On the chloride lability in electron-rich second-generation ruthenium benzylidene complexes

Article abstract of DOI:10.1007/s00706-015-1484-x

A series of electron-rich second-generation cis-dichloro ruthenium aldehyde-chelating benzylidene complexes was prepared, characterized, and tested in typical ring-opening metathesis polymerization (ROMP) experiments. The benzylidene precursors were prepa

Full text of DOI:10.1007/s00706-015-1484-x

Monatsh Chem
DOI 10.1007/s00706-015-1484-x
ORIGINAL PAPER
On the chloride lability in electron-rich second-generation
ruthenium benzylidene complexes
1
1
2
1
Simone Strasser
•
Eva Pump
•
Roland C. Fischer
•
Christian Slugovc
Received: 19 March 2015 / Accepted: 23 April 2015
Ó Springer-Verlag Wien 2015
Abstract A series of electron-rich second-generation cis-
dichloro ruthenium aldehyde-chelating benzylidene com-
plexes was prepared, characterized, and tested in typical
ring-opening metathesis polymerization (ROMP) ex-
periments. The benzylidene precursors were prepared via
etherification of the hydroxyl group and vinylation at po-
sition 2 of 2-bromo-5-hydroxy-4-methoxybenzaldehyde.
The corresponding ruthenium complexes were obtained
from a carbene exchange reaction and were characterized
by a cis-dichloro arrangement. A pronounced lability of the
chloride ligand trans to the N-heterocyclic carbene ligand
in methanol was observed and it was shown that this fea-
ture is responsible for a particularly slow ROMP in this
solvent.
Graphical abstract
Keywords Olefin metathesis Á Ruthenium Á
Structure–activity relationships Á Polymerizations
Introduction
Ruthenium-based olefin metathesis catalysts/initiators tol-
erate a wide array of functional groups including water and
to some extend oxygen and are therefore widely used in
carbon–carbon double bond forming reactions [1, 2]. Well-
defined ruthenium olefin metathesis catalysts/initiators
typically feature a square pyramidal coordination geometry
generally made up by a carbene as the apex and two neutral
ligands such as phosphines or N-heterocyclic carbenes
Dedicated to Franz Stelzer and his contributions to the field of Olefin
Metathesis.
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-015-1484-x) contains supplementary
material, which is available to authorized users.
(NHCs) as well as two anionic ligands (in most cases
chlorides) forming the base. Most prominent, yet most
metathetically active examples exhibit a trans-dichloro
arrangement, but also complexes with a thermodynamic
preference for the cis-dichloro isomer are known [3, 4].
The latter class is characterized by a slower initiation and a
higher thermal stability in comparison to their trans-
dichloro counterparts which can be rationalized by the
widely accepted hypothesis that the cis-dichloro species
&
Christian Slugovc
slugovc@tugraz.at
1
Institute of Chemistry and Technology of Materials, NAWI
Graz, Graz University of Technology, Stremayrgasse 9, 8010
Graz, Austria
2
Institute of Inorganic Chemistry, NAWI Graz, Graz
University of Technology, Stremayrgasse 9, 8010 Graz,
Austria
123

S. Strasser et al.
itself is not metathesis active but has to isomerize to its
metathesis active trans-dichloro counterpart [5, 6]. The
isomerization process occurs in a dissociative or a con-
certed manner [3]. Second-generation (i.e., bearing an
N-heterocyclic carbene coligand) cis-dichloro ruthenium
benzylidenes with, e.g., oxygen- [7–9], vinyl- [10], sulfur-
position 5 (see Scheme 1). Carbene precursors 3a–3d were
prepared in a two-step procedure starting from commercially
available 2-bromo-5-hydroxy-4-methoxybenzaldehyde (1).
In the first step, etherification of the phenolic hydroxyl group
using the corresponding alkyl bromides or iodides was car-
ried out following a slightly modified procedure [20].
Instead of acetone, dimethylformamide was used as the
solvent and additionally to K CO , 2.5 mol % Cs CO (in
[
11], or nitrogen-based [12, 13] neutral coligands are
known. A comprehensive overview including calculated
relative thermodynamic stabilities of the cis- and the trans-
isomers has been published recently [3]. The combination
of slow initiation and thermal stability makes cis-dichloro
pre-catalysts/initiators interesting for olefin metathesis re-
actions in which slow dosing at elevated temperatures is
desired [14–18] or when a thermally triggered polymer-
ization is intended [8, 12, 13].
2
3
2
3
respect of K CO ) were added to the reaction mixture. The
2
3
reactions were performed at room temperature for 24 h.
Compounds 2a–2d were obtained in 80–83 % yield after
chromatographic purification.
