Mono- and binuclear ruthenium(II) complexes containing pyridine-2,6-diimine (Pydim) ligands: Synthesis, characterization and catalytic activity in the transfer hydrogenation of acetophenone

Article abstract of DOI:10.1016/j.molcata.2007.02.026

A series of neutral mono- and binuclear Ru(II) complexes: [PydimCl₂RuL] (Pydim (1) pyridine-2,6-diimine; (2) L = NCMe; (3) L = PPh₃) and [PydimCl₂Ru(L-L)RuCl₂Pydim] (4) L-L = pyrazine; (5) L-L = 4,4′-bipyridine) have been synthesized from the corresponding (p-cymene)ruthenium dichloride dimer, pydim and ancillary ligands L and L-L, respectively. The Pydim-Ru(II) complexes have been employed as catalysts for the transfer hydrogenation of acetophenone in the presence of KOH using 2-propanol as a hydrogen source. Ligand substitution studies indicate that there is a significant difference in reactivity between complexes containing L/L-L and Pydim. Yields of up to 93% were obtained after 5 min at 82 °C.

Full text of DOI:10.1016/j.molcata.2007.02.026

Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
Mono- and binuclear ruthenium(II) complexes containing
pyridine-2,6-diimine (Pydim) ligands: Synthesis,
characterization and catalytic activity in the
transfer hydrogenation of acetophenone
Osman Dayan, Bekir C¸ etinkaya∗
Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey
Received 25 January 2007; received in revised form 16 February 2007; accepted 19 February 2007
Available online 23 February 2007
Abstract
A series of neutral mono- and binuclear Ru(II) complexes: [PydimCl2RuL] (Pydim (1) pyridine-2,6-diimine; (2) L = NCMe; (3) L = PPh3) and
[PydimCl2Ru(L-L)RuCl2Pydim] (4) L-L = pyrazine; (5) L-L = 4,4ꢀ-bipyridine) have been synthesized from the corresponding (p-cymene)ruthenium
dichloride dimer, pydim and ancillary ligands L and L-L, respectively. The Pydim-Ru(II) complexes have been employed as catalysts for the transfer
hydrogenation of acetophenone in the presence of KOH using 2-propanol as a hydrogen source. Ligand substitution studies indicate that there
is a significant difference in reactivity between complexes containing L/L-L and Pydim. Yields of up to 93% were obtained after 5 min at
82 ◦C.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Tridentate triamine ligands; Pyridine-2,6-diimines; Ru(II) complexes; Transfer hydrogenation of acetophenone
1. Introduction
Heterocyclic ligands containing nitrogen atoms are drawing
a great deal of attention in coordination chemistry and homo-
geneous catalysis [1–3] because of the versatility of their steric
and electronic properties, which can be modified by choosing
the appropriate ring substituents [4].
ˇ
Recently, planar tridentate pyridine-bridged N,Nı,N lig-
ands, such as 2,2ꢀ:6,2ꢀ-terpyridines (A) [5], 2,6-bis(oxazolinyl)
pyridines (Pybox) (B) [6,7]; 2,6-bis(pyrazol-1-yl)pyridine (C)
[8] and Pydims (D) [9,10] have been synthesized and their Ru(II)
complexes have been studied [11].
More recently, trans and cis-[RuCl2(PPh3){␬3-N,N,N-(R,R)-
Ph-Pybox}] have been prepared and used as highly efficient
enantioselective transfer hydrogenation catalysts [12]. This
report prompted us to study the catalytic activity of Ru(II) com-
plexes with the pydims, some of which have good efficiency
in the catalytic epoxydation of alkenes [9]. While the present
study was in progress, a related paper on the catalytic activity of
∗
Corresponding author. Tel.: +90 232 3881092; fax: +90 232 3881036.
E-mail address: bekir.cetinkaya@ege.edu.tr (B. C¸ etinkaya).
1381-1169/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2007.02.026

O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
135
C in the transfer hydrogenation of aryl ketones was published
[13].
24.94; 122.52; 123.47; 125.44; 126.28; 128.16; 131.81; 137.11;
148.38; 155.33; 167.40. IR (KBr; cm−1): 1640(␯C N).
Wearenotawareofanypreviousreportsabouttransferhydro-
genation of ketones with Pydim-Ru(II) complexes. Thus, it was
the goal of this work to prepare well-defined Pydim-Ru(II) cat-
alyst precursors incorporating pydim ligands for the transfer
hydrogenation of acetophenone. These complexes were found
to be active catalysts for transfer hydrogenation, leading to the
formation of sec-alcohol in high conversions.
2.2. Synthesis of complexes
2.2.1. General procedure for the synthesis of Type 2
complexes
An ethanolic solution (15 mL) of 1.10 eq. of 1 was mixed
with [RuCl2(p-cymene)]2 (306 mg, 0.50 mmol). The reaction
mixture was heated under reflux for 10 h. The refluxing dark
brown solution was cooled to room temperature. Ethanol was
removed by distillation and then the residue was dissolved in
dichloromethane (15 mL) containing acetonitrile (1 mL) and
precipitated by addition of diethyl ether (30 mL). The micro-
crystalline solid was filtered off and washed with diethyl ether
(3 × 10 mL) and pentane (3 × 10 mL). The desired products
were dried under reduced pressure at 50 ◦C for 1 h.
