New light-harvesting molecular systems constructed with a Ru(II) complex and a linear-shaped Re(I) oligomer

Article abstract of DOI:10.1021/ja104601b

A novel type of light-harvesting complexes was synthesized with a linear-shaped Re(I) oligomer as a photon absorber and a Ru(II) polypyridyl complex as an energy acceptor. The Re(I) oligomer and the Ru(II) complex are connected to each other with a bisdiimine ligand, that is, 1,2-bis[4-(4′- methyl-2,2′-bipyridinyl)]ethane (C2dmb). These Ru(II)-Re(I) multinuclear complexes, [Ru(dmb)₂(C2dmb)Re(CO)₂{-PP-Re(dmb)(CO) ₂-PP-Re(dmb)(CO)₃}₂](PF₆) ₇, [Ru(dmb)₂(C2dmb)Re(CO)₂{-PP-Re(dmb)(CO) ₃}₂](PF₆)₅, and [Ru(dmb) ₂(C2dmb)Re(CO)₃-PP-Re(dmb)(CO)₂-PP-Re(dmb)(CO) ₃](PF₆)₅ (dmb = 4,4′-dimethyl-2,2′- bipyridine; PP = bis(diphenylphosphino)acetylene), can strongly absorb a wide range of UV-vis light and emit mostly from the ³MLCT excited state of the Ru(II) unit at room temperature in solution even when the Re chain absorbs the light. Comparison of their photophysical properties with those of the corresponding model complexes shows that a highly efficient energy transfer from the Re chain to the Ru(II) unit occurs, and the energy transfer rate constants from each Re(I) unit were determined.

Full text of DOI:10.1021/ja104601b

Published on Web 07/28/2010
New Light-Harvesting Molecular Systems Constructed with a
Ru(II) Complex and a Linear-Shaped Re(I) Oligomer
Youhei Yamamoto,†,‡,§ Yusuke Tamaki,† Tatsuto Yui,†,‡ Kazuhide Koike,*,|,‡ and
Osamu Ishitani*,†,‡
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of
Technology, 2-12-1-E1-9 O-okayama, Meguro-ku, Tokyo 152-8551, Japan, CREST, Japan
Science and Technology Agency, and National Institute of AdVanced Industrial Science and
Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan
Received May 27, 2010; E-mail: ishitani@chem.titech.ac.jp
Abstract: A novel type of light-harvesting complexes was synthesized with a linear-shaped Re(I) oligomer
as a photon absorber and a Ru(II) polypyridyl complex as an energy acceptor. The Re(I) oligomer and the
Ru(II) complex are connected to each other with a bisdiimine ligand, that is, 1,2-bis[4-(4′-methyl-2,2′-
bipyridinyl)]ethane (C2dmb). These Ru(II)-Re(I) multinuclear complexes, [Ru(dmb)2(C2dmb)Re(CO)2-
{-PP-Re(dmb)(CO)2-PP-Re(dmb)(CO)3}2](PF6)7, [Ru(dmb)2(C2dmb)Re(CO)2{-PP-Re(dmb)(CO)3}2](PF6)5,
and [Ru(dmb)2(C2dmb)Re(CO)3-PP-Re(dmb)(CO)2-PP-Re(dmb)(CO)3](PF6)5 (dmb ) 4,4′-dimethyl-2,2′-
bipyridine; PP ) bis(diphenylphosphino)acetylene), can strongly absorb a wide range of UV-vis light and
emit mostly from the 3MLCT excited state of the Ru(II) unit at room temperature in solution even when the
Re chain absorbs the light. Comparison of their photophysical properties with those of the corresponding
model complexes shows that a highly efficient energy transfer from the Re chain to the Ru(II) unit occurs,
and the energy transfer rate constants from each Re(I) unit were determined.
Introduction
photon-collection systems have been reported. Polypyridyl
complexes of d6 transition metal ions such as ruthenium(II),16
Photon collection is one of the most important functions in
solar energy harvesting devices such as solar batteries1-3 and
photocatalysts for CO2 reduction and hydrogen evolution.4-12
When photosynthesis occurs in nature, well-ordered assemblies
that contain many chlorophylls collect the solar light and transfer
it to the reaction center.13-15 Some artificial molecular-based
osmium(III),17 iridium(III),18 and rhenium(I)19 are the light
absorbers that are used most often because of their outstanding
photophysical properties, which include the long lifetime of the
triplet metal-to-ligand charge transfer (3MLCT) excited state and
the high emission quantum yield at ambient temperature even
in solution. Polymers that include these metal complexes have
been synthesized for use in light collection systems. However,
† Tokyo Institute of Technology.
‡ CREST/JST.
§ Present address: Department of Pharmacy, College of Pharmaceutical
Sciences, Ritsumeikan University, 1-1-1 Nojihigasi, Kusatsu, Shiga 525-
8577, Japan.
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10.1021/ja104601b  2010 American Chemical Society
J. AM. CHEM. SOC. 2010, 132, 11743–11752 11743

A R T I C L E S
Yamamoto et al.
Scheme 1. Structures and Abbreviations of the Linear-Shaped
the metal complexes often hang from an organic polymer chain
as pendant groups20,21 or π-conjugated heteroaromatic polymers
with diimine parts in a main chain coordinated with metal
complexes.22-24 On the other hand, only a few emissive
polymers have been reported with main chains that are held
together by transition-metal complexes.25-32 These complexes
should have unique properties because of the contribution of
the d-orbitals in the transition metal ions to the main polymer
chain.
Re(I) Multinuclear Complexes and the Ru(II)-Re(I) Dinuclear
Complex as Model Compounds
We recently reported the systematic synthesis of linear-shaped
Re(I) multinuclear complexes bridged with bidentate phosphorus
ligands that have 2-20 Re(I) units in the backbone of the
polymer chain (Scheme 1).33 These complexes can strongly emit
at ambient temperature even in solution. Furthermore, in these
oligomers and polymers, the photochemical energy transfer
occurs efficiently from the edge unit to the interior units.
Here, we report a new series of light-harvesting systems with
the linear-shaped Re(I) oligomer as a photon absorber and a
Ru(II) polypyridyl complex as an energy acceptor. The Re(I)
oligomer and Ru(II) complex are connected to each other by a
bisdiimine ligand (Scheme 2).
2,2′-bipyridinyl)]ethane) (Ru-Re(CO)3(CF3SO3)2+), can be
quantitatively obtained by the reaction of [Ru(dmb)2(C2dmb)-
Re(CO)3Cl]2+ (Ru-Re(CO)3Cl2+) with an equal amount of
Tl(CF3SO3) in CH2Cl234 followed by excess bis(diphenylphos-
phino)acetylene (PP) in CH2Cl2. The result is [Ru(dmb)2(C2dmb)-
Re(CO)3(η1-PP)]3+ (Ru-Re(CO)3(η1-PP)3+), where PP works
as a monodentate ligand and can potentially coordinate with
another metal center.
