Transfer hydrogenation reaction using novel ionic liquid based Rh(I) and Ir(III)-phosphinite complexes as catalyst

Article abstract of DOI:10.1016/j.jorganchem.2016.09.006

Hydrogen transfer reduction methods are attracting increasing interest from synthetic chemists in view of their operational simplicity. Thus, interaction of [Rh(μ-Cl)(cod)]₂and Ir(η⁵-C₅Me₅)(μ-Cl)Cl]₂with phosphinite ligand [(Ph₂PO)-C₇H₁₁N₂Cl]Cl, 1 gave new monodendate (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ?⁴-1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro ?⁵-pentamethylcyclopentadienyl iridium(III))], 3 complexes, which were characterized by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis.¹H-{³¹P} NMR,¹H-¹³C HETCOR or¹H-¹H COSY correlation experiments were used to confirm the spectral assignments. The novel catalysts were applied to transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with high activity (up to 99%) under mild conditions. Notably, (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ?⁴-1,5-cyclooctadiene rhodium(I))], 2 complex is much more active than the other analogous complex, 3 in the transfer hydrogenation. Furthermore, compound, 2 acts as excellent catalysts, giving the corresponding alcohols in 97–99% conversions in 5?min (TOF?≤?1176?h^?1).

Full text of DOI:10.1016/j.jorganchem.2016.09.006

Accepted Manuscript
Transfer hydrogenation reaction using novel ionic liquid based Rh(I) and Ir(III)-
phosphinite complexes as catalyst
Duygu Elma Karakaş, Feyyaz Durap, Akın Baysal, Yusuf Selim Ocak, Khadichakhan
Rafikova, Eda Çavuş Kaya, Alexey Zazybin, Hamdi Temel, Cezmi Kayan, Nermin
Meriç, Murat Aydemir
PII:
S0022-328X(16)30382-5
10.1016/j.jorganchem.2016.09.006
JOM 19618
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 20 June 2016
Revised Date: 1 September 2016
Accepted Date: 8 September 2016
Please cite this article as: D.E. Karakaş, F. Durap, A. Baysal, Y.S. Ocak, K. Rafikova, E.E. Kaya, A.
Zazybin, H. Temel, C. Kayan, N. Meriç, M. Aydemir, Transfer hydrogenation reaction using novel ionic
liquid based Rh(I) and Ir(III)-phosphinite complexes as catalyst, Journal of Organometallic Chemistry
(2016), doi: 10.1016/j.jorganchem.2016.09.006.
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ACCEPTED MANUSCRIPT
Transfer Hydrogenation Reaction Using Novel Ionic Liquid Based Rh(I) and Ir(III)-
Phosphinite Complexes as catalyst
Duygu ELMA KARAKAŞa, Feyyaz DURAPb,c, Akın BAYSALb, Yusuf Selim OCAKc, Khadichakhan RAFIKOVAd, Eda ÇAVUŞ KAYAc,
b,c
Alexey ZAZYBİNd, Hamdi TEMELc,e, Cezmi KAYANb, Nermin MERİÇb,* , Murat AYDEMIR
e
Science and Technology Application and Research Center, Siirt University, Siirt, 56100, Turkey
b
Department of Chemistry, Faculty of Science, University of Dicle, 21280 Diyarbakir, Turkey
c
Science and Technology Application and Research Center (DUBTAM) , Dicle University, Diyarbakir, 21280, Turkey
d
Department of Chemical Engineering, Kazakh-British Technical University, 050000 Almaty, Kazakhstan
e
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Dicle University, Diyarbakir, 21280, Turkey
For the first time, (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite
chloride)
(chloro ɳ4-1,5-cyclooctadiene rhodium(I))] and (1-chloro-3-(3-methylimidazolidin-1-
(dichloro ɳ5-pentamethylcyclopentadienyl
yl)propan-2-yl diphenylphosphinite chloride)
iridium(III))] complexes have been synthesized with high yields. The novel catalysts were applied to
transfer hydrogenation of various using 2-propanol as a hydrogen source. Notably, rhodium(I)
complex is much more active in the transfer hydrogenation, giving the corresponding alcohols up to
99% conversions in 5 min (TOF ≤ 1176 h-1).

