Tuning of redox potentials by introducing a cyclometalated bond to bis-tridentate ruthenium(II) complexes bearing bis(N -methylbenzimidazolyl) benzene or -pyridine ligands

Article abstract of DOI:10.1021/ic2016885

A series of asymmetrical bis-tridentate cyclometalated complexes including [Ru(Mebib)(Mebip)]⁺, [Ru(Mebip)(dpb)]⁺, [Ru(Mebip)(Medpb)]⁺, and [Ru(Mebib)(tpy)]⁺ and two bis-tridentate noncyclometalated complexes [Ru(Mebip)₂]²⁺ and [Ru(Mebip)(tpy)]²⁺ were prepared and characterized, where Mebib is bis(N-methylbenzimidazolyl)benzene, Mebip is bis(N-methylbenzimidazolyl) pyridine, dpb is 1,3-di-2-pyridylbenzene, Medpb is 4,6-dimethyl-1,3-di-2- pyridylbenzene, and tpy is 2,2′:6′,2″-terpyridine. The solid-state structure of [Ru(Mebip)(Medpb)]⁺ is studied by X-ray crystallographic analysis. The electrochemical and spectroscopic properties of these ruthenium complexes were studied and compared with those of known complexes [Ru(tpy)(dpb)]⁺ and [Ru(tpy)₂]²⁺. The change of the supporting ligands and coordination environment allows progressive modulation of the metal-associated redox potentials (Ru ^II/III) from +0.26 to +1.32 V vs Ag/AgCl. The introduction of a ruthenium cyclometalated bond in these complexes results in a significant negative potential shift. The Ru^II/III potentials of these complexes were analyzed on the basis of Lever's electrochemical parameters (E _L). Density functional theory (DFT) and time-dependent DFT calculations were carried out to elucidate the electronic structures and spectroscopic spectra of complexes with Mebib or Mebip ligands.

Full text of DOI:10.1021/ic2016885

Article
pubs.acs.org/IC
Tuning of Redox Potentials by Introducing a Cyclometalated Bond to
Bis-tridentate Ruthenium(II) Complexes Bearing Bis(N-
methylbenzimidazolyl)benzene or -pyridine Ligands
†
,†
‡
†
§
Wen-Wen Yang, Yu-Wu Zhong,* Shinpei Yoshikawa, Jiang-Yang Shao, Shigeyuki Masaoka,
§
†
,‡
Ken Sakai, Jiannian Yao, and Masa-aki Haga*
†Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, People’s Republic of China
‡
Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo
1
12-8551, Japan
§
Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan
S Supporting Information
*
ABSTRACT: A series of asymmetrical bis-tridentate cyclo-
+
metalated complexes including [Ru(Mebib)(Mebip)] , [Ru-
+
+
(
(
[
Mebip)(dpb)] , [Ru(Mebip)(Medpb)] , and [Ru(Mebib)-
+
tpy)] and two bis-tridentate noncyclometalated complexes
Ru(Mebip)2]2 and [Ru(Mebip)(tpy)] were prepared and
+
2+
characterized, where Mebib is bis(N-methylbenzimidazolyl)-
benzene, Mebip is bis(N-methylbenzimidazolyl)pyridine, dpb
is 1,3-di-2-pyridylbenzene, Medpb is 4,6-dimethyl-1,3-di-2-
+
pyridylbenzene, and tpy is 2,2′:6′,2″-terpyridine. The solid-state structure of [Ru(Mebip)(Medpb)] is studied by X-ray
crystallographic analysis. The electrochemical and spectroscopic properties of these ruthenium complexes were studied and
+
2+
compared with those of known complexes [Ru(tpy)(dpb)] and [Ru(tpy) ] . The change of the supporting ligands and
2
II/III
coordination environment allows progressive modulation of the metal-associated redox potentials (Ru ) from +0.26 to +1.32
V vs Ag/AgCl. The introduction of a ruthenium cyclometalated bond in these complexes results in a significant negative potential
II/III
shift. The Ru
potentials of these complexes were analyzed on the basis of Lever’s electrochemical parameters (E ). Density
L
functional theory (DFT) and time-dependent DFT calculations were carried out to elucidate the electronic structures and
spectroscopic spectra of complexes with Mebib or Mebip ligands.
INTRODUCTION
Polyazine transition-metal complexes, particularly ruthenium-
II) complexes, have attracted tremendous interest because of
determines their suitability for specific applications such as
biomediators for electron shuttles between active sites of
oxidoreductases and the electrode.
■
(
6
Recently, cyclometalated ruthenium complexes have been
their distinguished electrochemical and photophysical proper-
7
1
the focus of many research activities. These complexes contain
ties. They intensely absorb visible light from the metal-to-
a covalent Ru−C bond between the metal center and one
supporting ligand. Because of the presence of the anionic
cyclometalating ligand, the metal center of cyclometalated
complexes is much more electron-rich than that of non-
cyclometalated analogues. As a result, the metal-associated
redox potentials of these complexes are much less positive than
ligand charge-transfer (MLCT) transitions, which makes them
good candidates as light-harvesting dyes and sensitizers. Some
2
ruthenium complexes with bright emission and long excited-
2
+
state lifetimes, e.g., [Ru(bpy)3] (bpy = 2,2′-bipyridine; Φ =
3
9
.5% in oxygen-free acetonitrile; τ = 1150 ns), are benchmark
emissive organometallic complexes. They have been widely
used in photoinduced electron- or energy-transfer processes
II/III
8
the noncyclometalated ones. For example, the Ru
process
2+
4
of noncyclometalated complex [Ru(tpy) ] occurs at +0.89 V
and photocatalysis. Bis-tridentate octahedral complexes such
2
+
9
as [Ru(tpy)2]2 (tpy = 2,2′:6′,2″-terpyridine) can be readily
incorporated into supramolecular architectures with well-
defined structures via easy and reliable functionalization at
+
vs Fc/Fc (+1.3 V vs Ag/AgCl ), while this process could take
place around at +0.12 V vs Fc/Fc (corresponding to +0.57 V
+
+
vs Ag/AgCl) for the cyclometalated analogue [Ru(tpy)(dpb)]
8
5
(dpb = 1,3-di-2-pyridylbenzene). In this context, we also note
the 4′ position of the tpy ligand, and linear multimetallic
that bis(triazole)- or bis(tetrazole)pyridine, as reported by Vos
and co-workers, could also act as σ-donor ligands, and
coordination arrays as potential molecular wires could be
produced. However, it should be noted that the coordination
environment and nature of the supporting ligands play
significant roles in determining the electrochemical and
photophysical properties of these complexes. This, in turn,
Received: August 3, 2011
Published: December 28, 2011
©
2011 American Chemical Society
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Inorganic Chemistry
Article
Scheme 1. Synthesis of Compounds Studied
II
+
2+
corresponding Ru (tpy)-type complexes show appealing
with those of [Ru(tpy)(dpb)] , [Ru(Mebip)(tpy)] , [Ru-
1
0
2+
2+
emissive properties. Recent investigations have proved that
cyclometalated ruthenium complexes could be used as efficient
(Mebip) ] , and [Ru(tpy) ] . In addition, density functional
2 2
theory (DFT) and time-dependent DFT (TDDFT) calcu-
lations were performed on these complexes to elucidate their
electronic structures and aid in the assignment of absorption
spectra. The presence of strong electron-donating benzimida-
zole rings is believed to substantially decrease the redox
potential of ruthenium complexes. The combination of
cyclometalated and noncyclometalated ruthenium complexes
with Mebib and Mebip would allow systematic tuning of the
metal-centered redox potentials.
