8-Quinolinolato complexes of ruthenium(II) and (III)

Article abstract of DOI:10.1016/j.ica.2008.05.036

Reduction of RuQ₃ (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ₂L₂ (L₂ = (dimethylsulfoxide)₂ (2); (4-picoline)₂ (3); N,N′-dimeth

Full text of DOI:10.1016/j.ica.2008.05.036

Inorganica Chimica Acta 362 (2009) 1149–1157
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
8-Quinolinolato complexes of ruthenium(II) and (III)
Chi-Fai Leung a, Chun-Yuen Wong a, Chi-Chiu Ko a, Man-Chong Yuen a, Wing-Tak Wong b,
Wai-Yeung Wong c, Tai-Chu Lau a,
*
a Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong, China
b Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
c Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Reduction of RuQ3 (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various p-acceptor ligands in
ethanol affords RuQ2L2 (L2 = (dimethylsulfoxide)2 (2); (4-picoline)2 (3); N,N0-dimethyl-1,4-diazabuta-1,3-
diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an
equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chroma-
tography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the
corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been
determined by X-ray crystallography.
Received 27 February 2008
Received in revised form 19 May 2008
Accepted 28 May 2008
Available online 4 June 2008
Keywords:
Ruthenium
8-Quinolinolate
Alkene
Ó 2008 Elsevier B.V. All rights reserved.
Nitrogen ligands
1. Introduction
including RuQ3 (1a), Ru(Me-Q)3 (1b, Me-Q = 2-methyl-8-quinoli-
nolato) and Ru(Cl-Q)3 (1c, Cl-Q = 5-chloro-8-quinolinolato). These
8-Hydroxyquinoline (HQ) and its derivatives are among the
most versatile and useful ligands with a variety of applications
[1]. They form stable complexes with most metals, and they have
been used as complexing agents and organic precipitants for the
separation of metal-ions from mixtures in analytical chemistry
[2–4]. They are also used for the spectrophotometric analysis of
metal ions. The luminescent properties of many complexes of 8-
hydroxyquinoline have also made these ligands useful for the sens-
ing of metal ions [5,6]. Electroluminescence from AlQ3 and GaQ3
has potential applications in organic light emitting devices (OLEDs)
[7–15]. Rare-earth complexes such as ErQ3, NdQ3, YbQ3 are also
useful for infrared electroluminescence devices [16–19]. The
luminescent properties of PtQ2 and IrQ2 make them useful photo-
sensitizers in solar energy conversion and photocatalytic processes
[20–22].
complexes are convenient starting materials for the preparation a
variety of bis(8-quinolinolato)ruthenium(II) complexes containing
p-acceptor ligands such as pyridine, alkene, dimethylsulfoxide and
diazadiene. In the case of RuQ2(nbd) (norbornadiene) both the cis,-
trans or trans,cis isomers have been isolated and structurally char-
acterized. These two isomers have significantly different properties
including redox potentials and energies of electronic transitions,
and DFT calculations have been performed on these two com-
plexes. Stable bis(8-quinolinolato)ruthenium(III) complexes con-
taining 4-picoline or norbornadiene have also been isolated.
2. Experimental
2.1. Materials and physical measurements
Although 8-quinolinolato complexes of many metals have been
extensively studied, only a few complexes of ruthenium have been
reported. These include RuQ3 (HQ = 8-hydroxyquinone) [23],
RuQ2(COD) (COD = 1,5-cyclooctadiene) [24], RuQ2(PPh3)2 [25],
[RuQ2(PPh3)2]PF6 [25] and [RuL2(Q)]+ (L = 2,20-bipyridine, 1,10-
phenanthroline and its derivatives) [26], which were prepared by
different methods.
Ru(acac)3 [27] and bis(1,3-dimethylimidazolidin-2-ylidene)
[28] were prepared according to literature methods. The
8-hydroxyquinoline ligands were purchased from Aldrich. Other
chemicals were of reagent grade and used without further purifica-
tion. IR spectra were obtained from KBr discs by using a Bomen
MB-120 FTIR spectrophotometer. UV–Vis spectra were recorded
on either a Perkin–Elmer Lamda 19 or a Shimadzu UV3100 spectro-
photometer. 1H NMR spectra were recorded on a Varian (300 MHz)
FT-NMR spectrometer. The chemical shifts (d ppm) were reported
with reference to tetramethylsilane (TMS). Elemental analyses
were done on an Elementar Vario EL Analyzer. Electrospray ioniza-
tion mass spectra (ESI/MS) were obtained with a PE-SCIEX API 300
We report herein a general, high-yield (>75%) synthetic method
for
a series of tris(8-quinolinolato)ruthenium(III) complexes,
* Corresponding author. Tel.: +852 27887811; fax: +852 27887406.
E-mail address: bhtclau@cityu.edu.hk (T.-C. Lau).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.05.036

1150
C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
triple quadruple mass spectrometer. Cyclic voltammograms were
recorded on a PAR model 273 potentiostat, using ferrocene (Fc)
as internal reference. A glassy carbon disk working electrode and
a Ag/AgNO3 reference electrode were used. The supporting electro-
lyte was 0.1 M ½NBunꢀPF6 in CH3CN. ½NBunꢀPF6 (Aldrich) was recrys-
(m
CH, 4-picoline). 1H NMR (300 MHz, CDCl3): d 2.19 (s, 6H, CH3 of
3
3
pic), 6.64 (d, JHH = 7.8 Hz, 2H, Q), 6.85 (d, JHH = 6.0 Hz, 4H, pic),
3
6.89 (d, JHH = 8.7 Hz, 2H, Q), 7.02 (d,3JHH = 8.1 Hz, 2H, Q), 7.23 (d,
3JHH = 12.6, 2H, Q), 7.60 (d, 3JHH = 8.4 Hz, 2H, Q), 8.35
3
(d,3JHH = 4.8 Hz, 2H, Q), 8.58 (d, JHH = 6.0 Hz, 4H, pic).
4
4
tallized three times from ethanol and dried in vacuo at 120 °C for
24 h before use. Acetonitrile was first refluxed over calcium
hydride and then distilled under argon.
2.2.6. RuQ2(dab) (4)
A mixture of 1a (80 mg, 0.15 mmol), bis(1,3-dimethylimidazoli-
din-2-ylidene) (30 mg, 0.15 mmol) and a few pieces of zinc amal-
gam in dichloromethane (15 ml) was refluxed under argon for
5 h. The resulting purple solution was stirred in air for 0.5 h to pro-
duce a red solution, which was then evaporated to dryness. The
residue was dissolved in dichloromethane and loaded onto a silica
gel column. Elution with acetone/dichloromethane (1:5) and slow
evaporation of the resulting solution afforded red crystals suitable
for X-ray crystallography. Yield 22 mg (32%). Anal. Calc. for
RuC22H20N4O2: C, 55.80; H, 4.26; N, 11.84. Found: C, 55.68; H, 4.55;
2.2. Synthesis of complexes
2.2.1. RuQ3 (1a)
A solid mixture of Ru(acac)3 (0.5 g, 1.26 mmol) and 8-hydroxy-
quinoline(HQ)(1 g, 6.89 mmol)was heated to a melt at 180 °C under
argon for 1 d. After cooling to room temperature the green residue
was washed with diethyl ether and the excess 8-hydroxyquinoline
was recovered by sublimation. The residue was then dissolved in
dichloromethane and purified by column chromatography (silica
gel) with chloroform as the eluent. The green crystals of the com-
pound were obtained by recrystallization from chloroform/n-hex-
ane. Yield 0.52 g (78%). Anal. Calc. for RuN3O3C27H18Cl: C, 60.78; H,
N, 12.01%. UV–Vis (CH2Cl2)kmax
,
nm
(
e
,
Mꢁ1 cmꢁ1 dmꢁ3) = 529
CH, dab).
