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[求助] 由于本人英文能力有限，求助虫友翻译一片化学方面的英文文献

Synthesis, Reactivity and Photophysical Properties of Quinolinolato Ruthenium(II) Complexes

Jing Xiang, Larry Tso-Lun Lo, Chi-Fai Leung, Shek-Man Yiu, Chi-Chiu Ko,* and Tai-Chu Lau*

Introduction
The excellent electron-transporting and emissive properties of 8-quinolinolato aluminum complex (AlQ3) in the electroluminescent devices have attracted enormous attention. In order to tune the functional properties of the AlQ3, considerable efforts have been made to study the relationship between properties of AlQ3-related complexes with their electronic and structural properties of the quinolinolato ligands. These studies have led to the development of AlQ3 derivatives with tunable HOMO-LUMO energy gaps and emission colors from blue to red.2 To explore quinolinolato complexes with different excited state properties, a number of quinolinolato transition metal complexes have also been synthesized and their photophysical properties were investigated. In contrast to AlQ3 derivatives, which only exhibit singlet emission, luminescence derived from both the singlet and triplet emissive excited states have also been reported in some of these quinolinolato complexes with heavy transition metal centers.3 With the quinolinolato ruthenium(II) complexes, their applications as photosensitizer for dye-sensitized solar cell have also been explored. To extend our recent work on the development of quinolinolato ruthenium(II) complexes,3f herein, we report the synthesis, characterization, reactivity and photophysical properties of a new class of quinolinolato ruthenium(II) complexes with different substituents on quinolinolato ligand and ancillary ligands of diverse electronic properties.

Physical measurements and Instrumentation.
IR spectra were recorded as KBr pellets on a Nicolet Avatar 360 FT-IR spectrometer at 4 cm–1 resolution. UV–Vis absorption spectra were recorded on either a Perkin–Elmer Lamda 19 or a Shimadzu UV3100 spectrophotometer. 1H NMR spectra were recorded on a Varian (300 MHz) NMR spectrometer or a Bruker (400 MHz) NMR spectrometer. The chemical shifts (δ ppm) were reported with reference to tetramethylsilane (TMS). Electrospray ionization mass spectra (ESI-MS) were obtained on a PE SCIEX API 365 mass spectrometer. Elemental analyses were done on an Elementar Vario EL III analyzer. Steady-state emission and excitation spectra were recorded on a Horiba Jobin Yvon Fluorolog-3-TCSPC spectrophotometer. Measurements of the EtOH/MeOH/CH2Cl2 (4:1:1, v/v/v) glassy samples at 77 K were carried out with samples contained in a quartz tube inside a quartz-walled Dewar flask. Luminescence quantum yields were determined using the optical dilution method described by Demas and Crosby with an aqueous solution of [Ru(bpy)3]Cl2 (em = 0.042 with 436 nm excitation) as reference. Luminescence lifetimes of the samples were determined using the time correlated single photon counting (TCSPC) technique on the TCSPC spectrofluorometer in a TCSPC mode using a NanoLED-375LH excitation source, which has its excitation peak wavelength at 375 nm and a pulse width shorter than 750 ps.

X-ray crystallography. The crystal structures were determined on an Oxford Diffraction Gemini S Ultra X-ray single crystal diffractometer using graphite monochromatized Cu–Kα (λ = 1.54178 Å

. Details of the crystal data and structure refinement are summarized in Table 1. The structures were resolved by the heavy-atom Patterson methods or direct methods and refined by full-matrix least-squares using SHELX-97  and expanded using Fourier techniques.  All non-hydrogen atoms were refined anisotropically. H atoms were generated by the program SHELXL-97.7 The positions of H atoms were calculated on the basis of riding mode with thermal parameters equal to 1.2 times that of the associated C atoms, and participated in the calculation of final R-indices.
Table 1. Crystal data and structure refinement details for compounds 3, 4, 8 and 12.
3•2CH2Cl2 4 8•0.25CH2Cl2•H2O 12
Formula C53H51NO8P2Ru•2CH2Cl2
C48H41NO2P2Ru C55.25H45.50Cl0.50N3O3P2Ru C43H45N3O2PRuF6P

Mr 1162.81 826.83
980.18
912.83

T /K 133 (2) 173 (2)
133 (2)
133 (2)