ACCEPTED MANUSCRIPT

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Transfer Hydrogenation Reaction Using Novel Ionic Liquid Based Rh(I) and
Ir(III)-Phosphinite Complexes as catalyst
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Duygu ELMA KARAKAŞa, Feyyaz DURAPb,c, Akın BAYSALb, Yusuf Selim OCAKc, Khadichakhan RAFIKOVAd, Eda ÇAVUŞ KAYAc,
Alexey ZAZYBİNd, Hamdi TEMELc,e, Cezmi KAYANb, Nermin MERİÇb,*, Murat AYDEMIRb,c
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Science and Technology Application and Research Center, Siirt University, Siirt, 56100, Turkey
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Department of Chemistry, Faculty of Science, University of Dicle, 21280 Diyarbakir, Turkey
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Science and Technology Application and Research Center (DUBTAM) , Dicle University, Diyarbakir, 21280, Turkey
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Department of Chemical Engineering, Kazakh-British Technical University, 050000 Almaty, Kazakhstan
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Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Dicle University, Diyarbakir, 21280, Turkey
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ABSTRACT
Hydrogen transfer reduction methods are attracting increasing interest from synthetic chemists in view of their
operational simplicity. Thus, interaction of [Rh(ꢀ-Cl)(cod)]2 and Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 with phosphinite
ligand [(Ph2PO)-C7H11N2Cl]Cl, 1 gave new monodendate (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))],
2
and (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro ɳ5-pentamethylcyclopentadienyl
iridium(III))], 3 complexes, which were characterized by a combination of multinuclear NMR spectroscopy, IR
spectroscopy, and elemental analysis. 1H-{31P} NMR, 1H-13C HETCOR or 1H-1H COSY correlation experiments
were used to confirm the spectral assignments. The novel catalysts were applied to transfer hydrogenation of
acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding
alcohols could be obtained with high activity (up to 99 %) under mild conditions. Notably, (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))],
2 complex is much more active than the other analogous complex, 3 in the transfer hydrogenation. Furthermore,
compound, 2 acts as excellent catalysts, giving the corresponding alcohols in 97-99% conversions in 5 min (TOF
≤ 1176 h-1).
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Keywords: Ionic Compound, Phosphinite, Rhodium, Iridium, Transfer Hydrogenation, Catalysis
*
To whom correspondence should be addressed: Department of Chemistry, Dicle University, TR-21280 Diyarbakır, Turkey. Tel: +90 412
248 8550 (ext. 3028), Fax: +90 412 248 8300, e-mail: nmeric@dicle.edu.tr
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1. Introduction
Ketones are the most common unsaturated substrates used in organic synthesis. Extensive
efforts have been devoted to their reduction into secondary alcohols especially via
hydrogenation [1]. Catalytic transfer hydrogenation (TH) with the aid of a stable hydrogen
donor is a useful alternative process for catalytic hydrogenation by molecular hydrogen for
the reduction of ketones [2,3]. In transfer hydrogenation, organic molecules such as primary
and secondary alcohols [4] or formic acid and its salts [5,6] 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 risks and constrains associated with hydrogen gas as well
as the necessity for pressure vessels and other equipment.
Transition metal complexes are powerful catalysts for organic transformations and when
the suitable ligands are associated with the metal center, they can offer chemio, regio or stereo
selectivity under mild conditions [7]. However, the appropriate choice of metal precursors and
the reaction conditions are crucial for catalytic properties [8]. A number of transition metal
complexes are known to be catalyzing hydrogen transfer from an alcohol to a ketone
[9,10,11]. Over the last three decades, most effort on hydrogenation has been focused on the
use of ruthenium [12,13,14], rhodium and iridium catalysts [15,16,17]. Rhodium and iridium
complexes have been proven to lead to very efficient processes along with potential industrial
applications [18,19,20].
In the past few years room temperature ionic liquids, consisting of 1,3-dialkylimidazolium
cations and their counter ions, have attracted growing interest [21,22,23,24]. These ionic
liquids are potential replacements for organic solvents both on laboratory and industrial scales
due to their green characteristics such as thermal stability, lack of vapor pressure, non-
flammability, wide liquid range, wide range of solubility and miscibility [25]. They can be
readily recycled; have profound effect on the activity and selectivity in reactions and in some
cases, facilitate the isolation of products. Therefore, ionic liquids are considered viable
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substitute for volatile organic solvents [26]. An unusual feature of ionic liquids is the
tunability of their chemical and physical properties by selection of appropriate anion–cation
combinations [27]. Metal-containing ionic liquids are regarded as promising new materials
that combine the properties of ionic liquids with additional intrinsic magnetic, spectroscopic,
or catalytic properties, depending on the incorporated metal ion [28].
The chemistry of P-based ligands has also been intensively explored in recent years [29].
