A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene moiety: Synthesis, characterization and its applications in transfer hydrogenation of ketones and dye sensitized solar cells

Article abstract of DOI:10.1016/j.poly.2014.12.046

The ruthenium(II) complex [Ru(bpy)₂L](PF₆)₂, where bpy is 2,2′-bipyridine and L is 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b′]dipyridine-2-one, was synthesized from the reaction of cis-Ru(bpy)₂Cl₂·2H₂O with L, and isolated as the hexafluorophosphate salt. The structure of L was unequivocally elucidated by single-crystal X-ray diffraction analysis. The new ruthenium(II) complex was thoroughly characterized by ¹H and ¹³C NMR spectroscopy, along with FTIR, UV-Vis and LC MS/MS Triple Quadrupole Mass spectroscopy and elemental analysis. The catalytic activity of [Ru(bpy)₂L](PF₆)₂ was tested in the transfer hydrogenation of various ketones in 2-propanol as both the solvent and hydrogen donor. The usage of [Ru(bpy)₂L](PF₆)₂ for the formation of a dye sensitized solar cell is also presented.

Full text of DOI:10.1016/j.poly.2014.12.046

Polyhedron 89 (2015) 55–61
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
A ruthenium(II) bipyridine complex containing a 4,5-diazafluorene
moiety: Synthesis, characterization and its applications in transfer
hydrogenation of ketones and dye sensitized solar cells
c
d
Akın Baysal a, Murat Aydemir a,b, Feyyaz Durap a,b, , Saim Özkar , Leyla Tatar Yıldırım ,
⇑
Yusuf Selim Ocak b,e
a Dicle University, Science Faculty, Department of Chemistry, TR-21280 Diyarbakır, Turkey
b Science and Technology Application and Research Center (DUBTAM), Dicle University, TR-21280 Diyarbakir, Turkey
c Middle East Technical University, Department of Chemistry, TR-06800 Ankara, Turkey
d Hacettepe University, Department of Engineering Physics, Beytepe, TR-06800 Ankara, Turkey
e Dicle University, Faculty of Education, Department of Science, TR-21280 Diyarbakir, Turkey
a r t i c l e i n f o
a b s t r a c t
The ruthenium(II) complex [Ru(bpy)2L](PF6)2, where bpy is 2,20-bipyridine and L is 1,5-dihydro-2-H-
cyclopenta[1,2-b:5,4-b0]dipyridine-2-one, was synthesized from the reaction of cis-Ru(bpy)2Cl2ꢀ2H2O
with L, and isolated as the hexafluorophosphate salt. The structure of L was unequivocally elucidated
by single-crystal X-ray diffraction analysis. The new ruthenium(II) complex was thoroughly characterized
by 1H and 13C NMR spectroscopy, along with FTIR, UV–Vis and LC MS/MS Triple Quadrupole Mass spec-
troscopy and elemental analysis. The catalytic activity of [Ru(bpy)2L](PF6)2 was tested in the transfer
hydrogenation of various ketones in 2-propanol as both the solvent and hydrogen donor. The usage of
[Ru(bpy)2L](PF6)2 for the formation of a dye sensitized solar cell is also presented.
Article history:
Received 12 September 2014
Accepted 29 December 2014
Available online 14 January 2015
Keywords:
N ligand
Catalyst
Transfer hydrogenation
DSSC
Ó 2015 Elsevier Ltd. All rights reserved.
X-ray
1. Introduction
Transition metal catalyzed transfer hydrogenation is a versatile
process for the reduction of multiple bonds to the corresponding
Ruthenium(II) complexes containing polypyridine ligands have
been investigated by many researchers due to their high catalytic
performance in homogeneous catalysis [1–3] and high solar power
conversion efficiency [4,5]. 4,5-Diazafluorene was reported over
four decades ago, but there exist only a few papers reporting the
use of 4,5-diazafluorene and its derivatives as ligands in catalytic
processes [6]. Jiang and Song [7] have reported the catalytic activ-
ity of [Rh(cod)(4,5-diazafluorenide)] in the hydrogenation of ole-
fins. The complex has been found to promote the hydrogenation
of terminal olefins, though it is not as active as Wilkinson’s catalyst
[7], without affecting the carbonyl groups in the substrates.
[Rh(4,5-diazafluorenide)(PPh3)2(H)2]Cl has also been found to be
an active catalyst in the hydrogenation of a variety of olefins,
including non-terminal ones [8]. Palladium-catalyzed aerobic
dehydrogenation in the presence of 4,5-diazafluoren-9-one as a
saturated compounds due to its easier and safer operation com-
pared to the classical hydrogenation by using molecular hydrogen
[15]. Carbonyls are known as one of the most versatile functional
groups for organic transformations. A general, mild and direct cat-
alytic route to convert a carbonyl group into the corresponding
alcohol would be highly desirable [3]. Over the last two decades,
a considerable amount of effort has been devoted to the design
and synthesis of new rhodium, ruthenium and iridium complexes
bearing C, N, O and P donor ligands for the transfer hydrogenation
of ketones [16,17].
