Trans- and cis-Ru(II) aminophosphine complexes: Syntheses, X-ray structures and catalytic activity in transfer hydrogenation of acetophenone derivatives

Article abstract of DOI:10.1016/j.ica.2010.12.028

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer hydrogenation process is a valuable synthetic tool. For this aim, a novel Ru(II) complex with the P-N ligand [(Ph ₂P)₂NCH₂

Full text of DOI:10.1016/j.ica.2010.12.028

Inorganica Chimica Acta 367 (2011) 166–172
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Inorganica Chimica Acta
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trans- and cis-Ru(II) aminophosphine complexes: Syntheses, X-ray structures
and catalytic activity in transfer hydrogenation of acetophenone derivatives
a
b
c
Murat Aydemir a, , Akın Baysal , Saim Özkar , Leyla Tatar Yıldırım
⇑
a Dicle University, Department of Chemistry, TR-21280 Diyarbakır, Turkey
b Middle East Technical University, Department of Chemistry, TR-06531 Ankara, Turkey
c Hacettepe University, Department of Engineering Physics, Beytepe, TR-06800 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2010
Received in revised form 29 November 2010
Accepted 10 December 2010
Available online 24 December 2010
The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer
hydrogenation process is a valuable synthetic tool. For this aim, a novel Ru(II) complex with the P–N
ligand [(Ph2P)2NCH2–C4H3S] derived from thiophene-2-methylamine was synthesized starting with the
complex [Ru(g l-Cl)Cl]2 and isolated in two isomeric forms: trans- and cis-
6-p-cymene)(
[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and 3, respectively. The structures of both isomers were also determined
by single crystal X-ray diffraction. The cis-isomer 3 can be isolated from the solution of major trans-iso-
mer 2 as yellow crystals. However, upon dissolution 3 is rapidly converted to the trans-isomer 2. The new
ruthenium(II) complex provides high catalytic activity in the transfer hydrogenation of acetophenone
derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. This
transfer hydrogenation is characterized by low reversibility under the experimental conditions.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Transfer hydrogenation
Crystal structures
Aminophosphine
Bis(phosphino)amine
Ru(II)
1. Introduction
hydrogenation by molecular hydrogen [22,23]. In transfer hydro-
genation, organic molecules such as primary and secondary alco-
Aminophosphine ligands have been studied for the last three
decades and found to be of considerable interest due their wide
range of applications in organometallic chemistry for the develop-
ment of industrial processes involving a great number of catalytic
reactions [1]. A large number of complexes with aminophosphine
ligands have been tested in different catalytic reactions including
allylic alkylation [2], amination [3], Heck [4], Sonogashira [5], Su-
zuki [6], hydroformylation [7], hydrogenation [8] and polymeriza-
tion [9] reactions. Some aminophosphines and derivatives have
also found application as anticancer drugs [10], herbicides and
antimicrobial agents, as well as neuroactive agents [11]. To date,
a number of such systems with a variety of backbone frameworks
have been synthesized and their transition metal chemistry has
been explored [12,13]. Aminophosphines and bis(phos-
phino)amines with P–NH and P–N–P skeletons, respectively, have
proved to be much more versatile ligands, and varying the substit-
uents on both the P- and N-centers gives rise the changes in the P–
N–P angle and the conformation around the P-centers [14–17].
Small variations in these ligands can cause significant changes in
their coordination behavior and the structural features of the
resulting complexes [18–21].
hols [24] or formic acid and its salts [25] have been employed as
the hydrogen source. The use of the hydrogen donor has some
advantages over the use of molecular hydrogen since it avoids
no risks and the constrains associated with hydrogen gas as well
as the necessity for pressure vessels and other equipments. 2-
Propanol is a popular reactive solvent for transfer hydrogenation
reactions since it is easy to handle and is relatively non-toxic,
environmentally benign and inexpensive. The volatile acetone
by-product can also be easily removed to shift unfavorable equi-
libria and can be converted to 2-propanol back by catalytic
hydrogenation [26]. In general, asymmetric hydrogenation is
mediated by a complex bearing Rh, Ru, or Ir, among which our
focus has been Ru. One reason is that the Ru catalysts have
excellent performances [27,28]. Another reason is that Ru en-
joyed a cost advantage relative to other asymmetric hydrogena-
tion metals such as Rh [29].
