Synthesis and properties of 5-(3-pyridyl)porphyrinatoruthenium(II) tetramers

Article abstract of DOI:10.1246/bcsj.80.1556

5-(3-Pyridyl)porphyrinatoruthenium(II) tetramers, [{Ru(3-PyT ₃porph)(CO)}₄] (1), [{Ru(3-PytB₃porph)(CO)} ₄] (2), [{Ru(3-PyHex₃porph)(CO)}₄] (3), and [{Ru(3-PytB₃porph)(py)}₄] (4) were prepared. The structures of the isolated tetramers were determined to be rhombic shaped with two chemically nonequivalent porphyrinatoruthenium(II) subunits by ¹HNMR, IR, and ESI-MS measurements. The tetramers were stable in benzene at 70 °C. However, the tetramers reacted with a large excess of pyridine to give two geometrical isomers of porphyrinatoruthenium(II) in dichloromethane at room temperature as observed by ¹H NMR spectrometry. U V-vis spectra of the tetramers showed splitting or broadening of the Soret band due to excitonic interactions. Stepwise oxidations of the porphyrin rings or the ruthenium ions in the cyclic tetramer skeleton were observed in cyclic voltammograms.

Full text of DOI:10.1246/bcsj.80.1556

1556 Bull. Chem. Soc. Jpn. Vol. 80, No. 8, 1556–1562 (2007)
ꢀ 2007 The Chemical Society of Japan
Synthesis and Properties of
5-(3-Pyridyl)porphyrinatoruthenium(II) Tetramers
Kenji Funatsu,1 Naomi Yasuda,1 Akio Ichimura,2 Ryoko Santo,2
ꢀ1
Yoichi Sasaki,1 and Taira Imamura
1Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810
2Department of Chemistry, Faculty of Science, Osaka City University, Osaka 558-0022
Received December 27, 2006; E-mail: timamura@sci.hokudai.ac.jp
5-(3-Pyridyl)porphyrinatoruthenium(II) tetramers, [{Ru(3-PyT3porph)(CO)}4] (1), [{Ru(3-PytB3porph)(CO)}4]
(2), [{Ru(3-PyHex3porph)(CO)}4] (3), and [{Ru(3-PytB3porph)(py)}4] (4) were prepared. The structures of the isolated
tetramers were determined to be rhombic shaped with two chemically nonequivalent porphyrinatoruthenium(II) subunits
by 1H NMR, IR, and ESI-MS measurements. The tetramers were stable in benzene at 70 ꢁC. However, the tetramers re-
acted with a large excess of pyridine to give two geometrical isomers of porphyrinatoruthenium(II) in dichloromethane
at room temperature as observed by 1H NMR spectrometry. UV–vis spectra of the tetramers showed splitting or broaden-
ing of the Soret band due to excitonic interactions. Stepwise oxidations of the porphyrin rings or the ruthenium ions in
the cyclic tetramer skeleton were observed in cyclic voltammograms.
oblique transition dipole geometry
Studies of metalloporphyrin oligomers have been used to
gain useful information on various systems. For example, they
have been used as model systems for photo-induced electron
transfer in photosynthetic reaction centers,1 as enzymatic cata-
lysts,2,3 and as models for the intramolecular interactions in
the metalloporphyrin subunits.3–7 In order to gain even more
information, new metalloporphyrin oligomers having unique
structures and characters must be prepared. The approaches
to construct those oligomers include non-covalent ligation and
self-assembly of metallo- or free-base-porphyrins with oxo-,
pyridyl-, or imidazolyl-substituents.4–13
inclined coplanar
transition dipole
geometly
L
N
N Ru N
N
4'
L
5'
N 6'
N
N
N
N
N
Ru
N
N
Ru
N N
Above all, arylporphyrins with pyridyl groups are very use-
ful for coordinative substituent-directed assembly of multipor-
phyrins by varying the pyridyl substituents from 2-pyridyl
groups to 4-pyridyl groups, because of the relative linear direc-
tion of metal–pyridyl bonds. Indeed, metal (Zn,13 Mg,14
Ru,15,16 and Rh17) 2-pyridylporphyrins as well as imidazole-
tethered porphyrinatozincs5 have been assembled to give
unique slipped-cofacial porphyrin dimers, which have strong
intramolecular interactions. On the other hand, in 5-(4-pyri-
dyl)porphyrins, square tetramers for Zn,18 Ru,19 and Rh17 have
been prepared. For a 5-(3-pyridyl)porphyrinatozinc with hy-
droxyphenyl groups20 and 5-(3-pyridyl)porphyrinatozincs,21
tetrameric structures with a rhombic shape have been reported.
