New N,N,N-donors resulting in highly active ruthenium catalysts for transfer hydrogenation at room temperature

Article abstract of DOI:10.1002/ejic.201100459

A series of ruthenium complexes of the general formula [RuCl ₂(L)(NNN)] were synthesized starting from tridentate N,N,N-ligands containing pyridine and allylated pyrazole donor groups and [RuCl ₂(PPh₃)₃]. The N,

Full text of DOI:10.1002/ejic.201100459

FULL PAPER
DOI: 10.1002/ejic.201100459
New N,N,N-Donors Resulting in Highly Active Ruthenium Catalysts for
Transfer Hydrogenation at Room Temperature
Leila Taghizadeh Ghoochany,[a] Saeid Farsadpour,[a] Yu Sun,[a] and Werner R. Thiel*[a]
Keywords: Ruthenium / Homogeneous catalysis / Hydrogenation / Transfer hydrogenation / N ligands
A series of ruthenium complexes of the general formula
[RuCl2(L)(NNN)] were synthesized starting from tridentate
N,N,N-ligands containing pyridine and allylated pyrazole
[RuCl2(CO)(NNN)], by bubbling CO into a solution in tolu-
ene at elevated temperatures. All ruthenium complexes were
investigated as catalysts for the transfer hydrogenation of
donor groups and [RuCl2(PPh3)3]. The N,N,N-donors intro- aryl ketones. The phosphane complexes show high activities
duced herein are accessible in a few steps from versatile pre-
cursors. The primary products, [RuCl2(NNN)(PPh3)], can be
converted into the corresponding carbonyl complexes,
with turnover frequency values of up to 1200 h–1 in the pres-
ence of just one equivalent of KOH, whereas the carbonyl
complexes are only poorly active.
dipyridine ligand),[6] [RuCl2(P)2(PN)] (PN = amino- or imi-
nophosphane ligands, oxazolinylferrocenylphosphane),[7]
[RuCl2(PN)2],[7a,8] [RuCl(η6-p-cymene)(PN)][BF4] (PN =
phosphole–pyridine),[9] [RuCl(η6-p-cymene)(NN)][BF4],[10]
[RuCl2(NPN)(P)],[11] {RuCl2(NPN)},[12] [RuCl2(NNN)(P)]
(NPN and NNN = oxazoline-based ligands),[13] [RuCl-
(CNN)(PP)] [PP = (R,S)-1-{2-[bis(4-methoxy-3,5-dimeth-
ylphenyl)phosphanyl]ferrocenyl}ethyldicyclohexylphos-
phane (Josiphos-type diphosphane) and CNN = amine/
aryl/pyridine-based ligands][14] and [RuCl2(PNNP)] systems
(PNNP = diphosphane/diamine ligands).[15]
Herein, we describe the synthesis and characterization of
ruthenium complexes of the type [RuCl2(L)(NNN)] (L =
PPh3 or CO), with tridentate dipyrazolpyridines as N,N,N-
ligands. These complexes efficiently catalyze the transfer hy-
drogenation of ketones in the presence of basic 2-propanol
at room temperature with high turnover frequencies (TOFs)
of up to 1200 h–1.
Introduction
Aliphatic and aromatic nitrogen donors have emerged as
important ligands in homo- and heterogeneous catalysis.[1,2]
Among them, tridentate aromatic nitrogen donors have
been used for nickel-catalyzed asymmetric Negishi cross-
couplings[2e,2f] or for iron/cobalt-catalyzed ethylene poly-
merization.[3] Furthermore, polydentate imino and amino
ligands have provided a considerable improvement on the
catalyst performance in the catalytic transfer hydrogenation
of ketones.[4]
In this transformation, the substrates are reduced to
alcohols with 2-propanol or formic acid as the hydrogen
source.[5] Highly active catalytic systems make this ap-
proach attractive for the preparation of alcohols because
the direct hydrogenation process requires handling of dan-
gerous dihydrogen, often under elevated pressure. The most
active systems are based on ruthenium, rhodium, and irid-
ium as the catalytically active metal site coordinated by ni-
trogen and/or phosphorus ligands. In particular, ruthenium
complexes containing suitable combinations of P- and N- Results and Discussion
or mixed P,N-ligands turned out to be efficient catalysts for
Synthesis and Characterization of Ligands and Complexes
the hydrogenation and transfer hydrogenation of carbonyl
compounds. Thus, bi-, tri-, and tetradentate achiral and chi-
ral ligands have successfully been used for the preparation
of these catalysts. A few general types should be mentioned
here: [RuCl2(NN)(P)2] and [RuCl2(NN)(PP)] (P = phos-
phane ligand; PP = diphosphane ligand; NN = diamine,
The tridentate N,N,N-ligands 2a,b employed herein are
accessible from versatile starting materials in good yields by
regioselective allylation of 2,6-bis(1H-pyrazol-3-yl)pyridine
(1a) or 2,6-bis(5-butyl-1H-pyrazol-3-yl)pyridine (1b;
Scheme 1).[3h,16,17] We decided to introduce allylic side
chains in the 1- and 1Ј-positions of the pyrazole rings to
functionalize the ligand with substituents of moderate
bulkiness. Furthermore, the allylic side chains should offer
a chelating π-donating element, which is able to stabilize
a 16 valence-electron (VE) ruthenium(II) intermediate in a
hemilabile manner, but will not be hydrogenated itself under
the given reaction conditions of transfer hydrogenation. De-
[a] Technische Universität Kaiserslautern, Fachbereich Chemie,
Kaiserslautern,
Erwin-Schrödinger-Str., Geb. 54, 67663 Kaiserslautern,
Germany
Fax: +49-631-2054676
E-mail: thiel@chemie.uni-kl.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100459.
