Structure and properties of carbonyl-coordinated ruthenium(II) and osmium(II) porphyrin dimers bridged by aza ligands

Article abstract of DOI:10.1246/bcsj.80.1955

Carbonyl-coordinated ruthenium(II) and osmium(II) porphyrin dimers bridged with aza ligands, [{M(por)-(CO)}₂](BL), (M = Ru^II, Os ^II; por = ttp (5,10,15,20-tetra-p-tolylporphyrinato dianion), oep (2,3,7,8,12,13,17,18-octa-ethylporphyrinato dianion); BL = pz (pyrazine), bpy (4,4′-bipyridine), dabco (l,4-diazabicyclo[2,2,2]octane)), were prepared and characterized, and their structures were determined by using single-crystal X-ray crystallography. The metal-metal distances of the pz-, bpy-, and dabco-bridged dimers in [{M(por)(CO)}₂(BL)] were about 7.1-7.3, 11.5, and 7.3-7.4 A, respectively. From electrochemical measurements, the first oxidation waves of the ruthenium and osmiumporphyrin dimers with the pz and dabco, except the Ru-oep systems, were split, although the first oxidation in the Rucomplexes occurs at the porphyrin rings and in the Os complexes occurs at the metal centers. The extent of the potential splits at the first oxidation processes, which reflects magnitude of the intramolecular redox interactions, was in the orders: ttp > oep and Os (metal oxidation) > Ru (ring oxidation), and dabco ≥ pz ? bpy.

Full text of DOI:10.1246/bcsj.80.1955

ꢀ 2007 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 80, No. 10, 1955–1964 (2007) 1955
Structure and Properties of Carbonyl-Coordinated Ruthenium(II)
and Osmium(II) Porphyrin Dimers Bridged by Aza Ligands
Chika Bando, Atsushi Furukawa, Kiyoshi Tsuge, Kazumi Takaishi,
ꢀ
Yoichi Sasaki, and Taira Imamura
Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810
Received February 22, 2007; E-mail: timamura@sci.hokudai.ac.jp
Carbonyl-coordinated ruthenium(II) and osmium(II) porphyrin dimers bridged with aza ligands, [{M(por)-
(CO)}2](BL), (M = RuII, OsII; por = ttp (5,10,15,20-tetra-p-tolylporphyrinato dianion), oep (2,3,7,8,12,13,17,18-octa-
ethylporphyrinato dianion); BL = pz (pyrazine), bpy (4,40-bipyridine), dabco (1,4-diazabicyclo[2,2,2]octane)), were
prepared and characterized, and their structures were determined by using single-crystal X-ray crystallography. The
metal–metal distances of the pz-, bpy-, and dabco-bridged dimers in [{M(por)(CO)}2(BL)] were about 7.1–7.3, 11.5,
˚
and 7.3–7.4 A, respectively. From electrochemical measurements, the first oxidation waves of the ruthenium and osmium
porphyrin dimers with the pz and dabco, except the Ru–oep systems, were split, although the first oxidation in the Ru
complexes occurs at the porphyrin rings and in the Os complexes occurs at the metal centers. The extent of the potential
splits at the first oxidation processes, which reflects magnitude of the intramolecular redox interactions, was in the
orders: ttp > oep and Os (metal oxidation) > Ru (ring oxidation), and dabco ꢁ pz ꢂ bpy.
Multiporphyrin assemblies have been extensively studied in
order to obtain more information on functional materials,1 such
as catalysts,2 receptors,3 and diverse photophysical devices.4,5
In such assemblies, arrangement of porphyrin subunits that
control intramolecular interaction plays a key role in the emer-
gence of the above functionality. For intramolecular inter-
action, close arrangement of two porphyrins is required. One
way to accomplish this is to use metal porphyrins with coordi-
nating groups, such as pyridyl groups.5,6 Introduction of metal
ions into pyridylporphyrins has afforded a variety of self-as-
sembled oligomers, which frequently show intramolecular
interactions as observed by electrochemical and UV–vis spec-
tral measurements. For example, unique slipped-cofacial di-
mers, which are formed by the introduction of ruthenium(II)
ions into 2-pyridylporphyrin, show a remarkable intramolecu-
lar interaction.7 The two central ruthenium ions of the dimers
having pyridine as axial ligands are electrochemically oxidized
at the first process step-by-step (potential split ꢃ300 mV),
giving a stable mixed-valence state that shows a unique cou-
pling phenomenon between ground-state molecular vibrations
and low-energy electronic transition (electron-molecular vibra-
tion coupling).7,8 The other way for effective arrangement
is the use of bridging ligands,9–14 that is, the shish-kebab
approach.13 Linear chain-like porphyrin oligomers thus con-
structed by bridging two metalloporphyrin subunits (FeII, RuII,
and OsII) with aza ligands, such as pz,15 also show distinct
intramolecular redox interactions, that is, large splits of the
redox waves at the metal centers. The extent of the splits fol-
lows the order of Os > Ru > Fe in metals and pz > bpy, ex-
cept dabco systems.14 However, aza ligand-bridged molecular
ruthenium oep–porphyrin dimers having CO as an axial ligand,
which are very similar in structure to the dimer unit constitut-
ing above the chain-like polymers, shows no distinct splits in
the cyclic voltammograms of the first electrochemical oxi-
dation process of the porphyrin ring, that is, two one-electron
transfers proceeded almost simultaneously.16
These results motivated us to investigate in detail the prop-
erties of discrete ruthenium(II) and osmium(II) porphyrin
dimers with pz, bpy, or dabco as a bridging ligand and CO
as an axial ligand illustrated in Fig. 1, focusing especially on
their intramolelular interactions, which can be evaluated by
electrochemical or UV–vis spectral measurements. Effects of
different metal centers, porphyrin rings, and bridging ligands
on the intramolecular interaction are interesting subjects,
because the first oxidations of monomeric ruthenium(II) and
H3C
CO
CO
CH3
CH3
N
N
N
N
M
N
N
M
N
N
N
N
N
N
N
N
H3C
H3C
H3C
BL
CH3
CH3
BL
N
N
M
M
CO
CO
[{M(ttp)(CO)}2(BL)] [{M(oep)(CO)}2(BL)]
M = Ru (II), Os (II)
N
N
N
N
N
BL =
, ,
N
Fig. 1. Carbonyl-coordinated metalloporphyrin dimers.
Published on the web October 12, 2007; doi:10.1246/bcsj.80.1955

1956 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007)
RuII and OsII Porphyrin Dimers
635612–635619. Copies of the data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK; Fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk).
osmium(II) porphyrins with a CO axial ligand occur at the por-
phyrin rings17 and metal centers,18 respectively, and the metal
porphyrin dimers with a dabco bridging ligand show no intra-
molecular redox interactions, as far as we know.
