Synthesis, structure, redox property and ligand replacement reaction of ruthenium(II) complexes containing a terpyridyl ligand with a redox active moiety

Article abstract of DOI:10.1016/j.poly.2009.12.024

Ruthenium(II) complexes bearing a redox-active tridentate ligand 4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine (tpyOMe), analogous to terpyridine, and 2,2′-bipyridine (bpy) were synthesized by the sequential replacement of Cl by CH₃CN and CO on the complex. The new ruthenium complexes were characterized by various methods including IR and NMR. The molecular structures of [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ and two kinds of [Ru(tpyOMe)(bpy)(CO)]²⁺ were determined by X-ray crystallography. The incorporation of monodentate ligands (Cl, CH₃CN and CO) regulated the energy levels of the MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]⁺ to [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ proceeds by a solvent-assisted dissociation process.

Full text of DOI:10.1016/j.poly.2009.12.024

Polyhedron 29 (2010) 1337–1343
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Synthesis, structure, redox property and ligand replacement reaction
of ruthenium(II) complexes containing a terpyridyl ligand
with a redox active moiety
b
c
a
Dai Oyama a, , Masato Kido , Ai Orita , Tsugiko Takase
*
a Cluster of Science and Technology, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan
b Graduate School of Science and Technology, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan
c Faculty of Education, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan
a r t i c l e i n f o
a b s t r a c t
Ruthenium(II) complexes bearing a redox-active tridentate ligand 40-(2,5-dimethoxyphenyl)-2,20:60,200-
terpyridine (tpyOMe), analogous to terpyridine, and 2,20-bipyridine (bpy) were synthesized by the
sequential replacement of Cl by CH3CN and CO on the complex. The new ruthenium complexes were
characterized by various methods including IR and NMR. The molecular structures of [Ru(tpy-
OMe)(bpy)(CH3CN)]2+ and two kinds of [Ru(tpyOMe)(bpy)(CO)]2+ were determined by X-ray crystallog-
raphy. The incorporation of monodentate ligands (Cl, CH3CN and CO) regulated the energy levels of the
MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed
in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]+ to [Ru(tpy-
OMe)(bpy)(CH3CN)]2+ proceeds by a solvent-assisted dissociation process.
Article history:
Received 4 November 2009
Accepted 15 December 2009
Available online 23 December 2009
Keywords:
Ruthenium complex
Terpyridine
Crystal structure
Redox property
Ligand replacement reaction
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
has been previously prepared by Colbran and co-workers [4].
Changes have also be made in the sixth ligand so that it exhibits
Ruthenium(II) complexes containing polypyridyl ligands such
as 2,20-bipyridine (bpy) and 2,20:60,200-terpyridine (tpy) have been
extensively studied as photo- and electrocatalysts due to their
accessible redox states [1,2]. Recently, we have reported several
ruthenium(II) complexes bearing redox active azopyridyl ligands
[3]. In comparison to the corresponding bpy complexes, the azo-
pyridyl ligands caused a shift in the ligand centered reduction to
more positive potentials by 0.8–1.2 V [3]. To explore these results
furthermore, more complex systems containing other redox active
polypyridyl ligands, needed to be constructed. In line with those
results, the desired complex should (i) introduce a redox active
substituent to the central pyridyl unit of a tpy ligand and (ii) intro-
duce new monodentate ligands to the sixth position of the com-
plexes to control the electron density of the metal center.
Combining both of these desired features will make it possible to
change the redox potentials and charge transfer energies of the
complexes as desired. The aim is to produce a complex which dem-
onstrates a new functionality derived from electronic communica-
tion between the metal center and ligand redox active site.
one of three different electronic properties:
p-electron donor (Cl),
p-electron acceptor (CO) and an intermediate (CH3CN). In this
paper, the synthesis, structures and redox properties of [Ru(tpy-
OMe)(bpy)L]n+ (tpyOMe = 40-(2,5-dimethoxyphenyl)-2,20:60,200-ter-
pyridine, L = Cl ([1]+), CH3CN ([2]2+), CO ([3]2+)) complexes is
described. Furthermore, the kinetic studies regarding ligand
replacement reactions are also reported to elucidate the Cl dissoci-
ation rate and mechanistic assignments under various conditions.
