New active ruthenium(II) complexes based N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester ligands for transfer hydrogenation of aromatic ketones by propan-2-ol

Article abstract of DOI:10.1016/j.jorganchem.2009.04.015

The dimeric starting material [Ru(η⁶-p-cymene)(μ-Cl)Cl]₂ reacts with N3,N3′-bis(diphenylphosphino)-2,2′-bipyridine-3,3′-diamine, 1 and P,P′-diphenylphosphinous acid-P,P′-[2,2′-bipyridine]-3,3′-diyl ester, 2 ligands to afford bridged

Full text of DOI:10.1016/j.jorganchem.2009.04.015

Journal of Organometallic Chemistry 694 (2009) 2488–2492
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New active ruthenium(II) complexes based
N3,N30-bis(diphenylphosphino)-2,20-bipyridine-3,30-diamine
and P,P0-diphenylphosphinous acid-P,P0-[2,20-bipyridine]-3,30-diyl ester ligands
for transfer hydrogenation of aromatic ketones by propan-2-ol
*
Murat Aydemir , Akin Baysal, Nermin Meric, Bahattin Gümgüm
Department of Chemistry, University of Dicle, 21280 Diyarbakır, Turkey
a r t i c l e i n f o
a b s t r a c t
The dimeric starting material [Ru(g l
6-p-cymene)( -Cl)Cl]2 reacts with N3,N30-bis(diphenylphosphino)-
Article history:
Received 9 March 2009
Received in revised form 9 April 2009
Accepted 15 April 2009
Available online 23 April 2009
2,20-bipyridine-3,30-diamine, 1 and P,P0-diphenylphosphinous acid-P,P0-[2,20-bipyridine]-3,30-diyl ester,
2
ligands to afford bridged dinuclear complexes [C10H6N2{NHPPh2-Ru(
g 3 and
6-p-cymene)Cl2}2],
[C10H6N2{OPPh2-Ru( in quantitative yields. These bis(aminophosphine) and
g
6-p-cymene)Cl2}2],
4
bis(phosphinite) based Ru(II) complexes serve as active catalyst precursors for the transfer hydrogenation
of acetophenone derivatives in 2-propanol and especially 4 acts as a good catalyst, giving the correspond-
ing alcohols in 99% yield in 20 min (TOF 6 280 hꢀ1).
Keywords:
Ketone hydrogenation
Transfer hydrogenation
Aminophosphine
Phosphinite ruthenium
Catalysis
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Electron rich phosphines are now recognized to greatly enhance
the rate of ketone hydrogenation by rhodium complexes [11,12].
Transition metal-catalyzed procedures for transfer hydrogena-
tion of a wide variety of functional groups by different hydrogen
donors are an interesting alternative to conventional hydrogena-
tion [1,2]. Ketones are the most common unsaturated substrates
used in organic synthesis. Extensive efforts have been devoted to
their reduction into secondary alcohols especially via hydrogena-
tion [3]. Transfer hydrogenation of ketones by propan-2-ol is con-
venient in large-scale synthesis since there is no need to employ a
high hydrogen pressure or to use hazardous reducing agents [4]. In
addition, the enantioselective hydrogenation of prochiral ketones,
which is one of the most exciting and powerful method of synthe-
sing chiral alcohols, has been receiving increased attention as well
and has led to notable success [5]. Although very frequently ruthe-
nium-based catalysts have been applied in the enantioselective
hydrogenation of prochiral ketones [6], rhodium complexes have
proven to lead very efficient processes along with potential indus-
trial applications [7–9].
The chemistry of aminophosphines and phosphinites has been
intensively explored in recent years [13]. These compounds are ex-
tremely attractive as potential ligands since various structural
modifications are accessible via simple P–N and P–O bond forma-
tion [14]. Many modified phosphine ligands and a variety of chiral
aminophosphine–phosphinite ligands have important applications
in organomatallic chemistry and catalysis, giving selective cata-
lysts for hydroformylation, hydrosilylation and asymmetric trans-
fer hydrogenation [15,16]. While much effort has been devoted
to the synthesis of aminophosphines and their metal complexes,
similar studies on the analogous bis(phosphinites) are less exten-
sive [17], even though some of their complexes has proved to be
efficient catalysts [18].
