Trans/cis isomerization of [RuCl2(diphosphine)(diamine)] complexes: Synthesis, X-ray structure and catalytic activity in hydrogenation

Article abstract of DOI:10.1016/j.saa.2012.11.108

The diamine (NN) co-ligand 2,2-dimethyl-1,3-propanediamine and 2,3-diaminophathalene react individually with [RuCl₂(dppb) ₂(μ-dppb)] to afford complexes with kinetically stable trans-[Cl₂Ru(dppb)(NN)] as the favoured isomer. The thermodynamically stable cis-[Cl₂Ru(dppb)(NN)] isomer of complex 1 was formed from the trans-1 isomer. The trans to cis isomerization reaction was conducted in CHCl₃ at RT and monitored by ³¹P{¹H} NMR. The structures of the desired complexes were characterized via elemental analyses, IR and, UV-visible spectroscopy, FAB-MS and NMR. The structure of the cis-1 isomer was determined by single crystal X-ray measurements. Both the trans-1 and cis-1 isomers were shown to have a significant catalytic role in selective hydrogenation reactions under mild conditions using cinnamic aldehyde as typical model reaction.

Full text of DOI:10.1016/j.saa.2012.11.108

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Trans/cis isomerization of [RuCl2(diphosphine)(diamine)] complexes: Synthesis,
X-ray structure and catalytic activity in hydrogenation
a
a
a
b
Ismail Warad a, , Hanan AlHussen , Hamdah Alanazi , Refaat Mahfouz , Belkheir Hammouti ,
⇑
Mohammad A. Al-Dosari c, Rawhi Al-Far d, Taibi Ben Hadda e
a Department of Chemistry, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia
b LCAE-URAC18, Faculté des Sciences, Université Mohammed Ier, Oujda 60000, Morocco
c National Nanotechnology Research Center, King Abdulaziz City for Science and Technology, PO Box 6086, Riyadh 11442, Saudi Arabia
d Department of Applied Sciences, Faculty of Applied Sciences and I.T., Al-Balqa’ Applied University, Salt 19117, Jordan
e Laboratoire LCM, Faculté Sciences, Université Mohammed Ier, Oujda 60000, Morocco
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
Two new ruthenium(II) complexes
of type trans-[RuCl2(dppb)(NAN)]
were made available.
Trans to cis isomerization reaction of
complex 1 was monitored by 31P{1H}
NMR.
The thermodynamically favored cis-
1 isomer of complex 1 was
confirmed by XRD crystal
measurements.
"
Synthesized complexes have showed
very good catalytic activity in the
hydrogenation of cinnamic
aldehyde.
a r t i c l e i n f o
a b s t r a c t
Article history:
The diamine (NAN) co-ligand 2,2-dimethyl-1,3-propanediamine and 2,3-diaminophathalene react
Received 2 September 2012
Received in revised form 6 November 2012
Accepted 30 November 2012
Available online 20 December 2012
individually with [RuCl2(dppb)2(l-dppb)] to afford complexes with kinetically stable trans-[Cl2-
Ru(dppb)(NAN)] as the favoured isomer. The thermodynamically stable cis-[Cl2Ru(dppb)(NAN)] isomer
of complex 1 was formed from the trans-1 isomer. The trans to cis isomerization reaction was conducted
in CHCl3 at RT and monitored by 31P{1H} NMR. The structures of the desired complexes were characterized
via elemental analyses, IR and, UV–visible spectroscopy, FAB-MS and NMR. The structure of the cis-1 isomer
was determined by single crystal X-ray measurements. Both the trans-1 and cis-1 isomers were shown to
have a significant catalytic role in selective hydrogenation reactions under mild conditions using cinnamic
aldehyde as typical model reaction.
Keywords:
Ruthenium(II) complexes
Trans/cis isomerism
Diamine
Ó 2012 Elsevier B.V. All rights reserved.
