Ruthenium-catalyzed transfer hydrogenation of aromatic ketones with aminophosphine or bis(phosphino)amine ligands derived from isopropyl substituted anilines

Article abstract of DOI:10.1016/j.poly.2009.12.035

A series of new highly active Ru(II) complexes with two new (N-diphenylphosphino)isopropylanilines, having an isopropyl substituent at carbon 2- (1) or 2,6- (2) and two new bis(diphenylphosphino)isopropylanilines, having an isopropyl substituent at carbon

Full text of DOI:10.1016/j.poly.2009.12.035

Polyhedron 29 (2010) 1219–1224
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Ruthenium-catalyzed transfer hydrogenation of aromatic ketones with
aminophosphine or bis(phosphino)amine ligands derived from isopropyl
substituted anilines
*
Murat Aydemir , Akın Baysal
Department of Chemistry, Dicle University, 21280 Diyarbakır, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new highly active Ru(II) complexes with two new (N-diphenylphosphino)isopropylanilines,
having an isopropyl substituent at carbon 2- (1) or 2,6- (2) and two new bis(diphenylphosphino)isopro-
pylanilines, having an isopropyl substituent at carbon atom 2- (3) or 4- (4), were prepared starting from
Received 5 August 2009
Accepted 18 December 2009
Available online 13 January 2010
the dimeric complex [Ru(g l-Cl)Cl]2. All the compounds have been fully characterized by
6-p-cymene)(
microanalysis, IR, 31P{1H} NMR, 1H NMR and 13C NMR spectroscopies. Following activation by NaOH,
complexes 5–8 were tested in the transfer hydrogenation of acetophenone derivatives with iso-PrOH
as the hydrogen source. Catalytic studies showed that the complexes are excellent catalytic precursors
for the transfer hydrogenation of acetophenone derivatives.
Keywords:
Catalysis
Transfer hydrogenation
Aminophosphine
Bis(phosphino)amine
Ruthenium
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Organic synthesis needs economically and technically more
benign methods that are very general. From an industrial
The chemistry of compounds containing phosphorus and nitro-
gen, with direct bonds between the two elements, has been known
for many years, but continues to attract considerable attention,
with applications in increasingly diverse fields [1,2]. Potentially this
ligand family is extremely attractive since preparative routes en-
able access to various structural modifications via simple P–N bond
formation [3]. Aminophosphines and bis(phosphine)amines, with
P–NH and P–N–P skeletons respectively, have proved to be much
more versatile ligands, and varying the substituents on both the
P- and N centres gives rise to changes in the P–N–P angle and the
conformation around the P-centres [4,5]. Small variations in these
ligands can cause significant changes in their coordination behav-
iour and the structural features of the resulting complexes [6].
There has been recently an increasing interest in the synthesis
of new and highly active transition-metal based catalysts derived
from aminophosphines that can be used in different catalytic
reactions including allylic alkylation [7,8], amination [9,10], Heck
[11–13], Suzuki [14–16], hydroformylation [17,18], Sonogashira
[19], polymerization [20] and hydrogenation reactions [21,22].
Some aminophosphines and derivatives have also found applica-
tion as anticancer drugs [23], herbicides and antimicrobial agents,
as well as neuroactive agents [24].
point of view, catalytic transfer hydrogenation is an attractive
alternative for high-pressure catalytic hydrogenation with molecu-
lar hydrogen [25]. Transition metal catalyzed transfer hydrogena-
tion with 2-propanol is a convenient method to reduce ketones
since there is no need for high hydrogen pressure or hazardous
reducing agents [26,27]. Homogeneous ruthenium complexes are
considered to be the most attractive catalysts for transfer hydroge-
nation reactions, though other metal complexes have also been
used successfully [28,29]. Varying levels of efficiency were
observed for ruthenium complexes with ligands such as diamines
[30], amino alcohols [31,32], phosphanes [33] and aminophos-
phines [34].
