Synthesis, characterization, and reactivity of ruthenium(II) complexes containing η6-arene-η1-pyrazole ligands

Article abstract of DOI:10.1016/j.tet.2012.07.058

New ruthenium(II) complexes containing η⁶-arene- η¹-pyrazole ligands were synthesized and characterized by elemental analysis and spectroscopic methods. In addition, the molecular structure of dichloro-3,5-dimethyl-1-(pentamethylbenz

Full text of DOI:10.1016/j.tet.2012.07.058

Tetrahedron 68 (2012) 8655e8662
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Synthesis, characterization, and reactivity of ruthenium(II) complexes containing
h
6-arene-
h
1-pyrazole ligands
a
a
,
b
a
_
*
€
Belgin Tunc¸ el Kırkar , Hayati Turkmen , Ibrahim Kani , Bekir C¸ etinkaya
a Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey
b Department of Chemistry, Anadolu University, 26470 Eskisehir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 May 2012
Received in revised form 19 June 2012
Accepted 17 July 2012
Available online 27 July 2012
New ruthenium(II) complexes containing
h h
6-arene- 1-pyrazole ligands were synthesized and charac-
terized by elemental analysis and spectroscopic methods. In addition, the molecular structure of di-
chloro-3,5-dimethyl-1-(pentamethylbenzyl)-pyrazoleeruthenium(II), [Ru]L3b, was determined by X-ray
diffraction studies. These complexes were applied in the transfer hydrogenation of acetophenone by
isopropanol in the presence of potassium hydroxide. The activities of the catalysts were monitored by
NMR.
Keywords:
Areneeruthenium(II) complexes
Pyrazole
Ó 2012 Elsevier Ltd. All rights reserved.
Transfer hydrogenation
Half-sandwich complexes
1. Introduction
the metal centre, preventing rapid oxidation to ruthenium(III).
Moreover, the arene ligands are relatively inert towards sub-
The asymmetric version of transfer hydrogenation reaction was
reported first as an enantioface discriminating reduction in the
1970s from the groups of Ohkubo and Sinou, who explored the
catalysis with [RuCl2(PPh3)3] in the presence of either a chiral
monophosphine or a chiral hydrogen donor.1 Since then, a wide
range of metal complexes coupled with various chiral phosphorus
and nitrogen ligands have been explored to catalyze the asym-
metric transfer hydrogenation of ketones and olefins.2 There is little
doubt that the last decade has witnessed the most celebrated
achievements in transfer hydrogenation/asymmetric transfer hy-
drogenation chemistry, highlighted by the advent of highly active,
selective and productive catalytic systems.3 Among the catalysts
developed for asymmetric transfer hydrogenation, the most im-
portant and significant are Ru(II) complexes containing mono-
tosylated 1,2-diamines, discovered by Hashiguchi, Ikariya, Noyori
and co-workers in 1995.4
stitution reactions and consequently are often considered as
spectator ligands. However, the arene moiety, which is strongly
coordinated to the ruthenium atom can be customized by simply
attaching different substituents. These functionalized substituents
can be modified to tune the properties of the areneeruthenium
complexes. The three remaining coordination sites opposite to the
arene ligand can be used to introduce a wide variety of ligands
with N-, O-, S- or P-donor atoms. The resulting complexes are
neutral, mono- or dicationic, and often these ligands are labile.
Among the arene-based ligands those containing
h -
6-arene-h1
pyrazole is limited to only two examples5 despite their obvious
interest in preparation of stable and rigid molecules as potential
catalyst.
The main purpose of this study was synthesize arene ligand in
which the arene bears pyrazole substituents and to synthesize of
new tethered areneeruthenium(II) derivatives that contain these
ligands. In addition, the influence of linker length of the donor to
the arene ring and nature of the donor ligand has been studied.
Ligands that contained different substituted phenyl rings and
pyrazole or 3,5-dimethylpyrazole were also used. The synthesis of
new complexes exploited arene exchange at high temperature to
afford arene complexes with coordinating pendant groups. New
half-sandwich ruthenium complexes that have pyrazole
substituted derivatives have been studied in a comprehensive
manner.
Areneeruthenium complexes play an increasingly important
role in organometallic chemistry. They appear to be good starting
materials for access to reactive arene metal hydrides intermediates
that have been used recently for carbonehydrogen bond activa-
tion. The presence of the aromatic p-ligand stabilizes and protects
* Corresponding author. Tel.: þ90 232 3881713; fax: þ90 232 3888264; e-mail
€
address: hayatiturkmen@hotmail.com (H. Turkmen).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.07.058

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B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
2+
2.2. X-ray structure of complex [Ru]L3b
-
2 PF6
The solid state structure of complex [Ru]L3b has been de-
termined by single X-ray analysis. The complex crystallizes in P21c
space group in a monoclinic crystal system. ORTEP diagram of
complex [Ru]L3b including atom numbering is shown in Fig. 1.
Details of crystallographic data collection parameters are summa-
rized in Table 1. Selected bond lengths and bond angles are listed in
Table 2. The geometry around the ruthenium atom can be regarded
as pseudo octahedral with p-cymene occupying six coordination
N
N
N
Ru
N
N
N
A
sites in h
6-fashion while the remaining coordination sites are oc-
cupied by two chlorine and nitrogen atom of coordinated ligand.
The complex adopts the well-known ‘piano stool’ structure as ev-
ident by the nearly 90ꢀ bond angles for N1eRu1eCl2 (88.91 (9)ꢀ)
and Cl1eRu1eCl2 (89.01 (10)ꢀ).
In addition, it has been envisioned that the resulting complexes
should be compared as catalysts for the transfer hydrogenation of
acetophenone by isopropanol in the presence of potassium hy-
droxide, since this indicates electron-donating properties of the
ligand on the ruthenium complex. The encapsulated are-
neeruthenium complex5 (A) has structural similarities with our
new ruthenium complexes. For that reason catalytic transfer hy-
drogenation has been studied with this complex too. Results of the
experiments were compared with catalytic activity results of our
new ruthenium complexes.
