Synthesis and catalytic applications of Ru and Ir complexes containing N,O-chelating ligand

Article abstract of DOI:10.1016/j.jorganchem.2020.121486

A series of monometallic complexes (Ru_1–3, Ir_1–3) which have N,O-chelating ligand (pyrazine-2-carboxylate (1), pyridine-2-carboxylate (2), quinoline carboxylate(3) and bimetallic complexes (Ru_4,5, Ir_4,5) bridged by pyrazine-2,3- dicarboxylate (4) and imidazole-4,5-dicarboxylate(5) were synthesized and characterized by ¹H-, ¹³C NMR, FT-IR, and elemental analysis. The crystal structure of Ir₂ was determined by X-ray crystallography. The complexes (Ru_1–5, Ir_1–5) were applied to investigate the electronic and steric effect of ligand in their catalytic activities in transfer hydrogenation and alpha(α)-alkylation reaction of ketones with alcohols. The activities of iridium complexes (Ir_1–5) were much more efficient than ruthenium complexes (Ru_1–5). The highest activity for both reactions was observed for the complex (Ir₂) with pyridine-2-carboxylate. The Ir hydride species was monitored for both reactions.

Full text of DOI:10.1016/j.jorganchem.2020.121486

Journal of Organometallic Chemistry 925 (2020) 121486
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and catalytic applications of Ru and Ir complexes containing
N,O-chelating ligand
Bilge Pakyapana, Serdar Batıkan Kavukcua, Zarife Sibel S¸ ahinb, Hayati Türkmena,∗
a University of Ege, Faculty of Science, Department of Chemistry, 35100 Izmir, Turkey
b University of Sinop, Scientific and Technological Research Application and Research Center, Sinop, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of monometallic complexes (Ru1–3
, Ir1–3) which have N,O-chelating ligand (pyrazine-2-
Received 15 May 2020
Revised 18 August 2020
Accepted 19 August 2020
Available online 23 August 2020
carboxylate (1), pyridine-2-carboxylate (2), quinoline carboxylate(3) and bimetallic complexes (Ru4,5, Ir4,5
)
bridged by pyrazine-2,3- dicarboxylate (4) and imidazole-4,5-dicarboxylate(5) were synthesized and char-
acterized by 1H-, 13 C NMR, FT-IR, and elemental analysis. The crystal structure of Ir2 was determined by
X-ray crystallography. The complexes (Ru1–5, Ir1–5) were applied to investigate the electronic and steric
effect of ligand in their catalytic activities in transfer hydrogenation and alpha(α)-alkylation reaction of
ketones with alcohols. The activities of iridium complexes (Ir1–5) were much more efficient than ruthe-
nium complexes (Ru1–5). The highest activity for both reactions was observed for the complex (Ir2) with
pyridine-2-carboxylate. The Ir hydride species was monitored for both reactions.
Keywords:
Transfer hydrogenation
Alpha alkylation of ketones
N,O-chelate ligand
Bimetallic complex
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
Alpha alkylated ketones are important concerns in organic syn-
thesis as intermediates and also for their biological activity [4].
Ruthenium and iridium complexes are one of the most produc-
tive areas among the transition metal chemistry as a catalyst [1].
The arene ligands such as p-cymene and pentamethylcyclopenta-
diene (Cp∗) coordinate to the metal center very intense and their
advantage is that the easy modification by adding or changing the
substituents. Also, the other available coordination sites of these
metals can be filled with donor atoms like N, O, S, P, C or as a
chelating ligand with combinations of the two atoms [2]. Chelat-
ing ligands are commonly formed by linking donor groups via or-
ganic linkers. Thus, this property makes them highly versatile and
very useful for the important catalytic transformations. The ne-
cessity of green processes in order to maintain a healthy nature
is an impulse to the scientists. To achieve this aim, both iridium
and ruthenium complexes have been successfully applied for cat-
alytic hydrogen transfer and this success motived the researchers
try these complexes on new catalytic transformations [3]. Espe-
cially, Ir(I) complexes have shown remarkable performance on the
(α)-alkylation of ketones with alcohols yet the Ir(III) complexes are
not very well-known [3]. Furthermore, high catalyst loading, ex-
pensive base usage and long reaction times still pose a problem
for this transformation.
