Rhodium-catalyzed transfer hydrogenation with aminophosphines and analysis of electrical characteristics of rhodium(I) complex/n-Si heterojunctions

Article abstract of DOI:10.1002/aoc.3140

A series of novel neutral mononuclear rhodium(I) complexes of the P-NH ligands have been prepared starting from [Rh(cod)Cl]₂ complex. Structural elucidation of the complexes was carried out by elemental analysis, IR and multinuclear NMR spectroscopic data. The complexes were applied to the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol derivatives in the presence of 2-propanol as the hydrogen source. Catalytic studies showed that all complexes are also excellent catalyst precursors for transfer hydrogenation of aryl alkyl ketones in 0.1m iso-PrOH solution. In particular, [Rh(cod)(PPh₂NH-C₆H₄-4-CH(CH ₃)₂)Cl] acts as an excellent catalyst, giving the corresponding alcohols in excellent conversion up to 99% (turnover frequency≤588h^-1). Furthermore, rhodium(I) complexes have been used in the formation of organic-inorganic heterojunction by forming their thin films on n-Si and evaporating Au on the films. It has been seen that the structures have rectifying properties. Their electrical properties have been analyzed with the help of current-voltage measurements. Finally, it has been shown that the complexes can be used in the fabrication of temperature and light sensors. Copyright

Full text of DOI:10.1002/aoc.3140

Full Paper
Received: 14 December 2013
Revised: 29 January 2014
Accepted: 18 February 2014
Published online in Wiley Online Library: 15 April 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3140
Rhodium-catalyzed transfer hydrogenation
with aminophosphines and analysis of electrical
characteristics of rhodium(I) complex/n-Si
heterojunctions
Murat Aydemira,b*, Yusuf Selim Ocakb,c, Khadichakhan Rafikovad,
Nurzhamal Kystaubayevad, Cezmi Kayana, Alexey Zazybind, Fatih Oka,
Akın Baysala and Hamdi Temelb,e
A series of novel neutral mononuclear rhodium(I) complexes of the P―NH ligands have been prepared starting from [Rh(cod)
Cl]2 complex. Structural elucidation of the complexes was carried out by elemental analysis, IR and multinuclear NMR spectro-
scopic data. The complexes were applied to the transfer hydrogenation of acetophenone derivatives to 1-phenylethanol
derivatives in the presence of 2-propanol as the hydrogen source. Catalytic studies showed that all complexes are also
excellent catalyst precursors for transfer hydrogenation of aryl alkyl ketones in 0.1 M iso-PrOH solution. In particular,
[Rh(cod)(PPh2NH―C6H4―4-CH(CH3)2)Cl] acts as an excellent catalyst, giving the corresponding alcohols in excellent con-
version up to 99% (turnover frequency ≤ 588 hꢀ1). Furthermore, rhodium(I) complexes have been used in the formation
of organic–inorganic heterojunction by forming their thin films on n-Si and evaporating Au on the films. It has been seen
that the structures have rectifying properties. Their electrical properties have been analyzed with the help of current–
voltage measurements. Finally, it has been shown that the complexes can be used in the fabrication of temperature
and light sensors. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: aminophosphine; rhodium; transfer hydrogenation; heterojunction; temperature sensor
of the most exciting and powerful methods of synthesizing
Introduction
alcohols, has been receiving increased attention as well and
has led to extraordinary success.[25] Specifically, the catalytic
Since the discovery that functional P-based ligands increase
considerably the activity and/or selectivity of metal catalysts,
transfer hydrogenation[26] of ketones is one of the most
the preparation of this type of ligand has been the subject of
extensive investigations.[1–4] Small variations in these ligands
can cause noteworthy changes in their coordination behavior
and the structural features of the formed complexes.[5–9]
Among these ligands, P―NH-containing ones have particular
use in catalysis where it is necessary for part of the ligand to
dissociate to allow an organic fragment to coordinate and undergo
transformations. The presence of P―N ligands enables many differ-
ent and important catalytic processes to occur including Heck[10,11]
and Suzuki[12,13] reactions. A large number of complexes with
aminophosphine ligands have also been evaluated in different
catalytic reactions, including allylic alkylation,[14] amination,[15]
Sonogashira,[16] hydroformylation,[17] hydrogenation[18] and poly-
merization[19] reactions.
attractive methods for synthesizing secondary alcohols, which
form an important class of intermediates for fine chemicals and
pharmaceuticals.[27,28]
There are several metal sources available that have to mediate
the hydride transfer from the donor to the substrate. Even if
main-group metals such as aluminum have historically been used
in the transfer hydrogenation reactions,[29,30] today’s catalysts of
*
Correspondence to: Murat Aydemir, Department of Chemistry, Faculty of Science,
University of Dicle, 21280 Diyarbakir, Turkey. E-mail: aydemir@dicle.edu.tr
a Department of Chemistry, Faculty of Science, University of Dicle, 21280,
Diyarbakir, Turkey
Catalytic hydrogenation with the aid of a stable hydrogen
donor is a useful alternative method for catalytic hydrogena-
tion by molecular hydrogen.[20,21] In transfer hydrogenation,
organic molecules such as primary and secondary alcohols[22] or
formic acid and its salts[23] have been employed as the hydrogen
source. In particular, transition-metal-catalyzed procedures for
transfer hydrogenation of a wide variety of functional groups by
different hydrogen donors are an interesting alternative to molecu-
lar hydrogenation.[24] The hydrogenation of ketones, which is one
b Science and Technology Application and Research Center, University of Dicle,
21280, Diyarbakir, Turkey
c
Department of Science, Faculty of Education, University of Dicle, 21280,
Diyarbakir, Turkey
d Department of Chemical Engineering, Kazakh–British Technical University,
050000, Almaty, Kazakhstan
e Faculty of Pharmacy, University of Dicle, 21280, Diyarbakir, Turkey
Appl. Organometal. Chem. 2014, 28, 396–404
Copyright © 2014 John Wiley & Sons, Ltd.

