Mixed isobutylphobane/n-heterocyclic carbene ruthenium- Indenylidene complexes: Synthesis and catalytic evaluation in olefin metathesis reactions

Article abstract of DOI:10.1002/adsc.201000207

Two new second generation ruthenium(II) dichloride-indenylidene complexes [RuCl₂(9- isobutylphosphabicyclo [3.3.1]nonane) (NHC)(3-phen- yl-1-indenylidene)], where NHC=1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene (SIMes) or its unsaturated imidazol-2-ylidene analogue (IMes), were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl₂(isobutylphobane) ₂(3-phenyl-1-indenylidene)]with a two-fold excess of the corresponding imidazol- (in)ium-2-carboxylate zwitterions. Both products were characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, and the molecular structure of [RuCl₂(isobutylphobane) (SIMes)(3-phenyl-1-indenylidene)]was determined by X-ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra- and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand. The catalytic activity of both compounds was assessed in olefin metathesis using benchmark ring-opening metathesis polymerization, ring-closing metathesis (RCM), and cross-metathesis reactions, and compared with those of related first and second generation ruthenium-benzylidene and indenylidene catalyst precursors. Kinetic studies confirmed the high thermal stability of the mixed isobutylphobane/ N-heterocyclic carbene complexes, which suffered from a slow initiation efficiency compared to other catalytic systems based on the tricyclohexylphosphane ligand. However, the remarkable robustness of [RuCl₂(isobutylphobane) (SIMes)(3-phenyl-1- indenylidene)]was beneficial for performing the RCM of diethyl 2,2-bis(2-methylallyl)malonate. Monitoring the formation of the ruthenium-methylidene active species [RuCl ₂(isobutylphobane)- (SIMes) (=CH₂)]derived from this precursor further demonstrated its ability to sustain long reaction times and high temperatures required to carry out the RCM of tetrasubstituted olefins.

Full text of DOI:10.1002/adsc.201000207

FULL PAPERS
DOI: 10.1002/adsc.201000207
Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-
Indenylidene Complexes: Synthesis and Catalytic Evaluation in
Olefin Metathesis Reactions
a
b
a
Xavier Sauvage, Guillermo Zaragoza, Albert Demonceau,
a,
and Lionel Delaude *
Laboratory of Macromolecular Chemistry and Organic Catalysis, Institut de Chimie (B6a), Universitꢀ de Liꢁge,
Sart-Tilman par 4000 Liꢁge, Belgium
a
Fax : (+32)-4-366-3497; e-mail: l.delaude@ulg.ac.be
Unidade de Difracciꢂn de Raios X, Edificio CACTUS, Universidade de Santiago de Compostela, Campus Sur, 15782
Santiago de Compostela, Spain
b
Received: March 16, 2010; Published online: August 16, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000207.
Abstract: Two new second generation ruthenium(II) benchmark ring-opening metathesis polymerization,
dichloride-indenylidene
complexes
[RuCl (9- ring-closing metathesis (RCM), and cross-metathesis
2
isobutylphosphabicyclo[3.3.1]nonane)
A
H
U
G
R
N
U
G
A
T
N
T
E
N
N
(NHC)(3-phen-
reactions, and compared with those of related first
ACHTUNGTRENNUNGy l-1-indenylidene)], where NHC=1,3-bis(2,4,6-tri- and second generation ruthenium-benzylidene and
methylphenyl)imidazolin-2-ylidene (SIMes) or its un- indenylidene catalyst precursors. Kinetic studies con-
saturated imidazol-2-ylidene analogue (IMes), were firmed the high thermal stability of the mixed isobu-
isolated in high yields upon heating a tetrahydrofur- tylphobane/N-heterocyclic carbene complexes, which
an (THF) solution of the diphosphane complex suffered from a slow initiation efficiency compared
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[RuCl (isobutylphobane) (3-phenyl-1-indenylidene)]
to other catalytic systems based on the tricyclohexyl-
with a two-fold excess of the corresponding imidazol- phosphane ligand. However, the remarkable robust-
(in)ium-2-carboxylate zwitterions. Both products ness of [RuCl (isobutylphobane)(SIMes)(3-phenyl-1-
2
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
2
1
13
31
were characterized by H, C, and P NMR spec- indenylidene)] was beneficial for performing the
troscopy, and the molecular structure of RCM of diethyl 2,2-bis(2-methylallyl)malonate.
[
RuCl (isobutylphobane)
A
H
U
G
R
N
U
G
Monitoring the formation of the ruthenium-methyli-
2
2
sis. A close inspection of the packing structure re-
ACHTUNGENTRNUNG( SIMes) ACHTNUGTRENNU(GN =CH )] derived from this precursor further
2
vealed the presence of different types of intra- and demonstrated its ability to sustain long reaction
intermolecular interactions that enhanced the global times and high temperatures required to carry out
stability of the crystals, while low temperature NMR the RCM of tetrasubstituted olefins.
experiments showed the existence of two distinct ro-
tational isomers due to the unsymmetrical nature of Keywords: ethenolysis; homogeneous catalysis; N-
the phobane ligand. The catalytic activity of both heterocyclic carbenes; phosphane ligands; ring-clos-
compounds was assessed in olefin metathesis using ing metathesis; ruthenium
[
3]
Introduction
clohexylphosphane) (Scheme 1). Countless structur-
al alterations have been made to this archetypal com-
[6]
[
4,5]
Thanks to the development of well-defined rutheni- pound in order to tailor its activity,
stability,
[9]
[
7]
[8]
um-alkylidene catalysts initiated by Grubbs in the late water-solubility, recoverability, or latency toward
[1]
1
990s, olefin metathesis has become a key method- specific catalytic processes, sometimes in an asymmet-
[
2]
[10]
ology in organic synthesis and in polymer chemistry.
ric fashion. Replacement of one phosphane ligand
Most catalytic systems investigated so far derive from with an N-heterocyclic carbene (NHC) was quickly
the Grubbs first generation ruthenium-benzylidene recognized to increase the catalyst stability and effi-
complex [RuCl
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(=CHPh)
A
H
U
G
R
N
N
(PCy ) ] (1) (PCy is tricy- ciency, thereby affording a new subset of ruthenium
2
3
2
3
1934
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
[
21]
lation of alkenes (with Pd), the arylation of hetero-
[
22]
cycles (with Rh),
or various atom transfer radical
[
23]
reactions (with Ru), to name just a few.