Diphosphine
Hydrogenation
Introduction
and asymmetrical catalytic hydrogenation [5–19]. Mixed-ligand
[Ru(II)-(diamine)(phosphine)] complexes also serve as excellent
A variety of phosphines and diphosphines have been studied re-
cently due to their ability to chelate transition metals [1–18]. These
studies, in turn, offer a broad framework for the design of new ap-
proaches for electro-catalysis, photolysis, bioinorganic chemistry,
hydrogen transfer catalysts [1–9]. The exchange of monoden-
tate phosphine ligands, such as triphenylphosphine (PPh3) or
ether-phosphine (P–O), and bidentate phosphine ligands, such as
1,3-bis-diphenylphosphinepropane (dppp) or 1,1-bis(diphenyl-
phosphino-methyl)ethane; (dppme), ligands of ruthenium(II)
complexes with several types of diamine ligands to synthesize
[Ru(II)-(diamine)(phosphine)] complexes represents one ongoing
⇑
Corresponding author. Tel./fax: +966 61 4675992.
E-mail address: warad@ksu.edu.sa (I. Warad).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.108

I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
467
area of investigation [1–5]. Due to their remarkable performance in
Experimental
the selective hydrogenation of unsaturated carbonyl compounds,
mixed [Ru(II)-(diamine)(phosphine)] complexes have received
considerable attention in recent years [7–18].
Conditions, materials and physical measurements
Improvements in catalytic reactivities can be achieved by the
appropriate design of structural, electronic, and stereochemical
features surrounding the coordination sphere of complexes, and
dramatic changes in the catalytic activity in certain reactions can
be attributed to small differences in the coordination sphere of
the transition metals [19–21].
All reactions were performed under an inert atmosphere
(argon) using standard high vacuum and Schlenk-line techniques.
The compounds 1,4-bis(diphenylphophino)butane (dppb), 2,2-di-
methyl-1,3-propanediamine and 1,2-diaminphathaline were
obtained from Merck and used as received. The [RuCl2(dppb)2-
(l-dppb)] was previously prepared in our lab. [30]. Elemental
The trans/cis isomerism of ruthenium complexes of disubsti-
tuted-2,20-bipyridine derivatives have been extensively investi-
gated, although to date, bidentate biphosphine-based ligands
with mixed diamine ligands have not been studied yet in details
yet [22–24]. Due to the presence of the P-ligand in the backbone
of such coordinated complexes, the trans/cis isomerism behavior
during reaction processes can be easily monitored by 31P{1H}
NMR [2–5].
As a part of our ongoing studies on the synthesis of new ligands
and complexes for their structural coordination and studies of their
applications [1–5,25–29], herein we report the synthesis and struc-
tural characterization of two new complexes and offer facile prob-
ing of structural isomerization of trans-1 to cis-1 via 31P{1H} NMR
single-crystal X-ray crystallography. Both cis and trans-1 isomeres
were shown to have a significant catalytic role in the selective
hydrogenation of the carbonyl group of cinnamic aldehyde under
mild conditions.
analyses were performed using an Elementar Varrio EL analyzer.
High-resolution 1H, 13C{1H}, DEPT 135, and 31P{1H} NMR
spectra were recorded on a Bruker DRX 250 spectrometer at
298 K. FT-IR and FAB-MS data were obtained on a Bruker IFS 48
FT-IR spectrometer and Finnigan 711A (8 kV), modified by AMD
and reported as mass/charge (m/z), respectively. The analyses of
the hydrogenation experiments were performed on a GC 6000
Vega Gas 2 (Carlo Erba Instrument) with a FID and capillary col-
umns PS 255 [10 m, carrier gas, He (40 kPa), integrator 3390 A
(Hewlett–Packard)].
