Synthesis of ruthenium(II) complexes containing tridentate triamine (′NNN′) and bidentate diamine ligands (NN′): As catalysts for transfer hydrogenation of ketones

Article abstract of DOI:10.1021/om200470p

A series of neutral and cationic Ru(II) complexes (1-10), bearing pyridine-based tridentate (′NNN′), pyridine-based bidentate (NN′), and mixed ′NNN′ + NN′ ligands, were synthesized by starting from [RuCl ₂(DMSO)₄] and [RuCl₂(p-cymene)]₂ precursors. Solid-state structures of mixed-ligand complexes 9 and 10 were determined by single-crystal X-ray diffraction. Both complexes are unusual in that NN′ ligands were spontaneously oxidized in air under base-free conditions to give imine-amine bidentate ligands upon replacement of p-cymene by meridional ′NNN′. The complexes 1-10 were screened for transfer hydrogenation (TH) of aryl ketones with 2-propanol. The highest catalytic activity was obtained with the complexes containing tridentate ′NNN′ and 7, which contain nonsulfonated 2-(aminomethyl)pyridine. However, for complexes 6_a-c, containing p-cymene (a facial tridentate ligand), a slower reaction rate was observed.

Full text of DOI:10.1021/om200470p

ARTICLE
pubs.acs.org/Organometallics
Synthesis of Ruthenium(II) Complexes Containing Tridentate
Triamine (0NkNkN0) and Bidentate Diamine Ligands
(NkN0): as Catalysts for Transfer Hydrogenation of Ketones
Salih G€unnaz, Namık Ozdemir, Serkan Dayan, Osman Dayan,* and Bekir Çetinkaya*
†
‡
§
,
||
,†
€
·
†Department of Chemistry, Ege University, 35100 Izmir, Turkey
‡Department of Physics, Faculty of Art and Sciences, Ondokuz Mayıs University, 55139 Samsun, Turkey
§Department of Chemistry, Faculty of Science, Erciyes University, 38039 Kayseri, Turkey
Laboratory of Inorganic Synthesis and Molecular Catalysis, Çanakkale Onsekiz Mart University, 17020 Çanakkale, Turkey
S Supporting Information
b
ABSTRACT: A series of neutral and cationic Ru(II) complexes
(1ꢀ10), bearing pyridine-based tridentate (0NkNkN0), pyridine-
based bidentate (NkN0), and mixed 0NkNkN0 + NkN0 ligands, were
synthesized by starting from [RuCl2(DMSO)4] and [RuCl2-
(p-cymene)]2 precursors. Solid-state structures of mixed-ligand
complexes 9 and 10 were determined by single-crystal X-ray
diffraction. Both complexes are unusual in that NkN0 ligands
were spontaneously oxidized in air under base-free conditions
to give imine-amine bidentate ligands upon replacement of
0
p-cymene by meridional NkNkN0. The complexes 1ꢀ10 were
screened for transfer hydrogenation (TH) of aryl ketones with
0
2-propanol. The highest catalytic activity was obtained with the complexes containing tridentate NkNkN0 and 7, which contain
nonsulfonated 2-(aminomethyl)pyridine. However, for complexes 6aꢀc, containing p-cymene (a facial tridentate ligand), a slower
reaction rate was observed.
’ INTRODUCTION
variability of Ar groups.64ꢀ68 Neutral sulfonamide ligands are
expected to be poor ligands. Thus, the pyridyl-2-alkylsulfona-
mides generally coordinate to the metal center through the
pyridyl nitrogen atom and the deprotonated nitrogen of the
sulfonamide group.69 However, Soltani et al. have recently shown
that cationic Ir complexes containing neutral sulfonamide ligands
are active catalysts for the TH of acetophenone derivatives in
water.70 More recently, Baratte and co-workers have shown that
Ru(II) complexes containing nonsulfonated (2-aminomethyl)-
pyridine ligands display excellent catalytic activity in the TH of
ketones.71 With the aim of contributing to the understanding of
how geometric and electronic factors imposed by a combination
of mixed tri- and bidentate ligands influence the catalyst perfor-
mance, herein a series of novel Ru(II) complexes (1ꢀ10) were
characterized and employed as catalysts for the TH of ketones.
Pyridine-based tridentate triamine compounds (0NkNkN0) are
very attractive ligands for coordination chemistry, and their
transition-metal (TM) complexes have been successfully applied
in homogeneous catalysis.1ꢀ28 Although examples of the related
Ru complexes are scarce, such complexes recently gained at-
tention due to their use in catalysis and in other chemical applica-
tions.29ꢀ48 For example, NNN -containing neutral Ru(II) com-
kk
d
d
plexes of the general formula [RuCl ( NNN )L] (L = monodentate
kk
2 d
d
ligands such as CH3CN, PPh3, and CO) are effective catalysts for
the transfer hydrogenation (TH) of ketones.29,32 During the
preparation of this paper, a report on unsymmetrical and
asymmetrical [RuCl(0NNN00)(PPh ) ]Cl complexes which
kk
3 2
showed excellent TH activity has appeared.49
On the other hand, Ru(II) complexes bearing chelating amine
ligands such as N-sulfonated 1,2-diamines have been successfully
used in the TH of acetophenone by Noyori and others.50ꢀ63
However, in spite of these developments, there is still demand for
stable and easily handled complexes prepared from cheap start-
ing materials which make them preferred catalyst precursors. In
comparison with the extensive chemistry of sulfonated 1,2-
diamines, little research has been performed on pyridylsulfona-
mide compounds of the type C5H4NCH2NHSO2Ar, which are
versatile bidentate ligands due to their ease of synthesis and
’ EXPERIMENTAL SECTION
The manipulations were performed under air unless otherwise stated.
All reagents and solvents were obtained from commercial suppliers
and used without further purification. [RuCl2(p-cymene)]2,72
[RuCl2(DMSO)4,73 dNkNkNd;74 bNkNkNb (R = H),75 pNkNkNp,76 and
Received: June 1, 2011
Published: July 12, 2011
r
2011 American Chemical Society
4165
dx.doi.org/10.1021/om200470p Organometallics 2011, 30, 4165–4173
|

Organometallics
ARTICLE
66
NkN0a were synthesized according to published procedures. NMR
7.43 (t, 2H, J = 7.4 Hz, H-10), 7.54 (t, 2H, J = 7.6 Hz, H-9), 8.19 (d, 2H,
J = 7.8 Hz, H-11), 8.49 (t, 1H, J = 7.8 Hz, H-4), 8.65 (d, 2H, J = 8.0 Hz,
H-3). 13C NMR (100 MHz, DMSO-d6): δ 45.63, 110.03, 119.82,
123.11, 137.12, 143.91, 151.42, 152.13, 156.21.
spectra were recorded at 297 K on a Bruker 300 MHz Ultrashield TM
NMR spectrometer at 300 MHz (1H) and 75.48 MHz (13C) or at 297 K
on a Varian Mercury AS 400 NMR spectrometer at 400 MHz (1H) and
100.56 MHz (13C). Chemical shifts (δ) are given in parts per million and
coupling constants (J) in hertz. The C, H, and N analyses were
performed using a CHNS-932 (LECO) instrument. Infrared spectra
were measured with a Perkin-Elmer Spectrum One FTIR system and
recorded using a universal ATR sampling accessory within the range
550ꢀ4000 cmꢀ1. Melting points were determined in open capillary
tubes on a digital Stuart SMP10 melting point apparatus or an Electro-
thermal 9100 melting point detection apparatus and are uncorrected.
