Mono- and Diruthenium, Symmetrical and Unsymmetrical Complexes Bridged by Pyrene Derivatives: Experimental and Theoretical Studies

Article abstract of DOI:10.1002/ejic.201700621

New mono- and diruthenium, symmetrical and unsymmetrical complexes, bridged by a new cyclometalating 1,3,6,8-tetra(4-substituted-2-pyridyl)pyrene derivative containing the solubilizing group 2,2-dimethylpropyloxy, with the terminal 4′-phenyl-2,2′:6′,2′′-terpyridine ligands containing diethylamine and a 2-ethynyl-9,9-dioctylfluorene moiety, were synthesized and thoroughly characterized. Thermal studies show that the obtained complexes retain high thermal stability. Spectroscopic studies show the metal-to-ligand charge-transfer excitation. Further, electrochemical studies show delocalization of the electronic charge (mixed valance). In addition, density functional theory and time-dependent density functional theory calculations have provided more detail about the structural properties and a deeper understanding of the experimental results. All of the obtained results show the considerable differences between the mono- and diruthenium and symmetrical and unsymmetrical complexes.

Full text of DOI:10.1002/ejic.201700621

A Journal of
Accepted Article
Title: Mono- and bisruthenium, symmetrical and unsymmetrical
complexes bridged by pyrene derivative - experimental and
theoretical studies
Authors: Dawid Zych, Aneta Slodek, Michał Pająk, Stanisław
Krompiec, Grzegorz Spólnik, and Witold Danikiewicz
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700621
Link to VoR: http://dx.doi.org/10.1002/ejic.201700621

10.1002/ejic.201700621
European Journal of Inorganic Chemistry
FULL PAPER
Mono- and bisruthenium, symmetrical and unsymmetrical
complexes bridged by pyrene derivative - experimental and
theoretical studies
Dawid Zych*[a], Aneta Slodek[a], Michał Pająk[a], Stanisław Krompiec[a], Grzegorz Spólnik[b],
Witold Danikiewicz[b]
donating and electron-withdrawing groups) [13]. The influence of
the changing of substituents in the bridge pyrene ligand has
Abstract: New mono- and bisruthenium, symmetrical and
unsymmetrical complexes bridged by new cyclometalating 1,3,6,8-
been relatively unexplored, only two were checked. Binuclear
tetra(4-substituted-2-pyridyl)pyrene derivative containing solubilizing
complexes of ruthenium are comprehensively experimentally as
group - 2,2-dimethylpropyloxy with the terminal 4'-phenyl-2,2':6',2''-
well as theoretically studied while the monoruthenium
complexes need to be more investigated. What is more, all
described in the literature binuclear complexes containing
pyrene as a bridge are symmetrical.
In this study, we present the synthesis with efficient way of
purification of novel mono- (3)Ru(TPY1) (A1) and bisruthenium,
terpyridine ligands containing diethylamine and 2-ethynyl-9,9-
dioctylfluorene moiety were synthesized and thoroughly
characterized. Thermal studies showed that obtained complexes
retain high thermal stability. Spectroscopic studies showed the
metal-to-ligand-charge-transfer (MLCT) excitation. What is more, the
electrochemical studies showed delocalization of the electronic
charge (mixed-valance). In addition, density functional theory (DFT)
and time-dependent-density functional theory (TD-DFT) calculations
were performed to provide more details about structural properties
and deeper understanding of the experimental results. All obtained
results showed the considerable differences between mono- and
bisruthenium and symmetrical and unsymmetrical complexes.
symmetrical
(TPY1)Ru(3)Ru(TPY1)
(A2),
(TPY2)Ru(3)Ru(TPY2)
(A3) and
unsymmetrical
(TPY1)Ru(3)Ru(TPY2) (A4) complexes bridged by new 1,3,6,8-
tetra(4-substituted-2-pyridyl)pyrene derivative (3) containing
solubilizing group i.e. 2,2-dimethylpropyloxy. The terminal
ligands contain electron-rich substituents, namely N,N-
diethylamine (TPY1) and 2-ethynyl-9,9-dioctylfluorene (TPY2), in
the para position of the phenyl ring of terpyridine. The ligands
TPY1 and TPY2 were intentionally chosen to examine their
effect on optical and electronic properties of the formed
complexes. These substituents have emerged to examine the
influence of replacement fluorene group by diethylamine unit
possessing stronger electron-donating ability on photophysical
properties of the desired complexes A1–A4, including
absorption, band gaps, HOMO and LUMO. On the other hand,
the presence of acetylene linker in TPY2 can affect the
geometry of resulting complexes and cause better delocalization
of the excited electron on the ligand connected with the
conjugated unit which better stabilizes the LUMO orbital [14].
Moreover, spectroscopic, electrochemical and theoretical
studies have been investigated in details.
Introduction
Ruthenium
complexes
bridged
by
1,3,6,8-
tetrasubstituted pyrene, 2,3,5,6-tetrasubstituted pyrazine, and
1,2,4,5-tetrasubstituted benzene derivatives have been the
subject of studies of a number of research groups for twenty
years [1-4]. The interest of this kind of compounds is due to their
appealing and unique electronic properties, such as wide
electronic absorption spectra in the UV/Vis range, tunable
potential energy and possible change between different
oxidation states [5]. Moreover, ruthenium complexes have the
ability to undergo metal-to-ligand-charge-transfer (MLCT)
excitation and delocalization of the electronic charge (mixed-
valance) [6]. What is more, they can be used in many
applications, such as information storage [7], molecular wires [8],
dynamic aircraft camouflage [9], electrochromic uses [10] and
others. The wide range of interesting properties and potential
applications is a reason that various ruthenium complexes have
drawn great interest and new systems should be still developed.
