Synthesis and characterization of ruthenium complexes with substituted pyrazino[2,3-f][1,10]-phenanthroline (= RPPL; R = ME, COOH, COOME)

Article abstract of DOI:10.1002/hlca.200390168

A series of substituted pyrazino[2,3-f][1,10]-phenanthroline (Rppl) ligands (with R = Me, COOH, COOMe) were synthetized (see 1-4 in Scheme 1). The ligands can be visualized as formed by a bipyridine and a quinoxaline fragment (see A and B). Homoleptic [Ru(R¹ppl)₃](PF₆)₂ and heteropleptic [Ru(R¹ppl){(R²)₂bpy}₂] (PF₆)₂ (R¹ = H, Me, COOMe and R² = H, Me) metal complexes 5-7 and 8-13, respectively, based on these ligands were also synthesized and characterized by conventional techniques (Schemes 2 and 3, resp.). In the heteroleptic complexes, the R¹-ppl ligand reduces at a less-negative potential than the bpy ligand, reflecting the acceptor property conferred by the quinoxaline moiety. The potentiality of some of these complexes as solar-cell dyes is discussed.

Full text of DOI:10.1002/hlca.200390168

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Synthesis and Characterization of Ruthenium Complexes with Substituted
Pyrazino[2,3-f][1,10]-phenanthroline (ˆ Rppl; R ˆ Me, COOH, COOMe)
by Alvaro Delgadillo, Paola Romo, Ana Maria Leiva, and Ba¬rbara Loeb*
¬
Facultad de QuÌmica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago, Chile
(phone: 56-2-6864404; fax: 56-2-6864744; e-mail: bloeb@puc.cl)
A series of substituted pyrazino[2,3-f][1,10]-phenanthroline (Rppl) ligands (with R ˆ Me, COOH,
COOMe) were synthetized (see 1 4 in Scheme 1). The ligands can be visualized as formed by a bipyridine
and
a quinoxaline fragment (see A
and B). Homoleptic [Ru(R1ppl)3](PF 6)2 and heteropleptic
[Ru(R1ppl){(R2)2bpy}2](PF 6)2 (R1 ˆ H, Me, COOMe and R2 ˆ H, Me) metal complexes 5 7 and 8 13,
respectively, based on these ligands were also synthesized and characterized by conventional techniques
(Schemes 2 and 3, resp.). In the heteroleptic complexes, the R1-ppl ligand reduces at a less-negative potential
than the bpy ligand, reflecting the acceptor property conferred by the quinoxaline moiety. The potentiality of
some of these complexes as solar-cell dyes is discussed.
Introduction. Transition-metal complexes with polypyridines have been widely
studied in the last decades mainly because of their special photophysical, photo-
chemical, and electrochemical properties [1]. These properties make them potential
candidates to be used as dyes in artificial solar-energy-conversion devices, e.g., in
photo-electrochemical solar cells [2]. Specifically, (polypyridine)ruthenium(II) com-
plexes have been anchored to semiconductor oxide electrodes, such as TiO2 electrodes,
and used to improve the light-to-electricity-conversion yield of the cell. The dye is
attached to the semiconductor surface by anchoring groups, such as carboxylates or
phosphonates; this anchor is a substituent at a polypyridine ligand of the complex.
Gr‰tzel×s [Ru(NCS)2{bpy(COOH)2}2] dye (bpy ˆ 2,2'-bipyridine), known as N3, is an
archetype for this type of complex [2a d].
The efficiency of the solar cell depends
among other parameters
on the
spectroscopic and electrochemical properties of the polypyridine complexes used to
sensitize the semiconductor oxide [3]. It is a well known fact that these properties can
be tuned by an adequate choice of ligands [1]. This makes the search for new complexes
with suitable anchoring ligands one of the most important issues of research on solar-
cell dyes.
