A redox asymmetric, cyclometalated ruthenium dimer: Toward upconversion dyes in dye-sensitized TiO2 solar cells

Article abstract of DOI:10.1021/om100865k

We have prepared the dinuclear ruthenium complexes [(R₃-tpy) Ru(N^C^N-tpy)Ru(tpy)]³⁺ (R = H ([5a]³⁺), CO₂Me ([6a]³⁺), N^C(H)^N-tpy = 4′-(3,5-dipyridylphenyl)-2,2′: 6′,2″-terpyridine, tpy = 2,2′:6′,2″-terpyridine) and [(R₃-tpy)Ru(N′^C^N′-tpy)Ru(tpy)]³⁺ (R = H ([5b]³⁺), CO₂Me ([6b]³⁺), N′^C(H) ^N′-tpy = 4′-(3,5-di(4-tert-butylpyridyl)phenyl)-2,2′: 6′,2″-terpyridine) in a stepwise manner. The directional nature of the bridging ligand, which is potentially cyclometalating on one side, induces large redox asymmetry in the resulting dinuclear complexes. One-electron oxidation gives rise to a strong metal-to-metal charge transfer transition from the [Ru(tpy₂)]²⁺ moiety to the cycloruthenated group, centered at 1034 nm for [6b]⁴⁺. The localized nature of the oxidation processes, the shape of the NIR band, and TD-DFT calculations allow assignment of these systems to localized Robin-Day class II. Exclusive substitution of the terminal tpy ligand on the cyclometalated ruthenium with acid moieties allows selective attachment of the dye to a semiconductor surface, whereby a possible two-step upconversion path is created in dye-sensitized solar cells for the utilization of low-energy photons.

Full text of DOI:10.1021/om100865k

Organometallics 2010, 29, 5635–5645 5635
DOI: 10.1021/om100865k
A Redox Asymmetric, Cyclometalated Ruthenium Dimer: Toward
Upconversion Dyes in Dye-Sensitized TiO2 Solar Cells^
Sipke H. Wadman,† Y. M. van Leeuwen,† Remco W. A. Havenith,§,‡
Gerard P. M. van Klink,† and Gerard van Koten*,†
†Chemical Biology & Organic Chemistry, §Theoretical Chemistry, Faculty of Science,
Utrecht University, Padualaan 8, 3584 Ch Utrecht, The Netherlands . ‡Also associated
with Electronic Structure of Materials, Radboud University Nijmegen,
Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
Received September 7, 2010
We have prepared the dinuclear ruthenium complexes [(R3-tpy)Ru(N∧C∧N-tpy)Ru(tpy)]3þ (R = H
([5a]3þ), CO2Me ([6a]3þ), N∧C(H)∧N-tpy∧=∧40-(3,5-dipyridylphenyl)-2,20:60,200-terpyridine, tpy =
2,20:60,200-terpyridine) and [(R3-tpy)Ru(N0 C N0-tpy)Ru(tpy)]3þ (R = H ([5b]3þ), CO2Me ([6b]3þ),
∧
N0 C(H)∧N0-tpy = 40-(3,5-di(4-tert-butylpyridyl)phenyl)-2,20:60,200-terpyridine) in a stepwise man-
ner. The directional nature of the bridging ligand, which is potentially cyclometalating on one side,
induces large redox asymmetry in the resulting dinuclear complexes. One-electron oxidation gives
rise to a strong metal-to-metal charge transfer transition from the [Ru(tpy2)]2þ moiety to the cyclo-
ruthenated group, centered at 1034 nm for [6b]4þ. The localized nature of the oxidation processes, the
shape of the NIR band, and TD-DFT calculations allow assignment of these systems to localized
Robin-Day class II. Exclusive substitution of the terminal tpy ligand on the cyclometalated
ruthenium with acid moieties allows selective attachment of the dye to a semiconductor surface,
whereby a possible two-step upconversion path is created in dye-sensitized solar cells for the
utilization of low-energy photons.
Introduction
sensitizer molecule and the following charge injection into
the conduction band of a semiconductor, usually anatase
TiO2, Figure 1. Several different sensitizers have been prepared
and tested such as organic molecules,7,8 porphyrins,9 phthalo-
cyanines,10,11 and transition metal complexes.12-15 Among
these sensitizers, polypyridine complexes of ruthenium have
displayed superior properties. The most well-known pigments
Solar energy is the most abundant renewable energy source
available to mankind. In fact, the resource base represented
by terrestrial irradiation exceeds by far that of all other
renewable energy sources combined.1,2 Semiconductor solar
cells offer high conversion efficiencies and long-term stabil-
ity, but the need for high-purity materials renders them expen-
€
3
sive. In 1991, Gratzel and co-workers showed that wide-
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T.; Karlsson, K. M.; Humphry-Baker, R.; Sun, L. C.; Hagfeldt, A.;
bandgap semiconductors can be sensitized to visible light
and that cheap and efficient solar cells can be obtained in this
way.4 With these dye-sensitized solar cells (DSSCs) energy
power conversion efficiencies (ηsun) up to 11% have been
reached.5,6 The crux of DSSCs is light absorption by a
€
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^ Part of the Dietmar Seyferth Festschrift. Dedicated to Prof. Dietmar
Seyferth in honor of his dedicated work and numerous inspiring contributions
to organometallic chemistry and its dissemination.
*To whom correspondence should be addressed. E-mail: g.vankoten@
uu.nl.
€
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2010 American Chemical Society
Published on Web 10/13/2010
pubs.acs.org/Organometallics

5636 Organometallics, Vol. 29, No. 21, 2010
Wadman et al.
Intervalence charge transfer (IVCT) transitions are known
to occur in symmetric bimetallic complexes upon partial
oxidation and are observed at very long wavelengths.25-27
When the bimetallic complex possesses redox asymmetry
between the metal moieties, the IVCT band is shifted to
higher energy, corresponding to the difference in oxidation
potential, which makes this type of transition very interesting
for regenerating the primary dye. Sufficient electronic com-
munication has to be ensured by covalently linking the indi-
vidual dye moieties. However, electronic coupling should not
be so strong that the redox centers lose their individuality
and form a Robin-Day class III delocalized system.28-30
Cyclometalation is an excellent tool to destabilize the
ground state of a complex as a result of the strong σ-donation
by a formally anionic carbon atom.31-36 The initial oxida-
tion potential can be significantly negatively shifted without
dramatically changing the overall geometry of the system. In
a bimetallic complex cyclometalation of only one metal
center will result in the necessary redox asymmetry in the
system. Moreover, we have already demonstrated that prop-
erly designed cyclometalated ruthenium complexes are effi-
cient and stable sensitizers for DSSC.37 More recently also
others have shown that other cyclometalated ruthenium
complexes are efficient sensitizers indeed.38,39
Figure 1. Operational scheme for DSSC (left) and upconversion
scheme employed (right). Please note that the photoelectrochemical
experiments described later utilize an HTM material that possesses
an energy level that is actually above the ground state of D1.
are the N719 dye [Ru(NCS)2(dcbpy)2] (dcbpy = 4,40-
dicarboxy-2,20-bipyridine)12 and the black dye [Ru(NCS)3-
(tctpy)]- (tctpy = 4,40,400-tricarboxy-2,20:60,200-terpyridine).13
Amphiphilic analogues of these dyes have been prepared in
order to decrease sensitivity toward water-induced decom-
position by forming a shielding hydrophobic layer. Exten-
sion of the conjugated system on the peripheral bpy ligand is
used to increase the extinction coefficient of the dye, and this
allows for the use of thinner, more efficient layers. The ideal
sensitizer for a single layer cell should absorb all light below
920 nm and convert it into electricity with unit efficiency.
Photons that do not possess sufficient energy to bridge this
threshold will not contribute to the current, resulting in a low
theoretical maximum efficiency. In multilayered semicon-
ductor stacked cells, low-energy photons are used to increase
the voltage, but matching of the current from the individual
layers is necessary. Using this approach power conversion
efficiencies as high as 40% have been reached upon concen-
tration of the solar light.3 We propose a similar way to utilize
low-energy photons in DSSCs, Figure 1.16 The setup consists
of two dye moieties, one of which is attached to the TiO2
surface. Upon excitation of this primary dye, it injects an
electron into the TiO2 CB, replicating a standard sensitizer.
This is rather similar to antennae or donor-acceptor systems
that have been utilized earlier, in which the excitation energy
is transferred to the titania surface, where the actual charge
injection takes place, a principle that has been utilized since
the early days of sensitized solar cells.4,17-24 However, this
dye, D1, is not regenerated by electron transfer from the
electrolyte, as is common practice. Instead it is regenerated
by optical electron transfer from a second dye moiety,
D2, which is in turn regenerated from the electrolyte.