Because of the disadvantages of conventional methods such as
low yields of product and toxic reagents usage leads the re-
searchers to produce these products with greener methods. Al-
pha alkylation of ketones with alcohols is a very favorable pro-
cess when it is compared to the common alkylation methods be-
cause of the fact that it has atom economy and water is formed
as a only byproduct [5]. To solve the alkylation problems, hy-
drogen auto transfer or as known borrowing hydrogen process,
which is the source of the atom efficiency, has been carried out.
The mechanism commonly build upon three steps, (i) dehydro-
genation, (ii) intermediate reaction, and (iii) hydrogenation [6].
These very well-known steps make this process more preferable
when the synthesis, environment and economy parameters are
considered.
Transfer hydrogenation (TH) is an essential alternative way to
obtain a wide variety of pharmaceutically and industrially impor-
tant chemicals because the usage of the pressurized hydrogen gas
in direct hydrogenation puts this important transformation in a
dangerous position. Thus, TH is a notably green method due to the
properties which are high atom efficiency, simple mechanism, and
low-cost hydrogen donors. Transition metal complexes, Ru [7], Ir
[8] and Rh [9] in the first place, with ligand systems bearing donor
atoms such as NN, NNN, CN, NO have successfully being applied in
this transformation [10].
∗
Many studies, such as characterization, catalytic or biological
activity, have been made on nitrogen and the phenoxy oxygen
Corresponding author.
E-mail address: hayati.turkmen@ege.edu.tr (H. Türkmen).
https://doi.org/10.1016/j.jorganchem.2020.121486
0022-328X/© 2020 Elsevier B.V. All rights reserved.

2
B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
hydrogenation reaction [12]. McGowan et al. examined cytotoxic
activity of the Ru2 complex in various cancer cell lines [13]. Also,
Schmidt et al. characterized Ir2 with the X-ray diffraction method
(Fig. 1) [14]. We aimed to observe that the effect of the hetero-
cyclic pyridine, pyrazine or imidazol carboxylate ligand on the cat-
alytic reactions. For this purpose, we presented the synthesis and
characterization of Ru(II) and Ir(III) arene complexes (arene = p-
cymene, Cp∗) bearing N,O-donor ligands. The activity of the
complexes has been investigated in the transfer hydrogenation re-
action and the alpha alkylation reactions of ketones with alcohols.
The ketone product yield in the α-alkylation reaction was very
promising with a low solvent volume and also low base – catalyst
ratio in a short period of time in comparison with the literature
[15]. The effect of the ligands such as additional benzene ring
or nitrogen atom to these important transformations were also
investigated.
Fig. 1. Previously reported complexes [12–14].
2. Results and discussions
As shown in the Schemes 1 and 2, the complexes were syn-
thesized by the reaction of the related ligand (1–5) and the
[RuCl2(p-cymene)]2 or [IrCl2Cp∗]2 in acetonitrile in the presence
of a base (triethylamine or sodium bicarbonate) for 24 h at room
temperature. The complexes were obtained in 81–94% yields and
they were air- and moisture-stable yellow solids. The solubility of
the monometallic complexes (Ru1–3 and Ir1–3) was good in apolar
and polar solvents. The bimetallic complexes (Ru4,5 and Ir4,5) are
poor soluble even in polar solvents because of this reason 1H-
and 13C NMR studies could not be performed except the 1H NMR
of Ru4 and Ir4. The characterization studies of the monometallic
complexes (Ru1–3 and Ir1–3) were made by 1H- and 13C NMR
spectroscopy and elemental analysis. NMR chemical shifts were
found to be in a good agreement with experimental values. In the
1H NMR spectra, the p-cymene aromatic protons were detected
as four doublets and the Cp∗ methyl protons were detected as
Fig. 2. Molecular structure of the complex Ir2.
coordinated metal complexes [11] but nitrogen and carboxylate
oxygen donor coordinated metal complexes are limited in the
literature. Çetinkaya et al. have reported this type of Ru complexes
(Ru2 and Ru3) and investigated their catalytic activity on transfer
Fig. 3. The effects of different catalysts on the transfer hydrogenation of 6.a
a
Reaction conditions: 6 (1.00 mmol), KOH (1 mmol), Cat. (0.5%), IPA (1.00 mL), time (0.5 h), temperature (82 °C), under argon. Conversions were determined by using GC.

B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
3
Fig. 4. The Ir-H species in the catalytic transfer hydrogenation reaction via 1H NMR spectroscopy.