Eur. J. Inorg. Chem. 2011, 3431–3437
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3431

L. Taghizadeh Ghoochany, S. Farsadpour, Y. Sun, W. R. Thiel
FULL PAPER
protonation of the pyrazole units with LiH in THF and ionic nature of the active site and to steric hindrance be-
subsequent allylation with allylic bromide gives 2a,b. It tween the two triphenylphosphane ligands.
1
should be noted here that the use of NaH for the deproton-
In the H NMR spectra of 3a,b, the resonances of the
ation of 1a,b leads to the formation of quite stable six-coor- allylic methylene protons, which become diastereotopic due
dinate sodium complexes, which hamper the isolation of the to the coordination of the ruthenium center, are now split
target ligands.
into two doublets of doublets at δ = 5.80 and 4.76 ppm for
3a and at δ = 6.20 and 4.21 ppm for 3b, which requires cis
coordination of the two chloro ligands. Recrystallization of
3a from CH2Cl2/Et2O resulted in the formation of single
crystals suitable for X-ray analysis. As already indicated by
the NMR spectra, the ruthenium centers were found in a
distorted octahedral coordination environment with the tri-
dentate N,N,N-ligand adopting a meridional geometry and
the two chloro ligands in a cis arrangement (Figure 1).
Compound 3a crystallizes with two crystallographically in-
dependent units in the solid state. The structural parameters
of these two units are almost identical (see the Supporting
Information), therefore, we take just one of the two units
for discussion of the geometry.
Scheme 1. Allylation of dipyrazolylpyridines and subsequent for-
mation of ruthenium(II) complexes.
By functionalizing the pyrazole ring with a butyl group
(as in 2b), the resonance of the proton in the 4-position of
the pyrazole ring shifts about 0.75 ppm towards a higher
field relative to 2a, indicating an increased electron density
in the pyrazole ring, which is also reflected in the 13C NMR
resonances of this compound. The methylene protons of
the allylic side chains are doublets at δ = 4.83/4.62 ppm for
compounds 2a/2b, indicating that these hydrogen atoms are
magnetically equivalent.
Treatment of 2a,b with one equivalent of the rutheni-
um(II) precursor [RuCl2(PPh3)3] in dichloromethane at
room temperature leads to the formation of the correspond-
ing red-colored ruthenium(II) complexes 3a,b in almost
quantitative yields (Scheme 1). Typical for octahedral ru-
thenium(II) monophosphane complexes, the 31P NMR res-
onances of 3a,b are observed a δ = 44.20 and 42.71 ppm.[18]
Figure 1. Molecular structure of the ruthenium(II) complex 3a in
the solid state. Characteristic bond lengths [Å] and angles [°] for
one of the crystallographically independent units are given: Ru1–
Cl1 2.4577(9), Ru1–Cl2 2.4665(8), Ru1–P1 2.2799(9), Ru1–N1
1.985(3), Ru1–N2 2.081(3), Ru1–N4 2.093(3), Cl1–Ru1–Cl2
88.99(3), Cl1–Ru1–P1 175.03(3), Cl1–Ru1–N1 90.40(7), Cl1–Ru1–
N2 83.59(7), Cl1–Ru1–N4 89.00(7), Cl2–Ru1–P1 86.27(3), Cl2–
Ru1–N1 178.65(8), Cl2–Ru1–N2 103.78(7), Cl2–Ru1–N4 100.71(7),
P1–Ru1–N1 94.37(7), P1–Ru1–N2 96.08(7), P1–Ru1–N4 93.34(7),
N1–Ru1–N2 77.35(10), N1–Ru1–N4 78.07(10), N2–Ru1–N4
154.24(10).
