Indian Journal of Chemistry
Vol. 49A, February 2010, pp. 167-170
Notes
Synthesis and structural characterization of a
new ruthenium hydride ethylene complex
C M Nagaraja, Munirathinam Nethaji & Balaji R Jagirdar*
Department of Inorganic & Physical Chemistry
Indian Institute of Science, Bangalore 560 012, India
Email: jagirdar@ipc.iisc.ernet.in
Received 20 October 2009; accepted 12 January 2010
A ruthenium(II) ethylene complex, trans-[Ru(H)(C2H4)(dppm)2][BF4], bearing two 1,1-bis(diphenylphosphino) methane
(dppm) ligands has been synthesized and structurally
characterized using X-ray crystallography. In the molecular
structure, the RuII center shows a distorted octahedral coordination
geometry formed by four P atoms of the two chelating dppm
ligands, a hydride, and an ethylene ligands. The four dppm
P atoms are almost co-planar with the hydride and the ethylene
ligands perpendicular to this plane. The C-C bond distance of the
bound ethylene is 1.375(6) Å, which is elongated by 0.042 Å as
compared to free ethylene (1.333(2) Å). The packing diagram of
the complex shows two voids or channels, which are occupied by
BF4– counterion and water molecules.
Keywords: Coordination chemistry, Ruthenium, Dihydrogen
complexes, Hydrides
IPC Code: Int. Cl.9 C007F15/00
Ever since the discovery of the first transition
metal dihydrogen complex by Kubas and co-workers
in 19841, a large number of such complexes have
been synthesized and well characterized2. The coordinated dihydrogen ligand can be substituted in
a facile manner by Lewis bases and this property
can be exploited in catalysis. Transition metal
hydride-olefin complexes are important since the
insertion of olefin into the metal-hydride bond is
a significant step in several catalytic processes
such as olefin hydrogenation and isomerization
reactions 3 . The bonding in a transition metalethylene complex can be elaborated using the
Dewar-Chatt-Duncanson (DCD) model4. It involves
σ-donation from the ethylene ligand to an empty
d(σ) orbital on the metal which is reinforced via
metal to ligand π-back donation from the occupied d(σ) orbital of the metal into the empty π* orbital
of ethylene. When the π-back donation is considerably great, the C-C bond lengthens enormously in
which case the metal ethylene system approaches the
metallocyclopropane extreme5. Herein, we report the
synthesis and structural characterization of the first
example of a ruthenium(II) hydride-ethylene complex
bearing 1,1-bis(diphenylphosphino)methane (dppm)
ligand, trans-[Ru(H)(C2H4)(dppm)2][BF4] (1), from
trans-[Ru(H)(η2-H2) (dppm)2][BF4]6 via substitution
of the coordinated dihydrogen ligand with
ethylene.
Experimental
All the reactions were carried out under an atmosphere of dry and oxygen free N2 at room temperature using standard Schlenk and inert atmosphere
techniques unless otherwise specified7. The 1H and
31
P{1H} NMR spectral data were obtained using an
Avance Bruker 400 MHz instrument. The 31P NMR
spectra were recorded relative to 85% H3PO4 (aqueous solution) as an external standard. Ethylene gas
(99.98%) was obtained from Bhoruka Gases Limited,
Bangalore, India. Elemental analysis was carried
out at the RSIC, CDRI, Lucknow, India.
1,1-Bis(diphenylphosphino)methane
(dppm)8,
9
cis-[RuCl2(dppm)2] ,
cis/trans-[Ru(H)2(dppm)2]10,
2
trans-[Ru(H)(η -H2)(dppm)2][BF4]5 were prepared by
literature methods.
