Syntheses, characterization, and photochemical properties of amidate-bridged Pt(bpy) dimers tethered to Ru(bpy)32+ derivatives

Article abstract of DOI:10.1039/c0dt01548b

Amidate-bridged diplatinum(ii) entities [Pt₂(bpy) ₂(μ-amidato)₂]²⁺ (amidate = pivalamidate and/or benzamidate; bpy = 2,2′-bipyridine) were covalently linked to one or two Ru(bpy)₃²⁺-type derivatives. An amide group was introduced at the periphery of Ru(bpy)₃²⁺ derivatives to give metalloamide precursors [Ru(bpy)₂(BnH)]²⁺ (abbreviated as RuBnH, n = 1 and 2), where deprotonation of amide BnH affords the corresponding amidate Bn, B1H = 4-(4-carbamoylphenyl)-2,2′-bipyridine, and B2H = ethyl 4′-[N-(4-carbamoylphenyl)carbamoyl]-2,2′- bipyridine-4-carboxylate. From a 1:1:1 reaction of [Pt₂(bpy) ₂(μ-OH)₂](NO₃)₂, RuBnH, and pivalamide, trinuclear complexes [Pt₂(bpy)₂(μ-RuBn) (μ-pivalamidato)]⁴⁺ (abbreviated as RuBn-Pt₂) were isolated and characterized. Tetranuclear complexes [Pt₂(bpy) ₂(μ-RuBn)₂]⁶⁺ (abbreviated as (RuBn) ₂-Pt₂) were separately prepared and characterized in detail. The quenching of the triplet excited state of the Ru(bpy) ₃²⁺ derivative (i.e., Ru*(bpy)₃ ²⁺) upon tethering the Pt₂(bpy)₂(μ-amidato) ₂²⁺ moiety is strongly enhanced in RuB1-Pt₂ and (RuB1)₂-Pt₂, while it is only slightly enhanced in RuB2-Pt₂ and (RuB2)₂-Pt₂. These are partly explained by the driving forces for the electron transfer from the Ru*(bpy)₃²⁺ moiety to the Pt₂(bpy) ₂(μ-amidato)₂²⁺ moiety (ΔG° _ET); the ΔG°_ET values for RuB1-Pt₂, (RuB1)₂-Pt₂, RuB2-Pt₂, and (RuB2) ₂-Pt₂ are estimated as -0.01, 0.00, +0.22, and +0.28 eV, respectively. The considerable difference in the photochemical properties of the B1- and B2-bridged systems were further examined based on the emission decay and transient absorption measurements, which gave results consistent with the above conclusions.

Full text of DOI:10.1039/c0dt01548b

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PAPER
Syntheses, characterization, and photochemical properties of amidate-bridged
2
+
Pt(bpy) dimers tethered to Ru(bpy) derivatives†
3
Masanari Hirahara, Shigeyuki Masaoka and Ken Sakai*a
a
a,b
Received 7th November 2010, Accepted 25th February 2011
DOI: 10.1039/c0dt01548b
2
+
Amidate-bridged diplatinum(II) entities [Pt
2
(bpy)
2
(m-amidato)
2
] (amidate = pivalamidate and/or
2+
benzamidate; bpy = 2,2¢-bipyridine) were covalently linked to one or two Ru(bpy)
3
-type derivatives.
derivatives to give metalloamide
(BnH)] (abbreviated as RuBnH, n = 1 and 2), where deprotonation of amide BnH
affords the corresponding amidate Bn, B1H = 4-(4-carbamoylphenyl)-2,2¢-bipyridine, and B2H = ethyl
¢-[N-(4-carbamoylphenyl)carbamoyl]-2,2¢-bipyridine-4-carboxylate. From a 1 : 1 : 1
reaction of [Pt (bpy) (m-OH) ](NO , RuBnH, and pivalamide, trinuclear complexes
Pt (bpy) (m-RuBn)(m-pivalamidato)] (abbreviated as RuBn-Pt
Tetranuclear complexes [Pt
and characterized in detail. The quenching of the triplet excited state of the Ru(bpy)
2
+
An amide group was introduced at the periphery of Ru(bpy)
3
2
+
precursors [Ru(bpy)
2
4
2
2
2
3 2
)
4
+
[
2
2
2
) were isolated and characterized.
(abbreviated as (RuBn) -Pt ) were separately prepared
6
+
2
(bpy)
2
(m-RuBn)
2
]
2
2
2
+
3
derivative (i.e.,
moiety is strongly enhanced in RuB1-Pt and
, while it is only slightly enhanced in RuB2-Pt and (RuB2) -Pt . These are partly
explained by the driving forces for the electron transfer from the Ru*(bpy)
2
+
2+
Ru*(bpy)
RuB1) -Pt
3
) upon tethering the Pt
2
(bpy)
2
(m-amidato)
2
2
(
2
2
2
2
2
2
+
3
moiety to the
, (RuB1) -Pt , RuB2-Pt
are estimated as -0.01, 0.00, +0.22, and +0.28 eV, respectively. The considerable difference
2
+
◦
◦
Pt
2
(bpy)
2
(m-amidato)
2
moiety (DG ET); the DG ET values for RuB1-Pt
2
2
2
2
, and
(
RuB2)
2
-Pt
2
in the photochemical properties of the B1- and B2-bridged systems were further examined based on the
emission decay and transient absorption measurements, which gave results consistent with the above
conclusions.
Introduction
Visible light-induced water splitting into molecular oxygen and
hydrogen has been considered as one of the most attractive
2+
2+
Scheme 1 Three-component system consisting of Ru(bpy)
an H -evolving catalyst.
3
, MV , and
1,2
solar energy conversion processes. In this context, tris(2,2¢-
2
2
+
bipyridine)ruthenium(II) (Ru(bpy)
3
) has attracted considerable
attention for many years due to its capability of driving both
3
photoinduced water oxidation and reduction processes. Scheme
2
+
dimers [Pt(II)
2
(NH
3
)
4
(m-amidato)
2
]
(amidate = acetamidate, 2-
7a–c
1
depicts one of the most widely studied half-cell systems
fluoroacetamidate, a-pyrrolidinonate, a-pyridonate, etc.)
also highly active as catalysts for HER. During our on-going
studies on the catalytic activities of various mononuclear and
are
for hydrogen evolution reaction (HER), where methylviologen
2
+
(
N,N¢-dimethyl-4,4¢-bipyridinium, abbreviated as MV ) is used
as an electron relay and EDTA (ethylenediaminetetraacetic acid
7
4
dinuclear platinum(II) complexes, the major concern has been
disodium salt) is adopted as a sacrificial electron donor.
4,5a
focused on the catalytic enhancement arising from the filled-filled
interaction between the Pt(II) dz2 orbitals within the dimeric units.
Our recent study further demonstrated that the formation of a
hydridodiplatinum(II,III) intermediate, stabilized with a metal–
metal bond, plays a crucial role in the catalytic enhancement.
On the other hand, attempts have also been made by us and
others to develop hybrid molecules driving both photoinduced
charge separation and catalytic reduction of water into molecular
hydrogen. The first active model of such a ‘photo-hydrogen-
evolving (abbreviated as PHE) molecular device’, developed in
As catalysts for HER, colloidal platinum, Co- and Rh-based
molecular systems, and hydrogenase were reported to be active.
5
6
We later found that amidate-bridged cis-diammineplatinum(II)
8
a
Department of Chemistry, Faculty of Science, Kyushu University,
9
Hakozaki 6-10-1, Higashi-ku, Fukuoka, 812-8581, Japan. E-mail: ksakai@
chem.kyushu-univ.jp
10
b
PRESTO, Japan Science and Technology Agency (JST), Honcho 4-1-8,
Kawaguchi, Saitama, 332-0012, Japan
†
1
Electronic supplementary information (ESI) available: H NMR spectra,
transient absorption spectra, ESI-TOF mass spectra, and additional
absorption spectral data. See DOI: 10.1039/c0dt01548b
9
our group, is depicted below (RuPt in Scheme 2).
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3967–3978 | 3967

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2
+
single Ru(bpy)
3
derivative. In this work, two bridging spacer
ligands B1 and B2 have been prepared to develop such RuPt
systems, i.e., RuB1-Pt and RuB2-Pt (illustrated below). Each
2
2
2
trinuclear compound was prepared through a one-pot reaction of
2
+
2+
[
Pt
2
(bpy)
2
(m-OH)
2
] , [Ru(bpy)
2
(BnH)] (abbreviated as RuBnH)
(
n = 1 and 2), and pivalamide followed by separation of the trin-
from three possible diplatinum products
uclear product RuBn-Pt
2
Scheme 2 Photo-hydrogen-evolving molecular device.
(i.e., Pt , RuBn-Pt , and (RuBn) -Pt ). The tetranuclear derivative
2
2
2
2
of each ligand system (i.e., (RuBn)
from a reaction of [Pt (bpy)
2
-Pt
2
2+
) was separately prepared
and RuBnH. Although all
Importantly, the HER driven by such hybrid systems has
2
2
(m-OH)
2
]
also been shown to proceed via the formation of a diplatinum
of these compounds have been found to exhibit no PHE activity,
we have succeeded in establishing a facile synthetic strategy
applicable to the development of such asymmetric and symmetric
supramolecular architectures. More importantly, through exam-
ining the photochemical and electrochemical properties of these
compounds, some important concepts have been established with
regard to the design strategies to the more efficient PHE molecular
devices.
9
a,e,h
intermediate.
An important new approach would be to replace the catalyst
core with the more highly active one to improve the PHE activity.