Although pyridines are generally considered to be better
We recently published the reaction of the N,N,N-ligand 1b donors than pyrazoles, the large Ru–N bond length differ-
(see Scheme 1), with N–H instead of N-allyl functions, with ence of about 10 pm can be explained simply by the steric
[RuCl2(PPh3)3].[19] This leads to a cationic ruthenium(II) requirements of the tridentate ligand.[19,20] Bidentate pyr-
complex of the type [RuCl(1b)(PPh3)2]Cl with the two phos- azolylpyridine complexes show less-pronounced differences
phane ligands trans to each other (31P NMR: δ = in the M–N bond lengths.[19,21] Due to the tridentate coor-
25.5 ppm). The ionic structure of this compound is stabi- dination of the N,N,N-donor, the central nitrogen atom,
lized by H···Cl interactions between the acidic N–H units N1, is pushed closer to the ruthenium(II) center. It there-
at the two pyrazole rings and both the coordinated chloro fore applies a trans influence to Cl2 comparable to the trans
ligand and the free chloride counteranion. In contrast to influence of the phosphane donor to Cl1, which explains
3a,b (see below), [RuCl(1b)(PPh3)2]Cl shows just moderate the almost identical Ru–Cl bond lengths found in this solid-
transfer hydrogenation activities, which we assign to the cat- state structure. All P–Ru–N angles are larger than 90°,
3432
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Eur. J. Inorg. Chem. 2011, 3431–3437

N,N,N-Donors Resulting in Highly Active Ruthenium Catalysts
showing the steric influence of bulky triphenylphosphane
on the chelating ligand.
As in 3a, the ruthenium center in 5a is again coordinated
in a distorted octahedral geometry with the tridentate
Bubbling CO into a solution of 3a,b in toluene at reflux N,N,N-donor adopting a mer arrangement. The Ru–N
results in the formation of the carbonyl complexes 4a,b in bond on one side and the Ru–Cl distances on the other side
quantitative yields (Scheme 1); a color change from red to are almost identical; slight differences are related to packing
yellow indicates the end of the reaction. The 31P NMR effects in the solid-state structure. The bond angle Cl3–Ru–
spectroscopy signals of the triphenylphosphane ligands N approaches 90°, corroborating the discussion of the steric
have disappeared, proving that the phosphane is substituted influence of the triphenylphosphane ligand on the structure
1
by CO, which is in contrast to previous findings.[19] The H of 3a.
NMR spectra of 4a and 4b recorded in [D6]DMSO again
show two diastereotopic methylene protons (4a: δ = 6.12,
Catalytic Transfer Hydrogenation
5.20 ppm; 4b: δ = 5.55, 5.03 ppm), which means that the
chloride ligands are still cis coordinated. In the 13C NMR
spectrum, the resonances of the carbonyl ligand are ob-
served at δ = 191.01 ppm for 4a and at δ = 191.22 ppm
for 4b. Intense CO absorptions in the infrared spectrum at
1936 cm–1 for 4a and at 1948 cm–1 for 4b confirm the at-
tachment of one carbonyl ligand to the ruthenium center.
The slight difference of 12 cm–1 can be explained by the
steric influence of the bulky butyl chain attached to com-
pound 4b, which increases the Ru–CO distance, decreases
back donation to the carbonyl ligand, and therefore,
strengthens the C=O bond. Attempts to obtain single crys-
tals of 4a suitable for X-ray structure determination by
recrystallization from dichloromethane over a long period
of time and in the presence of light resulted in oxidation
to ruthenium(III) and replacement of the carbonyl with a
chloride ligand (Scheme 2 and Figure 2).
Acetophenone has been chosen as a model substrate to
explore the catalytic performance of compounds 3 and 4 in
transfer hydrogenation. The reaction conditions were opti-
mized by first using 3a (Table 1). Due to the poor solubility
of the catalyst in 2-propanol, dichloromethane was added
to obtain a homogeneous solution. All reactions were car-
ried out at room temperature and the catalyst generally
showed high activities even under these very mild condi-
tions. It seemed that too much base and diluting the solu-
tion of the reaction reduced the reaction rate (entries 8 and
5, Table 1). As expected, the rate of the reaction increased
dramatically by increasing the temperature (entry 7,
Table 1). A blank experiment carried out in the absence of
the catalyst gave no hydrogenation of acetophenone at all
(entry 9, Table 1).