In the second step, a Suzuki–Miyaura cross-coupling
using 2,4,6-trivinylcyclotriboroxane anhydride pyridine
complex as the coupling partner, 3 mol % Pd(PPh ) as the
3
4
Herein we report on our investigations to increase the
electron density of the oxygen chelated benzylidene ligand
used in previously disclosed (SPY-5-31) dichloro(2-
catalyst, and K CO as the base was carried out. Com-
2 3
pounds 3a–3d were obtained in 77–96 % yield upon
column chromatographic purification. The desired ruthe-
nium benzylidene derivatives 4a–4d were then prepared by
stirring a solution of 1 eqiv. M31 and 1.15 eqiv. 3a–3d in
dichloromethane at room temperature for several hours,
whereupon the color of the solution turned from wine-red
to deep green (see Scheme 2). Extraction of the reaction
mixture with aqueous HCl was carried out to remove
pyridine from the reaction mixture to avoid the occurrence
of some pyridine coordinated impurities [19]. Complexes
4a–4d were then obtained upon column chromatographic
purification, followed by a second extraction procedure
with aqueous HCl in 53–73 % yield. The second extraction
was necessary to remove an unknown second carbene-
bearing complex which emerged during the chromato-
graphic purification (vide infra).
2
formylbenzylidene-j (C,O))(1,3-bis(2,4,6-trimethylphenyl)-
4
,5-dihydroimidazol-2-ylidene)ruthenium (5) [8]. The
study was conducted following two goals; first, the parent
compound 5 is not particularly soluble in nonpolar solvents
and upon introduction of long alkyl chains an increase of
solubility can be expected. Second, as it is known that the
initiation efficacy can be reduced by increasing the electron
density in related ester chelated benzylidene complexes
[19], a further reduction of the initiation efficacy of 5 might
be feasible [8].
Results and discussion
1
13
Aiming at the preparation of aldehyde-chelating benzyli-
dene complexes with different solubility in apolar media, a
series of differently substituted 2-vinyl-5-alkoxy-4-
methoxybenzaldehyde derivatives was envisaged. Carbene
precursors should feature a benzyloxy (3a), an n-butyloxy
The complexes were characterized by H and C NMR
spectroscopy, elemental analysis, and an exemplary single
crystal X-ray crystallographic structure determination of
1
4a. H NMR spectroscopy in CDCl as the solvent im-
mediately suggested cis-dichloro structures in all cases.
3
(
3b), an n-hexyloxy (3c), or an n-octyloxy group (3d) in
Distinct signals for all 4 aromatic mesityl protons and all 6
Scheme 1
1
23

On the chloride lability in electron-rich second-generation…
Scheme 2
˚
Table 1 Important bond lengths/A of complexes 4a and 5 [21]
mesityl methyl groups as well as a diastereotopic splitting
of the methylene group attached to the oxygen in position 5
were observed indicating a chiral ruthenium center as it is
4
a
5
Ru–C(1)
Ru–C(22)
Ru–O(1)
Ru–Cl(1)
Ru–Cl(2)
2.013(1)
1.830(1)
2.0583(9)
2.3877(3)
2.3654(3)
2.004(2)
present in cis-dichloro configured complexes of this type
1
4, 8, 9, 12]. Characteristic H NMR signals comprised the
1.827(2)
[
2.0487(16)
2.3600(6)
2.3548(6)
carbene’s proton at 18.59 ppm in case of 4a and 18.43–
1
9
4
8.44 ppm in case of 4b–4d, the aldehyde’s protons at
.59 ppm in case of 4a and 9.72–9.73 ppm in case of 4b–
1
d. Characteristic signals in the C{ H} NMR spectra
3
1
were observed at 283.7 ppm (4a) and 284.1 ppm (4b–4d)
and assigned to the carbene carbon. The aldehyde carbons
of all four complexes gave resonance at 213.95 ± 0.5 ppm
and all NHC-carbene carbons were observed at
2
04.15 ± 0.5 ppm. These data suggest that the substitution
at the oxygen in position 5 has only minor consequences
for the electronic properties of the atoms coordinated to the
ruthenium center. Furthermore, data make evident, that the
electron density in these derivatives is increased compared
1
to the not alkoxylated parent derivative 5 [8]. In 5, the H
NMR shifts for the carbene and the aldehyde are 18.86 and
1
0.03 ppm, the C{ H} NMR shifts for the carbene, the
3
1
1
aldehyde, and the NHC are 285.8, 213.4, and 206.4 ppm.
The suggested solution structure was also found in the solid
state when determining the single crystal X-ray structure of
crystals of complex 4a grown upon slow evaporation of
CH Cl solution of 4a. Compound 4a co-crystallizes with 1
2 2
Fig. 1 ORTEP plot of 4a CH Cl (displacement ellipsoids at 50 %
probability level, hydrogen omitted for clarity)
2
2
of 4a and 5 in aprotic solvents is generally worse than the
solubility of 4b–4d. As expected, 4d exhibits the best
solubility in nonpolar media and its good solubility in di-
equiv. of CH Cl in the centrosymmetric space group P1
2
2
and displays a distorted square pyramidal coordination
geometry of the ruthenium central atom with the two
chlorides in cis arrangement, the carbonyl oxygen O(1),
cyclopentadiene (DCPD) makes this compound
a
potentially attractive initiator for the bulk-polymerization
of this monomer (vide infra). All derivatives show an ap-
pealing solubility in methanol, which is surprising due to
the fact that methanol is often used as non-solvent in pu-
rification procedures of similar complexes [18, 22].
Initiators 4a–4d and 5 were tested in the polymerization
and the C(1) atom of the H IMes ligand forming the base.