These compounds are extremely attractive as potential ligands since various structural
modifications are accessible via simple P-N, P-C and P-O bond formation [30]. Many
modified P-based ligands have important applications in organometallic chemistry and
catalysis, giving selective catalysts for hydroformylation, hydrosilylation and transfer
hydrogenation [31,32,33,34]. While much effort has been devoted to the synthesis of
aminophosphines and their metal complexes, similar studies on the analogous phosphinites
are less extensive [35,36], even though some of their complexes have proved to be efficient
catalysts [37,38]. In addition, well-known phosphine ligands have also found widespread
applications in transition metal catalyzed transformations [39,40]. Phosphinites provide
different chemical, electronic and structural properties compared to phosphines. The metal-
phosphorus bond is often stronger for phosphinites compared to the related phosphine due to
the presence of electron-withdrawing P-OR group. In addition, the empty σ*-orbital of the
phosphinite P(OR)R2 is stabilized, making the phosphinite a better acceptor [41]. Although
some phosphinite ligands and their derivatives have been employed successfully as ligands in
the transfer hydrogenation of ketones [42,43,44, references therein), a screening of catalytic
activities of ionic liquid based phosphinites in this reaction is not common in the literature. To
the best of our knowledge, there is no report on the utility of these complexes including
phosphinite ligands based on ionic liquid in Rh(II) and Ir(III) catalyzed transfer
hydrogenation reaction. Extending our study to develop useful and very magnificent catalysts,
in this paper, we report (i) the synthesis and full characterization of two rhodium and iridium
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complexes, and (ii) for the first time their subsequent application in transfer hydrogenation of
the ketones.
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2. Experimental
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2.1. Materials and methods
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Unless otherwise stated, all reactions were carried out under an atmosphere of argon using
conventional Schlenk glassware, solvents were dried using established procedures and
distilled under argon immediately prior to use. Analytical grade and deuterated solvents were
purchased from Merck. PPh2Cl, epichlorohydrin, 1-methylimidazole, [Rh(ꢀ-Cl)(cod)]2 and
Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 are purchased from Fluka and were used as received. In addition, 1-
chloro-3-(3-methylimidazolidin-1-yl)propan-2-ol chloride and [(Ph2PO)-C7H11N2Cl]Cl [45]
were prepared according to the literature procedures [46,47].The infrared spectra was
measured by a Perkin Elmer FT-IR Spectrum one and a Perkin Elmer Lambda 25,
respectively. The FTIR spectra were recorded using a universal ATR sampling accessory
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(4000–550 cm-1). H (400.1 MHz), 13C NMR (100.6 MHz) and 31P-{1H} NMR spectra (162.0
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MHz) were recorded spectra on a Bruker AV400 spectrometer, with δ referenced 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 a Gallenkamp Model apparatus with
open capillaries.
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2.2. Transfer Hydrogenation of Ketones
Typical procedure for the catalytic hydrogen transfer reaction: a solution of cataysts (1-
chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ4-
1,5-cyclooctadiene rhodium(I))], 2 or (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride)
(dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3
(0.005 mmol), NaOH (0.025 mmol) and the corresponding ketone (0.5 mmol) in degassed 2-
propanol (5 mL) were refluxed until the reactions were completed. Then, a sample of the
reaction mixture was taken off, diluted with acetone and analyzed immediately by GC. The
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conversions are related to the residual unreacted ketone. GC analyses were performed on a
Shimadzu 2010 Plus Gas Chromatograph equipped with capillary column (5% biphenyl, 95%
dimethylsiloxane) (30m x 0.32mm x 0.25ꢀm). The GC parameters for transfer hydrogenation
of ketones were as follows; initial temperature, 50 ºC; initial time, hold min 1 min; solvent
delay, 4.48 min; temperature ramp 15 ºC/min; final temperature, 270 ºC, hold min 5 min; final
time, 20.67 min; injector port temperature, 200 ºC; detector temperature, 200 ºC, injection
volume, 2.0 ꢀL.