(18400), 401 (13370). IR (KBr, cmꢁ1): 2953 and 2922 (
m
1H NMR (300 MHz, CDCl3): d 3.40 (s, 6H, CH3 of dab), 6.85 (s, 2H,
N@CH of dab), 6.96 (m, 2H, Q), 7.20 (m, 2H, Q), 7.30 (m, 2H, Q)
7.91 (m, 2H, Q), 8.46 (m, 4H, Q).
3.40; N, 7.88. Found: C, 61.14; H, 3.24; N, 7.54%. UV–Vis (CHCl3) kmax
,
nm (
e
, Mꢁ1 cmꢁ1 dmꢁ3): 428 (14230), 341 (7490). IR (KBr, cmꢁ1):
1568, 1496, 1458, 1372, 1314, 1107.
2.2.7. Ru(Q)2(COD) (5)
This was obtained by a procedure similar to that for 3 using 1,5-
cyclooctadiene (1 ml). The yellow product was recrystallized from
dichloromethane/diethyl ether. Yield 46 mg (61%). Anal. Calc. for
RuC25H20O2N2: C, 62.36; H, 4.16; N, 5.82. Found: C, 62.08; H, 4.10;
2.2.2. Ru(Me-Q)3 (1b)
Green needle-shaped crystals of the complex were obtained by
a procedure similar to that for 1a using 8-hydroxy-2-methylquin-
oline. Yield 0.53 g (73%). Anal. Calc. for RuC30H24N3O3: C, 62.60;
H,4.20; N,7.30. Found: C, 63.01; H, 4.54; N, 7.56%. UV–Vis (CHCl3)
N, 5.97%. UV–Vis (CH2Cl2) kmax, nm (
e
, Mꢁ1 cmꢁ1 dmꢁ3) = 351
(7300), 427 (9660). IR (KBr, cmꢁ1): 2960, 2915 (
m
CH, cod). 1H
kmax, nm (
e
, Mꢁ1 cmꢁ1 dmꢁ3) = 427 (9870), 352 (7240). IR (KBr,
NMR (300 MHz, CDCl3): d 2.31 (m, 4H, CH2 of COD), 2.51 (m, 2H,
CH2 of COD), 2.75 (m, 2H, CH2 of COD), 3.40 (m, 2H, @CH of
COD), 4.45 (m, 2H, @CH of COD), 6.84 (m, 2H, Q), 7.14 (m, 2H,
Q), 7.30 (m 2H, Q), 7.40 (m, 2H, Q), 7.85 (m, 2H, Q), 8.48 (m, 2H, Q).
cmꢁ1): 1566, 1493, 1451, 1366, 1303, 1084.
2.2.3. Ru(Cl-Q)3 (1c)
Green needle-shaped crystals of the complex were obtained by
a procedure similar to that for 1a using 5-chloro-8-hydroxyquino-
line. Yield 0.61 g (76%). Anal. Calc. for RuC27H15N3O3Cl3: C, 50.92;
H,2.37; N,6.60. Found: C, 51.23; H, 2.60; N, 6.86%. UV–Vis
2.2.8. cis,trans-[RuIIQ2(nbd)] (6a) and trans,cis-[RuIIQ2(nbd)] (6b)
A mixture containing 1a (160 mg, 0.3 mmol), 2,5-norbornadi-
ene (2 ml) and a few pieces of zinc amalgam in ethanol (15 ml)
was refluxed under argon for 24 h. The resulting solution was fil-
tered and slow evaporation of the filtrate afforded a mixture of
red and yellow crystals. X-ray crystallography showed that the
red crystals consist of an equimolar mixture of 6a and 6b co-crys-
tallized together, whereas the yellow crystals consist of 6a only.
The red crystals were then dissolved in dichloromethane loaded
onto a neutral alumina column. 6a was obtained by elution with
dichloromethane while 6b was obtained by elution with dichloro-
methane/acetone (10:1).
(CHCl3)kmax, nm (e
, Mꢁ1 cmꢁ1 dmꢁ3) = 443 (15200), 347 (8610).
IR (KBr, cmꢁ1): 1563, 1492, 1452, 1362, 1303, 1084.
2.2.4. RuQ2(dmso)2 (2)
A mixture of 1a (80 mg, 0.15 mmol), dimethylsulfoxide (1 ml)
and a few pieces of zinc amalgam in ethanol (15 ml) was refluxed
under argon for 18 h. The resulting yellow solution was filtered and
diethyl ether (30 ml) was added to the filtrate. Yellow crystals
were obtained on standing the solution at 0 °C for 12 h. Yield
46 mg (56%). Anal. Calc. for RuC24H24O4N2S2: C, 48.42; H, 4.43; N,
The combined yield of the yellow compound 6a is 61 mg (42%).
Anal. Calc. for RuC26H24O2N2: C, 62.36; H, 4.19; N, 5.82. Found: C,
5.14. Found: C, 48.56; H, 4.58; N, 5.06%. UV–Vis (CH2Cl2) kmax
,
nm (
1078 (
e
, Mꢁ1 cmꢁ1 dmꢁ3) = 347 (5470), 435 (4100). IR (KBr, cmꢁ1):
62.64; H, 4.15, N, 5.91%. UV–Vis (CH2Cl2) kmax
ꢁ1 cmꢁ1 dmꢁ3) = 350 (1210), 427(1920). IR (KBr, cmꢁ1): 2950
CH, nbd). 1H NMR (300 MHz, CDCl3): d 1.64 (s, 2H, CH2 of nbd),
3.95 (m, 2H, @CH of nbd,), 4.14 (s, 2H, CH of nbd), 4.84 (m, 2H,
,
nm
(e,
m
SO), 2970 (
m
CH, dmso). 1H NMR (300 MHz, CDCl3): d 2.66
M
(m
3
(s, 6H, dmso), 2.97 (s, 6H, dmso), 6.87 (dd, JHH = 6.9 Hz,
4JHH = 0.9 Hz, 2H), 6.91(dd, JHH = 8.1 Hz, JHH = 1.2 Hz, 2H, ), 7.30–
3
4
3
4
3
4
7.36 (m, 4H), 8.10 (dd, JHH = 8.4 Hz, JHH = 1.2 Hz, 2H), 9.42 (dd,
@CH of nbd), 6.83 (dd, JHH = 7.8 Hz, JHH = 1.2 Hz, 2H, Q), 7.09
4
3
4
3JHH = 4.8 Hz, JHH = 1.2 Hz, 2H).