It should be noted that the coordination chemistry of Mebib
and Mebip and their derivatives is well documented. For
instance, Haga and co-workers have prepared a large number of
noncyclometalated ruthenium and cyclometalated iridium
complexes with Mebib and/or Mebip ligands and studied the
11
sensitizers for solar cell applications, benefiting from the
energetic match between the metal-based highest occupied
molecular orbital (HOMO) level of the dye and the conduction
band edge of TiO . Besides, numerous mixed-valence systems
with cyclometalated ruthenium as the charge-bearing sites have
been reported and an enhanced electronic coupling between
metal centers was found to be present. Encouraged by their
interesting properties and promising application in dye-
sensitized solar cells and molecular electronics, we recently
set out to design and synthesize new cyclometalated ruthenium
2
12
1
3
complexes. A cyclometalating tridentate ligand 1,3-di-1,2,3-
14
triazol-4-ylbenzene (dtab) has previously been reported, and
corresponding complexes [Ru(tpy)(dtab)]+ were found to
exhibit electrochemical and spectroscopic properties similar to
those of [Ru(tpy)(dpb)] . In this paper, we describe the
synthesis and characterization of new cyclometalated ruthenium
properties of these complexes both in solution and on the
electrode surface. The reaction of Mebib and Pd(OAc) was
found to give a cyclometalated palladium(II) complex where
Mebib behaved as a cyclometalating bidentate ligand. In
+
15
2
+
+
16
complexes [Ru(Mebib)(Mebip)] , [Ru(Mebip)(dpb)] , [Ru-
+
+
17
18
19
(
Mebip)(Medpb)] , and [Ru(Mebib)(tpy)] , where Mebib is
addition, copper(I), platinum(II), rhodium(III), and
20
bis(N-methylbenzimidazolyl)benzene, Mebip is bis(N-
methylbenzimidazolyl)pyridine, and Medpb is 4,6-dimethyl-
,3-di-2-pyridylbenzene. The electrochemical and photophys-
ical properties of these complexes were studied and compared
lanthanide complexes of Mebip or derivatives have been
reported to form stable coordination complexes with appealing
emissive or liquid-crystalline properties. It should also be
mentioned that some Mebip- or Mebib-containing ruthenium
1
8
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Inorganic Chemistry
Article
complexes were successfully used as solar cell sensitizers or
Table 1. Crystal Data and Structure Refinement for 8
21
water oxidation catalysts recently. However, cyclometalated
ruthenium complexes with either Mebib or Mebip ligands have
[
Ru(Mebip)(Medpb)](BPh )CH CN (8)
4 3
21d
empirical formula
fw
C H RuN ·C H B·C H N
39 32 7 24 20 2 3
1060.05
rarely been reported.
crystal color, habit
cryst dimens
cryst syst
a (Å)
red, needle
RESULTS AND DISCUSSION
Synthesis and X-ray Structure. The complexes studied in
■
3
0.30 × 0.03 × 0.01 mm
orthorhombic
17.0541(19)
14.2024(15)
20.996(2)
5085.5(10)
Pca21
the paper were synthesized as outlined in Scheme 1. Detailed
synthetic procedures and characterization data are provided in
the Experimental Section. Ligands Mebib and Mebip were
prepared according to reported procedures with slight
modifications from the condensation of N-methyl-1,2-phenyl-
enediamine with benzene-1,3-dicarboxylic acid and pyridine-
b (Å)
c (Å)
3
V (Å )
space group
15f,21b
Z value
4
2
,6-dicarboxylic acid, respectively.
The reaction of RuCl
3
21b
D
calc (g/cm3)
1.385
with Mebip afforded (Mebip)RuCl in good yield, which was
3
F000
2200
used as a common intermediate for the synthesis of asymmetric
complexes 1, 2, 6, and 8. The chloride atoms of (Mebip)RuCl3
were first replaced with solvent molecules (acetone in this case)
in the presence of AgOTf. The obtained intermediate was
heated in indicated solvents in the presence of Mebib, dpb, or
Medpb to give cyclometalated complexes 1, 2, and 8,
a
R1 [I > 2.00σ(I)]
0.0383
b
wR2
0.0771
c
GOF
1.007
a
R1 = ∑||F | − |F ||/|F |. wR2 = [∑w(|F | − |F | )] /∑w(|F | ) ]1/2.
b
2
2
2
2 2
o
c
o
o
c
o
c
2
1/2
GOF = [∑w(|F | − |F |) /(N − N )] , where N = number of
o
c
o
v
o
observations and N = number of variables.
v
respectively, after anion exchange with KPF . Similar
6
procedures were previously used for the synthesis of a number
Table 2. Selected Bond Lengths and Bond Angles of 8
7
,11−14
of cyclometalated ruthenium complexes.
The reaction of
(
tpy)RuCl and Mebib provided complex 3 in 33% yield.
bond lengths (Å)
bond angles (deg)
3
8
Known cyclometalated complex 4 was also prepared for a
comparison study. Two noncyclometalated complexes, 5 and 6,
could be prepared starting from Mebip. Complex 5 has been
reported in the literature. However, full characterization data
are not available. Complex 6 is a new compound. However, it
should be noted that similar complexes with substituents on the
Ru1−N1
2.066(3)
2.068 (3)
2.068(3)
2.055(3)
2.075 (3)
1.955(3)
N1−Ru1−C7
79.2(1)
Ru1−N2
Ru1−N3
Ru1−N4
Ru1−N5
Ru1−C7
N2−Ru1−C7
N3−Ru1−N4
N4−Ru1−N5
N4−Ru1−C7
N5−Ru1−C7
79.0(1)
77.4(1)
22
76.5 (1)
175.2 (1)
107.2 (1)
15
tpy ligand are known.
+
Suitable single crystals of [Ru(Mebip)(Medpb)] (8) with a
being slightly distorted because of repulsion between the N-
methyl groups and the hydrogen atoms of the pyridine moiety.