2.3. Synthesis of Compounds
2.3.1. Synthesis and Characterization of (1-chloro-3-(3-methylimidazolidin-1-yl)propan-
2-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))], (2)
[Rh(ꢀ-Cl)(cod)]2 (0.062 g, 0.127 mmol) and [(Ph2PO)-C7H11N2Cl]Cl, 1 (0.100 g, 0.253
mmol) were dissolved in dry CH2Cl2 (25 ml) under argon atmosphere and stirred for 1 h at
room temperature. The volume was concentrated to ca. 1–2 mL under reduced pressure and
addition of petroleum ether (20 ml) gave the corresponding rhodium(I) complex as a yellow
microcrystalline solid. The product was collected by filtration and dried in vacuo. Yield:140
1
mg, 86.3 %; m.p.:146-147oC); H NMR (400.1 MHz, CDCl3, ppm): δ 10.37 (s, 1H, -
(CH3)NCHN-), 6.93-7.85 (m, 12H, P(C6H5)2+-NCHCHN-), 6.05 (br, 1H, -CHOP), 5.73 (br,
2H, CH of cod), 4.90 (br, 1H, NCH2, (a)), 4.70 (m, 1H, NCH2, (b)), 4.37 (br, 1H, -CH2Cl,
(a)), 4.12-4.15 (m, 1H, -CH2Cl, (b)), 3.95 (s, 3H, NCH3), 3.30 (br, 1H, CH of cod), 2.98 (br,
1H, CH of cod), 2.44 (br, 4H, CH2 of cod ), 2.12 (br, 2H, CH2 of cod ), 1.90 (br, 2H, CH2 of
cod); 13C NMR (100.6 MHz, CDCl3, ppm): δ 28.07, 28.80, 32.46, 33.69 (CH2 of cod), 36.73
(NCH3), 46.10 (-CH2Cl), 51.21 (NCH2), 77.40 (d, 2J = 22.1 Hz, (-CHOP), 71.70 (d, 1J = 13.1
1
Hz, CH of cod ), 111. 01 (d, J = 7.0 Hz, CH of cod), 122.46, 122.77 (-NCHCHN-), 127.96
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2
(d, J31P–13C = 11.1 Hz, m-P(C6H5)2), 131.50 (p-P(C6H5)2), 133.33 (d, J31P–13C = 15.1 Hz, o-
P(C6H5)2)), (not observed i-P(C6H5)2), 138.86 (-(CH3)NCHN-); assignment was based on the
1
1H-13C HETCOR, DEPT and H-1H COSY spectra; 31P-{1H} NMR (162.0 MHz, CDCl3,
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ppm): δ 124.22 (d, J(103Rh–31P) =175.8 Hz, OPPh2); IR: υ 3055 (aromatic C-H), 2942, 2879,
2830 (aliphatic C–H), 1433 (P-Ph), 1047 (O-P) cm-1; C27H33N2OCl3PRh (641.81 g/mol):
calcd. C 50.53, H 5.18, N 4.37; found C 50.18, H 4.91, N 4.08 %.
2.3.2. Synthesis and Characterization of (1-chloro-3-(3-methylimidazolidin-1-yl)propan-
2-yl diphenylphosphinite chloride)
iridium(III))], 3
(dichloro ɳ5-pentamethylcyclopentadienyl
[Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 (0.101 g, 0.127 mmol) and [(Ph2PO)-C7H11N2Cl]Cl, 1 (0.100 g, 0.253
mmol) were dissolved in dry CH2Cl2 (25 ml) under argon atmosphere and stirred for 1 h at
room temperature. The volume was concentrated to ca. 1–2 mL under reduced pressure and
addition of petroleum ether (20 ml) gave the corresponding iridium (III) complex as an orange
microcrystalline solid. The product was collected by filtration and dried in vacuo.
Yield:171mg, 85.2 %; m.p.:133-134oC); 1H NMR (400.1 MHz, CDCl3, ppm): δ 9.96 (s, 1H,
-(CH3)NCHN-), 7.53-7.87 (m, 12H, P(C6H5)2+-NCHCHN-), 5.34 (br, 1H, -CHOP), 4.67 (br,
1H, NCH2, (a)), 4.54 (m, 1H, NCH2, (b)), 4.09 (s, 3H, NCH3), 3.29 (br, 2H, -CH2Cl), 1.34 (s,
15H, CH3 of Cp∗(C5Me5); 13C NMR (100.6 MHz, CDCl3, ppm): δ 8.19 (C5Me5), 36.78
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(NCH3), 43.46 (-CH2Cl), 50.47 (NCH2), 74.52 (-CHOP), 94.27 (d, J = 12.0 Hz, C5Me5),,
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123.28, 123.40 (-NCHCHN-), 128.54 (d, J31P–13C = 9.5 Hz, m-P(C6H5)2), 131.99 (p-
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P(C6H5)2), 134.73 (d, J31P–13C = 12.1 Hz, o-P(C6H5)2)), (not observed i-P(C6H5)2), 138.22 (-
(CH3)NCHN-); assignment was based on the H-13C HETCOR, DEPT and H-1H COSY
spectra; 31P-{1H} NMR (162.0 MHz, CDCl3, ppm): δ 96.36 (s, OPPh2); IR: υ 3055 (aromatic
C-H), 2945, 2912 (aliphatic C–H), 1437 (P-Ph), 1042 (O-P) cm-1; C29H36N2OCl4PIr (793.62
g/mol): calcd. C 43.89, H 4.57, N 3.53; found C 43.75, H 4.45, N 3.44 %.
3. Results and Discussion
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3.1. Synthesis of the new complexes
First of all, the synthesis of 1-(3-chloro-2-(hydroxypropyl)-3-methyl-imidazolium chloride,
[C7H12N2OCl]Cl, was accomplished in one step from the reaction of 1-methylimidazole and
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epichlorohydrin in ethanol at room temperature, according to a reported procedure [48].