(m, 2H, Q), 7.30 (dd, JHH = 5.1 Hz, JHH = 1.2 Hz, 2H, Q), 7.39 (d,
3JHH = 7.8, 2H, Q6), 7.80 (dd, JHH = 8.1Hz, JHH = 0.9Hz, 2H, Q),
3
4
3
4
2.2.5. RuQ2(pic)2 (3)
8.45 (dd, JHH = 4.8 Hz, JHH = 1.5Hz, 2H, Q).
A mixture of 1a (80 mg, 0.15 mmol), 4-picoline (1 ml) and a few
pieces of zinc amalgam in ethanol (15 ml) was refluxed under ar-
gon for 18 h. The resulting green solid was filtered and washed
with diethyl ether. Yield 66 mg (76%). Crystal suitable for X-ray
crystallography were obtained by diffusion of n-hexane into a
dichloromethane solution of the green solid at 4 °C. Anal. Calc. for
RuC30H26O2N4: C, 62.59; H, 4.55; N, 9.74. Found: C, 62.85; H,
The yield of the red compound 6b is 51 mg (35%). Anal. Calc. for
RuC26H24O2N2: C, 62.36; H, 4.19; N, 5.82. Found: C, 62.53; H, 4.01, N,
5.70%. UV–Vis (CH2Cl2), kmax, nm (e
, Mꢁ1 cmꢁ1 dmꢁ3) = 357 (1030),
500 (1000). IR (KBr, cmꢁ1): 2950 (CH, nbd). 1H NMR (300 MHz,
CDCl3): d 1.64 (s, 2H, CH2 of nbd), 3.85 (m, 2H, @CH of nbd), 3.95
(s, 2H, CH of nbd), 4.57 (m, 2H, @CH of nbd), 6.72 (d, 3JHH = 7.8 Hz,
2H, Q), 6.84 (d, 3JHH = 6.0 Hz, 2H, Q), 7.26 (d, 3JHH = 15.9 Hz, 2H, Q),
3
4.67; N, 9.90%. UV–Vis (CH2Cl2) kmax, nm (
e
, Mꢁ1 cmꢁ1 dmꢁ3) = 300
7.53 (m, 2H, Q), 8.21 (dd, JHH = 7.5 Hz, 2H, Q), 9.44 (dd,
(6790), 368 (6730), 410 (8020), 476 (17280). IR (KBr, cmꢁ1): 2960
3JHH = 5.7 Hz, 2H, Q2). ESI-MS (CH3OH) m/z: 481.5, [M]+.

C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
1151
Table 2
2.2.9. [RuQ2(pic)2]BPh4 (7)
Selected bond lengths (Å) and bond angles (°) of 2
A solution of FeCl3 ꢂ 6H2O (68 mg, 0.25 mmol) in methanol
(3 ml) was slowly added to a solution containing 3 (120 mg,
0.21 mmol) and NaBPh4 (76 mg, 0.25 mmol) in methanol (10 ml).
After stirring for 30 min the resulting dark green crystalline solid
was filtered, washed with methanol and then with diethyl ether.
Yield 133 mg (71%). Anal. Calc. for RuBC49H40O2N2: C, 73.40; H,
4.99; N, 3.50. Found: C, 73.03; H, 4.96; N, 3.76. ESI/MS (CH3OH) m/
z: 575.6, [M]+.
Bond
Bond length (Å)/bond angle (°)
Ru(1)–S(1)
Ru(1)–S(2)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–N(1)
Ru(1)–N(2)
S(1)–O(3)
2.224(5)
2.233(5)
2.077(12)
2.094(11)
2.07(1)
2.08(2)
1.481(12)
1.457(13)
S(2)–O(4)
2.2.10. [Ru(Q)2(nbd)]BPh4 (8)
O(1)–Ru(1)–N(1)
O(2)–Ru(1)–N(2)
S(1)–Ru(1)–S(2)
N(1)–Ru(1)–N(2)
O(1)–Ru(1)–O(2)
Ru(1)–S(1)–O(3)
Ru(1)–S(2)–O(4)
79.7(6)
81.1(5)
90.1(2)
164.7(6)
86.9(5)
117.7(6)
118.0(6)
This compound was prepared by the oxidation of 6a (120 mg,
0.25 mmol) with FeCl3 ꢂ 6H2O (81 mg, 0.30 mmol) in the presence
of NaBPh4 (99 mg, 0.30 mmol), similar to that for 7. Yield 150 mg
(75%). Anal.Calc. for RuBC49H40O2N2: C, 73.40; H, 5.04; N, 3.50. Found:
C, 73.03; H, 4.96; N, 3.76%. ESI/MS (CH3OH) m/z: 481.5, [M]+.
2.3. Crystal structure determination
Intensity data were collected at ambient temperature using a
Bruker Smart 1000 CCD diffractometer with graphite-monochro-
Table 3
Selected bond lengths (Å) and angles (°) for 3
mated Mo Ka radiation (k = 0.71073 Å) in the x-scan mode. Details
Bond
Distance (Å)/angle (°)
of the intensity data collection and crystal data are given in Table 1.
Selected bond lengths and angles for 2, 3, 4 and 6 are given in Ta-
bles 2–5, respectively. The data were corrected for Lorentz and
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–N(3)
Ru(1)–N(4)
Ru(1)–O(1)
Ru(1)–O(2)
2.024(5)
2.040(5)
2.079(5)
2.059(5)
2.080(4)
2.095(4)
polarization effects. Absorption corrections by the
w-scan method
or an approximation by inter-image scaling were applied. The
structures were resolved by Heavy-atom Patterson method [29]
or direct methods (SIR92 [30] or SHELXS-86 [31]), and expanded using
Fourier techniques (DIRDIF94 [32] or DIRDIF99 [33]). Hydrogen atoms
are included but not refined. All calculations were performed using
the Crystal Structure [34] or TEXSAN [35] crystallographic software
package from Molecular Structure Corporation.
O(1)–Ru(1)–N(1)
O(2)–Ru(1)–N(2)
N(3)–Ru(1)–N(4)
N(1)–Ru(1)–N(2)
N(2)–Ru(1)–N(3)
N(1)–Ru(1)–N(4)
O(1)–Ru(1)–O(2)
81.32(19)
80.9(2)
87.17(19)
91.93(18)
174.2(2)
172.95(19)
174.38(16)
2.4. Computational methodology
atom [38] and its valence basis set was (8s, 7p, 6d)/[6s, 5p, 3d] with
Z = 16.0. For H, C, N, and O atoms, the split valence with polariza-
tion basis sets 6-31G* were employed [39]. The DFT calculations
were accomplished using the GAUSSIAN 03 program [40]. Tight SCF
convergence (10ꢁ8 au) was used for all calculations. Charge
Decomposition Analysis (CDA) [41] was performed to investigate
Density functional theory (DFT) calculations were performed on
the complexes 6a and 6b. Their electronic ground states were fully
optimized from the X-ray determined geometries (without sym-
metry imposed) using Becke’s three-parameter hybrid functional
[36] with the Lee–Yang–Parr correlation functional [37] (B3LYP).