In the field of olefin metathesis, the first report on
the use of ruthenium-alkylidene complexes bearing
phobane ligands originated from the group of Forman
[
24]
in 2004. Thus, complexes 5 and 6 were synthesized
by ligand exchange between [RuCl (=CHPh)(PCy ) ]
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
2
3 2
(
1) or [RuCl (=CHÀCH=CMe )
ACHTUNGTRNNGE(U PPh ) ] and 9-cyclo-
2
2 3 2
hexyl-9-phosphabicyclo ACHUTNGRENNUG[ 3.3.1]nonane (Scheme 2). The
catalytic activity of benzylidene precatalyst 5 was
evaluated in various types of metathetical reactions,
[
24,25]
including ring-closing metathesis (RCM), [24,25c] ross-
[
24,26]
metathesis (CM),
self-metathesis (SM),
and
[
24]
ethenolysis. In many cases, the first generation pho-
bane complex 5 outperformed its tricyclohexylphos-
phane-based analogue (1) and behaved more like the
second generation Grubbs catalyst (2). Indeed, DFT
calculations showed that the substrate-induced de-
composition of propagating species decreased in the
order 1>5>2, in good agreement with experimental
Scheme 1. First and second generation ruthenium-benzyli-
dene and indenylidene complexes bearing tricyclohexylphos-
phane ligands.
[
27]
metathesis initiators, exemplified by the second gener- observations. Further enhancement of the catalytic
ation Grubbs catalyst, [RuCl (=CHPh)(PCy )(SIMes)] efficiency of 5 could be achieved by the addition of
A
H
U
G
R
N
U
G
A
T
N
T
E
N
N
ACHTUNGTRENNUNG
3
2
[
28]
(
2
2) [SIMes is 1,3-bis(2,4,6-trimethylphenyl)imidazolin- diverse co-catalysts, such as phenols,
tin and iron
[11]
[29]
[30]
-ylidene]. Numerous variations on the alkylidene halogenides, or ionic liquids. A stoichiometric re-
[
12]
fragment have also been performed. Among other action of 5 with 2-isopropoxystyrene afforded the che-
things, they led to the emergence of first and second lated alkoxybenzylidene compound 7, which was
generation ruthenium-indenylidene complexes, such found to be highly active at promoting the RCM of
[
31]
as 3 and 4, whose straightforward synthesis makes N,N-diallyltosylamide.
In the indenylidene series,
them an attractive alternative to benzylidene-based the first generation di(cyclohexylphobane) complex 8
[13]
precatalysts.
was synthesized and characterized by Forman et al. in
Although the dissociation of a phosphane ligand is 2006, starting from [RuCl (3-phenyl-1-indenylidene)-
2
supposed to be a crucial step in the mechanism of
[
14]
olefin metathesis initiated by complexes 1–4, only a
few studies have aimed at modifying this key compo-
[
15]
nent. Early reports from Grubbs and co-workers
[
16]
and related work from our group showed that both
strongly basic and bulky phosphanes were required to
achieve high catalytic efficiencies. Hence, tricyclohex-
ylphosphane has been the ligand of choice for most of
the ruthenium catalyst precursors investigated so far.
Recently, however, another class of phosphane li-
gands displaying similar steric and electronic proper-
ties has generated much interest as a viable alterna-
tive to PCy in olefin metathesis catalysts. The first
3
representatives of this family known collectively as 9-
phosphabicyclononanes or phobanes date back to
[17]
1966.
They are prepared on a large scale via the
radical addition of 1,5-cyclooctadiene to PH or pri-
3
mary alkylphosphanes and are usually obtained as a
mixture of [3.3.1]- and [4.2.1]-bridged isomers in vari-
[
17,18]
able proportions.
These relatively inexpensive li-
gands are currently used industrially in the cobalt-cat-
alyzed hydroformylation process developed by
[19]
Shell.
They have also found applications in other
transition metal-catalyzed reactions, such as the oligo- Scheme 2. First generation ruthenium-alkylidene complexes
[
20]
merization of ethylene (with Ni), the hydrocarbony- bearing cyclohexylphobane ligands.
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1935

Xavier Sauvage et al.
FULL PAPERS
sors for the synthesis of second generation ruthenium
[
33]
metathesis catalysts.
Because these stable zwitter-
ionic adducts can be stored and handled with no par-
ticular precautions, they are particulary attractive sur-
rogates to air and moisture-sensitive free carbenes. In
order to further illustrate their potentials in organo-
[
34]
metallic chemistry,
we used them as NHC ligand
precursors for this work. Thus, we have performed a
phosphane/NHC ligand exchange starting from [Ru-
Cl (isobutylphobane) (3-phenyl-1-indenylidene)] (Ne-
2
2
olystꢄ M11) (9) and a two-fold excess of either
SIMes·CO or IMes·CO [IMes is 1,3-bis(2,4,6-trime-
2
2
thylphenyl)imidazol-2-ylidene] (Scheme 3). The reac-
tions were carried out in refluxing THF using a
round-bottom flask fitted with a reflux condenser
topped with a gas bubbler and flushed by a slow
stream of argon. We reasoned that this experimental
set-up would help displace carbon dioxide and speed
[
35]
up the decarboxylation process. Attempts to moni-
3
1
Scheme 3. Synthesis of second generation ruthenium-indeny- tor the phosphane exchange by P NMR analysis of
lidene catalysts bearing isobutylphobane ligands.
samples removed from the reaction media at various
time intervals remained largely unsuccessful. Indeed,
both the substrate and the products gave very broad
ACHTUNGTRENNUNG( PPh ) ] and an isomeric mixture of cyclohexylpho- resonances at room temperature (vide infra), and only
3 2
[
32]
banes.
It should be pointed out that the related the signal assigned to free isobutylphobane was ob-
3
1
compound 9 bearing two isobutylphobane ligands served at À39.1 ppm in P NMR spectra acquired
(
see Scheme 3) is commercially available but, to the from a few scans in THF spiked with C D . Yet, the
6
6
best of our knowledge, its preparation has not been remarkable stability of the first and second generation
described in the open literature. Catalyst precursors 8 ruthenium-phobane complexes under investigation al-
and (to a lesser extent) 9, were found to be more effi- lowed us to use TLC analysis to monitor the reaction
cient promoters for the SM of terminal alkenes or the course. With both SIMes·CO and IMes·CO , a quan-
2
2
RCM of a wide variety of a,w-dienes and enynes than titative conversion was achieved within 4 h. The prod-
[
25]
the Grubbs first generation catalyst (1). In addition, ucts were then separated and purified by flash chro-
ruthenium-indenylidene complex 8 was also success- matography on silica gel. Mixed isobutylphobane/
fully applied to SM and ethenolysis reactions of NHC complexes 10 and 11 bearing, respectively, the
methyl oleate under low catalyst loading condi- saturated ligand SIMes and its unsaturated counter-
[32]
tions.
part IMes, were isolated as red powders in high yields
Surprisingly, the synthesis and catalytic evaluation (ca. 90%) and purities. These results were deemed
of second generation ruthenium-alkylidene catalyst very satisfactory. Therefore, we did not investigate the
precursors bearing phobane ligands has not been direct reactions between complex 9 and a stoichio-
documented yet. Thus, in this contribution, we report metric amount of the IMes or SIMes free carbenes,
on the preparation and characterization of two new although we are confident that they would lead to
mixed isobutylphobane/NHC Ru-indenylidene com- similar outcomes.
plexes and we assess their catalytic activity in various
Compounds 10 and 11 proved to be particularly
types of olefin metathesis transformations using stable in the solid state, as well as dissolved in aprotic
benchmark reactions. In order to shed light on their solvents. These observations are in good agreement
remarkable stability, we have also monitored their de- with previous work by Nolan et al., who found that
composition rate in the presence of ethylene.
indenylidene complexes 3 and 4 bearing PCy ligands
3
did not show any sign of decomposition in toluene-d
8
[
36]
13
1
at 808C for at least 10 days.
