A novel ruthenium carbene dimer that is active in the metathesis of internal alkenes; The crystal structure of Ru2(=CHPh)2(CF3CO2) 2(μ-CF3CO2)2(PCy 3)2(μ-H2O)

Article abstract of DOI:10.1016/S0022-328X(99)00376-9

The reaction of Ru(=CHPh)Cl₂(PCy₃)₂ (1) with two equivalents of CF₃CO₂Ag gives Ru₂(=CHPh)₂(CF₃CO₂) ₂(μ-CF₃CO₂)₂(PCy ₃)₂(μ-H₂O) (2) in high yield. The crystal structure of 2 reveals that the ruthenium atoms are bridged by two trifluoroacetate groups and one water molecule, and that the ruthenium coordination is distorted octahedral. Complex 2 is active in the metathesis of internal alkenes.

Full text of DOI:10.1016/S0022-328X(99)00376-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 588 (1999) 205–210
A novel ruthenium carbene dimer that is active in the metathesis
of internal alkenes; the crystal structure of
Ru (ꢀCHPh) (CF CO ) (m-CF CO ) (PCy ) (m-H O)
2
2
3
2 2
3
2 2
3 2
2
a
a,
b
b
W. Buchowicz , J.C. Mol *, M. Lutz , A.L. Spek
a
Institute of Molecular Chemistry, Faculty of Chemistry, Uni6ersiteit 6an Amsterdam, Nieuwe Achtergracht 166,
NL-1018 WV Amsterdam, The Netherlands
b
Bij6oet Center for Biomolecular Research, Department of Crystal and Structural Chemistry, Utrecht Uni6ersity, Padualaan 8,
NL-3584 CH Utrecht, The Netherlands
Received 4 May 1999; received in revised form 14 June 1999
Abstract
The reaction of Ru(ꢀCHPh)Cl (PCy ) (1) with two equivalents of CF CO Ag gives Ru (ꢀCHPh) (CF CO ) -
2
3 2
3
2
2
2
3
2 2
(
m-CF CO ) (PCy ) (m-H O) (2) in high yield. The crystal structure of 2 reveals that the ruthenium atoms are bridged by two
3
2 2
3 2
2
trifluoroacetate groups and one water molecule, and that the ruthenium coordination is distorted octahedral. Complex 2 is active
in the metathesis of internal alkenes. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium; Carbene complex; Metathesis; Methyl oleate; Trans-4-decene
fore, we investigated the reaction of 1 with CF CO Ag,
which is well known to abstract halogens from transi-
1. Introduction
3
2
tion metal complexes.
The development of well-defined ruthenium carbene
complexes of the general formula Ru(ꢀCHR)Cl (PR%)
2
3 2
has opened up new prospects for the alkene metathesis
reaction [1]. The most active among them,
2
. Experimental
Ru(ꢀCHPh)Cl (PCy ) (1), is now widely used as a
2
3 2
All manipulations were performed under an atmo-
catalyst in organic syntheses, in particular for ring-clos-
ing metathesis reactions [2,3]. However, due to certain
limitations of 1, such as its moderate stability to oxygen
and high temperatures and its lack of stereoselectivity,
there have been considerable efforts to develop the next
generation of metathesis catalysts [4–7].
sphere of purified nitrogen using standard Schlenk tube
techniques. All solvents were purified by standard pro-
cedures (hexane and THF were distilled from sodium
benzophenone ketyl). Compound 1 was prepared ac-
cording to Ref. [9]. CF CO Ag (Merck) was used as
3
2
received; alkenes (Fluka) were purified by passing
through activated alumina and distillation. NMR spec-
tra were measured with a Bruker AMX-300 spectrome-
ter (at room temperature (r.t.), unless stated otherwise).
The mass spectrum was measured with a Jeol JMS
SX/SX102A mass spectrometer.