2. Experimental
All manipulations were performed under argon using stan-
dard Schlenk Techniques. All reagents were obtained from
commercial suppliers and used without further purification. Sol-
vents were dried by standard methods and distilled under argon
before use. [RuCl2(p-cymene)]2 [14], 1a and 2a [15], 1c [9],
1d [16], 1e [17], 2f [18], 1g [19] were synthesized accord-
ing to published procedures. NMR spectra were recorded at
297 K on a Varian Mercury AS 400 NMR spectrometer at
400 MHz (1H), 100.56 MHz (13C). The C, H and N analy-
ses were performed using a CHNS-932 (LECO) instrument
at the Technical and Scientific Research Council of Turkey,
TUBITAK. Melting points were determined using an Elec-
trothermal 9100 melting point detection apparatus and are
uncorrected. IR spectra (KBr pellets) were recorded in the range
400–4000 cm−1 on an ATI UNICAM 2000 spectrophotome-
ter. GC measurements for catalytic experiments were performed
using an Agillent 6890N GC instrument with a HP5 capillary
column.
2.2.2. {(Acetonitrile)(2,6-bis[1-(4-fluorophenylimino)
ethyl]pyridine)dichlororuthenium(II)}
[Ru(1b)(CH3CN)Cl2] (2b)
Yield: 430 mg, 77%. mp 218–220 ◦C. Anal. calcd. for
C23H20Cl2F2N4Ru: C 49.12; H 3.58; N 9.96%; found: C 49.36;
1
H 3.77; N 9.58%. H NMR (δ, CDCl3): 2.13 [s, 3H, MeCN];
2.75 [s, 6H, N C-Me]; 7.04 [d, 4H, J = 7.8, Ph-Hm]; 7.27 [d,
4H, J = 8.0, Ph-Ho]; 7.90 [t, 1H, J = 7.8, Py-Hp], 8.03[d, 2H,
J = 7.8, Py-Hm]. 13C NMR (δ, CDCl3): 5.85; 18.29; 113.36;
118.54;120.93;130.63;141.44;148.05;158.22;165.03;171.14.
IR (KBr; cm-1): 1637 (␯C N).
2.2.3. {(Acetonitrile)(2,6-bis[1-(2-methyl-4-N,N-
diethylaminophenylimino)ethyl]pyridine)
2.1. General procedure for the synthesis of ligands
dichlororuthenium(II)} [Ru(1d)(CH3CN)Cl2] (2d)
Yield: 460 mg, 67%. mp 182 ◦C (dec.). Anal. calcd. for
C32H42Cl2N6Ru: C 56.30; H 6.20; N 12.31%; found: C 55.96; H
6.59; N 11.92%. 1H NMR (δ, CDCl3): 1.14 [t, 12H, J = 7.0 Hz,
2-Me-4-N(CH2Me)2-Ph]; 2.05 [s, 3H, MeCN]; 2.18 [s, 6H, 2-
Me-4-N(CH2Me)2-Ph]; 2.63 [s, 6H, N C-Me]; 3.32 [q, 8H,
J1 = 14 Hz, J2 = 6.4, 2-Me-4-N(CH2Me)2-Ph]; 6.50 [br, 4H, Ph-
Hm]; 7.41 [d, 2H, J = 8.4, Ph-Ho]; 7.51 [t, 1H, J = 8.0 Hz, Py-Ho],
7.72 [d, 2H, J = 8.0 Hz, Py-Hm]. 13C NMR (δ, CDCl3): 0.21;
8.85; 13.70; 15.73; 40.74; 106.09; 109.63; 118.22; 120.74;
121.96; 123.92; 126.63; 135.49; 142.17; 159.60; 166.71. IR
(KBr; cm−1): 1596 (␯C N).
A mixture of substituted aniline (10 mL) and 2,6-
diacetylpyridine (1.00 g, 6.12 mmol) was heated at 95 ◦C for 2
days. Then, the excess of aniline was distilled off under reduced
pressure and the residue was dissolved in hot ethanol. Upon
cooling to room temperature yellow crystals formed which were
filtered off, washed with diethyl ether (3 × 5 mL) and dried.
2.1.1. 2,6-Bis[1-(4-fluorophenylimino)ethyl] pyridine 1b
1
Yield: 1.95 g, 91%. mp 138–140 ◦C. H NMR (δ, CDCl3):
2.33 [s, 6H, N C-Me]; 6.73 [dd, 4H, J1 = 8.8 Hz, J2 = 4.8 Hz, Ph-
Ho]; 6.94 [dd, 4H, J1 = 8.8 Hz, J2 = 4.8 Hz, Ph-Hm]; 7.87 [t, 1H,
J = 7.8 Hz, Py-Hp], 8.34[d, 2H, J = 8.0 Hz, Py-Hm]. 13CNMR(δ,
CDCl3): 16.39; 115.83; 120.99; 122.61; 137.08; 147.42; 158.62;
161.03; 168.21. IR (KBr; cm−1): 1651(␯C N).
2.2.4. {(Acetonitrile)(2,6-bis[1-(2,4,6-
trimethylphenylimino)ethyl]pyridine)dichlororuthenium(II)}
[Ru(1e)(CH3CN)Cl2] (2e)
Yield: 450 mg, 74%. mp 130 ◦C (dec.). Anal. calcd. for
C29H34Cl2N4Ru: C 57.05; H 5.61; N 9.18%; found: C 56.96; H
5.93; N 9.24%. 1H NMR (δ, CDCl3): 2.23 [s, 12H, 2,6-(Me)2-4-
Me-Ph]; 2.24 [s, 3H, MeCN]; 2.26 [s, 6H, 2,6-(Me)2-4-Me-Ph];
2.60 [s, 6H, N C-Me]; 6.84 [s, 4H, Ph-Hm]; 7.56 [t, 1H,
J = 8.0 Hz, Py-Hp], 7.81 [d, 2H, J = 8.4 Hz, Py-Hm]. 13C NMR
(δ, CDCl3): 4.97; 18.51; 21.12; 123.79; 127.50; 128.24; 129.43;
131.88; 135.45; 145.68; 163.47; 172.99. IR (KBr; cm−1):
1605(␯C N).