Complexes of type [(tpy)M(NCN-pyrene-NCN)M(tpy)]n+ where
tpy is a terpyridine ligand, NCN-pyrene-NCN is a polydentate
cyclometalating pyrene ligand and M is ruthenium metal have
been investigated only by one research group. Yu-Wu Zhong, et
al. began studies with cyclometalated mono- and bisruthenium
complexes bridged by the simple derivative of pyrene, 1,3,6,8-
tetra(2-pyridyl)pyrene [11]. The same research team showed the
other bridging ligand 1,3,6,8-tetrakis(1-butyl-1H-1,2,3-triazol-4-
yl)pyrene [12]. Using this kind of ligands as a core of complex do
not provide good solubility, what is important in further research
for the application. It was found that electronic properties of the
mentioned above complexes are strongly dependent on the
substituents in terminal ligands and their nature (electron-
Results and Discussion
Synthesis and structural characterization
The synthesis of the bridge i.e. 1,3,6,8-tetra(4-(2,2-
dimethylpropyloxy)-2-pyridyl)pyrene 3 is presented in Scheme 1.
The first step was based on well-known reaction bromination of
commercially available pyrene, what resulted in 1,3,6,8-
tetrabromopyrene 1 in 98% yield [15]. The Suzuki-Miyaura
coupling reaction between 1 and bis(pinacolato)diboron with
catalyst [Pd(pddf)2Cl2] afforded to 1,3,6,8-tetrakis(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene 2 in 75% yield [16].
The target derivative 3 was synthesized in Suzuki-Miyaura Pd-
catalyzed cross-coupling reaction between tetrasubstituted
boronic
acid
pyrene
derivative
2
and
4-(2,2-
dimethylpropyloxy)pyridine what resulted in the product as a
yellow solid in 62% yield (for a detailed description of synthesis
see Supporting Information).
[a]
[b]
Institute of Chemistry, Faculty of Mathematics, Physics and
Chemistry, University of Silesia, Szkolna 9, 40-007 Katowice,
Poland
E-mail: dawidzych92@gmail.com
Institute of Organic Chemistry, Polish Academy of Sciences,
Kasprzaka 44/52, 01-224 Warszawa 42, Poland
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.201700621
European Journal of Inorganic Chemistry
FULL PAPER
CH
O
H C
3
3
H C
CH
3
3
O
O
N
N
H C
CH
CH
3
3
H3
C
CH3
B
B
Br
Br
H C
3
O
O
3
O
O
O
H3
C
CH3
H3
H3
C
C
CH3
CH3
a
b
c
H3
C
CH3
CH3
O
O
H C
3
CH
3
B
B
O
Br
Br
H3
C
H C
3
CH
3
N
N
O
H C
CH
3
3
CH
H C
3
3
1 (Y=98%)
Scheme 1. Synthesis route to tetrasubstituted pyrene intermediates 1,
2 (Y=75%)
3 (Y=62%)
and 3. Reagents and reaction conditions: a) Br2, PhNO2, reflux, 16 h;
2
b) bis(pinacolato)diboron, KOAc, [PdCl2(dppf)], PhMe, 90 ⁰C, 24 h; c) 2-bromo-4-(2,2-dimethylpropyloxy)pyridine, K3PO4*3H2O, [Pd(PPh3)4], DME/H2O, 105 ⁰C,
48 h.
cross-coupling reaction of 4 with trimethylsilylacetylene (TMSA)
catalyzed by [Pd(PPh3)4] gave 4'-(4-ethynylphenyl)-2,2':6',2''-
terpyridine 5 in 92% yield which was reacted with 2-iodo-9,9-
dioctylfluorene by using [Pd]/[Cu]-catalyzed Sonogashira cross-
coupling reaction what resulted in TPY2 as a dark yellow oil in
60% yield [18,19].
Scheme 2 shows the synthesis routes to terpyridine ligands
TPY1 and TPY2. First step was conducted based on described
in the literature procedure from commercially available
appropriate 4-substituted benzaldehyde and 2-acetylpyridine in
Kröhnke reaction and resulted in TPY1 as a green solid in 34%
yield or 4'-(4-bromophenyl)-2,2':6',2''-terpyridine 4, respectively,
whereas 4 was used in the next step [17]. The Sonogashira
H C
3
N
CH
3
H C
N
CH
3
3
a
H
C
8
17
H
O
H
C
8
17
N
N
N
H
TPY1 (Y=34%)
CH
3
N
Br
O
H
O
b
c, d
e
N
N
N
N
N
N
N
N
N
Br
5 (Y=92%)
TPY2 (Y=60%)
4 (Y=42%)
Scheme 2. Synthesis of compounds TPY1, TPY2 and 4, 5. Reagents and conditions: a) KOH, NH3 aq, EtOH, reflux, 16 h; b) KOH, NH3 aq, EtOH, room temp.,
24 h; c) TMSA, [Pd(PPh3)4], CuI, NEt3, reflux, 16 h; d) KF, THF, MeOH, room temp., 24 h; e) 2-iodo-9,9-dioctylfluorene, [Pd(PPh3)4], CuI, THF, NEt3, 78 ⁰C, 48 h.
