Synthesis, structural characterization and catalytic transfer hydrogenation of ruthenium(II) carbonyl complexes bearing N,N,O pincer type benzoylhydrazone ligands

Article abstract of DOI:10.1016/j.poly.2014.12.016

The convenient synthesis of four new octahedral ruthenium(II) carbonyl benzoylhydrazone complexes of the general molecular formula [Ru(L)Cl(CO)(PPh₃)] (where HL = substituted 2-acetylpyridine benzoylhydrazones; the H represents the dissociable

Full text of DOI:10.1016/j.poly.2014.12.016

Accepted Manuscript
Synthesis, structural characterization and catalytic transfer hydrogenation of
ruthenium(II) carbonyl complexes bearing N,N,O pincer type benzoylhydra-
zone ligands
Pandimuni Kalpaga Suganthy, Rupesh Narayana Prabhu, Venugopal
Shanmugham Sridevi
PII:
S0277-5387(14)00781-5
DOI:
http://dx.doi.org/10.1016/j.poly.2014.12.016
POLY 11104
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
11 October 2014
8 December 2014
Please cite this article as: P.K. Suganthy, R.N. Prabhu, V.S. Sridevi, Synthesis, structural characterization and
catalytic transfer hydrogenation of ruthenium(II) carbonyl complexes bearing N,N,O pincer type benzoylhydrazone
ligands, Polyhedron (2014), doi: http://dx.doi.org/10.1016/j.poly.2014.12.016
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Synthesis, structural characterization and catalytic transfer hydrogenation of
ruthenium(II) carbonyl complexes bearing N,N,O pincer type benzoylhydrazone ligands
a
b
Pandimuni Kalpaga Suganthy, Rupesh Narayana Prabhu, Venugopal Shanmugham
a,*
Sridevi
a
Department of Chemistry, Periyar E.V.R. College, Tiruchirappalli 620 023, Tamil Nadu,
India
b
School of Chemistry, University of Hyderabad, Hyderabad 500 046, Telangana, India
∗
Corresponding author. Tel.: +91–431–242–0079; fax: +91–431–2332010; e-mail:
sridevi.evr@gmail.com (V.S. Sridevi)
Abstract
The convenient synthesis of four new octahedral ruthenium(II) carbonyl
3
benzoylhydrazone complexes of the general molecular formula [Ru(L)Cl(CO)(PPh )] (where
HL = substituted 2−acetylpyridine benzoylhydrazones; the H represents the dissociable
proton) has been described. The characterization of the complexes was accomplished by
1
spectroscopic (FT-IR, H NMR, UV-Vis) techniques as well as by elemental (C,H,N)
analysis. A single crystal X-ray diffraction study of a representative complex,
[
3
Ru(L1)Cl(CO)(PPh )] (1), confirms a pincer-like N,N,O coordination mode of the
benzoylhydrazone ligand via the pyridine N, the azomethine N and the deprotonated amide O
atoms, with the formation of two five-membered fused chelate rings, and indicates a distorted
octahedral geometry around the ruthenium(II) centre. Further, the catalytic efficiency of
complex 1 has been investigated for the transfer hydrogenation of substituted acetophenones
to the corresponding secondary alcohols. The influence of base and catalyst loading in the
transfer hydrogenation reaction was also evaluated. The complexes were found to be efficient
catalysts in the presence of iso-propanol/KOH with conversions up to 99.2%.
Keywords: Benzoylhydrazone ligands, Pincer-type, Ru(II) carbonyl complexes, Crystal,
Catalysis, Transfer hydrogenation of ketones
1