Relativistic small effective core potential was employed for Ru
Table 1
Crystallographic data for compound 2, 3, 4 and 6
Compound
2
3
4
6a + 6b
Empirical formula
Formula weight
k (Å)
T (°C)
Space group
a (Å)
b (Å)
c (Å)
C22H24N2O4RuS2
545.63
0.7107
C30H26N4O2Ru
575.62
0.71073
25
C22H20N4O2Ru
473.50
C50H42N4O5Ru2
981.05
0.71069
25
0.71073
28
25
ꢀ
ꢀ
Pbca (#61)
19.554(3)
10.648(2)
26.059(4)
P21/c
P1ð#2Þ
P1ð#2Þ
12.683(3)
13.410(3)
15.195(4)
90
100.869(4)
90
2538.1(11)
4
1.506
1176
6.53
0.054
0.129
8.156(1)
10.962(2)
11.859(2)
97.87(1)
98.37(1)
102.22(1)
1009.7(3)
2
11.804(2)
12.730(0)
15.123(2)
106.12(1)
111.81(1)
92.82(1)
1992.8(5)
2
a
(°)
b (°)
c
(°)
V (Å3)
5425.8(16)
8
1.336
2224
7.58
0.048
0.087
1.00
Z value
Dcalc (g cmꢁ1
F000
)
1.557
480
8.02
0.036
0.048
1.39
1.635
996
8.154
0.0259
0.0301
1.003
l
(Mo K
a
) (cmꢁ1
)
Ra
Rwb
Goodness of fit
0.839
P
P
a
R = kFoj ꢁ jFck/ jFoj.
P
P
b
R
x
= [
x
(jFoj ꢁ jFc)2/
x
(Fo)]1/2
.

1152
C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
Table 4
The cyclic voltammograms of 1a–c exhibit two reversible cou-
ples which are assigned to RuIV/III and RuIII/II couples. The redox
potentials for 1a and 1b are similar to those reported in the litera-
ture [23]. As expected the redox potentials follow the order
1b > 1a > 1c, i.e. the potentials increase with the electron-donating
ability of the substituent.
Selected bond lengths (Å) and bond angles (°) of 4
Bond
Bond length (Å)/bond angle (°)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–N(3)
Ru(1)–N(4)
C(20)–N(3)
C(21)–N(4)
2.061(2)
2.060(2)
2.070(3)
2.079(3)
1.998(3)
2.001(3)
1.303(5)
1.318(5)
3.2. Synthesis and characterization of bis(8-quinolinolato)ruthenium
(II) complexes
Compound 1a is a convenient starting material for the synthesis
of a variety of bis(8-quinolinolato)ruthenium(II) complexes con-
O(1)–Ru(1)–N(1)
O(2)–Ru(1)–N(2)
N(3)–Ru(1)–N(4)
C(20)–N(3)–C(19)
C(21)–N(4)–C(22)
N(3)–C(20)–C(21)
N(4)–C(21)–C(20)
80.31(9)
80.33(9)
78.8(1)
119.8(3)
119.1(4)
115.5(4)
115.4(3)
taining
p-acceptor ligands, including dimethylsulfoxide (dmso),
4-picoline (pic), dienes and diazadiene, as outlined in Scheme 1.
The general synthetic method involves reduction of 1a with zinc
amalgam in the presence of excess
p-acceptor ligand in refluxing
ethanol under argon. These compounds have been characterized
by elemental analysis, IR and 1H NMR, and the data are consistent
with the proposed formulae. For an octahedral complex of the type
Ru(Q)2L2 where the two L ligands are cis, there are three possible
geometric isomers, as shown in Scheme 2:
Table 5
Selected bond lengths (Å) and bond angles (°) of 6a and 6b (co-crystallized)
Isomer
Bond
Distance (Å)/angle (°)
3.2.1. RuIIQ2(dmso)2
cis,trans (6a)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–C(20)
Ru(1)–C(21)
Ru(1)–C(23)
Ru(1)–C(24)
C(20)–C(21)
C(23)–C(24)
2.082(2)
2.0876(18)
2.106(2)
2.0825(19)
2.190(3)
2.189(2)
2.170(3)
2.169(3)
1.378(4)
1.381(4)
The 1H NMR spectrum of RuIIQ2(dmso)2 (2) shows that the
methyl protons (2.974 and 2.660 ppm) of the two dmso ligands
are chemically non-equivalent. The ratio between the integrals in
the aromatic and the aliphatic regions is 1:1, consistent with the
proposed formula. In the IR spectrum, a strong band occurs at
1078 cmꢁ1, which is in the region expected for S@O stretch of
S-bonded ruthenium(II) dmso complexes (1020–1134 cmꢁ1
)
[42b,42c,42d,42e]. The S@O stretch for O-bonded ruthenium(II)
dmso complexes occur at lower wavelengths (885–954 cmꢁ1
[42c,42d,42e].
)
O(3)–Ru(2)–O(4)
N(3)–Ru(2)–N(4)
160.08(9)
91.68(8)
The structure of 2 was established by X-ray crystallography.
Fig. 1 shows a perspective view of the molecule. Selected bond
lengths and bond angles are shown in Table 2. The two quinoli-
nolato ligands adopt a trans,cis configuration, and the two cis
dmso ligands are S-bonded to the ruthenium center. The two
Ru–S(dmso) (2.224(5) and 2.233(5) Å) and S–O (1.457(13) and
1.481(12) Å) bond distances are comparable to those in other
Ru(II) dmso complexes (2.241–2.364 Å and 1.459–1.50 Å,
respectively) [42]. The Ru–N(Q) distances (2.07(1) Å and
2.08(2) Å) are similar to those in RuQ3 (2.0527–2.0742 Å) [23b],
but the Ru–O(Q) distances (2.077(12) and 2.094(11) Å) are
slightly longer than those in RuQ3 (1.9932–2.0392 Å) [23b] and
is consistent with the lower atomic charge on the ruthenium
(II) center.
trans,cis (6b)
Ru(2)–O(3)
Ru(2)–O(4)
Ru(2)–N(3)
Ru(2)–N(4)
Ru(2)–C(45)
Ru(2)–C(46)
Ru(2)–C(48)
Ru(2)–C(49)
C(45)–C(46)
C(48)–C(49)
2.071(2)
2.0760(17)
2.112(2)
2.121(2)
2.192(3)
2.190(2)
2.160(2)
2.172(2)
1.380(4)
1.374(4)
O(3)–Ru(1)–O(4)
N(3)–Ru(1)–N(4)
94.62(8)
152.75(8)
the interaction between the close-shelled [RuQ2] core and the 2,5-
norbornadiene ligand for both complexes.
This complex in 77K EtOH/MeOH glass is found to show a long
lived (
k = 300 nm (Fig. 2). This emission are tentatively assigned as orig-
inated from the metal-perturbed intraligand (IL)
to p* phospho-
rescence derived from quinolate moieties mixed with the triplet
metal-to-ligand charge transfer (MLCT) [d (Ru) to
*(Q)] character,
s0 = 439 ls) emission at ca. 594 nm upon excitation with
3. Results and discussion
p
3.1. Synthesis and characterization of RuIII Q3
p
p
similar to those reported in the related PtQ2, IrQ3 and PbQ2 sys-
tems [20]. The strong spin–orbit coupling introduced by the ruthe-
nium metal center enhances the accessibility of the 3IL excited
states. The long-lived lifetime in the microsecond range is also
indicative of its triplet parentage.