Since the amidate-bridged diplatinum(II) cores have been proven
to exhibit higher H
PtCl (bpy) unit in RuPt (Scheme 2), the diplatinum(II) systems
tethered to Ru(bpy)
higher PHE activity. In this context, a tetranuclear complex Ru
Scheme 3) was previously prepared by reacting the original RuPt
system with pivalamidate ligand. Nevertheless, Ru Pt was found
Moreover, the Ru Pt system
depicted in Scheme 3 was also found to show no PHE activity.
2
-evolving activity in comparison with the
2
2
+
3
derivatives have been considered to exhibit
Pt
2
2
(
Results and discussion
2
2
7d,9c
to exhibit no PHE activity at all.
2
7d,9c
Syntheses
3
Consequently, we postulated that deactivation of the MLCT
excited state is greatly enhanced through the energy transfer (ENT)
Hybrid systems RuBn-Pt
prepared according to the synthetic scheme illustrated in Scheme
. In the synthesis of RuBn-Pt , an aqueous solution containing
Pt (bpy) (m-OH) ](NO , RuBnH, and pivalamide in a 1 : 1 : 1
2
and (RuBn)
2
-Pt (n = 1 and 2) were
2
2
+
or electron transfer (ET) among the closely located Ru(bpy)
moieties in these systems.
3
4
2
[
2
2
2
3 2
◦
)
ratio was reacted at 70 C to yield three types of diplatinum(II)
complexes (Scheme 4, route I). If RuBnH and pivalamide are
similar in the rate of ligand substitution, the distribution of
product (i.e., Pt
2
, RuBn-Pt
2
, and (RuBn)
2
2
-Pt ) should be in a
1
: 2 : 1 ratio. Indeed, ESI-TOF MS revealed that all these three
diplatinum species were involved in the crude product (data not
shown). For each ligand system, only the monoruthenium complex
RuBn-Pt
chromatography. On the other hand, each diruthenium com-
plex (RuBn) -Pt was separately prepared from a 1 : 2 reaction
of [Pt (bpy) (m-OH) ](NO and RuBnH in aqueous media to
2
was isolated from the crude product by gel permeation
2
2
2
2
2
)
3 2
improve the synthetic yield and the purity (Scheme 4, route II).
It must be also noted that the diplatinum(II) complexes of this
series have been extensively investigated in our group with the aim
11
of developing new one-dimensional platinum chain complexes,
which involves the study on a reference compound Pt .
2
11h
Absorption spectra
Theabsorptionspectraof RuBn, RuBn-Pt
2
, (RuBn)
2
-Pt
2
2
, andPt in
acetonitrile are shown in Fig. 1. The insets show the magnifications
2
+
of the MLCT bands for the Ru(bpy)
3
chromophores and the
MMLCT (metal-metal-to-ligand charge transfer) band for the
11h,12
Pt
2
(bpy)
2
(m-amidato)
2
choromophore.
The maximum absorp-
tion wavelengths and the molar absorptivities are summarized
in Table 1. For each system, the ligand-based absorption bands
corresponding to the p→p* transitions in the UV region, and the
7d,9c
2+
3
Scheme 3 Diruthenium models exhibiting no PHE activity.
MLCT bands for the Ru(bpy) chromophore are fundamentally
2
+
unaffected by linking the Ru(bpy)
3
and Pt
2
(bpy)
2
(m-amidato)
2
In the above context, our prediction has been to realize
improved PHE activity in a trinuclear RuPt system in which
the amidate-bridged type of diplatinum(II) core is tethered to a
moieties. The MLCT band of the B2-bridged system is ca. 20 nm
2
red-shifted in comparison with that of the B1-bridged system (see
2
+
Table 1), indicating that the lowest p* orbital of the Ru(bpy)
3
3
968 | Dalton Trans., 2011, 40, 3967–3978
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Scheme 4 Synthetic strategies to the hybrid compounds prepared in this work, exemplified with use of RuB1H.
moiety in the B2-bridged system is lower in energy than that in the
B1-bridged system. This is clearly due to the electron-withdrawing
effects of both ethoxycarbonyl and carbamoyl groups attached to
duced electron transfer (PET) leading to HER is effectively
promoted. In other words, no PHE activity has been exhibited by
3
the RuPt-based system whose MLCT emission intensity is rather
7e
the bpy ligand of B2. The spectra of RuBn-Pt
both fundamentally similar to that of the corresponding precursor
RuBnH. The absorptivity in the visible region of (RuBn) -Pt is
roughly twice as large as that of RuBn-Pt . It must be also noted
that both (RuBn) -Pt and RuBn-Pt involve a weak component
based on the MMLCT transition at the Pt (bpy) (m-amidato)
in Fig. 1c.
2
and (RuBn)
2
-Pt
2
are
comparable to that of the non-platinated ruthenium precursor.
The emission bands of the B1- and B2-bridged systems are
2
2
centered at 620 and 675 nm, respectively (Fig. 2a,b; see also Table
3
2
1). Note that [Pt
2
](PF
6
)
2
exhibits phosphorescence (i.e., MMLCT
2
2
2
emission) in the solid state at 720 nm (see Fig. S17†), even though
emission from the acetonitrile solution of the complex is extremely
2
2
2
chromophore, as shown by the spectrum of Pt
2
weak (see Table 1 and Fig. S18†). Therefore, the Pt
amidato) core in (RuBn) -Pt and RuBn-Pt must be considered as
potentially emissive. However, due to the extremely low emission
2
(bpy)
2
(m-
2
2
2
2
Emission spectra
3
2
quantum yield of Pt in acetonitrile (see Table 1), the MMLCT
9
b–h
emission component must have a negligible contribution to the
As recently reported,
platination-induced quenching of the
3
3
emission bands for the hybrid systems. The MLCT emission
MLCT emission is considerably enhanced when the photoin-
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a
Table 1 Absorption and emission spectral data
Absorption
Emission at room temperature
Emission at 77 K
4
-1
-1
c
Complex
l
max/nm (e/10 M cm )
l
max/nm
U
U
rel
t/ms
l
max/nm
t/ms
RuB1H
455 (1.77)
456 (2.15)
456 (3.59)
477 (1.46)
477 (1.82)
476 (3.01) f
472 (0.185)
620
623
619
667
669
666f
620
0.178
0.052
0.128
0.117
0.092
0.110
0.004
1
1.63
594
594
593
621
617
621
626
5.50
5.12
4.93
5.14
5.24
4.64
b
b
RuB1-Pt
2
0.29
0.62
1
0.79
0.94
0.35 (73%)
0.42 (44%)
1.01
0.90
1.02
1.41 (27%)
1.38 (56%)
(
RuB1)
RuB2H
RuB2-Pt
RuB2) -Pt
Pt
2
-Pt
2
2
b
b
f
2
(
2
2
1.07
1.44,
g
5
.83
2
+d
Ru(bpy)
Ru(bpy)
3
2
450
611
0.095
0.074
0.89
1.03
2+e
(debpy)
a
Measured for the PF -
◦
6
salts in CH
The luminescence quantum yields of RuB1H and RuB2H were determined by using the absolute luminescence quantum yield measurement system (see
Experimental section). The quantum yields for the platinated systems were determined by the relative method based on the values determined for RuB1H
3
CN at 25 C. Absorption spectra were measured in air and emission data were observed under degassed condition.
b
c
d
and RuB2H. Relative quantum yields, estimated by comparing its quantum yield with that for the parent complex RuBnH. Values taken from ref. 13.
Values taken from ref. 14. Measured for the nitrate salt of the complex. The quantum yield was estimated by the relative method using Ru(bpy)
Two decay components were observed at 77 K (see Fig. S23).
e
f
2+
3
.
g
bands of the B2-bridged systems are red-shifted relative to those
of the B1-bridged systems, clearly due to the lower lying p* level
of B2, as discussed above.
concentration, indicating that the PET occurs in a unimolecular
(i.e., intramolecular) fashion (Fig. S20†).
For RuB1-Pt at room temperature, the long-lived species (t =
2
2
The emission quantum yields are comparable to the re-
1.4 ms; 27%) has a minor contribution to the overall decay process
and may not be correlated with any PET events, since the lifetime is
quite consistent with that of the non-platinated precursor RuB1H
13b
lated polypyridyl ruthenium complexes; e.g., U = 0.095 for
1
4
[
(
Ru(bpy)
debpy = 4,4¢-bis(ethoxycarbonyl)-2,2¢-bipyridine). The emission
intensities of RuB2-Pt and (RuB2) -Pt are decreased by only 6–
1% upon platination of the corresponding Ru-only precursor (see
3
](PF
6
)
2
, and U = 0.074 for [Ru(bpy)
2
(debpy)](PF
6
)
2
(t = 1.63 ms). On the other hand, the short-lived species (t =
1
2
2
2
0.35 ms; 73%) must be relevant to the PET giving rise to the
platination-induced quenching (71% of quenching in Fig. 2a).
2
the Urel values in Table 1), indicating that PET is little enhanced in
the B2-bridged systems. This also confirms that the intramolecular
quenching of the triplet due to ET or ENT among the two
Similarly, (RuB1)
2
-Pt
2
shows a biexponential feature; t = 0.42 ms
1
(44%) and t = 1.38 ms (56%).
2
2
+
Ru(bpy)
hand, the emission quenching is relatively large in RuB1-Pt
emission intensity is decreased by 71% upon platination of RuB1H
into RuB1-Pt (see Fig. 2a). Similarly, relatively large quenching
38%) is induced upon platination of RuB1H into (RuB1) -Pt (see
Fig. 2a).