Ruthenium complexes with appropriate terpyridine ligand
(TPY)RuCl3 were synthesized in satisfactory yields according to
the well-known procedure [20] and used without any purification
in reaction with silver triflate (AgOTf) what resulted in a product
with labile triflate group [21]. Obtained in this way intermediate
was reacted with neutral pyrene ligand 3 (Scheme 3). The final
obtained based on the same procedure described above with
minor modification; monoruthenium complex A1 was added
instead of neutral pyrene ligand (Scheme 4). The product A4
was obtained in 17% yield as a black solid.
All compounds were fully characterized by nuclear magnetic
resonance spectroscopy NMR (1H for A1–A4 and 13C for A1),
high-resolution mass spectrometry (HRMS), and elemental
analysis. The experimental isotopic patterns compared with
theoretical for A1 and A2 are depicted in Figure 1, for more
details see Experimental section and Supporting Information
(Figure S6-S14).
complexes A1–A3 were precipitated by addition of KPF6(aq)
.
Sequential column chromatography (silica gel chromatography
followed by size-exclusion chromatography) was required to
isolate the pure product. Respective proportions of reactants
allowed to obtain monoruthenium A1 in 56% yield and
bisruthenium A2 (48%) and A3 (50%) complexes as black solids.
Moreover, the unsymmetrical bisruthenium complex A4 was
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10.1002/ejic.201700621
European Journal of Inorganic Chemistry
FULL PAPER
PF
6
CH3
CH3
H3
H3C
C
H3
C
CH3
O
O
+
N
N
CH
N
N
N
3
3
N
Ru
+
N
N
CH
CH3
CH3
H3
H3C
C
H3
C
CH3
O
O
O
O
CH3
CH3
H3
C
H3
C
CH3
H3
C
(TPY1)RuCl3 (0.8 eq.)
or (TPY1)RuCl3 (4 eq.)
AgOTf, acetone, reflux, 3h
N
N
N
A1 (Y=56%)
KPF6
(PF
)
2
6
CH3
CH3
H3
H3C
C
DMF:t-BuOH (2:1)
130 °C, 48 h
H3
C
CH3
N
O
O
O
O
+
+
CH3
CH3
H3
C
N
N
N
H
C
N
C
CH
N
N
N
3
3
H3
C
CH3
H3
C
N
Ru
N
Ru
3
+
+
(TPY2)RuCl3 (4 eq.)
N
N
N
H
3
CH
3
AgOTf, acetone, reflux, 3h
DMF:t-BuOH (2:1)
130 °C, 48 h
O
O
CH3
CH3
H3
C
KPF6
H3
C
CH3
H3
C
A2 (Y=48%)
(PF
)
2
6
CH3
CH3
H3
H3C
C
H3
C
CH3
O
O
+
+
N
N
N
N
N
Ru
N
Ru
N
+
+
N
N
N
C
8
H
H
C
8
17
H
C
17
8
C
H
17
17
8
O
O
CH3
CH3
H3
C
H3
C
CH3
H3
C
A3 (Y=50%)
Scheme 3. Synthesis of designed complexes A1, A2, and A3.
PF
6
(PF
)
2
6
CH3
H3C
CH3
H3C
H3C
CH3
H3C
CH3
CH3 H3C
CH3 H3C
O
O
O
O
+
+
+
N
N
N
CH
N
N
CH
N
N
3
(TPY2)RuCl3 (1.5 eq.)
N
N
N
3
KPF6
AgOTf, acetone, reflux, 3h
N
N
Ru
N
N
Ru
Ru
N
DMF:t-BuOH (2:1)
130 °C, 48 h
+
+
+
N
CH
CH
3
N
N
N
3
H
C
17
8
C
H
17
8
O
O
O
O
CH3 H3C
CH3 H3C
CH3 H3C
CH3 H3C
H3C
CH3
H3C
CH3
A4 (Y=17%)
Scheme 4. Synthesis of the designed unsymmetrical complex A4.
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10.1002/ejic.201700621
European Journal of Inorganic Chemistry
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A1
A2
Figure 1. Theoretical and experimental isotopic patterns for A1 and A2.
comparison to binuclear complexes A2–A4 and exalts 299 °C.
The temperature of 5% decomposition for A2–A4 is in the range
of 198 - 233 °C whereas the temperature of unsymmetrical
binuclear complex A4 is located between the temperatures of
symmetrical complexes A2 and A3 built from the same terminal
ligands. The char residue observed at 900 °C is the highest for
monoruthenium complex A1 and then for A4. Symmetrical
complexes A2 and A3 generated similar percent of residue.
DSC investigations for all compounds did not show any
transitions in the range of -145 °C – 195 °C.
Thermal properties
The thermal properties of the investigated compounds A1–A4
were examined by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA) under a nitrogen atmosphere;
the obtained results are shown in Table 1, whereas Figure 2
presents representative TGA and DTG thermograms for
mononuclear A1 and binuclear unsymmetrical A4 complexes.