The synthesis of RuQ3 (1a) and Ru(Me-Q)3 (1b) from RuCl3 ꢂ x-
H2O have been reported [23a]. In this work we have reinvestigated
the synthesis and have developed a general and high yield (>75%)
method for the preparation a series of tris(8-quinolinolato)ruthe-
nium(III) complexes, including 1a, 1b, and Ru(Cl-Q)3 (1c). This
method involves the reaction of Ru(acac)3 with the neat ligand at
180 °C followed by chromatographic purification. The excess li-
gand can be readily recovered by sublimation.
The cyclic voltammogram of 2 exhibits a quasi-reversible cou-
ple at 0.31 V (versus Fc+/0).
3.2.2. RuIIQ2(pic)2
The UV–Vis spectra of 1a and 1b are similar to those reported in
the literature [23]. The X-ray crystal structure of RuQ3 has been re-
cently reported, which shows that the compound has a meridonal
configuration [23b].
Reduction of 1a with zinc amalgam in the presence excess 4-
picoline (pic) in refluxing ethanol produced a green crystalline so-
lid. Elemental analysis and 1H NMR spectroscopy are consistent
with the formula RuIIQ2(pic)2 (3).

C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
1153
O
S
Ru
O
O
S
N
O
[RuIIIQ2(pic)2]BPh4
7
[RuIIIQ2(nbd)]BPh4
8
N
2
FeCl3 / NaBPh4
FeCl3 / NaBPh4
dmso
RuIIIQ3 1a
+ Zn/ Hg
in EtOH
N
2,5-norbornadiene
4-picoline
O
N
N
O
O
N
N
O
+
Ru
Ru
O
Ru
N
N
O
N
N
N
N
1,5-cyclooctadiene
N
3
6a
6b
N
O
N
N
O
O
Ru
N
Ru
O
N
N
5
4
Scheme 1. Reactions of RuQ3 (1a) with various p-acceptor ligands under reducing condition.
L
L
L
L
L
L
O
N
N
O
N
N
O
O
O
N
O
N
cis, trans
trans, cis
cis, cis
Scheme 2. Three possible geometric isomers of the complex RuQ2L2.
C(15)
C(6)
C(16)
C(7)
C(5)
C(14)
C(13)
C(17)
C(8)
O(2)
O(1)
C(4)
C(3)
C(18)
C(9)
C(2)
N(2)
N(1)
C(12)
575
600
625
650
675
700
725
750
Wavelength (nm)
C(11)
Ru(1)
Fig. 2. Emission spectrum of 2 in ethanol/methanol (4:1) glass 77 K.
C(1)
C(10)
S(2)
C(20)
C(21)
C(22)
similar to those in trans-[RuII(phen)2(py)2][PF6]2 (2.097(5) Å), and
trans-RuII(CN)2(py)4 (2.090(4)–2.093(4) Å) [43]. The Ru–N(Q) and
Ru–O(Q) distances (2.024(5), 2.040(5) and 2.080(4), 2.095(4) Å,
respectively) are similar to those in 2.
S(1)
C(19)
O(3)
O(4)
The cyclic voltammogram of 3 (Fig. 4) exhibits a reversible
couple at ꢁ0.56 V and a quasi-reversible couple at 0.56 V (versus
Fc+/0), which are assigned to RuIII/II and RuIV/III couples, respectively.
Fig. 1. ORTEP drawing of 2, thermal ellipsoids are drawn at the 50% probability
(hydrogen atoms are omitted for clarity).
The X-ray crystal structure of 3 shows that the two quinolinola-
to ligands have a cis,trans configuration, in contrast to the trans,cis
arrangement in 2, and the two picoline ligands are cis (Fig. 3). The
Ru–N(picoline) distances of 2.079(5) and 2.059(5) Å (Table 3) are
3.2.3. RuIIQ2(dab)
Bis(1,3-dialkylimidazolidin-2-ylidene) has been used as a car-
bene precursor for the preparation of various transition metal car-
bene complexes [44]. Attempts were made to prepare a carbene

1154
C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
C(30)
C(21)
C(20)
C(24)
C(20)
C(27)
C(28)
N(4)
C(22)
C(17)
C(21)
N(3)
C(19)
C(8)
C(26)
C(22)
C(29)
C(25)
O(2)
O(1)
C(19)
N(4)
O(2)
C(23)
Ru(1)
N(3)
O(1)
C(7)
C(4)
N(1)
N(2)
C(16)
C(6)
C(5)
C(15)
C(8)
C(17)
C(9)
C(2)
C(18)
C(13)
Ru(1)
C(16)
C(1)
C(7)
C(10)
N(2)
N(1)
C(15)
C(6)
C(11)
C(3)
C(9)
C(13)
C(14)
C(18)
C(12)
C(10)
C(1)
C(4)
Fig. 5. ORTEP drawing of 4, thermal ellipsoids are drawn at the 50% probability
C(5)
C(2)
(hydrogen atoms are omitted for clarity).
C(14)
C(11)
C(3)
C(12)
Fig. 3. ORTEP drawing of 3, thermal ellipsoids are drawn at the 50% probability
(hydrogen atoms are omitted for clarity).
in ruthenium(II) diazabutadiene complexes (2.01–2.15 Å) [45]. The
imine bond distances (N(4)–C(21) and N(3)–C(20)) (1.303(5) and
1.318(5) Å) are within the reported range for other ruthenium(II)
diazabutadiene complexes (1.25(1)–1.34(2) Å) [45]. The C(21)–
N(4)–C(22) and C(20)–N(3)–C(19) bond angles (119.1(4) and
119.8(3)) are consistent an sp2 imine nitrogen.
III/II
Ru
IV/III
Ru
The cyclic voltammogram of 4 shows a reversible RuIII/II couple at
0.77 V (versus Fc+/0) (Fig. 6). Two reversible couples also appear at
E = ꢁ1.64 and ꢁ1.80 V, these are assigned as the dab0/ꢁ and
dabꢁ/2ꢁ couples [46].
3.2.4. RuIIQ2(COD)
The synthesis and X-ray crystal structure of this compound have
been reported recently [24]. The two quinolinolato ligands adopt a
cis,trans configuration. The reported synthesis uses [Ru(COD)Cl2]2
as the starting material. In this work the same compound has been
prepared from RuQ3, the spectroscopic properties agree with that
prepared from [Ru(COD)Cl2]2.
1.0
0.5
0.0
-0.5
-1.0
Potential (V)vsFc+/Fc
3.2.5. RuIIQ2(nbd)
The reaction of RuQ3 with 2,5-norbornadiene (nbd) in ethanol
in the presence of zinc amalgam produces a mixture of red and
yellow crystalline solids. Elemental analysis of both solids are
Fig. 4. Cyclic voltammogram of 3 (0.1 M ½NBunꢀPF6 in CH3CN).