We previously reported the preparation of the N3,N30-
bis(diphenylphosphino)-2,20-bipyridine-3,30-diamine and P,P0-
diphenylphosphinous acid-P,P0-[2,20-bipyridine]-3,30-diyl ester
and their chalcogenides [19]. As a part of our interest in designing
new ligand systems with different spacers to control the electronic
attributes at phosphorus centers and to explore their coordination
chemistry, we report here the synthesis of bridged dinuclear Ru(II)
Three decades ago, it has been shown by Schrock and Osborn
that the use of rather basic alkyl phosphines allowed the hydroge-
nation of simple ketones in the presence of rhodium catalysts [10].
complexes [C10H6N2{NHPPh2-Ru(
H6N2{OPPh2-Ru(
6-p-cymene)Cl2}2], 4 and their catalytic evalua-
tion in the transfer hydrogenation of ketones.
g -
6-p-cymene)Cl2}2], 3 and [C10
g
* Corresponding author. Fax: +90 412 2488300.
E-mail address: aydemir@dicle.edu.tr (M. Aydemir).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.04.015

M. Aydemir et al. / Journal of Organometallic Chemistry 694 (2009) 2488–2492
2489
OH
O
2. Results and discussion
Synthesis and characterization of bis(aminophosphine), 1 and
bis(phosphinite), 2 ligands with rigid backbones, prepared from
the starting materials 3,30-diamino-2,20-bipyridine and 3,30-dihy-
droxy-2,20-bipyridine by the aminolysis and hydrolysis methods,
respectively, were previously reported [19] (Scheme 1).
[Ru(II)]
R
R
iPrOH
[Ru(II)]= 3 or 4 + NaOH; Ru : NaOH = 1 : 5
3 = [C10H6N2{NHPPh2-{Ru(p-cymene)Cl2}2]
The reaction of stoichiometric amounts of [Ru(p-cymene)Cl2]2
and [(Ph2PNH)2-C10H6N2], 1 affords complex [C10H6N2{NHPPh2-
4 = [C10H6N2{OPPh2-{Ru(p-cymene)Cl2}2]
R = H, p-F, p-Cl, p-Br, o-OCH3, p-OCH3
Ru(g
6-p-cymene)Cl2}2], (3) in high yield as a red microcrystalline
powder, this compound being stable in air. Complex 1 was
expected to cleave the [Ru(p-cymene)Cl2]2 dimer to give the corre-
sponding complex 3 via monohapto coordination of the amino-
phosphine group. Analysis by 31P–{1H} NMR exhibits a unique
signal in the spectrum, indicative of both phosphorus being equiv-
alent as a result of the high symmetry of the complex. The 31P–{1H}
NMR spectrum of 3 shows a single resonance at 52.00 ppm, in line
with the values previously observed for similar compounds [20].
Analysis by 1H NMR reveals this compound to be diamagnetic,
exhibiting signals corresponding to the aromatic rings for 3 at
8.04–7.41 ppm. Another set of signals consisting of two doublets
centered at 5.20 and 5.11 ppm are due to the presence of the aro-
matic protons in the p-cymene group, this information is comple-
mented by the presence of signals at 2.66 and 0.90 ppm due to the
CH and CH3 of the iso-propyl groups of the p-cymene moiety. Final-
ly, a signal due to the presence of the methyl in the p-cymene
group is observed at 1.73 ppm. Furthermore in the 13C–{1H} NMR
spectrum of 3, J(31P–13C) coupling constants of the carbons of the
phenyl rings was observed, which is consistent with the literature
values [21]. The structures of the 3 was further confirmed by IR
spectroscopy and microanalysis, and found to be in good agree-
ment with the theoretical values.
Scheme 2. Hydrogen transfer from iPrOH to acetophenone derivatives.
ters are very rare. In the 13C NMR spectrum through-space P–C
coupling was observed. Furthermore, 1H NMR spectral data of 4
is consistent with the structure proposed. In the 1H NMR spectrum,
4 is characterized by isopropyl methyl doublets, at d 0.88 ppm and
g
6-arene doublets at d 5.59 and 5.35 ppm. The structural composi-
tion of the complex has been confirmed by IR and elemental anal-
ysis. Although, single crystals of 3 and 4 were obtained by slow
diffusion of diethylether into a solution of the compound in dichlo-
romethane over several days, unfortunately we were not able to
protect the crystals from rapid decomposition in air.