Transfer hydrogenation with aminophosphines and electrical features
choice are transition metal complexes predominantly of ruthe-
nium, rhodium[31] or iridium.[32–34] Although very frequently
ruthenium- or iridium-based catalysts have been applied in the
hydrogenation of various ketones,[35] rhodium complexes have
proven to lead very efficient processes along with potential
industrial applications.[36–38] Furthermore, organic electronics
have advanced in recent years because of the easy and low-cost
application processes.[39] Organic compounds have been used
in the fabrication of different kinds of electrical and optical
devices, including organic field effect transistors,[40] organic
light-emitting diodes,[41] Schottky diodes,[42] temperature and
light sensors[43,44] and solar cells.[45,46] Interest in the devices
formed by metal complexes has been increasing rapidly because
of their high thermal and mechanical stability.[47] Many studies
have been performed to use them with suitable structures and
for synthesis of new compounds that can be used for this pur-
pose.[45,48] Therefore, it can be said that both synthesis and usage
of metal complexes in the formation of electrical and optical
devices have great importance.
GC Analyses
GC analyses were performed on a Shimadzu 2010 Plus gas chro-
matograph equipped with capillary column (5% biphenyl, 95%
dimethylsiloxane) (30 m × 0.32 mm × 0.25 μm). The GC parame-
ters for transfer hydrogenation of ketones were as follows: initial
temperature, 110°C; initial time, 1 min; solvent delay, 4.48 min;
temperature ramp 80°C minꢀ1; final temperature, 200°C; final
time, 21.13 min; injector port temperature, 200°C; detector tem-
perature, 200°C, injection volume, 2.0 μl.
General Procedure for the Transfer Hydrogenation of Ketones
A typical procedure for the catalytic hydrogen transfer reaction is as
follows. A solution of rhodium complexes, [Rh(cod)(PPh2NH―
C6H4―2-CH(CH3)2)Cl] (1), [Rh(cod)(PPh2NH―C6H4―4-CH(CH3)2)Cl]
(2) or [Rh(cod)(PPh2NH―C6H3―2,6-(CH(CH3)2))2Cl] (3), NaOH
(0.05 mmol) and the corresponding ketone (1.0 mmol) in degassed
iso-PrOH (10 ml) were refluxed until the reactions were completed.
After this period a sample of the reaction mixture was withdrawn,
diluted with acetone and analyzed immediately by GC. The conver-
sions are related to the residual unreacted ketone.
The design and synthesis of aminophosphine ligands[49–52]
have played a significant role in the development of transition-
metal-catalyzed reactions.[53–55] In recent years, we have reported
upon the synthesis and applications of a number of modified
rhodium(I)–aminophosphine catalysts containing the arene rings
for transfer hydrogenation.[56–58] In view of the promising results,
the rhodium complexes were shown to be efficient homoge-
neous hydrogenation catalysts toward various substrates.[59,60]
By taking into account that the easily prepared aminophosphine
ligands were also found to be effective ligands for the rhodium-
catalyzed transfer hydrogenation, we thought that Rh(I)–
aminophosphine catalysts would be valuable material for
study. Herein we report the synthesis of novel [Rh(cod)
(PPh2NH―C6H4―2-CH(CH3)2)Cl] (1), [Rh(cod)(PPh2NH―C6H4―4-
CH(CH3)2)Cl] (2) and [Rh(cod)(PPh2NH―C6H3―2,6-(CH(CH3)2))2Cl]
(3) complexes and their presentation in the transfer hydrogenation
of various ketones. Another aim of this study was to show fabrica-
tion of organic–inorganic rectifying heterojunctions by novel
rhodium(I) complexes, determine their electrical properties by
current–voltage (I–V) measurements and present their tempera-
ture- and light-sensing properties.
Fabrication and Characterization of Heterojunctions
In the study, an n-Si semiconductor with (100) orientation and
1–10 Ω cm resistivity was used in the fabrication of devices.
First, the wafer was degreased by boiling in trichloroethylene
for 5 min and ultrasonically vibrated in 2-propanol and acetone
for 5 min. The wafer was rinsed in 0.4% HF–H2O solution to re-
move the native oxide of the wafer. After each step the wafer
was cleaned by deionized water. The n-Si semiconductor was
then dried under nitrogen atmosphere. An ohmic contact for
n-Si was formed by evaporating an Au contact on the
unpolished side of the semiconductor and annealing at 420°C
for 3 min under nitrogen atmosphere. Before the formation of
rhodium(I) complex thin films, the wafer was cut into several
parts. The thin films of rhodium(I) complexes were formed by
SCS G3P-8 spin coater. The thicknesses of the films were
measured as 112, 120 and 116 nm for rhodium(I) complexes,
respectively, with the help of a PHE-102 spectroscopic ellipsometer.
The front contacts on thin films were also obtained by evaporating
Au at high vacuum. The electrical properties of the devices were
obtained and compared by means of I–V data obtained at room
temperature in the dark using a Keithley 2400 source meter.