Fig. 5. The effects of different catalysts on the alpha alkylation of acetophenone with benzyl alcohol.
a
Reaction conditions: Acetophenone (1.00 mmol), Benzyl Alcohol (1.00 mmol), KOH (0.20 mmol), Cat. (0.20 mol%), toluene (1.00 mL), time (2 h), temperature (120 °C),
under air, analyzed by NMR.
Table 1
C-H stretching. Furthermore, the vibrations appearing in the range
of 1650 and 1670 cm−1 were associated with the aromatic C=O
peaks. Also, the vibrations appearing around 1600 cm−1 were link
to the aromatic C=C peaks. Single crystals of Ir2 were obtained by
the diffusion of pentane into saturated chloroform solution of the
complex.
FTIR frequencies of the complexes.
Complex
νC=O
νC-H(Aromatic, Aliphatic)
νC=C(Aromatic)
Ru1
Ru2
Ru3
Ru4
Ir1
1666
1652
1656
1656
1662
1653
1661
1661
3037;2868,2931
3058;2876,2929
3037;2923
1586
1567
1597
1597
1583
1563
1593
1595
3037; 2971
3059;2983
The molecular structure of complex Ir2 with the atom number-
ing is shown in Fig. 2. The asymmetric unit of complex Ir2 contains
Ir(III) ion, pentamethylcyclopentadiene, pyridine-2-carboxylate, and
coordinated chlorine anion. The bond distances of Ir-N, Ir-O and Ir-
Ir2
3054;2910
Ir3
3051;2922
Ir4
3051;2988
˚
˚
˚
Cl are 2.104(12) A, 2.108(10) A, 2.398(4) A, respectively.
a singlet. The complexes exhibit piano-stool geometry. The IR
spectrums of complexes (Ru1–5 and Ir1–5) showed a band, approx-
imately 2900–3100 cm−1 region, which was correspond to νC-H
vibrations (Table 1). Successively, the peaks observed at region of
2800 cm−1 and 3100 cm−1 correspond to aromatic and aliphatic
2.1. Transfer hydrogenation (TH)
To explore the effect of the catalysts (Ru1–5 and Ir1–5) on the
ꢀ
transfer hydrogenation of ketones, the 4 Cl-acetophenone (6) was
chosen as a model substrate to evaluate the influence of mono-

4
B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
Scheme 1. Synthesis of the monometallic complexes.
Scheme 2. Synthesis of the bimetallic complexes.
and bi-metallic complexes. The reaction was carried out in IPA at
82 °C (bath temp.) for 0.5 h using KOH as the base under argon
atmosphere to find the most active catalyst. Monometallic complex
Ir2 was determined as the most active catalyst among all com-
plexes (Fig. 3). The amount of metal complexes was an important
parameter to perform the catalytic reaction which carried out with
0.5 mol% monometallic complex, 0.25 mol% bimetallic complex.
Also, in metal species, the catalytic activity of iridium complexes
was better than those with ruthenium ones. The dehalogenation
reaction did not take place under these conditions. The changes
in the aromatic ring of chelating ligand did not have a significant
effect on the catalytic yield.
In addition, a mercury poisoning experiment was performed for
the complex (Ir2) to determine whether the reaction was homoge-
neous or heterogeneous. The yield was significantly reduced as the
activities for Ir2 dropped from 93% to 62% for TH (Table 2, 16). This
experiment showed that the reaction was homogenously catalyzed.
The effect of different electron-withdrawing or -donating
groups on acetophenone was analyzed, after the optimum con-
ditions were decided and the most active catalyst was chosen.
The results are summarized in Table 3. The presence of electron-
withdrawing groups like chlorine (7a) and bromine (7b) on the
aromatic ring of acetophenone gave the corresponding products
with a yield of 93 and 87%, respectively. The electron-rich groups
such as methoxy (7c) provided the desired products with a >99%
yield. When ethyl (7f) was used for R2 substituent the conversion
was nearly the same. The yield for heptane-2-one (7i), an aliphatic
ketone, was found to be 98%. Additional ring on the aromatic ring
of acetophenone (7d) gave also a good result. The different ketone
analogs like benzophenone (7e) and caprolactone (7 g) resulted in
the corresponding products with the yields of 83 and 97%, respec-
tively.
