Widening the latency gap in chelated ruthenium olefin metathesis catalysts

Article abstract of DOI:10.1021/om200323c

The synthesis of novel sulfur-chelated ruthenium benzylidenes afforded latent catalysts with a wider range of activities and new isomeric forms. A ruthenium complex with a tridentate ligand displayed latency for even one of the most reactive ROMP monomers

Full text of DOI:10.1021/om200323c

ARTICLE
pubs.acs.org/Organometallics
Widening the Latency Gap in Chelated Ruthenium Olefin Metathesis
Catalysts
Yakov Ginzburg,† Aviel Anaby,† Yuval Vidavsky,† Charles E. Diesendruck,† Amos Ben-Asuly,†,‡
Israel Goldberg,§ and N. Gabriel Lemcoff*,†
†Chemistry Department, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
‡Achva Academic College, Shikmim 79800, Israel
§School of Chemistry, Tel-Aviv University, Tel-Aviv 69978, Israel
S Supporting Information
b
ABSTRACT: The synthesis of novel sulfur-chelated ruthenium
benzylidenes afforded latent catalysts with a wider range of
activities and new isomeric forms. A ruthenium complex with a
tridentate ligand displayed latency for even one of the most
reactive ROMP monomers, dicyclopentadiene, while a room
temperature latent trifluoromethyl-substituted thioether deri-
vative was shown to be the most active sulfur-chelated pre-
catalyst to date in several metathesis reactions at higher
temperatures. These new complexes widen the spectrum of
activity for this family of catalysts, enabling several practical applications and enhancing the understanding for the mechanisms of
activation in strongly chelated ruthenium alkylidenes.
’ INTRODUCTION
at room temperature, and in many cases the nature of the active
species and the mechanism of activation are not fully understood.
Complexes 18f and 68h are the only physically activated precatalysts
reported to be fully inert at room temperature to a series of ROMP
monomers such as substituted norbornenes and cyclooctenes.
However, prolonged exposure to norbornene and, more impor-
tantly, dicyclopentadiene (DCPD), produces polymers even at
room temperature.11 An additional issue with physically activated
initiators is that normally only a small fraction of the precatalysts
become active,12 contributing to an overall lower effectiveness of the
system.
Olefin metathesis1 in the past decade has advanced several
synthetic applications, particularly in the synthesis of special
polymers by ring-opening metathesis polymerization (ROMP) of
strained rings2 and in the preparation of drugs, where ring-closing
metathesis (RCM) is useful in the formation of ubiquitous
macrocycles.3 This recent success is mostly a consequence of the
remarkable development of well-defined carbene catalysts based
on molybdenum4 and ruthenium.5 Nonetheless, several technical
problems arise when mixing commercial catalysts with very
reactive ROMP monomers.6 For instance, high reaction rates
impede introduction of homogeneous solutions into the desired
mold.7 Thus, several latent olefin metathesis precatalysts were
developed.8,9 When is a catalyst latent? Catalytic latency may be
defined as the property of a precatalyst presenting negligible activity
at a given temperature (usually room temperature) and significant
reaction progress when suitable stimuli are applied. Naturally,
several parameters influence the “latency” of a catalyst in a specific
reaction, such as substrate and solvent. Activating methods may be
divided into two subcategories: chemical9 and physical.8 The first
case usually presents excellent interconversion between inactive
and active forms, but an extra chemical needs to be added to the
final product, which may be undesirable in some cases. With regard
to the latter, the introduction of foreign products is not necessary,
and several recent examples have shown numerous effective ways
to activate latent catalysts, such as heat,8bꢀg light,8h,10 and even
ultrasound.8a
In this work we present further development of sulfur-chelated
precatalysts geared to address two problems: on one hand to
make a precatalyst latent to DCPD and on the other hand to
enhance the activity of the active form of the dormant catalyst.
’ RESULTS AND DISCUSSION
We have shown in previous work that sulfur-chelated ruthe-
nium catalysts are latent to several substrates in RCM, cross-
metathesis (CM), and ROMP reactions, showing reasonable
rates upon heating8f or irradiating with UV light.13 However,
DCPD and unsubstituted norbornene are highly active sub-
strates, and their polymerization occurs at room temperature
with all known sulfur-chelated complexes. Due to the significance
of the high-performance materials derived from these monomers,
Even though many latent olefin metathesis catalysts have been
studied, the vast majority are not completely inert to most substrates
Received: April 16, 2011
Published: May 27, 2011
r
2011 American Chemical Society
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Figure 1. Latent ruthenium olefin metathesis catalysts.6,7
Scheme 1. Preparation of Olefin Metathesis Precatalysts 14a
a Conditions: (a) mercaptoethanol, K2CO3, DMF, 60 °C; (b) CH3PPh3I, KOtBu, ether; (c) CH3I, NaH, THF at room temperature; (d)
(SIMes)(PCy3)(Cl)2RudCHPh, CuCl, CH2Cl2, room temperature.
ways to increase the latency of S-chelated Ru benzylidenes were
explored.