Furthermore, the temperature-sensing properties of the Au/1/n-Si
device were examined using I–V measurements between 300 and
380 K and light-sensing properties of the structure were tested un-
der a solar simulator with AM1.5 global filter and 40–100 mWcmꢀ2
illumination intensity.
Experimental
Materials and Methods
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,
2-isopropylaniline, 4-isopropylaniline and 2,6-diisopropylaniline
Synthesis of Rhodium(I)–Aminophosphine Complexes
Synthesis of [Rh(cod)(PPh2NH―C6H4―2-CH(CH3)2)Cl] (1)
were purchased from Fluka and used as received. The starting
[61]
material [Rh(cod)(μ-Cl)]2
was prepared according to the liter-
ature procedure. IR spectra were recorded on a Mattson 1000
ATI UNICAM FT-IR spectrometer as KBr pellets. 1H (400.1 MHz),
13C NMR (100.6 MHz) and 31P-{1H} NMR spectra (162.0 MHz)
A mixture of [Rh(cod)(μ-Cl)]2 (0.1 g, 0.20 mmol) and [Ph2PNH―
(C6H4) ―2-CH(CH3)2) ] (0.13 g, 0.41 mmol) in 20 ml THF was stirred
at room temperature for 1 h. The volume of the solvent was then
reduced to 0.5 ml before addition of petroleum ether–hexane
(15 ml). The precipitated product was filtered and dried in
vacuo, yielding 1 as a yellow microcrystalline powder. Yield
0.20 g, 89.1%; m.p. 180–182°C. 1H NMR (δ in ppm relative to
TMS, J Hz, in CDCl3): 7.85–7.81 (m, 4H, o-protons of phenyls),
were recorded on a Bruker AV400 spectrometer, with
δ
referenced to external TMS and 85% H3PO4 respectively. Ele-
mental analysis was carried out on a Fisons EA 1108 CHNS-O
instrument. Melting points were recorded by Gallenkamp
model apparatus with open capillaries.
Appl. Organometal. Chem. 2014, 28, 396–404
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Aydemir et al.
7.46–7.39 (m, 6H, m- and p-protons of phenyls), 7.08 (d, 1H, JH–
H = 7.6Hz, H-3), 6.85–6.80 (m, 1H, H-4), 6.72 (t, 1H, JH–H = 7.6 Hz, H-
5), 6.53 (d, 1H, H-6, J = 7.6Hz), 5.59 (s, 2H, CH―cod), 3.77 (s, 1H,
NH), 3.24–3.27 (m,1H, CH(CH3)2― aniline), 2.94 (s, 2H, ―CH―cod),
2.43–1.86 (m, 8H, ―CH2―cod), 1.09 (d, 6H, JH–H = 6.7Hz, CH(CH3)
2― aniline); 13C NMR (δ in ppm relative to TMS, J Hz, in CDCl3):
140.10 (C-1), 139.23 (C-2), 139.09 (i-carbons of phenyls),132.91
(o-carbons of phenyls), 130.56 (p-carbons of phenyls), 128.25
(m-carbons of phenyls), 125.66 (C-3), 125.19 (C-5), 121.92 (C-4),
120.37 (C-6), 104.70 (CH―cod), 72.03 (CH―cod), 32.67 (CH2―cod),
28.61 (CH2―cod), 27.13 (CH(CH3)2―aniline), 23.07 (CH(CH3)2―ani-
0.41 mmol) was added. The reaction mixture was allowed to
proceed with stirring at room temperature for 1 h. After this time,
the solution was filtered and the solvent evaporated under
vacuum. The solid residue thus obtained was washed with
diethyl ether (3 × 10 ml) and then dried under vacuum. Following
recrystallization from petroleum ether–hexane (15 ml), a light-
brown crystalline powder was obtained. Yield 0.20 g, 82.2%; m.
p. 190°C (dec). 1H NMR (δ in ppm relative to TMS, J Hz, in CDCl3):
7.62–7.58 (m, 4H, o-protons of phenyls), 7.41–7.33 (m, 6H, m- and
p-protons of phenyls), 7.28 (m, 1H, H-3), 7.04 (t, 1H, H-4, JH–H =7.6Hz),
6.89 (d, 1H, H-5, J=7.6 Hz), 5.77 (s, 1H, J= 9.0 Hz, NH), 5.60 (s, 2H,
CH―cod), 3.37–3.30 (m, 2H, CH(CH3)2, 2.82 (s, 2H, CH―cod),
2.45–2.33 (m, 4H, CH2―cod), 2.09–2.07 (m, 2H, CH2―cod),
1.91–1.87 (m, 2H, CH2―cod), 0.78 (d, 12H, JH–H = 6.7Hz, CH(CH3)2,
aniline); 13C NMR (δ in ppm relative to TMS, J Hz, in CDCl3): 146.90
(C-1), 136.29 (i-carbons of phenyls), 133.75 (o-carbons of phenyls),
131.54 (C-2), 131.07 (C-6), 130.31 (p-carbons of phenyls), 127.68
(m-carbons of phenyls), 125.86 (C-4), 123.17 (C-3), 123.15 (C-5),
104.66 (CH―cod), 71.80 (CH―cod), 32.63 (CH2―cod), 28.87 (CH
(CH3)2―aniline), 28.59 (CH2―cod), 23.73 (CH (CH3)2―aniline);
assignment was based on 1H–13C HETCOR and 1H–1H COSY
spectra; 31P-{1H} NMR (δ in ppm relative to H3PO4, in CDCl3):
65.63 (d, JRhP = 157.1 Hz); selected IR data (KBr pellet, in
cmꢀ1): υ 930 (PN), υ 1435 (PPh), υ 3250 (NH); [C32H40NPRhCl]
(607.99 g molꢀ1): calcd C 63.21, H 6.63, N 2.30; found C
63.12, H 6.56, N 2.28%.