The C{ H} NMR
(IMes)(3-
Results and Discussion
spectrum of [RuCl (isobutylphobane)ACTHUNGTRENNNUG
2
phenyl-1-indenylidene)] (11) featured a doublet at
186.9 ppm for the C-2 carbon of the NHC ligand
bound to the metal center. The corresponding signal
in complex 10 was found at 217.9 ppm. Hence, satura-
Synthesis and Characterization of Complexes 10 and
11
Recently, we have shown that imidazol(in)ium-2-car- tion of the imidazole ring caused a 31 ppm shift of the
boxylates could act as convenient NHC ligand precur- carbene carbon to lower field, consistent with a
1936
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
higher anisotropy due to a lower population of the mixed phobane/NHC ruthenium-indenylidene com-
[
37]
31
carbene p -orbital. This difference of chemical shift plexes is in line with the P chemical shift gap ob-
p
between coordinated IMes and SIMes ligands is served between various other second generation
slightly larger than the values computed for the free ruthenium-alkylidene catalysts, where the IMes or
1,3-dimesitylimidazol(in)-2-ylidenes
(Dd=24 ppm) IDip ligands always lead to a more pronounced de-
and their imidazol(in)ium salt precursors (Dd= shielding of the trans-phosphane than SIMes or
[38]
2
2
5 ppm). In both complexes, the J coupling con- SIDip, even if the difference is sometimes less than
C,P
stant measured for the (S)IMes C-2 carbon was great- 1 ppm [IDip is 1,3-bis(2,6-diisopropylphenyl)imidazol-
er than 80 Hz, indicative of a trans relationship be- 2-ylidene, SIDip is 1,3-bis(2,6-diisopropylphenyl)imi-
[
36,40–43]
tween the phobane and the NHC ligand. Another dazolin-2-ylidene].
1
doublet located at 294.9 ppm in both complexes was
It should be noted that the interpretation of H and
C NMR spectra was complicated by the presence of
1
3
assigned to the indenylidene C-1 carbon atom. In this
2
case, the J coupling constant was reduced to ca. many hardly differentiable signals in the aliphatic and
C,P
4
Hz, due to a cis arrangement relative to the pho- aromatic regions due to the phobane and indenyli-
[
44]
bane ligand.
dene ligands, respectively.
Yet, elemental analysis
31
1
At room temperature, the P{ H} NMR spectrum confirmed the identity and purity of complexes 10
of complex 10 consisted of a very broad singlet cen- and 11. Moreover, we were able to grow crystals of
tered at 7.8 ppm. A likely shaped signal was observed [RuCl (isobutylphobane) ACHUTNGRNENUG( SIMes)(3-phenyl-1-indenyli-
2
at 10.2 ppm for complex 11. This difference of chemi- dene)] (10) suitable for X-ray diffraction analysis by
cal shift might be explained by a stronger s-donor slow diffusion of isopropyl alcohool into a saturated
ability of the saturated imidazolin-2-ylidene ligand dichloromethane solution at room temperature. Their
compared to its aromatic imidazol-2-ylidene counter- molecular structure is depicted in Figure 1, along with
part, which would increase the electron density selected bond lengths and angles. The coordination
around the phosphorus nucleus via a trans effect. De- geometry around the ruthenium center is a distorted
tailed investigations of the steric and electronic prop- square pyramid with the indenylidene moiety occupy-
erties of NHCs suggest, however, that saturated het- ing the apical position, while the two chloro substitu-
erocycles are slightly less electron-donating than their ents and the donor atoms of the phobane and NHC li-
[
39]
unsaturated analogues,
in apparent contradiction gands form the basal plane. Bond lengths and angles
with our correlation. At this point, we prefer not to are similar to those observed in first generation com-
[
24]
[32]
draw any definite conclusion from these data, al- plexes 6 and 8, or in related second generation
though we note that the tendency observed here for ruthenium-indenylidene catalysts bearing PCy3 and
Figure 1. ORTEP representation of complex 10 with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms
were omitted for the sake of clarity. Selected bond lengths (ꢅ) and angles (deg): Ru1ÀCl1 2.3911(16), Ru1ÀCl2 2.3999(15),
Ru1ÀC1 2.090(6), Ru1ÀP1 2.4161(15), Ru1ÀC22 1.874(6), C1ÀRu1-C22 102.4(2), C1ÀRu1-Cl1 87.91(16), C1ÀRu1ÀCl2
9
1.57(16), C1ÀRu1ÀP1 161.61(17), C22ÀRu1ÀP1 96.01(16), Cl1ÀRuÀCl2 162.68(5).
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1937

Xavier Sauvage et al.
FULL PAPERS
[
36,43]
the IDip or SIDip ligands.
It is noteworthy, how-
ever, that the 3-phenyl group and the cyclopentene
ring of the indenylidene ligand in complex 10 are in
the opposite orientation with respect to the other
compounds examined. Indeed, the 3-phenyl group lies
in front of another terminal phenyl group from an ad-
jacent molecule, whereas in compound 8 and in
[
RuCl (isobutylphobane) AHCTUNGTERNNUNG( SIDip)(3-phenyl-1-indenyli-
2
dene)], it is in front of the core six-membered ring of
the indenylidene ligand from an adjacent molecule.
Inspection of the packing structure of complex 10 fur-
ther reveals the presence of two intramolecular hy-
drogen bonds between the indenylidene hydrogen
atoms flanking the Ru=C bond and the chlorine
atoms, and an intermolecular hydrogen bond between
the para-hydrogen of the terminal phenyl group and
the Cl(1) atom of an adjacent molecule. More impor-
tant is the existence of intramolecular p-p stacking in-
teractions between the indenylidene ligand and the
mesityl group of the NHC above it, a common feature
in ruthenium-alkylidene complexes bearing NHC li-
gands with aromatic substituents, which may have im-
portant implications in terms of catalyst stability and
[45]
activity. Terminal phenyl rings of two adjacent mol-
ecules are also involved in a weak intermolecular p-p
stacking interaction, whereas various aliphatic CÀH
3
1
Figure 2. P NMR spectra of complex 10 in CDCl (a) at
2
bonds interact with aromatic rings either intra- or in-
termolecularly (see the Supporting Information for
more details about the crystallographic analysis of
complex 10 and color illustrations).
3
58C and (b) at À408C.