Because energy demand and environmental pollution are
increasing all over the world, renewable energy sources have
become one of the most promising subjects. Among the other
renewable energy sources, dye-sensitized solar cells (DSSCs) repre-
sent the possibility of low cost and large-scale power production.
Ruthenium(II) complexes have been preferred as photosensitizers
or dyes in the fabrication of DSSCs. The most commonly used
photosensitizers are 2,20-bipyridine ruthenium(II) (2,20-bipyridine)
complexes with thiocyanate (NCS) ligands, such as cis-dithiocy-
ligand converts aliphatic aldehydes to
at ambient temperature [9–14].
a,b-unsaturated aldehydes
⇑
Corresponding author at: Department of Chemistry, Dicle University, TR-21280
Diyarbakır, Turkey. Tel.: +90 412 248 8550; fax: +90 412 248 8300.
E-mail address: fdurap@dicle.edu.tr (F. Durap).
anatobis-(2,20-bipyridine-4,40-dicarboxylate)ruthenium(II)
and N719) [18]. Many studies have been performed using NCS free
(N3
http://dx.doi.org/10.1016/j.poly.2014.12.046
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

56
A. Baysal et al. / Polyhedron 89 (2015) 55–61
complexes for DSSC because NCS is an ambidentate ligand, which
can coordinate either at the sulfur or at the nitrogen atom, and is
a monodentate ligand, which can be easily replaced [18–22].
Previously, we have designed a series of catalysts containing P-
donor ligands, such as aminophosphine, bis(phosphinoamine),
phosphinite and aminophosphine-phosphinite, for ketone reduc-
tion [23–28]. Herein we report the synthesis and characterization
of the [Ru(bpy)2L](PF6)2 complex, where bpy is 2,20-bipyridine
the reaction. After this period, a sample of the reaction mixture
was taken, diluted with acetone and analyzed immediately by
GC. Conversions obtained were related to the residual unreacted
ketone. The GC parameters were as follows: initial temperature,
110 °C; initial time, 1 min; solvent delay, 4.48 min; temperature
ramp 80 °C/min; final temperature, 200 °C; final time, 21.13 min;
injector port temperature, 200 °C; detector temperature, 200 °C;
injection volume, 2.0 lL.
and
L
is 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-
one, as shown in Scheme 1, with the aim of using it as an efficient
catalyst in the transfer hydrogenation of ketones.
2.3. Synthesis of [Ru(bpy)2L](PF6)2
Our report also includes the construction of a dye sensitized
solar cell (DSSC) using the NCS free [Ru(bpy)2L](PF6)2 complex as
photosensitizer on a nanocrystalline TiO2 film in light of previous
studies reporting efforts to develop new highly efficient sensitizers
which can absorb sunlight and inject an electron into the conduc-
tion band of nanocrystalline TiO2 [29–31].
To a hot solution of the ligand (0.10 g, 0.54 mmol) in ethanol, a
solution of cis-Ru(bipy)2Cl2ꢀ2H2O in the same solvent (5 mL) was
added dropwise over 15 min. The mixture was heated to reflux
temperature with stirring for 5 h, then the ethanol was removed.
The residue obtained was dissolved in a minimum amount of
water, then a saturated aqueous solution of [NH4][PF6] was added
dropwise until no more precipitate formed. The mixture was left to
stand overnight and filtered. The resulting bright red precipitate
was filtered off, dried and recrystallized from ethanol to afford
the pure complex (0.48 g, 73%). C31H24N6ORuP2F12 (887.49 g/
mol), calcd.: C 41.95, H 2.73, N 9.47; found: C 42.07, H 2.78, N
9.56%. ESI-MS m/z: 597.10 [Mꢂ2PF6]+. IR (KBr, cmꢂ1) ˆ: 3634 (O–
H), 1414, 1448 (Aromatic), 829 (PF6). 1H NMR (400.1 MHz,
DMSO-d6) d: {11.96 (br, 1H, OH), 8.81 (m, 3H), 8.73 (d, 1H,
J = 8.1 Hz), 8.23 (d, 1H, J = 5.4 Hz), 8.15–8.19 (m, 4H), 8.05 (t, 2H,
J = 7.82 Hz), 8.00 (d, 1H, J = 5.3 Hz), 7.8 (d, 2H, J = 5.3 Hz), 7.63 (t,
1H, J = 6.3 Hz), 7.57 (t, 1H, J = 6.3 Hz), 7.52 (t, 1H, J = 6.3 Hz),
7.44–7.42 (m, 3H), 6.67 (d, 1H, J = 8.1 Hz), dipyridine and aromatic
protons}, 4.29 (s, 2H, CH2); 13C NMR (100.6 MHz, DMSO-d6) d:
{173.67, 167.75, 166.23, 164.36, 163.44, 163.39, 162.94, 162.24,
161.15, 157.77, 157.06, 153.68, 151.12, 145.67, 143.05, 142.80,
142.61, 142.10, 140.01, 134.05, 133.26, 132.97, 132.67, 131.73,
131.23, 129.39, 128.94, 128.58, 121.40, 117.57, dipyridine and aro-
2. Experimental
2.1. Materials
Unless otherwise stated, solvents and materials were used as
received and the manipulations were performed in air. cis-Ru
(bipy)2Cl2ꢀ2H2O
and
1,5-dihydro-2H-cyclopenta[1,2-b:5,4-b0]
dipyridine-2-one (L) were prepared according to the published pro-
cedures [32,33]. NMR spectra were obtained in DMSO-d6 using a
Bruker AV 400 spectrometer. TMS (d: 0.00 ppm) was used as an
internal standard for the 1H NMR acquisition. A Shimadzu LC MS
8040, LC MS/MS Triple Quadrupole Mass Spectra instrument was
used for mass spectra analysis due to its inherent characteristics
of accurate mass measurements. UV–Vis spectra were recorded
with a Perkin Elmer Lambda 25 spectrometer; FTIR-ATR spectra
were recorded with a Perkin Elmer Spectrum 100 spectrometer.
