Light-and Thermal-Activated Olefin Metathesis of Hindered Substrates

Article abstract of DOI:10.1021/acs.organomet.7b00677

Efficient light-and thermal-Activated metathesis reactions of tetra-substituted olefins were obtained by the S-chelated ruthenium precatalyst Tol-SCF₃. Its reactivity in a series of benchmark olefin metathesis reactions was compared to previous

Full text of DOI:10.1021/acs.organomet.7b00677

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Light- and Thermal-Activated Olefin Metathesis of Hindered
Substrates
Elisa Ivry,† Alexander Frenklah,† Yakov Ginzburg,† Efrat Levin,† Israel Goldberg,‡ Sebastian Kozuch,†
N. Gabriel Lemcoff,†,§ and Eyal Tzur*,∥
†Department of Chemistry, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel
‡School of Chemistry, Tel-Aviv University, Tel-Aviv 69978, Israel
§Ilse Katz Institute for Nanotechnology, Beer Sheva 8410501, Israel
∥Department of Chemical Engineering, Shamoon College of Engineering, Ashdod 77245 Israel
S
* Supporting Information
ABSTRACT: Efficient light- and thermal-activated metathesis reactions of tetra-substituted olefins were obtained by the S-
chelated ruthenium precatalyst Tol-SCF3. Its reactivity in a series of benchmark olefin metathesis reactions was compared to
previously reported Mes-SCF3 and a novel sterically congested S-chelated complex, Dipp-SCF3. Tol-SCF3 is thus the first latent
catalyst proven to be capable of promoting olefin metathesis of demanding substrates upon light stimulation at room
temperature.
steric properties of the N-heterocyclic carbene (NHC) ligand
on the course of the metathesis reaction.1 For example, the use
of bulky ligand 1,3-bis(2,6-diisopropylphenyl) imidazolidine-2-
ylidene (b, SIDipp) increased thermal stability and improved
activity in metathesis of standard substrates.2 In contrast, the
reduction of steric bulk around the NHC ligand, by using 1,3-
bis(2-methylphenyl)imidazolidine-2-ylidene (c, SITol) to
produce 1c, 2c,3 and 3c,4 allowed increased efficiency in
metathesis reactions of sterically demanding olefins.5 Other
ruthenium scaffolds that may benefit from this strategy are
latent ruthenium precatalysts,6 such as the sulfur-chelated
benzylidenes.7 These complexes exhibit a cis-dichloro config-
uration,8 which is unreactive toward ring-closing metathesis
(RCM), cross-metathesis (CM) and many ring-opening
metathesis polymerization (ROMP) reactions at ambient
conditions. Activation of these precatalysts has been achieved
by means of heat or UV irradiation, which results in the
isomerization of the dormant cis-dichloro complexes to the
active trans configuration.7a,b The ability to exploit light as a
INTRODUCTION
■
Although pioneered decades ago, the world of olefin
metathesis is still undergoing continuous development,
providing important research and synthetic tools to the field
of organic chemistry. One such aspect is the formation of tetra-
substituted carbon−carbon double bonds, which was originally
found to be challenging when promoted by standard
commercially available ruthenium precatalysts, such as 1−3a
(Figure 1). Extensive studies disclosed the great impact of the
Figure 1. Ruthenium complexes bearing NHC ligands with varying
steric hindrance.
Received: September 6, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00677
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Article
convenient and powerful energy resource in novel metathesis
applications, such as three-dimensional printing of ROMP
polymers9 or guiding of orthogonal organic reactions,10 has
given quite an impetus to the field of latency. Thus, the
expansion of the methodology to include metathesis of
sterically demanding substrates is highly desirable.