The ruthenium atom is
average RueC distance of 2.179(4) A. The average CeC bond length
in the p-cymene ring is 1.435 A with alternating short and long
p bonded to the p-cymene ring with an
ꢀ
ꢀ
bonds. Bonds C(2)eC(3), C(4)eC(5), C(6)eC(1) are shorter than
C(1)eC(2), C(3)eC(4), C(5)eC(6), which could be due to the loss of
planarity of the p-cymene ring. The largest ring torsion is ꢁ7.07ꢀ
(C5eC4eC3eC2). Similar patterns of alternate short and long CeC
bonds of the p-cymene ring are reported in other p-cyme-
neeruthenium complexes9,10 and are indicative of a contribution
from the cyclohexatriene resonance structures to the overall res-
onance hybrid. The p-cymene ligand is very close to planer ge-
ometry: the largest ring torsion of 3.01ꢀ (C8eC1eC2eC7). The
pyrazole ligand is almost perpendicular to the p-cymene ligand;
the mean plane angle of the ligands is 81.76ꢀ. The ruthenium
2. Results and discussion
2.1. Synthesis, characterization of pyrazole ligands and their
complexes
The pyrazole-functionalized arene ligands were synthesized
according to the steps illustrated in Scheme 1. Pyrazole derivatives
and 2,4,6-trimethylbenzyl bromide, 2,3,5,6-tetramethylbenzyl bro-
mide, 2,3,4,5,6-pentamethylbenzyl bromide, 1,3-bis(bromomethyl)-
ꢀ
arene centroid ring distance (1.642 A) is shorter than for analogous
ruthenium(II)earene complexes containing chelated ethylenedi-
11
amine ligands (e.g., [(h6-p-cym)Ru(en)Cl]PF6, 1.6692(14) A, [(h6
-
ꢀ
12
ꢀ
2,4,6-trimethylbenzene
or
1,4-bis(bromomethyl)-2,3,5,6-
bip)Ru(en)Cl]PF6, 1.662(3) A) and phenylazo-pyrazole ligands
ꢀ
tetramethylbenzene were heated in the presence of K2CO3 in tolu-
ene at reflux. All new ligands have been isolated as colourless and air
stable solids. Compounds L1a,b, L2a,b, L3a,b, L4a,b and L5a,b have been
characterized by 1H and 13C NMR spectroscopy. In 1H NMR spectra for
(e.g., [(h6-p-cym)Ru(azpy)Cl]PF6, 1.7203(16) A; [(
h
6-bip)Ru(azpy)
Cl]PF6, 1.707(2) A; and [(
h
6-p-cym)Ru(azpyeNMe2)Cl]PF6,
ꢀ
13
ꢀ
ꢀ
1.7107(15) A). The RueN bond (2.131(2) A) in complex [Ru]L3b is
longer than the phenylazo-pyrazole chlorido Ru(II) arene com-
ꢀ
L
1a, L2a, L3a, L4a and L5a the benzylic CH2 and CH protons at 4-position
ofpyrazolewere observed as singlet andtriplets in 2:1 ratio ataround
5.44e5.33 ppm and
6.19e6.16 ppm, respectively. In 1H NMR
spectra for L1b, L2b, L3b, L4b and L5b the CH2 and pyrazole-CH protons
observed as singlet and singlet in 2:1 ratio at around 5.26e5.17 ppm
and
5.73e5.77 ppm. The 1H NMR spectra of L1b, L2b, L3b, L4b and L5b
plexes (2.026(3)e2.046(5) A).
In the extended structure, no classical hydrogen bond in-
teractions have been determined whereas the strong CeH/N,
CeH/Cl intermolecular interactions have been observed. These
interactions are effective in forming a pseudo multi-dimensional
polymer chains (Fig. 2). Molecules are linked by pairs of
d
d
d
d
ꢀ
ꢀ
showedsignificantdifferences fromL1a, L2a, L3a, L4a andL5a:a marked
effect of methyl groups on pyrazole ring was observed. CH2 and
pyrazole-CH protons for L1b, L2b, L3b, L4b and L5b compounds were
observed to shift towards higher fields as compared to L1a, L2a, L3a, L4a
and L5a ligands.
C11eH11B/N2 (2.741 A) and C17eH17A/Cl2 (2.857 A),
ꢀ
ꢀ
C17eH17B/C15 (2.757 A), C11eH11C/Cl2 (2.784 A),
C16eH16A/Cl2 (2728 A) hydrogen bonds.
ꢀ
3. Catalytic studies
Ru(II)epyrazole complexes were synthesized by reaction of
[Ru(p-cymene)Cl2]2 with the pyrazole ligands (L1a,b, L2a,b, L3a,b
,
Ru(II)epyrazole complexes are efficient catalytic precursors for
the transfer hydrogenation of ketones to alcohols with 2-propanol
as hydrogen donor in the presence of base. In order to improve the
reactivity of our catalytic system, we examined the influence of the
base. The bases were screened in the model reaction (acetophe-
none in IPA at 82 ꢀC, reaction time 3 h, [Ru]L2a as catalyst). With the
organic base triethylamine (NEt3) and pyridine (Py), we observed
only poor yields. Using the inorganic bases Cs2CO3, K2CO3, KOH,
NaOH, and t-BuOK the conversion showed a dependency upon the
base strength. In general, the conversion rate: NEt3 (23%)<
Py(28%)<Cs2CO3(49%)<K2CO3(63%)<t-BuOK(81%)<NaOH(89%)<
KOH (95%). As in the previous study the best results were obtained
with KOH.14 Hence, it is decided that base KOH is the best com-
promise between optimum reaction rate in isopropanol and
reaching 95% conversion for acetophenone within 3 h. In the ab-
sence of a base no transfer hydrogenation of the ketones was ob-
served. The behaviour of the complexes in the transfer
L4b and L5a) in DMF (Scheme 1). All new complexes have been
isolated as orange and air stable solids. They are insoluble non-
polar solvents such as diethyl ether, hexane and pentane. The
new complexes were characterized by 1H and 13C NMR, and [Ru]
L3a by elemental analysis. The structure of [Ru]L3b was de-
termined by X-ray diffraction. All complexes gave 1H and 13C
NMR spectra corresponding to the proposed formulation. The 1H
NMR spectra of these complexes showed some differences from
their respective ligands. CH2 protons of [Ru]L1a,b, [Ru]L2a,b, [Ru]
L
3a,b, [Ru]L4b and [Ru]L5a were observed to shift towards higher
fields as compared to respective ligands. On the other hand
pyrazole-CH for [Ru]L1a,b, [Ru]L2a,b, [Ru]L3a,b, [Ru]L4b and [Ru]
L5a were observed as general shift towards lower fields as com-
pared to respective ligands: effect of five-membered ring bond
formations between metal and areneepyrazole ligand in ruth-
enium(II) complexes.