The elemental analyses for carbon, hydrogen and nitrogen were car-
ried out on a Costech Combustion System CHNS-O instrument. Anal-
yses by gas chromatography (GC) were performed on a Schimadzu
2010 Plus gas chromatography equipped with a capillary column
matic carbons}, 41.51 (CH2); assignment was based on 1H–13
C
HETCOR and 1H–1H COSY spectra. UV–Vis, nm (
e
, L/mol cm); 243
(24850), 286 (75200), 344 (22100), 428 (12380), 459 (sh) (9730).
(5% biphenyl, 95% dimethylsiloxane) (30 m ꢁ 0.32 mm ꢁ 0.25
lm).
2.4. X-ray diffraction structure analysis
2.2. General procedure for the transfer hydrogenation of ketones
X-ray diffraction data were collected on an STOE IPDS 2 two cir-
cle diffractometer equipped using graphite-monochromated MoK
a
A typical procedure for the catalytic hydrogen transfer reaction
was as follows: A solution of the complex [Ru(bpy)2L](PF6)2], NaOH
(0.025 mmol) and the corresponding ketone (0.5 mmol) in
degassed iso-Pr-OH (5 mL) were refluxed until the completion of
radiation at room temperature. The structure was solved by direct
methods and refined using the programs SHELXS97 and SHELXL97
[34] respectively, in the WinGX package [35]. A full-matrix
least-squares refinement on F2 converged at R = 0.0334. For all
Scheme 1. Synthesis of [Ru(bpy)2L](PF6)2.

A. Baysal et al. / Polyhedron 89 (2015) 55–61
57
Table 1
non-hydrogen atoms anisotropic displacement parameters were
refined. All hydrogen atoms were taken from a difference Fourier
map and refined.
Crystal data and results of the structure refinement for 1,5-dihydro-2H-cyclo-
penta[1,2-b:5,4-b0]dipyridine-2-one, L.
Formula
C11H8N2O
189.19
293(2)
0.71073
monoclinic
P21/c
Formula weight (g/mol)
Temperature (K)
Wavelength (Å)
Crystal system
Space group
2.5. Formation and characterization of DSSC using the
[Ru(bpy)2L](PF6)2 complex
The DSSC structure was fabricated using a Solaronix test cell
titania photoanode. The electrode was sintered at 450 °C in quartz
tube furnace for 20 min to remove pollutants, was then cooled to
room temperature and immersed in a 1 mM ethanol solution of
the Ru complex for 4 h. The titania photoanode was removed from
the solution, washed with ethanol and dried with a heat-gun. A
Solaronix platinum coated glass cathode was used as a counter
electrode and it was fired at 450 °C in a quartz tube furnace for
10 min to reactivate the catalytic platinum layer. The dye coated
TiO2 and Pt electrodes were sealed together with a gasket so that
the electrolyte is confined in the cavity. The space left between
the two electrodes was filled with an electrolyte (iodide/tri-iodide
in a nitrile solvent from Solaronix) that ensures charge transporta-
tion through a redox couple. The solar cell area was 0.36 cm2. The
current–voltage measurements of the sample were performed by
means of a Keithley 2400 source meter under a solar Simulator
with 100 mW/cm2 illumination intensity and an AM1.5 global fil-
ter. The results were compared with a reference DSSC structure
formed by means of the N719 dye using same fabrication
procedures.
Unit cell dimensions
a (Å)
b (Å)
10.3155(7)
9.7068(4)
17.7402(13)
105.747(13)
1709.67(18)
8
1.431
yellow
c (Å)
b (°)
Cell volume (Å3)
Z
Calculated density [g/cm3]
Crystal colour
Crystal shape
Crystal size (mm)
F(000)
prism
0.52 ꢁ 0.47 ꢁ 0.41
768
Absorption coefficient (mmꢂ1
h-range for data collection (°)
Limiting indices
)
0.095
2.05–27.12
ꢂ13 6 h613, ꢂ11 6 k 6 12,
ꢂ22 6 l 6 22
Reflections collected/unique
Refinement method
Parameters
3768/2225
Full-matrix least-squares on F2
317
Goodness-of-fit (GOF) on F2
0.816
Final R indices [I > 2
r
(I)]
R1 = 0.0334, wR2 = 0.0658
0.128, ꢂ0.123
Largest difference in peak and hole
(e Å3)
Additional material available from Cambridge Crystallographic Data Center as
deposition No: CCDC 1008611 containing H-atom coordinates, thermal parameters
and the remaining bond lengths and angles.
