Comparative transfer hydrogenation performance of homogeneous and heterogeneous ruthenium (II) catalysts derived from a Schiff base ligand

Article abstract of DOI:10.1016/j.jorganchem.2016.12.027

A new Schiff base ligand (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol (L₁H) 1 was synthesized and grafted to solid support successfully. Mononuclear Ru(II) complex 2, its solid supported analogue 4 and heterogeneous complex 5 were synthesized with [RuCl₂(p-cymene)]₂and RuCl₂(PPh₃)dppb. According to the UV–visible, IR and NMR data, the Ru (II) complexes are formed by the coordination of both nitrogen atoms of the ligand. Molecular structures of the L₁H 1 was determined by single crystal X-ray diffraction study. The Ruthenium (II) complexes 2, 4 and 5 were used as catalysts for the transfer hydrogenation of various ketones in 2-propanol. Following the comparison of complexes 2, 4 and 5 between each other, it was observed that immobilized complexes have higher catalytic activity against the homogeneous structure. The results showed that the diphosphine incorporated complex 5 is more efficient than the other Ru (II) complexes.

Full text of DOI:10.1016/j.jorganchem.2016.12.027

Accepted Manuscript
Comparative transfer hydrogenation performance of homogeneous and
heterogeneous ruthenium (II) catalysts derived from a Schiff base ligand
Esin Ispir, Ertan Sahin, Mesut İkiz, Arif Aktas
PII:
S0022-328X(16)30588-5
10.1016/j.jorganchem.2016.12.027
JOM 19750
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 20 October 2016
Revised Date: 22 December 2016
Accepted Date: 22 December 2016
Please cite this article as: E. Ispir, E. Sahin, M. İkiz, A. Aktas, Comparative transfer hydrogenation
performance of homogeneous and heterogeneous ruthenium (II) catalysts derived from a Schiff base
ligand, Journal of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2016.12.027.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Comparative transfer hydrogenation performance of
homogeneous and heterogeneous ruthenium (II) catalysts derived
from a Schiff Base ligand
Esin Ispir*a, Ertan Sahinb, Mesut İkiza, Arif Aktasa
*E-mail: esinispir@ksu.edu.tr; Tel: 0090 3442801451
aDepartment of Chemistry, Kahramanmaraş Sütçü Imam University, Kahramanmaraş,
46050–9, Turkey
bDepartment of Chemistry, Faculty of Science, Atatürk University, 25240, Erzurum, Turkey
Abstract:
A new Schiff base ligand (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol (L1H)
1 was synthesized and grafted to solid support successfully. Mononuclear Ru(II) complex 2,
its solid supported analogue 4 and heterogeneous complex 5 were synthesized with [RuCl2(p-
cymene)]2 and RuCl2(PPh3)dppb.
According to the UV-visible, IR and NMR data, the Ru (II) complexes are formed by
the coordination of both nitrogen atoms of the ligand. Molecular structures of the L1H 1 was
determined by single crystal X-ray diffraction study. The Ruthenium (II) complexes 2, 4 and
5 were used as catalysts for the transfer hydrogenation of various ketones in 2-propanol.
Following the comparison of complexes 2, 4 and 5 between each other, it was observed that
immobilized complexes have higher catalytic activity against the homogeneous structure. The
results showed that the diphosphine incorporated complex 5 is more efficient than the other
Ru (II) complexes.
Keywrds: Ru(II) complex, Schiff base, transfer hydrogenation, heterogeneous catalyst,
Corresponding author:
E-mail: esinispir@ksu.edu.tr. (E. İspir).
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1. Introduction
The reduction of ketones and aldehydes to alcohols by a catalyst [1] and a stable
hydrogen donor [2, 3] is called catalytic transfer hydrogenation and is an significant synthetic
conversion both in academic and industrial applications [4]. The design the effective catalysts
for transfer hydrogenation reactions have received considerable attention in the 1960s with
Henbest, the first time, reported iridium catalyst gave moderate rates and turnovers for in
transfer hydrogenation reactions [5]. Following that, RuCl2(PPh3)3 was used as catalyst in the
presence of trace amount of a base in hydrogen transfer reaction [6]. In the light of these
studies, several various catalysts were designed with various metal ions such as Pd [7], Ru
[1], Rh [8], Ir [9] and Os [10]. Among the transition metal ions, ruthenium is used in a wide
range of applications such as transfer hydrogenation because of its characteristic features
especially different oxidation states [11]. In addition to this, ligand design is another
important factor and ligand structure has great electronic and steric and influence in the
activity of catalyst. Within the pool of ligands, N containing molecules are drawing more
attention in the area of organometallic catalysts due to its potential in the catalytic activity
[12, 13].