Three-Point Chelates. Thus, with the intent to form an 18e
precatalyst, a tridentate styrene ligand with both sulfide and ether
functionalities was designed (Scheme 1).
Mercaptoethanol was reacted with 2-fluorobenzaldehyde
(10) in the presence of K2CO3 by nucleophilic aromatic
substitution using the same conditions previously developed
by us.8f Wittig olefination of 11 followed by methylation of the
hydroxyl group gave the desired styrene ligand precursor (13).
Commercially available second-generation Grubbs catalyst was
reacted with 13 in the presence of CuCl to give new complex
14. As expected, and according to the 1H NMR analysis, 14 was
assigned a cis-dichloro geometry.8f Unfortunately, structural
Figure 2. X-ray structure of complex 14.
analysis by X-ray diffraction revealed that only the sulfur atom
was bound to the metal (Figure 2), similar to a previous study
by Grubbs et al.14 The insignificant deviation of the OꢀCH3
13C NMR signal in the spectra of free ligand 13 and complex 14
(∼0.1 ppm) also supports the suggestion that there are no
significant RuꢀO interactions in solution. The strong trans
influence of the benzylidene ligand likely destabilizes the
coordination of the oxygen atom at this position.15
In order to enhance the binding of the additional chelating
atom, an analogous ligand with an extra sulfur atom (instead of
oxygen) was proposed. Thus, methylation of 1,2-ethanedithiol to
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Scheme 2. Preparation of Olefin Metathesis Precatalyst 19a
a Conditions: (a) CH3I, NaH, DMF at room temperature; (b) 10, DMF, 60 °C; (c) CH3PPh3I, KOtBu, ether; (d) (SIMes)(PCy3)(Cl)2RudCHPh,
CuCl, CH2Cl2, room temperature.
Table 1. DCPD Conversion at Various Temperatures in the
Presence of 19
entrya temp (°C) conversion after 1 h (%) conversion after 3 h (%)
1
2
3
4
5
20
40
<1
<1
20
36
36
<1
8
60
44
46
37
80
110
a Conditions: 0.1 mol % 19.; substrate 0.45 M, in chlorobenzene.
Conversion determined by GC-MS using mesitylene as internal
standard.
Figure 3. X-ray structure of complex 19.
observed (Table 1). At very high temperatures (Table 1, entry 5),
decomposition becomes significant and conversion decreases.
This type of behavior has been recently observed by Schanz et al.
with a Ru vinylvinylidene complex.18
In addition, RCM of diethyldiallylmalonate (DEDAM) with
catalysts 14 and 19 was also conducted. As expected no reaction
was observed at 25 °C, and both displayed negligible activity also
upon heating to 80 °C (<1% for both complexes after 24 h).
UV irradiation did not improve RCM conversions either. These
results indicate that both initiators are active only toward ROMP
reactions. Thus, the goal of reducing the activity of S-chelated
ruthenium benzylidenes toward DCPD was achieved by the
addition of an additional chelating sulfur atom.
Faster Latent Precatalyst. We have recently advocated that
cis-dichloro S-chelated olefin metathesis complexes are inactive
and reactions occur only through their trans counterparts.13
These precatalysts open an interesting possibility, where active
(trans) forms may be modified to enhance activity without
modifying the latent status of the cis forms.19
For example, we have shown that a 4-nitro substitution in the
benzylidene ring does not influence the latency of complex 1,
while in the latent trans N-chelated complex 20 the effect is very
significant,16b as demonstrated by Grela et al. previously for
oxygen-chelated complexes (Figure 4).20 Thus, we decided to
design a highly active sulfur-chelated trans dichloro olefin
metathesis catalyst, while keeping the cis isomer latent. We
envisioned that the replacement of methyl with a trifluoromethyl
group on the sulfur would significantly weaken the RuꢀS bond in
23 and make it a more active catalyst.
afford thioether 16 was followed by nucleophilic aromatic
substitution of 2-fluorobenzaldehyde. A Wittig olefination reac-
tion completed the synthesis of styrene 18 in good yields. The
novel three-point-chelated ruthenium-based complex 19 was
prepared by mixing the ligand precursor with second-generation
Grubbs catalyst in the presence of CuCl.