The IPA was the best hydrogen donor among other alcohol
derivatives (Table 2, entry 1) and the reaction was not achieved
in H2O. The KOH was the best base for the TH [16]. The reac-
tion did not occur well in lower temperatures than 82 °C such
as 60 °C and 25 °C (Table 2, entries 12,13). The conversion of
ꢀ
4 Cl-acetophenone to the desired product decreased on lowering
the amount of base (Table 2, entry 10) In the absence of either Ir2
or base, no conversion was observed (Table 1, entry 14–15).

B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
5
Table 2
The effects of solvent, base and catalyst on the transfer hydrogenation of 6.a.
a
Reaction conditions: 6 (1.00 mmol), base, cat. Ir2, IPA (1.00 mL), time (0.5 h), temperature (82 °C), under
argon. Yield was determined by using GC. bT= 60 °C. cT= 25 °C.d Hg drop was added to the reaction medium.
The mechanism of catalytic transfer hydrogenation reaction of
ketones to alcohols with catalyst Ir2 including N,O ligand system is
summarized in Scheme 3. The mechanism begins with the removal
of the halogen from the metal center with the aid of potassium hy-
droxide and a vacant coordination site is created (Ir2-I). Isopropox-
ide coordinates to the iridium metal thanks to this vacant coordi-
nation site (Ir2-II). At this step, there is a possibility that IIa and
IIb types may occur in low concentrations. After removal of iso-
propoxide as acetone from Ir2-II, the iridium monohydride species
Ir2-III is formed. The iridium dihydride species (Ir2-V) is formed
due to the second coordination of isopropoxide to Ir2-III and sub-
sequent separation of acetone (Ir2-IV). The dihydride Ir2-V is the
active species. Iridium provides the transfer of hydrogen atoms to
ketone to form Ir2-VI. The cycle is followed by the release of alco-
hol and coordination of a new isopropoxide to form intermediate
Ir2-II [17,22].
Formation of the Ir-H species was monitored in the transfer hy-
drogenation reaction of acetophenone to 1-penyletanol via 1H NMR

6
B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
Table 3
Transfer hydrogenation of different substrates.
aReaction conditions: 6 (1.00 mmol), KOH (1.00 mmol), Ir2 (0.5 mol%), 2-propanol
(1.00 mL), 0.5 h, 82 °C. Yields were determined by GC.
Table 4
Base/Catalyst Ratio.a
this reason, we decided to investigate different ketone substrates
with this condition (Table 5). Moreover, when the amount of cat-
alyst was reduced the conversion was also decreased. In con-
sequence, we can say that the conversion in this reaction de-
pends on the catalyst as well as the base amount. The prod-
uct yields were good with both electron-withdrawing or electron-
donating groups. When the reaction was carried out under ar-
gon atmosphere, the selectivity was changed (Table 4, entry 6).
This is why the reaction was performed under air atmosphere be-
cause oxygen of the air makes easier the oxidation step of the
11aa to 10aa.
Li et al. reported that the Cp∗Ir complex bearing a bipyridonate
ligand as an active catalyst on the reaction of alpha alkylation of
ketones with primary alcohols [18]. Their statement was the pres-
ence of the carbonyl group has a significant effect on the catalytic
hydrogen transfer by making easier the formation of hydroxy irid-
ium species. However, the procedure for the alpha alkylation reac-
tion of ketones with alcohols has some disadvantages such as high
catalyst loading (1 mol%), long reaction time (6 h) and usage of
Cs2CO3 which is costly with reference to KOH. Our reaction condi-
tions were milder when a comparison was made with the litera-
ture [18,23].
Entry
Base(mmol)/ Cat. (%)
Yield% (10aa/11aa)
1
0.2/1
98/2
2
0.2/0.5
0.2/0.2
0.2/0.1
0.1/0.1
0.2/0.2
91/9
3
81/19
69/31
74/16
69/31
4
5
6b
a
Reaction conditions: Acetophenone (1.00 mmol),
Benzyl Alcohol (1.00 mmol), KOH, Ir2, toluene (1.00 mL),
time (2 h), temperature (120 °C), under air, analyzed by
NMR. bUnder argon atmosphere.
spectroscopy. The reaction was carried out in CD3OD, 0.1 mmol
ꢀ
4 -chloroacetophenone, one drop IPA, 0.05 mol KOH and 2 mmol%
Ir2. The mixture was refluxed in 5 min and then analyzed with 1H
NMR spectroscopy. We observed one doublet at -13.4 ppm which
is Ir2-V dihyride species (J = 19.2 Hz) and one singlet at -16.5 ppm
which is Ir2-III hydride species (Fig. 4).