B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
8657
Br
Br
Br
Br
Br
Br
Br
C
A
D
E
B
R
H
N
N
R
a: R = H
b: R = Me
(i)
R
R
R
R
R
R
N
N
N
R
N
N
N
N
R
N
N
N
N
N
N
N
R
R
R
R
R
R
L1
L4
L3
L5
L2
[Ru(p-cymene)Cl2]2
(ii)
N
N
N
Ru
R
N
N
N
Ru
Ru
R
Ru
Cl
Ru
Cl
N
N
N
R
R
R
R
N
R
N
N
N
Cl
R
Cl
Cl
Cl
Cl
N
Cl
Cl
Cl
R
R
R
R
R
R
[Ru]L3
[Ru]L2
[Ru]L1
[Ru]L5a
[Ru]L4b
Scheme 1. Synthesis of ligands L1eL5: (i) toluene, K2CO3, 10 h, reflux and their Ru(II) complexes; (ii) DMF, 140 ꢀC, 40 h.
hydrogenation of acetophenone in the presence of KOH by 2-
propanol was studied. The catalytic reactions were performed un-
der identical conditions to allow comparison of the results. To in-
vestigate the influence of auxiliary ligands on catalytic activity the
time dependency on [Ru]L1a,b, [Ru]L2a,b, [Ru]L3a,b, [Ru]L4b, [Ru]L5a
and A was also studied (Fig. 3).
As can be seen from Fig. 3, the Ru(II)epyrazole complexes
([Ru]L1a,b, [Ru]L2a,b, [Ru]L3a,b, [Ru]L4b, [Ru]L5a, A) are found to

8658
B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
Table 2
Selected bond lengths and angles of complex [Ru]L3b
Bond angles [ꢀ]
ꢀ
Bond lengths [A]
Ru1eCl2
Ru1eCl1
Ru1eN1
Ru1eC2
Ru1eC3
Ru1eC6
Ru1eC1
Ru1eC5
Ru1eC4
N1eN2
2.4182(7)
2.4235(7)
2.131(2)
2.220(3)
2.188(2)
2.220(3)
2.193(3)
2.173(3)
2.083(3)
1.375(3)
1.335(4)
1.472(3)
Cl2eRu1eCl1
N1eRu1eCl2
N1eRu1eCl1
N1eRu1eC2
N1eRu1eC3
N1eRu1eC6
N1eRu1eC1
N1eRu1eC5
89.01(3)
88.92(6)
92.43(6)
124.65(10)
91.08(10)
140.19(10)
160.08(9)
102.21(10)
N1eC13
N2eC10
dentate ligands bound to ruthenium over N atom and than arene
Fig. 1. Molecular structure of complex [Ru]L3b. All hydrogen atoms have been omitted
for clarity. Displacement ellipsoids are drawn at the 50% probability level.
ring to form five-membered ring. The encapsulation of the ruthe-
nium atom by a
atoms of pyrazole was carried out: [
h
6-arene ligand linked to one or two nitrogen
h
6-: 1-(C,N)Ru(areneCH2pyr-
h
be active catalysts in transfer hydrogenation of acetophenone.
Better behaviour of the tetramethylbenzyl derivatives against
other complexes was observed. The introduction of methyl sub-
stituents on the pyrazole rings has a positive effect. When the
existence of three pyrazole group on the complex (A), a negative
effect was observed. After 3 h reaction time; activity of the
complexes decreases in the following order: [Ru]L2a>[Ru]
azole)Cl2]. In the cases where the arene ring bears two pyrazole
moieties as in [Ru]L4 and [Ru]L5, the N of the second pyrazole does
not involve in the coordination, which may impose some strain in
the complexes. However, halide displacement by silver salts such as
AgBF4 may bring about the formation of cationic [
Ru(areneCH2pyrazole)Cl]BF4.
The unique structures displayed by these ruthenium complexes
promised some interesting chemistry. We have used catalytic
transfer hydrogenation reactions to probe the influence of sub-
stituent methyl groups both on pyrazole and the arene of new
h h
6-: 1-(C,N)
L
2b>[Ru]L3b>[Ru]L5a>[Ru]L3a>[Ru]L1b>[Ru]L4b>[Ru]L1a>A.
Additional transfer hydrogenation experiments with different
ketones are in progress.
areneeruthenium(II) complexes ([Ru]L1a,b, [Ru]L2a,b, [Ru]L3a,b
,
4. Conclusion
[Ru]L4b, [Ru]L5a) and also on the encapsulated areneeruthenium
complexes (A). The described Ru(II) complexes bearing pyrazole
and arene ligands reveal differences in their behaviour as pre-
catalysts for transfer hydrogenation of acetophenone. The best re-
sult in the transfer hydrogenation of acetophenone was obtained
with [Ru]L2a and the worst result was found with the cationic A.
Presumably, the presence of H atom at p-position of the arene ring
is playing an important role in the transfer hydrogenation reaction.
More attempts remain to be carried out for future.
In the ruthenium literature the chelating (h h
1-pyrazole): 6-arene
binding mode is limited to only two examples. Therefore, in this
work, arene ligands that contain different substituted 2,4,6-
trimethylbenzyl bromide, 2,3,5,6-tetramethylbenzyl bromide,
2,3,4,5,6-pentamethylbenzyl bromide,1,3-bis(bromomethyl)-2,4,6-
trimethylbenzene or 1,4-bis(bromomethyl)-2,3,5,6-tetramethyl
benzene and pyrazole or 3,5-dimethylpyrazole were used for syn-
thesis of areneeruthenium(II) complexes. The synthesis of new
complexes exploited arene exchange at high temperature and bi-
5. X-ray structural analyses of complex [Ru]L3b
Diffraction data for the complex were collected with Bruker
Table 1
SMART APEX-II CCD area-detector diffractometer using Mo Ka ra-
Crystal data and structure refinement for complex [Ru]L3b
ꢀ
diation (k¼0.71073 A) at T¼100 K. Diffraction data were collected
over the full sphere and were corrected for absorption. The data
reduction was performed with the Bruker SAINT15 program pack-
age. For further crystal and data collection details see Table 1.
Structure solution was found with the SHELXS-9716 package using
the direct-methods and were refined SHELXL-9717 against F2 using
first isotropic and later anisotropic thermal parameters for all non-
hydrogen atoms. Hydrogen atoms were added to the structure
model on calculated positions. Geometric calculations were per-
formed with Platon.18
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C17H24Cl2N2Ru
428.35
374(2)
monoclinic
P21/c
10.3137(8)
11.0544(8)
15.1129(11)
ꢀ
a/A
ꢀ
b/A
ꢀ
c/A
ꢀ
ꢀ
a
/
90.00
98.739(4)
90.00
b
/
ꢀ
g
/
3
ꢀ
Volume/A
1703.0(2)
Z
4
rcalcd/Mg mmꢁ3
1.671
1.232
6. Experimental
6.1. General
m/mmꢁ1
F(000)
872
Crystal size/mm3
0.384ꢂ0.205ꢂ0.151
2
Q Range for data collection
4e56.88ꢀ
Index ranges
ꢁ13ꢃhꢃ13, ꢁ14ꢃkꢃ11, ꢁ19ꢃlꢃ20
14,850
Unless otherwise noted, all operations were performed without
taking precautions to exclude air and moisture. All solvents and
chemicals were used as received without any further treatment if
not noted otherwise. Starting compounds and reagents were ob-
tained from Merck, Fluka, Alfa Aesar and Acros Organics; pyrazole
was obtained from Alfa Aesar and solvents like dichloromethane,
ethanol, diethyl ether, toluene, N,N-dimethylformamide, hexane,
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
4230[R(int)¼0.0400]
4230/0/206
0.775
Final R indexes [I>2
s(I)]
R1¼0.0305, wR2¼0.0921
R1¼0.0439, wR2¼0.1058
0.521/ꢁ0.766
Final R indexes [all data]
ꢀꢁ3
Largest diff. peak/hole [e A
]

B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
8659
Fig. 2. Hydrogen bonding interactions in complex [Ru]L3b along the b direction.