Immobilization of a homogeneous catalyst to a solid material up ligand design has
attracted much attention [14-16] due to their potential industrial applications. For this
purpose, silica gel is the most used support material due to its excellent properties such as
large pore size, low cost, high stability, thermal endurance and easy separation [17]. In
addition to that, silica gel has an inert structure and does not solubilize in solvents; as a
consequence, it can be used at harsh reaction medias such as high temperatures and pressures
[18, 19]. Generally, organic ligand or metal complex is linked to silica via organosiloxane that
was grafted on silica surface. Especially 3-cholorpropyl-triethoxysilane is used as linking
agent for OH bearing ligands to graft them on the silica surface [20]. The pore size of the
solid state support has been shown to affect the activity of some hydrogenation catalysts. On
occasion heterogeneous catalysts have shown higher catalytic activity towards to the
unimmobilized analogues [19].
In the literature, there are a great number of studies on ruthenium complexes as
catalysts. Studies on ruthenium based catalysts have still taken considerable attention [3, 21].
In this study, we report the synthesis and catalytic application of homogeneous and
heterogeneous ruthenium (II) complexes in transfer hydrogenation of various ketones. In
order to compare the catalytic activity of homogeneous and heterogeneous analogues, first of
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all we synthesized mononuclear Ru(II) complex 2 and its solid supported analogue 4 with
[RuCl2(p-cymene)]2. Silica supported Ru(II)-p-cymene complex 4 was found to be more
effective than its non-silica supported Ru(II)-p-cymene complex 2. Furthermore, diphosphine
ligand was incorporated into silica supported Ru(II) complex 4 to obtain complex 5. Catalytic
activity results show that diphosphine incorporated complex 5 is the most effective catalyst in
transfer hydrogenation reactions.
2. Experimental
2.1. Materials and methods
All chemicals were purchased from chemical suppliers and purified to match the
reported physical and spectroscopic data. The solvents were carefully dried using standard
methods. Kiesegel gel 60 (Merck 0.2–0.5 mm) was used as solid supporting material for
immobilization of the homogeneous catalysts.
Infrared spectra were obtained using KBr discs (4000-400 cm-1) on a Shimadzu 8300 FTIR
spectrophotometer. Elemental analyses (C, H, N) were performed using a Carlo Erba 1106
elemental analyzer. The electronic spectra in the 200–900 nm range were obtained using
DMF on a Hithachi U-3900 spectrophotometer. Melting points were determined with an
1
13
Electrothermal 9200 apparatus. H and C NMR spectra were recorded on a Varian AS-
400 MHz instrument. Magnetic measurements were carried out by the Gouy method using
Hg[Co(SCN)4] as calibrant. Metal contents in heterogeneous complexes 4 and 5 were
determined by Perkin Elmer Optima 2100 DV ICP-OES. The thermal behavior characteristic
of the immobilized compounds 2, 4, and 5 were collected on a SII thermal analysis system
under nitrogen atmosphere at a heating rate of 10 °C/min in the range 30–900 °C. The surface
morphology of the silica-supported ligand 3 and complexes 4, 5 were analyzed using Jeol
Neoscope Benchtop Scanning Electron Microscope and Zeiss Evo LS10 SEM attached with
Bruker Quantax EDS. The catalytic conversions were determined by GC analysis with
YL6500 Instrument.
