Rodlike bimetallic ruthenium and osmium complexes bridged by phenylene spacers. Synthesis, electrochemistry, and photophysics

Article abstract of DOI:10.1021/ic0483141

In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl complexes of linear structure with the general formula [M(bpy)₃-BL-M(bpy)₃]⁴⁺ [M = Ru(II) or Os(II); BL = polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy = 2,2′-bipyridine]. By using a chemistry on the complex approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 A for the shortest and longest complex, respectively. For one of the ruthenium precursors, [RUbpy-ph₂-Si(CH₃) ₃][PF₆]₂, single crystals were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported. All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more positive potential than for the reference complexes [M(bpy)₃]²⁺ (M = Ru, Os). This result confirms that the best acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the phenylene units, in the two series of complexes, for the ground and excited states is discussed.

Full text of DOI:10.1021/ic0483141

Inorg. Chem. 2005, 44, 4706−4718
Rodlike Bimetallic Ruthenium and Osmium Complexes Bridged by
Phenylene Spacers. Synthesis, Electrochemistry, and Photophysics
Steve Welter,† Nunzio Salluce,‡ Arianna Benetti,† Nicolette Rot,† Peter Belser,‡ Prashant Sonar,§
Andrew C. Grimsdale,§ Klaus Mullen,§ Martin Lutz,| Anthony L. Spek,| and Luisa De Cola*,†
1
Molecular Photonics Materials, UniVersity of Amsterdam, Nieuwe Achtergracht 166, 1018 WV
Amsterdam, The Netherlands, UniVersity of Fribourg Pe´rolles, CH-1700 Fribourg, Switzerland,
Max-Planck-Institut fu¨r Polymerforschung, Ackermannweg 10, D-55128 Mainz, Germany, and
BijVoet Center for Biomolecular Research, Department of Crystal and Structural Chemistry,
Utrecht UniVersity, Padualaan 8, 3584CH Utrecht, The Netherlands
Received November 30, 2004
In the search for light-addressable nanosized compounds we have synthesized 10 dinuclear homometallic trisbipyridyl
+
complexes of linear structure with the general formula [M(bpy)3-BL-M(bpy)3]4 [M
) Ru(II) or Os(II); BL )
polyphenylenes (2, 3, 4, or 5 units) or indenofluorene; bpy
) 2,2′-bipyridine]. By using a “chemistry on the complex”
approach, different sizes of rodlike systems have been obtained with a length of 19.8 and 32.5 Å for the shortest
and longest complex, respectively. For one of the ruthenium precursors, [Rubpy-ph2-Si(CH3)3][PF6]2, single crystals
were obtained by recrystallization from methanol. Their photophysical and electrochemical properties are reported.
All the compounds are luminescent both at room and low temperature with long excited-state lifetimes due to an
extended delocalization. Nanosecond transient absorption showed that the lowest excited state involves the chelating
unit attached to the bridging ligand. Electrochemical data indicated that the first reduction is at a slightly more
+
positive potential than for the reference complexes [M(bpy)3]2 (M
) Ru, Os). This result confirms that the best
acceptor is the bipyridine moiety connected to the conjugated spacers. The role of the tilt angle between the
phenylene units, in the two series of complexes, for the ground and excited states is discussed.
I. Introduction
objects which recently have attracted a lot of attention. In
many cases, conjugated systems have been developed leading
to materials having a significant impact on emerging
technologies for biotechnology,10 electronics,11 and opto-
electronics.12 An attractive external input to trigger molecular
Functional molecular components able to be addressed
with an external stimulus are the key structures for building
up electronic circuits and devices. Molecular wires,1-4
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* To whom correspondence should be addressed. Fax: +31 20 525 6456.
E-mail: ldc@science.uva.nl.
† University of Amsterdam. Nieuwe Achtergracht 166, 1018 WV
Amsterdam, The Netherlands, Fax: +31 20 525 6456, ldc@science.uva.nl
(L. De Cola).
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‡ University of Fribourg Pe´rolles, CH-1700 Fribourg, Switzerland.
§ Max-Planck-Institut fu¨r Polymerforschung, Ackermannweg 10, D-55128
Mainz, Germany.
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| Bijvoet Center for Biomolecular Research, Department of Crystal and
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4706 Inorganic Chemistry, Vol. 44, No. 13, 2005
10.1021/ic0483141 CCC: $30.25
© 2005 American Chemical Society
Published on Web 05/24/2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
devices is light, and we expect a major development of
systems capable of elaborating light for signal generation,
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Welter et al.
Chart 1. Schematic Formula, Abbreviations, and Metal-to-Metal Distances of the Investigated Compounds
homometallic complexes containing an indenofluorene spacer
that force the phenyl rings in a coplanar geometry are also
reported. In particular, the synthetic strategy to prepare the
unsubstituted phenyl complexes using the “chemistry on the
complex” approach,60-62 the electrochemical and photophysi-
cal properties of all the compounds, and the crystal structure
of one of the ruthenium complexes are reported. The
possibility of varying the tilt angle between adjacent phenyls
opens new perspectives in the modulation of the electronic
interactions between the terminal units.
4708 Inorganic Chemistry, Vol. 44, No. 13, 2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
Scheme 1. Synthetic Scheme for the Dinuclear Ruthenium Complexes Containing Two, Three, Four, and Five Phenyls as Bridging Liganda
a (a) K2CO3, DMF, 120 °C, 24 h, 74%; (b) Ru(bpy)2Cl2, ethylene glycol, microwave irradiation (450 W, 3 × 2 min.), 78%; (c) K2CO3, Pd(PPh3)4, DMF,
95 °C, 16 h, 77-80%.
II. Results and Discussion
Synthesis. As a result of the low solubility and difficult
preparation of “bare” polyphenylene-substituted 2,2′-bi-
pyridines, bpy, the general procedure based on the complex-
ation of [Ru(bpy)2Cl2] with the chelating substituted bpy was
not employed. Instead, we used the “chemistry on the metal”
approach where the charged metal complex helps to solu-
bilize the polyphenylene chain and hence allows a stepwise
construction of the bridge with Suzuki cross-coupling reac-
tions.63 The starting compound for all the ruthenium com-
plexes is a derivative of ruthenium tris-bipyridine, [Rubpy-
ph-Br]2+ [18], containing two unsubstituted and one
All the complexes synthesized and investigated, including
their abbreviations, are shown in Chart 1. They have been
-
isolated and used as PF6 salts. For comparison purposes,
2+
the M(bpy)3 (M ) Ru or Os) and/or the mononuclear
compounds containing two phenylene units, [Mbpy-ph2-
bpy]2+, have been employed.
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Inorganic Chemistry, Vol. 44, No. 13, 2005 4709

Welter et al.
a
Scheme 2. Synthesis of [Ru-Flu-Ru](PF6)4 and [Os-Flu-Os](PF6)4
a Na2CO3, Pd(PPh3)4, DMF, 90 °C, 16 h.
functionalized 4-(4′-bromophenyl)-[2,2′]bipyridinyl ligand64
(Scheme 1). The cross-coupling reaction with 1,4-benzene-
diboronic acid and 4,4′-biphenyldiboronic acid, using Pd(0)
as catalyst, readily yields the bimetallic ruthenium complexes
connected by three and four phenylene units, respectively
(Scheme 1). The same approach was also used for the [Ru-
Flu-Ru]4+ complex containing an indenofluorene type of
bridging ligand. For the latter complex the indenofluorene
derivative [22] with two boronic acids was used in a Suzuki-
type cross-coupling reaction to give the bimetallic complex
in good yield (Scheme 2). For the longest bimetallic complex
with five phenylene units [7], we previously synthesized the
monometallic ruthenium complex with two phenylene units
by coupling [Rubpy-ph-Br]2+ with 4-trimethylsilylphenyl-
boronic acid followed by deprotection of the trimethysilyl
group with iodine chloride (ICl). This halogen-functionalized
ruthenium complex can further undergo a cross-coupling
reaction with 1,4-benzenediboronic acid to obtain the bime-
tallic ruthenium complex with five phenyl units (Scheme 1).
