Syntheses and X-ray crystal structures of two ruthenium(II) complexes derived from acetonitrile and dimethylphenylphosphonite

Article abstract of DOI:10.1016/j.jorganchem.2013.04.015

The ruthenium acetonitrile complex [RuCl₂(NCCH₃) ₂{P(OCH₃)₂C₆H₅} ₂] (1) and the stable salt [Ru(CH₃CN) ₄{P(OCH₃)₂C₆H₅} ₂][BF₄]₂ (2) have been prepared from [RuCl ₂(NCCH₃)₂(COD)] and the salt [Ru(COD)(CH ₃CN)₄][BF₄]₂ respectively. The two compounds have been characterized by IR, microanalytical, NMR measurements and single-crystal X-ray diffraction studies. The ruthenium in both compounds has almost ideal octahedral coordination geometry. One of the complexes, [RuCl ₂{P(OCH₃)₂C₆H₅} ₂(NCCH₃)₂] (1) has shown significant catalytic activity for the transfer hydrogenation of simple ketones while the other, [Ru{P(OCH₃)₂C₆H₅} ₂(NCCH₃)₄][BF₄]₂ (2) did not show any catalytic activity for this reaction.

Full text of DOI:10.1016/j.jorganchem.2013.04.015

Journal of Organometallic Chemistry 739 (2013) 21e25
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses and X-ray crystal structures of two ruthenium(II) complexes
derived from acetonitrile and dimethylphenylphosphonite
,
a
a
b
Samson O. Owalude a , Ezekiel O. Odebunmi , Uche B. Eke , Arnold L. Rheingold ,
*
Naftali Opembe c, Steven L. Suib c
a Department of Chemistry, University of Ilorin, P.M.B. 1515, Ilorin, Nigeria
b Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0358, USA
c Department of Chemistry, University of Connecticut, U-3060, 55 North Eagleville Road, Storrs, CT 06269-3060, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The ruthenium acetonitrile complex [RuCl2(NCCH3)2{P(OCH3)2C6H5}2] (1) and the stable salt
[Ru(CH3CN)4{P(OCH3)2C6H5}2][BF4]2 (2) have been prepared from [RuCl2(NCCH3)2(COD)] and the salt
[Ru(COD)(CH3CN)4][BF4]2 respectively. The two compounds have been characterized by IR, microana-
lytical, NMR measurements and single-crystal X-ray diffraction studies. The ruthenium in both com-
pounds has almost ideal octahedral coordination geometry. One of the complexes, [RuCl2
{P(OCH3)2C6H5}2(NCCH3)2] (1) has shown significant catalytic activity for the transfer hydrogenation of
simple ketones while the other, [Ru{P(OCH3)2C6H5}2(NCCH3)4][BF4]2 (2) did not show any catalytic ac-
tivity for this reaction.
Received 6 February 2013
Received in revised form
4 April 2013
Accepted 10 April 2013
Keywords:
Ruthenium
Single-crystal X-ray diffraction
Hydrogenation
Ketones
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
biological activities have been reported [13e19]. The use of this
derivative as a precursor to ruthenium organometallic compounds
The polymer [{RuCl2(COD)}x] has been often applied as a useful
synthetic precursor to a wide range of ruthenium compounds in
the past [1e3]. This compound is highly insoluble in most organic
solvents; therefore reactions with it are usually carried out under
extreme conditions which require filtration steps, long reaction
times etc [1] and often give products in moderate to low yields [4].
Its suspensions in methanol or ethanol have however been found
to react rapidly with hydrazines to produce clear solutions from
which cationic ruthenium(II) salts were isolated in quantitative
yield on addition of suitable counter anions [1]. Such derivatives of
the polymer contain labile hydrazine groups in solution making
them ideal precursors for the synthesis of an extensive range of
ruthenium(I1) salts [1,5]. Treatment of the polymer [{RuCl2(-
COD)}x] with acetonitrile at reflux also produced a soluble aceto-
nitrile solvate compound [RuCl2(NCCH3)2(COD)] which has a great
potential as precursor for ruthenium compounds [6e12]. A range
of useful organometallic compounds have been prepared using this
soluble precursor, in particular, compounds with medicinal and
has not been given prominent attention despite its great potential,
probably due to low yields. We have recently reported an efficient
synthetic procedure for [RuCl2(COD)(NCCH3)2] [20]. Transition
metal complexes with coordinated phosphinite and phosphonite
ligands have remained one of the most studied systems. This is
attributed to their simple synthetic methods, versatile coordina-
tion behavior and more importantly their wide applications as
catalysts for several organic functional groups transformations
[21,22]. Ruthenium complexes with phosphinite and phosphonite
ligands in particular have been reported as being very active cat-
alysts in the transfer of hydrogen from alcohols in the form of
hydrides to ketones [23]. Metal complexes with chiral bidentate
ligands are the most frequently used in the transfer hydrogenation
reactions [24] with those ligands containing nitrogen as donor
atoms exhibiting greater catalytic activity [25,26]. Since the mon-
odentate ligands are less expensive and more readily available
than most chiral bidentate ligands, we hereby report our findings
in the reactivity of ruthenium starting materials [RuCl2(-
COD)(CH3CN)2] and [Ru(COD)
(CH3CN)4][BF4]2 with the monodentate dimethylphenylphos-
phonite ligand P(OCH3)2C6H5, data on the catalytic activity of the
resulting complexes in the transfer hydrogenation of ketones are
also presented.