2. Experimental
2.1. Physical and kinetic measurements
Elemental analyses were carried out at the Research Center for
Molecular-Scale Nanoscience, Institute for Molecular Science. IR
spectra were obtained as KBr pellets with a JASCO FT-IR 4100 spec-
trometer. Mass spectra were obtained with a Bruker Daltonics
microTOF mass spectrometer equipped with electrospray ioniza-
tion (ESI) interface. Electronic absorption spectra were obtained
in 1 cm quartz cuvettes on a JASCO V-570 UV/VIS/NIR spectropho-
tometer. NMR spectra were recorded on a JEOL JMN-AL300 spec-
trometer operating at the 1H and 13C frequencies of 300 and
75.5 MHz, respectively. Chemical shifts were reported in parts
per million downfield from tetramethylsilane (TMS) as referenced
A candidate for substitution on the terpyridine unit is the redox
active p-dimethoxyphenyl unit positioned at the 40-position, which
* Corresponding author. Tel./fax: +81 24 548 8199.
E-mail address: daio@sss.fukushima-u.ac.jp (D. Oyama).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.024

1338
D. Oyama et al. / Polyhedron 29 (2010) 1337–1343
from the residual solvent peaks. Electrochemical measurements
were conducted on an ALS/Chi model 620A electrochemical ana-
lyzer. Measurements on complexes were made in CH3CN contain-
ing tetra-n-butylammonium perchlorate (0.1 M) as a supporting
electrolyte, in a one-compartment cell consisting of a platinum
working electrode, a platinum wire counter electrode, and an Ag/
AgNO3 (0.01 M in CH3CN) reference electrode. Cyclic voltammo-
grams were obtained at a sweep rate of 0.1 V/s. All potentials are
reported in volts versus ferrocenium/ferrocene couple (Fc+/Fc) at
25 °C under N2. The E1/2 values were calculated as an average of
the oxidative and reductive peak potentials, (Epa + Epc)/2. Kinetic
measurements were carried out at 40, 50 or 60 1 °C in a constant
temperature bath. Stock solutions of [Ru(tpyOMe)(bpy)Cl]+ ([1]+)
were prepared in RCN (R = CH3, C2H5, C3H7 or C6H5)–CH3OH (or
H2O) mixtures under N2. The complex concentration was
1.0 ꢀ 10ꢁ4 M. A portion of the solution was transferred by syringe
to the UV–Vis spectral cuvette and the spectrum of the sample was
recorded at appropriate intervals. Rate data for the substitution
were obtained by monitoring the absorbance increase at ca.
460 nm and absorbance decrease at 508 nm. Af was measured
when the intensity changes stopped. Values of pseudo-first order
rate constants (kobs) were obtained from the slopes of the plots
of ln(Af ꢁ At) or ꢁln(Af ꢁ At) against time [5].
2.2.3. [Ru(tpyOMe)(bpy)(CH3CN)](PF6)2 ([2](PF6)2)
[1]Cl (60 mg, 0.09 mmol) was dissolved in water (10 mL)-meth-
anol (10 mL)-acetonitrile (4 mL) mixture. This was refluxed for 2 h,
before being reduced to 6 mL using a rotary evaporator. Red crys-
tals precipitated when a saturated aqueous solution of KPF6 was
added to the concentrated mixture. The precipitate was collected
by filtration, washed with diethyl ether and dried in vacuo. The
crude product was recrystallization from methanol/diethyl ether
to give large crystals of [Ru(tpyOMe)(bpy)(CH3CN)](PF6)2. Yield
53 mg (64%). Anal. Calc. for C35H30N6O2F12P2Ruꢂ0.5CH3CN: C,
44.20; H, 3.25; N, 9.31. Found: C, 43.77; H, 3.36; N, 9.27%. ESI-MS
(CH3CN): m/z = 328 ([MꢁCH3CN+N2]2+). 1H NMR (CD3CN): d 9.61
(d, 1H), 8.78 (s, 2H), 8.62 (d, 1H), 8.47 (d, 2H), 8.35 (t, 2H), 8.02–
7.94 (m, 3H), 7.81 (t, 1H), 7.69 (d, 2H), 7.37–7.08 (m, 7H), 3.95 (s,
3H) and 3.90 (s, 3H) ppm. 13C{1H} NMR (CD3CN): d 159.48–
158.60 (multiple signals), 157.90, 156.88, 155.32, 155.05, 154.10,
153.38, 151.95, 148.05, 139.87, 139.39, 138.54, 138.29, 128.83,
128.67, 128.44, 127.60, 127.20, 126.12, 125.20–124.85 (multiple
signals), 124.46, 124.21, 117.71, 117.13, 114.25, 56.98 and
56.55 ppm.