Functionalized 2,2'-bipyridine has been the main ligand used in [Ru(polypyridine)]
dyes. In this work, the synthesis of derivatives A of the pyrazino[2,3-f][1,10]phenan-
thraline ligand, Rppl (R ˆ Me, COOH, or COOMe), is reported. This ligand can be
visualized as a fusion of a bipyridine and a quinoxaline moiety (see B), where the
quinoxaline part would also play the role of acceptor group.1)
1
)
The Rppl ligand with R ˆ H has been reported in the literature with different names, see, e.g., [4].

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Enhancement of rigidity and aromaticity in the polypyridine ligand should conduct
to improvement in the excited-state properties of the complex [5]. In metal complexes,
delocalization and rigidity in the acceptor ligand lead to decreased structural changes in
the excited state. This, in turn, decreases the nonradiative decay constant and can
greatly enhance excited-state lifetimes [5][6].
The synthesis and characterization of homoleptic and heteroleptic ruthenium(II)
complexes with these ligands is also reported. Based on the observed properties, the
potentiality of the complexes as solar-cell dyes is discussed.
Results and Discussion. Synthesis. The synthesis of pyrazino[2,3-f][1,10]phenan-
throline (1) and 2-methylpyrazino[2,3-f][1,10]phenanthroline (2) was achieved in high
yield by a condensation reaction of 1,10-phenanthroline-5,6-dione [7] with ethane-1,2-
diamine and propane-1,2-diamine, respectively, in MeOH (Scheme 1). The corre-
sponding carboxylic acid ligand 3 was obtained by oxidation of the methyl group of 2
with chromium oxide in concentrated sulfuric acid. Due to the insolubility of this ligand
Scheme 1

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in most common solvents, 3 was esterified in MeOH/H2SO4 according to the method of
Garelli and Vierling [8]. The ester 4 obtained is a well and more managable model,
suitable to study the behavior of the carboxylate ligand.
The homoleptic complexes 5 6 were generated by reaction of the respective ligand
with ruthenium trichloride in MeOH/H2O in the presence of hydroquinone
(Scheme 2). The complexes were isolated by precipitation from aqueous solution with
ammonium hexafluorophosphate.
The heteroleptic complexes 8 13 were obtained by chloro substitution in cis-
[RuCl2{(R2)2bpy}2] [9] with R1ppl in MeOH/H2O (Scheme 3) and were isolated by the
same procedure as described for the homoleptic complexes.
1
NMR Spectroscopy. The H-NMR spectra of the ligand ppl (1) shows the three
magnetically nonequivalent protons of the bipyridine moiety and the s of the
quinoxaline proton, Fig. 1,a. The lowest-field signal is assigned to HÀC(5) and
HÀC(12) (see A for numbering) due to the proximity of the quinoxaline N-atoms that
increase the para effect of the bipyridine N-atoms [10], shifting this signal to lower field
than that of the ortho protons HÀC(7) and HÀC(10) of the bipyridine part. This
behavior is not reproduced in the 13C-NMR spectra, where the chemical shift for C(5)
and C(12) appears at higher field than that of C(7), and C(10), according to the order
expected for a bipyridine-type ligand [10b]. On the other hand, HÀC(6) and HÀC(11)
as well as C(6) and C(11) of the bipyridine part appear at high field as expected. In the
substituted R-ppl ligands, the signal of HÀC(5) and HÀC(12) as well as that of
HÀC(7) and HÀC(10) split, due to the loss of symmetry in the compound.
As expected, in the 1H-NMR spectra of 2 (R ˆ Me) and 4 (R ˆ COOMe) (Fig. 1,b
and c, resp.), the signal corresponding to the quinoxaline proton HÀC(3) is strongly
affected by the nature of the substituent. In ligand 2, its shielding is enhanced (0.2 ppm)
Scheme 2

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Scheme 3
compared to the unsubstituted ligand 1, whereas, for ligand 4, this proton is manifestly
unshielded (0.8 ppm) because of the electron-acceptor properties of the ester group.