3
moieties is not enhanced in (RuB2)
2
-Pt
2
. On the other
Considerations for the two decay components
2
; the
For the first active model of a molecular device, i.e., Ru–Pt in
Scheme 3, the emission decay profile exhibited a triple exponential
2
9g
(
2
2
feature, which was in part attributed to the presence of several
conformers based on the rotation around the C(carbamoyl)–
2
+
C(bpy) bond connecting the Ru(bpy)
2
(phen-carbamoyl) unit
(bpy) unit. However, such a consideration is not
applicable to RuB1-Pt and (RuB1) -Pt , since the rotation around
9e
and the PtCl
2
Emission decay
The RuB2-Pt and (RuB2)
2
2
2
2
2
-Pt
2
systems were confirmed to possess
either the C(pyridine)-C(benzene) or C(benzene)–C(amidate)
an emission lifetime consistent with that of the precursor RuB2H
see Table 1; Fig. S24†). On the other hand, the RuB1-Pt
and (RuB1) -Pt systems, which show considerable quenching
bond in B1 is not likely to give a considerable change in the
(
2
net distance between the Ru center and the Pt
core. Nevertheless, the double-exponential features observed for
RuB1-Pt and (RuB1) -Pt indicate that each compound affords
2
(bpy)
2
(m-amidate)
2
2
2
in the steady-state emission, both exhibit a double exponential
decay profile. The PET in such hybrid systems were reported
to be considerably retarded in a frozen medium due to the high
reorganization energy required for the ET events, while such an
2
2
2
two major species exhibiting different excited-state properties in
solution.
A possible interpretation may be that the so-called head-to-
head (HH) and head-to-tail (HT) isomers exist in solution, and
the ET rates in these isomers are different to each other due
15
effect is much smaller for the ENT processes. In other words,
the activation free energy for an ET process considerably increases
in a frozen medium. As summarized in Table 1 (see also Fig.
16
to the considerable difference in the bridged Pt–Pt distance
leading to an effective difference in the electronic coupling between
S19†), the double exponential features observed for RuB1-Pt
2
and
2
+
16
(
RuB1) -Pt at room temperature are completely lost in the decay
2
2
the Ru(bpy)
3
and bpy(Pt) moieties. As previously reported,
profiles for the frozen samples at 77 K. These results strongly
support that the considerable quenching of emission for RuB1-
some of such diplatinum compounds doubly bridged by amidates
16b
are extremely slow in the HH-HT isomerization, while others
are quite rapid and reaches its equilibrium immediately after
Pt
2
and (RuB1)
2
2
-Pt at room temperature clearly arises from the
1
6c
PET events. In addition, it was also confirmed that the lifetimes
for both components are essentially insensitive to the complex
dissolution. Complex [Pt
2
](NO
3
)
2
·5H
2
O was shown to possess
the HT isomerism in the crystal (unpublished results) and to show
3
970 | Dalton Trans., 2011, 40, 3967–3978
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Fig. 2 (a) Emission spectra of [RuB1H](PF
and [(RuB1) -Pt ](PF ( ◊ ◊ ◊ ) in acetonitrile at 25 C under degassed condi-
tion. The excitation wavelength was 455 ± 2.5 nm and the solutions had an
equal absorbance (0.1) at 455 nm. (b) Emission spectra of [RuB2H](PF
6 2 2 6 4
) ( ), [RuB1-Pt ](PF ) (---),
◦
2
2
6 6
)
6 2
)
(
), [RuB2-Pt
2
](PF
6
)
4
(---), and [(RuB2)
2
-Pt
2
](PF
6
)
6
( ◊ ◊ ◊ ) in acetonitrile
◦
at 25 C under degassed condition. The excitation wavelength was 475 ±
2
.5 nm and the solutions had an equal absorbance (0.1) at 475 nm.
1
S3 and S4†), even though it is rather ambiguous in the H NMR
spectrum of (RuB2)
2
2
-Pt (Fig. S5†). Thus, it is obvious that all
these diplatinum systems are considered as a mixture of the HH
and HT isomers. However, lack of more concrete evidence prevents
us from firmly concluding that the two decay components arise
from the presence of these two isomers.
◦
Fig. 1 Absorptivity spectra in acetonitrile, in air, at 25 C. (a)
RuB1H](PF ), [RuB1-Pt ](PF (---), and [(RuB1) -Pt ](PF ( ◊ ◊ ◊ ).
](PF (---), and [(RuB2) -Pt ](PF
[
(
(
6
)
2
(
2
6
)
4
2
2
6
)
6
As an alternative possibility, an ion-paired species and a non-
ion-paired species may be different in the ET rate if there is a
prominent difference in the conformational feature of the two
b) [RuB2H](PF
6
)
2
(
), [RuB2-Pt
2
6
)
4
2
2
6 6
)
◊ ◊ ◊ ). (c) [Pt ](NO
2
3
)
2
(
).
17
species, as described elsewhere.
1
95
a singlet in the Pt NMR at -2064 ppm right after dissolution
11h
of the complex in water (D
undergoes gradual HT→HH isomerization in either water (D
or acetone ((CD CO) over a day, which was confirmed by Pt
2
O).
Moreover, the compound
Transient absorption spectra
2
95
O)
1
3
)
2
Fig. 3 shows the transient absorption spectra of all the compounds,
taken at 25 ns after laser pulse excitation at 266 nm, showing
NMR (unpublished results). However, the compound is now
2
+
shown to give a mixture of the HH and HT isomers right after
the decay of the triplet (i.e., Ru*(bpy)
3
). The spectral features
1
dissolution to acetonitrile (CD
3
CN), as observed by both H and
are fundamentally similar to each other except that the absorp-
tion intensities at around 550 nm for the B1-bridged systems
are considerably higher than those for the B2-bridged systems.
The B1-bridged systems show positive absorptions at 370 and
550 nm and bleaching at 455 and 620 nm. On the other hand,
the B2-bridged systems show positive absorptions at 385 nm
and bleaching at 475 and 620 nm, which is characteristic of
1
95
1
Pt NMR (see Fig. S1†). Based on the H NMR features observed
for [Pt ](NO O in CD CN (Fig. S1†), the hybrid compounds
·5H
prepared in this work are also suggested to give a mixture of the
HH and HT isomers in CD CN, even though their Pt NMR
spectra could not be acquired due to the limitation of samples
2
3
)
2
2
3
1
95
3
1
available for the measurements. In the H NMR spectrum of RuB1-
2
+ 18
Pt
2
(Fig. S2†), two sets of bpy ligands attached to the Pt(II) ions,
Ru(bpy)
3
.
The absorption intensities at 550 nm for the B1-
-
∑
attributable to the presence of the HH and HT isomers, are clearly
observable with the integrated intensity ratio being ca. 37 : 63 in
three domains; 8.70–8.61, 8.51–8.43 and 8.39–8.28 ppm. Similar
bridged systems, corresponding to the absorption of bpy , are
relatively strong compared with that observed for Ru(bpy)
suggesting that the MLCT excited state of RuB1H may be
described as [Ru(III)(bpy)
2
+ 18b
3
,
3
-
∑
2+
features are also observed for RuB2-Pt
2
and (RuB1)
2
-Pt
2
(Figs.
2
(B1H )] . Very similar descriptions can
This journal is © The Royal Society of Chemistry 2011
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As shown in Fig. 3, the degree of quenching of the triplet at
the early stage of the decay process is much larger in RuB1-Pt
compared to that in RuB1H. Moreover, the triplet of RuB1-Pt
2
2
decays much faster than that of RuB1H (Fig. S24a; see also Figs.
S6 and S7†). These are consistent with the results obtained by
the steady-state emission spectroscopy together with the emission
decay measurements.
Electrochemistry
The electrochemical parameters determined are summarized in
Table 2. Complex Pt
2
displays irreversible oxidation at 0.66 V
vs. Fc/Fc , assignable to the Pt(II) /Pt(III) couple, as previously
reported. The diplatinum(III) species are, in general, axially
+
2
2
20
1
1h,20d
ligated at both ends of the unit
and therefore the irreversible
character must be relevant to the relatively slow axial ligation
upon oxidation. On the other hand, two reversible reduction peaks
appear at -1.34 and -1.52 V, assignable to the reductions at the
bpy ligands bound to the Pt(II) ions (abbreviated as bpy(Pt)).
The reversible oxidation and reduction at 0.86 and -1.66 V
2
+
for RuB1H are consistent with those reported for Ru(bpy)
3
(see
2
+
Table 2). Since RuB1H and Ru(bpy)
3
show quite similar spectral
features at the MLCT band (Fig. S16†), the assignment of the first
reduction site of RuB1H is not straightforward. However, B1H is
likely to have a slightly lower p* level in comparison with the non-
substituted bpy because of its more extended aromatic character as
well as the electron-withdrawing effect of the peripheral carbamoyl
group. On the other hand, the corresponding redox potentials
of RuB2H (oxidation at 0.96 V and reduction at -1.43 V) are
both shifted to the positive potential, reflecting the electron-
withdrawing effects of the ethoxycarbonyl and carbamoyl groups
at the 4,4¢-positions of bpy in B2H.
Fig. 3 Transient absorption spectra of (a) RuB1H (black), RuB1-Pt
blue), and (RuB1) -Pt (red), and (b) RuB2H (black), RuB2-Pt (blue),
and (RuB2) -Pt (red) in acetonitrile at room temperature under Ar
atmosphere, where the fourth-harmonic (266 nm) of a Nd:YAG pulsed
laser was used as a pump source. All the solutions had an equal absorbance
at 266 nm (1.0). Each spectrum was recorded after 25 ns laser pulse
excitation.
