2808
Organometallics 2010, 29, 2808–2814 DOI: 10.1021/om1000919
Synthesis, Characterization, and Properties of Binuclear Gold(I) Phosphine Alkynyl Complexes Yan Lin, Jun Yin, Jingjing Yuan, Ming Hu, Ziyong Li, Guang-Ao Yu, and Sheng Hua Liu* Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P.R. China Received February 4, 2010
Reactions of gold salts with various π-conjugated dialkynes have led to two homologous series of binuclear alkynylgold(I) complexes, linear rigid-rod Cy3PAu-CC-(CHdCH)n-CC-AuPCy3 (n = 1-3, all-trans) (2a-c) and photochromic LAu-CC-DTE-CC-AuL (DTE = 1,2-di(2methylthien-3-yl)cyclopentene or 1,2-di(2-methylthien-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene) (L=PCy3, tricyclohexylphosphine or PPh3, triphenylphosphine) (4a-d). The photophysical properties of these complexes have been investigated. The emission spectra exhibited a progressive red-shift with increasing length of the bridge between the two Au(I) in the linear metal complexes 2. Photochromic alkynylgold(I) complexes 4 also exhibited fluorescence properties, and the emission wavelength was found to change upon variation of the dithienylethene (DTE) linkers as well as of the auxiliary phosphine ligands. It is revealed that the binuclear alkynylgold complexes with DTE units show photochromic behavior and that the efficiencies of the photochromic processes and conversions from the open- to the closed-ring isomers in the photostationary state (PSS) are greatly improved upon the introduction of gold. The photochromic process was also found to show complete reversibility, with restoration of the luminescence and NMR signals upon exposure to visible light.
Introduction Conjugated bimetallic acetylide complexes are attracting considerable current interest1 because of their potential applications in many areas of material science. The linear geometry of the alkynyl unit together with its π-unsaturated *To whom correspondence should be addressed. E-mail: chshliu@ mail.ccnu.edu.cn. (1) (a) Beck, W.; Niemer, B.; Wieser, M. Angew. Chem., Int. Ed. Engl. 1993, 32, 923. (b) Bunz, U. H. F. Angew. Chem., Int. Ed. Engl. 1996, 35, 969. (c) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605. (d) Lang, H. Angew. Chem., Int. Ed. Engl. 1994, 33, 547. (e) Bruce, M. I. Coord. Chem. Rev. 1997, 166, 91. (f) Paul., F.; Lapinte, C. Coord. Chem. Rev. 1998, 178, 431. (g) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350. (h) Beeby, A.; Findlay, K.; Low, P. J.; Marder, T. B. J. Am. Chem. Soc. 2002, 124, 8280. (i) Levitus, M.; Schmieder, K.; Ricks, H.; Shimizu, K. D.; Bunz, U. H. F.; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2001, 123, 4259. (g) Tour, J. M. Acc. Chem. Res. 2000, 33, 791. (2) (a) Bruce, M. I.; Low, P. J.; Costuas, K.; Halet, J.-F.; Best, S. P.; Heath, G. A. J. Am. Chem. Soc. 2000, 122, 1949. (b) Dembinski, R.; Bartik, T.; Bartik, B.; Jaeger, M.; Gladysz, J. A. J. Am. Chem. Soc. 2000, 122, 810. (3) (a) Xu, G.-L.; DeRosa, M. C.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2004, 126, 3728. (b) Xi, B.; Xu, G.-L.; Fanwick, P. E.; Ren, T. Organometallics 2009, 28, 2338. (c) Gao, L.-B.; Kan, J.; Fan, Y.; Zhang, L.-Y.; Liu, S.-H.; Chen, Z.-N. Inorg. Chem. 2007, 46, 5651. (d) Neil, R.; Craig, A. M. Chem. Soc. Rev. 2003, 32, 96. (4) (a) Liu, S. H.; Chen, Y.; Wan, K. L.; Wen, T. B.; Zhou, Z.; Lo, M. F.; Williams, I. D.; Jia, G. Organometallics 2002, 21, 4984. (b) Liu, S. H.; Xia, H. P.; Wen, T. B.; Zhou, Z. Y.; Jia, G. Organometallics 2003, 22, 737. (c) Yuan, P.; Liu, S. H.; Xiong, W.; Yin, J.; Yu, G.; Sung, H. Y.; Williams, I. D.; Jia, G. Organometallics 2005, 24, 3966. (d) Liu, S. H.; Hu, Q. Y.; Xue, P.; Wen, T. B.; Williams, I. D.; Jia, G. Organometallics 2005, 24, 769. (e) Yuan, P.; Wu, X. H.; Yu, G.; Du, D.; Liu, S. H. J. Organomet. Chem. 2007, 692, 3588. (f) Yuan, P.; Yin, J.; Yu, G.; Hu, Q. Y.; Liu, S. H. Organometallics 2007, 26, 196. (g) Liu, S. H.; Xia, H.; Wan, K. L.; Yeung, R. C.Y.; Hu, Q. Y.; Jia, G. J. Organomet. Chem. 2003, 683, 331. (h) Xia, H. P.; Yeung, R. C. Y.; Jia, G. Organometallics 1998, 17, 4762. pubs.acs.org/Organometallics
Published on Web 05/28/2010