Synthesis of the [RuCl2(dppb)diamine complexes]
The complex [RuCl2(dppb)2(l-dppb)] was treated in situ with
one equivalent of diamine ligands in chloroform under an inert
atmosphere. The green color directly turned yellow or brown after
the diamine addition. Air-sensitive mixed-ligand complexes
Cl
Ph2
P
NH
2
H C
3
NH2
C
H
CHCl3
CH3
3
NH
2
Ru
CH3
20 h
P
Ph2
NH2
CH2Cl2
Cl
(1)
trans-(Cl/Cl)
N
Ph2
P
Cl
Ph2
P
Ph2
P
Cl
N
Ph2
P
Ru
Cl
Ru
Ru
P
P
Ph2
Cl
P
Ph2
P
Ph2
Ph2
Cl
Cl
cis-(Cl/Cl)
Ph2
P
Cl
NH2
CH2Cl2
X
CHCl3
20 h
Ru
NH
NH
2
2
P
Ph2
NH2
Cl
(2)
trans-(Cl/Cl)
Scheme 1. Synthesis of complexes 1–2.

468
I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
{Ru(II)-(diamine)(bis-[diphenylphosphino] butane)} were obtained
in good yields (Scheme 1).
General procedure for the preparation of cis-1 from trans-1
Trans-1 (0.1 g, 1 mmol) was dissolved in 15 mL of CHCl3. The
reaction mixture was stirred at room temperature under an inert
atmosphere for approximately 20 h. During the reaction, the sam-
ples were taken periodically and subjected to 31P{1H} NMR until all
of the trans-1 was converted to cis-1.
General procedure for the preparation of the complexes
Cis-1-: m.p. 256 °C. IR (KBr,
l
cmꢀ1): 34250, 3120, 2890 and
The corresponding diamine (at 10% excess) was dissolved in
10 mL of dichloromethane and the resulting solution was added
drop-wise to a stirred solution of [RuCl2(dppb)2(l-dppb)] in
315, 255 cmꢀ1, assigned to ANH2, PhACH, alkylACH and RuACl,
respectively 31P{1H}(CDCl3): d (ppm) dd AX pattern dA = 45.8 and
dX = 55.2 ppm (JPP = 48.2 Hz).
10 mL of dichloromethane. The reaction mixture was stirred at
room temperature under an inert atmosphere for 30 min until
the green color of the solution changed. The resulting solution
was concentrated by vacuum to 1 mL followed by the addition of
20 mL of n-hexane to precipitate compounds 1 and 2. The resulting
precipitates were washed three times with diethyl ether and n-
hexane (10 mL each) to remove off the free ligands and other
impurities.
General procedure for the catalytic studies
The respective complexes (0.02 mmol), and the co-catalysts
(0.20 mmol) (KOH or K2CO3) and cinnamic aldehyde (2.0 mmol)
were placed together in a 100 mL a Schlenk pressure tube. The so-
lid mixture was stirred and warmed during the evacuation process,
during which the Schlenk tube was filled and refilled with argon
several times to assure an inert atmosphere, 2-propanol (40 mL)
was added to the reaction mixture, which was then sonicated for
10 min to completely dissolve the reaction mixture. The mixture
was vigorously stirred, degassed by two freeze–thaw cycles, and
then pressurized with dihydrogen at 3 bars. The reaction mixture
was vigorously stirred at RT for 1 h. During the hydrogenation pro-
cess samples were taken from the reaction mixture after the gas
was removed to control the conversion and turnover frequency.
The samples were inserted into a gas chromatograph using a spe-
cial glass syringe, and the various type of kind of reaction products
were compared with authentic samples.
Trans-1: [RuCl2(dppb)2(l-dppb)] (0.1 g, 0.069 mmol) was
treated with the 2,2-dimethyl-1,3-propanediamine ligand (0.01 g,
0.07 mmol), to produce 1. Yield (88%), yellow crystal, m.p. 276 °C
(decomp.). IR (KBr,
l
cmꢀ1): 3350, 3150, 2870 and 315, 255
cmꢀ1, assigned to ANH2, PhACH, alkylACH and RuACl, respec-
tively. 1H NMR (CDCl3 d (ppm) 0.73 (s, 6H, CH3), 1.48 (m, 4H, PCH2-
CH2), 2.47 (m, 4H, PCH2), 2.74, 2.82 (b, 8H, CH2N, NH2), 7.19–7.60
(2 m, 20H, C6H5), 31P{1H}(CDCl3): @ (ppm) 46.87. 13C{1H} NMR
(CDCl3): o (ppm) 22.70 (s, PCH2CH2), 25.13 (s, CH3), 26.03 (m,
PCH2), 49.92 (s, NCH2), 128.13 (m, m-C6H5), 128.96 (s, p-C6H5),
133.92 (m, o-C6H5), 136.59 (m, i-C6H5). FAB-MS; (m/z) 700.4
[M+]. Anal. Found: C, 56.26; H, 6.17; N, 3.87; Cl, 10.74. Calc. for C33-
H42Cl2N2P2Ru: C, 56.57; H, 6.04; N, 4.00; Cl, 10.12%, UV–Vis CHCl3:
330, 480 nm.