3. Results and discussion
3.1. Synthesis and characterization of [Ru(bpy)2L](PF6)2
Table 2
Selected bond lengths (Å) and angles (°).
1,5-Dihydro-2H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-one,
L,
was prepared in two steps according to the literature procedure
[32]. An X-ray quality crystal of L was grown from the slow diffu-
sion method in a chloroform-diethyl ether solution. Compound L
crystallizes in the monoclinic system (P21/c), including two inde-
pendent molecules of the formula C11H8N2O in the asymmetric
O1–C1
N1–C1
N1–C5
N2–C10
N2–C11
C5–N1–C1
C11–N2–C10
C4–C6–C7
1.2448(15)
1.3736(16)
1.3629(16)
1.3470(17)
1.3344(15)
121.68(11)
114.23(12)
102.52(11)
O1A–C1A
N1A–C1A
N1A–C5A
N2A–C10A
1.2424(15)
1.3823(17)
1.3599(16)
1.3456(17)
1.3422(16)
122.22(12)
114.49(12)
102.86(11)
N2A–C11A
C5A–N1A–C1A
C11A–N2A–C10A
C4A–C6A–C7A
unit, with the cell parameters: a = 10.3155(7), b = 9.7068(4),
c = 17.7402(13) Å, b = 105.747(13)°, V = 1709.67(18) Å3 and Z = 8.
The ORTEP [36] drawing of the molecule is shown in Fig. 1.
The data collection details, crystal data and refinement param-
eters are listed in Table 1. Selected bond lengths and angles are
given in Table 2. Hydrogen bonding and the molecular packing
geometry of the ligand molecule was calculated with PLATON
[37] and hydrogen bonding geometries are summarized in Table 3.
The two independent molecules in the asymmetric unit are
stacked along the a/b-axis. The two diazafluorenylidene fragments
are each nearly planar, excluding the H atoms of the CH2 group,
and are almost parallel each other, the dihedral angle between
these planes is 7.79(2)° [38].
The single crystal X-ray structural analysis of the ligand reveals
that it has a porous geometry which is stabilized by intermolecular
interactions of both hydrogen-bonds and stacking between the
diazafluorene moieties (Fig. 2).
The molecular packing in the solid state is porous structure
along the c-axis, as shown in Fig. 3a, where green and blue colours
represent M1and M2, respectively. Some special distances of the
packing are given in Fig. 3b.
Fig. 1. The molecular structure of 1,5-dihydro-2H-cyclopenta[1,2-b:5,4-b0]dipyri-
dine-2-one, (L) with the atomic numbering scheme (the crystal structure has two
independent molecules in the asymmetric unit).
A cationic ruthenium(II) complex was prepared by the reaction
of 1,5-dihydro-2H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-one (L)

58
A. Baysal et al. / Polyhedron 89 (2015) 55–61
Table 3
Structural parameters of the hydrogen bonds between the donor (D), acceptor (A) and
hydrogen (H).
D–Hꢀ ꢀ ꢀA
D–H (Å)
Aꢀ ꢀ ꢀH (Å)
Dꢀ ꢀ ꢀA (Å)
D–Hꢀ ꢀ ꢀH (°)
N1–H1ꢀ ꢀ ꢀN2Ai
0.900(16)
0.952(17)
1.006(15)
0.957(15)
1.002(15)
2.329(16)
1.788(17)
2.278(15)
2.572(15)
2.574(15)
3.1999(16)
2.7274(15)
3.2705(17)
3.3896(19)
3.5495(19)
162.9(13)
168.5(14)
169.0(12)
143.5(12)
164.4(11)
N1A–H1Aꢀ ꢀ ꢀO1ii
C3–H3ꢀ ꢀ ꢀO1iii
C8A–H8Aꢀ ꢀ ꢀO1Aiv
C10A–H10Aꢀ ꢀ ꢀN2ii
Symmetry codes [i: x, 1 + y, z; ii: x, ꢂ1 + y, z; iii: 1 ꢂ x, ꢂ1/2 + y, 1/2 ꢂ z; iv: x,
1/2 ꢂ y, ꢂ1/2 + z].
Fig. 4. Keto-enol form of 1,5-dihydro-2H-cyclopenta[1,2-b:5,4b0]dipyridine-2-one,
L.
Table 4
Transfer hydrogenation of acetophenone with iso-PrOH, catalyzed by [Ru(bpy)2L]
(PF6)2.
Fig. 2. Stacking geometry and details of the distances in the crystal structure of
1,5-dihydro-2H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-one, L [38].
e
Entry
S/Cat/NaOH
Time (h)
Conversion (%)d
TOF (hꢂ1
)
1
2
3
100:1:5a
100:1b
24
48
4
Trace
<3
99
–
–
25
100:1:5c
Reaction conditions:
a
At room temperature; acetophenone/Cat./NaOH, 100:1:5.