* Corresponding author. Tel.: þ234 8033639273.
E-mail addresses: owalude1412@yahoo.com, owalude@unilorin.edu.ng (S.O. Owalude).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.04.015

22
S.O. Owalude et al. / Journal of Organometallic Chemistry 739 (2013) 21e25
2. Experimental
to check the conversion. The samples were inserted by a special
glass syringe into a gas chromatograph and the reaction products
were compared with authentic samples. The results of the catalytic
reactions are collected in Table 2.
2.1. General comments
All manipulations were performed using standard Schlenk-tube
techniques under an atmosphere of purified nitrogen. All solvents
were purified by standard procedures [27]. RuCl3$xH2O was pur-
chased from Acros Organics. Dimethylphenylphosphonite and
acetonitrile were commercially obtained from Aldrich. The starting
materials [{RuCl2(COD)}x] [3], [RuCl2(COD)(NCCH3)2] [20] and
[Ru(COD)(NCCH3)4][BF4]2 [28] were synthesized according to
literature methods. Elemental analyses were performed with an
Elementar Vario EL analyzer at the Institute of Materials Science,
University of Connecticut. High-resolution 1H, 31P{1H}, and 13C{1H}
NMR spectra were recorded on a Bruker DRX 250 spectrometer at
298 K. The 1H and 13C{1H}chemical shifts were calibrated to solvent
peaks, which are reported relative to TMS. 31P NMR chemical shifts
were measured relative to 85% H3PO4. GCeMS analyses were per-
formed on Agilent 5975 Series MSD and 7820A GC System. All re-
ported yields in transfer hydrogenation experiments are GC yields
and were averages of at least two runs.
2.4. X-ray diffraction measurements
Crystals of 1 and 2 were mounted on a Cryoloop with Paratone-
N oil and data were collected at 90 K with a Bruker APEX II CCD
using Mo K alpha radiation. Data were corrected for absorption
with SADABS [30] and the structures solved by direct methods. All
non-hydrogen atoms were refined anisotropically by full matrix
least squares on F2. Hydrogen atoms on acetonitrile were found
from a Fourier difference map and were then fixed in position with
suitable riding parameters. Hydrogen atoms on phosphorus atoms
were found from a Fourier difference map and were refined iso-
tropically with distances of 1.33(1) angstroms and ꢁ1.20 Ueq of
parent P atom. All other hydrogen atoms were placed in calculated
positions with appropriate riding parameters.
3. Results and discussion
2.2. Preparations
3.1. Structural characterization of [RuCl2{P(OCH3)2C6H5}2(NCCH3)2]
(1)
2.2.1. [RuCl2{P(OCH3)2C6H5}2(NCCH3)2] (1)
In a 100 mL Schlenk flask, [RuCl2(COD)(NCCH3)2] (0.20 g,
0.5 mmol) and P(OCH3)2C6H5 (0.18 g, 1 mmol) were dissolved in
20.0 mL of acetonitrile and the orange solution was stirred at 78 ꢀC
for 19 h during which time a bright yellow solution formed. The
solution was reduced in volume to 5 mL under vacuum and kept at
Complex 1 was obtained in good yield from a ligand exchange
reaction of [RuCl2(COD)(NCCH3)2] with 2 M equivalents of the
P(OCH3)2C6H5 ligand. The physical properties and elemental anal-
ysis of the complex are given in the experimental section. Once
isolated, the complex was found to be relatively stable in air over a
period of two weeks and was therefore stored in an inert atmo-
sphere. The complex is soluble in CHCl3, CH2Cl2, DMF and DMSO
solvents but not in methanol, ethanol, hexane, pentane, THF and
ether.