2.2. Alpha alkylation reaction of ketones with alcohols
The encouraging results lead us to try different ketone and alco-
hol substrates as summarized in Tables 5 and 6 in determined con-
ditions according to the optimization examinations. The effect of
electron-donating or electron-withdrawing groups had been stud-
ied. The general yields for both substrate group were in between
72–95%. It was found that the different substitution patterns do
not have a significant effect on the formation of desired prod-
ucts. The electron-withdrawing groups on the ketone substrate’s
para position caused relatively less yield (Table 5, 10ba) in com-
parison to its ortho position analogue (Table 5, 10ca). Substrates
bearing electron-donating group such as methyl gave higher yields
The reaction between acetophenone (8a) and benzyl alcohol
(9a) was used as a model reaction for investigation of alpha alky-
lation of ketones with alcohols (Fig. 5) [23]. Toluene was chosen
as solvent according to the literature [15]. Base is also a very im-
portant factor on this reaction therefore, KOH was determined as
base when we consider its strength, availability and price. In ad-
dition, different base and catalyst ratio trials were investigated.
The best result was obtained with the 0.2 mmol base / 1% cat-
alyst ratio (Table 4). However, the 0.2 mmol base / 0.2% cat-
alyst also gave a satisfactory alpha alkylated ketone yield. For

B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
7
Scheme 3. Proposed mechanism for the catalytic transfer hydrogenation reaction.
(Table 5, 10fa). Cyclic and aliphatic ketone derivatives such as cy-
clohexanone and isobutyl methyl ketone also gave good results.
In addition to the ketone substrate assay, selected alcohols were
also allowed to react with acetophenone. Moderate to good yields
were obtained for different substrates with electron-withdrawing
or electron-donating groups. The substrates which bears electron-
donating group such as methoxy gave good results (Table 6, 10ac)
while aliphatic group such as heptanol gave the desired product in
moderate yield (Table 6, 10ai).
effort as we used cheap commercially available ligands and mild
reaction conditions [21,23].
As known, the borrowing hydrogen mechanism constitute the
basis of the alpha alkylation of ketones. The plausible mechanism
starts with the decoordination of Cl with the help of basic me-
+
dia provided by KOH as a result [IrCp∗
]
is produced. Dehydro-
2
genation of benzyl alcohol produce the active hydrogen which is
the foundation of the formation of Ir-H intermediate. Then, the
aldol condensation between the benzaldehyde, which is given by
the dehydrogenation of benzyl alcohol, and acetophenone is oc-
cured. Thereupon, rehydrogenation, using the hydrogen from the
Ir-H species, generates the final alkylated ketone product. The reac-
tion monitored by 1H NMR and three singlets at -14.46, -15.23 and
-15.96 ppm were observed in the hydridic region which reveals
the occurrence of the iridium hydride species (Scheme 4) (The full
spectrums are in SI).
In our work Ru(II) and Ir(III) complexes were used for both
transfer hydrogenation and alpha alkylation reactions. In the lit-
erature Çetinkaya et al. reported the highly active Ir(I) catalyst for
the alpha alkylation of ketones with primary alcohols. The results
of our study were also satisfying with relatively similar conditions
in comparison with the mentioned study. Although the amount of
catalyst is high in our work, the synthesis of the catalysts need less

8
B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
Scheme 4. The reaction mechanism of the alpha alkylation of ketones (left) and Ir-H formation in 1H NMR (right).
Table 5
Alpha alkylation of different ketones with benzyl alcohol.
a
Reaction conditions: Ketones (8) (1.00 mmol), 9a (1.00 mmol), KOH (0.20 mmol), Cat.
Ir2 (0.2 mol%), toluene (1.00 mL), time (2 h), temperature (120 °C), under air, analyzed
by NMR.
3. Conclusions
4. Experimental section
Ru(II) and Ir(III) complexes (M1–5) bearing N,O - donor ligands
were synthesized. The catalytic properties of the complexes were
investigated in the TH of ketones and α-alkylation reaction of ke-
tones with alcohols. The activity of synthesized bimetallic com-
plexes was lower than the monometallic complexes in the trans-
fer hydrogenation and α-alkylation of ketones with alcohols. Com-
plex Ir2 has been found that the most active complex among
the synthesized complexes for both transfer hydrogenation and α-
alkylation reaction. The Ir(III) complexes gave higher yields in a
shorter time than the Ru(II) complexes in the transfer hydrogena-
tion and α-alkylation reaction. The ketone product yield was af-
fected by the catalyst amount in the α-alkylation reaction. Also,
the ketone product yield decreased when the amount of catalyst
was reduced. The differences in the ligands such as additional ben-
zene ring or nitrogen atom did not affect the catalytic activity
prominently.