In the present work, a variety of aza ligand-bridged ruthe-
nium(II) and osmium(II) porphyrin dimers with CO as an axial
ligand, [{M(por)(CO)}2(BL)], were prepared, characterized,
and studied with respect to intramolecular interactions by
using electrochemical and UV–vis spectral measurements. The
structures of eight dimers were determined by single-crystal
X-ray crystallography. In the pz and dabco bridging systems,
almost all ruthenium and osmium porphyrin dimers, except
Ru–oep systems, clearly showed electrochemical and UV–vis
spectral intramolecular interactions.
Materials.
Silica gel, alumina (neutral, activity III), and
CH2Cl2 as an eluant were used for column chromatography. The
monomer complexes with ruthenium(II) ion or osmium(II) ion,
that is, [Ru(ttp)(CO)(CH3OH)],22 [Ru(ttp)(CO)(py)],23 [Os(ttp)-
(CO)(py)],24 [Os(ttp)(CO)(mpy)], and [Os(oep)(CO)(py)], were
prepared by reference to the reported methods as the source of
corresponding porphyrin dimers and in order to compare their
properties. The preparation methods for [Os(ttp)(CO)(py)] and
[Os(ttp)(CO)(mpy)] are given as examples.
[OsII(ttp)(CO)(py)].
The complex was prepared from
[Os(ttp)(CO)]. [Os(ttp)(CO)] was prepared from H2(ttp) and Os3-
(CO)12 by using the reported methods (yield: 33%).24 A CH2Cl2
solution (100 mL) containing [Os(ttp)(CO)] (100 mg, 110 mmol)
and pyridine (0.5 mL, 6.2 mmol) was stirred for 1 h at room tem-
perature and evaporated to dryness. The resulting solid was chro-
matographed using silica gel to give a single band. The eluent was
concentrated and the resulting solid was recrystallized from
CH2Cl2–pentane. The crystals obtained were collected by filtra-
tion and dried for 3 h at 80 ꢄC under reduced pressure (yield:
62.5 mg, 57%).
Experimental
Instrumentation. IR spectra (KBr pellet) were measured with
a JASCO FT/IR-660 Plus. UV–vis spectra were recorded on a
Hitachi U-3000 spectrophotometer. 1H NMR spectra were recorded
on a JEOL model JNM-EX270 spectrometer. Mass spectra were
measured with a JEOL JMS-HX110 for FAB-MS and a JEOL
JMS-700TZ for ESI-MS at the Center for Instrumental Analysis
in Hokkaido University. Cyclic voltammograms and differential
pulse voltammograms were recorded with a Hokutodenko model
HZ-3000 voltammetry analyzer at 20 ꢄC with a scan rate of 100
mV sꢅ1 and a BAS model CV-50, respectively. The working
and the counter electrodes were a platinum disk electrode (inside
diameter of 1.6 mm) and a platinum wire, respectively. The same
electrolyte (0.1 M TBA(PF6)) and solvent (CH2Cl2) were used in
order to compare the potentials, unless otherwise specified. The
sample solutions were deoxygenated by a stream of argon. The
reference electrode was Ag/AgCl. The redox potentials obtained
were corrected for a ferrocenium/ferrocene couple (Fcþ/Fc =
0.000 V). The numbers of transferred electrons were determined
by the wave heights of CV and DPV.
Anal. Calcd for C54H41N5OOs: C, 67.13; H, 4.28; N, 7.25%.
Found C, 66.96; H, 4.32; N, 7.36%. 1H NMR (CDCl3, 270 MHz):
ꢃ HCH 2.67 (s, 12H), Hm 7.48 (ddd, 8H), Ho 7.98 (ddd, 8H), H
ꢄ
3
8.50 (s, 8H), Hpy 1.60 (dt, 2H), 5.23 (t, 2H), 6.12 (t, 1H). FAB-
MS: 967 m=z [M]þ.
[OsII(ttp)(CO)(mpy)]. The complex was prepared by the
same method as that for the [Os(ttp)(CO)(py)] (yield: 59%),
except using mpy in place of py.
Anal. Calcd for C55H43N5OOs: C, 67.39; H, 4.42; N, 7.15%.
Found: C, 67.30; H, 4.37; N, 7.33%. 1H NMR (CDCl3, 270 MHz):
ꢃ HCH 2.67 (s, 12H), Hm 7.48 (ddd, 8H), Ho 7.98 (ddd, 8H), H
ꢄ
3
X-ray Crystallography. The single crystals of the present
dimer complexes suitable for X-ray analysis were obtained from
CH2Cl2–pentane or CHCl3–pentane solutions. Structure data were
collected on a Rigaku AFC-8S diffractometer or a Rigaku AFC-
7R diffractometer with a Mercury CCD Area detector using
8.49 (s, 8H), Hmpy 1.22 (s, 3H), 1.46 (dd, 2H), 5.03 (dd, 2H). FAB-
MS: 981 m=z [M]þ.
[{RuII(ttp)(CO)}2(pz)]. The complex was prepared by using
a reported method.25 To the CH2Cl2 (50 mL) solution of [Ru(ttp)-
(CO)(CH3OH)] (41 mg, 49 mmol), pz (1.9 mg, 24 mmol) in a CH2-
Cl2 solution was slowly added. The solution was stirred for 3 h
and evaporated to dryness. The products were isolated by column
chromatography using silica gel. The first band eluted with
CH2Cl2 was concentrated, followed by recrystallization of the
residue from CH2Cl2–pentane and dried in vacuo for 3 h (yield:
21 mg, 50%).
˚
graphite-monochromated Mo Kꢀ radiation (ꢁ ¼ 0:71073 A) at
153 K and processed using the CrystalClear software program.19
Final cell parameters were obtained from a least-square analysis
of reflections with I > 10ꢂðIÞ. The crystal structures were solved
by direct methods and expanded using Fourier and difference
Fourier techniques. All calculations were performed using the
CrystalStructure20 and SHELXL-97 software.21
Anal. Calcd for C102H76N10O2Ru2: C, 73.10; H, 4.57; N,
8.36%. Found: C, 72.70; H, 4.25; N, 8.32%. 1H NMR (CDCl3,
270 MHz): ꢃ Htolyl 2.68 (s, 24H), Hm 7.37 (s, 16H), Ho 7.63 (dd,
For the ttp complexes, non-hydrogen atoms in the complex
molecules were refined anisotropically, and the hydrogen atoms
were fixed at the calculated positions, except those of disordered
bridging ligands. The crystals of the ttp complexes contained
crystal solvents, which were disordered partially and refined with
isotropic displacement parameters. The hydrogen atoms of the
crystal solvents were not included in the calculations.