Our research focuses on the preparation of analogues
of 1 that are suitable for immobilisation on a solid
support. Since immobilisation of Ru(ꢀCHꢁCHꢀCPh )-
2
Cl (PPh ) on phosphine-functionalized polystyrenes
2
3 2
was only moderately successful [8], we assumed that
introduction of carboxylic groups around the Ru(II)
centre would be more useful for this purpose. There-
2
(
.1. Synthesis of Ru (ꢀCHPh) (CF CO ) (v-CF CO ) -
2
2
3
2 2
3
2 2
PCy ) (v-H O) (2)
3
2
2
*
Corresponding author. Tel.: +31-20-5256490; fax: +31-20-
A solution of 58.8 mg of CF CO Ag (0.266 mmol) in
5
256456.
3
2
E-mail address: jcmol@anorg.chem.uva.nl (J.C. Mol)
4 ml of THF was added to a solution of 1 (109.6 mg,
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00376-9

206
W. Buchowicz et al. / Journal of Organometallic Chemistry 588 (1999) 205–210
0
.133 mmol) in 80 ml of hexane at 0°C in 15 min.
reaction was monitored by sampling through a septum
at suitable time intervals. The catalyst in these samples
was immediately quenched with an excess of ethyl vinyl
Formation of a white precipitate and a change of
colour from purple to light-green followed. The mixture
was stirred for another 30 min at 0°C and then it was
filtered. The green filtrate was evaporated to dryness to
yield a green solid (92.4 mg, 98%). Crystalline 2 was
1
ether . The samples were analysed by GC (Carlo Erba
Top
8000 ) on a DB-5 (J&W Scientific) column. Trans/cis
ratios were measured on
(Chrompack).
a CP-Sil 88 column
obtained from hexane at −22°C (73.9 mg, 76%). M.p.
1
1
30°C (dec.). H-NMR (CD Cl ): l (ppm) 20.68 (d,
2
2
3
JPH=5.7 Hz, 2H, RuꢀCH), 11.75 (s, 2H, H O), 8.15
2
3
3
(
d, J =7.5 Hz, 4H, o-H of Ph), 7.76 (t, JHH=7.5
HH
3
. Results and discussion
3
Hz, 2H, p-H of Ph), 7.44 (t, J =7.8 Hz, 4H, m-H of
Ph), 2.03–0.84 (m, 74H, PCy and C H ). C-NMR
HH
1
3
3
6
14
2
3.1. Synthesis
(
CD Cl , −20°C): l (ppm) 327.1 (d, JPC=16 Hz,
2 2
2
RuꢀCH), 172.7 (q, J =38 Hz, CO CF ), 169.2 (q,
CF
2
3
2
Grubbs et al. [11] substituted chlorine ligands in
Ru(ꢀCHꢁCHꢀCPh )Cl (PPh ) with trifluoroacetate
J
=37 Hz, CO CF ), 158.5 (s, ipso-C of Ph), 134.7,
33.4, 133.3 (all s, Ph), 116.6 (q, JCF=283 Hz,
CF
2 3
1
1
2
2
3 2
groups by reacting a CH Cl solution of this complex
CO CF ), 35.04 (s, ipso-C of PCy ), 30.85 (d, JPC=9.8
Hz), 29.31 (bs), 26.12 (s), all PCy . P-NMR (CD Cl ):
l (ppm) 43.97 (s). F-NMR (CD Cl ): l (ppm) −
7
2
1
2
2
2
3
3
3
1
with a THF solution of CF CO Ag. However, when we
3
2
3
2
2
1
9
applied the same procedure to complex 1 complete
decomposition of the carbene ligand resulted. There-
fore, we turned our attention to a solvent in which 1
shows the lowest catalytic activity for metathesis and is
more stable, viz. hexane [12].
2
2
−
1
5.38 (s), −76.14 (s). IR (KBr): (cm ) w(CH) 2932,
854; wasym(COO) 1690, 1656; wsym(COO) 1448; 1266,
202, 1147, w(CF ) 726. MALDI-TOF MS: m/z (rel.
3
+
intensity) 1168 ([Ru (ꢀCHPh) (CF CO ) (PCy ) ] ,
9
2
2
3
2 2
+
3 2
3 2
%), 1055 ([Ru (ꢀCHPh) (CF CO )(PCy ) ] , 7%), 667
2
2
3
2
+
Table 1
(
100%), 371 (61%), 281 ([HPCy ] , 100%). Anal. Calc.