The TGA results showed that molecules retain high thermal
stability. Decomposition temperature corresponding to 5%
weight loss (T5%) for mononuclear complex A1 is higher in
Table 1. Thermal properties of the synthesized derivatives A1–A4.
TGA
Code
T5% [°C]
299
T10% [°C]
378
Tmax [°C]
Char residue at 900 °C [%]
425, 705
54
15
17
41
A1
A2
A3
A4
198
282
220, 416, 499, 716
272, 431, 496
233
278
202
268
209, 286, 429, 713
T5%, T10% – temperature of 5% and 10% weight loss, respectively; Tmax - the maximum
decomposition rate from DTG thermograms
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10.1002/ejic.201700621
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(a)
(b)
Figure 2. (a) TGA and (b) DTG curves of A1–A4.
carbon in presented complexes are showed in Table 2, the
length of Ru-C for monoruthenium complex A1 is the shortest.
Electrostatic potential energy maps for A1–A4 are showed in
Figure S2 in Supporting Information, they illustrate the charge
distributions of molecules three-dimensionally. It can
determinate how molecules interact with others.
What is more, representation of the frontier molecular orbitals
(HOMOs and LUMOs) and energy gap (ΔE) for described
compounds were also calculated. The obtained results are listed
in Table 2. The value of ΔE for A1–A4 is respectively 2.61 eV,
2.22 eV, 2.26 eV and 2.24 eV. The energy gap for
monoruthenium complex A1 is the highest whereas the
difference between HOMO and LUMO for bisruthenium
unsymmetrical complex A4 is between the energy of
symmetrical binuclear complexes A2 and A3 which are built
from the same terminal ligands.
Theoretical studies
In order to gain the information about the geometry and optical
properties of the mono- and bisruthenium complexes A1–A4
density functional theory (DFT) and time-dependent-density
functional theory (TD-DFT) calculations were performed by
using Gaussian 09 program [22]. The B3LYP exchange-
correlation functional with Def2-TZVP basis set for ruthenium
and 6-31G(d) for others atoms was employed. All calculations
were carried out in CH3CN as a solvent in the polarisable
continuous model (PCM). The B3LYP/Def2-TZVP; 6-31G(d)
optimized structures for A1–A4 are presented in Supporting
Information as Figure S1. In the presented structures terminal
ligands are in a perpendicular plane to the bridging ligand. The
substituents in terpyridines are not coplanar in relation to the
central pyridine ring. The bonds length between ruthenium and
Table 2. Calculated frontier orbitals HOMO and LUMO, energy gap and bond length Ru-C for A1-A4.
A1
A2
A3
A4
-4.87
HOMO [eV]
LUMO [eV]
ΔE [eV]
-5.01
-2.40
2.61
-4.83
-2.61
2.22
-4.90
-2.64
2.26
-2.63
2.24
1.986/1.989
Ru-C [Å]
1.985
1.987
1.989
The frontier orbitals for A1–A4 are presented in Figure 3. In the
case of monoruthenium complex A1, the electrons in the
Highest Occupied Molecular Orbital (HOMO) are mainly
localized on terpyridine ligand and ruthenium atom but the
Lowest Unoccupied Molecular Orbital (LUMO) is delocalized on
pyrene ligand. Separation of frontier orbitals for monoruthenium
complex was achieved. In the case of bisruthenium complex A4,
the HOMO and LUMO are localized on the core of the molecule,
bridging ligand, the part of the occupied frontier orbital is also
localized on the ruthenium metal. The same distribution of
frontier orbitals is for binuclear, symmetrical complexes A2 and
A3. The pyridines in the bridging pyrene ligand in mono- and
bisruthenium complexes take a slight part in the creation of
frontier orbitals whereas alkoxy chains do not participate at all.
The same results of theoretical studies for binuclear,
symmetrical complexes are described by Yu-Wu Zhong, et al.
[13]. The contours of other selected orbitals for A1 and A4 are
depicted in Figure S3 and S4 in Supporting Information.
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10.1002/ejic.201700621
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HOMO
LUMO
A1
A2
A3
A4
Figure 3. The HOMOs and LUMOs of A1-A4.
Optical properties and TD-DFT study
Moreover, the time-dependent-density functional theory
calculations were performed for compounds A1–A4. The
obtained results are discussed in the part concerning optical
properties and TD-DFT study.
The UV/Vis spectra of the new complexes A1–A4 were
investigated in acetonitrile (CH3CN) solutions at room
temperature. The obtained results are presented in Figure 6.
The absorption maxima and molar extinction data are shown in
Table 3. The assignment of bands is discussed based on the
results from theoretical studies (TD-DFT calculations) which
were also carried out using the same level of theory as DFT
study.
Figure 6. The UV/Vis spectra of complexes A1–A4 and NCN-coordinating pyrene ligand 3 in acetonitrile solution (c = 10–5 mol/L).
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10.1002/ejic.201700621
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Table 3. Absorption data for A1–A4 and 3.
