Crystal structure of trans- and cis-bis(acetylacetonato)bis(trimethylphosphite)ruthenium(II) complexes and testing their catalytic activity in hydrogen generation from the hydrolysis of sodium borohydride

Article abstract of DOI:10.1016/j.ica.2010.03.023

Both the trans and cis isomers of [Ru(acac)₂{P(OMe)₃}₂] were isolated in the form of single crystals and characterized by single crystal X-ray diffraction, UV-Vis, MS, ¹H, ¹³C and ³¹P NMR s

Full text of DOI:10.1016/j.ica.2010.03.023

Inorganica Chimica Acta 363 (2010) 1713–1718
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Crystal structure of trans- and cis-bis(acetylacetonato)bis(trimethylphosphite)-
ruthenium(II) complexes and testing their catalytic activity in hydrogen generation
from the hydrolysis of sodium borohydride
a
b
a,*
Mehdi Masjedi , Leyla Tatar Yildirim , Saim Özkar
a
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Department of Engineering Physics, Hacettepe University, 06800 Ankara, Turkey
b
a r t i c l e i n f o
a b s t r a c t
Article history:
2 3 2
Both the trans and cis isomers of [Ru(acac) {P(OMe) } ] were isolated in the form of single crystals and
Received 26 September 2009
Received in revised form 5 March 2010
Accepted 11 March 2010
1
13
31
characterized by single crystal X-ray diffraction, UV–Vis, MS, H, C and P NMR spectroscopy. The com-
ꢀ
pounds of ruthenium(II), both mononuclear complexes, crystallize in triclinic P1 space group. The metal
ion in both compounds has similar, slightly distorted octahedral coordination geometry. Both complexes
were tested as catalyst in hydrogen generation from the hydrolysis of sodium borohydride. When used
Available online 16 March 2010
alone, none of the trans- and cis-[Ru(acac)
However, the catalytic activity of cis-[Ru(acac)
significantly enhanced by the addition of two equivalents of trimethylphosphite per ruthenium into
the medium.
2
{P(OMe)
3
}
2
] complexes shows significant catalytic activity.
] in the hydrolysis of sodium borohydride is
Keywords:
Crystal structure
Ruthenium
Acetylacetonate
Trimethylphosphite
Sodium borohydride
Hydrolysis
2
{P(OMe) }
3 2
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
A recent study [1] has shown that ruthenium(III) acetylaceto-
of 2 shows usually high activity prompted us to synthesize ruthe-
nium acetylacetonato complexes containing two trimethylphosph-
ite ligands and test them as homogeneous catalysts in the
hydrolysis of sodium borohydride.
nate acts as homogeneous catalyst at room temperature in the
hydrolysis of sodium borohydride, which has been considered as
solid hydrogen storage materials [2–6]. We have also shown that
It has been reported that the alkene ligands of cis-[Ru(a-
2
cac)
2
(g
-alkene)
2
] [alkene = ethylene or cyclooctene) are easily
when two equivalents of P(OCH
reaction solution containing 450 mM NaBH
in 50 mL H O–THF solution, the hydrogen generation rate was
practically stopped (or reduced to the level of self hydrolysis) [7].
However, the catalytic hydrolysis of sodium borohydride restarts
at an unexpectedly high rate in a certain period of time (induction
time) after addition of trimethylphosphite. Accordingly, phospho-
rus ligand, known to be a poison in the hydrolysis, is involved in
the formation of a new ruthenium species containing trim-
ethylphosphite which has higher catalytic activity in comparison
3
)
3
per ruthenium is added to the
displaced by ligands (L) such as tertiary phosphines, phosphites,
pyridine or tert-butyl isocyanide, to yield trans-[Ru(acac) ] as
4
and 2 mM Ru(acac)
3
2 2
L
2
the kinetic products, which then usually isomerize to the thermo-
dynamically more stable cis-products on heating [8,9]. All of these
complexes undergo reversible one-electron oxidations, without
trans–cis interconversion; the resulting ruthenium(III) cationic
complexes can either be isolated or generated electrochemically
and detected by UV–Vis and ESR spectroscopy [10–12]. For the
preparation of ruthenium acetylacetonato complexes containing
3
two trimethylphosphite ligands, at first Ru(acac) is reduced by
with Ru(acac)
with the mole ratio of phosphorus to ruthenium. In other words,
changing the mole ratio of P(OMe) to Ru(acac) in the range of
–4 does not affect the mechanism of reaction or the structure of
active catalyst formed during hydrolysis of sodium borohydride
3
alone. The rate of hydrolysis varies very slightly
zinc amalgam in the presence of cyclooctene to form cis-[Ru(a-
2
cac)
from cis-[Ru(acac)
trans-[Ru(acac) {P(OMe)
cis counterpart. Both isomers of [Ru(acac)
isolated as single crystals and characterized by X-ray diffraction,
2 8 14 2
(g -C H ) ]. Then, the ready displacement of cyclooctene
2
3
3
2
(g
-C
}
3 2
8
H
14
)
2
]
by trimethylphosphite yields
] which isomerizes on heating to its
{P(OMe) ] could be
1
2
2
3 2
}
[
7]. The observation that the phosphorus to ruthenium molar ratio
1
13
31
UV, MS, H, C and P NMR spectroscopy [8]. Herein we also
report the results of their catalytic test in hydrogen generation
from the hydrolysis of sodium borohydride.
