Alkynyl-Bridged Ruthenium(II) 4′-Diferrocenyl-2,2 ... - ACS Publications

Jun 8, 2011 - Electrochemical data and UV absorption and emission spectra indicate that the insertion of an ethynyl group causes delocalization of ele...
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Alkynyl-Bridged Ruthenium(II) 40-Diferrocenyl-2,20:60 ,200 -terpyridine Electron Transfer Complexes: Synthesis, Structures, and Electrochemical and Spectroscopic Studies Kai-Qiang Wu,† Jian Guo,† Jian-Feng Yan,† LiLi Xie,† Feng-Bo Xu,‡ Sha Bai,§ Peter Nockemann,*,|| and Yao-Feng Yuan*,†,‡,^ †

State Key Laboratory Breeding Base of Photocatalysis, Fuzhou University, Fuzhou 350002, People's Republic of China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China § Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States School of Chemistry and Chemical Engineering, Queen’s University of Belfast, The QUILL research centre, Belfast BT9 5AQ, United Kingdom ^ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People's Republic of China

)

‡

bS Supporting Information ABSTRACT: The novel ligand 40 -diferrocenylalkyne-2,20 :60 ,200 -terpyridine (7; Fc-CtC-Fc-tpy; tpy = terpyridyl; Fc = ferrocenyl) and its Ru2þ complexes 810 have been synthesized and characterized by single-crystal X-ray diffraction, cyclic voltammetry, and UVvis and luminescence spectroscopy. Electrochemical data and UV absorption and emission spectra indicate that the insertion of an ethynyl group causes delocalization of electrons in the extended π* orbitals. Cyclic voltammetric measurements of 7 show two successive reversible oneelectron-oxidation processes with half-wave potentials of 0.53 and 0.78 V. The small variations of the E1/2 values for the Fe2þ/Fe3þ redox couples after the coordination of the Ru2þ ion suggest a weak interaction between the Ru2þ and Fe2þ centers. After insertion of an ethynyl group, UVvis absorption spectra show a red shift of the absorption peak of the 1[(d(π)Fe)6] f 1[(d(π)Fe)5(π*tpyRu)1] MMLCT of the Ru2þ complexes. The Ru2þ complex 8 exhibits the strongest luminescence intensity (λmaxem 712 nm, Φem = 2.63  104, τ = 323 ns) relative to analogous ferrocene-based terpyridine Ru(II) complexes in H2O/CH3CN (4/1 v/v) solution.

’ INTRODUCTION The design and synthesis of substituted 2,20 :60 ,200 -terpyridine transition-metal complexes are of great current interest, due to their wide applications in supramolecular chemistry and photochemistry.1 Among the 2,20 :60 ,200 -terpyridine ligands, 40 functionalized 2,20 :60 ,200 -terpyridines are currently attracting much attention, since they are suitable from a geometric viewpoint for the construction of supramolecular systems which show fascinating redox and photophysical properties based on intramolecular electron and energy transfer.13 A number of 40 functionalized 2,20 :60 ,200 -terpyridines have been utilized as spacers when incorporated into d6 transition-metal complexes with Ru,4 Fe,4 Co,5 and Ln6 cores. For the ruthenium(II) complexes, which exhibit unique photophysical, photochemical, electrochemical, electron transfer, and energy transfer properties and have been demonstrated for use in molecular assembly and recognition,7 it is worthwhile to mention that rigid coplanar groups attached to the 40 -position can delocalize the π electrons of molecules, leading to a decrease of the 3MLCT level of the complexes and consequently an increase of the energy gap between the 3MLCT and 3MC levels. Thus, a reduction of the r 2011 American Chemical Society

radiationless deactivation through 3MC greatly improves the optical properties of such metal complexes.8,9 Ferrocene derivatives show distinguished properties in applications including catalysis, materials science, and biomedicinal chemistry.6,10 The 40 -ferrocenyl-functionalized terpyridine ligands, especially those containing extensively conjugated substituents, are particularly interesting, since this type of ligand displays a high binding affinity to many metal ions, offering a thermodynamic driving force for the formation of stable metallosupramolecular assemblies. Furthermore, these ligands can be used for the construction of geometrically well-defined functional complexes which show fascinating properties based on intramolecular electron and energy transfer. The photoelectronic properties can be easily modulated by tuning the length and the nature of the spacer.9 In recent years, a number of research groups have been focusing their attention on the investigation of 40 -ferrocenylfunctionalized terpyridine ligands and their Ru2þ complexes. Received: February 6, 2011 Published: June 08, 2011 3504