1. Introduction
The interest in ruthenium complexes bearing Schiff bases remains unwavering due to
their multi-electron transfer properties, ability to have a wide range of oxidation states and
potential catalytic activity [1-6]. Aroylhydrazones are Schiff bases that have synthetic
flexibility, exhibit amide-imidol tautomerism, have a large number of potential donor atoms
and hence display versatility in metal coordination. They coordinate to a metal ion through
the imine nitrogen atom of the hydrazone moiety and the protonated/deprotonated amide
oxygen atom [3,4,7]. The binding capacity of the Schiff base is further increased by having
an additional donor atom (usually N or O) in a suitable position for chelation, normally
resulting in tricoordination [3,7-11]. The mode of coordination depends on the nature of the
central metal atom, the type of ligand as well as on the presence of other species capable of
competing for coordination sites.
Transfer hydrogenation is a convenient and versatile method for the reduction of
carbonyl compounds to their corresponding alcohols and is safe, highly selective,
environmentally friendly and requires inexpensive reagents or mild conditions for the
preparation of a broad scope of alcohols [12-14]. 2-Propanol is the most commonly used
solvent and hydrogen source since it is easy to handle, inexpensive, relatively non-toxic and
environmentally benign. Among the various metal complexes employed for transfer
hydrogenation reactions, ruthenium complexes have a long pedigree as catalysts for
homogeneous transfer hydrogenation reactions [15,16]. Ruthenium complexes containing
cyclometallated and N-heterocyclic carbene ligands [17,18], pincer ligands [19,20], Schiff
base ligands [3,21,22], tripodal ligands [23,24], arene ligands [25,26] and phosphine- or
amine-based ligands [27,28] have been extensively investigated and well established as
homogeneous catalysts for this transformation. Many reviews have appeared on the scope
and versatility of ruthenium catalyzed hydrogen transfer reactions, giving emphasis to the
design and nature of the coordinated ligands, reaction conditions (such as solvents, hydrogen
donors, bases, additives, temperature), kinetic studies and mechanistic aspects [13-16,28-34].
Though a few Ru(II) complexes with tridentate N,N,O-donor aroylhydrazones have been
structurally characterized [8-10], to the best of our knowledge there is no report on the
structural characterization of a carbonyl Ru(II) complex containing a tridentate N,N,O−donor
aroylhydrazone and its use as a catalyst for transfer hydrogenation reactions.
As a part of our ongoing research on the synthesis, characterization and catalytic
applications of transition metal complexes [35,36], the present report accounts for the
2

synthesis and characterization of four new octahedral Ru(II) carbonyl complexes with pincer-
like substituted 2-acetylpyridine benzoylhydrazones, with chloride and triphenylphosphine
incorporated as ancillary ligands. The structure of a representative complex has been probed
with the help of single crystal X-ray diffraction analysis and to the best of our knowledge this
is the first example of a structurally characterized Ru(II) carbonyl complex incorporating a
monoanionic tridentate N,N,O donor benzoylhydrazone ligand. Further, the catalytic
efficiency of the complex has been investigated for the transfer hydrogenation of
acetophenones containing different electronic effects to the corresponding secondary alcohols
under optimized conditions of base and catalyst loading.
2. Experimental section
2.1 Materials
RuCl ·3H O was purchased from Loba Chemie Pvt. Ltd and used as received.
3
2
Triphenylphosphine, 2-acetylpyridine, benzoylhydrazide derivatives and the ketones used for
the catalysis were obtained from Sigma-Aldrich and were used without further purification.
The solvents were freshly distilled prior to use following standard procedures [37]. All other
reagents used were purchased from commercially available sources and used as supplied. The
2-acetylpyridine benzoylhydrazones (HL1-HL4) were prepared by the condensation of 2-
acetylpyridine and 4-substituted benzoylhydrazide by following a procedure reported earlier
[
38]. The purity and identities of all the benzoylhydrazones were authenticated by FT-IR and
1
H NMR measurements. [RuHCl(CO)(PPh
39].
3 3
) ] was prepared by the reported literature method
[
2
.2 Physical measurements and instrumentation
The microanalyses (C,H,N) were recorded by an analytic function testing Vario EL III
CHN elemental analyzer. Infrared spectra were recorded in KBr pellets with a Perkin-Elmer
-1
1
5
97 spectrophotometer in the range 4000-400 cm . The H NMR spectra were recorded with
a Bruker 400 MHz spectrometer. Chemical shifts, given in ppm, are referenced to the
deuterated solvents. Electronic spectra of the complexes in chloroform solution were
recorded with a Cary 300 Bio UV-Vis Varian spectrophotometer in the range 800-230 nm
using cuvettes of 1 cm pathlength. Organic compounds in the catalysis were identified by
GC-MS using a Shimadzu Japan QP2010 S spectrometer using an RTX−5 MS detector
3

