Synthesis and photophysical properties of ruthenium(II) isocyanide complexes containing 8-quinolinolate ligands

Article abstract of DOI:10.1021/om900253h

A series of ruthenium(II) bis(8-quinolinolato) complexes bearing isocyanide ligands (RNC) have been synthesized by the reaction of [RuQ₃] (Q = 8-quinolinolate) with RNC in the presence of Zn/Hg. These complexes have the general formula [RuQ

Full text of DOI:10.1021/om900253h

Organometallics 2009, 28, 5709–5714 5709
DOI: 10.1021/om900253h
Synthesis and Photophysical Properties of Ruthenium(II) Isocyanide
Complexes Containing 8-Quinolinolate Ligands
Chi-Fai Leung,† Siu-Mui Ng,† Jing Xiang,† Wai-Yeung Wong,‡ Michael Hon-Wah Lam,†
Chi-Chiu Ko,*,† and Tai-Chu Lau*,†
†Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong,
Hong Kong, People’s Republic of China, and ‡Department of Chemistry, Hong Kong Baptist University,
Waterloo Road, Kowloon, Hong Kong, People’s Republic of China
Received April 3, 2009
A series of ruthenium(II) bis(8-quinolinolato) complexes bearing isocyanide ligands (RNC) have
been synthesized by the reaction of [RuQ3] (Q=8-quinolinolate) with RNC in the presence of Zn/Hg.
These complexes have the general formula [RuQ2(RNC)2] (1, R = tert-butyl; 2, R = 4-MeOPh; 3,
R=4-ClPh; 4, R=2,4,6-Br3Ph). Both the yellow cis,cis,trans (a) and orange-red trans,trans,trans (b)
isomers have been isolated for complexes 1-4. trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (6, HTol-Q=
8-hydroxyl-5-tolylquinoline) has also been prepared from [Ru(PPh3)2Cl2]. The structures of 2a, 3a,
and 4b have been determined by X-ray crystallography. These complexes exhibit an intense
absorption band in the UV region (λmax = 320-390 nm) with molar extinction coefficients (ε) on
the order of 104 dm3 mol-1 cm-1 and a moderately intense absorption with ε on the order of 103 dm3
mol-1 cm-1 at 400-492 nm. The intense absorption at 320-390 nm is assigned to the ligand-centered
πfπ* transitions of the quinolinolate ligands, probably mixed with the πfπ* transitions of the
isocyanide ligands. The lower energy absorptions at 400-492 nm are assigned to Ru(dπ)fπ*(Q)
metal-to-ligand charge transfer (MLCT) transitions. Upon excitation at λ > 350 nm, 1a-3a in
dichloromethane solution exhibit orange-red luminescence (645-680 nm). In 77 K EtOH/MeOH
glass, complexes 1-4 and 6 give intense structured emission spectra (593-638 nm). The cyclic
voltammograms (CV) of 1a-4a generally exhibit an irreversible or quasi-reversible RuIII/II couple at
the potential range of 0.02-0.38 V vs Fcþ/Fc, except in the case of 1a, where a reversible RuIII/II and a
quasi-reversible RuIV/III (0.68 V vs Fcþ/Fc) couple are observed. The potential for the RuIII/II couple
increases with the π-accepting ability of the isocyanide ligands. In the CV of 1b-4b, a reversible RuIII/II
(-0.16 to 0.065 V) and quasi-reversible RuIV/III (0.70-0.85 V) couple are observed.
Introduction
of bis(8-quinolinolato)ruthenium(II) complexes of general
formula [RuQ2L2] (L2=(DMSO)2, COD, (4-Mepy)2, etc.)14
We report here the synthesis and photophysical properties of
a series of bis(8-quinolinolato)ruthenium(II) complexes
bearing isocyanide ligands, with the general formula [RuQ2-
(RNC)2]. Polypyridyl ruthenium(II) and osmium(II) bearing
isocyanide or carbonyl ligands are known to possess inter-
esting emissive properties.10-13
Luminescent transition metal complexes have attracted
much attention in recent years because of their potential
applications in optical sensing and sensitization, electrolu-
minescent (EL) devices such as organic light-emitting
diode (OLED) and light-emitting electrochemical cells
(LEC), and photovoltaics.1,2 Since the first study of tris-
(8-quinolinolato)aluminum (AlQ3)-based multilayer EL
devices,3 considerable attention has been focused on the
study of various metal 8-quinolinolates and their deriva-
tives.4-9 We have recently developed the synthesis of a series
Experimental Section
Materials and Physical Measurements. 8-Hydroxyl-5-tolyl-
quinoline (HTol-Q), [RuQ3], and [Ru(Tol-Q)2(PPh3)2] were pre-
pared according to literature methods.8,14,15 The 4-chloro- and
*Corresponding author. E-mail bhtclau@cityu.edu.hk.
(1) Baranoff, E.; Collin, J. P.; Flamigni, L.; Sauvage, J. P. Chem. Soc.
Rev. 2004, 33, 147.
(2) Chou, P. T.; Chi, Y. Eur. J. Inorg. Chem. 2006, 3319.