X-ray structural analyses for complexes
2-: RuCl2(dppb)2(
the 2,3-diaminophathalene ligand (0.012 g, 0.07 mmol), to produce
2 Yield (83%), yellow crystal, m.p. 305 °C. IR (KBr,
cmꢀ1): 3380,
l-dppb) (0.1 g, 0.069 mmol) was treated with
All measurements were performed in the
on a CAD4 (Nonius) automatic diffractometer with graphite mono-
chromatized Mo K radiation [31]. The cell parameters were ob-
tained by fitting a set of 25 high-theta reflections. The details of
the data collection and refinement are given in Table 1. The control
of the intensity without appreciable decay (1.2%) yielded 7367 un-
ique reflections, of which 6516 exhibited I > 2.0(I). After Lorenz and
polarization corrections, the absorption corrections were applied
using -scans [32,33]. The structure was solved by direct methods
using the program SIR-97 [24]. The non-hydrogen atoms were re-
x/2h-scan technique
l
3110, 2880 and 314, 254 cmꢀ1, assigned to ANH2, PhACH, al-
kylACH and RuACl, respectively. 1H NMR (CDCl3); d (ppm) 1.52
(m, 4H, PCH2CH2), 2.57 (m, 4H, PCH2), 2.920(b, 4H, NH2), 7.00–
7.80 (3 m, 26H, C6H5), 31P{1H}(CDCl3): @ (ppm) for trans @ (ppm)
46.87. 13C{1H} NMR (CDCl3): @ (ppm) 23.80 (s, PCH2CH2), 26.55
(m, PCH2), 128.00–137.00 (8s, Ph), FAB-MS; (m/z) 756.1 [M+]. Anal.
Found: C, 60.52; H, 5.16; N, 3.55; Cl, 9.48. Calc. for C38H38Cl2N2P2Ru:
C, 60.32; H, 5.06; N, 3.70; Cl, 9.37. 62%; UV–Vis CHCl3: 325, 495 nm.
a
Table 1
Crystal data and structure refinement for cis-1.
C33H40Cl2N2P2Ru CHCl3
Mr = 817.95
Monoclinic, P21/n
a = 12.377 (2) Å
b = 19.394 (3) Å
c = 15.427 (2) Å
V = 3621.18 (3) Å3
Z = 4
Dx = 1.504 g cmꢀ3
Mo Ka radiation: (k = 0.71073 Å)
Cell parameters from 25 reflections
h = 2.0–27.0°
a
= 90.00 (3)°
b = 102.012 (12)°
= 90.00 (1)°
CAD4 (Nonius) diffractomer
/2h scan
l
= 0.917 mmꢀ1
T = 173 K
c
Crystal size = 0.8 ꢁ 0.4 ꢁ 0.4 mm3
Rint = 0.0216
x
hmax = 2.10–25.25°
h = ꢀ1 ? 14
Absorption correction: numerical
Tmin = NN, Tmax = NN
7971 Measured reflections
7367 Independent reflections
k = ꢀ23 ? 1
l = ꢀ18 ? 18
3 Standard reflections
Every 100 reflections
H atoms constrained to parent site
6545 Reflections with I > 2
r(I)
Refinement on F2
R[F2 > 2 (F2)] = 0.048
r
Calculated weights w = 1/[r
2(Fo2) + (0.0631P)2 + 1.5015P] where P = ((Fo2 + 2(F2c )/3
wR(F2) = 0.1255 (6545)
S = 1.093
(D/r)max = 0.997
D
D
q
q
max = 1.74 e Åꢀ1
6545 Reflections
429 Parameters
CCDC number
min = ꢀ0.67 e Åꢀ1
Extinction correction: SHELXL
784617

I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
469
fined anisotropically by the full-matrix least-square techniques
using the program SHELXL-97 [34]. All of the hydrogen atoms
bonded to C atoms were geometrically located and treated using
a
riding model, with CAH = 0.93–0.97 Å and Uiso(H) = 1.2 or
1.5Ueq(C).