Furthermore, as shown in Scheme 1, [(Ph2PO)-C7H11N2Cl]Cl, 1 was prepared from the
commercially available starting material PPh2Cl and [C7H12N2OCl]Cl, in the presence of
triethylamine by hydrolysis [49,50]. In Scheme 1, phosphinite ligand [(Ph2PO)-
C7H11N2Cl]Cl, 1 was synthesized from the starting material PPh2Cl, in CH2Cl2 solution by
the hydrolysis method as in a previously described procedure [51]. The LiCl salt was
separated by filtration and the ligand was obtained by extracting the solvent in vacuo in good
yields. The progress of this reaction was conveniently followed by 31P-{1H} NMR
spectroscopy. The signals of the starting material PPh2Cl at δ 81.0 ppm disappeared and new
singlet appeared downfield due to the corresponding phosphinite ligand. The 31P-{1H} NMR
spectrum of 1 show no unexpected features. As expected, the 31P-{1H} NMR spectra of
phosphinite, [(Ph2PO)-C7H11N2Cl]Cl, 1 shows single resonances due to phosphinite at δ
118.46, (see Figure 1), [52,53,54,55,56] in line with the values previously observed for
1
similar compounds [57,58,59,60]. The appropriate assignment of the H chemical shifts was
derived from 2D HH-COSY spectra and that of the 13C chemical ones from DEPT and 2D
HMQC spectra. Furthermore, characteristic J(31P-13C) coupling constants of the carbons of the
phenyl ring are observed in the 13C NMR spectra (including i-, o-, m-, p- carbons of phenyl
rings, for details see experimental section), which are consistent with the literature values
[61]. The structures for these ionic based monodendate phosphinite ligands are consistent
with the data obtained from IR spectra and elemental analyses (for details see experimental
section).
Insert Scheme 1 Here
Firstly, we investigated simple coordination chemistry of [Rh(ꢀ-Cl)(cod)]2 with [(Ph2PO)-
C7H11N2Cl]Cl, 1 ligand. Reactions of [Rh(ꢀ-Cl)(cod)]2 with [(Ph2PO)-C7H11N2Cl]Cl, 1 in
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CH2Cl2 in a ratio of 1/2:1 at room temperature for 1 h gave micro-crystalline precipitate of
complex (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-cyclooctadiene rhodium(I))], 2. Complexation reactions were straightforward,
with coordination to rhodium being carried out at room temperature. This ligand was expected
to cleave the [Rh(ꢀ-Cl)(cod)]2 dimer to give the corresponding complex via monohapto
coordination of the phosphinite. Bridge cleavage of the dimer [Rh(ꢀ-Cl)(cod)]2 with
phosphinite gave the mononuclear complexes in high yield. This complex is highly soluble in
CH2Cl2 and slightly soluble in hexane and they can be crystallized from CH2Cl2/hexane
solution. The coordination of the ligand through the P donor was confirmed by the 31P-{1H}
NMR spectroscopy. The complex, 2 were isolated as indicated by doublets in the 31P-{1H}
NMR spectra at (δ) 124.22 (d, 1JRhP: 175.8 Hz), [62,63] (Figure 1), indicating that ionic based
1
phosphinite ligand acting as monodendate ligand. H and 13C NMR spectra of compound 2
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display all the signals of coordinated ligands. The H NMR spectrum 2 displays the
anticipated multiplets at δ 7.85-6.93 ppm for the protons of phenyls, broad singlets at δ 5.73,
3.30, 2.98, 2.44, 2.12 and 1.90 ppm for cod protons. In the 13C-{1H} NMR spectrum of
compound 2, J(31P-13C) coupling constants of the carbons of the phenyl rings were observed,
which are consistent with the literature values [64] (for details see experimental section). The
structural compositions of the complex 2 were further confirmed by IR spectroscopy and
microanalysis, and found to be in good agreement with the theoretical values.
Insert Figure 1 Here
Reactions of the ionic based monodendate phosphinite with metal [Ir(η5-C5Me5)(ꢀ-Cl)Cl]2
precursor is also depicted in Scheme 1. (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride)
(dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3
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was obtained by the reaction of ligand with [Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 in a molar ratio of 2/1 at
room temperature for 1 h. In the 31P-{1H} NMR spectrum, resonance at δ 96.36 ppm may be
attributed to complex of 3 (Figure 1). The 1H NMR spectra are consistent with the anticipated
1
structure. Analysis by H NMR reveals this compound to be diamagnetic, exhibiting signals
corresponding to the aromatic rings for 3 at 7.87-7.53 ppm. Another signal consisting of a
singlet centered at 1.34 ppm are due to the presence of the methyl protons in the Cp* group,
this information is complemented by the presence of signal at 9.96 ppm (s, 1H, -
(CH3)NCHN-). Furthermore, in the 13C NMR spectrum of the complex 3 displays singlet at δ
8.19 ppm attributable to methyl carbons of Cp* and doublet at δ 94.27 due to carbons of Cp*
ring. The structural composition of the complex 3 was further confirmed by IR spectroscopy
and microanalysis, and found to be in good agreement with the theoretical values (for details
see experimental section). Although, single crystals of both complexes were obtained by slow
diffusion of diethyl ether into a solution of the compound in dichloromethane over several
days, unfortunately we were not able to protect them from rapid decomposition in air.