The Ru−C bond length is 1.955(3) Å. Bond lengths between
−
BPh4 counteranion for structure determination were obtained
by recrystallization from an acetonitrile−water solution. An
ORTEP plot of 8 is represented in Figure 1. Crystal data and
ruthenium and coordinated nitrogen atoms are in the range of
II
2
.066(3)−2.075(3) Å, except the Ru −N4 bond. The present
py
Ru−N4 bond length is 2.055(3) Å, which is slightly longer
py
II
than the values of 1.98−2.02 Å reported for Ru −N bond
py
2
+
2+
lengths in bis-tridentate [Ru(tpy) ] and [Ru(Mebip)2]
2
8
complexes. This result indicates that the trans influence of
carbon anion coordination induces elongation of the Ru−N4
py
bond trans to the Ru−C7 bond.
Electrochemical Studies and DFT Calculation. The
electronic properties of these complexes were studied by
electrochemical analysis and compared with those of [Ru(tpy)-
+
2+
(
dpb)] and [Ru(tpy) ] (Figure 2 and Table 3). To assist in
2
the determination of their electronic structures, DFT
calculations were performed on the B3LYP/LANL2DZ level.
Some frontier orbital structures with electron density
distribution are provided in Figures 3 and S1−S4 in the
Supporting Information. The frontier orbital energy level
diagram for complexes 1−3, 5, and 6 is shown in Figure 4.
The cyclic voltammetry (CV) profiles of cyclometalated
complexes 1−3 show some similarities albeit with a distinct
difference. All of them display a cathodic wave around −1.60 V
vs Ag/AgCl and two anodic waves within the solvent potential
window. The cathodic event is assigned to reduction of the
noncyclometalating ligand Mebip for complexes 1 and 2 and
tpy for complex 3. The anionic cyclometalating ligand is more
electron-rich and thus sluggish to be reduced than the
noncyclometalating ligand. This assignment is corroborated
Figure 1. ORTEP diagram of 8 with a BPh4− counteranion. Solvents
and anion are omitted for clarity.
selected bond lengths are given in Tables 1 and 2, respectively.
∧
∧
The Medpb ligand binds to ruthenium in a tridentate N C N
coordination mode with a covalent Ru−C bond. The
coordination geometry of the ruthenim(II) center was a
distorted octahedron. The Mebip ligand was not planar,
8
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Inorganic Chemistry
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+
that of [Ru(tpy)(dpb)] (4; +0.56 V vs Ag/AgCl). Complex 1
coordinated with four benzimidazole rings could be oxidized at
the lowest potential. It should be pointed out here that the
II/III
Ru
process must involve some degree of ligand-based
oxidation. It is supported by the DFT results that the HOMOs
of 2 and 3 and HOMO−1 of complex 1 exhibit high electron
delocalization between ruthenium and the cyclometalating
phenyl ring. This phenomenon is commonly observed in the
7
,11
DFT results of cyclometalated ruthenium complexes.
The
second oxidation waves of complexes 1−3 at around +1.50 V
III/IV
are ascribed to the Ru
process. Similarly, some content of
ligand oxidation must be present in this process. Importantly, in
the cases of complexes 1 and 3 (especially 1), this process
exhibits well-defined chemical reversibility. We note that this
process is clearly irreversible for most known cyclometalated
7
,11−14
ruthenium complexes
except in those bonded to
7f
oligothiophenes, as reported by Wolf and co-workers. This
again attests to the importance of benzimidazole ligands, which
stabilize the higher oxidation state because of their stronger σ-
donor nature than pyridines. Because of the considerably low
II/III
Ru
potential of complex 1, it could be easily transformed to
ruthenium(III) complex 9 in the presence of silver salt. The
characterization data of 9 are available in the Experimental
Section.
The CV profiles of complexes 5−7 are given in Figure 2b.
II/III
They all display two ligand-based reduction waves and a Ru
process. For the asymmetric complex 6, the Mebip ligand is
thought to be first reduced, as suggested by the DFT results
(
Figure S4 in the Supporting Information), which gives a
Mebip-associated LUMO level and a tpy-based LUMO+1 level.
II/III
Figure 2. Cyclic voltammograms of 1−7 in acetonitrile containing 0.1
The Ru
process of complexes 5−7 occurs at +0.86, +1.07,
M Bu NClO as the supporting electrolyte at a scan rate of 100 mV/s.
and +1.32 V vs Ag/AgCl, respectively. The significantly low
potential of benzimidazole-containing noncyclometa-
lated ruthenium complexes has been documented previously.
By taking together the Ru
successfully realize the systematic regulation of the metal-based
oxidation potential from +0.26 to +1.32 V vs Ag/AgCl (Figure
4
4
II/III
The working electrode was a glassy carbon, the counter electrode was
a platinum wire, and the reference electrode was Ag/AgCl in saturated
aqueous NaCl.
Ru
15
II/III
processes of complexes 1−7, we
by DFT calculations. The lowest unoccupied molecular orbitals
(LUMOs) of complexes 1−3 are all predominantly associated
2
c). Correspondingly, the HOMO levels of these complexes
with the noncyclometalating ligand (Figures 3 and S1 and S2 in
the Supporting Information). The anodic events of complexes
vary in a progressively descending order. We have carried out
DFT calculations on five complexes, 1−3, 5, and 6. Their
HOMO levels are found to reside at −6.96, −7.15, −7.31,
−10.00, and −10.50 eV, respectively (Figure 4). However, it
should be pointed out we did not consider the compensation
for counteranions during calculations. The relative energy level
1
+
−3 are rather interesting. The first oxidation waves (+0.26,
0.43, and +0.48 V vs Ag/AgCl for complexes 1−3,
II/III
respectively) could be attributed to the mixed Ru /ligand
oxidation process.
7,11−14
They are noticeably less positive than
Table 3. Observed and Calculated Electrochemical Data of Complexes 1−7
a
number of ligand parts
E1/2 for RuII/III, RuIII/IV
b
E1/2 for L0/−
b
ΔE (eV)
c
pytpy
pyphenyl
pybzim
Ph anion
bzim
E1/2(calcd)
b
complex
1
2
3
4
5
6
7
8
, [Ru(Mebib)(Mebip)]+
, [Ru(Mebip)(dpb)]+
, [Ru(Mebib)(tpy)]+
, [Ru(tpy)(dpb)]+
+0.26, +1.50
−1.60
−1.56
−1.55
−1.51
−1.24, −1.55
−1.24, −1.50
−1.22, −1.46
−1.57
1.86
1.92
1.95
2.07
2.10
2.31
2.54
1.95
1
1
1
1
1
1
4
2
2
+0.29
+0.39
+0.49
+0.60
+0.87
+1.07
+1.27
d
+0.43, +1.49
2
2
+0.48, +1.47
3
3
d
+0.56, +1.60
, [Ru(Mebip) ]2+
+0.86
+1.07
+1.32
2
1
4
2
2
, [Ru(Mebip)(tpy)]2+
3
6
, [Ru(tpy) ]2+
2
, [Ru(Mebip)(Medpb)]+
+0.38, +1.57
d
a
The following Lever electrochemical parameters (V vs NHE) were used: pytpy (pyridine of tpy) = 0.25, pyphenyl (pyridine with a adjacent phenyl
group) = 0.23, pybzim (pyridine with a adjacent benzimidazole group) = 0.20, Ph anion (carboanion) = −0.40, and bzim (bibenzimidazole) = 0.17.
b
The potential values for E1 (calcd) (V vs Ag/AgCl) was obtained by subtracting 0.22 V from those vs NHE. The potential is reported as the E
/2
1/2
c
value vs Ag/AgCl. The electrochemical energy gap is determined by the potential difference between the first oxidation and first reduction waves.
d
Ep,anodic, irreversible.
