Synthesis of novel ruthenium complexes of 2,2′-bis(diphenylphosphinomethyl)-1,1′-biphenyl and their catalytic hydrogenation reactions to α,β-unsaturated aldehydes

Article abstract of DOI:10.1016/S0022-328X(97)00726-2

Three ruthenium complexes containing BISBI [2,2′-bis(diphenylphosphinomethyl)-biphenyl], RuCl₂(PPh₃)(BISBI) 1, RuHCl(CO)(PPh₃)(BISBI) 2 and RuH₂(CO)(PPh₃)(BISBI) 3, had been prepared. Their compositions and structures were characterized by ³¹P{¹H}-NMR, ¹H-NMR and elemental analysis. Results of ³¹P{¹H}-NMR showed that the PPh₃ in complex 1 was completely dissociated and a dimer complex [RuCl₂(BISBI)]₂ was generated in CDCl₃ and C₆D₆ solutions. Molecular structure of 3 was also confirmed by single-crystal X-ray diffraction, the crystal belonged to a monoclinic system, P2₁/n space group, a=16.771(3) A, b=20.688(4) A, c=17.139(3) A, β=106.03(3)°, V=5715(3) A³ and Z=4. The hydrogenation results revealed that the three complexes showed much higher activities and selectivities than their analogous triphenylphosphine complexes for the hydrogenation of C=O bond in citral (3,7-dimethyl-2,6-octadienal) and cinnamaldehyde.

Full text of DOI:10.1016/S0022-328X(97)00726-2

Journal of Organometallic Chemistry 557 (1998) 207–212
Synthesis of novel ruthenium complexes of
2,2%-bis(diphenylphosphinomethyl)-1,1%-biphenyl and their catalytic
hydrogenation reactions to h,i-unsaturated aldehydes
Rui-Xiang Li a,*, Kam-Chung Tin a, Ning-Bew Wong a, Thomas C.W. Mak b, Ze-Ying Zhang b,
Xian-Jun Li c
a Department of Biology and Chemistry, City Uni6ersity of Hong Kong, Tatchee A6enue, Kowloon, Hong Kong, China
b Department of Chemistry, Chinese Uni6ersity of Hong Kong, Satin, Hong Kong, China
c Department of Chemistry, Sichuan Uni6ersity, Chengdu 610064, China
Received 23 July 1997; received in revised form 18 November 1997
Abstract
Three ruthenium complexes containing BISBI [2,2%-bis(diphenylphosphinomethyl)-biphenyl], RuCl2(PPh3)(BISBI) 1, RuH-
Cl(CO)(PPh3)(BISBI) 2 and RuH2(CO)(PPh3)(BISBI) 3, had been prepared. Their compositions and structures were characterized
by 31P{1H}-NMR, 1H-NMR and elemental analysis. Results of 31P{1H}-NMR showed that the PPh3 in complex 1 was completely
dissociated and a dimer complex [RuCl2(BISBI)]2 was generated in CDCl3 and C6D6 solutions. Molecular structure of 3 was also
˚
confirmed by single-crystal X-ray diffraction, the crystal belonged to a monoclinic system, P21/n space group, a=16.771(3) A,
3
˚
˚
˚
b=20.688(4) A, c=17.139(3) A, i=106.03(3)°, V=5715(3) A and Z=4. The hydrogenation results revealed that the three
complexes showed much higher activities and selectivities than their analogous triphenylphosphine complexes for the hydrogena-
tion of CꢀO bond in citral (3,7-dimethyl-2,6-octadienal) and cinnamaldehyde. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium complex; 2,2%-bis(diphenylphosphinomethyl)-1,1-biphenyl; Hydrogenation; Citral; Cinnamaldehyde
of the carbonyl function in the multistep synthesis to new
products [12]. Hydrogenation of the carbon–carbon
double bond is readily achieved under mild conditions
with high selectivity [13–15] whereas catalytic reduction
of aldehyde group remains a challenging problem, and
a few samples are reported for the formation of unsatu-
rated alcohols [16–20]. The heterogeneous hydrogena-
tion selectivity of CꢀO double bond in h,i-unsaturated
aldehyde molecule over Ru/Al2O3 is very poor [21,22].