equipped with a capillary column (30 m x 0.25 mm x 0.25 µm) and high purity helium as the
carrier gas.
2
.3 Synthesis of [Ru(L1)Cl(CO)(PPh
3
)] (1)
[
RuHCl(CO)(PPh ] (95 mg, 0.1 mmol) and Et N (0.5 mL) were added to a benzene
3
)
3
3
solution (20 mL) of HL1 (24 mg, 0.1 mmol). The reaction mixture was refluxed for 6 h under
an atmosphere of nitrogen and the progress of the reaction was monitored using TLC. At the
end of the reaction, the solution was concentrated to ca. 3 mL and n-hexane was added,
whereby a solid separated out. This material was collected by filtration and transferred to a
silica gel column packed with n-hexane. The first moving yellow band eluted with ethyl
acetate/n-hexane (1:9) was discarded. The following red band containing complex 1 was
eluted using methanol/chloroform (1:4). The red solution thus obtained was evaporated to
dryness and the complex was collected as a dark red solid (Scheme 1). Yield: 52 mg (78%).
-1
Anal. Calc. for C H ClN O PRu (665.08 g mol ): C, 59.59; H, 4.09; N, 6.32. Found: C,
33
27
3
2
-1
5
9.65; H, 4.12; N, 6.37 %. Selected IR bands (KBr, cm ): 1595 s ν(C=N-N=C), 1241 m ν(C-O),
1
1
946 s ν(C≡O). H NMR (400 MHz, DMSO-d
6
, δ ppm): 8.2-7.2 (m, 24H, aromatic), 2.7 (s, 3H,
3
-1
-1
CH
3
). UV-Vis (CHCl
3
, λmax/nm; ε/dm mol cm ): 420 (4,070), 315 (8,180), 243 (15,010).
Insert Scheme 1 here
2
.4 Synthesis of [Ru(L2)Cl(CO)(PPh
This complex was synthesized by following the same procedure as described above
for 1, but using HL2 instead of HL1. Colour: Red. Yield: 51 mg (73%). Anal. Calc. for
3
)] (2)
-1
C
33
H
26Cl
2 3 2
N O PRu (699.53 g mol ): C, 56.66; H, 3.75; N, 6.01. Found: C, 56.75; H, 3.80; N,
-1
1
5
.95 %. Selected IR bands (KBr, cm ): 1591 s ν(C=N-N=C), 1259 s ν(C-O), 1942 s ν(C≡O). H
6 3
NMR (400 MHz, DMSO-d , δ ppm): 8.2-7.2 (m, 23H, aromatic), 2.7 (s, 3H, CH ). UV-Vis
3
-1
-1
(
CHCl
3
, λmax/nm; ε/dm mol cm ): 424 (4,010), 310 (10,230), 247 (14,890).
2
.5 Synthesis of [Ru(L3)Cl(CO)(PPh
The procedure used for the synthesis of 3 was identical to that described for 1, except
for the use of HL3 instead of HL1. Colour: Red. Yield: 54 mg (71%). Anal. Calc. for
3
)] (3)
-1
33 3 2
C H26BrClN O PRu (743.98 g mol ): C, 53.27; H, 3.52; N, 5.65. Found: C, 54.75; H, 3.80;
-1
1
N, 5.95 %. Selected IR bands (KBr, cm ): 1591 s ν(C=N-N=C), 1259 s ν(C-O), 1942 s ν(C≡O). H
4