Results and Discussion
Synthesis. Scheme 2 summarizes the synthesis procedure for
the Ru(II)-Re(I) multinuclear complexes. The Ru(II)-Re(I)
dinuclear complex, [Ru(dmb)2(C2dmb)Re(CO)3(CF3SO3)]2+ (dmb
) 4,4′-dimethyl-2,2′-bipyridine, C2dmb ) 1,2-bis[4-(4′-methyl-
Photochemical ligand substitution of the Re(I) unit in this
binuclear complex is one of the key steps for synthesis of
Ru-Re3A3+ and Ru-Re57+. Irradiation of a THF-CH2Cl2
mixed solution containing Ru-Re(CO)3(η1-PP)3+ and excess
PP at 50-60 °C gave [Ru(dmb)2(C2dmb)Re(CO)2(η1-PP)2]3+
(Ru-Re(CO)2(η1-PP)23+). We have reported the photochemical
ligand substitution reaction of the Re(I) mononuclear complexes
with a phosphorus ligand, where only the CO ligand in the trans
position to the phosphorus ligand is substituted via a thermal
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ligand field (LF) excited state.35,36 In the case of the Ru(II)-Re(I)
binuclear complex, however, the ligand substitution of the Re(I)
unit competed with the energy transfer from the 3MLCT excited
state of the Re(I) unit to the Ru(II) unit. Irradiation at a higher
temperature made the photochemical ligand substitution more
favorable than the energy transfer.
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A dichloromethane solution containing Ru-Re(CO)2(η1-
3+
PP)2 and 2 equiv of fac-Re(dmb)(CO)3(CF3SO3) was stirred
at room temperature for 1 day and then heated at 40 °C for 1
more day. The result was Ru-Re3A3+ in a 16% isolated yield
based on the starting dinuclear complex Ru-Re(CO)3Cl2+ used.
A similar method was successfully applied to synthesize
Ru-Re57+ using the Re(I) dimer [Re(dmb)(CO)3-PP-
Re(dmb)(CO)2(CF3SO3)]+, which has an easily replaceable
CF3SO3- anion coordinated in the trans position to a phosphorus
bridge ligand, instead of fac-Re(dmb)(CO)3(CF3SO3). The
isolated yield was 13%. Another tetranuclear complex,
Ru-Re3B5+, has the Ru(II) unit attached to one of the
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11744 J. AM. CHEM. SOC. VOL. 132, NO. 33, 2010

New Light-Harvesting Molecular Systems
A R T I C L E S
Scheme 2. Synthesis of the Ru(II)-Re(I) Multinuclear Complexesa
a Reagents and reaction conditions: (i) Tl(CF3SO3) (1 equiv) in CH2Cl2 reflux for 2 days; (ii) an excess PP in CH2Cl2 at room temperature for 1 day
and then at 40 °C for
1 day; (iii) hV (>330 nm) in CH2Cl2/THF (1:1) containing an excess PP at 50-60 °C for 8 h; (iv)
[Re(dmb)(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+ (1 equiv) in CH2Cl2 at room temperature for 1 day and then at 40 °C for 1 day; (v) fac-Re(dmb)(CO)3(CF3SO3)
(2 equiv) in CH2Cl2 at room temperature for 1 day and then at 40 °C for 1 day; and (vi) [Re(dmb)(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+ (2 equiv) in CH2Cl2
at room temperature for 1 day and then at 40 °C for 1 day.
Figure 1. UV/vis absorption spectra of MeCN solutions containing (a) Ru-Re3A5+ (black line), Re33+ (red line), and Ru2+ (blue line); and (b) Ru-Re57+
(black line), Re55+ (red line), and Ru2+ (blue line).
edges of the trinuclear Re(I) unit. This complex was ob-
tained by the reaction of the Ru-Re(CO)3(η1-PP)3+ with
[Re(dmb)(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+. The isolated
yield was 21%. All of the Ru(II)-Re(I) multinuclear complexes
were isolated by size exclusion chromatography (SEC)37 and
identified by 1H NMR, IR, electrospray ionization mass
spectrometry, analytical SEC, and elemental analysis (see the
Supporting Information).
Photophysical Properties. As a typical example, Figure 1a
shows the UV/vis absorption spectra of Ru-Re3A5+ and the
corresponding model complexes, that is, the Ru(II) mononuclear
complex [Ru(dmb)3]2+ (Ru2+
)
and the Re(I) trimer
(37) Takeda, H.; Yamamoto, Y.; Nishiura, C.; Ishitani, O. Anal. Sci. 2006,
22, 545–549.
[Re(dmb)(CO)3-PP-Re(dmb)(CO)2-PP-Re(dmb)(CO)3]3+
9
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A R T I C L E S
Yamamoto et al.
(ε350 nm ) 10.0 × 103 M-1 cm-1) and Ru2+ (ε350 nm ) 7.4 × 103
M-1 cm-1). This emission spectrum was similar to both the
spectrum of Ru-Re3A5+ that was excited using 480 nm light,
which is absorbed by only the Ru(II) unit, and the spectrum of
the model of Ru(II) unit (Ru2+).
Table 1. Absorption Maxima and Molar Extinction Coefficients of
Ru(II)-Re(I) Multinuclear Complexes and the Corresponding
Model Complexesa
complex
λabs nm (ε/104 M-1 cm-1
)
Ru-Re3A5+ 286 (12.1) 314 (5.1) 350 (1.8) 390 (1.1) 460 (1.5)
Ru-Re3B5+ 285 (13.8) 315 (5.7) 350 (1.8) 390 (1.1) 460 (1.5)
These results clearly indicate that the emission occurs mainly
from the Ru(II) unit in Ru-Re3A5+ even when the Re chain is
excited because efficient intramolecular energy transfer occurs
from the excited Re chain to the Ru(II) unit. If the shapes and
efficiencies of both emission from the Re chain and the Ru(II)
Ru-Re57+
Re22+
285 (16.1) 314 (8.9) 350 (2.6) 390 (1.5) 460 (1.5)
315 (2.6) 350 (0.7)
Re33+
315 (4.1) 350 (1.0) 390 (0.3)
314 (7.8) 350 (1.8) 390 (0.7)
Re55+
Ru2+
286 (8.6)
460 (1.5)
unit of Ru-Re3A5+ are the same as those of Re33+ and Ru2+
,
a Measured in an MeCN solution at 25 °C.
then the emission spectrum of Ru-Re3A5+ (IRu-Re3A ) that is
5+
excited using 350 nm light can be simulated by the linear sum
of spectra of Re33+ and Ru-Re3A5+ that is excited using 480
38
3+
2+
nm light (IRe3 and IRu ) as shown in the following equation:
εRe33+
εRu2+
IRu-Re3A5+
)
× IRe33+ × R +
× IRu2+ × ꢀ
εRu-Re3A5+
εRu-Re3A5+
(1)
5+
2+
3+
where εRu-Re3A , εRe , and εRu are the molar extinction
coefficients of Ru-Re3A5+, Ru2+, and Re33+ at 350 nm, and
R and ꢀ are the ratios of the emission intensities from the Re
chain and the Ru(II) unit in Ru-Re3A5+ to those of Re33+
and the Ru(II) unit when the photons absorbed by them are
equal to those absorbed by the Ru(II) unit and the Re chain in
Ru-Re3A5+, respectively. The nonlinear least-squares method
was applied for fitting the spectral data shown in Figure 2, giving
R ) 0.033 and ꢀ ) 2.134 as the best-fitted data. These data
strongly indicate that the energy transfer occurred from the
excited Re chain to the Ru(II) unit with an efficiency of 86%.