Code
λmax/nm (ε/105 M−1 cm−1)
593 (0.22), 502 (0.23), 441 (0.33), 409 (0.36), 391 (0.37), 343 (0.44), 316 (0.65), 290 (0.49), 277sh
(0.39)
A1
652sh (0.26), 602 (0.30), 488 (0.46), 458 (0.41), 427 (0.37), 384 (0.49), 339sh (0.63), 317 (0.94), 289sh
A2
(0.72), 277sh (0.60)
657sh (0.20), 601 (0.26), 490 (0.33), 455 (0.27), 396sh (0.42), 316 (0.93), 284 (0.77)
651sh (0.28), 602 (0.34), 489 (0.44), 457 (0.33), 404sh (0.45), 338sh (0.85), 317 (1.06), 289 (0.84)
381 (0.34), 295 (0.43), 254 (0.45)
A3
A4
3
sh - shoulder
The predicted electronic transitions for A1 and A4 compared
with experimental spectra are shown in Figure 7 and for A2 and
A3 in Supporting Information (Figure S5). The calculated
wavelength in absorption spectra, oscillator frequencies (f) and
character of dominant transitions are listed in Table S1-S4 in
Supporting Information.
The absorption band with the lowest energy for A2–A4 are
shown as a shoulder.
In the case of monoruthenium complex A1, the band at 593 nm
is associated with H-1→LUMO and HOMO→LUMO transitions
(593.8 nm, f=0.0612). It is the mixed character of metal-to-
ligand-charge-transfer (MLCT) transitions from ruthenium to
pyrene and charge transfer from terpyridine to pyrene ligand.
The rest bands can be interpreted as intraligand transitions as
well as transitions between terpyridine and pyrene ligands,
whereas excitations at 391 nm (379.6 nm, f=0.1185;
HOMO→L+3) and 343 nm (334.4 nm, f=0.3969; HOMO→L+8)
have also the partial character of MLCT transition. In
unsymmetrical bisruthenium complex A4, the band at 651 nm is
associated with HOMO→LUMO transitions (697.3 nm, f=0.1179)
what correspond to mix of MLCT from ruthenium to pyrene and
intraligand charge transfer of pyrene. The other bands can be
described as intraligand transitions and transitions between
various part of molecule i.e. TPY1→TPY2, pyrene→TPY. The
trend of predicted excitations of bisruthenium complexes A2–A4
show that they have similar assignments for their absorption
bands.
In general, predicted excitations are in accordance with the
experimental data with differences up to 50 nm what can be
related to solvent polarity and explained by specific solvent
effects. What is more, the difference may be caused by a large
π-conjugated system of examined compounds A1–A4. In the
range of spectra, the same number of main bands was seen.
For all complexes absorption bands in UV region between 240
and 427 nm are connected with intraligand transitions π→π*
from NCN-coordinating pyrene ligand 3 and terminal terpyridine
ligands. In Vis region four for bisruthenium complexes A2–A4
and three for mononuclear complex A1 main absorption bands
are seen. The intensity of monoruthenium complex A1 in
comparison to bisruthenium complexes A2–A4 is even one and
a half less. It is worth mention that similar phenomenon is
observed for monoruthenium and bisruthenium complexes with
1,3,6,8-tetra(2-pyridyl)pyrene as bridging ligand [11].
Figure 7. UV/Vis spectra in CH3CN and TD-DFT predicted excitations (B3LYP/Def2-TZVP; 6-31G(d)/CH3CN) for A1 and A4.
Electrochemical Properties
peaks were recorded in the potential range from -2.11 to -1.21 V.
It is worth noting that for all of the examined complexes multi-
step reduction was observed. All the observed reduction
processes are fully reversible. It can be noted that all the
reduction processes occur on pyrene and terpyridine ligands.
The reduction processes of bisruthenium unsymmetrical
complex A4 occur harder (at about 100 mV lower potential) than
the same reduction processes of symmetrical complex A3 but
slightly easier than monoruthenium complex A1 with
diethylamine substituent at the terpyridine. It is probably related
to electron donating character of amine moiety in the terpyridine
ligand.
The electrochemical behavior of ruthenium complexes A1–A4 in
N,N-dimethylformamide (DMF) solution was examined by cyclic
voltammetry (CV) and differential pulse voltammetry (DPV). The
obtained electrochemical data are presented in Table 5 and 6.
The electrochemical oxidation and reduction onset potentials
were used to estimate ionization potentials (IP) and electron
affinities of the materials (it was assumed that the IP of
ferrocene (Fc) equals -5.1 eV) [23]. The calculated ionization
potentials values, electron affinities together with the
electrochemical band gaps energy (Eg) are presented in Table 5
and Table 6. For all of the examined compounds, the reduction
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10.1002/ejic.201700621
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For all of the examined compounds A1–A4 the oxidation peaks
were recorded at a potential range between -0.07 and 0.52 V.
Undoubtedly, the first oxidation occurs at the ruthenium atoms,
which corresponds well with the literature [3]. All the observed
oxidation processes are fully reversible. It is worth noting that
the first oxidation peak of A1 is recorded between two oxidation
peaks of A2 (Table 6). It may be that the delocalization of
electrons along the pyrene ligand is more favored in the mixed-
valence states than in the homovalent ones. It is the common
electrochemical behavior of those complexes [24].
The electrochemical band gaps (Eg el) for examined compounds
vary from 1.29 to 1.54 eV which corresponds well with the band
gaps calculated from UV/Vis spectra (1.62 eV for A1 and 1.53
eV for A2–A3).