In the spectra of the complexes, the complete bipyridine-part pattern remains at
almost the same position, except for the signals of HÀC(7) and HÀC(10), which are
shifted to drastically higher field (by ca. 0.8 ppm). This effect due to the electronic
current of the heterocycles in an octahedral configuration [11] is appreciable only in
the 1H-NMR spectra, since the 13C-NMR chemical shifts do not suffer major alterations
compared to those of the free ligand. The general pattern of the spectra also show the
equivalence of the three Rppl ligands in the complex, Fig. 2,b.
The 1H-NMR spectra of the heteroleptic [Ru{(R2)2bpy}2(R1ppl)]2‡ type complexes
show, in addition to the ppl pattern, two sets of signals for the bpy ligands. When R2 ˆ
H, the spectra are converted to a higher order, introducing some uncertainty in the
exact chemical-shift value.
UV/VIS Spectroscopy. The UV/VIS spectra of the free ligands show a series of low-
intensity bands in the 280 350-nm region and a strong band at 260 nm, all assigned to
p ! p* transitions. The homoleptic and heteroleptic complexes show UV/VIS spectra
quite similar to those of [Ru(bpy)3](PF 6)2 (Fig. 3). The 400 500-nm region is
dominated by a MLCT (metal-to-ligand charge transfer) broad manifold. In the case of
the ppl complexes, some enhancement of the intensity of the absorption at higher
energy is observed. This can be explained by the acceptor properties of ppl that
produces a destabilization of the dp level of the metal [1c]. The tris(bpy) complex
shows two additional bands at 285 and 240 nm; the first one is assigned to a LC band,
and the latter to a MLCT [1b]. In the ppl complexes, two bands at ca. 290 and ca.

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Fig. 1. 1H-NMR Spectra of a) ppl (1), b) (Me)ppl (2), and c) (COOMe)ppl (4) in CDCl3
260 nm also appear, but, in this case, they are assigned to LC transitions; the MLCT
band probably present in this region is overlapped by the intense LC band.
Electrochemistry. The electrochemical data for all the ligands and complexes are
shown in the Table. In the cyclic voltammogram of the free ligands, the position of the
reversible first reduction is very sensible to the substituent group: the less-negative
potential is observed for R ˆ COOMe, while the ligand with R ˆ Me shows the most
negative potential.
For the homoleptic complexes, a broad reduction peak is observed, followed by a
sharp reversible oxidation. Compared to the free ligand, the ligand reduction in the
complexes appears at less-negative potentials, due to the coordination effect that
lowers the energy of the p* orbitals. Nevertheless, the relative ordering of the ligands
remains unaltered. The RuII/RuIII oxidation potential is relatively constant along the
series, evidencing little effect of the substituents on the d-orbital energy of the metal. In
the heteroleptic complexes, the reversible-oxidation signal for the RuII/RuIII couple is

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Fig. 2. 1H-NMR Spectra of a) [Ru(bpy)2(ppl)](PF6)2 (8) and b) [Ru(ppl)3](PF6)2 (5) in CD3CN
Fig. 3. UV/VIS Spectra of [Ru{(COOMe)ppl}3](PF6)2 (7) and [Ru(bpy)3](PF6)2 in MeCN

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Table. Redox Potentials (V vs. Ag/AgCl) for the Rppl Ligands (RˆH, Me, COOMe) and Their Corresponding
RuII Complexes in MeCN
E1/2 (Ru3‡/Ru2‡
)
E1/2 (L/LÀ
)
1a)
2a)
4a)
5
6
7
8
10
12
9
11
13
À 1.50
À 1.60
À 1.16
À 1.16
À 1.21
À 0.86
À 1.18
À 1.20
À 0.94
À 1.23
À 1.24
À 0.96
‡ 1.44
‡ 1.41
‡ 1.45
‡ 1.37
‡ 1.37
‡ 1.38
‡ 1.24
‡ 1.26
‡ 1.29
a) DMSO vs. saturated calomel electrode (SCE).
observed in the same way as for the homoleptic compounds. Most of the cases show
three reductions, as can be seen in Fig. 4 for the complex [Ru(bpy)2{(COOMe)-
ppl}](PF 6)2 (12), the first one assigned to the ppf ligand and the others to bpy. This
behavior is a clear evidence for the acceptor properties of ppf. The assignment is based
on comparison with the ligand reduction in the homoleptic complexes.