6 3
NMR (400 MHz, DMSO-d , δ ppm): 8.3-7.2 (m, 23H, aromatic), 2.8 (s, 3H, CH ). UV-Vis
3
-1
-1
(
CHCl , λ /nm; ε/dm mol cm ): 429 (4,080), 319 (10,260), 242 (14,820).
3
max
2
.6 Synthesis of [Ru(L4)Cl(CO)(PPh
Complex 4 was synthesized in 70% yield by following the same procedure as
described above for 1, but using HL4 instead of HL1. Colour: Red. Anal. Calc. for
3
)] (4)
-1
C
34
H
29ClN
3 3
O PRu (695.11 g mol ): C, 58.75; H, 4.21; N, 6.05. Found: C, 58.68; H, 4.15; N,
-1
1
5
.93 %. Selected IR bands (KBr, cm ): 1594 s ν(C=N-N=C), 1245 s ν(C-O), 1944 s ν(C≡O). H
NMR (400 MHz, DMSO-d
H, CH ). UV-Vis (CHCl
14,680).
6
, δ ppm): 8.2-7.1 (m, 23H, aromatic), 3.8 (s, 3H, OCH
3
), 2.8 (s,
3
-1
-1
3
3
3
, λmax/nm; ε/dm mol cm ): 421 (4,110), 314 (9,290), 240
(
2.7 X-ray crystallography
Single crystals of [Ru(L1)Cl(CO)(PPh )]·H O (1·H O) suitable for X-ray diffraction
3
2
2
analysis were obtained by slow evaporation of an ethanol solution of the complex at room
temperature. The data collection was carried out using a Bruker AXS Kappa APEX II single
crystal X-ray diffractometer using monochromated Mo K
α
radiation (λ = 0.71073 Å). The
absorption corrections were performed by the multi-scan method using SADABS software
[
40]. Corrections were made for Lorentz and polarization effects. The structure was solved by
2
SIR92 [41] and refined by full-matrix least squares on F using SHELXL 97 [42]. All non-
hydrogen atoms were refined anisotropically and the hydrogen atoms in these structures were
located from the difference Fourier map and constrained to ideal positions in the refinement
procedure. The unit cell parameters were determined by the method of difference vectors
using reflections scanned from three different zones of the reciprocal lattice. The intensity
data were measured using ω and ϕ scans with a frame width of 0.5°. Frame integration and
data reduction were performed using the Bruker SAINT-Plus (Version 7.06a) software [43].
The crystal and structure refinement data of complex 1 are given in Table 1.
Insert Table 1 here
2.8 Typical procedure for transfer hydrogenation of ketones
The ketone (2.5 mmol), catalyst (5 µmol), base (20 µmol) and i-PrOH (5 mL) were
placed in an oven-dried round bottom flask at room temperature. The reaction mixture was
5

heated under reflux for the required reaction time under an atmosphere of nitrogen. The
reaction was then cooled to room temperature and the catalyst precipitated from the reaction
mixture by the addition of diethyl ether. The organic layer was neutralized with 1 N HCl,
2 4
washed with water and dried over anhydrous Na SO . The combined organic layer was
passed through a short path of silica gel and then subjected to GC−MS analysis. The
conversions obtained are related to the residual unreacted ketone and are averages of two runs
in the case of all catalytic reactions.
3. Results and Discussion
3.1 Synthesis and some properties
[
RuHCl(CO)(PPh ) ] was allowed to react with the substituted 2-acetylpyridine
3 3
benzoylhydrazones (HL) in an equimolar ratio in the presence of triethylamine as a base,
resulting in the formation of new neutral complexes of the general formula
[
Ru(L)Cl(CO)(PPh )] in reasonably good yields (Scheme 1). Structural studies of the
3
complexes showed that the ligands behave as mono anionic tridentate donors, replacing one
hydride and two PPh ligands from the ruthenium(II) precursor. Further, the oxidation state of
3
ruthenium remains unchanged during the formation of the complex. The analytical data of all
the ruthenium(II) complexes are in good agreement with the stoichiometries concluded from
their elemental analysis data. All the complexes are red in colour, found to be non-
hygroscopic and air stable in solution and in the solid state at room temperature. They are
highly soluble in solvents such as benzene, toluene, chloroform, dichloromethane,
acetonitrile, methanol, dimethylformamide, dimethyl sulfoxide etc., producing intense red
coloured solutions.
3
3
.2 Spectroscopic characteristics
.2.1 IR spectroscopy
The selected infrared absorption bands for all the complexes are given in the
experimental section. The IR spectra of the free Schiff bases (HL1-HL4) showed a medium
-1
to strong band in the regions 3176-3195 cm which is characteristic of the N–H functional
−1
group. The free ligands also display νC=N and νC=O absorptions in the region 1632-1650 cm .
The IR spectra of the complexes did not display any bands due to νN–H and νC=O stretching
vibrations, suggesting that the Schiff bases undergo tautomerization and subsequent
coordination of the imidolate oxygen to the ruthenium(II) ion. This is further supported by
6