2
The apex is formed by the carbene carbon atom C(1). The
˚
Ru–Cl bonds differ ca. 0.022 A in the solid state, with the
longer Cl(1)–Ru(1) distance found for the chlorine atom
trans to the NHC-ligand. Important structural features of
1
4a are listed in Table 1 and set into comparison with the
according values from the parent complex 5 [21]. Notice-
able are the higher bonding distances around ruthenium in
of monomer 6 (see Fig. 2) by following the reaction via H
NMR spectroscopy at room temperature. The polymeriza-
tion was generally slow and polymerization half-lifes were
determined to be 1 days 18 ± 1 h for initiators 4b–4d,
2 days 12 ± 1 h for initiator 5, and 7 days 6 ± 3 h for
initiator 4a. Because the propagating species is the same in
all cases, the different polymerization speeds can be
4a when compared to 5, which are a consequence of the
higher electron density in 4a (Fig. 1).
In a next step, the solubility of complexes 4a–4d and 5
was investigated. As can be seen in Table 2, the solubility
123

S. Strasser et al.
Table 2 Solubility of complexes 4a–4d and 5 determined at 25 °C
compound 5. This finding is in strong contrast to the results
obtained for similar ester-chelating complexes. In these
cases, electron-rich derivatives exhibited a lower initiation
efficacy [19]. The slow polymerization with 4a is readily
-
3
-3
(
low means \0.1 mg cm , fair means 0.1–0.5 mg cm , good
-3 -3
means 0.5–1 mg cm , high means [1 mg cm
)
4
a
4b
4c
4d
5
explained by the poor solubility of 4a in CDCl which is
3
Cyclohexane
Low
Low
Low
Fair
Low
Fair
Low
Fair
Fair
Low
Fair
similar to the solubility in CH Cl .
2
a
2
Dicyclopentadiene
Good
Fair
A similar trend for the initiation efficacy can be gained
when polymerizing 300 eqiv. monomer 6 with 1 eqiv. of
initiators under investigation in refluxing CH Cl
Et
2
O
Low
High
High
Low
High
High
Low
Good
High
CH
2
Cl
2
High
High
2
2
MeOH
Good
-3
(
cMonomer = 1 mol dm ). Reaction time was 48 h and
a
Determined at 33 °C
monomer 6 was completely consumed after that time in all
cases. The number-average molecular mass (M ) of the
n
resulting polymers, determined via size exclusion chro-
matography in THF relative to poly(styrene) standards, is
-
10,000 g mol in case of initiator 5 and in the range of
1
7
6
-
1
00,000–750,000 g mol
when using initiators 4a–4d.
The polydispersity index (PDI) was in all cases 2.0 ± 0.2.
For comparison, full initiation would release poly6 char-
-
acterized by a M of 45,000 g mol and a PDI of 1.07
1
n
[
23]. Switching to toluene as the solvent and polymerizing
at 80 °C no significant differences in the M values for
n
polymers prepared with all five initiators could be retrieved
-
1
(
M = 86,000 ± 6000 g mol ; PDI = 2.3 ± 0.2). Poly-
n
merizations were completed in less than 2 h under these
conditions. Further, initiators were tested in the polymer-
ization of neat DCPD. For this purpose, the polymerization
was monitored by simultaneous thermal analysis (STA)
[24]. An initiator loading of 40 ppm was investigated
Fig. 2 Time conversion plot of the polymerization of monomer 6
with initiators 4a–4d and 5 in CDCl at 20 °C under inert atmosphere
3
-3
-
1
2
of N ; cMonomer = 0.06 mol dm ; [Monomer]:[Initiator] = 10:1;
maintaining a heating rate of 3 °C min . Under these
conditions the heat evolvement of the polymerization
peaked at 90 ± 5 °C in case of initiators 4a–4d and
70 ± 5 °C in case of 5. Due to the concurring thermally
induced retro-Diels–Alder reaction of DCPD [24], a mass
loss occurred which amounts to 25 ± 5 % for tries initiated
exp. data shown as symbols; solid lines visual aids
deduced to a different initiation efficacy under the chosen
reaction conditions. The electron-rich derivatives 4b–4d
exhibited a higher initiation efficacy than the parent
Scheme 3
1
23

On the chloride lability in electron-rich second-generation…
with 4a–4d and to 10 ± 2 % when 5 is used as the ini-
tiator. Both results lead to the conclusion that the initiation
efficacy of the complexes is switched under these condi-
tions, i.e., 5 initiates faster than 4a–4d. The improved
solubility of 4d in DCPD did not translate into a better
performance under the studied conditions. Accordingly, the
initiators solubility in DCPD seems to be uncritical under
the tested conditions (generally, the solubility of the ini-
tiators in DCPD is an important factor for the performance
of the polymerization; see [25]).