In this paper, we report the ready synthesis of bis(phos-
phino)amine ligand [(Ph2P)2NCH2–C4H3S] and its corresponding
ruthenium(II) complexes, trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2],
2
and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 3. The structures of both
complexes were determined by single crystal X-ray diffraction
analyses. As a part of our continuing interest in developing
highly active efficient and stable catalysts [30–33], we report
here the catalytic activity of trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2],
Catalytic transfer hydrogenation with the aid of a stable
hydrogen donor is
a useful alternative method for catalytic
2
complex in the transfer hydrogenation of acetophenone
⇑
Corresponding author.
E-mail address: aydemir@dicle.edu.tr (M. Aydemir).
derivatives.
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.12.028

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172
167
CH2–); 13C NMR (100.6 MHz, CDCl3): d = 48.14 (–CH2–), 125.23
(C-5), 126.38 (C-4), 126.78 (m-carbons of phenyls), 127.76 (C-3),
129.61 (p-carbons of phenyls), 134.83 (o-carbons of phenyls),
137.30 (i-carbons of phenyls), 141.16 (C-2); assignment was based
on the 1H–13C HETCOR and 1H–1H COSY spectra; 31P NMR
2. Experimental
2.1. Materials and methods
Unless otherwise stated, all reactions were carried out under an
atmosphere of argon using conventional Schlenk glass-ware, sol-
vents were dried using established procedures and distilled under
argon immediately prior to use. Analytical grade and deuterated
solvents were purchased from Merck. PPh2Cl and thiophene-2-
methylamine are purchased from Fluka and were used as received.
(162 MHz, CDCl3): d = 78.05 (s); IR, (KBr):
m = 993 (P–N–P), 1436
(P–Ph) cmÀ1. Anal. Calc. for C58H50N2S2P4RuCl2 (1135.1 g/mol): C,
61.37; H, 4.44; N, 2.47. Found: C, 61.29; H, 4.39; N, 2.41%.
2.4. Synthesis of [Ru((PPh2)2NCH2–C4H3S)(
g
6-p-cymene)Cl]Cl (4)
[Ru(g l-Cl)Cl]2 [34] was prepared according to litera-
6-p-cymene)(
6-p-cymene)(
-Cl)Cl]2 (0.596 g,
ture procedure. The IR spectra were recorded on a Mattson 1000
ATI UNICAM FT-IR spectrometer as KBr pellets. 1H (400.1 MHz),
13C NMR (100.6 MHz) and 31P-{1H} NMR spectra (162.0 MHz) were
recorded spectra on a Bruker Avance 400 spectrometer, with d ref-
erenced to external TMS and 85% H3PO4 respectively. Elemental
analysis was carried out on a Fisons EA 1108 CHNS-O instrument.
Melting points were recorded by Gallenkamp Model apparatus
with open capillaries.