In the present report, from readily available starting materials,
such as isopropyl substituted anilines, two Ru(II)–aminophosphine
and two Ru(II)-bis(phosphino)amine complexes have been
prepared and characterized. As a part of our interest in designing
new ligand systems with different spacers to control the electronic
attributes at the phosphorus centers and to explore their coordina-
tion chemistry, we report here the synthesis of the Ru(II)
complexes [Ru(
g
6-p-cymene)(PPh2NH–C6H4-2-CH(CH3)2)Cl2] (5),
[Ru(g
6-p-cymene)(PPh2NH–C6H3-2,6-(CH(CH3)2)2)Cl2] (6), [Ru-
((PPh2)2N–C6H4-2-CH(CH3)2)2Cl2] (7) and [Ru((PPh2)2N–C6H4-4-
CH(CH3)2)2Cl2] (8), and these complexes were also evaluated in
the ruthenium-catalyzed transfer hydrogenation of acetophenone
derivatives.
* Corresponding author.
E-mail address: aydemir4921@hotmail.com (M. Aydemir).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.035

1220
M. Aydemir, A. Baysal / Polyhedron 29 (2010) 1219–1224
(4), were easily prepared from the reaction of H2N–C6H4-2-
2. Results and discussion
CH(CH3)2 or H2N–C6H4-4-CH(CH3)2, respectively, with two equiva-
lents of chlorodiphenylphosphine in the presence of triethylamine
in thf solution at 0 °C [44]. Attempts to prepare N,N-bis(diphenyl-
phosphino)-2,6-diisopropylaniline did not succeed, possibly due to
the steric repulsion between the two isopropyl groups and phenyl
rings of the phosphine. We also examined some simple coordina-
2.1. Synthesis and characterization of the Ru(II) complexes
Following our previous studies [35,36], we prepared a series of
ruthenium complexes 5–8 from the reaction of [RuCl(l-Cl)(p-cym-
ene)]2 with the monodendate 1, 2 and chelate ligands 3, 4 as
tion chemistry of 3 and 4 with the [Ru(g l-Cl)Cl]2
6-p-cymene)(
shown in Scheme 1.
precursor. The complexation reactions were straightforward, with
coordination to ruthenium being carried out at room temperature.
Complexes 7 and 8 were formed as fine powders (Scheme 1). The
reactions between the Ru(II) precursor and the bis(phos-
phino)amine ligands 3 and 4 were not affected by the molar ratio
(N-diphenylphosphino)isopropylanilines, having an isopropyl
substituent at carbon 2- (1) or 2,6- (2), were easily prepared from
the aminolysis of H2N–C6H4-2-CH(CH3)2 or H2N–C6H3-2,6-
(CH(CH3)2)2, respectively, with one equivalent of chlorodiphenyl-
phosphine in the presence of triethylamine at 0 °C, using thf/
CH2Cl2 (1/2) and CH2Cl2 as the solvent, respectively [37]. The reac-
of [Ru(g l-Cl)Cl]2 nor by the steric and electronic
6-p-cymene)(
tions of [Ru(g l-Cl)Cl]2 with PPh2NH–C6H4-2-
6-p-cymene)(
properties of the donor phosphorus atoms. The reaction of
(PPh2)2N–C6H4-2-CH(CH3)2, 3 and (PPh2)2N–C6H4-4-CH(CH3)2, 4
CH(CH3)2, 1 and PPh2NH–C6H3-2,6-(CH(CH3)2)2, 2 in CH2Cl2 in a ra-
tio of 1/2:1 at room temperature for 3 h gave a yellow insoluble
micro-crystalline precipitate of the neutral complexes 5 and 6,
respectively. The 31P{1H} NMR spectra of 5 and 6 show single
peaks at 51.62 and 57.69 ppm, respectively, in line with the values
previously observed for similar compounds [38,39] (see Supple-
mentary information Fig. 1). In the 13C{1H} NMR spectra of 5 and
6, J(31P–13C) coupling constants for the carbons of the phenyl rings
were recorded, which are consistent with the literature values [40–
43]. The most relevant signals of the 13C{1H} NMR spectra of com-
plexes 5 and 6 are those corresponding to the arene ligands (p-
cymene). The carbon atoms of the arene rings in the p-cymene li-
gands are observed as two singlets at 91.35 and 85.41 ppm in com-
pound 5 and 89.53 and 86.90 ppm in compound 6. Furthermore, 1H
NMR spectral data of 5 and 6 are consistent with the structures
proposed. In the 1H NMR spectra, 5 and 6 are characterized by
the isopropyl methyl doublets of the p-cymene groups, at d 0.88
with Ru(g l-Cl)Cl]2 in CH2Cl2 solution in a molar ratio
6-p-cymene)(
of 1:1/4 at room temperature for 4 h gives an orange/red solution.
