Readily available ferrocenyl-phosphinite ligands for Ru(II)-catalyzed enantioselective transfer hydrogenation of ketones and fabrication of hybrid heterojunctions

Article abstract of DOI:10.1016/j.ica.2013.09.037

A variety of phosphinite based on ferrocenyl moiety possessing central chirality have been screened as ligands for ruthenium(II)-catalyzed transfer hydrogenation of acetophenone derivatives using iso-PrOH as the hydrogen source to afford the corresponding product, (R) or (S)-1-phenylethanol derivatives with high conversions and good enantioselectivities. These complexes were also employed in the asymmetric reduction of different prochiral ketones (up to 85% ee). A comparison of the catalytic properties of amino alcohols and other analogs based on ferrocenyl backbone is also discussed briefly. The structures of these ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. Furthermore, organic-inorganic hybrid heterojunctions were also fabricated by forming thin films of ruthenium(II) complexes on n-Si and evaporation of Au as front contact. Current-voltage (I-V) characteristics of the structures showed excellent rectification properties. Electrical parameters including ideality factor, barrier height and series resistance were determined using I-V and capacitance-voltage (C-V) data. Finally, photoelectrical properties of the structures were examined by means of a solar simulator with AM1.5 global filter.

Full text of DOI:10.1016/j.ica.2013.09.037

Inorganica Chimica Acta 409 (2014) 244–253
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Readily available ferrocenyl-phosphinite ligands for Ru(II)-catalyzed
enantioselective transfer hydrogenation of ketones and fabrication
of hybrid heterojunctions
a
a,
⇑
b
a
a
a
Bünyamin Ak , Murat Aydemir , Yusuf Selim Ocak , Feyyaz Durap , Cezmi Kayan , Akin Baysal ,
Hamdi Temel
a
c
Department of Chemistry, Faculty of Science, University of Dicle, 21280 Diyarbakir, Turkey
Department of Science, Faculty of Education, University of Dicle, 21280 Diyarbakir, Turkey
Department of Chemistry, Faculty of Education, University of Dicle, 21280 Diyarbakir, Turkey
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 May 2013
Received in revised form 2 September 2013
Accepted 22 September 2013
Available online 29 September 2013
A variety of phosphinite based on ferrocenyl moiety possessing central chirality have been screened as
ligands for ruthenium(II)-catalyzed transfer hydrogenation of acetophenone derivatives using iso-PrOH
as the hydrogen source to afford the corresponding product, (R) or (S)-1-phenylethanol derivatives with
high conversions and good enantioselectivities. These complexes were also employed in the asymmetric
reduction of different prochiral ketones (up to 85% ee). A comparison of the catalytic properties of amino
alcohols and other analogs based on ferrocenyl backbone is also discussed briefly. The structures of these
ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR
spectroscopy, IR spectroscopy and elemental analysis. Furthermore, organic–inorganic hybrid hetero-
junctions were also fabricated by forming thin films of ruthenium(II) complexes on n-Si and evaporation
of Au as front contact. Current–voltage (I–V) characteristics of the structures showed excellent rectifica-
tion properties. Electrical parameters including ideality factor, barrier height and series resistance were
determined using I–V and capacitance–voltage (C–V) data. Finally, photoelectrical properties of the struc-
tures were examined by means of a solar simulator with AM1.5 global filter.
Keywords:
Homogeneous catalysis
Enantioselective transfer hydrogenation
Ferrocenyl-phosphinite
Heterojunction
Electrical properties
Photovoltaic application
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
Homogeneous asymmetric catalysis with transition metal com-
Furthermore, the unique structure of ferrocenes allows one to de-
sign a variety of chiral ferrocenyl phosphine ligands, which are
useful tools in metal-catalyzed asymmetric reactions [9]. These li-
gands are very efficient catalysts for a wide range of reactions, such
as hydrogenation [10], hydrosilylaton [11], allylic alkylation [12],
Grignard cross-coupling reactions [13] and cycpropanation [14].
Ferrocenyl phosphine ligands have found widespread applications
in transition metal catalyzed asymmetric transformations [15–18]
on comparison with the phosphinite derivatives. However, com-
pared to phosphines, phosphinites provide different chemical, elec-
tronic and structural properties. For example, the metal-
phosphorus bond is often stronger for phosphinites compared to
the related phosphine due to the presence of electron-withdrawing
P-OR group [19].
There is a great interest in the usage of organic semiconductors
in the fabrication of electrical and photoelectrical devices as active
components because they can attain new roles not realized by con-
ventional inorganic semiconductors [20,21]. Fabrication methods
and alternative materials have been examined with the purpose
of producing high performance electrical devices and low cost
and highly efficient solar cells [22,23]. Compared with organic
dyes, metal complex dyes have higher thermal and chemical
plexes is an active area of research [1] and great interest is directed
toward the design and development of efficient ligands [2]. An
increasing number of chiral compounds and enantiomerically pure
drugs are prepared through transition metal-catalyzed asymmetric
reactions [3]. Since the reactivity and stereoselectivity of an asym-
metric transformation are highly dependent on the structure of the
chiral ligand coordinated to the transition metal, the design and
synthesis of efficient chiral ligands are important in this area and
have attracted a great deal of attention from both academia and
industry [4–7].
The ferrocene moiety has been extensively explored as a back-
bone of chiral phosphine ligands due to its easy modifiability and
highly electron donating property [8] In addition, the ferrocene de-
rived ligands generally crystallize readily and they are relatively air
stable compared to their nonferrocenyl analogous. These features
are beneficial for purification and usage of the ligands.
⇑
Corresponding author. Tel.: +90 412 248 8550; fax: +90 412 248 8300.
E-mail address: aydemir@dicle.edu.tr (M. Aydemir).
0
020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.09.037

B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
245
stability [24]. Many studies have been performed to obtain suitable
compounds for the usage of electrical and optical devices and
determine electrical and photovoltaic parameters of the devices
The wafer cut into several parts. Before the formation of organic
interlayer on the substrates, the native oxide on front of n-Si sur-
face was removed by solution of H
2
O/HF (10:1) and dried under
[
25–31]. Therefore both the synthesis and the usage of these com-
N
2
atmosphere. The thin films of the 13–16 were formed on n-Si
pounds have great importance.
substrates using a SCS G3 spin coater. The front metal dots were
formed by evaporation of Au dots with diameter of 1.5 mm by
the help of shadow mask in a vacuum coating unit at about
2 ꢀ 10 Torr. The cross section of the devices is presented in
Fig. 1. The electrical properties of the devices were determined
from their current–voltage (I–V) and capacitance–voltage (C–V)
measurements by Keithley 2400 sourcemeter and Agilent 4294A
Impedance Analyzer, respectively. The photovoltaic measurements
were carried out under a solar simulator with AM1.5 global filter.
Considering the advantage of phosphinites, herein, we describe
the synthesis of novel ferrocenyl-phosphinite ligands. As far as we
know, there is no report on asymmetric transfer hydrogenation of
ketones by using chiral ferrocenyl-phosphinites as ligands. This
study was started with synthesis and full characterization of amino
alcohols, ferrocenyl phosphinite ligands and neutral ruthenium(II)-
ꢁ6
(p-cymene) complexes. Organic–inorganic heterojunctions were
also obtained using ruthenium compounds and their electrical
and photoelectrical properties were determined by their current–
voltage (I–V) and capacitance–voltage (C–V) measurements. It
was seen that these devices behave as good rectifying diodes and
they can be used in the electrical and photovoltaic applications.
2.3. General procedure for the transfer hydrogenation of ketones
Typical procedure for the catalytic hydrogen-transfer reaction:
a solution of the ruthenium complexes 13–16 (0.005 mmol), NaOH
(0.025 mmol) and the corresponding ketone (0.5 mmol) in de-
gassed iso-PrOH (5 mL) was refluxed until the reaction completed.
Then, a sample of the reaction mixture is taken off, diluted with
acetone and analyzed immediately by GC, conversions obtained
are related to the residual unreacted ketone.
2
. Experimental
2.1. Materials and methods
Unless otherwise mentioned, all reactions were carried out un-
der an atmosphere of argon using conventional Schlenk glass-ware,
solvents were dried using established procedures and distilled un-
der argon immediately prior to use. Analytical grade and deuter-
ated solvents were purchased from Merck. The starting materials
2.4. Procedures for the preparation of the amino alcohols, chiral
phosphinite ligands and their ruthenium(II) complexes
D
-,
purchased from Fluka and used as received. [Ru(
Cl)Cl] was prepared according to literature procedures [32].