16H), H 8.32 (s, 16H), Hpz ꢅ0:61 (s, 4H). FAB-MS: 1675 m=z
ꢄ
[M]þ.
[{RuII(ttp)(CO)}2(bpy)]. The dimer was prepared by a meth-
od similar to that of [{RuII(ttp)(CO)}2(pz)] and dried in air (yield:
56%).
Two oep complexes afforded isomorphous crystals. The por-
phyrin ring was disordered around the C4 axis over two positions.
The hydrogen atoms were not included in the calculations of the
oep complexes, because the disorder caused positional overlap
of the hydrogen and carbon atoms.
Anal. Calcd for C108H80N10O2Ru2: C, 74.04; H, 4.60; N,
8.00%. Found: C, 74.07; H, 4.64; N, 8.09%. 1H NMR (CDCl3,
270 MHz): ꢃ Htolyl 2.63 (s, 24H), Hm 7.39 (dd, 16H), Ho 7.81 (dd,
16H), H 8.45 (s, 16H), Hbpy 1.21 (d, 4H), 4.36 (d, 4H).
ꢄ
[{RuII(ttp)(CO)}2(dabco)]. The complex was prepared by a
method similar to that for [{OsII(ttp)(CO)}2(dabco)] (vide infra).
A CH2Cl2 solution of dabco (11 mg, 99 mmol) was added to a
Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre: Deposition numbers CCDC-

C. Bando et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1957
CH2Cl2 (50 mL) solution of [Ru(ttp)(CO)(CH3OH)] (61 mg,
73 mmol). The solution was stirred for 30 min, and the solvent
was evaporated to dryness. The resulting solid was suspended
in methanol. After filtration, the solid was thoroughly washed
with methanol and dried under reduced pressure at 100 ꢄC for
3 h (yield: 42 mg, 67%).
Anal. Calcd for C104H84N10O2Ru2: C, 73.13; H, 4.96; N,
8.20%. Found: C, 72.38; H, 5.05; N, 8.22%. 1H NMR (CDCl3,
270 MHz): ꢃ Htolyl 2.70 (s, 24H), Hm 7.44 (q, 16H), Ho 7.59 (ddd,
Anal. Calcd for C104H84N10O2Os2: C, 66.22; H, 4.49; N,
7.43%. Found: C, 65.77; H, 4.60; N, 7.51%. 1H NMR (CDCl3,
270 MHz): ꢃ HCH 2.70 (s, 24H), Hm 7.44 (dd, 16H), Ho 7.57 (dd,
3
16H), H 8.19 (s, 16H), Hdabco ꢅ5:28 (s, 12H). FAB-MS: 1886.6
ꢄ
m=z [M]þ.
[{OsII(oep)(CO)}2(pz)]. A CH2Cl2 solution of pz (3.1 mg, 39
mmol) was slowly added to a CH2Cl2 solution of [Os(oep)(CO)]
(40 mg, 53 mmol). The solution was stirred for 2 h and column-
chromatographed using silica gel. The first band was collected
and the solvent was evaporated. The residue was crystallized from
CH2Cl2–pentane. The product in the solid state was dried in vacuo
for 3 h at 50 ꢄC under reduced pressure (yield: 30 mg, 72%).
Anal. Calcd for C78H92N10O2Os2: C, 59.22; H, 5.86; N, 8.55%.
Found: C, 58.97; H, 5.99; N, 8.83%. 1H NMR (CDCl3, 270 MHz):
ꢃ Hmeso 9.11 (s, 8H), HCH CH 3.65 (q, 32H), HCH CH 1.63 (t, 48H),
16H), H 8.29 (s, 16H), Hdabco ꢅ5:43 (s, 12H). FAB-MS: 1708.5
ꢄ
m=z [M]þ.
[{RuII(oep)(CO)}2(pz)] and [{RuII(oep)(CO)}2(dabco)].16
These dimers were prepared for a comparison to other dimers
by methods similar to those above for the corresponding ttp com-
plexes and characterized.
2
3
2
3
[{OsII(ttp)(CO)}2(pz)]. To a CH2Cl2 solution of [Os(ttp)(CO)]
(80 mg, 90 mmol), a CH2Cl2 solution of pz (6.0 mg, 75 mmol) was
slowly added. The solution was stirred for 30 min and column-
chromatographed using silica gel. The first band was collected
and the solvent was evaporated. The residue was recrystallized
from CH2Cl2–pentane. The product in the solid state was dried in
vacuo for 3 h at 50 ꢄC under reduced pressure (yield: 53 mg, 63%).
Anal. Calcd for C102H76N10O2Os2: C, 66.07; H, 4.13; N,
7.55%. Found: C, 65.78; H, 4.26; N, 7.88%. 1H NMR (CDCl3,
Hpz ꢅ1:55 (s, 4H). ESI-MS: 1582 m=z (Mþ).
[{OsII(oep)(CO)}2(bpy)]. This complex was prepared by a
method similar to that for [{OsII(oep)(CO)}2(pz)] (yield: 70%).
Anal. Calcd for C84H96N10O2Os2: C, 60.84; H, 5.83; N, 8.45%.
Found: C, 60.84; H, 5.46; N, 8.38%. 1H NMR (CDCl3, 270 MHz):
ꢃ Hmeso 9.40 (s, 8H), Hbpy,NCHCH 3.97 (d, 4H), HCH CH 3.74 (q,
2
3
32H), HCH CH 1.73 (t, 48H), Hbpy,NCHCH 0.35 (d, 4H). ESI-MS:
2
3
1658 m=z [M]þ.
[{OsII(oep)(CO)}2(dabco)]. This complex was prepared by a
method similar to that for [{OsII(ttp)(CO)}2(dabco)] (yield: 34%).
Anal. Calcd for C80H100N10O2Os2: C, 59.53; H, 6.23; N,
8.66%. Found: C, 58.94; H, 6.23; N, 8.66%. 1H NMR (CDCl3,
270 MHz): ꢃ Hmeso 9.08 (s, 8H), HCH CH 3.63 (q, 32H), HCH CH
270 MHz): ꢃ HCH 2.64 (s, 24H), Hm 7.34 (s, 16H), Ho 7.63 (dd,
3
16H), H 8.23 (s, 16H), Hpz ꢅ0:56 (s, 4H). FAB-MS: 1855 m=z
ꢄ
[M]þ.