To solution of [Ru( l
a
g
0.980 mmol) in 10 mL thf, a solution (thf, 15 mL) of [(PPh2)2NCH2–
C4H3S], 1 (0.469 g, 0.980 mmol) was added. The resulting reaction
mixture was allowed to proceed under stirring at room temperature
for 1 h. After this time, the solution was filtered off and the solvent
evaporated under vacuum, the solid residue thus obtained was
washedwithdiethylether(3 Â 15 mL)andthendriedundervacuum
(Scheme 2). Following recrystallization from diethylether/CH2Cl2, a
red crystalline powder was obtained (yield: 0.71 g, 92%; m.p.: 250 °C
(dec.); 1H NMR (d in ppm rel. to TMS, J Hz, in CDCl3): 7.72 (dd, 8H,
3J = 7.2 and 13.6, o-protons of phenyls), 7.54 (dd, 4H, 3J = 6.6 and
12.4, p-protons of phenyls), 7.32 (m, 8H, m-protons of phenyls),
7.03 (d, 1H, 3J = 5.2 Hz, H-5), 6.66 (dd, 1H, 3J = 3.6 and 5.2 Hz, H-4),
6.39 (d, 1H, 3J = 3.6, H-3), 5.45 (d, 2H, 3J = 5.6 Hz, aromatic hydrogens
of p-cymene), 5.28 (d, 2H, 3J = 5.6 Hz, aromatic hydrogens of p-cym-
ene), 4.45 (t, 2H, 3J = 11.6 Hz, –CH2–), 2.81 (m, 1H, –CH– of p-cym-
ene), 2.26 (s, 3H, CH3-Ph of p-cymene), 1.23 (d, 6H, 3J = 6.8 Hz,
(CH3)2CHPh of p-cymene); 13C NMR (d in ppm rel. to TMS, J Hz, in
CDCl3): 18.63 (CH3Ph of p-cymene), 22.21 ((CH3)2CHPh of p-cym-
ene), 31.01 (–C H– of p-cymene), 47.68 (–CH2–), 77.97, 79.05
(aromatic carbons of p-cymene), 95.92, 100.20 (quaternary carbons
of p-cymene), 125.32 (C-5), 126.55 (C-4), 127.86 (C-3), 127.41
(t, 3J = 4.0 Hz, m-carbons of phenyls), 129.84 (d, 1J = 57.3 Hz, i-car-
bons of phenyls), 132.83 (t, 4J = 6.0 Hz, p-carbons of phenyls),
134.31 (t, 2J = 5.5 Hz, o-carbons of phenyls), 140.54 (C-2); assign-
ment was based on the 1H–13C HETCOR and 1H–1H COSY spectra;
31P NMR (d in ppm rel. to H3PO4, in CDCl3): 88.21 (s); Selected IR
2.2. GC analyses
GC analyses were performed on a HP 6890 N Gas Chromato-
graph equipped with capillary column (5% biphenyl, 95% dimethyl-
siloxane) (30 m  0.32 mm  0.25
lm). The GC parameters were
as follows for transfer hydrogenation of ketones; initial tempera-
ture, 110 °C; initial time, 1 min; solvent delay, 4.48 min; tempera-
ture ramp 80 °C/min; final temperature, 200 °C; final time,
21.13 min; injector port temperature, 200 °C; detector tempera-
ture, 200 °C; injection volume, 2.0 lL.
2.3. Synthesis of trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2] (2)
6-p-cymene)(
l-Cl)Cl]2 (149 mg,
To
a
solution of [Ru(
g
0.243 mmol) in 10 mL thf, a solution (thf, 30 mL) of (PPh2)2-
NCH2–C4H3S, 1 (469 mg, 0.972 mmol) was added. The resulting
reaction mixture was allowed to proceed under stirring at room
temperature for 1 h. After this time, the solution was filtered off
and the solvent evaporated under vacuum, the solid residue thus
obtained was washed with diethyl ether (3 Â 15 mL) and then
dried under vacuum (Scheme 1). Following recrystallization from
diethylether/CH2Cl2, a scarlet crystalline powder was obtained
(yield 506 mg, 91.5%), m.p. 251–253 °C. 1H NMR (400.1 MHz,
CDCl3) d = 7.11–7.56 (m, 40H, o-, m- and p- protons of phenyls),
6.96 (d, 2H, 3J = 4.20 Hz, H-5), 6.60 (dd, 2H, 3J = 2.80 and 4.20 Hz,
H-4), 6.43 (d, 2H, 3J = 2.80 Hz, H-3), 4.66 (t, 4H, 3J = 5.20 Hz, –
(KBr pellet, in cmÀ1):
39H39NSP2RuCl2 (787.7 g/mol): C, 59.47; H, 4.99; N, 1.78. Found:
m(P–N–P) 984, m(P–Ph) 1440; Anal. Calc. for
C
C, 59.39; H, 4.93; N, 1.74%.