Having established a principal activity profile of the new
initiators, we focused our attention on the carbene-bearing
by-products which were formed during the synthesis of 4a–
4
4
d. Exemplified by a closer discussion of the synthesis of
b, two side-products were observed. In the crude reaction
mixture two carbene-bearing complexes (approx. in 8:2
ratio) were present, which can be separated by column
chromatography. The main product was identified to be 4b,
while the identity of the by-product could not be fully
established. However, NMR data suggest the coordination
of a pyridine to the ruthenium center and a carbene-proton
Fig. 3 Time conversion plot of the polymerization of monomer 8
at 20 °C under inert
with initiator 4b in CDCl
atmosphere of N ; c
tor] = 70:1; exp. data shown as symbols; solid lines visual aids
3
and in methanol-d
4
-3
2
Monomer
= 0.13 mol dm ; [Monomer]:[Initia-
shift of 17.91 ppm (CDCl ) was observed. In analogy to
3
at 19.11 ppm. Diastereotopic splitting of the O–CH group,
2
prior work [19, 26], the compound is tentatively identified
as the cationic species 7a. A full characterization and
especially tries to crystallize 7a failed. A second carbene-
bearing by-product, not present in the crude reaction
mixture, was observed after column chromatography when
sampling the fraction containing 4b. This by-product oc-
curred in approx. 10 mol% and is characterized by a
resonance for the carbene-proton at 19.16 ppm and can be
easily removed by extracting a CH Cl solution of a mix-
but also of the mesityl signals, were indicative for a chiral
Ru-center consistent with the proposed structure 7c (see
Scheme 3). Removal of methanol-d
, drying in vacuum
allowed for
4
and acquisition of NMR spectra in CDCl
3
observing the same product mixture as present in unpuri-
fied 4b, indicating the reversibility of the process.
Performing the above described benchmark polymerization
of monomer 6 with unpurified 4b in the NMR tube led to a
similar time-conversion profile for the polymerization.
Additionally, the carbene region was monitored and a slow
vanishing of the carbene signal at 19.16 ppm in favor of
the formation of a novel aldehyde signal at 10.57 ppm was
found, suggesting that the cationic species 7b is sensitive
towards residual oxygen in the solution. To address the
question if 4b or 7b is the actual initiator, the course of the
polymerization of the methanol and chloroform-soluble
monomer 8 (resulting in the chloroform and methanol
soluble poly8) [28] was studied via NMR spectroscopy in
both solvents. Results are depicted in Fig. 3. The poly-
2
2
ture of 4b and 7b with aqueous HCl.
Therefore, we assume that during chromatography the
most labile halogen [27] is exchanged for another (un-
known) anion which either coordinates to the ruthenium
center or, more likely, is dissociated and the fifth coordi-
nation site of ruthenium is coordinated by a donor
molecule, e.g., methanol. To substantiate this hypothesis,
we dissolved purified and unpurified 4b (containing the
unknown impurity 7b) in methanol-d and recorded NMR
4
1
spectra of both solutions. The corresponding H NMR
spectra were identical, showing a single carbene-resonance
merization of 8 in CDCl at room temperature was slow
3
Scheme 4
123

S. Strasser et al.
(
half-life: approx. 6 days) and reached a conversion of
5 % after 19 days. In contrast, the polymerization in
molecular weights (M ) and polydispersity indices (PDI)
n
8
were determined by size exclusion chromatography (SEC)
using THF as solvent in the following arrangement: Merck
Hitachi L6000 pump, separation columns of Polymer
Standards Service, 8 9 300 mm STV 5 lm grade size
methanol-d was even slower and only 7 % conversion of 8
4
was found after 5 days and 12 h. After that time, methanol-
d was removed and the residue was dissolved in CDCl ,
4
3
6
4
3
˚
leading to an acceleration of the further course of the
reaction.
(10 , 10 , and 10 A), refractive index detector from Wyatt
Technology, model Optilab DSP interferometric refrac-
tometer. Polystyrene Standards purchased from Polymer
Standard Service were used for calibration. NMR spectra
were recorded on Bruker Avance 300 MHz or Varian
INOVA 500 MHz spectrometers. STA measurements were
performed with a Netzsch Simultaneous Thermal Analyzer
STA 449C (crucibles: aluminum from Netzsch) and was
The observed solvent effect can be either explained by a
competition of methanol-d with the monomer for the vacant
4
coordination site or, more likely, with the inactivity of the
cationic species 7c in olefin metathesis. As it is known, that
the actual active initiator is a trans-dichloro derivative
which is in equilibrium with its cis-dichloro isomer. The
latter features a pronounced lability of the chloride ligand
trans to the NHC-ligand [29] leading to the observed ca-
tionic species in polar medium. Accordingly, a concurring
reaction pathway is operating which shifts the equilibrium
apart from the formation of the trans-dichloro derivative
3
-1
operated with a helium flow rate of 50 cm min used in
-1
3
combination with a protective gas flow of 8 cm min
.
(SPY-5-31) Dichloro(4-benzyloxy-2-formyl-5-methoxybenz-
2
ylidene-j (C,O))(1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene)ruthenium
(
see Scheme 4). The lability of the chloride ligand and the
corresponding pre-equilibrium might also be the reason for
solvent effects previously observed in olefin metathesis [30].
In conclusion, we disclosed a family of electron-rich
aldehyde-chelating cis-dichloro configured benzylidene
complexes. Their electron-richness results in a pronounced
lability of the chloride in trans-position to the N-hetero-
cyclic carbene ligand. The resulting cationic complexes
exhibit a good solubility in the polar protic solvent
methanol. The formation of such cationic species is detri-
mental for catalyzing (or initiating) olefin metathesis
reactions as their existence lowers the relative concentra-
tion of the actual active pre-catalyst (or initiator) in
solution. The findings disclosed here might be of general
significance for any ruthenium-mediated olefin metathesis
transformation and constitute a further building-block for
explaining hitherto ununderstood solvent effects.