nature make the rigid metal alkynyl moiety an attractive and promising candidate for the construction of linear-chain metal-containing materials, which may possess unique properties such as electrical conductivity,2-4 liquid-crystalline properties,5 or nonlinear-optical behavior.6 Among these, alkynylgold(I) complexes, especially those with tertiary phosphine ligands, have received much attention, not only due to their stability and ease of preparation but also because of their rich photophysical properties.7,8 (5) (a) Altmann, M.; Bunz, U. H. F. Angew. Chem., Int. Ed. Engl. 1995, 34, 569. (b) Irwin, M. J.; Jia, G.; Payne, N. C.; Puddephatt, R. J. Organometallics 1996, 15, 51. (c) Alejos, P.; Coco, S.; Espinet, P. New J. Chem. 1995, 19, 799. (6) (a) Whittall, I. R.; Humphrey, M. G.; Samoc, M.; Luther-Davies, B. Angew. Chem., Int. Ed. Engl. 1997, 36, 370. (b) Vicente, J.; Chicote, M.-T.; Abrisqueta, M.-D.; Ramírez de Arellano, M. C. Organometallics 2000, 19, 2968. (7) (a) Yam, V. W.-W.; Cheng, E. C. C. Chem. Soc. Rev. 2008, 37, 1806. (b) Yam, V. W.-W.; Cheng, E. C. C. Top. Curr. Chem. 2007, 281, 269. (c) Che, C.-M.; Chao, H.-Y.; Miskowski, V. M.; Li, Y.; Cheung, K.-K. J. Am. Chem. Soc. 2001, 123, 4985. (d) Lu, W.; Xiang, H.-F.; Zhu, N.; Che, C.-M. Organometallics 2002, 21, 2343. (e) Lu, W.; Zhu, N.; Che, C.-M. J. Am. Chem. Soc. 2003, 125, 16081. (f) Yam, V. W.-W.; Cheung, K.-L.; Yip, S.-K.; Cheung, K.-K. J. Organomet. Chem. 2003, 681, 196. (g) Ho, S. Y.; Cheng, E. C.-C.; Tiekink, E. R. T.; Yam, V. W.-W. Inorg. Chem. 2006, 45, 8165. (h) Yam, V. W.-W.; Yip, S.-K.; Yuan, L.-H; Cheung, K.-L.; Zhu, N.; Cheung, K.-K. Organometallics 2003, 22, 2630. (i) He, X.; Zhu, N.; Yam, V. W.-W. Organometallics 2009, 28, 4792. (8) (a) Wong, W.-Y.; Choi, K.-H.; Lu, G.-L.; Shi, J.-X.; Lai, P.-Y.; Chan, S.-M.; Lin, Z. Organometallics 2001, 20, 5446. (b) Irwin, M. J.; Jia, G.; Payne, N. C.; Puddephatt, R. J Organometallics 1996, 15, 51. (c) Lohan, M.; Ecorchard, P.; R€uffer, T.; Justaud, F.; Lapinte, C.; Lang, H. Organometallics 2009, 28, 1878. (d) Bruce, M. I.; Jevric, M.; Skelton, B. W.; Smith, M. E.; White, A. H.; Zaitseva, N. N. J. Organomet. Chem. 2006, 691, 361. (e) Liu, L.; Poon, S.-Y.; Wong, W.-Y. J. Organomet. Chem. 2005, 690, 5036. r 2010 American Chemical Society
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Scheme 1
In recent years, much attention has been paid to the switching of physical properties by using appropriate stimuli to obtain functional materials.9 Chromism is regarded as an effective switching mechanism. Application of simple stimuli such as light or electricity to chromic compounds brings about changes of their structures, which eventually affect their physicochemical properties. Dithienylethene (DTE) derivatives are recognized as highly efficient organic photochromism compounds with respect to such features as fast response and fatigue resistance.10 Because metal-coordination complexes provide their own diverse assortment of photophysical and electrochemical characteristics, the combination of a DTE system with a metal ion should facilitate such application of switching devices.11 In our previous work, we constructed a photoswitchable organometallic molecular wire by combining a DTE unit with a redox-active ruthenium metal center. It was found that binuclear ruthenium vinyl complexes with dithienylethene units exhibited switching behavior triggered by either photochemical or electrochemical stimuli.12 Despite numerous studies on the luminescence of alkynylgold(I) species, to the best of our knowledge there have not hitherto been any reports of such systems incorporating a DTE unit in the main skeleton. Inspired by recent reports on the successful development of new photochromic materials that combine metals and dithienylethene moieties, we considered it an attractive goal to synthesize new gold(I) complexes with photoswitchable dithienylethene linkers. Herein, we report the first examples of binuclear alkynylgold(I) complexes {Au}-( μ-CC-DTE-CC)-{Au} containing dithienylethene. It is revealed that these complexes show photochromic behavior and that the efficiencies of their photochromic processes and conversions of the open-ring to the closed-ring isomers in the photostationary state (PSS) are greatly improved by the introduction of the metal. The luminescent properties of these complexes have been found to be perturbed by exposure to UV and visible light. The closed isomers of the (9) Feringa, B. L. Molecular Switches; Wiley-VCH: Weinheim, 2001. (10) (a) Irie., M. Chem. Rev. 2000, 100, 1683. (b) Tian, H.; Yang, S. Chem. Soc. Rev. 2004, 33, 85. (c) Tian, H.; Wang, S. Chem. Commun. 