2.2. X-ray Structure Determination
The data collections were performed on a Rigaku R-AXIS RAPID-S diffractometer with
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). Integration of the intensities,
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correction for Lorentz and polarization effects and cell refinement was performed using
Crystal Clear software [22].The structure was solved by direct methods and refined
against F2 by full-matrix least-squares calculations [23]. All non-H atoms have been refined
anisotropically, whereas the H atoms have been treated with a riding model. Crystal data
for1(L1H): C13H12N2O, crystal system, space group: monoclinic, P21/c; (no:14); unit cell
dimensions: a = 8.620 (4), b = 14.637(7), c = 9.120(4) Å, α= 90, β = 94.058(3), γ = 90º;
volume: 1147.80 (15) Å3; Z = 4; calculated density: 1.23 g/cm3; absorption coefficient: 0.080
mm-1; F(000): 448; θ-range for data collection 3.4–29.6º; refinement method: full matrix
least-square on F2; data/parameters:2988/147; goodness-of-fit on F2: 1.015; final R-indices [I
> 2σ(I)]: R1 = 0.043, wR2 = 0.111; largest diff. peak and hole: 0.170 and -0.133 e Å-3.
Crystallographic data were deposited in CSD with CCDC-1486601 registration number.
These data can be obtained free of charge from the Cambridge Crystallographic Data Centre
(CCDC) via www.ccdc.cam.ac.uk/data_request/cif and are available free of charge upon
request to CCDC, 12 Union Road, Cambridge, UK (fax: +441223 336033, e-mail:
deposit@ccdc.cam.ac.uk).
2.3. General procedure for the synthesis of ligand and complexes
2.3.1. Synthesis of (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 (L1H)
(E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 (L1H) (Fig. 1) was synthesized
as follow; 10 mmol (1.23 g) 4-(aminomethyl)phenol and 10 mmol (1.07 g) of picolinaldehyde
were condensed by refluxing in 70 ml of absolute ethanol for 3 h. The solution was left at
room temperature. (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 was obtained as
brown micro crystals; the micro crystals were filtered off, washed with 10 ml of absolute
1
ethanol and then recrystallized from DMF. Mp: 130oC. H NMR (400 MHz, CDCl3) δ 10.02
(s, 1H), 8.64 (d, J = 64.7 Hz, 1H), 8.35 (s, 1H), 7.99 (s, 1H), 7.69 (s, 1H), 7.28 (s, 1H), 6.98
13
(s, 2H), 6.60 (s, 2H), 4.71 (s, 2H). C NMR (101 MHz, CDCl3) δ 161.92, 155.84, 153.96,
148.89, 137.07, 129.84, 128.70, 125.00, 121.48, 115.58, 63.81. FT-IR (KBr, cm-1): 3027,
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2876-2789, 1639. Anal. Cald. For: [C13H12N2O], C: 73.56, H: 5.70, N: 13.20. Found: C:
73.29, H: 5.59, N: 13.01. UV-Vis. (λmax, nm) in MetOH: 255, 273, 280, 391.
2.3.2. Synthesis of immobilized ligand L2H 3
N
N
O
O
Silica
O Si
gel
O
SiCPTMS (5 g) which was prepared according to the reported method [24] was
immersed in 30 ml of dry toluene. (E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1
(L1H) (5 mmol, 1.06 g) was solved in 5 ml toluene was added to slurry. The suspension was
stirred for 24 h under reflux. The ligand grafted silica 3 was filtered and washed with ethanol
thoroughly to remove unreacted L1H. FT-IR (KBr, cm-1): 3030, 2879-2779, 1639, 1092, 910.
Solid UV-Vis. (λmax, nm): 257, 273, 281, 394.