Crystal system Monoclinic Triclinic Triclinic
Monoclinic

Space group P21/n
Pī
Pī
P21/n

a/Å 12.4343 (3) 9.2381 (3)
12.5278 (5)
12.4298 (3)

b/Å 28.1257 (5) 12.5884 (4)
13.1009 (5)
24.7828 (6)

c/Å 15.6486 (3) 17.4284 (5)
16.4148 (5)
13.3653 (3)

α, (°) / 82.761 (2)
101.879 (3)
/
β, (°) 101.690 (2) 86.015 (3)
92.797 (3)
94.183 (2)

γ, (°) / 74.412 (3)
111.000 (3)
/
V/ Å3 5359.18 (18) 1935.36 (10)
2439.04 (15)
4106.15 (17)

Z 4 2 2 4
ρcalcd, g cm–3 1.441
1.419
1.335
1.477

F(000) 2392 852 1009 1872
Collected refl. 23013
12258
16693
29571

Unique refl. 10291
6737
8596
7306

R(int) 0.025
0.027
0.018
0.026

Final R indices, I > 2σ(I) R1(obs) = 0.048
wR(all) = 0.139
R1(obs) = 0.034
wR(all) = 0.118
R1(obs) = 0.036
wR(all) = 0.108
R1(obs) = 0.040
wR(all) = 0.099

GOF 1.11
1.23
1.08
1.03

No.of par. 733
489
589
578

Synthesis and Characterization
Materials and Reagents. The 8-hydroxyquinoline (QH) and its derivatives, 2-methyl-8-hydroxyquinoline (MeQH), 5-chloro-8-hydroxyquinoline (ClQH) and 5-phenyl-8-hydroxyquinoline (PhQH), were purchased from Aldrich Chemical Company. [RuII(PPh3)3Cl2],  [RuII(PPh3)3(CO)(H)2]  and [RuII(PPh3)3(CO)(H)(Cl)]  were synthesized according to literature procedures. Other chemicals were of reagent grade and used without further purification.
[RuII(MeQ)(H)(CO)(PPh3)2] (1)
MeQH (79 mg, 0.5 mmol) in MeOH (20 mL) was slowly added to a suspension of [RuII(PPh3)3Cl2] (500 mg, 0.5 mmol) in MeOH (150 mL) containing Et3N (0.5 mL). The resulting mixture was refluxed for 5 hours under an inert atmosphere of argon, during which pale yellow solid was precipitated. Thereafter, the pale yellow solid was collected by suction filtration and air dried. It was further purified by recrystallization from slow evaporation of CH2Cl2/MeOH (1:3, v/v) solution of the complex. Yield: (300 mg, 73%). IR (KBr, cm–1): (C≡O) 1904, (Ru-H) 1950. ESI-MS: m/z 812 [M – H]+, 655 [M – MeQ]+. 1H NMR (400 MHz, CDCl3): δ 7.46-7.51 (m, 14H; Ar-H), 7.12-7.23 (m, 18H; Ar-H), 6.79 (t, J = 7.8 Hz, 1H; Ar-H), 6.58 (d, J = 7.8 Hz, 1H; Ar-H), 6.31 (s, 1H; Ar-H), 6.19 (s, 1H; Ar-H), 1.97 (s, 3H; -CH3), –10.62 (t, J = 20.0 Hz, 1H; Ru-H). Elemental analysis calcd (%) for C47H39NO2P2Ru: C 69.45, H 4.84, N 1.72; found: C 69.10, H 4.72, N 1.77. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 265sh (24350),  354 (6930), 421 (3710).