Trans-[Ru(H)(η2-H2)(dppm)2][BF4] (0.200 g,
0.18 mmol) was dissolved in 5 mL of CH2Cl2 under
H2 atmosphere. The mixture was subjected to three
cycles of freeze-pump-thaw degassing using a high
vacuum line. Ethylene gas (1 atm) was condensed into
the Schlenk tube at liquid N2 temperature. The
Schlenk tube was sealed and shaken overnight. During this period, the greenish-yellow solution paled
down. The solution was filtered through a Celite pad
on a filter frit. Addition of diethyl ether (5 mL) led to
the
precipitation
of
colorless
power
of
compound (1) which was isolated and dried in
vacuo. Yield; 85% (0.170 g). Anal.: Calc. for
C52H49P4BF4Ru·CH2Cl2: C, 59.45; H, 4.80. Found: C,
59.35; H, 5.48. 1H NMR spectral data of (1) (298 K,
CD2Cl2,): δ –3.75 (qnt, 1H, Ru−H, J(H, Pcis) = 20 Hz),
2.74 (s, 4H, C2H4), 4.59 (m, 2H, CH2), 5.14 (m, 2H,
CH2), 6.80-7.67 (m, 40H, P(C6H5)2). 31P{1H} NMR
spectral data (CD2Cl2): δ 1.3 (s, 4P, PCH2P).
168
INDIAN J CHEM, SEC A, FEBRUARY 2010
Single crystals of trans-[Ru(H)(C2H4)(dppm)2]
[BF4] (1) suitable for X-ray diffraction study were
obtained by layering diethyl ether over a
dichloromethane solution of the complex. Good
quality crystal was carefully selected after
examination under an optical microscope and coated
with paraffin oil and then mounted on the Goniometer
head. The unit cell parameters and intensity data were
collected at room temperature using a Bruker SMART
APEX CCD diffractometer equipped with a fine focus
MoKα X-ray source (50 kV, 40 mA). The data
acquisition was done using SMART software and
SAINT software was used for data reduction.11 The
empirical absorption corrections were made using the
SADABS program.12 The structure was solved and
refined using the SHELXL-97 program.13 The
ruthenium atom was located from the Patterson map,
the hydride, ethylene H atoms and all the non H atoms
were located from the difference Fourier map and
refined anisotropically. All other H atoms were fixed
in idealized positions and refined in a riding model.
The selected crystallographic data are given in
Table 1.
Results and discussion
Introduction of ethylene gas (1 atm) to a CH2Cl2
solution of trans-[Ru(H)(η2-H2)(dppm)2][BF4] under
H2 atmosphere resulted in the formation of an
ethylene complex (1) via the substitution of η2-H2
Table 1—Selected crystallographic data and structure
refinement for trans-[Ru(H)(C2H4)(dppm)2][BF4] (1)
Formula
FW
Crystal system
Space group
a (Ǻ)
b (Ǻ)
c (Ǻ)
α (º)
β (º)
γ (º)
V (Ǻ3)
Z
Dcalcd (g/cm3)
T (K)
λ (Ǻ)
µ (mm-1)
Ra
Rwa
C52H49BF4O2P4Ru
1017.67
Monoclinic
C2/c
30.016(12)
21.713(9)
19.674(8)
90.00
125.725(6)
90.00
10409(7)
8
1.3
293(2)
0.71073
0.475
0.054
0.078
R = Σ(|Fo|-|Fc|)/Σ|Fo|, Rw = [Σw(|Fo|-|Fc|)2/Σw|Fo|2]1/2 (based on
reflections with I >2σ(I)
with ethylene molecule (Scheme 1). This is evident by
the disappearance of the peak due to the dihydrogen
ligand and the appearance of a new hydride peak in
the 1H NMR spectrum of the sample. The hydride
trans to η2-C2H4 shows a quintet at δ –3.75 ppm
(J(H,Pcis) = 20 Hz), and the bound ethylene shows a
singlet at δ 2.74 for all the four hydrogen atoms
rendered equivalent at room temperature due to the
rapid rotation of the ethylene molecule about the
Ru-C2H4 bond at a rate greater than the NMR time
scale. The 31P{1H} NMR spectrum shows a singlet at
δ 1.3 ppm for all the four dppm P atoms indicating
their co-planarity.