Refluxing in iso-PrOH; acetophenone/Cat. 100:1, in the absence of base.
Refluxing in iso-PrOH; acetophenone/Cat./NaOH, 100:1:5.
Determined by GC (three independent catalytic experiments).
Referred at the reaction time indicated in column; TOF = (mol product/mol
(a)
b
c
d
e
Cat.) ꢁ hꢂ1
.
see experimental section). The 1H NMR spectrum of the complex
shows peaks for the protons of both ligands. It is noteworthy that
the observation of a broad 1H NMR signal at d(H) 11.96 ppm is due
to the hydroxyl H-atom. This suggests that the OH group in the
ligand L does not participate in metal binding. Compared with
the IR spectrum of the ligand, the band at 1651 cmꢂ1 due to
ˆ(CO) in the ligand L disappeared upon complex formation. The
weak absorption at 3634 cmꢂ1 is attributed to ˆ(O–H) in the com-
plex. The disappearance of a sharp signal at 1651 cmꢂ1 and the
appearance of new broad band at 3634 cmꢂ1 in the IR spectrum
and a broad signal at 11.96 ppm in the 1H NMR spectrum indicate
the isomerisation of the C@O group to its enol form with the
involvement of the NH group prior to complex formation. The pres-
ence of the PFꢂ6 group in the complex is also evident from the IR
absorption band at 829 cmꢂ1. In the electron spray ionization mass
3.647 Å
4.987 Å
2.381Å
(b)
3.577 Å
spectrum of the complex,
a signal for the complex cation
[Mꢂ2PF6]+ was observed at m/z 597.10 for the complex, consistent
with the expected value.
The electronic absorption spectrum of complex in methanol is
mainly dominated by absorptions at 243, 286 and 344 nm, and a
weak low energy band at 428 nm together with a shoulder at
459 nm, typical of ruthenium(II) tris(bipyridine) derivatives [39],
with reference to earlier studies on related ruthenium(II) polypyr-
idine systems [40]. The higher energy absorption bands are attrib-
uted to intra ligand transitions, while the low energy bands are
assigned to metal-to-ligand charge transfer transitions, which are
not observed in the electronic absorption spectrum of the free
ligand.
Fig. 3. Molecular packing geometry of the structure along the c-axis [38].
with cis-dichlorobis(2,20-bipyridine) ruthenium(II) in ethanol. The
ruthenium(II) complex was isolated as the analytically pure hexa-
fluorophosphate salt, [Ru(bpy)2L](PF6)2, where L is the enol form of
1,5-dihydro-2H-cyclopenta[1,2-b:5,4b0]dipyridine-2-one (Fig.
and Scheme 1).
4
The red complex [Ru(bpy)2L](PF6)2 was characterized by 1H and
13C NMR, FTIR, LC–MS, UV–Vis and elemental analysis (for details

A. Baysal et al. / Polyhedron 89 (2015) 55–61
59
Table 5
[Ru(bpy)2L](PF6)2 as a catalyst in 2-propanol both as a solvent
and hydrogen source. Initially, to an iso-PrOH solution of the Ru(II)
complex, an appropriate amount of acetophenone and NaOH/iso-
PrOH solution were added at room temperature (acetophenone/
Cat./NaOH; 100:1:5 M ratios). At room temperature no noticeable
formation of 1-phenylethanol was observed (Table 4, entry 1). A
blank experiment was performed to demonstrate that the transfer
hydrogenation does not occur in the absence of catalyst. The cata-
lytic activity of the complex is improved by increasing the reaction
temperature to 82 °C (Table 4, entry 3). As seen in Table 4, the com-
plex is very active, leading to a quantitative transformation of the
acetophenone with a complex/NaOH ratio of 1:5 at 82 °C. Further-
more, as can be inferred from Table 4 (entry 2), the presence of
base (NaOH) is necessary to observe an appreciable conversion.
The base most likely facilitates the formation of ruthenium alkox-
ide by abstracting the proton of the alcohol and subsequently the
alkoxide undergoes b-elimination to give hydride, which is an
active species in this reaction [41,42]. The results of the optimiza-
tion studies showed clearly that excellent conversions were
achieved in the reduction of acetophenone to 1-phenylethanol
when the complex [Ru(bpy)2L](PF6)2 was used as a catalytic pre-
cursor with a substrate to catalyst molar ratio of 100:1 at reflux
temperature in iso-PrOH (Table 4).
Transfer hydrogenation results for substituted acetophenones with the catalyst
[Ru(bpy)2L](PF6)2.a
c
Entry
R
Time (h)
Conversion (%)b
TOF (hꢂ1
)
1
2
3
4
5
6
7
4-F
4-Cl
4-Br
4-NO2
4-Me
2-MeO
4-MeO
3
4
4
3
9
7
10
98
98
1
1
33
25
25
33
11
14
<10
99 0.5
99 0.5
97
99 0.5
98
2
1
Reaction conditions:
a
Catalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 mL), NaOH
(0.025 mmol), 82 °C, the concentration of the acetophenone derivatives is 0.1 M.
b
The purity of the compounds was checked by 1H NMR and GC (three inde-
pendent catalytic experiments), yields are based on aryl ketone.
c
TOF = (mol product/mol Cat.) ꢁ hꢂ1
.