pentane were obtained from Merck and Ridel de Haen. [Ru(p-cym-
ene)Cl2]2
according to the literature. 2,4,6-Trimethylbenzyl bromide, 2,3,5,6-
tetramethylbenzyl bromide, 2,3,4,5,6-pentamethylbenzyl bromide,
cooling to ꢁ20 ꢀC. Yield: 1.89 g, 92%; mp: ca. 20 ꢀC. 1H NMR
6
and 3,5-dimethyl-1H-pyrozole7 were synthesized
(400 MHz, CDCl3):
d
7.52 (d, J¼1.95 Hz, 1H, HPzeH), 7.01 (d,
J¼2.34 Hz, 1H, HPzeH), 6.91 (s, 2H, AreH), 6.16 (t, J¼2.15 Hz, 1H,
HPzeH), 5.33 (s, 2H, CH2eAr), 2.28 (s, 9H, AreCH3). 13C NMR
1,3-bis(bromomethyl)-2,4,6-trimethylbenzene
bis(bromomethyl)-2,3,5,6-tetramethylbenzene
and
were
1,4-
prepared
(100 MHz, CDCl3): d 139.8, 138.2, 129.6, 128.9, 128.1, 109.9, 105.4
(AreC, HPzeC), 50.1 (CH2eAr),19.8, 21.2 (AreCH3). IR, nmax (CH2Cl2):
2989, 1650, 1613, 1463, 1383, 1313, 1254, 1134, 1091, 746 cmꢁ1. Anal.
Calcd for C13H16N2 (M¼200.28): C, 77.96; H, 8.05; N,13.19. Found: C,
78.01; H, 8.13; N, 13.29%.
according to literature.8 The complex (A) was prepared at according
to the literature.5 Melting points were recorded with Gallenkamp
electrothermal melting point apparatus. Elemental analysis data
were recorded with CHNS Elemental Analysis. 1H NMR and 13C NMR
spectra were recorded on a Varian AS 400 Mercury instrument. As
solvents CDCl3 and DMSO-d6 were employed. FTIR spectra were
recorded on a Perkin Elmer spectrum 100 series.
6.3. Synthesis of 3,5-dimethyl-1-(2,4,6-trimethylbenzyl)-1H-
pyrazole, L1b
Prepared according to the procedure of 1a except that 3,5-
dimethyl-1H-pyrazole (0.96 g; 10.0 mmol), 2,4,6-trimethylbenzyl
bromide (2.13 g, 10.0 mmol) and K2CO3 (1.80 g, 13 mmol) were
used. The residue was crystallized from hot hexane to give the title
compound as a colourless crystalline solid. Yield: 1.82 g, 80%; mp:
6.2. Synthesis of 1-(2,4,6-trimethylbenzyl)-1H-pyrazole, L1a
A
mixture of pyrazole (0.27 g; 4.00 mmol), 2,4,6-
trimethylbenzyl bromide (2.13 g; 10.0 mmol) and K2CO3 (1.80 g,
13.0 mmol) was refluxed 10 h in toluene (10 mL). Following the
completion of the process, the mixture was cooled to room tem-
perature, filtered and all volatiles of filtrate were removed. The
residue was crystallized from hexane to give colourless solid upon
99e101 ꢀC. 1H NMR (400 MHz, CDCl3):
d 6.85 (s, 2H, AreH), 5.74 (s,
1H, MePzeH), 5.17 (s, 2H, CH2eAr), 2.26 (s, 3H, AreCH3), 2.22 (s, 6H,
AreCH3), 2.17 (s, 3H, MePzeCH3), 2.00 (s, 3H, MePzeCH3). 13C NMR
(100 MHz, CDCl3):
d 147.1, 139.3, 137.8, 137.6, 129.9, 129.6, 105.5
(AreC, MePzeC), 48.3 (CH2eAr), 21.2, 20.3, 13.8, 11.4 (AreCH3,
MePzeCH3). IR, nmax (CH2Cl2): 2978, 1652, 1599, 1460, 1303, 1244,
1119, 1051, 777 cmꢁ1. Anal. Calcd for C15H20N2 (M¼228.33): C,
78.90; H, 8.83; N, 12.27. Found: C, 78.88; H, 8.74; N, 12.22%.
O
OH
0.1 mol % Ru(II)
1 mol % KOH
O
OH
+
+
82 °C
100
90
80
70
60
50
40
30
20
10
0
6.4. Synthesis of 1-(2,3,5,6-tetramethylbenzyl)-1H-pyrazole,
L2a
[Ru]L1a
[Ru]L1b
[Ru]L2a
[Ru]L2b
[Ru]L3a
[Ru]L3b
[Ru]L4b
[Ru]L5a
A
Prepared according to the procedure of L1a except that pyrazole
(0.68 g, 10.0 mmol), 2,3,5,6-tetramethylbenzyl bromide (2.27 g,
10.0 mmol) and K2CO3 (1.80 g, 13 mmol) were used. The residue
was crystallized from hot hexane to give the title compound as
a colourless crystalline solid. Yield: 1.99 g, 93%; mp: 67e69 ꢀC. 1H
NMR (400 MHz, CDCl3):
d
7.53 (s, 1H, AreH), 7.01 (d, J¼1.56 Hz, 1H,
HPzeH), 6.99 (d, J¼1.56 Hz, 1H, HPzeH), 6.16 (t, J¼1.56 Hz, 1H,
HPzeH), 5.40 (s, 2H, CH2eAr), 2.25 (s, 6H, AreCH3), 2.18 (s, 6H,
0
1
2
3
4
5
6
AreCH3). 13C NMR (100 MHz, CDCl3):
d 139.3, 134.5, 134.3, 132.4,
131.6, 128.2, 125.3 (AreC, HPzeC), 50.8 (CH2eAr), 20.7, 15.7
(AreCH3). IR, nmax (CH2Cl2): 2978, 1644, 1618, 1453, 1366, 1288,
1134, 1086, 769 cmꢁ1. Anal. Calcd for C14H18N2 (M¼214.30): C,
78.46; H, 8.47; N, 13.07. Found: C, 78.43; H, 8.53; N, 13.00%.
time (h)
Fig. 3. Time dependency of transfer hydrogenation of acetophenone catalyzed by the
complexes [Ru]L1a,b, [Ru]L2a,b, [Ru]L3a,b, [Ru]L4b, [Ru]L5a and A. Reactions were carried
out at 82 ꢀC using 10 mmol acetophenone with 0.1 mol % Ru(II) in 20 mL of 2-propanol.