dx.doi.org/10.1021/om200113d | Organometallics 2011, 30, 3504–3511

Organometallics Such multicomponent systems are of great current interest to model the photoinduced energy and electron transfer and charge separation of natural photosynthesis11 and for applications as molecular wires, for energy conversion and information storage.12 The 40 -p-ferrocenyl-2,20 :60 ,200 -phenylterpyridine (Fcphtpy) ligand and its Ru2þ complex were first synthesized in 1992 by Sauvage et al.,13 and the interaction between the ferrocene moiety and [Ru(tpy)2]2þ in the excited state was confirmed. Soon after that, almost at the same time, the preparation of 40 -ferrocenyl-2,20 :60 ,200 -terpyridine (Fc-tpy) via the Kr€onke method was reported independently by the groups of Constable14 and Walsh.15 Electrochemistry and UVvis spectra of the Ru2þ complexes indicate the electron transfer between the ferrocene moiety and terpyridine. Specially, the phenomenon of luminescence of these Ru2þ complexes was first observed ([Ru(tpy)(Fc-tpy)]2þ, λmaxem 601, 646 nm, Φem ≈ 0.003, τ < 0.025 ns; [Ru(Fc-tpy)2]2þ, λmaxem 599, 648 nm, Φem < 0.003, τ < 0.025 ns) at 77 K in 1999.16 The “back-to-back” ligands incorporating two tpy moieties (T-S-T) have found particular favor in supramolecular chemistry.9,17 The Constable group18 reported the bis(terpyridine) ligand 1,10 -bis(2,20 :60 ,200 -terpyridine-40 -yl)ferrocene (tpy-Fc-tpy). Dong and co-workers have focused on the electrochemical, photochemical, and photophysical aspects of multinuclear 40 -ferrocenyl-(bis-)2,20 :60 ,200 -terpyridines and their Ru2þ complexes since 2004.19,20 Heinze et al. reported on multielectron storage and photoinduced electron transfer in ruthenium(II)-containing complexes of terpyridine with a ferrocene attached via an amide link.21 Combining the rigid and linear alkynyl to the 40 -ferrocenyl2,20 :60 ,200 -terpyridine may lead to interesting optoelectronic properties. Siemeling et al.3,22 have prepared derivatives of 2,20 :60 ,200 -terpyridine with ferrocenyl and octamethylferrocenyl groups attached to the 40 -position by means of a p-phenylene and an acetylene spacer unit. They reported on the synthesis of these compounds and first results regarding their coordination chemistry as well as preliminary electrochemical investigations. This study recognized first the phenomenon of room-temperature luminescence of this type of Ru2þ complex. The Dong group2325 has undertaken systematic studies of the electrochemical and photophysical properties to probe the electronic states of complexes containing bis(2,20 :60 ,200 -terpyridine)polyferrocene redoxactive spacers that are end-capped with photoactive Ru2þ-terpyridine terminals. They have found that the insertion of an ethynyl group into the main chain can lead to an increase in the excitedstate lifetimes. The Ru2þ complexes 1 and 2 (Chart 1) have been found to be luminescent at room temperature. In order to investigate in which way the photoelectronic properties of Ru2þ complexes are affected by an alkynyl-bridged ferrocenyl substituent, we herein prepared the rigid π-conjugated ligand 7 and its Ru2þ complexes 810. We expected that the insertion of an ethynyl unit in the ligand could enhance the effective π-delocalization, thus lowering the energy levels of the molecular assembly. In this paper, we focus our attention on the electrochemical and room-temperature photoluminescent properties of the Ru2þ complexes. The molecular structure of the ligand, UVvis spectra, and the possible excited-state energy level of its Ru2þ complexes are also discussed.

’ EXPERIMENTAL SECTION General Conditions. All reactions involving air-sensitive materials were carried out under an atmosphere of nitrogen using standard

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Chart 1

Schlenk techniques. Chromatography was performed on neutral alumina (100200 mesh) or silica gel (100200 mesh). Diisopropylamine, acetonitrile, and CH2Cl2 were dried over CaH2 and freshly distilled under nitrogen prior to use. Instruments. Infrared spectra were recorded with a Perkin-Elmer Spectrum 2000 spectrophotometer (4000400 cm1). Melting points were determined on a Shenguang WRS-1B apparatus and are uncorrected. NMR spectra were recorded on a Bruker AV 400 (1H at 400 MHz) or a Bruker AV 500 (13C at 125.8 MHz) spectrometer. The ESIMS spectra were obtained on a Finnigan LCQ spectrometer. UV spectra were recorded from 200 to 800 nm in CH2Cl2 with a Perkin-Elmer Lambda 900 UV/vis/near-IR spectrophotometer. Photoluminescence spectra were measured on an Edinburgh F920 fluorescence spectrophotometer. Luminescence quantum yields were measured with reference to Ru(bpy)32þ (Φ = 0.059). Lifetime studies were performed on a single-photon-counting spectrometer from Edinburgh Instruments (FLS920) with a hydrogen-filled pulse lamp as the excitation source. Elemental analysis was performed on an Elementar Vario MICRO instrument. Reagents. Iodoferrocene,26 ethynylferrocene,27 Ru(tpy)Cl3,28 and 40 -ferrocenyl-2,20 :60 ,200 -terpyridine (Fc-tpy)14 were prepared according to literature procedures. All other chemicals were purchased from commercial suppliers and were used as received. Preparation of 10 -Iodoferrocenecarboxaldehyde (4).29 Iodoferrocene (3.12 g, 10.0 mmol) was added at room temperature under nitrogen to a stirred solution of N-methylformanilide (3.60 g, 26.6 mmol) and POCl3 (2.60 g, 17.1 mmol). Stirring was continued for 1 h at ambient temperature and at 6570 C for an additional 2 h. The mixture was cooled to 0 C, and then a solution of sodium acetate (8.5 g) in water (65 mL) was added dropwise. The mixture was stirred overnight at room temperature and then filtered. The filtrate was extracted with chloroform. The combined extracts were washed with water, dried over MgSO4, and evaporated under reduced pressure. The residue was chromatographed on silica gel. The first band that eluted with petroleum ether was the iodoferrocene. The second band, containing 4, eluted with petroleum ether/ethyl acetate (9/1), affording an orange-red solid (2.07 g, 61%). Mp: 3536 C (lit.30 mp 3435 C). IR (KBr): 1679 cm1 (νCdO). 1H NMR (CDCl3): δ 10.00 (s, 1 H), 4.77 (t, 2 H, Cp), 4.59 (t, 2 H, Cp), 4.50 (t, 2H, Cp), 4.26 (t, 2 H, Cp) ppm. MS: [M þ 1]þ at m/z 340.

Preparation of 2-[3-(10 -Iodoferrocenyl)-1-oxoprop-2-enyl]pyridine (5). 2-Acetylpyridine (0.60 g, 5.0 mmol) was added to a

3505

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Organometallics solution of 4 (1.36 g, 4.0 mmol) in ethanol (50 mL). After 5 min, aqueous sodium hydroxide (2 mol L1, 10 mL) was added and the mixture was stirred for 2 h. A deep purple precipitate appeared. The ethanol was evaporated under reduced pressure. After the addition of water, the mixture was extracted with CH2Cl2. The combined extracts were dried over MgSO4 and evaporated under reduced pressure. The residue was chromatographed on Al2O3. The second deep purple band that eluted with ethyl acetate/CH2Cl2 (1/9) afforded 5 as a deep purple solid (1.43 g, 81%). 1H NMR (CDCl3): δ 8.76 (d, 1H, Py), 8.26 (d, 1H, Py), 7.92 (dt, 1H, Py), 7.87 (s, 2H, CHdCH), 7.51 (ddd, 1H, Py), 4.67 (dd, 2H, Cp), 4.49 (dd, 2H, Cp), 4.40 (dd, 2H, Cp), 4.21 (dd, 2H, Cp) ppm. MS: [M þ 1]þ at m/z 444. Anal. Calcd for C18H14FeINO: C, 48.80; H, 3.18; N, 3.16. Found: C, 48.78; H, 2.92; N, 3.47.