Table 5. Electrochemical data for A1–A4 recorded in DMF solution.
HOMO
Eox(CV)[V] Eox(DPV)[V] Ered(CV)[V] Ered(DPV)[V]
LUMO [eV]2 Eg el [eV]3 Eg opt [eV]4 Eg (DFT) [eV]
[eV]1
A1
A2
A3
A4
0.08
0.04
0.09
-0.07
-0.05
-0.08
0.04
-1.46
-1.36
-1.21
-1.36
-1.43
-1.27
-1.29
-1.42
-5.18
-5.14
-5.19
-5.03
-3.64
-3.74
-3.89
-3.74
1.54
1.40
1.30
1.29
1.62
1.53
1.53
1.53
2.61
2.22
2.26
2.24
-0.17
1EHOMO= - 5.1 - Eox, onset
;
2 ELUMO= - 5.1 - Ered, onset; 3Eg el = Eox, onset - Ered, onset = EHOMO - ELUMO
4calc. from: Eg=1240/λabs
Table 6. Comparison of peak onsets (CV) for A1–A4 recorded in DMF solution.
Ered1[V] Ered2[V] Ered3[V] Ered4[V] Eox1[V]
Eox2[V]
Eox3[V]
A1
A2
A3
A4
-1.46
-1.36
-1.21
-1.36
-1.67
-1.65
-1.45
-1.56
-1.93
-1.72
-1.73
-1.86
-2.11
0.08
0.04
0.09
-0.07
0.23
0.19
0.29
0.17
-
-
-
-
-
-
0.52
Figure 8. DPV scans for A1–A4 in DMF with 0.1 M Bu4NPF6; sweep rate ν = 10 mV/s. The measurements were performed with a glassy carbon working
electrode and referenced against the Fc/Fc+ couple. The arrows show the scan direction.
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10.1002/ejic.201700621
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Figure 9. Cyclic voltammograms recorded during the reduction of A1–A4 in DMF. The measurements were performed with a glassy carbon working electrode
and referenced against the Fc/Fc+ couple; sweep rate v= 100 mV/s. The arrows show the scan direction.
Figure 10. Cyclic voltammograms recorded during the oxidation of A1–A4 in DMF. The measurements were performed with a glassy carbon working electrode
and referenced against the Fc/Fc+ couple; sweep rate v =100 mV/s. The arrows show the scan direction.
be of interest for
a
further test for the application.
Monoruthenium complexes in comparison to bisruthenium
complexes shown the meaningful differences what was proofed
in presented work.
Conclusions
We presented the synthesis with efficient way of purification and
comprehensive characterization of novel mono- (A1) and
bisruthenium, symmetrical (A2 and A3) and unsymmetrical (A4)
complexes bridged by new 1,3,6,8-tetra(4-substituted-2-
pyridyl)pyrene derivative containing solubilizing group 2,2-
dimethylpropyloxy with the terminal 4'-phenyl-2,2':6',2''-
terpyridine ligands containing amine and 2-ethynyl-9,9-
dioctylfluorene moiety. The described molecules A1–A4 were
prepared with moderate yields in the range of 17-56%. All
reported in this article compounds are soluble and thermally
stable. The presented experimental, as well as theoretical
studies, showed the considerable differences between mono-
and bisruthenium complexes whereas the difference between
symmetrical and unsymmetrical complexes are definitely less
significant. The absorption spectra are consistent in comparison
with results obtained from TD-DFT studies. What is more, the
electrochemical investigation showed that the first oxidation
peak of monoruthenium complex A1 is recorded between two
oxidation peaks of bisruthenium A2. It showed delocalization of
the electronic charge (mixed-valance). This kind of complex may
Experimental Section
Materials
All chemicals and starting materials were commercially available and
were used without further purification. Solvents were distilled as per the
standard methods and purged with nitrogen before use. All reactions
were carried out under argon atmosphere unless otherwise indicated.
Column chromatography was carried out on Merck silica gel. Size-
exclusion chromatography was carried out on Sephadex LH-20 GE
Healthcare. Thin layer chromatography (TLC) was performed on silica
gel (MerckTLCSilicaGel60).
General Procedure for the synthesis of mono- and bisruthenium
complexes A1–A3: To 50 mL of acetone appropriate (TPY)RuCl3 (0.024
mmol for A1; 0.12 mmol for A2 and A3) and AgOTf (0.08 mmol for A1;
0.40 mmol for A2 and A3) were added and the mixture was stirring at
65 °C for 3 h. After cooling to room temperature the mixture was filtered
through Celite and the filtrate was evaporated. The obtained residue,
1,3,6,8-tetrakis(4-(2,2-dimethylpropyloxy)-2-pyridyl)pyrene (0.026 g, 0.03
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10.1002/ejic.201700621
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mmol), t-BuOH (8 mL) and DMF (8 mL) were placed in 20 mL vial and
capped. The mixture was saturated with argon, heated to 130 ⁰C and
stirred for 48 h. After cooling to a room temperature aqua solution of
KPF6 (10 mL) was added and resulting precipitate was collected by
vacuum filtration and washed with water. The crude product was purified
by column chromatography (silica gel; CH3CN:H2O:KPF6(aq) (100:1:2))
followed by size-exclusion chromatography on Sephadex LH-20
(CH3CN:MeOH (2:1)). The trailing edge of the product band contained
small traces of other species was discarded. Fractions with the pure
product were evaporated to dryness.