3.2. Catalytic studies
After optimization of the reaction conditions, we also examined
acetophenone derivatives as substrates for transfer hydrogenation
using the [Ru(bpy)2L](PF6)2, complex in 2-propanol. A variety of
In a preliminary study, we examined the transfer hydrogenation
of acetophenone to produce 1-phenylethanol using the complex
Table 6
Transfer hydrogenation results for substituted alkyl phenyl ketones with the catalyst.
Entry
1
Time (h)
5
Substrate
Product
Conversion (%)a
98
1
O
O
O
O
OH
OH
OH
OH
2
3
4
5
6
7
8
99 0.5
98
97
98
97
1
2
1
1
12
4
O
O
OH
OH
4
7
8
7
9
98 0.5
O
OH
96
1
O
OH
Reaction conditions: [Ru(bpy)2L](PF6)2 catalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 mL), NaOH (0.025 mmol), 82 °C, the concentration of alkyl phenyl ketones is
0.1 M.
a
The purity of the compounds was checked by 1H NMR and GC (three independent catalytic experiments), yields are based on aryl ketone.

60
A. Baysal et al. / Polyhedron 89 (2015) 55–61
cated using the N719 photosensitizer were evaluated as 720 mV,
25.74 mA/cm2, 0.45% and 8.15%, respectively. The lower power con-
version efficiency can be attributed the weaker binding of
[Ru(bpy)2L](PF6)2 to TiO2 with respect to the N719 dye. Zalas
et al. [50] synthesized a new dinuclear dendritic-like ruthenium
dye which consists of two trisbipyridyl ruthenium(II) derivatives
clipped with an ethyl 3,5-diethynylbenzoate group. They have pre-
sented spectroscopic and electrochemical characterization of the
new compound and used it in the fabrication of a DSSC. They have
reported that the solar cell formed using the new dinuclear den-
dritic-like ruthenium dye had 60.5% FF and 0.32% photon-to-cur-
rent conversion efficiency values. Furthermore, Pellegrin et al.
[51] obtained ruthenium polypyridine complexes as sensitizers in
NiO based p-type dye-sensitized solar cells and analyzed the effects
of the anchoring groups. They determined the efficiency of the solar
cells as being between 0.0065 and 0.025%. The FF values of the cells
were about 0.34% for all samples. Therefore, it can be said that the
efficiency of the cell based on [Ru(bpy)2L](PF6)2 is satisfying on
comparison with cells formed using similar compounds.
Fig. 5. Current density–voltage measurement of the DSSC structure.
simple ketones (substrate/catalyst = 100:1) can be transformed
into their corresponding secondary alcohols with high conversions,
as illustrated in Table 5. An examination of the catalytic activity of
[Ru(bpy)2L](PF6)2 showed that it is an efficient catalyst affording
almost quantitative transformation of the ketones within a short
time (Table 5). As expected, the electronic properties (the nature
and position) of the substituents on the phenyl ring of the ketone
caused the changes in the extent of reduction. To ensure that the
observed results could be attributed to purely electronic effects
[43–45], para- and ortho-substituted acetophenone derivatives
were tested for transfer hydrogenation. The results indicated that
strong electron withdrawing substituents, such as F, NO2 and Cl,
speed up the reaction (Table 5). Conversely, the most electron-
donating substituents, (2- or 4-methoxy) led to lower conversions.
It is well-known that the presence of an electron withdrawing
group can ease hydrogen transfer reactions [46,47], which has
been attributed to the hydridic nature of the reducing species
involved. As such, substrates with fluoro or nitro groups undergo
higher conversions owing to rapid hydride transfer, while sub-
strates with electron-donating substituents (2- or 4-methoxy)
undergo a slower reaction in a more controlled manner [48,49].
The results indicate that high conversions were achieved in the
reduction of acetophenone derivatives when [Ru(bpy)2L](PF6)2
was used as the catalyst precursor.
4. Conclusions
In the present study, the cationic Ru(II) complex [Ru(bpy)2L]2+
was synthesized in high yield by the reaction of cis-Ru(bpy)2Cl2
ꢀ2H2O with 1,5-dihydro-2H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-
one, L. The crystal structure of L was also determined by single
crystal X-ray diffraction. The [Ru(bpy)2L](PF6)2 complex was found
to be a highly active homogeneous catalyst in the reduction of var-
ious ketones via hydrogen transfer from 2-propanol and readily
lead to secondary alcohols in high yields. In addition, a dye sensi-
tized solar cell based on the [Ru(bpy)2L](PF6)2 complex with 0.82%
solar conversion efficiency is reported.