*
Corresponding author. Tel.: +90 312 210 3212; fax: +90 312 210 3200.
E-mail address: sozkar@metu.edu.tr (S. Özkar).
0
020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.03.023

1
714
M. Masjedi et al. / Inorganica Chimica Acta 363 (2010) 1713–1718
2
. Experimental
was carried out using CAD-4 EXPRESS. Data reduction was carried out
using XCAD4 [16]. The trans structure was solved by SIR92 [17] and
the cis structure solved by SHELXS-97 [18]. Both structures refine-
ment were done by SHELXL-97. A full matrix least-squares refine-
ment on F was done. For all non-hydrogen atoms anisotropic
displacement parameters were refined. All H atoms of the both
compounds were placed in calculated positions and refined using
2
.1. Materials
2
Ruthenium(III) acetylacetonate, Ru(acac)
3
(97%), sodium boro-
were pur-
hydride, NaBH
4
(98%) and trimethylphosphite, P(OCH
3
)
3
chased from Aldrich, and cyclooctene, tetrahydrofuran, THF were
purchased from Merck. Liquid zinc amalgam (2–3% Zn) was pre-
pared by the appropriate literature procedure [13]. Zinc dust was
a
riding model. C–H(acac) = 0.93 Å/Uiso(H) = 1.2Ueq(C) and C–
H(methyl) = 0.96 Å/Uiso(H) = 1.5Ueq(C). Crystal and experimental
data are given in Table 1, selected bond lengths and angles are gi-
ven in Table 2. The graphical representations of the structure were
made with ORTEP [19] and MERCURY [20].
2 4
treated immediately before use with dilute H SO and washed suc-
cessively with water, alcohol and diethyl ether. All glassware and
Teflon-coated magnetic stir bars were cleaned with acetone, fol-
lowed by copious rinsing with distilled water before drying at
1
50 °C in oven for a few hours.
2 3 2
2.5. Catalytic activity of trans- and cis-[Ru(acac) {P(OMe) } ] in the
hydrolysis of sodium borohydride
2.2. Equipment
2 3 2
A solution of trans- or cis-[Ru(acac) {P(OMe) } ] was prepared
by dissolving 16.5 mg (0.03 mmol) ruthenium complex in a mix-
ture of 5 mL THF and 5 mL water under vigorous stirring. In a sep-
arate glass vial, 852 mg (22.5 mmol) NaBH was dissolved in 40 mL
4
water and the solution was transferred into the reaction flask
thermostated at 25.0 ± 0.1 °C. Then, the ruthenium solution in
0 mL THF/water was transferred into the reaction flask, yielding
a solution with ruthenium concentration of 0.6 mM and sodium
All reactions involving air sensitive compounds were performed
under argon or nitrogen atmospheres. H, C and P NMR spectra
were measured on a Bruker Avance (III) 400 MHz spectrometer,
1
13
31
4
chemical shifts are given in ppm (d) relative to Me Si as internal
1
13
31
standard for H, C and H
3
PO
4
(85% in glass capillary) for
P
NMR. UV–Vis electronic absorption spectra were recorded on a
Varian Carry-100 double beam spectrometer. Positive ion fast atom
bombardment mass spectrometry (FAB-MS) data was acquired on
a VG AutoSpec (Fisons Instruments).
1
The experimental setup [14] used for performing the hydrolysis
of sodium borohydride and measuring the hydrogen gas generated
from the reaction consists of a 75 mL jacketed reaction flask con-
taining a Teflon-coated stir bar placed on a magnetic stirrer (Hei-
dolph MR-301) and thermostated to 25.0 ± 0.1 °C by circulating
water through its jacket from a constant temperature bath (RL6
LAUDA water bath). A graduated glass tube (50 cm in height and
Table 1
Crystal data and results of structure refinement for trans- and cis-
2 3 2
[Ru(acac) {P(OMe) } ].