2.1.2. 2,6-Bis[1-(2-methyl-6-ethylphenylimino)ethyl]
pyridine 1f
1
Yield: 2.24 g, 92%. mp 160–161 ◦C. H NMR (δ, CDCl3):
1.08 [t, 6H, J = 7.6 Hz, 2-Me-6-CH2Me-Ph]; 1.98 [s, 6H,
2-Me-6-CH2Me-Ph]; 2.18 [s, 6H, N C-Me]; 2.33 [m, 4H, 2-
Me-6-CH2Me-Ph]; 6.92 [t, 2H, J = 7.6 Hz, Ph-Hp], 7.03 [t, 4H,
J = 8.6 Hz, Ph-Hm], 7.85 [t, 1H, J = 8.0 Hz, Py-Hp], 8.14 [d, 2H,
J = 8.0 Hz, Py-Hm]. 13C NMR (δ, CDCl3): 14.06; 16.90; 18.22;

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4.93; N 7.95%. 1H NMR (δ, CDCl3): 1.28 [t, 12H, J = 7.4 Hz, 2-
Me,4-N(CH2-Me)2-Ph]; 2.47 [s, 6H, 2-Me,4-N(CH2Me)2Ph];
3.34 [s, 6H, N C-Me]; 3.72 [m, 8H, 2-Me,4-N(CH2Me)2Ph];
6.89 [br, 6H, Ph-H]; 7.22[t, 6H,J = 7.6, PPh3-Hm]; 7.49 [t, 6H,
J = 7.6 PPh3-Hp]; 7.72 [t, 1H, J = 7.8, Py-Hp] 7.81 [t, 6H, J = 7.6,
PPh3-Ho]; 8.67 [d, 2H, J = 8.0, Py-Hm] 13C NMR (δ, CDCl3):
10.78; 14.12; 16.75; 42.33; 112.37; 113.80; 115.12; 119.38;
122.43; 124.13; 128.44; 130.27; 132.74; 133.48; 138.53;
145.64; 157.12; 165.73. IR (KBr; cm−1): 1602(␯C N).
2.2.5. {(Acetonitrile)(2,6-bis[1-(phenylimino)ethyl]
pyridine)dichlororuthenium(II)} [Ru(1g)(CH3CN)Cl2] (2g)
Yield: 405 mg, 77%. mp 217–219 ◦C. Anal. calcd. for
C23H22Cl2N4Ru: C 52.48; H 4.21; N 10.64%; found: C 52.58;
H 4.76; N 10.34%. 1H NMR (δ, CDCl3): 1.96 [s, 3H, MeCN];
2.72 [s, 6H, N C-Me]; 6.94 [d, 4H, J = 7.2, Ph-Ho]; 7.05-7.21
[m, 6H, Ph-Hm-p] 7.65 [t, 1H, J = 8.0, Py-Hp]; 7.88 [d, 2H,
J = 8.4 Hz, Py-Hm]. 13C NMR (δ, CDCl3): 5.43; 16.34; 121.51;
127.92;130.37;135.13;137.71;145.13;151.91;156.35;163.22.
IR(KBr; cm−1): 1639 (␯C N).
2.4. General procedure for the synthesis of Type 4
complexes
2.3. General procedure for the synthesis of Type 3
complexes
An ethanolic solution (15 mL) of 1.10 eq. of 1 was mixed with
[RuCl2(p-cymene)]2 (306 mg, 0.50 mmol). The reaction mix-
ture was heated under reflux for 10 h. The resulting dark brown
solution was cooled to room temperature and pyrazine (40 mg,
0.50 mmol) was added. The mixture was heated under reflux
for a further 2 h. The volatiles were removed under reduced
pressure and then the residue was dissolved in dichloromethane
(15 mL) and precipitated by addition of diethyl ether (30 mL).
The microcrystalline solid was filtered off and washed with
diethyl ether (3 × 10 mL) and pentane (3 × 10 mL). The desired
products were dried under reduced pressure at 50 ◦C for 1 h.
An ethanolic solution (15 mL) of 1.10 eq. of 1 was mixed with
[RuCl2(p-cymene)]2 (306 mg, 0.50 mmol). Thereactionmixture
was heated under reflux for 10 h. The resulting dark brown solu-
tion was cooled to room temperature and PPh3 (262 mg, 1 mmol)
was added. The mixture was heated under reflux for a further 2 h.
The volatiles were removed under reduced pressure and then the
residue was dissolved in dichloromethane (15 mL) and precipi-
tated by addition of diethyl ether (30 mL). The microcrystalline
solid was filtered off and washed with diethyl ether (3 × 10 mL)
and pentane (3 × 10 mL). The desired products were dried under
reduced pressure at 50 ◦C for 1 h.