The excellent catalytic performance of phosphinite- and amino-
phosphine-based transition metal complexes [27] prompted us to
develop new Ru(II) complexes with well-shaped ligands. To this
end, we examined the catalytic activation of complexes 3 and 4
in the transfer hydrogenation of aryl ketones to the corresponding
alcohols (Scheme 2).
Complexes 3 and 4 were used as precatalysts, iPrOH/NaOH as
the reducing system, and acetophenone as the model substrate.
2-Propanol is the conventional hydrogen source having favorable
properties; it is stable, easy to handle (b.p. 82 °C), non-toxic, envi-
ronmentally friendly, inexpensive and dissolves in many organic
compounds. Moreover, the acetone product is readily removable
[28]. The catalytic activities of complexes 3 and 4 were not deeply
investigated, because of their instability in solutions. All the cata-
lytic reactions were interrupted after 10, 20, 30 and 60 min. The
catalytic results are collected in Table 1. At room temperature no
appreciable formation of 1-phenylethanol was observed (Table 1,
We also examined simple coordination chemistry of 2 with
[Ru(p-cymene)Cl2]2. Complexation reaction was straightforward,
with coordination to ruthenium being carried out at room temper-
ature. The reaction of [Ru(p-cymene)Cl2]2 with one equivalent of
[(Ph2PO)2-C10H6N2], 2 affords the corresponding monodendate
[C10H6N2{OPPh2-Ru(g
6-p-cymene)Cl2}2] 4, in high yield as the
main product. The initial color change, i.e., from clear orange to
deep red [22], attributed to the dimer cleavage most probably by
the bis(phosphinite) ligand. The 31P–{1H} NMR spectrum is quite
consistent with the structure [23], that of contain 4 shows single
resonance at d 119.09 ppm. To the best of our knowledge Ceron-
Camacho and co-workers [24] have been reported the first crystal-
lographic determination of a bimetallic bridged structure using
this sort of ligands. Furthermore, a related structure has been in-
voked by Balakrishna and co-workers [25] for the formation of
the ruthenium complex where the ligands also serves as bridge be-
tween two metal centers, however no crystallographic evidence
was presented. Most recently [26] a similar structure has been
determined for a BINAP-based phosphinite ligand BINAPO, where
as is the case for complex 4, it is noted by the authors that com-
pounds bearing binaphtyl-based ligands bridging two metal cen-
Entries 1 and 2) and also the catalytic activity of [Ru(
ne)( -Cl)Cl]2 under the applied experimental conditions is negligi-
g
6-p-cyme-
l
ble. However, when the temperature was increased to 82 °C
smooth reduction of acetophenone into 1-phenylethanol occured,
with conversion ranging from 92% to 99% after 1 h for 3 and
20 min for 4 of reaction. The catalytic activities of 3 and 4 are com-
parable, with the values referred to 10 min of 135 and 275.4 hꢀ1
,
respectively (Table 1, Entries 3 and 4). These values correspond
to 22.5% and 45.9% conversions, respectively. As can be inferred
from the Table 2 (Entries 5 and 6) the precatalysts as well as the
presence of NaOH are necessary to observe appreciable conver-
Ph2
P
Cl
N
N
N
PPh2
Cl
X
Y
Ru
i
ii
Y
X
Ru
Y
Cl
Y
N
P
N
Ph2P
N
Ph2
Cl
Y: NH 1; O 2
Y: NH 3; O 4
g
6-p-cymene)Cl2}2], 3 and [C10H6N2{OPPh2-Ru( 6-p-cymene)Cl2}2], 4 complexes (i) 2 equiv. Ph2PCl, 2 equiv. Et3N, CH2Cl2
X: NH2, OH
Scheme 1. Synthesis of the [C10H6N2{NHPPh2-Ru(
g
for 1 and toluene for 2 and (ii) 1 equiv. [Ru(p-cymene)Cl2]2, thf.

2490
M. Aydemir et al. / Journal of Organometallic Chemistry 694 (2009) 2488–2492
Table 1
species in this reaction. This is the mechanism proposed by several
workers on the studies of ruthenium catalyzed transfer hydrogena-
tion reaction by metal hydride intermediates [29,30].