We have prepared a redox asymmetric, dinuclear ruthe-
nium compound with a bridging ligand that is N,C,N0-
cyclometalated to one ruthenium center and N,N0,N00-coor-
dinated t∧o the second ruthenium center. The bridging ligand
N∧C(H) N-tpy (40-(3,5-dipyridylphenyl)-2,20:60,200-terpyr-
idine) is reported in the literature, and the redox symmetric
complexes support sufficient electronic communication to
observe a well-defined IVCT transition at 2360 nm.40-42
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Article
Organometallics, Vol. 29, No. 21, 2010 5637
These systems are defined as Robin-Day class II,28 since
electronic communication is present but the system is well
described using localized states. We have prepared the com-
plexes [(R3-tpy)Ru(N∧C∧N-tpy)Ru(tpy)]3þ (R = H ([5a]3þ),
CO2M∧e ([6a]3þ)) and its t-Bu-subst∧ituted analogue [(R3-tpy)-
Ru(N0 C∧N0-tpy)Ru(tpy)]3þ (N0 C(H)∧N0-tpy = 40-(3,5-
di(4-tert-butylpyridyl)phenyl)-2,20:60,200-terpyridine), R =
H ([5b]3þ), CO2Me ([6b]3þ)) in a stepwise manner. The new
t-Bu-substituted ligand aids tremendously in raising the solubil-
ity of the resulting complexes, which is otherwise problematic at
best. A number of experimental techniques are used to analyze
the electronic properties of these complexes, which are supported
by TD-DFT calculations. The individual electron transfer pro-
cesses necessary for the upconversion scheme to be exerted are
demonstrated. Selective introduction of anchoring groups on the
cyclometalated moiety allows grafting of the complexes to a
semiconductor surface in a well-defined manner. After deprotec-
tion of the esters in [6b]3þ to free carboxylates in [8b] thecomplex
can be incorporated in an operational dye-sensitized solar cell.
Scheme 1. Synthesis and NMR Numbering Scheme of Free
Ligands 3aH and 3bHa
Results
Synthesis. The bridging ligands 3aH and 3bH were pre-
pared as outlined in Scheme 1. Starting from 3,5-dibromo-
a Conditions: (i) 2-acetylpyridine, NaOH, MeOH, room temperature,
1 h, (ii) 1-(2-oxo-2-(pyridin-2-yl)ethyl)pyridinium iodide, NH4OAc,
MeOH, reflux, 20 h, (iii) N,N-dimethylethanolamine, n-BuLi, SnClBu3,
hexane, -70 ꢀC, (iv) LiCl, [Pd(PPh3)4], toluene, reflux, 24 h.
43
benzaldehyde using a two-step Krohnke -type condensa-
€
tion reaction, 1 could be obtained in 75% overall yield.
3,5-Dibromobenzaldehyde was first converted to a chal-
cone by aldol condensation with acetylpyridine, which was
then reacted with 1-(2-oxo-2-(pyridin-2-yl)ethyl)pyridinium
iodide in the presence of NH4OAc as nitrogen source to form
the central pyridine ring. The resulting dibromide was reacted
with stannane 2a, and the desired ligand was obtained in 89%
yield and ultimately prepared on a multigram scale. The pres-
ence of copper44 or lithium salts45 in this catalyzed C-C cou-
pling reaction is beneficial, since they compete with palladium
for coordination to the product, which is a good ligand for
platinum group metals and inhibits the catalyst. For the pre-
paration of the t-Bu-substituted bridging ligand the same
methodology was adopted, using stannane 2b in the final step.
Stannane 2b was prepared directly from 4-tert-butylpyridine by
selective lithiation using n-BuLi/LiDMAE aggregate46 instead
of first introducing a bromine atom at the 2 position.47
The bimetallic complexes were prepared in a two-step
procedure, Scheme 2. By reacting ligand 3aH with [RuCl3-
(tpy)] the monometallic complex [4aH]2þ was obtained. Addi-
tional species were also synthesized, including the compound
in which the bridging ligand is coordinated in a cyclometa-
lated fashion, [7a]þ. The desired compound [4aH]2þ could
be isolated by sequential column chromatography on SiO2
and Al2O3 in 19% yield. Reaction of [4aH]2þ with another
equivalent of [RuCl3(tpy)] or [RuCl3((CO2Me)3tpy)] allows
the preparation of the cyclometalated compounds [5a]3þ and
[6a]3þ, respectively. Increased yields of [6a]3þ could be obtained
using μ-wave-assisted heating. Reaction of the substituted
ligand 3bH is more selective and allows the isolation of the
monometallic complex [4bH]2þ in 56% yield. Using μ-wave-
assisted heating, cyclometalated [5b]3þ could be prepared by
reaction of [4bH]2þ with [RuCl3(tpy)] in ethylene glycol. The
ester-substituted [6b]3þ was prepared using μ-wave irradia-
tion in MeOH at 97 ꢀC in a closed vessel. Deprotection of the
ester functionalities in [6a]3þ and [6b]3þ to the free deproto-
nated acids [8a] and [8b] (see Scheme 2), respectively, could
be performed by heating a solution of the complex in MeCN
solution in the presence of H2O and using NEt3 as base.
Electrochemical Data. The half-wave oxidation and reduc-
tion potentials in MeCN solution as determined by cyclic
voltammetry (CV) for the complexes are summarized in
Table 1. For the more soluble t-Bu-substituted complexes,
[4bH]2þ, [5b]3þ, and [6b]3þ, it was also possible to determine
the respective electrode potentials in CH2Cl2. For the mono-
metallic complexes a single metal-based48 oxidation is present,
while for the bimetallic complexes two distinct waves are ob-
served. Cyclometalation shifts the oxidation potential by about
0.7 V to less positive values. The oxidation process correspond-
ing to the [Ru(tpy)2]2þ moiety is rather constant throughout
the series. The redox asymmetry, as defined by ΔE1/2(ox)=
E1/2(ox2) - E1/2(ox1), is slightly solvent dependent.
Electronic Absorption Spectroscopy. The UV-vis ab-
sorption spectra of complexes in this study are depicted in
Figure 2 and summarized in Table 2.
Polypyridine complexes of ruthenium are characterized
by strong ligand-centered (LC) π-π* transitions in the UV
region and moderately intense metal-to-ligand charge trans-
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5638 Organometallics, Vol. 29, No. 21, 2010
Scheme 2. Synthesis and NMR Numbering Scheme of Complexes Used in This Studya
Wadman et al.
a Conditions: (i) [RuCl3(tpy)], AgBF4, MeOH, reflux, 20 h, (ii) [RuCl3(tpy)], N-methylmorpholine, ethylene glycol, μ-wave, 150 ꢀC, 30 min or
[RuCl3((CO2Me)3tpy)], N-methylmorpholine, MeOH, μ-wave, closed vessel, 97 ꢀC, 30 min, (iii) NEt3, MeCN, H2O, 70 ꢀC, 40 h.
Table 1. Electrochemical Dataa for [4aH]2þ, [4bH]2þ, [7a]þ,
[5a]3þ, [5b]3þ, [6a]3þ, and [6b]3þ
E1/2 (V) (ΔEp (mV))
ΔE1/2(ox)
II
III
•-
cation Ru0 /Ru0
RuII/RuIII
L/L•-
L0/L0
(V)b
[4aH]2þ
[4bH]2þ
0.88 (59) -1.65 (66) -1.93 (100)
0.88(64)
0.93 (68)c -1.61 (70)c
-1.63 (60) -1.88 (73)
[7a]þ
0.16 (59) -1.91 (73)
[5a]3þ
[5b]3þ
0.89 (69)
0.89 (89)
0.20 (63) -1.67 (58) -1.91 (86)d
0.17 (59) -1.67 (60) -1.93 (95)e
690
710
800
530
560
610
0.92 (93)c 0.12 (64)c -1.67 (75)c
[6a]3þf
[6b]3þg
0.90 (65)
0.90 (61)
0.37 (58) -1.48 (68) -1.68 (50)
0.34 (59) -1.48 (58) -1.61 (55)
0.93 (80)c 0.32 (59)c -1.56 (63)c -1.69 (63)c
a Data collected in MeCN with [n-Bu4N]PF6 as supporting electrolyte
at 100 mV/s; potentials reported vs ferrocene/ferrocenium (Fc/Fcþ) used
as internal reference. b Redox asymmetry, separation between the two
successive RuII/RuIII couples (ΔE1/2(ox) = E1/2(ox1) - E1/2(ox2)).
c Data collected in CH2Cl2. d Product adsorbs on electrode surface.
e Two overlapping one-electron processes. f Two overlapping one-
electron processes observed at -1.89 (210) V. g Two overlapping one-
electron processes observed at -1.83 V (140 mV).
Figure 2. Electronic absorption spectra of [4aH]2þ (dotted, black),
[4bH]2þ (dotted, red), [7a]þ (dash dot, black), [5a]3þ (dash,
black), [5b]3þ (dash, red), [6a]3þ (solid, black), [6b]3þ (solid, red)
in MeCN.
The different tpy and N∧C∧N groups result in the presence of
many overlapping LC absorptions in the UV. The mono-
nuclear complex [4aH]2þ displays visible MLCT features
non-cyclometalated analogues.36,53-55 The absorption spec-
tra of the dinuclear, cyclometalated complexes [5a]3þ and
[6a]3þ are clearly not a superimposition of the spectra of the
mononuclear units. Obviously, many different transitions
are involved in the visible absorption feature. An especially
large increase in absorption is observed at the low-energy
side of the MLCT band. These low-energy features are most
likely assigned to transitions from the cyclometalated ruthe-
nium center to the terminal tpy ligand. Introduction of the
very similar to those observed for [Ru(tpy)2]2þ 52
As is
.
commonly observed for cycloruthenated complexes, the
visible absorption features of the mononuclear, cyclometa-
lated complex [7a]þ are red-shifted, broadened, and slightly
decreased in molar absorption coefficient compared to the
(52) Maestri, M.; Armaroli, N.; Balzani, V.; Constable, E. C.;
Thompson, A. M. W. C. Inorg. Chem. 1995, 34 (10), 2759–2767.