2
(
2
2
2
2
2
2
+
The redox properties of the Ru(bpy)
amidato) moieties in the hybrid systems are roughly consistent
with those of their individual precursor or reference complexes
(see Fig. S25† and Table 2). For RuB1-Pt and RuB2-Pt , the
first and the second oxidations are attributed to those of the
3
and Pt
2
(bpy)
2
(m-
2
be applied to the platinated derivatives; RuB1-Pt
The time course of absorbance changes at each band for RuB1-Pt
and (RuB1) -Pt
S7 and S8†), consistent with the observed emission decay profiles
vide supra). On the other hand, a monoexponential feature is
seen in the time course of absorbance changes for RuB2-Pt and
RuB2) -Pt (see Figs. S9 and S10†).
2
and (RuB1)
2
-Pt
2
.
2
2
2
2
+
2
2
follows a double-exponential function (see Figs.
Pt
for (RuB1)
centers are overlapped, showing that the oxidation potentials at the
Pt (bpy) (m-amidato) moieties are shifted to the positive potential
2
(bpy)
2
(m-amidato)
2
and Ru(bpy)
3
moieties, respectively. As
2
-Pt and (RuB2)
2
2
-Pt , the oxidations at the Ru and Pt
2
(
2
2
2
2
(
2
2
due to the electron-withdrawing effect of the positively charged
a
Table 2 Redox potentials for the B1- and B2-bridged systems, together with the related compounds
b
E
1/2/V (DE
p
)
0
Complex
Oxidation
Reduction
DG ET/eV
RuB1H
0.86 (78)c
0.69 (irr)
0.83 (77)
-1.66 (66)
-1.33 (71)
-1.38 (79)
-1.43 (78)
-1.87 (70)
-1.53 (66)
-1.55 (68)
RuB1-Pt
2
0.86 (70)
0.95 (79)
-1.70 (138)
-0.01
c
(
RuB1)
RuB2H
RuB2-Pt
RuB2) -Pt
2
-Pt
2
2
-1.72(irr)
0.00
0.96 (71)c
c
c
c
c
2
0.84 (irr)
-1.34 (irr)
-1.38 (irr)
-1.34 (67)
-1.41 (irr)
-1.54 (irr)
-1.52 (75)
-1.55(irr)
0.22
0.28
c
(
Pt
2
0.95 (78)c
0.66 (irr)
0.905 (79)
2
2
+d
Ru(bpy)
3
-1.725 (69)
-1.915 (72)
a
◦
+
Measured for the acetonitrile solutions of the complexes containing 0.1 M TBAP at 25 C under Ar atmosphere. Potentials are given in volts vs. Fc/Fc .
b
c
DE
DE
S25†). Values taken from ref. 19.
p
denotes the peak-to-peak separation between the anodic and cathodic waves. The values are those for the irreversible processes. For such cases,
is written as irr. The redox potentials reported for such cases are taken from the peak potentials in each differential pulse voltammogram (see Fig.
p
d
3
972 | Dalton Trans., 2011, 40, 3967–3978
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2
+
2+
Ru(bpy)
3
moiety covalently linked to the bridging amidate. Such
diagrams in Scheme 5. The ET from the Ru*(bpy)
3
moiety (i.e.,
2
+
trends are also seen in the trinuclear systems (see Fig. S25†); the Pt-
based oxidations are shifted to the positive potential in comparison
with that of Pt
Pt show the first and the second reductions at the bpy(Pt) units
and the third one at those attached to the Ru(II) ion (abbreviated
donor) to the Pt
2
(bpy)
2
(m-amidato)
2
moiety (i.e., acceptor) is an
uphill process in the B2-bridged systems, while it is neither an
uphill nor a downhill process in the B1-bridged systems. This can
be correlated with the higher emission energies observed for the
B1-bridged systems (vide supra) as well as the more negative first
reduction potentials at the bpy moieties bound to the Ru(II) ion
in the B1-bridged systems (vide supra). Thus, it seems probable
that the prominent difference in the ET rate between the two
geometrically different species (e.g., the HH and HT isomers) only
2
(see Table 2). Importantly, RuB1-Pt
2
and (RuB1)
2
-
2
as bpy(Ru)). These indicate that the p*(bpy(Pt)) orbital could be
2
+
used to mediate ET from the Ru*(bpy)
evolving event, as well discussed for the RuPt derivatives. On
the other hand, reductions at B2 and bpy(Pt) in RuB2-Pt and
are overlapped. However, since the first reduction of
is observed at a much more positive potential compared to
3
moiety prior to the H
2
-
7
e,9
2
(
RuB2)
2
-Pt
2
appears in the case of RuB1-Pt
2
and (RuB1)
2
2
-Pt due to the shorter
distance between the donor and the acceptor and also due to the
larger driving forces for the ET.
Pt
2
that of RuB2H (see Table 2), the first and the second reductions
for RuB2-Pt and (RuB2) -Pt are reasonably assigned to those
2
2
2
for bpy(Pt) and B2, respectively. In these systems, the third one
is assignable to the reduction at bpy(Pt). These suggest that the
p*(bpy(Pt)) orbital rather than the p*(B2) orbitals becomes the
LUMO. Using the observed electrochemical and spectroscopic
parameters, the driving force for the intramolecular ET from the
Photochemical hydrogen production
As mentioned above, none of these new hybrids evolves H
presence of EDTA at pH = 5 under visible light illumination. It
must be also noted that the H -evolving activity of [Pt (bpy) (m-
) is fundamentally lower than that of
2
in the
2
2
2
2
+
◦
2+
Ru*(bpy)
based on the Rehm–Weller equation,
3
moiety to the bpy(Pt) moiety (DG ET) is estimated
(CH
[Pt (NH
; see also Fig. S21b†).
As recently demonstrated by us,
3
)
3
CCONH)
2
]
(Pt
2
21
2+
2
3
)
4
(m-CH
3
CONH)
2
]
(compare the U(H
2
) values in Table
3
0
2
7e,9f
2+
DG ET = Eox - Ered - E
T
- e /ed
(1)
if the Ru(bpy)
3
moiety
incorporated in the hybrid preserves activity as a photosensitizer,
2
+
where Eox is the first oxidation potential of the Ru center, Ered is
the reduction potential of the bpy(Pt) moiety, E is the energy of
oxidative quenching of the Ru*(bpy)
3
moiety will be promoted
2
+
+∑
T
by addition of MV to give MV . A simple dark reaction
3
+∑
the MLCT excited state, e is the dielectric constant of acetonitrile,
and d is the distance between the donor and the acceptor. Since the
e values are high for polar solvents like acetonitrile, the last term is
of an active Pt(II)-based catalyst and MV must then result
in catalytic H evolution from water at this pH, as recently
2
7g
2+
communicated. If the Ru*(bpy)
3
moiety in a hybrid is ef-
2
+
negligible. In addition, E
T
is estimated from a tangent to the high-
ficiently quenched even in the absence of MV , addition of
2
+
2+
+∑
energy side of the corresponding emission spectrum (see Table
both [Ru(bpy) ] and MV is required to generate MV . These
3
2
2
◦
1
.). As a result, the DG ET values for RuB1-Pt
RuB2-Pt , and (RuB2) -Pt are estimated as -0.01, 0.00, +0.22,
and +0.28 eV, respectively. These clearly indicate that the PET
processes in RuB2-Pt and (RuB2) -Pt are much less favorable in
comparison with those in RuB1-Pt and (RuB1) -Pt , consistent
2
, (RuB1)
2
-Pt
2
,
methods were adopted to evaluate the functionality of each
component incorporated in these hybrids. As a result, only a
2
2
2
trace amount of H was detected for all the hybrids even in
2
2
+
2
2
2
the presence of MV , in spite of the development of a dark
+
∑
2
2
2
blue chromophore of MV during the photolysis. These clearly
2
+
with the results obtained by the emission and transient absorption
spectroscopy (vide supra).
Based on the results described so far, the observed photochem-
ical events for the hybrid systems can be illustrated by the energy
indicate that the Pt
2
(bpy)
2
(m-amidato)
2
cores incorporated in
these hybrids are not active as catalysts for HER. Moreover, no
2
+
2+
H
2
evolves from the EDTA/Ru(bpy)
3
/MV /RuB1-Pt
2
system
as
(see Table 3), reconfirming the ineffectiveness of RuB1-Pt
2
Scheme 5 Energy level diagrams of the photochemical events for RuB1-Pt
2
, (RuB1)
2
-Pt
2 2 2 2
, RuB2-Pt , and (RuB2) -Pt .
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a
Table 3 PHE activities of hybrid systems and standard catalysts under various conditions
2+
2+
b
Photosystem (concentration of (RuBn)
in mM) (m = 1 or 2)
m
-Pt
2
Ru(bpy)
(mM)
3
MV
Pt
2
Catalyst
Photolysis
Time (h)
H
(mL)
2
evolved
Initial Rate of
-1
d
(mM) (mM)
TON
H
2
(mL h )
2
U(H )
2
+
+
2+
b
EDTA/Ru(bpy)
EDTA/Ru(bpy)
EDTA/RuB1-Pt
EDTA/RuB1-Pt
EDTA/RuB1-Pt
EDTA/RuB1-Pt
3
/MV /Pt
2
2
0.04
0.04
—
—
0.04
—
—
—
—
—
2.0
2.0
—
2.0
2.0
2.0
—
2.0
—
2.0
—
0.05
0.05
—
—
—
0.05
—
—
—
—
6
3.5
4
215
1982
—
<1.0
<1.0
184
—
—
—
—
—
9.3
85.8
—
<0.1
<0.1
7.96
—
—
—
—
—
140
1180
—
—
—
61
—
—
—
0.037
0.31
—
—
—
0.016
—
—
—
2
2+
c
e
3
/MV /Pt
-STD
2
(0.1)
2
+
2
2
2
/MV (0.1)
/Ru(bpy)
/MV /Pt
4
2+
2+
3
/MV (0.1)
(0.1)
3.5
3.5
3
3.5
3
3.5
3
3.5
2
+
b
2
EDTA/(RuB1)
EDTA/(RuB1)
2
-Pt
-Pt
2
(0.1)
/MV (0.1)
2
+
2
2
EDTA/RuB2-Pt
EDTA/RuB2-Pt
2
(0.1)
2
+
2
/MV (0.1)
—
—
—
—
—
—
EDTA/(RuB2)
EDTA/(RuB2)
2
-Pt
-Pt
2
(0.1)
/MV (0.1)
—
—
—
—
2
+
2
2
2.0
—
—
a
All the measurements were carried out using an aqueous acetate buffer solution containing 30 mM EDTA (disodium salt) at pH = 5.0 (0.03 M CH
3
COOH
·3H
(see Experimental
formation is estimated based on the relative method by comparing the initial slope of H formation
◦
and 0.07 M CH
and MV(NO
section for details). The quantum efficiency for the H
3
COONa) under Ar atmosphere at 20 C, in the presence of additional components listed in this table, where [Ru(bpy)
3
](NO
3
)
2
2
O
2+
2+
b
c
2+
3
)
2
were used as Ru(bpy)
3
and MV , respectively. [Pt
2
](NO
3
)
2
·5H
-1
2
O. Pt
2
-STD denotes [Pt
2
(NH
3
)
4
(m-CH
3 2
CONH) ]
d
2
2
2+
e
7c
for the each solution with that for the [Pt
2
(NH
3
)
4
(m-CH CONH) ] (1180 mL h per 10 mL solution). Taken from the literature.