-1
the appearance of new stretching frequencies in the regions 1241-1259 and 1591-1599 cm
in the complexes, which may be attributed to the C–O and C=N–N=C fragments respectively
of the coordinated ligand [3,4,8-10,44]. The typical strong band for the terminally
-1
coordinated carbonyl group in 1-4 is observed in the range 1940-1948 cm [3-5]. In addition,
-1
three strong bands displayed by all the complexes at ~520, ~695 and ~745 cm are attributed
to the metal coordinated PPh ligand [3,6,8-11,24,44].
3
3.2.2 NMR spectroscopy
Further, to confirm the coordination of the benzoylhydrazone ligands to the Ru(II)
1
ion, the H NMR spectra of the complexes were compared to the spectra of the free Schiff
bases. A sharp singlet that appeared for the –NH proton of free HL (δ 12.0-11.7 ppm) is
absent in all the complexes, supporting enolisation and coordination of the imidolate oxygen
atom to the ruthenium(II) ion [3,4]. The signal due to the azomethine methyl group appears
as a sharp singlet in the complexes (δ 2.9-2.8 ppm) and is slightly downfield in comparison
with those of free HL (δ 2.4-2.3 ppm), suggesting deshielding of these methyl protons due to
the coordination of the azomethine nitrogen atom to the metal centre. In addition, for
complex 4, the methoxy signal of the benzoylhydrazone ring resonates as a singlet at δ 3.8
ppm [3,4,8]. The remaining aromatic protons of the coordinated benzoylhydrazone ligand and
3
PPh appear as multiplets in the region δ 8.3-7.1 ppm.
3.2.3 Absorption spectroscopy
The absorption spectra of 1-4 were recorded in chloroform solution in the range 230-
00 nm at room temperature. The spectral profiles of the complexes are comparable, except
8
for some small shifts in the band positions. They display three intense absorptions in the
wavelength range 240-429 nm. The high intensity bands in the region 240-319 nm region
were assignable to ligand-centered (LC) transitions and have been designated as π-π* and n-
π* transitions. In the visible region, the major feature displayed by these complexes is a band
~
425 nm which was attributed to metal-to-ligand-charge-transfer (MLCT) transitions. Based
on the pattern of the electronic spectra of all the complexes, an octahedral environment
around the ruthenium(II) ion has been proposed, similar to that for other octahedral
ruthenium(II) complexes [3-5,8,9].
7