A porphyrinatozinc with a 2-aminopyrimidine moiety, which is
similar to the 3-pyridyl group in the position of N-atoms, also
forms a tetramer complex.22 The latter two complexes show a
large change in UV–vis spectra at variable temperatures due to
dissociation/association equilibria. This behavior results from
the breakage of the coordination bonds between zinc ions and
nitrogen atoms of pyridyl21 or aminopyrimidine groups,22 as
generally observed by UV–vis absorption dilution studies on
pyridylporphyrinatozinc oligomers.23 These results motivated
us to study metal 3-pyridylporphyrins with robust metal–pyri-
N
N
N
L
N Ru N
N
L
parallel transition
dipole geometry
: transition dipole moment
Fig. 1. Proposed structure and excitonic interactions in
cyclic tetramers with a rhombic shape. L denotes axial
ligands such as CO and pyridine.
dyl bonds without dissociation/association equilibria.
In the present work, new 5-(3-pyridyl)porphyrinatoruthe-
nium(II) tetramers were prepared and characterized. H NMR
measurements proved that these tetramers had a rhombic struc-
ture as shown in Fig. 1. UV–vis and electrochemical data
showed that there were strong intramolecular interactions be-
tween the constituent porphyrin subunits.
1
Experimental
Instrumentation. UV–vis spectra were recorded on a Hitachi
Published on the web August 10, 2007; doi:10.1246/bcsj.80.1556

K. Funatsu et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007) 1557
U-3000 spectrophotometer. 1H NMR spectra were recorded on
a JEOL-EX270 spectrometer. ESI-MS spectral measurements
were carried out at Center for Instrumental Analysis, Hokkaido
University and GC-MS and NMR Laboratory, Faculty of
Agriculture, Hokkaido University using a JEOL JMS-700TZ and a
JEOL JMS-SX102 combined with a JEOL MS-ESI 10L2, respec-
tively. Cyclic voltammograms (CVs) were recorded with a BAS
model CV-50W voltammetry analyzer with a scan rate of 100
mV sꢂ1 at 20 ꢁC. The reference electrodes were an aqueous Ag/
AgCl or an Ag/Agþ (CH3CN). The working and the counter elec-
trodes for the CV measurements were a platinum disk (i.d. = 1.6
mm) and a platinum wire, respectively. The sample solutions in
dichloromethane containing 0.1 M Bu4N(PF6) were deoxygenated
by a stream of argon. Redox potentials obtained were referenced
due was filtered off, and the filtrate was chromatographed on a
silica-gel column using dichloromethane as an eluent. The first
band was collected and evaporated to dryness. The product was
dried at 80 ꢁC in vacuo for 1 h (yield: 12 mg, 19%).
Anal. Calcd for C188H132N20O4Ru4: C, 71.92; H, 4.24; N,
8.92%. Found: C, 72.22; H, 4.59; N, 8.69%. UV–vis ꢀmax ("
104 Mꢂ1 cmꢂ1/" per subunit in CH2Cl2): 404 (59.2/14.8), 418
(sh. 51.8/13.0), 535 (7.26/1.82), 570 (2.30/0.58).
[{Ru(3-PytB3porph)(CO)}4] (2). Complex 2 was synthesized
by a method similar to that of 1 using H2(3-PytB3porph) in place
of H2(3-PyT3porph). Ru3(CO)12 (150 mg, 235 mmol) and H2(3-
PytB3porph) (100 mg, 128mmol) were reacted (yield: 35mg, 30%).
Anal. Calcd for C224H204N20O4Ru4: C, 73.82; H, 5.64; N,
7.69%. Found: C, 74.01; H, 5.93; N, 7.82%. UV–vis ꢀmax ("
104 Mꢂ1 cmꢂ1/" per subunit in CH2Cl2): 407 (65.0/16.3), 415
(sh. 58.7/14.7), 537 (7.63/1.91), 572 (2.45/0.61). ESI-MS: 3644
m=zþ (Mþ).
0
to the redox potential of a ferrocenium/ferrocene couple Eo (Fcþ/
Fc). A digital simulation of CVs was made with the simulation
package DigiSim 3.0 (Bioanalytical Systems).
Porphyrin Ligands.
5-(3-Pyridyl)-10,15,20-tri-p-tolylpor-
[{Ru(3-PyHex3porph)(CO)}4] (3).