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Figure 3. Isodensity plots of frontier orbitals of complex 1. All orbitals have been computed at an isovalue of 0.02.
phenyl anion indicates that the phenyl anion of the cyclo-
metalated bond acts as a strong π base.
Spectroscopic Studies and TDDFT Calculation. The
UV/vis absorption spectra of the above compounds were
recorded (Figures 5 and S5 in the Supporting Information) to
Figure 4. Frontier orbital energy level alignment of complexes 1−3, 5,
and 6.
difference between the cyclometalated and noncyclometalated
series may be overestimated. It should also be noted that the
energy gap of complexes 1−7, determined by the potential
difference between the first cathodic and first anodic waves, is
varied in an ascending order from 1.86 to 2.54 eV (Table 3).
Lever’s electrochemical parameter, E , has been used to
L
II/III
predict Ru
redox potentials by assuming that all of the
ligand contributions are additive. For the observed Ru
23
II/III
couple in acetonitrile (V vs NHE), the following equation
applies:
Figure 5. UV/vis absorption spectra of complexes 1−7 in acetonitrile.
further probe their electronic properties. To aid in the
assignment of absorption bands, TDDFT calculations were
performed on these complexes, and related results are collected
in Table 4, together with experimentally observed transitions.
Predicted absorption spectra are provided in Figure S6 in the
Supporting Information. It is well-known that polypyridine
ruthenium complexes display strong intraligand (IL) absorp-
tions in the UV region and MLCT transitions in the visible
region. One common feature for the complexes studied is
that, for complexes with the Mebip ligand, no matter
cyclometalated (1 and 2) or noncyclometalated (5 and 6),
intense Mebip-based IL transitions could be observed around
Eobs = 0.97[
∑
EL] + 0.04
(1)
In the present study, we have prepared a series of
cyclometalated and noncyclometalated ruthenium complexes
bearing Mebib and/or Mebip ligands. By using the reported
Lever’s parameters for the nitrogen-coordinating ligands such
as the pyridine (0.25 for tpy and 0.20 for benzimidazole) or
benzimidazole ligand (0.17 for bibenzimdazole) and eq 1, we
can derive the electrochemical parameter for the phenyl anion
in ruthenium cyclometalated complexes as −0.40. The
1
,2
predicted E1 values are listed in Table 3, together with the
/2
experimental values. The large negative value of E for the
L
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Table 4. Observed Absorption Data and Calculated Excitation Energy (E), Oscillator Strength (f), Dominant Contributing
a
Transitions, and the Associated Percent Contribution and Assignment of Complexes 1−3, 5, and 6
5
−1
−1
b
complex
Sn
E/eV
E/nm
f
λmax/nm obsd
ε (×10 M cm )
dominant transitions (percent contribution )
assignment
1
6
8
2.65
2.89
3.65
3.84
3.92
2.71
468
428
339
322
315
458
0.101
0.151
0.181
0.213
0.177
0.139
571
515
353
334
0.077
0.13
0.27
0.32
HOMO−2 → LUMO (58%)
HOMO−1 → LUMO+2 (91%)
HOMO−7 → LUMO (89%)
HOMO−8 → LUMO+1 (86%)
HOMO−4 → LUMO+2 (82%)
HOMO−2 → LUMO (44%)
HOMO−1 → LUMO+1 (23%)
HOMO → LUMO+2 (84%)
HOMO−1 → LUMO+3 (76%)
HOMO−4 → LUMO (88%)
HOMO−5 → LUMO+1 (72%)
HOMO−2 → LUMO (60%)
HOMO → LUMO+2 (90%)
HOMO−1 → LUMO+3 (89%)
HOMO−1 → LUMO+4 (68%)
HOMO−4 → LUMO+2 (73%)
HOMO−7 → LUMO (64%)
HOMO → LUMO+3 (87%)
HOMO−2 → LUMO (29%)
HOMO−1 → LUMO+1 (29%)
HOMO−3 → LUMO (92%)
HOMO−3 → LUMO+1 (92%)
HOMO−4 → LUMO (91%)
HOMO−4 → LUMO+1 (91%)
HOMO−2 → LUMO+1 (50%)
HOMO−2 → LUMO+3 (76%)
HOMO−3 → LUMO (84%)
HOMO−4 → LUMO+3 (34%)
MLMebipCT
MLMebibCT
ILMebip
23
27
30
6
ILMebip
ILMebib
2
3
5
516
457
0.17
MLMebipCT
MLMebipCT
MLdpbCT
MLdpbCT
ILMebip
7
1
8
4
6
7
7
0
0
7
4
7
2.84
3.18
3.57
3.79
2.59
2.95
3.28
3.40
3.91
4.17
2.52
2.84
436
390
347
327
478
419
378
364
317
297
491
437
0.072
0.086
0.239
0.12
0.115
1
1
2
349
334
0.39
0.29
ILMebip
0.069
0.156
0.045
0.034
0.153
0.168
0.016
0.094
MLtpyCT
MLMebibCT
MLtpyCT
MLtpyCT
ILMebib
497
394
0.11
1
2
3
3
0.082
319
275
0.44
0.47
ILtpy
MLMebipCT
MLMebipCT
MLMebipCT
ILMebip
491
357
342
480
354
0.16
0.66
0.48
0.14
0.38
0.31
1
1
1
1
4
5
6
7
7
9
4
6
1
3.30
3.30
3.39
3.39
2.91
3.01
3.36
3.71
3.86
375
375
365
365
425
411
369
334
321
0.104
0.104
0.14
ILMebip
ILMebip
0.14
ILMebip
6
0.12
MLtpyCT
MLMebipCT
ILMebip
0.019
0.345
0.080
0.18
1
2
3
ILMebip
336
b
HOMO−6 → LUMO+3 (83%)
ILMebip
a
2
Computed at the TDDFT/LANL2DZ level of theory. The actual percent contribution = (configuration coefficient) × 2 × 100%.
