular structure of the cation of [H2L1]Cl2.
Fig. 2. Perspective view of the molecular structure of [Ag3(L2)2(CH3CN)]3+. Thermal ellipsoids are drawn at 30% probability level. Selected bond ˚ ] and angles [°]: Ag(1)–Ag(2) 3.2695(7), Ag(2)–Ag(3) 3.2404(7), Ag(1)–C(44) 2.082(7), Ag(1)–C(23) 2.089(7), Ag(2)–N(9) 2.208(5), Ag(2)–N(3) distances [A 2.235(5), Ag(2)–N(13) 2.496(7), Ag(3)–C(55) 2.086(7), Ag(3)–C(12) 2.094(7), C(44)–Ag(1)–C(23) 171.0(3), N(9)–Ag(2)–N(3) 166.6(2), N(9)–Ag(2)–N(13) 93.3(2), N(3)–Ag(2)–N(13) 100.0(2), C(55)–Ag(3)–C(12) 171.5(3), Ag(3)–Ag(2)–Ag(1) 147.29(2).
trating that acetonitrile molecule is loosely bonded. The two naphthyridine rings coordinated to Ag(2) atom are also approximately perpendicular with the dihedral angle of 86°. The naphthyridine ring and its attached imidazolylidene rings are not co-planar with the dihedral angles ranging from 26.77° to 51.09° because of complexation to silver ions. The silver–silver interactions have been found in a few silver complexes containing imidazolylidene ligands [8– 11]. The three silver atoms are linearly arranged with two ˚ ). No intershort Ag–Ag contacts (3.2695(7), 3.2404(7) A molecular silver–silver interaction was observed because of the steric hindrance of the substituents. Although compound [Ag3(L3)2(CH3CN)]3+ (2) crystallizes in different space group from 1, the two compounds have essentially the same structures. As shown in Fig. 2,
the compound also has a Ag3 core with a Ag–Ag–Ag angle of 145.59(4)° similar to 1. The Ag–C bond distances for Ag(1) and Ag(2) atoms do not show significant difference as compared to 1. However, the silver–silver bond dis˚ ) are 0.1 A ˚ shorter than those of tances (av. 3.14 A [Ag3(L2)2(CH3CN)]3+. Another feature of 2 is that the Ag–Nnaphthyridine and Ag–Nacetonitrile distances are also distinctly shorter. Argentophilic interaction is a topic of recent research in the field of coordination and organometallic chemistry [17]. Short Ag–Ag contacts have been found in a few silver clusters stabilized by NHC ligands and the Ag–Ag distances ˚ [14]. The Ag–Ag distances cover a wide range of 2.7–3.3 A in 1 and 2 fall in this range illustrating weak Ag–Ag interactions. However, it is not easy to clearly demonstrate that if the close approach of silver atoms is ascribed to
J. Ye et al. / Inorganic Chemistry Communications 11 (2008) 404–408
Fig. 3. Perspective view of the molecular structure of [Ag3(L3)2(CH3CN)]3+. Thermal ellipsoids are drawn at 30% probability level, and ˚ ] and angles phenyl rings are omitted for clarity. Selected bond distances [A [°]: Ag(1)–Ag(2) 3.1902(14), Ag(2)–Ag(3) 3.1063(14), Ag(1)–C(9) 2.098(10), Ag(1)–C(47) 2.117(10), Ag(2)–N(7) 2.255(9), Ag(2)–N(1) 2.262(10), Ag(2)–N(13) 2.598(12), Ag(3)–C(19) 2.081(16), Ag(3)–C(37) 2.093(12), C(9)–Ag(1)–C(47) 168.3(4), N(7)–Ag(2)–N(1) 167.3(3), N(7)– Ag(2)–N(13) 91.6(4), N(1)–Ag(2)–N(13) 101.0(4), C(19)–Ag(3)–C(37) 169.2(6), Ag(3)–Ag(2)–Ag(1) 145.59(4).
407
respectively. These vibronically structured bands with spacing between the local maxima of the emission bands of about 17 nm may indicate the involvement of the naphthyridine rings in the emission processes [18]. The similarities of the emission spectra of 1 and 2 suggest that these emissions originate from the same electronic states assignable to ligand-to-ligand charge transfer and MLCT (d–p) transitions. The silver complexes of NHC often show their emission bands below 500 nm [9–11], thus the low-energy bands around 513 nm for 1 and 523 nm for 2 may be attributed to metal-centered charge transfer processes. The solid state photoluminescent properties of these materials have not been well explored, and more work is needed to elucidate the nature of the emission. In summary, we described structural characterization and luminescent properties of the trinuclear silver complexes [Ag3(L)2(CH3CN)](PF6)3 stabilized by novel naphthyridine-functionalized N-heterocyclic carbenes. Short silver–silver contacts are observed for these two compounds. They represent the first examples of linearly arranged Ag3 clusters containing NHC ligands. We are currently exploring application of these complexes to the synthesis of multinuclear nickel and palladium complexes which are potentially useful catalysts. Acknowledgements The authors thank the National Natural Science Foundation of China (20572096), Natural Science Foundation of Zhejiang Province (R405066), and Qianjiang project (2007R10006) for financial support. Appendix A. Supplementary material CCDC 665444, 664078 and 664079 contains the supplementary crystallographic data for [H2L1]Cl2, 1 and 2. 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.2008.01.010. References
Fig. 4. Solid-state emission spectra of 1 (dashed line) and 2 (solid line) upon excitation at 230 nm.