For the shortest complex with two phenylene units, a
different approach was used: [Rubpy-ph-Br]2+ was cross-
coupled with bpy-ph-B(OR)2 [12] bearing a boronic ester to
give the monometallic complex with the biphenylene spacer
[19] and a free complexing site where the second ruthenium
or other metal complexes can be coordinated.40
The synthetic approach described for the bimetallic
ruthenium complexes could not be readily adopted for the
corresponding osmium complexes. In fact, the coupling of
two [Osbpy-ph-Br]2+ units with bisboronic acids of mono-
and biphenyl, using Pd(0) as catalyst, only gave poor yields
for the bimetallic complexes in most cases. Only in the case
of [Os-Flu-Os]4+ and [Os-ph3-Os]4+ was this approach used
(Schemes 2 and 4). In fact, in most of the cases an undesired
side-product was obtained as the final osmium complex when
reacting [Osbpy-ph-Br]2+ in a 2:1 stoichiometry with a mono-
or biphenyl unit, containing two boronic acids and using Pd-
(PPh3)4 as catalyst in DMF. On the basis of mass spectros-
copy results, we tentatively assigned the structure to an
osmium complex containing a diphenylphosphine (originat-
ing from the catalyst, Pd(PPh3)4) linked to the phenylene.
However, under the same reaction conditions, [Osbpy-ph-
Br]2+ has coupled with an excess of 4-trimethylsilylphenyl-
boronic acid in high yield (∼90%). To avoid the previously
described problems, we opted for a more classical approach
to obtain the bimetallic osmium complexes. Indeed, most
homometallic dinuclear complexes reported in the literature
are obtained by complexing two osmium units to the finished
bridging ligand that contains two free coordinating sites. The
free bis-bipyridine bridging ligands with two, four, and five
phenylenes were synthesized according to the procedure
sketched in Scheme 3. The longer ligands were almost
insoluble and were further used without purification. The
bimetallic osmium complexes were obtained by microwave
irradiation of a mixture of the ligand and [Os(bpy)2Cl2] in
ethylene glycol (Scheme 4). Only relatively low yields of
20-24% were obtained for the complexes with four and five
phenylene units, probably as a result of the low solubility
of the ligand. Indeed, for the shortest ligand with two
phenylene units, a much higher yield of 84% was obtained.
It is therefore interesting to notice that the “chemistry on
the complex” approach is very effective in the case of the
bimetallic ruthenium complexes. However, this method is
not suitable for the synthesis of dinuclear osmium complexes
and yields large amounts of undesired side-products. So far
we have no explanation for the different chemical behavior
of Ru and Os. All the details on the synthesis and the full
characterization of the complexes are reported in the
Experimental Section.
Photophysical Properties. The absorption spectra of the
dinuclear complexes as well as the complexes containing
the indenofluorene bridging ligand are shown in Figures 1
and 2 for the ruthenium and osmium series, respectively.
Also, the spectra of the reference compounds M(bpy)32+ (M
) Ru or Os) are shown for comparison. The spectra of both
(64) Bossart, O.; De Cola, L.; Welter, S.; Calzaferri, G. Chem.-Eur. J.
2004, 10, 5771-5775.
4710 Inorganic Chemistry, Vol. 44, No. 13, 2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
Scheme 3. Synthetic Protocol for the Preparation of the Bridging Ligandsa
a (a) AcOK, DMSO, PdCl2(dppf), 105 °C, 17 h, 85%; (b) Na2CO3, toluene, Pd(PPh3)4, 95 °C, 48 h, 70%; (c) AcOK, DMSO, PdCl2(dppf), 105 °C, 25 h,
94%; (d) K2CO3, DMF, Pd(PPh3)4, 120 °C, 20 h, 55%; (e) Na2CO3, toluene, Pd(PPh3)4, 95 °C, 50 h, 87%; (f) Na2CO3, toluene, Pd(PPh3)4, 95 °C, 48 h, 80%.
series recorded in air-equilibrated acetonitrile show the
typical features of the reference complexes with additional
bands corresponding to the bridging ligand. In the UV region,
the band at 290 nm is assigned to a singlet intraligand (1IL)
π-π* transition of the three bipyridine units. The region
300-350 nm shows the absorbance of the oligophenylene
spacers (1IL, π-π*). With an increase in the number of
phenylene units, the conjugation length increases and results
in a red-shift for the maxima (320-350 nm), corresponding
to a lowering of the LUMO orbital, and therefore of the
HOMO-LUMO gap, and a simultaneous increase of the
molar extinction coefficient. In the case of [M-Flu-M]4+ (M
) Ru, Os) complexes, a remarkable red-shift of the phe-
nylene band is observed due to the forced planarization of
the phenylene units resulting in a larger π-conjugation
between the aromatic moieties. The influence of the pla-
narization of the phenylene units in the indenofluorene
bridging ligand can be easily seen by comparing the π-π*
transition bands in the [M-Flu-M]4+ and the [M-ph5-M]4+
complexes. In fact, for the ground state, the tilt angle in the
phenylene compounds is 23° while it is 0° for the indenof-
luorene units. This effect results in a strong red-shift (3690
and 3080 cm-1 for the corresponding ruthenium and osmium
complexes, respectively) of the band attributed to phenylene
units of the indenofluorene in the [M-Flu-M]4+ compared
with the phenylene moieties for the [M-ph5-M]4+ complexes
(Figures 1 and 2).
In the visible region, the comparison between the mono-
metallic complex [Rubpy-ph-Br]2+ and the bimetallic com-
plex [Ru-ph2-Ru]4+ shows no appreciable red-shift of the
absorption bands, indicating that the electronic coupling
between the two terminal metal units is very small. The
lowest energy absorption, at about 460 nm, is attributed to
singlet metal-to-ligand charge transfer (1MLCT) transitions
involving both the bipyridine on the bridging ligands (BL),
M(dπ) f BL(π*) and the ancillary bpy’s M(dπ) f bpy-
(π*). In fact, all the chelating ligands are expected to have
very similar energies, as can also be seen from the electro-
Inorganic Chemistry, Vol. 44, No. 13, 2005 4711

Welter et al.
Scheme 4. Synthesis of [Os-phn-Os](PF6)4 Complexes (n ) 2, 3, 4,
5)a
Figure 2. Absorption spectra of the homometallic osmium complexes in
acetonitrile, [Os-ph2-Os]4+ (-‚-), [Os-ph3-Os]4+ (---), [Os-ph4-Os]4+
(‚‚‚), [Os-ph5-Os]4+ ___), and [Os-Flu-Os]4+ (-‚‚-).
(
Table 1. Photophysical Properties of Dinuclear Ruthenium Complexes
Bridged by Oligophenylene Spacers
luminescence
abs.a
298 Ka
77 Kb
λ, nm
[Rubpy-ph2-bpy]2+ 456
λ, nm λ, nm τ, ns τ, µsc æem λ, nm τ, µs
626 207 1.7
625 213 1.9
625 198 1.7
625 206 1.7
625 210 1.7
624 195 1.7
0.079
0.075
0.073
0.071
0.070
0.084
590 6.4
595 6.4
596 6.1
595 6.4
595 6.1
594 6.1
[Ru-ph2-Ru]4+
[Ru-ph3-Ru]4+
[Ru-ph4-Ru]4+
[Ru-ph5-Ru]4+
[Ru-Flu-Ru]4+
[Ru(bpy)3]2+
457
457
457
457
466
451
616 160 0.89 0.062d 579 4.8 d
a Air-equilibrated acetonitrile (λexc ) 435 nm). b Butyronitrile solid
matrix. c Deaerated acetonitrile solution. d Ref 73.
Table 2. Photophysical Properties of Dinuclear Osmium Complexes
Bridged by Oligophenylene Spacers
luminescence
abs.a
298 Ka
77 Kb
λ, nm λ, nm τ, ns τ, nsc
æ
em 10-3 λ, nm τ, µs
a (a) K3PO4, Pd(PPh3)4, ethanol, dioxane, 95 °C, 16 h, 70%; (b) ethylene
glycol, microwave irradiation (450 W, 3 × 2 min).