Table 1. Transfer hydrogenation of acetophenone with 3a.[a]
Entry Substrate/catalyst/base Solvent Yield [%] after
ratios
[mL]
0.5 h
1 h
1.5 h
1
2
3
4
200
200
200
200
200
500
200
200
200
1
1
1
1
1
1
1
1
–
–
1
2.5
5
5
5
5
10
5
25
25
25
25
50
25
25
25
25
0
0
0
92
88
73
69
48
100[d]
22
0
93
92
87
92
62
0
94
92
99[b]
92
71
0
5
Scheme 2. Chlorination of the carbonyl complex 4a.
6
7[c]
8
37
0
49
9
0[e]
[a] Reaction conditions: 3a (2.5ϫ10–2 mmol), 2-propanol (20 mL),
CH2Cl2 (5 mL), room temp., N2, monitored by GC. [b] Reaction
completed after 80 min. [c] Reaction carried out at 82 °C. [d] Reac-
tion completed after 5 min. [e] Even after about 3 h no product was
detected without catalyst.
According to these results, the catalysis reactions were
carried out by using a 0.5 m solution of the substrate,
0.5 mol-% of catalyst, and 0.025 m of KOH. For this pur-
pose, a solution of the substrate in 2-propanol was added
at room temperature to a solution in 2-propanol/CH2Cl2
containing the catalyst and the base. With the addition of
the base, the color of the solution turned to a more intense
red color, but during the reaction the color of the solution
remained unchanged.
Complex 3a was found to catalyze the reduction of
acetophenone to 1-phenylethanol quantitatively in 80 min
at room temperature. Substitution of the protons in the 5-
position of the pyrazole ring with n-butyl groups dramati-
cally increases the performance: in the presence of catalyst
Figure 2. The molecular structure of the ruthenium(III) complex
5a in the solid state, characteristic bond lengths [Å], and angles [°]
are shown; the co-crystallized dichloromethane molecule is omitted
for clarity. Ru1–Cl1 2.4159(18), Ru1–Cl2 2.405(5), Ru1–Cl3
2.358(2), Ru1–N1 2.039(5), Ru1–N2 2.089(5), Ru1–N4 2.043(5),
Cl1–Ru1–Cl2 93.88(11), Cl1–Ru1–Cl3 177.59(6), Cl1–Ru1–N1
87.82(15), Cl1–Ru1–N2 89.66(15), Cl1–Ru1–N4 89.56(16), Cl2–
Ru1–Cl3 87.79(12), Cl2–Ru1–N1 177.92(18), Cl2–Ru1–N2
101.86(18), Cl2–Ru1–N4 104.24(18), Cl3–Ru1–N1 90.55(16), Cl3–
Ru1–N2 91.70(15), Cl3–Ru1–N4 88.34(16), N1–Ru1–N2 76.9(2),
N1–Ru1–N4 77.0(2), N2–Ru1–N4 153.9(2).
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L. Taghizadeh Ghoochany, S. Farsadpour, Y. Sun, W. R. Thiel
FULL PAPER
3b, the transformation is completed in less than 15 min at SN2Ј reaction with the base leading to an anionic pyrazolate
room temperature (Table 2), giving a minimum TOF of donor (Scheme 3) and a vacant coordination site at the ru-
800 h–1. We assign this finding to an increase in steric hin- thenium(II) center. This reaction would generate an inter-
drance by the n-butyl groups, which will force the allyl mediate suitable for a ligand-assisted, outer-coordination
chains to be oriented away from the rear side of the catalyst. mechanism.
This will probably enable the dissociation of the tri-
phenylphosphane ligand and activate the catalyst for the
transfer hydrogenation process. This mechanistic idea is
corroborated by replacing the triphenylphosphane ligand
with a carbon monoxide ligand (compounds 4a,b), which
makes the catalyst almost inactive even at 82 °C.
Table 2. Transfer hydrogenation of acetophenone with different ru-
thenium catalysts.[a]
Scheme 3. Cleavage of the allyl–N bond by the base.
Entry
Catalyst
Time [min]
Yield [%]
Treatment of 3a,b with KOH did not result in cleavage
of the N–allyl bond. Cleaving the Ru–P bond, further pro-
moted by the steric demand of the butyl chain in complex
3b, should therefore be the initial step to generate a reactive
16-VE ruthenium(II) species, which then leads to the for-
mation of the catalytically active ruthenium hydride species.