2.4.1. {(μ-Pyrazine)bis-[{2,6-bis[1-(4-N,N-
2.3.1. {(2,6-Bis[1-(4-N,N-dimethylaminophenylimino)
ethyl]pyridine)(triphenylphosphine) dichlororuthenium(II)}
[Ru(1a)(PPh3)Cl2] (3a)
methylaminophenylimino)ethyl]pyridine}
dichlorodiruthenium(II)]} [Ru2(1a)2Cl4(C4H4N2)] (4a)
Yield: 400 mg, 65%. mp = 323 ◦C (dec.). Anal. calcd. for
C60H66Cl4N12Ru2: C 53.03; H 5.11; N 13.74%; found: C 53.12;
Yield: 514 mg, 62%. mp > 350 ◦C. Anal. calcd. for
C43H44Cl2N5PRu: C 61.94; H 5.32; N 8.40%; found: C 61.13;
1
H 5.87; N 13.96%. H NMR (δ, CDCl3): 2.78 [s, 12H, N C-
1
H 4.93; N 7.95%. H NMR (δ, CDCl3): 2.34 [s, 6H, N C-
Me]; 2.86 [s, 12H, 4-NMe2-Ph]; 2.89 [s, 12H, 4-NMe2-Ph];
6.49 [d, 8H, J = 8.0 Hz, Ph-Hm]; 6.89 [d, 8H, J = 7.8 Hz, Ph-Ho];
7.59 [t, 2H, J = 7.4 Hz, Ph-Hp]; 7.80 [d, 4H, J = 7.8 Hz, Py-Hm];
7.94 [d, 4H, J = 4.3 Hz, Pyz-H]. 13C NMR (δ, CDCl3): 18.17;
40.96; 112.85; 122.86; 124.15; 124.60; 144.16; 148.77; 150.85;
163.44; 170.06. IR (KBr; cm−1): 1605(␯C N).
Me]; 2.97 [s, 12H, 4-N(Me)2-Ph]; 6.48-6-53 [br, 8H, Ph-H];
6.85 [t, 3H, J = 7.2 Hz, PPh3-Hm]; 7.08 [t, 6H, J = 7.2 Hz, PPh3-
Hp]; 7.18 [t, 6H, J = 8.0 Hz, PPh3-Ho]; 7.28 [d, 2H, J = 7.8 Hz,
Py-Hm]; 7.35 [t, 1H, J = 7.8 Hz, Py-Hp].13C NMR (δ, CDCl3):
18.46; 40.96; 111.08; 112.35; 123.55; 127.85; 128.74; 133.11;
135.39; 137.98; 148.64; 149.57; 163.56, 169.27. IR (KBr;
cm−1): 1617(␯C N).
2.4.2. {(μ-Pyrazine)bis-[{2,6-bis[1-(4-
fluorophenylimino)ethyl]pyridine}dichloro
2.3.2. {(2,6-Bis[1-(4-fluorophenylimino)ethyl]pyridine}
(triphenylphosphine) dichlororuthenium(II)}
diruthenium(II)]} [Ru2(1b)2Cl4(C4H4N2)] (4b)
Yield: 480 mg, 86%. mp > 350 ◦C. Anal. calcd. for
C46H38Cl4F4N8Ru2: C 49.21; H 3.41; N 9.98%; found: C 49.55;
H 3.76; N 9.66%. 1H NMR (δ, CDCl3): 2.77 [s, 12H, N C-Me];
6.87–7.11 [m, 16H, Ph-H]; 7.68 [t, 2H, J = 7.8, Py-Hp]; 7.91
[d, 4H, J = 8.0, Py-Hm]; 8.02 [d, 1H, J = 4.8, Pyz-H]; 8.21 [d,
1H, J = 4.8, Pyz-H]; 8.42 [d, 1H, J = 5.6, Pyz-H]; 8.71 [d, 1H,
J = 5.2, Pyz-H]. 13C NMR (δ, CDCl3): 19.12; 121.93; 126.09;
128.13; 129.30; 146.26; 147.73; 150.60; 163.56; 171.67. IR
(KBr; cm−1): 1613(␯C N).
[Ru(1b)(PPh3)Cl2] (3b)
Yield: 630 mg, 80%. mp > 350 ◦C. Anal. calcd. for
C39H32Cl2F2N3PRu:C59.77;H4.12;N5.36%;found:C59.95;
H 4.23; N 5.04%. 1H NMR (δ, CDCl3): 2.30 [s, 6H, N C-Me];
6.86 [t, 4H, J = 8.0, Ph-Hm]; 7.06–7.20 [m, 19H, PPh3-H and Ph-
Ho]; 7.24[t, 1H, J = 7.8, Py-Hp]; 7.37 [d, 2H, J = 7.8, Py-Hm].
13C NMR (δ, CDCl3): 17.33; 118.44; 121.74; 125.82; 129.46;
133.65;134.15;138.04;139.91;145.61;157.67;162.13;170.32.
IR (KBr; cm−1): 1635 (␯C N).
2.3.3. 2,6-Bis[1-(2-methyl-4-N,N-
2.4.3. {(μ-Pyrazine)bis-[{2,6-bis[1-(4-tert-
diethylaminophenylimino)ethyl]pyridine(triphenylphosphine)
dichlororuthenium(II)} [Ru(1d)(PPh3)Cl2] (3d)
buthylphenylimino)ethyl]pyridine}
dichlorodiruthenium(II)]} [Ru2(1c)2Cl4(C4H4N2)] (4c)
Yield: 510 mg, 80%. mp > 350 ◦C. Anal. calcd. for
C62H74Cl4N8Ru2: C 58.39; H 5.85; N 8.79%; found: C 57.92;
Yield: 610 mg, 66%. mp > 350 ◦C. Anal. calcd. for
C49H56Cl2N5PRu: C 64.11; H 6.15; N 7.63%; found: C 61.13; H

O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
137
H 5.67; N 9.86%. IR (KBr; cm−1): 1576 (␯C N). H NMR (δ,
CDCl3): 1.27 [s, 36H, 4-C(Me)3Ph]; 2.75 [s, 6H, N C-Me]; 2.78
[s, 6H, N C-Me]; 6.88 [d, 4H, J = 8.4 Hz, Ph-Hm]; 6.94 [d, 4H,
J = 8.4 Hz, Ph-Hm]; 7.20 [d, 4H, J = 8.4 Hz, Ph-Ho]; 7.25 [d, 4H,
J = 8.8 Hz, Ph-Ho]; 7.58 [t, 2H, J = 8.0 Hz, Py-Hp]; 7.82 [d, 4H,
J = 8.8 Hz, Py-Hm]; 7.89 [s, 4H, Pyz-H]. 13C NMR (δ, CDCl3):
18.02; 31.55; 34.77; 122.26; 125.75; 128.44; 129.25; 146.02;
147.48; 149.97; 162.35; 170.61. IR (KBr; cm−1): 1576(␯C N).
was heated under reflux for 10 h. The resulting dark brown solu-
tion was cooled to room temperature and 4,4ꢀ-bipyridine (40 mg,
0.50 mmol) was added. The mixture was heated under reflux
for a further 2 h. The volatiles were removed under reduced
pressure and then the residue was dissolved in dichloromethane
(15 mL) and precipitated by addition of diethyl ether (30 mL).