[Os-ph2-Os]4+ 592
[Os-ph3-Os]4+ 593
[Os-ph4-Os]4+ 593
[Os-ph5-Os]4+ 591
[Os-Flu-Os]4+ 592
751
744
746
746
748
743
44
42
44
42
42
40
64
63
62
62
64
60
4.2
4.1
4.3
4.6
4.7
3.5d
722
720
719
719
720
710
1.1
1.1
1.0
1.0
1.0
0.83
[Os(bpy)3]2+
583
a Air-equilibrated acetonitrile (λexc ) 435 nm). b Butyronitrile solid
matrix. c Deaerated acetonitrile solution. d Ref 65.
complexes show a weak absorption band (560-670 nm) that
is assigned to spin-forbidden electronic transitions (3MLCT),
partly allowed due to strong spin-orbit coupling in the
osmium complexes.65
The emission spectra of all the metal complexes were
recorded in acetonitrile at room temperature and in butyro-
nitrile glass at 77 K upon excitation at 435 nm. The
spectroscopic data are summarized in Tables 1 and 2 for the
ruthenium and osmium series, respectively. The room-
temperature luminescence spectra for the complexes contain-
ing the longest phenylene spacer, [Ru-ph5-Ru]4+, the inde-
nofluorene spacer, [Ru-Flu-Ru]4+, and the reference compound
[Ru(bpy)3]2+ are shown in Figure 3. All the ruthenium
bimetallic complexes show the same maximum (625 nm)
Figure 1. Absorption spectra of the homometallic ruthenium complexes
in acetonitrile, [Ru-ph2-Ru]4+ (-‚-), [Ru-ph3-Ru]4+ (‚‚‚), [Ru-ph4-Ru]4+
(---), [Ru-ph5-Ru]4+ (s), and [Ru-Flu-Ru]4+ (-‚‚-). With increasing
numbers of phenyl rings, the maxima at 325 nm are shifted to the red and
increase in intensity.
chemical investigations (vide infra). The MLCT absorption
bands of the [Os-phn-Os]4+ complexes are red-shifted
compared to the analogous ruthenium complexes because
of the higher energy of the HOMO orbital as a result of the
presence of the heavier atom. Additionally, the osmium
(65) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722-3734.
4712 Inorganic Chemistry, Vol. 44, No. 13, 2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
Figure 3. Luminescence spectra of the complexes [Rubpy3]2+ ___), [Ru-
(
Figure 4. Luminescence spectra of the complexes [Osbpy3]2+ ___),
(
ph5-Ru]4+ (‚‚‚), and [Ru-Flu-Ru]4+ (---) in acetonitrile solution at 293 K
(λexc ) 435 nm). The inset shows the emission spectra at 77 K in
[Os-ph5-Os]4+ (‚‚‚), and [Os-Flu-Os]4+ (---) in acetonitrile solution at 293
K (λexc ) 435 nm). The inset shows the emission spectra at 77 K in
butyronitrile rigid matrix of [Rubpy3]2+
[Ru-ph2-Ru]4+ (---).
(
___), [Rubpy-ph-Br]2+ (‚‚‚), and
butyronitrile rigid matrix of [Osbpy3]2+
[Os-ph2-Os]4+ (---).
(
___), [Osbpy-ph-Br]2+ (‚‚‚), and
and band-shape for the emission. Compared to [Ru(bpy)3]2+,
we observe a small red-shift for all the bimetallic complexes
of about 10 nm, indicating a lowering in energy of the
emissive 3MLCT state. The same red-shift of 10 nm is also
observed for the mononuclear [Rubpy-ph2-bpy]2+ complex,
clearly indicating that the shift in emission is not due to the
second metal center. This result already suggests that the
LUMO of the substituted bipyridine is lower in energy than
those of the ancillary bipyridines. This observation is in
accordance with the reduction potentials obtained for the
bimetallic complexes and with the transient absorption
spectra (vide infra). The excited-state lifetimes and quantum
yields of the bimetallic complexes at room temperature in
aerated conditions are higher than for [Ru(bpy)3]2+, whereas
in deaerated conditions the lifetime for the bimetallic
complexes is almost double that for [Ru(bpy)3]2+. The
emission quantum yields mirror these results (see Table 1),
indicating that the polyphenylene units appended to the
bipyridine play a major role in the delocalization of the
exciton but do not affect dramatically the energetics of the
MLCT state nor that of the metal-centered MC state.
The emission spectra of the [Os-ph5-Os]4+ and [Os-Flu-
Os]4+ complexes and the reference compound [Os(bpy)3]2+
in acetonitrile solution are shown in Figure 4. For the osmium
bimetallic complexes, the maximum of emission is around
745 nm and shows only a slight red-shift compared to [Os-
in the bridging ligand, are slightly red-shifted compared with
the corresponding mononuclear complexes, [Rubpy-ph2-
bpy]2+ (590 nm), suggesting a weak but nonnegligible
electronic interaction between the two metal centers. The
emission lifetimes of the ruthenium complexes at low
temperature are relatively long (6.1 to 6.4 µs) compared with
that of the reference compound [Ru(bpy)3]2+ (4.8 µs). Again,
such data indicate a strong contribution of the delocalization
due to the presence of the conjugated moieties on the
bipyridine and that the lowest excited state is localized on
the bridging ligand. A similar behavior is observed for the
osmium dinuclear complexes.
Transient Absorption Spectroscopy. More detailed in-
formation about the electronic nature of the lowest excited
state is provided by time-resolved transient absorption
spectroscopy. Upon excitation, both in the ruthenium and
osmium tris-bipyridine complexes, the lowest excited state
is an MLCT state. A charge is formally localized on the bpy
ligand with the lowest reduction potential, and the ruthenium
or osmium unit is formally oxidized. In a differential transient
spectrum this can be easily visualized by the appearance of
a bleaching corresponding to the 1MLCT band in the
absorbance spectrum and formation of the bands correspond-
ing to the bipyridine radical anion, bpy•-. If the bridging
ligand is involved in the excitation, it is expected that the
transient absorption spectra of [Ru(bpy)3]2+ and the dinuclear
complexes would differ. Figure 5 displays the transient
absorption spectra of [Ru(bpy)3]2+ (Figure 5a) and [Ru-ph4-
Ru]4+ (Figure 5b). All the other dinuclear complexes show
similar features as [Ru-ph4-Ru]4+. In the spectra, the negative
band at 460 nm is due to the bleaching of the ground state
of the Ru(bpy)3 moieties of the complexes (dπ f π*
transition). In the case of [Ru-Flu-Ru]4+, this bleaching band
is more structured and shows the bleaching of the indeno-
fluorene unit (Figure 5c). The strong absorption band at 375
nm is due to the formation of the bpy•- radical anion, since
the MLCT state is the lowest excited state. An additional
intense and very broad feature appears in the region from
500 to 850 nm for [Ru-ph4-Ru]4+ and [Ru-Flu-Ru]4+ with a
lifetime of 200 ns corresponding to the emission decay. A
more extended delocalization of the excited state, due to the
(bpy) ]2+ (743 nm). The emission for both systems containing
3
the different bridging ligands is similar and exhibits a typical
3MLCT character. As in the case of the ruthenium complexes,
the osmium compounds have all the same excited state
lifetimes (see Table 2) at room temperature and show only
a weak, not spectroscopic visible, electronic interaction
between the two terminal units.
At 77 K, in glassy butyronitrile matrixes, all the complexes
exhibit a structured emission with a maximum centered on
595 and 720 nm for the ruthenium and osmium complexes,
respectively (see Figures 3 and 4 insets and Tables 1 and
2). It is interesting to notice that for both series there is a
red-shift in the dinuclear species compared to [Ru(bpy)3]2+
and [Os(bpy)3]2+. Furthermore, the shortest member of the
families, the compounds containing only two phenylene units
Inorganic Chemistry, Vol. 44, No. 13, 2005 4713

Welter et al.
Table 3. Electrochemical Data for the Dinuclear Ruthenium
Complexesa
E
1/2(V)
Ru(II/III)
bpy
[Ru-ph2-Ru]4+
[Ru-ph3-Ru]4+
[Ru-ph4-Ru]4+
[Ru-ph5-Ru]4+
[Ru-Flu-Ru]4+
[Ru(bpy)3]2+
+1.27
+1.27
+1.28
+1.26
+1.28
+1.28
-1.31
-1.31
-1.30
-1.31
-1.30
-1.33
-1.52
-1.53
-1.52
-1.51
-1.51
-1.56
-1.84
-1.84
-1.83
-1.84
-1.84
-1.87
a Butyronitrile solution with 0.1 M Bu4NPF6, room temperature, potential
values vs SCE.