Similar measurements and analyses were applied to
Ru-Re3B5+ and Ru-Re57+. In both cases, efficient energy
transfer from the excited Re chain to the Ru(II) unit was
observed, and energy transfer efficiencies of 85% and 77% were
obtained for Ru-Re3B5+ and Ru-Re57+, respectively (Figure
S5).
Figure 2. Emission spectra of degassed MeCN solutions containing
Ru-Re3A5+ by excitation at 350 nm (black line) and 480 nm (red line),
Re33+ by excitation at 350 nm (blue line), and Ru2+ by excitation at 350
nm (brown line). They are standardized by the number of absorbed photons
at the excitation wavelength.
(Re33+). The spectrum of Ru-Re3A5+ was almost identical to
the 1:1 summation spectrum of Ru2+ and Re33+. This result
indicates that no strong electronic interaction occurred in the
ground state between the Ru(II) and Re(I) units, and the
absorptions at 330-400 and 410-490 nm of Ru-Re3A5+ can
Using the single-photon-counting technique, the emission
lifetimes of the Ru-Re multinuclear complexes and their models
were measured using 350 nm excitation light. The emission
decay of Ru-Re3A5+ could be fitted with triple-exponential
functions with lifetimes of 8, 133, and 902 ns (Figure 3) as
follows:39
1
be assigned to the MLCT absorption bands of the Re chain
and the Ru(II) unit, respectively. The strong absorption around
290 nm is attributed to the π-π* absorption bands of the
diimine ligands on both the Re(I) and the Ru(II) units. Similar
results were obtained for both Ru-Re3B5+ and Ru-Re57+
(Figure S4). Table 1 summarizes the UV/vis absorption proper-
ties of the Ru(II)-Re(I) multinuclear complexes and the
corresponding model complexes. It is noteworthy that these
multinuclear complexes strongly absorb a very wide range of
UV and visible light. For example, Ru-Re57+ absorbs light
with ε > 104 M-1 cm-1 at all UV-vis wavelengths shorter than
480 nm (Figure 1b).
I(t) ) A1e-t/τ + A2e-t/τ + A3e-t/τ
(2)
1
2
3
where I(t), An, and τn are intensities of the emission at time t,
pre-exponential factors, and lifetimes, respectively. The propor-
(38) The emission spectra from the Ru(II) units in Ru-Re3A5+, Ru-
Re3B5+, and Ru-Re57+ were slightly different from that from Ru2+
(∆λmax ) 3 nm) because of very week interaction between the Ru(II)
unit and the Re(I) unit attached to the Ru(II) unit through the bridge
ligand: Koike, K.; Naito, S.; Sato, S.; Tamaki, Y.; Ishitani, O. J.
Photochem. Photobiol., A 2009, 207, 109. The emission spectra from
the Re chain in the Ru-Re systems might be also slightly different
from the corresponding Re oligomers because of the same interaction;
even so, we have to use the emission spectra from the corresponding
Re oligomers because emission only from the Re chain in the Ru-
Re systems cannot be obtained due to the energy transfer. However,
an error caused by this should not conspicuously affect the estimation
of the energy transfer efficiency because the fitting data were much
more strongly dependent on the emission from the Ru(II) unit than
that from the Re chain.
All of the Ru(II)-Re(I) multinuclear complexes emit, mostly
from the Ru(II) unit, at room temperature in solution even when
the Re chain absorbs light. Figure 2 shows the emission spectra
of Ru-Re3A5+ using 350 nm light for excitation. The emission
spectra of both Re33+ upon excitation at 350 nm and
Ru-Re3A5+ at 480 nm (the light is only absorbed by the Ru(II)
unit in the complex) are also illustrated in Figure 2. The emission
spectrum of Re33+, which is the model compound for the Re
chain in Ru-Re3A5+, had a broad band with an emission
maximum at 560 nm (Φ ) 0.16). On the other hand, emission
of Ru-Re3A5+ had a maximum at 638 nm using the same
excitation light that was absorbed by both the Re(I) units and
the Ru(II) unit with a 5.7:4.3 ratio, which was calculated using
both molecular extinction coefficients of the models Re33+
(39) Although the time resolution of the emission decay measurements was
sub nanosecond, no faster decay was detected than those shown in
Figure 3.
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11746 J. AM. CHEM. SOC. VOL. 132, NO. 33, 2010

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A R T I C L E S
Figure 3. Emission decay curves of Ru-Re3A5+ obtained at an excitation wavelength of 350 nm. Monitor wavelengths were 470 nm (a), 570 nm (b), and
620 nm (c).
Table 2. Photophysical Properties of Ru(II)-Re(I) Multinuclear Complexes and the Corresponding Re(I) Oligomersa
pre-exponential factorsd/%
lifetime/ns
observed at 480 nm
observed at 570 nm
observed at 620 nm
b
λem
c
complex
Φem
τ1
τ2
τ3
a1
a2
a3
a1
a2
a3
a1
a2
a3
Ru-Re3A5+
Ru-Re3B5+
Ru-Re57+
638
638
638
0.087
0.093
0.090
8 ( 0.1
11 ( 0.1
11 ( 0.1
133 ( 4.9
108 ( 0.4
71 ( 2.2
902 ( 1.9
856 ( 0.7
861 ( 1.1
55
90
91
11
9
7
34
1
1
e
e
e
39
66
55
18
61
34
27
e
e
e
9
e
0
4
91
100
96
150 ( 10.1
1
Re22+
Re33+
Re55+
515
570
570
0.084
0.156
0.113
537 ( 2.0
15 ( 0.2
16 ( 0.3
100
96
93
100
e
e
893 ( 2.2
803 ( 1.3
4
7
100
100
a Measured in a degassed MeCN solution at 25 °C. The excitation wavelength was 350 nm. b Emission maximum. c Quantum yield of emission.
d Percentages of pre-exponential factors, that is, an ) An/∑m3 )1Am (see eq 2). e A rise of emission was observed at the first stage. See Figure 3c.
tion of the pre-exponential factors of each component was
shaded by changes in the detection wavelength. By monitoring
at 470 nm, which is close to the emission maximum of the
terminal Re(I) units,40,41 the decay component with a lifetime
of 8 ( 0.1 ns was dominant (Figure 3a). This component
increased with the detected wavelength to 570 and 620 nm,
which are the emission maxima of the interior Re(I) unit and
the Ru(II) unit, respectively (see the inset in Figure 3c). The
pre-exponential factors with lifetimes of 133 ( 4.9 and 902 (
1.9 ns were similar to each other during monitoring at 570 nm,
and the 902 ns component was dominant at 620 nm. Using 480
nm excitation light, which can be absorbed only by the Ru(II)
unit, the emission decay curves could be fitted with a single-
exponential function with a lifetime of 902 ( 1.9 ns. These
results indicate that the three components with lifetimes of 8,
133, and 902 ns are a result of the emission from the terminal
Re(I) units, the interior Re(I) unit, and the Ru(II) unit,
respectively.