Preparation of 40 -(10 -Iodoferrocenyl)-2,20 :60 ,200 -terpyridine (6). A solution of 5 (1.09 g, 2.5 mmol), N-[2-oxo-2-(2-pyri-

dyl)ethyl]pyridinium iodide (0.88 g, 2.7 mmol), and NH4OAc (about 5 g) in ethanol (50 mL) was heated to reflux for 2 h. The solvent was removed under reduced pressure. After the addition of water, the mixture was extracted with CH2Cl2. The combined extracts were dried over MgSO4 and evaporated under reduced pressure. The residue was chromatographed on Al2O3, with CH2Cl2 as eluent and afforded 6 as a saffron powder (0.51 g, 81%). 1H NMR (CDCl3): δ 8.75 (d, 2H, H6,600 ), 8.66 (d, 2H, H3,300 ), 8.57 (s, 2H, H30 ,50 ), 7.88 (dt, 2H, H4,400 ), 7.36 (ddd, 2H, H5,500 ), 5.02 (dd, 2H, Cp), 4.47 (dd, 2H, Cp), 4.32 (dd, 2H, Cp), 4.07 (dd, 2H, Cp) ppm. MS: [M þ CH3OH]þ at m/z 575. Anal. Calcd for C25H18FeIN3: C, 55.28; H, 3.34; N, 7.74. Found: C, 55.31; H, 3.53; N, 7.83.

Preparation of 40 -[10 -(Ferrocenylethynyl)ferrocenyl]-2,20 : 60 ,200 -terpyridine (Fc0 -tpy, 7). A deoxygenated solution of 6 (1.09 g,

2.0 mmol), ethynylferrocene (0.42 g, 2.0 mmol), Pd(PPh3)2Cl2 (14.04 mg, 0.02 mmol), and CuI (7.62 mg, 0.04 mmol) in diisopropylamine (30 mL) was stirred under reflux for 24 h. The mixture was cooled to room temperature and extracted with CH2Cl2. The combined extracts were evaporated to dryness under reduced pressure. The residue was chromatographed on Al2O3. The first band that eluted with petroleum ether/CH2Cl2 (1/1) was identified as 1,4-diferrocenyl-l,3-butadiyne. The second band that eluted with CH2Cl2 afforded 7 as a yellow powder (1.12 g, 89%). 1H NMR (CDCl3): δ 8.72 (d, 2H, H6,600 ), 8.62 (d, 2H, H3,300 ), 8.54 (s, 2H, H30 ,50 ), 7.87 (dt, 2H, H4,400 ), 7.35 (ddd, 2H, H5,500 ), 5.03 (dd, 2H, Cp), 4.52 (dd, 2H, Cp), 4.40 (dd, 2H, Cp), 4.31 (dd, 2H, Cp), 4.24 (dd, 2H, Cp), 4.14 (s, 5H, Cp), 4.08 (dd, 2H, Cp) ppm. 13C{1H} NMR (CDCl3): δ 65.92 (Fc), 68.06 (Fc), 68.39 (Fc), 68.90 (Fc), 69.91 (Fc), 70.06 (Fc), 70.65 (Fc), 71.24 (Fc), 71.97 (Fc), 72.31 (Fc), 72.73 (Fc), 82.60 (CtC), 82.76 (CtC), 85.01 (Fc), 117.81 (tpy-C3,300 ), 121.43 (tpy-C30 ,50 ), 123.69 (tpy-C5,500 ),136.79 (tpyC4,400 ), 149.07 (tpy-C40 ), 149.39 (tpy-C6,600 ), 155.32 (tpy-C20 ,60 ), 156.46 (tpy-C2,200 ) ppm. MS: [M þ 1]þ at m/z 626. Anal. Calcd for C37H27Fe2N3: C, 71.07; H, 4.35; N, 6.72. Found: C, 71.22; H, 4.64; N, 6.32. Preparation of [Ru(Fc0 -tpy)(tpy)](PF6)2 (8). A mixture of compound 7 (50 mg, 0.08 mmol), Ru(tpy)Cl3 (35 mg, 0.08 mmol), anhydrous ethanol (40 mL), and 10 drops of N-ethylmorpholine was heated under nitrogen at reflux temperature for 5 h. The reaction mixture was cooled to room temperature, and the solvent was removed under reduced pressure until the volume was reduced by half. A solution of NH4PF6 (0.13 g, 0.8 mmol) in water (10 mL) was added, and the mixture was stirred for 1 h. The precipitate was collected by filtration and successively washed with distilled water, anhydrous ethanol, and anhydrous ether. The residue was chromatographed on neutral Al2O3 using a 14:2:1 mixture of acetonitrile, saturated aqueous KNO3 solution, and water. An excess of a NH4PF6 aqueous solution was added to the dark red major collection, affording 8 as a dark red powder (0.08 g, 80%). Mp: 209 C dec. IR (KBr): 3436, 3087, 1609, 1431, 1397, 841, 557, 487 cm1. 1H NMR (CD3CN): δ 8.76 (d, 2H, tpy-H30 ,50 ), 8.74