Transfer hydrogenation of acetophenone catalyzed by 3 and 4.
f
Entry
Complex
Time (min)
Conversion (%)e
TOF (hꢀ1
)
Results obtained from optimization studies indicate clearly that
the excellent yields were achieved in the reduction of acetophe-
none to 1-phenylethanol when 3 and 4 were used as the catalytic
precursor in 60 min and 20 min, respectively, with a substrate–cat-
alyst molar ratio (100:1) in 2-propanol containing a small amount
of NaOH at 82 °C (Table 1). The catalytic reduction of acetophenone
derivatives were all tested with the conditions optimized for aceto-
phenone. The reaction with the bis(aminophosphine)-Ru(II), 3 cat-
alytic system proceeded more slowly than bis(phosphinite)-Ru(II),
4. But ruthenium(II) complex with bis(aminophosphine) ligand
also gave the same yields in 1 hour. It thus appears that the nature
of the bis(phosphinite) and bis(aminophosphine) ligand can also
play a crucial role in the transfer hydrogenation reactions. These
results indicate that the O–P and NH–P linkages possibly can stabi-
lize a catalytic transition state [31].
1
2
3
4
5
6
7
8
3a
4a
3b
4b
3b
4b
3b
3c
4c
3d
4d
30
30
10
10
20
20
60
60
60
10
10
<1
<1
22.5
45.9
42.5
99.0
95.2
135
275.4
127.5
297.0
95.2
9
10
11
3.2
6.5
192
390
a
Reaction conditions: at room temperature. acetophenone/Ru/NaOH, 100:1:5.
Reaction conditions: refluxing in iPrOH; acetophenone/Ru/NaOH, 100:1:5.
In the absence of base.
Reaction conditions: refluxing in iPrOH; acetophenone/Ru/NaOH, 1000:1:5.
Determined by GC (three independent catalytic experiments).
b
c
d
e
f
Referred at the reaction time indicated in column; TOF = (mol product/mol
Ru(II) Cat.) ꢁ hꢀ1
.
Complexes 3 and 4 showed very good activity for most of the
ketones. The introduction of electron withdrawing substituents,
such as F, Cl and Br to the para position of the aryl ring of the
ketone decreased the electron density of the C@O bond so that
the activity was improved giving rise to easier hydrogenation
[32].
sions. The base facilitates the formation of ruthenium alkoxide by
abstracting proton of the alcohol and subsequently alkoxide under-
goes b-elimination to give ruthenium hydride, which is an active
Table 2
Transfer hydrogenation of substituted acetophenones catalyzed by [C10H6N2{NHPPh2-Ru(g g
6-p-cymene)Cl2}2], 3 and [C10H6N2{OPPh2-Ru( 6-p-cymene)Cl2}2], 4.
c
Entry
1
Substrate
Product
Catalyst
Yield (%)a,b
95.2
TOF (hꢀ1
95.2
)
O
OH
3
2
4
99.0
297.0
OH
O
3
4
3
4
98.3
99.1
98.3
297.3
F
F
O
OH
5
6
3
4
96.5
95.1
96.5
285.3
Cl
Cl
O
OH
7
8
3
4
97.9
98.0
97.9
294.0
Br
Br
O
OH
OMe
OMe
9
3
4
96.4
98.9
96.4
10
296.7
O
OH
11
3
4
92.5
93.7
92.5
12
281.1
H3CO
H3CO
a
Catalyst (0.005 mmol), substrate (0.5 mmol), iPrOH (5 mL), NaOH (0.025 mmol), 82 °C, 1.0 h for 3 and 1/3 h for 4.
b
c
Purity of compounds is checked by NMR and GC, yields are based on methyl aryl ketone.
TOF = (mol product/mol Cat.) ꢁ hꢀ1
.

