Synthesis, structural characterization, and catalytic activity of ruthenium(II) monocarbonyl complexes with bidentate Schiff base and triphenylphosphine ligands

Article abstract of DOI:10.1080/00958972.2013.831843

Treatment of [RuHCl(CO)(PPh3)3] with equal amounts of equiv bidentate Schiff base 2[(4-chloro-phenylimino)-methyl]-phenol (HL-Cl) or 2(p-tolylimino-methyl)-phenol (HL-Me) or 2[(4-nitro-phenylimino)-methyl]-phenol (HL-NO2) in the presence of triethylamine afforded [RuCl(²-N,O-L-Cl) (CO)(PPh3)2] (1), [RuCl(²-N,O-L-Me)(CO)(PPh3)2] (2), and [RuCl( ²-N,O-L-NO2)(CO)(PPh3)2] (3), respectively The molecular structures of 1, 2, and 3·1.5C6H14 have been determined by single-crystal X-ray crystallography Complexes 1-3 were used for oxidation of primary and secondary alcohols to aldehydes and ketones as catalysts in the presence of N-methylmorpholine-N-oxide 2013

Full text of DOI:10.1080/00958972.2013.831843

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Synthesis, structural characterization,
and catalytic activity of ruthenium(II)
monocarbonyl complexes with
bidentate Schiff base and
triphenylphosphine ligands
Xiao-Feng Yina, Hui Linab, Ai-Quan Jiab, Qun Chena & Qian-Feng
Zhangab
a Department of Applied Chemistry, School of Petrochemical
Engineering, Changzhou University, Jiangsu, P.R. China
b Institute of Molecular Engineering and Applied Chemistry, Anhui
University of Technology, Ma’anshan, P.R. China
Accepted author version posted online: 05 Aug 2013.Published
online: 02 Sep 2013.
To cite this article: Xiao-Feng Yin, Hui Lin, Ai-Quan Jia, Qun Chen & Qian-Feng Zhang (2013)
Synthesis, structural characterization, and catalytic activity of ruthenium(II) monocarbonyl
complexes with bidentate Schiff base and triphenylphosphine ligands, Journal of Coordination
Chemistry, 66:18, 3229-3240, DOI: 10.1080/00958972.2013.831843
To link to this article: http://dx.doi.org/10.1080/00958972.2013.831843
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 18, 3229–3240, http://dx.doi.org/10.1080/00958972.2013.831843
Synthesis, structural characterization, and catalytic activity of
ruthenium(II) monocarbonyl complexes with bidentate Schiff
base and triphenylphosphine ligands
XIAO-FENG YIN†, HUI LIN†‡, AI-QUAN JIA‡, QUN CHEN† and
QIAN-FENG ZHANG*†‡
†Department of Applied Chemistry, School of Petrochemical Engineering, Changzhou University,
Jiangsu, P.R. China
‡Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology,
Ma’anshan, P.R. China
(Received 5 March 2013; in final form 12 July 2013)
Treatment of [RuHCl(CO)(PPh3)3] with equal amounts of equiv. bidentate Schiff base
2[(4-chloro-phenylimino)-methyl]-phenol (HL-Cl) or 2(p-tolylimino-methyl)-phenol (HL-Me) or
2[(4-nitro-phenylimino)-methyl]-phenol (HL-NO2) in the presence of triethylamine afforded [RuCl
(κ2-N,O-L-Cl)(CO)(PPh3)2] (1), [RuCl(κ2-N,O-L-Me)(CO)(PPh3)2] (2), and [RuCl(κ2-N,O-L-NO2)
(CO)(PPh3)2] (3), respectively. The molecular structures of 1, 2, and 3·1.5C6H14 have been
determined by single-crystal X-ray crystallography. Complexes 1–3 were used for oxidation of
primary and secondary alcohols to aldehydes and ketones as catalysts in the presence of
N-methylmorpholine-N-oxide.