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Chim. Acta 1991, 186 (1), 91–93.
(54) Constable, E. C.; Hannon, M. J. Inorg. Chim. Acta 1993, 211 (1),
101–110.
(55) Barigelletti, F.; Ventura, B.; Collin, J. P.; Kayhanian, R.;
Gavina, P.; Sauvage, J.-P. Eur. J. Inorg. Chem. 2000, No. 1, 113–119.

Article
Organometallics, Vol. 29, No. 21, 2010 5639
Table 2. Electronic Absorption Data for [4aH]2þ, [4bH]2þ, [7a]þ, [5a]3þ, [5b]3þ, [6a]3þ, and [6b]3þ
max (nm) in MeCN max (nm) in CH2Cl2
λ
λ
complex
(ε (103 M-1 cm-1)) (ε (103 M-1 cm-1))
[4aH]2þ
482 (19.5), 307 (67.3),
484, 309, 283, 242a
281 (82.6), 241 (69.9)
[4bH]2þ
[7a]2þ
[5a]3þ
[5b]3þ
482 (23.7), 308 (75.3),
282 (70.1), 240 (59.8)
540 (sh), 502(15.7), 379 (19.2),
278 (72.3), 241 (63.6)
540 (35.6), 481(sh), 350 (sh),
309 (99.5), 280 (76.8), 235 (68.9)
545 (39.8), 500 (sh), 350 (sh),
309 (107.1), 278 (83.4), 233 (sh)
768 (sh), 570 (sh), 511 (35.4), 423 (22.8), 308 (82.5), 295 (84.6).
779 (sh), 575 (sh), 515 (39.3),
424 (sh), 308 (92.0), 295
483 (24.1), 309 (79.4), 283
(69.0), 275 (70.0)
590 (sh), 544 (sh), 505, 377,
281a
554, 523 (sh), 485 (sh),
309, 282, 235a
560 (sh), 528 (34.2), 310
(11.3), 282 (89.9)
[6a]3þ
[6b]3þ
805(sh), 655 (sh), 585 (sh), 517, 427, 309, 296.a
813 (sh), 670 (sh), 589 (sh),
522 (34.4), 491 (sh), 436
(31.7), 309 (99.6), 297 (100.0)
(92.1), 210 (115.4)
a ε was not determined due to low solubility in CH2Cl2.
Table 3. Low-Energy Bands for [5a]4þ, [5b]4þ, [6a]4þ, and [6b]4þ
upon Chemical Oxidation in MeCN
λ
max(exp) (nm) (ν~max(exp) (cm-1))
(Δν~1/2 (cm-1)) (ε (103 M-1 cm-1))
calc λ0max (cm-1 a
Δν~1/2, calc (cm-1 b
)
)
MeCN
CH2Cl2
MeCN
[5a]4þ
[5b]4þ
[6a]4þ
[6b]4þ
956 (10 460)
(4174) (5.0)
939 (10 650)
(5097) (6.2)
1057 (9461)
(3828) (6.3)
1034 (9671)
(4000) (7.2)
945 (10 582)
(4155)
904 (11 062)
(4260) (5.3)
1061 (9425)
(3955)
4895
3355
4925
3365
5185
3450
5155
3440
1014 (9862)
(4405) (6.4)
a Calculated using λ0max = λmax þ ΔE1/2, ox
.
b Calculated using the
Hush formula using the reduced value for the absorption maxima; see
main text.
t-Bu moiety results in a small bathochromic shift as it further
destabilizes the metal center by electron donation. Addition-
ally, the t-Bu moiety seems to have a small hyperchromic
effect. The electronic spectrum of fully protonated [H38b]Cl3
in DMSO in the presence of an excess of HCl closely re-
sembles that of [6b]2þ, while the shape of the visible features
is distinctively changed when [8b] is fully deprotonated by an
excess of NaOH (Figure 4).
Figure 3. UV-vis-NIR spectra recorded during chemical oxi-
dation of [6b]3þ to [6b]4þ in MeCN (red to blue). The absorptions
of [5a]4þ predicted by TD-DFT in vacuo are given as black bars.
formula, and it is thus considered a Robin-Day class II
system.28 On the other hand, the band for bis-cyclometalated
[(Ru(tpy))2(μ-N∧C∧N-N∧C∧N)]2þ is rather narrow and,
moreover, solvent independent, and the system can be
considered borderline class II-III.25-27 To an approxima-
tion the Hush formula can be extended to asymmetric
systems, where the Gaussian-shaped band is0 shifted by the
Near-Infrared Spectra. The near-infrared (NIR) spectra of
the singly oxidized dinuclear complexes [5a]4þ, [5b]4þ, [6a]4þ
,
and [6b]4þ were recorded in MeCN and CH2Cl2, Table 3.
Oxidation was performed by titration with a concentrated
solution of (NH4)2[Ce(NO3)6] in MeCN or SbCl5 in CH2Cl2,
and the original spectrum was fully regenerated upon addi-
tion of an excess of ferrocene. Representative results ob-
tained for [6b]4þ are depicted in Figure 3. Upon oxidation,
the MLCT features are partly diminished and a broad band
arises in the NIR. One-electron oxidation of the symmetric
complexes [(Ru(tpy))2(μ-tpy-tpy)]4þ and [(Ru(tpy))2(μ-
N∧C∧N-N∧C∧N)]2þ into the mixed valence state resulted
in the observation of an IVCT transition at 1580 and 1936
nm, respectively.42 For symmetric, weakly coupled, class II
mixed valence systems the bandwidth of the NIR IVCT tran-
redox asymmetry and is centered at λ0max (λ max = λmax
þ
ΔE1/2(ox)).25 Using ΔE1/2(ox) obtained from CV in the
appropriate solvent as an upper limit, the theoretical band-
widths can be derived, Table 3. Compared to the reported
λmax for the symmetric compounds, λ0max is consequently
calculated at decreased energy, indicating that ΔE1/2(ox) is
overestimated from CV data. Data collected in CH2Cl2 are
also represented in Table 3, with all low-energy bands
showing solvatochromism.
Being very much aware of the severe limitations of TD-
DFT in these systems, we utilized it nonetheless as an indi-
cative tool for the nature of the IVCT transition in [5a]4þ. A
complete listing of the applied methodology, electronic
transitions, energy levels, isovalue plots,56 and Mulliken
sition can be predicted from the Hush formula (Δν1/2
=
(16RTln 2(λmax))1/2, R = 0.695 cm-1 K-1, T = 298 K (e.g.,
=
for [5a]4þ; Δν1/2 = (16 ꢀ 0.695 ꢀ 298 ꢀ 0.693 ꢀ 4895)1/2
3355 cm-1)).27 In the case of the nonmetalated [(Ru(tpy))2(μ-
(56) Schaftenaar, G.; Noordik, J. H. J. Comput. Aided Mater. Des.
2000, 14 (2), 123–134.
tpy-tpy)]4þ the bandwidth is well predicted by the Hush

5640 Organometallics, Vol. 29, No. 21, 2010
Wadman et al.
population analysis57 of the frontier molecular orbitals can
be found in the Supporting Information. In [5a]3þ the three
highest occupied molecular orbitals (HOMOs) are asso-
ciated with the cyclometalated ruthenium, while HOMO-4,
HOMO-5, and HOMO-6 are associated with the all-
N-coordinated metal. The lowest unoccupied spin orbital
(LUSO) is localized on the cyclometalated ruthenium in
[5a]4þ. The highest occupied spin orbitals (HOSOs) are
localized on the second ruthenium center. A strong transi-
tion is predicted for [5a]4þ at 1060 nm ( f = 0.173) assigned to
β-HOMO-1 f β-LUMO, Figure 3.
Photoelectrochemical Experiments. A solid-state dye-sen-
sitized solar cell was constructed using the soluble [H28b]Cl2
precipitated from DMSO solution as sensitizer and 2,20-7,70-
tetrakis(N,N-bis(4-methoxyphenyl)amino)-9,90-spirobifluo-
rene (spiro-MeOTAD) as solid hole-conducting material.58,59
It has to be noted that the exact degree of protonation of [8b]
is unknown, as HCl slowly escapes from the dry solid (the
degree of protonation can be judged from NMR spectros-
copy but changes over time as the compound is dried). Under
sunlight simulated by a LumiLED lightsource (mismatch
15-20%) the cell reached a power conversion efficiency of
1.37% with open circuit voltage Voc = 724 mV, short circuit
current Isc = 2.6 mA, and fill factor ff = 0.73. The incident
photon-to-current conversion efficiency (IPCE) spectrum of
this cell was measured using a 300 W Xe lamp with 10 nm
step width (Figure 4).
Figure 4. Photocurrent action spectrum of [H28b](Cl)2 in a solid-
state DSSC (squares). Normalized absorption spectra of [Hx8b]xþ
in DMSO in the presence of NaOH (black) or HCl (red).
the free carboxylates, the resulting complex, i.e., [8b], is
soluble in MeOH and DMSO, especially upon addition of
two additional equivalents of aqueous HCl. Its identity and
purity could be confirmed using 1H and 13C NMR spectros-
copy.
Discussion
Electrochemical Data. It has already been put forward that
care has to be taken in using localized descriptions of molec-
ular orbitals and transitions in cyclometalated complexes,60-63
because orbitals formally associated with the metal center
may have a significant component on the cyclometalated
ligand and vice versa. However, the HOMOs are still well
described as metal-based, and for ease of discussion we will
continue to use terms associated with localized descriptions.