Conclusions and Outlook.
A series of ligands derived from pyrazino[2,3-f]-
[1,10]phenanthroline and their corresponding homo- and heteroleptic complexes were
synthetized and characterized. As was previously mentioned, R1-ppl ligands behave as
being formed by a 2,2-bipyridine and a quinoxaline moiety. This assumption is
supported by theoretical calculations performed with the −Spartan× package [12]. Fig. 5
Fig. 4. Cyclic voltagram of [Ru(bpy)2{(COOMe)ppl}](PF6)2 (12) in MeCN

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Fig. 5. Frontier orbitals of ppl and their relationship to 2,2'-bipyridine and quinoxaline orbitals
shows the electronic-density distributions for the frontier orbitals of ppl and their
relationships to the corresponding orbitals for the 2,2'-bipyridine and quinoxaline
components. The quinoxaline region dominates the first ligand reduction, as can be
concluded from the resemblance of the ppl LUMO and the quinoxaline LUMO. This
explains the sensitivity of this region to a change in the R substituent, as observed
experimentally.
Interesting to point out is the fact that, in the heteroleptic [Ru{(R2)2bpy}2(R1ppl)]2‡
type complexes, modification of R2 on the bpy ligands has a strong effect on the metal
oxidation potential, evidencing that these ligands have the most marked influence on
the metal center.
The capacity to modify the redox potential of the quinoxaline region by substitution
with adequate acceptors can be used to introduce directionality to the electron flux
after the MLCTabsorption. In this way, charge separation in the excited state should be
enhanced, and consequently the behavior of the complex as a potential solar-cell dye
should be improved. In this context, ligands substituted with an ester group such as 4
are very promising. First, because of their manageability and solubility, the study of
their excited-state properties should be straightforward; second, they can be considered
good models for the corresponding carboxylated complexes. Moreover, they can be
converted by base hydrolysis to the mentioned carboxylated derivatives, and
subsequently tested as solar-cell dyes. Both studies, the photophysical behavior of
the complexes and their use as solar-cell dyes, are in progress.

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Experimental Part
1. General. The 1,10-phenanthroline-5,6-dione and the complexes [RuCl2(bpy)2] and [RuCl2(Me2bpy)2]
were synthesized according to [7][9]. UV/VIS Spectra: Shimadzu UV-3101PC spectrophotometer; l in nm. IR
Spectra: KBr pellets; Bruker Vector-22-FTIR spectrometer; in cmÀ1 1H-NMR Spectra: Bruker AC/200
.
(200 MHz) or Bruker Aspect 400-MHz spectrometer; in CD3CN or CDCl3 with SiMe4 as reference; d in ppm, J
in Hz. NMR spectra were processed with the −Mestre-C× software package [13]. Cyclic voltammetry: Bas CV-
50W-2.3-MF-9093 equipment.
2. Theoretical Calculations. Geometry optimization of ligands were performed by using the semi-empirical
methods implemented in the −Spartan× package [12]. Total energy and molecular surfaces were obtained by
using Hartree-Fock calculations (6-31G**) on the equilibrium geometry previously obtained.