This is supported by the fact that addition of an excess of
PPh3 to the catalyst strongly decreases the reaction rates of
3a,b, which is similar to findings reported in the litera-
ture.[22] Comparing the activity of 3b (TOF Ն 1200 h–1) at
room temperature makes it clear that we have obtained a
highly active structural motif. It already had been shown
in the literature that ruthenium(II) complexes with trans-
coordinated chloro ligands are less active in the transfer
hydrogenation of ketones than ruthenium(II) complexes
with cis-coordinated chloro ligands (such as 3a,b).[18a,18b,23]
1
2
3
3a
3b
4a
4b
4a
80
15
1080
1080
60
180
60
99
100
0
traces
0
traces
13
4
5[b]
6[b]
4b
180
16
[a] Reaction conditions: catalyst (5ϫ10–3 mmol), substrate
(1.0 mmol), KOH (2.5ϫ10–2 mmol), 2-propanol (4 mL), CH2Cl2
(1 mL), room temp., N2, monitored by GC. [b] Reaction carried
out at 82 °C.
Finally the activity of 3b was tested with a few different
ketones to show its general applicability in transfer hydro-
genation (Table 3). The results prove that increasing the
electron density at the aromatic ring reduces the reaction
rate. Complete conversion for the first two substrates was
observed after 10 min at room temperature resulting in a
minimum TOF of 1200 h–1.
Conclusions
We have described new ruthenium complexes of the type
[RuCl2(L)(NNN)] with tridentate dipyrazolylpyridine
N,N,N-ligands. The triphenylphosphane complexes turned
out to be highly efficient catalyst precursors for the transfer
hydrogenation of aromatic ketones. The introduction of a
butyl group in the 5-positions of the pyrazoles led to a pro-
nounced increase in catalytic activity.
Table 3. Transfer hydrogenation of different ketones with 3b[a]
.
Experimental Section
General: Solvents were purified and dried by standard methods. All
reactions were carried out under an atmosphere of dinitrogen. The
ligand precursors 1a and the ruthenium(II) complex [RuCl2-
(PPh3)3] were synthesized according to procedures published in the
literature.[16a,24] The NMR spectra are assigned according to
Scheme 4.
[a] Reaction conditions: substrate (1.0 mmol), 3b (5ϫ10–3 mmol),
KOH (2.5ϫ10–2 mmol), 2-propanol (4 mL), CH2Cl2 (1 mL), room
temp., N2, reactions monitored by GC, samples were taken after
10 min.
Concerning the mechanism of the transfer hydrogenation
catalyzed by 3a,b, we suggest a reaction sequence following
an inner coordination of the substrate. We have no evidence
for a ligand-assisted process, which could be initiated by
splitting one or both of the allylic chains through an SN2 or Scheme 4. Atom numbering used for NMR signal assignments.
3434 Eur. J. Inorg. Chem. 2011, 3431–3437
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N,N,N-Donors Resulting in Highly Active Ruthenium Catalysts
2,6-Bis(5-butyl-1H-pyrazol-3-yl)pyridine (1b): A solution of hexan-
2-one (15.41 g, 154 mmol) in dry THF (40 mL) was added at room
temperature dropwise to a solution of pyridine-2,6-dicarboxy-
licacid dimethylester (15 g, 76.9 mmol) and NaOMe (8.35 g,
154 mmol) in dry THF (170 mL). Then, the reaction mixture was
heated for 5 h to reflux. After cooling to room temperature, the
solvent was evaporated under vacuum and the resulting orange col-
ored solid was dissolved in a 1:1 mixture of chloroform (100 mL)
and water (100 mL). While vigorously stirring the reaction mixture,
1 m sulfuric acid was added until a pH value of 5 was reached.
The organic phase was separated, washed three times with water
(50 mL), and then dried with Na2SO4. After the solvent was re-
moved in vacuo, a light-brown oil resulted, which was dissolved in
ethanol (200 mL) and reacted for 4 h under reflux conditions with
N2H4·H2O (8.86 g, 177 mmol). The solvent and the excess hydraz-
ine were removed in vacuo and the light-yellow solid product was
recrystallized from ethyl acetate (15 g, 60%). C19H25N5 (323.44):
calcd. C 70.56, H 7.79, N 21.65; found C 70.60, H 7.70, N 21.70.
1H NMR (400.1 MHz, CDCl3, 20 °C): δ = 7.43 (t, JHH = 7.43 Hz,
1 H, H1), 7.20 (br. s, 2 H, H2), 6.25 (br. s, 2 H, H5), 2.50 (br. s, 4
H, Hbu), 1.52 (m, 4 H, Hbu), 1.29–1.23 (m, 4 H, Hbu), 0.81 (t, JHH
= 7.44 Hz, 6 H, Hbu) ppm. 13C{1H} NMR (100.6 MHz, CDCl3,
20 °C): δ = 153.0 (s, C3), 148.3 (s, C1), 144.3 (s, C4), 137.0 (s, C6),
117.8 (s, C2), 101.4 (s, C5), 31.6 (s, Cbu), 27.3 (s, Cbu), 22.7 (s, Cbu),
14.0 (s, Cbu) ppm.