Trans
Cis
Chemical formula
C
16
H
32
O
10
P
2
Ru
16 32 10 2
C H O P Ru
F(0 0 0)
564
1128
M
r
547.43
1.528
7.018
547.43
1.532
0.841
triclinic, P1ꢀ
Mo K 0.71073
D
x
(Mg mꢀ3)
2
5 cm in diameter) filled with water was connected to the reaction
ꢀ
1
l
(mm )
flask to measure the volume of the hydrogen gas to be evolved
from the reaction.
Crystal system, space group
Radiation (Å)
triclinic, P1ꢀ
Cu K 1.54184
a
a
Unit cell determination: number 25, 19.13–42.50
15, 9.88–11.10
of reflections used, h range
2 3 2
2.3. Synthesis of trans- and cis-[Ru(acac) {P(OMe) } ]
(°)
A (Å)
B (Å)
C (Å)
8.4916(10)
8.744(2)
16.186(3)
97.897(15)
90.936(10)
91.125(18)
1190.0(4)
10.9781(16)
12.709(2)
17.896(2)
89.074(14)
73.279(10)
83.039(13)
2373.2(6)
Trans- and cis-[Ru(acac)
by using the literature procedure [8]. Red-brown crystals of trans-
Ru(acac) {P(OMe) ] were obtained by crystallization from the
hexane–dichloromethane solution at 0 °C after 1 day, which were
separated by filtration and washed with hexane. Yellow-brown
2 3 2
{P(OMe) } ] complexes were prepared
a
(°)
b (°)
(°)
[
2
3 2
}
c
3
Cell volume (Å )
crystals of cis-[Ru(acac)
2
{P(OMe)
3
}
2
] were obtained by the crystal-
Z
2
4
lization from hexane at 0 °C after 1 week. Trans-[Ru(acac)
2
-
Crystal shape, red
Crystal size (mm)
Absorption correction (
prism, red-brown
0.40 ꢁ 0.10 ꢁ 0.10
prism, light-red
0.40 ꢁ 0.35 ꢁ 0.15
1
{
P(OMe)
3
}
2
]: H NMR (C
6 6
D , ppm): d 1.95 (s, 12H, 4Me), 3.72 (t,
w
-scan)
T
T
min = 0.422,
max = 0.493
T
T
min = 0.712,
max = 0.844
13
1
1
2
8H, 6OMe), 5.38 (s, 2H, 2CH). C { H} NMR (C
6
D
6
, ppm): d
31
1
7.01, 50.29, 99.64, 186.08. P { H} NMR (C D , ppm): d 138.05.
6 6
h-Range for data collection (°)
Dataset
2.76–74.21
2.89–26.29
ꢀ13 6 h 6 13,
0 6 k 6 15,
ꢀ22 6 k 6 22
10,063/9612
(Rint = 0.0196)
6182
+
Mass: m/z 548 (M , 15%), 424 (100), 300 (14). UV: kmax (THF, nm)
(e in dm mol cm ) 280 (31 900), 340 (15 300), 510 (4200).
ꢀ10 6 h 6 10,
ꢀ10 6 k 6 0,
ꢀ20 6 k 6 20
4640/4365
(Rint = 0.0376)
3428
3
ꢀ1
ꢀ1
1
2 3 2 6 6
cis-[Ru(acac) {P(OMe) } ]: H NMR (C D , ppm): d 1.62 (s, 6H,
Reflections collected/unique
2
Me), 1.82 (s, 6H, 2Me), 3.52 (t, 18H, 6OMe), 5.21 (s, 2H, 2CH).
1
3
1
C { H} NMR (C
6
D
6
, ppm): d 27.52, 27.86, 51.02, 99.12, 185.73,
Unique reflections [I > 2
Number of data/parameters/
r
(I)]
3
1
1
+
1
86.51. P { H} NMR (C
6
D
6
, ppm): d 154.74. Mass: m/z 548 (M ,
max (THF, nm) in
4365/270/0
9612/543/0
restraints
1
5%), 424 (100), 300 (14). UV:
k
(e
3
ꢀ1
ꢀ1
R [I > 2
r(I)]
R
1
= 0.0506,
wR = 0.1259
= 0.0730,
wR = 0.1381
1
R = 0.0482,
dm mol cm ) 240 (41 600), 280 (40 800), 530 (5100).
a
b
2
wR
= 0.0985,
wR = 0.1376
2
= 0.1173
R (all data)
R
1
R
1
2
2
2.4. Crystal structure analysis
S
1.055
1.026
(
D
/
r
)
max
0.001
1.118 and ꢀ1.616
SHELXL, 0.0021(3)
0.002
To determine the crystal structures of the compounds, trans-
and cis-[Ru(acac) {P(OMe) ], X-ray diffraction data were col-
lected at room temperature with graphite-monochromated Cu K
and Mo K radiation, respectively on an Enraf-Nonius CAD4 dif-
fractometer [15] operating in /2h scan mode. Cell refinement
qmax and qmin (e Åꢀ3
)
1.448 and ꢀ0.591
2
3
}
2
Extinction correction and
None
coefficient
a
a
a
2
2
2
2
) + (0.0788P)2 + 0.9482P].
w = 1/[
w = 1/[
r
r
(F
(F
o
o
b
) + (0.0659P)2 + 2.4157P] where P = (F + 2F 2
2
x
o c
)/3.