GC measurements for catalytic experiments were performed using a
Younglin Acme 6100 GC instrument with an Optima 5MS capillary
column or an Agilent 6890N GC instrument with a HP5 capillary
column.
1
Complex 2. Yield: 71%. Mp: 210ꢀ212 °C. H NMR (400 MHz,
DMSO-d6): δ 2.24 (s, 6H, (CH3)2SO), 6.23 (s, 4H, N-CH2-Ar),
7.16ꢀ7.61 (m, 16H, H-8, H-9, H-10, and Ar-H), 7.82 (d, 2H, J = 7.9
Hz, H-11), 8.16 (t, 1H, J = 7.8 Hz, H-4), 8.53 (d, 2H, J = 8.0 Hz, H-3).
13C NMR (100 MHz, DMSO-d6): 45.58, 50.88, 111.28, 116.03, 118.05,
132.0, 134.13, 135.51, 135.71, 137.89, 144.67, 146.43, 151.01, 159.33.
1
Complex 3. Yield: 70%. Mp: 226ꢀ228 °C. H NMR (400 MHz,
CDCl3): δ 2.11 (s, 6H, 4-Me-Ar), 2.45 (s, 12H, 2,6-(Me)2-Ar), 2.53
(s, 6H, (CH3)2SO), 6.18 (s, 4H, N-CH2-Ar); 6.58 (d, 2H, J = 7.6 Hz, H-
8), 6.84 (t, 2H, J = 7.8 Hz, H-10), 7.21 (s, 4H, 3,5-H-Ar) 7.51 (t, 2H, J =
7.7 Hz, H-9), 7.82 (d, 2H, J = 7.9 Hz, H-11), 8.26 (t, 1H, J = 7.8 Hz, H-4),
8.72 (d, 2H, J = 7.6 Hz, H-3). 13C NMR (100 MHz, CDCl3): δ 19.53,
20.01, 45.28, 50.17, 105.83, 116.03, 119.18, 120.32, 134.01, 134.86,
148.51, 151.63, 157.14, 165.91.
General Procedure for the Synthesis of bNkNkNb Deriva-
tives. A solution of 2,6-bis(benzimidazol-2-yl)pyridine (0.5 mmol) and
KOH (1.15 mmol) in acetone (20 mL) was refluxed for 1 h under argon.
Then benzyl halide (1.1 mmol) was added and the resulting solution was
refluxed for a further 8 h. Volatiles were removed, and the residue was
treated with CH2Cl2 (DCM) (10 mL) and filtered. The volume of the
filtrate was reduced to ∼5 mL; n-hexane (10 mL) was added and cooled
to obtain cream-colored crystals.
1
Complex 4. Yield: 77%. Mp: 244ꢀ246 °C. H NMR (400 MHz,
CDCl3): δ 2.11 (s, 12H, 2,6-(Me)2-Ar), 2.24 (s, 12H, 3,5-(Me)2-Ar),
2.79 (s, 6H, (CH3)2SO), 5.74 (s, 4H, N-CH2-Ar), 6.33 (d, 2H, J =
7.7 Hz, H-8), 6.64 (s, 2H, 4-H-Ar), 7.03 (t, 2H, J = 7.6 Hz, H-10), 7.39
(t, 2H, J = 7.5 Hz, H-9), 7.81 (d, 2H, J = 7.7 Hz, H-11), 8.21 (t, 1H, J =
7.7 Hz, H-4), 8.92 (d, 2H, J = 7.8 Hz, H-3). 13C NMR (100 MHz,
CDCl3): δ 14.02, 15.38, 45.39, 49.31, 112.06, 122.04, 124.08, 126.14,
142.18, 145.38, 150.17, 165.21, 168.09.
bNkNkNb (R = CH2C6H5). Yield: 83%. Mp: 240ꢀ242 °C. 1H NMR (400
MHz, DMSO-d6): δ 6.51 (s, 4H, N-CH2-Ar), 7.26 (m, 16H, Ar H), 7.81
(d, 2H, J = 7.9 Hz, H-8), 7.93 (t, 1H, J = 7.7 Hz, H-4), 8.41 (d, 2H,
J = 7.9 Hz, H-3). 13C NMR (100 MHz, DMSO-d6): δ 51.81, 110.01,
121.02, 122.61, 124.0, 127.03, 128.27, 129.66, 130.18, 135.51, 137.89,
139.85, 144.67, 151.01, 159.33.
1
Complex 5. Yield: 78%. Mp: 260ꢀ262 °C. H NMR (400 MHz,
CDCl3): δ 2.08 (s, 12H, 2,6-(Me)2-Ar), 2.19 (s, 12H, 3,5-(Me)2-Ar),
2.23 (s, 6H, 4-(Me)-Ar), 2.65 (s, 6H, (CH3)2SO), 6.08 (s, 4H, N-CH2-
Ar), 6.38 (d, 2H, J = 7.6 Hz, H-8), 6.85 (t, 2H, J = 7.6 Hz, H-10), 7.21 (t,
2H, J = 7.7 Hz, H-9), 7.82 (d, 2H, J = 7.8 Hz, H-11), 8.18 (t, 1H, J = 7.8
Hz, H-4), 9.13 (d, 2H, J = 7.8 Hz, H-3). 13C NMR (100 MHz, CDCl3): δ
17.76, 18.02, 19.03, 45.23, 48.63, 108.03, 114.28, 120.07, 126.12, 137.03,
143.38, 144.47, 155.94, 159.07.
bNkNkNb (R = CH2C6H2Me3-2,4,6). Yield: 71%. Mp: 248ꢀ250 °C. 1H
NMR (400 MHz, CDCl3): δ 1.93 (s, 12H, 2,6-(Me)2-Ar), 2.19 (s, 6H,
4-Me-Ar), 6.26 (s, 4H, N-CH2-Ar); 6.67 (d, 2H, J = 7.6 Hz, H-8), 6.71
(s, 4H, 3,5-H-Ar), 6.98 (t, 2H, J = 7.7 Hz, H-10), 7.19 (t, 2H, J = 7.6 Hz,
H-9), 7.76 (d, 2H, J = 7.9 Hz, H-11), 8.07 (t, 1H, J = 7.8 Hz, H-4), 8.42
(d, 2H, J = 7.6 Hz, H-3). 13C NMR (100 MHz, CDCl3): δ 19.88, 46.83,
105.88, 115.03, 120.58, 121.08, 134.0, 135.07, 135.23, 142.02, 142.26,
149.0, 155.41, 163.18.