(3) Tang, C. W.; Vanslyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
(4) Chen, C. H.; Shi, J. Coord. Chem. Rev. 1998, 171, 161.
(5) Wang, Y.; Zhang, W.; Li, Y.; Ye, L.; Yang, G. Chem. Mater. 1999,
11, 530.
(6) Wang, L.; Jiang, X.; Zhang, Z.; Xu, S. Displays 2000, 47.
(7) Khreis, O. M.; Gillin, W. P.; Sommeton, M.; Curry, R. J. Org.
Electron. 2001, 2, 45.
(10) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2007, 36, 1421.
(11) Li, E. Y.; Cheng, Y. M.; Hsu, C. C.; Chou, P. T.; Lee, G. H.
Inorg. Chem. 2006, 45, 8041.
(12) Villegeas, J. M.; Stoyanov, S. R.; Huang, W.; Lockyear, L. L.;
Reibenspies, J. H; Rilema, D. P. Inorg. Chem. 2004, 43, 6383.
(13) Stoyanov, S. R.; Villegeas, J. M.; Rilema, D. P. Inorg. Chem.
Commun. 2004, 7, 838.
(14) Leung, C. F.; Wong, C. Y.; Ko, C. C.; Yuen, M. C.; Wong,
W. T.; Wong, W. Y.; Lau, T. C. Inorg. Chim. Acta 2009, 362, 1149.
(15) Menon, M.; Pramanik, A.; Bag, N.; Chakravorty, A. J. Chem.
Soc., Dalton Trans. 1995, 1417.
(8) Montes, V. A.; Pohl, R.; Shinar, J.; Anzenbacher, P., Jr. Chem.;
Eur. J. 2006, 12, 4523.
(9) Curry, R. J.; Gillin, W. P. Appl. Phys. Lett. 1999, 75, 1380.
r
2009 American Chemical Society
Published on Web 09/16/2009
pubs.acs.org/Organometallics

5710 Organometallics, Vol. 28, No. 19, 2009
Leung et al.
1
2,4,6-tribromophenyl isocyanide ligands were synthesized by
reported procedures.16 tert-Butyl isocyanide, 4-methoxyphenyl
isocyanide, and 8-hydroxyquinoline were purchased from Al-
drich. Other chemicals were of reagent grade and used without
further purification. IR spectra were obtained from KBr discs by
using a Bomen MB-120 FTIR spectrophotometer. UV/visible
spectra were recorded on a Perkin-Elmer Lamda 19 spectro-
photometer. Steady-state emission and excitation spectra were
recorded on a Horiba Jobin Yvon Florolog-3-TCSPC spectro-
photometer. Measurements of the EtOH/MeOH (4:1, v/v) glass
samples at 77 K were carried out with samples contained in a
quartz tube inside a quartz-walled Dewar flask. 1H NMR
spectra were recorded on a Varian (300 MHz) FT-NMR spec-
trometer. The chemical shifts (δ ppm) were reported with
reference to tetramethylsilane (TMS). Elemental analyses were
done on an Elementar Vario EL III analyzer. Cyclic voltammo-
grams were recorded on a PAR model 273 potentiostat, using
ferrocene (Fc) as internal reference. A glassy carbon disk work-
ing electrode and a Ag/AgNO3 reference electrode were used.
The supporting electrolyte was 0.1 M [nBu4N]PF6 in CH3CN.
[nBu4N]PF6 (Aldrich) was recrystallized three times from etha-
nol and dried in vacuo at 120 °C for 24 h before use. Acetonitrile
was first refluxed over calcium hydride and then distilled under
argon.
Synthesis of Complexes. cis,cis,trans- (1a) and trans,trans,
trans-[RuQ2(tBuNC)2] (1b). A mixture of [RuQ3] (120 mg, 0.225
mmol), tert-butyl isocyanide (47 mg, 0.56 mmol), and a few
pieces of Zn/Hg in 25 mL of ethanol was refluxed under argon
for 18 h. After cooling to room temperature, the orange-red
solution was filtered and the volatiles were then removed by
rotary evaporation. The residue was dissolved in dichloro-
methane and loaded onto a silica gel column. A yellow band
eluted with dichloromethane was collected and dried under
reduced pressure to give a yellow crystalline solid (1a). The red
band eluted with dichloromethane/acetone (10:1) was also
collected and dried under reduced pressure to give a red crystal-
line solid (1b).
cm-1): 2074 (νNC), 2127 (νNC). H NMR (300 MHz, CDCl3):
δ 3.80 (s, 6H, MeO), 6.76 (m, 4H, Q þ 4-MeOPhNC), 6.87
(d, 3JHH = 7.20, 2H, Q), 7.16 (m, 8H, Q þ 4-MeOPhNC), 7.38
(t, 2H, 3JHH=8.10, Q), 8.0 (dd, 3JHH=8.53, 4JHH=1.35, 2H, Q),
8.44 (dd, 3JHH =4.80, 4JHH =1.50, 2H, Q).