3. Syntheses of Ligands. Pyrazino[2,3-f][1,10]-phenanthroline (1). Ethane-1,2-diamine (0.5 ml) was added
to a suspension of 1,10-phenanthroline-5,6-dione (0.50 g, 2.38 mmol) in MeOH (25 ml). After 5 min, a red soln.
appeared, which was stirred overnight at r.t. The solid formed was filtered off and washed with small amounts of
MeOH. Recrystallization from toluene gave 0.43 g (79%) of 1. IR (KBr): 1581, 1467, 1391, 740. 1H-NMR
(CDCl3): 9.51 (dd, J ˆ 8.2, 1.8, HÀC(5), HÀC(12)); 9.30 (dd, J ˆ 4.4, 1.8, HÀC(7), HÀC(10)); 9.00 (s, HÀC(2),
HÀC(3)); 7.81 (dd, J ˆ 8.2, 4.4, HÀC(6), HÀC(11)). 13C-NMR (CDCl3): 152.71; 147.79; 144.94; 140.983;
133.64; 127.48; 124.40. Anal. calc. for C14H8N4 ¥ 0.5 H2O: C 69.70, H 3.76, N 23.33; found: C 70.09, H 3.37,
N 23.54.
2-Methylpyrazino[2,3-f][1,10]phenanthroline (2). To a suspension of 1,10-phenanthroline-5,6-dione (1.00 g,
4.76 mmol) in MeOH (25 ml), propane-1,2-diamine (0.5 ml) was added. The red soln. was stirred overnight at
r.t. Evaporation gave an orange tar. The suspension of this tar in H2O was stirred for 2 days. A white solid was
formed, which was filtered off and washed with H2O. Recrystallization from toluene gave 0.93 g (80%) of 2. IR
(KBr): 1581, 1469, 1400, 1366, 744. 1H-NMR (CDCl3): 9.5 (dd, HÀC(12)); 9.41 (dd, HÀC(5)); 9.26
(m, HÀC(7), HÀC(10)); 8.82 (s, HÀC(3)); 7.78 (m, HÀC(6), HÀC(11)); 2.9 (s, Me). 13C-NMR (CDCl3):
154.06; 152.09; 151.805; 144.94; 133.15; 132.79; 123.90; 123.81; 22.33. Anal. calc. for C15H10N4: C 73.16, H 4.09,
N 22.75; found: C 73.15, H 4.13, N 22.79.
Pyrazino[2,3-f][1,10]phenanthroline-2-carboxylic Acid (3). To 2 (0.9 g, 3.65 mmol) placed in an ice bath,
conc. H2SO4 soln. (10 ml) was slowly added, followed by small portions of chromium oxide (total of 1.2 g,
12 mmol), with vigorous stirring. The resulting mixture was refluxed for 4 h and then stirred overnight at r.t. The
green soln. was poured over ice, and the white precipitated formed was filtered off and thoroughly washed with
H2O. The product was dried under vacuum: 0.38 g (38% of 3). IR (KBr): 3500 2250, 1721, 1379, 727.
Pyrazino[2,3-f][1,10]phenanthroline-2-carboxylic Acid Methyl Ester (4). To a suspension of 3 (0.35 g,
1.27 mmol) in MeOH (20 ml), conc. H2SO4 soln. (1 ml) was added. After refluxing some time, a clear soln.
appeared, and refluxing was continued for 24 h. Then H2O was added and the soln. neutralized with NaHCO3.
Finally, the aq. soln. was extracted with CHCl3 (3 Â 15 ml), the org. layer dried (Na2SO4) and evaporated, the
white residue re-extracted with CHCl3, and the org. phase dried (Na2SO4) and evaporated: 0.38 g (98%) of 4.
IR (KBr): 1743, 1723, 1098, 1021, 798. 1H-NMR (CDCl3): 9.67 (s, HÀC(3)); 9.62 (dd, HÀC(12)); 9.55
(dd, HÀC(5)); 9.35 (m, HÀC(7), HÀC(10)); 7.85 (m, HÀC(6), HÀC(11)); 4.17 (s, MeO). 13C-NMR (CDCl3):
164.55; 153.26; 152.89; 148.27; 145.11; 142.39; 142.22; 139.66; 133.93; 133.71; 126.62; 126.39; 124.22; 53.28. Anal.
calc. for C16H10N4O2 ¥ 3 H2O: C 55.81, H 4.68, N 16.27; found: C 54.62, H 3.25, N 15.55.