3.2. Catalytic transfer hydrogenation of ketones
Because of the good catalytic performance and the higher structural permutability of
phosphinite based transition metal complexes in the reduction of ketones [65,66], recently, we
have reported that the novel half-sandwich complexes, based on ligands with P-O backbone
[67,68]. The observed activity of these complexes has encouraged us to investigate other
analogous ligands and other transition metal complexes of these ligands. In this context,
complexes (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-3-(3-methylimidazolidin-1-
yl)propan-2-yl diphenylphosphinite chloride)
(dichloro ɳ5-pentamethylcyclopentadienyl
iridium(III))], 3 were selected as catalysts, 2-propanol/NaOH as the reducing system and
acetophenone as a model substrate (Scheme 2), and the results are listed in Table 1. In a
preliminary study, when the reaction temperature was increased to 82 °C, smooth reduction of
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241
242
243
244
245
246
247
248
249
acetophenone into 1-phenylethanol occurred with conversion up to 99 % after 1/3 h for 2 and
1 h for 3 of reaction Table 1 (Entries 1 and 2). From the results, it is noteworthy that the
complexes 2 and 3 display the differences in reactivity, with a complex/NaOH ratio of 1/5.
Complex 2 is more active, quantitatively converting acetophenone with a high TOF of 297 h-
1. From these preliminary results, it can be concluded that (1-chloro-3-(3-methylimidazolidin-
1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))],
2
is
more
effective
than
(1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride)
complex.
(dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3
250
251
252
Insert Scheme 2 Here
253
254
255
256
257
258
259
260
261
262
263
264
265
At room temperature no appreciable formation of 1-phenylethanol was detected (Table 1,
entries 3 and 4). As can be inferred from the Table 1 (Entries 5 and 6) the catalysts as well as
the presence of NaOH are necessary to observe appreciable conversions. The base facilitates
the formation of alkoxide by abstracting proton of the alcohol and subsequently alkoxide
undergoes β-elimination to give metal hydride, which is an active species in this reaction.
This is the mechanism proposed by several workers on the studies of transition metal
catalyzed transfer hydrogenation reaction by metal hydride intermediates [69,70]. In addition,
the replacement of the reaction atmosphere from an inert gas to an ambient atmosphere had no
negative effect on the activity of the catalyst (Table 1, Entries 7 and 8). Therefore, the
hydrogenation reactions were performed in air. Although, performing the reaction with the
addition of water slowed the reaction, it had no influence on conversion of the product (Table
1, entries 9 and 10). As shown in Table 1 (Entries 11-14), increasing the substrate-to-catalyst
ratio do not lower the conversions of the product in most cases except the time lengthened.
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266
267
Remarkably, the transfer hydrogenation of acetophenone could be achieved up to 99 %
conversion even when the substrate-to-catalyst ratio reached to 1000:1.
268
269
270
271
Insert Table 1 Here
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
The catalytic activity of complexes (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-
3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(dichloro ɳ5-
pentamethylcyclopentadienyl iridium(III))], 3 were also extensively investigated with
acetophehone derivatives. The catalytic reduction of acetophenone derivatives was all tested
with the conditions optimized for acetophenone and the results are summarized in Table 2.
The fourth column in Table 2 illustrates conversions of the reduction performed in a 0.1 M of
2-propanol solution containing 2 or 3 and NaOH (Ketone:Cat.:NaOH = 100:1:5). As
expected, electronic properties (the nature and position) of the substituents on the phenyl ring
of the ketone caused the changes in the reduction rate. An ortho- or para- substituted
acetophenone with an electron-donor substituent, i.e., 2-methoxy or 4-methoxy is reduced
more slowly than acetophenone (Table 2, entry 5, 6, 11 and 12) [71]. In addition, the
introduction of electron withdrawing substituents, such as NO2, F, Cl and Br to the para-
position of the aryl ring of the ketone decreased the electron density of the C=O bond so that
the activity was improved giving rise to easier hydrogenation (Entries 1-4 and 7-10) [72,73].