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(s, 2H, tpy0 -H30 ,50 ), 8.548.49 (m, 4H, tpy and tpy0 -H3,300 ), 8.41 (t, 1H, tpy-H40 ), 7.967.92 (m, 2H, tpy-H4,400 ), 7.887.84 (t, 2H, tpy0 H4,400 ), 7.427.41 (d, 3JH,H = 4 Hz, 2H, tpy-H6,600 ), 7.317.29 (d, 3 JH,H = 8 Hz, 2H, tpy0 -H6,600 ), 7.237.19 (m, 2H, tpy-H5, 500 ), 7.157.13 (m, 2H, tpy0 -H5,500 ), 5.37 (s, 2H, Cp), 4.86 (s, 2H, Cp), 4.54 (s, 2H, Cp), 4.47 (s, 2H, Cp), 4.33 (s, 2H, Cp), 4.20 (s, 5H, Cp), 4.08 (s, 2H, Cp) ppm. ESI-MS: [M  PF6]þ at m/z 1105. Anal. Calcd for C52H38F12Fe2N6P2Ru: C, 49.98; H, 3.07; N, 6.73. Found: C, 49.93; H, 3.22; N, 6.34. Preparation of [Ru(Fc0 -tpy)(Fc-tpy)](PF6)2 (9). A mixture of compound 7 (29.4 mg, 0.047 mmol) and Ru(DMSO)4Cl2 (22.8 mg, 0.047 mmol) in anhydrous ethanol (13 mL) was heated under nitrogen at reflux temperature for 24 h. After the mixture was cooled, the precipitate was collected by filtration, washed with anhydrous ether, and dried under vacuum. The product was mixed with Fc-tpy (20.8 mg, 0.05 mmol) in anhydrous ethanol (30 mL) and heated under nitrogen at reflux temperature for 5 h. The reaction mixture was cooled to room temperature, and the solvent was removed under reduced pressure until the volume was reduced by half. A solution of NH4PF6 (0.08 g, 0.47 mmol) in water (10 mL) was added, and the mixture was stirred for 1 h. The precipitate was collected by filtration and successively washed with distilled water, anhydrous ethanol, and anhydrous ether. The residue was chromatographed on neutral Al2O3 using a 14:2:1 mixture of acetonitrile, saturated aqueous KNO3 solution, and water. An excess of a NH4PF6 aqueous solution was added to the dark red major collection, affording 9 as a dark red powder (0.035 g, 52%). Mp 185 C dec. IR (KBr): 3435, 3088, 1609, 1432, 1388, 842, 557, 487 cm1. 1H NMR (CD3CN): δ 8.778.76 (s, 4H, tpy-H30 ,50 and tpy0 -H30 ,50 ), 8.668.57 (m, 4H, tpy and tpy0 -H3,300 ), 7.987.94 (t, 4H, tpy and tpy0 -H4,400 ), 7.447.36 (d, 3JH,H = 5.2 Hz, 4H, tpy and tpy0 -H6,600 ),7.227.18 (m, 4H, tpy and tpy0 -H5,500 ), 5.37 (s, 2H, Cp), 5.04 (s, 2H, Cp), 4.86 (s, 2H, Cp), 4.80 (s, 2H, Cp), 4.64 (s, 2H, Cp), 4.54 (s, 2H, Cp), 4.47 (s, 2H, Cp), 4.36 (s, 5H, Cp), 4.20 (s, 5H, Cp), 4.10 (s, 2H, Cp) ppm. ESI-MS: [M  PF6]þ at m/z 1288. Anal. Calcd for C62H46F12Fe3N6P2Ru: C, 51.94; H, 3.23; N, 5.86. Found: C, 51.81; H, 3.58; N, 6.18. Preparation of [Ru(Fc0 -tpy)2](PF6)2 (10). A mixture of compound 7 (17.5 mg, 0.028 mmol) and Ru(DMSO)4Cl2 (13.6 mg, 0.028 mmol) in anhydrous ethanol (8 mL) was heated under nitrogen at reflux temperature for 24 h. After the mixture was cooled, the precipitate was collected by filtration, washed with anhydrous ether, and dried under vacuum. The product was mixed with 7 (18.8 mg, 0.03 mmol) in anhydrous ethanol (30 mL) and heated under nitrogen at reflux temperature for 5 h. The reaction mixture was cooled to room temperature, and the solvent was removed under reduced pressure until the volume was reduced by half. An aqueous solution (10 mL) of NH4PF6 (47.7 mg, 0.28 mmol) was added, and the mixture was stirred for 1 h. The precipitate was collected by filtration and successively washed with distilled water, anhydrous ethanol, and anhydrous ether. The residue was chromatographed on neutral Al2O3 using a 14:2:1 mixture of acetonitrile, saturated aqueous KNO3 solution, and water. An excess of an aqueous solution of NH4PF6 was added to the dark red major collection, affording 10 as a dark red powder (0.032 g, 70%). Mp: 285 C dec. IR (KBr): 3431, 3088, 1607, 1431, 1388, 843, 557, 486 cm1. 1H NMR (CD3CN): δ 8.78 (s, 4H, tpy-H30 ,50 ), 8.548.49 (m, 4H, tpy0 -H3,300 ), 7.967.92 (m, 4H, tpy-H4,400 ), 7.427.41 (m, 4H, tpy-H6,600 ), 7.157.13 (m, 4H, tpy-H5,500 ), 5.37 (s, 4H, Cp), 4.88 (s, 4H, Cp), 4.55 (s, 4H, Cp), 4.47 (s, 4H, Cp), 4.31 (s, 4H, Cp), 4.20 (s, 10H, Cp), 4.08 (s, 4H, Cp) ppm. ESI-MS: [M  PF6]þ at m/z 1497, [M  2PF6]þ at m/z 1351. Anal. Calcd for C74H54F12Fe4N6P2Ru 3 4H2O: C, 51.86; H, 3.65; N, 4.90. Found: C, 51.74; H, 3.67; N, 4.90. Crystallography. Single crystals of 7 suitable for X-ray diffraction studies were obtained by slow diffusion of hexane into a CH2Cl2 solution at room temperature. Data were collected on a Rigaku-Weissenberg IP diffractometer. The structure was solved by direct methods and refined 3506

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Scheme 1. Synthesis of Ligand 7a

a Legend: (a) 2-acetylpyridine, NaOH, EtOH; (b) N-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide, NH4OAc, EtOH; (c) ethynylferrocene, Pd(PPh3)2Cl2, CuI, i-Pr2NH.

by full-matrix least squares on F2 using the SHELX program package.31 Non-hydrogen atoms were anisotropically refined, and the hydrogen atoms were refined in the riding mode with isotropic temperature factors fixed at 1.2 times the U(eq) values of the parent atoms (1.5 times for methyl groups). Electrochemistry. Electrochemical measurements were performed on a CHI 620C electrochemical analyzer at 25 C. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were carried out using a three-electrode system with glassy carbon as the working electrode, a platinum electrode as the counter electrode, and Ag/AgCl (3.0 mol L1 KCl) as the reference electrode. These experiments were carried out with a 0.3 mmol L1 solution of ferrocene derivatives in CH2Cl2 or CH2Cl2/ CH3CN (19/1) containing 0.1 mol L1 of tetrabutylammonium hexafluorophosphate (TBAHFP) as supporting electrolyte.