2 3
L-valine, L-leucine, L-isoleucine, PPh Cl, ferrocene and Et N were
6
g
-p-cymene)(
l
H
-
2.4.1. General procedure for synthesis of ferrocene based amino
alcohols (5–8)
1
2
1
3
31
1
(
at 400.1 MHz),
C
(at 100.6 MHz) and
P–{ H} NMR (at
Ferrocenecarboxaldehyde (856 mg, 4.0 mmol) and amino alco-
hol (4.2 mmol) were dissolved in previously dried chloroform
(40 mL; dried over K CO ) and the resulting solution was heated
2 3
at reflux under argon for 90 min. Then, the solution was cooled
to room temperature, the solvent was removed under reduced
pressure and the red–brown residue immediately re-dissolved in
dry methanol (40 mL; distilled from a MeONa solution). The meth-
anolic solution was cooled in an ice bath and treated slowly with
1
62.0 MHz) spectra were recorded on a Bruker AV400 spectrome-
1
ter, with TMS (tetramethylsilane) as an internal reference for
H
1
3
31
NMR and C NMR or 85% H
3
PO
4
as external reference for P–
1
{
H} NMR. The IR spectra were recorded on a Mattson 1000 ATI
UNICAM FT-IR spectrometer as KBr pellets. Specific rotations were
taken on a Perkin–Elmer 341 model polarimeter. Elemental analy-
sis was carried out on a Fisons EA 1108 CHNS-O instrument. Melt-
ing points were recorded by a Gallenkamp Model apparatus with
open capillaries. GC analyses were performed on a Shimadzu GC
4
solid NaBH (756 mg, 20 mmol over 30 min). After adding all the
NaBH , the mixture was stirred at 0 °C for 1 h and at room temper-
4
2
010 Plus Gas Chromatograph equipped with cyclodex B (Agilent)
capillary column (30 m ꢀ 0.32 mm I.D. ꢀ 0.25 m film thickness).
Racemic samples of alcohols were obtained by reduction of the
corresponding ketones with NaBH and used as the authentic sam-
ature for further 90 min. Then, the cooled mixture was quenched
with an aqueous solution of NaOH (10%, 40 mL) and extracted with
l
CH
2
Cl
2
(2 ꢀ 40 mL). The combined organic layer was washed with
brine (2 ꢀ 40 mL), dried over anhydrous MgSO
4
, and evaporated,
4
ples for ee determination. The GC parameters for asymmetric
transfer hydrogenation of ketones were as follows; initial temper-
ature, 50 °C; initial time 1.1 min; solvent delay, 4.48 min; temper-
ature ramp 1.3 °C/min; final temperature, 150 °C; initial time
leaving the crude product as a yellow–brown solid. Subsequent
purification by column chromatography (silica gel, dichlorometh-
ane–methanol 10:1) led to the development of two bands: the first
(minor) one containing mostly ferrocenyl methanol, followed by
the major band of the amino alcohol. Careful evaporation of the
2
2
.2 min; temperature ramp 2.15 °C/min; final temperature,
50 °C; initial time 3.3 min; final time, 44.33 min; injector port
temperature, 200 °C; detector temperature, 200 °C, injection vol-
ume, 2.0 L.
l
2.2. General procedure for fabrication and characterization of hybrid
heterojunctions
An n-Si wafer with (100) orientation and 0.1–1
X cm resistivity
were used for the fabrication of heterojunctions. To degrease the
wafer, it was boiled in trichloroethylene and rinsed in acetone
and isopropanol for ultrasonic vibration. The wafer was etched
by a solution of H
oxide layers on the surface. Preceding each step, the wafer was
rinsed in 18 M deionized water. The ohmic contact was made
by evaporation of Au on the unpolished side of the wafer followed
by a temperature treatment at 420 °C for 3 min in a N atmosphere.
2
O/HF (10:1) for 30 s in order to remove native
X
2
Fig. 1. The cross section of fabricated organic–inorganic hybrid heterojunctions.

2
46
B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
second fraction afforded pure ferrocene based amino alcohol as an
amber oil, which slowly solidifies to a brown solid.
2.4.2. General procedure for synthesis of ferrocene based phosphinites
(9–12)
Ferrocene based amino alcohol (0.33 mmol) and triethylamine
(
0.33 mmol) were dissolved in dry toluene (20 mL) under argon
atmosphere. Monochlorodiphenylphosphine, PPh Cl (73.2 mg,
.33 mmol) was added dropwise with a syringe to this solution.
2
.4.1.1.
[(2R)-2-[(Ferrocenylmethyl)amino]-3-methyl-butan-1-ol]
2
20
(
5). (Yield: 950 mg, 79%; mp: 63–65 °C); [
a
]
D
ꢁ35.8 (c 1.2,
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.95 (d, 3H,
J = 7.2 Hz, (CH CH, (a)), 1.00 (d, 3H, J = 6.8 Hz, (CH CH, (b)),
.86–1.93 (m, 1H, CH(CH ), 2.54–2.57 (m, 1H, CHNH), 2.88 (br,
H, NH and OH), 3.44–3.51 (m, 1H, CH OH, (a)), 3.64–3.69 (m,
H, CH NH+1H, CH OH (b)), 4.16 (br, m, 5H, C +2H, C ),
.25–4.28 (m, 2H, CHC ); C NMR (100.6 MHz, CDCl3, ppm) d:
8.49, 19.69 ((CH CH), 28.72 (CH(CH ), 46.45 (CH NH), 60.14
OH), 68.11, 68.26, 68.52, 68,68 (C ), 68.51
: (OH) = 3330,
0
1
The mixture was stirred at room temperature for 30 min. The
white precipitate was filtered under argon and remaining organic
phase dried in vacuo to produce a white viscous oily product.
3
)
2
3 2
)
1
2
2
4
1
3 2
)
2
2
2
5
H
5
5
H
4
2
.4.2.1.
[(2R)-2-(Ferrocenylmethylamino)-3-methylbutyl
diph-
ꢁ42.8 (c 1.2,
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.93 (d, 3H,
J = 6.9 Hz, CH(CH (a)), 0.96 (d, 3H, J = 6.9 Hz, CH(CH (b)),
.88–1.93 (m, 1H, CH(CH ), 2.68 (m, 1H, CHNH), 3.48 (d, 1H,
NH, (a)), 3.53 (d, 1H, J = 12.8 Hz, CH NH, (b)),
OP, (a)), 3.89–3.94 (m, 1H, CH OP, (b)),
), 7.36–7.44 (m,
13
5
H
4
enylphosphinite] (9). (Yield: 150 mg, 93%); [
a]
D
20
3
)
2
3
)
2
2
1
(CHNH), 64.02 (CH
2
5 4
H
3
)
2
3 2
)
ꢁ1
(C
H
5 5
), 86.25 (i-C
5
H
4
); IR (KBr pellet in cm
)
m
1
3 2
)
(
NH) = 3183, (C–Cp) = 3090, (C@C–Cp) = 1458; Anal. Calc. for C16-
J = 12.8 Hz, CH
2
2
ꢁ1
H
6
23NOFe (301.21 gmol ): C, 63.80; N, 4.65; H, 7.70. Found: C,
3.72; N, 4.60; H 7.62%.
3
4
6
.82–3.86 (m, 1H, CH
.09 (br, 2H C +5H, C
H, m- and p-C P), 7.54 (m, 4H, o-C
2
2
5
H
4
5
H
5
), 4.13 (m, 2H, C
5
H
4
13
6
H
5
6
H
5
P);
C
NMR
), 29.10
NH), 63.40 (d, J = 8.0 Hz, CHNH), 67.62,
), 68.54 (C ), 69.94 (d, J = 18.1 Hz, CH2-
), 128.35 (d, J = 6.5 Hz, m-C P), 129.34 (s,
P), 130.42 (d, J = 21.8 Hz, o-C P), 142.03 (d, J = 18.1 Hz,
P); P–{ H} NMR (162.0 MHz, CDCl3, ppm) d: 115.23 (s,
(
100.6 MHz, CDCl3, ppm) d: 18.68, 18.92 (CH(CH
CH(CH ), 47.06 (CH
8.14, 68.30, 68.38 C
OP), 87.59 (i-C
p-C
i-C
O-P(Ph)
3 2
)
2
.4.1.2.