Results and discussion
Synthesis of the complexes
Complexes 1 and 2 were isolated in good yield using a simple,
1 h, RT reaction of excess diamine with the green RuCl2(dppb)2-
(l-dppb) starting complex in chloroform under an inert atmo-
sphere. The reaction was monitored by the green color change
upon the addition of the diamine ligands, as well as by UV–Vis,
IR and 31P{1H} NMR spectral analyses (Scheme 1).
IR spectral investigations
Fig. 2. UV–Vis spectra of (a) green Rucl2(dppb)2(
l-dppb), (b) yellow 1, (c) brown 2
complexes direct dissolved in CHCl3 At RT. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
The IR spectra of the desired complexes were examined in com-
parison relative to the spectra of free ligands. The IR spectra of the
RuCl2(dppb)2(l-dppb) starting complex and complex 1 are shown
in Fig. 1, RuCl2(dppb)2(
l
-dppb) showed no peaks at 3400; and
of complexes 1 and 2, respectively. These complexes formed inten-
sely colored solutions, and thus very low concentrations were used
(10ꢀ4 M). The desired complexes displayed intense transitions in
the UV–Vis region. Bands at the high-energy end at 200–340 nm
1560 cmꢀ1, which are attributed to ANH2, stretching and bending
vibrations, respectively, as shown in Fig. 1a. The vibration of this
functional group appeared upon the addition of diamine to
range have been previously assigned to intra-ligand
p–
pꢂ/n–pꢂ
RuCl2(dppb)2(l-dppb) for the preparation of complex 1, as shown
in Fig. 1b. In particular, complexes 1 and 2 revealed four main sets
of characteristic absorptions in the ranges of 3400–3200, 3190–
3000, 2950–2820 and 270–285 cmꢀ1, which can be assigned to
ANH2, PhACH, alkylACH and RuACl stretching vibrations, respec-
tively. All other function group vibrations appeared at their ex-
pected positions as in Fig. 1.
transitions [22,29]. Base on the intensity and position, the lowest
energy transitions in the visible region at 400–520 nm have been
tentatively assigned to Md –L metal to ligand charge transfer
p
pꢂ
transitions (MLCTs) [35,36]. Additionally, the RuCl2(dppb)2(l-
dppb) complex revealed a visible broad band at 680 nm, which
can be primarily attributed to d–d electron transfer [36].
Electronic absorption spectral studies
Mass spectra
The electronic absorption spectra of green RuCl2(dppb)2(l-
dppb), and complexes 1 and 2 were acquired in chloroform at room
temperature. To avoid any structural changes, the electronic
absorption spectra of the [RuCl2(dppb)2(l-dppb)] complexes were
recorded before and after the direct addition of diamine to prepare
complexes 1 and 2, as in Fig. 2, the coordination process is visually
detected by observing the change in color from green to yellow and
brown upon addition of the diamine, consistent with the formation
The observed molecular ion peak (s) at m/z 700.4 and 756.1 cor-
responding to complexes 1 and 2, respectively, are consistent with
the proposed molecular formula. The FAB-MS spectrum of complex
1 shows a molecular ion peak [M+] m/z = 700.4, which corresponds
to the molecular formula of its parent ion [C31H42Cl2N2P2Ru]+ at
50% of the base peak intensity. The main first three fragments that
appeared in the spectrum correspond to m/z = 665.1 ([C31H38ClN2-
P2Ru]+, 80%, [M+]-Cl), and 629.9 ([C31H38N2P2Ru]+, 50%, [M+]-HCl2)
(Fig. 3).