4. Homoleptic Complexes [Ru(R1ppl)3](PF6): General Method: The appropiate ligand (1.5 mmol), RuCl3 ¥
H2O (0.7 mmol), and hydroquinone (0.7 mmol) were dissolved in a MeOH/H2O 2 :1 (25 ml). The soln. was
refluxed for 3 h. After filtration, NH4PF6 was added to precipitated the complex. The solid was filtered off,
washed with H2O and Et2O, and dried under vacuum.
Tris(pyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium(2‡)
Bis[hexafluorophosphate(1 À)]
([Ru(ppl) 3](PF 6)2; 5). Yield 70%. UV/VIS (MeCN): 253, 290, 448. IR (KBr): 1443, 1383, 840, 557. 1H-NMR
(CD3CN): 9.5 (dd, 6 H); 9.2 (s, 6 H); 8.2 (dd, 6 H); 7.7 (m, 6 H).
Tris(2-methylpyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium(2‡) Bis[hexafluorophosphate(1À)]
([Ru{(Me)ppl}](PF 6)2; 6). Yield 69%. UV/VIS (MeCN): 257, 291, 449. IR (KBr): 1408, 1370, 840, 557. 1H-NMR
(CD3CN): 9.5 (t, 6 H); 9.1 (s, 3 H); 8.2 (m, 6 H); 7.7 (m, 6 H); 2.9 (s, 9 H).
Tris(methyl pyrazino[2,3-f][1,10]phenanthroline-2-carboxylate-kN8,kN9)ruthenium(2‡) Bis[hexafluoro-
phosphate(1À)] ([Ru{(COOMe)ppl} 3](PF 6)2; 7). Yield 65%. UV/VIS (MeCN): 260, 300, 450. IR (KBr):
1743, 1726, 839, 557. 1H-NMR (CD3CN). 9.8 (s, 3 H); 9.6 (m, 6 H); 8.3 (t, 6 H); 7.8 (m, 6 H); 4.1 (s, 9 H).
5. Heteroleptic Complexes [Ru{(R2)2bpy}2(R1ppl)](PF6)2 : General Method.
A
soln. of R1ppl
[RuCl2{(R2)2bpy}2] (0.5 mmol), and H2O/MeOH (25 ml) was refluxed for 4 h. The solvent was evaporated

Helvetica Chimica Acta Vol. 86 (2003)
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close to dryness, then H2O was subsequently added. The soln. was filtered off, and NH4(PF 6) was added to give
the desired product. The solid was filtered off and washed with Et2O.
Bis(2,2'-bipyridine-kN1,kN1')(pyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium(2‡) Bis[hexa-
fluorophosphate(1À)] ([Ru(bpy) 2(ppl)](PF 6)2; 8). Yield 45%. UV/VIS (MeCN): 255, 288, 450. IR (KBr):
839, 557. 1H-NMR (CD3OD): 8.1 (d, 2 H); 7.7 (s, 2 H); 7.2 (t, 4 H); 6.8 6.4 (m, 6 H); 6.2 (d, 2 H); 6.0 (t, 2 H);
5.8 (t, 2 H).
Bis(4,4'-dimethyl-2,2'-bipyridine-kN1,kN1')(pyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium(2‡)
Bis[hexafluorophosphate(1À)] ([Ru(Me 2bpy)2(ppl)](PF 6)2; 9). Yield 48%. UV/VIS (MeCN): 256, 285, 450.