[(2S)-2-[(Ferrocenylmethyl)amino]-3-methyl-butan-1-ol]
(
6
3
)
2
2
20
(
6). (Yield: 860 mg, 71%; mp: 63–65 °C); [
a]
D
+35.8 (c 1.2,
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.85 (d, 3H,
J = 6.8 Hz, (CH CH), (a)), 0.91 (d, 3H, J = 6.8 Hz, (CH CH), (b)),
.75–1.82 (m, 1H, CH(CH ), 2.29 (br, 2H, NH and OH), 2.39–
.43 (m, 1H, CHNH), 3.32 (m, 2H, CH OH, (a)), 3.47 (m, 1H, CH NH),
.56 (m, 1H, CH OH, (b)), 4.06 (br, 5H, C +2H, C ), 4.14 (s, 2H,
); C NMR (100.6 MHz, CDCl3, ppm) d: 18.56, 19.67 (CH
), 46.39 (CH NH), 60.34 (CHNH), 64.02 (CH2-
OH), 67.85, 67.96, 68.11, 68.29 (C ), 68.43 (C ), 86.93
: (OH) = 3275, (NH) = 3190,
C–Cp) = 3091, (C@C–Cp) = 1465; Anal. Calc. for 23NOFe
301.21 gmol ): C, 63.80; N, 4.65; H, 7.70. Found: C, 63.74; N,
H
5 4
5 5
H
1
5
H
4
6 5
H
3
)
2
3 2
)
6
H
5
6 5
H
1
2
3
C
3 2
)
3
1
1
6
H
5
2
2
ꢁ1
2
); IR (KBr pellet in cm
)
m
: (NH) = 3334, (C–Cp) = 3072,
2
5
H
5
5 4
H
(
H
6
C@C–Cp) = 1464, (P–Ph) = 1434, (O–P) = 1024; Anal. Calc. for C28-
1
3
5
H
4
3 2-
)
ꢁ1
32NOPFe (485.38 gmol ): C, 69.28; N, 2.88; H, 6.65. Found: C,
CH), 28.95 (CH(CH
3
)
2
2
9.25; N, 2.85; H, 6.62%.
5
H
4
5 5
H
ꢁ1
(
(
(
5 4
i-C H ); IR (KBr pellet in cm ) m
2
.4.2.2. [(2S)-2-(Ferrocenylmethylamino)-3-methylbutyl
diph-
16
C H
2
0
enylphosphinite] (10). (Yield: 160 mg, 90%); [
a
]
D
+42.8 (c 1.2,
ꢁ
1
1
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 1.00 (d, 3H,
J = 6.9 Hz, CH(CH , (a)), 1.03 (d, 3H, J = 6.9 Hz, CH(CH (b)),
.95–2.00 (m, 1H, CH(CH ), 2.74 (m, 1H, CHNH), 3.54 (d, 1H,
NH (a)), 3.59 (d, 1H, J = 12.8 Hz, CH NH (b)), 3.89–
4
.59; H. 7.63%.
3
)
2
3 2
)
1
3 2
)
J = 12.8 Hz, CH
2
2
2
.4.1.3.
[(2S)-2-[(Ferrocenylmethyl)amino]-4-methyl-pentan-1-ol]
20
2 2
3.94 (m, 1H, CH OP, (a)), 3.96–4.01 (m, 1H, CH OP, (b)), 4.15 (br,
2H C H +5H, C H ), 4.21 (d, 2H, J = 1.4 Hz C H ), 7.39–7.46 (m,
(7). (Yield: 1020 mg, 81%; mp: 72–73 °C); [
a]
D
+23.8 (c 1.2,
1
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.84 (pseudo triplet,
6
1
5
4
5
5
5
4
13
6
H, m- and p-C
6
H
5
P), 7.60 (m, 4H, o-C
6
H
5
P);
C
NMR
), 29.16
NH), 63.46 (d, J = 8.0 Hz, CHNH), 67.63,
), 68.42 (C ), 69.69 (d, J = 17.1 Hz, CH2-
OP), 87.69 (i-C H ), 128.42 (d, J = 7.2 Hz, m-C H P), 129.40 (s, p-
H, J = 6.4 Hz, (CH
.36 (m, 1H, CH CHNH (b)), 1.52–1.59 (m, 1H, CH(CH )
3
)
2
CH), 1.17–1.24 (m, 1H, CH
2
CHNH (a)), 1.29–
), 2.35
OH
OH, (b)), 4.10 (br,
); C NMR (100.6 MHz,
), 24.95 (CH(CH ), 40.93
NH), 56.35 (CHNH), 62.90 (CH OH), 67.92,
), 68.46 (C ), 86.20 (i-C ); IR (KBr pel-
: (OH) = 3305, (NH) = 3177, (C–Cp) = 3091, (C@C–
(
(
6
100.6 MHz, CDCl3, ppm) d: 18.75, 18.97 (CH(CH
CH(CH ), 47.11 (CH
7.68, 68.16, 68.32 (C
3 2
)
2
3 2
3
)
2
2
(
br, 2H, NH and OH), 2.68–2.74 (m, 1H, CHNH), 3.22 (m, 1H, CH
a)), 3.44–3.52 (m, 2H, CH NH), 3.59 (m, 1H, CH
H, C +2H C ), 4.13 (m, 2H, C
CDCl3, ppm) d: 22.66, 23.02 (CH(CH
CHCH ), 45.94 (CH
7.98, 68.23, 68.34 (C
2
5
H
4
5 5
H
(
5
2
2
13
5
H
5
5
H
4
5
H
4
5
4
6
5
C
C
6
H
H
5
P), 130.50 (d, J = 21.6 Hz, o-C
6
H
5
P), 142.10 (d, J = 18.8 Hz i-
3
)
2
3 2
)
3
1
1
P); P–{ H} NMR (162.0 MHz, CDCl3, ppm) d: 115.11 (s, O-
(
6
2
2
2
6
5
ꢁ1
P(Ph)
2
); IR (KBr pellet in cm ) m: (NH) = 3334, (C–Cp) = 3070,
H
5 4
5
H
5
5 4
H
ꢁ
1
(C@C–Cp) = 1464, (P–Ph) = 1435, (O–P) = 1035; Anal. Calc. for C
H32NOPFe (485.38 gmol ): C, 69.28; N, 2.88; H, 6.65. Found: C,
6
let in cm
Cp) = 1438; Anal. Calc. for C17
N, 4.44; H, 8.00. Found: C, 64.73; N, 4.40; H, 7.96%.
)
m
28-
ꢁ1
ꢁ
1
H25NOFe (315.23 gmol ): C, 64.77;
9.24; N, 2.84; H, 6.61%.
2
.4.2.3. [(2S)-2-(Ferrocenylmethylamino)-4-methylpentyl
diph-
2
0
2
.4.1.4. [(2S,3S)-2-[(Ferrocenylmethyl)amino]-3-methyl-pentan-1-ol]
enylphosphinite] (11). (Yield: 150 mg, 91%); [
a]
D
+32.6 (c 1.2,
20
1
(
8). (Yield: 1070 mg, 85%; mp: 64–66 °C); [
a]
D
+26.2 (c 1.2,
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.90 (d, 3H,
J = 7.0 Hz, CH(CH )), 0.95 (d, 3H, J = 14.8 Hz, (CH )CH ), 1.64–1.67
), 1.22 (m, 1H, CH CH , (a)), 1.49 (m, 1H, CH CH
b)), 2.21 (br, 2H, NH and OH), 2.61–2.63 (m, 1H, CHNH), 3.35–3.40
m, 1H, CH OH, (a)), 3.49–3.64 (m, 2H, CH NH+1H, CH OH, (b)),
.15 (br, 5H, C +2H, C ), 4.22 (br, 2H, C
100.6 MHz, CDCl3, ppm) d: 11.75 (CH CH ), 14.54 (CHCH
CH CH ), 35.35 (CH CHCH ), 46.34 (CH NH), 60.13 (CHNH),
2.21 (CH OH), 67.81, 67.91, 68.04, 68.27 (C ), 68.42 (C ),
6.75 (i-C (OH) = 3268,
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.94 (d, 3H,
J = 6.6 Hz, CH(CH ), (a)), 0.99 (d, 3H, J = 6.6 Hz, CH(CH ), (b)),
1.36–1.45 (m, 2H, CH CHNH), 1.71–1.76 (m, 1H, CH(CH , 2.99
(m, 1H, CHNH), 3.57 (s, 2H, CH NH), 3.83–3.89 (m, 1H, CH OP,
(a)), 3.94–3.99 (m, 1H, CH OP, (b)), 4.16 (m, 2H C ),
4.22 (m, 2H, C ), 7.25–7.45 (m, 6H, m- and p-C P), 7.58–7.62
(m, 4H, o-C
23.04 (CH(CH
NH), 56.21 (d, J = 8.1 Hz, CHNH), 67.72, 68.26, 68.44, 68.51 (C
68.59 (C ), 72.19 (d, J = 17.1 Hz, CH OP), 87.45 (i-C ), 128.42
(d, J = 6.7 Hz, m-C P), 129.43 (s, p-C P), 130.54 (d,
J = 21.9 Hz, o-C P), 142.05 (d, J = 18.2 Hz, i-C
NMR (162.0 MHz, CDCl3, ppm) d: 115.35 (s, O-P(Ph)
1
3
3
3
3
2
2
3 2
)
(
(
(
m, 1H, CH
2
CHCH
3
2
3
2
3
,
2
2
2
5
4 5 5
H +5H, C H
2
2
2
1
5
H
4
6
H
5
3
13
4
(
(
6
8
5
H
5
5
H
4
5
H
4
);
C NMR
), 26.39
6
H
5
P); C NMR (100.6 MHz, CDCl3, ppm) d: 21.56,
), 25.02 (CH(CH ), 41.19 (CH CHNH), 46.27 (CH2-
),
2
3
3
3
)
2
3
)
2
2
2
3
3
2
2
5 4
H
2
5
H
4
H
5 5
5
H
5
2
5 4
H
ꢁ1
5
4
H ); IR (KBr pellet in cm
)
m
:
6
H
5
6 5
H
P); 31P–{ H}
); IR (KBr pel-
let in cm ) m: (NH) = 3323, (C–Cp) = 3069, (C@C–Cp) = 1478,
1
(
H
6
NH) = 3152 (C–Cp) = 3100, (C@C–Cp) = 1461; Anal. Calc. for C17-
25NOFe (315.23 gmol ): C, 64.77; N, 4.44; H, 8.00. Found: C,
4.71; N, 4.38; H, 7.94%.