2007, 781. (11) (a) Kim, H. J.; Jang, J. H.; Choi, H.; Lee, T.; Ko, J.; Yoon, M.; Kim, H.-J. Inorg. Chem. 2008, 47, 2411. (b) Lee, J. K.-W.; Ko, C.-C.; Wong, K. M.-C.; Zhu, N.; Yam, V. W.-W. Organometallics 2007, 26, 12. (c) Roberts, M. N.; Nagle, J. K.; Finden, J. G.; Branda, N. R.; Wolf, M. O. Inorg. Chem. 2009, 48, 19. (d) Lee, P. H.-M.; Ko, C.-C.; Zhu, N.; Yam, V. W.-W. J. Am. Chem. Soc. 2007, 129, 6058. (e) Matsuda, K.; Shinkai, Y.; Irie, M. Inorg. Chem. 2004, 43, 3774. (f) Motoyama, K.; Koike, T.; Akita, M. Chem. Commun. 2008, 5812–5814. (g) Liu, Y. F.; Lagrost, C.; Costuas, K.; Tchouar, N.; Bozec, H. L.; Rigaur, S. Chem. Commun. 2008, 6117. (h) Tanaka, Y.; Inagaki, A.; Akita, M. Chem. Commun. 2007, 1169. (i) Uchida, K.; Inagaki, A.; Akita, M. Organometallics 2007, 26, 5030. (12) Lin, Y.; Yuan, J.; Hu, M.; Cheng, J.; Yin, J.; Jin, S.; Liu, S. H. Organometallics. 2009, 28, 6402.
bimetallic complexes, obtained upon irradiation with UV light, have extended π-conjugated systems similar to that of {Au}(μ-CC-(CdC)4-CC)-{Au} (Scheme 1). To better understand their luminescence behavior, the analogous bimetallic polyenediyl complexes {Au}-(μ-CC-(CdC)n-CC){Au} (n = 1, 2, 3) have also been synthesized and have been found to exhibit rich photophysical behavior. The properties of all of the complexes have been compared in detail in order to probe the effects of the various linking units and phosphine auxiliaries.
Results and Discussion Synthesis and Characterization. The ligand precursors polyenediynes 1a,4b 1b,4a and 1c,4d and the photochromic terminal diacetylenes 3a12 and 3b13 were prepared according to the previously reported procedures. Scheme 2 outlines the general synthetic route used to obtain the binuclear alkynylgold(I) complexes. The precursor diacetylene ligands were used to form binuclear alkynylgold(I) complexes by the classical dehydrohalogenation reaction between alkynes and chlorogold(I) phosphine complexes in the presence of a base.14 Treatment of diacetylenes HCC-(CdC)n-CCH (n = 1-3, all-trans) and HCC-DTE-CCH with 2 equiv of [AuCl(L)] in the presence of excess NaOH in MeOH solution gave the desired complexes as air-stable solids in high purity. The products were found to be highly soluble in chlorinated solvents such as CH2Cl2. All of the newly synthesized alkynylgold(I) complexes were characterized by 1H and 31P{1H} NMR spectroscopies and gave satisfactory elemental analyses. The structure of 2a was also verified by X-ray crystallography (Figure 1). The 31P NMR spectrum of 2a displays a sharp singlet at δ = 56.63 ppm, which is slightly downfield from that of Au(PCy3)Cl (δ = 54.46 ppm), indicating a symmetrical arrangement of PAuCC groups in solution. The 1H NMR spectrum in CD2Cl2 shows a singlet at δ=5.84 ppm, characteristic of an alkenic H. The 13C NMR spectrum in CD2Cl2 features two doublets at δ= 144.90 ppm (2JPC = 131.9 Hz) and δ = 102.75 ppm (3JPC = 24.4 Hz), attributable to the R- and β-acetylide carbon atoms of AuCC, respectively. The other complexes (2b, 2c) display similar chemical shifts in their spectra, in accordance with those of other previously reported alkynylgold(I) complexes.7c-f Several related photochromic alkynylgold(I) complexes 4 have similar NMR spectral properties to those of the above (13) Osuka, A.; Fujikane, D.; Shinmori, H.; Kobatake, S.; Irie, M. J. Org. Chem. 2001, 66, 3913. (14) (a) Coates, G. E.; Parkin, C. J. Chem. Soc. 1962, 3220. (b) Bruce, M. I.; Horn, M. I.; Matisons, J. G.; Snow, M. R. Aust. J. Chem. 1984, 37, 1163. (c) Cross, R. J.; Davidson, M. F.; McLennan, A. J. J. Organomet. Chem. 1984, 265, C37. (d) Bolletta, F.; Fabbri, D.; Lombardo, M.; Prodi, L.; Trombini, C.; Zaccheroni, N. Organometallics 1996, 15, 2415.