3
50 nm (denoted as ILMebip, two sharp peaks). They originated
The room-temperature emission spectra of complexes 3 and 6
from relatively high occupied levels, e.g., HOMO−4, HOMO−
in butyronitrile are shown in Figure 6. They weakly emit at 790
7
, and HOMO−8 for complex 1 and HOMO−3, HOMO−4,
and HOMO−6 for complex 6. Transitions in the visible region
for all complexes consist of MLCT bands associated with both
coordinating ligands, either cyclometalated or noncyclometa-
lated. Complex 1 shows ML CT and ML CT transitions at
bip
bib
5
71 and 515 nm, respectively. They are associated with
excitation of HOMO−2 → LUMO and HOMO−1 → LUMO
2, respectively. In comparison, the Mebip- and dpb-targeted
+
MLCT absorptions of complex 2 are found at 516 and 457 nm
and dominated by HOMO−2 → LUMO and HOMO →
LUMO+2 transitions, respectively. The absorption spectrum of
+
3
is somewhat similar to that of [Ru(tpy)(dpb)] . The major
band around 500 nm is attributed to an admixture of both
Mebib- and tpy-targeted MLCT transitions. However,
ML CT transitions play a more important role, as predicted
bib
by TDDFT calculations. Transitions around 400 nm are
assigned to the tpy-targeted MLCT bands. It should be noted
that MLCT transitions of cyclometalated complexes (1−4) are
relatively bathochromically shifted and more broadened than
those of noncyclometalated complexes (5−7). This feature has
been previously documented on cyclometalated ruthenium
Figure 6. Emission spectra of complexes 3 (blue line) and 6 (red line)
in butyronitrile at room temperature.
and 680 nm and have 16 and 30 ns lifetimes at room
temperature, respectively. Compared to the emission properties
1
1,12
complexes.
Transitions at 480 nm of the asymmetric
2
+
of [Ru(tpy)2]
(λmax,em = 629 nm; τ = 0.25 ns) and
complex 6 contain MLCT transitions of both Mebip and tpy
0
[
λ
Ru(L3)(tpy)] (L3 = 2,6-bis([1,2,3,4]tetrazol-5-yl)pyridine;
ligands. However, ML CT has the major contribution. Finally,
tpy
10
it is found that all complexes studied are weakly emissive or
virtually nonemissive at room temperature in a fluidic solution.
max,em = 680 nm; τ = 42 ns) at room temperature, the
introduction of the Ru−C bond in complex 3 leads to a longer
8
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Inorganic Chemistry
Article
wavelength shift on emission. In order to get the information
3
3
about the MLCT− MC energy gap at the excited state, a
detailed study for the temperature dependence of the
luminescence lifetime is now underway, which will be published
as a separate paper.
Oxidative Spectroelectrochemistry. Oxidative spectroe-
II/III
lectrochemistry for the Ru
process was measured using a
thin-layer spectroelectrochemical cell. The original ruthenium-
+
(
II) complex 1, [Ru(Mebib)(Mebip)] , shows several broad
MLCT bands at 515 and 571 nm. The UV/vis spectral changes
of the thin-layer spectroelectrochemical oxidative electrolysis of
1
at +0.5 V and then +1.6 V vs Ag/AgCl for the first and
second oxidations are displayed in Figure 7. For the first
Figure 8. UV/vis spectral changes of complexes 3 (a) and 6 (b) during
oxidative thin-layer spectroelectrochemistry in 0.1 M TBAPF6 in
CH CN.
3
CONCLUSION
■
In summary, a number of cyclometalated and noncyclometa-
lated ruthenium complexes containing Mebip and/or Mebib
ligands are presented in this paper. The electronic properties of
these complexes were studied with electrochemical, spectro-
scopic, and spectroelectrochemical analysis and theoretical
calculations. A key finding is that, by using benzimidazole-
containing ligands, the metal-based oxidation potential of the
corresponding ruthenium complexes could be systematically
tuned in a wide scope (+0.26 to +1.32 V vs Ag/AgCl). As a
result, HOMO levels and energy gaps of these complexes are
varied in a controlled fashion. This feature is of importance and
interest for the design and synthesis of new organometallic
Figure 7. UV/vis spectral changes of complex 1 at applied potentials
of +0.5 V (a) and +1.6 V (b) vs Ag/AgCl during oxidative thin-layer
spectroelectrochemistry in 0.1 M TBAPF in CH CN.
11
materials for applications in dye-sensitized solar cells. We are
currently carrying out the synthesis of new mixed-valent
6
3
12−15
dimetallic systems with Mebip or Mebib ligands.
The
oxidation (Figure 7a), the disappearance of the MLCT bands at
15 nm and the appearance of new bands at 412 and 715 nm
are clearly seen along with several isosbestic points at 297, 324,
39, 447, 637, and 790 nm. The latter band at 715 nm might be
presence of the electron-rich benzimidazole ligands is thought
to greatly enhance the metal−metal coupling in these systems.
These results will be reported in due course in the near future.
5
3
EXPERIMENTAL SECTION
assigned to the ligand-to-metal charge-transfer band. The
■
original ππ* band at 281 nm was shifted to a longer wavelength
General Procedure. NMR spectra were recorded in the
designated solvent on a Bruker Avance 400 or 500 MHz spectrometer.
Spectra are reported in ppm values from residual protons of a
III
at 299 nm after oxidation to the Ru state. From analysis of the
Nernst plot, the number of electrons, n, and the standard
oxidation potential, E°, were determined as n = 1 and E° =
1
deuterated solvent for H NMR. Mass spectrometry (MS) data were
obtained with a Bruker Daltonics Inc. ApexII FT-ICR or Autoflex III
MALDI-TOF mass spectrometer. Microanalysis was carried out using
a Flash EA 1112 or Carlo Erba 1106 analyzer at the Institute of
Chemistry, Chinese Academy of Sciences.
1,3-Bis(1-methylbenzimidazol-2-yl)benzene (Mebib). A mix-
ture of isophthalic acid (680 mg, 4.1 mmol) and N-methyl-1,2-
phenylenediamine (1.64 g, 8.4 mmol) in 20 mL of poly(phosphoric
acid) was stirred at 210 °C for 4 h. After cooling to room temperature,
the reaction mixture was poured into 50 mL of water and neutralized
with 5 M aqueous NaOH. The precipitate was collected by filtration
and washing with water. The resulting solid was subjected to flash
+
0.24 V vs Ag/AgCl. The second oxidation led to a decrease of
the band at 412 nm and the broadening of all of the bands and
a small broad band appeared around 830 nm. Because
ruthenium(IV) examples are rare except those of ruthenium-
24
(
IV) oxo complexes, no strong characteristic bands were
observed. Similar spectral changes were observed for complexes
and 6 (Figure 8a,b). The trial to get the spectrum of the RuIV
3
state for complex 3 has failed so far because of decomposition
of the complex.