Keywords: Ruthenium; Schiff base; Synthesis; Crystal structure; Catalytic property
1. Introduction
Ruthenium Schiff base complexes have been found to be catalytically active for various
organic transformations such as cyclopropanation, ring opening of epoxides, oxidation of
sulfides, aziridination, the Diels–Alder reaction, and epoxidation of olefins [1, 2, 4, 5].
Ruthenium complexes containing tri- and tetradentate Schiff bases have been well studied
[6–9], whereas, those with bidentate Schiff base ligands have received comparatively less
attention [10]. There has been an increasing interest during recent years in ruthenium com-
plexes with bidentate ligands containing π-acceptor and σ-donor groups [10, 12]. The
N,O-donor Schiff bases in this study have been prepared from salicylaldehyde and substi-
tuted phenylamines [13]. These Schiff bases bond bidentate to the ruthenium(II) center
which forced the aryl rings of the Schiff base into a conformation, leading to an
approximately coplanar six-membered ring with the basal plane of octahedral ruthenium(II)
[10, 12, 14]. Ruthenium triphenylphosphine and ruthenium carbonyl complexes containing
*Corresaponding author. Email: zhangqf@ahut.edu.cn
© 2013 Taylor & Francis

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X.-F. Yin et al.
Schiff base have shown good activity and selectivity in oxidation and sulfimidation
processes, respectively [5, 15–17]. Hence, we synthesize a series of ruthenium(II)
complexes with N,O-bidentate Schiff base ligands and study their reactivity. Selective and
efficient catalysts have been reported, such as ruthenium(II) carbonyl complexes with N-[di
(alkyl/aryl)carbamothioyl]benzamide derivatives reported by Karvembu [18], copper(II)-azo
complexes by Shoair [19], multi-walled carbon nanotube-bound nickel Schiff base
complexes by Bhat [20], chromium(VI) complexes by Saha [21], inorganic/organic hybrid
catalyst based on zinc-substituted polyoxometalate, ionic liquid by Mirkhani, Yadollahi, and
Moghadam [22], and vanadium(IV) Schiff base complexes by Bagherzadeh [23], for
oxidation of alcohols to aldehydes or ketones in the presence of different oxidants including
NMO [18], H2O2 [19, 22], periodic acid H5IO6, [20] and oxone [23]. Herein, we report the
synthesis, structural characterization, and catalytic activity of ruthenium(II) monocarbonyl
complexes with N,O-bidentate Schiff base and triphenylphosphine.
2. Experimental
2.1. General
All synthetic manipulations were carried out under dry nitrogen by standard Schlenk
techniques. Salicylaldehyde, 4-chloro-phenylamine, 4-methyl-phenylamine, and 4-nitro-
Figure 1. Molecular structure of [RuCl(κ2-N,O-L-Cl)(CO)(PPh3)2] (1). Selected bond lengths (Å) and angles (°):
Ru(1)–C(1) 1.831(4), Ru(1)–O(2) 2.078(2), Ru(1)–N(2) 2.114(3), Ru(1)–P(2) 2.4098(9), Ru(1)–P(1) 2.4230(9), Ru
(1)–Cl(1) 2.4294(10); C(1)–Ru(1)–O(2) 174.12(13), C(1)–Ru(1)–N(2) 98.28(14), O(2)–Ru(1)–N(2) 87.49(10), C
(1)–Ru(1)–P(2) 90.50(11), O(2)–Ru(1)–P(2) 88.36(7), N(2)–Ru(1)–P(2) 90.25(8), P(2)–Ru(1)–P(1) 175.01(3), C
(1)–Ru(1)–Cl(1) 84.90(12), O(2)–Ru(1)–Cl(1) 89.32(7), N(2)–Ru(1)–Cl(1) 176.82(9).