2.3.3. Synthesis of homogeneous Ru complex 2
Dichloro(p-cymene)ruthenium(II) dimer (0.28 g,0.47 mmol) was added to the solution of (E)-
4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 (L1H) (0.2 g, 0.94 mmol) in methanol (10
ml) for 6 h under nitrogen atmosphere in a schlenk tube. The precipitate was filtered and
rinsed with petroleum ether (20 mL) and diethyl ether (20 mL). The complex 2 was obtained
as brown solid. The Ru(II) complex is soluble in solvents such as EtOH and MetOH. Mp:
1
190oC. H NMR (300 MHz, DMSO) δ 9.95 (s, 1H), 9.65 (t, J = 23.4 Hz, 1H), 8.31 (d, J =
38.2 Hz, 1H), 8.23 (s, 2H), 7.78 (s, 1H), 7.28 (d, J = 7.7 Hz, 2H), 6.91 (d, J = 7.8 Hz, 2H),
6.31 (d, J = 5.7 Hz, 1H), 6.08 (d, J = 5.4 Hz, 1H), 5.92 (dd, J = 12.0, 5.8 Hz, 1H), 5.65 (d, J =
16.1 Hz, 1H), 5.30 (d, J = 16.1 Hz, 1H), 2.70 – 2.36 (m, 2H), 2.14 (s, 3H), 0.96 (dd, J = 28.6,
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13
6.4 Hz, 6H). C NMR (75 MHz, DMSO) δ 165.99, 157.96, 155.90, 154.53, 139.60, 131.31,
129.14, 128.08, 124.24, 115.83, 104.18, 103.58, 87.64, 84.50, 84.09, 83.81, 68.30, 30.40,
22.00, 21.48, 18.36.FT-IR (KBr, cm-1): 3037, 2866-2785, 1630. Anal.Cald. For:
[C23H26Cl2N2ORu], C: 53.28, H: 5.05, N: 5.40. Found: C: 53.16, H: 5.09, N: 5.31. UV-Vis.
(λmax, nm) in DMF: 274, 328, 363, 396, 404. µeff, BM: Diamagnetic.
2.3.4. Synthesis of heterogeneous Ru complexes 4-5
Complexes 4 and 5 were synthesized with same synthetic procedure. The complexes
were prepared by stirring mixture of ligand-grafted silica 3 (1 g) and Ru(II) compounds
o
[[RuCl2(p-cymene)]2, RuCl2(PPh3)dppb] (0.5 mmol) in toluene (20 mL) at 60 C for 24 h.
After stirring, complexes were filtered, washed with diethyl ether and hexane till washings
were colorless. They were dried in air. The proposed structures of complexes are shown in
Fig.1.
Complex 4: FT-IR (KBr, cm-1): 3446, 2925, 2853, 1636, 1092, 802,476. Solid UV-Vis. (λmax
,
nm): 210, 286, 439.
ICP: Ru, 6788 mg/kg.
Complex 5: FT-IR (KBr, cm-1): 3444, 2925, 2857, 1632, 1090, 905, 486. Solid UV-Vis. (λmax
,
nm): 222, 338, 443.
ICP: Ru, 32660 mg/kg.
2.3.5. General procedure for the transfer hydrogenation of ketones
Under nitrogen atmosphere, aromatic ketone (1 mmol), KOH (1 mL, 0.1 M) and complex 2 (1
mg, 0.003 mmol) were dissolved in degassed 2-propanol (9.75 mL) with nitrogen and the
mixture was refluxed for 180 min. The same reaction conditions were used for complex 4 (10
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mg) and complex 5 (10 mg). They were added in degassed 2-propanol as solid. The
hydrogenation of the ketone was followed by GC using HP-5 column.
3. Result and Discussion
3.1. Synthesis, Characterization and Immobilization of L1H
(E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 (L1H) (Fig. 1) was synthesized from
the reaction of 4-(aminomethyl)phenol and picolinaldehyde. The ligand is soluble in common
organic solvents such as EtOH, MeOH, DMF, CH2Cl2 and stable at room temperature. The
structure of L1H was further characterized by UV-visible spectra, FTIR, elemental analyses,
NMR and X-Ray analyses.
The 1H NMR spectra of the L1H is shown in Fig. S6. L1H has one phenolic OH group
and its NMR signal was seen at 10.02 ppm as a singlet. Azomethine proton (CH=N) was
observed at 8.64 ppm [25]. The singlet at 4.71 ppm was assigned to the –CH2- protons. The
aromatic protons were observed in the region of 8.35–6.60 ppm. At the IR spectra of the L1H,
bands at 3037 cm–1 and 2866–2785 cm–1 that are assignable to ν(OH) and ν(Ar-CH) [26]. The
sharp band at 1639 cm-1 is due to the vibration of the azomethine group (-CH=N-). The
electronic absorption spectral data for L1H was obtained in DMF solutions at room
temperature.