8
96
dx.doi.org/10.1021/ic2016885 | Inorg. Chem. 2012, 51, 890−899

Inorganic Chemistry
Article
column chromatography on silica gel (eluent: 4:1 CH Cl /acetone) to
give 960 mg of Mebib as a yellow solid (69%). H NMR (400 MHz,
(d, J = 8.2 Hz, 2H), 6.76 (t,J = 7.7 Hz, 2H), 6.90 (t, J = 6.7 Hz, 2H),
7.08 (t, J = 7.6 Hz, 2H), 7.16 (d, J = 5.5 Hz, 2H), 7.38 (d, J = 8.3 Hz,
2H), 7.55 (m, overlapped, 3H), 8.31 (d, J = 7.9 Hz, 2H), 8.36 (t, J =
8.3 Hz, 1H), 8.41 (d, J = 7.8 Hz, 2H), 8.78 (d, J = 8.0 Hz, 2H). ESI-
2
2
1
CDCl ): δ 3.91 (s, 6H), 7.35 (m, 4H), 7.42 (d, J = 7.0 Hz, 2H), 7.71
3
(
7
t, J = 7.8 Hz, 1H), 7.84 (d, J = 6.8 Hz, 2H), 7.93 (d, J = 7.6 Hz, 2H),
.14 (s, 1H).
,6-Bis(1-methylbenzimidazol-2-yl)pyridine (Mebip). A mix-
+
MS: m/z 672.3 for [M − PF ] . Anal. Calcd for C H F N PRu: C,
6
37 28
6
7
2
54.41; H, 3.46; N, 12.01. Found: C, 54.25; H, 3.61; N, 12.03.
Complex 5. To 15 mL of ethylene glycol were added Mebip (84.8
mg, 0.25 mmol) and RuCl ·3H O (32.6 mg, 0.125 mmol). The
ture of pyridine-2,6-dicarboxylic acid (0.68 g, 4.1 mmol) and N-
methyl-1,2-phenylenediamine (1.73 g, 8.9 mmol) in 20 mL of
poly(phosphoric acid) was stirred at 210 °C for 4 h. After cooling
to room temperature, the reaction mixture was poured into 50 mL of
water and neutralized with 5 M aqueous NaOH. The precipitate was
collected by filtration and washing with water. The resulting solid was
subjected to flash column chromatography on silica gel (eluent: 5:1
CH Cl /methanol) to give 1.31 g of Mebip as a yellow solid (95%).
3
2
mixture was heated with microwave radiation (power 375 W) for 40
min. After cooling to room temperature, 10 mL of water and an excess
of KPF6 were added. The resulting precipitate was collected by
filtration and washing with water and Et O. The obtained solid was
2
subjected to flash column chromatography on silica gel (eluent:
200:5:1 acetone/H O/aqueous KNO ) followed by anion exchange
2
2
2
3
1
1
H NMR (400 MHz, CDCl ): δ 4.25 (s, 6H), 7.39 (m, 4H), 7.47 (d, J
with KPF to give 37 mg of complex 5 (28%). H NMR (400 MHz,
3
6
=
7.7 Hz, 2H), 7.88 (d, J = 7.5 Hz, 2H), 8.06 (t, J = 7.8 Hz, 1H), 8.42
CD CN): δ 4.38 (s, 12H), 6.14 (d, J = 8.3 Hz, 4H), 6.99 (t, J = 7.8 Hz,
3
(
d, J = 7.8 Hz, 2H).
Complex 1. To 10 mL of dry acetone were added Ru(Mebip)Cl3
4H), 7.30 (t, J = 7.8 Hz, 4H), 7.47 (d, J = 8.3 Hz, 4H), 8.56 (t, J = 8.3
Hz, 2H), 8.89 (d, J = 8.2 Hz, 4H). ESI-MS: m/z 390.1 for [M −
2+
(55 mg, 0.1 mmol) and AgOTf (78 mg, 0.3 mmol). The mixture was
2PF
6
]
(z = 2). Anal. Calcd for C42H F N P Ru·2H O: C, 45.62;
34 12 10 2 2
refluxed for 2 h before cooling to room temperature. The precipitate
was removed by filtration, and the filtrate was concentrated to dryness.
To the residue were added Mebib (33 mg, 0.1 mmol), N,N-
dimethylformamide (DMF; 8 mL), and tert-butyl alcohol (t-BuOH; 8
mL). The mixture was then refluxed for 24 h. After cooling to room
temperature, the solvent was removed under reduced pressure, and the
residue was dissolved in the proper amount of methanol. After the
H, 3.46; N, 12.67. Found: C, 45.28; H, 3.11; N, 12.80.
Complex 6. To 10 mL of dry acetone were added Ru(Mebip)Cl
3
(33.9 mg, 0.06 mmol) and AgOTf (78 mg, 0.3 mmol). The mixture
was refluxed for 2 h before cooling to room temperature. The
precipitate was removed by filtration, and the filtrate was concentrated
to dryness. To the residue were added 2,2′:6′,2″-terpyridine (24 mg,
0.1 mmol) and 15 mL of ethylene glycol. The mixture was then heated
with microwave radiation (P = 375 W) for 40 min. After cooling to
addition of an excess of KPF , the resulting precipitate was collected by
6
filtration and washing with water and Et O. The obtained solid was
room temperature, 10 mL of water and an excess of KPF
The resulting precipitate was collected by filtration and washing with
water and Et O. The obtained solid was subjected to flash column
chromatography on silica gel (eluent: 200:5:1 CH CN/H O/aqueous
KNO ) followed by anion exchange with KPF to give 30 mg of
complex 6 (52%). H NMR (400 MHz, CD CN): δ 4.40 (s, 6H), 5.97
6
were added.
2
subjected to flash column chromatography on silica gel (eluent: 10:1
1
CH Cl /CH CN) to give 45 mg of complex 1 (49%). H NMR (400
2
2
2
3
MHz, CD CN): δ 4.51 (s, br, 6H), 4.60 (s, br, 6H), 5.80 (m, br, 2H),
3
2
3
6
2
7
.11 (d, J = 7.5 Hz, 2H), 6.76 (t, J = 7.5 Hz, 2H), 6.81 (t, J = 7.6 Hz,
H), 6.93 (m, 2H), 7.13 (t, J = 7.7 Hz, 2H), 7.26 (d, J = 8.2 Hz, 2H),
3
6
1
3
.36 (d, J = 8.3 Hz, 2H), 7.70 (t, J = 7.6 Hz, 1H), 8.15 (br, 2H), 8.40
(d, J = 8.3 Hz, 2H), 6.99 (t, J = 7.8 Hz, 2H), 7.12 (t, J = 6.6 Hz, 2H),
7.35 (m, overlapped, 4H), 7.58 (d, J = 8.4 Hz, 2H), 7.79 (t, J = 7.9 Hz,
2H), 8.41 (m, overlapped, 3H), 8.55 (t, J = 8.1 Hz, 1H), 8.78 (d, J =
8.3 Hz, 2H), 8.82 (d, J = 8.1 Hz, 2H). ESI-MS: m/z 336.9 for [M −
+
(
t, J = 7.4 Hz, 1H), 8.50 (br, 2H). ESI-MS: m/z 778.4 for [M − PF ] .
6
Anal. Calcd for C H F N PRu·H O: C, 54.89; H, 3.86; N, 13.40.
43
34
6
9
2
Found: C, 55.27; H, 3.66; N, 13.57.