2.2.4. [Ru(tpyOMe)(bpy)(CO)](PF6)2 ([3](PF6)2)
A suspension of [2](PF6)2 (50 mg, 0.05 mmol) in 2-methoxyeth-
anol (30 mL) was heated to 100 °C under an atmosphere of CO
(25 atm) for 1 week. The reaction mixture was reduced to 5 mL
using a rotary evaporator. Addition of diethyl ether to the solution
resulted in the formation of a light brown precipitate of [Ru(tpy-
OMe)(bpy)(CO)](PF6)2. The product was collected by filtration
and washed with diethyl ether and dried in vacuo. The crude prod-
uct was purified by diffusion of diethyl ether into an acetone solu-
tion of the compound. Yield 33 mg (67%). Anal. Calc. for
C34H27N5O3F12P2Ru: C, 43.23; H, 2.88; N, 7.42. Found: C, 43.15;
H, 3.03; N, 7.48%. ESI-MS (CH3CN): m/z = 328 ([M]2+). IR (KBr):
2.2. Preparation of compounds
All solvents were purchased as anhydrous solvents for organic
synthesis and used without further purification. CH3CN for electro-
chemical experiments was further distilled over CaH2 under N2 just
prior to use. 40-(2,5-dimethoxyphenyl)-2,20:60,200-terpyridine (tpy-
OMe) and [Ru(DMSO)4Cl2] (DMSO = dimethyl sulfoxide) were pre-
pared according to known procedures or a modification of such a
method [4,6].
1982 and 1995 (sh) cmꢁ1 C„O). 1H NMR (CD3CN): d 9.58 (d,
(m
2.2.1. [Ru(tpyOMe)(DMSO)Cl2]
1H), 8.81 (s, 2H), 8.64 (d, 1H), 8.52–8.48 (m, 3H), 8.39 (t, 1H),
8.16–8.06 (m, 3H), 7.95 (t, 1H), 7.73 (d, 2H), 7.45–7.17 (m, 7H),
3.94 (s, 3H) and 3.90 (s, 3H) ppm. 13C{1H} NMR (CD3CN): d
194.65 (CO), 158.38, 156.46, 156.17, 155.82, 155.04, 154.75,
151.98–151.93 (multiple signals), 148.63, 141.63, 141.32, 140.55,
129.52–129.42 (multiple signals), 128.87, 126.47–126.09 (multiple
signals), 125.20, 117.89, 117.62, 114.36, 57.03 and 56.56 ppm.
The complex was prepared by modification of a previously re-
ported method [7]. [Ru(DMSO)4Cl2] (100 mg, 0.21 mmol) was dis-
solved in methanol (5 mL) under Ar, and the mixture was refluxed
for 10 min. TpyOMe (77 mg, 0.21 mmol) was slowly added to the
refluxing solution. The solution was refluxed for a further 10 h.
The mixture was allowed to cool, and the brown precipitate was col-
lected by filtration, washed with water (to remove [Ru(tpy-
OMe)2]2+) and methanol, and then dried in vacuo. Yield 95 mg (71%).
2.3. X-ray crystallography
2.2.2. [Ru(tpyOMe)(bpy)Cl]X ([1]Cl and [1]PF6)
The single crystals of [2]2+ and [3]2+ were obtained by a week-
[Ru(tpyOMe)(DMSO)Cl2] (60 mg, 0.10 mmol) and bpy (16 mg,
0.10 mmol) were added to methanol (50 mL) and the suspension
was refluxed for 1 h. The volume was reduced to 10 mL using a ro-
tary evaporator, and purple crystals were precipitated by addition
of diethyl ether. The precipitate was collected by filtration, washed
with diethyl ether and dried in vacuo. The crude product was final-
ly recrystallized from acetonitrile and diethyl ether, yielding
[Ru(tpyOMe)(bpy)Cl]Cl as a purple powder. Yield 56 mg (80%).