Single crystals of L1H 1 were grown from slow evaporation of DMF solution of ligand
(Fig. 2.). Molecule crystallizes monoclinic P21/c space group. The N1-C6 distance of 1.261
(3) Å shows a typical C=N double bon character. The molecules display intermolecular O-
H…N (2.85 Å) and weak C-H…O (3.42 Å) hydrogen bonds, which stabilize the crystal
structure.
Supporting material (SiCPTMS) was prepared according to literature from treating
activated silica with 3-chloropropyltriethoxysilane. Then it was used to synthesize the
immobilized ligand 3. Immobilized ligand 3 was characterized with FTIR, Thermal and EDX
analyses. As distinct from LıH’s FTIR spectrum, immobilized ligand 3 shows characteristic
bands at 1092 and 910 cm–1 corresponding to the stretching vibrations of Si-O-Si bands,
respectively. In the thermal analyze spectrum the ~ 14% mass loss can be attributed to the
grafted L1H structure. In addition, N and C atoms seen at EDX analyze prove that L1H was
grafted to SiCPTMS successfully.
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3.2. Synthesis and Characterization of homogeneous 2 and heterogeneous catalysts 4, 5
The homogeneous catalyst complex 2 has been prepared by the condensation between
(E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1 (L1H) and [RuCl2(p-cymene)]2. The
heterogeneous catalysts complexes 4 and 5 were obtained by the reaction of immobilized
ligand 3 and ruthenium compounds [RuCl2(PPh3)dppb, [RuCl2(p-cymene)]2], respectively.
1
The homogeneous catalyst 2 was characterized by H, 13C NMR, IR and UV-Vis
analyses. In order to better determine the structure of the complex 2 1H and 13C NMR spectral
1
studies was performed (Fig.S7). The H NMR spectrum of complex 2 shows a singlet in the
1
9.95 ppm can be attributed to the proton of the –OH group [27]. The H NMR resonance of
azomethine proton (CH=N) was observed at 9.65 ppm. The singlet signal at 2.14 ppm was
attributed to the –CH3 protons. The IR spectra of the complexes were also studied and
compared with ligand spectrum in order to determine the linkage of Schiff base ligands to the
metal center in the complexes. Complex 2 and L1H have similar bands but especially the
azomethine ν(C=N) stretching shifted to lower frequency (1630), indicating the coordination
of azomethine nitrogen to metal ion. The electronic spectrum of complex 2 was recorded in
DMF in the range 800-200 nm. By comparing the spectra of the L1H and the complexes 2, the
absorption band above 404 nm was assigned to ligand to metal charge transfer transitions
[28].
The structures of complexes 4 and 5 were characterized with IR, solid UV-Vis, SEM,
EDX and thermal analyses. The IR spectra of heterogeneous complexes 4 and 5 were similar
to the homogeneous complex 2 spectrum. In addition to complex 2 spectrum, complexes 4
and 5 have characteristic vibrations at around 1092 and 802 cm–1 corresponding to the
stretching vibrations of Si-O-Si bands, respectively. Also the lowering in frequencies of the
C=N peaks at complexes 4 and 5 spectra is indicative of the formation of metal-ligand bonds.
Complexes 4 and 5 exhibit absorption bands above 439 and 443 nm and these were assigned
to L M charge transition.
The EDX analyses (Fig. 3.) prove that ligand 3 was grafted on solid surface and
heterogeneous complexes 4 and 5 were synthesized on the solid support with the expected
atom peaks.
Thermal behaviors of immobilized ligand 3 and heterogeneous complexes 4 and 5
have been studied using thermo gravimetric analysis (TG) and differential thermal analysis
(DTA) equipments. The thermal curves are given in Fig. 4. The main 14% weight loss in the
temperature range of 400-700oC for immobilized ligand 3 corresponds to the breakage of the
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Schiff base molecule grafted to the activated silica. For heterogeneous complexes main mass
loses are 22% and 68% respectively. Increased mass loses implying a higher amount of
ruthenium compounds [RuCl2(PPh3)dppb, [RuCl2(p-cymene)]2] are derived from the size of
these compounds. The difference at % residues and % mass losses for the compounds
suggested that heterogeneous Ru(II) complexes 4, 5 were synthesized successfully on the
solid support. For higher temperatures, the weight loss followed a slower rate, and the final
peaks in the region of 700-1100oC are due to partly thermal decompositions of the silica
structure and formation of metal oxides for complexes 4 and 5.