4.1. General information
All experimental manipulations of complexes were carried out
under inert atmosphere using standard Schlenk line techniques
unless otherwise stated. The glass equipment was heated under
vacuum in order to remove oxygen and moisture and then they
were filled with argon. The other reagents were used as received
from suppliers without further purification. [RuCl2(p-cymene)]2
was prepared according to the method reported by Bennett and
Smith through the reaction of ruthenium (III) chloride with α–
terpinene [19]. Catalytic reactions for α-alkylation were carried out
under air and catalytic reactions for transfer hydrogention were
carried out under argon gas on Carousel 12 Plus Reaction Station
system. 1H and 13C NMR spectra of compounds were recorded
by Varian 400 and 600 MHz spectrometers and chemical shifts
were recorded in ppm. J values were given in Hz. NMR chemical
shifts were referenced to the solvent signal in CDCl3. The reactions

B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
9
Table 6
Alpha alkylation of different alcohols with acetophenone.
a
Reaction conditions: 8a (1.00 mmol), alcohols (9) (1.00 mmol), KOH (0.20 mmol), Cat.
Ir2 (0.20 mol%), toluene (1.00 mL), time (2 h), temperature (120 °C), under air, ana-
lyzed by NMR.
of alpha alkylation of ketones with alcohols were also monitored
by Nuclear Magnetic Resonance (NMR). Reagents were purchased
from Aldrich or Merck. Melting points measured on Gallenkamp
electrothermal melting point apparatus without correction. FT-IR
spectra were recorded on Perkin Elmer Spectrum 100 series.
5.44 (dd, J = 5.6 Hz, 1 H, cym-Ar-H), 2.79 (m, 1 H cym-CH), 2.20
(s, 3 H, cym-CH3), 1.17 (d, J = 6.4 Hz, 6 H, cym-(CH3)2). 13C NMR
(100 MHz, DMSO – d6) δ 170.9, 154.2, 150.9, 140.0, 128.5, 125.8,
101.4, 98.6, 83.0, 82.8, 81.5, 80.5, 45.9, 40.4, 40.2, 40.0, 39.8, 39.6,
39.4, 30.9, 22.3, 22.2, 18.6, 8.9. Anal. Calcd for C16 H20ClN2O2Ru (M:
408,87): C, 46.91; H, 4.84; N, 6.75%; Found: C, 47.00; H, 4.93; N,
6.85%.
4.2. Synthesis and characterization of compounds
Complex Ru3: The compound Ru3 was prepared in the same
manner as Ru1 using 3 as ligand. Yield = 79%, 187 mg. IR (KBr
pellet), ʋmax/cm−1: 1656 (C=O). 1H NMR (400 MHz, CDCl3): δ 8.69
(d, J = 8.8 Hz, 1 H, Ar-H), 8.37 (d, J = 8.8 Hz, 1 H, Ar-H), 8.16 (d,
J = 8.4 Hz, 1 H, Ar-H), 7.94 (m, 1 H, Ar-H), 7.76 (t, J = 6.8 Hz,
1 H, Ar-H), 5.74 (d, J = 6 Hz, 1 H, cym-Ar-H), 5.56 (dd, J = 6, 2
H, cym-Ar-H), 5.43 (d, J = 6 Hz, 1 H, cym-Ar-H), 2.63 (m, 1 H,
cym-CH), 2.27 (s, 3 H, cym-CH3), 1.12 (d, J = 7.2 Hz, 3 H, cym-
CH3) 1.02 (d, J = 6.8 Hz, 3 H, cym-CH3). 13C NMR (100 MHz,
CDCl3): δ 178.1, 171.1, 147.5, 139.8, 131.5, 130.7, 129.1, 128.9, 128.9,
122.6, 103.3, 100.1, 86.1, 86.1, 84.9, 81.1, 80.8, 80.7, 51.2, 46.2, 46.2,
45.8, 30.9, 22.5, 21.8, 21.7, 18.7, 13.1, 8.6, 7.0, 6.9. Anal. Calcd for
C22H27ClNO2Ru (M: 474,08): C, 55.65; H, 5.64; N, 2.88%; Found: C,
55.75; H, 5.74; N, 2.96%.