General Procedure for the Synthesis of NkN0aꢀc. 2-(Amino-
methyl)pyridine (NkN0a) was used as supplied. The compound NkN0b
was prepared by modification of the published procedure.77
A solution of arylsulfonyl chloride (10 mmol) in 20 mL of dry
tetrahydrofuran (THF) was added dropwise to a solution of (2-amino-
methyl)pyridine (1.04 mL, 10 mmol) and triethylamine (2.82 mL,
20 mmol) in 50 mL of dry THF under argon. The reaction mixture was
refluxed for 6 h, and then the volatiles were removed under reduced
pressure. The residue was dissolved in DCM (20 mL) and washed with
H2O (3 ꢁ 50 mL) at room temperature. The organic layer was separated
and dried over anhydrous MgSO4, filtered, and concentrated under
reduced pressure. The residue was recrystallized from a DCM/hexane
(1/3) mixture. The desired products were dried under reduced pressure
at 50 °C for 1 h.
bNkNkNb (R = CH2C6HMe4-2,3,5,6). Yield: 73%. Mp: 262ꢀ264 °C. 1H
NMR (400 MHz, CDCl3): δ 1.98 (s, 12H, 2,6-(Me)2-Ar), 2.18 (s, 12H,
3,5-(Me)2-Ar), 6.19 (s, 4H, N-CH2-Ar), 6.63 (d, 2H, J = 7.6 Hz, H-8),
6.91 (s, 2H, 4-H-Ar), 7.01 (t, 2H, J = 7.5 Hz, H-10), 7.21 (t, 2H, J =
7.6 Hz, H-9), 7.81 (d, 2H, J = 7.6 Hz, H-11), 8.14 (t, 1H, J = 7.7 Hz, H-4),
8.52 (d, 2H, J = 7.8 Hz, H-3). 13C NMR (100 MHz, CDCl3): δ 16.0,
21.18, 47.11, 111.97, 120.03, 122.91, 124.08, 126.0, 131.27, 134.21,
134.68, 138.07, 138.22, 142.11, 150.08.
1
bNkNkNb (R = CH2C6Me5). Yield: 82%. Mp: 270ꢀ272 °C. H NMR
(400 MHz, CDCl3): δ 2.02 (s, 12H, 2,6-(Me)2-Ar), 2.13 (s, 12H,
3,5-(Me)2-Ar), 2.21 (s, 6H, 4-(Me)-Ar), 6.18 (s, 4H, N-CH2-Ar), 6.59
(d, 2H, J = 7.6 Hz, H-8), 7.01 (t, 2H, J = 7.5 Hz, H-10), 7.22 (t, 2H, J =
7.6 Hz, H-9), 7.81 (d, 2H, J = 7.6 Hz, H-11), 8.11 (t, 1H, J = 7.8 Hz, H-4),
8.72 (d, 2H, J = 7.8 Hz, H-3). 13C NMR (100 MHz, CDCl3): δ 15.94,
17.73, 19.92, 47.82, 112.0, 120.0, 122.51, 123.89, 126.07, 128.21, 133.41,
134.87, 136.03, 138.71, 142.38, 150.67.
NkN0b. Yield 66%. Mp: 68ꢀ70 °C. 1H NMR (300 MHz, DMSO-d6):
δ 4.03 (d, 2 H, J = 6.0 Hz, Hf), 7.24 (t, 1 H, J = 7.5 Hz, Ph-Hp), 7.35 (d,
1 H, J = 7.5 Hz, Hd), 7.54ꢀ7.66 (m, 2 H, Ph-Ho), 7.72 (t, 1 H, J = 7.8 Hz,
Hb), 7.79ꢀ7.83 (m, 2 H, Ph-Hm), 8.30 (t, J = 6.0 Hz, 1 H, Hc), 8.43 (d,
J = 4.8 Hz, 1 H, Ha). 13C NMR (75 MHz, DMSO-d6): δ 48.4, 122.1,
122.9, 127.0, 129.6, 132.9, 137.2, 141.0, 149.2, 157.6. IR (cmꢀ1): 3060,
2973, 2936, 2858, 2846, 1596, 1576, 1479, 1463, 1479, 1463, 1444, 1436,
1328; 1298, 1229, 1157, 1090, 1071, 1052, 1008, 851, 830, 750, 733, 690.
NkN0c. Yield: 67%. Mp: 89ꢀ91 °C. 1H NMR (300 MHz, DMSO-d6): δ
2.19 (s, 6 H, SO2-Ar-(CH3)2), 2.44 (s, 6 H, SO2-Ar-(CH3)2), 4.09 (d, J=
6.3 Hz, 2 H, Hf), 7.15 (s, 1 H, SO2ꢀAr-Hp), 7.27 (d, J= 8.1 Hz, 1 H, Hd),
7.66 (t, J = 8.1 Hz, 1 H, Hb), 8.10 (t, 1 H, J = 6.3 Hz, Hc), 8.39 (d, 1 H, J =
4.8 Hz, Ha). 13C NMR (75 MHz, DMSO-d6): δ 17.6, 20.5, 47.2, 121.4,
122.2, 134.2, 134.9, 135.3, 136.4, 138.7, 148.5, 157.2. IR (cmꢀ1): 3091,
3007, 2973, 2943, 2853, 1597, 1572, 1479, 1458, 1442, 1386, 1376,
General Procedure for the Synthesis of 1ꢀ5. bNkNkNb
(0.165 mmol) derivatives and Ru(DMSO)4Cl2 (0.080 mg, 0.165 mmol)
were placed in the same Schlenk tube, and ethanol (5 mL) was added
under argon. Then the mixture was stirred and heated under reflux for
1 day. The volatiles were removed under reduced pressure, and the
residue was dissolved in CHCl3 (5 mL). Diethyl ether (10 mL) was
added to the solution to precipitate the complexes (1ꢀ5). The brown
solid that formed was filtered off and dried under reduced pressure.
1
Complex 1. Yield: 62%. Mp: 318ꢀ320 °C. H NMR (400 MHz,
DMSO-d6): δ 2.61 (s, 6H, (CH3)2SO), 7.29 (d, 2H, J = 7.6 Hz, H-8),
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Organometallics
ARTICLE
Table 1. Crystal Data and Structure Refinement Parameters for Complexes 9 and 10
param
9
10
CCDC deposition no.
color/shape
chem formula
formula wt
785422
785421
black/plate
black/prism
[RuCl(C19H13N5)(C12H10N2O2S)] Cl
[RuCl(C11H9N5)(C12H10N2O2S)] Cl H2O
3
3
3
729.59
647.50
temp (K)
296
296
wavelength (Å)
cryst syst
0.71073 (Mo KR)
monoclinic
P21 (No. 4)
0.71073 (Mo KR)
monoclinic
P21 (No. 4)
space group
unit cell params
a, b, c (Å)
8.1576(5), 18.6367(9), 10.1442(7)
8.3674(2), 16.1181(3), 10.4014(3)
R, β, γ (deg)
V (Å3)
90, 91.002(6), 90
90, 106.616(2), 90
1541.99(16)
1344.22(6)
Z
2
2
Dcalcd (Mg/m3)
1.571
1.600
μ (mmꢀ1
)
0.791
0.899
abs cor
integration (X-RED32)
0.7815, 0.9854
integration (X-RED32)
0.6149, 0.8677
Tmin, Tmax
F000
736
652
cryst size (mm3)
0.52 ꢁ 0.25 ꢁ 0.01
STOE IPDS II/rotation (ω scan)
ꢀ10 e h e 10, ꢀ23 e k e 23, ꢀ12 e l e 12
2.01 e θ e 26.77
10616
0.62 ꢁ 0.38 ꢁ 0.16
STOE IPDS II/rotation (ω scan)
diffractometer/measurement method
index ranges
ꢀ10 e h e 10, ꢀ20 e k e 20, ꢀ13 e l e 13
2.04 e θ e 27.55
22438
θ range for data collecn (deg)
no. of rflns collected
no. of indep /obsd rflns
Rint
6478/3411
6098/5518
0.1534
0.0456
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
ΔFmax, ΔFmin (e/Å3)
full-matrix least squares on F2
full-matrix least squares on F2
6478/1/397
6098/4/340
1.121
1.012
R1 = 0.0876, wR2 = 0.1568
R1 = 0.1605, wR2 = 0.1783
0.748, ꢀ0.783
R1 = 0.0291, wR2 = 0.0620
R1 = 0.0339, wR2 = 0.0632
0.725, ꢀ0.626
1320, 1255, 1205, 1142, 1093, 1069, 1008, 879, 849, 834, 810, 761,
724, 675.