2-(2-Methoxyethoxy)-
phyrin (H2(3-PyT3porph)), 5-(3-pyridyl)-10,15,20-tris(p-t-butyl-
phenyl)porphyrin (H2(3-PytB3porph)), and 5-(3-pyridyl)-10,15,20-
tris(p-hexyloxyphenyl)porphyrin (H2(3-PyHex3porph)),24 were
synthesized by combining 3-pyridinecarbaldehyde and p-tolualde-
hyde, 3-pyridinecarbaldehyde and 4-tert-butylbenzaldehyde, and
3-pyridinecarbaldehyde and 4-(hexyloxy)benzaldehyde, respec-
tively, with reference to the literature,6 and characterized by spec-
tral methods and elemental analyses.
ethanol (300 mL) was heated to 80 ꢁC under Ar, and H2(3-Py-
Hex3porph) (150 mg, 164 mmol) was added. After complete disso-
lution, Ru3(CO)12 (300 mg, 470 mmol) was added, and the tempera-
ture was increased to 150 ꢁC. When no UV–vis spectral changes
were observed after 1.5 h, the solution was cooled to room tem-
perature and salted out with an aqueous solution of sodium chlo-
ride. After filtering and thoroughly washing with water, the result-
ing solid material was dried over P2O5 under reduced pressure
for 12 h and then dissolved in dichloromethane. To the solution,
DDQ was added and stirred until no UV–vis peaks of rutheni-
um–chlorin complexes were observed, and the solution was sub-
jected to chromatography with silica gel. The first red-band that
eluted with dichloromethane was collected, and the solvent was
evaporated to dryness. The resulting solid was recrystallized from
dichloromethane–hexane and dried for 2.5 h under reduced pres-
sure (yield: 25 mg).
A typical preparation method for H2(3-PyHex3porph) is as fol-
lows. A propionic acid (200 mL) solution containing 4-(hexyloxy)-
benzaldehyde (12.5 mL, 60 mmol), 3-pyridinecarbaldehyde (19
mL, 20 mmol), and pyrrole (5.6 mL, 80 mmol) was refluxed for
3.5 h and cooled to room temperature. The solution was filtered
off. The resulting solid was dried at 100 ꢁC in vacuo (yield: 1.9 g).
The solid (0.9 g) was dissolved in a small amount of dichloro-
methane and column-chromatographed on silica gel. After the first
band of H2(Hex4porph) was eluted with neat dichloromethane
(yield: 750 mg), the second band containing the desired ligand was
eluted with 1% MeOH–CH2Cl2. The solvent was evaporated, and
the residue was dried at 100 ꢁC in vacuo (yield: 170 mg).
Anal. Calcd for C61H65N5O3 (H2(3-PyHex3porph)): C, 79.97;
H, 7.15; N, 7.64%. Found: C, 79.65; H, 7.16; N, 7.36%. UV–vis
ꢀmax (" 104 Mꢂ1 cmꢂ1 in CH2Cl2): 421 (49.0), 518 (1.72), 555
(1.12), 593 (0.54), 650 (0.63). 1H NMR (CDCl3, 270 MHz, 23 ꢁC):
ꢁ ꢂ2:77 (2H, s, NH), 0.98 (9H, t, OCH2CH2(CH2)3CH3), 1.44–
1.66 (18H, m, OCH2CH2(CH2)3CH3), 1.99 (6H, quin, OCH2CH2-
(CH2)3CH3), 4.23 (6H, t, OCH2CH2(CH2)3CH3), 7.30 (6H, d, m-
Ph), 7.73 (1H, m, 5-Py), 8.11 (6H, d, o-Ph), 8.51 (1H, m, 4-Py),
8.75–8.93 (8H, m, ꢂ), 9.03 (1H, m, 6-Py), 9.45 (1H, m, 2-Py).
FAB-MS: 916 m=zþ (Mþ).
Anal. Calcd for C248H252N20O16Ru4: C, 71.38; H, 6.09; N,
6.71%. Found: C, 71.05; H, 6.11; N, 6.79%. UV–vis ꢀmax ("
104 Mꢂ1 cmꢂ1/" per subunit in CH2Cl2): 407 (64.0/16.0), 419
(sh. 56.5/14.1), 537 (7.38/1.85), 574 (2.82/0.71). IR (KBr mull):
ꢃCO 1951 cmꢂ1, ESI-MS: 4173 m=zþ (Mþ).
[{Ru(3-PytB3porph)(py)}4] (4). A toluene solution (700 mL)
containing 2 (25 mg, 6.9 mmol) and pyridine (2.2 mL, 27 mmol) was
irradiated with visible light using a medium-pressure mercury
lamp for 4 h under vigorous Ar bubbling and stirring at tempera-
tures from 0 to 5 ꢁC. Upon irradiation, the solution color changed
from red to brown. The brown solution was filtered and evaporat-
ed to dryness. The resulting solid was dissolved in a small amount
of toluene and separated by an alumina column (Activity III) with
toluene as an eluent. The first eluted brown-band was collected,
and the solvent was evaporated to dryness. The resulting deep-
purple solid was recrystallized from toluene–methanol and dried
at 110 ꢁC in vacuo for 3 h (yield: 23 mg, 85%).
[{Ru(3-PyT3porph)(CO)}4] (1).