[RuII(MeQ)(H)(CO){P(C6H4Me)3}2] (2)
The compound was synthesized according to a procedure similar to that for 1 except [RuII{P(C6H4Me)3}3Cl2]  was used in place of [RuII(PPh3)3Cl2]. Yield: (268 mg, 59%). IR (KBr, cm–1): (C≡O) 1907, (Ru-H) 1944. ESI-MS: m/z 896 [M – H]+, 739 [M – MeQ]+. 1H NMR (400 MHz, CDCl3): δ 7.35-7.40 (dt, J = 8.0, 4.9 Hz, 12H, Ar-H), 6.90 (d, J = 6.8 Hz, 12H, Ar-H), 6.76 (t, J = 7.8 Hz, 1H, Ar-H), 6.54 (d, J = 8.4 Hz, 1H, Ar-H), 6.22 (d, J = 7.8 Hz, 1H, Ar-H), 6.15 (d, J = 8.2 Hz, 1H, Ar-H), 5.30 (s, 1H, Ar-H), 2.23 (s, 18H, -CH3), 2.04 (s, 3H, -CH3), –10.69 (t, J = 20.2 Hz, 1H, Ru-H). Elemental analysis calcd (%) for C53H51NO2P2Ru: C 70.97, H 5.73, N 1.56; found: C 70.78, H 5.82, N 1.60. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 271sh (27990), 352 (6440), 425 (3630).

[RuII(MeQ)(H)(CO){P(C6H4OMe)3}2] (3)
The compound was synthesized according to a procedure similar to that for 1 except [RuII{P(C6H4OMe)3}3Cl2] was used in place of [RuII(PPh3)3Cl2]. Yield: (275 mg, 55%). IR (KBr, cm–1): (C≡O) 1902, (Ru-H) 1964. ESI-MS: m/z 992 [M – H]+, 835 [M – MeQ]+. 1H NMR (400 MHz, CD2Cl2): δ 7.51 (d, J = 8.4 Hz, 1H; Ar-H), 7.36-7.42 (m, 12H, Ar-H), 6.80 (t, J = 7.8 Hz, 1H, Ar-H), 6.65-6.71 (m, 13H, Ar-H), 6.25 (d, J = 7.7 Hz, 1H, Ar-H), 6.18 (d, J = 7.1 Hz, 1H, Ar-H), 3.74 (s, 18H, CH3O-), 2.07 (s, 3H, -CH3), –10.75 (t, J = 20.4 Hz, 1H, Ru-H). Elemental analysis calcd (%) for C53H51NO8P2Ru: C 64.11, H 5.18, N 1.41; found: C 64.20, H 5.22, N 1.37. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 272sh (30750), 341 (6370), 424 (3010).

[RuII(MeQ)(Me)(CO)(PPh3)2] (4)
The compound was synthesized similar to that for 1 except EtOH (150 mL) was used as solvent instead of MeOH. Yield: (279 mg, 67%). IR (KBr, cm–1): (C≡O) 1894.  ESI-MS: m/z 812 [M – H]+, 669 [M – MeQ]+. 1H NMR (400 MHz, CD2Cl2): δ 7.53 (d, J = 8.6 Hz, 1H; Ar-H), 7.28-7.30 (m, 19H, Ar-H), 7.15-7.20 (m, 12H, Ar-H), 6.92 (t, J = 7.8 Hz, 1H; Ar-H), 6.68 (d, J = 8.4 Hz, 1H; Ar-H), 6.48 (d, J = 7.1 Hz, 1H; Ar-H), 6.35 (d, J = 8.4 Hz, 1H; Ar-H), 1.80 (s, 3H; Ar-CH3), 0.52 (t, J = 6.5 Hz, 3H; Ru-CH3). Elemental analysis calcd (%) for C48H41NO2P2Ru: C 69.72, H 5.00, N 1.69; found: C 69.66, H 5.12, N 1.72. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]):  249sh (39610), 356 (5810), 426 (3390).

[RuII(Q)(H)(CO)(PPh3)2] (5)
8-Hydroxyquinoline (HQ) (61 mg, 0.42 mmol) was added to a suspension [RuII(PPh3)3(CO)(H)2] (200 mg, 0.21 mmol) in MeOH (150 mL). The resulting mixture was refluxed for 1 day under an inert atmosphere of argon to give a suspension of yellow microcrystalline solid, which was collected and washed with ice-cold methanol (3 × 4 mL). Yield: (120 mg, 71%). IR (KBr, cm–1): (C≡O) 1904, (Ru-H) 1955. ESI-MS: m/z 798 [M – H]+, 655 [M – MeQ]+. 1H NMR (300 MHz, CDCl3): δ 7.73 (d, J = 4.9 Hz, 1H, Ar-H), 7.43-7.51 (m, 13H, Ar-H), 7.10-7.21 (m, 18H, Ar-H), 6.91 (t, J = 7.9 Hz, 1H, Ar-H), 6.50 (dd, J = 8.3, 4.7 Hz, 1H, Ar-H), 6.27-6.31 (m, 2H, Ar-H), –9.88 (t, J = 19.9 Hz, 1H, Ru-H). Elemental analysis calcd (%) for C46H37NO2P2Ru: C 69.16, H 4.67, N 1.75; found: C 69.20, H 4.80, N 1.77. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 268sh (23790), 353 (7660), 424 (4440).