Suitable crystals for X-ray diffraction were successfully
obtained by slow diffusion of pentane into a dichloromethane
solution of the complexes at −20 °C. Both Dipp-SCF3 and
Tol-SCF3 exhibit the predicted cis-dichloro configuration with
Cl−Ru−Cl angles near 90° (Figure 3). As could be expected,
Herein we report the synthesis of sterically reduced latent
precatalyst Tol-SCF3, and its application in light and also
thermal activated metathesis of hindered olefins. Sterically
encumbered Dipp-SCF3 was synthesized as well, and the
activities of the two novel complexes were compared to those
11
of previously reported Mes-SCF3 (Figure 2).
Figure 3. ORTEP diagram of Tol-SCF3 and Dipp-SCF3. Ellipsoids
are drawn at 50% probability. Hydrogens are omitted for clarity.
the solid-state structure of Tol-SCF3 appears as a single
conformer, in which the methyl substituents of the tolyl rings
are syn to one another on the sulfur atom side (complex syn-a,
Figure S8). Notably, Tol-SCF3 is a considerably stable example
of a SITol-bearing ruthenium complex. Previously reported
complexes bearing NHCs with vacant ortho positions on the
N-aryl substituent were shown to easily undergo C−H
activation, leading to various decomposition products.14 Such
processes are promoted by rotation of the N-substituents to
achieve the geometry required for the C−H activation. In
previous reports, the rotation of the N-aryl substituent was
restricted by placing substituents on the NHC backbone to
minimize this decomposition.15 Interestingly, the rigid
structure of Tol-SCF3 in its cis configuration efficiently
prevents rotation of the N-aryl group and thus bestows the
complex with additional thermal stability.13
Figure 2. Latent SCF3-chelated precatalysts bearing NHC ligands
varying in size investigated in this work.
RESULTS AND DISCUSSION
The new complexes were synthesized by mixing 1b and 1c
with a slight excess of ligand 4 (Scheme 1) and duly
■
Scheme 1. Synthesis of Complexes Tol-SCF3 and Dipp-SCF3
A very important aspect of the S-chelated ruthenium
complexes is the cis/trans isomer interplay. Usually, the trans
isomer is first obtained as the kinetic product, and heating the
solution affords the cis-dichloro isomer.16 While cis-dichloro
Tol-SCF3 was obtained in 10 h, Dipp-SCF3 required much
harsher conditions, and even after a prolonged heating period
of 3 weeks in DCM, some of the kinetic trans-isomer could still
be observed (Scheme 1). As steric congestion has been shown
to influence the trans-cis isomerization equilibrium,1b,16 it
would seem that the high steric hindrance of Dipp-SCF3
increases the energy of the transition state between the trans
and cis isomers, thus slowing the isomerization process. To test
this hypothesis, the isomerization events were computed using
DFT17 calculations with Gaussian16.18 Two mechanisms were
taken into consideration:8 (1) A concerted mechanism,
including a pseudorotation of the benzylidene moiety,
concomitant with a displacement of the chloride trans to the
NHC. (2) A dissociative mechanism, where a 14e−
intermediate is formed by dissociation of the chelated sulfur,
which in turn may recoordinate in a cis configuration after
rotation of the benzylidene and relocation of the chloride
ligand (Figure S9).
characterized by NMR, HR-MS, and single crystal X-ray
spectroscopy analyses. While the H NMR spectra of Dipp-
1
SCF3 and Mes-SCF3 exhibited a single benzylidene signal for
the cis-complex (16.76 and 16.85 ppm, respectively), a careful
inspection of the carbene region of Tol-SCF3 revealed a main
peak at 16.71 ppm accompanied by broad signals at 16.87
ppm. The additional peaks expose the cohabitation of 4
possible rotamers (for full details see the Supporting
Information) which can be observed due to hindered rotation
around the CAr−N and Ru−CNHC bonds. A similar behavior
was seen in complex 3c, where the relatively strong interactions
of the indenylidene aromatic system with the N-tolyl
substituents also prevented free rotation, and heating to 70
°C was required in order to observe the coalescence of the
NMR signals.4 In contrast, complex 2c enjoys a high degree of
freedom, and all rotamers were averaged at room temperature
in the NMR.12 In line with these observations, a high
coalescence temperature was also seen in Tol-SCF3, where
the benzylidene and the NHC aromatic rings are stacked upon
each other. Heating to 80 °C sharpened the signals to clearly
observe two of the rotamers, in a 1:3 ratio (Figure S8 in the
Supporting Information). Upon further heating to 130 °C,
beginning of coalescence for these two peaks was observed.13
Further characterization of the complexes was carried out by
crystallographic studies.