8660
B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
6.5. Synthesis of 3,5-dimethyl-1-(2,3,5,6-tetramethylbenzyl)-
1H-pyrazole, L2b
739 cmꢁ1. Anal. Calcd for C17H20N4 (M¼280.37): C, 72.83; H, 7.19; N,
19.98. Found: C, 72.80; H, 7.15; N, 20.02%.
Prepared according to the procedure of L1a except that 3,5-
6.9. Synthesis of 1,10-[(2,4,6-trimethylbenzene-1,4-diyl)dime-
dimethyl-1H-pyrazole
(0.96
g,
10.0
mmol),
2,3,5,6-
thanediyl]bis(3,5-dimethyl-1H-pyrazole), L4b
tetramethylbenzyl bromide (2.27 g, 10.0 mmol) and K2CO3
(1.80 g, 13.0 mmol) were used. The residue was crystallized from
hot hexane to give the title compound as a colourless crystalline
solid. Yield: 2.06 g, 85%; mp: 119e121 ꢀC. 1H NMR (400 MHz,
Prepared according to the procedure of L1a except that 3,5-
dimethyl-1H-pyrazole (1.92 g, 20.0 mmol), 1,4-bis(bromomethyl)-
2,4,6-trimethylbenzene (3.05 g, 10.0 mmol) and K2CO3 (1.80 g,
13.0 mmol) were used. The residue was crystallized from hot
hexane to give the title compound as a colourless crystalline solid.
Yield: 2.68 g, 80%; mp: 235e238 ꢀC. 1H NMR (400 MHz, CDCl3):
CDCl3):
d
6.94 (s, 1H, AreH), 5.76 (s, 1H, MePzeH), 5.25 (s, 2H,
CH2eAr), 2.25 (s, 6H, MePzeCH3), 2.19 (s, 9H, AreCH3, MePzeCH3),
2.01 (s, 3H, MePzeCH3). 13C NMR (100 MHz, CDCl3):
d 147.1, 139.2,
134.1, 134.09, 132.7, 131.9, 105.1 (AreC, MePzeC), 49.0 (CH2eAr),
20.8, 15.9, 13.9, 11.5 (AreCH3, MePzeCH3). IR, nmax (CH2Cl2): 2982,
1677, 1603, 1513, 1403, 1299, 1224, 1117, 1086, 758 cmꢁ1. Anal. Calcd
for C16H22N2 (M¼242.36): C, 79.29; H, 9.15; N, 11.56. Found: C,
79.23; H, 9.13; N, 11.61%.
d
6.92 (s, 1H, AreH), 5.73 (s, 2H, MePzeH), 5.18 (s, 4H, CH2eAr), 2.28
(s, 6H, AreCH3), 2.15 (s, 6H, MePzeCH3), 2.14 (s, 3H, AreCH3). 13C
NMR (100 MHz, CDCl3): d 147.1, 139.2, 138.2, 137.7, 131.1, 131.1, 105.5
(AreC, MePzeC), 48.5 (CH2eAr), 20.6, 16.1, 13.8, 11.5 (AreCH3,
MePzeCH3). IR, nmax (CH2Cl2): 2980, 1656, 1612, 1454, 1387, 1311,
1240,1103, 1065, 768 cmꢁ1. Anal. Calcd for C21H28N4 (M¼336.47): C,
74.96; H, 8.39; N, 16.65. Found: C, 74.99; H, 8.44; N, 16.60%.
6.6. Synthesis of 1-(pentamethylbenzyl)-1H-pyrazole, L3a
Prepared according to the procedure of L1a except that pyrazole
(0.27 g, 4.0 mmol), 2,3,4,5,6-pentamethylbenzyl bromide (0.97 g,
4.0 mmol) and K2CO3 (0.83 g, 6.0 mmol) were used. The residue was
crystallized from hot hexane to give the title compound as a cream
solid. Yield: 0.87 g, 95%; mp: 76e78 ꢀC. 1H NMR (400 MHz, CDCl3):
6.10. Synthesis of 1,10-[(2,3,5,6-tetramethylbenzene-1,4-diyl)
dimethanediyl]bis(1H-pyrazole), L5a
Prepared according to the procedure of L1a except that pyrazole
(1.36
g,
20.0
mmol),
1,4-bis(bromomethyl)-2,3,5,6-
d
7.56 (d, J¼2.15 Hz, 1H, HPzeH), 7.03 (d, J¼2.15 Hz, 1eH, HPzeH),
tetramethylbenzene (3.20 g, 10.0 mmol) and K2CO3 (1.80 g,
13.0 mmol) were used. The residue was crystallized from hot
hexane to give the title compound as a colourless crystalline solid.
Yield: 2.72 g, 93%; mp: 160e162 ꢀC. 1H NMR (400 MHz, CDCl3):
6.17 (t, J¼2.15 Hz, 1H, HPzeH), 5.44 (s, 2H, CH2eAr), 2.28 (s, 3H,
AreCH3), 2.26 (s, 6H, AreCH3), 2.25 (s, 6H, AreCH3). 13C NMR
(100 MHz, CDCl3):
d 139.3, 136.0, 133.9, 133.3, 128.9, 128.3, 105.2
(AreC, HPzeC), 51.3 (CH2eAr), 17.4, 17.1, 16.7 (AreCH3). IR, nmax
(CH2Cl2): 2977, 1648, 1619, 1473, 1412, 1319, 1240, 1130, 1077,
763 cmꢁ1. Anal. Calcd for C15H20N2 (M¼228.33): C, 78.90; H, 8.83;
N, 12.27. Found: C, 78.83; H, 8.88; N, 12.33%.