Diethylene glycol mono-
methylether suspension (100 mL) containing H2(3-PyT3porph) (50
mg, 81 mmol) and Ru3(CO)12 (150 mg, 240 mmol) was refluxed
for 2 h under N2 atmosphere. The reaction was monitored by visi-
ble spectroscopy and then heating was stopped when the charac-
teristic band of H2(3-PyT3porph) at around 650 nm was no longer
evident. After standing at room temperature, the solution was
passed through sintered glass. To the solution was added a saturat-
ed NaCl aqueous solution (100 mL). The resulting precipitate was
filtered through sintered glass, washed with water, and dried at
100 ꢁC in vacuo for 1 h. Since the crude product showed a UV–
visible band of chlorin at around 600 nm, DDQ was added to a
dichloromethane solution of 1. The suspension was stirred at room
temperature until the characteristic band disappeared. DDQ resi-
Anal. Calcd for C240H224N24Ru4: C, 74.89; H, 5.87; N,
8.74%. Found: C, 74.85; H, 6.35; N, 8.52%. UV–vis ꢀmax (" 104
M
ꢂ1 cmꢂ1/" per subunit in CH2Cl2): 411 (42.6/10.7), 424 (sh.
41.5/10.4), 510 (7.61/1.90), 534 (sh. 2.70/0.68), 582 (0.89/
0.22), 658 (0.38/0.10). ESI-MS: 3849 m=zþ (Mþ).
Results and Discussion
Characterization of Porphyrin Tetramers 1–4. These
complexes could not be obtained as single crystals suitable
for X-ray crystallography. However, complexes 2–4 were

1558 Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007)
5-(3-Pyridyl)porphyrinatoruthenium(II)
Table 1. 1H NMR Chemical Shift Values of 3-Pyridylporphyrinatoruthenium(II) Tetramersa)
tert-Bu
or Hexyloxy
Pyridine
(axial ligand)
Complex
3-Pyridyl
ꢂ-Pyrrole
Phenyl (o, m)
2
2-Py: 2.31 (s, 2H), 20-Py: 2.75 (s, 2H)
4-Py: 5.72 (d, 2H), 40-Py: 6.18 (d, 2H)
5-Py: 3.97 (t, 2H), 50-Py: 4.70 (t, 2H)
6-Py: 1.07 (d, 2H), 60-Py: 2.14 (d, 2H)
7–9b)
7–9b)
0.98 (s, 18H)
1.44 (s, 36H)
1.58 (s, 36H)
1.62 (s, 18H)
(at 70 ꢁC)
3
2-Py: 2.38 (s, 2H), 20-Py: 2.91 (s, 2H)
4-Py and 40-Py: 5.92 (m, 4H)
5-Py: 4.31 (t, 2H), 50-Py: 4.50 (t, 2H)
6-Py: 1.13 (d, 2H), 60-Py: 2.08 (d, 2H)
7–9b)
7–9b)
0.79–1.95 (m, 132H)
3.16 (t, 4H)
3.63–4.05 (m, 20H)
(at 23 ꢁC)
4
2-Py: 3.34 (s, 2H), 20-Py: 3.82 (s, 2H)
4-Py: 5.58 (d, 2H), 40-Py: 6.32 (d, 2H)
5-Py: 4.05 (t, 2H), 50-Py: 4.72 (t, 2H)
6-Py: 1.98 (d, 2H), 60-Py: 3.13 (d, 2H)
8.24
8.31
8.37
8.44
8.74
8.90
7–9b)
0.98 (s, 18H)
1.45 (s, 36H)
1.50 (s, 36H)
1.63 (s, 18H)
ꢄ-Py: 2.75 (d, 4H)
ꢂ-Py: 4.88 (t, 4H)
ꢅ-Py: 5.44 (t, 2H)
ꢄ-Py0: 2.39 (d, 4H)
ꢂ-Py0: 4.21 (t, 4H)
ꢅ-Py0: 4.88 (t, 2H)
(at 70 ꢁC)
a) In C6D6. Chemical shift values in ꢁ were corrected with respect to C6H6 (7.2 ppm). b) These proton signals were not precisely
analyzed due to broadening.
characterized to be tetramers with a rhombic structure by
1H NMR spectroscopy, IR spectroscopy, electrospray ioniza-
tion mass spectrometry (ESI-MS), and elemental analysis, as
described later in detail. In 1, its significantly low solubility
in organic solvents, such as dichloromethane, chloroform, tolu-
ene, and benzene, inhibited the measurements of 1H NMR
spectrum for structural analysis. However, mass spectrometry
and elemental analysis, and the similarities in UV–vis and
IR spectra, and the CVs to those of 2 and 3 supported the for-
mation of the self-assembled porphyrinatoruthenium tetramer
with a rhombic shape. The solubility of 2 was much higher
than that of 1, because of the tert-butyl substituents. However,
contrary to our expectation, the solubility of 2 was lower than
the monomeric complex [Ru(tpp)(CO)(py)]. Complex 4 was
also less soluble in the solvents, compared to the correspond-
ing monomer analogue of [Ru(tpp)(py)2]. Complex 3 was the
spacing of 0.33 amu was also obtained at 1282.5948 (7.40%).