47.70; H, 4.86; N:5.85; S, 5.39. 1H NMR (300 MHz, DMSO-d6):
δ 1.17 (d, 6 H, J = 6.6 Hz, Hk), 2.25 (s, 3 H, Hg), 2.78ꢀ2.87 (m, 1H, Hj),
4.23 (d, 2H, J = 6.0 Hz, Hf), 7.09 (d, 2H, J = 6.6 Hz, Hi), 7.54ꢀ7.66 (m,
6H, Ph-H + Hd), 7.79ꢀ7.85 (d, 2H, J = 6.6 Hz, Hh), 8.09 (t, J = 7.5 Hz,
General Procedure for the Synthesis of 6aꢀc. An ethanolic
solution (15 mL) of 1.10 mmol of NkN0aꢀc was mixed with [RuCl2(p-
cymene)]2 (0.306 g, 0.50 mmol). The reaction mixture was heated
under reflux for 6 h. The volatiles were removed under reduced pressure,
and then the residue was dissolved in DCM (15 mL) and precipitated by
addition of diethyl ether (30 mL). The 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.
Complex 6a. Yield: 64%. Mp: 140ꢀ142 °C dec. Anal. Calcd for
C16H22Cl2N2Ru: C, 46.38; H, 5.35; N, 6.76. Found: C, 47.38; H, 5.86;
N, 6.39. 1H NMR (300 MHz, DMSO-d6): δ 1.12 (d, 6H, J = 6.9 Hz, Hk),
1.97 (s, 3H, Hg), 2.69ꢀ2.78 (m, 1H, Hj), 4.11ꢀ4.21 (m, 2H, Hf),
4.31ꢀ4.39 (m, 2H, ꢀNH2), 5.78 (t, 2H, J1 = 6.9 Hz, J2 = 6.6 Hz, Hi),
5.99 (d, 1H, J = 6.0 Hz, Hh), 6.04 (d, 1H, J = 5.7 Hz, Hh), 7.50ꢀ7.58
(m, 2H, Hd + Hb), 7.97 (t, 1H, J = 7.8 Hz, Hc), 9.15 (d, 1 H, J = 5.4 Hz,
Ha). 13C NMR (75 MHz, DMSO-d6): δ 18.17, 21.95, 22.90, 30.70,
52.52, 82.28, 82.87, 83.50, 85.25, 98.37, 103.45, 121.63, 125.28, 139.54,
155.05, 161.94. IR (cmꢀ1): 3375, 3209, 3061, 2965, 2926, 2873, 1608,
1471, 1441, 1386, 1321, 1282, 1252, 1199, 1155, 1105, 1091, 1057, 1033,
1015, 946, 880, 804, 768, 728, 672.
1H, Hb), 8.47 (t, 1H, J = 6.0 Hz, Hc), 8.61 (d, 1H, J = 6.0 Hz, Ha). 13
C
NMR (75 MHz, DMSO-d6): δ 22.0, 24.5, 33.5, 45.8, 126.1, 126.6, 127.1,
129.3, 132.3, 133.3, 135.0, 140.3, 142.8, 145.8, 158.2. IR (cmꢀ1): 3077,
2968, 2938, 2924, 2874, 2845, 2830, 1626, 1611, 1583, 1569, 1543, 1473,
1448, 1365, 1345, 1287, 1234, 1165, 1053, 1033, 1002, 935, 884, 850,
756, 727, 686.
Complex 6c. Yield: 82%. Mp: 201ꢀ203 °C dec. Anal. Calcd for
C26H34Cl2N2O2RuS: C, 51.14; H, 5.61; N, 4.59; S, 5.25. Found: C,
50.23; H, 6.02; N, 4.82; S, 4.95. 1H NMR (300 MHz, DMSO-d6): δ 1.17
(d, 6 H, J = 7.2 Hz, Hk), 2.19 (s, 6H, SO2-Ar-(CH3)2), 2.26 (s, 3 H, Hg),
2.43 (s, 6H, SO2-Ar-(CH3)2), 2.79ꢀ2.88 (m, 1H, Hj), 4.17 (d, 2H, J=
6.3 Hz, Hf), 7.07ꢀ7.14 (m, 4H, Hi), 7.18 (s, 1H, SO2-Ar-Hp), 7.39ꢀ7.47
(m, 1H, Hd), 7.99 (t, 1H, J = 7.2 Hz, Hb), 8.20 (t, 1H, J = 6.3 Hz, Hc), 8.52
(d, 1H, J = 4.5 Hz, Ha). 13C NMR (75 MHz, DMSO-d6): δ 18.1, 20.9,
22.0, 24.5, 33.5, 45.4, 124.4, 124.6, 126.6, 129.3, 134.8, 135.0, 135.6,
136.0, 138.6, 142.2, 145.1, 145.7, 155.4. IR (cmꢀ1): 3121, 3086, 2967,
2931, 2875, 1627, 1611, 1571, 1543, 1465, 1447, 1388, 1361, 1340, 1285,
1250, 1206, 1163, 1052, 1032, 934, 884, 848, 830, 751, 723, 674.
General Procedure for the Synthesis of 7ꢀ10. An ethanolic
solution (15 mL) of 1.10 equiv of 0NkNkN0 was mixed with 6 (1 mmol).
Complex 6b. Yield: 69%. Mp: 187ꢀ189 °C dec. Anal. Calcd for
C22H26Cl2N2O2RuS: C, 47.65; H, 4.73; N, 5.05; S, 5.78; found: C,
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The reaction mixture was heated under reflux for 10 h. The volatiles were
removed under reduced pressure, and then the residue was dissolved in
DCM (15 mL) and precipitated by addition of diethyl ether (30 mL).
The brown-black 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.