(4a, C37
H40Cl N O Ru)
2 2 3
Complex M31 (373.9 mg, 0.50 mmol) was dissolved in
Cl in a Schlenk flask and
2
3
5 cm dry degassed CH
2
3
161.0 mg 3a (0.60 mmol) dissolved in 2 cm CH
Cl
2
2
was added under inert atmosphere of nitrogen. The reaction
mixture was stirred at room temperature for 4 h, where-
upon its color turned from deep red to deep green. The
reaction mixture was transferred into a separation funnel
3
and two times extracted with 5 cm HCl (0.5 M) and
3
subsequently with 5 cm
collected, dried over Na
H
O. The organic phase was
2
SO , and the volume of the
4
2
3
solvent was reduced to about 1 cm . Upon precipitation
with n-pentane a green powder formed, which was
collected on a glass frit and dried in vacuo. Subsequent
purification by column chromatography (SiO
CH Cl /MeOH, 20:1–10:1, (v:v)) and sampling the spot at
R = 0.62 [CH Cl /MeOH, 10:1, (v:v)] gave the crude
, CH Cl and
2
2 2
2
2
f
2
2
3
product. This product was redissolved in 5 cm CH Cl
2
2
3
and two times extracted with 5 cm HCl (0.5 M) and
Experimental
3
subsequently with 5 cm H O. Removal of the solvent and
2
Umicore M31 was received from Umicore AG [23].
2
drying in vacuum gave pure 4a. Yield: 213.2 mg (62 %)
1
-Bromo-5-hydroxy-4-methoxybenzaldehyde (1), 2,4,6-
trivinylcyclotriboroxane-pyridine complex, and Pd(PPh ) ,
green microcrystals;
H NMR (300 MHz, CDCl ):
3
d = 18.59 (s, 1H, Ru = CH), 9.59 (s, 1H, CHO), 7.52 (s,
1H, bz), 7.50 (s, 1H, bz), 7.39–7.24 (m, 3H , 1H ), 7.20
3
4
bz
mes
were purchased from Aldrich and were used as received.
endo,exo-Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid
dimethyl ester (6) [31], endo,exo-bicyclo[2.2.1]hept-5-ene-
6
(bs, 1H, mes), 6.95 (s, 1H, ph ), 6.82 (bs, 1H, mes), 6.54 (s,
3
1H, ph ), 5.48 (bs, 1H, mes), 5.15 (m, 1H, CH
bz
2
), 5.07 (m,
), 2.70
mes
bz
2
2
,3-dicarboxylic acid bis[2-[2-(2-ethoxyethoxy)ethox-
1H, CH
), 4.28-3.43 (m, 4H, Im), 3.95 (s, 3H, OCH
3
mes
3
mes
), 2.45 (s, 6H, CH
3
y]ethyl] ester (8) [28], and (SPY-5-31)-dichloro(2-
2
formylbenzylidene-j (C,O))(1,3-bis(2,4,6-trimethylphe-
(s, 3H, CH
), 2.00 (s, 3H, CH ),
3
mes
3
mes
13
1
1.58 (s, 3H, CH
), 0.88 (s, 3H, CH ) ppm; C{ H}
3
nyl)-4,5-dihydroimidazol-2-ylidene)ruthenium (5) [8] were
prepared according to literature methods. Elemental ana-
lyses (C, H, N) were conducted on an Elementar vario EL
machine, and results were found to be in agreement
NMR (75 MHz, CDCl ): d = 283.7 (1C, Ru = CH), 213.9
3
5
(1C
, CNN), 204.1 (1C, CHO), 156.8 (1C
, ph ), 147.0
), 138.2, 137.9, 137.8,
, C ), 130.9, 130.1, 129.3, 128.4
q
q
q
4
mes-N
(1C
, ph ), 140.4, 139.9 (2C , C
q
q
mes
135.2, 135.4, 131.6 (6C
1
1
(
± 0.3 %) with the calculated values. The number-average
(4C, mes), 136.0 (1C , bz ), 130.8 (1C , ph ), 128.7, 128.1
q q
1
23

On the chloride lability in electron-rich second-generation…
2
,3,5,6
4
), 128.2 (1C, bz ), 121.8 (1C , ph ), 120.0
2
mes
3H, CH3 ), 1.83 (m, 2H, OCH CH (CH ) CH ), 1.52 (m,
2 2 2 3 3
(
4C, bz
q
bz
2
3
1C , ph ), 108.1 (1C , ph ), 70.5 (1C, CH ), 56.3 (1C,
6
(
2H, O(CH ) CH (CH ) CH ), 1.37 (m, 4H, O(CH ) (CH )
2 2 2 2 2 3 2 3 2 2-
q
q
3
OCH ), 53.6, 51.0 (2C, Im), 21.6, 20.7, 20.3, 18.5, 18.4,
mes
3
CH ), 1.06 (s, 3H, CH ), 0.93 (t, 3H, J = 6.7 Hz,
3 3 HH
mes
6.6 (6C, CH3 ) ppm.