3
Crystal data and structure refinement for 2
for C H F O P Ru ·0.5C H : C, 50.3; H, 6.02%.
Found: C, 50.4; H, 6.11%.
5
8
80 12
9
2
2
6
14
a
Formula
C58H80F12O P Ru ·0.5C H
9 2 2 6 14
The solid remaining on the filter was washed with
Mr
1456.39
150(2)
Nonius KappaCCD
Temperature (K)
Diffractometer
Radiation
Crystal system
Space group
a (A
b (A)
c (A
CH Cl (5×2 ml) to produce a pale-yellow solution
2
2
and an insoluble residue (AgCl). An off-white solid was
obtained after solvent removal. It was purified by crys-
tallisation from CH Cl –hexane and identified as
Mo–Ka (u=0.71073 A
Triclinic
P1
,
)
2
2
(
1
AgClPCy (46.9 mg, 84% yield). H-NMR (CDCl ): l
ppm) 2.0–1.6 (m, 18H), 1.5–1.1 (m, 15H). C-NMR
,
,
)
12.2484(5)
16.9499(9)
17.2405(8)
97.750(2)
96.165(3)
96.146(3)
3499.1(3)
2
3
3
13
(
(
2
(
,
)
CDCl ): l (ppm) 31.60 (2d, J =17 Hz), 31.02 (s),
3
PC
3
h (°)
i (°)
k (°)
1
6.88 (d, JPC=12 Hz), 25.57 (s). P-NMR (CD Cl ): l
ppm) 43.28 (2d, JAgP=599 and 691 Hz). Anal. Calc.
2 2
1
for C H AgClP: C, 51.0; H, 7.85%. Found: C, 50.6;
V (A
,
3)
1
8
33
Z
H, 7.65%. Molecular weight determination in CH Cl2
2
z (g cm 3)
−
1.382
0.558
0.20×0.20×0.08
0.595
showed the complex to be monomeric.
v (mm−1)
3
Crystal size (mm )
2
.2. X-ray structure determination
,
−1
(
sin w/u)max (A
)
Reflections collected/unique
Parameters/restraints
S
Final R indices [I\2|(I)]
R indices (all data)
Structure solution
Structure refinement
Structure drawings and
checking
15002/11071 [Rint=0.0348]
778/61
1.035
Crystals suitable for X-ray study were grown from
n-hexane at −22°C. Crystal data and details of refine-
ment are shown in Table 1.
R =0.0505, wR =0.1262
1
2
R =0.0670, wR =0.1369
1
2
SIR-97 [13]
2
.3. Metathesis experiments
SHELXL-97 [14] (refinement on F2)
PLATON [15]
The glassware used in these experiments was dried
for several hours at 120°C and cooled to the reaction
temperature under nitrogen. In a typical experiment,
trans-4-decene (0.15 ml, 0.79 mmol) was added to a
solution of complex 2 (2.1 mg, 1.44×10 mmol) in an
appropriate solvent (0.48 ml). The resulting solution
was vigorously stirred. The progress of the metathesis
a
The positions of the hexane solvent molecules are only partially
occupied.
−
3
1
Ru(ꢀCHꢁCHꢀCPh )X (PR ) (X=Cl, CF CO , R=Ph, Cy) re-
2
2
3 2
3
2
acts with ethyl vinyl ether to yield metathesis-inactive ethoxy-substi-
tuted carbene species [9,10].

W. Buchowicz et al. / Journal of Organometallic Chemistry 588 (1999) 205–210
207
Fig. 1. Molecular plot of 2. Hydrogen atoms and solvent molecules are omitted for clarity. Only one conformation of the disordered CF group
3
at C(32) is shown.
The reaction of 1 with CF CO Ag in hexane pro-
to 1, where the carbene ligand is perpendicular to the
PꢁRuꢁP plane, the corresponding angles between car-
bene ligands and PꢁRuꢁC(carbene) planes (i.e.