d
7.55 (d,
d
¼2.68 Hz, 2H, HPzeH), 7.05 (d,
d
¼2.34 Hz, 2H, HPzeH),
6.19 (t,
d
¼1.04 Hz, 2H, HPzeH), 5.44 (s, 4H, CH2eAr), 2.27 (s, 12H,
AreCH3). 13C NMR (100 MHz, CDCl3):
d 139.5, 135.1, 132.5, 128.3,
105.4 (AreC, HPzeC), 51.2 (CH2eAr), 16.7 (AreCH3). IR, nmax
(CH2Cl2): 2987, 1661, 1623, 1472, 1379, 1322, 1259, 1130, 1077,
760 cmꢁ1. Anal. Calcd for C18H22N4 (M¼294.39): C, 73.44; H, 7.53; N,
19.03. Found: C, 73.38; H, 7.54; N, 19.11%.
6.7. Synthesis of 3,5-dimethyl-1-(pentamethylbenzyl)-1H-
pyrazole, L3b
Prepared according to the procedure of L1a except that 3,5-
6.11. Synthesis of 1,10-[(2,3,5,6-tetramethylbenzene-1,4-diyl)
dimethyl-1H-pyrazole
(1.20
g,
12.4
mmol),
2,3,4,5,6-
dimethanediyl]bis(3,5-dimethyl-1H-pyrazole), L5b
pentamethylbenzyl bromide (3 g, 12.44 mmol) and K2CO3 (2.07 g,
15 mmol) were used. The residue was crystallized from hot ethanol
to give the title compound as a colourless crystalline solid. Yield:
Prepared according to the procedure of L1b except that 3,5-
dimethyl-1H-pyrazole (1.92 g, 20.0 mmol), 1,4-bis(bromomethyl)-
2,3,5,6-tetramethylbenzene (3.20 g, 10.0 mmol) and K2CO3 (1.80 g,
13.0 mmol) were used. The residue was crystallized from hot
hexane to give the title compound as a colourless crystalline solid.
Yield: 2.98 g, 85%; mp: 248e250 ꢀC. 1H NMR (400 MHz, CDCl3):
2.71 g, 85%; mp: 139e141 ꢀC. 1H NMR (400 MHz, CDCl3):
d 5.77 (s,
1H, MePzeH), 5.26 (s, 2H, CH2eAr), 2.28 (s, 3H, AreCH3), 2.27 (s, 6 H
AreCH3), 2.26 (s, 6H, AreCH3), 2.21 (s, 3H, MePzeCH3), 2.06 (s, 3H,
MePzeCH3). 13C NMR (100 MHz, CDCl3):
d 147.1, 138.7, 135.2, 133.8,
132.9, 130.0, 105.5 (AreC, MePzeC), 49.3 (CH2eAr), 17.4, 17.1, 16.9,
13.1, 11.6 (AreCH3, MePzeCH3). IR, nmax (CH2Cl2): 2979, 1633, 1599,
1455, 1375, 1334, 1245, 1124, 1087, 754 cmꢁ1. Anal. Calcd for
C17H24N2 (M¼256.39): C, 79.64; H, 9.44; N, 10.93. Found: C, 79.66;
H, 9.35; N, 11.02%.
d
5.75 (s, 2H, MePzeH), 5.24 (s, 4H, CH2eAr), 2.23 (s, 12H, AreCH3),
2.17 (s, 6H, MePzeCH3), 2.04 (s, 6H, MePzeCH3). 13C NMR (100 MHz,
CDCl3):
d
147.2, 139.1, 134.6, 132.7, 105.5 (AreC, MePzeC), 49.2
(CH2eAr), 16.9, 13.9, 11.5 (AreCH3, MePzeCH3). IR, nmax (CH2Cl2):
2984, 1647, 1614, 1476, 1334, 1304, 1261, 1133, 1088, 743 cmꢁ1. Anal.
Calcd for C22H30N4 (M¼350.50): C, 73.44; H, 7.53; N, 19.03. Found:
C, 73.41; H, 7.62; N, 19.06%.
6.8. Synthesis of 1,10-[(2,4,6-trimethylbenzene-1,4-diyl)dime-
thanediyl]bis(1H-pyrazole), L4a
6.12. Synthesis of ruthenium(II) complexes
Prepared according to the procedure of L1a except that pyrazole
(1.36 g, 20 mmol), 1,4-bis(bromomethyl)-2,4,6-trimethylbenzene
(3.05 g, 10 mmol) and K2CO3 (1.8 g, 13 mmol) were used. The res-
idue was crystallized from hot hexane to give the title compound as
a colourless crystalline solid. Yield: 1.96 g, 70%; mp: 78e80 ꢀC. 1H
6.12.1. Synthesis
of
dichloro-1-(2,4,6-trimethylbenzyl)-pyr-
azoleeruthenium(II), [Ru]L1a. [Ru(p-cymene)Cl2]2 (105.0 mg,
0.17 mmol) wasadded to a solutionof 1-(2,4,6-trimethylbenzyl)-1H-
pyrazole (106.2 mg, 0.53 mmol) in DMF (5 mL), the mixture was
stirred for 60 min at room temperature and then was heated to
140 ꢀC and stirred vigorously at this temperature for 48 h under
argon. A change in colour of the solution from orange to dark-brown
was observed. After cooling the mixture, diethyl ether added, then
the precipitated orange solid was collected by filtration. A residue
was solved in CH2Cl2 and diethyl ether diffusion into the solution
NMR (400 MHz, CDCl3):
d
7.52 (d, J¼2.16 Hz, 2H, HPzeH), 7.03 (s, 1H,
AreH), 7.02 (d, J¼2.16 Hz, 2H, HPzeH), 6.18 (t, J¼2.16 Hz, HPzeH),
5.37 (s, 4H, CH2eAr), 2.33 (s, 6H, AreCH3), 2.23 (s, 9H, AreCH3). 13
C
NMR (100 MHz, CDCl3):
d 141.3, 138.9, 138.7, 131.3, 130.6, 128.1,
105.5 (AreC, HPzeC), 50.5 (CH2eAr), 20.2, 15.6 (AreCH3). IR, nmax
(CH2Cl2): 2982, 1638, 1616, 1569, 1379, 1322, 1244, 1123, 1077,

B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
8661
give the orange crystals of dichloro-1-(2,4,6-trimethylbenzyl)-pyr-
(M¼400.31): C, 45.01; H, 5.04; N, 7.00. Found: C, 45.06; H, 5.12; N,
azoleeruthenium(II). Yield: 69.6 mg, 55%; mp: 225 ꢀC (decomp.). 1H
7.10.