The corresponding PF6 salt was prepared by addition of a saturated
aqueous solution of KPF6 to a methanolic solution of [Ru(tpy-
long diffusion of diethyl ether into an acetonitrile solution ([2]2+
)
or an acetone solution ([3]2+) of the complexes. An orange crystal
of [2](PF6)2ꢂCH3CN with the dimensions 0.3 ꢀ 0.2 ꢀ 0.1 mm was
mounted on a glass fiber. The crystals of [3]2+ exhibited two dis-
tinct colors and habits. A yellow needle-like crystal with the
dimensions
0.4 ꢀ 0.1 ꢀ 0.1 mm
was
revealed
to
be
[3](PF6)2ꢂ(CH3)2CO. A red block-like crystal with the dimensions
0.6 ꢀ 0.2 ꢀ 0.2 mm was revealed to be [3](PF6)2. All data were col-
lected on a Rigaku RAXIS-RAPID diffractometer with graphite
monochromated Mo Ka radiation (k = 0.71075 Å). Data were col-
OMe)(bpy)Cl]Cl.
Yield
58 mg
(72%).
Anal.
Calc.
for
lected to a maximum 2h value of 55.0°. All calculations were car-
ried out using the CRYSTALSTRUCTURE crystallographic software
package [8]. The structures were solved either by direct methods
([2](PF6)2ꢂCH3CN and [3](PF6)2) [9] or by the Patterson method
([3](PF6)2ꢂ(CH3)2CO) [10], and both were expanded using Fourier
techniques. Multi-scan absorption corrections were applied [11].
The non-hydrogen atoms (other than F atoms of counter anions
and C and N atoms of the solvent molecule (CH3CN) in the case
of [2](PF6)2ꢂCH3CN) were refined anisotropically, and hydrogen
atoms included as riding atoms. One of the anions was disordered
over two positions around an F–P–F bond axis in [2](PF6)2ꢂCH3CN.
C33H27N5O2F6PClRuꢂH2O: C, 48.04; H, 3.54; N, 8.49. Found: C,
47.72; H, 3.50; N, 8.50%. ESI-MS (CH3CN): m/z = 662 ([M]+). 1H
NMR (CD3CN): d 10.22 (d, 1H), 8.70 (s, 2H), 8.62 (d, 1H), 8.44 (d,
2H), 8.33 (d, 1H), 8.25 (t, 1H), 7.94–7.84 (m, 3H), 7.70–7.65 (m,
3H), 7.37–7.09 (m, 6H), 6.97 (t, 1H), 3.94 (s, 3H) and 3.89 (s,
3H) ppm. 13C{1H} NMR (CD3CN): d 159.78–159.69 (multiple sig-
nals), 158.28, 157.11, 155.01, 153.39–152.85 (multiple signals),
151.95, 144.78, 138.89, 137.82, 137.32, 136.36, 128.27–127.73
(multiple signals), 126.93, 124.43–123.90 (multiple signals),
116.58, 114.08, 56.93 and 56.50 ppm.

D. Oyama et al. / Polyhedron 29 (2010) 1337–1343
1339
Table 1
Crystallographic data for [2](PF6)2ꢂCH3CN, [3](PF6)2ꢂ(CH3)2CO and [3](PF6)2.