The extra electron density at the ruthenium nucleus from the
strong σ-donation of the anionic carbon places the oxidation
potential of [7a]þ at 700 mV less positive values than that of
[4aH]2þ, similar to the negative shifts for the oxidation
potential of other cyclometalated ruthenium complexes.36,53-55
Introduction of the t-Bu and CO2Me moieties shifts the
oxidation potential of the ruthenium center negatively and
positively, respectively, in line with the respective Hammett64
parameters σp=-0.20 and 0.45. Several reduction processes
are observed that are assigned to successive reduction of the
different tpy ligands in the complexes. In the dinuclear
complexes [5a]3þ-[6b]3þ two successive and electrochemi-
cally reversible one-electron oxidation waves are observed,
which are assigned to the stepwise oxidation of the two metal
centers.
Synthesis. Ligand 3aH has been previously reported, but
was prepared on a 25 mg scale with 2% overall yield, using a
pyridine condensation and Negishi cross-coupling methodo-
logy.42 The methodology applied here allows easy prepara-
tion of the bridging ligands on a multigram scale. Further-
more, it allows for easy functionalization of the ligand.
Introduction of the t-Bu moieties increases the solubility of
the ligands and corresponding complexes. As a result 3bH is
soluble in common organic solvents, while 3aH is soluble
only in halogenated solvents but sparingly in other solvents.
Reaction of 3aH with [RuCl3(tpy)] is only slightly selective
toward the N,N0,N00-coordinating side. As a result, a mixture
of several complexes was obtained, but the desired product
[4aH]2þ could be isolated by repeated column chromatogra-
phy. Reaction with 3bH is more selective, probably as a
result of the decreased reactivity of the potentially cyclome-
talating moiety by steric interference, electronic effects on the
coordinating nitrogen, or changed acidity of the C-H bond.
The bimetallic compounds could be obtained by reaction of
the monometallic complexes with the appropriate ruthenium
precursor. Fast and effective reactions could be achieved
using μ-wave-assisted heating in a closed vessel. Whereas the
unsubstituted [5a]3þ is rather insoluble in MeCN and its 13
C
In symmetric, dinuclear metal complexes, splitting of the
individual oxidation waves is usually taken as an indication
NMR spectrum could be obtained only in DMSO-d6, the
t-Bu- and ester-substituted [6b]3þ are highly soluble in MeCN,
acetone, and CH2Cl2. Deprotection of [6a]3þ resulted in the
formation of a dark solid that is insoluble in common organic
solvents. After deprotection of the ester moieties in [6b]3þ to
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Article
Organometallics, Vol. 29, No. 21, 2010 5641
of metal-metal interaction, although other effects may
play a non-negligible role.65-67 In [{Ru(ttpy)}2(μ-tpy-tpy)]4þ
and [{Ru(ttpy)}2(μ-N∧C∧N-N∧C∧N)]2þ (ttpy = 40-tolyl-
2,20:60,200-terpyridine) the separation between the two oxida-
tion waves is 70 and 170 mV, respectively, and the IVCT
band is indeed much stronger in the latter.41,42,68 Delocaliza-
tion of the metal states over the cyclometalated bridging
ligand increases the electronic communication between the
metal centers. In unsymmetric complexes, the redox asym-
metry (ΔE1/2(ox)) hampers direct determination of the inter-
action-induced splitting between the respective redox waves.
The difference between the two waves in [5a]3þ is smaller
than the difference observed between the oxidation poten-
tials of [4aH]2þ and [7a]þ. This is a result of the positive shift
of the oxidation potential of the cyclometalated ruthenium
moiety upon coordination of the tpy moiety on the bridging
ligand.
Near-Infrared Spectra. Upon one-electron oxidation of
the bimetallic complexes [5a]3þ-[6b]3þ, the MLCT feature
is partly diminished, with the remaining MLCT band very
akin to the band observed for the mononuclear complexes
[4aH]2þ and [4bH]2þ. This corresponds with an initial anodic
step localized on the cyclometalated ruthenium center. The
new low-energy transition is assigned IVCT character. It has
to be noted that the term IVCT is strictly speaking not
applicable to unsymmetric systems, where the diabatic states
are of different energy. But we will continue to use the term
for ease of discussion. As a result of the redox asymmetry, the
IVCT bands are observed at increased energy compared to
that observed for the redox symmetric analogues. The redox
asymmetry ΔE1/2(ox) as obtained from CV data can be used
to estimate the theoretical bandwidth with the Hush for-
mula. All observed bandwidths are larger than the calculated
values, which indicates localized Robin-Day class II behav-
ior.28 The IVCT NIR band is therefore expected to possess
significant charge transfer character, which should result in
strong solvent dependence of the energy of this excitation.
Indeed, the low-energy absorption feature is solvatochromic.
However, the energy shift of this transition can also be
ascribed to the dependence of ΔE1/2(ox) on the solvent.
Extreme care has to be taken in using DFT for extended
binuclear systems, as DFT often results in artificial over-
estimation of delocalization.69-71 The energy of CT excita-
tions can be strongly underestimated by TD-DFT, especially
for weakly interacting systems.71 Additionally, spurious
charge transfer states might be present. Indeed, for [5a]3þ
two strong excitations are predicted around 680 nm, viz., at
lower energy than the main experimental MLCT features.
These transitions are assigned large CT character from the
cyclometalated ruthenium to the tpy moiety of the bridging
ligand, which is unlikely to be a transition of high inten-
sity. However, even with the tendency of DFT toward
delocalization, the metal levels are localized on the individual
ruthenium centers. In silico one-electron oxidation results in
a LUSO associated with the cyclometalated ruthenium
center and HOSOs associated with the second metal center.
These results corroborate metal-based initial and secondary
oxidation processes. The predicted strong NIR transition for
the one-electron-oxidized [5a]4þ at 1060 nm is assigned
metal-to-metal charge transfer character with some involve-
ment of the bridging ligand. For all the uncertainty involved
in applying TD-DFT in this fashion, this excitation supports
the experimental assignment of the absorption as an unsym-
metric class II IVCT transition.
Photoelectrochemical Experiments. A simple DSSC was
constructed to investigate some of the sensitizing properties
of the dinuclear dye [8b]. With the dye complex attached to
the TiO2 surface, many individual processes can occur. Upon
absorption of the first photon, either dye moiety D1 or D2 is
excited, eqs 1 and 2, respectively. D1 represents the cyclo-
metalated moiety of [8b], D2 the [Ru(tpy)2]2þ moiety, and
HTM the hole transfer medium. As dye moiety D1 is directly
attached to the TiO2 surface, electron injection into the TiO2
conduction band (CB) from its excited state is fast, eq 3.
Direct electron injection from the second dye moiety D2 can
also occur, reaction 4. It has previously been demonstrated
that in a [{RuCl(dcbpy)2}BL{OsCl(bpy)2}]2þ (dcbpy = 4,40-
dicarboxyl-2,20-bipyridine, BL = 1,2-bis(4-pyridyl)ethane)
direct electron transfer from the osmium moiety to the TiO2
conduction band occurred, eq 4, mediated by the flexible BL
that allows proximity to the surface.18 Direct electron trans-
fer is unlikely to occur in [8b], as the D2 moiety is remote
from the surface and, moreover, efficient energy transfer can
occur to the D1 moiety, eq 5. After excitation transfer, the
dye moiety D1 can inject an electron into the TiO2 CB.
ꢁ
TiO2-D1-D2- HTM þ hν f TiO2-D1 -D2- HTM ð1Þ
ꢁ
TiO2-D1-D2- HTM þ hν f TiO2-D1-D2 - HTM ð2Þ
-
þ
ꢁ
TiO2-D1 -D2- HTM f TiO2ðe Þ-D1 -D2- HTM
ð3Þ
ð4Þ
ð5Þ
TiO2-D1-D2 - HTM f TiO2ðe Þ-D1-D2þ- HTM
-
ꢁ
ꢁ
ꢁ
TiO2-D1-D2 - HTM f TiO2-D1 -D2- HTM
The thus formed TiO2(e-)-D1þ-D2-HTM can undergo
several processes. Depending on the redox level of the HTM,
D1 can be directly regenerated, eq 6. Spiro-MeOTAD was
used as hole-conductor material, as with its oxidation po-
tential of E1/2(ox1) = 0.11 V and E1/2(ox2) = 0.23 V in
CH2Cl272 only a small driving force is present for regenera-
tion of the primary dye [6b]2þ with E1/2(ox1) = 0.32 V vs Fc/
Fcþ, which should thus be slow. Additionally to the small
driving force, the D1 moiety is shielded from the solid-state
HTM by D2, further slowing direct regeneration according
to eq 6. However, in the current setup direct regeneration
cannot be excluded as the main transfer pathway to regen-
erate D1. Future investigations will focus on alternative
HTM materials that could utilize the potential increase in
open circuit voltage as well as time-resolved data that could
clarify the time-scale of each of these processes.
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5642 Organometallics, Vol. 29, No. 21, 2010
Wadman et al.