287
288
289
290
Insert Table 2 Here
We also carried out further experiments to study the effect of bulkiness of the alky groups
on the catalytic activity and the results were given in Table 3 (entries 1-12). A variety of
simple aryl alkyl ketones were transformed to the corresponding secondary alcohols. It was
291
292
11

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293
294
295
296
found that the activity is highly dependent on the steric bulk of the alkyl group. The reactivity
gradually decreased by increasing the bulkiness of the alkyl groups [74]. That’s to say, when
the size of alkyl group is increased, the activity was remarkable decreased [75,76].
Insert Table 3 Here
297
298
299
Encouraged by the high catalytic activities obtained in these preliminary studies, we next
extended our investigations to include hydrogenation of various simple ketones (Table 4).
Investigation of catalytic activity of these (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(dichloro ɳ5-
pentamethylcyclopentadienyl iridium(III))], 3 has shown that they are efficient catalysts
affording almost quantitative transformation of the ketones in short times and 2 is more active
than 3 (Table 3). However, their efficiency was lower leading to longer conversion times. For
instance, hydrogenations of cyclohexanone could be achieved in 30 min and 2 h by (1-chloro-
3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-
cyclooctadiene rhodium(I))], 2 and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
(dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3,
diphenylphosphinite chloride)
respectively. In addition, conversion of methyl isobutyl ketone occurred in 1 h and 3 h by 2
and 3, respectively, while that of diethyl ketone occurred in 2 h and 4 h by 2 and 3,
respectively.
Insert Table 4 Here
315
316
317
318
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319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
4. Conclusions
In summary, for the first time (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))] and (1-chloro-3-
(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(dichloro ɳ5-
pentamethylcyclopentadienyl iridium(III))] complexes have been synthesized with high
yields. The complexes were characterized using multi nuclear NMR, IR and microanalysis.
The use of the new complexes for the reduction of the ketonic C=O bond of ketones under
hydrogen transfer conditions was also investigated. We found that these complexes are
efficient homogeneous catalytic systems that can be readily implemented and lead to
secondary alcohols from good to excellent conversions. Especially, (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-
cyclooctadiene rhodium(I))] was a more efficient catalyst in the transfer hydrogenation
reaction. The modular construction of these catalysts and their flexibility toward transfer
hydrogenation make these systems to pursue. Further studies of other transition metal
complexes of this ligand are in progress and will be reported in due course.
Acknowledgement
Partial support from Dicle University (Project number: FEN.15.021 and FEN.15.022), and
the analysis conducted by the Dicle University Science and Technology Research
Center (DUBTAM) is gratefully acknowledged. The authors also thank the Ministry of
Education and Science of the Republic of Kazakhstan for financial support (1318/GF4, 1752/
GF4).
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3
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2
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3
23.1 Hz, (-CHOP), 122.59, 122.90 (-NCHCHN-), 129.53 (d, J31P–13C = 10.1 Hz, m-P(C6H5)2),
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1
131.41 (p-P(C6H5)2), 135.26 (d, J31P–13C = 19.6, o-P(C6H5)2)), 140.65 (d, J31P–13C = 47.8 Hz, i-
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Captions
Scheme 1 Synthesis of the [(Ph2PO)-C7H11N2Cl]Cl, 1, (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl
diphenylphosphinite chloride)
(chloro ɳ4-1,5-cyclooctadiene rhodium(I))],
2 and (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro ɳ5-pentamethylcyclopentadienyl
iridium(III))], 3 (i) 1 equiv. Ph2PCl, 1 equiv. n-BuLi, CH2Cl2; (ii) 1/2 equiv. [Rh(ꢀ-Cl)(cod)]2, CH2Cl2; (iii) 1/2
equiv. [Ir(η5-C5Me5)(ꢀ-Cl)Cl]2, CH2Cl2.
Figure 1 The 31P-{1H} NMR spectra of ligand and its complexes, [(Ph2PO)-C7H11N2Cl]Cl, 1, (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-cyclooctadiene
rhodium(I))], and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
2
(dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3.
Scheme 2 Hydrogen transfer from 2-propanol to acetophenone.
20

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Table
1
Transfer hydrogenation of acetophenone with 2-propanol catalyzed by (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
(chloro ɳ4-1,5-cyclooctadiene
rhodium(I))], 2 or (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro
ɳ5-pentamethylcyclopentadienyl iridium(III))], 3.
Entry
Catalyst
S/C/NaOH
Time
Conversion(%)[i]
TOF(h-1)[k]
[a]
1
2
2
3
100:1:5
100:1:5
1/3 h
1 h
99
99
297
99
[a]
[b]
3
4
2
3
100:1:5
100:1:5
1 h
1 h
trace
trace
….
….
[b]
[c]
5
6
2
3
100:1
100:1
1 h
1 h
<5
<5
….
….