3.3. X-ray molecular structure of 1
Attempts to grow single crystals of all the complexes (1-4) were made to confirm the
coordination modes of the benzoylhydrazone ligands towards ruthenium(II) and the overall
coordination geometry in these complexes by X-ray crystallography. However, only X-ray
2
quality single crystals of complex 1 as a solvate (1·H O) could be obtained. The ORTEP
view of 1⋅H O is shown in Fig.1. The selected bond parameters involving the metal centre are
2
listed in Table 2. As seen from the ORTEP diagram, the benzoylhydrazone ligand
coordinates meridionally to the Ru(II) ion in a tridentate manner via the pyridine N,
azomethine N and deprotonated amide O atoms in the benzoylhydrazone fragment, forming
two five membered fused chelate rings. The carbonyl C atom occupies the fourth equatorial
coordination site and forms a CN O square plane (basal plane). One chloride ion and the
2
phosphine atom of a PPh
3
ligand occupy the two axial sites. The ruthenium ion is therefore
sitting in a CN OClP coordination environment and has a distorted octahedral geometry, as
2
reflected from the bond parameters around the Ru(II) ion. The N–N, N–C and C–O bond
–
lengths in the =N–N=C(O )– fragment of the coordinated ligand are consistent with the
enolate form of the amide functionality [3,4,9,10]. The phenyl ring of the coordinated ligand
is twisted from the basal plane, resulting in a dihedral angle of 21.25°. Around the Ru(II) ion,
the chelate bite angle in the five membered ring formed by the azomethine N and
deprotonated amide O atoms (76.19°) is slightly smaller than that in the five membered ring
formed by the azomethine N and the pyridine N atoms (78.77°), indicating better chelation in
the former ring [9,10]. The Ru–N(pyridine) bond length of 2.068(3) Å is slightly longer than
the Ru–N(azomethine) bond length (2.023(3) Å). Most likely this difference could be due to
the rigidity of the tridentate ligand and due to better π–back-bonding in the Ru–
N(azomethine) bond compared to that in the Ru–N(pyridine) bond [9,10]. The other bond
angles (°) around the Ru(II) ion are N3–Ru–O1 = 154.90(12), N1–Ru–C19 = 175.28(13) and
P–Ru–Cl = 173.35(3), whereas the bond lengths (Å) are 1.882(4) for Ru–C19, 2.105(2) for
Ru–O1, 2.4528(10) for Ru–Cl and 2.3046(10) for Ru–P. The bond lengths and bond angles
are in good agreement with reported data on other octahedral Ru(II) benzoylhydrazone
complexes [3,4,8,9]. Since the spectral properties of all the four complexes are similar,
analogous molecular structures are assumed for the other three complexes.
Insert Fig. 1 here
8

Insert Table 2 here
3.4 Catalytic transfer hydrogenation reaction
In a transfer hydrogenation reaction hydrogen is transferred from one organic
molecule to another, and it is of great importance as it has become an efficient tool in organic
synthesis. A wide range of ruthenium complexes have used as effective homogeneous
catalysts for transfer hydrogenation reactions and this encouraged us to carry out this type of
reaction with the new ruthenium(II) benzoylhydrazone complexes.
3.4.1 Effect of bases
One of the complexes, 1, was taken as a model catalyst and the conversion of
acetophenone (as the substrate) to 1-phenylethanol using iso-PrOH as the solvent in the
presence of different bases was initially screened (Table 3). The conversion was found to be
strongly dependent on the base employed. In presence of a strong base like KOH, the
2 3 3 3
conversion was high after 4 h. When weak bases such as Na CO , CH COONa or Et N were
used, the conversion of the product was reduced drastically, even with longer timescales.
Also, controlled experiments indicated that no conversion was observed in the absence of the
3 2
base or catalyst even after longer reaction times. In addition, when RuCl ·H O, the Ru(II)
precursor or benzoylhydrazone ligands alone or as a mixture were used, no conversion was
observed, ascertaining the necessity of the Ru(II) benzoylhydrazone complex for this
reaction. From the above results it is observed that a reasonably good conversion can be
achieved in the transfer hydrogenation of acetophenone by using i-PrOH/KOH at 82 °C.
Insert Table 3 here
3.4.2 Effect of catalyst loading
To ascertain the catalytic efficiency of the complex, different catalyst:substrate (C:S)
ratios were tested in the transfer hydrogenation reaction of acetophenone using complex 1 as
a model catalyst with i-PrOH/KOH and the results are summarized in Table 4. It is observed
that the formation of 1-phenylethanol is excellent when a C:S ratio of 1:250 is used. Also, the
reaction still proceeds smoothly but is accompanied by a drop in the conversion upon
changing the C:S ratio to 1:500, 1:750 or 1:1000. Since the conversions are good with
9