Fig. 1. IR-KBr disk spectra of (a) RuCl2(dppb)2(
l
-dppb) and (b) complex 1.
Fig. 3. FAB-MS spectrum of complex 1.

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NMR investigation
attributed to the diamines and dppb ligands. The chemical shifts
and integration of the DEPT 135 13C{1H} and 1H NMR resonances
confirms the dppb to diamine coordination ratio which is in agree-
ment with the structural composition, as shown in Fig. 4.
The NMR spectra also corroborate the structure of the desired
complexes. The 1H and 13C{1H} NMR spectra were recorded di-
rectly after dissolving the complexes in CDCl3 solution as described
in ‘Experimental’. Several characteristic sets of observed signals are
The 31P{1H} NMR spectra of direct dissolved complexes 1 and 2
in CDCl3, showed only one signal at 46.87 and 47.15 ppm, respec-
Fig. 4. (a) 1H and (b) 135 dept 13C{1H} NMR spectra corroborates the structure of trans-1 in CDCl3 at RT.

I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
471
Fig. 5. Time-dependent 31P{1H} NMR spectroscopic of: (a) trans-1 complex with C2v equivalent P atoms at dp = 46.8 ppm, direct dissolved in CDCl3 (b) after 2 h of stirring,
mixture of trans-1 and cis-1 isomers with trans-1 predominate, (c) after 12 h, mixture of trans-1 and cis-1 isomers with dd in-equivalent P atoms cis-1 predominate isomer, (d
and c) after 20 h, only cis-1 isomer was recorded.
tively as shown in Fig. 5. This result is expected for a kinetically fa-
vored trans-1 configuration with C2v symmetrical arrangements of
the P atoms, where the nitrogen atoms are trans to the phosphorus
atoms, as shown in Scheme 1. In our studies of such complexes, we
demonstrated that the trans-Cl2Ru isomer, which the nitrogen
atoms trans to the phosphorus atoms (trans effect) is chemically
and structurally favoured over any other isomers.
It is interesting to point out that the process of isomerization
the from trans to the cis isomer was first observed through
31P{1H} NMR experiments. In the case of the spectrum for trans-1

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I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
a fresh solution of complex 1 in CHCl3 showed one singlet at
46.87 ppm for the kinetically favored trans-1 isomer. The intensity
of this singlet decreased with time as the complex became dy-
namic in the chloroform solution. Two doublets indicating the for-
mation of cis-1 (the thermodynamically favored isomer) with
unequivalent number of phosphorus atoms were observed by
31P{1H} NMR at room temperature (AX pattern with dA = 45.8 and
dX = 55.2 ppm, coupling constant of PAP atoms, JAX = 48.2 Hz)
(Fig. 5). The 31P chemical shifts and the 31PA31P coupling con-
stants are consistent with a cis arrangement of the P atoms in dppb.
To verify the spatial molecular structure of the cis-1 isomer, ob-
tained from trans-1, we performed an X-ray structure analysis for
crystal of complex 1.
X-ray structure determination of complex 1
A suitable single crystal of cis-1 was obtained by evaporating
the concentrated parent solution of full cis-1, as confirmed by 31P
NMR, using a soft-vacuum desiccator, several trials were per-
formed until suitable crystals were collected. A yellow crystal of
cis-1 having approximate dimensions of 0.8 ꢁ 0.4 ꢁ 0.4 mm3 was
mounted on a glass fiber.
The structure shows two independent diamine and diphosphine
ligands and one solvated chloroform molecule per asymmetric
unit. The orientations of the diamine and diphosphine ligands are
different which indicates that the structure belongs to the cis-Cl2Ru
isomer. The diphosphine portion of atomic numbering scheme is
shown in Fig. 6.