13
1
1
O(CH ) CH ) ppm; C{ H} NMR (75 MHz, CDCl ):
2 5 3 3
d = 284.1 (1C, Ru = CH), 214.0 (1C , CNN), 204.1 (1C,
q
(
SPY-5-31) Dichloro(4-butyloxy-2-formyl-5-methoxybenz-
2
5
CHO), 156.6 (1C , ph ), 148.6 (1C , ph ), 140.4, 134.0 (2C ,
4
q
q
q
ylidene-j (C,O))(1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene)ruthenium
mes-N
C
C
), 138.4, 138.2, 137.8, 135.2, 135.7, 131.6 (6C ,
q
mes 1
), 130.9 (1C , ph ), 130.1, 129.8, 129.6, 128.5 (4C,
q
(4b, C H Cl N O Ru)
34 42 2 2 3
2
3
6
mes), 122.2 (1C , ph ), 118.3 (1C , ph ), 108.2 (1C , ph ),
q
q
q
Complex 4b was synthesized similarly to 4a using
50.0 mg M31 (0.33 mmol) and 90.1 mg 3b (0.38 mmol)
as the starting materials. Yield: 151.8 mg (65 %) green
69.7 (1C, OCH (CH ) CH ), 56.3 (1C, OCH ), 51.0 (2C,
2 2 4 3 3
2
Im), 31.7 (1C, OCH CH (CH ) CH ), 29.0 (1C, O(CH )
2 2-
2
2
2 3
3
CH (CH ) CH ), 25.9 (1C, O(CH ) CH CH CH ), 22.8
3
2
2 2
3
2 3
2
2
crystals; TLC: R = 0.45 (SiO , CH Cl /MeOH, 10:1,
f
2
2
2
(
1C, O(CH ) CH CH ), 21.5, 20.9, 20.3, 18.5, 18.4, 16.8
2 3
1
2 4
mes
6C, CH3 ), 14.2 (1C, O(CH ) CH ) ppm.
(
v:v)); H NMR (300 MHz, CDCl ): d = 18.43 (s, 1H,
3
(
2 5
3
Ru = CH), 9.72 (s, 1H, CHO), 7.29 (bs, 1H, mes), 7.18
6
bs, 1H, mes), 7.00 (s, 1H, ph ), 6.90 (bs, 1H, mes), 6.53 (s,
(
(SPY-5-31) Dichloro(2-formyl-5-methoxy-4-octyloxybenz-
2
ylidene-j (C,O))(1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene)ruthenium
3
H, ph ), 5.95 (bs, 1H, mes), 4.33–3.49 (m, 4H, Im), 4.01-
1
3
3
.78 (t, 2H, OCH (CH ) CH ), 3.93 (s, 3H, OCH ), 2.72 (s,
2
2 2
3
3
mes
mes
3
mes
H, CH3 ), 2.50 (s, 3H, CH ), 2.44 (s, 6H, CH3 ), 2.06
(4d, C H Cl N O Ru)
38 50
2 2 3
mes
s, 3H, CH3 ), 1.80 (m, 2H, OCH CH CH CH ), 1.52 (m,
(
Complex 4d was synthesized similarly to 4a using
250.0 mg M31 (0.33 mmol) and 100.9 mg 3d (0.38 mmol)
as the starting materials. Yield: 185.3 mg (73 %) green
microcrystals; TLC: R = 0.57 (SiO , CH Cl /MeOH,
2
2
2
mes
3
2
3
H, O(CH ) CH CH ), 1.05 (s, 3H, CH ), 0.99 (t, 3H,
2 2 2 3 3
13
1
C{ H} NMR
JHH = 7.4 Hz, O(CH ) CH ) ppm;
2 3
3
(
75 MHz, CDCl ): d = 284.1 (1C, Ru=CH), 213.9 (1C ,
3
q
f
2
2
2
5
CNN), 204.2 (1C, CHO), 156.5 (1C , ph ), 148.5 (1C ,
1
10:1, (v:v)); H NMR (300 MHz, CDCl ): d = 18.44 (s,
q
q
3
4
ph ), 140.3, 139.9 (2C , C
mes-N
), 138.24, 138.20, 137.8,
1H, Ru=CH), 9.73 (s, 1H, CHO), 7.29 (bs, 1H, mes), 7.19
6
(bs, 1H, mes), 7.02 (s, 1H, ph ), 6.91 (bs, 1H, mes), 6.56 (s,
3
1H, ph ), 5.98 (bs, 1H, mes), 4.31–3.49 (m, 4H, Im),
q
mes
35.6, 135.2, 131.6 (6C , C ), 130.9, 130.1, 129.5, 128.4
2
4C, mes), 130.8 (1C , ph ), 122.2 (1C , ph ), 118.3 (1C ,
1
q
1
(
q
6
q
q
3
ph ), 108.1 (1C , ph ), 69.4 (1C, OCH (CH ) CH ), 56.3
4.05–3.79 (t, 2H, OCH (CH ) CH ), 3.93 (s, 3H, OCH ),
3
q
2
2 2
3
2
2 4
3
mes
mes
(
1C, OCH ), 51.04, 50.97 (2C, Im), 31.1 (1C, OCH CH
3
2.73 (s, 3H, CH ), 2.52 (s, 3H, CH ), 2.43 (s, 6H,