3
2
7c,11b
an H
EDTA/RuB1-Pt
RuB1-Pt preserves activity as a photosensitizer but does not
2
-evolving catalyst. In addition, H
2
does evolve from the
is much higher than that of the latter (0.42 V vs. SCE
the other hand, the PET is more or less enhanced in RuB1-Pt
and (RuB1) -Pt due to the higher driving force for the PET as
). On
2
+
2
/MV /Pt
2
system (Table 3; Fig. S22d†). Thus,
2
2
2
2
possess catalytic activity for HER.
As reported so far, such hybrid systems can be classified into
four categories as follows. For those possessing a catalytically
well as the closer location of the donor and the acceptor. These
provide somewhat reasonable directions for developing and testing
new model systems applicable to the PHE cycle. An important new
approach would be to develop and examine the compounds having
9
active Pt(II) center, (i) H
promoted, (ii) the amount of H
if the PET becomes much less favorable, and (iii) no H
no PET takes place. As for those whose Pt(II) centers are inactive
towards HER, (iv) no H evolves regardless of the PET efficiency.
2
may evolve if the PET is efficiently
evolved may be greatly diminished
evolves if
2
+
2
a [Pt
2
(NH
3
)
4
(m-amidato)
2
]
moiety as an H
2
-evolving site, even
2
though some electron reservoirs accepting the electron transferred
2
+
from the Ru*(bpy)
3
moiety must be introduced as additional
2
tethers. Further studies are still in progress in our laboratory.
In this context, all the four hybrids prepared in this work belong
to group (iv), even though there is a marked difference in the PET
efficiency between the B1- and B2-bridged systems.
Experimental section
Materials
2
4
25
4
-Bromo-2,2¢-bipyridine, cis-RuCl
2
(bpy)
2
27
·2H
[Ru(bpy)
(m-CH CONH)
CCONH) ](NO
2
O, [Pt
2
(bpy)
2
-
·
-
·
Conclusions
26
(
m-OH)
2
7c
](NO
3
)
2
,
[Ru(bpy)
2
(B2H)](PF
(NH
(m-(CH
6
)
2
,
3
](NO
3
2
3
)
2
In the present study, we have succeeded in the syntheses and
7c
3H
2
O,
MV(NO
3
)
2
,
[Pt(2.25+)
(bpy)
2
3
)
4
3
]
4
characterization of four new RuPt
-evolving sites are made up of a Pt
All the compounds have been shown to preserve photosensitizing
2
and Ru
2
Pt
2
complexes whose
11a,b
(
NO
3
)
10·4H
2
O,
and [Pt
2
2
3
)
3
2
)
2
H
2
2
(bpy)
2
(m-amidato) core.
2
11h
5H
2
O
were prepared as previously described. Ligands BnH and
the ruthenium complexes [RuBnH] were prepared according to
the scheme illustrated below.
2+
2
+
ability at the Ru(bpy)
to the loss of H -evolving activity at the diplatinum cores. At the
3
moieties but exhibit no PHE activity due
2
moment, we assume that the ineffectiveness at these diplatinum
cores may be caused by the electron-withdrawing effect of the
2,2¢-bipyridyl-4-boronic acid. This compound was prepared
28
by the ‘in situ quench’ protocol, as previously described. To
a Schlenk-type flask (200 mL) equipped with a rubber septum
was added 4-bromo-2,2¢-bipyridine (2.14 g, 9.1 mmol). The flask
was purged with Ar followed by charging with THF (40 mL)
2
+
positively charged Ru(bpy)
3
tethers, giving rise to the electron
poor character at the Pt(II) centers and to the elongation of the
bridged Pt(II) ◊ ◊ ◊ Pt(II) distance, as previously observed for the
23
analogous dimers tethered to viologen or pyridinium moieties.
and triisopropyl borate (3.2 mL, 13.9 mmol). The mixture was
◦
These must be viewed as related to our previous indications that
the catalytic activity is enhanced by (i) the destabilization of the
HOMO corresponding to the filled dz2 orbital and also by (ii)
cooled to -78 C using a liquid N
2
/acetone bath. n-Buthyllithium
(1.6 M in hexane, 6.5 mL; 10.4 mmol) was added using a syringe
over 25 min followed by stirring it for an additional 30 min.
7d
the shortening in the bridged Pt(II) ◊ ◊ ◊ Pt(II) distance. Moreover,
these are also relevant to the fact that the H -evolving activity of
is an order of magnitude lower
The liquid N
2
/acetone bath was removed and then the reaction
◦
2
mixture was allowed to warm to -20 C followed by addition
of 1 N HCl solution (27 mL). After raising the temperature to
room temperature, the mixture was washed with ethyl acetate by
extraction (50 mL ¥ 3). The aqueous layer was collected and its
pH was adjusted to 7 using an aqueous 1 N NaOH solution.
2
+
[
Pt
2
(bpy)
2
(m-(CH
3
)
3
CCONH)
(m-CH
2
]
2
+
than that of [Pt
2
(NH
3
)
4
3
CONH) ] (see Table 3), since the
2
oxidation potential, corresponding to the Pt(II)
for the former (0.66 V vs. Fc/Fc , regarded as 1.13 V vs. SCE)
2
/Pt(III) couple,
2
+
3
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The colorless solid deposited was collected by filtration, washed
with acetonitrile (ca. 10 mL ¥ 2), and dried in vacuo to yield the
product as a colorless solid (Yield: 65%, 1.18 g). Anal. calcd. for,
C
10
H
9
N
2
O B: C, 60.05; H, 4.54; N, 14.01. Found: C, 59.94; H,
2
1
4.55; N, 14.01. H NMR (300.50 MHz, CD OD) d ppm 8.81 (m,
3
J = 4.8 Hz, 1H, H-6), 8.64 (s, 1H, H-3), 8.54 (d, 1H, H-6¢, J = 5.5
Hz), 8.33 (dt, 1H, H-3¢, J = 7.9, 1.0 Hz), 8.06 (td, 1H, H-4¢, J = 7.8,
1
.7 Hz), 7.96 (m, 1H, H-5), 7.57 (dd, 1H, H-5¢, J = 7.4, 5.2 Hz).
4
-(4-carbamoylphenyl)-2,2¢-bipyridine (B1H). 2,2¢-bipyridyl-
-boronic acid (0.74 g, 3.7 mmol), 4-bromobenzamide (1.1 g,
.5 mmol), Pd(OAc) (66 mg 8 mol%), dppf (326.2 mg, 16 mol%),
4
5
2
and DMF (14 mL) were added to a Schlenk-type flask (100 mL)
equipped with a rubber septum. The solution was first degassed
by the conventional freeze–pump–thaw technique, followed by
purging with Ar. An aqueous 1 M Cs
2
CO solution (8.0 mL,
3
8
.0 mmol), similarly degassed and purged with Ar, was added
to the mixture using the syringe technique. The mixture was then
◦
stirred at 100 C for 60 h. After cooling it to room temperature,
the solvent was removed by evaporation. The crude product was
added to a mixture of an aqueous 0.5 N NaOH solution (30 mL)
and ethyl acetate (30 mL). The aqueous layer was washed with
ethyl acetate (30 mL ¥ 3) to remove the unreacted boronic acid.
The combined organic layers were washed with an aqueous 0.5 N
NaOH solution (40 mL ¥ 3). Then, the organic layer was extracted
with an aqueous 3 N HCl solution (40 mL ¥ 3). The washings were
combined and the pH of the solution was adjusted to 5 using an
aqueous 0.5 N NaOH solution. The resulting colorless precipitate
was collected by filtration and dried in vacuo (Yield: 29%, 0.23 g).