The microcrystalline solid was filtered off and washed with
diethyl ether (3 × 10 mL) and pentane (3 × 10 mL). The desired
products were dried under reduced pressure at 50 ◦C for 1 h.
1
2.4.4. {(μ-Pyrazine)bis-[{2,6-bis[1-(2-methyl-4-N,N-
diethylaminophenylimino)ethyl]pyridine}
2.5.1. {(μ-4,4ˇı-Bipyridine)bis-[{2,6-bis[1-(4-N,N-
methylaminophenylimino)ethyl]pyridine} dichloro
dichlorodiruthenium(II)]} [Ru2(1d)2Cl4(C4H4N2)] (4d)
Yield: 940 mg, 68%. mp 355 ◦C (dec.). Anal. calcd. for
C66H86Cl4N12Ru2: C 56.97; H 6.23; N 12.08%; found: C 56.20;
diruthenium(II)]} [Ru2(1a)2Cl4(C10H8N2)] (5a)
Yield: 420 mg, 68%. mp 368 ◦C (dec.). Anal. calcd. for
C60H66Cl4N12Ru2: C 55.47; H 5.12; N 12.94%; found: C 55.12;
H 5.05; N 13.11%. 1H NMR (δ, CDCl3):): 2.77 [s, 12H, N C-
Me]; 2.84 [s, 24H, 4-NMe2-Ph]; 6.46 [d, 8H, J = 8.4 Hz, Ph-Hm];
6.90–6.93 [m, 12H, Ph-Ho, Bpy-Hm]; 7.54 [t, 2H, J = 7.8 Hz, Py-
Hp]; 7.81 [d, 4H, J = 8.4 Hz, Py-Hm]; 8.55 [d, 4H, J = 5.3 Hz,
Bpy-Ho]. 13C NMR (δ, CDCl3): 17.89; 40.98; 112.53; 123.70;
127.67;134.54;139.56;143.20;149.09;155.72;163.43;173.84.
IR (KBr; cm−1): 1609 (␯C N).
1
H 6.32; N 11.92%. H NMR (δ, CDCl3): 0.95–1.11 [m, 24H,
2-Me,4-N(CH2-Me)2-Ph]; 1.76–2.09 [m, 12H, 2-Me,4-N(CH2-
Me)2-Ph]; 2.65 [d, 12H, J = 5.6 Hz, N C-Me]; 2.97–3.31
[m, 16H, 2-Me,4-N(CH2-Me)2-Ph]; 6.06-6.18 [m, 4H, Ph-
Hm]; 6.27–6.34 [m, 4H, Ph-Hm]; 6.68–6.86 [m, 4H, Ph-Ho];
7.45–7.64 [m, 6H, Py-H]; 7.70–7.74 [m, 4H, Pyz-H]. 13C NMR
(δ, CDCl3): 12.77; 15.98; 18.31; 44.34; 109.63; 115.11; 117.64;
121.31;129.00;135.46;138.72;145.78;148.36;158.97;170.31.
IR (KBr; cm−1): 1583 (␯C N).
2.5.2. {(μ-4,4ˇı-Bipyridine)bis-[{2,6-bis[1-(2-methyl-4-
N,N-diethylaminophenylimino)ethyl] pyridine}
2.4.5. {(μ-Pyrazine)bis-[{2,6-bis[1-(2,4,6-
dichlorodiruthenium(II)]} [Ru2(1d)2Cl4(C10H8N2)] (5d)
Yield: 510 mg, 70%. mp 330 ◦C (dec.). Anal. calcd. for
C72H90Cl4N12Ru2: C 58.93 H 6.18; N 11.45%; found: C
trimethylphenylimino)ethyl]pyridine}dichloro
diruthenium(II)]} [Ru2(1e)2Cl4(C4H4N2)] (4e)
Yield 457 mg, 75%. mp 182 ◦C (dec.). Anal. calcd. for
C58H66Cl4N8Ru2: C 57.14; H 5.46; N 9.19%. found: C 56.78;
1
59.10; H 6.11; N 11.41%. H NMR (δ, CDCl3): 1.04 [t, 24H,
J = 6.6 Hz, 2-Me,4-N(CH2-Me)2-Ph]; 2.19 [s, 12H, 2-Me,4-
N(CH2-Me)2-Ph]; 2.73 [s, 12H, N C-Me]; 3.18–3.30 [m, 16H,
2-Me,4-N(CH2-Me)2-Ph]; 6.17 [d, 4H, J = 8.8 Hz, Ph-Ho]; 6.45
[s, 4H, Ph-Hm]; 6.86 [d, 4H, J = 6.4 Hz, Bpy-Hm]; 6.93 [t, 4H,
J = 8.2 Hz, Ph-Hm]; 7.59 [t, 2 H, J = 8.0 Hz, Py-Hp]; 7.84 [d, 4H,
J = 8.0, Py-Hm]; 8.55 [d, 4H, J = 4.8, Bpy-Ho]. 13C NMR (δ,
CDCl3): 12.63; 16.01; 18.34; 45.94; 110.56; 115.49; 118.67;
120.21; 121.72; 129.96; 136.54; 140.01; 144.32; 146.16;
155.22; 162.42; 172.12. IR (KBr; cm−1): 1600(␯C N).