[{OsII(ttp)(CO)}2(bpy)]. The bpy dimer was prepared by a
similar method to that for the pz dimer. [Os(ttp)(CO)] (40 mg,
45 mmol) was dissolved in CH2Cl2 (60 mL). To the solution, a
CH2Cl2 solution containing bpy (8.7 mg, 56 mmol) was slowly
added. The mixed solution was agitated for 5 h, and the solvent
was evaporated to dryness. The resulting solid was again dis-
solved in a small amount of CH2Cl2 for purification by column
chromatography using silica gel. The first band was collected
and concentrated to give the dimer complex. The complex was
recrystallized from CH2Cl2–pentane and dried in vacuo for 3 h
(yield: 25 mg, 57%).
2
3
2
3
1.55 (t, 48H), Hdabco ꢅ5:28 (s, 12H). ESI-MS: 1614 m=z [M]þ.
Results and Discussion
Structure. The crystal structures of [{M(ttp)(CO)}2(pz)],
[{M(ttp)(CO)}2(bpy)], [{M(ttp)(CO)}2(dabco)], and [{M-
(oep)(CO)}2(pz)] were determined by X-ray structure analysis.
Structures and crystal data of the complexes are shown in
Fig. 2 and Table 1, respectively. The porphyrin rings were
almost planar in the complexes. The deviations of 24 atoms
of each porphyrin ring from their mean planes were less than
Anal. Calcd for C108H80N10O2Os2: C, 67.20; H, 4.18; N,
7.26%. Found: C, 67.29; H, 4.30; N, 7.30%. 1H NMR (CDCl3,
˚
0.23 A. The M–M separations reflect the size of the bridging
ligands. In case of smaller bridging ligands, such as pz and
270 MHz): ꢃ HCH 2.62 (s, 24H), Hm 7.39 (dd, 16H), Ho 7.79 (ddd,
3
˚
dabco, the M–M separations were 7.1–7.3 A, whereas for the
˚
bpy complexes the separations were 11.4–11.5 A. The bridging
16H), H 8.34 (s, 16H), Hbpy 1.21 (d, 4H), 4.43 (d, 4H). FAB-MS:
ꢄ
1930 m=z [M]þ.
[{OsII(ttp)(CO)}2(dabco)].
The preparation of the dabco
bpy adopted a planar structure in [{M(ttp)(CO)}2(bpy)].
The structures of the ttp complexes consisted of a pair of
parallel porphyrin rings with a bridging aza-ligand, except
for [{Ru(ttp)(CO)}2(pz)], in which two porphyrin rings were
tilted from each other by 37ꢄ. Other than this pz complex,
the Ru– and Os–ttp complexes with the same bridging ligands
adopted quite similar structures and had a crystallographical or
complex was initially tried by a method similar to the pz complex.
However, different from the pz system, purification by column
chromatography was unsuccessful, because of strong adsorption
of dabco onto silica gel. Column chromatography gave only a
mixture of the target dimer and the original [Os(ttp)(CO)]. After
many trials of purification, the crude product was purified without
column chromatography. Namely, the mixture obtained by a
method similar to the pz dimer was suspended in methanol, fil-
tered through a fritted filter, and washed thoroughly with methanol
to give directly the dabco dimer (yield: 52 mg, 59%).
The properties of [{OsII(ttp)(CO)}2(dabco)] are a little different
in several points from those of [{OsII(ttp)(CO)}2(pz)] and [{OsII-
(ttp)(CO)}2(bpy)], the behavior on columns, lower solubility in
CH2Cl2, and instability in CHCl3. A CHCl3 solution of the dabco
dimer gave unknown precipitates, when it was left to stand for one
day. Extra addition of CHCl3 to the solution causes no dissolution
of the precipitates. However, the CH2Cl2 solution of the dabco
complex gave no such precipitation in a few days.
substantial mirror plane horizontal to the OC–M M–CO axis.
Namely, the two ttp rings in each complex adopted an eclipsed
ꢆꢆꢆ
form along the OC–M M–CO axis to bring the tolyl groups in
ꢆꢆꢆ
the pz- and dabco-bridged complexes close together. Although
the close contact of tolyl ligands is unfavorable due to steric
hindrance, the mutual arrangement between the bridging
ligands and the porphyrin rings resulted in the eclipsed form.
The closest H H distances26 between the neighboring tolyl
ꢆꢆꢆ
˚
groups of upper and lower porphyrins were 3.01 and 2.70 A
in the pz and dabco complexes, respectively, which are still
slightly larger than twice of the van der Waals radius of H

1958 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007)
RuII and OsII Porphyrin Dimers
the tight packing in the crystal lattice (Fig. S1). The sticking
tolyl groups support the molecular arrangements by touching
ones of the neighboring molecules. The eclipsed arrangement
of porphyrins in the crystals should result from these weak
steric interactions.
( a )
( b )
As an exceptional case, [{Ru(ttp)(CO)}2(pz)] had a highly
distorted structure. The dihedral angles between the porphyrin
rings and the pz deviated from ideal 90ꢄ by 15.9(2) and
19.8(2)ꢄ, whereas the deviation of = N(por)–M–N(pz) from
À
ideal 90ꢄ was only 0.1–7.5ꢄ. The larger deviation of the di-
hedral angles between the pz and the porphyrin rings than
( c )
( d )
= N(por)–M–N(pz) shows that the pz plane tilted to the M–N
bond to cause the distorted structure of [{Ru(ttp)(CO)}2(pz)].
À
Although the bridging pz ligand can rotate around the M M
ꢆꢆꢆ
axis even in this distorted form, the pz was not disordered in
the structure. Like a cover board for the open space formed
between the two porphyrin subunits, the plane of pz faced
toward the inside of the wedge-shape structure as shown in
Fig. 2b. Rotation of the bridging pz ligand around the M M
ꢆꢆꢆ
( e )
( f )
axis from the observed position brings two of the four hydro-
gen atoms of pz close to the porphyrin rings, leading to desta-
bilization of the Ru–N(pz) bonds. In the crystal lattice, these
distorted molecules were arranged so that pinched and open
sides alternated in order to minimize the steric repulsion
between the molecules. The weak interactions between the
porphyrin rings and the bridging ligand and among the neigh-
boring molecules in the crystal lattice resulted in the regular
molecular structures of the five ttp complexes or the distorted
structure of [{Ru(ttp)(CO)}2(pz)].
The pz-bridged oep complexes [{M(oep)(CO)}2(pz)] af-
forded isomorphous crystals with an I4=mmm space group.