2.5. X-Ray Crystallography
X-ray diffraction data of single crystal for trans- and cis-
[Ru((PPh2)2NCH2–C4H3S)2Cl2] were collected at room temperature
Scheme 1. Synthesis of the trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 3 complexes: (i) 2 equivalent Ph2PCl, 2 equivalent Et3N, thf; (ii) 1/4
equivalent [Ru( -Cl)Cl]2, thf; (iii) in CH2Cl2, 48 h; (iv) 1 equivalent [Ru( -Cl)Cl]2, thf.
6-p-cymene)( 6-p-cymene)(
g
l
g
l

168
M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172
3. Results and discussion
3.1. Synthesis and characterization of the metal complexes
The ligand thiophene-2-(N,N-bis(diphenylphosphino))methyl-
amine, [(Ph2P)2NCH2–C4H3S], 1 was prepared from the aminolysis
of two equivalents of PPh2Cl with one equivalent thiophene-2-
methylamine in the presence of triethylamine at 0 °C, as outlined
in Scheme 1 [39]. The 31P NMR spectrum of 1 gives single reso-
nance at 59.83 ppm, similar to those found for closely related com-
pounds [40]. 1 is not stable and rapidly oxidized to P(O)Ph2PPh2 on
exposure to air or moisture as monitored by 31P NMR spectroscopy,
which gives two doublets at 34.60 and À24.30 ppm with a cou-
pling constant of 1J(PP) = 226 Hz.
Scheme 2. Hydrogen transfer from iso-PrOH to acetophenone derivatives.
with graphite monochromated Mo K
an Enraf-Nonius CAD4 diffractometer operating in
a
(k = 0.71073 Å) radiation on
/2h scan
x
mode. Unit cell parameters were refined from the setting angles
of (trans) 25 and (cis) 17 centered reflections in the range of (trans)
10.00 6 h 6 18.03° and (cis) 10.10 6 h 6 17.96°. Cell refinement
was carried out using CAD-4 EXPRESS [35]. Data reduction was car-
ried out using XCAD4 [36]. The structure was solved by direct meth-
ods using SHELX97 and refined by the full-matrix least-squares
method on F2 assuming anisotropic thermal parameters for non-
hydrogen atoms using SHELXL97 [37] in the WINGX package [38].
Hydrogen atoms on the methylene of the trans structure were ta-
ken from a difference Fourier map and refined with isotropic ther-
mal parameters. All other hydrogen atoms of both molecules were
placed geometrically and a riding model was used on their carrier
atom. Selected crystal and experimental data are given in Table 1.
Selected bond lengths and angles are given in Tables 2 and 3.
We examined some simple coordination chemistry of 1 with
[Ru(g l-Cl)Cl]2 precursor. The reaction between
6-p-cymene)(
Ru(II) precursor and bis(phosphino)amine, 1 is profoundly affected
by the molar ratio of the reactants. Reaction of (PPh2)2NCH2–C4H3S,
1 with [Ru(g l-Cl)Cl]2 in thf solution in a molar ratio
6-p-cymene)(
of 1:1/4 at room temperature for 1 h yielded trans-
[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 as crystalline orange powders
(Scheme 1). By slow diffusion of diethylether into a solution of
the complex 2 in the dichloromethane, complex 2 was obtained
as scarlet crystals. In addition to the complex 2, a few yellow crys-
tals of complex 3 were also obtained, which were suitable for X-ray
diffraction studies. From these single crystals, the structures of
both compounds were elucidated by X-ray diffraction studies.
Crystal structure studies showed that major and minor products
are trans- (2) and cis- (3) isomer of [Ru((PPh2)2NCH2–C4H3S)2Cl2],
respectively. The trans isomer, 2 was isolated and characterized
by observing a singlet at 78.05 ppm in the 31P NMR spectrum in
line with the values previously observed for similar compounds
[41,42]. This indicates that (PPh2)2NCH2–C4H3S is acting as a
bidendate chelating ligand. The IR bands observed at 993 and
2.6. General procedure for the transfer hydrogenation of ketones
Typical procedure for the catalytic hydrogen transfer reaction: a
solution
of
ruthenium
complex
trans-[Ru((PPh2)2NCH2–
C4H3S)2Cl2], 2 (0.01 mmol), NaOH (0.05 mmol) and the correspond-
ing ketone (1.0 mmol) in degassed iso-PrOH (10 mL) was refluxed
for 60 min for 2. After this period a sample of the reaction mixture
was taken off, diluted with acetone and analyzed immediately by
GC. Conversions obtained are related to the residual unreacted
ketone.