Monometallic complexes M1–3 were prepared from [Ru(p-
cymene)Cl2]2 or [IrCl2Cp∗]2 with pyrazine-2-carboxylic acid(1),
pyridine-2-carboxylic acid (2), quinoline carboxylic acid(3). Ace-
tonitrile (10 mL) was used as solvent and reactions were per-
formed in the presence of NEt3 for 24 h at room temperature. The
yellow solid was filtrated and washed with diethyl ether (20 mL).
The product was dried under vacuum. The reaction of [RuCl2(p-
cymene)]2 and [IrCl2Cp∗]2 with imidazole-4,5-dicarboxylic acid
gave the bimetallic complexes (Ru4 and Ir4) respectively. The com-
plexes (Ru5, Ir5) were synthesized according to literature [20].
Complex Ru1: This compound has been synthesized from
[RuCl2(p-cymene)]2 (0.153 g, 0.25 mmol) and 1 (0.50 mmol) lig-
and in acetonitrile in the presence of triethylamine for 24 h at
room temperature. The yellow solid has been obtained, washed
with diethylether and dried under vacuum. Yield = 78%, 159 mg.
m.p = 208 °C. IR (KBr pellet), ʋmax/cm−1: 1652 (C=O). 1H NMR
(400 MHz, CDCl3): δ 9.03 (d, J = 4.4 Hz, 1 H, py-H), 7.96 (m, 1 H,
py-H), 7.89 (t, J = 7.6 Hz, 1 H, py-H) 7.57 (m, 1 H, py-H), 5.62 (d,
J = 6.4 Hz, 2 H, cym-Ar-H), 5.45 (dd, J = 5.6 Hz, 2 H, cym-Ar-H),
2.83 (m, 1 H, cym-CH), 2.25 (s, 3 H, cym-CH3), 1.19 (d, J = 6.4 Hz, 6
H, cym-(CH3)2). 13C NMR (100 MHz, CDCl3): δ 170.9, 154.2, 150.9,
140.1, 128.5, 125.8, 101.4, 98.6, 82,9, 81.5, 80.5, 40.3, 39.6, 30.9,
22.3, 18.0. Anal. Calcd for C17 H21ClNO2Ru (M: 408,03): C, 49.92;
H, 5.09; N, 3.34%; Found: C, 50.06; H, 5.19; N, 3.43%.
Complex Ru4: This compound has been synthesized by the re-
action of [RuCl2(p-cymene)]2 and ligand (4) in acetonitrile in the
presence of NaHCO3 for 24 h at room temperature. The yellow
solid has been obtained, washed with diethylether (20 mL) and
dried under vacuum. Yield = 80%, 145 mg. 1H NMR (400 MHz,
DMSO–d6): δ 8.42 (s, 1 H, Im-H), 5.65 (m, 2 H, cym-Ar-H), 5.50
(dd, J = 17.6, 5.9 Hz, 1 H, cym-Ar-H), 5.38 (dd, J = 16.4, 5.9 Hz,
1
H, cym-Ar-H), 2.66 (m,
1
H, cym-CH), 2.10 (dd,
J
=
14.0,
1.1 Hz, 3 H, cym-CH3), 1.13 (m, 6 H, cym-(CH3)2). Anal. Calcd for
C27H36Cl2N2O4Ru2 (M: 726,01): C, 44.56; H, 4.92; N, 3.76%; Found:
C, 44.69; H, 5.00; N, 3.86%.
Complex Ru5: This compound was synthesized according to the
literature [20].