of the lifetimes of Ru-Re3A5+ with those of the model
complexes indicates that the intramolecular energy transfer
proceeded both from the excited interior Re(I) unit to the Ru(II)
unit and also from the excited terminal Re(I) unit to both the
interior Re(I) unit and the Ru(II) unit (Scheme 3a). The lifetime
of the terminal Re(I) unit in Ru-Re3A5+ (τ1 ) 8 ( 0.1 ns)
was shorter than that of Re33+ (15 ( 0.2 ns), because of the
additional energy transfer pathway to the Ru(II) unit (Scheme
3a). The energy transfer in Re33+ occurs from the terminal Re(I)
unit only to the interior Re(I) unit (Scheme 3e). The energy
transfer rate constant from the excited terminal Re(I) unit to
the interior Re(I) unit (k1(Re33+) in Scheme 3e) and the summed
rate constant of the radiative and nonradiative decays from each
Re(I) units in Re33+ can be determined as k1(Re33+) ) 6.5 ×
107 s-1, kr(Re33+, terminal) + knr(Re33+, terminal) ) 1.9 × 106
s-1, and kr(Re33+, interior) + knr(Re33+, interior) ) 1.1 × 106
s-1 using the same procedures that were reported previously33
(Supporting Information). These data are used as the energy
transfer rate constant k1(Ru-Re3A5+) in Scheme 3a, and
radiative and nonradiative decay rate constants form each
Re(I) unit in Ru-Re3A5+ (kr(Ru-Re3A5+, terminal) +
knr(Ru-Re3A5+, terminal)) because there is no strong electrical
interaction between the Ru(II) unit and the Re chain in
Ru-Re3A5+. Therefore, the direct energy transfer rate from
the terminal Re(I) unit to the Ru(II) unit (k3(Ru-Re3A5+)) can
be estimated with the following equation:
Table 2 summarizes the emission properties of the Ru(II)-Re(I)
multinuclear complexes and the corresponding model com-
plexes, that is, Ru2+ for the Ru(II) unit, Re22+ for the terminal
Re(I) unit, and Re33+ and Re55+ for the Re chain. A comparison
(40) Koike, K.; Hori, H.; Ishizuka, M.; Westwell, J. R.; Takeuchi, K.;
Ibusuki, T.; Enjouji, K.; Konno, H.; Sakamoto, K.; Ishitani, O.
Organometallics 1997, 16, 5724–5729.
(41) Tsubaki, H.; Tohyama, S.; Koike, K.; Saitoh, H.; Ishitani, O. Dalton
Trans. 2005, 385–395.
9
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A R T I C L E S
Yamamoto et al.
Scheme 3. Energy Transfer Processes and Their Rate Constants in the Ru(II)-Re(I) Multinuclear and the Corresponding Model Complexesa
a Assumptions for the calculation are written in brackets.
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A R T I C L E S
Scheme 4. Fates of the Excited States of the Re(I) Units Produced
1
k3(Ru-Re3A5+) =
- [kr(Re33+, terminal)
a
in Ru-Re3A5+
τ1(Ru-Re3A5+
)
+ knr(Re33+, terminal)] - k1(Re33+) ) 5.8 × 107 s-1 (3)
Although energy transfer from the terminal Re(I) unit to the
interior Re(I) unit affected the emission profile of the excited
state of the interior Re(I) unit, its decay curve can be easily
separated from the rise caused by the energy transfer because
the time scales were very different. Eenergy transfer should not
proceed from the excited interior Re(I) unit to the terminal Re(I)
unit because the energy transfer is endothermic (∆E ) 0.23
eV). Therefore, the following method can be applied to calculate
the rate constant of the energy transfer from the interior Re(I)
unit to the Ru(II) unit (k2(Ru-Re3A5+) in Scheme 3a):
1
k2(Ru-Re3A5+) )
-
τ2(Ru-Re3A5+
)
[kr(Ru-Re3A5+, interior) + knr(Ru-Re3A5+, interior)]
a The black arrows are absorbed photons processes, and the red arrows
are energy transfer processes.
1
=
- [kr(Re33+, interior) +
τ2(Ru-Re3A5+
)
knr(Re33+, interior)] ) 6.4 × 106 s-1 (4)
the two terminal Re(I) units of Ru-Re3A5+ should obstruct
the collision, and, consequently, the energy transfer slowed
down.
Using these energy transfer rates, we can estimate the fates
of the excited states of the Re(I) units produced in Ru-Re3A5+
(Scheme 4). We have reported that linear-shaped Re(I) oligo-
mers such as Re33+ have no strong interaction between the Re(I)
units. Therefore, the ratio of the absorbed photons between the
two terminal Re(I) units and the interior Re(I) unit was 7:3 at
350 nm using the data for Re22+. Because the spectrum of
Ru-Re3A5+ was very similar to the 1:1 summation of the
spectra of Ru2+ and Re33+ (Figure 1), the ratio of the absorbed
photons between the terminal and the interior Re(I) unit in the
Re chain of Ru-Re3A5+ is also approximately 7:3. When 100
photons are absorbed by the Re chains of Ru-Re3A5+, 70 of
those photons are absorbed by the terminal Re(I) units. The
ratio of the energy transfer rates from the terminal Re(I) unit to
theinteriorRe(I)unitandtotheRu(II)unit,thatis,k1(Ru-Re3A5+):
k3(Ru-Re3A5+), was 6.5:5.8 (Scheme 3a). Because 99% of the
excited terminal Re(I) units was quenched by the energy transfer
(see the Supporting Information), energy transfer from the
produced excited state makes both 36.5 of the excited interior
Re(I) units and 32.5 of the excited Ru(II) units. Although 15%
of the excited states of the internal Re(I) units, that is, (30 +
36.5) × 0.15 = 10, are deactivated via radiative and nonradiative
decays, energy transfer also occurs to make 56.5 of the excited
Ru(II) units (Supporting Information). Therefore, 89 of the
excited Ru(II) units are finally produced. The energy transfer
efficiency from the Re chain to the Ru(II) unit calculated by
this manner (89%) is consistent with the energy transfer
efficiency that was estimated from the emission spectra using
eq 1 as described above (86%).
The emission and lifetime data of Ru-Re3B5+, to which the
Ru(II) unit is connected with one of the terminal Re(I) units,
were compared to those of Ru-Re3A5+. Because the energy
transfer from the excited Re(dmb)(CO)2 unit to the Re(dmb)-
(CO)3 unit is a highly endergonic reaction, it should be very
slow. For Ru-Re3B5+, therefore, we can obtain the direct
energy transfer rate constant from the excited interior Re(I) unit,
which has the Re(dmb)(CO)2 structure, to the Ru(II) unit by
using the decay rate constants of excited Re33+ and the
following equation:
1
k3(Ru-Re3B5+) =
- [kr(Re33+, interior) +
τ2(Ru-Re3B5+
)
knr(Re33+, interior)] ) 8.1 × 106 s-1 (5)
The rate constant k2(Ru-Re3A5+) is slightly but obviously
slower than k3(Ru-Re3B5+), although the structures of the
energy donor and the acceptor are very similar between
Ru-Re3B5+ and Ru-Re3A5+. These results also indicate that
the energy transfer from the excited Re(I) unit to the Ru(II)
unit occurs via collision but the Fo¨rster-type mechanism is not
dominant. In Ru-Re3B3+, two kinds of the tricarbonyl Re(I)
units [Re(LL)(CO)3P-]+ occur (Re-I and Re-II in Figure 3b).