As demonstrated by the solution experiments, when D1 is
oxidized, the MLCT features of the D2 moiety remain and
this group can absorb another photon to form the excited
state TiO2(e-)-D1þ-D2*-HTM. Excited-state electron
transfer can now occur, as D2* is a stronger reductant than
both D1 and D2, thus forming TiO2(e-)-D1-D2þ-HTM,
eq 7. Perhaps a more interesting process is the direct regen-
eration of D1 by optical electron transfer from D2, eq 8,
which corresponds to the metal-to-metal charge transfer
transition that was demonstrated in solution and occurs
around 1000 nm (i.e., at energies below the threshold
assumed for conventional sensitizers).
tations can have a tremendous influence on the rate or
intensity of the absorption associated with the individual
processes. For instance, decreasing the electronic coupling
will decrease the intensity of the NIR band associated with
eq 8, but will also decrease the rate of eq 10, viz., the
corresponding back electron transfer. Tuning of these levels,
as well as further decreasing the position of the HTM level, is
necessary to use the low-energy photons in this fashion to
increase the open circuit voltage in dye-sensitized solar cells.
Conclusion
We have prepared a series of redox asymmetric diruthe-
nium complexes using the monocyclometalating bridging
ligand N∧C(H)∧N-tpy and its t-Bu-substituted analogue.
The t-Bu moieties ensure higher solubility of the ligand and
the corresponding complexes and increase the selectivity of
formation of the mononuclear nonmetalated complex. Sub-
sequent cyclometalation could be performed by direct C-H
activation in methanol using μ-wave-assisted heating. The
bimetallic complexes undergo reversible metal localized first
and second oxidation processes. Cyclometalation induces
strong redox asymmetry by positively shifting the electrode
potential of the oxidation of the affected ruthenium center.
The visible electronic absorption spectra are dominated by
strong MLCT features, resulting from the presence of many
different transitions. One-electron oxidation into the mixed
valence state diminishes the visible absorption band, while
the MLCT features of the nonmetalated moiety are pre-
served. Additionally, a strong NIR absorption band arises
that is associated with a metal-to-metal charge transfer
transition. The localized nature of the oxidation processes,
the shape of the NIR band, and TD-DFT calculations allow
assignment of these systems as Robin-Day class II. Initial
tests in a solid-state DSSC indicate that the proposed two-
photon process could be operational, but no direct evidence
was obtained and additional tests are necessary. As it stands,
the asymmetric dinuclear ruthenium compound described
here represents the first model for a sensitizer for an upcon-
version scheme in DSSCs that could greatly increase the
maximum theoretical efficiency of these solar cells.
TiO2ðe- Þ-D1þ-D2- HTM f TiO2ðe- Þ-D1-D2- HTMþ ð6Þ
þ
TiO2ðe- Þ-D1þ-D2- HTM þ hν f TiO2ðe- Þ-D1 -D2
ꢁ
- HTM f TiO2ðe- Þ-D1-D2þ- HTM
ð7Þ
ð8Þ
TiO2ðe- Þ-D1þ-D2- HTM þ hν
f TiO2ðe- Þ-D1-D2þ- HTM
The TiO2(e-)-D1-D2þ-HTM state can either be regen-
erated by the electrolyte according to eq 9 or can relax back
to the TiO2(e-)-D1þ-D2-HTM state, eq 10. Additionally,
back electron transfer from the TiO2 CB to either the D1þ or
D2þ cation or to the HTM itself (eqs 11-13) can occur,
which is generally a slow process, especially when the dis-
tance between the surface and the cation is increased.
TiO2ðe- Þ-D1-D2þ- HTM f TiO2ðe- Þ-D1-D2- HTMþ ð9Þ
TiO2ðe- Þ-D1-D2þ- HTM f TiO2ðe- Þ-D1þ-D2- HTM ð10Þ
TiO2ðe- Þ-D1þ-D2- HTM f TiO2-D1-D2- HTM
ð11Þ
TiO2ðe- Þ-D1-D2þ- HTM f TiO2-D1-D2- HTM
TiO2ðe- Þ-D1-D2- HTMþ f TiO2-D1-D2- HTM
ð12Þ
ð13Þ
It should be noted that the IPCE curve is measured
monochromatically and is sensitive only to photons of
sufficient energy to produce current. In this aspect, no IPCE
is expected for the low-energy absorption feature, as no
pathway is available in which photons of this energy inject
electrons, and photons of higher energy are essential to
produce current. Also in efficiency measurements, no up-
conversion process would be measurable, as no wavelength-
dependent information is available. Direct regeneration of
D1 by the electrolyte according to eq 6 is probably a slow
process, resulting in low efficiency. Thus, no direct evidence
is available that the two-photon process as proposed in
Figure 1 is operational in the cell. However, the individual
processes that are necessary for such a scheme have been
demonstrated in a single bimetallic cyclometalated complex.
Additional tests that allow, for instance, time-resolved ob-
servation of the stepwise processes are necessary. Also IPCE
determination under bias illumination (in the presence of
photons of sufficiently low energy) would be instrumental in
the analysis. Obviously, tuning of the electronic interaction
between the metal centers and the respective oxidation
potentials can be achieved by modification of the bridging
and peripheral ligands in the dinuclear complex. Such adap-
Experimental Section
General Procedures. All air-sensitive reactions were per-
formed under a dry nitrogen atmosphere using standard
Schlenk techniques. Absolute solvents were dried over appro-
priate drying agents and distilled before use. All other solvents
and reagents were purchased and used as received. Microwave
reactions have been carried out in an Ethos Sel micro-
wave solvent extraction labstation using closed pressure vessels.
The temperature was controlled via a reference vessel containing
the same amount of solvent but no reactants. 1H and 13C{1H}
NMR spectra were recorded at 298 K on a Varian 300 MHz
Inova spectrometer and on a Varian 400 MHz NMR system.
NMR spectra were referenced to the solvent residual signal.73
Spectral assignments were based on chemical shift and integral
considerations as well as COSY and NOESY two-dimensional
experiments. Elemental analyses were carried out by Kolbe
€
Mikroanalytisches Laboratorium (Mulheim an der Ruhr,
Germany). 1-(2-Oxo-2(pyridin-2-yl)ethyl)pyridinium iodide,74
(73) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62 (21), 7512–7515.
(74) Ballardini, R.; Balzani, V.; Clemente-Leon, M.; Credi, A.;
Gandolfi, M. T.; Ishow, E.; Perkins, J.; Stoddart, J. F.; Tseng, H. R.;
Wenger, S. J. Am. Chem. Soc. 2002, 124 (43), 12786–12795.

Article
Organometallics, Vol. 29, No. 21, 2010 5643
2-pyridyltributylstannane,75 [RuCl3(tpy)],76 and [RuCl3(4,40,400-
(MeO2C)3-tpy)]13 were prepared following literature proce-
dures.
CH), 7.67 (t, 1H, 3J = 1.6 Hz, Ar4H), 7.51 (dd, 1H, 3J = 7.6 Hz,
5
3J = 4.8 Hz, Ar0 H). 13C NMR (100 MHz, CDCl3): δ 189.1,
153.9, 149.2, 141.3, 138.9, 137.4, 135.6, 130.3, 127.5, 123.6, 123.6,
Electronic Spectroscopic Measurements and Electrochemical
Experiments. Solution UV-vis spectra were recorded on a Cary
50 Scan UV-vis spectrophotometer or on a Cary 5 UV-
vis-NIR spectrophotometer. Chemical oxidation of samples
was performed by titration with freshly prepared concentrated
solutions of [Ce(NO3)6](NH4)2 in MeCN or SbCl5 in CH2Cl2.
Cyclic voltammograms were recorded in a single compartment
cell under a dry nitrogen atmosphere. The cell was equipped
with a Pt microdisk working electrode, a Pt wire auxiliary
electrode, and a Ag/AgCl wire pseudoreference electrode. The
working electrode was polished with alumina nanopowder be-
tween scans. The potential control was achieved with a PAR model
263A potentiostat. All redox potentials are reported against the
ferrocene-ferrocenium (Fc/Fcþ) redox couple used as an inter-
nal standard.77,78 All electrochemical samples were 10-1 M in
[n-Bu4N]PF6 as the supporting electrolyte in MeCN distilled over
KMnO4 and Na2CO3 or in CH2Cl2 distilled over CaH2.
123.3.
40-(3,5-Dibromophenyl)-2,20:60,200-terpyridine, 1. A suspension
of (E)-3-(3,5-dibromophenyl)-1-(pyridin-2-yl)prop-2-en-1-one
(10.4 g, 28 mmol), 1-(2-oxo-2(pyridin-2-yl)ethyl)pyridinium
iodide (14.6 g, 45 mmol), and NH4OAc (29.7 g, 385 mmol) in
MeOH (400 mL) was heated under reflux for 20 h. The mixture
was diluted with H2O (200 mL) and filtered. The product was
isolated with CH2Cl2, washed with aqueous NaOH (0.2 M, 100
mL), dried over MgSO4, filtered, and evaporated in vacuo,
1
yielding the product as a white solid (12.3 g, 94%). H NMR
(400 MHz, CDCl3): δ 8.72 (d, 2H, 3J = 4.8 Hz, F6), 8.65 (d, 2H,
3J = 8.0 Hz, F3), 8.62 (s, 2H, E3,5), 7.96 (s, 2H, D2,6), 7.89 (dd,
2H, 3J = 8.0 Hz, 3J = 7.6 Hz, F4), 7.74 (s, 1H, D4), 7.37 (dd, 2H,
3J = 7.6 Hz, 3J = 4.8 Hz, F5). 13C NMR (100 MHz, CDCl3): δ
156.4, 155.9, 149.3, 147.8, 142.3, 137.3, 134.6, 129.4, 124.4,
123.8, 121.7, 118.9. Anal. Calcd for C21H13Br2N3: C, 53.99; H,
2.80; N, 8.99. Found: C, 54.10; H, 2.86; N, 9.05.