In 2006, researchers from Sasol have shown that gesting that the conformer with a transoid orientation
31
1
the very broad peak observed in P{ H} NMR spec- of the isobutyl group relative to the indenylidene
troscopy at room temperature for the first generation moiety is more stable than the cisoid one in the solid
di(cyclohexylphobane) ruthenium-benzylidene com- state.
plex 5 and related compounds was due to the slow ro-
tation of its unsymmetrical phobane ligands around
[46]
the RuÀP bonds. Three distinct rotational isomers Catalytic Tests
were detected at À408C in 72/25/3 proportions. Based
on experimental results and DFT calculations, they In order to assess the ability of complexes 10 and 11
were assigned, respectively, to structures with (trans- to promote olefin metathesis, we have tested them in
oid, transoid), (transoid, cisoid), and (cisoid, cisoid) benchmark ROMP, RCM, and CM reactions using
orientations of the cyclohexyl groups relative to the standard protocols defined by Grubbs and co-workers
benzylidene unit. In the case of second generation to ease the comparison between different catalytic
[
47]
complex 10 bearing only one isobutylphobane ligand, systems.
Thus, in a first series of experiments, we
lowering the temperature to À408C led to the re- have carried out the ROMP of 1,5-cyclooctadiene in
placement of the broad signal observed at room tem- CD Cl at 308C using 0.1 mol% of various ruthenium
2
2
perature by two sharp singlets at 9.7 and À0.3 ppm in
a 87/13 ratio (Figure 2). Thus, we tentatively assign
the major peak to the transoid conformer 10a and the
minor one to its cisoid congener 10b. The same ex-
planation also holds true for complex 11, whose
3
1
P NMR spectrum at À408C comprised a major peak
at 11.3 ppm and a minor one at 0.5 ppm in a 92/8 initiators [Eq. (1)]. As observed previously by the
ratio (not shown). It is supported by the crystal struc- group of Verpoort,
[
42]
consumption of the monomer
ture depicted in Figure 1, which shows that the isobu- occurred much faster with the second generation ben-
tyl chain of the phobane ligand points in the opposite zylidene catalyst 2 than with the known bis(tricyclo-
direction of the indenylidene fragment, thereby sug- hexylphosphane) ruthenium-indenylidene complex 3
1938
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
608C and the monomer-to-catalyst ratio was 250 [Eq.
(
2)]. Under these conditions, no significant difference
was observed in the polymerization outcome, whether
complex 10 or 11 was employed as catalyst precursor.
In both cases, a high molecular weight polymer with a
polydispersity index close to 1.5 and a backbone that
contained mostly trans double bonds was isolated in
almost quantitative yield (Table 1).
Next, we have investigated the RCM of diethyl 2,2-
diallylmalonate [Eq. (3)]. Preliminary experiments
Figure 3. Time course of the ROMP of 1,5-cyclooctadiene
using various catalyst precursors (0.1 mol%) in CD Cl at
2
2
3
08C (2: ^, 3: *, 9: *, 10: ~, 11: !).
were carried out using 1 mol% of ruthenium initiator
and a 0.1M stock solution of substrate in CD Cl at
2
2
(
Figure 3). The analogous first generation Ru-indeny- 308C, as recommended by Grubbs et al. for the com-
lidene complex 9 bearing two isobutylphobane ligands parative evaluation of catalyst precursors in the RCM
[
47]
was even less active. Introduction of the SIMes ligand of a,w-dienes.
Under these conditions, complexes
in second generation complex 10 slightly increased 10 and 11 were considerably less active than their first
the polymerization rate compared to 9, whereas sub- generation parent 9 (Figure 4). The latter catalyst af-
stitution of an isobutylphobane ligand with the unsa- forded a 96% conversion after 30 min. Within the
turated IMes donor led to a dramatic reduction of ac- same period of time, consumption of the starting ma-
tivity. Complete consumption of 1,5-cyclooctadiene terial did not exceed 6% with complex 10 and 3%
was, however, achieved within 24 h with complexes 3, with complex 11. Yet, with these two compounds, sat-
9
, and 10. In the case of complex 11, it took 9 days to isfactory conversions were eventually reached after a
reach a 78% conversion. Although we stopped the ex- few days. The same trend was already observed by
periment at this point, the catalyst was still active, Clavier and Nolan when comparing first and second
which indicates a great stability and a poor initiation generation ruthenium-indenylidene catalysts based on
efficiency.
the tricyclohexylphosphane ligand (3 and 4, respec-
[49]
Because no information on the polymer microstruc- tively).
Subsequent work by Verpoort et al. con-
ture could be obtained from the NMR kinetic meas- firmed that first generation catalysts 1 and 3 afforded
urements, we decided to perform the ROMP of cyclo- higher conversions of diethyl 2,2-diallylmalonate in
octene on a millimolar scale and to characterize the shorter reaction times than their second generation
polyoctenamer formed using catalyst precursors 10 analogues 2 and 4 when the RCM was carried out at
[
42,44]
and 11. The standard procedure used in our laborato- 208C.
ry to appraise new catalytic systems was applied.
[
48]
To compensate for the slow initiation rate displayed
Polymerizations were carried out in chlorobenzene at by complexes 10 and 11 at 308C, we decided to per-
[a]
Table 1. ROMP of cyclooctene catalyzed by complexes 10 and 11.
[b]
À1 [c]
[c]
scis[d]
Complex
Monomer Conversion [%]
Polymer Yield [%]
M [kgmol ]
M /Mn
w
n
1
1
0
1
>99
>99
91
88
195
207
1.6
1.5
0.18
0.14
[
[
[
[
a]
Experimental conditions: Ru catalyst (0.03 mmol), PhCl (5 mL), cyclooctene (7.5 mmol), 2 h at 608C.
Determined by GC using the cyclooctane impurity of cyclooctene as an internal standard.
Determined by SEC in THF with polystyrene calibration.
b]
c]
d]
13
Fraction of cis double bonds within the polyoctenamer, determined by C NMR.
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1939

Xavier Sauvage et al.
FULL PAPERS
bane complexes 10 and 11 (1 mol%) in toluene-d at
8
508C instead of 308C with the more active diphobane
precursor 9. Under these conditions, an almost quanti-
tative conversion of the b-substituted a,w-diene took
place within 4 h with all three catalysts (Figure 5).
Small differences in reaction rates were, nevertheless,
clearly visible from the kinetic plots. They confirmed
the trends already observed for the RCM of
DEDAM, as complex 9 displayed a higher catalytic
activity at 308C than complex 10 at 508C, which was
in turn slightly more efficient than its sibling 11. It
should be pointed out that metathesis reactions are
limited to an equilibrium that does not always allow a
1
00% conversion to be reached (especially when
Figure 4. Time course of the RCM of diethyl 2,2-diallylmalo-
RCM is performed in a closed system that does not
allow removal of the ethylene by-product), thereby
explaining the levelling off at ca. 95% observed with
complexes 9 and 10.
nate using various catalyst precursors (1 mol%) in CD Cl at
2
2
3
1
08C (9: *, 10: ~, 11: !) or in toluene-d at 508C (10: ~,
8
1: !).