2+
Complex 2. To 10 mL of dry acetone were added Ru(Mebip)Cl3
55 mg, 0.1 mmol) and AgOTf (78 mg, 0.3 mmol). The mixture was
2PF
3.23; N, 11.21. Found: C, 43.38; H, 3.12; N, 11,40.
Complex 8. A mixture of Ru(Mebip)Cl (0.15 g, 0.27 mmol) and
6 28 12 8 2 2
] (z = 2). Anal. Calcd for C36H F N P Ru·2H O: C, 43.25; H,
(
refluxed for 2 h before cooling to room temperature. The precipitate
was removed by filtration, and the filtrate was concentrated to dryness.
To the residue were added 1,3-di-2-pyridylbenzene (23.2 mg, 0.1
mmol), DMF (8 mL), and t-BuOH (8 mL). The mixture was then
refluxed for 24 h. After cooling to room temperature, the solvent was
removed under reduced pressure, and the residue was dissolved in the
proper amount of methanol. After the addition of an excess of KPF6,
the resulting precipitate was collected by filtration and washing with
3
silver trifluoromethanesulfonate (AgOTf, 0.21 g, 0.82 mmol) was
heated in 60 mL of acetone with stirring under light-protecting
conditions for 2 h. After removal of the resulting AgCl precipitate by
filtration, the solvent was evaporated. 4,6-Dimethyl-1,3-di-2-pyridyl-
benzene (Medpb, 95 mg, 0.41 mmol) and n-butanol (n-BuOH; 60
mL) were then added to the filtrate, and heating at 140 °C was
continued for 15 h. After cooling to room temperature, the solvent was
evaporated in vacuo. The brown residue was purified by column
chromatography with CH CN/aqueous 0.5 M KNO (9:1, v/v) as the
water and Et O. The obtained solid was subjected to flash column
2
chromatography on silica gel (eluent: 10:1 CH Cl /CH CN) to give
2
2
3
3
3
1
2
8.5 mg of complex 2 (35%). H NMR (400 MHz, CD CN): δ 4.38
eluent. The addition of a saturated KPF aqueous solution to the main
3
6
(
7
(
s, 6H), 6.06 (d, J = 8.2 Hz, 2H), 6.57 (t, J = 6.5 Hz, 2H), 6.81 (t, J =
.7 Hz, 2H), 7.07 (d, J = 5.5 Hz, 2H), 7.22 (t, J = 7.7 Hz, 2H), 7.46
m, overlapped, 4H), 7.61 (t, J = 7.6 Hz, 1H), 8.03 (d, J = 8.0 Hz, 2H),
eluate resulted in precipitation of the product, which was collected by
filtration. Purification by recrystallization from CH CN/water afforded
3
1
48 mg of complex 8 in a yield of 20%. H NMR (500 MHz, DMSO-
8
2
.21 (t, J = 8.1 Hz, 1H), 8.34 (d, J = 7.6 Hz, 2H), 8.75 (d, J = 8.1 Hz,
d6): δ 4.15 (s, 6H), 4.48 (s, 6H), 5.95 (d, J = 8.6 Hz, 2H), 6.63 (t, J =
6.6 Hz, 2H), 6.85 (t, J = 7.4 Hz, 2H), 7.02 (d, J = 5.7 Hz, 2H), 7.19 (s,
1H), 7.21 (t, J = 7.7 Hz, 2H), 7.48 (t, J = 7.7 Hz, 2H), 7.67 (d, J = 8.6
+
H). ESI-MS: m/z 672.4 for [M − PF ] . Anal. Calcd for
6
C H F N PRu: C, 54.41; H, 3.46; N, 12.01. Found: C, 54.11; H,
37
28
6
7
3
.42; N, 12.04.
Hz, 2H), 8.12 (d, J = 8.0 Hz, 2H), 8.31 (t, J = 8.2 Hz, 1H), 8.92 (d, J =
+
Complex 3. To 10 mL of dry acetone were added Ru(tpy)Cl (52
8.0 Hz, 2H). ESI-MS: m/z 700.284 for [M − PF ] (M =
3
6
mg, 0.1 mmol) and AgOTf (78 mg, 0.3 mmol). The mixture was
refluxed for 2 h before cooling to room temperature. The precipitate
was removed by filtration, and the filtrate was concentrated to dryness.
To the residue were added Mebib (33 mg, 0.1 mmol), DMF (8 mL),
and t-BuOH (8 mL). The mixture then refluxed for 24 h. After cooling
to room temperature, the solvent was removed under reduced
pressure, and the residue was dissolved in the proper amount of
C H N PF Ru). Anal. Calcd for C H N PF Ru: C, 54.27; H,
39
32
7
6
39 32
7
6
3.97; N, 11.37. Found: 54.50; H, 4.00; N, 11.23. For X-ray
crystallographic analysis, a BPh salt of 8 was used instead of a PF
4
6
salt. [Ru(Mebip)(Medpb)](BPh ) was easily obtained by anion
4
exchange.
Complex 9. To 20 mL of dry n-BuOH were added complex 1
(93.8 mg, 0.1 mmol) and AgBF (260 mg, 1.3 mmol). The mixture
4
methanol. After the addition of an excess of KPF , the resulting
precipitate was collected by filtration and washing with water and
was refluxed for 5 h. After cooling to room temperature, the solvent
was removed under reduced pressure and the residue was dissolved in
the proper amount of methanol. After the addition of an excess of
6
Et O. The obtained solid was subjected to flash column chromatog-
2
raphy on silica gel (eluent: 10:1 CH Cl /CH CN) to give 27 mg of
KPF , the resulting precipitate was collected by filtration and washing
2
2
3
6
1
complex 3 (33%). H NMR (400 MHz, CD CN): δ 4.31 (s, 6H), 5.73
with water and Et O. The obtained solid was subjected to flash column
3
2
8
97
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Inorganic Chemistry
Article
chromatography on silica gel (eluent: 100:10:0.3 CH CN/H O/
3
2
AUTHOR INFORMATION
■
aqueous KNO ) to give 60.9 mg of complex 9 (65%). This complex is
3
Corresponding Author
*E-mail: zhongyuwu@iccas.ac.cn (Y.-W.Z.), mhaga@kc.chuo-u.
ac.jp (M.H.).
paramagnetic because of the presence of ruthenium(III) species, as
1
proved by the broadening of H NMR signals. MALDI-TOF: m/z
+
7
4
78.1 for [M − 2PF ] . Anal. Calcd for C H F N P Ru·C H O: C,
6
43 34 12
9
2
4
10
9.43; H, 3.88; N, 11.04. Found: C, 49.37; H, 3.79; N, 11.23. The UV/
vis absorption spectrum of complex 9 (Figure S7 in the Supporting
Information) is virtually identical with that of one-electron-oxidized
species of 1 recorded during spectroelectrochemical measurements
ACKNOWLEDGMENTS
■
Y.-W.Z. thanks the National Natural Science Foundation of
China (Grant 21002104), the National Basic Research 973
program of China (Grant 2011CB932301), and Institute of
Chemistry, Chinese Academy of Sciences (“100 Talent”
Program), for funding support. M.H. is grateful for the partial
financial support received from Chuo University Joint Research
Grant 2009 and thanks the Ministry of Education, Culture,
Sports, Science and Technology for a Grant-in-Aid for Priority
Area “Coordination Programming” (Grant 21108003) and also
for Scientific Research (Grant 21350082). We thank Prof.