[2](PF6)2ꢂCH3CN
[3](PF6)2ꢂ(CH3)2CO
[3](PF6)2
Chemical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell parameters
a (Å)
C37H33N7O2F12P2Ru
998.71
173(1)
C37H33N5O4F12P2Ru
1002.70
173(1)
C34H27N5O3F12P2Ru
944.62
173(1)
monoclinic
P21/n (no. 14)
triclinic
triclinic
ꢀ
ꢀ
P1 (no. 2)
P1 (no. 2)
8.8827(8)
12.4297(12)
19.3308(18)
71.420(3)
85.567(2)
87.007(3)
2016.1(3)
2
9.1389(5)
14.9718(7)
15.3166(7)
103.6671(17)
95.1080(16)
104.5294(14)
1946.58(17)
2
8.84218(16)
25.0491(5)
16.3475(3)
b (Å)
c (Å)
a
(°)
b (°)
90.3548(7)
c
(°)
V (Å3)
3620.72(12)
4
6.276
Z
l
(Mo K
a
) (cmꢁ1
)
5.681
5.910
Number of measured reflections
Number of observed reflections
Refinement method
18831
19031
5972 (I > 1.0
34966
6883 (I > 2.0r(I))
5355 (I > 1.2
r(I))
r(I))
Full-matrix least-squares on F2
Parameters
532
0.0872
0.2308 (I > 1.2
583
0.0549
0.1192 ((I > 1.0
541
0.0348
0.1087 (I > 2.0r(I))
a
R1
b
wR2
r(I))
r(I)))
S
1.002
1.015
1.008
a
R1 (I > 2
r
(I)) =
R
||Fo| ꢁ |Fc||/
R|Fo|.
b
2
wR2 = {Rw(Fo ꢁ Fc2)2/Rw(Fo2)2}1/2
.
tion 3.3. Although [2]2+ has a labile CH3CN molecule as a ligand, it
required severe conditions (high pressure of CO, high temperature
and longer reaction time) to form [3]2+ using a ligand replacement
reaction in CO gas. The IR spectrum of [3]2+ displays a strong
Table 2
UV–Vis spectral and electrochemical data for the present complexes.
Complexes
[1]+
[2]2+
[3]2+
m
(C„O) band at 1982 cmꢁ1. This value is 22 cmꢁ1 lower than that
kmax/nma
(e
/Mꢁ1 cmꢁ1
)
508 (11600)
362 (sh)
318 (28800)
292 (37100)
283 (42200)
464 (13500)
308 (33800)
283 (44500)
387 (8700)
315 (25900)
287 (43000)
267 (32700)
of the corresponding tpy complex ([Ru(tpy)(bpy)(CO)]2+) [12] due
to the presence of the electron donating dimethoxyphenyl moiety.
In addition to this band, a small shoulder band at higher wavenum-
ber side was observed. ESI-MS and 1H NMR spectra show only a
single species in solution; however two different solid states would
exist from the IR measurement.
E/Vb
RuIII/IIc
0.38
1.04
0.88
1.02
tpyOMe+/0d
1.04
The electronic spectra of [1]+, [2]2+ and [3]2+ in acetonitrile are
shown in Fig. 1, and the data are summarized in Table 2. The in-
tense bands in the visible region result from the metal-to-ligand
charge transfer (MLCT) transitions, and terpyridyl- and bipyridyl-
(bpy or tpy)0/ꢁ (1)e
(bpy or tpy)0/ꢁ (2)e
ꢁ1.84
ꢁ1.70
ꢁ1.45
ꢁ1.98
ꢁ2.01
ꢁ1.76
a
b
c
In CH3CN.
In CH3CN, versus Fc+/Fc.
E1/2 values.
centered
p–p* transitions are observed in the region between
d
e
Epa values.
Epc values.
200 and 350 nm [13]. Although no significant substituent effect
was observed between [Ru(tpyOMe)2]2+ and [Ru(tpy)(tpyOMe)]2+
in the energy of the MLCT transition [4b], the present complex sys-
tem exhibited very different energies: the absorption at
Crystallographic parameters of [2](PF6)2ꢂCH3CN, [3](PF6)2ꢂ(CH3)2CO
and [3](PF6)2 are summarized in Table 1 and selected bond lengths
and angles are listed in Table 3.
kmax = 508 nm of [1]+ is red-shifted by 44 nm relative to [2]2+
,
and the MLCT band of [3]2+ (kmax = 387 nm) is blue-shifted by
77 nm relative to [2]2+. The change in the MLCT transitions to high-
er energies (L = CO > CH3CN > Cl) obeys the spectrochemical series.