IR (KBr): 1619, 842, 557. 1H-NMR (CD3CN): 9.5 (d, 2 H); 9.2 (s, 1 H); 8.4 (s, 2 H); 8.35 (s, 2 H); 8.2 (d, 2 H);
7.85 (m, 2 H); 7.6 (d, 2 H); 7.45 (d, 2 H); 7.25 (d, 2 H); 7.0 (d, 2 H); 2.6 (s, 6 H); 2.45 (s, 6 H).
Bis(2,2'-bipyridine-kN1,kN1')(2-methylpyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium(2‡) Bis-
[hexafluorophosphate(1À)] ([Ru(bpy) 2{(Me)ppl}](PF 6)2; 10). Yield 50%. UV/VIS (MeCN): 256, 287, 450.
IR (KBr): 840, 557. 1H-NMR (CD3CN): 9.5 (t, 2 H); 9.1 (s, 1 H); 8.5 (t, 4 H); 7.8 8.2 (10 H); 7.6 (d, 2 H); 7.4
(t, 2 H); 7.2 (t, 2 H); 2.9 (s, 3 H).
Bis(4,4'-dimethyl-2,2'-bipyridine-kN1,kN1')(2-methylpyrazino[2,3-f][1,10]phenanthroline-kN8,kN9)ruthenium-
(2‡) Bis[hexafluorophosphate(1À)] ([Ru(Me 2bpy)2{Meppl}](PF 6)2; 11). Yield 49%. UV/VIS (MeCN): 256,
1
285, 450. IR (KBr): 1619, 842, 557. H-NMR (CD3CN): 9.5 (dd, 2 H); 9.1 (s, 1 H); 8.4 (s, 2 H); 8.38 (s, 2 H); 8.2
(t, 2 H); 7.85 (m, 2 H); 7.7 (d, 2 H); 7.4 (m, 2 H); 7.3 (d, 2 H); 7.05 (d, 2 H); 2.9 (s, 3 H); 2.6 (s, 6 H); 2.5 (s, 6 H).
Bis(2,2'-bipyridine-kN1,kN1')(methylpyrazino[2,3-f][1,10]phenanthroline-2-carboxylate-kN8,kN9)ruthenium-
(2‡) Bis[hexafluorophosphate(1À)] ([Ru(bpy) 2{(COOMe)ppl}](PF6)2; 12). Yield 45%. UV/VIS (MeCN):
259, 286, 450. IR (KBr): 1744, 1726, 840, 558. 1H-NMR (CD3CN): 9.8 (s, 1 H); 9.55 (t, 2 H); 8.55 (t, 4 H); 8.25
(m, 2 H); 8.15 (t, 2 H); 8.05 (t, 2 H); 7.95 (m, 2 H); 7.9 (d, 2 H); 7.7 (t, 2 H); 7.5 (t, 2 H); 7.25 (t, 2 H); 4.1 (s, 3 H).
Bis(4,4'-dimethyl-2,2'-bipyridine-kN1,kN1')(methyl pyrazino[2,3-f][1,10]phenanthroline-2-carboxylate-
kN8,kN9)ruthenium(2‡) Bis[hexafluorophosphate(1À)] ([Ru(Me2bpy)2{(COOMe)ppl}](PF6)2 ; 13). Yield
50%. UV/VIS (MeCN): 259, 284, 447. IR (KBr): 1744, 1726, 843, 557. 1H-NMR (CD3CN): 9.8 (s, 1 H); 9.5
(t, 2 H); 8.4 (s, 2 H); 8.35 (s, 2 H); 8.2 (m, 2 H); 7.9 (m, 2 H); 7.6 (d, 2 H); 7.4 (t, 2 H); 7.3 (d, 2 H); 7.05 (d, 2 H);
4.1 (s, 3 H); 2.55 (s, 6 H); 2.45 (s, 6 H).
Support from Conicyt (doctoral thesis support grant to A.D.) and Fondecyt (Lineas Complementarias
8980007, and Project 1020517) is gratefully acknowledged.