(0.268 g, 100%). C35H32Cl2N5PRu (725.62): calcd. C 57.93, H 4.45,
N 9.65; found C 57.64, H 4.45, N 9.65. 1H NMR (400.1 MHz,
CDCl3, 20 °C): δ = 7.35 (d, JHH = 2.72 Hz, 2 H, H6), 7.29 (t, JHH
= 7.49 Hz, 1 H, H1), 7.25–7.18 (m, 5 H, H2,HPh), 7.09–7.06 (m,
12 H, HPh), 6.75 (d, JHH = 2.72 Hz, 2 H, H5), 6.15–6.04 (m, 2 H,
H8), 5.80 (dd, 4 H, H7), 5.32 (m, 4 H, H9,H10), 4.76 (dd, 2 H,
H7) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ = 155.8
(s, C1), 152.6 (s, C4), 134.1 (d, JCP = 41.62 Hz, Cph), 133.4 (d, JCP
= 9.24 Hz, Cph), 133.0 (s, C8), 132.5 (s, C6), 132.0 (s, C3), 129.0
(br. s, Cph), 127.8 (d, JCP = 8.33 Hz, Cph), 120.2 (s, C2), 116.9 (s,
C9), 105.5 (s, C5), 56.2 (s, C7) ppm. 31P{1H} NMR (162.0 MHz,
CDCl3, 20 °C): δ = 44.2 ppm.
[2,6-Bis(1-allyl-5-butyl-1H-pyrazol-3-yl)pyridine]dichloro(triphen-
ylphosphane)ruthenium(II) (3b): The same procedure as that used
for 3a was applied to give 3b as a red solid (0.31 g, 100 %).
C43H48Cl2N5PRu (837.84): calcd. C 61.67, H 5.73, N 8.36; found
1
C 61.95, H 5.68, N 7.68. H NMR (400.1 MHz, CDCl3, 20 °C): δ
= 7.34 (t, JHH = 8.22 Hz, 1 H, H1), 7.21 (m, 3 H, Hph), 7.15 (d,
JHH = 7.44 Hz, 2 H, H2), 7.11–7.07 (m, 12 H, HPh), 6.47 (s, 2 H,
H5), 6.22–6.19 (m, 4 H, H7,H8), 5.14–5.10 (m, 4 H, H9,H10), 4.24–
4.18 (m, 2 H, H7), 2.59–2.54 (m, 4 H, Hbu), 1.60–1.56 (m, 4 H,
Hbu), 1.39–1.34 (m, 4 H, Hbu), 0.94 (t, JHH = 7.05 Hz, 6 H, Hbu).
13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ = 156.2 (s, C1), 151.6
(s, C4), 148.0 (s, C3), 134.5 (d, JCP = 40.69 Hz, Cph), 134.4 (s, C8),
133.4 (d, JCP = 9.24 Hz, Cph), 131.8 (s, C6), 128.8 (br. s, Cph), 127.6
(d, JCP = 9.25 Hz, Cph), 117.6 (s, C2), 116.5 (s, C9), 104.0 (s, C5),
53.8 (s, C7), 30.1 (s, Cbu), 25.8 (s, Cbu), 22.4 (s, Cbu), 14.00 (s, Cbu).
31P{1H} NMR (162.0 MHz, CDCl3, 20 °C): δ = 42.7 ppm.