Acknowledgements
Partial support from the Dicle University Research Fund (Project
Nos. 02-FF-33, DÜBAP-14-FF-75) and the Turkish Academy of
Sciences is gratefully acknowledged. The analysis was conducted
at Dicle University Science and Technology Application and
Research Center (DUBTAM). The authors thank Canan Kazak for
the X-ray single crystal data collection.
Appendix A. Supplementary data
We also carried out further experiments to investigate the effect
of the bulkiness of the alkyl groups on the catalytic activity and the
results were given in Table 6. A variety of simple aryl alkyl ketones
were transformed to the corresponding secondary alcohols. It was
observed that the activity is considerably dependent on the steric
hindrance of the alkyl group. The reactivity is gradually reduced
by increasing the bulkiness of the alkyl groups [45–49]. Prompted
by the high catalytic activities obtained in these studies, we next
extended our studies to include hydrogenation of various simple
ketones. An investigation of the catalytic activity of [Ru(bpy)2L]
(PF6)2 showed that it is an effective catalyst, enabling almost quan-
titative transformation of the ketones in short times (Table 6).
CCDC 1008611 contain the supplementary crystallographic
data for 1,5-dihydro-2-H-cyclopenta[1,2-b:5,4-b0]dipyridine-2-
one. These data can be obtained free of charge via http://www.
ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
References
[1] S.A. Moya, M. Vidal, G. Abarca, C. Martinez, V. Guerchais, H. Le Bozec, M.T.
Garland, S. Rodriguez, P. Aguirre, Inorg. Chem. Commun. 13 (2010) 1519.
[2] S.A. Moya, M. Vidal, K. Brown, C. Negrete-Vergana, G. Abarca, P. Aguirre, Inorg.
Chem. Commun. 22 (2012) 146.
[3] P. Stepnicka, J. Ludvik, J. Canivet, G. Süss-fink, Inorg. Chim. Acta 359 (2006)
2369.
3.3. Photovoltaic properties of DSSC based on [Ru(bpy)2L](PF6)2
[4] D. Martineau, M. Beley, P.C. Gros, S. Cazzanti, S. Caramori, C.A. Bignozzi, Inorg.
Chem. 46 (2007) 2272.
[5] D. Martineau, M. Beley, P.C. Gros, J. Org. Chem. 71 (2) (2006) 566.
[6] K. Kloc, J. Mlochowski, Z. Szule, Heterocycles 9 (1978) 849.
[7] H. Jiang, D. Song, Organometallics 27 (2008) 3587.
[8] H. Jiang, E. Stepowska, D. Song, Eur. J. Inorg. Chem. (2009) 2083
[9] W. Gao, Z. He, Y. Qian, J. Zhao, Y. Huang, Chem. Sci. 3 (2012) 883.
[10] M. Piotrowicz, J. Zakrzewski, Organometallics 32 (2013) 5709.
[11] A.N. Campbell, S.S. Stahl, Acc. Chem. Res. 45 (2012) 851.
[12] T.N. Diao, J.J. Wadzinski, S.S. Stahl, Chem. Sci. 3 (2012) 887.
The current voltage measurements of the DSSC structure formed
using the Ru complex are presented in Fig. 5. The open circuit
photovoltage (VOC) and short circuit photocurrent density (JSC) are
determined as 435 mV and 3.05 mA/cm2 from Fig. 5, respectively.
Using the VOC and JSC values, the fill factor (FF) and solar to electric-
ity conversion efficiency (
g) were calculated as 0.56% and 0.82%,
respectively. The VOC, JSC, FF and
g
of the reference solar cell fabri-

A. Baysal et al. / Polyhedron 89 (2015) 55–61
61
[13] A.N. Campbell, P.B. White, I.A. Guzei, S.S. Stahl, J. Am. Chem. Soc. 132 (2010)
[32] A. Baysal, F. Durap, B. Gümgüm, L.T. Yıldırım, D. Ülkü, A.D. Bog˘a, S. Özkar, Helv.
Chim. Acta 90 (2007) 1211.
15116.
[14] A. Kilic, F. Durap, M. Aydemir, A. Baysal, E. Tas, J. Organomet. Chem. 693 (2008)
2835.
[33] B.P. Sullian, D.J. Salmon, T.J. Meyer, Inorg. Chem. 17 (1978) 3334.
[34] G.M. Shelx, Sheldrick, Acta Cryst. A 64 (2008) 112.
[35] G.X. Win, L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[36] ORTEP 3: L.J. Farrugia, J. Appl. Cryt. 30 (1997) 565.
[37] PLATON: A.L. Spek, Acta Cryst. D65 (2009) 148.
[15] Y. Himeda, N. Onozawa-Komatsuzaki, H. Sugihara, H. Arakawa, K. Kasuga, J.
Mol. Catal. A: Chem. 195 (2003) 95.
_
[16] H. Türkmen, I. Kani, B. Çetinkaya, Eur. J. Inorg. Chem. (2012) 4494
[17] O. Dayan, N. Özdemir, Z. Sßerbetçi, M. Dinçer, B. Çetinkaya, Inorg. Chim. Acta
[38] MERCURY: C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R.
Taylor, M. Towler, J. van de Streek, J. Appl. Cryst. 39 (2006) 453.