2b was recrystallized from dichloromethane/n-hexane. Yield:
62 mg (42%). Anal. Calcd for C34H26N4O4Ru: C, 62.28; H, 3.97;
N, 8.55. Found: C, 62.41, H, 4.06; N, 8.48. UV/vis (CH2Cl2)
λ
max, nm (ε, M-1 cm-1): 331 (25 100), 389 (18 200), 478 (5840).
IR (KBr, cm-1): 2088 (νNC). H NMR (300 MHz, CDCl3): δ
3.72 (s, 6H, MeO), 6.62 (d, 4H, Qþ4-MeOPhNC), 6.86 (m, 6H,
Qþ4-MeOPhNC), 7.03 (dd, 3JHH =7.80, 4JHH =1.20, 2H, Q),
7.34 (m, 4H, Q), 8.07 (dd, 3JHH=8.40, 4JHH=1.50, 2H, Q), 9.17
(dd, 3JHH =4.80, 4JHH =1.50, 2H, Q).
1
cis,cis,trans- (3a) and trans,trans,trans-[RuQ2(4-ClPhNC)2]
(3b). The complexes were synthesized by a similar procedure
to that for 1a and 1b using 4-chlorophenyl isocyanide (77 mg,
0.56 mmol). The yellow band eluted from a silica gel column
with dichloromethane/acetone (10:1) was collected and dried
in vacuo to give a yellow crystalline solid (3a). A red-orange band
eluted with acetone was also collected and dried to give a
reddish-orange crystalline solid (3b).
3a was recrystallized from dichloromethane/n-hexane. Yield:
49 mg (32%). Anal. Calcd for C32Cl2H20N4Ru: C, 64.75, H,
3.40, N, 9.44. Found: C, 64.81, H, 3.21, N, 9.37. UV/vis
(CH2Cl2) λmax, nm (ε, M-1 cm-1): 323 (23 700), 440 (8410). IR
(KBr, cm-1): 2052 (νNC), 2116 (νNC). 1H NMR (300 MHz,
CDCl3): δ 6.91 (d, 3JHH =6.90, 2H, Q), 7.16 (m, 8H, Qþ4-Cl-
PhCN), 7.25 (m, 6H, Qþ4-ClPhNC), 7.40 (t, 3JHH =7.80, 2H,
Q), 8.03 (dd, 3JHH = 8.40, 4JHH = 1.5), 8.43 (dd, 3JHH = 4.95,
4JHH =1.35, 2H, Q).
3b was recrystallized from dichloromethane/n-hexane. Yield:
57 mg (38%). Anal. Calcd for C32Cl2H20N4Ru: C, 64.75, H,
3.40, N, 9.44. Found: C, 64.82, H, 3.54, N, 9.37. UV/vis (CH3Cl)
λ
max, nm (ε, M-1 cm-1): 348 (25 100), 465 (6250). IR (KBr,
cm-1): 2077(νNC). H NMR (300 MHz, CDCl3): 6.86 (m, 6H,
1
3
Q þ 4-ClPhNC), 7.04 (d, JHH = 8.10, 2H, Q), 7.12 (m, 4H,
1a was recrystallized from dichloromethane/n-hexane. Yield:
43 mg (34%). Anal. Calcd for C28H30N4O2Ru: C, 60.53; H, 5.41;
N, 10.09. Found: C, 60.31; H, 5.33; N, 10.16. UV/vis (CH2Cl2)
4-ClPhNC), 7.36 (m, 4H, Q), 8.10 (dd, 3JHH=8.40, 4JHH=1.50,
2H, Q), 9.14 (dd, 3JHH =4.80, 4JHH =1.50, 2H, Q).
cis,cis,trans- (4a) and trans,trans,trans-[RuQ2(2,4,6-Br3PhNC)2]
(4b). The complexes were synthesized by a similar procedure
to that for 1a and 1b using 2,4,6-tribromophenyl isocyanide
(191 mg, 0.56 mmol). The reaction mixture was filtered to give a
red solid and a yellow filtrate. The solvent was removed and the
residue was dissolved in dichloromethane and purified by silica
gel column chromatography using dichloromethane/acetone
(10:1) as eluent to give 4a as a yellow crystalline solid. The red
solid was purified by alumina column chromatography using
acetone as eluent to give an orange-red crystalline solid (4b).
4a was recrystallized from dichloromethane/n-hexane. Yield:
63 mg (26%). Anal. Calcd for Br6C32H16N4O2Ru: C, 35.95, H,
1.51, N, 5.24. Found: C, 35.81, H, 1.67, N, 5.43. UV/vis (CH3Cl)
λ
max, nm (ε, M-1 cm-1): 345 (9280), 452 (6330). IR (KBr, cm-1):
2050 (νNC), 2123 (νNC), 2979 (νCH, tBuNC). 1H NMR (300 MHz,
CDCl3): δ 1.32 (s, 18H, tBuNC), 6.80 (d, 3JHH = 8.10 Hz, 2H,
Q), 7.08 (m, 4H, Q), 7.32 (t, JHH = 8.10, 2H, Q), 7.93 (dd,
3
3JHH=8.40, 4JHH=1.20, 2H, Q), 8.33 (dd, 3JHH=4.65, 4JHH
1.20, 2H, Q).