Calculated molecular weights from the peaks of [M]2þ
and [M]3þ were 3848.3668 and 3847.7844 amu, respectively.
These values are in excellent agreement with the theoretical
average mass of the porphyrinatoruthenium tetramer of 4
(3848.8823; error = 2.6 ppm for [M]2þ and 2.9 ppm [M]3þ).
In the porphyrin oligomers of 1 and 2, the peaks corresponding
to 1+ charge states of porphyrin tetramers were observed at
3139.5850 (13.73%) and 3644.2190 (8.01%), accompanied
by intense peaks at 1569.6252 (m=z, 100%) and 1821.8378
(100%), respectively. These latter peaks were ascribed to 2+
charge states of porphyrin tetramers, judging from the sharp-
ness of the intense peaks and ESI-MS features of 4.
Table 1 listed 1H NMR data of 2, 3, and 4. The spectra of 2
and 4 were measured at 70 ꢁC due to lower solubility in C6D6,
while the measurement on 3 with hexyloxy groups was carried
out at room temperature (23 ꢁC) as described above. At tem-
peratures lower than 90 ꢁC, no rotation of the bridging pyridyl
groups and axial pyridyl ligands took place.19,25 Although ꢂ-
pyrrole protons gave no clear results, because of broadening
of the signals at around 7–9 ppm, up-field shifts of pyridyl pro-
ton signals and signal patterns were diagnostic enough to char-
acterize of the porphyrinatoruthenium tetramers having a
rhombic form. The proposed structure, depicted in Fig. 1, sug-
gests that the tetramers are composed of geometrical porphyrin
isomers, that is, two porphyrin subunits in four porphyrins
have a pyridyl group with a cis-direction to the axial ligand
of L (Py or CO), and the other two porphyrin subunits have
a trans-pyridyl group (Fig. 2e). Indeed, as summarized in
Table 1, each pyridyl group of 2 and 3 showed two different
proton signals with the same intensity in the magnetic region
between 1–6 ppm. Namely, in 2, one set of the 3-pyridyl sig-
nals on phase sensitive H–H COSY possessed three signals at
1.07 ppm (doublet, 6-Py), 3.97 ppm (triplet, 5-Py), and 5.72
ppm (doublet, 4-Py), as shown in the solid line of Fig. S1. An-
other set of 3-pyridyl proton signals (60-Py, 50-Py, and 40-Py)
appeared at slightly lower fields than each of the signals with
1
most soluble and made it possible to obtain a H NMR spec-
trum at room temperature, while other complex systems were
measured at 70 ꢁC (vide infra).
Elemental analyses of all the tetramers agreed well with
their respective compositions. Infrared spectra of 1, 2, and 3
had characteristic carbonyl-stretches at 1956, 1958, and 1951
cmꢂ1, respectively. Complex 4 showed no carbonyl stretches,
indicating thorough decarbonylation from the axial site.
Mass spectroscopy supported the formation of the porphyrin
tetramers. ESI-MS of 2, 3, and 4 showed respective characteris-
tic peaks corresponding to the molecular weights at 3644.2,
4173.1, and 3848.5 when a mixed solvent of methanol/di-
chloromethane (4/1 (v/v) for 2 and 4, and 1/1 for 3) was used.
Under these conditions, 1 showed no clear ESI-MS spectra, be-
cause of insolubility in the mixed solvent. However, when di-
chloromethane was used in the ESI-MS measurements, these
porphyrin oligomers appeared as tetramers. The ESI-MS spec-
trum of 4 showed an intense peak centered at 1924.4412
(100%) with an m=z peak spacing of 0.5 amu (atomic mass
unit), corresponding to the 2+ charge state ([M]2þ). The peak
corresponding to 3+ charge state ([M]3þ) with an m=z peak

K. Funatsu et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007) 1559
pyridyl substituents were observed in the region of 2 to 6.5
ppm, as shown in Table 1 and Fig. S2. In addition, axial pyri-
dine exhibited two sets of signals (ꢄ-, ꢂ-, ꢅ-Py and ꢄ-, ꢂ-, ꢅ-
Py0) in the same region. Although some signals of pyridines
were overlapped, correlation of H–H COSY distinguished
the two sets of pyridine signals. Thus, no essential differences
exist between the NMR data of those tetramers, though the
L
Ru N
L
L
Ru
Ru
N
N
N
N
Ru
Ru
L
L
1
(b) cyclic trimer
(a) cofacial dimer
measurement temperatures were different. The H NMR and
ESI-MS results indicate that the porphyrin oligomers are cyclic
porphyrinatoruthenium tetramers with a rhombic shape. This
proposed structure is essentially the same with that of 5-(3-
pyridyl)porphyrinatozincs, which have been analyzed by using
single-crystal X-ray crystallography.20,21 1H NMR spectra of
monomeric porphyrins formed by dissociation of the tetramers
in the presence of a large excess of pyridine also support the
rhombic structure composed of two kinds of geometrical iso-
mers (see section of Reaction with Pyridine). This rhombic
structure was stable even at 70 ꢁC without dissociation/associ-
ation. Indeed, no UV–vis spectral changes occurred at different
temperatures.