NMR (400 MHz, CDCl3):
d
7.96 (d, J¼1.95 Hz, 1H, HPzeH), 7.42 (d,
J¼1.95 Hz, 1H, HPzeH), 6.24 (t, J¼1.95 Hz, 1H, HPzeH), 5.69 (s, 2H,
AreH), 5.01 (s, 2H, CH2eAr), 2.22 (s, 6H, AreCH3), 2.10 (s, 3H,
6.12.6. Synthesis of dichloro-3,5-dimethyl-1-(pentamethylbenzyl)-
pyrazoleeruthenium(II), [Ru]L3b. Prepared according to the pro-
cedure of [Ru]L1a except that [(p-cymene)RuCl2]2 (105.0 mg,
0.17 mmol) and 3,5-dimethyl-1-(pentamethylbenzyl)-1H-pyrazole
(135.9 mg, 0.53 mmol) were used. Yield: 105.3 mg, 72%; mp: 233 ꢀC
AreCH3). 13C NMR (100 MHz, CDCl3):
d 139.1, 138.2, 137.7, 130.7,
129.8, 129.6, 105.5 (AreC, HPzeC), 49.6 (CH2eAr), 21.2, 20.1
(AreCH3). IR, nmax (CH2Cl2): 3839, 3747, 3311, 2924,1614,1558,1370,
750 cmꢁ1. Anal. Calcd for C13H26Cl2N2Ru (M¼372.26): C, 41.94; H,
4.33; N, 7.53. Found: C, 41.96; H, 4.25; N, 7.60.
(decomp.). 1H NMR (400 MHz, CDCl3):
d
5.87 (s, 1H, MePzeH), 4.91
(s, 2H, CH2eAr), 2.41 (s, 3H, MePzeCH3), 2.22 (s, 3H, MePzeCH3), 2.16
(s, 6H, AreCH3), 2.10(s, 6H, AreCH3), 2.08 (s, 3H, AreCH3). 13C NMR
6.12.2. Synthesis of dichloro-3,5-dimethyl-1-(2,4,6-trimethylbenzyl)-
pyrazoleeruthenium(II), [Ru]L1b. Prepared according to the pro-
cedure of [Ru]L1a except that [(p-cymene)RuCl2]2 (105.0 mg,
0.17 mmol) and 3,5-dimethyl-1-(2,4,6-trimethylbenzyl)-1H-pyr-
azole (121.0 mg, 0.53 mmol) were used. Yield: 54.5 mg, 40%; mp:
(100 MHz, CDCl3): d 154.1, 140.2, 108.7, 102.7, 88.8, 86.4, 83.5 (AreC,
MePzeC), 48.4 (CH2eAr), 29.9, 16.0, 14.9, 14.3, 12.5 (AreCH3,
MePzeCH3). IR, nmax (CH2Cl2): 3815, 3747, 3649, 2919, 1737, 1559,
1376, 749 cmꢁ1. Anal. Calcd for C17H24Cl2N2Ru (M¼428.36); C,
47.67; H, 5.65; N, 6.54. Found: C, 47.56; H, 5.62; N, 6.61.
234 ꢀC (decomp.). 1H NMR (400 MHz, CDCl3): 5.90 (s,1H, MePzeH),
d
5.64 (s, 2H, AreH), 4.87 (s, 2H, CH2eAr), 2.43 (s, 3H, MePzeCH3 ), 2.28
(s, 3H, MePzeCH3), 2.22 (s, 6H, AreCH3), 2.21 (s, 3H, AreCH3). 13C
6.12.7. Synthesis of 1,10-[(2,4,6-trimethylbenzene-1,4-diyl)dimetha-
nediyl]bis(3,5-dimethyl-1H-pyrazole)eruthenium(II),
[Ru]
NMR (100 MHz, CDCl3):
d
147.8, 143.9, 140.6, 108.8, 94.4, 89.3, 87.3
L4b. Prepared according to the procedure of [Ru]L1a except that [(p-
(AreC, MePzeC), 46.9 (CH2eAr), 17.5, 16.7, 14.0, 12.6 (AreCH3,
MePzeCH3). IR, nmax (CH2Cl2): 3812, 3744, 3645, 2923, 1741, 1555,
1366, 748 cmꢁ1. Anal. Calcd for C15H20Cl2N2Ru (M¼400.31): C, 45.01;
H, 5.04; N, 7.00. Found: C, 45.06; H, 5.12; N, 7.09.
cymene)RuCl2]2 (105.0 mg, 0.17 mmol) and 1,10-[(2,4,6-
trimethylbenzene-1,4-diyl)dimethanediyl]bis(3,5-dimethyl-1H-
pyrazole) (269.3 mg, 0.53 mmol) were used. Yield: 103.7 mg, 60%;
mp: 225 ꢀC (decomp.). 1H NMR (400 MHz, CDCl3):
d 5.91 (s, 1H,
AreH), 5.80 (s, 1H, MePzeH), 5.67 (s, 1H, MePzeH), 5.07 (s, 2H,
CH2eAr), 4.88 (s, 2H, CH2eAr), 2.43, 2.37 (s, 6H, MePzeCH3), 2.26,
2.23, 2.19 (s, 9H, AreCH3), 2.14, 2.09 (s, 6H, MePzeCH3). 13C NMR
6.12.3. Synthesis
of
dichloro-1-(2,3,4,6-tetramethylbenzyl)-pyr-
azoleeruthenium(II), [Ru]L2a. Prepared according to the procedure
of [Ru]L1a except that [(p-cymene)RuCl2]2 (105.0 mg, 0.17 mmol)
(100 MHz, CDCl3): d 154.1, 148.5, 140.7, 140.1, 108.9, 105.3, 96.7, 95.5,
and
1-(2,3,5,6-tetramethylbenzyl)-1H-pyrazole
(113.6
mg,
89.8, 89.7, 89.6, 87.3 (AreC, MePzeC), 47.5, 46.4 (CH2eAr), 16.9, 16.8,
14.1, 13.9, 13.7, 12.6, 11.5 (AreCH3, MePzeCH3). IR, nmax (CH2Cl2):
3820, 3746, 3651, 2927, 1729, 1548, 1369, 753 cmꢁ1. Anal. Calcd for
C21H28Cl2N4Ru (M¼508.45): C, 46.61; H, 5.55; N, 11.02. Found: C,
46.58; H, 5.49; N, 11.08.
0.53 mmol) were used. Yield: 85.4 mg, 65%; mp: 254 ꢀC (decomp.).
1H NMR (400 MHz, CDCl3):
d
7.39 (d, J¼2.14 Hz, 1H, HPzeH), 7.38 (d,
J¼2.14 Hz, 1H, HPzeH), 6.95 (s, 1H, AreH), 6.16 (t, J¼2.14 Hz, 1H,
HPzeH), 5.33 (s, 2H, CH2eAr), 2.17 (s, 2H, AreCH3). 13C NMR
(100 MHz, CDCl3):
d 139.5, 131.1, 109.2, 105.8, 104.3, 88.9, 84.1
(AreC, HPzeC), 48.9 (CH2eAr), 18.3, 15.7 (AreCH3). IR, nmax
(CH2Cl2): 3811, 3750, 3652, 2924, 1728, 1565, 1373, 750 cmꢁ1. Anal.
Calcd for C14H18Cl2N2Ru (M¼386.28): C, 45.53; H, 4.70; N, 7.25.