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Figure 1. Molecular structure of 2b. Scheme 2
linear rigid-rod alkynylgold(I) species. The 31P NMR spectra of 4a-d each feature a sharp singlet at δ = 56.11, 40.73, 56.12, and 41.69 ppm, respectively. The presence of the DTE unit is indicated by the 1H and 13C NMR spectra, which feature characteristic singlet signals for the thiophene and methyl moieties in CDCl3 solution. X-ray Structure of 2a. The molecular structure of Cy3PAuCC-CHdCH-CC-AuPCy3 (2a) is depicted in Figure 1. The crystallographic details and selected bond distances as well as angles are given in Tables 1 and 2, respectively. As shown in Figure 1, the C-Au-P and Au-C-C dihedral angles are 177.6(3)° and 171.1(9)°, respectively, which indicate linear geometry, typical of the sp hybridization found in alkynylgold(I) complexes. The CC bond length is 1.181(11) A˚, and this bond length, along with those of the Au-C (2.018(8) A˚) and Au-P (2.2807(18) A˚) bonds, are comparable to those observed in other alkynylgold(I) (15) Bruce, M. I.; Grundy, K. R.; Liddell, M. J.; Snow, M. R.; Tiekink, R. T. J. Organomet. Chem. 1988, 344, C49–C52. (16) Muller, T. E.; Choi, S. W. K.; Mingos, D. M. P.; Murphy, D.; Williams, D. J.; Yam, V. W. W. J. Organomet. Chem. 1994, 484, 209. (17) Muller, T. E.; Mingos, D. M. P.; Williams, D. J. J. Chem. Soc., Chem. Commun. 1994, 1787. (18) (a) Angermaier, K.; Zeller, E.; Schmidbaur, H. J. Organomet. Chem. 1994, 472, 371. (b) Assefa, Z.; McBurnett, B. G.; Stables, R. J.; Fackler, J. P., Jr.; Assmann, B.; Angermaier, K.; Schmidhaur, H. Inorg. Chem. 1995, 34, 75. (c) M€uller, T. E.; Green, J. C.; Mingos, D. M. P.; McPartlin, C. M.; Whittingham, C.; Williams, D. J.; Woodroffe, T. M. J. Organomet. Chem. 1998, 551, 31.
phosphine analogues, R3PAu-CC-AuPR3 (R = Ph,15 NpPh2,16 Np2Ph,17 Cy7c). The longer Au-P bond distances compared to those in the chlorogold phosphine complexes are in line with the higher trans influence of the alkynyl group.18 Compound 2a contains a trans carbon-carbon double bond (C(21)-C(21a)); the C(21a)-C(21)-C(20) angle is 133.4(16)°, which is larger than the corresponding angles in the (CH)nbridged binuclear metallic complexes [RuCl(CO)(PMe3)3]2( μ-(CHdCH)n) (n = 4 (125.8°),3d n = 5 (125.5°)4d). Electronic Absorption and Emission Spectroscopy of Linear Rigid-Rod Alkynylgold(I) Complexes. The electronic absorption and emission data of complexes 2a-c are summarized in Table 3, while Figure 2 shows their respective absorption spectra in dichloromethane at 298 K. They all exhibit three absorption peaks with similarly structured absorption bands at lower energies, which may be assigned as metal-perturbed intraligand (IL) [πfπ*(CC)] transitions with some metalto-ligand charge-transfer (MLCT) character. These bands are significantly red-shifted compared to those of the free polyenediyl derivatives Me3SiCC-(CHdCH)n-CCSiMe3 (n = 1, 2, 3) (1a, 420 nm) by using cutoff filters. All of the metal complexes display similarly structured absorption bands, both in the open and closed forms. We find that the position of the absorption band shows a bathochromic shift after coordination of the metal entities to form the alkynylgold(I) complexes. These observations are consistent with increased π-delocalization through the metal groups due to metal-to-ligand back-donation to the π* orbital.