=
1b was recrystallized from dichloromethane/n-hexane. Yield:
50 mg (40%). Anal. Calcd for C28H30N4O2Ru: C, 60.53; H, 5.41;
N, 10.09. Found: C, 59.97; H, 5.39; N, 10.04. UV/vis (CH2Cl2)
λ
max, nm (ε, M-1 cm-1): 377 (11 300), 396 (11 500), 489 (5840).
t
IR (KBr, cm-1): 2098 (νNC), 2978 (νCH, BuNC). 1H NMR
(300 MHz, CDCl3): δ 1.02 (s, 18H, tBuNC), 6.76 (d, 3JHH=7.50,
2H, Q), 6.92 (d, 3JHH =7.50, 2H, Q), 7.28 (m, 4H, Q), 7.96 (dd,
λ
max, nm (ε, M-1 cm-1): 327 (24 200), 391 (18 600). IR (KBr,
3JHH=8.25, 4JHH=1.35, 2H, Q), 9.08 (dd, 3JHH=5.10, 4JHH
=
cm-1): 1997 (νNC), 2105 (νNC). 1H NMR (300 MHz, CDCl3): δ
6.93 (dd, 3JHH=7.80, 4JHH=1.20, 2H, Q), 7.21 (m, 4H, Q), 7.42
(t, 3JHH = 8.10, 2H, Q), 7.57 (s, 2H, 2,4,6-Br3PhNC), 8.06 (dd,
1.20, 2H, Q)
cis,cis,trans- (2a) and trans,trans,trans-[RuQ2(4-MeOPhNC)2]
(2b). The complexes were synthesized by a similar procedure to
that for 1a and 1b using 4-methoxylphenyl isocyanide (75 mg,
0.56 mmol). The yellow band eluted from a silica gel column
with dichloromethane/acetone (10:1) was collected and dried in
vacuo to give a yellow crystalline solid (2a). A red-orange band
eluted with acetone was also collected and dried to give a
reddish-orange crystalline solid (2b).
3JHH=8.55, 4JHH=1.35, 2H, Q), 8.55 (dd, 3JHH=4.65, 4JHH
=
1.35, 2H, Q).
4b was also recrystallized from dichloromethane/n-hexane.
Yield: 76 mg (32%). Anal. Calcd for Br6C32H16N4O2Ru: C,
35.95, H, 1.51, N, 5.24. Found: C, 35.79, H, 1.64, N, 5.15. UV/
vis (CH3Cl) λmax, nm (ε, M-1 cm-1): 377 (23 100), 472 (14 200).
IR (KBr, cm-1): 2040 (νNC). H NMR (300 MHz, CDCl3): δ
1
3
4
3
2a was recrystallized from dichloromethane/n-hexane. Yield:
54 mg (37%). Anal. Calcd for C34H26N4O4Ru: C, 62.28; H, 3.97;
N, 8.55. Found: C, 62.09, H, 4.13, N, 8.36. UV/vis (CH2Cl2)
6.85 (dd, JHH = 7.80, JHH = 0.90, 2H, Q), 7.05 (dd, JHH
=
8.25, 4JHH = 1.05, 2H, Q), 7.35 (m, 4H, Q), 7.49 (s, 2H, 2,4,6-
Br3PhNC), 8.09 (dd, 3JHH=8.70, 4JHH=1.50, 2H, Q), 9.12 (dd,
3JHH =4.80, 4JHH =1.20, 2H, Q).
λ
max, nm (ε, M-1 cm-1): 322 (27 300), 444 (8030). IR (KBr,
trans,trans,trans-[Ru(PPh3)2(Tol-Q)2] (5). [Ru(PPh3)2Cl2]
(120 mg, 0.17 mmol) was suspended in 25 mL of ethanol, and
8-hydroxyl-5-tolylquinoline (81 mg, 0.35 mmol) was added. The
(16) Ugi, I.; Fetzer, U.; Eholzer, U.; Knupfer, H.; Offerman, K.
Angew. Chem. 1965, 77 (11), 492.