1
H 6.32; N 10.18%. H NMR (δ, CDCl3): 2.01 [s, 24H, 2,6-
(Me)2 ,4-Me-Ph]; 2.13 [s, 12H, 2,6-(Me)2,4-Me-Ph]; 2.63 [s,
12H, N C-Me]; 6.59 [s, 8H, Ph-H]; 7.67 [t, 2H, J = 7.8 Hz,
Py-Hp]; 7.89 [d, 4H, J = 8.0 Hz, Py-Hm]; 8.24 [s, 4H, Pyz-H].
13C NMR (δ, CDCl3): 18.34; 20.54; 123.57; 128.51, 129.33,
131.36, 135.50; 144.60; 147.76; 162.26, 173.49. IR (KBr;
cm−1): 1635(␯C N).
2.4.6. {(μ-Pyrazine)bis-[{2,6-bis[1-(2-methyl-6-
ethylphenylimino)ethyl]pyridine}dichloro
2.5.3. {(μ-4,4ˇı-Bipyridine)bis-[{2,6-bis[1-(2,4,6-
diruthenium(II)]} [Ru2(1f)2Cl4(C4H4N2)] (4f)
trimethylphenylimino)ethyl]pyridine}
Yield 515 mg, 84%. mp 389 ◦C (dec.). Anal. calcd. for
C58H66Cl4N8Ru2: C 57.14; H 5.46; N 9.19%; found: C 57.88;
dichlorodiruthenium(II)]} [Ru2(1e)2Cl4(C10H8N2)] (5e)
Yield: 526 mg, 81%. mp 260 ◦C (dec.). Anal. calcd. for
C64H70Cl4N8Ru2: C 59.35; H 5.45; N 8.65%. found: C 59.87;
H 4.92; N 8.94%. 1H NMR (δ, CDCl3): 2.04 [s, 24H, 2,6-(Me)2
,4-Me-Ph]; 2.25 [s, 12H, 2,6-(Me)2,4-Me-Ph]; 2.68 [s, 12H,
N C-Me]; 6.76 [s, 8H, Ph-H]; 7.05 [d, 4H, J = 6.0, Bpy-Hm];
7.69 [t, 2H, J = 7.8 Hz, Py-Hp]; 7.93 [d, 4H, J = 8.0 Hz, Py-Hm];
8.52 [d, 4H, J = 6.0, Bpy-Ho]. 13C NMR (δ, CDCl3): 18.74;
20.92; 119.76; 123.70; 127.78; 129.42; 132.12; 135.36; 143.60;
144.63; 155.52; 162.97; 173.70. IR (KBr; cm−1): 1631(␯C N).
1
H 4.96; N 9.67%. H NMR (δ, CDCl3): 0.86–1.01 [m, 12H,
2-Me-6-(CH2-Me)-Ph]; 2.03–2.18 [m, 12H, 2-Me-6-(CH2-Me)-
Ph]; 2.53–2.69 [m, 16H, 2-Me-6-(CH2-Me)-Ph]; 2.63 [s, 12H,
N C-Me]; 6.76-6.95 [m, 12H, Ph-H]; 7.70 [t, 2H, J = 8.2 Hz,
Py-Hp]; 7.91 [d, 4H, J = 8.0 Hz, Py-Hm]; 8.24–8.30 [m, 4H, Pyz-
H]. 13C NMR (δ, CDCl3): 15.62; 18.83; 20.85; 25.14; 123.74,
126.65, 127.02;128.73;131.18;137.48;138.17;146.06;147.84;
162.35; 173.71. IR (KBr; cm−1): 1619(␯C N).
2.5. General procedure for the synthesis of Type 5
complexes
2.5.4. {(μ-4,4ˇı-Bipyridine)bis-[{2,6-bis[1-(2-methyl-6-
ethylphenylimino)ethyl]pyridine}
dichlorodiruthenium(II)]} [Ru2(1f)2Cl4(C10H8N2)] (5f)
Yield 503 mg, 78%. mp 370 ◦C (dec.). Anal. calcd. for
C64H70Cl4N8Ru2: C 59.35; H 5.45; N 8.65%; found: C 60.14;
An ethanolic solution (15 mL) of 1.10 eq. of 1 was mixed with
[RuCl2(p-cymene)]2 (306 mg, 0.50 mmol). Thereactionmixture

138
O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
1
J = 6.0, Ph-H]; 7.05 [d, 4H, J = 4.8, Bpy-Hm]; 9.03 [d, 4H,
J = 5.2, Bpy-Ho]. 13C NMR (δ, CDCl3): 16.79; 27.87; 35.41;
114.56; 120.36; 128.68; 131.47; 137.46; 149.45; 153.31.
H 5.23; N 8.87%. H NMR (δ, CDCl3): 0.68–0.92 [m, 12H,
2-Me,6-(CH2-Me)-Ph]; 1.99–2.16 [m, 12H, 2-Me-6-(CH2-Me)-
Ph]; 2.28–2.53 [m, 8H, 2-Me,6-(CH2-Me)-Ph]; 2.64 [d, 12H,
J = 5.2, N C-Me]; 6.82–7.04 [m, 16H, Ph-H, Bpy-Hm]; 7.65
[t, 2H, J = 8.0 Hz, Py-Hp]; 7.89 [d, 4H, J = 8.0 Hz, Py-Hm];
8.32–8.38 [m, 4H, Bpy-Ho]. 13C NMR (δ,CDCl3): 14.53; 19.34;
21.25; 25.86; 119.56; 123.04; 126.08; 127.48; 129.87; 133.23;
134.84; 146.29; 148.09; 155.53; 161.32; 168.30; 176.50. IR
(KBr; cm−1): 1625 (␯C N).