Table 4. Electrochemical Data for the Dinuclear Osmium Complexesa
E
1/2(V)
Os(II/III)
bpy
[Os-ph2-Os]4+
[Os-ph3-Os]4+
[Os-ph4-Os]4+
[Os-ph5-Os]4+
[Os-Flu-Os]4+
[Os(bpy)3]2+
+0.86
+0.83
+0.84
+0.83
+0.86
+0.85
-1.20
-1.23
-1.24
-1.23
-1.20
-1.20
-1.42
-1.45
-1.46
-1.45
-1.42
-1.41
-1.78
-1.83
-1.86
-1.87
-1.79
-1.77
a Butyronitrile solution with 0.1 M Bu4NPF6, room temperature, potential
values vs SCE.
Electrochemical Measurements. Electrochemical studies
employed cyclic voltammetry with a three-electrode system
consisting of a platinum working electrode, a platinum
counter electrode, and a silver pseudo-reference electrode.
The electrochemical data for the ruthenium compounds and
[Ru(bpy)3]2+ are reported in Table 3. Corresponding data
for osmium compounds and [Os(bpy)3]2+ are reported in
Table 4.
All the dinuclear complexes have a single, reversible bi-
electronic anodic wave for the Ru(II/III) and Os(II/III) redox
couple, almost at the same potential as for the reference
compounds, [Ru(bpy)3]2+ and [Os(bpy)3]2+. This supports
the fact that the electronic coupling between the metal centers
is relatively weak. All the complexes exhibit three well-
resolved reversible waves in the cathodic branch of the
voltammograms that are due to reductions centered on the
substituted and unsubstituted bipyridine ligands. For each
of the ruthenium complexes, the first reduction is shifted to
a more positive potential than the first reduction of [Ru-
(bpy)3]2+. This feature indicates that for the dinuclear
complexes the first reduction is localized on the phenylene-
substituted bipyridine.
Crystal Structure. For the precursor [Rubpy-ph2-Si-
(CH3)3](PF6)2, single crystals were obtained by recrystalli-
zation from methanol. The crystal structure is shown in
Figure 6; crystal and unit cell data as well as selected bond
distances and angles are presented in Tables 5 and 6,
respectively. Besides the main molecules, the structure
additionally contains disordered solvent molecules, which
were treated as diffuse electron density (see Experimental
Section). The three bipyridyl residues are approximately
coplanar with interplanar angles of 3.3(4), 11.3(5), and
1.4(4)°, respectively. Most importantly, the crystal structure
reveals that the first phenyl ring makes a dihedral angle of
22.0(4)° with the bipyridine plane, whereas the second phenyl
ring is almost coplanar with the bipyridine unit (dihedral
Figure 5. Transient absorption spectra of [Ru(bpy)3]2+ (a), [Ru-ph4-Ru]4+
(b), and [Ru-Flu-Ru]4+ (c) recorded in acetonitrile (λexc ) 435 nm). The
insets show the recovery of the ground-state bleaching.
presence of the oligophenylene structure, is responsible for
this absorption at lower energy. This was reported for other
conjugated structures.27 The intensity and energy of this band
depend partially on the number of phenylenes. By compari-
son with [Ru(bpy)3]2+ the difference is clearly seen as a shift
to lower energy of the bpy•- band around 380 nm and, in
the case of the unsubstituted bpy, a lack of such broad feature
in the visible. It is interesting to notice that such a band does
not change going from 3 to 5 phenylene units, probably
because the first 2 phenylene units are the only responsible
for the delocalization of the charge. Furthermore, the fact
that the excited state is localized on the bridging ligand, and
therefore directional, can be employed for vectorial energy
or electron transport in non covalently linked systems.64 It
is worth mentioning that the different planarization of the
p-phenylene units versus the indenofluorene derivatives does
not seem to play a major role. Such a behavior could be
explained by the fact that in the excited state the phenylenes
become planar despite the fact that in the ground state the
tilt angle is 23°. On the other hand, however, the HOMO-
LUMO gap for the indenofluorene spacer is expected to be
lower and could play a major role in systems where energy
or electron transfer take place.
4714 Inorganic Chemistry, Vol. 44, No. 13, 2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
-
Figure 6. Displacement ellipsoid plot (30% probability) of [Rubpy-ph2-Si(CH3)3](PF6)2. Hydrogen atoms, PF6 anions, and disordered solvent molecules
have been omitted for clarity.
pyridinyl66 and 4,4′′-dibromo-[1,1′;4′,1′′]terphenyl,67 [Rubpy-
Table 5. Crystal and Unit Cell Data for [Rubpy-ph2-Si(CH3)3](PF6)2
ph-Br]2+, [Rubpy-ph2-Si(CH3)3]2+, [Rubpy-ph2-I]2+ 64 and 2,8-bis-
formula
formula weighta
crystal system
space group
a/Å
C45H40F12N6P2RuSi + disordered solvent
1083.93
triclinic
P1h (No. 2)
11.6477 (2)
11.7793 (2)
19.5014 (3)
75.8460 (6)
77.0381 (6)
75.8165 (7)
2476.56 (7)
2
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)tetraalkylindeno-(1,2b)-
fluorene68 were prepared following literature procedures. All
experiments were carried out under N2 atmosphere using standard
Schlenk line techniques except where otherwise mentioned. Chro-
matographic purification was conducted using 40-63-µm silica gel
or neutral alumina 705C purchased from Fluka. Preparative thick-
layer chromatography was performed on ANALTECH silica gel
G Uniplates (soft layer, 20 × 20 cm, 1000 µm). NMR spectra were
recorded on a Varian Mercury-VX (300 MHz) using the residual
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
D
calc/g m-3 a
1.454
0.488
1096
1
nondeuterated solvent as reference in the case of H NMR. High-
µ/mm-1 a
resolution electron spray ionizaton (ESI) mass spectra were
measured with a Bruker FTMS 4.7 T Bio APEXII spectrometer.
Fast atom bombardment mass spectroscopy (MS-FAB) was per-
formed with a Vacuum Micromass VG 70/70E (nitrobenzyl alcohol
matrix).
F(000)a
crystal size/mm
(sin θ/λ)max/Å-1
measured reflections
unique reflections
Rint
0.09 × 0.12 × 0.27
0.53
28011
6088
0.041
Photophysical Measurements. Absorption and emission spectra
were obtained on air-equilibrated solutions using previously
described equipment.69 Time-resolved emission spectra were mea-
sured on a Hamamatsu C-5680 streak camera equipped with a M
5677 sweep unit. Excitation at 450 nm was achieved by a pulsed
Coherent Infinity XPO laser operating at a repetition rate of 10
Hz. The time resolution of this setup is about 200 ps, as limited by
the laser width. Estimated errors are as follows: band maxima,
(2 nm; relative luminescence intensity, (20%; lifetimes, (10%.
Transient Absorption Spectroscopy. Nanosecond transient
absorption spectra were obtained by irradiating the samples with
2-ns pulses (fwhm) of a continuously tunable (420-710 nm)
Coherent Infinity XPO laser using a setup that was reported
previously.69 All spectra were recorded in acetonitrile with 80 ns
between each frame with a minimum instrumental gate time of 5
ns. The first frame was recorded 1 ns after the laser pulse. Samples
were prepared to have optical density, at the excitation wavelength,
of about 0.5 in a 1-cm cuvette.
parameters/restraints
R1 [I > 2σ(I)]
wR2 [all refl.]
GoF
622/127
0.0671
0.1892
1.081
a Derived quantities do not contain the contribution of the disordered
solvent.
Table 6. Selected Distances (Å), Angles (°), and Torsion Angles (°)
for [Rubpy-ph2-Si(CH3)3](PF6)2
Ru(1)-N(12)
2.061 (6)
2.069 (6)
2.064 (6)
2.057 (6)
2.052 (6)
2.062 (6)
78.6 (2)
79.3 (3)
78.9 (2)
22.4 (10)
-24.2 (11)
Ru(1)-N(22)
Ru(1)-N(62)
Ru(1)-N(72)
Ru(1)-N(82)
Ru(1)-N(92)
N(12)-Ru(1)-N(22)
N(62)-Ru(1)-N(72)
N(82)-Ru(1)-N(92)
C(24)-C(25)-C(31)-C(32)
C(33)-C(34)-C(41)-C(32)
Electrochemical Measurements. Electrochemical studies were
performed using a PAR model 283 potentiostat employing a gas-
angle 6.9(4)°). This geometry ensures a good conjugation
of their π systems. The Ru-N bond lengths range from
2.052(6) Å for Ru-N(82) to 2.069(6) Å for Ru-N(22). This
might indicate that there is less electron density on N(22)
because of a higher conjugation of the bipyridine unit and
the phenylene in para position.