Article
Organometallics, Vol. 28, No. 19, 2009 5711
˚
Table 2. Selected Bond Lengths (A) and Bond Angles (deg)
for 2a, 3a, and 4b
Table 1. Crystal and Structural Determination Data for the
Complexes 2a, 3a, and 4b
2a Ru(1)-O(1)
Ru(1)-O(4)
Ru(1)-N(1)
Ru(1)-N(2)
Ru(1)-C(8)
2.059(4)
2.074(4)
2.133(5)
2.105(5)
1.893(6)
Ru(1)-C(27)
C(27)-N(4)
C(8)-N(3)
O(1)-O(5)
1.944(7)
1.192(8)
1.153(8)
2.866(8)
2a H2O
3a CH2Cl2
4b
3
3
formula
C
34H28N4-
O5Ru
C33H22Cl2N4- Br6C32H16N4-
O2Ru
607.632
triclinic
P1 (no. 2)
O2Ru
1069.02
monoclinic
I 1 2/a 1 (no. 15)
fw
crystal system
space group
673.689
monoclinic
P 1 21/n 1
(no. 14)
9.8044(4)
14.0508(6)
21.6146(9)
90.00
92.02(0)
90.00
2975.77(20)
4
1.504
1.43
1639
293(2)
0.71073
3.12, 25.00
4982, 3623
Ru(1)-C(27)-N(4) 173.77(54) N(1)-Ru(1)-O(1) 82.58(17)
Ru(1)-C(8)-N(3) 174.31(52) N(2)-Ru(1)-O(2) 80.82(17)
3a Ru(1)-O(1)
a/A
b/A
c/A
R/deg
β/deg
8.3101(4)
13.0622(7)
15.2027(5)
78.156(4)
83.45(0)
28.703(4)
1579.11(13)
2
1.576
3.885
1162
293(2)
23.0841(10)
6.9214(3)
23.5613(12)
90.00
112.32(1)
90.00
3482.52(30)
4
2.039
2.087(5)
2.073(5)
2.111(6)
2.110(6)
Ru(1)-C(25)
Ru(1)-C(26)
C(25)-N(2)
C(26)-N(3)
1.899(7)
1.915(7)
1.171(9)
1.164(8)
Ru(1)-O(2)
Ru(1)-N(1)
Ru(1)-N(4)
γ/deg
Ru(1)-C(25)-N(2) 174.86(56) N(1)-Ru(1)-O(1) 79.55(16)
Ru(1)-C(26)-N(3) 176.77(52) N(4)-Ru(1)-O(2) 79.81(17)
volume/A3
Z
Dcalc/g cm-3
μ(Mo KR)/mm-1
F(000)
4b Ru(1)-O(1)
Ru(1)-N(2)
2.098(7)
2.066(9)
Ru(1)-C(1)
C(1)-N(1)
1.975(10)
1.157(12)
3.00
506
293(2)
temperature/K
λ/A
θmin, θmax/deg
total, unique data
Ru(1)-C(1)-N(1)
178.11(83) N(2)-Ru(1)-O(1) 80.1(3)
0.71073
3.22, 25.00
5251, 4357
1.54178
6.82, 54.97
2054, 1834
Results and Discussions
R1(obsd/all)
wR2(obsd/all)
0.0588/0.0868 0.0566/0.0681 0.0631/0.0678
0.1275/0.1350 0.1795/0.1795 0.1690/0.1740
Syntheses and Characterizations. The reaction of [RuQ3]
with RNC in refluxing ethanol in the presence of Zn/Hg
under argon produces [RuQ2(RNC)2] as a mixture of cis,
cis,trans- (1a-4a) and trans,trans,trans-isomers (1b-4b)
(Scheme 1), which can be readily separated by column
chromatography. Similar methods have been used to synthe-
size bis(8-quinolinolato) and bis(acetylacetonato) ruthenium
complexes containing various π-acid ligands such as diene,
dmso, and pyridine.14,18 Attempts to synthesize the corre-
sponding [Ru(Tol-Q)2(RNC)2] via [Ru(Tol-Q)3] according
to Scheme 1 failed. Instead, the trans,trans,trans-isomer
of the complex was synthesized from trans,trans,trans-[Ru-
(Tol-Q)2(PPh3)2] (5), which was prepared by the reaction of
RuCl2(PPh4)3 with HTol-Q in ethanol.15 The reaction of 5
with an excess of tert-butyl isocyanide (tBuNC) gives
the corresponding trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (6)
(Scheme 2).
The IR spectra of the cis,cis,trans-isomers 1a-4a show
two strong νNC in the range 2000-2150 cm-1, indicative of a
mutually cis disposition of the isocyanide ligands.12,19-21
The trans,trans,trans-isomers 1b-4b and 6 exhibit only one
single νNC at ∼2040-2098 cm-1 in the same region.22 The
slightly lower νNC stretching frequencies observed in the
complexes compared to that of the free ligands can be
attributed to a π back-bonding interaction between ruthe-
nium(II) and isocyanide. The stretching frequencies follow
the order 4a (1997, 2105 cm-1)<3a (2052, 2116 cm-1)<2a
(2074, 2127 cm-1) and 4b (2040 cm-1)<3b (2077 cm-1)<2b
(2088 cm-1), which is in the reverse order of the π-accepting
ability of the isocyanide ligands: 2,4,6-Br3-C6H2NC>4-Cl-
C6H4NC>4-MeO-C6H4NC. The 1H NMR spectra of 1-4
and 6 reveal a 1:1 ratio of the 8-quinolinolate and the
isocyanide ligands, consistent with the proposed formula
[RuIIQ2(RNC)2].
goodness-of-fit on F2 1.113
1.047
1.054
mixture was refluxed under argon for 3 h. The golden yellow
crystalline solid formed was filtered, washed with ethanol, and
then air-dried. Yield: 103 mg (55%). Anal. Calcd for
C68H54N2O2P2: C, 74.64, H, 4.97, N, 2.56. Found: C, 74.45,
H, 4.81, N, 2.68.
trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (6). A mixture of 5
(80 mg, 0.091 mmol), tert-butyl isocyanide (30 mg, 0.37 mmol),
and a few pieces of Zn/Hg was refluxed under argon for 18 h to
give an orange-red solution. The mixture was filtered and the
solvent was removed by rotary evaporation. The orange-red
residue was purified by silica gel column chromatography using
ethyl acetate as eluent. The red-orange band was collected and
dried in vacuo to give an orange-red crystalline solid, which was
recrystallized from dichloromethane/n-hexane (6). Yield: 42 mg
(48%). Anal. Calcd for C42H42N4O2Ru: C, 68.55, H, 5.75, N,
7.61. Found: C, 68.69, H, 5.85, N, 7.64. UV/vis (CH3Cl) λmax
,
nm (ε, M-1 cm-1): 309 (19 100), 420 (11 500), 492 (6860). IR
(KBr, cm-1): 2098 (νNC). 1H NMR (300 MHz, CDCl3): δ 2.42
(s, 6H, Tol-Q), 2.59 (s, 18H, tBuNC), 6.83 (d, 2H, 3JHH =8.10,
Tol-Q), 7.17 (d, 2H, 3JHH =6.30, Tol-Q), 7.27 (m, 8H, Tol-Q),
3
3
7.36 (t, 2H, JHH = 7.80, Tol-Q), 8.23 (d, 2H, JHH = 9.00,
Tol-Q), 9.05 (dd, 2H, 3JHH = 5.10, 4JHH = 1.50, Tol-Q).
X-ray Structure Determination. Crystals suitable for X-ray
diffraction analysis were obtained for compounds 2a H2O,
3a CH2Cl2, and 4b. Crystal data and experimental details are
3
3
given in Table 1. X-ray diffraction data were collected at 293 K
on an Oxford CCD diffractometer using graphite-monochro-
mated Mo KR radiation (λ = 0.71073 A) for 2a H2O and
3
3a CH2Cl2 and Cu KR (λ = 1.54178 A) for 4b in the ω-scan
3
mode. Selected bond lengths and bond angles are given in
Table 2. Absorption corrections were done by the multiscan
method. The structures were resolved by the heavy-atom Pat-
terson method or direct methods and refined by full-matrix
least-squares using SHELX-97 and expanded using Fourier
techniques.17 All non-hydrogen atoms were refined anisotropi-
cally. H atoms were generated by the program SHELXL-97.
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.
(18) Bennett, M. A.; Heath, G. A.; Hockless, D. C. R.; Kovacik, I.;
Willis, A. C. J. Am. Chem. Soc. 1998, 120, 932.
(19) Cadierno, V.; Crochet, P.; Dıez, J.; Garcıa-Garrido, S. E.;
´ ´
Gimeno, J. Organometallics 2004, 23, 4836.
(20) Kawano, H.; Nishimura, Y.; Onishi, M. Dalton 2003, 1808.
(21) Ruiz, J.; Riera, V.; Vivanco, M. J. Chem. Soc., Dalton Trans.
1995, 1069.
€
€
€
(17) Sheldrick, G. M. SHELX-97; University of Gottingen: Gottingen,
(22) Linder, E.; Gesprags, M.; Gierling, K.; Fawzi, R.; Steimann, M.
Germany, 1998.
Inorg. Chem. 1995, 34, 6106.

5712 Organometallics, Vol. 28, No. 19, 2009
Scheme 1. Ligand Substitution Reaction of [RuQ3] with Isocyanide
Leung et al.
Scheme 2. Synthetic Routes for Compounds 5 and 6
X-ray Crystal Structures. Single crystals of 2a and 3a were
obtained by slow diffusion of n-hexane into a dichloro-
methane solution of the complexes at 4 °C. Single crystals of
4b were obtained by slow evaporation of a chloroform/
ethanol solution of the complex. The crystal data and experi-
mental details for these complexes are summarized in Table 1.
Structures of cis,cis,trans-RuQ2(4-MeOPhNC)2 (2a) and
cis,cis,trans-RuQ2(4-ClPhNC)2 (3a). The cis,cis,trans-con-
figuration of 2a and 3a and the trans,trans,trans-configura-
tion of 4b are revealed by X-ray crystallography. Perspective
views of these complexes are shown in Figures 1-3. Selected
bond distances and angles are listed in Table 2. Complexes 2a
and 3a have a distorted octahedral geometry with the two
8-quinolinolate ligands in a cis,cis,trans-configuration. The
two isocyanide ligands are cis to each other and trans to the
N atoms of the quinolinolate ligands. Complex 4b adopts an
octahedral geometry with an all-trans-configuration, consis-
tent with a single νNC in IR spectrum. The Ru-C (isocyanide)
and CtN (isocyanide) bond lengths in these complexes are in
the range 1.893-1.973 and 1.153-1.192 A, respectively.