Found: C, 45.51; H, 4.62; N, 7.30.
6.12.8. Synthesis of 1,10-[(2,3,5,6-tetramethylbenzene-1,4-diyl)dime-
thanediyl]bis(1H-pyrazole)-ruthenium(II),
according to the procedure of [Ru]L1a except that [(p-cymene)
RuCl2]2 (105.0 mg, 0.17 mmol) and
1,10-[(2,3,5,6-
[Ru]L5a. Prepared
tetramethylbenzene-1,4-diyl)dimethanediyl]bis(1H-pyrazole)
6.12.4. Synthesis of dichloro-3,5-dimethyl-1-(2,3, 5,6-
(156.0 mg, 0.53 mmol) were used. Yield: 90.4 mg, 57%; mp: 233 ꢀC
tetramethylbenzyl)-pyrazoleeruthenium(II),
[Ru]L2b. Prepared
(decomp.). 1H NMR (400 MHz, CDCl3):
d
7.71 (d, J¼2.34 Hz, 1H,
according to the procedure of [Ru]L1a except that [(p-cymene)
RuCl2]2 (105.0 mg, 0.17 mmol) and 3,5-dimethyl-1-(2,3,5,6-
tetramethylbenzyl)-1H-pyrazole (128.5 mg, 0.53 mmol) were
used. Yield: 87.3 mg, 62%; mp: 245 ꢀC (decomp.). 1H NMR
HPzeH), 7.55 (d, J¼1.95 Hz, 1H, HPzeH), 7.49 (d, J¼2.34 Hz, 1H,
HPzeH), 7.40 (d, J¼1.95 Hz, 1H, HPzeH), 6.43 (t, J¼1.95 Hz, 1H,
HPzeH), 6.30 (t, J¼2.34 Hz, 1H, HPzeH), 5.27 (s, 2H, CH2eAr), 5.24 (s,
2H, CH2eAr), 2.25 (s, 6H, AreCH3), 2.04 (s, 6H, AreCH3). 13C NMR
(400 MHz, CDCl3):
d
5.82 (s, 1H, AreH), 4.89 (s, 1H, MePzeH), 4.82 (s,
(100 MHz, CDCl3): d 140.6, 140.1, 130.6, 129.9, 109.2, 106.2, 105.0,
2H, CH2eAr), 2.34 (s, 3H, MePzeCH3), 2.20 (s, 3H, MePzeCH3), 2.14 (s,
6H, AreCH3), 2.01 (s, 6H, AreCH3). 13C NMR (100 MHz, CDCl3):
90.6, 79.6, 88.9 (AreC, HPzeC), 51.1, 50.4 (CH2eAr), 15.2, 14.9
(AreCH3). IR, nmax (CH2Cl2): 3811, 3739, 3637, 2926,1741,1560,1381,
747 cmꢁ1. Anal. Calcd for C18H22Cl2N4Ru (M¼466.37): C, 46.36; H,
4.75; N, 12.01. Found: C, 46.42; H, 4.62; N, 12.08.
d
151.7, 141.7, 107.9, 104.0, 92.5, 85.7, 75.8 (AreC, MePzeC), 48.1
(CH2eAr), 18.4, 14.4, 13.7, 12.3 (AreCH3, MePzeCH3). IR, nmax
(CH2Cl2): 3812, 3740, 3659, 2915, 1721, 1563, 1374, 755 cmꢁ1. Anal.
Calcd for C16H22Cl2N2Ru (M¼414.34): C, 46.38; H, 5.35; N, 6.76.
Found: C, 46.46; H, 5.26; N, 6.80.
6.13. General method for transfer hydrogenation of aceto-
phenone using Ru(II) complexes
6.12.5. Synthesis
of
dichloro-1-(pentamethylbenzyl)-pyr-
A mixture of acetophenone (10.0 mmol), the catalyst (0.01 mmol
Ru(II)), and propan-2-ol (19 mL) was stirred at 82 ꢀC for 10 min and
1 mL of 0.1 M KOH (0.1 mmol) solution in 2-propanol was then
introduced. The mixture was stirred at the refluxing temperature
under argon atmosphere. At the desired reaction times, aliquots
were withdrawn from reaction vessel, to follow the reaction by 1H
NMR spectroscopy.
azoleeruthenium(II), [Ru]L3a. Prepared according to the pro-
cedure of [Ru]L1a except that [(p-cymene)RuCl2]2 (105.0 mg,
0.17 mmol) and 1-(pentamethylbenzyl)-1H-pyrazole (120.0 mg,
0.53 mmol) were used. Yield: 95.2 mg, 70%; mp: 261 ꢀC
(decomp.). 1H NMR (400 MHz, CDCl3):
d
7.69 (d, J¼2.36 Hz, 1H,
HPzeH), 7.42 (d, J¼2.36 Hz, 1H, HPzeH), 6.41 (t, J¼2.36 Hz, 1H,
HPzeH), 5.23 (s, 2H, CH2eAr), 2.19 (s, 6H, AreCH3), 2.16 (s, 3H,
AreCH3), 2.04 (s, 6H, AreCH3). 13C NMR (100 MHz, CDCl3):
Acknowledgements
d
140.4130.1, 108.7, 101.9, 88.8, 84.5 (AreC, HPzeC), 50.9 (CH2eAr),
15.9, 15.4, 14.6 (AreCH3). IR, nmax (CH2Cl2): 3823, 3751, 3642,
Financial support from Ege University (Project 2010-FEN-046;
2011-FEN-091) and The Turkish Academy of Sciences (TUBA) is
2925, 1729, 1563, 1365, 751 cmꢁ1. Anal. Calcd for C15H20Cl2N2Ru

8662
B.T. Kırkar et al. / Tetrahedron 68 (2012) 8655e8662
Steiner, H.; Studer, M. Adv. Synth. Catal. 2003, 345, 103; (e) Qiu, L. Q.; Wu, J.;
Chan, S. S.; Au-Yeung, T. T. L.; Ji, J. X.; Guo, C. R. W.; Pai, C.; Zhou, Z. Y.; Li, X. S.;
Fan, Q. H.; Chan, A. S. C. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5815; (f) Fujita, K.;
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gratefully acknowledged. The authors are grateful to Anadolu Uni-
versity and the Medicinal Plants and Medicine Research Centre of
Anadolu University, Eskis¸ ehir, Turkey, for the use of X-ray
Diffractometer.
Supplementary data
Crystallographic data can be obtained from the Cambridge
Crystallographic Data Center, by quoting the reference number
CCDC-756923. The data can be obtained free of charge at
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found in the online version, at http://
dx.doi.org/10.1016/j.tet.2012.07.058.
8. Van der Made, A. W.; van der Made, R. H. J. Org. Chem. 1993, 58, 1262.
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