Scheme 2. Synthesis of Ru2þ Complexes

’ RESULTS AND DISCUSSION Synthesis. The new ligand 7 and its Ru2þ complexes 810

have been prepared as shown in Schemes 1 and 2. 7 was prepared by Sonogashira cross-coupling of 6 with ethynylferrocene in diisopropylamine in the presence of Pd(PPh3)2Cl2 and CuI as catalyst (Scheme 1). Among the raw materials, the multifunctional building block 4 has been prepared through an improved three-step procedure from ferrocene.29 This new protocol features the ready availability of the starting materials and a simple and straightforward synthetic pathway. The new ligand 7 is airstable in the solid state. In solution, the ligand is air-stable under exposure of a fluorescent lamp. However, the color of this compound changes from yellow to blue upon UV exposure because of a one-electron oxidation of the ferrocene moiety.3 Ru(II) complexes were isolated as the hexafluorophosphate salts and purified by column chromatography. Solid-State Structure of 7. The molecular structure of 7 in the solid state is shown in Figure 1. Selected bond distances, bond angles, and dihedral angles are summarized in the caption of Figure 1. Ligand 7 crystallizes in the monoclinic space group P21/c with two molecules in the asymmetric unit, as shown in Figure 1. The average distances of FeC (2.05 Å) and CpCp (3.3 Å) are close to those reported for analogous ferrocenes.32 The ethynyl moiety is almost linear and exhibits an average angle of 177. The CC triple-bond distance (about 1.21 Å) is close to those

reported for analogous compounds.3,24 The Cp rings coordinated to Fe2 adopt a staggered conformation, while Cp rings of the other three Fc groups are almost eclipsed. In molecule A (Figure 1, left), the four Cp rings are nearly parallel, with an average dihedral angle of 2.86. In molecule B (Figure 1, right), the two central axes of the ferrocene moieties are approximately perpendicular, with a dihedral angle of 72.16 of the two alkynyl-bridged Cp rings. For both molecules, the 2,20 :60 ,200 -terpyridine group is almost coplanar and exhibits a maximum dihedral angle of 7.62. The terpyridine group adopts the expected transtrans conformation about the interannular CC bonds.3,19 The directly bonded Cp ring of the ferrocene group is almost coplanar with the central ring of terpyridine, with dihedral angles of 3.27 and 7.49 for molecules A and B, respectively. Electrochemical Study of 7. The free ligand 7 was studied by cyclic voltammetry (CV) using CH2Cl2 as the solvent. The measurements were carried out at a scan rate of 100 mV s1. The CV curve is shown in Figure 2. Electrochemical data of 7 as well as of some related compounds are shown in Table 1. 3507

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Figure 1. ORTEP view of 7 (50% probability level). Hydrogen atoms are omitted for clarity. Selected bond distances (Å), bond angles (deg), and dihedral angles (deg): C1C11 = 1.455(10), C11C12 = 1.208(10), C12C13 = 1.414(10), C18C23 = 1.474(8), C25C26 = 1.479(8), C31 C33 = 1.492(8), C38C48 = 1.433(9), C48C49 = 1.204(9), C49C50 = 1.414(9), C55C60 = 1.478(8), C62C63 = 1.481(8), C68C70 = 1.510(8); C1C11C12 = 177.8(8), C11C12C13 = 178.9(9), C38C48C49 = 175.1(8), C48C49C50 = 176.5(8); Cp(5)Cp(15) = 4.54, tpy(2)Cp(20) = 3.27, tpy(2)tpy(1) = 3.22, tpy(2)tpy(3) = 6.40, Cp(40)Cp(50) = 72.16, tpy(5)Cp(55) = 7.49, tpy(5)tpy(4) = 2.57, tpy(5)tpy(6) = 7.62. Cp(n) and tpy(n) denote the planes of the cyclopentadienyl ring and the pyridyl ring containing Cn and Nn, respectively.

Table 1. CV Data of 710 and Related Compounds compd

E1/2(Ru2þ/3þ), V E1/2(Fe2þ/3þ), V E1/2(tpy0//2), V

ferrocenea

0.46

Fc-Fcb Fc-CtC-Fcb

0.44, 0.79 0.63, 0.76

bifc-tpyc

0.45, 0.90

7a

0.53, 0.78

[Ru(tpy)2]2þd

þ1.19

3c

þ1.36

0.48, 0.88

1.19, 1.52 1.16, 1.43

8a

þ1.35

0.58, 0.79

1.22, 1.46

9a

þ1.36

0.55, 0.79

1.20, 1.43

10a

þ1.38

0.58, 0.80

1.18, 1.45

a

Figure 2. Cyclic voltammogram at a scan rate of 100 mV s1 of 0.3 mmol L1 solutions of 7 in CH2Cl2/0.1 mol L1 TBAHFP at a glassy carbon electrode.

As shown in Figure 2, 7 undergoes two successive reversible one-electron-oxidation processes, corresponding to Fe(II)Fe(II) f Fe(II)Fe(III) and Fe(II)Fe(III) f Fe(III)Fe(III), respectively. All the binuclear compounds listed in Table 1 (from “FcFc” to “7”) exhibit two pairs of redox peaks, indicating that the two ferrocenyl fragments are not electrochemically equivalent. The terpyridyl substituent acts as an electron-withdrawing group, decreasing the electron density of the adjacent and the nonadjacent ferrocene moiety (through the electron-transferring alkynyl spacer), resulting in a positive shift of the half-wave potentials to 0.78 and 0.53 V, respectively. In comparison to FcCC-Fc, the redox peaks become more distinguishable as the ΔE1/2 value increased after the introduction of a terpyridyl substituent, a phenomenon observed likewise for bifc-tpy and bifc.19 The E1/2 value of the nonadjacent ferrocenyl of Fc-CtC-Fctpy (0.53 V) is more positive than that of bifc-tpy (0.45 V), while

Vs Ag/AgCl electrode in this work. b Vs SCE electrode.33 c Vs Ag/AgCl electrode;19 bifc = biferrocene. d Vs Ag/AgCl electrode.15,16

for the adjacent ferrocenyl it is more negative (0.78 V for FcCtC-Fc-tpy and 0.90 V for bifc-tpy). The comparison of redox potentials between 7 and the similar compound bifc-tpy19 indicates that the introduction of the alkynyl spacer enhances the electron transfer between the two ferrocene moieties. Thus, the electronic properties of the terpyridine ligand are perturbed. Electrochemical Results for the Ru2þ Complexes. The Ru2þ complexes 810 were studied by CV using CH2Cl2/ CH3CN (19/1) as the solvent. The CV curves are shown in Figure 3. Electrochemical data for the Ru(II) complexes 810 are collected in Table 1. The redox behavior of 810 is dominated by the Ru2þ/Ru3þ redox couple (E1/2 from 1.37 to 1.42 V), the Fe2þ/Fe3þ redox couples (E1/2 from 0.53 to 0.80 V), and the tpy/tpy/tpy2 redox couples (E1/2 from 1.18 to 1.50 V). The potential shifts of the E1/2 values for the Ru2þ/Ru3þ redox couples (160mV) and the tpy/tpy/tpy2 redox couples (3060 mV) of complex 8 compared with the values for [Ru(tpy)2]2þ indicate that there is an interaction between Ru2þ and the Fc-CtC-Fc 3508

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Figure 3. Cyclic voltammograms at a scan rate of 100 mV s1 of 0.3 mmol L1 solutions of complexes 810 in CH2Cl2/CH3CN (19/1 v/v)/0.1 mol L1 TBAHFP at a glassy carbon electrode.