2,6-Bis(1-allyl-1H-pyrazol-3-yl)pyridine (2a): LiH (0.16 g, 20 mmol)
was added to a solution of 1a (2.1 g, 10 mmol) in dry THF
(75 mL). After the evolution of dihydrogen ceased, allylic bromide
(1.2 g, 20 mmol) was added and the reaction mixture and was
stirred for 12 h. After removing the solvent in vacuo, the product
was extracted with chloroform and the organic phase was filtered
through sodium sulfate. Removing the solvent under reduced pres-
sure gave the product as a pale-yellow solid (1.9 g, 65%). C17H17N5
(291.35): calcd. C 70.08, H 5.88, N 24.04; found C 70.82, H 5.74,
[2,6-Bis(1-allyl-1H-pyrazol-3-yl)pyridine]carbonyldichlororuthen-
ium(II) (4a): Compound 3a (0.145 g, 0.2 mmol) was dissolved in
dry toluene/CH2Cl2 (10:1) and CO gas was bubbled into the solu-
tion heated at reflux. The color of the solution changed from red
to yellow. When the reaction mixture cooled to room temperature,
a yellow powder precipitated, which was filtered off washed with
dry diethyl ether to give the product as a yellow solid (0.098 g,
100 %). C18H17Cl2N5ORu·CH2Cl 2: calcd. C 39.60, H 3.32, N
12.15; found C 40.05, H 3.56, N 12.33. 1H NMR (400.1 MHz, [D6]-
1
N 23.44. H NMR (400.1 MHz, CDCl3, 20 °C): δ = 8.22 (br. s, 2
H, H2), 7.86 (br. s, 1 H, H1), 7.75 (d, JHH = 2.35 Hz, 2 H, H5),
7.55 (d, JHH = 2.35 Hz, 2 H, H6), 6.08–5.98 (m, 2 H, H8), 5.31–
5.24 (m, 4 H, H9,H10), 4.85 (d, JHH = 5.87 Hz, 4 H, H7) ppm.
13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ = 147.9 (s, C3), 144.
8 (s, C4), 143.3 (s, C1), 132.0 (s, C8), 131.7 (s, C6), 121.4 (s, C2),
119.7 (s, C9), 108. 9 (s, C5), 55.4 (s, C7) ppm.
DMSO, 20 °C): δ = 8.21–8.10 (m, 5 H, H1,H2,H6), 7.36 (d, JHH
=
2.19 Hz, 2 H, H5), 6.16–6.09 (m, 2 H, H8), 5.51–5.47 (dd, 2 H,
H7), 5.23–5.19 (m, 6 H, H7,H9,H10) ppm. 13C{1H} NMR
(100.6 MHz, [D6]DMSO, 20 °C): δ = 191.0 (s, CO), 152.8 (s, C3),
152.3 (s, C4), 138.8 (s, C8), 135. (s, C6), 133.7 (s, C1), 119.2 (s, C2),
2,6-Bis(1-allyl-5-butyl-1H-pyrazol-3-yl)pyridine (2b): The same pro-
cedure as that used for 2a was applied to give 2b as a pale-yellow
solid (2.8 g, 70%,). C25H33N5 (403.57): calcd. C 74.40, H 8.24, N
17.35; found C 74.29, H 8.25, N 17.40. 1H NMR (400.1 MHz,
CDCl3, 20 °C): δ = 7.79 (d, JHH = 7.83 Hz, 2 H, H2), 7.59 (t, JHH
= 7.82 Hz, 1 H, H1), 6.76 (s, 2 H, H5), 5.95–5.82 (m, 2 H, H8),
5.05 (d, JHH = 10.17 Hz, 2 H, H9), 4.88 (d, JHH = 17.22 Hz, 2 H,
H10), 4.62 (br. s, 4 H, H7), 2.46 (t, JHH = 7.83 Hz, 4 H, Hbu), 1.61–
1.54 (m, 4 H, Hbu), 1.35–1.26 (m, 4 H, Hbu), 0.84 (t, JHH = 7.43 Hz,
6 H, Hbu) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 20 °C): δ =
151.8 (s, C3), 150.7 (s, C4), 144.4 (s, C1), 136.5 (s, C6), 133.1 (s,
C8), 117.9 (s, C2), 116.5 (s, C9), 103.1 (s, C5), 51.6 (s, C7), 30.2 (s,
Cbu), 24.9 (s, Cbu), 22.1 (s, Cbu), 13.6 (s, Cbu) ppm.
118.3 (s, C9), 106.7 (s, C5), 53.9 (s, C7) ppm. IR (KBr): ν = 1936
˜
(C=O) cm–1.