(66) Querol, M.; Bozic, B.; Salluze, N.; Belser, P. Polyhedron 2003, 22,
655-664.
(67) Colonge, J.; Buendia, J.; Sabadie, J. Bull. Soc. Chim. Fr. 1967, 11,
4370-4374.
(68) Sonar, P.; Zhang, J.; Grimsdale, A. C.; Mu¨llen, K.; Surin, M.;
Lazzaroni, R.; Lecle`re, S.; Tierney, S.; Heeney, M.; McCulloch, I.
Macromol. 2004, 37, 709-715.
III. Experimental Section
(69) Kleverlaan, C. J.; Stufkens, D. J.; Clark, I. P.; George, M. W.; Turner,
J. J.; Martino, D. M.; van Willigen, H.; Vlcek, J. J. Am. Chem. Soc.
1998, 120, 10871-10879.
General. Reagents and solvents were all commercially available
and used as received. The ligand 4-(4-bromo-phenyl)-[2,2′]bi-
Inorganic Chemistry, Vol. 44, No. 13, 2005 4715

Welter et al.
tight, single-compartment, three-electrode cell under an argon
atmosphere. A platinum disk (apparent surface area of 0.42 mm2)
was employed as the working electrode. Before each measurement
the electrode was polished with diamond paste. A silver wire and
a platinum wire were used as pseudoreference and auxiliary
electrodes, respectively. The redox potentials were measured against
the ferrocene/ferrocenium (Fc/Fc+) redox couple that was used as
an internal standard (E1/2 ) 0.38 V vs SCE in acetonitrile).
Tetrabutylammonium hexafluorophosphate (0.1 M) was used as
supporting electrolyte.
Crystal Structure Determination of [Rubpy-ph2-Si(CH3)3]-
(PF6)2. X-ray intensities were measured on a Nonius Kappa CCD
diffractometer with rotating anode (graphite monochromator, λ )
0.71073 Å) at a temperature of 150(2) K. An absorption correction
was not considered necessary. The structure was solved with
automated Patterson methods70 and refined with SHELXL-9771
against F2 of all reflections. Non-hydrogen atoms were refined freely
with anisotropic displacement parameters. Hydrogen atoms were
introduced in calculated positions and refined as rigid groups. One
PF6- anion was refined with a disorder model. The crystal structure
contains voids (306 Å3/unit cell) filled with disordered solvent
molecules. Their contribution to the structure factors (78 electrons/
unit cell) was secured by back-Fourier transformation using the
SQUEEZE procedure of the PLATON package.72 Structure calcula-
tions, drawings, and checking for higher symmetry were performed
with PLATON.72 Further crystallographic details are given in Table
5.
Synthesis. Bpy-ph-B(OR)2 [12], 4-[4-(4,4,5,5-Tetramethyl-
[1,3,2]dioxaborolan-2-yl)-phenyl]-[2,2′]bipyridinyl. The ligand
bpy-ph-Br [11] (105 mg, 0.34 mmol), oven-dried potassium acetate
(99 mg, 1.01 mmol), and bis(pinacolato)diboron (99 mg, 0.39
mmol) were dissolved in DMSO (2 mL), and oxygen was removed
from the system by the freeze-pump-thaw technique. The catalyst,
PdCl2(dppf) (8.3 mg, 0.01 mmol), was added; the reaction mixture
was then heated to 105 °C for 17 h. After cooling to room
temperature, 3 mL of water were added to the dark-brown-reddish
solution. The resulting mixture was then extracted with CH2Cl2 (2
× 20 mL). The combined brownish-colored organic layer was
washed with water until the water phase became colorless. The
organic phase was evaporated under reduced pressure to afford a
black solid. Extraction with hexane isolated the desired compound
which was used without further purification (yield: 111 mg, 85%).
1H NMR (300 MHz, CDCl3): δ ) 8.74 (m, 2H), 8.71 (s, 1H),
8.47 (d, J ) 7.6 Hz, 1H), 7.96 (d, J ) 8.1 Hz, 2H), 7.86 (dd, J )
7.6 Hz, 2.0 Hz, 1H), 7.80 (d, J ) 8.5 Hz, 2H), 7.58 (dd, J ) 5.0
Hz, 2.0 Hz, 1H), 7.35 (ddd, J ) 7.6 Hz, 4.5 Hz, 1.0 Hz, 1H), 1.4
(s, 12H). 13C NMR (100 MHz, CDCl3): δ ) 157.1, 156.5, 150.0,
149.6, 141.2, 137.4, 135.9, 135.1, 126.8, 124.2, 122.1, 121.8, 119.5,
84.2, 25.5, 25.0. MS (FAB, m/z): 359 (M + H)+.
added under a mild flow of argon. The reaction mixture was heated
at 95 °C for 48 h. The reaction mixture was cooled to room
temperature. The layers were separated, and the aqueous layer was
extracted with toluene (2 × 20 mL). The combined organic phases
were dried (MgSO4) and evaporated under reduced pressure to yield
a yellow solid. The crude product was dissolved in CH2Cl2 (3 mL)
and purified over silica gel column chromatography (Kieselgel 60,
230-400 mesh ASTM deactivated by triethylamine, 12 × 3 cm)
using CH2Cl2/EtOAC (4:1) as eluent. After evaporation of the
solvents the desired compound was obtained as a white solid
(yield: 342 mg, 70%). 1H NMR (400 MHz, CDCl3): δ ) 8.79 (m,
3H), 8.58 (d, J ) 8.6 Hz, 1H), 7.91 (d, J ) 8.1 Hz, 3H), 7.73 (d,
J ) 8.6 Hz, 2H), 7.66 (dd, J ) 1.5 Hz, 5.1 Hz, 1H), 7.63 (d, J )
8.6 Hz, 2H), 7.54 (d, J ) 8.1 Hz, 2H), 7.41 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ ) 156.2, 155.4, 149.5, 144.1, 142.8, 141.4,
139.5, 137.9, 137.4, 132.4, 129.3, 129.1, 128.2, 127.5, 124.6, 122.5,
122, 121.5, 119.7. MS (FAB, m/z): 387.05 (M + H)+.
Bpy-ph2-B(OR)2 [14], 4-[4′-(4,4,5,5-Tetramethyl-[1,3,2]diox-
aborolan-2-yl]-biphenyl-4-yl]-[2,2′]bipyridinyl. A solution of bpy-
ph2-Br [13] (90 mg, 0.24 mmol), oven-dried potassium acetate (66
mg, 0.67 mmol), and bis(pinacolato)diboron (65 mg, 0.26 mmol)
in DMSO (3 mL) was evacuated and backfilled with argon (four
cycles). Finally, PdCl2(dppf) (8.3 mg, 0.01 mmol) was added over
a mild flow of argon. The reaction mixture was heated to 105 °C
for 25 h. Water (3 mL) was added to the dark-brown-reddish
solution, and the resulting mixture was extracted with CH2Cl2 (2
× 20 mL). The combined brownish organic layer was washed with
water (4 × 10 mL) until the water phase became colorless. The
organic phase was evaporated under reduced pressure to afford a
black solid. Addition of hexane to this solid solubilized the desired
compound that was used without further purification (yield: 98
1
mg, 94%). H NMR (400 MHz, CDCl3): δ ) 8.79 (m, 3H), 8.58
(d, J ) 8.1 Hz, 1H), 7.92 (m, 5H), 7.79 (d, J ) 8.1 Hz, 2H), 7.68
(m, 3H), 7.40 (ddd, J ) 8.1 Hz, 5.6 Hz, 1.0 Hz, 1H), 1.4 (s, 12H).