line); assignment was based on H–13C HETCOR and H–1H COSY
spectra; 31P-{1H} NMR (δ in ppm relative to H3PO4, in CDCl3): 56.68
(d, JRhP =157.1 Hz); selected IR (KBr pellet, in cmꢀ1): υ 917 (PN),
υ 1434 (PPh), υ 3239 (NH); [C29H34NPRhCl] (565.91 g molꢀ1):
calcd C 61.55, H 6.06, N 2.47; found C 61.49, H 5.96, N 2.44.%.
1
1
Synthesis of [Rh(cod)(PPh2NH―C6H3―4-CH(CH3)2)Cl] (2)
To a solution of [Rh(cod)(μ-Cl)]2 (0.35 g, 0.70 mmol) in THF, a solu-
tion (THF, 30 ml) of [Ph2PNH― (C6H4) ―4-CH(CH3)2] (0.45 g,
1.40 mmol) was added. The reaction mixture was allowed to
proceed with stirring at room temperature for 1 h. After this time,
the solution was filtered and the solvent evaporated under
vacuum. The solid residue thus obtained was washed with
diethyl ether (3 × 10 ml) and then dried under vacuum. Following
ecrystallization from petroleum ether–hexane (15 ml), a light crys-
talline powder was obtained. Yield 0.72 g, 90.1%; m.p. 153–156°C.
1H NMR (δ in ppm relative to TMS, J Hz, in CDCl3): 7.94–7.82
(m, 4H, o-protons of phenyls), 7.50–7.40 (m, 6H, m- and p-protons
of phenyls), 6.84 (d, 2H, H-3 and H-5, JH–H = 8.4Hz), 6.53 (d, 2H,
H-2 and H-6, J = 8.4 Hz), 5.64–5.54 (m, 2H, CH―cod), 4.60 (s, 1H,
NH), 3.36–2.96 (m, 2H, CH―cod), 2.43-2.39 (m, 2H, CH2―cod and
1H, CH(CH3)2), 2.33–1.88 (m, 6H, CH2―cod), 1.12 (d, 6H, ―CH
(CH3)2 aniline, JH–H = 6.8 Hz); 13C NMR (δ in ppm relative to TMS, J
Hz, in CDCl3): 141.32 (C-1), 139.81 (C-4), 139.52 (i-carbons of
phenyls),132.91 (o-carbons of phenyls), 130.60 (p-carbons of
phenyls), 128.32 (m-carbons of phenyls), 127.20 (C-2), 126.51 (C-6),
119.15 (C-3), 118.52 (C-5), 104.78 (CH―cod), 71.61 (CH―cod),
33.12 (CH2―cod), 28.60 (―CH(CH3)2―aniline), 28.03(CH2―cod),
23.97 (―CH(CH3)2―aniline); assignment was based on 1H–13C
HETCOR and 1H–1H COSY spectra; 31P-{1H} NMR (δ in ppm relative
to H3PO4, in CDCl3): 55.20 (d, JRhP = 157.1Hz); selected IR (KBr pellet,
in cmꢀ1): υ 921 (PN), υ 1435 (PPh), υ 3244 (NH); [C29H34NPRhCl]
(565.91 g molꢀ1): calcd C 61.55, H 6.06, N 2.47; found C 61.48,
H 5.94, N 2.42%.
Results and Discussion
Synthesis and Characterization of the Metal Complexes
As shown in Scheme 1, three (N-diphenylphosphino)-isopropy-
laniline ligands, having isopropyl substituent at carbon 2-, 4-, or
2,6-, were synthesized from the aminolysis[62] of chlorodiphenyl-
phosphine with 2-isopropylaniline, 4-isopropylaniline or 2,6-
diisopropylaniline, respectively, under anaerobic conditions It is
well known that aminolysis[63,64] appears to be the most common
method used for the synthesis of aminophosphines,[65,66] whereby
the solvent has a significant influence on the rate and product of
the aminolysis. (N-Diphenylphosphino)-isopropylanilines, having
isopropyl substituent at the carbon 2- or 2,6-, were easily
prepared from the aminolysis of H2N―C6H4―2-CH(CH3)2 or
H2N―C6H4―2,6-{CH(CH3)2}2, respectively, with
1 equiv. of
chlorodiphenylphosphine in the presence of triethylamine using
THF/CH2Cl2 (1/2) and CH2Cl2 as a solvent, respectively. Both
compounds were isolated as viscous oily substances in high yield
under anaerobic conditions. However, the attempt to synthesize
(N-diphenylphosphino)-4-isoprophylaniline hardly succeeded,
owing to the formation of N,N-bis(diphenylphosphino)-4-
isopropylaniline. Therefore, preparation of (N-
Synthesis of [Rh(cod)(PPh2NH―C6H3―2,6-(CH(CH3)2))2Cl] (3)
To a solution of [Rh(cod)(μ-Cl)]2 (0.10 g, 0.20 mmol) in THF, a solu-
tion (THF, 30 ml) of [Ph2PNH― (C6H3) ―2,6-{CH(CH3)2}2] (0.15 g,
diphenylphosphino)-4-isopropylaniline
was
achieved only with 1 equiv. of Ph2PCl, in the
presence of n-BuLi at ꢀ78°C as a yellow, viscous
oily compound (Scheme 1). These three
aminophosphines were fully characterized by
multinuclear NMR, IR spectroscopy and elemen-
tal analysis. The 31P-{1H} NMR spectra of ligands,
2-, 4- and 2,6- show single resonances at δ 29.0,
31.8 and 45.5 ppm, respectively, comparable to
those of other aminophosphines.[67] Further-
more, characteristic J(31P–13C) coupling con-
stants of the carbons of the phenyl rings were
Scheme 1. Synthesis of aminophosphine ligands and their [Rh(cod)(PPh2NH―C6H4―2-CH
(CH3)2)Cl] (1), [Rh(cod)(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) and [Rh(cod)(PPh2NH―C6H3―2,6-
(CH(CH3)2))2Cl] (3) complexes: (i) 1 equiv. Ph2PCl, 1 equiv. Et3N, THF/CH2Cl2 (1/2) for 1; 1 equiv.