M. Aydemir et al. / Journal of Organometallic Chemistry 694 (2009) 2488–2492
2491
130.62 (s, p-carbons of phenyls), 132.37 (d, J = 9.05 Hz, o-carbons
of phenyls), 134.90 (d, J = 34.00 Hz, i-carbons of phenyls), 95.41
(CH3-CCH2CH2C-CH(CH3)2 of p-cymene), 138.05 (C-6), 142.30 (C-
3), 110.60 (CH3-CCH2CH2C-CH(CH3)2 of p-cymene), 148.80 (C-2);
assignment was based on the 1H-13C HETCOR spectrum; 31P NMR
3. Conclusions
In summary, we have synthesized and characterized two new
bimetallic Ru(II) complexes based bis(aminophosphine) and
bis(phosphinite) monodendate ligands and investigated their use
in transfer hydrogenation of ketones. We have found that these
complexes are efficient homogeneous catalytic systems that can
be readily implemented and lead to secondary alcohols from good
to excellent yields. The catalytic activities in the studied hydrogen
transfer reactions were generally much higher for the bis(phosph-
inite) ligand than those for the bis(aminophosphine) ligand. This
higher catalytic activity can be explained by the inherent hemila-
bile character of the phosphinite ligand which can generate an
open coordination site at ruthenium more easily, thus allowing a
faster substrate complexation. The procedure is simple and effi-
cient towards various aryl ketones. Future investigations are aim-
ing at the development of an asymmetric version of this process.
(162 MHz, CDCl3): d = 51.94 (s); IR, (KBr):
t
= 925 (P–NH), 1439
Anal. Calc. for
(P–Ph), 1587 (C@N), 3363 (N–H) cmꢀ1
;
C54H56N4P2Ru2Cl4: C, 55.58; H, 4.84; N, 4.80. Found: C, 55.46; H,
4.81; N, 4.75%.
4.3. Synthesis of [C10H6N2{OPPh2-Ru(
g
6-p-cymene)Cl2}2], 4
To a solution of [(
thf,
g
6-p-cymene)RuCl2]2 (55 mg, 0.09 mmol) in
a
solution (thf, 10 mL) of (Ph2PO)2-C10H6N2, (50 mg,
2
0.09 mmol) was added. The resulting reaction mixture was allowed
to proceed under stirring at room temperature for 2 h. After this
time, the solution was filtered off and the solvent evaporated under
vacuum, the solid residue thus obtained was washed with diethyl
ether (3 ꢁ 10 mL) and then dried under vacuum (Scheme 1). Fol-
lowing recrystallization from diethylether/CH2Cl2, a red powder
was obtained (yield 96 mg, 91.4%), m.p. 143–145 °C. 1H NMR
(400.1 MHz, CDCl3): d = 8.67 (d, 2H, J = 4.40, H-6), 7.98 (d, 2H,
J = 8.40, H-4), 7.22–7.62 (m, 20H, o-, m- and p-protons of phenyls),
6.91 (dd, 2H, J = 4.42 and 8.60, H-5), 5.59 (d, 4H, J = 6.00 Hz, aro-
matic hydrogen of p-cymene), 5.35 (d, 4H, J = 6.00 Hz, aromatic
hydrogen of p-cymene), 2.46 (m, 2H, –CH– of p-cymene), 1.69
(s, 6H, CH3-Ph of p-cymene), 0.88 (d, 12H, J = 6.40 Hz, (CH3)2CHPh
of p-cymene); 13C NMR (100.6 MHz, CDCl3): d = 17.04 (CH3Ph of
p-cymene), 21.61 ((CH3)2CHPh of p-cymene), 30.00 (–CH– of
p-cymene), 80.50, 85.22 (CH3-CCH2CH2C-CH(CH3)2 of p-cymene),
122.50 (C-5), 128.04 (d, J = 10.03 Hz, m-carbons of phenyls),
129.03 (C-4), 130.80 (s, p-carbons of phenyls), 132.73 (d,
J = 9.03 Hz, o-carbons of phenyls), 136.00 (d, J = 40.50 Hz, i-carbons
of phenyls), 96.70 (CH3-CCH2CH2C-CH(CH3)2 of p-cymene), 141.80
(C-2), 144.21 (C-6), 110.71 (CH3-CCH2CH2C-CH(CH3)2 of p-cymene),
148.47 (C-3); assignment was based on the 1H-13C HETCOR
spectrum; 31P NMR (162 MHz, CDCl3): d = 119.09 (s); IR, (KBr):
4. Experimental
4.1. 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 sol-
vents were purchased from Merck. PPh2Cl, 2-chloro-3-nitropyridine
and 2-bromo-3-hydroxypyridine are purchased from Fluka and
were used as received. The starting materials 3,30-diamino-2,20-
bipyridine [33], 3,30-dihidroxy-2,20-bipyridine [34], [Ru(p-cyme-
ne)Cl2]2 [35], were prepared according to literature 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 recorded
spectra on a Bruker Avance 400 spectrometer, with d referenced to
external TMS and 85% H3PO4, respectively. GC analyses were per-
formed on a HP 6890N Gas Chromatograph equipped with capillary
column (%5 biphenyl, %95 dimethylsiloxane) (30 m ꢁ 0.32 mm ꢁ
t
= 893 (P–O), 1439 (P–Ph), 1580 (C@N) cmꢀ1. Anal. Calc. for
C54H54N2O2P2Ru2Cl4: C, 55.49; H, 4.66; N, 2.40. Found: C, 55.41;
H, 4.59; N, 2.36%.