The Ru-C-N(isocyanide) units are almost linear (173.77-
178.11°). These bonding parameters are similar to those
reported for other ruthenium(II) isocyanide complexes.12,19-22
The bite angles of the quinolinolato ligands in these complexes
are about 80°, and the Ru-N(Q) and Ru-O(Q) bond
distances are in the range 2.059-2.087 and 2.105-2.133 A,
respectively, which are typical of ruthenium(II) 8-quinolino-
lato complexes.14
Photophysical Properties of the [RuQ2(RNC)2]. Both cis,
cis,trans- and trans,trans,trans-isomers exhibit an intense
absorption band in the UV region (λmax = 320-390 nm) with
molar extinction coefficients (ε) on the order of 104 dm3 mol-1
cm-1 and a moderately intense absorption with ε on the order
of 103 dm3 mol-1 cm-1 at 400-492 nm (Figure 4). The intense
absorption at 320-390 nm is assigned to the ligand-centered
πfπ* transitions of the quinolinolate ligands, probably
mixed with the πfπ* transitions of the isocyanide ligands,
as much more intense absorptions are observed for complexes
2-4 and 6 with phenyl isocyanide ligands than for 1 with
Figure 1. ORTEP drawing of 2a H2O (thermal ellipsoids are
drawn at the 50% probability; solvent of crystallization (water)
and hydrogen atoms are omitted for clarity).
3
tert-butyl isocyanide. The lower energy absorptions at 400-
492 nm are assigned to Ru(dπ)fπ*(Q) metal-to-ligand
charge transfer (MLCT) transitions, probably mixed with
the intraligand charge transfer (ILCT) transitions of the
quinolinolate ligands, asthe ILCT transitions of quinolinolate
ligands of related complexes have also been reported to occur
in this region.23 These low-energy absorption bands for the
cis,cis,trans-isomers (1a-4a) are significantly blue-shifted
compared to the corresponding trans,trans,trans-isomers
(1b-4b) (see Experimental Section). This is attributed to
(23) (a) Ballardini, R.; Varani, G.; Indelli, M. T.; Scandola, F. Inorg.
Chem. 1986, 34, 3858. (b) Donges, D.; Nagle, J. K.; Yersin, H. Inorg. Chem.
1997, 36, 3040. (c) Kunkely, H.; Vogler, A. Inorg. Chem. Commun. 1998, 1,
398. (d) Yersin, H.; Donges, D.; Nagle, J. K.; Sitters, R; Glasbeek, M. Inorg.
Chem. 2000, 39, 770. (e) Czerwieniec, R.; Kapturkiewicz, A.; Anulewicz-
Ostrowska, R.; Nowacki, J. J. Chem. Soc., Dalton Trans. 2001, 2756.
(f) Cheng, Y.-M.; Yeh, Y.-S.; Ho, M.-L.; Chou, P.-T.; Chen, P.-S.; Chi, Y.
Inorg. Chem. 2005, 44, 4594.

Article
Organometallics, Vol. 28, No. 19, 2009 5713
Table 3. UV/Vis and Emission Data for Compounds 1-4 and 6
Emission
em / nm
glass 77 K CH2Cl2 298 K
Emission
Absorption λabs / nm
(ε / dm3 mol-1 cm-1
λ
λem / nm
)
1a 345(9280), 452(6330)
1b 377(11 300), 396(11 600) 489(5840) 625
2a 322(27 300), 444(8030) 599
2b 331(25 100), 389(18 200), 478(5840) 610
614
665
655
645
3a 323(23 600), 440(8910)
3b 348(25 100), 465(6250)
4a 327(24 200), 391(18 600)
4b 377(23 100), 472(14 200)
595
606
586
600
6
309(19 100), 420(11 500), 492(6860) 638
Figure 2. ORTEP drawing of 3a (thermal ellipsoids are drawn
at the 50% probability; solvent of crystallization (CH2Cl2) and
hydrogen atoms are omitted for clarity).
Figure 5. Emission spectra of 1a, 2a, and 3a in dichloromethane
solution at 298 K.
orbitals and hence in a higher energy MLCT transition. In the
trans,trans,trans-isomers the two RNC ligands would com-
pete for the same dπ(Ru) orbitals for π-back-bonding. The
energy of this band also increases with the π-accepting ability
of the isocyanide ligand: 2,4,6-Br3-C6H2NC (4a: 391 nm; 4b:
472 nm)>4-Cl-C6H4NC (3a: 440 nm; 3b: 465 nm)>4-MeO-
C6H4NC (2a: 444 nm; 2b: 478 nm)>tBuNC (1a: 452 nm; 1b:
489 nm) (Table 3). This trend is in agreement with the MLCT
[dπ(Ru)fπ*(Q)] assignment since the better π-accepting Br3-
C6H2NCwouldbetter stabilize the dπ(Ru) orbital, thus giving
rise to a higher energy MLCT [dπ(Ru)fπ*(Q)] transition.
The increased stabilization of the dπ(Ru) orbital with increas-
ing π-accepting ability of the isocyanide ligand is also reflected
in the RuIII/II redox potential (vide infra). Similarly, the red-shift
in the lower energy absorption for 6 compared to that of 4b
can be explained by a better π-conjugation in the tolyl quino-
linolate ligand, which renders the π*(Q) orbital lower lying in
energy and hence lower in MLCT [dπ(Ru)fπ*(Q)] energy.