argentophilic interaction or simple geometric requirement of the ligands. The trinuclear silver complexes are emissive in their solid states. The emission spectra are shown in Fig. 4. The emission spectra of 1 and 2 display unusual multiple bands (415, 436, 444, 470, 483, 496 and 515 nm for 1 and 432, 445, 471, 487, 496 and 523 nm for 2) with kmax = 470 nm and 471 nm upon excitation at 230 nm,
[1] D. Bourissou, O. Guerret, F.P. Gabbai, G. Bertrand, Chem. Rev. 100 (2000) 39. [2] (a) R.S. Simons, P. Custer, C.A. Tessier, W. Youngs, J. Organomet. Chem. 22 (2003) 1979; (b) Y.A. Wanniarachchi, M.A. Khan, L.M. Slaughter, Organometallics 23 (2004) 5881; (c) X.-Y. Yu, B.O. Patrick, B.R. James, Organometallics 25 (2006) 2359; (d) P.L. Chiu, C.Y. Chen, J.Y. Zeng, C.Y. Lu, H.M. Lee, J. Organomet. Chem. 690 (2005) 1682; (e) A. Flahaut, J.-P. Baltaze, S. Roland, P. Mangeney, J. Organomet. Chem. 691 (2006) 3498. [3] (a) A.J. Boydston, K.A. Williams, C.W. Bielawski, J. Am. Chem. Soc. 127 (2005) 12496; (b) C.K. Lee, K.M. Lee, I.J.B. Lin, Organometallics 21 (2002) 10.
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[14] [15]
[16] [17]
[18]
H, 3.66; N, 10.12.1H NMR (400 MHz, DMSO-d6): 8.32, 8.02 (both d, J = 8.4, naphthyridine, each 4H), 8.22, 7.88 (both s, NCHCHN, each 4H), 7.07 (s, C6H2(CH3)3, 8H), 2.47 (s, C6H2(CH3)3, 12H), 2.07 (s, CH3CN, 6H), 1.96 (s, C6H2(CH3)3, 24H).13C{1H}NMR (100.6 MHz, DMSO-d6): 152.9, 151.4, 141.1, 139.1, 136.0, 134.5, 129.2, 125.0, 121.5, 120.7, 118.4, 116.0, 21.0, 17.8, 1.5. [Ag3(L3)2(CH3CN)] (PF6)3: Yield: 60.6%. Anal. Calcd for C58H47Ag3F18N13P3: C, 41.35; H, 2.81; N, 10.81. Found: C, 41.25; H, 3.01; N, 10.42. 1H NMR (400 MHz, DMSO-d6): 9.22 (br. naphthyridine, 4H), 8.42, 8.36 (both br. imidazolylidene, each 4H), 7.93 (s, naphthyridine, 4H), 7.02–6.79 (m, C6H5, 20H), 5.22 (br., CH2, 8H), 2.05 (s, CH3CN, 3H). 13C{1H}NMR (100.6 MHz, DMSO-d6): 153.4, 150.3, 144.1, 136.3, 128.6, 128.2, 126.1, 118.8, 118.5, 65.2, 55.2, 16.1, 1.5. J.C. Garrison, W.J. Youngs, Chem. Rev. 105 (2005) 3978. Crystallographic data for [H2L1]Cl2: C16H22Cl2N6O3, Mr. = 417.30, ˚ , b = 13.408(3) A ˚ , c = 14.895(4) A ˚, triclinic, P 1, a = 10.485(3) A ˚ 3, a = 95.436(4)°, b = 91.399(4)°, c = 107.918(4)°, V = 1980.3(9) A Z = 4, Dcalc = 1.400 Mg/m3, F(0 0 0) = 872, 10453 reflections, collected, 6894 reflections unique (Rint = 0.0321), goodness-of-fit on F2 = 1.001, R [I > 2rI]: 0.0556, 0.1211. For 1: C68H70Ag3F18N14O2P3, ˚ , b = 14.5039(12) A ˚, Mr. = 1873.90, triclinic, P-1, a = 13.6814(12) A ˚ , a = 84.372(2)°, b = 74.770(2), c = 68.9510(10)°, c = 21.6420(19) A ˚ 3, Z = 2, Dcalc = 1.609 Mg/m3, F(0 0 0) = 1880, 19400 V = 3867.2(6) A reflections, 13353 collected, reflections unique (Rint = 0.0205), goodness-of-fit on F2 = 1.058, R [I > 2rI]: 0.0647, 0.1727. For 2: C58H47Ag3F18N13P3, Mr. = 1684.6, monoclinic, P21/c, a = ˚ , b = 13.1562(19) A ˚ , c = 27.3759(18) A ˚ , b = 122.922(5)°, 22.971(2) A ˚ 3, Z = 4, Dcalc = 1.611 Mg/m3, F(0 0 0) = 3335, V = 6944.7(13) A 21722 reflections collected, 11038 reflections unique (Rint = 0.0609), goodness-of-fit on F2 = 1.052, R [I > 2rI]: 0.0912, 0.2189. F. Liu, W. Chen, D. Wang, Dalton Trans. (2006) 3015. (a) T.C.W. Mak, X. Zhao, Q. Wang, G. Guo, Coord. Chem. Rev. 251 (2007) 2311; (b) C.-M. Che, M.-C. Tse, M.C.W. Chan, K.-K. Cheung, D.L. Phillips, K.-H. Leung, J. Am. Chem. Soc. 122 (2000) 2464; (c) K. Singh, J.R. Long, P. Stavropoulos, J. Am. Chem. Soc. 119 (1997) 2942. (a) A.A. Mohamed, J.M. Lo´pez-de-Luzuriaga, J.P. Fackler Jr., J. Clust. Sci. 14 (2003) 61; (b) Y. Zhou, W. Chen, Dalton Trans. (2007) 5123.