appreciable turnover numbers (TON) when the C:S ratio is 1:500, it was concluded that this
C:S ratio is the most suitable for the catalytic transfer hydrogenation reaction.
Insert Table 4 here
3.4.3 Transfer hydrogenation of ketones
In light of the results obtained, the transfer hydrogenation reactions of a series of
substituted acetophenones were carried out with complex 1 as the model catalyst, using i-
PrOH/KOH, and the results are summarized in Table 5. For a comparison of the results, all
the reactions were carried out under identical conditions. The complex catalyzes the transfer
hydrogenation of various acetophenones to their corresponding alcohols with good to
excellent conversions in all cases. It was observed that the conversion is dependent on the
substituent present on the acetophenone ring. The presence of an electron-withdrawing
substituent (nitro, cyano or chloro) on the aryl ring gave higher conversions (entries 1-3)
when compared to that of acetophenone (entry 4), whereas presence of an electron-donating
substituent (methyl, methoxy or hydroxy) on the ring (entries 5-7) decreased the conversion.
In terms of the TON/TOF, the catalytic efficiency of the new ruthenium(II) complexes is
higher than that of other ruthenium(II) complexes [23,24,26,27,45].
Insert Table 5 here
4
. Conclusions
The reactions of substituted 2-acetylpyridine benzoylhydrazone ligands with
RuHCl(CO)(PPh ] resulted in the formation of new octahedral ruthenium(II) carbonyl
benzoylhydrazone complexes of the general formula [Ru(L)Cl(CO)(PPh )] (where HL = the
[
3 3
)
3
substituted 2-acetylpyridine benzoylhydrazone ligand). The characterization of the complexes
1
was accomplished by analytical and spectral (FT-IR, H NMR, UV-Vis) methods. The
coordination of the benzoylhydrazone ligand via the pyridine N, the azomethine N and the
imidolate O atoms and the distorted octahedral geometry around the Ru(II) ion were
confirmed by single crystal X-ray diffraction studies of complex 1. In addition, complex 1
acts as an excellent catalyst for the transfer hydrogenation of a series of acetophenones to the
corresponding secondary alcohols using iso-propanol/KOH under optimized conditions, with
1
0

conversions of up to 99.2%. The turnover number and turnover frequency are up to 496 and
-1
1
24 h respectively.
Appendix A. Supplementary data
CCDC 891960 contains the supplementary crystallographic data for complex 1. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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1
3

Scheme and Figure Captions
Scheme 1. Synthesis of the ruthenium(II) benzoylhydrazone complexes
Fig. 1. The ORTEP diagram of the complex 1 with 30% probability elipsoids. The solvent
molecule is omitted for the sake of clarity.
1
4

PPh3
N
CO
N
[
RuHCl(CO)(PPh ) ]
3 3
Ru
Cl
C H , Et N
N
6
6
3
O
O
N
Reflux 6 h
H C
3
H C
3
N
N
H
R
HL1: R = H
HL2: R = Cl
HL3: R = Br
1
2
3
4
: R = H
: R = Cl
: R = Br
R
HL4: R = OCH3
: R = OCH3
Scheme 1
1
5

Fig. 1
1
6

Table 1. Crystal data and structure refinement for the complex 1⋅H O
2
Empirical formula
Formula weight
Colour
C H ClN O PRu
33 29 3 3
683.08
Red
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
293(2)
0.71073
Triclinic
P-1
8.9848(5)
b (Å)
c (Å)
10.7226(6)
17.4085(10)
96.253(5)
104.113(5)
108.399(5)
1511.56(15)
2
1.501
0.699
696
α (°)
β (°)
γ (°)
Volume (Å )
Z
Calculated density (Mg m )
Absorption coefficient (mm )
F(000)
3
–3
–1
Crystal size (mm)
Theta range (°)
Limiting indices
0.29 x 0.25 x 0.22
3.36 to 29.13
–9 ≤ h ≤ 12,
–
–
13 ≤ k ≤ 13,
19 ≤ l ≤ 23
Reflections collected/unique
Refinement method
6917/5053
Full–matrix least–squares on F
2
Data/restraints/parameters
Goodness–of–fit on F
6917/0/387
1.042
2
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff. peak and hole (e Å )
R
1
= 0.0506, wR
= 0.0799, wR
2
= 0.0991
= 0.1158
R
1
2
–
3
0.059 and 0.002
1
7