The solution was concentrated and cooled to 0 °C. The trans iso-
mers of 7 and 8 were isolated as indicated by singlets in the
31P{1H} NMR spectra at (d) 79.65 and 79.25 ppm, respectively, in
line with the values previously observed for similar compounds
[45,46] (see Supplementary information Fig. 1), indicating that 3
and 4 act as bis(bidendate) chelating ligands. Furthermore, the
1H and 13C{1H} NMR spectroscopies are in agreement with the
structures proposed, and the structural compositions of complexes
7 and 8 were further confirmed by IR spectroscopy and the micro-
analyses were found to be in good agreement with the theoretical
values.
2.2. Catalytic transfer hydrogenation of acetophenone derivatives
and 1.25 ppm and
g
6-arene doublets at d 5.28, 5.14 and 5.06,
The obtained complexes 5–8 were then examined for the ruthe-
nium catalyzed transfer hydrogenation of arylketones to the corre-
sponding alcohols in iso-PrOH solution (Scheme 2).
In a preliminary study, if the reaction was activated by an alk-
oxide base, the synthesized complexes 5–8 were evaluated as a
precursor for the catalytic transfer hydrogenation of acetophenone
4.84 ppm, respectively (for details see Section 3). In addition, the
structural compositions of complexes 5 and 6 have been confirmed
by IR and elemental analysis.
N,N-bis(diphenylphosphino)isopropylanilines (PPh2)2N–C6H4–
CH(CH3)2, having an isopropyl substituent at carbon 2- (3) or 4-
Scheme 1. Synthesis of the complexes [Ru(
CH(CH3)2)2Cl2] 7 and [Ru((PPh2)2N–C6H4-4-CH(CH3)2)2Cl2] 8 (i) 1 equiv. Ph2PCl, 1 equiv. Et3N, thf/CH2Cl2 (1/2) for 1 and CH2Cl2 for 2; (ii) 2 equiv. Ph2PCl, 2 equiv. Et3N, thf;
(iii) 1/2 equiv. [Ru( -Cl)Cl]2, thf; (iv) 1/4 equiv. [Ru( -Cl)Cl]2, thf.
6-p-cymene)( 6-p-cymene)(
g g
6-p-cymene)(PPh2NH–C6H4-2-CH(CH3)2)Cl2] 5, [Ru( 6-p-cymene)(PPh2NH–C6H3-2,6-(CH(CH3)2)2)Cl2] 6, [Ru((PPh2)2N–C6H4-2-
g
l
g
l

M. Aydemir, A. Baysal / Polyhedron 29 (2010) 1219–1224
1221
Scheme 2. Hydrogen transfer from iso-PrOH to acetophenone derivatives.
Table 1
by iso-PrOH/NaOH as a reducing system. The results are summa-
rized in Table 1. The activity of the ruthenium(II) p-cymene
complexes is well known in this catalytic process [47–49]. The
catalytic activities of complexes 5–8 were not deeply investigated,
because of their instability in solution. At room temperature no
appreciable formation of 1-phenylethanol was observed (Table 1,
Transfer hydrogenation of acetophenone with iso-PrOH catalyzed by
[Ru(g
6-p-cymene)(PPh2NH–C6H4-2-CH(CH3)2)Cl2] 5, [Ru( 6-p-cymene)(PPh2NH–
g
C6H3-2,6-(CH(CH3)2)2)Cl2] 6, [Ru((PPh2)2N–C6H4-2-CH(CH3)2)2Cl2] 7 and [Ru((PPh2)2-
N–C6H4-4-CH(CH3)2)2Cl2] 8.