DFT Calculations. DFT calculations were performed at the
DZ Dunning79,80 level of theory for carbon, nitrogen, and
hydrogen and using the Stuttgart RSC 1997 ECP relativistic
core potential81 for ruthenium using the B3LYP functional.
Geometries were optimized using the Gamess UK82 program
package. Subsequent TD-DFT calculations were run on the
optimized geometry at the same level of theory using the
Gaussian version 03 program package.83 Isovalue plots of the
frontier molecular orbitals were made using MOLDEN.56
Syntheses. (E )-3-(3,5-Dibromophenyl)-1-(pyridin-2-yl)prop-
2-en-1-one. A solution of 3,5-dibromobenzaldehyde (9.4 g, 36
mmol) and 2-acetylpyridine (4.0 mL, 36 mmol) in MeOH (400
mL) was treated with an aqueous NaOH solution (4 M, 13 mL,
42 mmol), and the resulting mixture stirred at room temperature
for 1 h. The suspension was filtered, and the product isolated
with CH2Cl2 (100 mL), washed with H2O (100 mL), dried over
MgSO4, and evaporated in vacuo. The product was obtained as a
white solid (10.4 g, 80%). 1H NMR (400 MHz, CDCl3): δ 8.75
(4-tert-Butylpyridin-2-yl)tributylstannane, 2b. A solution of
N,N-dimethylethanolamine (9.0 mL, 90 mmol) in hexane (200
mL) was treated with n-BuLi (1.6 M in hexane, 112.5 mL, 180
mmol) at 0 ꢀC. The mixture was stirred for 20 min, 4-tert-
butylpyridine (8.8 mL, 60 mmol) was added, and the mixture
was stirred for 1 h. After cooling to -70 ꢀC, SnCl(n-Bu)3 (90%
pure, 37 mL, 120 mmol) was added, and the mixture was allowed
to warm to room temperature and stirred for 2 h. The reaction
was quenched with aqueous NH4Cl, the phases were separated,
and the aqueous phase was extracted with Et2O (100 mL). The
combined organic layers were dried over MgSO4, filtered, and
concentrated in vacuo, yielding the product (48 g, 188%,
Sn(n-Bu)4 present as impurity) as a colorless oil. 1H NMR
3
(400 MHz, CDCl3): δ 8.62 (d, 1H, J = 5.2 Hz, Ar6H), 7.37
(s, 1H, Ar3H), 7.10 (d, 1H, 3J = 5.2 Hz, Ar5H), 0.70-1.60 (m,
36H, n-Bu þ t-Bu).
40-(3,5-Di(2-pyridinyl)phenyl)-2,20:60,200-terpyridine, 3aH. A
suspension of 1 (3.6 g, 7.7 mmol), tributyl-2-pyridylstannane
(17.5 g, 31 mmol), LiCl (3.1 g, 74 mmol), and Pd(PPh3)4 (0.5 g,
0.4 mmol) in toluene (80 mL) was degassed and heated under
reflux for 24 h. An aqueous solution of KF was added, the result-
ing mixture was filtered over Celite, and the solids were washed
with CH2Cl2. The combined organic fractions were dried over
K2CO3, and concentrated in vacuo. The product was purified by
washing with pentane (3 ꢀ 50 mL) and toluene (30 mL), yielding
the product as a white solid (3.16 g, 89%). 1H NMR (400 MHz,
CDCl3): δ 8.97 (s, 2H, E3,5), 8.77-8.83 (m, 5H, D4 þ C3 þ C6),
8.63 (s, 2H, D2,6), 8.02 (d, 2H, 3J = 8.0 Hz, F3), 7.94 (dd, 2H,
3J = 8.0 Hz, 3J = 7.6 Hz, C4), 7.86 (dd, 2H, 3J = 8.0 Hz, 3J =
7.6 Hz, F4), 7.39-7.43 (m, 4H, C5 þ F6), 7.33 (d, 2H, 3J = 7.6
6
(d, 1H, 3J = 4.8 Hz, Ar0 H), 8.27 (d, 1H, 3J = 16.0 Hz, CH), 8.17
3
(d, 1H, 3J = 8.0 Hz, Ar0 H), 7.88 (dd, 1H, 3J = 8.0 Hz, 3J = 7.6,
4
3
Ar0 H), 7.76 (d, 2H, 4 = 1.6, Ar2H), 7.72 (d, 1H, J = 16 Hz,
(75) Nierengarten, H.; Rojo, J.; Leize, E.; Lehn, J. M.; Van Dorsselaer,
A. Eur. J. Inorg. Chem. 2002, No. 3, 573–579.
(76) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg. Chem. 1980, 19
(5), 1404–1407.
(77) Kolthoff, I. M.; Thomas, F. G. J. Phys. Chem. 1965, 69 (9), 3049–
3058.
(78) Pavlishchuk, V. V.; Addison, A. W. Inorg. Chim. Acta 2000, 298
(1), 97–102.
(79) Dunning, T. H. J. Chem. Phys. 1970, 53 (7), 2823–2833.
(80) Dunning, T. H.; Hay, P. J. In Methods of Electronic Structure
Theory; 1977.
3
Hz, J = 5.2 Hz, F5). 13C NMR (100 MHz, CDCl3): δ 157.0,
156.4, 156.1, 150.6, 149.9, 149.2, 140.9, 140.1, 137.2, 137.1,
(81) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Theor. Chim. Acta 1990, 77 (2), 123–141.
126.8, 126.5, 124.1, 122.8, 121.7, 121.4, 119.6.
40-(3,5-Di(4-tert-butylpyridin-2-yl)phenyl)-2,20:60,200-terpyridine,
3bH. A suspension of 1 (5.0 g, 11 mmol), 2b (40.6 g, 30 mmol,
Sn(nBu)4 present), LiCl (5.4 g, 127 mmol), and Pd(PPh3)4 (0.9 g,
0.8 mmol) in degassed toluene (100 mL) was heated under reflux
for 3 days. After cooling to room temperature, an aqueous
solution of KF (20 mL) was added, the mixture was filtered, the
phases were separated, and the aqueous phase was extracted
with CH2Cl2 (100 mL) and concentrated in vacuo. The product
was purified by column chromatography on SiO2 (hexane/ethyl
acetate, 9:1) and Al2O3 (hexane/ethyl acetate, 9:1), yielding the
(82) Guest, M. F.; Bush, I. J.; Van Dam, H. J. J.; Sherwood, P.;
Thomas, J. M. H.; Van Lenthe, J. H.; Havenith, R. W. A.; Kendrick, J.
Mol. Phys. 2005, 103 (6-8), 719–747.
(83) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A.; J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople,
J. A. Gaussian 03; Gaussian, Inc: Madison, WI, 2004.
1
product as a white solid (1.4 g, 23%). H NMR (400 MHz,
C6D6): δ 9.30 (s, 2H, E3,5), 9.28 (s, 1H, D4), 8.88 (s, 2H, D2,6),
8.68 (d, 2H, 3J = 8.0 Hz, F3), 8.59 (d, 2H, 3J = 5.2 Hz, C6), 8.52
(d, 2H, 3J = 5.2 Hz, F6), 7.91 (s, 2H, C3), 7.34 (dd, 2H, 3J = 8.0
Hz, 3J = 7.6 Hz, F4), 6.85 (d, 2H, 3J = 5.2 Hz, C5), 6.77 (dd,
2H, 3J = 7.6 Hz, 3J = 5.2 Hz, F5), 1.05 (s, 18H, t-Bu). 13C NMR
(100 MHz, C6D6): δ160.3, 157.3, 156.6, 156.4, 150.8, 150.0, 149.3,

5644 Organometallics, Vol. 29, No. 21, 2010
Wadman et al.
141.7, 140.4, 136.3, 126.9, 126.7, 123.5, 121.2, 119.8, 119.6, 117.6,
34.5, 30.3. Anal. Calcd for C39H37N5: C, 81.36; H, 6.48; N, 12.16.
Found: C, 81.25; H, 6.43; N, 12.18.
dissolved in MeCN (50 mL) and precipitated by addition of
aqueous KPF6 and removal of MeCN. The product was purified
by column chromatography on SiO2 (MeCN/aqueous 0.5 M
NaNO3, 9:1, v/v), yielding the product as a dark purple solid (98
mg, 58%). 1H NMR (400 MHz, DMSO-d6): δ 9.76 (s, 2H, E3,5),
[Ru(3aH)(tpy)](PF6)2, [4aH](PF6)2. A suspension of [RuCl3-
(tpy)] (164 mg, 0.37 mmol) and AgBF4 (275 mg, 1.41 mmol) in
acetone (50 mL) was heated under reflux for 2 h. After filtration
over Celite, the solvent was removed in vacuo. The mauve solid
was dissolved in EtOH (150 mL), a solution of 3aH (174 mg, 0.37
mmol) in CH2Cl2 (40 mL) was added, and the solution was
heated under reflux for 2 h. The product was precipitated by
addition of an aqueous KPF6 solution. The product was puri-
fied by column chromatography on SiO2 (MeCN/aqueous 0.5
M NaNO3, 9:1, v/v) and on Al2O3 (MeCN:/toluene, 1:1, v/v),
during which [7a]þ was isolated as a side product. The product
was precipitated from MeCN with ethyl acetate, yielding the
product as an orange solid (76 mg, 19%). 1H NMR (400 MHz,
CD3CN): δ 9.15 (s, 2H, E3,5), 9.05 (s, 1H, D4), 8.91 (s, 2H,
D2,6), 8.79 (d, 2H, 3J = 8.0 Hz, H3,5), 8.77 (br, 2H, C6), 8.68 (d,
2H, 3J = 8.0 Hz, F3), 8.53 (d, 2H, 3J = 8.0 Hz, G3), 8.45 (t, 1H,
3J = 8.0 Hz, H4), 8.27 (d, 2H, 3J = 8.0 Hz, C3), 8.02 (dd, 2H,
3J = 8.0 Hz, 3J = 6.0 Hz, C4), 7.94-7.98 (m, 4H, F4þG4), 7.53
(d, 2H, 3J = 5.2 Hz, G6), 7.46 (dd, 2H, 3J = 6.0 Hz, 3J = 4.4 Hz,
C6), 7.3 (d, 2H, 3J = 6.2 Hz, F6), 7.19-5.25 (m, 4H, F5þG5).