The SEM images if SiO2, SiCPTMS, complex 4 and complex 5 are shown in Fig.5.
Silica gel has a clean-cut surface. The morphological differences between activated silica gel
and the ligand in SEM images are very important evidence of the grafting of ligand onto the
silica gel granules. The grafting of the ligand onto the silica gel causes a roughening on the
activated silica gel surface. Images of the metal complexes show further roughening on the
surface, which may be due to interaction of the ruthenium metal atoms with the ligand to
associate the fixed geometry of the complexes [22]
3.2. Catalytic Transfer Hydrogenation of Ketones
To examine and compare the catalytic capability of ruthenium (II) complexes of L1H, a
homogeneous 2 and two heterogeneous catalysts 4 and 5 were prepared and then employed
in the transfer hydrogenation reactions using acetophenone as the model substrate with 2-
propanol as the hydrogen donor and solvent (Table 1). Initially the reaction conditions were
optimized and KOH was selected as a base due to the 67% conversion where the C:S ratio
was 3/1000. When the homogeneous complex 2 was immobilized, the complex 4 was
obtained and 10 mg amount of complex 4 was used in transfer hydrogenation reaction using
acetophenone with the same ruthenium amount in complex. Interestingly enough, 54%
conversion was screened in 10 minutes. This result showed that complex 2 gave much better
result if it was immobilized on a solid state such as silica gel. In addition to this, complex 5
was synthesized with RuCl2(PPh3)dppb to see the influence of P atom on the activity and the
conversion was found to be 96% in only 10 minutes.
With these results complex 5 was found to be best catalyst even with lower catalyst
loading. Concurrently, a transfer hydrogenation reaction of a series of acetophenone
derivatives with the 2-propanol in the presence of catalyst 5 and KOH was studied and the
results are summarized in Table 2. The reduced products were defined by GC-MS.
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Complex 5 display good catalytic activity in the transfer hydrogenation of all
acetophenone derivatives. All ketones are efficiently reduced through transfer hydrogenation
reaction except 2-bromo acetophenone. Complex 5 catalyzed the complete reduction of 3-
bromo acetophenone with 96% conversion in 30 minute which is the shortest time among the
other reductions. The same 99% conversion was occurred from the reduction of 2-methy
acetophenone and 2-methoxy acetophenone both in 60 and 180 minutes, respectively. 4%
conversion was obtained from the reduction of 2-bromo acetophenone although the reduction
experiment was repeated for this ketone with several times. As seem probable, transfer
hydrogenation of ketones to the corresponding alcohols, are affected by electron-withdrawing
and electron-donating substituents [29]. The probable cause for this situation is methyl and
methoxy groups on the aryl ring of ketones have a powerful tendency to donate electrons. In
comparison, the average conversions of ketones having electron-donating substituents methyl
and methoxy are higher than the average conversion of ketones having electron- withdrawing
substituents. When the conversions of ketones including electron-donating substituents such
as methyl and methoxy compared between each other, ortho substituated ketones gave the
highest conversion (99%). In addition this, as seen from Table 2, substitute groups a para
position gave lower conversions 97% and 91%, respectively, than ortho and meta positions. It
is worth noting that the affect of electron-withdrawing substituent was analyzed, as expected,
para position substituent on the aryl ring of ketone gave higher conversion 97% than ortho
4% and meta 96% substitute ketones.
Conclusions
In summary, we have presented a new Schiff base ligand L1H 1 which was
characterized by single crystal X-ray analysis and its immobilized form L2H 3. Afterwards
one homogeneous complex 2 with ligand L1H 1 and two heterogeneous complexes 4 and 5
with ligand L2H 3 were prepared. [RuCl2(p-cymene)]2] was used in the preparation of
ruthenium complexes 2 and 4. Besides that [RuCl2(PPh3)dppb] was used to obtain the
complex 5 to show the impact of P atom on transfer hydrogenation reactions.