2
Table 2. Selected bond lengths (Å) and bond angles (°) for the complex 1⋅H O
Bond Length (Å)
2.3046(10)
2.105(2)
Bond Angle (°)
Ru–P
N3–Ru–O1
N1–Ru–C19
P–Ru–Cl
154.90(12)
175.28(13)
173.35(3)
78.77(13)
105.51(12)
99.32(14)
76.19(10)
87.88(9)
98.76(9)
86.01(9)
94.93(8)
88.71(7)
85.13(7)
89.61(11)
89.62(11)
125.9(3)
108.3(3)
121.9(3)
Ru–O1
Ru–N1
Ru–N3
2.023(3)
2.068(3)
N1–Ru–N3
O1–Ru–C19
N3–Ru–C19
N1–Ru–O1
N3–Ru–Cl
N3–Ru–P
Ru–C19
Ru–Cl
1.882(4)
2.4528(10)
1.146(4)
1.300(4)
1.382(4)
1.340(4)
1.297(4)
1.842(3)
1.827(3)
1.832(4)
O2–C19
N1–C25
N2–N1
N2–C27
O1–C27
P–C1
N1–Ru–Cl
N1–Ru–P
O1–Ru–Cl
O1–Ru–P
P–C7
P–C13
C19–Ru–Cl
C19–Ru–P
O1–C27–N2
C27–N2–N1
N2–N1–C25
ESD in parenthesis
1
8

a
Table 3. Effect of base in the transfer hydrogenation of acetophenone
O
Complex 1, Base
OH
o
i-PrOH, 82 C
b
Entry
Base
KOH
Na CO
Time (h) Conversion (%)
1
2
3
4
4
6
98.4
25
2
3
CH COONa
12
18
18
Trace
3
Et N
3
a
Reaction conditions: acetophenone (2.5 mmol), 1 (10 µmol), catalyst:base = 1:4 in i-
PrOH (5 mL) at 82 °C.
b
The conversion was determined by GC-MS analysis and is the average of two runs.
1
9

a
Table 4. Effect of catalyst loading
O
Complex 1
OH
i-PrOH, KOH
b
c
Entry
C:S ratio
1:250
1:500
1:750
1:1000
Conversion (%)
TON
246
464
525
481
1
2
3
4
98.4
92.8
70.0
48.1
a
Reaction conditions: acetophenone (2.5 mmol), 1 (10-2.5 µmol), catalyst:KOH = 1:4 in
i-PrOH (5 mL) at 82 °C for 4 h.
b
The conversion was determined by GC-MS analysis and is the average of two runs.
TON = Turnover number = ratio of moles of product formed to moles of catalyst used.
c
2
0

a
Table 5. Transfer hydrogenation of ketones using complex 4
O
OH
Complex 1
i-PrOH, KOH
o
R1
82 C, 4 h
R1
(
R = NO , CN, Cl, H, CH , OCH , OH)
1
2
3
3
b
c
d
Entry
No.
Ketones
Alcohols
Conversion
(%)
TON
TOF
O
OH
1
99.2
496
488
124
O N
2
O N
2
O
OH
2
97.6
122
NC
NC
O
O
OH
3
4
5
94.4
92.8
91.2
472
464
456
118
116
114
Cl
Cl
OH
H
H
O
OH
H C
3
H C
3
O
OH
OH
6
7
88.8
88.0
444
440
111
110
H CO
3
H CO
3
O
HO
HO
a
Reaction conditions: ketone (2.5 mmol), 1 (5 µmol), KOH (20 µmol) in i-PrOH (5 mL) at
2 °C for 4 h.
8
b
The conversion was determined by GC–MS analysis and is the average of two runs.
TON = Turnover number = ratio of moles of product formed to moles of catalyst used.
c
d
–1
TOF = Turnover frequency = TON h .
2
1

Graphical abstract – Pictogram
O
OH
i-PrOH, KOH
o
R
R
8
2 C, 4 h
2
3

Graphical abstract - Synopsis
A simple route for the synthesis of four new Ru(II) carbonyl benzoylhydrazone complexes is
described. The molecular structure was confirmed by a single crystal X-ray diffraction study. Further,
the catalytic efficiency of the complexes has been evaluated for the transfer hydrogenation of
substituted acetophenones to their corresponding secondary alcohols under optimized conditions.
2
4