1436 cmÀ1 represent
m(PNP) and m
(PPh), respectively. The 13C
NMR spectra gave signals in line with structures as explained in
Section 2 [43].
Table 1
Crystal data and experimental details for compounds trans- and cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2].
Compound
trans
cis
Formula
Formula weight
[C58H50Cl2N2P4RuS2]Á2(CHCl3)
1373.73
[C58H50Cl2N2P4RuS2]Á(CH2Cl2)(C4H10O)
1294.04
Crystal shape/color
prism/yellow
plate/yellow
0.4 Â 0.4 Â 0.1
295(2)
monoclinic/P21/c
12.532(2)
27.738(4)
17.7547(10)
90
101.378(8)
90
6050.5(14)
4
Crystal size (mm3)
0.15 Â 0.05 Â 0.03
T (K)
295(2)
triclinic/P1
ꢀ
Crystal system/space group
a (Å)
b (Å)
c (Å)
10.6451(10)
11.459(2)
13.580(2)
67.663(9)
75.767(7)
84.664(8)
1485.2(4)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
1.536
0.844
1.421
0.654
l
(mmÀ1
)
F(0 0 0)
698
2664
h range for data collection (°)
Reflections measured
2.27–26.29
6263
2.33–26.29
12 230
Independent observed reflections
5999
11855
Independent reflections [I > 2
Data/restraints/parameters
Rint
r]
4739
5999/5/335
0.0445
5538
11 855/4/664
0.0704
R indices (all data)
R1 = 0.1144, wR2 = 0.2802
R1 = 0.089, wR2 = 0.2582
1.069
À2.140, 2.293
R1 = 0.2254, wR2 = 0.1821
R1 = 0.730, wR2 = 0.2352
1.002
À1.019, 2.678
R indices [I > 2
Goodness of fit (GOF) on F2
qmin (e ÅÀ3
r(I)]
D
qmin
,
D
)

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172
169
g
6-p-cymene)Cl]Cl, 4, in high yield as
Table 2
Selected bond lengths for 2 and related bond length ranges for 3 (Å).
[Ru((PPh2)2NCH2–C4H3S)(
the main product (Scheme 1).
The title compounds trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 and
cis-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 3 both mononuclear Ru(II) com-
plexes, crystallize in the triclinic P1 and monoclinic P21/c space
group, respectively. In the trans- compound 2 the central Ru atom,
which is located on an inversion center, has disordered octahedral
coordination. In the cis- compound 3 the Ru atom has highly disor-
dered octahedral coordination. The ORTEP drawing [44] of the mol-
ecule is shown in Fig. 2.
In compound 2, the equatorial plane consists of two P atoms
and their symmetry related P atoms from N-diphenylphosphino
(PPh2) ligands [Ru–P1 2.3523(17), Ru–P2 2.3250(17) Å]. The Cl
atom and its symmetry related atom occupy the axial positions
of the octahedron [Ru–Cl1 2.4205(17) Å]. The coordination bond
angles are range of 69.39(6)–110.61(6)°. In compound 3, there
are two different coordination planes, A [P1/N1/P2/Cl2] and B
[P3/N2/P4/Cl1], which are consists of three P atoms from N-
diphenylphosphino (PPh2) ligands with Ru–P bond length range
of 2.282(2)–2.336(2) Å and one Cl atom with Ru–Cl bond length
range of 2.463(2)–2.464(2) Å. The A and B planes are nearly per-
pendicular to each other. Dihedral angle between them is 88.42°.
The coordination bond angles are range of 70.13(8)–102.68(8)°.