In contrast to previous results where both cis and trans isomers
could be obtained,8f,16 only one product was observed in this
case. The 1H NMR spectrum of the product disclosed the typical
asymmetric structure observed for cis-dichloro arrangements. In
this case the 13C NMR SꢀCH3 signal shifted from 15.4 ppm in
18 to 40.6 ppm in 19, indicative of sulfur binding to ruthenium.
Unexpectedly, the X-ray diffraction analysis showed a chloride
atom trans to the benzylidene moiety. This type of cis-dichloro
configuration has not been observed to date in ruthenium
alkylidenes and possesses a uniquely long ClꢀRu bond of
2.586(1) Å coerced by the trans influence of the benzylidene
ligand (Figure 3). The other ClꢀRu bond in 19 is of normal
length, 2.419(1) Å. For comparison, the RuꢀCl distances
observed in other compounds that contain a cis-dichloro-ruthe-
nium moiety, with the metal being coordinated in a
(pseudo)octahedral environment to two additional C-ligands
and two S-ligands, are 2.456, 2.393ꢀ2.408, 2.412ꢀ2.435,
2.432ꢀ2.449, and 2.418ꢀ2.432 Å.17
New complexes 14 and 19 were tested with respect to their
temperature dependency of ROMP and RCM activity. As
expected, the sulfurꢀoxygen complex 14 initiated ROMP of a
DCPD solution at room temperature, converting 40% of the
monomer after 2 h. In comparison, an insoluble gel was formed
after 15 min when the reaction was performed at 80 °C. Most
gratifyingly, the sulfurꢀsulfur chelated complex 19 showed less
than 1% monomer conversion after two hours at 20 °C, whereas
increased conversion by raising the temperature could be clearly
Thus, using an optimized version of the Suzuki coupling
previously reported by us,22 commercially available 21 was reacted
with vinyl boronic acid ester, giving styrene 22. Reaction with
(SIMes)py2(Cl)2RudCHPh21 gave a new complex, 23, as a single
isomer. Complex 23 was studied in solution by 1H NMR, showing
the expected spectrum observed for cis isomers. Single-crystal X-ray
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Figure 4. Effects of electron-withdrawing groups on latency of cis- versus trans-dichloro ruthenium benzylidenes.
Scheme 3. Preparation of Complex 23a
Table 2. Comparative Olefin Metathesis Activity of 23 and 1
a Conditions: (a) vinyl boronic acid, di(n-butyl)ester, PdCl2, S-Phos,
THF, NaOH, 80 °C; (b) (SIMes)py2(Cl)2RudCHPh,19 CH2Cl2,
45 °C.
a Conditions: 0.5 M substrate in toluene, 1 h at 80 °C. b Includes 12%
c
isomerization products. No reaction also after 24 h. d Polymerization
Figure 5. X-ray structure of complex 23 (only one of three crystal-
lographically independent molecular units is shown).
was also observed. e 0.15 M substrate in toluene. f Includes 30%
isomerization products.
diffraction analysis supported the proposed structure (Figure 5).
Whendissolvedinbenzene andirradiated, peaksofthecorrespond-
ing trans isomer could be observed in the H NMR spectrum,
demonstrating that a significant quantity of a viable active species
may be obtained.
1
Table 3. Comparative Activity of 23 and 1 at Room
Temperature
entrya
irradiationb
catalyst
conversion (%)c
To test the latency of novel precatalyst 23, it was added to a
solution of DEDAM in CH2Cl2 and stirred at 27 °C in the dark.
After 24 h, less than 1% conversion was observed. After 1 week,
only 1.5% product could be found, indicating that the precatalyst
displays good latency at room temperature for this substrate.
Table 2 summarizes the results of RCM and CM reactions of
the two complexes in hot toluene (the low polarity of toluene
compared to CH2Cl2 stabilizes the trans isomer, increasing the
relative amount of the active species in solution).8c,16a In order to
evaluate the activity of the active form, all metathesis reactions
were concurrently carried out with both 23 and 1.
1
2
3
4
dark
1
<1
<1d
<1
86
23
1
350 nm
23
a Conditions: 0.1 M DEDAM with 0.5 mol % precatalyst in CH2Cl2 for 2
h at room temperature. b Irradiation in a Rayonet apparatus. The “dark”
samples were covered with aluminum foil and set inside the Rayonet
apparatus for both irradiated and dark samples to be at the same
temperature/stirring rate. c Determined by GC-MS. d Conversion after
1 week was less than 2%.
Even though latent complex 1 reaches full conversion given
enough time, it is very slow even at high temperatures. CF3-
substituted complex 23 displayed improved rates, decreasing the
reaction time to full conversion from days to a few hours.