4
complex of RuIIQ2 by treatment of 1a with bis(1,3-dimethylimidaz-
olidin-2-ylidene) (L0) in the presence of Zn/Hg under argon. A pur-
ple solution was produced, but attempts to isolate pure products
from this solution were unsuccessful. However, the purple solution
readily turned red upon exposure to air, and the red complex
-/2-
dab
0/-
dab
RuQ2(dab)
(4)
(dab = N,N0-dimethyl-1,4-diazabuta-1,3-diene)
could be isolated. The reaction presumably occurs by initial forma-
tion of RuQ2L0, followed by cleavage and oxidation of L0. Attempts
to prepare 4 by using N,N0-dimethylethylenediamine (Me2en) in-
stead of L0 were unsuccessful, neither RuQ2(Me2en) nor 4 could
be isolated. Although there are numerous examples of ruthenium
1,4-diaza-1,3-butadiene complexes containing bulky substituents
such as isopropyl, tert-butyl and cyclohexyl on the imine nitrogen
[45], this is the first example of a ruthenium complex containing
the methyl-substituted diazabutadiene ligand.
III/II
Ru
The X-ray structure shows that the two quinolinolato ligands
are coordinated to the ruthenium center in a cis,trans fashion, sim-
ilar to 3; and the dab ligand functions as a bidentate ligand (Fig. 5).
Selected bond distances and bond angles are shown in Table 4. The
Ru–N(Q) (2.070(3) and 2.079(3) Å) and Ru–O(Q) (2.061(2) and
2.060(2) Å) distances are similar to those in 2 and 3. The Ru(1)–
N(dab) distances (1.998(3) and 2.001(3) Å) are among the shortest
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
+
Potential (V)vsFc /Fc
Fig. 6. Cyclic voltammogram of 4 (0.1 M ½NBunꢀPF6 in CH3CN).
4

C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
1155
consistent with the formula RuQ2(nbd). X-ray crystallography
0.30
0.25
0.20
0.15
0.10
0.05
0.00
showed that the yellow compound is the cis,trans isomer (6a),
whereas as the red crystals consist of co-crystallized cis,trans (6a)
and trans,cis (6b) isomers (Fig. 7). The bond distances and angles
for 6a in the red and yellow crystals are the same (Table 5). The
bond distances for 6a are also very similar to those for 6b. The
Ru–C(nbd) distances for 6a and 6b (2.160(2)–2.192(3) Å) are with-
in the range for other ruthenium 2,5-norbornadiene complexes
(2.150–2.220 Å) [47]. The olefinic C@C distances in 6a and 6b
(1.374(4)–1.381(4) Å) are also comparable to those in other ruthe-
nium 2,5-norbornadiene complexes (1.383–1.401 Å) [47], and are
longer than the length of 1.35 Å in the free olefin [47d], reflecting
6a
6b
the existence of ruthenium–olefin p-back bonding.
The mixture of 6a and 6b in the red crystals can be readily sep-
arated by column chromatography (neutral alumina) as yellow and
red solids. The 1H NMR spectra of both compounds have a ratio of
3:2 for the integrals in the aromatic and the aliphatic regions, con-
sistent with the presence of two 8-quinolinolato ligands and a 2,5-
norbornadiene ligand. In the UV–Vis spectrum the lowest energy
absorption band for 6a occurs at 427 nm, while that of 6b occurs
at a lower wavelength of 500 nm (Fig. 8).
300
400
500
600
700
800
Wavelength (nm)
Fig. 8. UV–Vis spectra of 6a and 6b.
The cyclic voltammogram of 6b in CH3CN shows a reversible
couple at ꢁ0.03 V and a quasi-reversible couple at 0.83 V versus
Fc+/0 which are assigned to the RuIII/II and the RuIV/III couples,
respectively (Fig. 9). In contrast, 6a shows only a quasi-reversible
RuIII/II couple at Epa = 0.41 V and no RuIV/III couple in the same
potential range (ꢁ1.0–1.0 V). However, there is a relatively small
6a
C(50)
C(47)
C(44)
6b
C(48)
C(46)
C(49)
C(45)
C(35)
C(26)
N(3)
C(27)
N(4)
C(28)
C(29)
C(36)
Ru(2)
1.5
1.0
0.5
0.0
-0.5
-1.0
C(34)
O(3)
C(43)
+
C(33)
C(30)
Potential (V)vsFc /Fc
C(37)
C(38)
O(4)
C(32)
Fig. 9. Cyclic voltammogram of 6a and 6b.
C(31)
C(42)
C(39)
couple at 0.64 V, which presumably is due to [RuQ2(CH3CN)2]2+/+
generated from loss of the alkene ligand from 6a upon oxidation
to RuIII.
C(3)
C(41)
C(2)
C(1)
C(40)
C(4)
C(5)
Since 6a and 6b have similar bond lengths and angles but differ
significantly in redox potentials and energies of electronic transi-
tions, theoretical calculations have been performed on these two
compounds in order to gain an insight into the nature of these dif-
ferences. The ground-state structures of complexes 6a and 6b were
optimized at the DFT level (B3LYP). Their optimized structural data
are in satisfactory agreement with their X-ray crystal structure
data. The highest-occupied molecular orbitals (HOMOs) for both
complexes are mainly contributed from the d orbitals of Ru(II)
and the orbitals of Q (6a, 19.8% d(Ru), 71.3% Q; 6b, 30.1% d(Ru),
59.7% Q). It is noted that the energy of the HOMO of 6a
(ꢁ4.82 eV) is lower than that of 6b (ꢁ4.41 eV) by 0.41 eV. This is
consistent with the experimental findings that (i) the first oxida-
tion wave for 6a (Epa = 0.41 V versus Fc+/0) is more anodic than that
of 6b (E1/2 = ꢁ0.03 V versus Fc+/0); (ii) the lowest energy transition
C(6)
C(9)
N(1)
C(7)
C(20)
O(2)
C(8)
C(16)
C(17)
C(21)
C(22)
C(15)
C(14)
Ru(1)
C(18)
C(10)
C(19)
O(1)
N(2)
C(13)
C(25)
C(12)
C(24)
C(23)
C(11)
Fig. 7. ORTEP drawing of co-crystallized 6a (bottom) and 6b (top) in the red
crystals, thermal ellipsoids are drawn at the 50% probability (hydrogen atoms are
omitted for clarity).
(presumably due to d [Ru(II)] to p* (Q) MLCT transition) of 6a
p

1156
C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
(kmax = 427 nm) is blue-shifted compared to 6b (kmax = 500 nm) by
0.42 eV. Charge decomposition analysis (CDA) calculations suggest
that the bonding interaction of the close-shelled [RuQ2] moiety and
the nbd ligand for both complexes can be described by the Dewar–
electronic transitions, despite their very similar bond distances. A
novel ruthenium(III) norbornadiene complexes [RuQ2(nbd)]BPh4
has also been isolated, indicating that there is a rich coordination
chemistry of ruthenium with 8-hydroxyquinoline.
Chatt–Duncanson donor–acceptor model as the residual terms (D)
are essentially zero (6a, ꢁ0.027; 6b, ꢁ0.022). The ratio of the val-
ues for [nbd ? Ru2+] donation (d) and [Ru2+ ? nbd] back-donation
(b), d/b, are 2.00 and 1.72 for 6a and 6b, respectively, suggesting an
overall charge donation from nbd to the Ru2+ centers, although the
Ru2+ centers are supported by the electron-donating ligands Q.
Acknowledgements
The work described in this paper was supported by the Re-
search Grants Council of Hong Kong (CityU 101403) and the City
University of Hong Kong (7001925).