The hydrogen bonding and molecular packing geometry was
calculated with PLATON [45]. In the crystal structure of 2 and 3, there
trans
cis
Ru–Cl1
Ru–P1
Ru–P2
P1–Ni
2.4205(17)
2.3523(17)
2.3250(17)
1.723(6)
1.714(6)
1.843(8)
1.821(7)
1.807(8)
1.830(7)
1.496(9)
1.695(10)
1.656(13)
2.663(3)
Ru–Cl
Ru–P
P–N
P–C
N–C
S–C
2.463(2)–2.464(2)
2.282(2)–2.336(2)
1.709(7)–1.743(7)
1.814(8)–1.833(9)
1.474(10)–1.486(9)
1.645(14)–1.707(10)
2.648(3)–2.656(3)
ꢀ
P2–N
P1–C1
P1–C7
P2–C13
P2–C19
N–C25
S–C26
S–C29
P1ÁÁÁP2i
PÁÁÁP
[i: Àx, Ày, Àz].
Table 3
Selected bond angles for 2 and related bond angle ranges for 3 (°).
trans
cis
Cl1–Ru–P1
Cl1–Ru–P1i
Cl1–Ru–P2
Cl1–Ru–P2i
P1–Ru–P2
P1–Ru–P2i
P1–N–P2i
85.73(6)
94.27(6)
92.02(6)
87.98(6)
110.61(6)
69.39(6)
101.5(3)
93.9(2)
Cl–Ru–P (neighbor)
Cl–Ru–P (opposite)
Cl1–Ru–Cl2
P1–Ru–P2
P3–Ru–P4
P1–Ru–P3
P2–Ru–P3
P2–Ru–P4
P2–Ru–P4
P–N–P
87.77(8)–100.71(8)
156.08(8)–157.89(8)
85.84(8)
71.18(8)
70.13(8)
101.15(8)
102.68(8)
102.58(8)
167.66(8)
exists X–HÁÁÁCg (
p-ring) interaction further stabilizes the structure
with the shortest intra and intermolecular hydrogen bondings. De-
Ru–P1–Ni
Ru–P2–N
C1–P1–C7
C13–P2–C19
tails of the hydrogen bonding geometry and
given in Tables 4 and 5, respectively.
p-ring interactions are
95.1(2)
101.8(4)
100.4(3)
100.2(3)–100.6(3)
93.7(2)–95.3(2)
98.5(4)–99.5(4)
Ru–P–N
C–P–C
3.2. Catalytic transfer hydrogenation of acetophenone derivatives
In preliminary study, the obtained complex trans-
[i: Àx, Ày, Àz].
a
[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2 was examined in the ruthenium
catalyzed transfer hydrogenation of acetophenone to the corre-
sponding alcohol in iso-PrOH solution (Scheme 2).
The reaction of 1 with 1/2 equivalent [Ru(g l-
6-p-cymene)(
Cl)Cl]2 yielded a dark yellow solid. The 31P NMR spectrum of the
crude product indicated that it is a mixture of two products, 2
and 4 as shown in (Fig. 1). In the 31P NMR spectrum, the singlet
at 78.05 ppm was assigned to compound 2. Complex 4 exhibits a
singlet at 88.2 ppm for monochelating (PPh2)2NCH2–C4H3S. Com-
pound 4 with one (PPh2)2NCH2–C4H3S ligand and compound 2
with two [C4H3S-CH2N(PPh2)2] ligands show two sets of 31P NMR
resonances with relative intensities of 1:2 (approximately) which
are consistent with these structural formulae. The compound 4
was also prepared in its pure form separately using different molar
The activity of Ru(II) arene complexes is well known in this cat-
alytic process [46,47, and references therein]. In a typical experi-
ment, 0.01 mmol of the complex 2 and 1 mmol of acetophenone
were added to a solution of NaOH in iso-PrOH (0.05 mmol of NaOH
in 10 mL iso-PrOH) and refluxed at 82 °C, the reaction being mon-
itored by GC. With a complex/NaOH ratio of 1/5, the complex leads
to a quantitative transformation of the acetophenone in 1 h, with a
moderate TOF of <100 hÀ1 (Table 6, entry 1). These results are sum-
marized in Table 6. It should be pointed out that complex 2 is more
active catalysts than the corresponding precursor: [Ru(
ne)( -Cl)Cl]2 (41% maximum conversion in 24 h) with a 1/14 com-
plex/NaOH ratio [48].