[39] I.K. Shoeb, E.B. Amy, D.S. Gregory, S. Milan, M.G. Mark, Inorg. Chem. 38 (1999)
2411.
[40] A. Juris, U. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. Von Zelewsky,
Coord. Chem. Rev. 84 (1988) 85.
[41] H. Doucet, T. Ohkuma, K. Murata, T. Yokozawa, M. Kozawa, E. Katayama, F.A.
England, T. Ikariya, R. Noyori, Angew. Chem. Int. Ed. 37 (1998) 1703.
[42] H. Zhang, B.C. Yang, Y.Y. Li, Z.R. Donga, J.X. Gao, H. Nakamura, K. Murata, T.
Ikariya, J. Chem. Com., Chem. Commun. (2003) 142
[43] R. Guo, X.H. Chen, C. Elphelt, D. Song, R.H. Morris, Org. Lett. 7 (2005) 1757.
[44] P. Pelagatti, M. Carcelli, F. Calbiani, C. Cassi, L. Elviri, C. Pelizzi, U. Rizzotti, D.
Rogolino, Organometallics 24 (2005) 5836.
392 (2012) 246.
[18] C. Dragonetti, A. Valore, A. Colombo, D. Roberto, V. Trifiletti, N. Manfredi, M.M.
Salamone, R. Ruffo, A. Abbotto, J. Organomet. Chem. 714 (2012) 88.
[19] K.C.D. Robson, B.D. Koivisto, A. Yella, B. Sporinova, M.K. Nazeeruddin, T.
Baumgartner, M. Gratzel, C.P. Berlinguette, Inorg. Chem. 50 (2011) 5494.
[20] C. Dragonetti, A. Colombo, M. Magni, P. Mussini, F. Nisic, D. Roberto, R. Ugo, A.
Valore, A. Valsecchi, P. Salvatori, M.G. Lobello, F.D. Angelis, Inorg. Chem. 52
(2013) 10723.
[21] T. Bessho, E. Yoneda, J.H. Yum, M. Guglielmi, I.T.H. Imai, U. Rothlisberger, M.K.
Nazeeruddin, M. Gratzel, J. Am. Chem. Soc. 131 (2009) 5930.
[22] S.H. Wadman, J.M. Kroon, K. Bakker, R.W.A. Havenith, G.P.M. van Klink, G.V.
Koten, Organometallics 29 (2010) 1569.
[23] M. Aydemir, N. Meriç, A. Baysal, J. Organomet. Chem. 720 (2012) 38.
[24] C. Kayan, N. Meriç, M. Aydemir, Y.S. Ocak, A. Baysal, H. Temel, Appl.
Organomet. Chem. 28 (2014) 127.
[45] J.W. Faller, A.R. Lavoie, Organometallics 20 (2001) 5245.
[46] J.-X. Gao, X.-D. Yi, P.-P. Xu, C.-L. Tang, H.-L. Wan, T. Ikariya, J. Organomet.
Chem. 592 (1999) 290.
[25] F. Ok, M. Aydemir, F. Durap, A. Baysal, Appl. Organomet. Chem. 28 (2014) 38.
[26] F. Durap, M. Aydemir, D. Elma, A. Baysal, Y. Turgut, C. R. Chimie 16 (2013) 363.
[27] F. Durap, M. Aydemir, A. Baysal, D. Elma, B. Ak, Y. Turgut, Inorg. Chim. Acta 411
(2014) 77.
[47] J.-X. Gao, H. Zhang, X.-D. Yi, P.-P. Xu, C.-L. Tang, H.-L. Wan, K.-R. Tsai, T. Ikariya,
Chirality 12 (2000) 383.
[48] J.-S. Chen, Y.-Y. Li, Z.-R. Dong, B.-Z. Li, J.-X. Gao, Tetrahedron Lett. 45 (2004)
8415.
[28] N. Meric, F. Durap, M. Aydemir, A. Baysal, Appl. Organomet. Chem. 28 (2014)
803.
[29] Y. Hou, D. Wang, X.H. Yang, W.Q. Fang, B. Zhang, H.F. Wang, H.G. Yang, Nat.
Commun. 4 (2013) 1583.
[49] Z.-R. Dong, Y.-Y. Li, J.-S. Chen, B.-Z. Li, Y. Xing, J.-X. Gao, Org. Lett. 7 (2005)
1043.
[50] M. Zalas, B. Gierczyk, M. Klein, K. Siuzdak, T. Pe˛dzin´ ski, T. Łuczak, Polyhedron
67 (2014) 381.
[30] X. Yin, Z. Xue, L. Wang, Y. Cheng, B. Liu, ACS Appl. Mater. Inter. 4 (3) (2012)
1709.
[51] Y. Pellegrin, L. Le Pleux, E. Blart, A. Renaud, B. Chavillon, N. Szuwarski, F.
Odobel, J. Photochem. Photobiol. A: Chem. 219 (2) (2011) 235.
[31] Y. Yu, K. Wu, K. Shen, K.D. Wang, Eur. Phys. J. Appl. Phys. 61 (01) (2013) 10201.