Scheme 1. Synthesis of Ru(II) Complexes 1ꢀ10 and Num-
bering Scheme for the Ligands 0NkNkN0 and NkN0
Complex 7. Yield: 187 mg, 64%. Mp: >280 °C. Anal. Calcd for
C27H27Cl2N5Ru: C, 54.64; H, 4.59; N, 11.80. Found: C, 53.88; H, 4.21;
N, 12.26. 1H NMR (300 MHz, DMSO-d6): δ 2.71 (d, 6H, J = 4.2 Hz, H-
6), 3.93 (t, 1H, J1 = 6.0 Hz, J2 = 5.7 Hz, Hf), 4.95 (t, 1H, J1 = 6.3 Hz, J2 =
6.0 Hz, Hf), 6.65 (d, 1H, J = 5.7 Hz, Hd), 7.02ꢀ7.61 (m, 13H,
Ar-H + ꢀNH2), 7.91 (t, 1H, J1 = 8.4 Hz, J2 = 7.8 Hz, Hc), 8.01 (t,
1H, J1 = 8.1 Hz, J2 = 7.8 Hz, H-4), 8.33 (d, 1H, J = 7.8 Hz, H-3), 8.46 (d,
1H, J = 8.1 Hz, H-3), 8.91 (d, 1H, J = 7.5 Hz, Ha). 13C NMR (75 MHz,
DMSO-d6): δ 17.84, 17.97, 49.79, 120.08, 120.98, 121.91, 123.17, 124.66,
125.08, 126.07, 126.33, 127.28, 128.63, 128.91, 129.17, 135.83, 136.69,
149.10, 149.43, 150.15, 151.54, 160.91, 161.63, 161.76, 164.04, 173.30,
173.87. IR (cmꢀ1): 3382, 3226, 3130, 3044, 2922, 1622, 1608, 1591, 1498,
1482, 1471, 1437, 1386, 1374, 1307, 1289, 1226, 1209, 1154, 1101, 1070,
1028, 1020, 865, 800, 782, 757, 736, 700, 671.
Complex 8. Yield: 65%. Mp: >280 °C. Anal. Calcd for
C33H29Cl2N5O2RuS: C, 54.17; H, 4.00; N, 9.57; S, 4.38. Found: C,
52.83; H, 4.25; N, 8.24; S, 3.96. 1H NMR (300 MHz, DMSO-d6): δ
2.44 (s, 6H, H-6), 6.96ꢀ7.09 (m, 10H, Ph-H), 7.49 (d, 2H, J = 7.2 Hz,
SO2-Ar-H), 7.60 (t, 1H, J1 = 7.5 Hz, J2 = 7.2 Hz, H-4), 7.66 (t, J = 8.1
Hz, 2 H, SO2-Ar-H), 7.84ꢀ7.92 (m, 2H, NkN0-H + SO2-Ar-H),
8.26ꢀ8.32 (m, 2H, NkN0-H), 8.51 (d, 2H, J = 8.4 Hz, H-3), 9.28 (d,
J = 5.1 Hz, 1 H, Ha), 9.74 (s, 1H, Hf). 13C NMR (75 MHz, DMSO-d6):
δ 18.0, 126.9, 127.2, 128.7, 129.0, 129.3, 131.0, 133.6, 134.7, 134.8,
135.6, 136.5, 146.4, 152.1, 152.7, 159.5, 174.7, 175.8. IR (cmꢀ1):
3074, 2960, 2874, 1695, 1630, 1601, 1484, 1463, 1448, 1425, 1407,
1377, 1359, 1271, 1235, 1169, 1136, 1052, 1034, 927, 903, 866, 844,
807, 753, 721, 689.
(296 K) using graphite-monochromated Mo KR radiation (λ = 0.71073 Å)
in ω-scanning mode. The structures were solved by direct methods
using SHELXS-9778 and refined through full-matrix least-squares meth-
ods using SHELXL-9779 implemented in the WinGX80 program suite.
All NH and CH hydrogen atoms were positioned geometrically and
treated using a riding model, fixing the bond lengths at 0.86 and 0.93 Å,
respectively. For complex 10, the coordinates of the water H atoms were
determined from a difference map and were refined isotropically subject
to a DFIX restraint of OꢀH = 0.82 Å. The displacement parameters of
the NH and CH hydrogen atoms were constrained to Uiso(H) = 1.2Ueq
(1.5Ueq for water) of their parent atoms. Data collection: X-AREA.81
Cell refinement: X-AREA. Data reduction: X-RED32.81 A summary of
the crystal data, experimental details, and refinement results are given in
Table 1. The general purpose crystallographic tool PLATON82 was used
for the structure analysis and presentation of the results.
Complex 9. Yield: 0.46 g; 63%. Mp: >280 °C. Anal. Calcd for
C31H23Cl2N7O2RuS: C, 51.03; H, 3.18; N, 13.44; S, 4.40. Found: C,
1
49.34; H, 3.89; N, 12.94; S, 3.89. H NMR (300 MHz, DMSO-d6):
δ 6.85ꢀ6.95 (m, 5 H, SO2-Ar-H), 7.06 (t, 2 H, J1 = 8.1 Hz, J2 = 7.2 Hz,
H-10), 7.35 (t, 2 H, J = 8.1 Hz, H-9), 7.46 (t, 1 H, J1 = 6.9 Hz, J2 = 7.2 Hz,
Hb), 7.63 (d, 2 H, J = 8.4 Hz, H-11), 8.28 (t, 1 H, J1 = 6.9 Hz, J2 = 6.3 Hz,
Hc), 8.36 (t, 1 H, J1 = 7.5 Hz, J2 = 7.8 Hz, H-4), 8.56 (d, 2 H, J = 7.8 Hz,
H-8), 8.74 (d, 1 H, J = 7.8 Hz, Hd), 9.05 (d, 1 H, J = 7.8 Hz, H-3), 9.12 (d,
1 H, J = 7.8 Hz, H-3), 10.14 (s, 1 H, Hf), 10.49 (d, 1 H, J = 5.1 Hz, Ha),
15.06 (br, 2H, N-H). 13C NMR (75 MHz, DMSO-d6): δ 101.8, 114.2,
115.5, 121.9, 124.7, 125.7, 126.6, 128.8, 129.4, 133.6, 134.5, 135.2, 136.4,
136.8, 141.1, 150.9, 152.2, 157.1, 175.0. IR (cmꢀ1): 3038, 3013, 2943,
1608, 1592, 1547, 1526, 1480, 1455, 1413, 1351, 1320, 1290, 1249, 1234,
1184, 1172, 1148, 1086, 1056, 1033, 1014, 980, 906, 894, 845, 811, 804,
779, 763, 735, 722, 680.
Complex 10. Yield: 84%. Mp: >250 °C. Anal. Calcd for
C23H19Cl2N7O2RuS: C, 43.88; H, 3.04; N, 15.58; S, 5.09. Found:
C, 45.07; H, 3.76; N, 14.47; S, 4.65. 1H NMR (300 MHz, DMSO-d6):
δ 6.93ꢀ6.96 (m, 4H, H-6 + H-7), 7.25 (t, 1H, J1 = 7.8 Hz, J2 = 8.1 Hz,
Hc), 7.58 (t, 1 H, J1 = 7.2 Hz, J2 = 7.5 Hz, H-4), 7.69 (d, 2 H, J = 2.4 Hz,
H-3), 7.97ꢀ8.08 (m, 5H, SO2-Ph-H), 8.30 (t, 1 H, J1 = 7.8 Hz, J2 = 7.5
Hz, Hb), 8.87 (d, 1 H, J = 8.1 Hz, Hd), 10.05 (d, J = 5.4 Hz, 1 H, Ha),
10.11 (s, 1H, Hf), 13.48 (s, 2H, pNkNkNp(N-H)). 13C NMR (75 MHz,
DMSO-d6): δ 105.5, 118.6, 126.8, 128.6, 130.0, 132.6, 134.0, 134.9,
135.4, 136.4, 153.2, 154.2, 154.9, 157.1, 175.9. IR (cmꢀ1): 3062,
3032, 2973, 2943, 2924, 2830, 1699, 1638, 1591, 1483, 1462, 1449,
1427, 1395, 1374, 1354, 1314, 1298, 1253, 1233, 1184, 1169, 1139,
1082, 1053, 1033, 1019, 930, 901, 787, 760, 751, 736, 724, 690.