g
6-p-cyme-
ratios. The reaction of (PPh2)2NCH2–C4H3S with excess of [Ru(
g
6-p-
l
cymene)( -Cl)Cl]2) affords only the corresponding monochelate
l
Fig. 1. The 31P NMR spectra of reaction mixture containing complexes 2 and 4; (i) reaction of 1 with 1/4 equivalent [Ru(
equivalent [Ru( -Cl)Cl]2; (iii) reaction of 1 with 1 equivalent (excess) [Ru( -Cl)Cl]2.
6-p-cymene)( 6-p-cymene)(
g l-Cl)Cl]2; (ii) reaction of 1 with 1/2
6-p-cymene)(
g
l
g
l

170
M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172
Fig. 2. The molecular structure and atomic labeling scheme of (a) trans compound and (b) cis compound. The thermal ellipsoids are drawn at 30% probability and hydrogen
atoms and solvents were omitted for clarity.
Table 4
Table 6
Structural parameters of hydrogen bonds between donor (D), acceptor (A) and
hydrogen (H).
Transfer hydrogenation of acetophenone with iso-PrOH catalyzed by trans-
[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2.
i
Compound D–HÁÁÁA
D–H (Å) AÁÁÁH (Å) DÁÁÁA (Å)
D–HÁÁÁA (°)
Entry
Catalyst
S/C/NaOH
Time (h)
Conversion (%)h
TOF (hÀ1
)
trans (2)
C2–H2ÁÁÁCl14a
0.93
0.93
0.98
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.59
2.78
2.65
2.57
2.77
2.87
2.52
2.49
2.74
2.86
2.56
2.66
3.364(10) 140
1
2
3
4
5
6
7
3a
3b
3c
3d
3e
3f
100:1:5
100:1:5
100:1
100:1:5
100:1:5
100:1:5
500:1:5
1
1
1
1
1.5
2
3.5
99
<1
<2
<1
99
–
–
C14–H14ÁÁÁS4a
C30–H30ÁÁÁCl4b
C8–H8ÁÁÁS
3.426(10) 128
3.605(19) 164
3.660(12) 168
3.496(9)
3.801(9)
3.410(9)
3.392(10) 164
3.553(10) 146
3.788(11) 173
3.418(13) 147
3.402(12) 133
–
cis (3)
C2–H2ÁÁÁCl2
136
175
159
98
65
49
28
C6–H6ÁÁÁS1
97 (96, 93, 92)k
99
C12–H12ÁÁÁCl1
C48–H48ÁÁÁCl1
C54–H54ÁÁÁCl1
C58–H58ÁÁÁS2
3g
a
Catalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (10 mL), NaOH
(0.05 mmol), 82 °C, for 2, the concentration of acetophenone derivatives is 0.1 M.
C63–H63AÁÁÁCl16a 0.97
Ketone/catalyst/NaOH ratio: 100/1/5. Yields were determined by GC.
b
C63–H63BÁÁÁCl26a 0.97
At room temperature; acetophenone/Ru/NaOH, 100:1:5.
Refluxing in iso-PrOH; acetophenone/Ru, 100:1, in the absence of base.
c
d
Symmetry codes: [4a: 2 À x, Ày, 1 À z; 4b: À1 + x, y, z; 6a: 1 À x, 1/2 + y, 1/2 À z].
Refluxing in iso-PrOH; acetophenone/Ru, 100:1:5, in the absence of catalyst.
e
Refluxing the reaction in air.
Added 0.1 mL of H2O.
Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 500:1:5.