One of these units (Re-I) is directly connected to the Ru(II)
unit. However, only one emission lifetime component was
attributed to the tricarbonyl units (τ ) 11 ns). Consequently,
the energy transfer rates from the excited Re-I and Re-II units
to the Ru(II) unit (k2(Ru-Re3B5+)) and k4(Ru-Re3B5+) should
be similar each other.
We synthesized [Ru(dmb)2(C2dmb)Re(CO)2{PPh2(Ct C-
t-Bu)}2]3+ (Ru-Re3+ in Scheme 3d) as a model of the central
Ru(II)-Re(I) part in Ru-Re3A5+ and determined that the
energy transfer rate from the excited Re(I) unit to the Ru(II)
unit in the model was k2(Ru-Re3+) ) 2.3 × 108 s-1, which is
much faster than k2(Ru-Re3A5+). This result strongly suggests
that the intramolecular energy transfer from the excited Re(I)
unit to the Ru(II) unit in both Ru-Re3+ and Ru-Re3A5+
proceeds via collision between them. The steric hindrance of
Four kinds of emitters in Ru-Re57+ exist (Scheme 3c): the
Ru(II) unit, two kinds of the [Re(dmb)(CO)2(PP)2] type units
(Re-III and Re-IV), and the terminal Re(I) unit. If the energy
transfer rate from the excited terminal Re(I) unit to the interior
unit Re-IV (k1(Ru-Re57+)) is the same to that of Re55+
(k1(Re55+) ) 6.1 × 107 s-1), k4(Ru-Re57+) can be estimated
as 2.8 × 107 s-1 by the same procedures used for
k3(Ru-Re3A5+). The energy migration phenomenon between
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A R T I C L E S
Yamamoto et al.
Photochemical Reactions. For the photochemical ligand sub-
stitution reaction, the solution was irradiated by an Eikosha 500
W high-pressure mercury lamp with a uranium glass filter (>330
nm) in a Pyrex doughnut-form cell. N2 gas was bubbled through
the solution at 50-60 °C.
Separation Using Size Exclusion Chromatography. Separation
of the multinuclear complexes was achieved by size exclusion
chromatography (SEC) using a pair of Shodex PROTEIN KW-
2002.5 columns (300 mm × 20.0 mm i.d.) with a KW-LG guard-
column (50 mm × 8.0 mm i.d.) and a JAI LC-9201 recycling
preparative HPLC apparatus with a JASCO 870-UV detector. The
eluent was a 1:1 (v/v) mixture of methanol and acetonitrile with
0.15 M CH3CO2NH4, and the flow rate was 5.0 mL min-1. Details
have been reported elsewhere.37
Emission Lifetime Measurement. An acetonitrile solution of
the metal complex was degassed by the freeze-pump-thaw method
and then transferred into a 10 × 10 × 40 mm quartz cuvette. The
emission lifetimes were measured using a Horiba NAES-1100 or
FluoroCube 3000U time-correlated single-photon-counting system.
The sample solutions were excited by an NFL-111 ns H2 lamp with
a proper band-pass filter (Toshiba U350) for the NAES-1100 or
by a Nano LED-370 (371 nm) for the FluoroCube. The decay profile
simulations were performed by a nonlinear least-squares method.
Materials. The THF was distilled from Na/benzophenone just
before use. The acetonitrile was dried three times over P2O5 and
then distilled from CaH2 prior to use. Dichloromethane was dried
over CaH2 prior to use. All purified solvents were kept under N2
before use. Spectral-grade solvents were used for the spectroscopic
measurements. Other reagents and solvents were purchased reagent-
grade and used without further purification.
the interior units in the linear-shaped Re oligomers and polymers
is not well understood.33a Two lifetime components of 71 and
150 ns were observed and attributable to the interior Re(I) units.
Therefore, the energy migration processes between the interior
Re(I) units should be much slower than energy transfers from
these Re(I) units to the Ru(II) unit (km , 3.73 × 106 s-1: see
the Supporting Information). We can estimate the energy transfer
rates as k3(Ru-Re57+) ) 1.3 × 107 s-1 and k2(Ru-Re57+) )
5.4 × 106 s-1 using τ ) 71 and 150 ns because of the structural
and environmental similarities to the interior Re(I) units in
Ru-Re3B5+ (k3(Ru-Re3B5+
)
)
8.1
×
106 s-1
) and
Ru-Re3A5+ (k2(Ru-Re3A5+) ) 6.4 × 106 s-1), respectively.
In Scheme 3, the energy transfer rate from each excited Re(I)
unit to the Ru(II) unit or to the other Re(I) unit can be
summarized. In Ru-Re3B5+ and Ru-Re57+, both of the energy
transfer efficiencies from the excited Re chain to the Ru(II) unit
were calculated as 89% by procedures similar to those for
Ru-Re3A5+
.
Conclusion
We have successfully synthesized linear Re(I) trinuclear and
pentanuclear complexes with the Ru(II) trisdiimine complex as
an energy acceptor. All of the Ru(II)-Re(I) multinuclear
complexes were emissive, mostly from the Ru(II) unit, at room
temperature in solution. In these complexes, photoinduced
intramolecular energy transfer proceeded efficiently from the
excited Re(I) units to the Ru(II) unit. All of these energy transfer
rate constants and efficiencies could be estimated using the
photophysical data of the corresponding model complexes.
Both the dmb ligand on the Ru(II) unit and the CO ligand
on the terminal Re(I) units can be substituted with various types
of ligands, and, therefore, this type of heteronuclear complex
can potentially be used as a constituent unit in a new series of
light-harvesting materials. We have already found that
Ru-Re3A5+ works as an effective photocatalyst for CO2
reduction. The possibilities including this preliminary result are
currently under investigation in our laboratory.