3.3. Synthesis and characterization of bis(8-quinolinolato)ruthenium
(III) complexes
Appendix A. Supplementary material
3.3.1. [RuIIIQ2(pic)2]BPh4
CCDC 670792, 670793, 670794, 670795 and 670796 contain the
supplementary crystallographic data for 2, 3, 4, 6 and 6a. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary material such as spectral data for 7 and 8; electro-
chemical data for 1–6; crystal data and selected bond lengths and
bond angles of 6a are also available. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2008.05.036.
In accordance with its relatively low RuIII/II redox potential
(E1/2 = 0.56 V versus Fc+/0), a solution of 3 in chloroform was oxi-
dized within minutes by air at room temperature. Oxidation of 3
can be efficiently carried out by FeCl3 in methanol in the presence
of excess NaBPh4 to give a dark green crystalline solid, formulated
as [RuIIIQ2(pic)2]BPh4 (7). Compound 7 has a room temperature
magnetic moment of leff = 2.04 lB (Gouy method), consistent with
a low-spin d5 RuIII complex. The ESI/MS in dichloromethane shows
peaks at m/z = 576, 483 and 390 which is due to [M]+, [M-pic]+ and
[M-2pic]+, respectively. The cyclic voltammogram of 7 is the same
as that of 3, suggesting that no isomerization has occurred during
the oxidation.
References
[1] R.G.W. Hollingshead, Oxine and its
London, 1954–1956.
Derivatives, vols. I–IV, Butterworths,
[2] E.B. Sandell, H. Onishi, Photometric Determination of Traces of Metals, General
Aspects; Fourth Edition of Part I of Colorimetric Determination of Traces of
Metals, Wiley, New York, 1978, p. 415.
[3] R. Ballardini, G. Varani, M.T. Indelli, F. Scandola, Inorg. Chem. 25 (1986) 3858.
[4] C. Bartocci, S. Sostero, O. Traverso, A. Cox, T.J. Kemp, W.J. Reed, J. Chem. Soc.,
Faraday Trans. 76 (1980) 797.
[5] K. Soroka, R.S. Vithanage, D.A. Phillips, B. Walker, P.K. Dasgupta, Anal. Chem. 59
(1987) 629.
[6] M.A. Palacios, Z. Wang, V.A. Montes, G.V. Zyryanov, B.J. Hausch, K. Jursíková, P.
Anzenbacher Jr., Chem. Commun. (2007) 3708.
[7] T. Moeller, A.J. Cohen, J. Am. Chem. Soc. 72 (1950) 3546.
[8] W.E.J. Ohnesorge, Inorg. Nucl. Chem. 29 (1967) 485.
[9] C.H. Chen, J. Shi, Coord. Chem. Rev. 171 (1998) 161.
[10] P.E. Burrows, L.S. Sapochak, S.R. Forrest, Appl. Phys. Lett. 64 (1994) 2718.
[11] Y. Wang, W. Zhang, Y. Li, L. Ye, G. Yang, Chem. Mater. 11 (1999) 530.
[12] W. Humbs, E. Veldhoven, H. Zhang, M. Glasbeek, Chem. Phys. Lett. 304 (1999)
10.
[13] Z. Chen, J. Yu, M. Sone, S. Miyata, Y. Lu, T. Watanabe, J. Phys. D: Appl. Phys. 34
(2001) 2679.
[14] W. Stampor, J. Kalinowski, G. Marconi, P. Di Marco, V. Fattori, G. Giro, Chem.
Phys. Lett. 283 (1998) 373.
[15] L. Wang, X. Jiang, Z. Zhang, S. Xu, Displays (2000) 47.
[16] O.M. Khreis, R.J. Curry, M. Somerton, W.P.J. Gillin, Appl. Phys. 88 (2000) 777.
[17] R.J. Curry, W.P. Gillin, Synth. Met. (2000) 35.
[18] O.M. Khreis, W.P. Gillin, M.P.M. Somerton, R.J. Curry, Org. Electron. 2 (2001)
45.
[19] R.J. Curry, W.P. Gillin, Appl. Phys. Lett. 75 (1999) 1380.
[20] R. Ballardini, G. Varani, M.T. Indelli, F. Scandola, Inorg. Chem. 25 (1986) 3858.
[21] D. Donges, J.K. Nagle, H. Yersin, Inorg. Chem. 36 (1997) 3040.
[22] C. Bartocci, S. Sostero, O. Traverso, J.C.S. Faraday I 76 (1980) 797.
[23] (a) G.K. Lahiri, S. Bhattacharya, B.K. Ghosh, A. Charkravorty, Inorg. Chem. 26
(1987) 4324;
(b) J.G. Małecki, M. Jaworska, R. Kruszynski, J. Kłak, Polyhedron 24 (2005)
3012;
(c) S.G. Rodman, J.K. Nagle, Inorg. Chim. Acta 105 (1985) 205.
[24] (a) P.J. Powell, Organomet. Chem. 65 (1974) 89;
(b) C. Slugovc, A. Koppitz, A. Pogantsch, F. Stelzer, Inorg. Chim. Acta 358 (2005)
2718.
3.3.2. [RuIIIQ2(nbd)]BPh4
In accordance with its redox potential (E1/2 = 0.03 V versus
Fc+/0), 6b can be readily oxidized by FeCl3 in methanol in the pres-
ence of excess NaBPh4 to give a dark brown crystalline solid formu-
lated as [RuIIIQ2(nbd)]BPh4 (8). As expected, no reaction occurred
when 6a (Epa = 0.41 V versus Fc+/0) was treated with FeCl3. Com-
pound 8 has a room temperature magnetic moment of leff = 2.2 lB
(Gouy method), consistent with a low-spin d5 RuIII complex. The
ESI/MS of 8 shows [M]+ at m/z = 482, there is also a minor peak
at 390 which is due to [M-nbd]+.
This is a rare example of a stable ruthenium(III) alkene complex.
Ruthenium (III) alkene complexes are usually unstable with re-
spect to loss of alkene, unless another donor atom is also present
to form a stable chelate [48]. Presumably Qꢁ is sufficiently elec-
tron-donating so that there is some p
-back bonding between RuIII
and the alkene. Another example of ruthenium(III) norbornadiene
complex, [Ru(Et2dtc)2(nbd)](I3), has been reported recently; where
Et2dtc is N,N-diethyldithiocarbamate [47d].
Since the 2,5-norbornadiene is coordinated to a ruthenium(III)
center, it is expected to be electrophilic. However, reaction of 8
with various nucleophiles (R2NH, CNꢁ) invariably resulted in the
reduction of 8 back to 6b, as monitored by UV–Vis spectroscopy.
When reactions were carried out on a preparatory scale, 6b could
be isolated in >90% yields. Even on standing, a dark purple solution
of 8 in CH2Cl2 gradually turned to orange 6b with a rate constant of
0.013 sꢁ1 at 25.0 °C.
4. Conclusion
[25] M. Menon, A. Pramanik, N. Bag, A. Charkravorty, J. Chem. Soc., Dalton Trans.
(1995) 1417.
A general, high-yield synthetic method for RuQ3 and its deriva-
tives has been developed. RuQ3 is a versatile starting material for
the preparation of a variety of bis(8-quinolinolato)ruthenium(II)
[26] J.T. Warren, W. Chen, D.H. Johnston, C. Turro, Inorg. Chem. 38 (1999) 6187.