0
ꢀC for three weeks to obtain yellow crystalline solids. Yield 76%;
mp 282e301 ꢀC; 1H NMR (CD2Cl2)
(ppm) 1.85 (s, 6H, CH3), 3.83 (s,
12H, OCH3), 7.47e7.92 (m, 10H, C6H5); 13C{1H} NMR (CD2Cl2),
(ppm) 3.50 (s, CH3), 53.01 (s, OCH3), 128.09 (s, CN), 130.23e131.30
(m, C6H5); 31P{1H} (CD2Cl2), (CN) 2279 cmꢁ1
154.81; IR (KBr)
(RueP) 526 cmꢁ1. Elemental analysis for C20H28Cl2N2O4P2Ru,
d
d
d
n
,
The IR spectrum of complex 1 has characteristic n(CN) bands at
n
2279 cmꢁ1 in the region higher in frequency than in the free nitrile
(2248 cmꢁ1) [31], as expected for coordination through the nitrile
nitrogen atom [7]. Absence of COD protons at the expected regions
in both compounds suggests that the COD ligand was substituted in
preference to the acetonitrile in contrast to literature report [5]. The
1H NMR spectrum of 1 displays singlets at 3.83 and 1.8 ppm which
are assigned to the protons on the methoxy groups on
P(OCH3)2C6H5 and acetonitrile methyl groups respectively. The
resonances attributable to the protons on the phenyl groups on
P(OCH3)2C6H5 were observed between 7.47 and 7.92 ppm. The 13C
NMR spectrum of 1 consist of lines at 3.50 ppm assigned to the
methyl groups on the acetonitrile while lines for CN were present at
128.09 ppm and aromatic carbons on P(OCH3)2C6H5 were observed
between 130 and 131 as multiplets. Appearance of a singlet at
154.81 ppm in the 31P{1H} NMR spectrum of 1 is indicative of
equivalent phosphorus of the two P(OCH3)2C6H5 ligands. The 31P
calcd. (found): C, 40.30 (40.40); H, 5.29 (4.71); N, 4.71 (4.71).
2.2.2. [Ru{P(OCH3)2C6H5}2(NCCH3)4][BF4]2 (2)
[Ru(COD)(NCCH3)4][BF4]2 (0.20 g, 0.37 mmol) and dimethox-
yphenylphosphine (0.14 g, 0.75 mmol) were dissolved in 15.0 mL of
acetonitrile and the yellow mixture was refluxed for 12 h. The
volume was reduced to 5 mL and kept at 0 ꢀC for two weeks. The
white precipitate obtained was collected by filtration, dried in the
vacuum and recrystallized from CH2Cl2/MeOH solution to give
colorless prisms. Yield 70%; mp 225e228 ꢀC; 1H NMR (CD2Cl2)
d
(ppm) 2.27 (s, 12H, CH3), 3.86 (s, 12H, OCH3), 7.66e7.69 (m, 10H,
C6H5); 13C{1H} NMR (CD2Cl2),
(ppm) 3.74 (s, CH3), 127.58 (s, CN),
129.50e132.20 (m, C6H5); 31P{1H} (CD2Cl2),
151.07 (s, P(OCH3)2
C6H5); IR (KBr)
(CN) 2081 cmꢁ1 (RueP) 529 cmꢁ1. Elemental
d
d
n
, n
analysis for C24H34P2O4N4B2F8Ru, calcd. (found): C, 36.97 (37.15); H,
4.37 (4. 42); N, 7.19 (7.28).
chemical shift of free P(OCH3)2C6H5 have been reported at
d
þ161.7
[32] and þ165.09 ppm [33]. The 31P NMR signal in the complex 1 is
2.3. General procedure for the transfer hydrogenation study
d
þ154.81 ppm, the coordination shift is between 8 and 11 units
upfield when the free P(OCH3)2C6H5 becomes coordinated in the
[RuCl2(NCCH3)2(P(OCH3)2C6H5)2] complex. The integration ratios in
the 1H NMR of 1 combined with the elemental analysis data sup-
port the stoichiometry [RuCl2(NCCH3)2(P(OCH3)2C6H5}2].
A published procedure was adopted [29] for the transfer hy-
drogenation studies of 1 and 2 as described here for 1. The ruthe-
nium complex 1 (0.004 mmol) was placed in a 50 mL flask
containing 15 mL of 2-propanol as solvent, and 5 mL of a NaOH
(0.096 mol/L) solution in 2-propanol was added as a co-catalyst.