M. Masjedi et al. / Inorganica Chimica Acta 363 (2010) 1713–1718
1715
Table 2
concentration of 450 mM. The experiment was started by closing
the reaction flask and turning on the stirring at 1000 rpm simulta-
neously. The volume of hydrogen gas evolved was measured by
recording the displacement of water level in the graduated glass
tube for every 5 min.
Selected bond lengths and angles for compounds (Å, °).
Trans
Cis
Ru–P1
2.3175(14)
2.066
1.597
2.3089(15)
2.065
1.597
Ru–P (aver)
Ru–O (aver)
P–O (aver)
2.2061
2.084
1.595
2.2106
2.084
1.580
Ru–O (aver)
P–O (aver)
0
0
0
0
0
0
Ru –P1
Ru –P (aver)
0
0
3
2.8. Catalytic activity of Ru(acac) in the hydrolysis of sodium
borohydride in the presence of trimethylphosphite
Ru –O (aver)
Ru –O (aver)
0
0
0
0
P –O (aver)
P –O (aver)
i
P1ꢂꢂꢂP1
4.635(2)
P1ꢂꢂꢂP2
3.152(2)
Trans
Based on literature procedure [7], a stock solution of P(OCH
)
)
3
3
3
0
0
0
0
0
0
0
0
0
P1–Ru–O4
P1–Ru–O5
O4–Ru–O5
O4–Ru–(O5)
91.82(11)
88.96(11)
92.96(15)
87.04(15)
P1 –Ru –O4
90.81(11)
91.30(12)
92.94(16)
87.06(16)
(
(
100 mM) in THF was prepared by dissolving 1.18 mL P(OCH
3
P1 –Ru –O5
Molecular weight = 124.08 g/mol, d = 1.052 g/mL) to 100 ml THF.
/Ru(acac)
ratio of 2, an aliquot of the stock solution (0.6 mL) was diluted to
5 mL by adding THF and, then, 12 mg of Ru(acac) complex was
0
0
O4 –Ru –O5
i
0
ii
For the preparation of catalysts solution with P(OCH
3
)
O4 –Ru –(O5 )
3
3
Cis
P1–Ru–P2
P–Ru–O (aver)
P–Ru–O (aver)
0
0
0
3
96.01(5)
91.42
173.00
P1 –Ru –P2
90.93(6)
93.03
173.44
0
0
0
P –Ru –O (aver)
P –Ru –O (aver)
added to this solution and dissolved completely by stirring the
solution. Then, the solution was transferred into the reaction flask
0
0
0
Wide angle
O4–Ru–O5
O9–Ru–O10
O5–Ru–O9
O5–Ru–O10
O4–Ru–O10
O4–Ru–O9
containing 852 mg (22.5 mmol) NaBH
and thermostated at 25.0 ± 0.1 °C. The initial concentration of
Ru(acac) complex in the reaction solution was 0.6 mM and the
concentration of P(OCH was 1.2 mM. The reaction was started
by closing reaction flask and turning on the stirrer at 1000 rpm
simultaneously. The volume of hydrogen gas generated was re-
corded every 5 min.
4
dissolved in 45 mL water
0
0
0
0
0
0
0
0
0
0
0
0
0
90.04(14)
89.98(14)
86.54(13)
83.01(14)
85.07(14)
174.30(13)
O4 –Ru –O5
90.94(13)
90.57(13)
83.46(13)
81.24(13)
84.20(13)
172.87(13)
0
O9 –Ru –O10
3
0
O5 –Ru –O9
0
0
3 3
)
O5 –Ru –O10
O4 –Ru –O10
0
O4 –Ru –O9
i = ꢀx, ꢀy, ꢀz and ii = 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
0
Atoms names written with ( ) symbol shows the second symmetry independent
molecule in the unit cell.)