L
L
Ru
N
Ru
N
Ru
N
L
N
Ru
L
Ru
L
L
N
Ru
N
N
Ru
N
L
Ru
L
(c) cyclic octamer
UV–Vis Spectra. UV–vis spectra of 1, 2, and 3 exhibited a
broad Soret band with an apparent shoulder and two Q bands
as shown in Figs. 3a and 3b. In every tetramer, the shape of the
Soret band reflected excitonic interactions, stronger than those
of square tetramers, [{Ru(4-PyP3porph)(CO)}4] and [{Ru(4-
PyT3porph)(CO)}4].19 Excitonic splittings in the Soret bands
of 1, 2, and 3 were evaluated from the wavelengths of the
peaks and shoulders as 829, 529, and 704 cmꢂ1, respectively.
Both the main interactions between inclined coplanar dipole–
dipoles and between obliquely arranged dipole–dipoles, illus-
trated in the Fig. 1, explain the splitting of the Soret band of
porphyrins 1, 2, and 3.26 Q bands of the porphyrin tetramers
were red-shifted slightly relative to those of monomers, such
as [Ru(tpp)(CO)(py)], as observed in many porphyrinatozinc
dimers aligned coplanarly.27 In the pyridine complex of 4,
the Soret band was also broader than that of the corresponding
monomer of [Ru(tB4porph)(py)2] as shown in Fig. 3c, reflect-
ing excitonic interactions. The Q band was shifted 4 nm from
506 nm of the monomer to lower energy (510 nm).
L
L
Ru
N
Ru
N
Ru
N
N
L
Ru
L
(d) proposed structure with a rhombic shape
L
L
N
Ru
Ru
N
trans-subunit
cis-subunit
(e) porphyrinatoruthenium subunits
Fig. 2. Topologically possible structures of self-assembled
5-(3-pyridyl)porphyrinatoruthenium(II) oligomers (a–d)
and their porphyrin subunits (e).
Reactions with Pyridine. By the addition of an excess
of pyridine (final concentration ratio: 104–105 times) to the di-
chloromethane solutions of 1, 2, and 3, the Soret band of each
complex became to sharp and intense. The final spectra were
almost the same as those of monomer analogues of [Ru(tpp)-
(CO)(py)], [Ru(tB4porph)(CO)(py)], and [Ru(Hex4porph)-
(CO)(py)] with ca. 18 nm half-widths. The maximum of the
Soret band of the monomer formed in each 3-pyridyl system
appeared at the midpoint of the broad Soret bands of the con-
stituent interacting porphyrin subunits as shown in Fig. 3a.
1H NMR measurements at room temperature, where no rota-
tion of pyridyl groups occurred, was used to monitor the prog-
ress of the dissociation reaction, that is, the addition of d5-pyri-
dine (concentration ratio: 250 times) to the CDCl3 solution of
3, followed by standing for 24 h to complete the dissociation
reaction, caused low-field shifts in all of the pyridyl proton sig-
nals upon dissociation and concomitantly gave two new sets of
signals with the same intensity (9.28 and 9.45 ppm for the pro-
tons at the 2nd position, 2-Py), due to constituent porphyrin
isomers. This NMR result from the reaction process concretely
similar correlations. Two additional singlet signals (2H integral
intensities) that appeared at 2.31 and 2.75 ppm were assigned
to 2-Py protons on 3-pyridyl substituents. These 1H NMR data
show that the 3-pyridyl substituents coordinate to ruthenium
ions and that two different kinds of porphyrinatoruthenium
subunits are present. The NMR results do not support the for-
mation of a slipped cofacial dimers and cyclic trimers illustrat-
ed in Figs. 2a and 2b, because these oligomers contain only the
same porphyrin subunits with a trans-3-pyridyl group, that is,
the direction of the each pyridyl N-atom is reverse to that of
the CO ligands. Although larger oligomers, such as an octamer,
composed of six cis-pyridylporphyrins and two trans-pyridyl-
porphyrins shown in Fig. 2c, are also topologically possible,
the NMR data exclude their formation, because of the differ-
ence in the composition ratio of porphyrin subunits.