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Figure 5. UVvis absorption spectra of 810 in CH2Cl2 solution at room temperature.

Table 2. UVVis Absorption Data of 710 and Related Compounds abs λmax, nm (103ε, M1 cm1)

compd ferrocenea

437 (0.096), 322 (0.056)

Ru(tpy)22þb

478 (14), 306 (61), 269 (39)

Fc-tpyb

454 (2.5), 363 (6.1), 280 (107), 248 (107)

(Fc-tpy)Ru2þ(tpy)b

515 (sh), 478 (15), 306 (61), 270 (41)

(Fc-tpy)2Ru2þb

526 (15), 482 (15), 310 (60), 284 (44), 274 (49)

Fc-CtC-tpyc

450 (1.6), 375 (sh), 321 (21.3), 280 (34.0), 253 (30.4)

(Fc-CtC-

525 (sh), 489 (28.7), 309 (81.4), 273 (63.6)

tpy)Ru2þ(tpy)c

Figure 4. UVvis absorption spectrum of 7 in CH2Cl2 solution at room temperature.

(Fc-CtC-tpy)2Ru2þc

505 (28.0), 314 (69.8), 277 (63.1)

bifc-tpyd

481 (4.3), 340 (sh), 281 (99), 276 (104), 272 (99),

3d

518 (8.8), 480 (14), 347 (sh), 308 (61), 270 (40),

7

467.1 (4.7), 377 (sh), 278.8 (125.2), 245.8 (136.5)

8

518 (sh), 480.9 (29.9), 308.1 (124.9), 271.9 (96.8)

9

526.7 (16.9), 483.6 (17.8), 308.4 (96.9), 276.4 (106.2)

10

581.7 (13.9), 510 (18.5), 309.7 (88.9), 281.2 (93.7)

253 (103) 263 (41)

group, possibly due to the lowered energy of the LUMO orbitals caused by the introduction of the 40 -substituent. Similar potential shifts have been previously reported for 3.19 The small variations of the E1/2 values for the Fe2þ/Fe3þ redox couples of 7 (0.53 and 0.78 V) compared to those of complexes 810 (0.550.58 and 0.790.80 V) suggest a weak interaction between the Ru2þ and Fe2þ centers. Although complex 9 possesses three asymmetric ferrocene moieties, only two redox peaks were observed, as shown in Figure 3. This can be explained by the similar chemical environments around those two ferrocene moieties attached to the terpyridyl. Thus, there is a redox peak masked by the other two peaks. A comparison with the complexes 8 and 10 demonstrates that the terpyridyl redox peaks of 9 are slightly different, probably due to the two different ferrocenyl substituents that are attached to the terpyridyl moieties. UVvis Spectroscopy. The UVvis absorption spectra of 710 in a CH2Cl2 solution at room temperature are shown in Figures 4 and 5. The UVvis spectral data of 710 and related compounds are summarized in Table 2. As shown in Figure 4, the UV absorption spectra of ligand 7 correspond to assembled spectra of the ferrocene moiety and the tpy moiety. The absorption bands at 322 nm (ε = 56 M1 cm1) and 437 nm (ε = 96 M1 cm1) of ferrocene have been assigned to the 1A1g f 1E1g and 1A1g f 1E2g ligand-field (dd) transitions,

a

From ref 16. b From ref 15. c From ref 3. d From ref 19.

respectively.19,34,35 The absorption band at 279 nm (ε = 125 200 M1 cm1) has been assigned to the πtpyπ*tpy transitions. The absorption bands at 377 nm (sh) and 467 nm (ε = 4700 M1 cm1) for the ferrocene moiety of 7 are redshifted and the molar absorptivities of the bands are considerably enhanced relative to those of ferrocene, which is consistent with the electron-withdrawing character of tpy15,34 attached to the ferrocene moiety and the expanded conjugated system. As shown in Figure 5, the visible absorption bands at ∼480 nm of 810 are dominated by the 1[(d(π)Ru)6] f 1[d(π)5(π*tpy)1] MLCT absorption. The broad visible absorption bands at 518 nm (sh) for 8, 526 nm (ε = 16 900 M1 cm1) for 9, and 581 nm (ε = 13 900 M1 cm1) for 10 are assigned to the 1 [(d(π)Fe)6] f 1[(d(π)Fe)5 (π*tpyRu)1] MMLCT transition.16 The peak position of this transition is red-shifted with an increasing number of ferrocenyl substituents. The insertion of the ethynyl group enlarges the π-electron system of the delocalization of the molecule and lowers the energy of the π*tpy orbitals, giving rise to a more red-shifted transition. 3509

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Figure 6. Luminescence spectra at λexc 490 nm of complexes 810 in H2O/CH3CN (4/1 v/v) solution at room temperature.

Table 3. Emission Maxima, Quantum Yields, and Lifetimes of 810 and Related Compoundsa compd

λmax, nm

[Ru(tpy)2]2þ

n.d.

104Φem

τ, ns

3b

n.d.