0.25 lm). Elemental analysis was carried out on a Fisons EA 1108
CHNS-O instrument; melting points by Gallenkamp Model appara-
tus with open capillaries.
4.4. Transfer hydrogenation of ketones
4.2. Synthesis of [C10H6N2{NHPPh2-Ru(
g
6-p-cymene)Cl2}2], 3
Typical procedure for the catalytic hydrogen transfer reaction:
a suspension of ruthenium complexes [C10H6N2{NHPPh2-Ru(
cymene)Cl2}2], 3 (0.005 mmol) or [C10H6N2{OPPh2-Ru(
6-p-cyme-
ne)Cl2}2], (0.005 mmol), NaOH (0.025 mmol) and the
g
6-p-
To a solution of [(
g
6-p-cymene)RuCl2]2 (55 mg, 0.09 mmol) in
g
CH2Cl2, solution (CH2Cl2, 30 mL) of (Ph2PNH)2-C10H6N2,
a
1
4
(50 mg, 0.09 mmol) was added. The resulting reaction mixture
was allowed to proceed under stirring at room temperature for
2 h. After this time, the solution was filtered off and the solvent
evaporated under vacuum, the solid residue thus obtained was
washed with diethyl ether (3 ꢁ 10 mL) and then dried under vac-
uum (Scheme 1). Following recrystallization from diethylether/
corresponding ketone (0.5 mmol) in degassed iso-propanol
(5 mL) was refluxed for 60 min for 3 and 20 min for 4. After this
time a sample of the reaction mixture is taken off, diluted with
acetone and analyzed by GC, yields obtained are related to the
residual unreacted ketone.
CH2Cl2,
a red powder was obtained (yield 94 mg, 89.4%),
m.p. > 200 °C (dec.). 1H NMR (400.1 MHz, CDCl3): d = 12.25 (d, 2H,
3JNHP = 10.80 Hz, NH-P), 8.06 (d, 2H, J = 3.60, H-6), 8.04 (dd, 8H,
J = 6.30 and 11.40 Hz, o-protons of phenyls), 7.41 (m, 12H, m- and
p-protons of phenyls), 7.20 (d, 2H, J = 8.40, H-4), 6.86 (dd, 2H,
J = 4.26 and 9.20, H-5), 5.20 (d, 4H, J = 5.60 Hz, aromatic hydrogen
of p-cymene), 5.11 (d, 4H, J = 5.20 Hz, aromatic hydrogen of p-cym-
ene), 2.66 (m, 2H, –CH– of p-cymene), 1.73 (s, 6H, CH3-Ph of p-cym-
ene), 0.90 (d, 12H, J = 6.60 Hz, (CH3)2CHPh of p-cymene); 13C NMR
(100.6 MHz, CDCl3): d = 17.48 (CH3Ph of p-cymene), 21.47
((CH3)2CHPh of p-cymene), 30.21 (–CH– of p-cymene), 86.95,
90.30 (CH3-CCH2CH2C-CH(CH3)2 of p-cymene), 122.50 (C-5),
127.20 (C-4), 128.15 (d, J = 10.06 Hz, m-carbons of phenyls),
Acknowledgment
Partial support from Dicle University (Project No.: DÜAPK
05-FF-27) is gratefully acknowledged.
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