The complexes occupy the 4=mmm position with the OC–
( g )
( h )
M M–CO axis on the 4-fold axis. The porphyrin rings were
ꢆꢆꢆ
disordered over two positions around the 4-fold axis with
20.5(2) and 20.5(1)ꢄ rotation for Os and Ru complexes, respec-
tively. As shown by the local 4=mmm symmetry, [{M(oep)-
(CO)}2(pz)] had a pair of parallel porphyrin rings as observed
for the ttp complexes. The eight ethyl groups on an oep ring
were all folded to the inner part of the molecule to make
a ‘‘capsule’’ with two CO ligands sticking out as shown in
Fig. 3. These capsules were piled up creating a body-centered
lattice. Because of the disorder, there were two possible ar-
rangements of the upper and the lower porphyrin rings, name-
ly, eclipsed and twisted ones. However, the eclipsed form
should be favorable as in the case of the ttp complexes, be-
cause the ring arrangements are determined by the steric repul-
sion between bridging ligands and porphyrins. In the eclipsed
form, the closest distance between C atoms in neighboring
Fig. 2. ORTEP drawings of [{M(por)(CO)}2(BL)] with
50% thermal ellipsoid. Hydrogen atoms are omitted for
clarity. (a) [{Os(ttp)(CO)}2(pz)], (b) [{Ru(ttp)(CO)}2-
(pz)], (c) [{Os(ttp)(CO)}2(dabco)], (d) [{Ru(ttp)(CO)}2-
(dabco)], (e) [{Os(ttp)(CO)}2(bpy)], (f) [{Ru(ttp)(CO)}2-
(bpy)], (g) [{Os(oep)(CO)}2(pz)], (h) [{Ru(oep)(CO)}2-
(pz)]. In the oep complexes, one set of oep pairs is depict-
ed (see text).
atom, and the overall structures appear to be determined by the
interaction between the porphyrin rings and the bridging
ligands. The pz and bpy planes bisected the N–M–N angle
in the porphyrin rings to avoid the steric repulsion between
porphyrin rings and hydrogen atoms of the bridging ligands.
In case of the dabco-bridged Os complex, dabco was disor-
dered. However, in the Ru complex, dabco was fixed in a po-
sition where less steric repulsion between the porphyrin rings
and the bridging ligand is achieved. To avoid the steric repul-
sion with the bridging dabco ligand, both the upper and lower
porphyrin rings adopted an eclipsed form with mirror symme-
try. The regular structures of each molecule also bring about
˚
methyl group was 3.35(1) and 3.381(9) A for Os and Ru com-
plexes,27 respectively, which again is very close but not too
close to cause the strong repulsion.28 The molecular structures
of [{M(oep)(CO)}2(pz)] in the crystals are the results of the
weak interactions as discussed for the ttp complexes.
UV–Vis Spectra and CO Stretches. UV–vis spectra of
the porphyrin dimers were similar to those of the correspond-
ing monomers. However, the Soret bands were shifted to
wavelengths shorter than those of [Os(ttp)(CO)(py)], [Os(oep)-
(CO)(py)], or [Ru(ttp)(CO)(py)] by several nanometers, ac-
companied by a decrease in molar extinction coefficients per

Table 1. Crystal Data and Metal–Metal Distancesa)
[{Os(ttp)(CO)}2(pz)] [{Os(ttp)(CO)}2- [{Os(ttp)(CO)}2(dabco)]
[{Os(oep)-
(CO)}2(pz)]
[{Ru(ttp)(CO)}2- [{Ru(ttp)(CO)}2- [{Ru(ttp)(CO)}2(dabco)]
(pz)] 1.5C5H12
[{Ru(oep)-
(CO)}2(pz)]
5.9CH2Cl2
(bpy)] 3CH2Cl2
ꢆ
0.4CH2Cl2 1.2C5H12
(bpy)] 6CHCl3
4.6CH2Cl2 1.3C5H12
ꢆ
ꢆ
ꢆ
ꢆ
10O2Ru2
ꢆ
ꢆ
ꢆ
C
105:9H87:8N10
-
C111H86N10O2-
Os2Cl6
2185.1
C110:4H99:2N10
O3Os2Cl0:8
2006.8
tetragonal
I4=m
-
C78H92N10
O2Os2
1582.1
-
C109:5H94
N
1784.2
triclinic
-
C114H86N10
O2Ru2Cl18
1911.2
triclinic
ꢀ
P1
-
C115:1H108:8N10
O2Ru2Cl9:2
2192.5
monoclinic
P21=m
-
Formula
C78H92N10O2Ru2
O2Os2Cl11:8
2331.3
monoclinic
I2=m
Mw
Crystal syst
Space group
1403.8
tetragonal
I4=mmm
13.3347(8)
13.3347(8)
19.965(1)
90
90
90
3550.1(4)
2
triclinic
ꢀ
P1
tetragonal
I4=mmm
13.3293(5)
13.3293(5)
19.9145(11)
90
90
90
3538.2(3)
2
ꢀ
P1
˚
a/A
14.200(6)
23.701(4)
15.659(4)
90
91.220(5)
90
10.29(2)
13.38(5)
19.12(4)
100.03(6)
95.56(6)
95.52(6)
2536(1)
1
14.6695(5)
14.6695(5)
23.456(2)
90
90
90
5047.5(5)
2
16.638(6)
16.995(6)
18.502(5)
68.312
70.79(1)
82.75(1)
4590(2)
2
16.74(2)
19.57(3)
10.76(1)
110.30(2)
94.914(4)
112.53(1)
2955(6)
1
14.165(1)
23.936(2)
15.648(1)
90
91.120(2)
90
˚
b/A
˚
c/A
ꢀ/deg
ꢄ/deg
ꢅ/deg
˚
V/A
3
5269(3)
2
5304.5(8)
2
Z
Crystal dimensions
/mm3
0:25 ꢇ 0:5 ꢇ 0:5 0:1 ꢇ 0:175 ꢇ 0:875 0:175 ꢇ 0:25 ꢇ 0:25 0:16 ꢇ 0:15 ꢇ 0:21 0:13 ꢇ 0:08 ꢇ 0:18 0:05 ꢇ 0:08 ꢇ 0:58
0:4 ꢇ 0:55 ꢇ 0:63
0:61 ꢇ 0:32 ꢇ 0:30
˚
ꢁ (Mo Kꢀ)/A
T/K
0.7107
153
0.7107
153
0.7107
153
0.7107
153
0.7107
153
0.7107
153
0.7107
153
0.7107
153
No. of total data
collected
No. of independent
rfln (F2 > 2ꢂðF2))
R1 (F2 > 2ꢂðF2))
wR2 (all)
9109
3931
12074
8611
17101
2780
9795
1170
19790
10221
10052
4891
24341
10402
10038
1197
0.065
0.192
7.2626(7)
0.050
0.1440
11.4791(3)
0.037
0.107
7.3444(3)
0.025
0.062
7.1676(3)
0.086
0.217
7.1387(9)
0.099
0.288
11.448(1)
0.0940
0.2660
7.3339(7)
0.038
0.100
7.1719(6)
˚
Metal–metal/A
a) CCDC No.: CCDC 635612–635619.