13C NMR (100 MHz, CD3CN): δ 159.2, 159.1, 156.7, 156.5,
156.4, 153.5, 153.4, 150.8, 149.1, 142.5, 139.2, 139.1, 139.0,
138.4, 136.8, 128.5, 128.4, 127.8, 127.6, 125.9, 125.4, 124.7,
124.3, 123.0, 121.9. Anal. Calcd for C46H32F12N8P2Ru: C,
50.79; H, 2.97; N, 10.30. Found: C, 50.71; H, 2.91; N, 10.29.
[Ru(3a)(tpy)](PF6), [7a](PF6). 1H NMR (400 MHz, acetone-d6):
δ 9.15 (s, 2H, E3,5), 9.04 (d, 2H, 3J = 8.0 Hz, A3,5), 8.93 (s, 2H,
D3,5), 8.87 (d, 2H, 3J = 8.0 Hz, F3), 8.84 (d, 2H, 3J = 4.8 Hz, F6),
8.71 (d, 2H, 3J = 8.0 Hz, B3), 8.57 (d, 2H, 3J = 8.0 Hz, C3), 8.43 (t,
1H, 3J = 8.0 Hz, A4), 8.09 (dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz, F4),
7.85 (dd, 2H, 3 = 7.6 Hz, 3J = 7.6 Hz, B4), 7.76 (dd, 2H, 3J = 7.6
Hz, 3J = 6.4 Hz, C4), 7.56 (dd, 2H, 3J = 7.6 Hz, 3J = 4.8 Hz, F5),
7.37 (d, 2H, 3J = 7.2 Hz, B6), 7.28 (d, 2H, 3J = 6.8 Hz, C6), 7.15
(dd, 2H, 3J = 7.6 Hz, 3J = 68 Hz, B5), 6.82 (dd, 2H, 3J = 7.2 Hz,
3J = 6.4 Hz, C5). 13C NMR (100 MHz, CD3CN): δ 225.8, 169.4,
160.0, 157.2, 157.1, 155.4, 153.7, 152.9, 152.8, 150.3, 143.8, 138.2,
136.6, 136.2, 133.3, 131.5, 127.3, 125.2, 124.5, 123.3, 123.1, 122.8,
122.1, 120.9, 119.4.
3
9.33 (s, 2H, D3,5), 9.16 (d, 2H, J = 8.0 Hz, F3), 9.12 (d, 2H,
3J = 8.0 Hz, A3,5), 9.11 (d, 2H, 3J = 8.0 Hz, H3,5), 8.87 (d, 2H,
3
3J = 8.0 Hz, G3), 8.79 (d, 2H, J = 8.0 Hz, C3), 8.66 (d, 2H,
3J = 8.0 Hz, B3), 8.55 (t, 1H, 3J = 8.0 Hz, H4), 8.45 (t, 1H, 3J =
8.0 Hz, A4), 8.13 (dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz, F4), 8.06
(dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz, G4), 7.82-7.90 (m, 4H, B4 þ
C4), 7.63 (d, 2H, 3J = 5.6 Hz, G6), 7.49 (d, 2H, 3J = 5.2 Hz, F6),
7.30-7.38 (m, 4H, B6 þ C6), 7.10-7.20 (m, 6H, B5 þ F5 þ G5),
3
3
6.90 (dd, 2H, J = 7.6 Hz, J = 5.2 Hz, C5). 13C NMR (100
MHz, dmso-d6): δ 228.6, 168.4, 159.4, 159.0, 158.7, 155.7, 155.6,
154.3, 153.0, 152.8, 152.7, 152.4, 149.8, 143.5, 138.8, 138.7,
136.4, 136.3, 133.9, 128.5, 128.4, 128.2, 127.4, 125.3, 125.2,
124.8, 124.7, 123.5, 123.3, 122.8, 121.0, 120.9. One additional
resonance could not be resolved.
[Ru2(μ-3b)(tpy)2](PF6)2, [5b](PF6)3. A mixture of [4bH](PF6)2
(33 mg, 0.025 mmol) and [RuCl3(tpy)] (29 mg, 0.066 mmol) was
suspended in ethylene glycol (25 mL) and heated to 150 ꢀC for
30 min using μ-wave radiation in a closed vessel. The product
was precipitated by addition of aqueous KPF6, filtered, and
collected with MeCN. The product was purified by column
chromatography on SiO2 (MeCN/aqueous 0.5 M NaNO3,
9:1, v/v) and recrystallized from MeCN and H2O, yielding the
1
product as a purple solid (28 mg, 67%). H NMR (400 MHz,
CD3CN),: δ 9.44 (s, 2H, E3,5), 9.12 (s, 2H, D3,5), 8.88 (d, 2H,
3J = 8.0 Hz, F3), 8.83 (d, 2H, 3J = 8.0 Hz, A3,5), 8.82 (d, 2H,
3J = 8.0 Hz, H3,5), 8.57 (d, 2H, 3J = 8.0 Hz, G3), 8.55 (d, 2H,
4J = 1.2 Hz, C3), 8.51 (d, 2H, 4J = 1.2 Hz, B3), 8.47 (t, 1H, 3J =
8.0 Hz, H4), 8.35 (t, 1H, 3J = 8.0 Hz, A4), 8.06 (dd, 2H, 3J = 8.0
Hz, 3J = 8.0 Hz, F4), 8.00 (dd, 2H, 3J = 8.0 Hz, 3J = 8.0 Hz,
G4), 7.79 (dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz, B4), 7.60 (d, 2H,
3J = 4.8 Hz, G6), 7.44 (d, 2H, 3J = 5.6 Hz, F6), 7.23-7.30 (m,
6H, B6þG5þF5), 7.06 (d, 2H, 3J = 6.8 Hz, C6), 7.05 (dd, 2H,
3J = 7.6 Hz, 3J = 5.6 Hz, B5), 6.85 (dd, 2H, 3J = 6.8 Hz, 4J =
1.2 Hz, C5), 1.38 (s, 18H, t-Bu). 13C NMR (100 MHz, CD3CN):
δ 228.7, 168.9, 161.4, 160.0, 159.5, 159.2, 156.5, 156.3, 155.0,
153.5, 153.5, 153.2, 152.3, 151.3, 148.7, 143.0, 139.1, 139.0,
136.7, 136.4, 133.6, 129.5, 128.6, 128.4, 127.3, 125.6, 125.5,
124.7, 123.5, 123.2, 122.1, 120.7, 118.4, 35.8, 30.7. Anal. Calcd
[Ru(3bH)(tpy)](PF6)2, [4bH](PF6)2. A suspension of [RuCl3-
(tpy)] (105 mg, 0.24 mmol), 3bH (75 mg, 0.12 mmol), and AgBF4
(160 mg, 0.82 mmol) in MeOH (40 mL) was heated under reflux
for 20 h. After cooling, the orange solution was filtered over
Celite, and the product was precipitated by addition of aqueous
KPF6 and removal of the MeOH in vacuo. The product was
purified by column chromatography on SiO2 (MeCN/aqueous
0.5 M NaNO3, 9:1, v/v) and on Al2O3 (MeCN/toluene, 1:1, v/v),
yielding the product as an orange solid (81 mg, 56%). 1H NMR
(400 MHz, CD3CN): δ 9.06 (s, 2H, E3,5), 8.98 (t, 1H, 4J = 1.6
Hz, D4), 8.91 (d, 2H, 4J = 1.6 Hz, D2,6), 8.80 (d, 2H, 3J = 8.0
Hz, H3,5), 8.50-8.58 (m, 6H, F3þC6þG3), 8.46 (t, 1H, 3J = 8.0
Hz, H4), 8.22 (d, 2H, 4J = 1.6 Hz, C3), 7.98 (dd, 2H, 3J = 8.0
Hz, 3J = 8.0 Hz, F4), 7.90 (dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz,
G4), 7.65 (d, 2H, 3J = 5.6 Hz, F6), 7.38-7.44 (m, 4H, C5þG6),
for C69H58F18N11O6P3Ru2 2H2O: C, 48.34; H, 3.65; N, 8.99.
Found: C, 48.78; H, 3.75; N, 8.62.