In a final series of RCM experiments, we have in-
form the RCM of diethyl 2,2-diallylmalonate at vestigated the cyclization of diethyl 2,2-bis(2-methyl-
higher temperatures. Because the boiling point of allyl)malonate into the corresponding tetrasubstituted
CD Cl is only 408C, we replaced it with toluene-d
(
cycloolefin [Eq. (5)]. The considerable steric hin-
bp 1118C) in these experiments. A first data set was drance of the b,y-disubstituted a,w-diene makes this
recorded at 508C (Figure 4). At this temperature, it reaction very challenging for most ruthenium initia-
2
2
8
[
47]
took approximately 1 h to achieve an almost quantita- tors currently available. Because an important ther-
tive conversion with complex 10, whereas complex 11 mal activation is required to perform the cyclization,
required ca. 140 min to reach equilibrium. A further
kinetic plot was recorded with this latter catalyst pre-
cursor at 808C. At this temperature, the reaction took
place almost instantaneously and led to a complete
conversion of the substrate before the first NMR
analysis could be performed. In order to quantify the
activities of the two complexes under scrutiny, we
have determined the rate constants observed in the
RCM of diethyl 2,2-diallylmalonate (DEDAM) at
508C. The formalism proposed by Grubbs et al. was
employed to extract the pseudo-first order rate con-
[
47,50]
stants from the plot of ln
A
H
U
G
E
N
N
As
expected, the k
obs
À1
(
(
0.0010 s ) was greater than for its counterpart 11
0.0004 s ), but lagged significantly behind the one
À1
À1
obtained with complex 9 at 308C (0.0019 s ).
Replacement of one allyl group with a branched 2-
methylallyl substituent in DEDAM affords diethyl 2-
allyl-2-(2-methylallyl)malonate, which is a standard
substrate to probe metathesis catalysts in the forma-
[
47]
tion of trisubstituted cycloolefins [Eq. (4)]. Due to
steric effects, this reaction is more demanding than
the corresponding RCM to form the disubstituted cy-
clopentene shown in Eq. (3). Thus, we chose to per- (1 mol%) in CD Cl at 308C (9: *) or in toluene-d at 508C
form the reaction with second generation isobutylpho-
Figure 5. Time course of the RCM of diethyl 2-allyl-2-(2-
methylallyl)malonate using various catalyst precursors
2
2
8
(10: ~, 11: !).
1940
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
rapid degradation of the active species is a major
issue in this transformation, and the second genera-
Scheme 4. Unhindered second generation ruthenium-alkyli-
tion complexes that are more able to withstand ele- dene complexes.
vated temperatures usually give better results than
[
5,36,40]
their first generation analogues.
In our hands,
despite the use of rather forcing conditions (5 mol% the corresponding ruthenium-benzylidene or indenyli-
catalyst loading at 808C), conversions remained, how- dene complexes 2 and 4 bearing the PCy3 ligand
ever, far from quantitative using common SIMes- (Figure 6). The validity of our approach was further
based catalyst precursors, such as complexes 2 and 4 strenghtened by recent reports from the groups of
(
Figure 6). To overcome these limitations, Grubbs Plenio and Nolan that appeared while this manuscript
[
52]
et al. have successfully introduced a new family of was under review.
The two teams showed that
second generation ruthenium-benzylidene and isopro- ruthenium-benzylidene or indenylidene catalyst pre-
poxybenzylidene catalyst precursors based on NHC li- cursors bearing two distinct NHC ligands were highly
gands designed to reduce the steric pressure around active for the RCM of tetrasubstituted cycloolefins. In
the metal center (Scheme 4). Thus, in compounds 12 both cases, an increased stability due to the strong in-
and 13, free ortho positions on the N-bound 2-tolyl teraction between the NHCs and the metal center
substituents provide more space around the rutheni- was held responsible for the slow generation of active
um atom, which is thought to account for their in- species at elevated temperatures.
creased activity toward sterically challenging sub-
strates.
The kinetic plots of our systems revealed that once
again, the SIMes-based complex 10 outperformed its
[51]
We reasoned that another strategy to achieve the IMes-based sibling 11: within 2 h at 808C, conversion
same goal would be to increase the catalyst stability reached 72% with the former catalyst but did not
through a modification of the phosphane ligand and exceed 55% with the latter one. No more evolution
that complexes 10 and 11 were ideal candidates to was recorded after that period of time, indicating a
probe the validity of this approach. Hence, we were complete decomposition of the active species. Compa-
very pleased to note that the two mixed isobutylpho- ratively, complexes 2 and 4 were far less resistant to
bane/NHC catalyst precursors were more active than thermal degradation and stopped working after 30 to
60 min under the experimental conditions adopted.
Adding the ruthenium initiator in small portions over
time and venting the ethylene produced upon RCM
of diethyl 2,2-bis(2-methylallyl)malonate should fur-
ther enhance the resilience of complexes 10 and 11,
but such modifications of the benchmark protocols
used to compare various catalytic systems fell outside
the scope of this study.
Last but not least, we have investigated the cross-
metathesis between allylbenzene and cis-1,4-diacet-
AHCTUNGTRENNUGNo xy-2-butene [Eq. (6)]. Because these two starting
materials display similar high reactivities toward self-
metathesis, and their homodimers or cross-products
ylallyl)malonate using various catalyst precursors (5 mol%) are prone to undergo secondary metathesis events, a
Figure 6. Time course of the RCM of diethyl 2,2-bis(2-meth-
in toluene-d at 808C (2: ^, 4:
&
, 10: ~, 11: !).
statistical mixture containing six different products
8
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1941

Xavier Sauvage et al.
FULL PAPERS
(
E/Z-heterocoupled 4-phenyl-2-buten-1-yl acetate, E/ erature that demonstrated the superior activity of
Z-1,4-diacetoxy-2-butene, and E/Z-homocoupled 1,4- second generation ruthenium-benzylidene or indenyli-
[
53]
diphenyl-2-butene) is obtained. In order to increase dene catalysts based on the PCy ligand, such as 2 or
3
the statistical yield for the desired heterocoupled 4, over their first generation counterparts (1 and 3, re-
[
47,54]
monoester 14, 2 equiv. of cis-1,4-diacetoxy-2-butene spectively) in several types of CM reactions.
corresponding to 4 equiv. of allyl acetate) were intro- discrepancy further suggests that complexes 10 and 11
duced relative to allylbenzene. The benchmark proce- are particularly stable in solution and are much
This
(
[
47]
dure proposed by Grubbs et al. (2.5 mol% of cata- slower initiators for olefin metathesis than most
lyst in CH Cl at 258C) was followed and the reaction ruthenium-alkylidene species investigated so far.