Ruthenium(II) monocarbonyl complexes
3231
Figure 2. Molecular structure of [RuCl(κ2-N,O-L-Me)(CO)(PPh3)2] (2). Selected bond lengths (Å) and angles (°):
Ru(1)–C(1) 1.835(4), Ru(1)–O(2) 2.087(2), Ru(1)–N(1) 2.111(3), Ru(1)–P(1) 2.4054(9), Ru(1)–P(2) 2.4184(9), Ru
(1)–Cl(1) 2.4245(9); C(1)–Ru(1)–O(2) 171.72(12), C(1)–Ru(1)–N(1) 99.90(13), O(2)–Ru(1)–N(1) 88.19(10), C(1)–
Ru(1)–P(1) 88.57(10), O(2)–Ru(1)–P(1) 89.64(6), N(1)–Ru(1)–P(1) 89.98(7), P(1)–Ru(1)–P(2) 177.40(3), C(1)–Ru
(1)–Cl(1) 85.18(10), O(2)–Ru(1)–Cl(1) 86.72(6),N(1)–Ru(1)–Cl(1) 174.91(8), P(1)–Ru(1)–Cl(1) 89.77(3).
Figure 3. Molecular structure of [RuCl(κ2-N,O-L-NO2)(CO)(PPh3)2] (3). Selected bond lengths (Å) and angles
(°): Ru(1)–C(1) 1.846(5), Ru(1)–O(2) 2.086(3), Ru(1)–N(1) 2.113(3), Ru(1)–P(2) 2.4073(11), Ru(1)–P(1) 2.4243
(11), Ru(1)–Cl(1) 2.4262(11); C(1)–Ru(1)–O(2) 174.60(15), C(1)–Ru(1)–N(1) 97.29(16), O(2)–Ru(1)–N(1) 87.94
(11), C(1)–Ru(1)–P(2) 89.28(13), O(2)–Ru(1)–P(2) 89.17(8), N(1)–Ru(1)–P(2) 92.14(9), P(2)–Ru(1)–P(1) 175.03
(4), C(1)–Ru(1)–Cl(1) 86.41(14), O(2)–Ru(1)–Cl(1) 88.36(8), N(1)–Ru(1)–Cl(1) 176.30(10), P(2)–Ru(1)–Cl(1)
87.75(4).

3232
X.-F. Yin et al.
phenylamine were purchased from Alfa Aesar Ltd. and used without purification. [RuHCl
(CO)(PPh3)3] was prepared according to the literature method [24]. NMR spectra were
1
recorded on a Bruker ALX 400 Plus spectrometer operating at 400 and 162 MHz for H
and 31P, respectively. Chemical shifts (δ, ppm) were reported with reference to SiMe4 (1H)
and H3PO4 (31P). Electronic absorption spectra were obtained on a Shimadzu UV-3000
spectrophotometer. Infrared spectra (KBr) were recorded on a Perkin–Elmer 16 PC FT-IR
spectrophotometer with the use of pressed KBr pellets and the positive FAB mass spectra
were recorded on a Finnigan TSQ 7000 spectrometer. Elemental analyzes were carried out
using a Perkin–Elmer 2400 CHN analyzer.
2.2. Synthesis and characterization
2.2.1. General procedure for preparation of Schiff base ligands (HL). A
methanol (25 mL) solution of salicylaldehyde (15 mM) was added to substituted aniline
(15 mM) in a round-bottomed flask equipped with a condenser. The reaction mixture was
stirred at reflux for 24 h. After completion of reaction, the yellow crystalline product pre-
cipitated upon cooling. The solid product was filtered, washed with cold methanol, and
dried in air.
2.2.2. 4-Chloro-phenylsalicylaldimine (HL-Cl). Yellow solid, yield: 96%; IR (KBr disk,
1
cm−1): 3574 (νO–H), 1635 (νC=N), 769 (νC–Cl); H NMR (CDCl3, 400 MHz): δ 6.97–7.14
(m, 6H, ArH), 7.45 (d, 2H, J = 5.7 Hz, ArH), 8.26 (s, 1H, –CH=N), 12.75 (s, 1H, OH)
ppm; MS (FAB): m/z 231 [M+], 196 [M+–Cl]. Anal. Calcd for C13H9NOCl (%): C, 67.69;
H, 3.93; N, 6.07. Found: C, 67.62; H, 3.91; N, 6.03.