The mixture was then freed from oxygen by three freeze-thaw
cycles. Subsequently the flask was filled with argon and the ke-
tone (5.0 mmol) was added. The reaction mixture was vigorously
stirred at 82 ꢀC for 4 h. During the transfer hydrogenation, samples
were taken from the reaction mixture at regular interval of 30 min
3.2. Structural characterization of [Ru{P(OCH3)2C6H5}2(NCCH3)4]
[BF4]2 (2)
The cationic tetrakisacetonitrile complex [Ru(CH3CN)4{-
P(OCH3)2C6H5}2][BF4]2 (2) has been obtained in 70% isolated yield
by the reaction of [Ru(CH3CN)4(COD)][BF4]2 with P(OCH3)2C6H5 in

S.O. Owalude et al. / Journal of Organometallic Chemistry 739 (2013) 21e25
23
CH3CN at 78 ꢀC. Compound 2 was isolated as air-stable colorless
solid and has been characterized by means of standard spectro-
scopic techniques (IR and 1H, 31P{1H}, and 13C{1H} NMR) as well as
elemental analysis. The IR spectrum of 2 contained weak n(CN)
absorption bands at 2081 cmꢁ1. In the 1H NMR spectrum of 2,
proton resonances for hydrogen atoms attached to the methoxy
groups of P(OCH3)2C6H5 were observed at 3.86 ppm while the
resonances attributable to the acetonitrile methyl groups appeared
at 2.27 ppm. The phenyl proton resonances in the complex were
observed between 7.66 and 7.69 ppm as multiplets. This is also
supported by the 13C {1H}NMR data giving rise to a single line at
3.74 ppm attributable to the CH3CN methyl carbons and a multiplet
of resonance between 129 and 132 ppm for the phenyl rings on
P(OCH3)2C6H5. The resonance of the nitrile group is found at
127.58 ppm, compared to 116.92 ppm in free CH3CN [34]. The signal
attributable to the two equivalent phosphorus atoms in 2 was
observed at 151.07 ppm in the 31P NMR spectrum. The coordination
shift when compared to the 31P chemical shift of the free
P(OCH3)2C6H5 at
d
þ161.7 [32] or þ165.09 ppm [33] is between 11
and 14 units upfield when the free P(OCH3)2C6H5 become coordi-
nated in the [Ru(NCCH3)4(P(OCH3)2C6H5)2][BF4]2 complex. All data
are in agreement with the proposed stoichiometry.
Fig. 2. ORTEP diagram of [Ru(NCCH3)4{P(OCH3)2C6H5}2][BF4]2 (2) with ellipsoids
drawn at 50% probability. One of the BF4 counterion has been omitted for clarity.
ꢀ
Selected bond distances (A) and angles (deg): Ru(1)eN(1) 2.0347(14), Ru(1)eN(2)
2.0226(14), Ru(1)eP(1) 2.3535(4), P(1)eO(2) 1.5981(12), P(1)eC(1) 1.8074(16), N(2A)e
Ru(1)eN(2) 180.00(6), N(2)eRu(1)eN(1) 89.35(5), N(2)eRu(1)eP(1) 89.87(4), N(1)e
Ru(1)eP(1A) 88.26(4), N(1)eRu(1)eP(1) 90.13(4), O(2)eP(1)eO(1) 106.79(6).
3.3. X-ray analysis of 1 and 2
Crystals suitable for X-ray structural analysis have been ob-
tained for complexes
1 and 2 by slow evaporation of
dichloromethane-methanol (1:3) solution of the complexes at
room temperature. The molecular structures of complexes 1 and 2
are shown in Figs. 1 and 2. Crystal data and structure refinement
details are presented in Table 1 while the selected bond distances
and bond angles of both complexes are listed as footnotes to each
figure.
The crystal structure of 1 (Fig. 1) consists of a mononuclear
[RuC20H28Cl2N2O4P2] unit. Ru2þ has an octahedral geometry with
the equatorial plane occupied by N1, N1A, P1 and P1A from two
CH3CN and two P(OCH3)2C6H5, and the axial positions are
completed by Cl1, Cl1A from the chlorides. The two Cl ligands in 1
are bound to the ruthenium center in trans positions, forming angle
180.00(3)ꢀ. The other two ligands, CH3CN and P(OCH3)2C6H5 are
also bound to the ruthenium center in similar fashion with angles
of 180.00(11) and 180.00(3)ꢀ respectively. The angles around the Ru
Table 1
Summary of X-ray parameters for compounds 1 and 2.