X-ray Crystallography. The single-crystal X-ray data of 9 and 10
were collected on a STOE diffractometer with an IPDS(II) image plate
detector. All diffraction measurements were performed at room temperature
’ RESULT AND DISCUSSION
Synthesis of Compounds. The ligands used and the synthesis
and reaction routes of the novel Ru(II) complexes are presented
in Scheme 1. Synthesized compounds were characterized by
elemental analysis and NMR and IR spectra. The structures of
9 and 10 were confirmed by X-ray crystallography.
NkN0b,c, NkNkNd, NkNkNb (R = H), and pNkNkNp were synthe-
d
b
sized according to a modified literature procedure in good
yield.66,74ꢀ77 bNkNkNb derivatives were obtained via alkylation
of the NkNkNb (R = H) with benzyl chloride, 2,4,6-trimethyl-
b
benzyl chloride, 2,3,5,6-tetramethylbenzyl bromide, and 2,3,
4,5,6-pentamethylbenzyl bromide in the presence of KOH in
acetone at reflux. The mononuclear six-coordinate Ru(II) com-
plexes 1ꢀ5 were synthesized by reaction of RuCl2(DMSO)4
with bNkNkNb derivatives in ethanol. On the other hand, NkN0a,b
ligands were obtained by the reaction of arylsulfonyl chloride
with (2-aminomethyl)pyridine in the presence of triethylamine
in THF at reflux. The monocationic chloro complexes 6aꢀc are
accessible in good yield by treatment of the [RuCl2(p-cymene)]2
with NkN0aꢀc at 78 °C in ethanol solution. The reaction of 6a with
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dNkNkNd in boiling ethanol gives complex 7. On the other hand,
the replacement reaction of 6b with dNkNkNd, NkNkNb, and
b
pNkNkNp in ethanol at 78 °C unexpectedly resulted in the cationic
six-coordinate Ru(II) imine complexes 8ꢀ10. As a matter of fact,
a number of ruthenium complexes with multidentate ligands are
known to give oxidative dehydrogenated ligands which remain
coordinated to the metal center.83 Furthermore, the oxidation of
amine complexes to imine complexes by molecular oxygen is
base-catalyzed and is strongly dependent on the ancillary ligands
coordinated to Ru(II).84 However, to our knowledge, there has
been no report on the metal-prompted oxidation of N-(2-
methylpyridyl)arenesulfonylamide.
All complexes are air- and moisture-stable both in the solid
state and in solution. 1ꢀ5 and 6aꢀc are soluble in chlorinated
solvents, DMSO, DMF, and MeOH, while 7ꢀ10 are soluble in
DMSO, DMF, and MeOH.
In 1H NMR spectra for the bNkNkNb derivatives, the H-3 and
H-4 protons were observed as doublets and triplets in a 2:1 ratio
at around δ 8.11ꢀ8.56 ppm. The protons of the phenyl rings of
each ligand appear as eight-proton multiplets around δ 6.6ꢀ
1
7.8 ppm. Upon coordination of Ru(II) (1ꢀ5), the H NMR
spectra of complexes showed some differences from their
respective ligands (bNkNkNb), especially the pyridine backbone.
H-3 and H-4 protons for complexes 1ꢀ5 were observed as
doublets and triplets in a 2:1 ratio with a general shift toward
lower fields as compared to their respective ligands. Moreover,
Figure 1. View of complex 9 showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 30% probability level. For the
sake of clarity, only the H atom involved in hydrogen bonding has been
included.
13C NMR signals shifted to higher fields. 1ꢀ5 gave 1H and 13
C
NMR spectra corresponding to the proposed formulation. With
reference to previous X-ray diffraction and DFT studies on other
related [RuCl2(0NkNkN0)(DMSO)] systems,85 we tentatively
assigned an S-bonded trans structure to 1ꢀ5.
Similarly, from the 1H NMR spectra, the effect of coordination
of the Ru(II) to the NkN0 ligand through the sulfonamide
nitrogen and pyridyl nitrogen for 6b,c could clearly be seen.
The Hf protons of NkN0b,c appear as a doublet at δ 4.03 and
4.09 ppm, respectively. Upon coordination to Ru(II) (6b,c), the
signals of Hf moved further downfield and appeared as a doublet
at δ 4.23 and 4.17 ppm, respectively. Also, the protons of the
pyridine ring of 6b,c, especially Ha, are shifted downfield com-
pared to those of free ligands (NkN0b,c). Similarly, aromatic
protons of the p-cymene group (Hh and Hi) on 6b,c are shifted
downfield in comparison to the [RuCl2(p-cymene)]2 dimer.
Moreover, in the 13C NMR spectra, the sulfonamide ligands
(NkN0b,c) exhibited a singlet at δ 48.4 and 47.2 ppm, which can be
assigned to the methylene carbons (NkN0b,c (Py-CH2-NH)).
Upon coordination to Ru(II) (6b,c), those peaks moved further
upfield and appeared at δ 45.8 and 45.4 ppm, respectively.
The main points of interest in the NMR spectra of 8ꢀ10 are
the loss of the peaks assignable to methylene protons (Hf) on the
sulfonamide group and the appearance of a new singlet around δ
9.74ꢀ10.15 ppm. This suggested that the sulfonamide was
converted to a sulfonimine group (NkN0b (Py-CHdNꢀ). The
Figure 2. View of the complex 10 showing the atom-numbering
scheme. Displacement ellipsoids are drawn at the 30% probability level.
For the sake of clarity, only H atoms involved in hydrogen bonding have
been included.
H-3 and H-4 protons arising from dNkNkNd, bNkNkNb, and pNkNkNp
were observed as doublets and a triplet in a 2:1 ratio at around
δ 7.58ꢀ9.12 ppm. From 13C NMR spectra of 8ꢀ10, ꢀCHdNꢀ
peaks appeared at 175.0ꢀ175.9 ppm.
1359 cmꢀ1 in 8, 1172 and 1351 cmꢀ1 in 9, and 1169 and
1354 cmꢀ1 in 10.
1
In the IR spectra, NH stretching frequencies shift from 3060
and 3091 cmꢀ1 in NkN0a,b to 3077 and 3121 cmꢀ1 in 6b,c,
respectively. Also, the SO2 stretches shift from 1157 and
1328 cmꢀ1 in NkN0a and 1142 and 1320 cmꢀ1 in NkN0b (for
the asymmetric and symmetric stretches, respectively) to 1165
and 1345 cmꢀ1 in 6b, 1163 and 1340 cmꢀ1 in 6c, 1169 and
In the H NMR spectra of 6a, Hf protons belonging to
(2-aminomethyl)pyridine were observed as multiplets around
4.11ꢀ4.39 ppm. Upon coordination to Ru(II) (7), those peaks
were observed as two triplets at 3.93 and 4.95 ppm and H-6
protons were observed as doublets at 2.71 ppm. In the 13C NMR
spectra of 7, ꢀNdC(CH3) peaks were observed at 17.84 and
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Table 2. Selected Geometric Parameters for Complexes
9 and 10
Table 3. Catalytic Activity for Transfer Hydrogenation of
Acetophenone Catalyzed by Ru(II) Complexes a
param
9
10
param
9
10
Bond Lengths (Å)
Ru1ꢀCl1
Ru1ꢀN1
Ru1ꢀN3
Ru1ꢀN5
Ru1ꢀN6
Ru1ꢀN7
S1ꢀO1
2.387(4) 2.3741(8) N3ꢀC6
1.286(17) 1.355(4)
1.435(16)
1.341(7)
1.383(17)
1.31(2)
1.971(11) 2.002(3)
2.062(11) 2.051(2)
2.093(11) 2.042(3)
2.053(13) 2.078(2)
2.022(12) 2.014(2)
1.427(10) 1.420(2)
1.420(11) 1.437(3)
1.676(11) 1.653(2)
1.769(3)
N3ꢀC12
N4ꢀC11
N4ꢀC13
N4ꢀC14
N5ꢀC9
entry
cat.