7.44 (dd, J = 7.3, 4.8 Hz, 2H), 7.38 (dt, J = 7.3, 2.4 Hz, 4H), 7.29 (ddd, J
= 9.1, 6.6, 3.2 Hz, 4H), 7.21 (dd, J = 7.2, 3.4 Hz, 1H), 7.14 (dd, J = 13.6,
6.3 Hz, 2H), 7.09 (dd, J = 10.1, 4.2 Hz, 1H), 7.04 (t, J = 6.1 Hz, 2H), 6.59
(ddd, J = 8.8, 6.4, 2.4 Hz, 4H), 3.91 (s, 8H), 3.61 (dd, J = 14.1, 7.0 Hz,
4H), 1.42 – 1.38 (m, 6H), 1.35 – 1.26 (m, 14H), 1.14 – 1.09 (m, 8H), 1.09
– 1.04 (m, 36H), 0.91 – 0.78 (m, 8H), 0.74 – 0.61 (m, 4H).
HRMS (ESI): m/z calcd. for C133H140N11O4Ru2 [M+H]2+ 1079.4589; found
1079.4600.
Anal. Cald. for C133H139F12N11O4P2Ru2: C, 65.26; H, 5.72; N, 6.30. Found:
C, 65.41; H, 5.77; N, 6.19.
Procedure for the synthesis of unsymmetrical bisruthenium
complex A4: To 25 mL of acetone (TPY2)RuCl3 (0.023 g, 0.025 mmol)
and AgOTf (0.025 g, 0.1 mmol) were added and the mixture was stirring
at 65 °C for 3 h. After cooling to room temperature the mixture was
filtered through Celite and the filtrate was evaporated. Obtained residue,
monoruthenium complex A1 (0.033 g, 0.023 mmol), t-BuOH (5 mL) and
DMF (5 mL) were placed in 20 mL vial and capped. The mixture was
saturated with argon, heated to 130 ⁰C and stirred for 48 h. After cooling
to a room temperature aqua solution of KPF6 (10 mL) was added and
resulting precipitate was collected by vacuum filtration and washed with
water. The crude product was purified by column chromatography (silica
gel; CH3CN:H2O:KPF6(aq) (100:1:2)) followed by size-exclusion
chromatography on Sephadex LH-20 (CH3CN:MeOH (2:1)). Fractions
with the pure product were evaporated to dryness.
Measurements: NMR spectra were recorded in CD3COCD3 with Bruker
Advance 400 MHz instruments (for 1H and 13C NMR).
High-resolution mass spectrometry (HRMS) measurements were
performed using Synapt G2-S mass spectrometer (Waters) equipped
with the electrospray ion source and quadrupole-Time-of-flight mass
analyzer. Methanol was used as a solvent with the flow rate 100 µl/min.
The measurement was performed in positive ion mode with the capillary
voltage set to 3 kV. The desolvation gas flow was 400 L/h and
temperature 150 °C. The sampling cone was set to 20 V and the source
temperature was 120 °C. To ensure accurate mass measurements, data
were collected in centroid mode and mass was corrected during
acquisition using leucine enkephalin solution as an external reference
(Lock-SprayTM), which generated reference ion at m/z 556.2771 Da ([M
+ H]+) in positive ESI mode. The results of the measurements were
processed using the MassLynx 4.1 software (Waters) incorporated with
the instrument.
Elemental analysis was performed by using Perkin Elmer Series II
CHNS/O Analyzer 2400 in CHN operating mode. The sample before the
measurement was dried for 6 h under vacuum (0,2 mbar, 60°C).
Differential Scanning Calorimetry (DSC) was measured with a TA-DSC
2010 apparatus, under a nitrogen atmosphere with heating/cooling rate
20 deg/min. Thermogravimetric analysis (TGA) was done using
TGA/DSC1 Mettler-Toledo thermal analyzer with a heating rate of
10 ºC/min in a stream of nitrogen (60 cm3/min1).
A1 (20 mg, 56%) as black solid
1H NMR (400 MHz, Acetone) δ 9.26 (s, J = 12.5 Hz, 2H), 9.11 (d, J = 9.5
Hz, 2H), 8.87 (d, J = 8.2 Hz, 2H), 8.75 (d, J = 9.4 Hz, 2H), 8.36 (d, J = 2.7
Hz, 2H), 8.30 (s, 1H), 8.21 (d, J = 8.7 Hz, 2H), 7.80 (t, J = 7.8 Hz, 2H),
7.56 (d, J = 1.8 Hz, 2H), 7.29 (t, J = 7.3 Hz, 2H), 7.23 (d, J = 6.4 Hz, 2H),
7.20 – 7.13 (m, 2H), 7.08 – 6.98 (m, 6H), 6.50 (dd, J = 6.5, 2.9 Hz, 2H),
3.97 (s, 4H), 3.81 (s, 4H), 3.66 – 3.54 (m, 4H), 1.28 (s, J = 10.1, 6.9 Hz,
6H), 1.11 (s, 18H), 1.00 (s, 18H).