Upon excitation at λ>350 nm, 1a-3a in dichloromethane
solution exhibit orange-red luminescence (645-680 nm)
(Figure 5). In 77 K EtOH/MeOH glass, complexes 1-4
and 6 produce intense structured emission spectra (593-
638 nm) (Figure 6). In contrast to the ligand-centered (LC)
emissions of other 8-quinolinolato complexes, which occur
in a similar region and are insensitive to the nature of the
ancillary ligands or the metal center,23 these emissions show
a similar energy dependence on the isomeric forms, π-accep-
ting ability of the isocyanide, and conjugation in the quino-
linolate ligand to the MLCT [dπ(Ru)fπ*(Q)] absorption.
This energy dependence strongly suggests the involvement of
the MLCT state. Therefore, with reference to previous spec-
troscopic studies on related 8-quinolinolato complexes,23
they are also tentatively assigned to be derived from the
MLCT [dπ(Ru)fπ*(Q)] excited state with ligand-centered
character.
Figure 3. ORTEP drawing of 4b (thermal ellipsoids are drawn
at the 50% probability; hydrogen atoms are omitted for clarity).
Figure 4. UV/vis spectra of 1a, 2a, and 3a in dichloromethane.
stronger π-back-bonding between Ru(II) and RNC in the cis,
cis,trans-isomers (as reflected in the shorter Ru-C(isocyanide)
bond distances), which would result in lower lying dπ(Ru)

5714 Organometallics, Vol. 28, No. 19, 2009
Leung et al.
Figure 6. Emission spectra of 1a, 1b, 2a, 3a, and 4a in ethanol/
methanol (4:1) glass at 77 K.
n
Figure 7. Cyclic voltammogram of 1a and 1b in 0.1 M Bu4-
Table 4. Electrochemical Data and Experimental Details for
Compounds 1-4 and 6
NPF6 in acetonitrile. Scan rate is 50 mV s-1
.
RuIII/IIE1/2/ V (ΔE/mV)a
RuIV/IIIEpa/Va
1a
1b
2a
2b
3a
3b
4a
4b
0.02 (62)
-0.16 (60)
0.17b
0.01 (63)
0.24b
0.03 (64)
0.38b
0.065 (75)
0.68
0.72
0.71
0.70
0.85
a Versus Fcþ/Fc. b Quasi-reversible or irreversible couple and only
Epa reported. All potentials were obtained in 0.1 M nBu4NPF6 in
acetonitrile, except 4a, for which 0.1 M nBu4NPF6 in CH2Cl2 is used.
Electrochemical Properties of RuQ2(RNC)2. The electro-
chemical data for compounds 1-4 are presented in Table 4.
The cyclic voltammograms (CV) of the cis,cis,trans-isomers
(1a-4a) generally exhibit an irreversible or quasi-reversible
RuIII/II couple at the potential range 0.02-0.38 V vs Fcþ/Fc,
except in the case of 1a, where a reversible RuIII/II and a
quasi-reversible RuIV/III (0.68 V vs Fcþ/Fc) couple are obser-
ved. The potential for the RuIII/II couple increases with the
π-accepting ability of the isocyanide ligands, 2,4,6-Br3-C6H2-
NC (4a: 0.38 V) > 4-Cl-C6H4NC (3a: 0.24 V) > 4-MeO-
C6H4NC (2a: 0.17 V) > tBuNC (1a: 0.02 V), in accordance
with stabilization of Ru(II) through π-back-bonding with
isocyanide. In the CV of the trans,trans,trans-isomers 1b-4b,
a reversible RuIII/II (-0.16 to 0.065 V) and quasi-reversible
RuIV/III (0.70-0.85 V) couple are observed. The potential
for the RuIII/II couple in 1b-4b also increases with the
π-accepting ability of the isocyanide ligand, and as expected
from the weaker π-back-bonding between Ru(II) and iso-
cyanide in these complexes, the potentials are lower than that
of the corresponding cis,cis,trans-isomers 1a-4a. The po-
tential of the RuIV/III couple is relatively insensitive to the
nature of the isocyanide ligand, except in 4b, where the
n
Figure 8. Cyclic voltammogram of 2a and 2b in 0.1 M Bu4-
NPF6 in acetonitrile Scan rate is 50 mV s-1
.
presence of three bromo substituents in the isocyanide ligand
should make it much less electron-donating, and hence the
potential of the RuVI/III couple is increased.
In conclusion, we report here general synthetic routes for the
preparation of a series of neutral ruthenium complexes of
general formula [RuQ2(RNC)2]. These complexes are air stable
and soluble in a variety of organic solvents, and they possess
interesting photophysical properties. They are therefore poten-
tially useful as materials for electroluminescent devices.
Acknowledgment. The work described in this paper
was supported by the Research Grants Council of Hong
Kong (CityU 2/06C) and the City University of Hong
Kong (7002095).
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.