[RuII(ClQ)(H)(CO)(PPh3)2] (6)
Complex 6 was prepared by a procedure similar to that for 5 except ClQH was used instead of QH. Yield: (135 mg, 77%). IR (KBr, cm–1): (C≡O) 1918, (Ru-H) 1945. ESI-MS: m/z 832 [M – H]+, 655 [M – MeQ]+. 1H NMR (300 MHz, CDCl3): δ 7.77 (d, J = 7.7 Hz, 2H, Ar-H), 7.47-7.54 (m, 10H, Ar-H), 7.11-7.28 (m, 20H, Ar-H), 6.93 (d, J = 8.6 Hz, 1H, Ar-H), 6.65 (m, 1H, Ar-H), 6.19 (d, J = 8.6 Hz, 1H, Ar-H), –10.75 (t, J = 20.3 Hz, 1H, Ru-H). Elemental analysis calcd (%) for C46H36ClNO2P2Ru: C 66.31, H 4.35, N 1.68; found: C 66.23, H 4.10, N 1.56. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 263sh (22270), 351 (5900), 441 (4190).
[RuII(PhQ)(H)(CO)(PPh3)2] (7)
Complex 7 was prepared by a procedure similar to that for 5 except PhQH was used instead of QH. Yield: (110 mg, 59%). IR (KBr, cm–1): (C≡O) 1914, (Ru-H) 1942. ESI-MS: m/z 874 [M – H]+, 655 [M – MeQ]+. 1H NMR (300 MHz, CDCl3): δ 7.85 (d, J = 4.6 Hz, 1H, Ar-H), 7.65 (d, J = 8.2 Hz, 1H, Ar-H), 7.52-7.58 (m, 12H, Ar-H), 7.40 (t, J = 7.3 Hz, 3H, Ar-H), 7.29 (d, J = 7.5 Hz, 1H, Ar-H), 7.25 (d, J = 1.5 Hz, 1H, Ar-H), 7.14-7.21 (m, 18H, Ar-H), 6.90 (d, J = 8.2 Hz, 1H, Ar-H), 6.51 (dd, J = 8.6, 4.6 Hz, 1H, Ar-H), 6.35 (d, J = 8.2 Hz, 1H, Ar-H), –9.80 (t, J = 19.6 Hz, 1H, Ru-H). Elemental analysis calcd (%) for C52H41NO2P2Ru: C 71.39, H 4.72, N 1.60; found: C 71.22, H 4.69, N 1.61. UV/Vis (CH2Cl2): λmax[nm] (ε [mol–1 dm3 cm–1]): 265sh (22280), 303sh (12790), 358 (7280), 440 (5820).