13C NMR (100 MHz, CDCl3): δ ) 149.4, 143.2, 142.5, 137.8,
137.3, 135.8, 135.1, 129.3, 128.3, 128.1, 127.5, 126.8, 124.6, 122.2,
122.0, 119.7, 84.3, 83.9, 25.4, 25.2. HRMS (ESI), m/z: [M + H]+
calcd for C28H28N2B(11)O2: 435.2238; found: 435.2235.
Bpy-ph2-bpy [15]. A dry flask was charged with bpy-ph-B(OR)2
[12] (193 mg, 0.54 mmol), bpy-ph-Br [11] (146 mg, 0.47 mmol),
and K2CO3 (500 mg, 3.61 mmol). The flask was evacuated and
backfilled with argon (four cycles). Degassed DMF (20 mL) and
Pd(PPh3)4 (12 mg, 0.01 mmol) were added over a mild flow of
argon. The reaction mixture was heated at 120 °C for 20 h. The
reaction mixture was then cooled to room temperature; more DMF
(10 mL) was then added to precipitate more of the free ligand,
which was isolated by suction filtration and washed with DMF (2
× 10 mL). The crude product was dissolved in CH2Cl2 (3 mL)
and purified using column chromatography (SiO2, CH2Cl2/MeOH
(9:1) as eluent). The fractions containing the desired compound
[TLC: Rf ) 0.10, support SiO2, CH2Cl2/MeOH (9:1) as eluent],
were collected and evaporated under reduced pressure to yield a
white solid (yield: 120 mg, 55%). 1H NMR (400 MHz, CDCl3): δ
) 8.58 (m, 4H), 8.52 (s, 2H), 8.23 (d, J ) 8.0 Hz, 2H), 7.80 (d, J
) 8.5 Hz, 6H), 7.70 (d, J ) 8.5 Hz, 4H), 7.55 (dd, J ) 5.3 Hz, 1.8
Hz, 2H), 7.32-7.24 (m, 2H). 13C NMR (75 MHz, CDCl3): δ )
157.3, 156.1, 149.6, 149.0, 148.85, 146.3, 137.14, 132.27, 128.3,
124.2, 123.5, 121.4, 121.2, 118.8. MS (FAB, m/z): 463 (M + H)+.
HRMS (ESI), m/z: [M + H]+ calcd for C32H23N4: 463.1917;
found: 463.1911.
Bpy-ph2-Br [13], 4-(4′-Bromo-biphenyl-4-yl)-[2,2′]bipyridinyl.
An oven-dried two-neck round flask was charged with bpy-ph-
B(OR)2 [12] (450 mg, 1.26 mmol) and 1-bromo-4-iodo-benzene
(355 mg, 1.26 mmol). The flask was evacuated and backfilled with
argon for four cycles. Degassed toluene (13 mL), Na2CO3 1M in
H2O (13 mL, 12.6 mmol), and Pd(PPh3)4 (12 mg, 0.01 mmol) were
(70) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. “The
DIRDIF99 program system, Technical Report of the Crystallography
Laboratory,” The Netherlands, 1999.
(71) Sheldrick, G. M. SHELXL-97. Program for crystal structure refine-
ment, Universita¨t Go¨ttingen, Germany, 1997.
(72) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7-13.
(73) Calvert, J. M.; Caspar, J. V.; Binstead, R. A.; Westmoreland, T. D.;
Meyer, T. J. J. Am. Chem. Soc. 1982, 104, 6620-6627.
Bpy-ph4-bpy [16]. A dry flask was charged with bpy-ph2-Br
[13] (302 mg, 0.78 mmol) and bpy-ph2-B(OR)2 [14] (280 mg, 0.78
mmol). Oxygen was removed from the closed system by evacuation
4716 Inorganic Chemistry, Vol. 44, No. 13, 2005

Rodlike Bimetallic Ru and Os Complexes Bridged by Phenylene
and argon backfilling (four cycles). To this system, degassed toluene
(7 mL) and a degassed aqueous solution of Na2CO3 1 M (7 mL, 7
mmol) and Pd(PPh3)4 (0.04 mol %) were added over a mild flow
of argon. The reaction mixture was refluxed for 50 h. The solution
was cooled to room temperature, and the insoluble solid was
recovered by suction filtration and washed with hexane (2 × 20
mL). The crude product was used in the next step without further
purification (yield: 417 mg, 87%).
4PF6). HRMS (ESI), m/z: [M-4PF6]4+ calcd for C72H54N12Ru-
(102)2: 322.5665; found: 332.5670.
[Ru-ph3-Ru](PF6)4 [3]. [Rubpy-ph-Br]2+ [18] (52 mg, 5.1 ×
10-5 mol), 4,4′-phenyldiboronic acid (4.2 mg, 2.55 × 10-5 mol),
and K2CO3 (35 mg, 2.6 × 10-4 mol) were dissolved in DMF (10
mL). Pd(PPh3)4 (4 mg, 3.5 × 10-6 mol) was added to the degassed
solution, and the reaction mixture was heated to 95 °C. After 16 h
the solvent was removed under vacuum (100 °C), and the residue
was purified as described before for [Ru-ph2-Ru](PF6)4. Evaporation
Bpy-ph5-bpy [17]. The same reaction procedure as described
for bpy-ph4-bpy was used, using 4,4′′-dibromo-[1,1′;4′,1′′]terphenyl
(100 mg, 0.26 mmol), bpy-ph-B(OR)2 [12] (185 mg, 0.52 mmol),
Na2CO3 0.5 M (10 mL, 5 mmol), and Pd(PPh3)4 (0.04 mol %).
The crude product was used in the next step without further
purification (yield: 144 mg, 80%).
1
of the solvent yielded an orange solid (yield: 42 mg, 78%). H
NMR (300 MHz, CD3CN): δ ) 8.82 (s, 2H), 8.73 (d, J ) 8.0 Hz,
2H), 8.54 (dd, J ) 8.3 Hz, J ) 2.0 Hz, 8H), 8.18-7.96 (m, 18H),
7.92 (s, 4H), 7.88-7.72 (m, 14H), 7.52-7.40 (m, 10H). HRMS
(ESI), m/z: [M-4PF6]4+ calcd for C78H58N12Ru(102)2: 341.5743;
found: 341.5751.
[Rubpy-ph2-bpy](PF6)2 [19]. A dry Schlenk flask was charged
with [Rubpy-ph-Br](PF6)2 (140 mg, 0.14 mmol), bpy-ph-B(OR)2
[12] (70 mg, 0.20 mmol), K2CO3 (94 mg, 0.68 mmol), and 20 mL
of DMF. The solution was degassed by the freeze-pump-thaw
technique, and Pd(PPh3)4 (0.04 mol %) was added. The reaction
mixture was heated at 120 °C for 24 h. The solvent was evaporated
under reduced pressure to afford a black solid. The crude product
was dissolved in water/acetone (10:1, 10 mL), and a saturated
aqueous solution (1 mL) of NH4PF6 was added. The acetone was
removed under reduced pressure from the water phase, and the
precipitated solid was filtered and washed with water (2 × 20 mL)
and diethyl ether (2 × 10 mL). The crude product was purified on
a silica gel column with MeCN/H2O/MeOH/KNO3, 4:1:1:0.1 as
eluent. An orange compound (TLC: Rf ) 0.20, support SiO2,
solvent MeCN/H2O/MeOH/KNO3, 4:1:1:0.1, as eluent) was isolated
and further purified by preparative thick-layer chromatography
(SiO2, MeCN/H2O/MeOH/KNO3, 4:1:1:0.1, as mobile phase).
Recrystallization from acetone/hexane yielded a crystalline orange
[Ru-ph4-Ru](PF6)4 [5]. A solution of [Rubpy-ph-Br]2+ [18] (310
mg, 0.30 mmol), 4,4′-biphenyldiboronic acid (37 mg, 0.15 mmol)
and Na2CO3‚10H2O (127 mg, 0.92 mmol) in DMF (10 mL) was
degassed by the freeze-pump-thaw technique. Subsequently, Pd-
(PPh3)4 (10 mg, 4.6 × 10-3 mmol) was added, and the reaction
mixture was heated to 90 °C. After 16 h the solvent was removed
under vacuum (100 °C), and the residue was purified as described
before for [Ru-ph2-Ru](PF6)4. The reaction yields an orange-red
1
solid (yield: 242 mg, 80%). H NMR (300 MHz, CD3CN): δ )
8.81 (s, 2H), 8.73 (d, J ) 8.0 Hz, 2H), 8.54 (dd, J ) 8.3 Hz, 2.0
Hz, 8H), 8.20-7.68 (br m, 40H), 7.52-7.40 (m, 10H). HRMS
(ESI), m/z: [M-4PF6]4+ calcd for C85H62N12Ru(101)Ru(102):
360.3324; found: 360.3336.