n-BuLi at ꢀ78°C, 1 equiv. Ph2PCl, 1 equiv. Et3N, CH2Cl2, for 2; 1 equiv. Ph2PCl, 1 equiv. Et3N,
CH2Cl2 for 3; (ii) 1/2 equiv. [Rh(μ-Cl)(cod)]2, THF, for 1–3.
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 396–404

Transfer hydrogenation with aminophosphines and electrical features
observed in the 13C NMR spectrum (including i-, o-, m-, p- carbons of
phenyl rings; for details see Experimental section) which were
consistent with literature values.[68] These compounds are unstable
in solution toward oxidation when exposed to air or moisture. Solu-
tion of ligands in CDCl3, prepared under anaerobic conditions, is ox-
idized gradually to give respective oxide and bis(diphenylphosphino)
monoxide [P(O)Ph2PPh2] derivatives.
Catalytic Transfer Hydrogenation of Acetophenone Derivatives
Recently we reported that the novel half-sandwich metal com-
plexes, based on the ligands with a P―NH backbone, are active
catalysts in the reduction of aromatic ketones.[72–76] The complex
with sp3-hybribized nitrogen containing N―H bonds displays a
higher reaction rate. On the other hand, the presence of an
N―H group in the ligands makes it possible to stabilize a six-
membered cyclic transition state by forming a hydrogen bond
with the oxygen atom of ketones.[77–79] Therefore, these kinds
of ligands are attractive and also widely used, especially in
ruthenium, rhodium and iridium complexes, for catalytic transfer
hydrogenation reactions.[80–83]
In a preliminary study, the catalytic activity of complexes 1–3
in transfer hydrogenation of aromatic ketones by iso-PrOH was
investigated. In a typical experiment, 0.01 mmol of the complex
and 1 mmol acetophenone were added to a solution of NaOH
in iso-PrOH (0.05 mmol NaOH in 10 ml iso-PrOH), refluxed at
82°C and the reaction was monitored by GC. Complexes 1–3
were employed as a precursor for the catalytic transfer hydro-
genation of the acetophenone by iso-PrOH /NaOH as a reduc-
ing system, and the results are summarized in Table 1. These
three complexes catalyzed the reduction of ketones to the
corresponding alcohols via hydrogen transfer from iso-PrOH
in all reactions. At room temperature no appreciable formation
of 1-phenylethanol was found (Table 1, entries 1–3). It is well
known that the base facilitates the formation of ruthenium alkoxide
by abstracting proton of the alcohol, and subsequently alkoxide
undergoes β-elimination to give ruthenium hydride, which is an
active species in this reaction. This is the mechanism proposed by
several research groups on studies of rhodium-catalyzed transfer
hydrogenation reaction by metal hydride intermediates.[84–91] The
role of the base is to generate a more nucleophilic alkoxide ion
which would rapidly attack the rhodium complex responsible for
dehydrogenation of iso-PrOH. As can be seen from Table 1 (entries
4–6), the pre-catalysts as well as the presence of NaOH are neces-
sary to observe appreciable conversions. As Table 1 shows, high
conversions can be achieved with the 1–3 catalytic systems. As seen
in Table 1, increasing the substrate–catalyst ratio does not lower
conversion of the product in most cases,
We examined simple coordination chemistry of [Rh(cod)(μ-Cl)]2
with [Ph2PNH― (C6H4) ―2-CH(CH3)2], [Ph2PNH― (C6H4) ―4-CH
(CH3)2] and [Ph2PNH― (C6H3) ―2,6-{CH(CH3)2}2] aminophosphine
ligands. Reactions of [Rh(cod)(μ-Cl)]2 with (N-diphenylphosphino)-
2-isopropylaniline, (N-diphenylphosphino)-4-isopropylaniline and
(N-diphenylphosphino)-2,6-diisopropylaniline in THF in a ratio of
1/2:1 at room temperature for 1 h gave a microcrystalline
precipitate of neutral complexes 1–3, respectively. Complexation
reactions were straightforward, with coordination to rhodium be-
ing carried out at room temperature. These ligands were expected
to cleave the [Rh(cod)(μ-Cl)]2 dimer to give the corresponding
complexes via monohapto coordination of the aminophosphine
groups. Bridge cleavage of the dimer, [Rh(cod)(μ-Cl)]2 with
aminophosphines gave the mononuclear complexes in high
yields. These complexes are highly soluble in CH2Cl2 and
slightly soluble in hexane, and they can be crystallized from
petroleum ether–hexane solution. The coordination of the ligand
through the P donor was confirmed by 31P-{1H} NMR spec-
troscopy. Compounds 1–3 were isolated as indicated by doublets
1
in the 31P-{1H} NMR spectra at δ 56.68 (d, JRhP: 157.1 Hz), 55.20
1
1
(d, JRhP: 157.1 Hz) and 65.63 (d, JRhP: 157.1 Hz) ppm, respec-
tively (Fig. 1),[69,70] indicating that aminophosphine ligands act
as monodentate ligands. Analysis by 1H NMR reveals these
compounds to be diamagnetic, exhibiting signals corresponding
to the aromatic rings for 1–3 at approximately 7.94–7.33 ppm
(for details see Experimental section). Furthermore, in the
13C-{1H} NMR spectrum of 1, J(31P–13C) coupling constants of the
carbons of the phenyl rings were observed which were consistent
with literature values.[71] The structural compositions of com-
plexes 1–3 were further confirmed by IR spectroscopy and
microanalysis, and were found to be in good agreement with
theoretical values.