3 3
2
2-
mes
mes
mes
CH CH ), 21.5, 20.8, 20.2, 18.5, 18.4, 16.8 (6C, CH ),
2
CH3 ), 2.08 (s, 3H, CH3 ), 1.83 (m, 2H, OCH CH (-
2 2
3
3
1
9.3 (1C, O(CH ) CH CH ), 14.1 (1C, O(CH ) CH ) ppm;
3
CH ) CH ), 1.50 (m, 2H, O(CH ) CH (CH ) CH ), 1.42-
2 5 3 2 2 2 2 4 3
mes
2
2
2
3
2 3
1
H NMR (300 MHz, CD OD): d = 19.11 (s, 1H, Ru=CH),
1.23 (m, 8H, O(CH ) (CH ) CH ), 1.06 (s, 3H, CH ),
2 3 2 4 3 3
3
6
.96 (s, 1H, CHO), 7.66 (s, 1H, ph ), 7.14 (s, 2H, mes),
3
13
1
9
0.90 (t, 3H, J = 6.6 Hz, O(CH ) CH ) ppm; C{ H}
HH 2 5 3
3
.96 (s, 1H, ph ), 6.67 (s, 2H, mes), 4.29 (m, 1H,
6
NMR (75 MHz, CDCl ): d = 284.1 (1C, Ru = CH), 214.0
3
5
(1C , CNN), 204.1 (1C, CHO), 156.6 (1C , ph ), 148.6
OCH (CH ) CH ), 4.19 (m, 1H, OCH (CH ) CH ), 4.08
2
2 2
3
2
2 2
3
mes
q
q
4
(1C , ph ), 140.4, 139.9 (2C , C
mes-N
(
(
s, 3H, OCH ), 3.84 (s, 4H, Im), 2.42 (s, 6H, CH ), 2.30
3
mes
), 138.4, 138.2, 137.8,
3
q
q
mes
mes
s, 6H, CH3 ), 1.94 (s, 6H, CH3 ), 1.91 (m, 2H,
1
135.2, 135.7, 131.6 (6C , C ), 131.0 (1C , ph ), 130.1,
q
q
2
OCH CH CH CH ), 1.60 (m, 2H, O(CH ) CH CH ),
2
129.8, 129.6, 128.5 (4C, mes), 122.2 (1C , ph ), 118.3
q
2
2
3
2 2
2
3
3
.05 (t, 3H, J = 7.4 Hz, O(CH ) CH ) ppm.
3
6
1
(1C , ph ), 108.2 (1C , ph ), 69.7 (1C, OCH (CH ) CH ),
q q 2 2 6 3
HH
2 3
3
5
6.3 (1C, OCH ), 51.0 (2C, Im), 32.0 (1C, OCH CH (-
3 2 2
(
SPY-5-31) Dichloro(2-formyl-4-hexyloxy-5-methoxybenz-
2
CH ) CH ), 29.5 (1C, O(CH ) CH (CH ) CH ), 29.4 (1C,
3
2 5
3
2 2
2
2 4
ylidene-j (C,O))(1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene)ruthenium
O(CH ) CH (CH ) CH ), 29.1 (1C, O(CH ) CH (CH )
2 2-
2
3
2
2 3
3
2 4
2
CH3), 26.2 (1C, O(CH ) CH CH CH ), 22.8 (1C,
2 5
2
2
3
(4c, C H Cl N O Ru)
36 46 2 2 3
O(CH ) CH CH ), 21.5, 20.9, 20.3, 18.5, 18.4, 16.8 (6C,
2
mes
CH3 ), 14.2 (1C, O(CH ) CH ) ppm.
6
2
3
Complex 4c was synthesized similarly to 4a using
50.1 mg M31 (0.33 mmol) and 100.9 mg 3c (0.38 mmol)
as the starting materials. Yield: 128.2 mg (53 %) green
2 7
3
2
2
Chloro(4-butyloxy-2-formyl-5-methoxybenzylidene-j -
(C,O))(pyridine)(1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydroimidazol-2-ylidene)ruthenium chloride
(7a, C H Cl N O Ru)
microcrystals; TLC: R = 0.55 (SiO , CH Cl /MeOH, 10:1,
f
2
2
2
1
(
v:v)); H NMR (300 MHz, CDCl ): d = 18.44 (s, 1H,
3
Ru=CH), 9.72 (s, 1H, CHO), 7.29 (bs, 1H, mes), 7.19 (bs,
6
H, mes), 7.01 (s, 1H, ph ), 6.91 (bs, 1H, mes), 6.56 (s, 1H,
3
9
47
2 3 3
1
Complex 7a was obtained during the purification of 4b via
column chromatography sampling the spot at R = 0.10
3
ph ), 5.97 (bs, 1H, mes), 4.31–3.50 (m, 4H, Im), 4.03–3.79 (t,
H, OCH (CH ) CH ), 3.93 (s, 3H, OCH ), 2.74 (s, 3H,
f
2
(CH Cl /MeOH, 10:1, (v:v)). Yield: 38.0 mg (16 %) deep
2
2
2 4
3
3
2
mes
CH3 ), 2.52 (s, 3H, CH3 ), 2.43 (s, 6H, CH3 ), 2.08 (s,
mes
mes
1
green microcrystals;
H NMR (300 MHz, CDCl3):
123