[Ru-ph5-Ru](PF6)4 [7]. This compound was prepared according
to the same conditions as described above for [Ru-ph4-Ru](PF6)4,
starting from 100 mg (0.088 mmol) of [Rubpy-ph2-I]2+ [20], 70
mg (0.35 mmol) of 4,4′-biphenyldiboronic acid, 73 mg (0.53 mmol)
of K2CO3, and 5 mg (0.004 mmol) of Pd(PPh3)4 in 20 mL of DMF,
to give [Ru-ph5-Ru](PF6)4, an orange solid (yield: 79 mg, 77%).
1H NMR (400 MHz, CD3CN): δ ) 8.83 (s, 2H), 8.75 (d, J ) 8.1
Hz, 2H), 8.55 (dd, J ) 7.6 Hz, 8H), 8.15-8.07 (m, 10H), 8.05 (d,
J ) 8.6 Hz, 4H), 7.99 (d, J ) 8.6 Hz, 4H), 7.90 (d, J ) 6.1 Hz,
12H), 7.82-7.73 (m, 14H), 7.48-7.42 (m, 10H). HRMS (ESI),
m/z: [M-4PF6]4+ calcd for C90H66N12Ru(101)Ru(102): 379.3403;
found: 379.3409.
1
powder (yield: 121 mg, 74%). H NMR (300 MHz, acetone-d6):
δ ) 8.81 (dd, J ) 0.9 Hz, 2.1 Hz, 1H), 8.76 (d, J ) 0.9 Hz, 4.8
Hz, 1H), 8.73 (ddd, J ) 0.9 Hz, 1.8 Hz, 4.8 Hz, 1H), 8.54 (dt, J )
1.2 Hz, 8.1 Hz, 1H), 7.99-7.88 (m, 5H), 7.75 (dd, J ) 1.8 Hz, 5.4
Hz, 1H) 7.45 (ddd, J ) 1.2 Hz, 5.0 Hz, 1H). HRMS (ESI),
m/z: [M-2PF6]2+ calcd for C52H38N8Ru(102): 438.1126; found:
438.1135.
[Ru-ph2-Ru](PF6)4 [1]. To a solution of Ru(bpy)2Cl2 (11 mg,
0.02 mmol) in ethylene glycol (5 mL) with 5% water content,
[Rubpy-ph2-bpy]2+ [19] (20 mg, 0.017 mmol) was added. The
suspension was repeatedly heated three times for two minutes in a
modified microwave oven (450 W). The solvents were removed
under reduced pressure. The solid residue was dissolved in water
(10 mL). The water phase was washed with CH2Cl2 (3 × 5 mL) in
order to remove starting materials. Evaporation of the water phase
gave a red solid that was purified by silica gel column chroma-
tography (MeCN/H2O/MeOH/NaCl, 4:1:1:0.1). After evaporation
of the organic solvents, the desired product was precipitated from
the remaining water-layer by adding NH4PF6 (100 mg). The orange
precipitate was filtered over Celite and washed several times with
water (2 × 20 mL) and diethyl ether (2 × 10 mL). Finally the
compound was eluted from Celite with acetone. Evaporation of
the solvent yielded an orange solid (yield: 25 mg, 78%). 1H NMR
(300 MHz, CD3CN): δ ) 8.83 (s, 2H), 8.75 (d, J ) 8.1 Hz, 2H),
8.55 (m, 8H), 8.15-8.07 (m, 10H), 8.06 (d, J ) 8.6 Hz, 4H), 8.00
(d, J ) 8.6 Hz, 4H), 7.85 (d, J ) 6.1 Hz, 2 H), 7.83-7.77 (m,
[Ru-Flu-Ru](PF6)4 [9]. This compound was prepared according
to the same conditions as described above for [Ru-ph4-Ru](PF6)4,
starting from 100 mg (9.86 mol) of [Rubpy-ph-Br]2+ [18], 43 mg
(4.5 × 10-5 mol) of [22], 37 mg (2.40 × 10-4 mol) of K2CO3, and
5 mg (4.5 × 10-6 mol) of Pd(PPh3)4 in 20 mL of DMF, to give an
orange solid (yield: 101 mg, 87%). 1H NMR (300 MHz, CD3CN):
δ ) 8.87 (s, 2H), 8.78 (d, J ) 4.8 Hz, 2H), 8.58 (dd, J ) 7.8 Hz,
8H), 8.20-8.05 (m, 18H), 8.00-7.93 (m, 4H), 7.90-7.75 (m, 18H),
7.54-7.42 (m, 10H), 2.02 (m, 8H), 1.23-1.00 (m, 40 H), 0.78 (t,
12H), 0.69 (m, 8H). HRMS (ESI), m/z: [M-4PF6]4+ calcd for
C124H130N12Ru(102)Ru(104): 498.2154; found: 498.2164.
[Osbpy-ph-Br](PF6)4 [21]. Os(bpy)2Cl2 (120.4 mg, 0.21 mmol)
and bpy-ph-Br [11] (50 mg, 0.16 mmol) were dissolved in 3 mL
of ethylene glycol. The mixture was placed in a modified microwave
oven and irradiated at 450 W for two minutes and, after a cooling
period, for another two minutes. The stage of conversion was
checked by TLC, and the reaction mixture was longer irradiated if
necessary. The solvent was distilled off under vacuum using a
“micro distillation head” at high temperature (90-110 °C). The
dark-green compound was dissolved in water ((20 mL), and the
water phase was extracted with chloroform to remove the excess
of Os(bpy)2Cl2. The compound was purified by column chroma-
tography on silica gel using MeCN/H2O/MeOH/KNO3, 4:1:1:0.1
10H), 7.74 (dd, J ) 6.1 Hz, 2.0 Hz, 2H), 7.48-7.42 (m, 10H). 13
C
NMR (100 MHz, CD3CN): δ ) 157.9, 157.4, 152.1, 149.1, 141.9,
140.0, 138.2, 135.7, 128.5, 128.0, 125.1, 124.9, 124.7, 122.1. MS
(ESI, m/z): 790.13 (M-2PF6), 478.09 (M+- 3PF6), 322.58 (M+-
Inorganic Chemistry, Vol. 44, No. 13, 2005 4717

Welter et al.
as eluent. The desired compound was collected, and the organic
solvents were evaporated. A quantity of 100 mg of NH4PF6 in 2
mL of water was added to the remaining water-layer to obtain a
dark-green precipitate. The precipitate was filtered over Celite and
washed several times with water (2 × 20 mL) and diethyl ether (2
× 10 mL). Finally the compound was eluted from Celite with
acetone. [Osbpy-ph-Br](PF6)2 was obtained as a dark-green powder
as eluent. Recrystallization from acetone/diethyl ether yielded a
crystalline green powder (yield: 9 mg, 24%). 1H NMR (400 MHz,
CD3CN): δ ) 8.81 (s, 2H), 8.73 (d, J ) 8.1 Hz, 2H), 8.53 (dd, J
) 7.6 Hz, 8H), 8.04 (d, J ) 8.6 Hz, 4H), 7.98 (d, J ) 8.6 Hz, 4H),
7.96-7.87 (m, 18H), 7.77-7.67 (m, 12H), 7.65 (dd, J ) 2.0 Hz,
6.1 Hz, 2H), 7.39-7.33 (m, 10H). 13C NMR (100 MHz, CD3CN):
δ ) 159.8, 159.4, 151.3, 151.1, 137.6, 137.4, 128.6, 128.4, 128.1,
127.9, 124.9, 122.2. HRMS (ESI), m/z: [M-4PF6]4+ calcd for
C84H62N12Os(190)Os(192): 405.1099; found: 405.1107
1
(yield: 150 mg, 85%). H NMR (300 MHz, CD3CN): δ ) 8.73
(s, 1H), 8.69 (d, J ) 8.0 Hz, 1H), 8.58-8.46 (d, J ) 8.3 Hz, 4H),
7.95-7.82 (m, 5H), 7.80 (s, 4H), 7.74-7.65 (m, 6H) 7.65 (d, J )
7.5 Hz, 1H), 7.36-7.27 (m, 5H).). HRMS (ESI), m/z: [M-4PF6]4+
calcd for C36H27N6Os(192)Br(79): 407.0542; found: 407.0534.