2.8. General method for transfer hydrogenation of
acetophenone using Ru(II)-pydim complexes as pre-catalyst
A mixture of acetophenone (10 mmol), the catalyst
(0.01 mmol Ru(II)) and propan-2-ol (19 mL) were stirred at
82 ◦C for 10 min. 1 mL of 0.1 M KOH (0.1 mmol) solution in
2-propanol was then introduced. The mixture was stirred at
refluxing temperature and the reaction was monitored by GC.
After the reaction had been heated for the appropriate time,
the mixture was concentrated and subjected to flash column
chromatography on silica gel (CH2Cl2/MeOH 9:1) to afford the
alcohol product. The solvent was removed under reduced pres-
sure to give an oily residue. The identity of the products were
confirmed by 1H NMR spectroscopy.
2.6. Synthesis of μ-(pyrazine)tetrachlorobis
(p-cymene)diruthenium(II), 6
A solution of pyrazine (1.00 mmol, 80 mg) in ethanol (10 mL)
was added dropwise to a solution of [RuCl2(p-cymene)]2
(1.00 mmol, 612 mg) in ethanol (40 mL). A yellow precipitate
formed immediately. The mixture was heated under reflux for 2 h
and then cooled to room temperature. A yellow precipitate was
filtered off, washed with diethyl ether (3 × 10 mL) and dried
under reduced pressure. Yield 600 mg, 86%; mp 228–230 ◦C
(dec.). Anal. calcd. for C24H32Cl4N2Ru2: C 41.63; H 4.66; N
4.05%; found: C 41.37; H 4.55; N 4.13%.
3. Results and discussion
3.1. Synthesis of ligands
1H NMR (δ, CDCl3): 1.28 [d, 12H, J = 6.4 Hz, Me-Ph-
CH(Me)2]; 2.13 [s, 6H, Me-Ph-CH-(Me)2]; 3.03 [m, 2H,
Me-Ph-CH(Me)2]; 5.31 [d, 4H, J = 6.0, Ph-H]; 5.47 [d,
4H, J = 6.0, Ph-H]; 8.21 [s, 4H, Pyz-H]. 13C NMR (δ,
CDCl3): 17.13; 26.19; 38.26; 119.21; 123.49; 125.54; 136.78;
139.44.
Pydim ligands (1a–g) were prepared in good yield by a
Schiff-base condensation reaction (Scheme 1). The prepara-
tion of ligands 1a, c, d, e, g have been described elsewhere
[9,15–17,19]. All compounds were characterized by NMR and
IR spectroscopy.
1
All the ligands gave H and 13C NMR spectra correspond-
2.7. Synthesis of μ-(4,4ˇı-bipyridine)tetrachlorobis
(p-cymene)diruthenium(II), 7
ing to the proposed formulations. The Py-Hp and -Hm protons
were observed as doublets and triplets in a 2:1 ratio at around
δ 7.75–8.48 ppm. The most notable observation in the 1H
NMR spectra of the free pydim ligands was that Py-Hm was
more sensitive to the p-substituent of the aryl ring. Thus,
Py-Hm signals moved further downfield as the electron with-
drawing property of the p-substituent increased. In the 13C
NMR spectra, the pydim ligands exhibited a singlet at about
166–168 ppm, which can be assigned to the imine (C N) carbon.
The pydim ligands also showed a singlet at 16–17 ppm, which
could be ascribed to the methyl groups in the backbone of the
ligand.
This compound was prepared in the same manner as 6 using
4,4ꢀ-bipyridine (156 mg, 1.00 mmol) and [RuCl2(p-cymene)]2
(612 mg, 1.00 mmol)). A yellow microcrystalline solid was
obtained. Yield: 720 mg, 93%. mp 244–246 ◦C (dec.). Anal.
calcd. for C30H36Cl4N2Ru2: C 46.88; H 4.72; N 3.64%; found:
C 46.97; H 4.59; N 3.72%.
1H NMR (δ, CDCl3): 1.32 [d, 12H, J = 6.4 Hz, Me-Ph-
CH(Me)2]; 2.08 [s, 6H, Me-Ph-CH(Me)2]; 2.99 [m, 2H,
Me-Ph-CH(Me)2]; 5.27 [d, 4H, J = 5.6, Ph-H]; 5.49 [d, 4H,
Scheme 1. Synthesis of the Pydim ligands.

O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
139
Scheme 2. Synthesis of mono- or binuclear Pydim-Ru(II) complexes.
3.2. Synthesis of complexes
–Hm protons for all Pydim-Ru(II) complexes were observed as
doublets and triplets in a 2:1 ratio which had shifted towards
higher fields when compared to their respective free ligands
except for 2b, 3d and 4d. Py-Hp for 2b and Py-Hm for 3d showed
a lower chemical shift than the free pydim ligands. Py-Hp and
Py-Hm for 4d were observed as multiplets. The stereochem-
istry was determined on the basis of 1H and 13C NMR spectra,
which exhibited the expected singlet resonances for C2 symme-
try. On the basis of X-ray diffraction studies the two chlorine
atoms were assigned to be in a trans-orientation in complex 2f
[18]. The same orientation has also been observed in an ani-
syl derivative of 2 (Ar 4-MeOC6H4) [9]. However, in the case
of the related complex [RuCl2(PPh3)(Me4BPy)] (Me4BPy: 2,6-
bis(3,5-dimethylprazol-1-yl)pyridine), a cis-configuration was
assigned by an X-ray crystallographic study [13]. In another
example, reaction of trans-[RuCl2(C2H4){N,N,N-(R,R)-Ph-
Pybox}] with PPh3 yields either the cis- or trans-isomer
depending on whether it is refluxed in MeOH or CH2Cl2
[12].