S. Strasser et al.
d = 17.80 (s, 1H, Ru=CH), 9.93 (s, 1H, CHO), 8.59 (d, 2H,
JHH = 5.0 Hz, py ), 7.76 (t, 1H, J = 7.0 Hz, py ),
ROMP experiments
4
2,6
3
4
HH
6
3
.60 (s, 1H, ph ), 7.47 (s, 1H, ph ), 7.33 (dd, 2H,
7
3
Monomer 6 (0.48 mmol, 300 eqiv.) was dissolved in the
respective solvent (CH Cl or toluene, under exclusion of
3,5
JHH = 5.9 Hz, py ), 6.96 (s, 2H, mes), 6.44 (s, 2H,
mes), 4.23 (m, 1H, OCH (CH ) CH ), 4.11 (m, 1H,
2
2
-
3
air) to obtain a solution with c = 0.1 mol dm , which
was heated to the desired reaction temperature (40 or 80 °C
oil bath temperature). The respective initiator (4a–4d or 5,
0.0015 mmol, 1 eqiv.) was added using a stock solution
2
2 2
3
OCH (CH ) CH ), 4.08 (s, 3H, OCH ), 3.96 (bs, 4H,
2
2 2
3
3
mes
mes
Im), 2.66 (s, 6H, CH3 ), 2.13 (s, 6H, CH3 ), 1.88 (m, 2H,
mes
OCH CH CH CH ), 1.64 (s, 6H, CH ), 1.53 (m, 2H,
2
2
2
3
3
3
O(CH ) CH CH ), 0.99 (t, 3H, J = 7.3 Hz, O(CH2)3-
-3
(4 mg cm ) in the according solvent. The polymerization
2
2
2
3
HH
CH ) ppm.
3
was monitored via thin layer chromatography and quen-
ched upon addition of excess ethyl vinyl ether (approx.
3
0.1 cm ) after the spot for the monomer was not detected
X-ray structure determination
X-ray data of 4aÁCH Cl were collected on a Bruker Kappa
anymore. The volume of the reaction mixture was reduced
3
to approx. 1.5 cm . The polymer was obtained upon pre-
2
2
8
APEX-2 CCD diffractometer using graphite-monochro-
cipitation in vigorously stirred methanol and drying in
vacuo. NMR spectroscopic data of the polymers are iden-
tical to those published previously [34, 35].
Polymerizations of monomers 6 and 8 in NMR tubes were
carried out at 20 °C similarly using either CDCl3 or
methanol-d4 as the solvents. Monomer 6 (10 eqiv.;
˚
mated Mo-Ka radiation (k = 0.71073 A) and 0.5° u- and
x-scan frames. Corrections for absorption and k/2 effects
were applied [32]. After structure solution with program
2
SHELXS97 and direct methods, refinement on F was
carried out with program SHELXL97 [33]. All non-hy-
drogen atoms were refined anisotropically. H atoms were
placed in calculated positions and thereafter treated as
riding. Crystallographic data are: 4ÁCH Cl , C H Cl N
-
3
c = 0.06 mol dm ) was polymerized with initiators 4a–
4d and (1 eqiv.). Monomer (70 eqiv.;
5
c = 0.13 mol dm ) was polymerized with 4b (1 eqiv.).
8
-
3
2
2
32 39
2 3-
ORuÁCH Cl ,
M = 817.61,
green
prism,
2
2
r
0
.35 9 0.26 9 0.13 mm, triclinic, space group P-1 (no. 2),
Simultaneous thermal analysis
˚
a = 8.0798(4) A, b = 14.5694(6) A, c = 16.5689(7) A,
˚
˚
a = 72.937(2)°,
V = 1845.97(14)
b = 81.987(2)°,
l = 0.753 mm
dx = 1.471 g cm , T = 100 K. 65819 reflections col-
c = 86.486(2)°,
A stock solution of the respective initiator in CH Cl was
2
2
3
˚
A ,
-1
Z = 2,
,
prepared so that the desired initiator amount (40 ppm) is
-
3
3
3
reached upon adding 0.06 cm of the solution to 1 cm of
molten DCPD at approx. 35 °C. Both liquids were mixed
and a weighed portion of the formulation was transferred to
an open crucible which was placed in the STA-machine. A
lected (hmax = 26.0°) and merged to 7228 independent
data (Rint = 0.0274); final
R
indices (all data):
R = 0.0218, wR = 0.0541, 440 parameters. CCDC
1
2
-
1
1
054954 contains the supplementary crystallographic data
heating run (heating ramp of 3 °C min ) was commenced
starting at 20 °C.
for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments Financial support by the European Community
(
grant no. CP-FP 211468-2 EUMET) is gratefully acknowledged. E.P.
is thankful for having received the ‘‘Chemical Monthly’’ stipend
013.
Testing of the solubility
2
3
After dissolving 1 mg of the respective compound in 5 cm
CH Cl , removal of the solvent under N stream, stirring,
2
2
2
3
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