2
2
course was monitored by GC using n-tetradecane as
internal standard. The conversions to heterocoupled
product 14 vs. time were recorded using various Mechanistic Indications
ruthenium-indenylidene
catalyst
precursors
(
Figure 7). The results of this kinetic study confirmed According to the well-established mechanism postu-
the trends already deduced from the RCM experi- lated for olefin metathesis, 16-electron ruthenium-al-
ments. Thus, the replacement of tricyclohexylphos- kylidene catalyst precursors must lose a phosphane
phane in complex 3 with the isobutylphobane ligand ligand in order to generate 14-electron complexes A
in the analogous first generation catalyst 9 led to a and D, which are the true active species leading to
small albeit significant reduction of activity. A fine the
distinction was also made between complexes 10 and (Scheme 5). The formation of A precedes the olefin
1, but the difference was less pronounced than in coordination and a first metathesis event that leads to
key
metallacyclobutane
intermediate
C
[
55]
1
RCM reactions. With these two catalysts, conversions complex B. The initial phosphane dissociation is not
did not exceed 5% after 5 h. When the reactions were related to the nature of the substrate and corresponds
prolonged overnight, the yield of cross-product 14 to the limiting step for NHC-containing precata-
[
14]
reached 79% with SIMes-based complex 10 and 76% lysts.
This explains why a thermal activation of
with its counterpart 11. In both cases, formation of second generation ruthenium-indenylidene complexes
the thermodynamically more stable trans-4-phenyl-2- 10 and 11 was required to perform the RCM of dieth-
buten-1-yl acetate was favored over its cis isomer (E/ yl 2,2-diallylmalonate and diethyl 2-allyl-2-(2-methyl-
Z ratio=6.7 with 10 and 6.3 with 11). Most strikingly, allyl)malonate, in sharp contrast with their diphos-
second generation complexes 10 and 11 were far less phane parent 9, which reacted faster at lower temper-
active than the first generation catalysts 3 and 9. This ature (cf. Figure 4 and Figure 5). Conversely, the for-
is in sharp contrast with previous results from the lit- mation of the metallacyclobutane C, and its conver-
sion to the methylidene species D upon extrusion of
the RCM product constitute the limiting step for first
generation precatalysts, which are therefore much
more sensitive to the steric hindrance of the substrate
and fail to accomplish the RCM of tetrasubstituted
[
56]
olefins.
We have no explanation to account for the superior
activity exhibited by SIMes-based complex 10 in com-
parison with its IMes-containing sibling 11 in the vast
majority of our catalytic tests. We note, however, that
related precursors 2 and 4 were also found better cat-
alysts than the corresponding PCy /IMes ruthenium-
3
alkylidene compounds for many RCM or CM reac-
[
47,49]
tions.
Based on DFT calculations, Jensen and co-
workers attributed this difference of behavior to both
[
57]
electronic and steric effects.
The specific s-donor
and p-acceptor properties of the NHC ligand are ex-
pected to have a large impact on the stability of 14-
electron complexes A and D. The non-planarity of
the imidazoline backbone in SIMes and differences in
the tilt angle of the mesityl groups may also be re-
sponsible for subtle steric modifications of the ruthe-
nium coordination sphere. Likewise, our investiga-
tions have shown that the replacement of tricyclohex-
ylphosphane with isobutylphobane had a dramatic in-
Figure 7. Time course of the CM between allylbenzene and
cis-1,4-diacetoxy-2-butene using various catalyst precursors
(
2.5 mol%) in CH Cl at 258C (3: *, 9: *, 10: ~, 11: !).
2 2
Lines are intended as visual aids only, not as curve fits.
1942
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
Scheme 5. Proposed mechanism and rate-determining steps (RDS) for the RCM of a,w-dienes catalyzed by ruthenium-in-
denylidene complexes.
fluence on the stability and activity of second genera-
tion ruthenium-indenylidene complexes. This result
was hardly predictable based on simple steric and
electronic considerations. As a matter of fact, tricyclo-
hexylphosphane is slightly more bulky than isobutyl-
phobane, as expressed by the Tolman cone angle (q=
[58]
[59]
1
708 for PCy3 and 1638 for i-BuPhob ). For non-
obvious reasons, it is also a better electron donor, as
measured from the values of n(CO) in trans-
À1
[60]
[
RhCl(CO) ACHTUNGTRENNUNG( PR ) ] complexes (1943 cm for PCy3
3 2
À1
[61]
vs. 1950 cm for i-BuPhob ).
Decomposition Studies
The steric and electronic robustness of the indenyli-
dene unit, together with the strong binding of PCy3
and NHC ligands are responsible for the high thermal the second generation isobutylphobane complex 11,
1
stability of ruthenium complexes 3 and 4, as pointed no sign of reaction was detected by H NMR analysis
[
36]
[42]
out by the groups of Nolan
and Verpoort.
The and the starting material was recovered unchanged
catalytic tests that we have carried with isobutylpho- upon work-up. This lack of reactivity confirms the re-
bane-based compounds 10 and 11 suggest that they markable stability and the poor initiation efficiency of
are even more stable. Because ruthenium-methyli- the isobutylphobane/NHC ruthenium-indenylidene
dene species are key propagating agents in many met- template.
athetical transformations and represent the thermally
least stable intermediates within the catalytic cycle,
We then decided to compare the ethenolysis rates
of two second generation ruthenium-indenylidene
[
62]
we reasoned that assessing their stability and decom- complexes bearing, respectively, a tricyclohexylphos-
position pathways would help us to better rank their phane and an isobutylphobane ligand. For these ex-
indenylidene precursors in terms of catalytic efficien- periments, complexes 4 and 10 were dissolved in C D6
6
cy. Thus, we tried to prepare the [RuCl (iso- saturated with ethylene at 258C and then heated to
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
butylphobane)
ACHTUNGTRENNUNG( IMes) ACTHUNGTRENNU(GN =CH )] complex by reacting in- 508C in sealed NMR tubes (Scheme 6). The disap-
2
denylidene compound 11 with ethylene in benzene at pearance of the indenylidene H-8 protons in the start-
1
5
08C for 2 h [Eq. (7)]. This procedure was successful- ing materials was followed by H NMR spectroscopy
ly applied by Forman et al. for the synthesis of meth- using triptycene as an internal standard. Concomitant-
ylidene complexes derived from first generation cy- ly, we also monitored the appearance of new signals
[
24]
clohexylphobane catalyst precursors 5 and 6. With at higher field (ca. 18.5 ppm), due to the formation of
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1943

Xavier Sauvage et al.
FULL PAPERS
Scheme 6. Decomposition path of ruthenium-indenylidene complexes under ethylene atmosphere.
ruthenium-methylidene active species 15 or 16 long reaction times and high temperatures required to
Figure 8). A rapid consumption of PCy -based inden- carry out the RCM of tetrasubstituted olefins.