Entry
Catalyst
S/C/NaOH
Time
Conversion (%)h
TOFi
1
2
3
4
5
6
7
8
5a
6a
7a
8a
5b
6b
7b
8b
5c
6c
7c
8c
5d
6d
7d
8d
5e
6e
7e
8e
5f
100:1:5
100:1:5
100:1:5
100:1:5
100:1
100:1
100:1
100:1
500:1:5
500:1:5
500:1:5
500:1:5
1000:1:5
1000:1:5
1000:1:5
1000:1:5
100:1:5
100:1:5
100:1:5
100:1:5
100:1:5
100:1:5
1 h
1 h
1 h
1 h
1 h (24 h)
1 h
1 h
1 h
2 h
2 h
4 h
4 h
3.5 h
3.5 h
6 h
<1
<1
<1
<1
entries 1, 2, 3 and 4) and also the catalytic activity of [Ru(
cymene)( -Cl)Cl]2 under the applied experimental conditions is
g
6-p-
l
negligible. In addition, as can be inferred from Table 1 (entries 5,
6, 7 and 8), the precatalysts as well as the presence of NaOH are
necessary to observe appreciable conversions. The base facilitates
the formation of ruthenium alkoxide by abstracting a proton of
the alcohol and subsequently the alkoxide undergoes b-elimina-
tion to give ruthenium hydride, which is an active species in this
reaction. This is the mechanism proposed by several workers on
the studies of the ruthenium-catalyzed transfer hydrogenation
reaction by metal hydride intermediates [50–52].
As Table 1 shows, high conversions can be achieved with the 5–8
catalytic systems. Next, we have expanded the substrate-to-cata-
lyst ratio to observe its effect on the catalytic efficiency. As shown
in Table 1, increasing the substrate-to-catalyst ratio does not dam-
age the yields of the product in most cases. Remarkably, the transfer
hydrogenation of acetophenone could be achieved in 95% yield
even when the substrate concentration was increased from 0.1 to
0.5 M and the substrate-to-catalyst ratio reached 1000:1. In addi-
tion, performing the reaction in air, slowed down the reaction but
did not affect yield of the product. Amazingly, the reaction was
not affected by the addition of water (Table 1, entries 21 and 22).
The results obtained from the optimization studies indicate clearly
that excellent yields were achieved in the reduction of acetophe-
none to 1-phenylethanol when 5–8 were used as the catalytic pre-
cursor with a substrate–catalyst molar ratio (100:1) in 2-propanol,
containing a small amount of NaOH at 82 °C.
<1 (60)
<1
<1
<1
9
98.7
97.6
96.8
97.4
98.7
98.0
96.6
97.4
49.7
44.6
23.6
24.4
99.2
98.8
49
49
24
24
28
28
16
16
199
178
94
98
25
49
10
11
12
13
14
15
16
17
18
19
20
21
22
6 h
15 min
15 min
15 min
15 min
4 h
5g
2 h
Reaction conditions:
a
At room temperature, acetophenone/Ru/NaOH, 100:1:5.
b
c
d
e
f
Refluxing in iso-PrOH, acetophenone/Ru/NaOH, 100:1, in the absence of base.
Refluxing in iso-PrOH, acetophenone/Ru/NaOH, 500:1:5.
Refluxing in iso-PrOH, acetophenone/Ru/NaOH, 1000:1:5.
Refluxing in iso-PrOH, acetophenone/Ru/NaOH, 100:1:5.
Added 0.1 mL H2O.
Carried out (refluxing) the reaction in air.
Determined by GC (three independent catalytic experiments).
Referred at the reaction time indicated in column; TOF = (mol product/mol
g
h
i
Ru(II) Cat.) ꢀ hꢁ1
.
Following the optimization studies, we also examined the trans-
fer hydrogenations of aromatic ketones using complexes 5–8. These
results are presented in Table 2. The catalytic reduction of aromatic
ketones was conducted with a substrate/catalyst molar ratio (S/C)
of 100 using a 0.1 M solution in iso-PrOH, containing small amount
of NaOH as a cocatalyst. The reduction of aromatic ketones under
identical conditions using complexes 5–8 led to the corresponding
alcohols in good to excellent yields (92–99%). As already stated, the
nature and position of the substituents in the aromatic ketones re-
sult in significant effects on the activity [53,54]. Ketones with an
electron-withdrawing substituent are reduced smoothly with a
high rate, while the introduction of an electron-donating substitu-
ent, such as methoxy, to the p-position tends to lower the rate. The
p-substituted acetophenone with the electron donor substituent
40-methoxy is reduced more slowly than acetophenone. Notably,
with an electron-donating methoxy group in the o-position the
reaction is accelerated, but when the p-position is substituted the
rate is lowered. Furthermore, the transfer hydrogenation of aro-
matic ketones with an electron-withdrawing group such as a fluoro,
chloro and bromo in the p-position led to high conversions (up to
99%). Among all the selected ketones, the best results were obtained
from the reduction of p-fluoroacetophenone, giving 99% conver-
sions (Table 2, entries 2, 8, 14 and 20).