Results and discussion
Synthesis and Characterization. Reaction of [RuII(PPh3)3Cl2] with MeQH in the presence of Et3N in MeOH produces a neutral carbonyl hydrido complex [RuII(MeQ)(PPh3)2(CO)(H)] (1). Under similar reaction conditions using [RuII{P(C6H4Me)3}3Cl2] or  [RuII{P(C6H4OMe)3}3Cl2] in place of [RuII(PPh3)3Cl2] also afforded the target carbonyl hydrido complexes with the corresponding phosphine ligands,  [RuII(MeQ){P(C6H4Me)3}2(CO)(H)] (2) and [RuII(MeQ){P(C6H4OMe)3}2(CO)(H)] (3), respectively (Scheme 1a). The carbonyl and hydride ligands of these complexes are derived from the decarbonylation of primary alcohol (MeOH). Similar decarbonylation of methanol, such as the formation of carbonyl hydrido complex [RuII(PPh3)3(CO)(Cl)(H)] from the reaction between 16e– ruthenium complex [RuII(PPh3)3(Cl)2] and MeOH in the presence of base,11 are commonly reported in other transition metals complexes, in particular for those with 16e– Ru(II) metal center.  To elucidate the role of methanol in the formations of these carbonyl hydrido complexes, the reaction between the [RuII(PPh3)3Cl2] and MeQH was also carried out in ethanol. The major product was then characterized to be the carbonyl methyl complex [RuII(MeQ)(PPh3)2(CO)(CH3)] (4), which is an air-stable and diamagnetic. This reaction is similar to the formation of corresponding carbonyl methyl complex [TpRuII(CH3)(CO)(PPh3)] from the reaction of [(Tp)RuIICl(PPh3)(CH3CN)] (Tp = hydrotris(pyrazolyl)borate) with NaBH4 in EtOH.  When the reaction of [RuII(PPh3)3Cl2] with MeQH was carried out in nPrOH, it also produces the ethyl carbonyl complex [RuII(MeQ)(PPh3)2(CO)(CH2CH3)]. However, the ethyl carbonyl complex is unstable in solution, presumably, due to spontaneous β-H elimination of Ru-CH2CH3 to form an alkene complex. On the other hand, when the reaction was carried out in PhCH2OH, it produced exclusively [RuII(MeQ)(PPh3)2(CO)(H)] (1) rather than [RuII(MeQ)(PPh3)2(CO)(Ph)].
Attempt to synthesize the carbonyl hydrido complexes with other substituted quinoline ligands (XQ) such as QH, ClQH and PhQH based on similar strategy for the preparation of the MeQ complexes was unsuccessful. These reactions result in the formation of di(quinolinolato) complexes ([RuII(XQ)2(PPh3)2]; XQ = Q, ClQ and PhQ) as the major product. The difference of their reactivity can be attributed to the steric hindrance of methyl substituent in the MeQ, which leads to the formation of [RuII(MeQ)(PPh3)2]+ with two vacant site for the coordination with alcohol. This suggestion is further supported by the formation of [RuII(MeQ)(PPh3)2(CH3CN)2]+, characterized by ESI mass spectrometry, in the reaction of [RuII(PPh3)3Cl2] with MeQ in CH3CN.

Scheme 1. Synthetic routes for different quinolinolato ruthenium(II) complexes

To prepare carbonyl hydrido complexes with different quinoline ligands, the reactions of the quinoline ligands with [RuII(PPh3)3(CO)(H)(Cl)] were attempted; however they afforded a mixture of [RuII(XQ)(PPh3)2(CO)(H)] and [RuII(XQ)(PPh3)2(CO)(Cl)], which are difficult to be separated as they have very similar solubility. It is found that the use of dihydrido complex [RuII(PPh3)3(CO)(H)2] in place of [RuII(PPh3)3(CO)(H)(Cl)] could eliminate the formation of the chloro complex as the impurity. Treatment of [RuII(PPh3)3(CO)(H)2] with XQ produce the corresponding carbonyl hydrido complexes [RuII(XQ)(PPh3)2(CO)(H)] (X = H, 5; Cl, 6; Ph, 7) (Scheme 1b) in moderate yield. Similar to 1 – 3, these complexes are diamagnetic and air-stable in the solid state but show slow decomposition in solutions.

All complexes were characterized by 1H NMR, IR, and ESI-MS, and gave satisfactory elemental analyses. The structures of 3, 4, 8 and 12 were unambiguously confirmed by X-ray crystallography. All the complexes show 1H NMR signals with chemical shifts and integral ratios consistent with their chemical formulations. For all hydride complexes (1 – 3 and 5 – 7), an upfield triplet signal at ca. –10.7 ppm, typical of metal hydride complexes, with coupling constants in the range of 19.6 – 20.4 Hz and integral ratio of one proton were observed. The observation of the triplet splitting is the result of the coupling between the hydride with two phosphines of the two chemically equivalent cis-triphenylphosphine ligands. These coupling constants are also in the typical range of related coupling reported for related phosphino ruthenium(II) hydride complexes.10
All carbonyl hydride complexes (1 – 3 and 5 – 7) show one weak and one strong absorptions in the region of 1900 – 1960 cm–1, corresponding to the ν(Ru-H) and ν(C≡O) stretches, respectively. These ν(C≡O) and ν(Ru-H) stretching frequencies are comparable with those in [RuII(CO)(H)2(PPh3)3]10 and are in the typical ranges of other related hydrido and carbonyl Ru(II) complexes.  Comparing these carbonyl stretches of the complexes with PPh3, the stretching frequency is in line with the electron withdrawing effect of the substituent on the trans-quinolinolato ligand [6 (1918 cm–1) > 7 (1914 cm–1) > 5 (1904 cm–1)]. Upon ligand substitutions of the hydrido and one phosphine ligands with two cyanide or isocyanide ligands, the complexes (8 – 12) show another strong ν(C≡N) stretch at ca. 2100 cm–1 for cyano complexes (8 – 11) or 2200 cm–1 for isocyano complex (12) in addition to the carbonyl stretch in the range of 1937 – 1988 cm–1. Moreover, the hexafluorophosphate (PF6–) counter anion in 12 is also characterized by the observation of strong v(P–F) stretch at ca. 840 cm–1.