3
. Results and discussion
2 3 2
The mononuclear trans- and cis-[Ru(acac) {P(OMe) } ] com-
borohydride concentration of 450 mM. The experiment was started
by closing the reaction flask and turning on the stirring at
plexes were prepared by using the literature procedure [8]. The
trans-[Ru(acac) {P(OMe) ] complex was crystallized from hex-
ane–dichloromethane solution. The cis-[Ru(acac) {P(OMe)
2
3 2
}
1
000 rpm simultaneously. The volume of hydrogen gas evolved
2
3 2
} ]
was measured by recording the displacement of water level in
the graduated glass tube for every 5 min.
complex formed from the thermal conversion of the trans-isomer
was crystallized from hexane solution. Single crystals of the com-
pounds were used for the XRD structure determination. ORTEP draw-
ing of the title compounds with the atomic numbering scheme
displacement ellipsoids are drawn at the 30% probability level for
2 3 2
2.6. Catalytic activity of trans- and cis-[Ru(acac) {P(OMe) } ] in the
hydrolysis of sodium borohydride in the presence of
trimethylphosphite
trans- and cis-[Ru(acac)
tively. Crystal data and results of structure refinement for trans-
and cis-[Ru(acac) {P(OMe) ] are summarized in Table 1. Both
2 3 2
{P(OMe) } ] in Fig. 1(a) and (b), respec-
A stock solution of P(OCH
dissolving 1.18 mL P(OCH
d = 1.052 g/mL) to 100 ml THF. For the preparation of catalyst solu-
tions with P(OCH /Ru molar ratio of 2, an aliquot of the stock
solution (0.6 mL) was diluted to 5 mL by adding THF and, then,
6.5 mg of ruthenium complex [Ru(acac) {P(OMe) ] was added
)
3 3
(100 mM) in THF was prepared by
2
3 2
}
3
)
3
(Molecular weight = 124.08 g/mol,
ꢀ
complexes crystallize in the triclinic P1 space group. The trans-
complex contains two half molecule in asymmetric unit without
symmetry related and two formula units of C16H O P Ru in the
32 10 2
unit cell. The cis-complex contains two molecules in asymmetric
unit without symmetry related as well and four formula units of
3 3
)
1
2
3 2
}
to this solution and dissolved completely by stirring the solution.
Then, the solution was transferred into the reaction flask contain-
C
16
32
H O
10
2
P Ru in the cell.
In both complexes, the coordination geometry around the Ru(II)
ion is a slightly distorted octahedron involving four O atoms of two
acac ligands and two P atoms of trimethylphosphites. Coordination
ing 852 mg (22.5 mmol) NaBH
thermostated at 25.0 ± 0.1 °C. The initial concentrations in the
reaction solution were 0.6 mM Ru, 1.2 mM P(OCH and
50 mM NaBH . The reaction was started by closing reaction flask
4
dissolved in 45 mL water and
3 3
) ,
environment of ruthenium(II) ion of the trans-[Ru(acac)
2
{-
4
4
P(OMe) ] structure involves four O atoms of two symmetry re-
3 2
}
and turning on the stirrer at 1000 rpm simultaneously. The volume
of hydrogen gas generated was recorded every 5 min.
lated acac ligands in the basal plane with the average Ru–O
coordination bond length of 2.066 Å. The axial positions are occu-
pied by the P atoms of two symmetry related trimethylphosphites
with the Ru–P bond range of 2.3089(15)–2.3175(14) and the aver-
3
2.7. Catalytic activity of Ru(acac) in the hydrolysis of sodium
i
borohydride
age P1ꢂꢂꢂP1 (i: ꢀx, ꢀy, ꢀz) distance of 4.6264 Å for two asymmetric
units. The bond angles within the coordination sphere are close to
the ideal value of 90° as shown in (Table 2) and Fig. 2(a).
Coordination environment of ruthenium(II) ion of the cis-[Ru(a-
3
Based on literature procedure [1], a solution of Ru(acac) was
prepared by dissolving 12 mg (0.03 mmol) ruthenium complex in
a mixture of 5 mL THF and 5 mL water under vigorous stirring.
After the preparation of ruthenium complex solution, 852 mg
2 3 2
cac) {P(OMe) } ] structure can be defined with two different basal
plane each involving two O atoms from an acac ligand and one O
atom of the other acac ligand and one P atom of a trim-
ethylphosphite. Two basal planes of cis structure are almost per-
pendicular to each other and dihedral angel between them is
86.08°. The axial positions are occupied by one O atom of the acac
ligand with the chelate ring out of the basal plane and the P atom
(
22.5 mmol) NaBH
was transferred into the reaction flask thermostated at
5.0 ± 0.1 °C. Then, the ruthenium complex solution in 10 ml
4
was dissolved in 40 mL water and the solution
2
THF/water was transferred into the reaction flask, yielding a solu-
tion with Ru concentration of 0.6 mM and sodium borohydride

1
716
M. Masjedi et al. / Inorganica Chimica Acta 363 (2010) 1713–1718
Fig. 1. ORTEP drawing of the title compounds with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. (a) Trans- and (b) cis-
Ru(acac) {P(OMe)
], where (i: ꢀx, ꢀy, ꢀz).