This paper presents three novel ruthenium complexes
containing bidentate phosphine BISBI as well as the
study the effect of coordination environment on catalytic
activity and selectivity. The initial results show that
ruthenium complexes containing BISBI have much
higher activities and selectivities than the analogous
ruthenium complexes of triphenylphosphine for the hy-
drognation of CꢀO bond in h,i-unsaturated aldehydes.
1. Introduction
In recent decades, the synthesis and catalytic reaction
of ruthenium complexes containing phosphines have
been one of the most active research areas. A great
number of papers have been published [1–4]. Ruthenium
complexes containing one chelating bis(tertiary phos-
phine) ligand per metal atom are key species for catalytic
homogeneous hydrogenation reactions, and spectacular
success of such Ru(P–P) complexes in asymmetric hy-
drogenation of certain olefins, ketones and imines (where
P–P is a chiral phosphine) have been demonstrated
[5–11]. h,i-unsaturated aldehydes are known to be
valuable intermediates in the field of fragrance and flavor
chemistry, and very often involve the selective reduction
* Corresponding author. Fax: +852 27887406.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00726-2

208
R.-X. Li et al. / Journal of Organometallic Chemistry 557 (1998) 207–212
2. Experimental
2.1. Materials
quickly from black to green during this time. At the
end of reaction, the product was filtered, washed with
acetone and diethyl ether, and recrystallized in toluene
and n-hexane to give 0.73 g (74%) yield of 1 as green
powder. Anal: calcd. for C56H47Cl2P3Ru: C, 68.30%; H,
4.82%. Found: C, 68.42%, H, 4.91%. 31P{1H}NMR: l
(ppm) 54.8 (d), 52.9 (d), −6.7 (s), JP–P=44 Hz.
All synthetic reactions were performed with standard
Schlenk technique and under nitrogen atmosphere. Sol-
vents were generally dried over appropriate drying
agents and distilled under nitrogen prior to use.
Reagent-grade PPh3 was purchased from Aldrich, citral
(97%) and cinnamaldehyde (98%) from Riedel–deHae¨n
and were distilled before used. RuCl3 · xH2O (more
than 42% Ru) was purchased from Kunming, China.
3.2. RuHCl(CO)(PPh3)(BISBI) 2
RuHCl(CO)(PPh3)3 0.19 g (0.2 mmol) and BISBI
0.11 g (0.2 mmol) were dissolved in 10 ml toluene. The
solution was refluxed for 3 h, and the solution slowly
changed from colorless to pale yellow during refluxing
time. After the reaction completion, 30 ml n-hexane
was added to the solution with syringe and no precipi-
tate was observed. Then the solution was kept in a
refrigerator overnight to form microcrystalline white
needles. The crystals were filtered, washed with n-hex-
ane and dried under vacuum to give 0.083 g (42%) of 2
as white needles. Anal.: Calc. for C57H48ClOP3Ru: C,
69.96%; H, 4.95%; Found: C, 69.83%; H, 4.90%.
31P{1H}-NMR: l (ppm) 48.5 (dd), 32.9 (dd), and 26.8
Starting
materials
RuCl2(PPh3)3
[23],
RuH-
Cl(CO)(PPh3)3 [24], RuH2(CO)(PPh3)3 [24] and BISBI
[25] were prepared according to the reported methods.
2.2. Analytical methods
The 1H- and 31P{1H}-NMR spectra were recorded on
Bruker DPX 400 spectrometer at room temperature,
400.13 MHz for 1H and 160.97 MHz for 31P. The
chemical shifts of 31P-NMR were relative to 85%
H3PO4 as external standard, 1H relative to TMS as
internal standard, with downfield shifts as positive.
Elemental analyses were done on LECO CHN 900
element analyser. IR was recorded on Perkin Elmer
1600 spectrometer with KBr plate.