Thus, changing the ligand L has changed the energies of the MLCT
bands, suggesting that substitution of these ligands has an effect
3. Results and discussion
3.1. Synthesis and characterization of [Ru(tpyOMe)(bpy)L]n+
on the metal center and moves the dp orbital energies of the ruthe-
nium(II). Other studies on ruthenium complexes with polypyridyl
ligands have attributed this change to a stabilization of the metal
Complexes [1]+, [2]2+ and [3]2+ containing the tpyOMe ligand
were prepared as shown in Scheme 1. [Ru(tpyOMe)(DMSO)Cl2]
was adopted as the precursor for the preparation of ruthenium(II)
complexes having both tridentate tpyOMe and bidentate bpy. The
reaction of [Ru(tpyOMe)(DMSO)Cl2] with bpy in hot methanol gave
[1]Cl, and the subsequent exchange of counter anion from Clꢁ to
dp orbitals by the p-acceptor ligands which decreases the d–p*
orbital separation [14]. CH3CN solutions of the complexes showed
no detectable room-temperature luminescence when excited at
their MLCT maxima.
Single crystal X-ray studies of [1]+, [2]2+ and two polymorphs of
[3]2+ have been conducted. The molecular structure of
[1]PF6ꢂCH3CN has been reported elsewhere [15]. Molecular projec-
tions of the structures are shown in Fig. 2 ([2]2+) and Fig. 3 ([3]2+),
and selected parameters can be found in Table 3. For all the cations,
the ligand environment about the ruthenium atom is identical to
other [Ru(tpy)(bpy)X]n+ complexes (Table 3) [15,16]. The pendant
ꢁ
PF6 gave [1]PF6 in a good yield. [1]+ can be also synthesized by
the reaction of bpy with [Ru(tpyOMe)Cl3] which is prepared from
RuCl3 and tpyOMe. However, the [Ru(tpyOMe)Cl3] route gave a
much lower yield. [1]+ reacts with CH3CN in H2O–CH3OH–CH3CN
mixtures at reflux to give [2]2+, but does not proceed in CH3CN
only. The details of this replacement reaction are described in Sec-

1340
D. Oyama et al. / Polyhedron 29 (2010) 1337–1343
Table 3
Selected bond lengths (Å) and angles (°) for [2](PF6)2ꢂCH3CN, [3](PF6)2ꢂ(CH3)2CO and [3](PF6)2.
[2](PF6)2ꢂCH3CN
[3](PF6)2ꢂ(CH3)2CO
[3](PF6)2
Bond lengths
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
Ru1–N5
Ru1–N6
O1–C21
O1–C23
O2–C18
O2–C22
2.079(7)
1.950(9)
2.067(6)
2.089(9)
2.024(8)
2.045(8)
1.361(12)
1.434(13)
1.371(13)
1.410(18)
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
Ru1–N5
Ru1–C34
C34–O3
C17–O1
O1–C22
C20–O2
O2–C23
2.078(3)
1.986(3)
2.090(3)
2.068(3)
2.102(4)
1.856(5)
1.152(10)
1.374(6)
1.436(6)
1.381(6)
1.425(5)
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
Ru1–N5
Ru1–C34
C34–O3
C18–O1
O1–C22
C21–O2
O2–C23
2.1025(19)
1.9848(18)
2.0841(18)
2.083(2)
2.1128(19)
1.882(2)
1.132(3)
1.377(3)
1.414(4)
1.373(3)
1.433(3)
Bond angles
C21–O1–C23
C18–O2–C22
116.8(9)
117.7(9)
Ru1–C34–O3
C17–O1–C22
C20–O2–C23
55.92(17)
177.0(3)
117.5(3)
117.2(4)
Ru1–C34–O3
C18–O1–C22
C21–O2–C23
45.01(9)
177.4(2)
117.6(2)
116.5(2)
Dihedral angle
43.0(3)
H3CO
OCH3
N
+
O
Me
Me
Ru
N
N
S
N
N
N
OCH3
OCH3
N
N
N
N
[Ru(DMSO)4Cl2]
N
Cl
N
Ru
N
H3CO
H3CO
Cl
Cl
[1]+
2+
2+
N
N
N
N
N
N
OCH3
OCH3
CH3CN
CO
N
Ru
N
N
Ru
N
H3CO
H3CO
NCCH3
CO
[2]2+
[3]2+
Scheme 1.
dimethoxyphenyl substituents are not coplanar with the terpyridyl
moiety; the dihedral angles between the central pyridyl and the
dimethoxyphenyl ring are 43.0–55.9°. This is comparable to that
found for the metal-free ligand (50.2°) [4b]. Fig. 2 depicts the
molecular structure of [2]2+. There are no significant differences
in the Ru–NCCH3 moiety compared with the analogous complex
([Ru(tpy)(bpy)(CH3CN)]2+) [16a].