[
2
3 2
}
Fig. 2. Basal planes of the coordination geometry for the Ru(II) ion in the trans (a) and in the cis (b) structures.
Table 3
of other trimethylphosphites as shown in Fig. 2(b). The average
Hydrogen-bonding geometry (Å, °).
0
0
bond distances are Ru–P = 2.2061, Ru –P = 2.2106 and Ru–
O = 2.084 Å (Table 2). Compared to the bond distances in the
trans-complex, the Ru–P distances of cis-structure are smaller
while the Ru–O distance are nearly the same. Ruthenium(II) coor-
dination involves bond angles ranging between 83.01(14)–
D–OꢂꢂꢂA
HꢂꢂꢂA
DꢂꢂꢂA
D–HꢂꢂꢂA
Trans
C1–H1BꢂꢂꢂO4
2.32
2.41
2.49
2.35
3.127(8)
3.191(8)
3.206(7)
3.146(9)
141
139
132
140
0
0
C1 –H1FꢂꢂꢂO4
C3–H3CꢂꢂꢂO5
0
0
C3 –H1EꢂꢂꢂO5
9
6.01(5)° and 81.24(13)–94.12(10)° for two asymmetric units of
C1–H1BꢂꢂꢂO4
C3–H3AꢂꢂꢂO9
C9–H9CꢂꢂꢂO9
2.44
2.37
2.41
2.52
3.165(8)
3.278(7)
3.166(9)
2.912(8)
133
157
135
104
cis-structure, the smallest values belonging to the O5–Ru–O10
0
0
0
8
3.01(14)° and O5 –Ru –O10 81.24(13)° and the largest values
0
0
0
belonging to the P1–Ru–P2 96.01(5)° and P1 –Ru –O5 94.12(10)°.
The average coordination wide angles are 173.43 and 173.25° for
asymmetric unit of cis-structure. The P1ꢂꢂꢂP2 distance is
C10–H10CꢂꢂꢂO8
C11–H11CꢂꢂꢂO4
Cis
2.53
2.37
2.56
2.33
2.38
3.180(9)
3.174(8)
2.959(9)
3.131(9)
2.803(10)
125
140
105
141
106
0
0
0
0
0
C1 –H1FꢂꢂꢂO4
3
.152(2) Å (Table 2).
C2 –H2FꢂꢂꢂO3
0
C3 –H3DꢂꢂꢂO9
Hydrogen bond and molecular packing geometry of the title
0
0
C10 –H10FꢂꢂꢂO8
molecules were calculated with PLATON [21] and hydrogen-bonding
geometry is summarized in Table 3. A maximum and minimum
ꢀ
3
ꢀ3
ꢀ3
residual electron density of 1.448 e Å and ꢀ0.591 e Å were ob-
respectively in the cis-structure. The highest peak 1.118 e Å
and deepest hole ꢀ1.616 e Å
0
ꢀ3
served at a distance of 0.86 Å from Ru and 0.66 Å from O6 atom,
were observed at distances of

M. Masjedi et al. / Inorganica Chimica Acta 363 (2010) 1713–1718
1717
2500
2000
1500
1000
a
b
c
d
e
f
500
0
0
2000
4000
6000
8000
10000
12000
time (s)
Fig. 3. Volume of H
plus two equivalents of P(OMe)
2
vs. time for the hydrolysis of NaBH
4
using compounds: (a) cis-[Ru(acac)
2
{P(OMe)
3
}
2
], (b) trans-[Ru(acac)
{P(OMe)
2
{P(OMe)
3 2 2 3 2
} ], (c) trans-[Ru(acac) {P(OMe) } ]
3
, (d) [Ru(acac)
3
], (e) [Ru(acac) ] plus two equivalents of P(OMe)
3
3
, (f) cis-[Ru(acac)
2
3
}
2
] plus two equivalents of P(OMe) .
3
0
1
.12 Å from P1 and 0.84 Å from Ru atom, respectively in the trans-
3
that changing the mole ratio of P(OMe) to trans- or cis-[Ru(a-
structure.