Table 1
Experimental data for the X-ray diffraction studies
Formula
C57H49OP3Ru
2.3. Catalytic hydrogenation
Formula weight
Space group
943.9
P21/n
˚
Appropriate amount of catalyst and substrate solu-
tions were introduced into a stainless steel autoclave
(100 ml) equipped with stirrer (Parr 4561 minireactor).
The autoclave was evacuated and flushed with high
purity hydrogen consecutively five times, then filled
with hydrogen to the desired pressure. After the reac-
tion solution was heated to the desired temperature, the
stirrer was started (400 rpm) and reaction time was
accounted. The reaction was quenched by immersing
the reactor in an ice bath at the end of hydrogenation.
The products were analyzed on GC (HP 5890 SERIES
II) with an FID and a capillary column (HP-FFAP, 25
m ×0.2 mm ×0.33 mm), and the GC graphs were
obtained with an HP 3396 INTEGRATOR. The com-
ponents were identified by authentic sample on GC and
GC–MS (HP 5890 GC with Series Mass Selective
Detector).
a (A)
16.771(3)
20.688(4)
17.139(3)
106.03(3)
5715(2)
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
Z
4
Dcalc (g cm−3
)
1.097
Crystal size (mm)
Radiation
Absorption coefficient
Transmition factor
F(000)
Temperature (K)
q range for data collection
Limiting indices
0.22×0.22×0.25
Mo Kh
0.391 mm−1
0.741–1.000
1952
293(2)
1.58–26.74°
05h521, −265k526,
−215l520
16 687
10 601 (Rint=0.1050)
3595
Reflections collected
Independent reflections
Observed reflection
(F\6.0|(F))
Transmission factor
Quantity minimized
Refinement method
Data/restraints/parameters
Final R indices [I\2|(I)]
R indices (all data)
Goodness of fit on F2
Extinction coefficient
Largest difference peak and
hole
0.613/1.553
Sw(Fo−Fc)2
Full-matrix least-squares on F2
6928/0/560
3. Preparation of complexes
R1=0.0690, wR2=0.1664
R1=0.1565, wR2=0.2224
0.900
0.0034(2)
0.622 and −0.628 eA
3.1. RuCl2(PPh3)(BISBI) 1
RuCl2(PPh3)3 0.96 g (1.0 mmol) and BISBI 0.54 g
(1.0 mmol) were suspended in acetone (15 ml) and were
refluxed for 1 h. The color of solid substance changed
−3
˚

R.-X. Li et al. / Journal of Organometallic Chemistry 557 (1998) 207–212
209
Table 2
peaks were presented in Tables 1 and 2 gave selected
bond distances and angles.
Selected bond lengths and angles for RuH2(CO)(PPh3)(BISBI)
˚
Bond
Lengths (A) or angles(°)
Ru–C(1)
Ru–P(1)
Ru–P(2)
Ru–P(3)
1.88 (1)
2.33 (1)
2.30 (1)
2.38 (1)
1.15 (1)
106.6(1)
96.0(1)
144.5(1)
91.7(1)
101.1(1)
105.4(1)
4. Results and discussion
4.1. Complex 1
C(1)–O
The green solid complex was quite stable in air, but
it was very unstable in solution when exposed in air,
and the color of solution quickly changed from yellow-
brown to brown and unidentified black precipitate was
formed. When the complex was dissolved in organic
solvents, such as, benzene and CHCl3 under nitrogen,
the color of solutions were brown, not green. The
carbon and hydrogen analysis of the green product was
consistent with the formula RuCl2(PPh3)(BISBI).
31P{1H}-NMR spectra in CDCl3 or C6D6 exhibited two
doublets at 54.8 and 52.9 ppm with coupling constant
C(1)–Ru–P(1)
C(1)–Ru–P(2)
P(1)–Ru–P(2)
C(1)–Ru–P(3)
P(1)–Ru–P(3)
P(2)–Ru–P(3)
(t), JP–Pcis=18 Hz, JP–Ptrans=296 Hz; 48.4 (dd), 32.8
(dd), and 27.2 (t), JP–Pcis=13 Hz, JP–Ptrans=296 Hz;
1H-NMR: l (ppm) −6.95 (dt), JH–Pcis=31 Hz, and
JH–Ptrans=108 Hz. IR: wCO=1930 cm−1 (vs), wRu–H
=
2038 cm−1 (w).