6
H
5
6 5
H
ꢁ1
2
ꢁ
1

B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
247
(
(
2
P–Ph) = 1435, (O–P) = 1022; Anal. Calc. for
499.38 gmol ): C, 69.74; N, 2.80; H, 6.86. Found: C, 69.70; N,
.76; H, 6.82%.
C
29
H
34NOPFe
(100.6 MHz, CDCl3, ppm) d: 17.55 (CH
18.63 (CH(CH ), 21.76, 22.01 ((CH
(CH(CH ), 30.11 (CH- of p-cymene), 47.22 (CH
CHNH), 69.13 (CH OP), 67.90, 68.50, 68.57, 68.90, (C
(C )), 87.50 (i-C ), 87.54, 87.73, 89.02, 90.32 (aromatic car-
bons of p-cymene), 97.43, 111.37 (quaternary carbons of p-cym-
3
Ph of p-cymene), 18.61,
ꢁ1
3
)
2
3
)
2
CH of p-cymene), 28.72
NH), 62.44
), 69.98
3
)
2
2
(
2
5 4
H
2
.4.2.4. [(2S-3S)-2-(Ferrocenylmethylamino)-3-methylpentyl diph-
5
H
5
5 4
H
2
0
enylphosphinite] (12). (Yield: 150 mg, 95%); [
MeOH)]; H NMR (400.1 MHz, CDCl3, ppm) d: 0.93–0.99 (m, 6H,
a
]
D
+29.6 (c 1.2,
1
31
ene), 127.88, 130.90, 131.01, 136.72 (m-, p-, o- and i-C
6
H
5
P); P–
{ H} NMR (162.0 MHz, CDCl3, ppm) d: 112.00 (s, O-P(Ph) ); IR
(NH) = 3275, (C–Cp) = 3091, (P–
Ph) = 1446, (O–P) = 1029, (C@C–Cp) = 1465; Anal. Calc. for [C38-
1
CHCH
b)), 1.69 (m, 1H, CH(CH
NH), 3.86–3.90 (m, 1H, CH
.13 (br, 2H C +5H, C
m- and p-C P), 7.57 (m, 4H, o-C
CDCl3, ppm) d: 12.18 (CH CH ), 14.83 (CHCH
NH), 62.19 (d, J = 8.1 Hz, CHNH), 67.61,
), 68.39 (C ), 69.90 (d, J = 17.2 Hz, CH2-
), 128.35 (t, J = 14.1 Hz, m-C P), 129.09 (s,
P), 130.42 (d, J = 22.1 Hz, o-C P), 142.06 (d, J = 18.1 Hz,
P); P–{ H}NMR (162.0 MHz, CDCl3, ppm) d: 114.37 (s,
3
+CH
2
CH
3
), 1.23 (m, 1H, CH
)), 2.82 (m, 1H, CHNH), 3.52 (m, 2H, CH2-
OP, (a)), 3.94–4.00 (m, 1H, CH OP, (b)),
), 4.19 (m, 2H, C ), 7.23–7.42 (m, 6H,
2
CH
3
(a)), 1.56 (m, 1H, CH
2
CH
3
2
ꢁ1
(
3
(KBr pellet in cm
) m:
2
2
ꢁ1
4
5
H
4
5
H
5
5
H
4
2
H46NOPFeRuCl ] (791.58 gmol ): C, 57.65; N, 1.76; H, 5.85.
13
6
H
5
6
H
5
P); C NMR (100.6 MHz,
), 26.11 (CH CH ),
Found: C, 57.60; N, 1.72; H, 5.81%.
2
3
3
2
3
3
6
3 2
5.91 (CHCH ), 46.84 (CH
8.14, 68.28, 68.33, (C
H
5 4
H
5 5
2.4.3.3. [(2S)-2-(Ferrocenylmethylamino)-4-methylpentyl diphenyl-
6
OP), 87.70 (i-C
p-C
i-C
O-P(Ph)
H
5 4
6
H
5
phosphinito(dichloro(
g
-p-cymene)ruthenium(II))]
(15). (Yield:
+39.4 (c 1.2, MeOH)]; 1
NMR (400.1 MHz, CDCl3, ppm) d: 0.80 (br, 6H, CH(CH ), 1.10
(m, 6H, (CH CH of p-cymene), 1.32 (br, 2H, CH CH), 1.89 (s,
3H, CH Ph of p-cymene), 1.47 (br, 1H, CH(CH ), 2.66 (br, 1H,
CH- of p-cymene), 2.80 (m, 1H, CHNH), 3.57 (br, 2H, CH NH),
3.70 (br, 1H, CH OP, (a)), 4.06 (br, 1H, CH OP, (b)), 4.14–4.25
br, 4H, C +5H, C ), 5.26 (br, 4H, aromatic protons of p-cym-
ene), 7.43 (m, 6H, m- and p-C P), 7.90–7.92 (m, 4H, o-C P);
C NMR (100.6 MHz, CDCl3, ppm) d: 17.53 (CH Ph of p-cymene),
21.97, 22.46, 22.94 (CH(CH +(CH CH of p-cymene), 24.68
(CH(CH ), 30.12 (CH- of p-cymene), 40.94 (CH CH), 46.25 (CH2-
NH), 55.28 (CHNH), 64.20 (CH OP), 68.11, 68.52, 68.97, 68.99
(C )), 69.13 (C )), 87.32 (i-C ), 87.46, 87.77, 90.36, 91.04
(aromatic carbons of p-cymene), 97.40, 111.42 (quaternary car-
bons of p-cymene), 128.01 (d, J = 22.0 Hz, m-C P), 131.03 (s,
p-C P), 133.16 (d, J = 25.9 Hz, o-C P), 138.20 (d, J = 49.6 Hz,
i-C
O-P(Ph)
2
0
6
H
5
6
H
5
205 mg, 80%; mp: 115–117 °C); [
a
]
D
H
3
1
1
6
H
5
3 2
)
ꢁ1
2
); IR (KBr pellet in cm
)
m
: (NH) = 3320, (C–Cp) = 3075,
3
)
2
2
(
H
6
C@C–Cp) = 1458, (P–Ph) = 1437, (O–P) = 1023; Anal. Calc. for C29-
3
3 2
)
ꢁ1
34NOPFe (499.38 gmol ): C, 69.74; N, 2.80; H, 6.86. Found: C,
2
9.69; N, 2.75; H, 6.81%.
2
2
(
5
H
4
5 5
H
2
1
.4.3. General procedure for synthesis of ruthenium(II) complexes (13–
6
H
5
6 5
H
1
3
6)
[
3
Ru(g
6-p-cymene)(
l
-Cl)Cl]
2
(0.17 mmol) and ferrocene based
3
)
2
3 2
)
phosphinite (0.33 mmol) were dissolved in 20 mL of toluene and
stirred for 1 h at room temperature. The volume was concentrated
3
)
2
2
2
1
(
–2 mL under reduced pressure and addition of petroleum ether
20 mL) gave the complex as a tile red solid. The product was col-
lected by filtration and dried in vacuum.