X-ray crystal structures. The geometric arrangements of the ligands in the carbonyl methyl complex, carbonyl hydrido complexes and their products from the ligand substitution reactions with cyanide or isocyanide ligands have been confirmed by the X-ray crystal structures of 3, 4, 8 and 12 (Figure 1). Selected bond distances and angles of these complexes are summarized in Table 2. The ruthenium metal centers in these crystal structures adopted a distorted octahedral geometry. All carbonyl ligands in these complexes are trans to the oxygen atom of quinolinoato ligand with Ru–C(CO) bond distances in the range of 1.827 – 1.877 Å, which is typically observed in other Ru(II) carbonyl complexes.14 In the structures of 3 and 4, the two triphenylphosphine ligands are trans to each other whereas the hydrido ligand in 3 and the methyl ligand in 4 are trans to nitrogen atom of the quinolinolato ligand with the Ru–H and Ru–CH3 bond distances of 1.49 and 2.15 Å, respectively, which are comparable with those of related ruthenium complexes.  The relatively longer Ru–N (quinolinolato ligand) bond lengths in 3 (2.205 Å

and 4 (2.213 Å

than the corresponding bond lengths in cis-trans-cis-[RuII(Q)2(PPh3)2] (2.10 Å

, rac-[Ru(bpy)2(Q)]PF6 (2.05 Å

, 8 (2.176 Å

and 12 (2.169 Å

are presumably due to the strong trans influence of the hydrido and methyl ligands. The X-ray crystal structures of 8 and 12 confirmed the rearrangement of the unsubstituted PPh3, which changed from cis- to trans-position relative to the quinolinolato ligand, in the ligand substitution reactions and the trans configurations of the two newly substituted ligands (CN– or CNR). The slight deviations of the CN–C bond angle (175.3

of isocyanide ligands from the linearity in 12 are attributed to the -back-bonding interaction from the Ru(II) metal centers as commonly observed in other metal isocyanide complexes.

(a) (b)
Figure 1. The perspective drawings of (a) 3, (b) 4, (Thermal ellipsoids are drawn at 50% probability)

Table 2. Selected bond distances (Å

and angles (°) with estimated standard deviations (e.s.d.s.) in parentheses for 3, 4, 8 and 12.
3
Ru(1)–P(1) 2.3510 (10) Ru(1)–N(1) 2.205 (3)
Ru(1)–P(2) 2.3441 (10) Ru(1)–C(1) 1.827 (4)
Ru(1)–O(2) 2.114 (3) Ru(1)–H(1) 1.49 (10)

N(1)–Ru(1)–P(1) 93.98 (8) C(1)–Ru(1)–P(2) 88.36 (13)
N(1)–Ru(1)–P(2) 91.06 (8) C(1)–Ru(1)–O(2) 176.75 (15)
N(1)–Ru(1)–H(1) 169 (4) C(1)–Ru(1)–N(1) 105.24 (15)
C(1)–Ru(1)–P(1) 95.37 (13) C(1)–Ru(1)–H(1) 86 (4)

4
Ru(1)–C(2) 1.829 (3) Ru(1)–N(1) 2.213 (2)
Ru(1)–O(1) 2.0902 (18) Ru(1)–P(1) 2.3712 (7)
Ru(1)–C(1) 2.156 (3) Ru(1)–P(2) 2.3820 (7)