[
RuB1-Pt
2
](PF
6
)
4
·H
2
O. [RuB1H](PF
6
)
2
·H
2
O
(100
mg,
0
.10 mmol) was dissolved in a minimum amount of a mixed
solvent consisting of acetonitrile, methanol and water (1 : 1 : 2
v/v/v) (ca. 3 mL) and the solution was treated with an Amberlite
00 ion exchange resin (nitrate form, obtained by treating
the chloride form with 1 N HNO ). The organic solvents
were removed by evaporation and the resulting aqueous layer
was freeze-dried to give [RuB1H](NO . To this was added
pivalamide (13 mg, 0.13 mmol), [Pt (bpy) (m-OH) ](NO (115
4
1
1
Anal. calcd. for B1H· /
2
HCl· /
2
H
2
O, C17
H
14.5
N
3
O
1.5Cl0.5: C, 67.49;
1
3
H, 4.83; N, 13.89. Found: C, 67.11; H, 4.85; N, 13.63. H NMR
(
(
(
300.50 MHz, CD
m, 2H, H-6¢ and H-3), 8.49 (d, 1H, H-3¢, J = 8.1 Hz), 7.97–7.85
m, 5H, H-4¢ and p-C ), 7.58 (d, 1H, H-5, J = 5.2 Hz), 7.37 (dd,
H, H-5¢, J = 7.5, 4.8 Hz) 6.15, 5.70 (s broad, 1H, -CONH ).
3
Cl) d ppm 8.77 (d, 1H, H-6, J = 5.2 Hz), 8.72
)
3 2
2
2
2
)
3 2
6
H
4
mg, 0.13 mmol), and water (6 mL). Then, the mixture was
stirred at 70 C for 5 days followed by filtration for the removal
1
2
◦
of insoluble materials. To the filtrate was added an aqueous
saturated NH
4
PF solution (1 mL). The black solid deposited was
6
[
RuB1H](PF
6
)
2
·H
2
O. A solution of RuCl
2
(bpy)
2
·2H
2
O (195
filtered and dried by suction. The crude product over the glass
filter was redissolved in a minimum amount of acetonitrile and
was purified on a Sephadex LH-20 column (60 cm ¥ 1.4 cm i.d.)
using a mixed solvent consisting of acetonitrile, methanol, and
water (10 : 10 : 1 v/v/v) as eluent. The first and the second red
bands corresponded to (RuB1)
and the third band corresponded to RuB1H and Pt
band was collected and dried in vacuo (Yield: 11%, 23 mg). Anal.
1
1
mg, 0.375 mmol) and B1H· /
2
HCl· /
2
H
2
O (103 mg, 0.342 mmol)
in ethanol (80 mL) was refluxed for 14 h. After the solution
was cooled down to room temperature, ethanol was removed by
evaporation followed by addition of water (2 mL). The solution
was then filtered for the removal of insoluble materials. Addition
2
-Pt
2
and RuB1-Pt
2
, respectively,
of an aqueous saturated NH
4
PF solution (1 mL) to the filtrate
6
2
. The second
resulted in prompt deposition of a red solid, which was collected
by filtration, washed with water (10 mL ¥ 2), and dried in
vacuo. The compound (316 mg) was recrystallized from a 4 : 1
water–ethanol mixture to give the product as orange crystals
calcd. for [RuB1-Pt
C, 35.66; H, 2.70; N, 8.05. Found: C, 35.47; H, 2.58; N, 8.01. H
2
](PF
6
)
4
·H
2
O, C62
H
54
N
12
O
2
RuPt
2
P
4
F
24·H
2
1
O:
NMR (600.13 MHz, CD
.7 Hz, 1H), 8.70–8.61 (m, 1H), 8.60–8.51 (m, 5H), 8.51–8.43
m, 1H), 8.39–8.28 (m, 1H), 8.24–8.16 (m, 2H), 8.16–8.02 (m,
3
CN) d ppm 8.83 (s, 1H), 8.75 (t, J =
(
C
4
8
Yield: 55%, 205 mg). Anal. calcd. for [RuB1H](PF
6
)
2
·H
2
O,
7
(
37
H
29
N
7
ORuP
2
F
12·H
2
O: C, 44.58; H, 3.14; N, 9.84. Found: C,
1
4.40; H, 3.10; N, 9.81. H NMR (300.50 MHz, CD CN) d ppm
.79 (s, 1H, substituted bpy H-3), 8.71 (d, 1H, substituted bpy
3
1
6
3
–
1H), 8.01–7.88 (m, 4H), 7.88–7.72 (m, 7H), 7.59–7.37 (m, 10H),
.86–6.52 (m, 1H), 1.46–1.24 (m, 9H). ESI-TOF MS m/z (calcd):
H-3¢, J = 8.0 Hz), 8.54, (d, 4H, bpy H-3 and H-3¢, J = 8.6 Hz),
.15–7.96 (m, 9H, bpy H-4, H-4¢ and –C -), 7.84–7.76 (m, 6H,
bpy H-6 and H-6¢), 7.70 (d, 1H, substituted bpy H-5, J = 6.0 Hz),
.47–7.41 (m, 5H, bpy H-5 and H-5¢), 6.89, 6.16 (s broad, 2H,
CONH ). ESI-TOF MS m/z (calcd): 344.43 (344.57, [M – 2PF
4
+
72.49 (372.57, [M – 4PF
6
– H
2
O]] ); 544.98 (545.08, [M – 3PF
6
8
6
H
4
3
+
2+
H
2
O] ); 889.99 (890.11, [M – 2PF
6
– H O] ).
2
7
-
–
[(RuB1) -Pt ](PF ·8H O. The freeze-dried sample of
2
2
6
)
6
2
2
6
[RuB1H](NO was prepared from [RuB1H](PF O (64.9
3
)
2
6
)
2
·H
2
2
+
+
H
2
O] ), 883.83 (834.11, [M – PF
6
– H
2
O] ).
mg, 59.4 mmol) in the same manner as described above for
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3967–3978 | 3975

View Article Online
[
RuB1-Pt
2
](PF
6
)
4
·H
2
O. To this was added [Pt
2
(bpy)
2
(m-
Measurements
OH) ](NO
2
3
)
2
(26.2 mg, 29.4 mmol), and water (3 mL). Then,
◦
1
the mixture was stirred at 70 C for 60 h followed by filtration
for the removal of insoluble materials. The crude product was
crushed out in the same manner as described above and was
similarly purified using Sephadex LH-20. The first reddish-brown
band was collected, evaporated to dryness, and dried in vacuo
H NMR spectra were acquired on a JEOL JNM-AL300 (300.50
MHz), a JEOL JNM-ESA600 (600.13 MHz), and, a JEOL JNM-
ECS400 (399.78 MHz) spectrometer, in which tetramethylsilane
was used as an internal standard. UV-Visible absorption spectra
were recorded on a Shimadzu UV-2450 spectrophotometer at
◦
(
C
Yield: 40%, 36 mg). Anal. calcd. for [(RuB1)
2
-Pt
2
](PF
6
)
6
·8H
2
O,
25 C, in air. Emission spectra were recorded on a Shimadzu
◦
H
72
N
18
O
2
Ru
2
Pt
2
P
6
F
36·8H
2
O: C, 36.51; H, 2.87; N, 8.15. Found:
RF5300PC spectrofluorophotometer at 25 C. Emission decays
were observed at 25 C on an Iwatsu DS-4262 digitizing oscillo-
94
◦
1
C, 36.21; H, 2.53; N, 8.26. H NMR (600.13 MHz, CD
3
CN)
d ppm 8.82 (s, 2H), 8.76 (d, J = 7.93 Hz, 2H), 8.70–8.63 (m,
scope equipped with a Hamamatsu R928 photomultiplier tube.
2
8
1
H), 8.61–8.44 (m, 10H), 8.29–8.19 (m, 4H), 8.17–8.03 (m, 18H),
.00 (d, J = 8.02 Hz, 2H), 7.97–7.90 (m, 2H), 7.89–7.76 (m,
2H), 7.76–7.65 (m, 4H), 7.53–7.36 (m, 14H). ESI-TOF MS m/z
The excitation source was an N laser (337 nm) (Usho KEN-
2
1520). The grating monochromator used was a Jobin Vyvon H-20
instrument. Data acquisitions were carried out up to 512 scans.
Electrospray ionization time-of-flight mass spectra (ESI-TOF MS)
were obtained for the acetonitrile solutions of the complexes using
a JEOL JMS-T100CS. The emission quantum yields of RuB1H
and RuB2H were determined using a Hamamatsu C9920-02
absolute photoluminescence quantum yield measurement system
with a 150 W Xe lamp coupled to a monochromator for wavelength
discrimination, an integrating sphere as a sample chamber, and
a Hamamatsu C10027-01 multichannel detector for the signal
detection. Luminescence quantum yields for the multinuclear
3
+
(
calcd): 346.29 (346.39, [RuB1-Pt] ); 536.92 (537.09, [(RuB1-Pt)
-
2+
+
OH + H
2
O] ).
[
RuB2-Pt
RuB2H](NO
07 mmol) in the same manner as described above for [RuB1-
Pt ](PF O. To this was added pivalamide (11.2 mg,
12 mmol), [Pt
2
](PF
6
)
4
·2H
2
O. The
freeze-dried
sample
of
[
1
3
)
2
was prepared from [RuB2H](PF
)
6 2
(117 mg,
2
6
)
4
·H
2
1
2
(bpy)
2
(m-OH)
2
](NO
3
)
2
(89.6 mg, 104 mmol), and
◦
water (2 mL). Then, the mixture was stirred at 70 C for 21 h
followed by filtration for the removal of insoluble materials. The
crude product was crushed out in the same manner as described
above and was similarly purified using Sephadex LH-20. The first
complexes RuBn-Pt
2
and (RuBn)
2
-Pt (n = 1, 2) were estimated
2
on the basis of the quantum yields determined for RuB1H and
RuB2H.
and the second red bands corresponded to (RuB2)
Pt , respectively. The second band was collected, evaporated to
dryness, and dried in vacuo (Yield: 8.7%, 11.8 mg). Anal. calcd.