(
3
ylidene complex 4 took place as soon as ethylene was
added to the reaction mixture. It led to the formation
of the corresponding methylidene species 15, whose Conclusions
maximum concentration peaked after 7 h and corre-
sponded to 45% of the initial precatalyst. Due to bi- By heating a THF solution of the commercially avail-
molecular decomposition processes, this intermediate able
[RuCl (isobutylphobane) (3-phenyl-1-indenyli-
2
2
then slowly decomposed into unidentified products dene)] catalyst precursor (9) with a two-fold excess of
and almost totally disappeared after 2 days. The de- either SIMes·CO or IMes·CO , we were able to iso-
2
2
composition path of isobutylphobane complex 10 was late two new second generation ruthenium-indenyli-
completely different. An induction period of ca. 9 h dene complexes bearing mixed isobutylphobane/NHC
was observed before it started reacting with ethylene ligands (10 and 11) in high yields. These compounds
to afford a small amount of [RuCl (isobutylphobane)- were highly stable in the solid state, as well as dis-
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(SIMes)
of this complex never exceeded 2%, it persisted after
almost 3 days, when the measurements were inter- structure
ACHTUNGTRENNUNG( =CH )] (16). Although the molar proportion solved in aprotic solvents. They were characterized by
2
1 13 31
H, C, and P NMR spectroscopy, and the molecular
of [RuCl (isobutylphobane)(SIMes)(3-
AHCTUNGTRENNUNG
2
rupted. This behavior explains why complex 10 ini- phenyl-1-indenylidene)] (10) was determined by X-
tiates RCM and CM reactions very slowly, but leads ray diffraction analysis. A close inspection of the
to robust active species that are able to sustain the packing structure revealed the presence of different
types of intra- and intermolecular interactions that
enhance the global stability of the crystals, while low
temperature NMR experiments showed the existence
of two distinct rotational isomers due to the unsym-
metrical nature of the phobane ligand.
The catalytic activity of compounds 10 and 11 was
probed in various types of ROMP, RCM, and CM re-
actions, and compared with those of related first and
second generation ruthenium-benzylidene and inden-
ylidene catalyst precursors. Kinetic studies confirmed
the high thermal stability of isobutylphobane com-
plexes 10 and 11, which suffered from a slow initia-
tion efficiency compared to other catalytic systems
based on the tricyclohexylphosphane ligand. Howev-
er, the remarkable robustness of [RuCl (iso-
2
ACTHNGUTRENNUGb utylphobane) ACTHUNGTRENNUNG( SIMes)(3-phenyl-1-indenylidene)] (10)
turned out to be beneficial for performing the RCM
of diethyl 2,2-bis(2-methylallyl)malonate, a challeng-
ing reaction that holds previously developed rutheni-
um-indenylidene catalysts in check. Monitoring the
formation of the ruthenium-methylidene active spe-
cies [RuCl (isobutylphobane) ACHUTNGREUNNG( SIMes) ACHTUNGTNERNUN(G =CH )] (16) de-
2
2
rived from this precursor further demonstrated its
ability to sustain long reaction times and high temper-
dene species derived thereof (15: &, 16: ~) in C D saturat- atures required to carry out the RCM of tetrasubsti-
Figure 8. Time course of the decomposition of ruthenium-in-
denylidene complexes (4: &
, 10: ~) and ruthenium-methyli-
6
6
ed with ethylene at 508C.
tuted olefins. Other types of metathetical processes,
1944
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Adv. Synth. Catal. 2010, 352, 1934 – 1948

Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium-Indenylidene Complexes
such as the self-metathesis or ethenolysis of renewa- down and the solvent was removed under vacuum. The resi-
due was purified by flash chromatography on a silica gel
ble fatty acid esters, are also in dire need for econom-
plug using the same eluent that was used for TLC to afford
ical, selective, and long-lived catalysts to be applied
on a large scale, and we envision that mixed phobane/
NHC ruthenium-indenylidene complexes might be
promising candidates to fulfill these duties.
the title compound (10) as a red powder; yield: 0.42 g
1
4
(
91%). H NMR (400 MHz, C D 298 K): d=9.18 (d, J =
6 6, 7,8
7
1
.2 Hz, 1H, H-8), 7.87 (s, 1H, Ph), 7.85 (s, 1H, Ph), 7.80 (s,
H, H-2), 7.33–7.30 (m, 2H), 7.24–7.20 (m, 3H), 7.12–7.08
(
m, 1H), 6.95 (s, 2H, CHar Mes), 6.48 (s, 1H, CH ), 6.04 (s,
ar
1
H, CH ), 3.39–3.33 (m, 2H, CH NHC), 3.27–3.13 (m, 2H,
ar 2
Experimental Section
CH NHC), 2.88, 2.83, 2.39, 2.22, 2.17, 1.76 (aliphatic part);
2
1
3
2
C NMR (101 MHz, C D , 298 K): d=294.9 (d, JP, C
=
6
6
2
General Information
3.9 Hz, C-1 indenylidene), 217.9 (d,
NHC), 145.1, 141.8, 139.5, 139.4, 138.4, 138.0, 137.7, 137.6,
1
1
listed); P NMR (101 MHz, C D , 298 K): d=7.8 (br s);
anal. calcd. for C H Cl N PRu (866.95): C 66.50, H 6.86, N
J
P, C =80.9 Hz, C-2
All reactions were carried out under a dry argon atmos-
phere using standard Schlenk techniques. Solvents were dis-
tilled from appropriate drying agents and deoxygenated
37.4, 137.2, 137.0, 136.9, 136.1, 130.3, 130.2, 129.4, 129.1,
28.9, 126.8, 116.5, 52.4, 52.0, (other aliphatic signals not
31
[
63]
6
6
prior to use. Diethyl 2-allyl-2-(2-methylallyl)malonate, di-
[63]
[35a]
48 59
2
2
ethyl 2,2-bis(2-methylallyl)malonate,
IMes·CO2,
were synthesized according to published pro-
cedures. Indenylidene complex 9 (Neolystꢄ M11) was ob-
tained from Umicore. Silica gel 60 (60 ꢅ nominal pore di- Synthesis of {Dichloro(9-isobutylphosphabicyclo-
and
3
.23; found: C 66.80, H 7.06, N 3.59.