J
PP=44 Hz and a strong singlet at −6.7 ppm. The
former was a typical AB splitting pattern of dimer
ruthenium-phosphine complexes with chloride bridges
[5,26], and the latter was assigned to free PPh3. The
integration ratio of two doublets to singlet was roughly
2. Moreover, except for the two doublets and the
singlet of free PPh3 in this solution, any peaks of 1
could not be observed on the spectra.
However, besides of the two doublets of dimer and
the singlet of free PPh3, the 31P-NMR spectra appeared
two very weak wide doublets at 13.2 and 47.2 ppm and
a wide singlet at 71.2 ppm at −20.0°C. When the
temperature was further decreased to −55°C, the in-
tensities of the three new wide peaks were greatly
increased and sharpened, the 31P{1H}-NMR spectra
clearly exhibited two doublets of doublet at 13.2 and
47.2 ppm and a unsymmetric quartet at 71.2 ppm.
Their coupling constants were JPx–Pa=20 Hz and JPb–
3.3. RuH2(CO)(PPh3)(BISBI) 3
It was synthesized by the same method as in complex
2, but RuH2(CO)(PPh3)3 0.18 g (0.2 mmol) and BISBI
0.11 g (0.2 mmol) were used as the starting materials.
Pale yellow microcrystals were obtained with 0.12 g
(65%) yield. Anal.: Calc. for C57H49OP3Ru: C, 72.52%,
H, 5.23%; Found: C, 72.08%, H, 5.10%. 31P{1H}NMR:
l (ppm) 58.9 (dd), 56.1 (dd) and 55.3 (t), JP–Pcis=14
1
Hz, JP–Ptrans=232 Hz; H-NMR: l (ppm) −7.9 (m, 1
H), JHa–Pcis=17 and 18 Hz, JHa–Hb=8.1 Hz; −9.5
(ds, 1 H), JHb–Pcis=33 Hz, JHb–Ptrans=71 Hz. IR,
wCO=1939 cm−1 (vs).
3.4. X-ray crystallographic analysis of 3
Pa=306 Hz at 13.2 ppm, JPx–Pb=38 Hz and JPa–Pb
308 Hz at 47.2 ppm, and Pa–Px=20 Hz and
Pb–Px=38 Hz at 71.2 ppm. This result confirmed that
=
The crystal used for X-ray diffraction were grown
from a 2:1 mixture solvent of toluene and n-hexane.
The colorless plate crystal (0.22×0.22×0.25 mm) was
covered with a thin layer of paraffin oil as a precaution
against decomposition in air, and was mounted on a
Rigaku RAXIS IIC imaging-plate diffractometer. In-
tensity data were collected at 293 K using graphite-
J
J
complex 1 was only stable in solution at very low
temperature. However, the peak intensity of the AB
splitting pattern of dimer was still greater than the new
ABX splitting pattern (the ratio was about 2:1) at
−55°C. Furthermore, when the equil molar ratio PPh3
was dissolved in the CDCl3 solution of 1, the color of
solution changed from brown to green-yellow, the sin-
glet peak of PPh3 was enhanced, two doublets at 54.8
and 52.9 ppm were not remarkable change, but three
very weak wide peaks with ABX splitting pattern were
appeared at 13.0, 47.2 and 71.2 ppm. Attempts to
isolate the dimer complex from its oganic solution by
adding diethyl ether or n-hexane were unsuccessful,
only the original green solid complex 1 was recovered.