Crystals, with two different habits (yellow needles and red
blocks) were separated from the recrystallization of [3]2+. The dif-
ferent crystal habits had different space groups with the yellow
ꢀ
crystals solving in P1 as [3](PF6)2ꢂ(CH3)2CO, and the red crystals
solving in P21/n as [3](PF6)2. A comparison of the ruthenium geom-
etries in the two structures is shown in Table 3 and Fig. 3a and b.
The geometries around the ruthenium atom are similar to each
other and are consistent with those observed in closely related
complex ([Ru(tpy)(bpy)(CO)](PF6)2: Ru–C, 1.844(4) Å; C–O,
1.160(4) Å; Ru–C–O, 175.2(3)°) [12]. However, the O–CH3 orienta-
tion of two methoxy groups are different: two O–CH3 groups point
in the same orientation in [3](PF6)2ꢂ(CH3)2CO (Fig. 3a), while in
[3](PF6)2 they point in opposite directions (Fig. 3b). The former
structure is identical to [1]+ and [2]2+. On the other hand, the latter
Fig. 1. Electronic spectra of [1]+, [2]2+ and [3]2+ (c = 1.0 ꢀ 10ꢁ4 M in CH3CN).

D. Oyama et al. / Polyhedron 29 (2010) 1337–1343
1341
when a wide variety of ligands are introduced into the complexes
(c.f. tpyOMe ? tpyOMe+ is oxidized at +1.05 V in [Ru(tpyOMe)2]2+
and at +1.06 V in [Ru(tpy)(tpyOMe)]2+ [4b]). On the other hand, the
potentials for the RuIII/II couple varies with the monodentate ligand
L: the RuIII/II couple in [2]2+ is 500 mV higher than that of [1]+, and
the RuIII/II couple of [3]2+ was not observed with the solvent win-
dow. The change in the potential is reasonably well correlated with
the electron-accepting ability of the ligand L. These results suggest
no electronic interaction between the L ligand and the dimethoxy-
phenyl moiety, but the substituent L does effect the metal-cen-
tered potentials of the complex. In addition to two oxidation
processes, two successive one-electron reduction processes were
observed at negative potentials. These are attributed to reduction
of the terpyridyl and bipyridyl centers.
C23
O1
C35
C21
C34
N6
C18
C22
O2
N2
N3
N4
Ru1
N5
N1
3.3. Ligand replacement reaction
In general, the chloride ligands in ruthenium(II) complexes are
inert and Ag+ ions or irradiation of light is required to effect substi-
tution. As described in Section 3.1, no replacement reaction of [1]+
was observed when CH3CN solutions were heated. On the other
hand, purple solutions of [1]+ became red in the presence of CH3OH
or H2O (Eq. (1)).
Fig. 2. ORTEP drawing of [Ru(tpyOMe)(bpy)(CH3CN)]2+ ([2]2+
numbering scheme. Hydrogen atoms have been omitted for clarity. The thermal
ellipsoids are shown at the 50% probability level.