3
2
ceeded within minutes and yielded a green solid after a
3
1
simple work-up. The
P-NMR spectrum of this
product showed only one peak at 43.97 ppm. The
presence of a carbene proton in the new compound
C1ꢁRu1ꢁP1/C11ꢁC12ꢁC16
and
C2ꢁRu2ꢁP2/
C21ꢁC22ꢁC26) are 68 and 55°, respectively. Accord-
ingly, the carbene protons of 2 are observed as a
1
was clearly established by H-NMR as a doublet at
2
0.68 ppm. Integration of cyclohexyl protons versus
3
doublet with JPH=5.7 Hz in the NMR spectrum.
the carbene proton showed that the reaction took a
somewhat unexpected course as only one tricyclo-
The bridging unit is similar to those of closely related
ruthenium dimers [16–18]. The water molecule is coor-
dinated in the cis position relative to both carbene
ligands. It is connected by two strong hydrogen bonds
with non-coordinated oxygen atoms of monodentate
trifluoroacetate groups (O···O distances of 2.546(5) and
2
hexylphosphine ligand remained in the product . The
presence of two different trifluoroacetate groups was
13
also concluded from the spectroscopic data ( C and
1
9
F-NMR, IR). However, it was not possible to deter-
mine the mode of coordination of these groups. There-
fore, we undertook an X-ray structure determination
of our product.
2
.510(5) A). In agreement with the solid-state structure
,
3
.2. X-ray structure
Table 2
Selected bond lengths (A
parentheses
,
) and angles (°) for 2 with estimated S.D. in
A perspective view of the molecule together with the
atom numbering scheme is shown in Fig. 1. Selected
bond lengths and bond angles are listed in Table 2.
The two carbene units are in cis position to each
other with the phosphine ligands located on the other
side of the molecule. The two RuꢀC bond lengths are
Bond lengths (A
Ru(1)ꢁC(1)
Ru(1)ꢁP(1)
Ru(1)ꢁO(1)
Ru(1)ꢁO(31)
Ru(1)ꢁO(51)
Ru(1)ꢁO(61)
,
)
1.859(5)
2.3625(13) Ru(2)ꢁP(2)
2.183(3)
2.113(3)
2.075(3)
2.228(4)
Ru(2)ꢁC(2)
1.858(5)
2.3345(14)
2.221(3)
2.099(3)
2.272(3)
2.080(3)
Ru(2)ꢁO(1)
Ru(2)ꢁO(41)
Ru(2)ꢁO(52)
Ru(2)ꢁO(62)
identical (1.859(5) and 1.858(5) A
,
) and comparable to
those of Ru(ꢀCH-p-C H Cl)Cl (PCy ) (1.839(3) A
,
) [9]
) [7]
6
4
2
3 2
Bond angles (°)
and [Ru(ꢀCHPh)Tp(PCy )(H O)][BF ] (1.878(4) A
,
3
2
4
C(1)ꢁRu(1)ꢁP(1)
C(1)ꢁRu(1)ꢁO(1)
P(1)ꢁRu(1)ꢁO(1)
C(1)ꢁRu(1)ꢁO(31)
C(1)ꢁRu(1)ꢁO(51)
89.90(16) C(2)ꢁRu(2)ꢁP(2)
98.58(18) C(2)ꢁRu(2)ꢁO(1)
171.27(10) P(2)ꢁRu(2)ꢁO(1)
86.70(19) C(2)ꢁRu(2)ꢁO(41)
94.90(19) C(2)ꢁRu(2)ꢁO(52) 172.57(18)
84.71(18)
89.84(16)
94.35(18)
175.22(10)
97.22(19)
(
Tp=tris(pyrazolyl)borate). The two RuꢁP distances
are slightly different (2.3625(13) and 2.3345(14) A) and
significantly shorter than the shorter RuꢁP bond in
Ru(ꢀCH-p-C H Cl)Cl (PCy ) (2.397(1) A). In contrast
,
,
6
4
2
3 2
C(1)ꢁRu(1)ꢁO(61) 171.39(19) C(2)ꢁRu(2)ꢁO(62)
O(31)ꢁRu(1)ꢁO(51) 175.29(13) O(41)ꢁRu(2)ꢁO(62) 176.35(14)
O(61)ꢁRu(1)ꢁO(51) 92.62(14) O(62)ꢁRu(2)ꢁO(52) 96.01(13)
Ru(1)ꢁO(1)ꢁRu(2) 122.47(16)
2
The other PCy3 ligand was isolated and characterised as a 1:1
complex with AgCl (see Experimental).