1960 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007)
RuII and OsII Porphyrin Dimers
c
b
a
Fig. 3. The crystal packing of [{Os(oep)(CO)}2(pz)] molecules. The other set of disordered oep is omitted for clarity.
Table 2. UV–Vis and IR Data of Osmium and Ruthenium Porphyrins
Complex
ꢁ
max/nm ("/104 Mꢅ1 cmꢅ1/" per subunit/104 Mꢅ1 cmꢅ1) in CH2Cl2
ꢆCO/cmꢅ1
[{Os(ttp)(CO)}2(pz)]
[{Os(ttp)(CO)}2(bpy)]
[{Os(ttp)(CO)}2(dabco)]
[Os(ttp)(CO)(py)]
404 (52.7/26.4), 520 (3.2/1.6)
408 (53.1/26.5), 520 (3.4/1.7)
405 (57.8/28.9), 517 (3.1/1.5)
410 (30.1), 521 (1.8)
1932
1932
1923
1920
1917
[Os(ttp)(CO)(mpy)]
410, 520
[{Os(oep)(CO)}2(pz)]
[{Os(oep)(CO)}2(bpy)]
[{Os(oep)(CO)}2(dabco)]
[Os(oep)(CO)(py)]
388 (40.3/20.2), 508 (2.32/1.16), 537 (3.28/1.64)
391 (55.4/27.7), 508 (2.67/1.34), 538 (3.94/1.97)
389 (49.7/24.9), 507 (2.14/1.07), 538 (3.45/1.73)
394 (32.4), 510 (1.29), 541 (2.23)a)
1915
1914
1905
1902b)
[{Ru(ttp)(CO)}2(pz)]
[{Ru(ttp)(CO)}2(bpy)]
[{Ru(ttp)(CO)}2(dabco)]
[Ru(ttp)(CO)(py)]
408, 531, 566
410, 532, 568
408, 530, 564
413, 533, 566
1959
1960
1952
1950
a) Ref. 29. b) Ref. 30, Nujol mull.
each constituent porphyrin subunit with considerable broaden-
ing, as listed in Table 2, which reflects the presence of intra-
molecular interactions. The blue shifts are due to the excitonic
interaction between two porphyrin rings facing each other, as
explained by the Kasha model.31 In every series of [{Os(ttp)-
(CO)}2(BL)], [{Os(oep)(CO)}2(BL)], and [{Ru(ttp)(CO)}2-
(BL)], the smallest blue shifts were observed in the bpy com-
1H NMR profiles between the ruthenium porphyrin dimers and
the corresponding osmium porphyrin dimers. The 1H NMR
signals of the bridging pz in [{M(por)(CO)}2(pz)] were ob-
served at around ꢅ0:6 and around ꢅ1:5 ppm as a single peak,
respectively, which were significantly shifted upfield com-
pared to the corresponding resonance shifts of non-coordinat-
ing pz observed at 8.6 ppm. The dabco-bridging ligands of
[{M(por)(CO)}2(dabco)] also showed a single peak at around
ꢅ5:3 and ꢅ5:3 (Os complex)– ꢅ6:3 (Ru-complex) ppm, re-
spectively, and a peak for free base of dabco was observed
at 2.8 ppm. On the other hand, [{M(ttp)(CO)}2(bpy)] gave two
signals, e.g., the [{Os(ttp)(CO)}2(bpy)] complex had signals at
1.21 and 4.43 ppm ascribed to ꢀ and ꢄ protons of the bpy
ligand. The upfield shifts were about 6.3 ppm from those of
˚
plexes with the largest metal–metal distance (ca. 11.5 A) sug-
gesting very weak interactions. This is consistent with Ru–
octaphenylporphyrazine–bpy dimers which show no interac-
tions.32 The CO stretches of all the complexes were observed
at wave numbers a little larger than the corresponding pyridine
monomer complexes.
1H NMR Spectra. There were no essential differences in

C. Bando et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1961
Table 3. Redox Potentials (E/mV) and Potential Differences (ꢁE)a)
II,II
Complex
Os2III,III/Os2
ꢁE
por2(+,+)/por2(0,0)f)
[{Os(oep)(CO)}2(pz)]
[{Os(oep)(CO)}2(bpy)]
[{Os(oep)(CO)}2(dabco)]
[{Os(ttp)(CO)}2(pz)]
[{Os(ttp)(CO)}2(bpy)]
[{Os(ttp)(CO)}2(dabco)]
179 [1], 259 [1]
83 [2]
148 [2] (broad)
364 [1], 438 [1]
249 [2]
80
ꢃ0
830 [2]
827 [2]
831 [2]
917 [2]
897 [2]
927 [2]
ꢃ50e)
74
ꢃ0
280 [1], 387 [1]
107
II,II
por2(+,+)/por2(0,0)f)
ꢁE
Ru2III,III/Ru2
[{Ru(oep)(CO)}2(pz)]b)
[{Ru(oep)(CO)}2(pz)]c)
[{Ru(oep)(CO)}2(pz)]d)
[{Ru(oep)(CO)}2(bpy)]b)
[{Ru(oep)(CO)}2(dabco)]b)
[{Ru(oep)(CO)}2(dabco)]c)
[{Ru(oep)(CO)}2(dabco)]d)
[{Ru(ttp)(CO)}2(pz)]
240 [2]
265 [2]
275 [2]
170 [2]
210 [2]
ꢃ0
ꢃ0
ꢃ0
ꢃ0
ꢃ0
ꢃ0
ꢃ0
60
690 [2]
699 [2]
746 [2]
690 [2]
750 [2]
660 [2]
806 [2]
830 [2]
800 [2]
840 [2]
205 [2]
265 [2]
390 [1], 450 [1]
300 [2]
350 [1], 420 [1]
[{Ru(ttp)(CO)}2(bpy)]
[{Ru(ttp)(CO)}2(dabco)]
ꢃ0
70
a) Potentials were obtained by DPV for the CH2Cl2 solutions containing 0.1 M
TBA(PF6) as an electrolyte and corrected for Fcþ/Fc (0.000 V) at 20 ꢄC, unless other-
wise specified. The numbers in brackets are the numbers of transferred electron.