In contrast to complex 1, the active form of new complex 23 is
very active and difficult to isolate, probably indicating that trans-23
readily undergoes decomposition reactions.8h Supporting this
assumption, ruthenium hydrides (typical ruthenium decomposition
products) have been shown to be effective in double-bond
isomerization,23 and this may explain the high quantity of isomer-
ized products observed in entries 6 and 3, Table 2.
Asinthecaseofcomplex1, photoactivation of complex 23 was also
determined.13 Table 3 shows RCM activity under UV irradiation.
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Figure 6. Benzylidene area in 1H NMR of complex 23: (a) no irradiation; (b) 20 min irradiation; (c) 100 min irradiation; (d) 200 min irradiation.
Table 4. Comparative ROMP Activity of 23 and 1
entrya
irradiationb
temp (°C)
reaction time (h)
conversion with 1 (%)c
conversion with 23 (%)c
1
2
3
none
∼35
80
24
1.5
1
<1
32
<1
<1
91
94
none
350 nm
∼35
a Conditions: 0.5 M cyclooctene with 0.3 mol % precatalyst in 1,2-dichloroethane. b Irradiation in a Rayonet apparatus. c Determined by GC-MS using
mesitylene as internal standard.
In order to verify that the trans isomer is truly the active
species, a solution of 23 in C6D6 was irradiated with UV light
(350 nm), and a 4:3 trans/cis mixture was obtained (Figure 6).
To this mixture was added hexane to selectively precipitate the cis
isomer, followed by filtration to remove it from the mixture. The
green solid residue after solvent evaporation was redissolved in
C6D6 and analyzed by 1H NMR, effectively showing that mainly
the trans isomer was obtained (see the Supporting Information).
DEDAM was added to this solution in the glovebox, and the
reaction was followed at 25 °C. After 35 min, 15% conversion was
observed, which increased to 62% in 15 h.
chelated ruthenium catalysts, a trifluoromethyl group was at-
tached to the chelating sulfur atom. Indeed, catalyst 23 in its
active form was found to be much more active than its sulfur-
chelated predecessors.8g
Expanding the window of reactivity in dormant precatalysts,
on one hand making the resting species less active toward the
most reactive substrates and, on the other, improving the active
state, advances our understanding of the mechanism of latent
catalysis and may result in important practical applications.
’ EXPERIMENTAL SECTION
Finally, the activity of complex 23 for ROMP was also tested.
cis-Cyclooctene was chosen as a model substrate (Table 4).
As shown in Table 4, complex 23 demonstrated a significantly
higher activity than 1 also for ROMP reactions.
General Procedures. All reagents were of reagent grade quality,
purchased commercially from Sigma-Aldrich, Alfa-Aesar, or Fluka, and
used without further purification. All solvents were dried and distilled
prior to use. Purification by column chromatography was performed on
Davisil chromatographic silica media (40ꢀ60 μm). TLC analyses were
performed using Merck precoated silica gel (0.2 mm) aluminum
’ CONCLUSIONS
Three new sulfur-chelated ruthenium benzylidenes are pre-
sented. These complexes were designed to improve two short-
comings of most latent olefin metathesis catalysts: the lack of true
latency toward reactive ROMP monomers and the slow kinetics
of the dormant catalysts when activated. To address the first
issue, the addition of a second sulfur-chelating atom resulted in a
complex (19) that displayed high latency at room temperature
for dicyclopentadiene ROMP. Moreover, this new complex
showed a novel cis-dichloro geometry with an unusually long
RuꢀCl bond. The use of an additional oxygen-chelating atom
instead of sulfur (complex 14) resulted in a bidentate chelate
that did not display enhanced latency, supporting the theory that
tridentate chelation is necessary. Seemingly, a strong trans
influence from the benzylidene ligand disfavors oxygen coordi-
nation in this case. In order to enhance the activity of sulfur-
[backed] sheets. NMR spectra were recorded on Bruker DPX200
,
DPX400, or DMX500 instruments; chemical shifts, given in ppm, are
relative to Me4Si as the internal standard or to the residual solvent peak.
HR-MS data were obtained using a Thermoscientific LTQU XL Orbi-
trap HRMS equipped with APCI (atmospheric-pressure chemical
ionization). Gas chromatography data were obtained using an Agilent
6850 GC equipped with an Agilent 5973 MSD working under standard
conditions and an Agilent HP5-MS column. Purification on preparative
HPLC was carried out on a Jasco instrument equipped with an MD-1515
photodiode array detector and a Phenomenex normal phase Luna 10 μm
column (250 ꢁ 21.2 mm) working at a 20 mL/min flow.