Koichi Nozaki at the University of Toyama for measuring the
emission spectra and lifetimes.
(Figure 7a).
Electrochemical Measurements. All cyclic voltammograms were
taken using a CHI620D potentiostat or an ALS/CHI model 660A
electrochemical analyzer with a one-compartment electrochemical cell
under an atmosphere of nitrogen. A glassy carbon electrode with a
diameter of 0.3 mm was used as the working electrode. The electrode
was polished prior to use with 0.05 μm alumina and rinsed thoroughly
with water and acetone. A large-area platinum wire coil was used as the
counter electrode. All potentials are referenced to a saturated Ag/AgCl
electrode without regard for the liquid-junction potential. All
measurements were carried out in acetonitrile at a scan rate of 100
mV/s, in 0.1 M of Bu NClO (TBAP) as the supporting electrolyte.
4
4
Spectroscopic Measurements. UV/vis and near-IR (NIR)
spectra were recorded on a TU-1810DSPC, Agilent 8453, or a
Hitachi U-4000 UV/vis spectrophotometer at room temperature in
acetonitrile, with a conventional 1 cm quartz cell. The emission spectra
were recorded using a grating monochromator (Triax 1900, Jobin
Yvon) with a CCD image sensor (S7031, Hamamatsu). The emission
lifetime measurements were obtained by exciting deoxygenated
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samples with the Nd:YVO laser, using the system previously
4
25
described.
(
Oxidative Spectroelectrochemistry. Oxidative spectroelectro-
chemistry was performed in a thin-layer cell (optical length = 0.05 cm)
in which a platinum mesh working electrode was set. A platinum wire
(
and Ag/AgNO (0.01 M AgNO in 0.1 M TBAPF in CH CN) were
3
3
6
3
used as a counter electrode and a reference electrode. The cell was put
into the spectrometer to monitor the spectral change during
electrolysis.
Computational Methods. DFT calculations are carried out using
26
the B3LYP exchange correlation functional and implemented in the
2
7
Gaussian 03 program package. The electronic structures of
complexes were determined using a general basis set with the Los
Alamos effective core potential LanL2DZ basis set for ruthenium and
28
(
c) Wadman, S. H.; Havenith, R. W. A.; Hartl, F.; Lutz, M.; Spek, A.
L.; van Klink, G. P. M.; van Koten, G. Inorg. Chem. 2009, 48, 5685.
d) Jager, M.; Smeigh, A.; Lombeck, F.; Gorls, H.; Collin, J.-P.;
Sauvage, J.-P.; Hammarstrom, L.; Johannsson, O. Inorg. Chem. 2010,
9, 374. (e) Duprez, V.; Launay, J.-P.; Gourdon, A. Inorg. Chim. Acta
003, 343, 395. (f) Moorlag, C.; Wolf, M. O.; Bohne, C.; Patrick, B. O.
6
-31G* for other atoms in the vacuum.
X-ray Crystallography. A high-quality single crystal of [Ru-
Mebip)(Medpb)](BPh ) (red, needle) was mounted on a glass fiber
(
̈
̈
(
4
̈
and transferred into the cold nitrogen stream, and the X-ray diffraction
data were collected using a Bruker SMART APEXII ULTRA CCD
detector diffractometer on a rotating anode (Mo Kα radiation,
graphite monochromator, λ = 0.710 73 Å). Corrections for absorption
4
2
J. Am. Chem. Soc. 2005, 127, 6382.
(8) Wadman, S. H.; Lutz, M.; Tooke, D. M.; Spek, A. L.; Hartl, F.;
Havenith, R. W. A.; van Klink, G. P.; van Koten, G. Inorg. Chem. 2009,
8, 1887.
9) Arana, C. R.; Abrun
10) (a) Duati, M.; Tasca, S.; Lynch, F. C.; Bohlen, H.; Vos, J. G.;
Stagni, S.; Ward, M. D. Inorg. Chem. 2003, 42, 8377. (b) Duati, M.;
Fanni, S.; Vos, J. G. Inorg. Chem. Commun. 2000, 3, 68.
11) (a) Wadman, S. H.; Kroom, J. M.; Bakker, K.; Lutz, M.; Spek, A.
L.; van Klink, G. P. M.; van Koten, G. Chem. Commun. 2007, 1907.
b) Bessho, T.; Yoneda, E.; Yum, J.-H.; Guglielmi, M.; Tavernelli, I.;
Imai, H.; Rothlisberger, U.; Nazeeruddin, M. K.; Gratzel, M. J. Am.
Chem. Soc. 2009, 131, 5930. (c) Bomben, P. G.; Robson, K. C. D.;
Sedach, P. A.; Berlinguette, C. P. Inorg. Chem. 2009, 48, 9631.
d) Koivisto, B. D.; Robson, K. C. D.; Berlinguette, C. P. Inorg. Chem.
009, 48, 9644. (e) Bomben, P. G.; Koivisto, B. D.; Berlinguette, C. P.
Inorg. Chem. 2010, 49, 4960. (f) Wadman, S. H.; Kroon, J. M.; Bakker,
K.; Havenith, R. W. A.; van Klink, G. P. M.; van Koten, G.
Organometallics 2010, 29, 1569. (g) Bomben, P. G.; Theriault, K. D.;
Berlinguette, C. P. Eur. J. Inorg. Chem. 2011, 1806. (h) Robson, K. C.
29
were made by SADABS. The structure was solved by direct methods
2
using SHELXS-97 and refined anisotropically on F with SHELXL-
4
(
(
30
9
7. All hydrogen atoms except those of water molecules were located
̃
a, H. D. Inorg. Chem. 1993, 32, 194.
in their idealized positions, with methyl C−H bond length 0.98 Å and
aromatic C−H bond length 0.95 Å, and included in the refinement
using a riding model approximation. The corresponding CIF file is
available in the Supporting Information.
(
(
ASSOCIATED CONTENT
■
*
S
Supporting Information
Isodensity plots of frontier orbitals for complexes 2, 3, 5, and 6,
Cartesian coordinates of all of the optimized geometries,
TDDFT-predicted UV/vis spectra of complexes 1−3, 5, and 6,
absorption spectra of 1, 8, and 9, NMR and MS spectra of new
complexes, and a CIF file for complex 8. This material is
available free of charge via the Internet at http://pubs.acs.org.
(
2
8
98
dx.doi.org/10.1021/ic2016885 | Inorg. Chem. 2012, 51, 890−899

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