2.2.3. 4-Methyl-phenylsalicylaldimine (HL-Me). Yellow solid, yield: 93%; IR (KBr disk,
1
cm−1): 3586 (νO–H), 1639 (νC=N); H NMR (CDCl3, 400 MHz): δ 2.23 (s, 3H, CH3), 7.02–
7.19 (m, 6H, ArH), 7.36 (d, 2H, J = 6.2 Hz, ArH), 8.37 (s, 1H, –CH=N), 12.94 (s, 1H, OH)
ppm; MS (FAB): m/z 210 [M+]. Anal. Calcd for C14H12NO (%): C, 79.98; H, 5.75; N,
6.66. Found: C, 79.70; H, 5.73; N, 6.61.
2.2.4. 4-Nitro-phenylsalicylaldimine (HL-NO2). Yellow solid, yield: 94%; IR (KBr disk,
1
cm−1): 3596 (νO–H), 1642 (νC=N), 1572, 1369 (νNO2); H NMR (CDCl3, 400 MHz): δ 6.93–
7.27 (m, 6H, ArH), 7.58 (d, 2H, J = 6.4 Hz, ArH), 8.71 (s, 1H, –CH=N), 13.02 (s, 1H, OH)
ppm; MS (FAB): m/z 241 [M+], 195 [M+–NO2]. Anal. Calcd for C13H9N2O3 (%): C, 64.73;
H, 3.76; N, 11.61. Found: C, 64.45; H, 3.73; N, 11.57.
2.2.5. General procedure for preparation of ruthenium complexes 1–3. To a round-bot-
tomed flask with a stir bar was placed [RuHCl(CO)(PPh3)3] (0.81 g, 0.85 mM) under nitro-
gen. Pre-dried THF (10 mL) was added and the resulting mixture was stirred at room
temperature. Then, ligand (0.85 mM) and excess triethylamine (1.05 g, 10.4 mM) in THF
(5 mL) were added. The reaction mixture was stirred at room temperature overnight. After
removal of solvents, dichloromethane (20 mL) was added and the solution was filtered. The
filtrate was concentrated and the residue was washed with diethyl ether (5 mL × 2) and

Ruthenium(II) monocarbonyl complexes
3233
hexane (5 mL × 2) to give the desired product. Recrystallization from CH2Cl2/hexane (1 : 1)
afforded yellow needle crystals in two days suitable for X-ray diffraction.
2.2.6. [RuCl(κ2-N,O-L-Cl)(CO)(PPh3)2] (1). Yield: 0.44 g, 56%. IR (KBr disk, cm−1):
1
1909 (νC≡O), 1621 (νC=N); 31P NMR (CDCl3, 400 MHz): δ 22.1 (s, PPh3) ppm. H NMR
(CDCl3, 400 MHz): δ 6.91–7.18 (m, 36H, ArH), 7.47 (d, 2H, J = 5.9 Hz, ArH), 8.35 (s, 1H,
–CH=N) ppm. MS (FAB): m/z 919 [M+], 891 [M+–CO], 884 [M+–Cl], 856 [Ru(κ2-N,O-L-
Cl)(PPh3)2]+, 594 [Ru(κ2-N,O-L-Cl)(PPh3)]+, 332 [Ru(κ2-N,O-L-Cl)]+. Anal. Calcd for
C50H39NO2Cl2P2Ru (%): C, 65.29; H, 4.27; N, 1.52. Found: C, 65.14; H, 4.23; N, 1.56.