[Ru2(p-cymene)2Cl4] reacts with pydim ligands (1) in reflux-
ing EtOH and the resulting air-stable six coordinated mono- or
binuclear complexes can be isolated if the ancillary ligand (L
or L-L) is added to the mixture towards the end of reaction
(Scheme 2). The binuclear complexes 4 and 5 could also be pre-
pared by reaction of the binuclear precursor complexes 6 and 7
with the appropriate pydim ligands (Scheme 2, the lower part).
All of the complexes were soluble in chlorinated solvents and
werefullycharacterizedbyelementalanalysisandspectroscopic
methods.
The 1H NMR spectra of these complexes showed some dif-
ferences from their respective ligands, especially in the pyridine
backbone. The chemical shift of the methyl groups in the pydim
backbone (complexes 3, 4 and 5) were singlets which had shifted
towards higher field in the complexes as compared to the free
ligands. In the case of type 2, the methyl protons showed a lower
chemical shift than the free pydim ligands. Similarly, Py-Ho and

140
O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
Table 1
CatalyticactivityfortransferhydrogenationofacetophenonecatalyzedbyRu(II)
complexes
Entries
Catalyst
Conversion (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
2a
2b
2d
2e
2f
2g
3a
3b
3d
4a
4b
4c
4d
4e
4f
70
99 (93)b(32)c
54
62
61
91
68
95
43
79
96
91
62
88
89
63
58
80
84
4
Fig. 1. Optimization of reaction conditions for transfer hydrogenation of ace-
tophenone catalyzed by 3e.
3.3. Catalytic studies
5a
5d
5e
5f
6
7
Studies of the transfer hydrogenation of acetophenone with
2-propanol catalyzed by the complexes were carried out under
identical conditions to allow comparison of results.
Preliminary studies were performed using complexes of
type 3 as a catalyst as these complexes were structurally sim-
ilar to ruthenium complexes containing bis(oxazolines) and
bis(pyrazolines) ligands [12,13]. Initial experiments using 3d
with ketone:Ru:base in the ratio 1000:1:50 showed limited reac-
tivity (40% yield after 1h). On the basis of these results, we
attempted the optimization of the reaction conditions using
4e as a catalyst (Fig. 1). Reactions were carried out at 82 ◦C
using 10 mmol acetophenone with 0.01 mmol 4e in 20 mL of
2-propanol for 1 h. As a general feature, a strong dependence
was observed on the KOH/catalyst molar ratio, which should
not be lower than approximately 10:1. Otherwise, the reaction
becomes slower.
7
Reactions were carried out at 82 ◦C using 10 mmol acetophenone with 0.1 mol%
Ru(II) in 20 mL of 2-propanol for 1 h.
b
Reactions were carried out at 82 ◦C using 10 mmol acetophenone solution
with 0.1 mol% Ru(II) in 20 mL of 2-propanol for 5 min.
c
Reactions were carried out at 25 ◦C using 10 mmol acetophenone solution
with 0.1mol% Ru(II) in 20 mL of 2-propanol for 1 h.
3. The efficiency of the catalyst seems to depend not only on the
imine fragment of the pydim ligands, but also on the ancillary
ligands.
4. Mononuclear complexes of type 2 are more active than type
3 complexes. Similarly, the binuclear complexes of type 4
are more active than type 5 complexes.
5. Although all of the Pydim-Ru(II) complexes are active cat-
alysts, 2b, 3b and 4b are much more efficient. Fluorine
substituent on the imine fragment of the pydim ligand has
been shown to be crucial in the catalytic activity.
6. Catalytic activity decreases when methyl groups are intro-
duced at the ortho positions of the aryl ring.
No attempts were made to optimize the catalyst loading,
although this could have a favorable bearing on the reactivity;
instead identical reaction conditions were used throughout the
present study.
To investigate the effect of ancillary ligands, the catalytic
ˇ
activity of MeCN, Pyrazine, and 4,4ı-bipyridine coordinated
complexes 2, 4 and 5 were also studied under the same con-
ditions. As a result, the Pydim-Ru(II) complexes of type 2–5
were found to be active catalysts in the transfer hydrogenation
of acetophenone, leading to the formation of sec-alcohol with
good to excellent conversions (43–99%) in 1 h. The results are
summarized in Table 1.
4. Conclusions
This work reports the preparation and characterization of
Pydim ligands, mono- and binuclear Pydim-Ru(II) complexes
and their catalytic activities for the hydrogen transfer reaction
of acetophenone. Useful information has been collected about
the influence of several structural factors, including the steric
bulkiness around the Ru(II) center and the presence of electron-
withdrawing groups on the aromatic ring of the imine fragment
of the pydim ligands: (i) if one or two methyl groups were intro-
duced into the ortho position of the imine fragment, a constant
The most remarkable features are:
1. Very rapid conversions are achieved at 82 ◦C. The reactions
become notably slower as the temperature decreases.
2. Under the same reaction conditions, binuclear Ru(II)-
arene complexes 6 and 7 furnished less than 7% yield of
product.

O. Dayan, B. C¸ etinkaya / Journal of Molecular Catalysis A: Chemical 271 (2007) 134–141
141
decrease in the catalytic yield was observed, which was probably
due to a steric effect. ii) When an electron withdrawing group
was introduced into the para position of the imine fragment, cat-
alytic yield increased. However, if an electron donating group
was introduced into the para position of the imine fragment,
catalytic yield was decreased.
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