Complex Ru2: The compound Ru2 was prepared in the same
manner as Ru1 using 2 as ligand. Yield = 79%, 160 mg. m.p = 195
°C . IR (KBr pellet), ʋmax/cm−1: 1666 (C=O). 1H NMR (400 MHz,
CDCl3): δ 9.04 (s, 1 H, pz-H), 8.96 (d, J = 1.6 Hz, 1 H, pz-H), 8.75
(d, J = 2.4 Hz, 1 H, pz-H), 5.61 (d, J = 5.6 Hz, 2 H, cym-Ar-H),
Complex Ir1: This compound has been synthesized by the reac-
tion of [IrCl2Cp∗]2 and ligand (1) in acetonitrile in the presence of
triethylamine for 24 h at room temperature. The yellow solid has

10
B. Pakyapan, S.B. Kavukcu and Z.S. S¸ ahin et al. / Journal of Organometallic Chemistry 925 (2020) 121486
been obtained, washed with diethylether (20 mL) and dried un-
der vacuum. Yield = 81%, 202 mg. IR (KBr pellet), ʋmax/cm−1: 1653
(C=O). 1H NMR (400 MHz, CDCl3): δ 8.56 (d, J = 4 Hz, 1 H, py-H),
8.15 (d, J = 8 Hz, 1 H, py-H), 7.95 (t, J = 8 Hz, 1 H, py-H), 7.56
(t, J = 8 Hz, 1 H, py-H), 1.72 (s, 15 H, Cp∗-H). 13C NMR (100 MHz,
CDCl3): δ 178.1, 149.1, 139.1, 128.4, 127.7, 85.4, 8.9. Anal. Calcd for
C17 H22ClIrNO2 (M: 500,10): C, 40.73; H, 4.32; N, 2.71%; Found: C,
40.83; H, 4.43; N, 2.80%. Crystals were obtained by solvent diffu-
sion method by diffusing pentane into a saturated chloroform so-
lution of the complex.
Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Declaration of Competing Interest
The authors declare no conflict of interest.
Complex Ir2: The compound Ir2 was prepared in the same
manner as Ir1 using 2 as ligand. Yield = 80%, 200 mg. IR (KBr pel-
let), ʋmax/cm−1: 1662 (C=O). 1H NMR (400 MHz, CDCl3): δ 9.29 (s,
1 H, pz-H), 8.84 (d, J = 4 Hz, 1 H, pz-H), 8.53 (dd, J = 4 Hz, 1 H,
pz-H), 1.72 (s, 15 H, Cp∗-H). 13C NMR (100 MHz, CDCl3): δ 178.1,
149.1, 139.1, 128.4, 127.7, 85.4, 77.3, 77.2, 76.9, 76.7, 8.9. Anal. Calcd
for C16 H21ClIrN2O2 (M: 501,09): C, 38.26; H, 4.11; N, 5.48%; Found:
C, 38.36; H, 4.22; N, 5.59%.
Acknowledgements
The authors thank to Ege University Scientific Research Fund
(17-FEN-058) for the financial support. The authors acknowledge
Scientific and Technological Research Application and Research
Center, Sinop University, Turkey, for the use of the Bruker D8
QUEST diffractometer.
Complex Ir3: The compound Ir3 was prepared in the same
manner as Ir1 using 3 as ligand. Yield = 80%, 220 mg. IR (KBr pel-
let), ʋmax/cm−1: 1661 (C=O). 1H NMR (400 MHz, CDCl3): δ 8.47
(d, J = 8.0 Hz, 1 H, Ar-H), 8.38 (d, J = 8.0 Hz, 1 H, Ar-H), 8.22
(d, J = 8.0 Hz, 1 H, Ar-H), 7.96 (d, J = 8.0 Hz, 1 H, Ar-H), 7.88
(t, 1 H, Ar-H), 7.76 (m, 1 H, Ar-H), 1.65 (s, 15 H, Cp∗-H). 13C NMR
(100 MHz, CDCl3): δ 174.8, 157.1, 145.2, 142.5,139.1, 136.6, 134.7,
132.8, 125.5, 123.9, 121.0, 85.4, 77.3, 77.2, 77.0, 76.6, 8.9. Anal. Calcd
for C21H24ClIrNO2 (M: 550,11): C, 45.75; H, 4.31; N, 2.44%; Found:
C, 45.85; H, 4.40; N, 2.55%.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2020.
121486.
Complex Ir4: This compound has been synthesized by the re-
action of [IrCl2Cp∗]2 and 4 ligand in acetonitrile in the presence
of NaHCO3 for 24 h at room temperature. The yellow solid has
been obtained, washed with diethylether (20 mL) and dried un-
der vacuum. Yield = 80%, 180 mg. 1H NMR (400 MHz, DMSO-
d6): δ 7.72 (s, 1 H, Im-H), 1.61 (s, 30 H, Cp∗-H). Anal. Calcd for
C27H38Cl2Ir2N2O4 (M: 910,15): C, 35.55; H, 4.11; N, 2.92%; Found:
C, 35.64; H, 4.21; N, 3.08%.
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