[2,6-Bis(1-allyl-1H-pyrazol-3-yl)pyridine]carbonyldichlororuthen-
ium(II) (4b): The same procedure as that used for 4a was applied
to give 4b as a yellow solid (0.121 g, 100%). C26H33Cl2N5ORu
(603.56): calcd. C 51.74, H 5.51, N 11.60; found C 50.73, H 5.54,
N 11.60. 1H NMR (400.1 MHz, [D6]DMSO, 20 °C): δ = 8.15 (t,
JHH = 7.49 Hz, 1 H, H1), 8.05 (d, JHH = 7.83 Hz, 2 H, H2), 7.21
(s, 2 H, H5), 6.05–5.96 (m, 2 H, H8), 5.58 (dd, 2 H, H7), 5.19 (dd,
4 H, H9,H10), 5.07 (d, JHH = 17.37 Hz, 2 H, H7), 2.76–2.66 (m, 4
H, Hbu), 1.70–1.62 (m, 4 H, Hbu), 1.43–1.36 (m, 4 H, Hbu), 0.96–
0.91 (m, 6 H, Hbu) ppm. 13C{1H} NMR (100.6 MHz [D6]DMSO,
20 °C): δ = 191.2 (s, CO), 153.0 (s, C3), 151.4 (s, C4), 148.3 (d, C6),
138.8 (s, C8), 133.3 (s, C1), 119.0 (s, C2), 117.1 (s, C9), 105.0 (s,
C5), 51.3 (s, C7), 29.3 (s, Cbu), 24.7 (s, Cbu), 21.8 (s, Cbu), 13.7 (s,
[2,6-Bis(1-allyl-1H-pyrazol-3-yl)pyridine]dichloro(triphenylphos-
phane)ruthenium(II) (3a): Compound 2a (0.15 g, 0.37 mmol) was
added to a solution of [RuCl2(PPh3)3] (0.355 g, 0.37 mmol) in dry
CH2Cl2 (10 mL). The reaction mixture was stirred at room tem-
perature for about 2 h. After concentrating the solution to about
5 mL, dry diethyl ether (25 mL) was added to precipitate the prod-
uct, which was filtered off and washed with diethyl ether to remove
liberated triphenylphosphane to give the final product as a red solid
Cbu) ppm. IR (KBr): ν = 1948 (C=O) cm–1.
˜
General Procedure for the Catalytic Transfer Hydrogenation: Solu-
tions containing the substrate (a), the catalyst (b), and KOH (c)
were prepared as follows: (a) the organic substrate (5 mmol) was
dissolved in 2-propanol (10 mL), (b) the ruthenium complex
Eur. J. Inorg. Chem. 2011, 3431–3437
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3435

L. Taghizadeh Ghoochany, S. Farsadpour, Y. Sun, W. R. Thiel
FULL PAPER
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(0.025 mmol) was dissolved in 2-propanol (5 mL) and CH2Cl2
(5 mL), and (c) KOH (0.125 mmol) was dissolved in 2-propanol
(5 mL). Solution (c) was added to solution (b), then solution (c)
was added to this mixture. The reactions were monitored by GC.
X-ray Structure Analyses: Crystal data and refinement parameters
for compounds 3a and 5a are collected in Table 4. The structures
were solved by direct methods (SIR92[25]), completed by subse-
quent difference Fourier syntheses, and refined by full-matrix least-
squares procedures.[26] For 3a and 5a, semi-empirical absorption
corrections from equivalents (Multiscan) were carried out.[27] All
non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were placed in calculated positions
and refined by using a riding model.
Table 4. Summary of the crystallographic data and details of data
collection and refinement.
3a
C35H32Cl2N5PRu C18H19Cl5N5Ru
725.60 583.70
0.19ϫ0.17ϫ0.06 0.20ϫ0.13ϫ0.03
5a
Empirical formula
Formula weight
Crystal size [mm]
T [K]
[4]
[5]
150(2)
150(2)
λ [Å]
1.54184
triclinic
P1
1.54184
triclinic
P1
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
¯
¯
13.0148(9)
14.8928(10)
16.8628(10)
102.805(6)
92.194(5)
93.225(5)
3177.8(4)
4
1.517
6.280
3.41–62.92
27114
8.0575(4)
10.4714(4)
14.3250(7)
71.813(4)
81.249(4)
76.049(4)
1110.51(9)
2
1.746
11.381
3.26–62.60
8213
γ [°]
V [Å3]
Z
ρcalcd. [gcm–3]
μ [mm–1]
θ-range [°]
Reflections collected
[6]
[7]
Independent reflections 9952
[Rint = 0.0352]
3539
[Rint = 0.0252]
3539/0/262
0.0556, 0.1596
Data/restr./parameters
Final R indices
[IϾ2σ(I)][a]
9952/0/793
0.0299, 0.0787
R indices (all data)
0.0362, 0.0823
0.985
0.880/–0.749
0.0595, 0.1626
1.096
1.573/–1.549
GooF[b]
Δρmax/min [eÅ–3]
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|, ωR2 = [Σω(F2o – Fc2)2/ΣωF2o]1/2. [b] GooF
= [Σω(F2o – F2c)2/(n – p)]1/2
.
CCDC-823928 (for 3a) and -823929 (for 5a) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Received: April 29, 2011
Published Online: July 15, 2011
Eur. J. Inorg. Chem. 2011, 3431–3437
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3437