1c

690

1.48

67

2c 8

690 712

1.13 2.63

24 323

9

712

0.83

10

712

0.66

In H2O/CH3CN (4/1) solution at room temperature: λmax = emission maximum and Φem = emission quantum yield (measured at λexc 490 nm), τ = triplet lifetime (measured at λexc 340 nm), n.d. = nondetectable. b From ref 19. c From ref 25. a

Luminescence Spectroscopy. Since the ferrocene moiety can act as an efficient quencher for the 3MLCT state, ferrocenylsubstituted analogues show almost negligible luminescence, except from a few complexes that have been reported.3,24,25 We studied the three ferrocenyl-functionalized terpyridine Ru2þ complexes in a H2O/CH3CN (4/1 v/v) solution at room temperature (Figure 6). The emission maxima, quantum yields, and lifetimes of 810 and related compounds are summarized in Table 3. The complexes 9 and 10 show a dramatic decrease in the luminescence intensity; thus, we were not able to study their luminescence lifetimes. As shown in Figure 6, all three Ru2þ complexes exhibit luminescence at room temperature with a maximum emission wavelength at 712 nm. Complex 8 shows the strongest luminescence intensity (λmaxem 712 nm, Φem = 2.63  104, τ = 323 ns) relative to the analogous ferrocene-based terpyridine Ru(II) complexes (see Table 3). The pronounced weak luminescence intensities of 9 and 10 have been attributed to the presence of additional ferrocene moieties, which provide additional channels for excited-state deactivation. In comparison with complex 3, which is nonluminescent at room temperature,19 the structure of ligand 7 has an inserted ethynyl group in the main chain. The insertion of the ethynyl group enlarges the electron delocalization in the extended π* orbitals and lowers the energy of the 3MLCT orbitals. As a consequence, the energy gap between the 3MLCT and 3MC levels increases and the radiationless deactivation through the 3MC is slower. Therefore, complexes 810 exhibit room-temperature luminescence.

Figure 7. Schematic Jablonski-type energy level diagram for complex 8.

MLCT Excited-State Decay. From the analysis of the UVvis absorption and fluorescence spectral data of complex 8, we propose the energy level diagram given in Figure 7. The excited-state energy of 8 is estimated to be 2.6 eV from the absorption maximum (480.9 nm), which is attributed to the 1 [(d(π)Ru)6] f 1[d(π)5(π*tpy)1] MLCT absorption, designated the 1[RuIII-tpy-FcII] state. The 1[(d(π)Fe)6] f 1[(d(π)Fe)5(π*tpyRu)1] MMLCT transition leading to the shoulder at 518 nm corresponds to an energy of 2.4 eV, designated the 1 [RuII-tpy-FcIII] state. The excited-state energy of 3[RuIII-tpyFcII] is estimated to be 1.7 eV from the emission maximum at 712 nm. An energy of 1.92.0 eV for the 3[RuII-tpy-FcIII] state was estimated from the low-energy onset of the 1[(d(π)Fe)6] f 1 [(d(π)Fe)5(π*tpyRu)1] MLCT band.36 The insertion of an ethynyl group enlarges the electron delocalization of the molecule in the extended π* orbitals and lowers the energy of the 3 [RuIII-tpy-FcII] energy level. There is less pronounced mixing between the 3[RuIII-tpy-FcII] state and the 3[RuII-tpy-FcIII] state in 8. Consequently, the Ru2þ complex 8 exhibits roomtemperature luminescence in a H2O/CH3CN (4/1) solution.

’ CONCLUSIONS In this paper, the novel ferrocene-based terpyridine ligand 7 and its Ru2þ complexes 810 have been synthesized and characterized using electrochemical and photophysical studies. Spectroscopic data show that the Ru2þ complexes can be regarded as promising candidates for building blocks of molecular wires. The crystal structure of the free ligand reveals two molecules in the asymmetric unit with different orientations of the terminal ferrocene moiety. Cyclic voltammetric measurements of 7 show two successive reversible one-electron-oxidation processes with half-wave potentials of 0.53 and 0.78 V. The small variations of the E1/2 values for the Fe2þ/Fe3þ redox couples after the coordination of the Ru2þ iron suggest a weak interaction between the Ru2þ and Fe2þ centers. The enlarged molecule delocalization lowers the energy of the π*tpy orbitals, giving a more red-shifted 1[(d(π)Fe)6] f 1[(d(π)Fe)5(π*tpyRu)1] MMLCT transition in the visible region of the UV spectra. The insertion of the ethynyl functionality enlarges the π-electron delocalization and lowers the energy of the 3MLCT level. As a consequence, the energy gap between the 3MLCT and 3MC levels increases and the activated radiationless deactivation 3510

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Organometallics through 3MC is slower. All three Ru2þ complexes show intense luminescence at room temperature with a maximum emission wavelength at 712 nm. To the best of our knowledge, complex 8 shows the strongest luminescence intensity (λmaxem 712 nm, Φem = 2.63  104, τ = 323 ns) relative to analogous ferrocenebased terpyridine Ru(II) complexes previously reported. However, the dramatic decrease of luminescence yields and the triplet lifetimes observed for 9 and 10 have been attributed to the presence of additional ferrocene moieties, which act as efficient quenchers. On the basis of these results, we are intending to design improved connecting spacers in subsequent research.

’ ASSOCIATED CONTENT Supporting Information. A CIF file and tables giving crystallographic data for 7 (CCDC 705110) and figures giving DPV plots of 710. This material is available free of charge via the Internet at http://pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (Y.-F.Y.); p.nockemann@ qub.ac.uk (P.N.).

’ ACKNOWLEDGMENT This work was supported financially by the NNSFC (Grant No. 20772016), the NSF of Fujian Province (Grant No. 2009J05028 and 2010J01036), the Science and Technology Key Project from Fujian Province (Grant No. 2009H0021), and the Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars from the Education Ministry of China. P.N. thanks the EPSRC for an RCUK fellowship. ’ REFERENCES (1) Schubert, U. S.; Hofmeier, H.; Newkome, G. R. Modern Terpyridine Chemistry; Wiley-VCH: Weinheim, Germany, 2006. (2) Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.; Thompson, A. M. W. C. Inorg. Chem. 1995, 34, 2759. (3) Siemeling, U.; Br€uggen, J. V. d.; Vorfeld, U.; Neumann, B.; Stammler, A.; Stammler, H.-G.; Brockhinke, A.; Plessow, R.; Zanello, P.; Laschi, F.; Biani, F. F. d.; Fontani, M.; Steenken, S.; Stapper, M.; Gurzadyan, G. Chem. Eur. J. 2003, 9, 2819. (4) Lim, Y.-K.; Wallace, S.; Bollinger, J. C.; Chen, X.; Lee, D. Inorg. Chem. 2007, 46, 1694. (5) Zhang, W.-W.; Yu, Y.-G.; Lu, Z.-D.; Mao, W.-L.; Li, Y.-Z.; Meng, Q.-J. Organometallics 2007, 26, 865. (6) Stepnicka, P. Ferrocenes: Ligands, Materials and Biomolecules; Wiley: Chichester, England, 2008. (7) (a) Du, P.; Schneider, J.; Li, F.; Zhao, W.; Patel, U.; Castellano, F. N.; Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 5056. (b) Manner, V. W.; Mayer, J. M. J. Am. Chem. Soc. 2009, 131, 9874. (c) Welter, S.; Brunner, K.; Hofstraat, J. W.; De Cola, L. Nature 2003, 421, 54. (8) (a) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. Rev. 1996, 96, 759. (b) Benniston, A. C.; Grosshenny, V.; Harriman, A.; Ziessel, R. Angew. Chem., Int. Ed. Engl. 1994, 33, 1884. (c) Poddutoori, P. K.; Poddutoori, P.; Maiya, B. G.; Prasad, T. K.; Kandrashkin, Y. E.; Vasil’ev, S.; Bruce, D.; Est, A. v. d. Inorg. Chem. 2008, 47, 7512. (d) Sauvage, J.-P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. Rev. 1994, 94, 993. (e) Shunmugam, R.; Tew, G. N. Chem. Eur. J. 2008, 14, 5409.