2-(2-Hydroxyethylthio)benzaldehyde (11). 2-Mercaptoetha-
nol (1.2 mL, 16.6 mmol) was added to K2CO3 (2.45 g, 7.8 mmol) in
10 mL of DMF. 2-Fluorobenzaldehyde (2.0 g, 16.1 mmol) was added,
and the mixture was stirred overnight at 60 °C. After cooling, the mixture
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was poured into 20 mL of saturated NaHCO3 and extracted with ether
(3 ꢁ 25 mL). The extracts were washed with water and dried over
MgSO4, and the solvent was removed under reduced pressure. The
crude product was purified by chromatography on silica gel (petroleum
etherꢀethyl acetate gradient from 10:1 to 4:1) to yield 11 as a colorless
oil (90%). 1H NMR (200 MHz, CDCl3, ppm): δ 2.06 (bs, 1H), 3.17 (t,
J = 6.1 Hz, 2H), 3.83 (t, J = 6.1 Hz, 2H), 7.29ꢀ7.37 (m, 2H), 7.45ꢀ7.57
(m, 1H), 7.55ꢀ7.51 (m, 2H), 7.83 (d, J = 7.6 Hz, 1H). 13C NMR (125
MHz, CDCl3, ppm): δ 36.1, 60.3, 125.8, 128.7, 132.2, 134.0, 134.2,
140.4, 191.6. C9H10O2S GC-MS (EI): m/z 182.00 (Mþ), calcd 182.04.
2-(2-Vinylphenylthio)ethanol (12). Methyl triphenylphospho-
nium iodide (8.6 g, 21.3 mmol) was dissolved in 25 mL of ether before
KOtBu (2.6 g, 23.2 mmol) was added in one portion at 0 °C. After
stirring for 10 min at room temperature, 11 (2.75 g, 15.1 mmol) was
added in one portion at 0 °C, and the reaction stirred at room
temperature until complete disappearance of the reactants (2ꢀ3 h).
The mixture was poured into 50 mL of saturated NaHCO3 and extracted
with ether (3 ꢁ 50 mL). The extract was dried over MgSO4, and the
solvent removed under reduced pressure. The crude product was further
purified by chromatography on silica gel (petroleum etherꢀethyl acetate
gradient from 10:1 to 4:1) to yield 12 as a colorless oil (82%). 1H NMR
(400 MHz, CDCl3, ppm): δ 2.25 (s, 1H), 3.03 (t, J = 6.0 Hz, 2H), 3.67
(s, 2H), 5.36 (dd, J = 11.0, 1.2 Hz, 1H), 5.70 (dd, J = 17.4, 1.2 Hz, 1H),
7.28ꢀ7.19 (m, 2H), 7.30 (dd, J = 17.4, 11.0 Hz, 1H), 7.46ꢀ7.42
(m, 1H), 7.55ꢀ7.51 (m, 1H). 13C NMR (100 MHz, CDCl3, ppm): δ
37.7, 60.2, 116.2, 126.3, 127.5, 128.1, 132.0, 132.8, 134.6, 139.5.
C10H12OS GC-MS (EI): m/z 180.06 (Mþ), calcd 180.06.
(2-Methoxyethyl)(2-vinylphenyl)sulfane (13). NaH (115
mg, 4.8 mmol) was added in one portion to 12 (433 mg, 2.40 mmol)
in DMF and stirred for 10 min. CH3I (450 μL, 7.2 mmol) was then
added dropwise, and the mixture stirred overnight at room temperature.
The mixture was poured into 20 mL of saturated NaHCO3 and extracted
with ether (3 ꢁ 25 mL). The extracts were washed with water and dried
over MgSO4, and the solvent was removed under reduced pressure. The
crude product was purified by chromatography on silica gel (petroleum
etherꢀethyl acetate gradient from 10:1 to 4:1) to yield as a colorless oil
(50%). 1H NMR (400 MHz, CDCl3, ppm): δ 3.04 (t, J = 6.7 Hz, 2H),
3.34 (s, 3H), 3.53 (t, J = 6.7 Hz, 2H), 5.34 (dd, J = 11.0, 1.3 Hz, 1H), 5.69
(dd, J = 17.4, 1.3 Hz, 1H), 7.24ꢀ7.20 (m, 2H), 7.28 (dd, J = 17.4, 11.3
Hz, 1H), 7.44ꢀ7.40 (m, 1H), 7.54ꢀ7.50 (m, 1H). 13C NMR (100 MHz,
CDCl3, ppm): δ 33.8, 58.7, 70.9, 115.9, 126.1, 127.1, 128.1, 131.2, 133.9,
134.8, 139.2. C11H14OS GC-MS (EI): m/z 194.10 (Mþ), calcd. 194.08.