conversn (%)
time (min)
10
1
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
74
13
22
33
47
91
58
72
80
86
94
89
92
94
97
2
1.363(5)
3
N5ꢀC13
N5ꢀC19
N7ꢀC17
N7ꢀC25
C6ꢀC7
1.331(17)
1.349(17)
1.406(4)
1.325(18)
1.386(5)
4
S1ꢀO2
5
S1ꢀN7
S1ꢀC18
S1ꢀC26
N2ꢀN3
N4ꢀN5
N2ꢀC6
N2ꢀC7
N2ꢀC8
6
30
60
1.754(14)
7
1.342(4)
1.331(4)
C7ꢀC8
1.351(6)
1.382(6)
1.365(8)
1.447(5)
8
C9ꢀC10
C10ꢀC11
C16ꢀC17
C24ꢀC25
9
1.391(18)
1.395(18)
10
11
12
13
14
15
1.354(5)
1.47(2)
Bond Angles (deg)
Cl1ꢀRu1ꢀN1 86.2(4)
Cl1ꢀRu1ꢀN3 89.8(3)
Cl1ꢀRu1ꢀN5 88.4(3)
Cl1ꢀRu1ꢀN6 94.8(3)
86.06(8)
88.72(8)
88.82(8)
94.08(8)
N1ꢀRu1ꢀN7 101.8(4) 101.17(10)
N3ꢀRu1ꢀN5 156.6(4) 155.88(11)
N3ꢀRu1ꢀN6 104.2(4) 101.38(10)
N3ꢀRu1ꢀN7 91.9(4)
93.36(10)
102.73(12)
92.09(10)
78.70(10)
a 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.
Cl1ꢀRu1ꢀN7 172.0(3) 172.74(7) N5ꢀRu1ꢀN6 99.2(4)
N1ꢀRu1ꢀN3 77.1(4)
N1ꢀRu1ꢀN5 79.5(5)
77.96(10) N5ꢀRu1ꢀN7 93.1(4)
77.93(12) N6ꢀRu1ꢀN7 77.2(4)
N1ꢀRu1ꢀN6 178.4(5) 179.33(12)
the NkNkN-tridentate ligand and the fact that the pyridine N atom
donor occupies the central position of the tridentate ligand.
Thus, the RuꢀNpyridine bond becomes shorter than other
RuꢀN bonds because of the restraints of the two chelating arms
on either side of the coordinating atom. In contrast to that
formed by the tridentate triamine ligands, the five-membered
chelate rings formed by the bidentate ligand deviate from
planarity. This nonplanar chelate ring has a twist conformation
in complex 9, with Ru1 and N6 displaced by 0.048(4) and
ꢀ0.067(6) Å above and below the N7ꢀC25ꢀC24 plane, while it
has an envelope conformation in complex 10, with N7 atom displaced
from the Ru1ꢀN6ꢀC16ꢀC17 mean plane by 0.065(2) Å
(puckering parameters: Q = 0.104(2) Å and j = 136.02(14)°).87
The bond lengths and bond angles of the phenyl and pyridine
rings are similar to those found in related pyridylarenesulfona-
mide ligands.88ꢀ92 The fact that the imine N7dC25 bond
distance in 9 is significantly shorter than the corresponding bond
in 10 can be considered as possible evidence of the conjugation of
the imine N7dC17 bond with the sulfonyl SdO bonds in 10.
The dihedral angle between the two coordinated pyridine rings is
86.42(5)° in 9 and 88.53(4)° in 10, indicating a nearly perpen-
dicular orientation. In both complexes, the benzene ring of the
sulfonamide ligand is almost parallel to the five-membered ring of
the tridentate ligand. This disposition allows an intramolecular
πꢀπ stacking interaction with an interplanar spacing of 3.640(4)
Å for 9 and 3.625(4) Å for 10 between the ring centroids.
17.97 ppm and ꢀNdC(CH3) peaks were observed at 173.30
and 173.87 ppm.
Crystal Structures of 9 and 10. The solid-state structures of
compounds 9 and 10 were verified by single-crystal X-ray
analysis. The perspective ORTEP-386 views of 9 and 10 with
the adopted atomic numbering scheme are depicted in Figures 1
and 2. Selected bond lengths and angles are given in Table 2.
Complexes 9 and 10 contain a bidentate NkN0a ligand with a
Ru(II) metal center and one Cl ligand. The two complexes differ
from each other in the symmetrical NkNkN-tridentate triamine
ligand: 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine (bNkNkNb) in
complex 9 and 2,6-bis(1H-pyrazol-3-yl)pyridine (pNkNkNp) in
complex 10. However, the crystallization characteristics of the
two cations are the same, with both crystallizing in the mono-
clinic space group P21. In the complexes, the charge is neutralized
h
by a Cl anion, and complex 10 also includes a water molecule in
the asymmetric unit.
The local structure around the Ru(II) ions is that of an
octahedron, the equatorial plane of which (N1/N3/N5/N6) is
formed by three nitrogen atoms from the tridentate ligand (N1,
N3, and N5) and one nitrogen atom of the bidentate ligand
(N6). The axial positions in the octahedron are occupied by one
chlorine ligand (Cl1) and one nitrogen atom of the bidentate
ligand (N7). As can be seen from the trans angles, which vary
from 156.6(4) to 178.4(5)° for 9 and from 155.88(11) to
179.33(12)° for 10, and the cis angles, which vary from
77.1(4) to 104.2(4)° for 9 and from 77.93(12) to 102.73(12)°
for 10, the coordination octahedron around the Ru(II) ions is
rather deformed, the major distortion arising via the N3ꢀ
Ru1ꢀN5 angle. This angle is considerably smaller than the ideal
angle of 180°. In each complex, the RuꢀNpyridine bond length of
the tridentate ligand is shorter than those of the other Ruꢀ
N bonds. This is probably due to the geometric requirements of
The two complexes show some similarities in hydrogen-
bonding interactions. In the molecular structure of the com-
plexes, there is one intramolecular hydrogen-bonding interaction
of the type CꢀH Cl, forming the five-membered ring S(5).93
3 3 3
The crystal structures are stabilized by NꢀH Cl, OꢀH Cl,
3 3 3
3 3 3
NꢀH O, CꢀH Cl, and CꢀH O intermolecular inter-
3 3 3
3 3 3
3 3 3
actions (see the Supporting Information for details).