In the H–H COSY spectrum of 4, two sets of signals for 3-

1560 Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007)
5-(3-Pyridyl)porphyrinatoruthenium(II)
0.8
(a)
trans- L
Ru
2
[Ru(3-PyT3porph)(CO)(Py)]
[{Ru(3-PyT3porph)(CO)}4] 1
L
0.6
0.4
0.2
0.0
N
L
Ru
Py
N
Py
Ru
+
N
N
Ru
N
Ru
Py
L
L
Ru
2
N
300
400
400
400
500
600
700
800
800
800
cis- L
Wavelength / nm
Fig. 4. Dissociation reaction of 3 in d5-pyridine–CDCl3 at
23 ꢁC.
(b)
1.2
0.8
0.4
0.0
(a)
ring oxidn. 2
ring oxidn. 1
-3
-2
-1
0
1
300
500
600
700
-500
-500
-500
0
500
E / mV vs Fc+ / Fc
ring oxidn. 2
1000
Wavelength / nm
(c)
(b)
0.5
0.4
0.3
0.2
0.1
0.0
-4
-3
-2
-1
0
ring oxidn. 1
1
0
500
E / mV vs Fc+ / Fc
ring oxidn.
1000
300
500
600
700
Wavelength / nm
(c)
-6
-4
-2
0
Fig. 3. (a) UV–vis spectral change of 1 by the addition of
excess pyridine to the CH2Cl2 solution at 23 ꢁC. (b) and
(c) are UV–vis spectra of 2 and 4, respectively, in CH2Cl2
at 23 ꢁC. The UV–vis spectrum of 3 is similar to (b).
Ru(III / II)
demonstrates that the tetramers are made from two geometrical
isomers of pyridylporphyrin subunits, cis- and trans-isomers,
as illustrated in Fig. 4. The two signals of the 2-Py proton
coalesce at around 90 ꢁC to give a single signal by the rotation
of the pyridyl groups.
Electrochemical Studies. CVs of the rhombic tetramers
and their simulation curves are shown in Figs. 5 and 6, and
the redox potentials (E00) are listed 0in Table 2 together with
the redox potential differences (ꢀE0 ) in each oxidation step.
All of the tetramers underwent two-stage electrochemical ox-
idations, each of which involved 4-electrons in a manner simi-
lar to the square tetramers constructed from 5-(4-pyridyl)por-
phyrinatoruthenium(II) subunits.19 By reference to the redox
behavior of carbonyl-coordinated porphyrinatoruthenium(II)
2
0
500
1000
E / mV vs Fc+ / Fc
Fig. 5. CVs of tetramers with a rhombic shape in 0.1 M
Bu4NPF6–CH2Cl2 solution at 23 ꢁC. (a) 1, (b) 2, and (c) 4.
analogues,28 the two oxidation stages in 1, 2, and 3 were as-
cribed to the first and second oxidation processes of their por-
phyrin rings. The difference in potentials between the first
stages and the second stages of the carbonyl-coordinated tetra-
mers was about 400 mV. The difference is almost the same

K. Funatsu et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007) 1561
Table 2. Redox Potentials (E00) and ꢀE00 Values of 3-Pyr-
(a)
idylporphyrinatoruthenium Tetramersa)
por. ring ox.
1e- x 4
E00Ru/mVb)
(ꢀE00/mV) (ꢀE00/mV) for the
E001/mVb)
ꢀE00total/mV E020 /mV
por
0.8
Complex
RuIII/II
por oxidn. 1 1st step
oxidn. 2
0.4
1
378
(85)
463
529
573
(66)
(44)
195
191
177
260
1016
1021
976
0
2
3
382
465
534
573
-0.2
(83)
(69)
(39)
-0.6
366
449
526
543
-0.20
0.30
E / V vs FC+ / FC
0.80
(83)
(77)
(17)
(b)
4
ꢂ275
Ru(III / II)
1e- x 4
(104)
(107)
(49)
1.5
1.0
ꢂ171
ꢂ64
ꢂ15
986
370
[Ru(tpp)(CO)]cÞ
770
a) Redox potentials were corrected with respect to E (Fcþ/Fc) =
0.000 V. b) The potentials were confirmed by CV simulation.
c) From Ref. 30, in 0.1 M Bu4N(ClO4)–CH2Cl2.
0.5
0
waves were also observed in the first oxidation stage of 4.
Simulation of the cyclic voltammogram exhibited that the first
stage of 4 consisted of stepwise four one-electron oxidations
-0.5
and the largest ꢀE00
value (260 mV). However, broadening
total
-0.65
-0.25
0.15
of the second oxidation stages for all the rhombic cyclic tetra-
mers was too small to estimate the redox potential of the four
one-electron steps, that is, it seems to be pseudo one-step four-
electron transfers similar to the square cyclic tetramer systems.