These results suggested that PPh3 in the complex was
almost completely dissociated in organic solvent and
˚
monochromatized Mo Kh (u=0.71073 A) radiation
from a rotating-anode generator operating at 50 kV
and 90 mA. The q range for data collection was 1.58–
26.74°, 45° oscillation frames was in the range 0–135°,
and the exposure was 10 min. per frame. A self-consis-
tent semi-empirical absorption correction was applied
by using the ABSCOR program. All calculation were
performed with Siemens SHELXTL PLUS (PC Version)
system. Structure refinement was based on F2 for all
10601 reflections. A final R-factor is 0.0690, wR 0.1664,
the largest and mean D/|, and the largest difference

210
R.-X. Li et al. / Journal of Organometallic Chemistry 557 (1998) 207–212
Fig. 1. Conversion of RuCl2(PPh3)(BISBI) to [RuCl2(BISBI)]2 in solution.
the unstable intermediate was subsequently dimerized
at room temperature, and the low temperature and
crystallization was favourable to the association of
PPh3 and dimer to form mononuclear complex 1 again.
The proposed conversion to dimer structure could be
seen in Fig. 1. This phenomenon has also been reported
in many phosphine complexes of ruthenium [26–28],
but the degree of dissociation of PPh3 was usually much
smaller at room temperature. According to our knowl-
edge, the complete dissociation of PPh3 in solution has
not yet been reported. The large chelating angle of the
ligand [29] and the big chelating ring (9-membered ring)
of 1 may be responsible for the unstable molecular
structure in solution.
in the molecule could not vary the chemical environ-
ment of the three phosphorus atoms. The two isomers
should result from the two distorted phenyl rings in the
chelating ring back-bone of BISBI. The steric structure
of 2 can be proposed in Fig. 2. Compared to the IR
spectra of RuHCl(CO)(PPh3)3 (wCO=1923 and wRu–
H=2014 cm−1), that the absorption peak of CO in 2
was shifted to higher wave number which indicated that
the back-donor electron from Ru was decreased in CO
y anti-bond orbit after triphenylphosphine was substi-
tuted with BISBI. The IR absorption peak of Ru–H
bond was also shifted to high wave number.
4.3. Complex 3
1H-NMR of this complex showed multiplets at −7.9
ppm with the coupling constants JHa–Pcis=17 and 18
Hz and JHa–Hbcis=8 Hz, and a doublet of sextet at
−9.5 ppm with coupling constants JHb–Pcis=33 Hz
and JHb–Ptrans=70 Hz, JHa–Hbcis=8 Hz. The integra-
tion ratio of Ha to Hb signals was 1:1. According to the
1H-NMR spectra and the coupling constants, it could
be reasonably suggested that the two coordinated hy-
drogen atoms were in cis-position to each other, Ha
was in cis-position to three phosphorus atoms, Hb was
in trans-position to one phosphorus atom and in cis-
position to two other phosphorus atoms.
4.2. Complex 2
The complex 2 was stable in solution as well as in
solid state. However, the yellow solution would gradu-
ally changed to dark brown color after it was exposed
1
in air for two days. H-NMR of this complex in C6D6
showed a doublet of triplets at −6.95 ppm and cou-
pling constants were JH–Pcis=31 Hz and JH–Ptrans=108
Hz. The results indicated that one phosphorus atom
was in the trans-position to the hydride and two phos-
phorus atoms were in the cis-position. This also
reflected that the two phosphorus atoms in the cis-posi-
tion to this hydride would be the two phosphorus
atoms of BISBI according to the symmetry of peaks.
However, 31P{1H}-NMR showed two sets of peaks with
the same intensity and the same splitting pattern. The
results suggested that the two sets of peaks should be
assigned to two isomers with the same phosphorus
31P{1H}-NMR spectra showed two doublets of dou-
blets at 58.8 and 56.1 ppm and a triplet at 48.7 ppm
with the coupling constants JP–Pcis=14 Hz and JP–
Ptrans=232 Hz. The result also indicated that two
phosphorus atoms were in trans-position to each other
and one in cis-position to another two phosphorus
1
atoms. According to the 31P{1H}-NMR and H-NMR
configuration in the steric structure. H- and 31P{1H}-
1
results, the molecule structure of 3 was proposed in Fig.