The molecular structure consists of discrete
trans-[Ru(H)(C2H4)(dppm)2]+ units and a [BF4]counterion, and two water molecules. An ORTEP
diagram is shown in Fig. 1 and the selected bond
lengths and angles are listed in Table 2. The complex
crystallized in the monoclinic space group C2/c with
the BF4– counterion sitting on the crystallographic
axes. The geometry around the ruthenium is nearly a
distorted octahedron with the four dppm P atoms
almost coplanar with the hydride and the ethylene
ligands in the fifth and sixth coordination sites
perpendicular to this plane. The C-C bond distance in
the bound ethylene ligand is 1.375(6) Å, which is
elongated by 0.042 Å compared to that in free
ethylene (1.333(2) Å).14 Similar lengthening of the
ethylene C-C bond (1.384(5) Å) upon coordination to
ruthenium center has been reported in the literature15.
The dppm bite angles P1-Ru1-P2 and P3-Ru1-P4 are
respectively, 70.79(5)º and 71.40(5)º. Interestingly,
the crystal packing down the c axis shows channels
which are occupied by the BF4– counterions and water
molecules (Fig. 2).
Ph2 H
P
Ru
P
Ph2
H
+
Ph2 H
P
Ru
P
Ph2 P
Ph2
Ph2
P
P
Ph2
1 equiv HBF4 . Et2O
CH2Cl2, H2
H
Ph2
H
Ph2
P
P
Ph2 P
Ru
H
H
CH2Cl2
P Ph2
Ph2
H
H 2C
a
Scheme 1
P
Ph2
C2H4 (1 atm)
P
Ph2 P
BF4
P
Ru
P
CH2
Ph2
Ph2
BF4
169
NOTES
Table 2—Selected bond lengths (Å) and angles (˚) of
complex (1)
Fig.
1—ORTEP
view
of
the
cation,
trans-[Ru(H)(C2H4)(dppm)2]+ (1) at the 50% probability level
showing atom numbering for selected atoms. All the
H atoms have been omitted for clarity.
Bond lengths (Å)
Ru(1)-H(1)
Ru(1)-C(52)
Ru(1)-P(3)
Ru(1)-P(4)
Ru(1)-C(51)
C(51)-C(52)
Ru(1)-P(2)
Ru(1)-P(1)
1.50(5)
2.289(4)
2.3197(13)
2.3364(12)
2.270(4)
1.375(6)
2.3362(13)
2.3420(13)
Bond angles (˚)
C(51)-Ru(1)-C(52)
P(3)-Ru(1) P(4)
C(51)-Ru(1)-P(3)
C(51)-Ru(1)-P(2)
P(3)-Ru(1)-P(2)
C(52)-Ru(1)-P(4)
C(51)-Ru(1)-P(1)
P(4)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
C(51)-Ru(1)-C(52)
C(52)-Ru(1)-P(3)
C(52)-Ru(1)-P(2)
C(51)-Ru(1)-P(4)
P(2)-Ru(1)-P(4)
C(52)-Ru(1)-P(1)
C(51)-Ru(1)-H(1)
35.11(16)
71.40(5)
87.38(13)
120.17(12)
105.65(5)
115.83(12)
96.22(13)
111.12(5)
70.79(5)
35.11(16)
95.56(13)
85.09(12)
80.84(12)
158.92(4)
86.29(13)
162.9(17)
of the η2-H2 ligand. The packing diagram as viewed
down the c axis reveals the presence of interesting
channels that are occupied by the BF4– counterions
and water molecules.
Supplementary data
CCDC 762869 contains the crystallographic data
for the complex reported herein. These data may be
obtained free of change from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK, (Fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk) via www.ccdc.cam.ac.uk/
datarequest.cif.
Fig. 2—The packing plot of complex (1) along the c axis, the
channels are occupied by two BF4– counterions and water
molecules.
The present study shows that substitution of
the bound η2-H2 ligand in trans-[Ru(H)(η2-H2)
(dppm)2][BF4] with ethylene results in an ethylene
complex trans-[Ru(H)(C2H4)(dppm)2][BF4]. The
X-ray crystal structure of the ethylene complex gives
evidence of the binding of the ethylene ligand in place
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