Synthesis. The standard Schlenk techniques were employed for
synthesis. Ru(dmb)2(C2dmb)Re(CO)3Cl (Ru-Re(CO)3Cl2+), fac-
Re(CO)3(dmb)(CF3SO3), [Re(dmb)(CO)3-PP-Re(dmb)(CO)2-
(CF3SO3)]+, and the corresponding model complexes were prepared
according to the method in the literature.33,34
[Ru(dmb)2(C2dmb)Re(CO)2{-PP-Re(dmb)(CO)2-PP-
Re(dmb)(CO)3}2](PF6)7, (Ru-Re57+)(PF6-)7. The synthesis
procedure for Ru-Re57+ is summarized in Scheme 5. A dichlo-
romethane solution (100 mL) of Ru-Re(CO)3Cl2+(PF6-)2 (100 mg,
0.07 mmol) with 1 equiv of Tl(CF3SO3) (25 mg, 0.07 mmol) was
refluxed for 1 day in dim light, giving [Ru(dmb)2(C2dmb)-
Re(CO)3(CF3SO3)]2+(PF6-)2 (Ru-Re(CO)3(CF3SO3)2+). A dichlo-
romethane solution (100 mL) of Ru-Re(CO)3(CF3SO3)2+ (90 mg,
0.06 mmol) with bis(diphenylphosphino)acetylene (PP) (118 mg,
0.30 mmol) was stirred at room temperature in dim light for 1 day,
giving [Ru(dmb)2(C2dmb)Re(CO)3(η1-PP)]3+ (Ru-Re(CO)3(η1-
PP)3+). Next, 100 mL of THF was added, and the solution was
irradiated at 50 °C for 8 h using a high-pressure mercury lamp
with a uranium glass filter (>330 nm). The result was [Ru(dmb)2-
(C2dmb)Re(CO)2(η1-PP)2]3+ (Ru-Re(CO)2(η1-PP)23+). The sol-
vent was evaporated, and the residual red solid was washed several
times with degassed ether. A dichloromethane solution (100 mL)
Experimental Section
Instrumentation and Measurements. The IR spectra were
recorded in an MeCN solution with a JASCO FT/IR-610 spec-
trometer at 1 cm-1 resolution. The 1H and H,H COSY NMR spectra
were measured in an acetone-d6 solution using a JEOL JNM-AL400
(400 MHz). The residual protons of the acetone-d6 were used as
internal standards for the measurements. The electrospray ionization
mass spectra (ESI MS) were measured using a Shimadzu LCMS-
2010A mass spectrometer or a Waters LCT Premier XE ESI
TOFMS spectrometer. The UV/vis absorption spectra were recorded
in an MeCN solution with a JASCO V-565 spectrophotometer. The
emission spectra were recorded at 25 °C using a JASCO FP-6500
spectrophotometer, and the correction data for the detector sensitiv-
ity were supplied by JASCO. The sample solutions were degassed
by the freeze-pump-thaw method before the emission measure-
ments. The emission quantum yields were evaluated with emission
containing Ru-Re(CO)2(η1-PP)2 and 2 equiv of [Re(dmb)-
3+
(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+ was stirred at room tem-
perature for 1 day and then at 50 °C for 1 day in dim light. After
the solution was evaporated, the residue was separated using SEC.
The band, which included the product, was evaporated under
reduced pressure and dissolved in a small amount of methanol. The
solution was added dropwise to a concentrated MeOH solution of
NH4PF6. The precipitated orange powder was filtered off, washed
with diethylether, and then dried in a vacuum. Yield: 13%. Anal.
Calcd for C212H172F42N16O12P15Re5Ru1: C, 46.89; H, 3.19; N, 4.13.
Found: C, 46.82; H, 3.41; N, 4.22. 1H NMR (δ, 400 MHz,
CD3COCD3): 8.73 (s, 1H, R-3), 8.67 (s, 1H, ꢀ-3), 8.65 (s, 4H, dmb-
3,3′ of Ru(dmb)2), 8.52, 8.48 (d, 4H, J ) 7.6 Hz, dmb-6,6′ of
terminal-Re(dmb)(CO)3), 8.20, 8.11 (s, 4H, dmb-3,3′ of terminal-
Re(dmb)(CO)3), 7.94 (d, 1H, J ) 5.4 Hz, R-6), 7.90 (s, 1H, γ-3),
7.84 (s, 1H, δ-3), 7.83 (d, 4H, J ) 5.6 Hz, dmb-6,6′ of Ru(dmb)2),
7.81 (d, 1H, J ) 5.4 Hz, ꢀ-6), 7.80 (d, 1H, J ) 5.1 Hz, δ-6), 7.77
from Ru(bpy)3 in degassed acetonitrile (Φem ) 0.095).42
2+
2+
(42) Recently, the emission quantum yield of Ru(bpy)3 has been
reevaluated from Φem ) 0.062 to Φem ) 0.095: Suzuki, K.; Kobayashi,
A.; Kaneko, S.; Takehira, K.; Yoshihara, T.; Ishida, H.; Shiina, Y.;
Oishi, S.; Tobita, S. Phys. Chem. Chem. Phys. 2009, 11, 9850–9860.
Although we used the new value (Φem ) 0.095) as the reference in
this Article, the older data (Φem ) 0.062) were used in our previous
paper23 about the photophysics of the linear Re(I) oligomers and
polymers. The readers should be careful about this point if they
compare emission quantum yields reported in the two papers.
9
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New Light-Harvesting Molecular Systems
A R T I C L E S
a
Scheme 5. Synthesis of Ru-Re57+
a Reagents and reaction conditions: (i) Tl(CF3SO3) (1 equiv) in CH2Cl2 reflux for 2 days; (ii) excess PP in CH2Cl2 at room temperature for 1 day and then
at 40 °C for 1 day; (iii) hV (>330 nm) in CH2Cl2 at 50 °C for 8 h; and (iv) [Re(dmb)(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+ (2 equiv) in CH2Cl2 at room
temperature for 1 day and then at 40 °C for 1 day.
a
a
Scheme 6. Synthesis of Ru-Re3A5+
Scheme 7. Synthesis of Ru-Re3B5+
a All complexes were PF6 salts. Reagents and reaction conditions: (i) 1
equiv of [Re(dmb)(CO)3-PP-Re(dmb)(CO)2(CF3SO3)]+ in CH2Cl2 at room
temperature for 1 day and then at 40 °C for 1 day.
a Reagents and reaction conditions: (i) [Re(dmb)(CO)3-PP-
Re(dmb)(CO)2(CF3SO3)]+ (2 equiv) in CH2Cl2 at room temperature for 1
day and then at 40 °C for 1 day.
4H, J ) 5.6 Hz, dmb-6,6′ of Ru(dmb)2), 7.81 (d, 1H, J ) 5.4 Hz,
ꢀ-6), 7.80 (d, J ) 5.1 Hz, 1H, δ-6), 7.77 (d, J ) 5.1 Hz, 1H, γ-6),
7.65-7.24 (m, 44H, R, ꢀ, δ, γ-5, and Ph), 7.37 (d, 4H, J ) 5.6
Hz, dmb-5 of Ru(dmb)2), 7.18, 7.15 (d, 4H, J ) 5.4 Hz, dmb-5 of
terminal-Re(dmb)(CO)3). IR (MeCN): νCO/cm-1 ) 2044 (s), 1960
(b), 1929 (m), 1884 (s). ESI MS in MeCN (m/z): 555.2 [M]5+, 730.2
(d, 1H, J ) 5.1 Hz, γ-6), 7.70, 7.61 (s, 4H, dmb-6 of Re-IV),
7.65-7.24 (m, 84H, R,ꢀ,δ,γ-5, and Ph), 7.58, 7.57 (d, 4H, J ) 5.6
Hz, dmb-6 in Re-IV), 7.37 (d, 4H, J ) 5.6 Hz, dmb-5 in
Ru(dmb)2), 6.92, 6.88 (d, 4H, J ) 7.6 Hz, dmb-5 of terminal-
Re(dmb)(CO)3), 6.48, 6.39 (d, 4H, J ) 5.6 Hz, dmb-5 of Re-IV).