The homogeneous and heterogeneous complexes were tested as catalyst in transfer
hydrogenation reactions of several ketones. From the comparison of homogeneous 2 and
heterogeneous complexes 4, it was seen that heterogeneous complex 4 was more active in
transfer hydrogenation reactions. Same study was made with heterogeneous complex 5 and
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the data have demonstrated that heterogeneous complex 5 shows higher catalytic activity than
complexes 2 and 4. Our experiences in these fields are ongoing and will be reported in the
course of time.
Acknowledgements
This work was financially supported by the Unit of Coordination of Scientific
Research Projects, Kahramanmaraş Sütçü Imam University, Kahramanmaraş, Turkey (Project
no: 2013/5-14M).
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Table 1.
Optimization studies for complexes in TH reaction of acetophenone
Entry
1*
Catalyst
C/S
Base
Time (min) Conversion ( %a)
2
2
4
5
3/1000
3/1000
3/1000
3/1000
NaOH
KOH
KOH
KOH
60
60
10
10
48
67
54
96
2*
3
4
a
Conditions:* 0.003 mmol 2, 1 mmol acetophenone, 1 mL 0.1 M base, reflux, C/S: catalyst (Ru)/substrate, determined by
GC,

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Table 2.
Catalytic transfer hydrogenation of ketones with ruthenium complex 5
Ketone
(1 mmol)
Alcohol
Time
(min.)
Conversion
(%)
Entry
1
C/S
10
60
96
99
3/1000
3/1000
O
2
3
Me
120
98
3/1000
4
5
180
60
97
4
3/1000
3/1000
3/1000
3/1000
3/1000
3/1000
3/1000
O
OH
Br
Br
6
30
96
97
99
98
91
O
7
120
180
120
180
Br
8
9
10

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NH2
+
O
+
N
N
ii
i
Cl-
N
N
N
HO
HO
Ru
HO
1
Cl
L1H
Cl
2
O
iii
Silica
gel
O Si
O
SiCPTMS
N
N
O
3
O
Silica
gel
O Si
O
iv
v
+
N
N
N
Cl
Cl-
Ru
Cl
O
N
Ru
O
O
Ph2P
Silica
gel
O
Cl
O Si
Silica
gel
O Si
PPh2
O
O
5
4
(i) Ethanol, rt, 3 h; (ii) [RuCl2(p-cymene)]2, MetOH, reflux, 6 h; (iii) SG-Cl, Toluene,
reflux, 24 h; (v, iv) [RuCl2(p-cymene)]2, RuCl2(PPh3)dppb, Toluene, 60°C, 24 h
Fig.1. General synthesis of L1H ligand and its homogeneous and heterogeneous Ru(II)
complexes.

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Fig.2. Molecular structure of(E)-4-(((pyridin-2-ylmethylene)amino)methyl)phenol 1(L1H).
Thermal ellipsoids are drawn at the 40% probability level.

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SiCPTMS
Complex 4
Complex 5
Fig.3. EDX images of complex 4 and complex 5

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(a)
(b)
(c)
Fig.4. T.G. and D.T.A. of immobilized ligand 3 (a), Complex 4 (b) and Complex 5 (c)

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(a)
(b)
(c)
(d)
Fig.5. SEM images of support material (a), SiCPTMS (b), Complex 4 (c), Complex 5 (d)

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►
A new Schiff base ligand L1H 1 was synthesized and grafted to solid support successfully.
And single-crystal X-ray analyse was performed for L1H 1.
► Mononuclear Ru(II) complex 2, its solid supported analogue 4 and heterogeneous complex
5 were synthesized with [RuCl2(p-cymene)]2 and RuCl2(PPh3)dppb.
►
The synthesized metal complexes were performed as catalysts for the transfer
hydrogenation of various ketones in 2-propanol.
► Following the comparison of complexes, it was observed that immobilized complexes have
higher catalytic activity against the homogeneous structure.
►
Catalytic activity results show that diphosphine incorporated complex 5 is the most effective
catalyst in transfer hydrogenation reactions.