It is noteworthy that the Ru–aminophosphine catalytic systems,
5 and 6, and Ru–bis(phosphino)amine catalytic systems, 7 and 8,
display differences in reactivity (Table 2). The Ru–aminophosphine
complexes have proved to be excellent catalyst precursors in trans-
fer hydrogenation of acetophenone derivatives, leading to the cor-
responding alcohols (in up to 94–99% yield). That is to say, the
catalyst activities in the studied hydrogen transfer reactions were
generally much higher for the Ru–aminophosphine complexes 5
and 6 than for the Ru–bis(phosphino)amine complexes 7 and 8.
For example, under identical conditions, transfer hydrogenation
of acetophenone derivatives with the system Ru–aminophosphines
led to 92–99% conversions within 30 min, whereas with Ru–
bis(phosphino)amines as the auxiliary, the same 92–99% conver-
sions were achieved only after a 1 h period (Table 2). The higher
catalytic activity can be explained by the inherent hemilabile char-
acter [55] of the aminophosphine ligands which can generate an
open coordination site at ruthenium more easily, thus allowing a
faster substrate complexation. Complex 5 or 6, with sp3-hybribized
nitrogen containing N–H bonds, displayed higher reaction rates. On
the other hand, with the presence of N–H groups in the ligands it is
possible to stabilize a six membered cyclic transition state by

1222
M. Aydemir, A. Baysal / Polyhedron 29 (2010) 1219–1224
Table 2
Transfer hydrogenation results for substituted acetophenones with the catalyst systems prepared from [Ru(
g
6-p-cymene)(
l
-Cl)Cl]2 and PPh2NH–C6H4-2-CH(CH3)2 1, PPh2NH–
C6H3-2,6-(CH(CH3)2)2 2, (PPh2)22N–C6H4-2-CH(CH3)2}2 3 and (PPh22N-C6H4-4-CH(CH3)2 4.a
O
OH
OH
Cat
O
R
R
+
+
c
Entry
Catalyst
5
R
Time
Yield (%)b
TOF (hꢁ1
)
1
2
3
4
5
6
7
8
H
4-F
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
30 min
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
95.6
98.9
97.5
96.3
96.0
95.0
94.3
98.4
97.0
95.9
93.3
92.8
96.2
98.5
96.3
95.2
93.4
90.8
97.8
99.3
97.7
96.5
94.4
92.6
191
198
197
193
192
190
189
197
194
192
187
186
96
99
96
95
93
91
98
99
98
4-Cl
4-Br
2-MeO
4-MeO
H
6
7
8
4-F
9
4-Cl
4-Br
2-MeO
4-MeO
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
4-F
4-Cl
4-Br
2-MeO
4-MeO
H
4-F
4-Cl
4-Br
2-MeO
4-MeO
1 h
1 h
1 h
97
94
93
a
Catalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 mL), NaOH (0.025 mmol %), 82 °C, 30 min for 5 and 6; 1.0 h for 7 and 8, the concentration of the acetophenone
derivatives is 0.1 M.
b
Purity of compounds is checked by NMR and GC (three independent catalytic experiments), yields are based on methyl arylketone.
c
TOF = (mol product/mol Cat.) ꢀ hꢁ1
.
forming a hydrogen bond with the oxygen atom of the ketones
[56–58].