5
H
5
5
H
5
5 4
H
6
H
5
6
H
5
6 5
H
3
1
1
2
.4.3.1. [(2R)-2-(Ferrocenylmethylamino)-3-methylbutyl diphenyl-
6
H
5
P); P–{ H} NMR (162.0 MHz, CDCl3, ppm) d: 112.02 (s,
6
ꢁ1
phosphinito(dichloro(
20 g, 84%; mp: 108–110 °C); [
NMR (400.1 MHz, CDCl3, ppm) d: 0.73–0.82 (m, 6H, CH(CH
.99 (m, 6H, (CH CH of p-cymene), 1.79 (br, 1H, CH(CH +3H,
CH Ph of p-cymene), 2.46 (br, 1H, CHNH), 2.54 (m, 1H, CH– of p-
cymene), 3.48 (br, 2H, CH NH), 3.65 (br, 1H, CH OP, (a)), 3.83 (br,
H, CH OP, (b)), 4.02–4.14 (m, 4H, C +5H, C ), 5.14 (br, 1H,
J = 5.6 Hz, aromatic protons of p-cymene, (a)), 5.20 (br, 3H, aro-
matic protons of p-cymene, (b)), 7.33 (m, 6H, m- and p-C P),
P); C NMR (100.6 MHz, CDCl3, ppm) d:
Ph of p-cymene), 18.60, 18.70 (CH(CH ), 21.77, 22.01
CH of p-cymene), 28.69 (CH(CH ), 30.11 (CH- of p-cym-
ene), 47.20 (CH NH), 62.36 (CHNH), 69.12 (CH OP), 67.97, 68.49,
), 69.12 (C ), 87.59 (i-C ), 87.54, 87.68,
0.36, 90.86 (aromatic carbons of p-cymene), 97.43, 111.33 (qua-
P),
P), 136.17
P); 31P–{ H} NMR (162.0 MHz, CDCl3, ppm) d:
g
-p-cymene)ruthenium(II))]
(13). (Yield:
2
); IR (KBr pellet in cm
) m: (NH) = 3305, (O–H) = 3177
20
1
2
a]
D
ꢁ56.8 (c 1.2, MeOH)];
H
(C–Cp) = 3091, (C@C–Cp) = 1438, (P–Ph) = 1446, (O–P) = 1024,
2
(C@C–Cp) = 1465; Anal. Calc. for 48NOPFeRuCl ]
3
)
2
),
[C39
H
ꢁ1
0
3
)
2
3
)
2
(805.58 gmol ): C, 58.14; N, 1.73; H, 6.00. Found: C, 58.12; N,
1.71; H, 5.98%.
3
2
2
1
2
5
H
4
5 5
H
2.4.3.4. [(2S-3S)-2-(Ferrocenylmethylamino)-3-methylpentyl diphe-
6
6
H
5
nylphosphinito(dichloro (
g
-p-cymene)ruthenium(II)] (16). (Yield:
13
20
+35.3 (c 1.2, MeOH)]; 1
CH + 3H,
7
1
(
.78–7.84 (br, 4H, o-C
7.55 (CH
H
6 5
197 mg, 77%; mp: 114–116 °C); [
NMR (400.1 MHz, CDCl3, ppm) d: 0.78–0.83 (m, 3H, CH
CH(CH )), 1.04 (d, 3H, J = 6.8 Hz, (CH CH of p-cymene, (a)), 1.10
(d, 3H, J = 6.8 Hz, (CH CH of p-cymene, (b)), 1.29 (m, 2H,
CHCH (CH )), 1.52 (m, 1H, CHCH (CH )), 1.88 (s, 3H, CH Ph of
p-cymene), 2.62 (m, 1H, CH– of p-cymene+1H, CHNH), 3.63 (m,
2H, CH NH), 3.73 (m, 1H, CH OP (a)), 3.96 (m, 1H, CH OP (b)),
4.15 (m, 2H, C +5H, C ), 4.28 (m, 2H, C ), 5.21 (br, 2H,
aromatic protons of p-cymene), 5.29 (br, 2H, aromatic protons
of p-cymene), 7.42–7.43 (m, 6H, m- and p-C P), 7.83–7.92
P); C NMR (100.6 MHz, CDCl3, ppm) d: 11.93
), 14.70 (CHCH ), 17.56 (CH Ph of p-cymene), 21.88,
22.51 ((CH CH of p-cymene), 25.79 (CHCH CH ), 30.10 (CH- of
p-cymene), 35.28 (CHCH CH ), 46.78 (CH NH), 60.90 (CHNH),
65.52 (CH OP), 67.03, 68.12, 68.54, 68.57 ((C ), 69.07 (C ),
87.04 (i-C ), 87.49, 87.76, 90.31, 91.21 (aromatic carbons of
p-cymene), 97.30, 111.22 (quaternary carbons of p-cymene),
127.89 (d, J = 11.0, m-C P), 130.91 (s, p-C P), 132.61 (d,
J = 11.1, o-C P), 136.60 (d, J = 49.6 Hz, i-C
(162.0 MHz, CDCl3, ppm) d: 111.87 (s, O-P(Ph)
a
]
D
H
3
3
)
2
2
3
(CH
3
)
2
3
)
2
3
3 2
)
2
2
3 2
)
6
9
8.71, 68.94 (C
5
H
4
5
H
5
5
H
4
2
3
2
3
3
ternary carbons of p-cymene) 127.92 (d, J = 10.0 Hz, m-C
31.00 (s, p-C P), 132.75 (d, J = 10.1 Hz, o-C
J = 48.3 Hz, i-C
11.65 (s, O-P(Ph)
Cp) = 3090, (P–Ph) = 1441, (O–P) = 1030, (C@C–Cp) = 1458; Anal.
H
6 5
2
2
2
1
(
1
6
H
H
6 5
5
6
H
5
5
H
4
5
H
5
5 4
H
1
ꢁ1
2
); IR (KBr pellet in cm
)
m
: (NH) = 3330, (C–
6 5
H
1
3
(m, 4H, o-C
(CH CH
6 5
H
ꢁ
1
Calc. for [C38
H, 5.85. Found: C, 57.62; N, 1.73; H, 5.82%.
H
46NOPFeRuCl
2
] (791.58 gmol ): C, 57.65; N, 1.76;
2
3
3
3
3
)
2
2
3
2
3
2
2
.4.3.2. [(2S)-2-(Ferrocenylmethylamino)-3-methylbutyl diphenyl-
2
5
H
4
5 5
H
6
phosphinito(dichloro(
38 mg, 90%; mp: 108–110 °C); [
NMR (400.1 MHz, CDCl3, ppm) d: 0.73–0.80 (m, 6H, CH(CH
.99 (m, 6H, (CH CH of p-cymene), 1.80 (br, 1H, CH(CH +3H,
CH Ph of p-cymene), 2.45 (br, 1H, CHNH), 2.55 (m, 1H, CH– of
p-cymene), 3.45 (br, 2H, CH NH), 3.65 (br, 1H, CH OP,(a)), 3.82
br, 1H, CH OP, (b)), 4.03–4.14 (br, 4H, C +5H, C ), 5.15–
.23 (br, 4H, aromatic protons of p-cymene), 7.33 (br, 6H, m-
g
-p-cymene)ruthenium(II))]
(14). (Yield:
5 4
H
20
+56.8 (c 1.2, MeOH)]; 1
2
a
]
D
H
3
)
2
),
6
H
5
6 5
H
3
1
1
0
3
)
2
3
)
2
6
H
5
6
H
5
P); P–{ H} NMR
); IR (KBr pellet
: (NH) = 3268, (C–Cp) = 3100, (C@C–Cp) = 1461, (P–
Ph) = 1446, (O–P) = 1027, (C@C–Cp) = 1465; Anal. Calc. for [C39-
3
2
ꢁ1
2
2
in cm
) m
(
5
2
5
H
4
5 5
H
ꢁ1
H
48NOPFeRuCl
2
] (805.58 gmol ): C, 58.14; N, 1.73; H, 6.00.
1
3
and p-C
6
H
5
P), 7.80–7.86 (m, 4H, o-C
6
H
5
P);
C
NMR
Found: C, 58.11; N, 1.70; H, 5.97%.