IR (MeCN): νCO/cm-1 ) 2044 (s), 1961 (s), 1929 (m), 1884 (m).
ESI MS in MeCN (m/z): 630.8 [M]7+, 760.1 [M + PF6]6+, 941.1
[M + PF6]4+
.
[Ru(dmb)2(C2dmb)Re(CO)3-PP-Re(dmb)(CO)2-PP-
Re(dmb)(CO)3](PF6)5, (Ru-Re3B5+)(PF6-)5. The synthesis
procedure for Ru-Re3B5+ is shown in Scheme 7. A dichlo-
romethane solution (100 mL) containing Ru-Re(CO)3(η1-PP)3+
(100 mg, 0.05 mmol) and an equivalent of [Re(dmb)(CO)3-PP-
Re(dmb)(CO)2(CF3SO3)]+ (81 mg, 0.05 mmol) was stirred at room
temperature in dim light for 1 day. The resulting Ru-Re3B5+ was
isolated using a method similar to the one used to isolate
Ru-Re57+(PF6-)7. Yield: 21%. Anal. Calcd for C132H110F30N12-
O8P9Re3Ru: C, 45.29; H, 3.17; N, 4.80. Found: C, 45.19; H, 3.47;
[M + 2PF6]5+
.
[Ru(dmb)2(C2dmb)Re(CO)2{-PP-Re(dmb)(CO)3}2](PF6)5,
(Ru-Re3A5+)(PF6-)5. A similar procedure for Ru-Re5 was
7+
applied to the synthesis of Ru-Re3A5+ using fac-
Re(dmb)(CO)3(CF3SO3) instead of [Re(dmb)(CO)3-PP-Re(dmb)-
(CO)2(CF3SO3)]+ (Scheme 6). Yield: 16%. Anal. Calcd for
C
132H110F30N12O8P9Re3Ru: C, 45.29; H, 3.17; N, 4.80. Found: C,
45.21; H, 3.39; N, 4.55. 1H NMR (δ, 400 MHz, CD3COCD3): 8.82
(s, 1H, R-3), 8.67 (s, 1H, ꢀ-3), 8.65 (s, 4H, dmb-3,3′ of Ru(dmb)2),
8.53, 8.47 (d, 4H, J ) 5.4 Hz, dmb-6,6′ of terminal-Re(dmb)(CO)3),
8.14, 8.10 (s, 4H, dmb-3,3′ of terminal-Re(dmb)(CO)3), 7.94 (d,
1H, J ) 5.4 Hz, R-6), 7.90 (s, 1H, γ-3), 7.84 (s, 1H, δ-3), 7.83 (d,
1
N, 4.64. H NMR (δ, 400 MHz, CD3COCD3): 8.82 (s, 1H, R-3),
8.70 (s, 1H, γ-3), 8.67 (s, 1H, ꢀ-3), 8.65 (s, 4H, dmb-3,3′ of
Ru(dmb)2), 8.61 (d, 1H, J ) 5.4 Hz, γ-6), 8.52, 8.48 (d, 4H, J )
9
J. AM. CHEM. SOC. VOL. 132, NO. 33, 2010 11751

A R T I C L E S
Yamamoto et al.
a
Scheme 8. Synthesis of Ru-Re3+
a Reagents and reaction conditions: (i) PPh2-Ct C-t-Bu (2 equiv) in toluene reflux for 1 day; (ii) Ag(CF3SO3) (1 equiv) in THF reflux for 3 h; and (iii)
in acetone/o-dichlorobenzene (1:3 v/v) reflux for 1 day.
7.6 Hz, dmb-6,6′ of Re(dmb)(CO)3), 8.20, 8.11 (s, 4H, dmb-3,3′
of Re-II), 7.94 (d, 1H, J ) 5.4 Hz, R-6), 7.83 (d, 4H, J ) 5.6 Hz,
dmb-6,6′ of Ru(dmb)2), 7.79 (s, 1H, δ-3), 7.81 (d, 1H, J ) 5.4 Hz,
ꢀ-6), 7.70 (s, 2H, dmb-3,3′ of interior Re(dmb)(CO)2), 7.60-7.27
(m, 49H, R, ꢀ, δ, γ-5, δ-6, and dmb-5,5′ in Ru(dmb)2), 7.58, 7.57
(d, 2H, J ) 7.08 Hz, dmb-6,6′ of interior Re(dmb)(CO)2), 7.08,
6.62 (d, 2H, J ) 7.08 Hz, dmb-5,5′ of interior Re(dmb)(CO)2),
6.92, 6.88 (d, 2H, J ) 7.56 Hz, dmb-5,5′ of Re-II). IR (MeCN):
light for 1 day, giving Re(CO)3(PPh2-Ct C-t-Bu)2Cl. The solvent
was evaporated under reduced pressure, and 50 mL of THF was
added to the residue. The THF solution of Re(CO)3(PPh2-Ct C-t-
Bu)2Cl with an equivalent of Ag(CF3SO3) was refluxed in dim light
for 3 h, giving Re(CO)3(PPh2-Ct C-t-Bu)2(CF3SO3). The solvent
was evaporated under reduced pressure, and 30 mL of acetone was
added to the residue. A mixed solution of acetone and o-
dichlorobenzene (1:3 v/v) of Re(CO)3(PPh2-Ct C-t-Bu)2(CF3SO3)
with an equivalent of [Ru(dmb)2(C2dmb)](PF6)2 was refluxed in
dim light for 1 day. The solution was evaporated, and the residue
was separated using SEC. The band that included the product was
evaporated under reduced pressure, and a methanol solution of the
residue was added dropwise to a concentrated MeOH solution of
NH4PF6. The precipitated yellow powders were filtered off, washed
with diethylether, and then dried in a vacuum. The yield based
on [Ru(dmb)2(C2dmb)](PF6)2 used: 34%. Anal. Calcd for
C86H84F18N8O2P5ReRu: C, 50.49; H, 4.14; N, 5.48. Found: C, 50.26;
ν
CO/cm-1 ) 2044 (s), 1960 (b), 1929 (m), 1884 (s). ESI MS in
MeCN (m/z): 555.2 [M]5+, 730.2 [M + PF6]4+, 1022.0 [M +
2PF6]3+
.
Synthesis and Identification of the Model Complexes. Similar
synthesis procedures for the corresponding 2,2′-bipyridine com-
plexes33 were applied for the synthesis of the linear-type of Re(I)
oligomers with 4,4′-dimethyl-2,2′-bipyridine (dmb), that is,
[Re(dmb)(CO)3-PP-Re(dmb)(CO)3]2+ (Re22+), [Re(dmb)(CO)3-
PP-Re(dmb)(CO)2-PP-Re(dmb)(CO)3]3+ (Re33+), and [Re(dmb)-
(CO)3{-PP-Re(dmb)(CO)2}3-PP-Re(dmb)(CO)3]5+ (Re55+).