[27] W.P. Griffith, D. Pawson, J. Chem. Soc., Dalton. Trans. (1973) 1315.
[28] H.E. Winberg, Chem. Abstr. 64 (1966) 15854h.
[29] DIRDIF 92: P.T. Beurskens, G. Admiraal, W.P. Bosman, S. Garcis-Granda, R.O.
Gould, J.M.M. Smits, C. Smykalla, PATTY: The DIRDIF Program System, Technical
Report of the Crystallography Laboratory, University of Nijmegen, The
Netherlands, 1992.
[30] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26
(1993) 343.
[31] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
complexes containing
p-acceptor ligands. The quinolinolato
complexes adopt either cis, trans or trans,cis configurations. In the
case of RuQ2(nbd) (6) both isomers have been isolated and
structurally characterized. These two isomers have significantly
different properties including redox potentials and energies of

C.-F. Leung et al. / Inorganica Chimica Acta 362 (2009) 1149–1157
S. Geremia, M. Calligaris, Inorg. Chem. 34 (1995) 4722;
1157
[32] DIRDIF 94: P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de Gelder,
R. Israel, J.M.M. Smits, The DIRDIF 94 Program System, Technical Report of the
Crystallography Laboratory, University of Nijmegen, The Netherlands, 1994.
[33] DIRDIF 99: P.T. Beurskens, G. Admiraal, G. Beurskens, W.P. Bosman, R. de Gelder,
R. Israel, J.M.M. Smits, The DIRDIF 99 Program System, Technical Report of the
Crystallography Laboratory, University of Nijmegen, The Netherlands, 1999.
[34] CRYSTALSTRUCTURE 3.00: Crystal Structure Analysis Package, Rigaku and Rigaku/
MSC, 2000–2002.
(f) T.J. Beasley, R.D. Brost, C.K. Chu, S.L. Grundy, S.R. Stobart, Organometallics
12 (1993) 4599;
(g) B.J. Coe, T.J. Meyer, P.S. White, Inorg. Chem. 32 (1993) 4012;
(h) D. Sellmann, J. Utz, F.R. Heinemann, Inorg. Chem. 38 (1999) 5314.
[43] (a) P. Bonneson, J.L. Walsh, W.T. Pennington, A.W. Cordes, B. Durham, Inorg.
Chem. 22 (1983) 1761;
(b) P. Desjardins, G.P.A. Yap, R.J. Crutchley, Inorg. Chem. 38 (1999) 5901;
(c) B.J. Coe, T.J. Meyer, P.S. White, Inorg. Chem. 34 (1995) 3600.
[44] (a) P.B. Hitchcock, M.F. Lappert, P.L. Pye, J. Chem. Soc., Chem. Commun. (1976)
644;
[35] TEXSAN: Crystal Structure Analysis Package, Molecular Structure Corporation,
The Woodlands, TX, USA, 1985 and 1992.
[36] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[37] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
(b) P.B. Hitchcock, M.F. Lappert, P.L. Pye, J. Chem. Soc., Chem. Commun. (1974)
679;
(c) P.B. Hitchcock, M.F. Lappert, P.L. Pye, J. Chem. Soc., Chem. Commun. (1977)
196.
[38] M. Dolg, H. Stoll, H. Preuss, R.M. Pitzer, J. Phys. Chem. 97 (1993) 5852.
[39] M.M. Francl, W.J. Pietro, W.J. Hehre, J.S. Binkley, M.S. Gordon, D.J. DeFrees, J.A.
Pople, J. Chem. Phys. 77 (1982) 3654.
[40] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O.
Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K.
Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.
Raghavachari, J.B. Foresman, J.W. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.
Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople, GAUSSIAN 03, Revision D.01, Gaussian, Inc., Wallingford CT, 2004.
[41] (a) G. Frenking, N. Fröhlich, Chem. Rev. 100 (2000) 717;
[45] (a) L.H. Staal, L.H. Polm, K. Vrieze, F. Ploeger, C.H. Stam, Inorg. Chem. 20 (1981)
3590;
(b) C.J. Kleverlaan, D.J. Stufkens, J. Fraanje, K. Goubitz, Eur. J. Inorg. Chem.
(1998) 1243;
(c) M.P. Aarnts, M.P. Wilms, K. Peelen, J. Fraanje, K. Goubitz, F. Hartl, D.J.
Stufkens, J.B. Baerends, A. Vlcek, Inorg. Chem. 35 (1996) 5468;
(d) B. de Klerk-Engel, J.G.P. Delis, K. Vrieze, Organometallics 13 (1994) 3269;
(e) M.P. Aarnts, D.J. Stufkens, A. Oskam, J. Fraanje, K. Goubitz, Inorg. Chim. Acta
256 (1997) 93;
(f) B. de Klerk-Engel, J.G.P. Delis, J. Ernsting, C.J. Elsevier, Frühauf, D.J. Stufkens,
K. Vrieze, K. Goubitz, J. Fraanje, Inorg. Chim. Acta 250 (1995) 273.
[46] (a) H.M. Tuononen, A.F. Armstrong, Dalton Trans. (2006) 1885;
(b) H.M. Tuononen, A.F. Armstrong, Inorg. Chem. 44 (2005) 8277.
[47] (a) D.C. Wilson, J.H. Nelson, J. Organomet. Chem. 682 (2003) 272;
(b) T. Hayashida, K. Miyazaki, Y. Yamaguchi, H. Nagashima, J. Organomet.
Chem. 634 (2001) 167;
(b) S. Dapprich, G. Frenking, J. Phys. Chem. 99 (1995) 9352.
[42] (a) A.A. Rachford, J.L. Petersen, J.J. Rack, Inorg. Chem. 45 (2006) 5953;
(b) E. Reisner, V.B. Arion, M.F.C. Guedes da Silva, R. Lichtenecker, A. Eichinger,
B.K. Keppler, V.Y. Kukushkin, A.J.L. Pombeiro, Inorg. Chem. 43 (2004) 7083;
(c) E. Alessio, G. Mestroni, G. Nardin, W.M. Attia, M. Calligaris, G. Sava,
S. Zorzet, Inorg. Chem. 27 (1988) 4099;
(c) J. Sutter, S.L. James, P. Steenwinkel, T. Karlen, D.M. Grove, N. Veldman, W.J.J.
Smeets, A.L. Spek, G. van Koten, Organometallics 15 (1996) 941;
(d) W.H. Leung, J.L.C. Chim, H. Hou, T.S.M. Hun, I.D. Williams, W.T. Wong,
Inorg. Chem. 36 (1997) 4432;
(e) K. Itoh, N. Oshima, G.B. Jameson, H.C. Lewis, J. Ibers, J. Am. Chem. Soc. 103
(1981) 3014.
(d) E. Alessio, B. Milani, M. Bolle, G. Mestroni, P. Faleschini, S. Geremia,
M. Calligaris, Inorg. Chem. 34 (1995) 4712;
(e) E. Alessio, B. Milani, M. Bolle, G. Mestroni, P. Faleschini, F. Todone
[48] M.A. Bennett, G.A. Heath, D.C.R. Hockless, I. Kovacik, A.C. Willis, J. Am. Chem.
Soc. 120 (1998) 932.