[c]
[d]
7
8
2
3
100:1:5
100:1:5
1/3 h
1 h
99
98
297
98
[d]
[e]
9
10
2
3
100:1:5
100:1:5
3/2 h
4 h
98
98
65
25
[e]
[f]
11
12
2
3
500:1:5
500:1:5
1 h
3 h
98
99
490
165
[f]
[g]
13
14
2
3
1000:1:5
1000:1:5
3 h
5 h
99
99
330
200
[g]
Reaction conditions:
[a]
[b]
Refluxing in 2-propanol; acetophenone/Cat./NaOH, 100:1:5;
At room temperature;
[c]
acetophenone/Cat./NaOH, 100:1:5;
base;
acetophenone/Cat./NaOH, 500:1:5;
Refluxing in 2-propanol; acetophenone/Cat., 100:1, in the absence of
[d]
[
e
]
[
f
]
Refluxing the reaction in air;
Added 0.1 mL of H2O;
Refluxing in 2-propanol;
[i]
[g]
Refluxing in 2-propanol; acetophenone/Cat/NaOH, 1000:1:5;
[k]
Determined by GC (three independent catalytic experiments);
Referred at the reaction time indicated in
column; TOF= (mol product/mol)Cat.)x h-1.

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Table 2 Transfer hydrogenation results for substituted acetophenones with the catalyst systems prepared from
[(Ph2PO)-C7H11N2Cl]Cl, 1 and [Rh(ꢀ-Cl)(cod)]2 or [Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 .[a]
OH
O
OH
O
Cat.
R
R
+
+
Entry
R
Time
Conversion(%)[b]
TOF(h-1)[c]
Cat: Rh(I) complex, 2
1
2
3
4
5
6
4-F
4-Cl
4-Br
4-NO2
2-MeO
4-MeO
5 min
98
99
96
97
95
92
1176
594
384
1164
95
10 min
15 min
5 min
1 h
2 h
46
Cat: Ir(III) complex, 3
7
8
9
10
11
12
4-F
4-Cl
4-Br
4-NO2
2-MeO
4-MeO
10 min
25 min
45 min
10 min
2 h
98
97
96
98
93
90
588
333
128
588
47
7/2 h
26
[a] Catalyst (0.005 mmol), substrate (0.5 mmol), 2-Propanol (5 mL), NaOH (0.025 mmol %), 82 °C, respectively,
[b]
the concentration of acetophenone derivatives is 0.1 M; Purity of compounds is checked by NMR and GC
[c]
(three independent catalytic experiments), yields are based on methyl aryl ketone;
Cat.) x h-1.
TOF = (mol product/mol

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Table 3 Transfer hydrogenation results for substituted alkyl phenyl ketones with the catalyst systems prepared
from [(Ph2PO)-C7H11N2Cl]Cl, 1 and [Rh(ꢀ-Cl)(cod)]2 and [Ir(η5-C5Me5)(ꢀ-Cl)Cl]2 .[a]
Entry
Cat.
Time
Substrate
Product
Conv. (%)[b]
TOF(h-1)[c]
O
OH
1
2
2
3
30 min
2 h
99
98
198
49
OH
O
3
4
2
3
1 h
3 h
98
98
98
33
O
O
OH
OH
5
6
2
3
2 h
5 h
97
99
49
20
7
8
2
3
4 h
9 h
98
99
25
11
[a] Catalyst (0.005 mmol), substrate (0.5 mmol), 2-propanol (5 mL), NaOH (0.025 mmol %), 82 °C, respectively,
the concentration of alkyl phenyl ketones is 0.1 M;
[b] Purity of compounds is checked by NMR and GC (three independent catalytic experiments), yields are based
on methyl aryl ketone;
[c] TOF = (mol product/mol Cat.) x h-1.

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Table 4 Transfer hydrogenation of various simple ketones with 2-propanol catalyzed by (1-chloro-3-(3-
methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))],
2 and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride)
pentamethylcyclopentadienyl iridium(III))], 3.[a]
(dichloro ɳ5-
Entry
Cat.
2
Substrate
Product
Time
30 min
2 h
Conv. (%)[b]
TOF(h-1)[c]
O
OH
1
2
98
99
196
50
3
O
OH
3
4
2
3
30 min
2 h
99
98
198
49
OH
O
5
6
2
3
1 h
3 h
98
99
98
33
O
OH
7
8
2
3
2 h
4 h
99
98
50
25
Reaction conditions:
[a] Refluxing in 2-propanol; acetophenone/Cat./NaOH, 100:1:5;
[b] Determined by GC (three independent catalytic experiments), purity of compounds is checked by NMR and
GC (three independent catalytic experiments), yields are based on methyl aryl ketone
[c] TOF = (mol product/mol Cat.) x h-1.
;

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