The syn rotamers of Tol-SCF3, i.e., syn-a (Tol-SCF3-α) and
syn-b (Tol-SCF3-β), were chosen as the thermodynamic
products due to the observed Tol-SCF3 configuration in the
solid state (vide supra) and as they were also shown to be the
dominant species in solution of 2c.12 According to Table 1, it
would appear that in DCM Tol-SCF3-α is predicted to show
no distinct preference for any of the mechanisms; however,
B
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Article
a
Table 1. ΔE [kcal/mol] for the SCF3-Chelated Species in the Two cis−trans Isomerization Mechanisms
DCM
toluene
pathway
complex
TS1
int.
TS2
cis
TS1
int.
TS2
cis
Tol-SCF3-α
Tol-SCF3-β
Mes-SCF3
Dipp-SCF3
29.3
26.3
26.3
29.2
−5.8
−4.3
−8.3
−4.3
29.5
26.8
26.4
31.0
−3.8
−2.2
−6.4
−2.8
concerted
Tol-SCF3-α
Tol-SCF3-β
Mes-SCF3
Dipp-SCF3
19.2
20.6
18.9
18.7
14.7
15.7
13.1
12.3
29.0
34.4
32.5
31.3
−5.8
−4.3
−8.3
−4.3
20.1
21.3
21.0
19.3
15.1
16.0
12.9
12.5
30.5
36.5
34.0
32.5
−3.8
−2.2
−6.4
−2.8
dissociative
a
Calculated for DCM and toluene, solvation model PCM with reference to the trans isomer.
Tol-SCF3-β showed a much lower energy for the transition
state in the concerted mechanism. The energy required for the
rotation of the NHC from trans-Tol-SCF3-α to trans-Tol-
SCF3-β is ∼14.50 kcal/mol. Therefore, it may be assumed that
the two rotamers can indeed interconvert in order to produce
the lower energy transition state required for the isomerization
process. Tol-SCF3, Mes-SCF3, and Dipp-SCF3 show a
preference toward the concerted mechanism, in which, the
ΔE for the isomerization of Dipp-SCF3 is higher by ∼3 kcal/
mol. This may account for the very slow isomerization of the
trans-Dipp-SCF3 to the cis-Dipp-SCF3 isomer.
Following their full structural characterization, the activities
of the precatalysts were compared in a series of benchmark
RCM reactions, including sterically hindered substrates. The
reactions were all run in toluene-d8 at 0.1 M substrate
concentration. At room temperature, no RCM activity was
observed for any of the catalysts and substrates checked,
confirming the expected latency of the precatalysts. Thermal
activation was effected by heating the reaction mixtures to 80
°C. The kinetic profiles of the reactions were monitored by 1H
NMR (500 MHz) and are presented in Figures 4−6. In
Figure 5. Kinetic profile of RCM of diethyl 2-allyl-2-(2-methylallyl)-
malonate. Toluene-d8, 0.1M, 80 °C, 2 mol % cat.