2
-Pt
2
and RuB2-
The cyclic voltammetric and differential pulse voltammetric
measurements were performed on a BAS CV-50 W electrochemical
analyzer for the argon-purged acetonitrile solutions of the com-
plexes (1 mM) in the presence of 0.1 M tetra(n-butyl)ammonium
perchlorate (TBAP) as a supporting electrolyte at room temper-
ature. The platinum working electrode was polished with BAS
polishing alumina suspension and rinsed with acetonitrile before
use. The counter electrode was a platinum wire. The measured
2
for [RuB2-Pt
2
](PF
6
)
4
·2H
2
O, C66
H
59
N
13
O
5
RuPt
2
P
4
F
24·2H
2
O: C,
1
3
5.69; H, 2.86; N, 8.20. Found: C, 35.56; H, 2.81; N, 8.27. H
NMR (600.13 MHz, CD CN) d ppm 9.42 (s, 1H), 9.15–9.05
3
(
m, 2H), 8.75–8.25 (m, 8H), 8.20–7.85 (m, 18H), 7.80–7.65
(
m, 4H), 7.60–7.20 (m, 8H), 6.80–6.50 (m, 2H), 4.55–4.45 (m,
+
2
H), 1.50–1.44 (m, 3H), 1.40–1.25 (m, 9H). ESI-TOF MS m/z
potentials were recorded with respect to an Ag/Ag reference
3
+
(
calcd): 384.64 (384.73, [RuB2-Pt] ); 401.25 (401.33, [M – 4PF
6
–
electrode (ca. 490 mV vs. NHE), but was corrected using the
4
+
3+
+
2H
2
O] ); 583.29 (583.43, [M – 3PF
6
– 2H
2
O] ); 947.41 (947.61,
ferrocene/ferrocenium (Fc/Fc ) couple as an internal standard.
2
+
[
M – 2PF
6
– 2H
2
O] ).
For the nanosecond flash photolysis experiments, sample solu-
tions were excited by a Nd:YAG laser (Minilite II-10, Continuum),
and transient absorbance changes were monitored by a 150
W Xe lamp and an amplified photomultiplier tube (R2949,
Hamamatsu). Transient absorption spectra were recorded using
multichannel detector with a gated image-intensifier, C9546-03
(Hamamatsu). Each sample solution was purged with Ar for at
least 20 min before the measurement.
[
(RuB2)
RuB2H](NO
9.4 mmol) in the same manner as described above for [RuB1-
Pt ](PF O. To this was added [Pt (bpy) (m-OH) ](NO (26.2
2
-Pt
2
](PF
6
)
6
·6H
2
O. The freeze-dried sample of
[
5
3
)
2
was prepared from [RuB2H](PF
)
6 2
(64.9 mg,
2
6
)
4
·H
2
2
2
2
)
3 2
mg, 29.4 mmol) and water (3 mL). Then, the mixture was stirred
at 70 C for 60 h followed by filtration for the removal of insoluble
◦
materials. The crude product was crushed out in the same manner
described above and was similarly purified using Sephadex
LH-20. The first red-brown band was collected, evaporated to
dryness, and dried in vacuo (Yield: 40%, 38 mg). Anal. Calcd.
Photochemical H
2
evolution from water was analyzed by using
an automatic H monitoring system developed in our group. In this
2
-
1
system, a continuous flow of Ar (10.0 mL min , controlled by an
STEC SEC-E40/PAC-D2 digital mass flow controller) was bub-
bled through a photolysis solution (10 mL) contained in a Pyrex
vial (ca. 20 mL). The vent gas from the vial was introduced into a
6-way valve which allowed the automatic injection of the sample
gas onto a gas chromatograph (Shimadzu GC-14A equipped with
a molecular sieve 5A column of 2 m ¥ 3 mm i.d., thermostatted
for [(RuB2)
2
-Pt
2
](PF
6
)
6
·6H
2
O, C102
H
82
N
20
O
8
Ru
2
Pt
2
P
6
F
36·6H
2
O:
C, 37.28; H, 2.88; N, 8.52. Found: C, 37.13; H, 2.77; N, 8.91.
1
H NMR (600.13 MHz, CD CN) d ppm 9.81–9.22 (m, 4H),
3
9
7
6
6
6
–
.19–9.01 (m, 4H), 8.93–8.21 (m, 16H), 7.62–7.19 (m, 14H),
.81–7.61 (m, 10H), 8.04–7.81 (m, 18H), 8.21–8.04 (m, 14H),
.96–5.68 (m, 2H), 4.49 (d, J = 6.8 Hz, 4H), 1.43 (t, J = 6.8 Hz,
◦
at 30 C). The injection of the sample gas and the output signal
H). ESI-TOF MS m/z (calcd): 384.58 (384.73, [M – 6PF
6
–
from the thermal conductivity detector of the gas chromatograph
were both controlled by control software operating on a Windows
system. Photolysis solutions were deaerated with Ar for at least
30 min prior to the photolysis. The photoirradiation was carried
6
+
3+
H
6H
2
O] , overlapped with [RuB2-Pt] ); 490.48 (490.47, [M – 5PF
6
5
+
4+
2
O] ); 649.37 (649.58, [M – 4PF
6
– 6H
2
O] overlapped with
2
+
3+
[(RuB2-Pt) + PF
6
] ); 914.11 (914.43, [M – 3PF
6
– 6H O] ).
2
3
976 | Dalton Trans., 2011, 40, 3967–3978
This journal is © The Royal Society of Chemistry 2011

View Article Online
out by an Ushio Xe short arc lamp UXL500D-O (operated
at 350 W). The photolysis vial was immersed in a water bath
thermostatted at 20 C to remove IR radiation and to eliminate
9 (a) H. Ozawa, M. Haga and K. Sakai, J. Am. Chem. Soc., 2006, 128,
4
926–4927; (b) H. Ozawa and K. Sakai, Chem. Lett., 2007, 36, 920–
◦
921; (c) H. Ozawa, Ph.D. Dissertation, Kyushu University, 2007; (d) S.
Masaoka, Y. Mukawa and K. Sakai, Dalton Trans., 2010, 39, 5868–
5876; (e) H. Ozawa, M. Kobayashi, B. Balan, S. Masaoka and K. Sakai,
Chem.–Asian J., 2010, 5, 1860–1869; (f) M. Kobayashi, S. Masaoka
and K. Sakai, Molecules, 2010, 15, 4908–4923; (g) B. Balan, H. Ozawa,
S. Masaoka, T. Katayama, Y. Nagasawa, H. Miyasaka and K. Sakai,
manuscript in preparation; (h) H. Ozawa and K. Sakai, Chem. Commun.,
2011, 47, 2227–2242.
the temperature effect. The photolysis solution of each hybrid
compound was prepared using the nitrate salt of the complex,
in situ prepared by the conventional ion-exchange technique, as
9d
-
previously described; a weighed amount of the PF salt was first
6
dissolved in a 1 : 1 water–methanol mixture and was treated with
-
10 (a) H. Rau, B. Sch a¨ fer, D. Gleich, E. Anders, M. Rudolph, M. Friedrich,
H. G o¨ rls, W. Henry and J. G. Vos, Angew. Chem., Int. Ed., 2006,
an anion-exchange resin (Amberlite IRA-400 in the NO
3
form)
followed by complete removal of solvents (finally freeze-dried).
4
5, 6215–6218; (b) M. Elvington, J. Brown, S. M. Arachchige and
2
+
The photolysis solution containing [Pt
Pt -STD), which was used to determine the quantum efficiency
of H
Pt(2.25+)
2
(NH
3
)
4
(m-CH
3
CONH)
2
]
K. J. Brewer, J. Am. Chem. Soc., 2007, 129, 10644–10645; (c) S. M.
Arachchige, J. R. Brown, E. Chang, A. Jain, D. F. Zigler, K. Rangan
and K. J. Brewer, Inorg. Chem., 2009, 48, 1989–2000; (d) A. Fihri, V.
Artero, M. Razavet, C. Baffet, W. Liebl and M. Fontecave, Angew.
Chem., Int. Ed., 2008, 47, 564–567.
(
2
2
formation catalyzed by Pt
(NH (m-CH CONH)
2
, was prepared by dissolving
[
2
3
)
4
3
2
]
4
(NO
3
)
10·4H
2
O into the pho-
7
c,e
tolysis solution. As previously described, this mixed-valence
octanuclear platinum complex was proven to give a pure solution
11 (a) K. Sakai and K. Matsumoto, J. Am. Chem. Soc., 1989, 111, 3074–
3075; (b) K. Matsumoto, K. Sakai, K. Nishio, Y. Tokisue, R. Ito, T.
Nishide and Y. Shichi, J. Am. Chem. Soc., 1992, 114, 8110–8118; (c) K.
Sakai, M. Takeshita, Y. Tanaka, T. Ue, M. Yanagisawa, M. Kosaka,
T. Tsubomura, M. Ato and T. Nakano, J. Am. Chem. Soc., 1998,
120, 11353–11363; (d) K. Sakai, E. Ishigami, Y. Konno, T. Kajiwara
and T. Ito, J. Am. Chem. Soc., 2002, 124, 12088–12089; (e) K. Sakai,
M. Kurashima, N. Akiyama, N. Satoh, T. Kajiwara and T. Ito, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun., 2003, C59, m345–m349;
2
+
of [Pt
2
(NH
3
)
4
(m-CH
3
CONH)
2
]
via the cleavage of the complex
into the dimeric species and complete reduction into the Pt(II)
species in the presence of an excess of EDTA.
2
Acknowledgements
(
f) M. Mizota and K. Sakai, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2004, E60, m473–m476; (g) K. Sakai, K. Yokokawa and Y.
Yokoyama, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2007,
C63, m36–m41; (h) K. Yokokawa and K. Saka, Acta Crystallogr., Sect.
C: Cryst. Struct. Commun., 2004, C60, m244–m247.