2
48
B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
3
. Results and discussion
under anaerobic condition, is stable (up to 24 h) and decomposes
very slowly gradually to give oxide and the hydrolysis product
diphenylphosphinous acid, Ph P(O)H [48]. Furthermore, the
P–{ H} NMR spectrum also displays formation of PPh PPh and
P(O)Ph PPh
, as indicated by signals at about d ꢁ15.2 ppm as sin-
3.1. Synthesis and characterization of the amino alcohols, ferrocenyl-
2
3
1
1
phosphinites and their ruthenium(II) complexes
2
2
2
2
1
The synthesis of
pounds 1–4) [33,34] were accomplished in one step from
line, -leucine or -isoleucine, respectively, according to the
procedures described in the literature [35,36]. The ferrocene based
amino alcohols 5–8 were synthesized by the condensation reaction
between ferrocenecarboxaldehyde [37] and amino alcohols in the
D
-,
L
-valinol,
L
-leucinol and
L
-isoleucinol (com-
glet and d 35.6 ppm and d ꢁ21.4 ppm as doublets with
J
(PP)
D
-, L-va-
226 Hz, respectively, after the 48 h [49]. The assignment of the
1
L
L
H chemical shifts was derived from 2D HH-COSY spectra and
1
3
the appropriate assignment of the C chemical shifts from DEPT
and 2D HMQC spectra. Again, the magnetic non-equivalence of
protons as well as carbons atoms of the monosubstituted Cp ring
was observed (see Section 2). Furthermore, IR spectra and C, H, N
elemental analyses are in agreement with the proposed structures
for ferrocenyl-phosphinite ligands.
1
presence of the base catalyst as shown in Scheme 1. The H NMR
spectra of compounds 5–8 show characteristic features: the
a
- and b-cyclopentadienyl protons in the amino alcohols with rel-
atively small non-resolved multiplets appear approximately at d
.00–4.50 ppm. The magnetic non-equivalence of protons as well
2
g l-Cl)Cl] , in
6-p-cymene)(
Treatment of ligands, 9–13 with [Ru(
2:1 M ratios were readily synthesized in good yields (Scheme 1).
4
6
as carbon atoms of the monosubstituted Cp ring was observed,
which is caused by their planar structure. The 13C-{ H} NMR spec-
tra also exhibit the typical signals for monosubstitued ferrocenes.
The structures for these ferrocene based chiral amino alcohols
are consistent with the data obtained from a combination of mul-
tinuclear NMR spectroscopy, IR spectroscopy and elemental analy-
sis (for details see Section 2 and SI (Supporting information)).
The synthetic procedure for the preparation of the ferrocenyl-
phosphinite ligands is shown in Scheme 1. Ferrocene based chiral
bis(phosphinite) ligands, 9–12 were synthesized by a hydrogen
abstraction from the described ferrocene based chiral amino alco-
hols 5–8, by a base (Et
equivalent of Ph PCl, in anhydrous toluene under inert argon
atmosphere, respectively (Scheme 1). The ammonium salt was sep-
arated by filtration and the ligands were obtained by extracting the
solvent in vacuo in good yields. The progress of this reaction was
conveniently followed by 31P–{ H} NMR spectroscopy. The signal
The starting ruthenium(II) complex, [Ru(
was prepared from the reaction of the commercially available
-phellandrene (5-isopropyl-2-methylcyclohexa-1,3-diene) with
2
g -p-cymene)(l-Cl)Cl] ,
1
a
6
3 2
RuCl [50]. Treatment of [Ru(g -p-cymene)(l-Cl)Cl] with ferro-
cene based phosphinite ligands 9–12 in 1:2 M ratio in toluene
resulted the formation of mononuclear complexes 13–16 as or-
ange-red crystalline solids. The reactions between Ru(II) precursor
and ferrocenyl-phosphinite ligands are not affected by the molar
6
ratio (2:1 or 1:1) of [Ru(
g
-p-cymene)(
l
-Cl)Cl]
2
as well as the ste-
ric and electronic properties of the substituents on the donor phos-
phorus atoms. The initial color change, i.e., from clear orange to
deep red, attributed to the dimer cleavage most probably by the
ferrocenyl-phosphinite ligand [51]. All the complexes were iso-
3
N) and the subsequent reaction with one
2
3
1
1
lated as indicated by singlets in the P–{ H} NMR spectra at d
111.65, 112.00, 112.02 and 111.87 ppm for 13–16, respectively,
in line with the values previously observed for similar compounds
1
1
[40] with a coordination shift of approximately d 3.0 ppm (SI). H
1
3
of the starting material PPh
new singlet appeared downfield due to the ferrocenyl-phosphinite
ligands. The P–{ H} NMR spectra of 9–12 show no unexpected
features. The P–{ H} NMR spectra of compounds, 9–12 show sin-
2
Cl at d 81.0 ppm disappeared and a
and C NMR spectra of complexes 13–16 display all the signals
1
of coordinated ligands. The H NMR spectra of compounds display
3
1
1
generally the p-cymene aromatic CH protons as two signals. It is
very well-known that the presence of one (broad) or two signals
corresponding to aromatic CH p-cymene protons in the 1H NMR
spectra of 13–16 is consistent with a Cs symmetry of complexes
and a free rotation of the arene (p-cymene) ligand [52,53]. In addi-
tion, the proton signals corresponding to amino alcohol moiety for
3
1
1
gle resonances due to phosphinite at 115.23, 115.11, 115.35 and
1
14.37, respectively in line with the values previously observed
for similar compounds [38–47]. Typical spectra of these ligands
are illustrated in SI. Solution of the ligands in CDCl , prepared
3
Scheme 1. Reagents and conditions: (i) NaBH
4
-I , THF, for 1–4; (ii) ferrocenecarboxaldehyde, K
2
2 3 3 4 2 3
CO , CHCl , NaBH , 1.5 h, for 5–8; (iii) 1 equiv Ph PCl, 1 equiv Et N, toluene for
6
9–12 (iv) 1/2 equiv [Ru(
g
-p-cymene)(
l-Cl)Cl] , toluene for 13–16.
2

B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
249
the ligands in complexes, 13–16 do not differ significantly from
those of the free ligand. The most relevant signals of C-{ H}
[68], Reetz [69], Feringa [70] and more recently Chan [71] and Zhao
[72] a large number of chiral monodendate phosphonite, phos-
phite, and phosphoramidite ligands have been found to induce
good to excellent enantioselectivities in asymmetric hydrogena-
tion reactions, comparable to or exceeding those obtained with
bidendate ligands. To comprise in an account, the most important
advantage of chiral phosphinite ligands over the corresponding
P-based ligands is the easiness of preparation, which leads to a
substantial interest to develop highly effective chiral monodendate
phosphinite ligands for asymmetric catalysis [73–75].
Ferrocenyl-phosphinites demonstrate good air stability relative
to the other analogous phosphinites and is designed to avoid using
any extreme conditions. Thus, this kind of ligands combines a
number of characteristics making them uniquely attractive for
asymmetric catalysis [76]. It is well-known that, the oxygen atom
in phosphinite ligand increases the distance between the chiral
1
3
1
NMR spectra of complexes are those corresponding to p-cymene
1
13
moiety (see Section 2) and in the H and C spectra of complexes
3–16, the characteristic signals of mono- and unsubstituted ferro-
1
cene units are observed [54–56]. Elemental analyses of the
complexes are also consistent with the suggested molecular
formulas. The absorption bands corresponding to Ru(II)-ferroce-
nyl-phosphinite ligands in the IR spectra of complexes do not exhi-
bit significant differences with respect to those of free ligands (see
Section 2). Although, single crystals of complexes were obtained by
slow diffusion of diethylether 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. Asymmetric transfer hydrogenation of acetophenone derivatives
with iso-PrOH
2
moiety and the PPh group. Consequently there is less control of
stereoselectivity in the catalyst-substrate interaction. Furthermore,
the presence of the C–O–P bond substantially increases the flexibil-
ity of the backbone and consequently decreases the enantioselec-
tivity of the catalyst. Despite these disadvantages, the excellent
catalytic performance and the higher structural permutability of
phosphinite based transition metal catalysts [77–79] prompted
us to develop new catalyst systems with well-shaped monoden-
date phosphinite ligands [80–83]. Encouraged by our recent
success in the development of new chiral and highly active ligands
Despite the encouraging performance of many ferrocene based
bidendate phosphorus-chelate ligands [57–61] the past few years
have witnessed a renewed interest in the development of chiral
monodendate phosphorus containing ligands for use in asymmet-
ric hydrogenation reactions [62–66]. This resurgence in monoden-
date ligands is due to the ready accessibility of a range of diverse
ligand structures, and often their lower cost compared to biden-
date ligands [67]. Following the studies from the groups of Pringle
Table 1
Transfer hydrogenation of acetophenone with iso-PrOH catalyzed by Ru-ferrocenyl based monodendate phosphinite complexes (13–16).
O
H
HO
Cat.