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(9) Qiu, D.; Cheng, Y.; Wang, L. Dalton Trans. 2009, 3247. (10) (a) Yuan, Y.-F.; Cardinaels, T.; Lunstroot, K.; Van Hecke, K.; Van Meervelt, L.; G€orller-Walrand, C.; Binnemans, K.; Nockemann, P. Inorg. Chem. 2007, 46, 5302. (b) Lu, M.; He, T.; Tour, J. M. Chem. Mater. 2008, 20, 7352. (c) H€usken, N.; Gasser, G.; K€oster, S. D.; Metzler-Nolte, N. Bioconjugate Chem. 2009, 20, 1578. (d) Landis, E. C.; Hamers, R. J. Chem. Mater. 2009, 21, 724. (11) Browne, W. R.; O’Boyle, N. M.; McGarvey, J. J.; Vos, J. G. Chem. Soc. Rev. 2005, 34, 641. (12) (a) Baranoff, E.; Collin, J.-P.; Flamigni, L.; Sauvage, J.-P. Chem. Soc. Rev. 2004, 33, 147. (b) Gr€atzel, M. Inorg. Chem. 2005, 44, 6841. (c) Meyer, T. J. Acc. Chem. Res. 1989, 22, 163. (13) Chambron, J.-C.; Coudret, C.; Sauvage, J.-P. New J. Chem. 1992, 16, 361. (14) Constable, E. C.; Edwards, A. J.; Martinez-Ma~ nez, R.; Raithby, P. R.; Thompson, A. M. W. C. J. Chem. Soc., Dalton Trans. 1994, 645. (15) Farlow, B.; Nile, T. A.; Walsh, J. L.; McPhail, A. T. Polyhedron 1993, 12, 2891. (16) Hutchison, K.; Morris, J. C.; Nile, T. A.; Walsh, J. L.; Thompson, D. W.; Petersen, J. D.; Schoonover, J. R. Inorg. Chem. 1999, 38, 2516. (17) (a) Thompson, A. M. W. C. Coord. Chem. Rev. 1997, 160, 1. (b) Wild, A.; Winter, A.; Schl€utter, F.; Schubert, U. S. Chem. Soc. Rev. 2011, 40, 1459. (18) Constable, E. C.; Edwards, A. J.; Marcos, M. D.; Raithby, P. R.; Martinez-Ma~ nez, R.; Tendero, M. J. L. Inorg. Chim. Acta 1994, 224, 11. (19) Dong, T.-Y.; Lin, M.-C.; Chiang, M. Y.-N.; Wu, J.-Y. Organometallics 2004, 23, 3921. (20) Dong, T.-Y.; Chen, K.; Lin, M.-C.; Lee, L. Organometallics 2005, 24, 4198. (21) Heinze, K.; Hempel, K.; Beckmann, M. Eur. J. Inorg. Chem. 2006, 2040. (22) Siemeling, U.; Vorfeld, U.; Neumann, B.; Stammler, H.-G.; Zanello, P.; Biani, F. F. d. Eur. J. Inorg. Chem. 1999, 1. (23) Dong, T.-Y.; Chang, S.-W.; Lin, S.-F.; Lin, M.-C.; Wen, Y.-S.; Lee, L. Organometallics 2006, 25, 2018. (24) Dong, T.-Y.; Lin, H.-Y.; Lin, S.-F.; Huang, C.-C.; Wen, Y.-S.; Lee, L. Organometallics 2008, 27, 555. (25) Dong, T.-Y.; Lin, M.-C.; Chang, S.-W.; Ho, C.-C.; Lin, S.-F.; Lee, L. J. Organomet. Chem. 2007, 692, 2324. (26) Fish, R. W.; Rosenblum, M. J. Org. Chem. 1965, 30, 1253. (27) (a) Polin, J.; Schottenberger, H. Org. Synth. 1996, 73, 262. (b) Rosenblum, M.; Brawn, N.; Papenmeier, J.; Applebaum, M. J. Organomet. Chem. 1966, 6, 173. (28) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg. Chem. 1980, 19, 1404. (29) (a) Guo, J.; Wu, K. Q.; Chen, X.; Yuan, Y. F. Chem. J. Chin. Univ. 2010, 31, 79. (b) Guo, J.; Zhuang, S.; Chen, S. H.; Zhang, S. B.; Yuan, Y. F. Chin. J. Org. Chem. 2009, 29, 1264. (30) Inouye, M.; Hyodo, Y.; Nakazumi, H. J. Org. Chem. 1999, 64, 2704. (31) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (32) Seiler, P.; Dunitz, J. D. Acta Crystallogr. 1979, B35, 1068. (33) Levanda, C.; Bechgaard, K.; Cowan, D. O. J. Org. Chem. 1976, 41, 2700. (34) (a) Bhadbhade, M. M.; Das, A.; Jeffery, J. C.; McCleverty, J. A.; Badiola, J. A. N.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1995, 2769. (b) Sohn, Y. S.; Hendrickson, D. N.; Gray, H. B. J. Am. Chem. Soc. 1971, 93, 3603. (35) Bozak, R. E. Adv. Photochem. 1971, 8, 227. (36) Benniston, A. C.; Goulle, V.; Harriman, A.; Lehn, J.-M.; Marczinke, B. J. Phys. Chem. 1994, 98, 7798.

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