except for lengthening the time.
Remarkably, transfer hydrogenation of
acetophenone could achieve up to
99% conversion even when the sub-
strate–catalyst ratio reached 1000:1
(Table 1, entries 7–9). In addition, the
choice of base, such as KOH and NaOH,
had little influence on the conversion
(Table 1, entries 10–12). Outcomes
obtained from optimization studies indi-
cated clearly that excellent conversions
were achieved in the reduction of ace-
tophenone to 1-phenylethanol when
Rh(I)–aminophosphine catalysts were
used as the catalytic precursor, with a
substrate–catalyst molar ratio (100:1) in
iso-PrOH at 82°C (Table 1, entries 13–15).
With a complex–NaOH ratio of 1/5, the
catalyst systems are very active, leading
to a quantitative transformation of the
Figure 1. The 31P-{1H} NMR spectra of [Rh(cod)(PPh2NH-C6H4-2-CH(CH3)2)Cl] (1), [Rh(cod)(PPh2NH-C6H4-4-
CH(CH3)2)Cl] (2) and [Rh(cod)(PPh2NH-C6H4-2,6-(CH(CH3)2))2Cl] (3) complexes.
acetophenone, with a good turnover
frequency (TOF) of <396 hꢀ1
.
Appl. Organometal. Chem. 2014, 28, 396–404
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Aydemir et al.
Table 1. Transfer hydrogenation of acetophenone with iso-PrOH cata-
lyzed by [Rh(cod)(PPh2NH―C6H4―2-CH(CH3)2)Cl] (1), [Rh(cod)
(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) and [Rh(cod)(PPh2NH―C6H3―2,6-
(CH(CH3)2))2Cl] (3)
Table 2. Transfer hydrogenation results for substituted acetophenones
with catalyst systems [Rh(cod)(PPh2NH―C6H4―2-CH(CH3)2)Cl]
(1), [Rh(cod)(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) and [Rh(cod)
(PPh2NH―C6H3―2,6-(CH(CH3)2))2Cl] (3)a
c
Conversion(%)f
TOF
g
Entry
R
Time
Conversion (%)b
TOF (hꢀ1
)
Entry
Catalyst S/C/NaOH
Time
(hꢀ1
)
Catalyst: [Rh(cod)(PPh2NH―C6H4―2-CH(CH3)2)Cl], (1)
1
1a
2a
100:1:5
100:1:5
100:1:5
100:1
1 h
1 h
1 h
2 h
<5
<5
<5
<5
1
2
3
4
5
6
4-F
30 min
45 min
45 min
30 min
1 h
98
99
99
99
98
97
198
132
132
198
98
2
4-Cl
3
3a
4-Br
4
1b
4-NO2
2-MeO
4-MeO
5[b]
6[b]
7[c]
8
100:1
100:1
1000:1:5
2c
2 h
<5
2 h
<5
2 h
49
3 h
99
33
99
20
98
99
99
99
99
98
Catalyst: [Rh(cod)(PPh2NH―C6H3―4-CH(CH3)2)Cl], (2)
1000:1:5
5 h
1 h
99
7
4-F
10 min
15 min
20 min
10 min
30 min
1 h
98
99
98
99
99
98
588
396
294
594
198
98
9[c]
10
11
12
13
14
15
1000:1:5
1d
98
8
4-Cl
100:1:5
100:1:5
100:1:5
100:1:5
100:1:5
100:1:5
45 min
15 min
1 h
33
99
9
4-Br
2d
10
11
12
4-NO2
2-MeO
4-MeO
3d
20
1e
45 min
15 min
1 h
131
396
98
2e
3e
Catalyst: [Rh(cod)(PPh2NH―C6H3―2,6-(CH(CH3)2))2Cl], (3)
13
14
15
16
17
18
4-F
30 min
45 min
1 h
99
99
98
98
99
98
198
125
98
Reaction conditions:
aAt room temperature; acetophenone/catalyst/NaOH, 100:1:5,
4-Cl
4-Br
bRefluxing in iso-PrOH; acetophenone/catalyst, 100:1, in the
4-NO2
2-MeO
4-MeO
30 min
2 h
196
50
absence of base,
cRefluxing in iso-PrOH; acetophenone/Ru/NaOH, 1000:1:5,
dRefluxing in iso-PrOH; acetophenone/catalyst/KOH, 100:1:5,
eRefluxing in iso-PrOH; acetophenone/catalyst/NaOH, 100:1:5,
fDetermined by GC (three independent catalytic experiments),
gReferred at the reaction time indicated in column; TOF = (moles
3 h
33
Reaction conditions:
aCatalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (10 ml),
NaOH (0.05 mmol%), 82°C, respectively; concentration of
acetophenone derivatives is 0.1 M.
product/moles catalyst) × hꢀ1
.
bPurity of compounds is checked by NMR and GC (three
independent catalytic experiments); yields are based on
methyl aryl ketone.
cTOF = (moles product/moles catalyst) × hꢀ1
.