3
[Ru2(μ-3a)((MeO2C)3-tpy)(tpy)](PF6)3, [6a](PF6)3. A mixture
of [4aH](PF6)2 (16.0 mg, 0.015 mmol) and [RuCl3((MeO2C)3-
tpy)] (19 mg, 0.031 mmol) was suspended in MeOH (25 mL) and
heated to 97 ꢀC in a closed vessel for 30 min using μ-wave
radiation. The product was precipitated by addition of aqueous
KPF6, filtered, and collected with MeCN. The product was
purified by column chromatography on SiO2 (MeCN/aqueous
0.5 M NaNO3, 9:1, v/v) and recrystallized from MeCN with
1
Et2O, yielding the product as a purple solid (23 mg, 90%). H
NMR (400 MHz, CD3CN): δ 9.50 (s, 2H, A3,5), 9.44 (s, 2H,
E3,5), 9.16 (s, 2H, D3,5), 9.10 (s, 2H, B3), 8.89 (d, 2H, 3J = 8.0
Hz, F3), 8.82 (d, 2H, 3J = 8.0 Hz, H3,5), 8.59 (d, 2H, 3J = 4.4
Hz, G3), 8.57 (d, 2H, 3J = 4.4 Hz, C3), 8.47 (t, 1H, 3J = 8.0 Hz,
H4), 8.05 (dd, 2H, 3J = 7.6 Hz, 3J = 7.6 Hz, F4), 7.99 (dd, 2H,
3J = 7.6 Hz, 3J = 7.6 Hz, G4), 7.82 (dd, 2H, 3J = 7.6 Hz, 3J =
7.2 Hz, C4), 7.54-7.60 (m, 6H, B5þB6þG6), 7.43 (d, 2H, 3J =
6.0 Hz, F6), 7.23-7.29 (m, 4H, F5þG5), 7.04 (d, 2H, 3J = 5.2
Hz, C6), 6.78 (dd, 2H, 3J = 7.6 Hz, 3J = 6.0 Hz, C5), 4.25 (s, 3H,
CO2CH3), 3.95 (s, 6H, CO2CH3). 13C NMR (100 MHz,
CD3CN): δ 224.7, 168.9, 166.2, 165.0, 160.6, 159.5, 159.2,
156.5, 155.8, 153.9, 153.6, 153.5, 153.4, 150.5, 143.9, 139.1, 137.8,
137.4, 136.6, 134.2, 130.8, 128.6, 128.4, 126.7, 125.6, 125.4, 124.7,
124.1, 123.9, 123.6, 123.5, 121.8, 121.6, 54.0, 53.8. Anal. Calcd for
C67H48F18N11O6P3Ru2: C, 46.24; H, 2.78; N, 8.85. Found: C,
45.20; H, 3.83; N, 8.88.
3
3
7.29 (dd, 2H, J = 8.0 Hz, J = 5.6 Hz, F5), 7.20 (dd, 2H,
3J = 7.6 Hz, 3J = 5.6 Hz, G5), 1.44 (s, 18H, t-Bu). 13C NMR
(100 MHz, CD3CN): δ 162.5, 159.1, 159.1, 156.9, 156.4, 156.3,
153.5, 153.5, 150.7, 149.2, 142.4, 139.2, 139.1, 139.0, 136.8, 128.5,
128.4, 128.0, 127.9, 125.4, 125.4, 124.7, 123.1, 121.4, 119.0, 35.8,
30.8. Anal. Calcd for C54H48F12N8P2Ru: C, 54.05; H, 4.03; N,
9.34. Found: C, 54.00; H, 4.10; N, 9.29.
[Ru2(μ-3a)(tpy)2](PF6)2, [5a](PF6)3. A mixture of [RuCl3(tpy)]
(143 mg, 0.32 mmol) and AgBF4 (211 mg, 1.08 mmol) in acetone
(30 mL) was heated under reflux for 2 h. The mixture was filtered
over Celite, and the solvent was removed in vacuo. The mauve
solid was dissolved in n-BuOH (20 mL), and 3aH (50 mg, 0.11
mmol) was added. The mixture was heated under reflux for 20 h.
The solvent was removed in vacuo, and the dark solid was

Article
[Ru2(μ-3b)((MeO2C)3-tpy)(tpy)](PF6)3, [6b](PF6)3. A mixture
Organometallics, Vol. 29, No. 21, 2010 5645
(d, 2H, J=8.0 Hz), 9.16 (s, 2H), 9.11 (d, 2H, 3J=8.0 Hz), 8.86
(d, 2H, 3J = 8.0 Hz), 8.69 (s, 2H), 8.53 (t, 1H, 3J = 8.0 Hz), 8.12
(dd, 2H, 3J = 8.0 Hz, 3J = 7.6 Hz), 8.06 (dd, 2H, 3J = 8.0 Hz,
3J = 7.6 Hz), 7.62 (d, 2H, 3J = 5.2 Hz), 7.58 (d, 2H, 3J = 5.2 Hz),
7.46 (d, 2H, 3J = 5.6 Hz), 7.30-7.40 (m, 6H), 6.93 (d, 2H, 3J =
6.4 Hz), 6.85 (d, 2H, 3J = 6.4 Hz), 1.28 (s, 18H). 13C NMR (100
MHz, DMSO-d6): δ 224.5, 167.3, 166.6, 165.3, 160.5, 159.2, 158.5,
158.1, 155.1, 155.0, 153.8, 152.3, 152.2, 152.0, 151.5, 149.9, 142.6,
140.9, 138.3, 135.9, 129.7, 128.0, 127.8, 126.2, 125.4, 124.8, 124.2,
123.6, 123.4, 122.9, 121.8, 120.2, 118.0, 35.1, 30.3. Two additional
resonances could not be resolved.
3
of [4bH](PF6)2 (57 mg, 0.047 mmol) and [RuCl3(tpy)] (47 mg,
0.071 mmol) was suspended in MeOH (50 mL) and heated to
97 ꢀC in a closed vessel for 30 min using μ-wave radiation. The
product was precipitated by addition of aqueous KPF6, filtered,
and collected with MeCN. The product was purified by column
chromatography on SiO2 (MeCN/aqueous 0.5 M NaNO3, 9:1,
v/v) and recrystallized from MeCN with Et2O, yielding the
1
product as a purple solid (51 mg, 58%). H NMR (400 MHz,
CD3CN): δ 9.50 (s, 2H, A3,5), 9.45 (s, 2H, E3,5), 9.15 (s, 2H,
D3,5), 9.11 (s, 2H, B3), 8.89 (d, 2H, 3J = 4.4 Hz, F3), 8.83 (d,
2H, 3J = 4.4 Hz, H3,5), 8.58 (d, 2H, 3J = 4.4 Hz, G3), 8.55 (d,
2H, 3J = 4.4 Hz, C4), 8.48 (t, 1H, 3J = 4.4 Hz, H4), 8.06 (dd, 2H,
3J = 4.4 Hz, 3J = 4.4 Hz, F4), 8.00 (dd, 2H, 3J = 4.4 Hz, 3J =
4.4 Hz, G4), 7.56-7.61 (m, 6H, G6þB5þB6), 7.45 (d, 2H, 3J =
4.4 Hz, F6), 7.24-7.30 (m, 4H, G5þF5), 6.89 (d, 2H, 3J = 4.4
Hz, G6), 6.79 (dd, 2H, 3J = 4.4 Hz, 3J = 4.4 Hz, C6), 4.25 (s, 3H,
CO2Me), 3.95 (s, 6H, CO2Me), 1.35 (s, 18H, t-Bu). 13C NMR
(100 MHz, CD3CN): δ 224.2, 168.5, 166.2, 165.0, 162.5, 160.6,
159.5, 159.2, 156.5, 156.4, 155.6, 153.8, 153.7, 153.3, 152.8, 150.8,
144.0, 139.1, 139.0, 137.3, 136.7, 133.7, 131.1, 128.6, 128.4, 126.6,
125.5, 125.4, 124.8, 124.0, 123.9, 123.6, 122.2, 120.9, 118.8, 53.9,
Acknowledgment. The authors gratefully acknowledge
support from the European Commission through the
funding of the project FULLSPECTRUM within the
Sixth Framework Program under number SES6-CT-
2003-502620. The work of R.W.A.H. is part of the
research program of the Stichting voor Fundamenteel
Onderzoek der Materie (FOM), which is financially
supported by the Nederlandse Organisatie voor Weten-
schappelijk Onderzoek (NWO). We acknowledge NWO/
NCF for supercomputer time on ASTER, SARA (The
Netherlands, project number SG-032). K. Nazeeruddin
53.8, 35.9, 30.6. Anal. Calcd for C75H64F18N11O6P3Ru2 7H2O:
3
C, 45.53; H, 3.97; N, 7.79. Found: C, 45.70; H, 4.24; N, 7.54.
[Ru2(μ-3b)((-O2C)3-tpy)(tpy)], [8b]. A solution of [6b](PF6)3
(23 mg, 0,012 mg), H2O (0.1 mL), and NEt3 (0.1 mL) in MeCN
(2 mL) was heated to 70 ꢀC for 40 h. The resulting suspension
was filtered, the solid was washed with acetone (1 mL), and the
product was collected with MeOH. Concentration of the solu-
tion in vacuo yielded the product as a dark purple solid (13 mg,
78%). 1H NMR (400 MHz, DMSO-d6 in the presence of 2 equiv
of aqueous HCl): δ 9.88 (s, 2H), 9.55 (s, 2H), 9.37 (s, 2H), 9.31
€
and Michael Gratzel are acknowledged for their aid in
performing the preliminary DSSC tests.
Supporting Information Available: Method description and
results for DFT calculations on [5a]3þ and [5a]4þ. This mate-
rial is available free of charge via the Internet at http://
pubs.acs.org.