*
iso-PrOH
acetone
f
% eeg
Configurationh
i
ꢁ1
Entry
Complex
13a
S/CNaOH
Time (h)
Conversion (%)
TOF (h
)
1
2
3
4
100:1:5
100:1:5
100:1:5
100:1:5
24
24
24
24
12 (36)d
16 (45)d
11
91 (63)d
76 (70)d
R
S
S
S
<5
<5
<5
<5
a
14
15
a
a
16
10
5
6
7
8
9
13b
100:1
100:1
100:1
100:1
100:1
1
1
1
1
<5
<5
<5
<5
<5
b
14
15
16
<50
<50
<50
b
b
c
e
e
70 (67)e
13
1/2 (1/2)
96 (95)
R
192 (190)
10
11
12
14c
100:1:5
100:1:5
100:1:5
1/2 (1/2)e
1/2
1/2
99 (97)e
97
95
80 (79)e
72
74
S
S
S
198 (194)
194
190
c
15
c
16
1
1
1
1
3
4
5
6
14
14
14
14
100:1:3
100:1:5
100:1:7
100:1:9
1/2
1/2
1/2
1/2
93
99
94
90
72
80
70
73
R
S
S
S
186
198
188
180
Reaction conditions
a
At room temperature; acetophenone/Ru/NaOH, 100:1:5.
b
c
d
e
f
Refluxing in iso-PrOH; acetophenone/Ru, 100:1, in the absence of base.
Refluxing in iso-PrOH; acetophenone/Ru/NaOH, 100:1:5.
At room temperature; acetophenone/Ru/NaOH, 100:1:5, (64 h).
Refluxing in iso-PrOH; acetophenone/Ru/KOH, 100:1:5.
Determined by GC (three independent catalytic experiments).
Determined by capillary GC analysis using a chiral cyclodex B (Agilent) capillary column.
g
h
i
Determined by comparison of the retention times of the enantiomers on the GC traces with literature values, (S) or (R) configuration was obtained in all experiments.
ꢁ1
TOF = (mol product/mol Cat.) ꢀ h
.

2
50
B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
[
84,85], we initiated a study of the synthesis of a series of
changed from orange to deep red. As a result of the reversibility at
room temperature the prolonging the reaction time (64 h) led to a
decreasing of enantioselectivity, as indicated by the catalytic re-
monodendate ferrocenyl-phosphinite ligands, and investigated
their efficiency in ruthenium catalyzed asymmetric transfer
hydrogenations.
d
sults collected with 13–16 (entries 1 and 2, ) [87,88]. Furthermore,
Chiral complexes 13–16 have been tested as catalyst precursors
for the asymmetric transfer hydrogenation of acetophenone under
variable conditions (Table 1). Furthermore, a comparison of
complexes as precatalysts for the asymmetric hydrogenation of
acetophenone by iso-PrOH in the presence of NaOH is summarized
in Table 1. Catalytic experiments were carried out under Ar atmo-
sphere using standard schlenk-line techniques. These systems
catalyzed the reduction of acetophenone to corresponding alcohol
as can be inferred from the Table 1, the presence of base is neces-
sary to observe appreciable conversions under refluxing (Table 1,
entries 9–12), otherwise little conversion (up to 5%, 1 h) occur in
all the reactions (Table 1, entries 5–8). The base facilitates the for-
mation of ruthenium alkoxide by abstracting proton of the alcohol
and subsequently alkoxide undergoes b-elimination to give ruthe-
nium hydride, which is an active species in this reaction. This is the
mechanism proposed by several research groups on the studies of
ruthenium catalyzed transfer hydrogenation reaction by metal
hydride intermediates [89–91]. In addition, the choice of base, such
as KOH and NaOH, had little influence on the conversion and
(
(S)-, (R)-1-phenylethanol) in the presence of NaOH as a promoter.
To an iso-PrOH solution of Ru(II)-monodendate phosphinite
complex, an appropriate amount of acetophenone and NaOH/iso-
PrOH solutions were added, respectively, at room temperature.
The solution was stirred for several hours, and then examined with
capillary GC analysis. At room temperature, transfer hydrogenation
of acetophenone occurred very slowly [86], with low conversion
e
enantioselectivity (entries 9 and 10, ).
Optimization studies of the catalytic reduction of acetophenone
in iso-PrOH showed that good activity was obtained with a base/li-
gand ratio of 5:1 (Table 1). Reduction of acetophenone into (S)- or
(R)-1-phenylethanol could be achieved in high yield by increasing
the temperature up to 82 °C (Table 1, entries 9–12). These
(
7
up to 16%, 24 h) and moderate to high enantioselectivity (up to
6% ee) in the reactions (entries 1–4). During this period, the color
Table 2
a
Asymmetric transfer hydrogenation results for substituted acetophenones catalyzed by Ru-ferrocenyl based monodendate phosphinite complexes, (13–16) .
O
OH
OH
O
Cat / NaOH
R
R
+
+
Entry
Complex
Substrate
Product
Time
Conv.b (%)
% eec
TOFd (hꢁ1
)
Configuratione
1
2
3
4
13
14
15
16
O
OH
*
1/3
1/3
1/3
1/3
97
99
98
9
74
80
76
72
291
297
294
288
R
S
S
S
F
F
5
6
7
8
13
14
15
16
O
OH
1/2
1/2
1/2
1/2
98
99
98
99
75
80
78
74
196
198
196
198
R
S
S
S
*
Cl
Br
Cl
Br
9
13
14
15
16
O
OH
*
1/2
1/2
1/2
1/2
98
98
97
99
73
79
74
75
196
196
194
198
R
S
S
S
10
11
12
13
14
15
16
13
14
15
16
O
OH
1/3
1/3
1/3
1/3
98
99
98
97
77
81
75
72
231
297
294
291
R
S
S
S
*
O N
O N
2
2
17
18
19
20
13
14
15
16
O
MeO
OH
*
1
1
1
1
97
99
98
99
76
85
73
78
97
99
98
99
R
S
S
S
MeO
2
2
2
2
1
2
3
4
13
14
15
16
O
OH
2
2
2
2
97
99
98
98
70
79
67
63
49
50
49
49
R
S
S
S
*
MeO
MeO
a
b
c
Catalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 mL), NaOH (0.025 mmol %), 82 °C, the concentration of acetophenone is 0.1 M.
Purity of compounds is checked by NMR and GC (three independent catalytic experiments), yields are based on aryl ketone.
Determined by capillary GC analysis using a chiral cyclodex B (Agilent) capillary column (30 m ꢀ 0.32 mm I.D. ꢀ 0.25
lm film thickness).
d
e
ꢁ1
TOF = (mol product/mol Cat.) ꢀ h
.
Determined by comparison of the retention times of the enantiomers on the GC traces with literature values.

B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
251
ꢀ
ꢁ
encouraged results show that the ferrocenyl based monodendate
phosphinite ligands with amino (NH) moiety show much higher
activity and enantioselectivity. Similar tendency was reported in
earlier studies [92–94] indicating that the NH functional moiety
in ligand plays an important role in Ru(II)-ligand catalytic system.
Higher activity and enantioselectivity of amino containing phosph-
inite ligand also may be due to the fact that NH moiety can stabi-
lize the catalytic transition state [95]. Furthermore, it is
noteworthy that the catalytic system, 13–16 displays the differ-
ences in reactivity. These results indicate that the structure of
the monodenate ferrocenyl-phosphinite ligands is a crucial factor
for acceleration of the reaction. Compared to the other complexes,
ꢂ
2
qU
b
kT
I
0
¼ AA T exp
ꢁ
ð2Þ
⁄
where A is the diode area, A Richardson constant and /
b
the barrier
height. The ideality factor and the barrier height of a device can be
determined using Eqs. (1) and (2) as
ꢀ
ꢁ
q
dV
n ¼
ð3Þ
ð4Þ
kT d ln I
and
!
ꢂ
2
kT
q
AA T
U
b
¼
ln
I
0
[
(2S)-2-(ferrocenylmethylamino)-3-methylbutyl diphenylphosphi-
6
nito(dichloro(g -p-cymene)ruthenium(II))], 14 appears to provide
a bit more effective chiral environment around the ruthenium. In
the context of the results, it could be reasonably argued that the
absolute configuration of the product is governed by the carbon
centered chirality.
Our study reveals that the activity and enantioselectivity of the
catalyst is sensitive to substrate structures. So, the complexes 13–
respectively. The ideality factors of the structures were calcu-
lated from the linear parts of all forward bias I–V plots using Eq.