[35a]
SIMes·CO2
ameter, 0.04–0.063 mm particle size) supplied by ROCC was
used for flash chromatography. Petroleum ether refers to
the hydrocarbon fraction of bp 40–608C and was purchased
from Labotec. All the other chemicals were purchased from
ACTHUNGERTNNUNG[ 3.3.1]nonane) ACHTUNGERTNNUNG[ 1,3-bis(2,4,6-trimethylphenyl)-
imidazol-2-ylidene](3-phenyl-1-indenylidene)-
ruthenium(II)} (11)
1
13
1
31
1
Using the same procedure as described above, [Ru-
Aldrich. H, C{ H}, and P{ H} NMR spectra were record-
ed with a Bruker DRX 400 or a Bruker Avance 250 spec-
trometer. Chemical shifts are listed in parts per million
downfield from TMS and are referenced from the solvent
Cl (isobutylphobane) (3-phenyl-1-indenylidene)] (9) (0.4 g,
2
2
0
.53 mmol) was reacted with IMes·CO (0.367 g, 1.05 mmol,
2
2
equiv.) to afford the title compound (11) as a red powder;
1
1
13
31
yield: 0.40 g (88%). H NMR (400 MHz, C D , 298 K): d=
9
residual peaks ( H, C) or external H PO ( P). Gas chro-
6
6
3
4
4
.13 (d, J =7.2 Hz, 1H, H-8), 7.87 (s, 1H, Ph), 7.85 (s, 1H,
matography was carried out with a Varian 3900 instrument
equipped with a flame ionization detector and a WCOT
fused silica column (stationary phase: CP-Sil 5CB, column
length: 15 m, inside diameter: 0.25 mm, outside diameter:
7,8
Ph), 7.82 (s, 1H, H-2), 7.31–7.24 (m, 2H), 7.23–7.19 (m,
3
1
H), 7.13–6.93 (m, 1H), 6.93 (s, 2H, CHar NHC), 6.47 (s,
H, CHar NHC), 6.18 (s, 2H, H-4,5 NHC), 6.03 (s, 1H, CH
ar
1
NHC), (other aliphatic signals not listed); H NMR
0.39 mm, film thickness: 0.25 mm). Size-exclusion chroma-
(
400 MHz, CD Cl , 223 K): d=0.7 (br s, CH phobane, 6H),
tography (SEC) was performed in THF at 458C with a SFD
S5200 autosampler liquid chromatograph equipped with a
SFD 2000 refractive index detector and a battery of 4 PL
gel columns fitted in series (particle size: 5 mm; pore sizes:
2
2
3
1
.50–2.50 (m, CH + CH phobane, 17H), 1.77 (s, CH , 3H),
2 3
1
.80 (s, CH , 3H), 1.96 (s, CH , 3H), 2.37 (s, CH , 6H), 2.89
3
3
3
1
3
(
s, CH , 3H), (aliphatic part only); C NMR (101 MHz,
3
2
5
4
3
2
À1
C D , 298 K): d=294.9 (d, J =3.5 Hz, C-1 indenylidene),
1
0 , 10 , 10 , and 10 ꢅ; flow rate: 1 mLmin ). The molecu-
6
6
P, C
2
1
1
1
86.9 (d, J =85.9 Hz, C-2 NHC), 145.2, 141.8, 139.1, 138.7,
38.5, 137.7, 137.5, 137.2, 136.3, 129.5, 129.3, 129.0, 128.3,
26.8, 126.6, 125.6, 125.3, 124.7, 116.6, (other aliphatic sig-
lar weights (not corrected) are reported versus monodis-
perse polystyrene standards used to calibrate the instrument.
Elemental analyses were carried out in the Laboratory of
Pharmaceutical Chemistry at the University of Liꢁge.
P, C
1
3
nals not listed); C NMR (101 MHz, CD Cl , 223 K): d=
2
2
1
7.7 [s, PÀCH ÀCH
ACHTUNGTRNENU(G CH ) ], 18.15, 18.23, 19.1, 19.2 (s, ortho-
3 2
3
2
CH , IMes), 20.8 (d, J =3.7 Hz, PÀCHÀCH ÀCH ), 20.9,
3
P, C
2
2
3
2
1.3 (s, para-CH , IMes), 21.4 (d, J =4.5 Hz, PÀCHÀCH À
3
P, C
2
Synthesis of {Dichloro(9-isobutylphosphabicyclo-
ACHTUNGTRENNUNG[ 3.3.1]nonane) ACHTUNGTRENNUNG[ 1,3-bis(2,4,6-trimethylphenyl)imid-
azolin-2-ylidene](3-phenyl-1-indenylidene)-
ruthenium(II)} (10)
1
CH ), 23.2 [d, JP,C =22 Hz, PÀCH ÀCH
ACHTUNGTNERNGNU( CH ) ], 24.3 (d,
3 2
2
2
3
3
JP, C =6.3 Hz, PÀCHÀCH ), 25.1 (d,
J
=8.9 Hz, PÀCHÀ
2
P, C
CH ), 26.8 [m, PÀCHÀCH , PÀCH ÀCH
ACHTUNGTNERNGNU( CH ) ], 27.2 (d,
2
2
2
3 2
2
2
J
=16.1 Hz, PÀCH), 32.9 (d, J =16.1 Hz, PÀCH), (ali-
P, C
P, C
3
1
phatic part only); P NMR (101 MHz, C D , 298 K): d=
A 100-mL, two-neck, round-bottom flask containing a mag-
netic stirring bar and fitted with a reflux condenser topped
6
6
1
6
0.2; anal. calcd. for C H Cl N PRu (864.93): C 66.65, H
.64, N 3.24; found: C 66.69, H 6.82, N 3.39.
48 57 2 2
with an oil bubbler was charged with [RuCl (iso-
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
butylphobane) (3-phenyl-1-indenylidene)]
(9)
(0.4 g,
2
0
.53 mmol) and SIMes·CO2 (0.369 g, 1.05 mmol, 2 equiv.).
X-Ray Crystal Structure Determination
The reactor was purged of air by applying three vacuum/
argon cycles before dry THF (20 mL) was added. The dark
red solution was refluxed in an oil bath at 808C under a
slow stream of argon. The reaction progress was monitored
by TLC on silica gel plates using petroleum ether/diethyl
ether (92/8 v/v) as eluent. When conversion of the starting
complex was complete (ca. 4 h), the solution was cooled
Orange crystals of complex 10 suitable for X-ray diffraction
analysis were obtained by slow diffusion of isopropyl alcohol
into a saturated dichloromethane solution at room tempera-
ture. Crystal data (d=0.95 ꢅ) were collected on a Bruker
APPEX II diffractometer using graphite-monochromated
Mo-Ka radiation (l=0.71073 ꢅ) from a fine-focus sealed
Adv. Synth. Catal. 2010, 352, 1934 – 1948
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1945

Xavier Sauvage et al.
FULL PAPERS
tube source at 100 K. Computing data and reduction was References
[
64]
made with the APPEX II software.
The structure was
[65]
solved using DIRDIF, and finally refined by full-matrix,
least-squares based on F by SHELXL. An empirical ab-
sorption correction was applied using SADABS. All non-
hydrogen atoms were anisotropically refined and the hydro-
gen atom positions were calculated and refined using a
riding model.
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crystal dimensions: 0.09ꢆ0.08ꢆ0.05 mm, monoclinic, a=
1
1
3.2609(10),
b=19.0101(12),
c=17.2004(11) ꢅ,
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À1
Z=4, l
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CCDC 766617 contains the supplementary crystallograph-
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from The Cambridge Crystallographic Data Centre via
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Decomposition of Ruthenium-Indenylidene Catalysts
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6
6
An NMR tube equipped with a screw-cap septum was
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The financial support of the “Fonds de la Recherche Scientifi-
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purchase of major instrumentation. We thank Umicore AG &
Co. KG for a generous donation of complex 9.
1946
asc.wiley-vch.de
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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