Figure 6. Kinetic profile of RCM of diethyl 2,2-bis(2-methylallyl)-
malonate. Toluene-d8, 0.1M, 80 °C, 2 mol % cat.
frame of 3 h. Interestingly, except for Tol-SCF3, a significant
induction period was observed. As this induction period is only
evident with the most hindered substrate, we propose that this
unexpected behavior is a result of steric hindrance within the
catalytic sphere.12,19 For the S-chelated precatalysts, two steps
are required to generate an active complex. First, the complex
must isomerize to an active species, i.e., the trans precatalyst or
directly the trans 14e− intermediate. Second, the olefin
substrate needs to coordinate (either in an associative or
dissociative manner)20 to the ruthenium center to produce a
species which will eventually lead to a productive RCM
pathway. It is reasonable to assume that the higher the steric
congestion, the slower the second coordination step. There-
fore, we suggest that in the case of hindered olefins the second
step has the highest transition state, causing initiation to be
significantly affected by steric volume. This may also explain
the reduced induction period observed for Tol-SCF3, which
can best accommodate the incoming olefin. In contrast, Dipp-
SCF3 initiates and performs more efficiently than Mes-SCF3.
Figure 4. Kinetic profile of RCM of N,N-diallyltosyl amine. Toluene-
d8, 0.1M, 80 °C, 2 mol % cat.
accordance with literature precedents, RCM reactions that
afford doubly (Figure 4) and triply (Figure 5) substituted
olefins were faster when catalyzed by Dipp-SCF3. Moreover,
the results obtained using Dipp-SCF3 make this new complex
the most efficient olefin metathesis catalyst in the family of S-
chelated benzylidenes for this type of reactions. However,
when diethyl bis(2-methylallyl)malonate was used as the
substrate, the trend was reversed, and Tol-SCF3 was the best
performer (Figure 6). Tol-SCF3 not only was the fastest to
initiate but also gave a substantially higher conversion
compared to the other complexes within the reaction time
C
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Table 1 suggests that a slightly lower energy is required to
obtain the 14e− intermediate of Dipp-SCF3 in toluene,
allowing for more productive metathesis encounters with the
substrate and diminishing the induction period. This is an
example of the delicate interplay between both processes
(precatalyst activation and substrate coordination) required to
promote latent olefin metathesis of hindered substrates.
The scope of the reaction was further explored with several
RCM and CM substrates, supporting the previously observed
trend (Table 2). Dipp-SCF3 was the fastest catalyst of the
(entry 7). When a hindered olefin was used as a CM partner
(entry 8), Tol-SCF3 and Mes-SCF3 maintained their
efficiency, while that of Dipp-SCF3 dropped dramatically.
The results highlight the usefulness of Tol-SCF3 in challenging
reactions where latency may be required.
Finally, the appealing light activation of the precatalysts by
UV irradiation at 350 nm was examined (Table 3). To our
Table 3. RCM Reactions Promoted by SCF3-Chelated
a
,
21
Complexes under 350 nm UV Irradiation
Table 2. RCM and CM Reactions Promoted by SCF3-
a
Chelated Complexes by Thermal Activation
a
Reactions were conducted in DCM-d2, 0.1M; conversions
b
1
determined by H NMR (500 MHz). Toluene-d8.
satisfaction, the behavior for light-promoted RCM of olefins
fell in line with the results obtained for the thermal activation
and provided good results with precatalysts Mes-SCF3 and
Dipp-SCF3 with unhindered olefins. Tol-SCF3 also maintained
its high effectiveness in the RCM of tetra-substituted olefins,
but Mes-SCF3 and Dipp-SCF3 substantially underperformed
compared to thermal activation (entries 5−6 in Table 2 and
entries 3 and 4 in Table 3). Although RCM under UV
irradiation required longer reaction periods, especially for
tetra-substituted olefins, our results show that Tol-SCF3 is the
only catalyst that can perform efficient light-promoted RCM
reactions in sterically challenging substrates.