Both trans-[Ru(acac)
complexes were readily identified by MS, H, C and P NMR
spectra compared to the literature values [8]. The FAB-MS of both
cac) {P(OMe) ] does not affect the rate of hydrogen generation
2
3 2
}
2
{P(OMe)
3
}
2
] and cis-[Ru(acac)
2
{P(OMe)
}
3 2
]
as observed in the previous study [7]. Regardless of phosphine to
ruthenium ratio in the range of 1–4, one active catalyst containing
more than two phosphine ligands is formed during hydrolysis of
1
13
31
trans-[Ru(acac)
2
{P(OMe)
3
}
2
] and cis-[Ru(acac)
2
{P(OMe)
3
}
2
] com-
sodium borohydride starting with cis-[Ru(acac)
2 3 2
{P(OMe) } ] or
+
plexes show M molecular ion peak at m/z = 548 along with two in-
Ru(acac) in the presence of P(OMe) [7].
3
3
+
tense peaks at m/z = 424 and m/z = 300 for the [MꢀP(OMe)
3
] and
+
[
Mꢀ2P(OMe)
3
] fragments, respectively. UV spectrum of the trans
isomer shows one broad band centered around 510 nm in addition
to two sharp absorptions at 340 and 280 nm which are close to
4. Conclusion
2 3 2
The mononuclear trans- and cis-[Ru(acac) {P(OMe) } ] com-
those of Ru(acac)
shows one broad absorption feature centered around 530 nm and
two sharp bands at 280 and 240 nm.
3
[22]
.
In the case of cis isomer, UV spectrum
ꢀ
plexes crystallize in the triclinic P1 space group. Two complexes
are geometrical isomers and the coordination around the ruthe-
nium(II) ion is a slightly distorted octahedron involving four O
atoms of two acac ligands and two P atoms of trimethylphosph-
ites. The Ru–P distances of cis structure are smaller than that of
2 3 2 2 3 2
The trans-[Ru(acac) {P(OMe) } ] and cis-[Ru(acac) {P(OMe) } ]
complexes were tested as homogeneous catalyst in hydrogen gen-
eration from the hydrolysis of sodium borohydride. Fig. 3 shows
the plots of hydrogen volume versus time for the hydrolysis of so-
the trans structure due to the lack of p-competition in the cis iso-
dium borohydride performed using (a) cis-[Ru(acac)
b) trans-[Ru(acac) {P(OMe) ], (c) trans-[Ru(acac)
plus two equivalents of P(OMe) , d) [Ru(acac) ], (e) [Ru(acac)
plus two equivalents of P(OMe) , (f) cis-[Ru(acac) {P(OMe)
two equivalents of P(OMe) all with 0.6 mM Ru and 450 mM
NaBH at 25 ± 0.1 °C. It is seen that none of the two complexes
2
{P(OMe)
3
}
2
],
mer. Moreover, trans and cis isomers have different crystallo-
graphic asymmetric units and basal planes as well as different
hydrogen bond and molecular packing geometry. None of the
trans- and cis-[Ru(acac) {P(OMe) } ] complexes was found to be
2 3 2
efficient catalyst in the hydrolysis of sodium borohydride. The
(
2
3
}
2
2
{P(OMe)
3
}
2
]
]
3
3
3
3
2
3
}
2
] plus
3
4
significant enhancement in the catalytic activity of cis-[Ru(a-
alone is an effective catalyst in the hydrolysis of sodium borohy-
dride. Amount of hydrogen gas evolved from the hydrolysis of so-
dium borohydride in the presence of one of these trans- and cis-
2 3 2
cac) {P(OMe) } ] in the presence of trimethylphosphite indicates
the formation of an active ruthenium species which involves
more than two phosphorus ligands. The active ruthenium species
might have a facial arrangement of three ligands which may be
[
Ru(acac)
is negligible compared to the amount of hydrogen obtained by
using [Ru(acac) ] (1200 mL) in the same time period. Since the
2 3 2
{P(OMe) } ] complexes alone is less than 100 mL, which
formed directly from Ru(acac)
3
2 3 2
or cis-[Ru(acac) {P(OMe) } ], but
3
not from trans-[Ru(acac) {P(OMe) }
2
3 2
] in the presence of trim-
addition of trimethylphosphite enhances remarkably the catalytic
activity of ruthenium(III) acetylacetonate [7], the catalytic activity
of trans- and cis-[Ru(acac) {P(OMe) } ] was also tested in the
2 3 2
hydrolysis of sodium borohydride in the presence of two equiva-
lents of trimethylphosphite. Fig. 3 shows that there is a slight
improvement in the catalytic activity of trans isomer in the pres-
ence of two equivalents of trimethylphosphite, though still lower
ethylphosphite. The latter one can form only a complex with
meridional arrangement of phosphorus ligands which is not as
active as the facial complex. This species containing more than
two trimethylphosphite ligands in most likely in facial arrange-
ment appears to be the active catalyst in the hydrogen generation
of sodium borohydride. The isolation and characterization of the
catalytically active ruthenium species would enlighten the mech-
anism of the homogeneous catalysis [23]. In an ongoing research,
we have been working on the isolation, stabilization and charac-
terization of ruthenium complex containing more than two phos-
phorus ligands which is either the active catalyst or forming the
active catalyst in the hydrolysis of sodium borohydride starting
than that of Ru(acac)
catalytic activity of cis-[Ru(acac)
3
alone. Different from the trans isomer, the
{P(OMe) ] is radically enhanced
2
3 2
}
in the presence of two equivalents of trimethylphosphite. Hence,
although the cis isomer is not an efficient catalyst in the hydrolysis
of sodium borohydride, the significant enhancement in its catalytic
activity achieved by addition of two equivalents of trim-
ethylphosphite indicates the formation of an active ruthenium spe-
cies involving more than two phosphine ligands. It is noteworthy
3
with Ru(acac) plus trimethylphosphite. This seems to be the
key for establishing the mechanism of the homogeneous catalytic
hydrolysis of sodium borohydride [23].