208
W. Buchowicz et al. / Journal of Organometallic Chemistry 588 (1999) 205–210
Table 3
the protons of the aqua ligand are found at 11.75 ppm
in a CD Cl solution.
a
Activity of 2 for the metathesis of internal alkenes
2
2
As for the source of this water molecule, we first
analysed the commercial CF CO Ag by weight loss on
Entry Substrate
Temperature Time (h)
(°C)
Conversion
(%)
3
2
prolonged drying as well as by determination of silver
content by direct titration. Both measurements showed
that amounts of water in this solid were one order of
magnitude too low to account for the formation of 2.
Therefore, we attribute the presence of water in 2 to the
residual water in hexane used as a solvent for its
preparation, which was determined at 40 ppm by coulo-
metric Karl–Fischer titration (20 ppm of water is re-
quired to form 2).
1
2
3
4
Trans-4-
decene
20
20
40
4
4
1
4
24
36
41
20
Methyl
b
oleate
Methyl
oleate
Methyl elai- 20
c
date
a
Reaction conditions: 3 mM solutions in CH Cl , molar ratio
2
2
In common with other adducts of Ru(II) carboxy-
2
substrate:2=550:1.
b
lates [19], the mass spectrum of 2 does not contain the
molecular peak. The peak with the highest mass (at m/z
Methyl cis-9-octadecenoate.
Methyl trans-9-octadecenoate.
c
1168 with the molecular pattern consistent with the
presence of two Ru atoms) corresponds to a fragment
derived from 2 by abstraction of the water molecule
and two (presumably monodentate) trifluoroacetate
groups. The next observed fragment is formed by ab-
straction of another trifluoroacetate group. Further
fragmentation pathways are not clear at the moment.
Compound 2 is well soluble in common organic
solvents. The molecular weight determination of 2 in
CH Cl and C H proves that the compound is also
2
2
6
6
dimeric in solution. We have not seen any decomposi-
tion of 2 in hexane; it decomposes, however, within
several hours in CH Cl at r.t. Solid samples of com-
2
2
plex 2 are handled in air and show no signs of decom-
position on a bench-top for weeks.
Fig. 2. Trans/cis composition of alkenes in the metathesis using
complex 2 as a catalyst: (a) dimethyl 9-octadecene-1,18-dioate formed
from methyl oleate; (b) 6-dodecene formed from trans-4-decene. All
runs performed at 20°C with 3 mM solutions of 2 in CH Cl and a
3.3. Catalytic acti6ity
2
2
substrate:2 molar ratio of 550:1.
We tested 2 for its metathesis activity with internal
alkenes, e.g. methyl oleate (Eq. (1)).
3
with 1 under the same conditions . Within the reaction
times shown in Table 3 the selectivity for the primary
metathesis products was very high as only traces of
other products (B0.1%) were detected by GC.
2
2
CH (CH ) CHꢀCH(CH ) CO CH X
3
2 7
2 7
2
3
CH (CH ) CHꢀCH(CH ) CH
3
2 7
2 7
3
We observed an interesting stereoselectivity of 2 for
the formation of carbonꢁcarbon double bonds. Ini-
tially, both metathesis products have predominantly the
opposite configuration of their double bond than has
the substrate. This is illustrated by analysis of the
trans/cis composition of the two compounds depicted
in Fig. 2. In the case of a cis-substrate (methyl oleate)
the product dimethyl 9-octadecene-1,18-dioate (Fig. 2,
curve a) is formed mostly as the trans-isomer. For the
metathesis of trans-4-decene equimolar amounts of cis-
and trans-6-octadecene were detected at 2% conversion
+
CH CO (CH ) CHꢀCH(CH ) CO CH
(1)
We first checked the activity of 2 in different solvents at
r.t. It appeared that 2 was the most active in CH Cl ;
3
2
2 7
2 7
2
3
2
2
conversion data in CH Cl are given in Table 3. The
activity of 2 was significantly lower in 1,2-dichloroben-
zene, THF and ethyl acetate, while almost no activity
was observed in Et O and hexane.