1
2
Formula
Mol wt
C20H28Cl2N2O4P2Ru
594.35
C24H34B2F8N4O4P2Ru
779.18
Cryst syst
Space group
T (K)
Monoclinic
P2(1)/n
100(2)
12.4227(11)
8.3978(8)
12.7477(13)
90
110.507(3)
90
Monoclinic
P2(1)/n
100(2)
8.4490(10)
11.2854(10)
17.1068(10)
90
98.305(4)
90
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
(deg)
(deg)
(deg)
3
ꢀ
V (A )
1245.6(2)
2
1.585
1614.0(5)
2
1.603
Z
Dcalcd (Mg/m3)
m(Mo K
a
) mmꢁ1
1.001
0.668
F(000)
Range
No. of rflns
604
2.84e26.38
10,607
788
2.56e26.38
14,884
q
, deg
No. of indep rflns
No. of refined params
2521
138
3309
209
RI (I > 2
s
(I))
R1 ¼ 0.0323
wR2 ¼ 0.0841
R1 ¼ 0.0339
wR2 ¼ 0.0856
1.074
R1 ¼ 0.0210
wR2 ¼ 0.0495
R1 ¼ 0.0248
wR2 ¼ 0,0517
1.024
Fig. 1. ORTEP diagram of [RuCl2{P(OCH3)2C6H5}2(NCCH3)2] (1) with ellipsoids drawn at
50% probability. Hydrogen atoms have been omitted for clarity. Selected bond dis-
R indices (all data)
ꢀ
tances (A) and angles (deg): Ru(1)eN(1) 2.023 (2), Ru(1)eN(2) 2.023(2), Ru(1)eP(1)
2.3321(6), P(1)eO(1) 1.6118(17), P(1)eC(1) 1.823 (2), Ru(1)eCl(1) 2.4091(6), N(1)e
Ru(1)eN(1A) 180.0, N(1A)eRu(1)eP(1A) 88.63 (5), N(1)eRu(1)eP(1) 91.37(5), N(1)e
Ru(1)eCl(1) 89.26(5), P(1)eRu(1)eCl(1) 87.29(2), N(1)eRueCl(1) 90.74(5), O(2)eP(1)e
O(1) 105.16(9).
GOF
Max peak, e A
CCDC no.
ꢀꢁ3
0.940
873004
0.439
884044

24
S.O. Owalude et al. / Journal of Organometallic Chemistry 739 (2013) 21e25
atom are all close to 90ꢀ in line with the octahedral coordination
arrangement. Bond distances found in this structure correspond to
related values from other similar structures. The average CeC bond
Table 2
Catalytic transfer hydrogenation of ketones catalyzed by complex 1.
Entry
1.
Substrate
Product
Yield (%)
99.5
ꢀ
ꢀ
distance of 1.391(3) A and CeCeC bond angles of 120 in the two
OH
O
O
O
phenyl rings in the structure are within the accepted values of
ꢀ
ꢀ
1.394 A and 120 for phenyl rings [35]. The average RueP bond
ꢀ
length of 2.3316(6) A is slightly shorter than the sum of their co-
valent radii (2.51 A) which indicates a strong mutual attraction
ꢀ
OH
between Ru and P [36]. Mean PeO and OeC distances are
2.
3.
97
ꢀ
1.6121(16) and 1.444(3) A respectively and are normal and requires
ꢀ
no comment [36]. The average RueCl bond length in 1 (2.4090(5) A)
is shorter than the values previously reported for a related octa-
hedral complex [29].
OH
The asymmetric unit of complex 2 comprises half the molecule
with the ruthenium atom situated on a center of symmetry. The X-
ray crystal structure shows (Fig. 2) four CH3CN and two
P(OCH3)2C6H5 ligands coordinated in an almost ideal octahedral
arrangement to the central Ru2þ cation. The cation within 2 is
monomeric, the equatorial plane is occupied by four CH3CN ligands
coordinated through the nitrogen atoms while the two coordinated
P-bonded P(OCH3)2C6H5 molecules occupy axial positions. The
100
O
OH
4.
100
ꢀ
mean RueP distance is 2.3535(4) A while the PeO distances range
ꢀ
between 1.5981(12)e1.6042(12) A. Average RueN bond distance of
ꢀ
2.02865 A in 2 is somewhat shorter than in the parent acetonitrile
species [28]. Associated with the Ru cation are two essentially
tetrahedral BF4 counter ions (only one illustrated). The geometry of
the counter ions is in agreement with that found in other structures
[37] but no interactions were found between these ions and the
ruthenium(II) core.