a
CONCLUSIONS
Reaction conditions: 0.1 M substrate in toluene, 1 mol % cat., 15
■
b
min at 80 °C. Conversions determined by GC-MS. Reaction
conditions: 5 mol % cat., 120 min. Reaction conditions: 0.4 mol %
cat. Mesitylene as internal standard and 2 equiv of cis-1,4-diacetoxy-
S-chelated complexes bearing NHC ligands varying in size
have been synthesized and fully characterized. Solid and
solution state analyses revealed the influence of the bulkiness
of the NHC ligand on the complexes’ structures and their
inherent stability. These characteristics directly affect key
process of the metathesis catalysis. The complex bearing the
smallest NHC, Tol-SCF3, provided excellent results in
thermal- and light-induced metathesis of hindered olefins. As
such, Tol-SCF3 is the first light-activated latent olefin
metathesis catalyst that can efficiently perform metathesis in
sterically demanding substrates. The complex bearing the
bulkiest NHC, Dipp-SCF3, provided the best results for di-
and trisubstituted benchmark RCM reactions. These novel
complexes expand the scope and efficiency of the sulfur-
chelated precatalyst family for latent olefin metathesis catalysis
applications.
c
d
e
2-butene. Reaction conditions: 5 mol % cat., 120 min, mesitylene as
f
internal standard and 3 equiv of allybenzene. Measured by 1H NMR.
group yielding almost complete conversions within 15 min
under the thermal activating conditions for di- and
trisubstituted olefins (entries 1−4). Once again, when
demanding tetra-substituted substrates were used, Tol-SCF3
excelled (entries 5−6). The limits of the RCM reaction of
N,N-bis-2-methylallyl tosyl amine using Tol-SCF3 (entry 6)
were also tested at lower catalyst loadings. Thus, 0.4 mol %
Tol-SCF3 promoted 83% conversion within 60 min at 100 °C.
In addition, a CM reaction produced satisfactory results as
well, with Dipp-SCF3 affording 85% conversion within 15 min
D
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1
the product in −20 °C. H NMR (400 MHz, CD2Cl2): δ 16.76 (s,
1H), 7.66 (d, J = 7.8 Hz, 1H), 7.56 (dd, J = 15.3, 7.6 Hz, 2H), 7.46
(dd, J = 7.8, 1.3 Hz, 1H), 7.37−7.33 (m, 2H), 7.28 (t, J = 7.5 Hz,
1H), 7.22 (t, J = 7.7 Hz, 1H), 6.86 (d, J = 7.6 Hz, 1H), 6.48 (dd, J =
7.7, 1.1 Hz, 1H), 4.33−4.03 (m, 5H), 3.91 (m, 1H), 3.33 (m, 1H),
2.29 (m, 1H), 1.65 (d, J = 6.5, 3H), 1.58 (m, 6H), 1.24 (d, J = 6.7,
6H), 1.24 (d, J = 6.8, 6H) 1.19 (d, J = 6.9, 3H) 0.97, (d, J = 6.7, 3H),
0.41 (d, J = 6.7, 3H). 13C NMR (100 MHz, CD2Cl2): δ 286.1, 213.8,
154.9, 151.2, 149.8, 147.7, 145.9, 136.4, 132.4, 132.2, 131.7, 131.3,
131.0, 130.7, 130.1, 127.0, 126.3, 125.6, 125.4, 124.9, 123.8, 54.6,
29.7, 29.6, 29.2, 28.8, 28.4, 28.1, 27.2, 26.6, 24.6, 23.2, 22.4, 21.6. 19F
NMR (377 MHz, CD2Cl2): δ −75.77. HRMS m/z calcd for
[C35H43Cl2F3N2RuSNa]+: 775.14118, found 775.13983.