The activity of 2 in the metathesis of methyl elaidate
or trans-4-decene was nearly the same (Table 3, entries
2
2
2
1
and 4). This means that, similar to 1, the Ru(II)
centre in 2 is not reactive towards the ester functional-
ity. The activity of 2 increased greatly when the temper-
ature was raised to 40°C (Table 3, entry 3). The catalyst
reacted significantly faster with a cis-substrate than
with a trans-substrate (Table 3, entries 2 and 4). The
conversions obtained with 2 are somewhat lower than
(
Fig. 2, curve b). The alkenes approached their trans/cis
3
The conversions after 4 h using 1 as a catalyst under the same
reaction conditions as in Table 3 were 36 and 40% with trans-4-
decene and with methyl oleate, respectively (see Ref. [12]).

W. Buchowicz et al. / Journal of Organometallic Chemistry 588 (1999) 205–210
209
troducing a large variety of ligands around the Ru(II)
centre.
5
. Supplementary material
Crystallographic data (excluding structure factors)
for the structure in this paper have been deposited
with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC 118783. Copies
of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
Fig. 3. Trans/cis isomerization of 4-decene during its metathesis using
complex 2 as a catalyst (at 20°C, 3 mM solutions of 2 in CH Cl ,
trans-4-decene:2 molar ratio of 550:1).
2
2
thermodynamic equilibrium value on prolonged reac-
tion times due to secondary reactions (i.e. trans/cis
isomerization via metathesis). At the same time the
substrates were isomerized towards their trans/cis ther-
modynamic composition, as shown in Fig. 3 for 4-
decene.
Acknowledgements
This work was financially supported in part (M.L.
and A.L.S.) by the Council for Chemical Sciences of
the Netherlands Organization for Scientific Research
The effect of the reaction conditions (solvent, sub-
strate and temperature) on the metathesis activity of 2
closely resembles that of 1. Therefore, we assume for
the mechanism of its catalytic activity the existence of
analogous species as shown for 1, i.e. with one phos-
phine bonded to the Ru(II) centre [20]. The enhanced
(
CW-NWO). Technical support by Ron Barendregt is
greatly acknowledged.
4
stereoselectivity of 2 compared to that of 1 suggests
References
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most likely dimeric. The detailed study of the crystal
structure of 2 points to the bridging water molecule as
the most likely ligand to be cleaved during the initia-
tion step. This proposal is supported by our observa-
tion that the catalytic activity of 2 is enhanced when
the presence of traces of water is avoided. When the
glassware used for the metathesis experiments was left
on a bench-top for several hours before the experi-
ment was performed, the conversion after 4 h with
trans-4-decene reached only 18%.
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4. Conclusions
(
[
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We have selectively converted Ru(ꢀCHPh)Cl (PCy3)2
2
(
(
1) into a novel carbene complex Ru (ꢀCHPh) -
[11] R.H. Grubbs, L.K. Johnson, S.T. Nguyen, US Patent 5 312
40 (1994).
[
[
2
2
9
CF CO ) (m-CF CO ) (PCy ) (m-H O)
(2),
which
3
2 2
3
2 2
3 2
2
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is active in the metathesis of internal alkenes. The
new catalyst displays increased product stereoselectiv-
ity compared to 1. The synthetic method applied
for the preparation of 2 provides possibilities for in-
[
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1
997.
4
The corresponding trans/cis ratios using 1 as a catalyst were, for
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. A multipurpose crystallographic tool.
instance, 4.9 at 7% conversion for dimethyl 9-octadecene-1,18-dioate
and 3.8 at 3% conversion for 6-dodecene, respectively. For more data
on trans/cis composition of alkenes in the metathesis using 1 see Ref.
Utrecht University, The Netherlands, 1998.
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