Experimental conditions: ketone, 5 mmol; NaOH, 0.096 mol; catalyst loading,
0.004 mmol; 2-propanol, 15 mL; temp, 82 ꢀC; time, 4 h. Yields were determined by
GCeMS and related to the unreacted ketone.
The activity of complex 2 was also investigated under the same
conditions as complex 1 but 2 showed no activity toward the
transfer hydrogenation of any of the ketones even at an extended
time of 24 h. This gives further support to the assertion that an
active dihydride species RuH2(NCCH3)2{P(OCH3)2C6H5}2 formed by
complex 1 through the loss of the two chlorides is likely to be the
true catalyst. The different catalytic performances of the two
complexes may therefore be due to the different coordination en-
vironments around the metal centers.
3.4. Catalytic transfer hydrogenation reactions
The simple synthetic routes to the isolated complexes prompted
us to investigate their catalytic activity in the transfer hydrogena-
tion of ketones (Scheme 1). The ruthenium complex 1 showed
remarkable performance in the conversion of both aliphatic and
aromatic ketones to alcohols and the results are presented in
Table 2. The complex efficiently catalyzed the reduction of ethyl
methyl ketone and hexanone to their corresponding alcohols with
99.5 and 97% conversion respectively. The conversion in case of
both acetophenone and cyclohexanone was 100%. No transfer hy-
drogenation was observed in the absence of base, suggesting loss of
the chlorides to form a reactive dihydride species in a similar
fashion to the formation of RuH2(PPh3)2(cydn) reported by Morris
et al. [38]. Therefore, it is believed that the base facilitated the
formation of a ruthenium alkoxide by abstracting the proton from
The results obtained in this study are similar to those reported
by Wills and co-workers with the complex [{P(OC10H6)2C6H4Br}2
-
RuCl2(DPEN)] (DPEN ¼ diphenylethylenediamine) for the transfer
hydrogenation of acetophenone [24(b)]. Using the complex at
50 bar hydrogen pressure and S/C ratio of 2000, acetophenone was
fully reduced in less than 4 h. The new catalyst system does not
require the presence of molecular hydrogen to function; the
hydrogen is rather transferred in form of hydride from isopropanol
to the ketones as proposed above. In another report, a Ru complex
containing BINOL-derived monodentate diphosphonite ligand
[{P(OC10H6)2}2C15H12O] was reported to efficiently catalyze the
asymmetric transfer hydrogenation of both aryl/alkyl and alkyl/
alkyl ketones [46]. However, the simple synthetic route and price
affordability will place this new catalyst system a better candidate
for asymmetric transfer hydrogenation of ketones.
the alcohol and subsequently the alkoxide underwent b-elimina-
tion to give the active species, ruthenium hydride [39]. The ketone
then coordinates to the hydride-ruthenium intermediate which
eventually led to the alcohol formation [40e45]. Complex 1 how-
ever, showed no activity toward the hydrogenation of nitrobenzene
after 48 h, therefore no further attempt was made to hydrogenate
compounds with similar functional groups.
The new catalyst system is also very effective and fast, achieving
100% yield in 4 h for acetophenone, there is therefore no problem of
chiral resolution of products with this new catalyst system.
OH
O
Ru-cat
4. Conclusions
NaOH, 2-iPrOH
R1
R2
R1
R2
The reaction of the ruthenium(II)-organonitrile precursor
[RuCl2(COD)(NCCH3)2] or [Ru(COD)(NCCH3)4][BF4]2 with dime-
thylphenylphosphonite gave new acetonitrileeRu(II) complexes.
The complexes were isolated as air and moisture stable solids and
have been characterized by IR and NMR spectroscopic techniques,
elemental analyses and X-ray crystal structure analyses. One of the
R1, R2 = alkyl or aryl
Scheme 1. Transfer hydrogenation reactions.

S.O. Owalude et al. / Journal of Organometallic Chemistry 739 (2013) 21e25
25
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Acknowledgment
This work was supported by the United States Institute of In-
ternational Education (IIE). The authors would like to thank Uni-
versity of Connecticut for the facilities to carry out the research
work and the University of California, San Diego for the X-ray
diffraction analysis. The University of Ilorin is also gratefully
acknowledged for a grant of Staff Development Award to SOO to
undertake the study. NO and SLS acknowledge the support of the
National Science Foundation under grant GOALI CBET number
0827800.
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