1
H, 4.00; N, 5.27. H NMR (δ, 400 MHz, CD3COCD3): 8.82 (s,
1
Re22+, yield: 90%. H NMR (δ, 400 MHz, CD3COCD3): 8.54
1H, R-3), 8.66-8.69 (m, 5H, ꢀ-3 and dmb-3,3′), 8.35 (s, 1H, γ or
δ-3), 8.32 (d, J ) 5.7 Hz, 1H, γ or δ-6), 8.29 (s, 1H, γ or δ-3),
8.12 (d, J ) 5.7 Hz, 1H, γ or δ-6), 7.94 (d, J ) 5.7 Hz, 1H, R-6),
7.80-7.84 (m, 5H, ꢀ-6, dmb-6,6′ of Ru(dmb)2), 7.27-7.60 (m,
28H, R, ꢀ, γ, and δ-5, dmb-5,5′ of Ru(dmb)2, and Ph), 3.15-3.28
(m, 4H, -CH2CH2-), 2.52-2.58 (m, 18H, R-dmb-CH3, δ-dmb-
CH3, dmb-CH3 of Ru(dmb)2), 1.14-1.15 (m, 18H, t-Bu). ESI-MS
in MeCN (m/z): 537 [M]3+, 879 [M + PF6]2+. FT-IR (in CH2Cl2)
νCO (cm-1): 1943, 1873.
(d, 4H, J ) 5.6 Hz, dmb-6,6′), 8.24 (s, 4H, dmb-3,3′), 7.68 (dd,
4H, J ) 7.2, 6.8 Hz, Ph-p), 7.53 (m, 8H, J ) 7.2, 6.8, 2.4 Hz,
Ph-m), 7.26 (d, 8H, J ) 6.8, Ph-o), 7.24 (d, 4H, J ) 5.6 Hz, dmb-
5,5′). IR (CH2Cl2): νCO/cm-1 ) 2045, 1962, 1930. ESI-MS in
MeCN (m/z): 652 [M]2+
.
Re33+, yield: 64%. Anal. Calcd for C96H74F18N6O8P7Re3Ru: C,
1
45.09; H, 2.92; N, 3.29. Found: C, 45.20; H, 3.01; N, 3.22. H
NMR (δ, 400 MHz, CD3COCD3): 8.52 (d, 4H, J ) 5.8 Hz, dmb-
6,6′ of Re(dmb)(CO)3), 8.11 (s, 4H, dmb-3,3′ of Re(dmb)(CO)3),
7.75 (d, 2H, J ) 6.1 Hz, dmb-6,6′ of Re(dmb)(CO)2), 7.73 (s, 2H,
dmb-3,3′ of Re(dmb)(CO)2), 7.64-7.58 (dd, 8H, J ) 7.2, 6.8 Hz,
Ph-p), 7.49-7.41 (m, 16H, Ph-m), 7.26 (d, 8H, J ) 6.8 Hz,Ph-o),
7.24 (d, 4H, J ) 5.6 Hz, dmb-5,5′ of Re(dmb)(CO)3), 7.11 (dd,
8H, J ) 7.2, 6.8 Hz, Ph-o), 6.58 (d, 2H, J ) 5.2 Hz, dmb-5,5′ of
Re(dmb)(CO)2). IR (CH2Cl2): νCO/cm-1 ) 2044, 1960, 1929, 1884.
[Re(dmb)(CO)2{PPh2(Ct C-t-Bu)}2](PF6). A procedure similar
to the one used for [Re(dmb)(CO)2{PPh2(Ct C-t-Bu)}2]+ was used
to synthesize Ru-Re3+. The reactant dmb was used instead of
[Ru(dmb)2(C2dmb)](PF6)2. Anal. Calcd for C50H50F6N2O2P3Re1: C,
1
54.39; H, 4.56; N, 2.54. Found: C, 54.63; H, 4.77; N, 2.50. H
NMR (δ, 400 MHz, CD3COCD3): 8.31 (s, 2H, dmb-3,3′), 8.18 (d,
J ) 5.8 Hz, 2H, dmb-6,6′), 7.32-7.49 (m, 20H, Ph), 7.28 (d, J )
5.8 Hz, 2H, dmb-5,5′), 2.56 (s, 6H, dmb-CH3), 1.14 (s, 18H,
-C(CH3)3). IR (CH2Cl2): νCO/cm-1 ) 1945, 1874. ESI MS in
MeCN (m/z): 960 [M]+.
ESI-MS in MeCN (m/z): 708.2 [M]3+, 1133.6 [M + PF6]2+
.
Re55+, yield: 52%. Anal. Calcd for C176H138F35N10O12P8Re5: C,
1
47.73; H, 3.14; N, 3.16. Found: C, 47.89; H, 3.22; N, 3.41. H
NMR (δ, 400 MHz, CD3COCD3): 8.50 (d, 4H, J ) 6.1 Hz, dmb-
6,6′ of Re(dmb)(CO)3), 8.10 (s, 4H, dmb-3,3′ of Re(dmb)(CO)3),
7.74 (d, 4H, J ) 6.1 Hz, dmb-6,6′ of Re(dmb)(CO)2), 7.72 (s, 4H,
dmb-3,3′ of Re(dmb)(CO)2), 7.64-7.58 (dd, 8H,, J ) 7.2, 6.8 Hz,
Ph-p), 7.49-7.41 (m, 16H, Ph-m), 7.26 (d, 8H, J ) 6.8 Hz,Ph-o),
7.24 (d, 8H, J ) 5.6 Hz, dmb-5,5′ of Re(dmb)(CO)3), 7.11 (dd,
8H, J ) 7.2, 6.8 Hz, Ph-o), 6.49 (d, 4H, J ) 6.1 Hz, dmb-5,5′ of
Re(dmb)(CO)2), 6.46 (d, 2H, J ) 6.1 Hz, dmb-5,5′ in Re(dm-
b)(CO)2). IR (CH2Cl2): νCO/cm-1 ) 2044, 1960, 1955, 1929, 1883.
Supporting Information Available: The ESI-MS and ESI-
TOFMS spectra of Ru-Re57+ (Figures S1 and S2), the ESI-
MS spectra of Ru-Re3A5+ (Figure S3), the UV/vis absorption
spectra of Ru-Re3B5+ and the corresponding model complexes
(Figure S4), the emission spectra of Ru-Re57+, Ru-Re3B5+
,
and the corresponding model complexes (Figure S5), and the
estimation methods for the energy transfer rate constant in Re33+
and the energy transfer efficiency in Ru-Re3A5+. This material
is available free of charge via the Internet at http://pubs.acs.org.
ESI-MS in MeCN (m/z): 753.3 [M]5+, 977.2 [M + PF6]4+
.
[Ru(dmb)2(C2dmb)Re(CO)2{PPh2(Ct C-t-Bu)}2]3+ (PF6-)3,
(Ru-Re3+)(PF6-)3. The synthesis procedure for Ru-Re3+ is shown
in Scheme 8. A toluene solution (100 mL) of Re(CO)5Cl (100 mg,
0.28 mmol) with 2 equiv of PPh2-Ct C-t-Bu was refluxed in dim
JA104601B
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11752 J. AM. CHEM. SOC. VOL. 132, NO. 33, 2010