2.2.7. [RuCl(κ2-N,O-L-Me)(CO)(PPh3)2] (2). Yield: 0.36 g, 47%. IR (KBr disk, cm−1):
1
1914 (νC≡O), 1627 (νC=N); 31P NMR (CDCl3, 400 MHz): δ 21.6 (s, PPh3) ppm. H NMR
(CDCl3, 400 MHz): δ 2.26 (s, 3H, CH3), 6.98–7.23 (m, 36H, ArH), 7.41 (d, 2H, J = 5.9 Hz,
ArH), 8.49 (s, 1H, –CH=N) ppm. MS (FAB): m/z 899 [M+], 871 [M+–CO], 864 [M+–Cl],
836 [Ru(κ2-N,O-L-Cl)(PPh3)2]+, 574 [Ru(κ2-N,O-L-Cl)(PPh3)]+, 312 [Ru(κ2-N,O-L-Cl)]+.
Anal. Calcd for C51H42NO2Cl–P2Ru (%): C, 68.11; H, 4.71; N, 1.56. Found: C, 68.03; H,
4.65; N, 1.52.
2.2.8. [RuCl(κ2-N,O-L-NO2)(CO)(PPh3)2] 1.5C6H14 (3·1.5C6H14). Yield: 0.35 g, 42%.
IR (KBr disk, cm−1): 1912 (νC≡O), 1630 (νC=N), 1587, 1373 (νNO2); 31P NMR (CDCl3, 400
1
MHz): δ 22.9 (s, PPh3) ppm. H NMR (CDCl3, 400 MHz): δ 6.93–7.36 (m, 36H, ArH),
7.49 (d, 2H, J = 5.9 Hz, ArH), 8.53 (s, 1H, –CH=N) ppm. MS (FAB): m/z 858 [M+], 830
[M+–CO], 823 [M+–Cl], 795 [Ru(κ2-N,O-L-NO2)(PPh3)2]+, 533 [Ru(κ2-N,O-L-NO2)
(PPh3)]+, 271 [Ru(κ2-N,O-L-NO2)]+. Anal. Calcd for C44H39N2O4ClP2Ru·3/2(C6H14) (%):
C, 64.46; H, 6.12; N, 2.84. Found: C, 64.27; H, 6.06; N, 2.79.
2.3. X-ray crystallography
A summary of crystallographic data and experimental details for 1, 2, and 3·1.5C6H14 is
summarized in table 1. Intensity data were collected on a Bruker SMART APEX 2000
CCD diffractometer using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) at
296(2) K. The collected frames were processed with SAINT [25]. The data were corrected
for absorption using SADABS [26]. Structures were solved by direct methods and refined
by full-matrix least-squares on F2 using the SHELXTL software package [28]. All non-
hydrogen atoms were refined anisotropically. The positions of all hydrogens were generated
geometrically (Csp3–H = 0.96 and Csp2–H = 0.93 Å) and included in the structure factor cal-
culations with assigned isotropic thermal parameters but were not refined. The hexane mol-
ecules in 3·1.5C6H14 were isotropically refined without hydrogens due to disorder, which
probably resulted in a relatively high R value in the final refinement.
2.4. Procedure for catalytic oxidation of alcohols
Oxidation of primary alcohols to aldehydes and secondary ones to ketones with NMO were
catalyzed in the presence of [RuCl(κ2-N,O-L-Cl)(CO)(PPh3)2] (1), [RuCl(κ2-N,O-L-Me)
(CO)(PPh3)2] (2), or [RuCl(κ2-N,O-L-NO2)(CO)(PPh3)2] (3). A typical reaction using 1, 2

3234
X.-F. Yin et al.
Table 1. Crystallographic data and experimental details for 1, 2, and 3·1.5C6H14
.