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a All absorption spectra were recorded in CH2Cl2 at 298 K. [2] = 2 10-5 mol 3 L-1. b Measured in CH2Cl2 at 298 K.
Figure 2. Absorption spectrum of (Cy3P)AuCC-(CHdCH)nCCAu(PCy3) (2) in CH2Cl2 solution at 298 K. ([2] = 2.0 10-5 mol dm-3; red, 2a; green, 2b; black, 2c).
Figure 3 shows the absorption spectral changes of compounds 3b and 4c. Upon illumination at a wavelength of 302 nm, the solutions of 3b and 4c in dichloromethane reached a photostationary state, whereby the colorless solutions of the open-ring isomers turned purple and dark blue, respectively, showing new bands at 379 and 577 nm (for 3b) and at 385 and 601 nm (for 4c). These colored solutions were bleached by subsequent irradiation with visible light (λ > 420 nm), owing to the compounds reverting to their original open-ring states. As is evident from Table 4, the absorption maxima of the open-ring and closed-ring forms were dependent on the central switching units at the reaction centers. The closed isomers of the hexahydro switches (4a, 4b) turned dark red, while the hexafluoro switches (4c, 4d) became dark blue upon UV irradiation. This was because the absorption maxima of the hexafluoro compounds were bathochromically shifted to the region 601-605 nm, while those of the hexahydro compounds were only shifted to 530-536 nm. Different ancillary phosphine ligands did not cause notable shifts of the absorption maxima of the open-ring and closed-ring forms. The photochromic process was reversible, and no apparent deterioration of 4c was observed after repeating the process several times (Figure 4). The photochromic alkynylgold(I) complexes also exhibited fluorescence in CH2Cl2 solutions. In each case, the emission energy was found to change upon variation of both the linking moieties and the auxiliary phosphine ligands. Table 4 shows the emission data for complexes 4a-d at 298 K. The emission wavelengths of the hexafluoro compounds (4c, 4d) are longer than those of their hexahydro analogues (4a, 4b). The emissions of 4a and 4c are also red-shifted relative to those of 4b and 4d, which can be rationalized by the fact that the PCy3 ligand is electron-donating in nature and renders the Au(I) center more electron-rich. The fluorescence intensity decreased along with the photochromism on going from the ring-opened to the ringclosed form upon irradiation at 302 nm, as shown in Figure 5. The obvious emission quench at the photostationary state (PSS) may be attributed to the formation of the closed isomers.
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Table 4. Electronic Absorption, Quantum Yields, Conversions (PSS) for Photochromic Compounds 3, 4 absorptiona λmax/nm (ε/104 L mol-1 cm-1) compd
open
3a
262(3.08)
3b
260(3.50)
4a
284(3.22) 305(3.02) 320(2.95)
4b
275(4.00) 288(4.07) 312(3.88)
4c
283(4.47) 297(5.27) 312(4.85)
4d
301(4.93) 316(4.72)
Φb
conversionc (open f closed) (%)
closed
Φo-c
Φc-o
340(0.84) 518(0.89) 379(0.38) 577(0.40) 349(1.39) 530(1.63) 355(1.74) 536(2.25) 385(1.40) 601(2.10) 387(1.29) 605(1.99)
0.49
0.045
50
0.39
0.012
78
0.61
0.0063
92
0.78
0.040
85
0.41
0.0096
95
0.72
0.011
>95
a All absorption spectra were recorded in CH2Cl2 at 298 K. C = 2 10-5 mol 3 L-1. b Quantum yields of cyclization (Φo-c) and cycloreversion (Φc-o). c Determined by 1H NMR in CDCl3.
Figure 3. UV-vis spectral changes upon 302 nm light irradiation (observed in CH2Cl2, 2.0 10-5 mol dm-3). (a) 3b; (b) 4c.
Figure 4. Reversible photochromism of 4c monitored by UV-vis spectroscopy ([4c] = 2.0 10-5 mol/L; alternating UV (20 S) and visible light (3 min) irradiations) in air atmosphere at room temperature.