1
718
M. Masjedi et al. / Inorganica Chimica Acta 363 (2010) 1713–1718
[
[
7] M. Masjedi, T. Demiralp, S. Ozkar, J. Mol. Catal. A: Chem. 310 (2009) 59.
8] M.A. Bennett, G. Chung, D.C.R. Hockless, H. Neumann, A.C. Willis, J. Chem. Soc.,
Dalton Trans. (1999) 3451.
Acknowledgement
Partial support of this work by Turkish Academy of Sciences and
TUBITAK (Project No. 105M357) is gratefully acknowledged. MM
thanks to the Scientific and Technological Research Council of Tur-
key (TUBITAK) for awarding a PhD fellowship.
[9] M.A. Bennett, M.J. Byrnes, A.C. Willis, Dalton Trans. (2007) 1677.
[10] M.A. Bennett, M.J. Byrnes, A.C. Willis, Organometallics 22 (2003) 1018.
[
11] M.A. Bennett, M.J. Byrnes, G. Chung, A.J. Edwards, A.C. Willis, Inorg. Chim. Acta
58 (2005) 1692.
3
[
[
12] M.A. Bennett, M.J. Byrnes, I. Kovacik, J. Organomet. Chem. 689 (2004) 4463.
13] G. Brauer, Handbook of Preparative Inorganic Chemistry, vol. 2, Academic
press, New york, 1965, p. 1806.
14] M. Zahmakiran, S. Ozkar, J. Mol. Catal. A: Chem. 258 (2006) 95.
15] Enraf-Nonius, CAD-4 EXPRESS, Enraf-Nonius, Delft, The Netherlands, 1994.
16] XCAD4: K. Harms, S. Wocadlo, XCAD4, University of Marburg, Germany, 1995.
17] SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G.
Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994) 435.
Appendix A. Supplementary material
[
[
[
[
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.03.023.
[
[
[
18] SHELX: G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
19] ORTEP-3: L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
20] MERCURY: C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R.
Taylor, M. Towler, J. van de Streek, J. Appl. Crystallogr. 39 (2006) 453.
21] PLATON: A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
References
[
[
[
1] E. Keceli, S. Ozkar, J. Mol. Catal. A: Chem. 286 (2008) 87.
2] A. Zuttel, Naturwissenschaften 91 (2004) 157.
3] S.C. Amendola, P. Onnerud, M.T. Kelly, P.J. Petillo, G.L. Sharp, M. Binder, J. Power
Sources 85 (2000) 186.
[
[
22] R. Grobelny, B. Jeowska-Trzebiatowska, W. Wojciechowski, J. Inorg. Nucl.
Chem. 28 (1966) 2715.
[
23] M. Masjedi, L.T. Yildirim, S. Ozkar, Isolation, stabilization and characterization
of ruthenium complexes containing trimethylphosphite ligands as novel and
long-lived homogeneous catalysts in hydrogen generation of sodium
borohydride, in preparation.
[
4] S.C. Ammendola, J.M. Janjua, N.C. Spencer, M.T. Kelly, P.J. Petillo, G.L. Sharp, M.
Binder, Int. J. Hydrogen Energy 25 (2000) 969.
[
[
5] J.Y. Lee, H.H. Lee, J.H. Lee, D.M. Kim, J.H. Kim, J. Electrochem. Soc. 149 (2002) 603.
6] H.I. Schlesinger, H.C. Brown, A.B. Finholt, J.R. Gilbreath, H.R. Hockstra, E.K.
Hydo, J. Am. Chem. Soc. 75 (1953) 215.