EXPERIMENTAL SECTION
■
General. All reagents were of reagent-grade quality, purchased
commercially from Sigma-Aldrich, Sterm, or Alfa Aesar, and used
without further purification. All solvents were dried and distilled prior
to use. Purifications by column chromatography were performed on
Davisil Chromatographic silica media (40−6 μm). TLC analyses were
performed using Merck precoated silica gel (0.2 mm) aluminum
[backed] sheets. Gas chromatography data was obtained using an
Agilent 6850 GC equipped with an Agilent 5973 MSD working under
standard conditions and an Agilent HP5-MS column. NMR spectra
were recorded on Bruker DPX400 or DPX500 instruments; chemical
shifts, given in ppm, are relative to the residual solvent peak. HRMS
data were obtained using a Bruker Daltonics Ion Trap MS Esquire
3000 Plus equipped with APCI (Atmospheric Pressure Chemical
Ionization). Irradiation experiments were carried out using a Rayonet
RPR-200 instrument with 350.0 nm lamp and were carried out in
NMR tube.
General Procedure for RCM Reaction. All substrates which
were not commercially available were synthesized according to known
procedures from the literature. In the glovebox, a solution of the
substrate in the appropriate solvent (0.1M) was added to ruthenium
complex (0.5, 1, 2, or 5 mol %). The mixture was then transferred to
an NMR tube or a vial, which in turn was placed in an 80 °C heating
bath or in a Rayonet photoreactor. Conversion was monitored by GC-
(Trifluoromethyl)(2-vinylphenyl)sulfane (4). New synthesis
procedure for 4:11 In a dry flask, methyl triphenylphosphonium iodide
(11.79 g, 29.02 mmol) was stirred in dry ether (100 mL), at 0 °C,
under N2 atmosphere. KOtBu (3.86 g, 34.40 mmol) was added in one
portion. The solution was stirred at 0 °C for 15 min. 2-
((Trifluoromethyl)thio)benzaldehyde (5.00 g, 24.25 mmol) was
added in one portion. The solution was stirred for 3 h, until the
reaction was judged complete by GC-MS. Saturated NaHCO3
solution (100 mL) was added, and the phases were separated. The
aqueous phase was extracted with ether (3 × 50 mL). The combined
organic layers were washed with water and brine and dried over
MgSO4. The drying reagent was filtered off, and the liquid was stored
at −18 °C overnight. The precipitated triphenylphosphine oxide was
filtered off, and the solvent was evaporated. The crude product was
purified on silica gel column with petroleum ether as eluent. 4 was
obtained as a colorless oil (2.64 g, 53%). The NMR and GC-MS
spectra were in agreement with previous results.11
1
MS or H NMR.
General Procedure for CM Reaction. All substrates which were
not commercially available were synthesized according to known
procedures from the literature. In the glovebox, a solution of the
substrates in the appropriate solvent (0.1M) was added to ruthenium
complex (1 or 5 mol %). The mixture was placed in an 80 °C heating
bath. Conversion was monitored by GC-MS using mesitylene (1.5
equiv) as internal standard.
Computational Details. The DFT geometry optimization was
performed using B97D3/Def2-SVP. Final geometries were confirmed
to be minimum energy structures through frequency calculations.
Reaction pathway was also confirmed using IRC calculations. Single
point calculations were performed using MN15/Def2-TZVP. Solvent
effects have been estimated in single point calculations based on PCM
model for DCM and toluene.
Ru(SIMes)(CHPhSCF3)Cl2 (Mes-SCF3). Prepared according to
previously reported literature procedure.11
ASSOCIATED CONTENT
■
Ru(SITol)(CHPhSCF3)Cl2 (Tol-SCF3). In the glovebox, Tol-
Grubbs (1c) (300 mg, 0.38 mmol) was dissolved in dry DCM (20
mL) followed by addition of ligand 4 (109 mg, 0.53 mmol). The
pressure tube was sealed, and the reaction mixture was refluxed
overnight. The solvent was removed under vacuum, and the crude was
redissolved in minimal amount of DCM. Ether was slowly added until
precipitation of a purple-blue solid was obtained. After the suspension
was sonicated a few minutes, the solvent was decanted. Benzene was
added, and the solution was sonicated for 2 h. The solid was filtered
and washed several times with benzene, followed by drying under
high vacuum for 5 days. Tol-SCF3 was obtained as a light blue solid
(162 mg, 70%). Crystals suitable for X-ray analysis were obtained by
slow diffusion of pentane into a DCM solution of the product in −20
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00677.