As seen in Table 1, catalytic activities in the studied hydrogen
transfer reactions were generally much higher for the [Rh(cod)
(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) than for the [Rh(cod)
(PPh2NH―C6H4―2-CH(CH3)2)Cl] (1) and [Rh(cod)(PPh2NH―
C6H3―2,6-(CH(CH3)2))2Cl] (3). Under identical conditions, trans-
fer hydrogenation of acetophenone derivatives with system 2
led to 99% conversion within 15 min whereas, with catalysts
1 and 3 as the auxiliary, similar (99% and 98%) conversions
were achieved only after periods of 45 min and 1 h, respec-
tively (Table 1).
Encouraged by the high catalytic activities obtained in these
preliminary studies, we next extended our investigations to in-
clude hydrogenation of various simple ketones. First, the
catalysts [Rh(cod)(PPh2NH―C6H4―2-CH(CH3)2)Cl] (1), [Rh(cod)
(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) and [Rh(cod)(PPh2NH―
C6H4―2,6-(CH(CH3)2))2Cl] (3) were extensively investigated with
acetophenone derivatives (Table 2). The catalytic reduction of
acetophenone derivatives was tested with the conditions opti-
mized for acetophenone, and the results are given in Table 2,
which illustrates conversions of the reduction performed in
0.1 M iso-PrOH solution containing complexes 1–3 and NaOH
(ketone:catalyst:NaOH = 100:1:5). It is well known that the nature
and position of the substituents on the phenyl ring of the ketone
cause significant changes in the reduction rate.[92] For instance,
the introduction of electron-withdrawing substituents, such as
F, Cl and NO2, 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
(Table 2, entries 1–4, 7–10 and 13–16).[93,94] Conversely, 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, entries 5, 6, 11, 12, 17 and 18).
Extensive research indicates clearly that with each of the tested
complexes the best yield was achieved in the reduction of
acetophenone derivatives when [Rh(cod)(PPh2NH–C6H4–4-CH
(CH3)2)Cl] (2) was used as the catalyst.
We also conducted further experiments to explore the effect
of bulkiness of the alkyl groups on catalytic activity, and the
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 396–404

Transfer hydrogenation with aminophosphines and electrical features
results are given in Table 3 (entries 1–12). A variety of simple
aryl alkyl ketones were transformed to the corresponding sec-
ondary alcohols, and it was found that catalytic activity was
highly dependent on the steric hindrance of the alkyl group.
The reactivity regularly decreased by increasing the bulkiness
of the alkyl groups.[95–97]
Determination of some Electrical Properties of Heterojunctions
Formed Using Rhodium(I) Thin Films
I–V plots of Au/1/n-Si, Au/2/n-Si and Au/3/n-Si structures are
presented in Fig. 2. The figure indicates that all structures have
rectifying behavior which is limited by the properties of the
inorganic semiconductor substrate and the magnitude of the
energy barrier at the hetero interface, i.e. while the reverse
current demonstrated excellent saturation, the forward current
increased exponentially with voltage.[98] Therefore the I–V data
can be analyzed by thermionic emission theory. According to
the theory, the relationship between applied voltage and cur-
rent may be written as[99]
Figure 2. ln I–V plots of the diodes formed using rhodium(I) complex
thin films.
ꢀ
ꢁ
ꢀ
ꢁ
ideality factor. The ideality factors of Au/1/n-Si, Au/2/n-Si and Au/
3/n-Si were determined from the slope of the linear parts of the
forward-bias I–V plots as 1.82, 1.37 and 1.88, respectively.
According to the theory, the ideality factor of a diode should
be close to unity. The deviation from unity for the structures
can be attributed to effects of series resistance, existence of
interface state densities and fabrication-induced defects. The
barrier heights of the Au/1/n-Si, Au/2/n-Si and Au/3/n-Si
heterojunctions were extracted from saturation current values
as 0.76, 0.76 and 0.74 eV, respectively, which imply very simi-
lar band structures at organic–inorganic interface. The small
difference between the values can be attributed to effects
of natural oxide layers on n-Si formed during fabrication pro-
cesses and interface states. Similar structures have also been
reported with different metal complexes in the litera-
ture.[48,100,101] Temel et al.[48] synthesized N2S2O2 thio Schiff
base ligand and its Cu(II), Co(III), Ni(II) and Pd(II) complexes,
and presented their usage in the fabrication of organic–inor-
ganic hybrid devices. They showed that the structures had
good rectifying properties and their barrier height values
changed between 0.78 and 0.88 eV, which is remarkably
higher than conventional Al/n-Si metal–semiconductor con-
tact. El-Nahass et al.[102] fabricated an Au/NiPc/n-Si hete-
rojunction by forming NiPc thin films on n-Si using an
evaporation technique. They calculated the ideality factor
and barrier height values of the Au/NiPc/n-Si diode as 1.68
and 0.55 eV, respectively.