Determined by GC (three independent catalytic experiments).
f
g
h
At room temperature no appreciable formation of 1-phenyleth-
anol was observed (Table 6, entry 2) and also the catalytic activity
i
Referred at the reaction time indicated in column; TOF = (mol product/mol
Ru(II)Cat.) Â hÀ1
.
of [Ru(g l-Cl)Cl]2 under the applied experimental
6-p-cymene)(
k
The amount of the water in different concentrations (0.5, 1.0 and 5.0 mL).
conditions is negligible. In addition, as can be inferred from the
Table 6 (entry 3 and 4), the precatalyst as well as the presence of
NaOH are necessary to observe appreciable conversion. Amazingly,
the conversion was not affected in the air or with the addition of
water. Performing the reaction in air slowed down the reaction
but did not affect conversions (Table 6, entry 5). For the transfer
hydrogenation of acetophenone, the catalyst system showed high
activity even in the presence of small amount (0.1 mL) of water.
When we increased the amount of water in the reaction system,
the high conversion remained intact (Table 6, entry 6). The transfer
hydrogenation of acetophenone could be achieved to up 99% con-
version even when the substrate-to-catalyst ratio reached to 500:1
except time of the reaction lengthened (Table 6, entry 7). Further-
more, in order to investigate the evolution of the catalyst, 2, 31P
NMR spectrum was recorded immediately after the catalytic reac-
tion. The observed singlet at 21.56 ppm is corresponding to hydro-
lysis product diphenylphosphinous acid, Ph2P(O)H [49–51].
This complex was also extensively investigated with a variety of
substrates. Electronic properties (the nature and position) of the
substituents on the phenyl ring of the ketone caused the changes
in the reduction rate. A ortho- or para-substituted acetophenone
with an electron-donor substituent, i.e., 2-methoxy or 4-methoxy
is reduced more slowly than acetophenone (Table 7, entry 4 and
5) [52]. In addition, the introduction of electron withdrawing
Table 5
Structural parameters of X–HÁÁÁCg (p-ring) interactions.
Compounds
X–H ÁÁÁCg
X–H (Å)
HÁÁÁCg (Å)
XÁÁÁCg (Å)
X–HÁÁÁCg (°)
2
C8–H8ÁÁÁCg41
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.63
2.98
2.76
2.81
2.96
2.70
2.60
3.520(12)
3.686(12)
3.559(9)
3.594(9)
3.264(9)
3.506(10)
3.470(12)
160
134
144
142
101
146
157
C29–H29ÁÁÁCg424c
C31–H31ÁÁÁCg61
C23–H23ÁÁÁCg62
C41–H41ÁÁÁCg62
C6–H6ÁÁÁCg63
3
C58–H58ÁÁÁCg64
Symmetry code: [4c: x, y, À1 + z].
[Cg41 = S/C26/C27/C28/C29; Cg42 = C19/C20/C21/C22/C23/C24; Cg61 = Ru1/P1/N1/P2; Cg62 = Ru1/P3/N2/P4; Cg63 = S1/C14/C15/C16/C17; Cg64 = S2/C43/C44/C45/C46].

M. Aydemir et al. / Inorganica Chimica Acta 367 (2011) 166–172
171
Table 7
Transfer hydrogenation results for substituted acetophenones with the catalyst system trans-[Ru((PPh2)2NCH2–C4H3S)2Cl2], 2.a
O
OH
OH
O
Cat
R
R
+
+
c
Entry
R
Time (h)
Conversion (%)b
TOF (hÀ1
)
Cat: Ru(II) complex, 2
1
2
3
4
5
4-F
4-Cl
4-Br
2-MeO
4-MeO
1
1
1
1
1
99
98
98
97
95
99
98
98
97
95
a
b
c
Catalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (10 mL), NaOH (0.05 mmol), 82 °C, 1 h for 2, the concentration of acetophenone derivatives is 0.1 M.
Purity of compounds is checked by NMR and GC (three independent catalytic experiments), yields are based on methyl aryl ketone.
TOF = (mol product/mol Cat.) Â hÀ1
.
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4. Conclusion
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This compound has proved to be efficient catalyst in the transfer
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not affected in the air or addition of water. When we increased
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mained intact.
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Partial support from Dicle University (Project number: DÜAPK
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Scientific Research Department (Project number: 04A602004) is
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