b) Ref. 16. The reported values are the half-wave potentials (E1=2 ¼ ðEpa ꢅ EpcÞ=2)
obtained by CV for the CH2Cl2 solutions with 0.1 M TBAP at 25 ꢄC and corrected
for Fcþ/Fc (0.000 V). c) This work. The values are the half-wave potentials (E1=2) ob-
tained by CV measurements using 0.1 M TBAP. d) This work. The values are the half-
wave potentials (E1=2) obtained by CV measurements using 0.1 M TBA(PF6). e) This
value was estimated from almost a linear relationship between the ꢁE values and
the FWHM (full width at half maximum from the top in mV) values obtained for
the dimer complexes which gave separated peaks at the first oxidation processes of
DPV measurements (Fig. S2). f) The plus and zero charges indicate the site of oxida-
tion, not the formal valence.
a free-base of the bpy ligand, indicating smaller shielding ef-
fects due to elongation of the distance between two porphyrins
compared to the pz and dabco systems. These signal patterns
demonstrate that all of the porphyrin dimer structures with
two facing porphyrins are maintained in solution, though from
X-ray crystallography, in the structure of [{Ru(ttp)(CO)}2-
(pz)], the two porphyrin subunits were not parallel.
to be 390 and 450 mV as listed in Table 3. The difference
(ca. 60 mV) corresponds to the comproportionation constant
(Kc) of ca. 11, indicating the presence of a weak intramolecu-
lar redox interaction. CV and DPV of the osmium porphyrin
dimers of [{Os(por)(CO)}2(pz)] more clearly showed the
stepwise two-redox waves at their first oxidation processes
of the metal centers. On the other hand, the oxidation waves
for [{Os(ttp)(CO)}2(pz)] observed at around 400 and 900 mV
were ascribed to the oxidations of osmium ion and porphyrin
rings respectively.18,29 The former broad oxidation wave at
around 400 mV corresponds two reversible one-electron oxida-
tions, whereas the second oxidation of the porphyrin rings in-
volves one-step two-electron transfers. The potential differ-
ence of the two stepwise oxidations at the first oxidation pro-
cess was determined to be 74 mV (Kc ¼ 19). An unexpected
result was obtained in both of the ruthenium and osmium
dabco systems. Although intramolecular redox interaction
was expected to be too weak to be detected in the dabco sys-
tems, because the bridging ligand does not resonate and the
distance between two osmium ions is larger than those of the
pz systems, the dabco systems showed a split in the first pro-
cesses. For example, from the CV and DPV data of [{Os(ttp)-
(CO)}2(dabco)], the osmium ions were oxidized at 280 and
387 mV, and the porphyrin rings were oxidized at 927 mV at
the second process. The split in the one-electron stepwise ox-
Electrochemistry. As described above, in carbonyl-coordi-
nated osmium porphyrin complexes, the first oxidation occurs
at the metal centers,18 whereas in carbonyl ruthenium por-
phyrin complexes, the first oxidation proceeds at the porphyrin
rings.17 Interplanar distances longer than 7 A exclude any
˚
direct porphyrin ring–porphyrin ring interaction, because
through-space interactions are negligible for interorbital sepa-
rations greater than 3 A.33a,34 First, the reported ruthenium por-
˚
phyrin systems of [{Ru(oep)(CO)}2(BL)] were reinvestigated
by CV and DPV under the same experimental conditions as
those using TBAP as an electrolyte.16 The results were essen-
tially the same with the reported data. Namely, no clear splits
were observed in the first oxidation process as shown in
Table 3. The use of TBA(PF6) as an electrolyte gave the same
result. However, the DPV of [{Ru(ttp)(CO)}2(pz)] showed a
broad wave at around 400 mV as shown in Fig. 4, suggesting
the Ru complex is oxidized stepwise during the first process.
Each of two waves composing the broad wave was estimated

1962 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007)
RuII and OsII Porphyrin Dimers
( a )
( b )
II,II
Os2II,III/Os2
por. ring
II,II
Os2II,III/Os2
por. ring
Os2III,III/Os2
II,III
15
10
5
Os2III,III/Os2
II,III
4
2
0
0
-5
-2
0.4
0.8
E / V
1.2
0.4
0.8
E / V
1.2
1.2
1.2
( c )
( d )
4
3
2
1
0
10
5
0
0.4
0.8
E / V
1.2
0.4
0.8
E / V
( e )
( f )
por. ring
10
8
por. ring
3
2
1
0
por. ring
por. ring
6
4
2
0
0.4
0.8
E / V
1.2
0.4
0.8
E / V
Fig. 4. Voltammograms of selected metalloporphyrin dimers by CV and DPV. Potentials were corrected for a ferrocenium/ferro-
cene couple (Fcþ/Fc = 0.000 V). (a) [{Os(ttp)(CO)}2(pz)] (CV), (b) [{Os(ttp)(CO)}2(dabco)] (CV), (c) [{Os(ttp)(CO)}2(pz)]
(DPV), (d) [{Os(ttp)(CO)}2(dabco)] (DPV), (e) [{Ru(ttp)(CO)}2(pz)] (DPV), (f) [{Ru(ttp)(CO)}2(dabco)] (DPV).
idation at the first process was 107 mV. This value (107 mV)
corresponds to 69 of Kc and is a little larger than those of
the [{Os(ttp)(CO)}2(pz)] (Kc ¼ 19) and [{Os(oep)(CO)}2(pz)]
(Kc ¼ 24) systems. In all of the [{Os(por)(CO)}2(bpy)] sys-
tems as well as the [{Ru(por)(CO)}2(bpy)] systems, there were
no splits in the first oxidation process of the osmium ions
as suggested by the large distance between two osmium ions
determined by X-ray crystallography.
tially show intramolecular interactions, but the dabco bridging
complex without a ꢇ-conjugated system shows only weak in-
tramolecular redox interaction through bonds or no interaction.