13C NMR (101 MHz, Acetone) δ 170.79, 167.01, 166.02, 161.85, 160.39,
155.52, 154.01, 153.26, 151.63, 149.89, 145.60, 137.93, 136.80, 135.54,
129.34, 129.01, 128.58, 128.50, 128.03, 128.00, 127.13, 124.34, 124.32,
123.91, 118.90, 113.17, 112.91, 111.63, 110.00, 109.31, 78.66, 78.56,
68.03, 44.99, 32.41, 32.30, 26.74, 26.61.
Spectroscopic Measurements: UV/Vis spectra were recorded by using
Perkin–Elmer Lambda Bio 40 UV/Vis spectrophotometer at room
temperature in denoted solvents with a conventional 1.0 cm quartz cell.
HRMS (ESI): m/z calcd. for C81H85N8O4Ru [M]+ 1335.5737; found
1335.5769.
Electrochemical Measurements: Electrochemical measurements were
carried out using Eco Chemie Autolab PGSTAT128n potentiostat, glassy
carbon electrode (diam. 2 mm), platinum coil and silver wire as working,
Anal. Cald. for C81H85F6N8O4PRu: C, 65.71; H, 5.79; N, 7.57. Found: C,
65.50; H, 5.93; N, 7.41.
auxiliary and
a reference electrode, respectively. Potentials are
A2 (30 mg, 48%) as black solid
referenced with respect to ferrocene (Fc), which was used as the internal
standard. Cyclic voltammetry experiments were conducted in a standard
one-compartment cell, in DMF (Carlo Erba, HPLC grade), under argon.
0.2M Bu4NPF6 (Aldrich, 99%) was used as the supporting electrolyte.
The concentration of compounds was equal 1.0·10-6 mol/dm3.
Deaeration of the solution was achieved by argon bubbling through the
solution for about 10 min before measurement. All electrochemical
experiments were carried out under ambient conditions.
1H NMR (400 MHz, Acetone) δ 9.37 (d, J = 17.9 Hz, 4H), 9.32 – 9.24 (m,
2H), 8.91 (d, J = 8.1 Hz, 6H), 8.52 (t, J = 7.8 Hz, 2H), 8.26 (d, J = 8.5 Hz,
8H), 7.91 (dd, J = 16.0, 9.1 Hz, 8H), 7.29 – 7.15 (m, 8H), 7.04 (d, J = 8.5
Hz, 6H), 7.00 – 6.90 (m, 2H), 6.61 – 6.36 (m, 4H), 3.91 (s, 8H), 3.61 (dd,
J = 14.0, 6.8 Hz, 14H), 1.05 (s, 36H).
HRMS (ESI): m/z calcd. for C106H108N12O4Ru2 [M]2+ 908.3352; found
908.3400.
Anal. Cald. for C106H108F12N12O4P2Ru2: C, 60.45; H, 5.17; N, 7.98. Found:
C, 60.55; H, 5.26; N, 7.86.
Acknowledgements
A3 (42 mg, 50%) as black solid
1H NMR (400 MHz, Acetone) δ 9.40 (s, J = 7.3 Hz, 4H), 9.36 (d, J = 10.6
Hz, 4H), 8.93 (d, J = 8.1 Hz, 4H), 8.50 (s, 4H), 8.26 (d, J = 7.9 Hz, 4H),
7.88 – 7.72 (m, 8H), 7.59 (d, J = 8.0 Hz, 4H), 7.43 – 7.34 (m, 6H), 7.34 –
This work was supported by the Ministry of Science and Higher
Education,
Poland
(Diamentowy
Grant
number
0215/DIA/2015/44).
7.24 (m, 4H), 7.17 (d, J = 6.5 Hz, 4H), 7.11 – 7.05 (m, 4H), 6.90 (d, J =
5.5 Hz, 2H), 6.81 (d, J = 12.1 Hz, 2H), 6.50 (d, J = 7.2 Hz, 4H), 3.85 (s,
8H), 1.35 (t, J = 4.8 Hz, 8H), 1.22 (s, 12H), 1.08 – 0.98 (m, 72H), 0.68 –
Calculations have been carried out using resources provided by
Wroclaw Centre for Networking and Supercomputing
(http://wcss.pl), grant No.18.
0.59 (m, 12H).
HRMS (ESI): m/z calcd. for C160H174N10O4Ru2 [M+4H]2+ 1251.5904;
found 1251.5953.
Keywords: Ru(II) complexes • Terpyridines • Electrochemistry •
Theoretical study • Absorption spectra
Anal. Cald. for C160H170F12N10O4P2Ru2: C, 68.90; H, 6.14; N, 5.02. Found:
C, 68.99; H, 6.30; N, 4.98.
A4 (10 mg, 17%) as black solid
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FULL PAPER
Mono- and bisruthenium complexes
Dawid Zych*, Aneta Slodek, Michał
Pająk, Stanisław Krompiec, Grzegorz
Spólnik, Witold Danikiewicz
Page No. – Page No.


Novel complexes bridged by pyrene derivative
New cyclometalating 1,3,6,8-tetra(4-substituted-2-pyridyl)pyrene derivative
containing solubilizing group - 2,2-dimethylpropyloxy
Differences between mono- and bisruthenium, symmetrical and
unsymmetrical complexes
Mono- and bisruthenium, symmetrical

and
unsymmetrical
complexes
bridged by pyrene derivative
experimental and theoretical studies
-
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