3. The IR of 3 showed that the absorption peak of
carbonyl shifted to lower wave number (wCO=1939
cm−1) in relative to RuH2(CO)(PPh3)3 (wCO=1942
NMR had exhibited that the hydrogen atom and the
three phosphorus atoms were on the same plane and
were arranged in meridian form with two phosphorus
atoms of BISBI. The position exchange of CO and Cl
Fig. 2. Proposed structure of 2.
Fig. 3. Proposed structure of 3.

R.-X. Li et al. / Journal of Organometallic Chemistry 557 (1998) 207–212
211
Fig. 4. An ORTEP drawing of the complex 3.
cm−1). However, the absorption of carbonyl group was
too strong, so that the Ru–H absorption was over-
lapped with the carbonyl peak and could be not ob-
served in IR spectra.
chelating ring (nine-membered chelating ring) enhanced
the dissociation of PPh3 in solution which had been
verified by 31P{1H}-NMR for 1. The generated dimer
could be easily transfered into active catalytic species
when it further reacted with hydrogen under ambient
conditions. Besides of the large chelating contributing
to improve the catalytic activities and selectivities, the
electronic factor seemed to play a important role. When
the coordination environment of ruthenium was further
modified with carbonyl and hydride, such as 2 and 3, 2
showed higher catalytic activity than 1. However, the
catalytic activity of 3 was sharply decreased. The car-
bonyl absorption of 3 in IR spectra was shifted to
higher wave number had indicated that back-donored
electron from ruthenium decreased when the chloride in
2 was substituted by the hydride. This means that the
electronic density of ruthenium in 3 was lower than in
2. It might be reasonable to suggest that the lower
electronic density of ruthenium in 3 was not favourable
to the catalytic reaction.
The results of single-crystal X-ray diffraction were
listed in Tables 1 and 2 and Fig. 4. It was consistent
with the structural analysis by NMR spectra. The two
phosphorus atoms of BISBI were in trans position. If
two hydrogen atoms were added in the structure, the
configuration of the complex was a distorted octahe-
dron. The bond angle between two P–Ru bonds coor-
dinated by BISBI was 144.6°, which was much less than
180° because of the distort tension of chelating ring and
pressure raised by the large volume of the
triphenylphosphine group.
4.4. Hydrogenation of citral and cinnamaldehyde
catalyzed by Ru complexes 1, 2 and 3
Hydrogenation results were shown in Table 3. The
substitution of PPh3 by BISBI had improved both the
catalytic activities and selectivities of ruthenium com-
plexes 1, 2 and 3 for the hydrogenation of CꢀO bond in
h,i-unsaturated aldehydes to form allylic alcohols. The
catalytic activities of 1 and 2 were much higher than the
analogous triphenylphosphine complexes. It was rea-
sonable to suggest that the large chelating angle and
Acknowledgements
This work was supported by City University of Hong
Kong, Chinese University of Hong Kong and Sichuan
University, China.

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R.-X. Li et al. / Journal of Organometallic Chemistry 557 (1998) 207–212
Table 3
Hydrogenation of h,i-unsaturated aldehydes
Catalysts
Citrala
Cinnamaldehydeb
Conversion (%)
Conversion (%)
Selectivityc (%)
Selectivityc (%)
RuCl2(PPh3)3
28
41
4.1
62
0.0
3.3
23
80
8.8
60
—
40
25
48
9.9
85
4.2
11
73
86
76
73
62
88
RuCl2(PPh3)(BISBI)
RuHCl(CO)(PPh3)3
RuHCl(CO)(PPh3)(BISBI)
RuH2(CO)(PPh3)3
RuH2(CO)(PPh3)(BISBI)
Reaction conditions: substrate 2.0 ml, temp.: 50°C.
a Benzene: 8.0 ml, time: 2 h, H2 pressure: 20 kg cm−2, catalyst conc. 2.0×10−3 M.
b Cyclohexane: 8.0 ml, time: 1 h, H2 pressure: 30 kg cm−2, catalyst conc. 1.0×10−3 M.
c Selectivity in allylic alcohol.
241.
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