C(2)–Ru(1)–O(1) 178.49 (10) C(1)–Ru(1)–P(1) 89.22 (7)
C(2)–Ru(1)–C(1) 94.56 (11) N(1)–Ru(1)–P(1) 91.56 (5)
O(1)–Ru(1)–C(1) 84.07 (9) C(2)–Ru(1)–P(2) 89.45 (8)
C(2)–Ru(1)–N(1) 103.47 (10) O(1)–Ru(1)–P(2) 91.18 (5)
O(1)–Ru(1)–N(1) 77.91 (8) C(1)–Ru(1)–P(2) 89.65 (7)
C(1)–Ru(1)–N(1) 161.97 (9) N(1)–Ru(1)–P(2) 90.23 (5)
C(2)–Ru(1)–P(1) 88.34 (8) P(1)–Ru(1)–P(2) 177.43 (2)
O(1)–Ru(1)–P(1) 91.00 (5)

UV-vis absorption and emission spectroscopy. The electronic absorption spectra of 1 – 12 show intense ligand centered -* transitions with molar absorption coefficients on the order of 104 mol–1 dm3 cm–1 in high energy UV region (  300 nm). In addition to these intense absorptions, all complexes also display two moderately intense absorption shoulders or bands with molar absorption coefficients on the order of 103 mol–1 dm3 cm–1 and abs in the region of 330 – 358 nm and 410 – 440 nm (Figure 2). These absorptions showed an energy dependence on the electronic nature of the quinolinolato ligand and are almost insensitive to the change of electronic nature of other ancillary ligands. Moreover, these absorptions are similar to π-π* transition of quinolinolato ligand observed in other related metal complexes such as [OsII(CO)3(XQ)(L)] (XQ = Q and MeQ; L = Cl, I, CF3CO2),3e AlQ33a and IrQ33a. With reference to previous spectroscopic studies and the absorption energy trends in these complexes, these absorptions are tentatively assigned to the metal-perturbed π-π* transitions of quinolinolato ligand.

Figure 3. Overlaid UV/Vis absorption spectra of 1, 5, 6 and 7 in CH2Cl2 at 298 K.

Unlike other homoleptic quinolinolato transition metal complexes such as RhQ3, PdQ2, IrQ3 and PtQ2, which show red emissions derived from their ligand-centered (LC) phosphorescence,3a,b,d and [Os(CO)3(XQ)(L)], which show dual emission band derived from the mixture of LC fluorescence and phosphorescence,3e all complexes in CH2Cl2 solution at room temperature only display green photoluminescence with emission maxima in the range of 500 – 530 nm. These emissions of these quinolinolato complexes are relatively insensitive to electronic effect of substituents on the phosphine ligands as well as the nature of the ancillary ligands as reflected from the similar emission energy for methylquinolinolato complexes 1 – 3, 8 and 12. In contrast, the emission energies of these complexes are much more sensitive to the substituents on the quinolinolato ligand as illustrated by the emission trends in the order of 1 (500 nm for MeQ) < 5 (504 nm for Q) < 6 (518 nm for ClQ)  7 (519 nm for PhQ) (Figure 3) for complex analogues with different quinolinolato ligands. Such emission energy dependence and the close resemblance of these emissions to the fluorescence of other quinolinolato metal complexes with different metal centers3a-e are suggestive of an assignment to the quinolinolato ligand-centered (LC) fluorescence. The short-lived emission lifetimes of less than 3 ns are consistent with the fluorescence assignment. To eliminate the possible mixing of the LC phosphorescence in the tail of the green emission, time-resolved emission spectroscopy has also been performed. However, no additional emission band was identified at different times (> 1 ns) after the laser excitation. The absence of the red LC phosphorescence in these complexes may be attributed to the inefficient intersystem crossing from the singlet to triplet state or very efficient non-radiative decay from the triplet state. The variation of the intersystem crossing efficiency with different substituent on the quniolinolato ligand and ancillary ligands has also been reported in the series of the quinolinolato osmium complexes [Os(CO)3(RQ)(X)].3e
On the other hand, these complexes show two emission bands in 77 K EtOH/MeOH/CH2Cl2 (4:1:1 v/v/v) glassy medium (Figure 3b). These are similar to the dual emissions, corresponding to the LC fluorescence and phosphorescence, observed in PbQ2 and BiQ3 in 77 K EtOH glassy medium. The high-energy emission bands of these complexes are structureless similar to those observed in AlQ3 and the high-energy emission bands in PbQ2 and BiQ3 in 77 K EtOH glassy medium, whereas the low-energy emissions show a structured emission band similar to the LC phosphorescence of RhQ2, IrQ3 and PtQ2 in 77 K EtOH glassy medium. Based on the previous spectroscopic study,3a-e the two emission bands of these complexes are also tentatively assigned to the LC fluorescence and phosphorescence.