3), and the results are given in Table 3. As seen from the Table 3,
(
all ideality factor values are higher than unity and they present the
deviation from ideal situation. The deviation from ideal diode may
due to the existence of fabrication induced defects at organic–inor-
ganic interface, the series resistance of devices and native oxide
layer on inorganic semiconductor. Increase of diffusion current
with applied voltage and recombination of electron and holes in
depletion region can be also another explanation [99]. The barrier
height values of the structures were calculated using saturation
current values and Eq. (4). The barrier height values vary between
1
6 were further investigated in transfer hydrogenation of substituted
acetophenone derivatives, and the results of this transformation are
presented in Table 2. The catalytic reduction of acetophenone deriva-
tives was all tested with the conditions optimized for acetophenone.
The results in Table 2 demonstrate that a range of acetophenone
derivativescanbehydrogenatedwithgoodenantioselectivities.Com-
plex 14 showed the highest activity with good enantioselectivity for
most of the ketones listed in Table 2. Furthermore, the position and
electronic property of the ring substituents also influenced hydroge-
nation results. The highest enantioselectivity was found for transfer
hydrogenationofo-methoxyacetophenone (85% ee), while the lowest
enantioselectivity was observed in transfer hydrogenation of
p-methoxyacetophenone. From the results, the introduction of an
electron-donating group such as methoxy group to the p-position
decelerates the reaction, but that to the o-position increases the rate
and improves the enantioselectivity. The introduction of electron-
0
.77 and 0.82 eV. The very small difference between barrier height
results can be attributed differences at band structures of hetero-
junctions, existence of interface states at the interface and the
native oxide layer on n-Si semiconductor.
As seen the Fig. 2, the forward bias I–V characteristics of the
heterojunctions deviate from linearity because of the series resis-
tance. The series resistance of the structures can be calculated
Cheung functions. According to the method the series resistance
of a diode can be determined using following equations derived
from Eq. (1) [100]
2
withdrawing substituents, such as F or NO , to the para positions of
the aryl ring of the ketone, resulted in improved activity with good
enantioselectivity (entries 1–4 and 13–16, Table 2). The introduction
of electron withdrawing substituents 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
dV
dðln IÞ
nkT
q
¼
þ IR
S
ð5Þ
and
ꢀ
ꢁ
ꢀ
ꢁ
nkT
q
I
[
96,97].
HðIÞ ¼ V ꢁ
ln
¼ nUb þ IRS
ð6Þ
2
AA T
3.3. Electrical and photoelectrical properties of heterojunctions
Although all the structures formed using 13–16 were analyzed
and their results are given in this text, only figures of [(2R)-2-
(
(
ferrocenylmethylamino)-3-methylbutyl
diphenylphosphinito
6
dichloro(g -p-cymene)ruthenium(II))], 13 are presented in the
manuscript. Current–voltage (I–V) characteristics of all organic–
inorganic heterojunctions showed excellent rectification. The I–V
characteristics of Au/13/n-Si in dark and various illumination condi-
tions are given in Fig. 2. The weak voltage dependence of the
reverse–bias current and the exponential increase of the forward-
bias current are the characteristic properties of rectifying contacts
[
26]. An organic–inorganic rectifying diode can be analyzed by
means of thermionic emission theory. According to the theory, the
forward–bias I–V characteristics of a contact determined as [98]
ꢀ
Þꢁ
qðV ꢁ IR
S
I ¼ I
0
exp
ð1Þ
nkT
where q is the electronic charge, V the voltage drop across the diode,
the series resistance, n the ideality factor, k the Boltzmann
R
S
constant, T the absolute temperature and I
0
the saturation current
Fig. 2. The I–V plots of Au/13/n-Si structure in dark and under various illumination
written as [106]
conditions.

2
52
B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
Table 3
Table 4
Some electrical parameters of the heterojunction in dark.
Open circuit voltage and short circuit current values of heterojunctions under 40 and
1
00 mW/cm2 illuminations.
Complex ln I–V
dV/dln(I)
H (I)
C–V
Complex
V
1
OC (mV) at
I
SC
(
l
A) at
V
OC (mV) at
2
SC
I (lA) at
40 mW/cm
n
/
b
n
R
S
/
b
R
S
V
d
/
b
N
d
00 mW/cm2
100 mW/cm
2
40 mW/cm
2
1
1
1
1
6
6
6
6
1
1
1
1
3
4
5
6
1.50 0.79 1.61
1.51 0.77 1.86
1.82 0.79 2.21
1.59 0.82 1.84 141 0.80 156 0.75 0.97 1.41 ꢀ 10
59 0.74
16 0.68
28 0.73
63 0.75 0.95 1.12 ꢀ 10
18 0.65 0.85 1.26 ꢀ 10
40 0.77 0.96 1.36 ꢀ 10
13
14
15
346
306
386
356
234
127
187
181
336
246
337
336
48
37
47
26
16
The dV/d(lnI)–I and H(I)–I plots are linear in series resistance
regions. The slopes of these plots give series resistance of the junc-
tions. These two R
method. Y-axis intercept of dV/d(lnI)–I and H(I)–I graphs give n(kT/
q) and / values, respectively. The plots of Cheung functions for
S
values are used to check the consistency of the
b
Au/13/n-Si heterojunction are given in Fig. 3. The ideality factor,
barrier height and series resistance values of all structures were
calculated by the help of dV/d(lnI)–I and H(I)–I plots using Eqs.
(
5) and (6). The calculated values are also given in Table 3. As pre-
sented in the table, the obtained n values from dV/d(lnI)–I plots are
higher than the one obtained from lnI–V plots, which is attributed
to the existence of series resistance and interface states and to the
voltage drop across the interface layer [101]
Fig. 2 also presents I–V measurements taken under 40, 60, 80
2
and 100 mW/cm . As seen from the Fig. 2, the photocurrent (ISC
)
of the structure increases from 48 to 234 lA and the open circuit
voltage increases (VOC) from 336 to 346 mV when the light inten-
2
sity is increased from 40 to 100 mW/cm , indicating that the light
forms carrier-contributing photocurrent because of the production
of electron hole pairs as a result of light absorption [102]. Similar
results were obtained for other compounds and presented in
Table 4.
Frequency dependent C–V characteristics of Au/13/n-Si hetero-
junction are presented in Fig. 4. As seen in the Fig. 4, the capaci-
tance at positive voltages decreases with increasing frequency. It
implies that the interface states does not follow AC signal in higher
frequencies and the high frequency capacitance does not make an
important contribution to the total capacitance [27]. The C–V char-
acteristics of the Au/13/n-Si structure can be determined using
Fig. 4. The C–V plots of Au/13/n-Si structure at various frequencies and C 2–V plot
at 500 kHz as inset.
ꢁ
The barrier height of a diode can be determined calculate by the fol-
lowing relation [111]
ꢀ
ꢁ
Nc
/
¼ Vbi þ kT ln
ð8Þ
bðCꢁVÞ
N
d
[
103]
where N
c
is density of states in the conduction band. Firstly, the Vbi
–2
and N values of all diodes were determined by the help of C –V
d
1
2ðVbi þ VÞ
ꢁ
2
¼
ð7Þ
plots at 500 kHz. (C –V plot of the Au/13/n-Si at 500 kHz is de-
2
2
C
A
s
e qN
d
picted in the inset of Fig 4). Then, barrier heights of the devices were
calculated using Eq. (10). The Vbi, N and / values are also given in
d b
Table 3.
where
e
s
is the dielectric constant of semiconductor, N
d
the donor
concentration and Vbi the built-in potential determined from the
ꢁ2
extrapolation of the linear reverse bias C –V plot to the V axis.
4
. Conclusions
In summary, we have synthesized and characterized a new ser-
ies of ruthenium(II)-ferrocenyl-phosphinite catalysts, which are
effective for the asymmetric transfer hydrogenation (ATH) of ace-
tophenone derivatives. High yield and moderate to good enanti-
oselectivities were obtained by using the complexes as catalyst.
The simplicity and efficiency clearly make it an alternative choice
of catalyst for the practical preparation of highly valued alcohols
via the catalytic asymmetric transfer hydrogenation of ketones.
In addition, it was seen that organic–inorganic heterojunctions fab-
ricated using 13–16 present excellent rectification properties.
Their electrical properties were analyzed using I–V and C–V meth-
ods. The photoelectrical properties were also reported.
Acknowledgement
Partial support from Dicle University (Project number: DÜBAP-
07-01-22 and 10-ZEF-165) is gratefully acknowledged.
Fig. 3. The dV/d(lnI)–I and H(I)–I plots of Au/13/n-Si heterojunction.

B. Ak et al. / Inorganica Chimica Acta 409 (2014) 244–253
253
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