2-(2-(Methylthio)ethylthio)benzaldehyde (17). Ethane-
dithiol (0.84 mL, 1.25 mmol) was added to K2CO3 (3.00 g, 21 mmol)
in 10 mL of DMF. CH3I (0.69 mL, 1.35 mmol) was then added
dropwise, and the mixture stirred overnight at room temperature.
2-Fluorobenzaldehyde (2.0 g, 16.1 mmol) was added, and the mixture
was stirred overnight at 60 °C. After cooling, the mixture was poured
into 20 mL of saturated NaHCO3 and extracted with ether (3 ꢁ 25 mL).
The extracts were washed with water and dried over MgSO4, and the
solvent was removed under reduced pressure. The crude product was
purified by chromatography on silica gel (petroleum etherꢀethyl acetate
gradient from 10:1 to 4:1) to yield 17 as a colorless oil (60%). 1H NMR
(400 MHz, CDCl3, ppm): δ 2.15 (s, 3H), 2.79ꢀ2.72 (m, 2H),
3.21ꢀ3.13 (m, 2H), 7.34 (t, J = 7.2, 7.2 Hz, 1H), 7.44 (d, J = 7.9 Hz,
1H), 7.53 (dt, J = 8.0, 7.9, 1.6 Hz, 1H), 7.85 (dd, J = 7.7, 1.2 Hz, 1H),
10.40 (s, 1H). 13C NMR (100 MHz, CDCl3, ppm): δ 15.6, 32.9, 33.0,
125.9, 128.7, 131.9, 134.0, 134.4, 140.4, 191.4. C10H12OS2 GC-MS (EI):
m/z 212.00 (Mþ), calcd 212.03.
temperature until complete disappearance of the reactants (2ꢀ3 h). The
mixture was poured into 50 mL of saturated NaHCO3 and extracted
with ether (3 ꢁ 50 mL). The extract was dried over MgSO4, and the
solvent removed under reduced pressure. The crude product was further
purified by chromatography on silica gel (petroleum etherꢀethyl acetate
gradient from 10:1 to 4:1) to yield 18 as a colorless oil (88%). 1H NMR
(500 MHz, CDCl3, ppm): δ 2.12 (s, 3H), 2.72ꢀ2.64 (m, 2H),
3.11ꢀ3.03 (m, 2H), 5.37 (dd, J = 11.0, 1.2 Hz, 1H), 5.72 (dd, J =
17.4, 1.2 Hz, 1H), 7.26 (ddt, J = 1.3, 6.8, 9.3, Hz, 2H), 7.31 (dd, J = 17.5,
11.0 Hz, 1H), 7.46ꢀ7.42 (m, 1H), 7.58ꢀ7.54 (m, 1H). 13C NMR
(MHz, CDCl3, ppm): δ 15.4, 33.5, 33.9, 115.9, 126.2, 127.3, 128.1,
131.6, 133.4, 134.7, 139.3. C11H14S2 GC-MS (EI): m/z 210.00 (Mþ),
calcd 210.05
General Procedure for cis-Dichloro Catalysts (14, 19). In a
glovebox, Grubbs second-generation catalyst (50 mg, 0.059 mmol) was
added to 2 equiv of the ligand (13 or 18) in 10 mL of CH2Cl2 in one
portion. The solution was stirred for 1 h at room temperature before
CuCl (10 mg, 0.101 mmol) was added, and the mixture was stirred for 24
h. The solvent was removed by evaporation, and the product purified by
silica gel chromatography (hexaneꢀacetone gradient from 5:1 to 1:1).
The fraction containing the product was evaporated, and the product
was recrystallized from DCMꢀpentane at ꢀ18 °C.
14: blue solid (19.0 mg, 50%). Crystals suitable for X-ray analysis
were obtained by slow diffusion of hexanes over a CH2Cl2 solution of 14
at ꢀ18 °C. 1H NMR (500 MHz, CD2Cl2, ppm, 256 K):23 δ 1.58 (s, 3H),
2.15 (s, 3H), 2.38 (s, 3H), 2.46 (s, 3H), 2.53 (s, 3H), 2.64 (s, 3H), 2.78
(ddd, J = 13.0, 8.8, 4.6 Hz, 1H), 3.46 (s, 3H), 3.58ꢀ3.47 (m, 3H),
4.21ꢀ3.76 (m, 4H), 5.96 (s, 1H), 6.76 (d, J = 7.7 Hz, 1H), 6.91 (s, 1H),
7.05 (s, 1H), 7.13 (s, 1H), 7.17 (t, J = 7.4 Hz, 1H), 7.51 (t, J = 7.5 Hz,
1H), 7.60 (d, J = 7.8 Hz, 1H), 17.05 (s, 1H). 13C NMR (125 MHz,
CD2Cl2, ppm): δ 13.9, 18.7, 20.9, 22.7, 26.0, 27.3, 31.6, 36.7, 123.3,
129.2, 129.4, 129.7, 130.1, 135.3, 137.3, 138.7, 139.8, 155.1, 213.8, 285.6.