The geometry surrounding the Ru(II) center has an octahedral
environment formed by two chlorine atoms in the cis geometric
configuration and two PAP and NAN ligands. The RuACl bond dis-
tances are 2.4404(4) and 2.5264(3) Å. The RuAN bond distances,
which in range from 2.1268(3) to 2.1978(3) Å are similar to those
of RuAN in the trans-Cl2Ru(PAP)(NAN)] complex with a range
2.1994(19)–2.2030(2) Å, where NAN0 is an analogs of NAN (the
PAP ligand is the same for both complexes) [29].
Fig. 7. View of packing of cis-1 in the unitcell.
P2AC27, respectively. We note
a
slight deformation around
Ru1; where the angles are different from 96°[N1ARu1A N2 =
84.21(6)°, N1ARu1AP1 = 94.72(9)°, N1ARu1A P2 = 98.78(10)°,
N2ARu1AP1 = 170.16(10)°,
N2ARu1AP2 =
96.78(9)°,
and
Cl1ARu1ACl2 = 90.74(5)°]. The deviation in this octahedral geom-
etry is also confirmed by the angles of the atoms in trans positions,
which are consistent different from 180°; P1ARu1AN2 =
170.16(1)° and P2ARu1ACl2 = 176.35(1)°. The crystal structure of
the title complex is stabilized by inter- and intra-molecular
CAH. . .ClACCl2H type-hydrogen bonding interactions that form a
3D network. The packing and hydrogen bonding interactions are
illustrated in Fig. 7.
Catalytic activity of complexes in the hydrogenation of cinnamic
aldehyde
Cinnamic aldehyde (trans-4-phenyl-3-propene-2-al) was se-
lected to determine the hydrogenation selectivity and activity of
the desired complexes. Three different regio-selective hydrogena-
tion was expected [1,29].
In the molecular structure of cis-1, the two central phenyl rings
of the two P atoms coordinated to the Ru metal form dihedral an-
gles of 34.8(5) and 68.8(6)° for C7AP1---P2AC23 and C1AP1---
The hydrogenation reaction using the complexes as the cata-
lysts were perform under identical conditions: 40 °C with a molar
substrate: to catalyst (TON, S/C) ratio of 1000/1; 3 bar of hydrogen
pressure, 40 ml of 2-propanol; Ru: co-catalysts (KOH, t-BOK or
K2CO3): cinnamic aldehyde ratio of [1:10:1000]. Data regarding
the reduction of cinnamic aldehyde to trans-4-phenyl-3-propene-
2-ol are presented in Table 2.
The hydrogenation reactions under the above condition using
complex 1 with both isomers (trans-1 and cis-1) as catalysts were
Table 2
Hydrogenation of cinnamic aldehyde using Ru(II) cat. in 2-propanol at 40 °C with a
molar substrate: catalyst (TON, S/C) ratio of 1000/1, under 3 bar of hydrogen pressure,
for 1 h.
Trial
Catalyst
Conversion (%)a
Co-cat.
TOFb
1
2
3
4
5
6
6
Trans-1
Cis-1
Trans-1
Trans-1
Trans-1
2
>99
>99
>99
20c
7d
KOH
KOH
t-KOBu
KOH
K2CO3
KOH
995
990
980
200
7
0d
0
0
RuCl2(dppb)2(
l-dppb)
0d
KOH
a
b
c
Yield and selectivity were determined by GC.
ꢀ1
TOF: turnover frequency (molsub molꢀ1
EtOH instead of 2-propanol solvent.
10 h reaction.
h
).
cat
Fig. 6. ORTEP view of the cis-1 with the atom numbering scheme. Displacement
ellipsoids for non-H atoms are drawn at the 30% probability level. H atoms were
omitted for clarity.
d

I. Warad et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 466–473
473
completed within 1 h which enhanced the TOF number. Both the
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Crystallographic data corresponding to the structural analysis
have been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 784617 for complex {[cis-Cl2Ru(PAP)-
(NAN)]ꢃHCCl3}. Copies of this information can be obtained free of
charge from The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk
or http://www.ccdc.cam.ac.uk).
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.11.108.