The blue fluorescence of the solution could be recovered by using visible light to induce the formation of the open-ring isomers. The photochromic behavior of the binuclear alkynylgold(I) complexes (4a-d) and their corresponding diacetyl precursors (3a, 3b) was examined by means of NMR spectrometry. The ratios between the closed and open isomers at the photostationary state were measured from the 1H NMR spectra. The characteristic shifts of their Me and thiophene groups were observed in the 1H NMR spectra (CDCl3, 1.0 10-2 mol dm-3). Irradiation with UV light caused the appearance of a new set of singlets with the concomitant disappearance of the singlets of the original state. As shown in Figure 6, the 1H NMR signal of the methyl
Figure 5. Emission spectral changes of compound 4b upon UV and Vis light irradiation.
groups attached to the thiophene rings appeared at δ = 1.73 ppm for 4cO and δ = 2.06 ppm for 4cC, and the 1H NMR signal of the protons attached to the thiophene rings appeared at δ = 7.17 ppm for 4cO and δ = 6.29 ppm for 4cC. Thus the chemical shift of the protons on the thiophene rings appeared at higher field compared to that in the case of 4cO, while the chemical shift of the methyl protons appeared at lower field, in accordance with our previous report.12 Similar shift changes have also been observed in the 1H NMR spectra of other dithienylethene compounds (Table 5). The
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Table 6. 1H NMR Chemical Shifts of Opened and Closed-Ring Isomers for 3, 4 open
closed
compd
δMe
δthiophene-H
δMe
δthiophene-H
3a 3b 4a 4b 4c 4d
1.89 1.90 1.71 1.76 1.73 1.79
6.97 7.24 6.92 6.95 7.17 7.18
1.95 2.13 1.97 1.94 2.06 2.10
6.18 6.45 6.01 6.05 6.29 6.32
Figure 7. Visible absorption changes of 3b, 4c, and 4d upon UV light irradiation. The absorptions were monitored at the maxima of the visible absorptions (3bO, 577 nm; 4cO, 601 nm; 4dO, 605 nm).
Figure 6. 1H NMR spectral changes upon 302 nm light irradiation (observed in CDCl3). (a) 3b; (b) 4c (* methyl signal). Table 5. Excitation and Emission Data for Photochromic Compounds 3, 4 compd
excitation λmax/nm
emissiona λmax/nm
compd
excitation λmax/nm
3a
364
409, 432
3b
343
4a 4c
368 385
416, 433 436, 460
4b 4d
350 352
emissionamax/ nm 378, 397, 419, 444 395, 422 398, 442
a All absorption spectra were recorded in CH2Cl2 at 298 K, C = 2 10-5 mol 3 L-1.
31
P NMR signal appears as the same sharp singlet in both the open-ring and closed-ring isomers, indicating that the spacer has little effect on the environment of the phosphine. As shown in Table 4 and Figure 6, the photocyclization yield of 3bC from 3bO was 78% according to 1H NMR analysis, while the yields of 4cC and 4dC from their corresponding open-ring isomers were improved to 95% (Table 6). Similar promotion was also observed for their hexahydro counterparts (from 50% (3a) up to 92% (4a) and 85% (4b)). The higher photocyclization yields of the metal alkynyl complexes can be ascribed to the metalation. Metalation led to notable differences both in the photocyclization yields and quantum yields compared with those of the free DTE alkynes. The quantum yields of the photocyclization and photocycloreversion reaction of these compounds
were summarized in Table 4. These values were evaluated by the standard procedure using 1,2-bis(2-methyl-5-phenyl-3thienyl)perfluorocyclopentene as a standard.19 The photocyclization quantum yield of 3a in CH2Cl2 solution was 0.49(302 nm) at room temperatue. When the metal groups attached to the reaction centers, the photocyclization quantum yields increased to 0.61 for 4a and 0.78 for 4b. The same promotion in the cyclization quantum yields was also observed for hexafluoro systems. However, the values of the photocycloreversion quantum yields were irregular. It is worth noting that the efficiencies of the cyclization and cycloreversion were also dependent on the metalation. As can be seen from Figure 7, the ring-closing rates for 3b, 4c, and 4d were comparable, but the metal complexes 4 reached photostationary states more efficiently than the free DTE molecules 3 (i.e., ca. 60 s for 3b; ca. 20 s for 4c and 4d). However, more significant differences were observed for the reverse ring-opening process, whereby the metal complexes 4 reverted to their open isomers more slowly than the metal-free species (i.e., ca. 2 min for 3b and within 3 min for 4c and 4d). It is notable that different ancillary phosphine ligands (Ph or Py) had little effect on the efficiency of this conversion. A similar tendency was also observed upon comparison of the photochemical efficiencies of 4a and 4b with that of 3a. This suggests that metalation has a significant impact on the stability of the ring-closed isomers, in accordance with the findings of Akita’s11i and our group12 on how different metal species influence the efficiencies of cyclization and cycloreversion.
(19) Irie, M.; Lifka, T.; Kobatake, S.; Kato, N. J. Am. Chem. Soc. 2000, 122, 4871.