isolated by filtration and dried in vacuo. Yield 180 mg, 92%,
m.p. = 175–177 °C. 1H NMR (400.1 MHz, CDCl3) d: 8.15–8.02 (dd,
4H, 5J = 6.60 and 3J = 8.40 Hz, o-protons of phenyls), 7.55–7.40
(m, 6H, m- and p-protons of phenyls), 7.05 (d, 1H, 3J = 6.80 Hz, H-
3), 6.68 (dd, 1H, 3J = 6.80 and 7.00 Hz, H-4), 6.59 (dd, 1H, 3J = 7.00
and 8.00 Hz, H-5), 6.29 (d, 1H, 3J = 8.00 Hz, H-6), 6.01 (d, 1H,
2JNHP = 12.40 Hz, NH-P), 5.28 (d, 2H, 3J = 4.80 Hz, aromatic protons
of p-cymene), 5.14 (d, 2H, 3J = 5.20 Hz, aromatic protons of p-cym-
ene), 3.36 (m, 1H, –CH– of aniline), 2.61 (m, 1H, –CH– of p-cymene),
1.85 (s, 3H, CH3-Ph of p-cymene), 1.20 (d, 6H, 3J = 6.40 Hz,
(CH3)2CHPh of aniline), 0.88 (d, 6H, 3J = 6.80 Hz, (CH3)2CHPh of p-
cymene); 13C NMR (100.6 MHz, CDCl3) d: 17.28 (CH3Ph of p-cym-
ene), 21.35 ((CH3)2CHPh of p-cymene), 23.04 ((CH3)2CHPh of ani-
line), 26.74 (–CH– of aniline), 30.23 (–CH– of p-cymene), 85.41,
91.35 (aromatics carbons of p-cymene), 93.66, 108.93 (quaternary
carbons of p-cymene), 117.97 (C-6), 120.60 (C-4), 124.83 (C-5),
125.41 (C-3), 128.12 (d, 3J = 10.06 Hz, m-carbons of phenyls),
130.79 (s, p-carbons of phenyls), 132.55 (d, 2J = 11.1 Hz, o-carbons
of phenyls), 133.28 (d, 1J = 52.3 Hz, i-carbons of phenyls), 138.45
(C-2), 138.63 (d, 2J = 5.5 Hz, C-1); assignment was based on
1H–13C HETCOR and 1H–1H COSY spectra; 31P NMR (162 MHz,
3. Experimental
3.1. Materials and methods
Unless otherwise stated, all reactions were carried out under an
atmosphere of argon using conventional Schlenk glass-ware, sol-
vents were dried using established procedures and distilled under
argon immediately prior to use. Analytical grade and deuterated
solvents were purchased from Merck. Ph2PCl, 2-isopropylaniline,
4-isopropylaniline and 2,6-di(isopropyl)aniline were purchased
from Fluka and used as received. The starting material [Ru(
cymene)( -Cl)Cl]2 [59,60] was prepared according to literature
g
6-p-
l
procedures. The 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) were re-
corded on a Bruker Avance 400 spectrometer with d referenced to
external TMS and 85% H3PO4. Elemental analysis was carried out
on a Fisons EA 1108 CHNS-O instrument. Melting points were re-
corded on a Gallenkamp Model apparatus with open capillaries.
CDCl3) d: 51.62 (s, –NH–P–(C6H5)2–Ru); IR, (KBr, cmꢁ1
) t: 926
(P–NH), 1440 (P–Ph), 3313 (N–H); Anal. Calc. for C31H36NPRuCl2:
3.1.1. Synthesis of [Ru(
(5)
g
6-p-cymene)(PPh2NH–C6H4-2-CH(CH3)2)Cl2],
6-p-cymene)(
C, 59.52; H, 5.80; N, 2.24. Found: C, 59.43; H, 5.75; N, 2.20%.
A mixture of [Ru(
g
l
-Cl)Cl]2 (0.096 g, 0.156 mmol)
3.1.2. Synthesis of [Ru(
g
6-p-cymene)(PPh2NH–C6H3-2,6-
and PPh2NH–C6H4-2-CH(CH3)2 (0.100 g, 0.313 mmol) in 30 mL of
thf was stirred at room temperature for 3 h. The volume of the sol-
vent was reduced to 0.5 mL before addition of diethyl ether
(10 mL) to precipitate an orange micro-crystalline solid that was
(CH(CH3)2)2)Cl2], (6)
A mixture of [Ru(
and PPh2NH–C6H3-2,6-(CH(CH3)2)2 (0.100 g, 0.277 mmol) in 30 mL
g
6-p-cymene)(