In practice, compared to the dimers of triruthenium complexes
bridged by pz (split ꢃ400 mV), the complexes bridged by
dabco show very weak splits of 0–60 mV on the reduction
waves obtained by CV.36 In the porphyrin polymers aligned
linearly, the Ru–oep–dabco complexes at carbon cloth elec-
trodes showed no clear intramolecular redox interactions,
and the potential split of the pz-bridged polymers were larger
than in the bpy-bridged polymers,14 which should result from
the difference in distance between two metal centers in each
dimer. These results are consistent with the concept that con-
duction in the partially oxidized ruthenium-complex polymers
occurs at metal center and the intramolecular redox interaction
mainly reflects the extension of ꢇ-conjugated bridging ligand
systems.14,37
Effects of Porphyrin Rings and Bridging Ligands. In the
series of porphyrin dimers having the same metal ions and por-
phyrin rings, the oxidation potentials increased in the order of
pz > dabco > bpy as shown in Table 3. The Creutz–Taube
ion, in which pz bridges two ruthenium units, shows a strong
intramolecular redox interaction through bonds.35 This strong
interaction results from the intramolecular interaction between
ꢀ
ꢇd orbitals of ruthenium ion and ꢇ orbitals of pz. This theory
suggests that both the pz and bpy bridging complexes poten-

C. Bando et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1963
In the present carbonyl-coordinated porphyrin dimers, in the
CV of the pz-bridged complexes of Os–ttp systems, there was
a split in the first oxidation process and the bpy bridged com-
plex exhibited no splits. The latter result is understandable due
to the above reasons, that is, the intramolecular redox interac-
tion of the bpy complex should be too small to observe a split
in the potential. On the other hand, the results of the dabco sys-
tem were surprising. Although the dabco complexes essential-
ly have no ꢇ-conjugated system in the molecules and the dis-
tances between the two metal ions are a little larger than those
of the pz complexes, the [{M(ttp)(CO)}2(dabco)] complexes
exhibited distinct intramolecular redox interactions with al-
most the same magnitude as that of the [{M(ttp)(CO)}2(pz)]
complexes. It has been reported that there are interactions
between the two nitrogen atoms of a dabco molecule through
the ꢂ bond of the C–C linkage and the lone pair of the nitrogen
atoms.33 However, this concept does not explain the split
as large as the pz porphyrin dimers at the first oxidation pro-
cesses. A great many dabco systems have to be studied in order
to make a definite conclusion.
Another striking result from the electrochemical studies is
that the interaction intensities for ruthenium systems are com-
parable to the corresponding osmium systems, although these
carbonyl-coordinated ruthenium and osmium complexes are
redox active at the porphyrin rings and metal centers, respec-
tively, in the first electrochemical oxidation process. This re-
sult suggests that the porphyrin ring-centered oxidation state
of the ruthenium complexes can be distinguished from the
metal-centered oxidation state, when electrons transfer to an-
other site of a ruthenium porphyrin subunit through the bridg-
ing ligands. The effects of the porphyrin rings, the central
metal ions, and the bridging ligands on the redox interactions
go in the orders of ttp > oep and Os (metal oxidation) > Ru
(ring oxidation), and dabco ꢁ pz ꢂ bpy, respectively, though
the oxidizing moieties in the first processes are different in the
carbonyl-coordinated ruthenium and osmium porphyrin com-
plexes. The order of ttp > oep seems to reflect the difference
in their redox potentials, that is, oep ring is oxidized more
easily than ttp systems. These orders rationalize the result that
the reported [{Ru(oep)(CO)}2(BL)] systems exhibit no appa-
rent splits.16 The separations must be <40 mV at the first oxi-
dation processes. All of the dimer complexes in the present
systems gave no corresponding pure mixed-valence com-
plexes, because of the relative small potential splits. This made
it impossible to study electron-molecular vibration coupling as
observed in the 2-pyridylporphyrin dimer complexes.8 Since
the axial CO ligand was thought to have large effects on the
interaction of the present systems, we tried to prepare and iso-
late the dimer complexes with axial ligands, such as pyridine
and 4-dimethylaminopyridine, instead of CO axial ligands,
but we were unsuccessful in getting pure samples, though
physicochemical measurements revealed the presence of the
target complexes in the solutions. Instead, anthracene-bridged
ruthenium porphyrin dimers with aza ligands at the axial
positions are now being prepared.
were prepared and characterized by using physicochemical
measurements and X-ray crystallography. X-ray crystallogra-
phy revealed that the central metal ions in the porphyrin sub-
units were located in each porphyrin plane and the distances
between two metal ions were in the order of bpy ꢂ dabco ꢁ
pz. All these complexes exhibited blue-shifted Soret bands
compared to the corresponding monomers, which indicates
the presence of intramolecular interactions in the cofacial
porphyrin dimers. Electrochemical measurements also demon-
strated that, in both of the ruthenium and osmium porphyrin
dimers, the pz and dabco complexes exhibited intramolecular
redox interactions, as observed by the split in each of the
waves for the first oxidation processes. The bpy complex
had no splits as was expected from the distance between two
metal ions. The interaction of the dabco complexes, which
have no ꢇ-conjugated system or have only a small amount
of conjugation between two nitrogen atoms through C–C
bonds in dabco, was not so different from that of the pz com-
plex, which has a ꢇ conjugation system in the molecule. In
addition, no essential difference in the magnitude of the intra-
molecular redox interactions was observed between ruthenium
and osmium complex systems, though in the former, the first
oxidation occurred at the porphyrin rings, and in the latter,
the oxidation occurred at the metal centers.
Supporting Information
The arrangement of [{Os(ttp)(CO)}2(pz)] molecules in the a–c
plane (Fig. S1) and plots of difference between two peaks (mV)
obtained by DPV vs. HWHM (full-width at the half-maximum
from the top) at the first oxidation processes (Fig. S2). Theses ma-
terial are available free of charge on the web at http://www.csj.jp/
journals/bcsj/.
References
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M. R. Wasielewski, X. Chen, J. Porphyrins Phthalocyanines
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M. L. Merlau, M. del P. Mejia, S.-B. Nguyen, J. T. Hupp,
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4
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Conclusion
Carbonyl-coordinated ruthenium(II) and osmium(II) por-
phyrin dimers bridged with aza-ligands of pz, bpy, and dabco

1964 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007)
RuII and OsII Porphyrin Dimers
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ꢆꢆꢆ
27 Because ethyl groups showed disorder and because the ter-
minal methyl groups can rotate around the C–C bonds, not the
H H distance but the C C distance was used for discussion of
ꢆꢆꢆ
ꢆꢆꢆ
13 J. P. Collman, J. T. McDevitt, G. T. Yee, C. R. Leidner,
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the oep complexes.
28 In this setting, the minimum H H separation becomes
ꢆꢆꢆ
˚
2.20 A if mirror symmetry is supposed. However, the ethyl group
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ion; py = pyridine; mpy = 4-methylpyridine; pz = pyrazine;
bpy = 4,40-bipyridine; dabco = 1,4-diazabicyclo[2,2,2]octane;
TBAP = tetrabutylammonium perchlorate; TBA(PF6) = tetra-
butylammonium hexafluorophosphate; DDQ = 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone; CV = Cyclic Voltammetry; DPV =
Differential Pulse Voltammetry.
is flexible and the small rotation of terminal methyl group can
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