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Organometallics, Vol. 29, No. 12, 2010
Conclusions Two new series of binuclear alkynylgold(I) complexes, linear rigid-rod and photochromic complexes, have been successfully synthesized and structurally characterized. The complexes have been shown to exhibit photoluminescence properties, and the emission wavelength was found to change upon variation of the linkers as well as of the auxiliary phosphine ligands. Photochromic alkynylgold(I) complexes show reversible photochromic behavior; the efficiencies of their photochromic processes and conversions from the open- to the closed-ring isomers in the photostationary state (PSS) are greatly improved by the introduction of gold.
Experimental Section General Materials. All manipulations were carried out under a nitrogen atmosphere by using standard Schlenk techniques unless otherwise stated. Solvents were distilled under nitrogen from sodium-benzophenone (diethyl ether, THF) or calcium hydride (dichloromethane). Triethylamine were freshly distilled over KOH pellets. The starting materials TMS-CC-(CHdCH)n-CCTMS (n = 1,2,3),4b,a,d [(R3P)AuCl],20,21 1,2-bis(5-ethynyl-2-methylthiophen-3-yl)cyclopentene (3a),12 and 1,2-bis(5-ethynyl-2-methylthiophen-3-yl)perfluorocyclopentene (3b)13 were prepared according to literature methods. Elemental analyses (C, H, N) were performed by the Microanalytical Services, College of Chemistry, CCNU. 1H, 13C, and 31P NMR spectra were collected on American Varian Mercury Plus 400 spectrometer (400 MHz). 1 H and 13C NMR chemical shifts are relative to TMS, and 31P NMR chemical shifts are relative to 85% H3PO4. UV-vis spectra were obtained on U-3310 UV spectrophotometer. Fluorescence spectra were recorded on a Hitachi-F-4500 fluorescence spectrophotometer. UV light was irradiated using ZF5 UV lamp (302 nm), and visible light irradiation (λ > 420 nm) was carried out by using a LZG 220 V 500W tungsten lamp with cutoff filters. The quantum yields were determined by comparing the reaction yields of the diarylethenes against 1,2-bis(2methyl-5-phenyl-3-thienyl)perfluorocyclopentene. General Synthesis of Compounds Cy3PAu-CC-(CHdCH)nCC-AuPCy3 (n = 1, 2, 3) (2). To a methanolic solution (30 mL) of TMS-CC-(CHdCH)n-CC-TMS (n = 1, 2, 3; 0.1 mmol) and Cy3PAuCl (0.2 mmol) was added an excess of NaOH (0.2 g, 5 mmol), and the mixture was stirred for 1 h. The brown solid was collected by filtration. Then the brown solid washed with water, methanol, and diethyl ether, in turn. The crude product was purified by column chromatography (Al2O3, CH2Cl2) to give a pale-yellow solid and dried under vacuum. 2a: Yield, 0.051 g, 50%. Anal. Calcd for C42H68P2Au2: C, 49.03; H, 6.66. Found: C, 49.63; H, 6.19. 1H NMR (400 MHz, CD2Cl2): δ 1.20-1.96 (m, 66 H, Cy), 5.84 (s, 2H, CHd). 31P NMR (160 MHz, CDCl3): δ 56.63 (s). 13C NMR (100 MHz, CD2Cl2): δ 26.23, 27.38, 31.02, 33.38, 102.75, 120.54, 144.90. 2b: Yield, 0.065 g, 61%. Anal. Calcd for C44H70P2Au2: C, 50.10; H, 6.69. Found: C, 50.04; H, 6.15. 1H NMR (400 MHz, CD2Cl2): δ 1.12-1.99 (m, 66 H, Cy), 5.60 (m, 2H, CCHdCH), 6.34 (m, 2H, CCHdCH). 31P NMR (160 MHz, CDCl3): δ 56.59 (s). 13C NMR (100 MHz, CD2Cl2): δ 26.23, 27.39, 31.03, 33.40, 103.19, 114.01, 139.66, 145.43. (20) McAuliffe, C. A.; Parish, R. V.; Randall, P. D. J. Chem. Soc., Dalton Trans. 1979, 1730. (21) Cross, R. J.; Davidson, M. F. J. Chem. Soc., Dalton Trans. 1986, 411.