l-Cl)Cl]2 (0.085 g, 0.138 mmol)
of thf was stirred at room temperature for 3 h. The volume of the

M. Aydemir, A. Baysal / Polyhedron 29 (2010) 1219–1224
1223
solvent was reduced to 0.5 mL before addition of diethyl ether
(10 mL) to precipitate an orange micro-crystalline solid that was
isolated by filtration and dried in vacuo. Yield 172.9 mg, 94%,
m.p. = 174–176 °C. 1H NMR (400.1 MHz, CDCl3) d: 7.70 (dd, 4H,
5J = 6.40 and 3J = 7.60 Hz, o-protons of phenyls), 7.41–7.26 (m,
6H, m- and p-protons of phenyls), 6.98 (t, 1H, 3J = 7.40 Hz, H-4),
6.79 (d, 2H, 3J = 7.20 Hz, H-3 and H-5), 5.23 (d, 1H, 2JNHP = 13.20 Hz,
NH–P), 5.06 (d, 2H, 3J = 6.00 Hz, aromatic protons of p-cymene),
4.84 (d, 2H, 3J = 6.40 Hz, aromatic protons of p-cymene), 3.35 (m,
2H, –CH– of aniline), 2.84 (m, 1H, –CH– of p-cymene), 1.89 (s,
3H, CH3-Ph of p-cymene), 1.34 (d, 6H, 3J = 6.80 Hz, (CH3)2CHPh of
aniline, (a)), 1.25 (d, 6H, 3J = 6.80 Hz, (CH3)2CHPh of aniline, (b))
0.63 (d, 6H, 3J = 6.80 Hz, (CH3)2CHPh of p-cymene); 13C NMR
(100.6 MHz, CDCl3) d: 17.94 (CH3Ph of p-cymene), 23.47 ((CH3)2-
CHPh of p-cymene), 22.29 ((CH3)2CHPh of aniline), 27.89
(–CH– of p-cymene), 30.38 (–CH– of aniline), 86.90, 89.53 (aromat-
ics carbons of p-cymene), 94.75, 100.60 (quaternary carbons of
p-cymene), 123.00 (C-4), 126.40 (C-3 and C-5), 134.80 (d, 2J =
4.5 Hz, C-1), 127.28 (d, 3J = 10.0 Hz, m-carbons of phenyls),
130.37 (s, p-carbons of phenyls), 134.01 (d, 2J = 11.0 Hz, o-carbons
of phenyls), 136.00 (d, 1J = 51.3 Hz, i-carbons of phenyls), 148.80
(C-2 and C-6); assignment was based on 1H–13C HETCOR and
1H–1H COSY spectra; 31P NMR (162 MHz, CDCl3) d: 57.69 (s,
Anal. Calc. for C66H62N2P4RuCl2: C, 67.23; H, 5.30; N, 2.38. Found: C,
67.15; H, 5.24; N, 2.32%.
3.2. Typical procedure for the transfer hydrogenation
Typical procedure for the catalytic hydrogen transfer reaction: a
solution of the ruthenium complex [Ru(
C6H4-2-CH(CH3)2)Cl2] (0.005 mmol), [Ru(
NH–C6H3-2,6-(CH(CH3)2)2)Cl2] 6 (0.005 mmol), [Ru((PPh2)2N–C6-
H4-2-CH(CH3)2)2Cl2] (0.005 mmol) or [Ru((PPh2)2N–C6H4-4-
CH(CH3)2)2Cl2] (0.005 mmol), NaOH (0.025 mmol) and the
g
6-p-cymene)(PPh2NH–
5
g
6-p-cymene)(PPh2-
7
8
corresponding ketone (0.5 mmol) in degassed iso-propanol (5 mL)
were refluxed for 30 min for 5 and 6, 60 min for 7 and 8. After this
time a sample of the reaction mixture was taken off, diluted with
acetone and analyzed immediately by GC. Yields obtained are
related to the residual unreacted ketone.
3.3. GC analyses
GC analyses were performed on a HP 6890 N Gas Chromatograph
equipped with a capillary column (5% biphenyl, 95% dimethylsilox-
ane) (30 m ꢀ 0.32 mm ꢀ 0.25
lm). The GC parameters 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/min; final temperature, 200 °C; final time, 21.13 min;
injector port temperature, 200 °C; detector temperature, 200 °C,
–NH–P–(C6H5)2–Ru); IR, (KBr, cmꢁ1
) t: 906 (P–NH), 1440 (P–Ph),
3319 (N–H); Anal. Calc. for C34H42NPRuCl2: C, 61.17; H, 6.34; N,
2.10. Found: C, 61.09; H, 6.27; N, 2.06%.
injection volume, 2.0 lL.