Figure 3. Overlaid emission spectra of selected complexes (1, 5, 6 and 7) in (a) CH2Cl2 at 298K and (b) EtOH/MeOH/CH2Cl2 (4:1:1 v/v/v) glassy medium at 77 K.

Conclusion. Different synthetic routes to substituted quinolinolato ruthenium(II) complexes with different ancillary ligands of diverse electronic properties have been developed. Based on these synthetic routes, ruthenium(II) complexes with substituted quinolinolate ligands and different ancillary ligands can be prepared. All newly synthesized complexes have been characterized by IR spectroscopy, 1H NMR spectroscopy, ESI mass spectrometry and elemental analysis. The photophysical properties of all these complexes were investigated. All complexes exhibit short-lived quinolinolate-based LC fluorescence in the solution state at room temperature and dual emissions derived from the LC fluorescence and phosphorescence at 77 K glassy medium. These emissions are relatively insensitive to the change of the ancillary ligands but are tunable through the change of the substituents on the quinolinolate ligand.

Acknowledgment. The work described in this paper was supported by . The flash photolysis system was supported by the Special Equipment Grant from the University Grants Committee of the Hong Kong (SEG_CityU02).

Supporting Information Available. CIF files giving crystallographic data for 3, 4, 8 and 12. This material is free of charge via the internet at https://pubs.acs.org.

Table 3. Photophysical data for complexes 1 – 12.
Medium
(T/K) Emissiona
λem/ nm emb Absorptionc  λabs/ nm (ε / dm3 mol–1 cm–1)
1 CH2Cl2 (298)
Glassd (77) 500
456, 580, 629 0.0291 265sh (24350), 354 (6930), 421 (3710)
2 CH2Cl2 (298)
Glassd (77) 500
0.0270 271sh (27990), 352 (6440), 425 (3630)
3 CH2Cl2 (298)
Glassd (77) 501
456, 582, 630 0.0287 272sh (30750), 341 (6370), 424 (3010)
4 CH2Cl2 (298)
Glassd (77) 500
463, 587, 633 0.0036 249sh (39610), 356 (5810), 426 (3390)
5 CH2Cl2 (298)
Glassd (77) 504
448, 578, 625 0.0227 268sh (23790), 353 (7660), 424 (4440)
6 CH2Cl2 (298)
Glassd (77) 518
472, 603, 653 0.0278 263sh (22270), 351 (5900), 441 (4190)
7 CH2Cl2 (298)
Glassd (77) 519
464, 602, 654 0.0573 265sh (22280), 303sh (12790), 358 (7280), 440 (5820)
8 CH2Cl2 (298)
Glassd (77) 512
456, 524, 576 0.0322 269 (23250), 276 (23890), 330 (7010), 346sh (2600), 410 (5564)
9 CH2Cl2 (298)

Glassd (77) 516

0.0274 262 (17160), 269 (17790), 275sh (15510), 331sh (3370), 347sh (2890), 428 (3500)
10 CH2Cl2 (298)

Glassd (77) 528

0.0247 262 (25300), 268 (24800), 275sh (21150), 341 (6400), 355 (6000), 438, (4370)
11 CH2Cl2 (298)

Glassd (77) 529

0.00324 262 (28870), 269 (29230), 276 (26900), 298sh (13930), 352 (6020), 433, (4790)
12 CH2Cl2 (298)
Glassd (77) 501
463, 580 0.0006 272 (24540), 412 (3010)
a Excitation at 400 nm. Emission maxima are uncorrected values. b Luminescence quantum yield with excitation at 436 nm. c In dichloromethane at 298 K. d EtOH–MeOH–CH2Cl2 (4:1:1 v/v/v).

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