2 (a) J. A. Bailey, M. G. Hill, R. E. Marsh, V. M. Miskowski, W.
P. Schaefer and H. B. Gray, Inorg. Chem., 1995, 34, 4591–4599;
This work was in part supported by Grants-in-Aid for Scientific
Research (A) (No. 17205008) and (B) (No. 21350036), a Grant-
in-Aid for Specially Promoted Research (No. 18002016), and a
Grant-in-Aid for the Global COE Program (‘Science for Future
Molecular Systems’) from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan.
1
(
b) S.-W. Lai, M. C. W. Chan, T.-C. Cheung, S.-M. Peng and C.-
M. Che, Inorg. Chem., 1999, 38, 4046–4055; (c) T.-C. Cheung, K.-K.
Cheung, S.-M. Peng and C.-M. Che, J. Chem. Soc., Dalton Trans.,
1
999, 1645–1651; (d) S.-W. Lai, T.-C. Cheung, M. C. W. Chan, K.-
K. Cheung, S.-M. Peng and C.-M. Che, Inorg. Chem., 2000, 39, 255–
62.
Notes and references
2
1
(a) V. Balzani, L. Moggi, M. F. Manfrin, F. Bolletta and M. Gleria,
Science, 1975, 189, 852–856; (b) J. R. Bolton, Science, 1978, 202, 705–
13 (a) K. Nakamaru, Bull. Chem. Soc. Jpn., 1982, 55, 1639–1640; (b) K.
Suzuki, A. Kobayashi, S. Kaneko, K. Takehira, T. Yoshihara, H. Ishida,
Y. Shiina, S. Oishi and S. Tobita, Phys. Chem. Chem. Phys., 2009, 11,
9850–9860.
7
11; (c) T. J. Mayer, Acc. Chem. Res., 1989, 22, 163–170; (d) M. Gr a¨ tzel,
Acc. Chem. Res., 1981, 14, 376–384; (e) E. Borgarello, J. Kiwi, E.
Pelizzetti, M. Visca and M. Gr a¨ tzel, Nature, 1981, 289, 158–160; (f) H.
B. Gray and A. W. Maverick, Science, 1981, 214, 1201–1205; (g) A. F.
Heyduk and D. G. Nocera, Science, 2001, 293, 1639–1641; (h) A. J.
Esswein and D. G. Nocera, Chem. Rev., 2007, 107, 4022–4047; (i) M.
Wang, Y. Na, M. Gorlov and L. Sun, Dalton Trans., 2009, 6458–6467;
14 O. Johansen, A. Launikonis, A. W. H. Mau and W. H. F. Sasse, Aust.
J. Chem., 1980, 33, 1643–1648.
15 (a) P. Chen and T. J. Meyer, Inorg. Chem., 1996, 35, 5520–5524; (b) M.
L. A. Abrahamsson, H. B. Baudin, A. Tran, C. Philouze, K. E. Berg,
M. K. Raymond-Johansson, L. Sun, B. A
˚
kermark, S. Styring and L.
(
j) M. Schwalbe, M. Karnahl, H. G o¨ rls, D. Chartrand, F. Laverdiere,
Hammarstr o¨ m, Inorg. Chem., 2002, 41, 1534–1544.
16 (a) T. V. O’Halloran and S. J. Lippard, J. Am. Chem. Soc., 1983, 105,
3341–3342; (b) T. V. O’Halloran and S. J. Lippard, Inorg. Chem., 1989,
28, 1289–1295; (c) K. Matsumoto, H. Miyamae and H. Moriyama,
Inorg. Chem., 1989, 28, 2959–2964; (d) K. Matsumoto, J. Matsunami
and H. Urata, Chem. Lett., 1993, 597–600; (e) K. Matsumoto and H.
Urata, Chem. Lett., 1994, 307–310; (f) K. Sakai, Y. Tanaka, Y. Tsuchiya,
K. Hirata, T. Tsubomura, S. Iijima and A. Bhattacharjee, J. Am. Chem.
Soc., 1998, 120, 8366–8379.
G. S. Hanan, S. Tschierlei, B. Dietzek, M. Schmitt, J. Popp, J. G. Vos
and S. Rau, Dalton Trans., 2009, 4012–4022.
2
3
K. R. Mann, N. S. Lewis, V. M. Miskowski, D. K. Erwin, G. S.
Hammond and H. B. Gray, J. Am. Chem. Soc., 1977, 99, 5525–5526.
(a) J.-M. Lehn and J.-P. Sauvage, Nouv. J. Chim., 1977, 1, 449–451;
(
b) K. Kalyanasundaram, Coord. Chem. Rev., 1982, 46, 159–244; (c) A.
Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A. von
Zelewsky, Coord. Chem. Rev., 1988, 84, 85–277.
4
5
J. Kiwi and M. Gr a¨ tzel, Nature, 1979, 281, 657–658.
17 M. Ogawa, B. Balan, G. Ajayakumar, S. Masaoka, H.-B. Kraatz, M.
Muramatsu, S. Ito, Y. Nagasawa, H. Miyasaka and K. Sakai, Dalton
Trans., 2010, 39, 4421–4434.
(a) M. Kirch, J.-M. Lehn and J.-P. Sauvage, Helv. Chim. Acta, 1979,
6
2, 1345; (b) S. F. Chan, M. Chou, C. Creutz, T. Matsubara and N.
Sutin, J. Am. Chem. Soc., 1981, 103, 369–379; (c) C. V. Krishnan, B.
S. Brunschwig, C. Creutz and N. Sutin, J. Am. Chem. Soc., 1985, 107,
18 (a) R. Bensasson, C. Salet and V. Balzani, J. Am. Chem. Soc., 1976,
98, 3722–3724; (b) P. S. Braterman, A. Harriman, G. A. Heath and
L. J. Yellowlees, J. Chem. Soc., Dalton Trans., 1983, 1801–1803; (c) E.
Taffarel, S. Chirayil, W. Y. Kim, R. P. Thummel and R. H. Schmehl,
Inorg. Chem., 1996, 35, 2127–2131.
19 R. Lomoth, T. H a¨ pul, O. Johansson and L. Hammarstr o¨ m, Chem.–Eur.
J., 2002, 8, 102–110.
2
005–2015.
6
7
I. Okura, M. Takeuchi and N. Kim-Thuan, Chem. Lett., 1980, 765–766.
(a) K. Sakai, Ph.D. Dissertation, Waseda University, 1993; (b) K. Sakai
and K. Matsumoto, J. Mol. Catal., 1990, 62, 1–14; (c) K. Sakai, K.
Kizaki, T. Tsubomura and K. Matsumoto, J. Mol. Catal., 1993, 79,
1
2
41–152; (d) K. Sakai and H. Ozawa, Coord. Chem. Rev., 2007, 251,
753–2766; (e) H. Ozawa, Y. Yokoyama, M. Haga and K. Sakai, Dalton
20 (a) L. S. Hollis and S. J. Lippard, J. Am. Chem. Soc., 1981, 103, 6761–
6763; (b) L. S. Hollis and S. J. Lippard, Inorg. Chem., 1983, 22, 2605–
2614; (c) K. Matsumoto and N. Matoba, Inorg. Chim. Acta, 1986, 120,
L1–L3; (d) K. Matsumoto and K. Sakai, Adv. Inorg. Chem., 1999, 49,
375–427.
Trans., 2007, 1197–1206; (f) R. Okazaki, S. Masaoka and K. Sakai,
Dalton Trans., 2009, 6127–6133; (g) K. Yamauchi, S. Masaoka and K.
Sakai, J. Am. Chem. Soc., 2009, 131, 8404–8406.
M. Ogawa, G. Ajayakumar, S. Masaoka, H.-B. Kraatz and K. Sakai,
Chem.–Eur. J., 2011, 17, 1148–1162.
8
21 D. Rehm and A. Weller, Ber. Bunsen-Ges. Phys. Chem., 1969, 73, 834–
839.
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3967–3978 | 3977

View Article Online
2
2
2 A. Islam, H. Sugihara, L. P. Singh, K. Hara, R. Katoh, Y. Nagawa,
M. Yanagida, Y. Takahashi, S. Murata and H. Arakawa, Inorg. Chim.
Acta, 2001, 322, 7–16.
24 T. Mizuno, M. Takeuchi, I. Hamachi, K. Nakashima and S. Shinkai,
J. Chem. Soc., Perkin Trans., 1998, 10, 2281–2288.
25 B. P. Sullivan, D. J. Salmon and T. J. Meyer, Inorg. Chem., 1978, 17,
3334–3341.
3 (a) K. Sakai, M. Shiomi, T. Tsubomura, K. Kato, Y. Yokoyama, T.
Kajiwara and T. Ito, Acta Crystallogr., Sect. E: Struct. Rep. Online,
26 S. Wimmer, P. Castan, F. L. Wimmer and N. P. Johnson, Inorg. Chim.
2
003, E59, m559–m561; (b) K. Sakai, Y. Ikuta, T. Tsubomura, K.
Acta, 1988, 142, 13–15.
Kato, Y. Yokoyama, T. Kajiwara and T. Ito, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2003, E59, m780–m783; (c) K. Sakai, Y. Yokoyama,
H. Hama, K. Kato, Y. Ikuta, T. Tsubomura and T. Tanase, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2004, E60, m664–m667.
27 M. Hirahara, S. Masaoka and K. Sakai, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2009, E65, m228–m229.
28 W. Li, D. P. Nelson, M. S. Jensen, R. S. Hoerrner, D. Cai, R. D. Larsen
and P. J. Reider, J. Org. Chem., 2002, 67, 5394–5397.
3
978 | Dalton Trans., 2011, 40, 3967–3978
This journal is © The Royal Society of Chemistry 2011