Complex
1
2
3·1.5C6H14
Empirical formula
C50H39NO2Cl2P2Ru
919.73
Monoclinic
36.4797(11)
9.1618(3)
C51H42NO2ClP2Ru
899.32
C53H60N2O4ClP2Ru
987.49
Formula weight
Crystal system
a (Å)
b (Å)
c (Å)
Triclinic
9.0870(2)
10.2937(2)
23.4627(5)
96.328(1)
94.825(1)
97.454(1)
2152.06(8)
P-1
Triclinic
9.0619(4)
12.7710(5)
20.3154(9)
80.336(3)
89.068(3)
89.575(3)
2303.16(17)
P-1
24.8066(7)
α (°)
β (°)
γ °)
97.445(2)
V (Å3)
Space group
Z
8221.0(4)
C2/c
8
2
2
DCalc (g cm−3
)
1.486
1.388
1.424
Temperature (K)
F (000)
296(2)
3760
0.633
39,275
9352
523
296(2)
924
0.542
27,123
8417
524
0.0657
0.0437, 0.0847
296(2)
1030
0.517
31,934
10,593
565
0.0574
0.0554, 0.1257
μ(Mo-Kα) (mm−1
Total refln.
)
Independent refln.
Parameters
Rint
0.0907
0.0490, 0.0830
b
R1a, wR2 (I >
2σ(I))
R1, wR2 (all data)
0.0641, 0.1009
0.981
0.0724, 0.0959
1.031
0.0755, 0.1511
0.933
GoFc
aR1 = Σ||Fo| – |Fc||/Σ|Fo|.
bwR2 = [Σw(|Fo2| – |Fc2|)2/Σw|Fo2|2]1/2
.
cGoF = [Σw(|Fo| – |Fc|)2/(Nobs–Nparam)]1/2
.
or 3 as catalyst is as follows. A solution of 1, 2 or 3 (1 M%) in 20 mL of CH2Cl2 was
added to the mixture of substrate (1 mM) and NMO (2 mM). The mixture was stirred at
room temperature for 9 h and the solvent was evaporated under reduced pressure with a
rotary evaporator resulting in a solid mass. It was shaken with petroleum ether (30–40 °C)
(20 mL). The oxidized product extracted into petroleum ether was analyzed by GC.
3. Results and discussion
2[(4-chloro-phenylimino)-methyl]-phenol (HL-Cl), 2(p-tolyimino-methyl)-phenol (HL-Me),
and 2[(4-nitro-phenylimino)-methyl]-phenol (HL-NO2) were easily prepared by condensa-
tion of salicylaldehyde with the appropriate substituted aniline in methanol. Interactions of
[RuHCl(CO)(PPh3)3] with HL-Cl, HL-Me and HL-NO2 at room temperature in THF in the
presence of organic base afforded [RuCl(κ2-N,O-L-Cl)(CO)(PPh3)2] (1), [RuCl(κ2-N,O-L-
Me)(CO)(PPh3)2] (2), and [RuCl(κ2-N,O-L-NO2)(CO)(PPh3)2] (3) in 56, 47, and 42%
yields, repectively, as shown in scheme 1. One PPh3 and the hydride in the starting ruthe-
nium hydride compound were replaced by one bidentate O,N-ligand.
The electronic spectra of 1–3 in dichloromethane showed three bands from 245 to 500
nm (see Supplementary material). The high intensity bands at 257 nm have been assigned
to intraligand transitions [29]. The low energy absorptions at 348 nm are due to charge
transfer transitions arising from the metal t2g level to the unfilled π* molecular orbital of the

Ruthenium(II) monocarbonyl complexes
3235
PPh
3
H
C
N
R
Cl
PPh
3
O
N
CO
Ru
Cl
CO
OH
Et N / T H F , r e f lu x
Ph P
HC
R
Ru
3
PPh
3
H
3
R = Cl
M e
NO
1
2
PPh
3
3
2
Scheme 1. Syntheses of ruthenium(II) monocarbonyl complexes with bidentate O,N-ligands.
ligand. The bands from 435 to 462 nm have been assigned to spin-allowed metal-ligand
charge transition and d→d transitions. The nature of electronic spectra is similar to those
observed for other octahedral ruthenium(II)-carbonyl triphenylphosphine complexes
[30–33]. IR spectra of HL-Cl, HL-Me, and HL-NO2 showed the CH=N at 1635, 1639, and
1642 cm−1, respectively. In their corresponding ruthenium complexes, the blue bandshifted
about 13 cm−1 (1, 1621 cm−1; 2, 1627 cm−1, 3 1630 cm−1), suggesting coordination of nitro-
gen to ruthenium. The phenolic O–H of HL (3574–3596 cm−1) could no longer be observed
in IR spectra of 1–3, presenting coordination of oxygen to ruthenium. The stretches of
terminal C≡O in 1–3 were found from 1909 to 1914 cm−1, comparable to ruthenium
carbonyl complexes with NOS Schiff base and triphenylphosphine (1919–1933 cm−1) [31].