C31H38Cl2N2ORuS HR-MS (ESI): m/z 623.1423 (M ꢀ Cl)þ, calcd
623.1431.
19: dark green solid (27.0 mg, 70%). Crystals suitable for X-ray
analysis were obtained by slow diffusion of hexanes over a CH2Cl2 solution
of 19 at ꢀ18 °C. 1H NMR (500 MHz, CD2Cl2, ppm): δ 1.75 (s, 3H), 2.12
(s, 6H), 2.26 (s, 6H), 2.29 (m, 1H), 2.52 (s, 6H), 2.66 (m, 1H), 2.94
(m, 1H), 3.63 (m, 1H), 3.93 (s, 4H), 6.52 (s, 2H), 6.80 (d, J = 7.5 Hz, 1H),
6.99 (s, 2H), 7.30 (t, J = 7.2 Hz, 1H), 7.70 (dt, J = 7.5, 7.2 Hz, 2H), 16.91
(s, 1H). 13CNMR(125MHz,CD2Cl2, ppm): δ18.7, 19.0, 21.2, 29.5, 31.9,
40.6, 52.2, 125.0, 129.7, 130.0, 130.2, 131.0, 131.3, 131.8, 135.6, 135.8,
136.5, 137.2, 137.4, 139.1, 156.0, 210.8, 302.0. C31H38Cl2N2RuS2 HR-MS
(ESI): m/z 639.1196 (M ꢀ Cl)þ, calcd 639.1203.
1-(Trifluoromethylsulfanyl)-2-vinylbenzene (22). Palladium
acetate (32.0 mg, 48 μmol) and 2-dicyclohexylphosphimo-20,60-
dimethoxy-1,10-biphenyl (39.0 mg, 95 μmol) were dissolved in 2.0 mL
of THF. 21 (120.0 μL, 0.460 mmol) was added, and the mixture was
stirred for 15 min. Vinylboronic acid di-n-butyl ester (0.50 mL, 23.1
mmol) was added, followed by 1.0 mL of a 3.75 M NaOH aqueous
solution, and the reaction mixture was heated to reflux (ca. 70 °C) for 4
h. After cooling, the mixture was extracted with 20 mL of n-hexane. The
extract was washed once with 10 mL of 1 M sodium hydroxide, followed
by a 3 ꢁ 10 mL wash with deionized water (to neutral pH). The organic
layer was filtrated over silica, dried over MgSO4, and evaporated. The
yellow oil residue of the crude product was further purified by normal
phase preparative HPLC using n-pentane as eluent to afford 22 as a pale
yellow oil (25.5 mg, 27% overall). 1H NMR(400 MHz, CDCl3, ppm):
δ 5.43 (dd, J = 1.0, 11.0 Hz, 1H), 5.77 (dd, J = 1.0, 17.5 Hz, 1H), 7.32 (dt,
J = 1.5, 7.6 Hz, 1H), 7.38 (dd, J = 11.0, 17.5 Hz, 1H), 7.45 (tdd, J = 0.65,
1.4, 7.9 Hz, 1H), 7.69 (m, 1H). 13C NMR (100 MHz, CDCl3, ppm): δ
77.2, 117.2, 122.7, 126.4, 128.5, 131.6, 134.4, 138.5, 143.0. 19F NMR
(375.5 MHz, CDCl3, ppm): δ ꢀ42.4. C9H7F3S GC-MS (EI): m/z
244.00 (Mþ), calcd 204.02.