This is a common feature in both the rhombic and square
cyclic tetramer series. This behavior may reflect the difference
in charge densities caused by oxidations in each stage, that is,
the charges of the tetramers change largely from zero to plus
four in the first oxidation stage but from plus four to plus eight
in the second stage.
E / V vs FC+ / FC
Fig. 6. Simulations of the CVs of (a) 2 and (b) 4. The solid
lines and the dotted lines are simulation curves and experi-
mental curves respectively.
with that of the [Ru(tpp)(CO)] monomer system.29 In 4, the
first and second stages were ascribed to the oxidation of four
ruthenium centers from the oxidation state of II to III and
the porphyrin rings, respectively.19,30 In the carbonyl-coordi-
nated complexes, relative broad waves were observed in the
first oxidation stage. Simulations demonstrated that the first
stages consisted of stepwise four-one-electron oxidations, as
listed in Table 2. The oxidation behavior signifies the presence
of electronic interactions among the porphyrinatoruthenium
subunits. There were no0essential differences among 1, 2, and
Conclusion
Self-assembled 5-(3-pyridyl)porphyrinatoruthenium oligo-
mers were synthesized and characterized. The structures were
determined to be cyclic tetramers with a rhombic shape by
1H NMR, ESI-MS, and analytical procedures. UV–vis studies
exhibited strong excitonic interactions between porphyrin
subunits. Electrochemical measurements of all these rhombic
tetramers showed a stepwise four-one-electron oxidation in
the first porphyrin ring oxidation of 1–3 and the Ru oxidation
of 4. As a whole, interactions observed in UV–vis and electro-
chemical studies between each porphyrinatoruthenium subunit
were significantly larger than those of square cyclic tetramers.
3 in both ꢀE00 and ꢀE0
in their first oxidation stages. The
total
first and second ꢀE00 values of ca. 80 and 70 mV were larger
than the third ꢀE00 values (17–44 mV). ꢀE00
of these tetra-
values were significant-
total
mers were 177–195 mV. The ꢀE00
total
ly larger by 47–65 mV than those of square cyclic tetramers,
[{Ru(4-PyP3porph)(CO)}4] and [{Ru(4-PyT3porph)(CO)}4].19
The large electronic interactions must result from less perpen-
dicular arrangements and more flexibilities between porphyrin
subunits in the present systems than in the 5-(4-pyridyl)por-
phyrin square complex systems. This feature is consistent with
the broadening of UV–vis spectra as described above. Broad
We acknowledge funds from a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology, Japan (Nos. 08454206 and
17655021).

1562 Bull. Chem. Soc. Jpn. Vol. 80, No. 8 (2007)
5-(3-Pyridyl)porphyrinatoruthenium(II)
Inorg. Chem. 1997, 36, 833. h) C. M. Drain, J.-M. Rehn, J. Chem.
Soc., Chem. Commun. 1994, 2313. i) H. Yuan, L. Thomas, K.
Woo, Inorg. Chem. 1996, 35, 2808. j) P. J. Stang, J. Fan, B.
Olenyuk, Chem. Commun. 1997, 1453.
Supporting Information
H–H COSY NMR spectra of 2 and 4. UV–vis spectrum and
simulated cyclic-voltammograms of 3. These materials are availa-
ble free of charge on the web at http://www.csj.jp/journals/bcsj/.
9
J.-C. Chambron, V. Heitz, J.-P. Sauvage, The Porphyrin
Handbook, ed. by K. M. Kadish, K. M. Smith, R. Guilard,
Academic Press, New York, 2000, Vol. 6, Chap. 40, pp. 1–42.
10 T. Imamura, K. Fukushima, Coord. Chem. Rev. 2000, 198,
133.
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24 Abbreviations:
3-PyT3porph = 5-(3-pyridyl)-10,15,20-
tri-p-tolylporphyrinato dianion, 3-PytB3porph = 5-(3-pyridyl)-
10,15,20-tris(p-t-butylphenyl)porphyrinato dianion, 3-PyHex3-
porph = 5-(3-pyridyl)-10,15,20-tris(p-hexyloxyphenyl)porphy-
rinato dianion, Hex4porph = 5,10,15,20-tetrakis(p-hexyloxyphen-
yl)porphyrinato dianion, 4-PyP3porph = 5-(4-pyridyl)-10,15,20-
triphenylporphyrinato dianion, 4-PyT3porph = 5-(4-pyridyl)-10,
15,20-tri-p-tolylporphyrinato dianion, tB4porph = 5,10,15,20-
tetrakis(p-t-butylphenyl)porphyrinato dianion, tpp = 5,10,15,20-
tetraphenylporphyrinato dianion. DDQ = 2,3-dichloro-5,6-dicya-
no-1,4-benzoquinone, py = pyridine.
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