) with the atom
½RuðtpyOMeÞðbpyÞClꢃþ þ CH3CN
form is consistent with that observed in the metal-free tpyOMe
and its copper(II) complex [4b]. These differences are most likely
due to different packing or intermolecular effects on the orienta-
tion of methoxy groups of the tpyOMe ligand [17].
kobs
!½RuðtpyOMeÞðbpyÞðCH3CNÞꢃ2þ þ Clꢁ
ð1Þ
The well-separated absorption maxima for [1]+ and [2]2+ allowed
their interchange to be followed spectrophotometrically. Therefore,
the kinetics of the reaction have been monitored by UV–Vis spec-
troscopy to determine the rate constants and to obtain mechanistic
evidence. Fig. 5 illustrates a set of curves which were obtained start-
ing with [1]+ in CH3CN–H2O at 60 °C. The original bands at 360 and
508 nm decreased, and new bands for [2]2+ increased at 308 and
464 nm with clear isosbestic points. Plots of the absorption data
3.2. Redox properties
The electrochemical potentials of [1]+, [2]2+ and [3]2+ were char-
acterized by cyclic voltammetry experiments in CH3CN solution,
and the results are summarized in Table 2. Fig. 4 shows cyclic vol-
tammograms for the present complexes. All three complexes show
a quasi-reversible one-electron oxidation attributed to the dime-
thoxyphenyl group at ca. +1.0 V. This value remains constant even
(ln(Dabsorbance)) versus time are linear, indicating that this reac-
tion can be described with a first-order rate constant kobs. In princi-
ple, the rate constants kobs are pseudo-first order because the
C22
(a)
(b)
C23
O1
C17
O2
O3
O3
C20
C21
C23
C34
C34
O2
C18
N2
N3
O1
N2
N1
N3
N4
Ru1
N4
Ru1
N5
N1
C22
N5
Fig. 3. ORTEP drawings of [Ru(tpyOMe)(bpy)(CO)]2+ ([3]2+) with the atom numbering scheme. (a) [3](PF6)2ꢂ(CH3)2CO, (b) [3](PF6)2. Hydrogen atoms have been omitted for
clarity. The thermal ellipsoids are shown at the 50% probability level.

1342
D. Oyama et al. / Polyhedron 29 (2010) 1337–1343
Table 4
Summary of the Cl-replacement reaction rate constants for [1]+.
T (°C)
Solvent
RCN
Solv:RCN (v/v)
105 k(sꢁ1
)
60
50
40
60
60
60
60
60
60
50
40
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
H2O
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
C2H5CN
C3H7CN
C6H5CN
CH3CN
CH3CN
CH3CN
1:1
1:1
1:1
5:1
10:1
1:1
1:1
1:1
1:1
1:1
1:1
2.7
1.5
0.6
4.3
4.5
2.7
2.7
2.7
9.4
7.2
2.9
H2O
H2O
Under the same conditions, the rate for the replacement reaction of
the chloride in the analogous complex ([Ru(tpy)(bpy)Cl]+) was
slower than that of [1]+. The strong electron donors could stabilize
the coordination number-decreasing state, that is, transition states
[18]. This result based on the spectator ligand effect, therefore, sug-
gests that increase of electron density of the metal due to the
replacement of the tpy ligand to the tpyOMe ligand (more electron
donor) caused an acceleration of both dissociation of the Ru–Cl
bond and formation of Clꢁ.
The reaction was also studied using different concentrations or
kinds of entering ligands (RCN). The values of kobs for all of the
reactions were found to be independent of concentration and the
nature of the entering ligands (Table 4). As a result, this system
is consistent with a dissociative (Id) mechanism rather than an
associative one. This replacement reaction proceeded in the pres-
ence of H2O or CH3OH. One explanation is that hydrogen bonds
form between the chloride ligand and a hydrogen from the solvent
reducing the binding energy of the Ru–Cl bond, leading to dissoci-
ation of the ligand [19]. Addition of H2O to the solution of [1]+
accelerated of the replacement reaction more than CH3OH (Ta-
ble 4). This is consistent with the strength of the hydrogen bond-
ing. This reaction, therefore, has been classified as a solvent-
assisted dissociation (SAD) [20].
Fig. 4. Cyclic voltammograms of [1]+, [2]2+ and [3]2+ (scan rate = 0.1 V sꢁ1).
Supplementary data
CCDC 749665, 749666 and 749667 contains the supplementary
crystallographic data for [2](PF6)2ꢂCH3CN, [3](PF6)2ꢂ(CH3)2CO and
[3](PF6)2. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
Professor Koji Tanaka of the Institute for Molecular Science is
acknowledged for helpful discussions and insight. The authors
thank the Joint Studies Program (2008–2009) of the Institute for
Molecular Science for generous financial support of this research.
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