qϕb
kT
qðV ꢀ IRsÞ
ꢁ
I ¼ AA T2 exp
exp
(1)
nkT
where
ꢀ
ꢁ
qϕb
kT
ꢁ
I0 ¼ AA T2 exp
(2)
is the saturation current, A is the effective diode area, A* is the
Richardson constant, q is the electronic charge, ϕb is the barrier
height of the diode, k is the Boltzmann constant, T is the absolute
temperature, Rs is the series resistance and n is the dimensionless
Table 3. Transfer hydrogenation results for substituted alkyl phenyl
ketones with the catalyst systems [Rh(cod)(PPh2NH―C6H4―2-CH
(CH3)2)Cl] (1), [Rh(cod)(PPh2NH―C6H4―4-CH(CH3)2)Cl] (2) and [Rh
(cod)(PPh2NH―C6H4―2,6-(CH(CH3)2))2Cl] (3)a
Entry Catalyst Time Substrate
Product Conversion TOF
(%)b
(hꢀ1
)
c
1
1
2
3
1
2
3
1
2
3
1
2
3
1 h
Substrate 1 Product 1
99
98
99
99
98
98
99
99
98
98
98
98
99
294
149
149
196
49
2
1/3 h
3/2 h
3
4
3/2 h Substrate 2 Product 2
5
1/2 h
2 h
6
The deviations from linearity in ln I–V plots in Fig. 2 show the
effect of series resistance. The series resistance of the diodes
can be calculated using one of the common equations proposed
by Norde:[103]
7
2 h
1 h
3 h
4 h
2 h
5 h
Substrate 3 Product 3
Substrate 4 Product 4
50
8
99
9
33
10
11
12
25
ꢀ
ꢁ
V
1
IðVÞ
49
FðVÞ ¼
ꢀ
(3)
ꢁ
AA T2
20
2
β
aCatalyst (0.01 mmol), substrate (1.0 mmol), iso-PrOH (5 ml), NaOH
(0.05 mmol%), 82°C, respectively; concentration of alkyl phenyl
ketones is 0.1 M.
where I(V) is the current obtained from I–V data. The barrier
height value is calculated using the following equation, with
the help of the minimum value of F vs. V plot:
bPurity of compounds is checked by NMR and GC (three
independent catalytic experiments); yields are based on
methyl aryl ketone.
V0 kT
cTOF = (moles product/moles catalyst) × hꢀ1
.
ϕb ¼ FðV0Þ þ
ꢀ
(4)
2
q
Appl. Organometal. Chem. 2014, 28, 396–404
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Aydemir et al.
where F(V0) is the minimum F(V) value and V0 is the corres-
ponding voltage value. F(V)–V plots of the structures obtained
using the rhodium(I) complexes are presented in Fig. 3. The series
resistance (Rs) of a diode is defined by the relation
where Imin is the corresponding current value at V0. The barrier
height values and series resistance values of Au/1/n-Si, Au/2/n-Si
and Au/3/n-Si heterostructures were calculated as 0.87, 0.81 and
0.85 eV and 138, 434 and 132 Ω, respectively.
Temperature- and Light-Sensing Properties of a Heterojunction
Formed Using Rhodium(I) Thin Film
kTð2 ꢀ nÞ
Rs ¼
(5)
qImin
The temperature-dependent I–V plot of Au/1/n-Si heterojunction
between 300 and 380 K in the dark is presented in Fig. 4(a). As
clearly seen from the figure, temperature has a strong effect,
especially on reverse-bias I–V characteristics of the diode. When
the temperature was increased at the same time, the reverse
current increased for fixed voltage. This shows that the structure
can be used as a temperature sensor. The temperature depen-
dence of ideality factor and barrier height values was executed
with the help of equations (1) and (2). As presented in Fig. 4(b),
the ideality factor value of the device decreased from 1.82 to
1.16 and the barrier height value of the structure increased from
0.76 to 0.85 eV with increase in temperature. When the therm-
ionic emission theory is considered, it can be seen that the
current transport has strong temperature dependence. Electrons
at low temperatures are able to overcome the lower barriers and
the current transport will be dominated by current flow through
the patches of lower Schottky barrier height and a larger ideality
factor.[104–106] When the temperature increases, more electrons
have sufficient energy to surmount the higher barrier. The
sensitivity of organic–inorganic diodes to temperature has been
Figure 3. F-V plots of the diodes formed using rhodium(I) complex
thin films.
Figure 4. (a) The temperature dependent I-V plot of Au/1/n-Si hetero-
junction between 300 and 380 K. (b) The temperature dependence of
ideality factor and barrier height values of Au/1/n-Si heterojunction.
Figure 5. (a) The light intensity dependent I-V plot of Au/1/n-Si
heterojunction. (b) The light intensity dependence of photoelectrical
parameters of Au/1/n-Si heterojunction.
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 396–404

Transfer hydrogenation with aminophosphines and electrical features
also reported by different authors.[105,107] For instance, the
References
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as a result of the light absorption. Figure 5(b) shows the effects of
light intensity on light sensitivity, open circuit current (Isc) and
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Acknowledgment
Partial support from Dicle University (Project number: DÜBAP-12-
FF-140) is gratefully acknowledged.
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