Catalytic Studies. TH has been studied extensively in the past
decade, and catalysts that combine known metal complexes with
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Table 4. Catalytic Activity for Transfer Hydrogenation of
Ketones Catalyzed by Ru(II) Complexesa
temperature, 1 mL of 0.1 M KOH (0.1 mmol) solution in
2-propanol was then introduced and the mixture was stirred at
82 °C. Reactions were monitored by GC. The results are sum-
marized in Table 3.
Similarly, the TH of ketones with 2-propanol catalyzed by the
cationic Ru(II) complexes 6ꢀ10 were carried out under identical
conditions to allow comparison of results (Table 4). Preliminary
studies were performed using 6b as catalyst and acetophenone as
a model substrate. In a typical experiment, 6b (0.01 mmol) and
acetophenone (1 mmol) were dissolved in 2-propanol (4 mL).
This mixture was stirred at 82 °C for 10 min. After the mixture
was cooled to room temperature, the base (0.1 mmol) was added
and the mixture was stirred at 82 °C. Reactions were monitored
by GC. Very rapid conversions were achieved at 82 °C. When the
temperature was decreased, the catalytic conversion became
noticeably slower.
On the basis of these results, the neutral Ru(II) complexes
1ꢀ5 are more active catalysts than the cationic complexes 6ꢀ10.
For the neutral complexes 1ꢀ5, time dependence is also notice-
able. For example, for the 10 and 30 min periods 1 is the best. In
other words, complexes with N-alkyl substitution show lower
activities than the complexes with NꢀH. However, for a 60 min
period the catalytic activity increases in the order 2 < 3 < 4, 1 < 5.
For cationic half-sandwich Ru(II) arene complexes, interest-
ingly, the sulfonamide-containing complexes 6b,c are more active
catalysts than the (2-aminomethyl)pyridine-containing complex
6a. On the other hand, 6b is a more active catalyst than 6c for all
ketones. These results might be related to the steric hindrance of
the sulfonamide ligands. Complexes 8ꢀ10 are generally more
active than 6b. However, unexpectedly, 6b is more active than
10 except for 40-Cl-acetophenone and 40-F-acetophenone. The
catalytic activities of complexes containing NkNkN ligands increase
in the following order for all ketones: 10 < 8 < 9. Complex 7 is a
more efficient catalyst than the other cationic Ru(II)-NkNkN
complexes (8ꢀ10). Ru(II) complexes are generally more effi-
cient catalysts for electron-withdrawing substituents such as F,
Cl, and Br on the para position of the aryl ring of the ketone.
When an electron-donating group is introduced in the aryl ring of
the ketone, the catalytic activity decreases.
’ CONCLUSIONS
In this work, we reported the preparation and characterization
of a series of neutral and cationic Ru(II) complexes bearing
tridentate and bidentate ligands and their catalytic activities for
the hydrogen transfer reaction of acetophenone derivatives with
the use of 2-propanol in the presence of KOH. When cationic
Ru(II) arene complexes containing sulfonamide ligands (6b,c)
were treated with NkNkN ligands, unexpectedly, a facile oxidative
dehydrogenation of sulfonamides (C5H4N-CH2-NH-SO2-Ph)
took place under base-free and mild conditions (0.2 atm of O2
at 78 °C) and in each case (8ꢀ10) the oxidized ligand remained
coordinated in the metal center. To our knowledge, this is the
first report of amine oxidation from the coordinated sulfonamide
ligands to the corresponding sulfonimine ligands on an Ru(II)
metal center. Catalytic experiments showed that the neutral
Ru(II) complexes 1ꢀ5 are more active catalysts than the cationic
complexes 6ꢀ10. On the other hand, cationic Ru(II) complexes
7ꢀ10, containing NkNkN ligands, are more active than the cationic
half-sandwich Ru(II) complexes 6aꢀc, bearing a p-cymene group. 7
is a more active complex than the other cationic Ru(II) complexes
(6, 8ꢀ10) for all ketones. The efficiency of the catalyst seems to
a Reactions were carried out at 82 °C using 1 mmol of substrate with
0.01 mmol of Ru(II) in 5 mL of 2-propanol for 1 h. b Carried out at 82 °C
using 1 mmol of substrate with 0.01 mmol of Ru(II) in 5 mL of
2-propanol for 30 min. c Carried out at 25 °C using 1 mmol of substrate
with 0.01 mmol of Ru(II) in 5 mL of 2-propanol for 1 h. d Carried out at
82 °C using 1 mmol of substrate with 0.01 mmol of Ru(II) in 5 mL of
2-propanol for 15 min. e Carried out at 82 °C using 10 mmol of substrate
with 0.01 mmol of Ru(II) in 5 mL of 2-propanol for 1 h.
new ligands are reported continuously. In this work, we described
the synthesis of a series of novel Ru(II) complexes (1ꢀ10)
employed as catalysts for the TH of ketones.
Catalytic studies with complexes of type 1ꢀ5 were performed
for the transfer hydrogenation of acetophenone in the presence
of KOH by 2-propanol. Reactions were performed under iden-
tical conditions to allow comparison of results. In a typical
experiment, 1 (0.01 mmol) and acetophenone (10 mmol) was
dissolved in 2-propanol (19 mL). This mixture was stirred at
82 °C for 10 min. After the mixture was cooled to room
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Organometallics
ARTICLE
depend not only on the ligands of the complex but also on the
substituent on the aromatic ketones. Electron-withdrawing groups
introduced into the para position of the acetophenone increased
the yield, whereas electron-donating groups at the para position of
the acetophenone decreased the yield. Moreover, when 20,40,60-
trimethylacetophenone was used as a substrate, a constant decrease
in the catalytic yield was observed, which was probably due to steric
effects.
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’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving crystallographic
b
data for 9 and 10. This material is available free of charge via the
Internet at http://pubs.acs.org. CCDC 785421 and 785422 also
contain the supplementary crystallographic data (excluding struc-
ture factors) for the structures reported in this article. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/data_
request/cif, by e-mailing data_request@ccdc.cam.ac.uk, or by con-
tacting The Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, U.K. (fax: +44-1223-336033).
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’ AUTHOR INFORMATION
(26) Coronado, E.; Dias, J. C.; Gimenez-Lopez, M. C.; Gimenez-
Saiz, C.; Gomez-Garcia, C. J. J. Mol. Struct. 2008, 890, 215–220.
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Corresponding Author
*O.D.: tel, +902862180018-1860; fax, +902862180533; e-mail,
osmandayan@comu.edu.tr. B.Ç.: tel, +902323112353; fax,
+902323881036; e-mail, bekir.cetinkaya@ege.edu.tr.
(29) Lu, X.-Y.; Xu, H.-J.; Chen, X.-T. Inorg. Chem. Commun. 2009,
9, 887–889.
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’ ACKNOWLEDGMENT
This research has been supported by The Scientific and
Technical Research Council of Turkey (TUBITAK; Project
Calorim. 2008, 3, 943–949.
_
€
(31) Oter, O.; Ertekin, K.; Dayan, O.; Çetinkaya, B. J. Fluoresc. 2008,
No. 107T808) and TUBA (Turkish Academy of Science). We
thank Professor Orhan B€uy€ukg€ung€or for his help with the data
collection and acknowledge the Faculty of Arts and Sciences,
Ondokuz Mayıs University, Samsun, Turkey, for the use of the
STOE IPDS II diffractometer (purchased under Grant No. F-279
of the University Research Fund).
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