NMR spectra, MS data and X-ray data of two complexes,
computational energy plot, and ΔG values of Table 1
(PDF)
Atomic coordinate files (XLSX, XYZ)
Accession Codes
1
°C. H NMR (400 MHz, CD2Cl2): δ 16.88−16.72 (m, 1H), 8.46 (s,
CCDC 1564124−1564125 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
0.5H), 7.76−7.62 (m, 3H), 7.51−7.47 (m, 3.5H), 7.40−7.36 (m,
1H), 7.33−7.25 (m, 3H) 6.80 (d, J = 7.6 Hz, 1H), 6.72 (d, J = 7.2,
1H), 4.27 (bs, 1H), 4.16−4.07 (m, 1H), 4.05−3.98 (m, 1H), 3.94−
3.86 (m, 1H), 2.58 (s, 3H), 1.26 (bs, 3H). 13C NMR (101 MHz,
CD2Cl2) δ 290.6, 208.8, 155.4, 138.9, 136.0, 133.2, 132.9, 131.4,
131.3, 131.1, 130.6, 129.8, 129.4, 128.8, 128.5, 127.7, 127.3, 127.2,
126.0, 125.6, 125.2, 122.7, 52.5, 52.0, 19.0, 16.4. 19F NMR (376 MHz,
CD2Cl2): δ −41.1. HRMS m/z calcd for [C25H23ClF3N2RuS]+ (M −
Cl)+: 577.0261, found: 577.0204. The fractions observed in the
AUTHOR INFORMATION
■
1
integrals of the H NMR spectrum are due to the presence of minor
Corresponding Author
*E-mail: eyalt@sce.ac.il.
and major rotamers.
Ru(SIDipp)(CHPhSCF3)Cl2 (Dipp-SCF3). In the glovebox,
Dipp-Grubbs (1b) (500 mg, 0.54 mmol) was dissolved in dry
DCM (20 mL) followed by addition of ligand 4 (190 mg, 0.93
mmol). The reaction mixture was refluxed for 3 weeks. The solvent
was removed under vacuum. cis-Dipp-SCF3 was purified by flash
chromatography using 7:1 to 7:2 hexane/acetone as eluent to give
gray-green solid (171.0 mg, 29%). Crystals suitable for X-ray analysis
were obtained by slow diffusion of pentane into a DCM solution of
ORCID
Israel Goldberg: 0000-0002-3117-0534
Sebastian Kozuch: 0000-0003-3070-8141
N. Gabriel Lemcoff: 0000-0003-1254-1149
Notes
The authors declare no competing financial interest.
E
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Levin, E.; Butilkov, D.; Goldberg, I.; Reany, O.; Lemcoff, N. G. Angew.
Chem., Int. Ed. 2016, 55, 764−767.
ACKNOWLEDGMENTS
■
E.T. acknowledges grant No. 14/Y16/T1/D3/Yr2 provided by
the Shamoon College of Engineering, Ashdod, Israel. The
Israel Science Foundation is gratefully acknowledged for partial
funding of this work (Grant No. 537/14).
(11) Ginzburg, Y.; Anaby, A.; Vidavsky, Y.; Diesendruck, C. E.; Ben-
Asuly, A.; Goldberg, I.; Lemcoff, N. G. Organometallics 2011, 30,
3430−3437.
(12) Stewart, I. C.; Benitez, D.; O’Leary, D. J.; Tkatchouk, E.; Day,
M. W.; Goddard, W. A., III; Grubbs, R. H. J. Am. Chem. Soc. 2009,
131, 1931−1938.
(13) The boiling point of the solvent (TCE-d2, 146.5 °C) prevented
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DOI: 10.1021/acs.organomet.7b00677
Organometallics XXXX, XXX, XXX−XXX