3.1.3. Synthesis of [Ru((PPh2)2N–C6H4-2-CH(CH3)2)2Cl2], (7)
A mixture of [Ru(g l-Cl)Cl]2 (0.030 g, 0.050 mmol)
6-p-cymene)(
4. Conclusion and perspectives
and (PPh2)2N–C6H4-2-CH(CH3)2 (0.100 g, 0.20 mmol) in 30 mL of
thf was stirred at room temperature for 4 h. The volume of the sol-
vent was reduced to 0.5 mL before addition of diethyl ether
(10 mL) to precipitate a bright yellow micro-crystalline solid that
was isolated by filtration and dried in vacuo. Yield 106.8 mg, 91%,
m.p. > 250 °C (dec.). 1H NMR (400.1 MHz, CDCl3) d: 7.56–6.85 (m,
40H, o-, m- and p-protons of phenyls and 8H, aromatic protons of
aniline), 3.32 (m, 2H, –CH– of aniline), 1.23 (d, 12H, 3J = 6.40 Hz,
(CH3)2CHPh of aniline); 13C NMR (100.6 MHz, CDCl3) d: 23.51
((CH3)2CHPh of aniline), 27.34 (–CH– of aniline), 124.12, 126.47,
126.98, 127.10, 134.38, 139.13 (aromatic carbons of aniline),
125.69 (m-carbons of phenyls), 128.57 (p-carbons of phenyls),
129.69 (i-carbons of phenyls), 134.38 (o-carbons of phenyls);
assignment was based on 1H–13C HETCOR and 1H–1H COSY spec-
tra; 31P NMR (162 MHz, CDCl3) d: 79.65 (s, –N–(P–(C6H5)2)2–Ru);
In conclusion, we have synthesized and characterized a series of
new ruthenium(II) complexes based on aminophosphine and
bis(phosphine)amine ligands which are valuable for the transfer
hydrogenation of aromatic ketones. The catalysis attains a high
efficiency using the ruthenium(II) complexes with aminophos-
phine monodendate ligands. The high catalytic activity is
contrasted to the slightly lower reactivity of a structurally similar
bis(phosphino)amine-based complex. The results suggest that the
NH moiety in the aminophosphine ligand is responsible for
the high reactivity. Further studies of other transition metal com-
plexes of these ligands and their application in catalytic reactions
are in progress. Furthermore, future investigations are aimed at
the development of an asymmetric version of this process.
IR, (KBr, cmꢁ1
) t: 1438 (P–Ph), 947 (P–N); Anal. Calc. for
C66H62N2P4RuCl2: C, 67.23; H, 5.30; N, 2.38. Found: C, 67.17; H,
Acknowledgement
5.23; N, 2.33%.
Partial support from Dicle University (Project number: DÜAPK
05-FF-27) is gratefully acknowledged.
3.1.4. Synthesis of [Ru((PPh2)2N–C6H4-4-CH(CH3)2)2Cl2], (8)
A mixture of [Ru(g l-Cl)Cl]2 (0.030 g, 0.050 mmol)
6-p-cymene)(
Appendix A. Supplementary data
and (PPh2)2N–C6H4-4-CH(CH3)2 (0.100 g, 0.20 mmol) in 30 mL of
thf was stirred at room temperature for 4 h. The volume of the sol-
vent was reduced to 0.5 mL before addition of diethyl ether
(10 mL) to precipitate a bright yellow micro-crystalline solid that
was isolated by filtration and dried in vacuo. Yield 103.8 mg, 89%,
m.p. > 250 °C (dec.). 1H NMR (400.1 MHz, CDCl3) d: 7.40–7.07 (m,
40H, o-, m- and p-protons of phenyls), 6.92 (d, 4H, 3J = 8.40 Hz,
H-3 and H-5), 6.83 (d, 4H, 3J = 8.00 Hz, H-2 and H-6), 2.75 (m, 2H,
–CH– of aniline), 1.14 (d, 12H, 3J = 6.80 Hz, (CH3)2CHPh of aniline);
13C NMR (100.6 MHz, CDCl3) d: 23.75 ((CH3)2CHPh of aniline),
33.27 (–CH– of aniline), 126.11 (C-2 and C-6), 127.10 (C-3 and C-
5), 126.78 (m-carbons of phenyls), 129.44 (s, p-carbons of phenyls),
133.29 (i-carbons of phenyls), 134.28 (o-carbons of phenyls),
141.29 (C-4), 145.30 (C-1); assignment was based on 1H–13C HET-
COR and 1H–1H COSY spectra; 31P NMR (162 MHz, CDCl3) d: 79.25
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2009.12.035.
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