Methyl(2-(2-vinylphenylthio)ethyl)sulfane (18). Methyl tri-
phenylphosphonium iodide (1.54 g, 3.81 mmol) was dissolved in 25 mL
of ether before KOtBu (0.458 g, 4.08 mmol) was added in one portion at
0 °C. After stirring for 10 min at room temperature, 17 (0.578 g, 2.72
mmol) was added in one portion at 0 °C and the reaction stirred at room
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ARTICLE
Catalyst (23). 22 (25.5 mg, 0.125 mmol) and pyridine third-
generation Grubbs catalyst (1.1 equiv) were dissolved in 4 mL of
chloroform. The resulting solution was refluxed for 4.5 h and then
evaporated to dryness. The crude product was purified by chromatog-
raphy on silica gel using acetoneꢀCH2Cl2 (1:10) as eluent to give 23 as
an indigo solid after evaporation (126.4 mg, 72%). Crystals suitable for
X-ray analysis were obtained by slow diffusion of hexanes over a CH2Cl2
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1
solution of 23 at 4 °C. H NMR (400 MHz, CDCl3, ppm): δ 1.56
(s, 3H), 2.10 (s, 3H), 2.28 (s, 3H), 2.38 (s, 3H), 2.52 (s, 3H), 2.61 (s, 3H),
3.86 (m, 2H), 4.09 (m, 2H), 5.92 (s, 1H), 6.71 (d, J = 7.1, 1H), 6.81
(s, 1H), 6.97 (2, 1H), 7.0 (s, 1H), 7.21 (t, J = 7.1 Hz, 1H), 7.53 (dt, J = 1.0,
7.8 Hz, 1H), 7.65 (d, J = 7.19, 1H), 16.85 (s, 1H). 13C NMR (125 MHz,
CDCl3, ppm): δ 17.3, 18.6, 19.2, 20.3, 20.9, 21.2, 51.3, 51.4, 124.0, 124.5
(q, J = 325 Hz), 128.8, 129.2, 129.6, 129.7, 129.8, 129.8 130.0, 131.0,
131.0, 134.7, 134.7, 135.9, 137.7, 138.6, 139.6, 140.9, 154.7, 210.5, 284.9.
19F NMR (375.5 MHz, CDCl3, ppm): δ ꢀ39.0. C29H31Cl2F3N2RuS
HR-MS (ESI): m/z 633.0873 (M ꢀ Cl)þ, calcd 633.0887.
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Buchmeiser, M. R.; Pieber, T. R. J. Chromatogr. A 2008, 1191, 274–281.
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Grubbs, R. H.; Schrodi, Y. Organometallics 2004, 23, 5399–5401.
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General Procedure for ROMP of DCPD. A 4 mL vial was
charged with initiator (0.45 μmol, 0.1%), DCPD (60 μL, 0.45 mmol),
mesitylene (internal standard, 50 μL), and chlorobenzene (1 mL). The
reaction mixture was stirred at the appropriate temperature. Monomer
conversion was monitored by GC-MS.
General Procedure for RCM and CM Reactions. A 4 mL vial
was charged with initiator (0.50 mmol, 1%), substrate (0.50 mmol), and
solvent (1 mL). The reaction mixture was stirred at the defined
temperature and irradiation (none or UV light at 350 nm) for the
defined time. Product formation was monitored by GC-MS.
(9) (a) Allaert, B.; Dieltens, N.; Ledoux, N.; Vercaemst, C.; Van Der
Voort, P.; Stevens, C. V.; Linden, A.; Verpoort, F. J. Mol. Catal. A: Chem.
2006, 260, 221–226. (b) Dunbar, M. A.; Balof, S. L.; Roberts, A. N.;
Valente, E. J.; Schanz, H. J. Organometallics 2011, 30, 199–203.
(10) Vidavsky, Y.; Lemcoff, N. G. Beilstein J. Org. Chem. 2010, 6,
1106–1119.
’ ASSOCIATED CONTENT
S
Supporting Information. NMR and MS spectra. This
b
material is available free of charge via the Internet at http://pubs.
acs.org.
(11) DCPD polymerization is very exothermic and is rapidly fin-
ished after the initial induction period seen in partially latent catalysts
(catalysts latent for less reactive substrates). For example, gel formation
is clearly observed after a few minutes of addition of 1 to a DCPD
solution in methylene chloride.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: lemcoff@bgu.ac.il.
(12) Diesendruck, C. E.; Vidavsky, Y.; Ben-Asuly, A.; Lemcoff, N. G.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4209–4213.
(13) Ben-Asuly, A.; Aharoni, A.; Diesendruck, C. E.; Vidavsky, Y.;
Goldberg, I.; Straub, B. F.; Lemcoff, N. G. Organometallics 2009,
28, 4652–4654.
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have been previously reported:(b) Bieniek, M.; Bujok, R.; Cabaj, M.;
Lugan, N.; Lavigne, G.; Arlt, D.; Grela, K. J. Am. Chem. Soc. 2006, 128,
13652–13653.
’ ACKNOWLEDGMENT
The Edmond J. Safra Foundation and the Israel Science
Foundation (Grant No. 54/09) are gratefully acknowledged for
financial support. Ms. Einav Barak is gratefully acknowledged for
skilled technical assistance, and Dr. Anna Aharoni is gratefully
acknowledged for stimulating scientific discussions on the
trifluoromethyl derivative.
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