Only one 31P signal was observed in the 31P NMR spectra of 1 (22.1 ppm), 2 (21.6 ppm),
and 3 (22.9 ppm) due to trans PPh3 ligands. The aldimine proton (–CH=N–) resonances of
1 (δ = 8.35 ppm), 2 (δ = 8.49 ppm), and 3 (δ = 8.53 ppm) shift downfield compared to the
free ligands HL-Cl (δ = 8.26 ppm), HL-Me (δ = 8.37 ppm), and HL-NO2 (δ = 8.71 ppm),
suggesting coordination of nitrogen to ruthenium. The positive ion FAB mass spectra of
1–3 display the expected peaks corresponding to the molecular ions {[M+], [M+–Cl] or
[M+–CO], and [ML(PPh3)2]+, [ML(PPh3)]+ or [ML]+} with the characteristic isotopic distri-
bution patterns.
The structures of 1, 2, and 3·1.5C6H14 have been established by X-ray crystallography.
Perspective views of the molecular structures of 1–3 are shown in figures 1–3, respectively.
The central ruthenium is bonded in a slightly distorted octahedral geometry, to a nitrogen, a
oxygen of the Schiff base, a carbon monoxide, two triphenylphosphines, and a terminal
chloride. The Schiff base is bidentate to ruthenium and forms a six-membered chelate ring
with O–Ru–N bite angles of 87.49(10)°, 88.19(10)° and 87.94(11)° for 1, 2, and
3·1.5C6H14, respectively. The trans P–Ru–P angles are 175.01(3)°, 177.40(3)°and 175.03
(4)° for 1, 2, and 3·1.5C6H14, respectively. The Ru–C bond lengths (1.831(4) Å in 1, 1.835
(4) Å in 2, and 1.846(5) Å in 3·1.5C6H14) and the Ru–C–O bond angles (174.8(4)° in 1,
173.5(3)° in 2, and 176.3(4)° in 3·1.5C6H14) are normal for ruthenium-carbonyl complexes
[30–34]. The average Ru–P lengths are 2.4164(9), 2.4119(9), and 2.4158(11) Å for 1, 2,
and 3·1.5C6H14, respectively, and the average Ru–Cl lengths are 2.4294(10), 2.4245(9),
and 2.4262(11) Å for 1, 2, and 3·1.5C6H14, respectively, in agreement with those in related
ruthenium(II) complexes [30–35].
Complexes 1–3 catalyze oxidation of primary alcohols to the corresponding
aldehydes and secondary alcohols to ketones in dichloromethane in the presence of
N-methylmorpholine-N-oxide (NMO) (scheme 2). Karvembu reported
a catalytic
system: [Ru(L)(CO)(PPh3)2]/NMO/DCM (L = binegative tridentate ONS Schiff base;

3236
X.-F. Yin et al.
OH
O
Catalyst: 1 mol%
R
R'
NMO / CH2Cl2, r.t., 12 h
R
R'
R = R' = Alkyl (or) aryl (or) H
Scheme 2. Catalytic oxidation reactions of alcohols to aldehydes/ketones.
NMO, 3 mM; DCM = dichloromethane), for oxidation of alcohols to carbonyl com-
pounds, and stated that neither the Ru complex nor the NMO alone causes the
organic transformation under defined conditions [31]. In our catalytic system, dichloro-
methane is also the best solvent and the Ru catalyst amount is 1 M%, but 2 mM of
NMO instead of 3 mM is enough for the catalysis. A series of alcohols, including
benzylic alcohol with different substituents, benzylic secondary alcohols with different
substituents, cyclohexanol, and 1-cyclohexyl-ethanol, have been chosen as substrates.