REFERENCES
[1] a) K. Kalyanasundarum, −Photochemistry of Polypyridine and Porphyrin Complexes×, Academic Press,
London, 1992; b) A. Juris, F. Barigelletti, S. Campagna, V. Balzani, P. Belser, A. von Zelewsky, Coord.
Chem. Rev. 1988, 84, 85; c) K. Kalyanasundaram, in −Photosensitization and Photocatalysis Using
Inorganic and Organometallic Compounds×, Eds. K. Kalyanasundaram, M. Gr‰tzel, Kluwer Academic
Publishers, London, 1993; d) U. Schubert, C. Eschbaumer, Angew. Chem., Int. Ed. 2002, 41, 2892.
[2] B. O×Regan, M. Gr‰tzel, Nature (London) 1991, 353, 737; M. K. Nazeeruddin, A. Kay, L. Rodicio, R.
Humphry-Baker, E. M¸ller, P. Liska, N. Vlachopoulos, M. Gr‰tzel, J. Am. Chem. Soc. 1993, 115, 6382; A.
Hagfeldt, M. Gr‰tzel, Chem. Rev. 1995, 95, 49; M. Gr‰tzel, A. Hagfeldt, Acc. Chem. Res. 2000, 33, 269; C.
Bignozzi, R. Argazzi, C. Kleverlaan, Chem. Soc. Rev. 2000, 29, 87; R. Argazzi, C. Bignozzi, G. Hasselmann,
G. Meyer, Inorg. Chem. 1998, 37, 4533; C. Bignozzi, E. Costa, M. Alebbi, I. Gillaizeau-Gauthier, F. Odobel,
P. Qu, G. Meyer, Inorg. Chem. 2001, 40, 6073.
[3] K. Kalyanasundaram, M. Gr‰tzel, Coord. Chem. Rev. 1998, 77, 374; B. V. Bergeron, G. J. Meyer, in
−Photovoltaics for the 21st Century II×, Eds. R. D. McConnell, and V. K. Kapur, The Electrochem. Soc. Inc.,
Pennington, NJ, 2001, p. 173.
[4] J. Aldrich-Wright, I. Greguric, R. Vagg, K. Vickery, P. Williams, J. Chromatogr., A 1995, 718, 436; X. He, L.
Wang, H. Chen, L. Xu, L. N. Ji, Polyhedron 1998, 17, 3161.
[5] J. Treadway, B. Loeb, R. Lopez, P. Anderson, F. Keene, T. Meyer, Inorg. Chem. 1996, 35, 2242.
[6] J. A. Treadway, G. F. Strouse, R. R. Ruminski, T. J. Meyer, Inorg. Chem. 2001, 40, 4508.
[7] W. Paw, R. Eisenberg, Inorg. Chem. 1997, 36, 2287.
[8] N. Garelli, P. Vierling, J. Org. Chem. 1992, 57, 3046.
[9] B. Sullivan, D. Salmon, T. Meyer, Inorg. Chem. 1978, 17, 3334; P. A. Lay, A. M. Sargeson, H. Taube, Inorg.
Synth. 1986, 24, 291.

2120
Helvetica Chimica Acta Vol. 86 (2003)
¬
[10] a) A. Arancibia, J. Concepcion, N. Daire, G. Leiva, A. M. Leiva, B. Loeb, R. Del Rio, R. Diaz, A. Francois,
M. Saldivia, J. Coord. Chem. 2001, 54, 323; b) H. Friebolin, −Basic One- and Two-Dimensional NMR
Spectroscopy×, VCH, Weinheim, 1991.
[11] G. Orellana, C. Alvarez, J. Santoro, Inorg. Chem. 1988, 27, 1025.
[12] −Spartan×, Version 5.0.3, Wavefunction Inc., 1998.
[13] J. C. Cobas, J. Cruces, J. Sardina, −MestRe-c 2.3a×, Universidad de Santiago de Compostela, 1995.
Received October 28, 2002