Lin et al. 2c: Yield, 0.050 g, 46%. Anal. Calcd for C46H72P2Au2: C, 51.11; H, 6.71. Found: C, 51.09; H, 6.20. 1H NMR (400 MHz, CD2Cl2): δ 1.21-1.97 (m, 66 H, Cy), 5.64 (d, 2H, J (HH) = 15.2 Hz, CCHdCH), 6.13 (m, 2H, CCHdCHCHd), 6.36 (m, 2H, CCHdCHCHd). 31P NMR (160 MHz, CDCl3): δ 56.62 (s). 13C NMR (100 MHz, CD2Cl2): δ 26.22, 27.37, 31.02, 103.49, 114.68, 133.34, 139.56, 146.29. General Synthesis of Compounds LAu-CC-DTE-CCAuL (4). The terminal diacetylene 3 (0.11 mmol) was dissolved in an anhydrous methanol (10 mL) under nitrogen. This solution was added to the dry THF solution (10 mL) of AuClL (0.20 mmol), and the mixture was stirred at room temperature. The methanol solution (5 mL) of NaOH (200 mg, 0.5 mmol) was added dropwise to the mixture. After 2 h, a precipitate (4a, 4b, light red; 4c, 4d, light blue) appeared in the solution. The precipitate was collected by filtration with a suction filter and washed with MeOH, H2O, and ether successively. The powder was dried under vacuum for 2 h. 4a: Yield, 0.080 g, 63%. Anal. Calcd for C55H80Au2P2S2: C, 52.38; H, 6.39. Found: C, 52.65; H, 6.63. 1H NMR (400 MHz, CDCl3): δ 1.26-1.99 (m, 74 H, Cy, CH3, CH2), 2.69 (t, J = 7.4 Hz, 4 H, CH2), 6.92 (s, 2 H, thiophene-H). 31P NMR (160 MHz, CDCl3): δ 56.11 (s). 13C NMR (100 MHz, CDCl3): δ 13.70 (CH3), 22.55, 26.75, 27.19, 30.56, 32.73, 38.71, 96.50, 121.07, 131.86, 132.34, 133.80, 134.44, 135.04, 139.97, 141.27. 4b: Yield, 0.088 g, 72%. Anal. Calcd for C55H44Au2P2S2: C, 53.93; H, 3.62. Found: C, 53.76; H, 3.53. 1H NMR (400 MHz, CDCl3): δ 1.76 (s, 6 H, CH3), 1.97-2.01 (m, 2 H, CH2), 2.71 (t, J = 7.4 Hz, 4 H, CH2), 6.95 (s, 2 H, thiophene-H), 7.45-7.57 (m, 30 H, Ph). 31P NMR (160 MHz, CDCl3): δ 40.73 (s). 13C NMR (100 MHz, CDCl3): δ 14.26 (CH3), 22.60, 38.71, 96.56, 120.62, 129.03, 129.31, 131.52, 132.37, 133.89, 134.33, 135.12. 4c: Yield, 0.12 g, 88%. Anal. Calcd for C55H74Au2F6P2S2: C, 48.25; H, 5.45. Found: C, 48.06; H, 5.65. 1H NMR (400 MHz, CDCl3): δ 1.26-1.99 (m, 72 H, Cy, CH3), 7.17(s, 2 H, thiopheneH). 31P NMR (160 MHz, CDCl3): δ 56.12 (s). 13C NMR (100 MHz, CDCl3): δ 14.30 (CH3), 25.85, 27.09, 30.71, 33.20, 94.48, 123.83, 124.30, 130.48, 140.92, 142.46, 143.75. 4d: Yield, 0.95 g, 71%. Anal. Calcd for C55H38Au2F6P2S2: C, 49.56; H, 2.87. Found: C, 49.38; H, 2.96. 1H NMR (400 MHz, CDCl3): δ 1.79 (s, 6 H, CH3), 7.18 (s, 2 H, thiophene-H), 7.46-7.57 (m, 30 H, Ph). 31P NMR (160 MHz, CDCl3): δ 41.69 (s). 13C NMR (100 MHz, CDCl3): δ 14.39 (CH3), 95.14, 123.29, 124.27, 129.19, 130.66, 131.60, 134.14, 134.28, 135.43, 141.35. Crystallographic Details for 2a. Crystals suitable for X-ray diffraction were grown from a dichloromethane of solution 2a layered with hexane. A crystal with approximate dimensions of 0.40 0.20 0.10 mm3 was mounted on a glass fiber for diffraction experiment. Intensity data were collected on a Nonius Kappa CCD diffractometer with Mo KR radiation (0.71073 A˚) at 293 K. The structure was solved by a combination of direct methods (SHELXS-97) and Fourier difference techniques and refined by full-matrix least-squares (SHELXL-97). All non-H atoms were refined anisotropically. The hydrogen atoms were placed in the ideal positions and refined as riding atoms. Further crystal data and details of the data collection are summarized in Table 1.
Acknowledgment. We acknowledge financial support from National Natural Science Foundation of China (nos. 20772039, 20931006) Supporting Information Available: Spectral changes upon UV irradiation of 4a, 4b, and 4d, and X-ray crystallographic file (CIF) for compound 2a. This material is available free of charge via the Internet at http://pubs.acs.org.