[RuHCl(CO)(PPh3)3] showed less catalysis than 1–3, exhibiting 64% conversion of
benzylic alcohol into benzaldehyde, whereas 1–3 showed approximately 95% transfor-
mation under the same conditions. The oxidation products were identified by GC.
The TON (%conversion) values are given in table 2 and indicate that the present
ruthenium(II) complexes are promising catalysts. All substrates were efficiently con-
verted to the corresponding ketones or aldehydes. Benzylic alcohol and substituted
benzylic alcohols (entries 6–10) bearing either electron-donating or electron-withdraw-
ing groups afforded the corresponding aldehydes in good conversions (93–99%), simi-
lar to previously reported Ru(II)-PPh3/NMO catalytic systems with tridentate ONS
Schiff base ligands (97–99%) [31] and Ru(II)-PPh3/NMO catalytic systems with N-[di
(alkyl/aryl)carbamothioyl] benzamide derivatives (94%) [18]. The efficiency of oxida-
tion of benzylic alcohols is higher than that reported for Ru(II)-PPh3 catalytic systems
with bi- or tridentate ONO Schiff base (70%) [36] and [Ru(PPh3)3Cl2]/hydroquinone/
air systems (80%) [37].
Benzylic secondary alcohols were smoothly oxidized to the corresponding ketones
with good yields (82–93%), comparable to the observed ruthenium complexes
containing N-[di(alkyl/aryl)carbamothioyl]-benzamide and triphenylphosphine ligands
(94–99%) [18], but the catalytic activity was lower than the tetrametallic ruthenium-
μ-oxo-μ-hydroxo catalyst (100%) [38] and heterogeneous nickel catalysts with Schiff
base ligands (about 95%) [20]. No further oxidation of aldehydes to acids was
observed even after extended reaction time, indicating good selectivity of 1–3. Unlike
benzylic alcohols and benzylic secondary alcohols, the conversion was not encourag-
ing for cyclohexanol and 1-cyclohexylethanol which were converted into their corre-
sponding ketones in 74–82% yields, similar to ruthenium complexes with tridentate
ONS Schiff base ligands (68–80%) [31], but slightly higher than that in Ru(II)-PPh3
catalytic systems with bi or tri-dentate ONO Schiff bases (42–85%) [36]. The
catalytic oxidation activities of the present three ruthenium(II)-monocarbonyl com-
plexes are not affected by the different electron-donating and electron-withdrawing
N,O-bidentate Schiff bases. Investigations to understand catalytic mechanisms and
properties of the ruthenium(II) complexes containing bidentate and tridentate Schiff
base ligands are in progress.

Ruthenium(II) monocarbonyl complexes
3237

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Ruthenium(II) monocarbonyl complexes
3239
4. Conclusion
Three new ruthenium(II) monocarbonyl complexes with bidentate Schiff base and triphenyl-
phosphines have been synthesized and characterized by microanalytical and spectroscopic
methods. Their molecular structures have been determined by single-crystal X-ray crystal-
lography. The ruthenium complexes exhibit excellent catalytic performance on oxidation of
alcohols to corresponding aldehydes or ketones in the presence of NMO, and the Schiff
base ligands with different electron-donating and electron-withdrawing groups have little
influence on the catalytic activity. It may provide a simple and alternative method for the
oxidation of different kinds of alcohols under mild conditions.
Supplementary material
Crystallographic data for 1, 2, and 3·1.5C6H14 have been deposited with the Cambridge
Crystallographic Data Center as Supplementary publication Nos CCDC 925317–925319,
respectively. Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (+44) 1233 336 033; Email:
deposit@ccdc.cam.ac.uk].
Acknowledgment
This project was supported by the Natural Science Foundation of China (20771003 and
21201003).
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