[Os-ph2-Os](PF6)4 [2]. To a solution of Os(bpy)2Cl2 (160 mg,
0.28 mmol) dissolved in ethylene glycol (5 mL) with 5% water
content, bpy-ph2-bpy [15] (55 mg, 0.13 mmol) was added. The
suspension was repeatedly heated in a modified microwave oven
(450 W) three times for two minutes and allowed to cool between
heating periods. The solvents were removed under reduced pressure
to form a solid residue, and redissolved in water (10 mL). The
water phase was washed with CH2Cl2 (3 × 5 mL) in order to
remove starting materials. The remaining CH2Cl2 was removed
under reduced pressure from the water phase, NH4PF6 (100 mg)
was added, and the resulting green precipitate was isolated by
suction filtration. The crude product was dissolved in acetone (3
mL) and purified by silica gel column chromatography using
MeCN/H2O/MeOH/KNO3, 4:1:1:0.1 as eluent. A green band
(TLC: Rf ) 0.32, support SiO2, MeCN/H2O/MeOH/KNO3, 4:1:1:
0.1, as eluent) was isolated, and the solvents were removed under
reduced pressure. The green solid was further purified by preparative
plate (SiO2, MeCN/H2O/MeOH/ KNO3, 4:1:1:0.1, as mobile phase).
The recrystallization from acetone/diethyl ether yielded a crystalline
green powder (yield: 223 mg, 84%). 1H NMR (400 MHz,
CD3CN): δ ) 8.80 (s, 2H), 8.73 (d, J ) 8.6 Hz, 2H), 8.53 (dd, J
) 7.1 Hz, 8H), 8.05 (d, J ) 8.6 Hz, 4H), 7.99 (d, J ) 8.6 Hz, 4H),
7.96-7.88 (m, 10H), 7.77-7.67 (m, 12H), 7.65 (dd, J ) 6.1 Hz,
2.0 Hz, 2H), 7.40-7.34 (m, 10H). 13C NMR (100 MHz, CD3CN):
δ ) 159.9, 159.4, 151.3, 151.1, 148.3, 141.9, 137.5, 135.4, 128.6,
128.3, 125.5, 125.1, 124.9, 122.2. HRMS (ESI), m/z: [M-4PF6]4+
calcd for C72H54N12Os(190)Os(192): 367.0943; found: 367.0949.
[Os-ph3-Os](PF6)4 [4]. [Osbpy-ph-Br]2+ [21] (33 mg, 2.99 ×
10-5 mol), 4,4′-phenyldiboronic acid (2.7 mg, 1.63 × 10-5 mol),
and K3PO4 (28 mg, 1.3 × 10-4 mol) were dissolved in a mixture
of ethanol (4 mL) and dioxane (5 mL). Pd(PPh3)4 (3 mg, 2.4 ×
10-6 mol) was added to the degassed solution and the reaction
mixture was heated to 95 °C. After 16 h the solvents were removed
under vacuum (100 °C), and the residue was purified as described
before for [Ru-ph2-Ru](PF6)4. A dark-green solid was obtained
(yield: 24 mg, 70%). 1H NMR (300 MHz, CD3CN): δ ) 8.81 (s,
2H), 8.72 (d, J ) 7.8 Hz, 2H), 8.55-8.51 (m, 8H), 8.05-7.88 (m,
21H), 7.76-7.64 (m, 15H), 7.39-7.33 (m, 10H). HRMS (ESI),
m/z: [M-4PF6]4+ calcd for C78H58N12Os(190)Os(192): 386.1021;
found: 386.1025.
[Os-ph5-Os](PF6)4 [8]. This compound was prepared by the same
procedure as that used for [Os-ph4-Os](PF6)4 with Os(bpy)2Cl2 (66
mg, 0.12 mmol) and bpy-ph5-bpy [17] (40 mg, 0.06 mmol). The
reaction yielded a crystalline dark-green powder (yield: 27 mg,
1
20%). H NMR (400 MHz, CD3CN): δ ) 8.81 (s, 2H), 8.73 (d, J
) 8.6 Hz, 2H), 8.53 (dd, J ) 8.1 Hz, 8H), 8.04 (d, J ) 8.6 Hz,
4H), 7.98 (d, J ) 8.6 Hz, 4H), 7.90 (d, J ) 7.1 Hz, 20H), 7.78-
7.67 (m, 14H), 7.66 (dd, J ) 7.1 Hz, 2.0 Hz, 2H), 7.39-7.32 (m,
10H). HRMS (ESI), m/z: [M-4PF6]4+ calcd for C90H66N12Os(190)-
Os(192): 424.1178; found: 424.1188.
[Os-Flu-Os](PF6)4 [10]. This compound was prepared according
to the same conditions as those described above for [Ru-ph4-Ru]-
(PF6)4, starting from 80 mg (7.25 × 10-5 mol) of [Osbpy-ph-Br]2+
[21], 35 mg (3.63 × 10-5 mol) of [22], 60 mg (2.40 × 10-4 mol)
of K2CO3, and 8 mg (7.25 × 10-6 mol) of Pd(PPh3)4 in 20 mL of
1
DMF, to give a dark-green solid (yield: 65 mg, 65%). H NMR
(300 MHz, CD3CN): δ ) 8.81 (s, 2H), 8.73 (d, J ) 8.0 Hz, 2H),
8.58-8.48 (m, 8H), 8.12-7.88 (m, 18H), 7.86-7.62 (m, 22H),
7.44-7.32 (m, 10H), 2.02 (m, 8H), 1.23-1.00 (m, 40 H), 0.78 (t,
12H), 0.69 (m, 8H). HRMS (ESI), m/z: [M-4PF6]4+ calcd for
C124H130N12Os(190)Os(192): 542.2430; found: 542.2427.
Conclusions
We have synthesized and investigated a series of dinuclear
homometallic ruthenium and osmium complexes containing
p-polyphenylene units as spacers. The “chemistry on the
complex” approach allows a very easy and straightforward
synthesis of the dinuclear ruthenium complexes. However,
for the osmium complexes this approach was not suitable
and in most of the cases yielded undesired byproducts. Thus
a more classical approach had to be used for the osmium
dinuclear homometallic complexes involving the complex-
ation of the bridging ligand to [Os(bpy)2Cl2]. The electro-
chemical data show that the first reduction takes place on
the bridging bipyridine ligand. The photophysical data
indicate in fact that the lowest excited state involves the bpy
of the bridging ligand. A weak interaction between the two
metal centers exists in the ground state. Time-resolved
emission and transient absorption spectroscopy reveal that
in the excited state the electronic density is delocalized over
the p-phenylene spacers. Such a strong directionality in the
excitation could be used for vectorial processes.
[Os-ph4-Os](PF6)4 [6]. To a solution of Os(bpy)2Cl2 (20 mg,
0.03 mmol), dissolved in ethylene glycol (5 mL) with 5% water
content, bpy-ph4-bpy [16] (10 mg, 0.016 mmol) was added. The
suspension was homogenized in an ultrasonic bath and then heated
in a modified microwave oven (3 × 2 min, 450 W). Water (10
mL) was added to the reaction solution, and the insoluble part was
filtered off over Celite; NH4PF6 (100 mg) was then added, and the
resulting green precipitate was isolated by suction filtration, washed
several times with water, and then with diethyl ether. The crude
product was dissolved in acetone (3 mL) and purified by silica gel
column chromatography with MeCN/H2O/MeOH/KNO3, 4:1:1:0.1
Acknowledgment. This research was supported by Phil-
ips Research (Contract RWC-061-JR-00084-jr) and the
European Union (MWFM G5RD-CT-2002-00776).
Supporting Information Available: Crystallographic data
including atomic positions and displacement parameters (cif) and
mass analysis data. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC0483141
4718 Inorganic Chemistry, Vol. 44, No. 13, 2005