A partially serendipitous discovery of thermo-switchable ruthenium olefin metathesis initiator that seem to be well suited for ROMP of monomers bearing vinyl pendant groups

Article abstract of DOI:10.1016/j.jorganchem.2017.04.003

A latent Ru olefin metathesis catalyst bearing a chelating ligand with an azoxybenzene fragment was obtained and characterized. The complex was inactive in the ring closing metathesis (RCM) reaction of a standard test diene: diethyl diallylmalonate at room temperature but can be subsequently activated by elevated temperature (up to 100 °C). The lack of activity of this azoxy catalyst in RCM of dienes containing terminal C-C double bonds at room temperature and high activity in ring opening metathesis polymerization (ROMP) of bicyclo [2.2.1]hept-2-ene (norbornene, NBE) permitted the ROMP of the challenging monomer: 5-vinyl-2-norbornene yielding soluble polymers with cyclopentenylenevinylene chains with vinyl pendant groups.

Full text of DOI:10.1016/j.jorganchem.2017.04.003

Accepted Manuscript
A partially serendipitous discovery of thermo-switchable ruthenium olefin metathesis
initiator that seem to be well suited for ROMP of monomers bearing vinyl pendant
groups
Katarzyna Szwaczko, Izabela Czeluśniak, Karol Grela
PII:
S0022-328X(17)30230-9
10.1016/j.jorganchem.2017.04.003
JOM 19890
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 31 January 2017
Revised Date: 4 April 2017
Accepted Date: 7 April 2017
Please cite this article as: K. Szwaczko, I. Czeluśniak, K. Grela, A partially serendipitous discovery
of thermo-switchable ruthenium olefin metathesis initiator that seem to be well suited for ROMP of
monomers bearing vinyl pendant groups, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2017.04.003.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
A partially serendipitous discovery of thermo-switchable ruthenium olefin metathesis
initiator that seem to be well suited for ROMP of monomers bearing vinyl pendant groups
Katarzyna Szwaczkoa§, Izabela Czeluśniakb, Karol Grelaa*
a Poland, Biological and Chemical Research Centre, Department of Chemistry, University of
Warsaw, Żwirki i Wigury Street 101, 02-089 Warsaw, Poland
§ Current address: Poland Department of Organic Chemistry, Faculty of Chemistry, Marie Curie-
Skłodowska University, Gliniana 33, 20-614 Lublin, Poland
b Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie, 50-383 Wrocław, Poland
This paper is dedicated to John Gladysz on the occasion of his 65th birthday, in appreciation of
his fine friendship, generosity, and approach to science.
ABSTRACT:
A latent Ru olefin metathesis catalyst bearing a chelating ligand with an azoxybenzene fragment
was obtained and characterized. The complex was inactive in the ring closing metathesis (RCM)
reaction of a standard test diene: diethyl diallylmalonate at room temperature but can be
subsequently activated by elevated temperature (up to 100 °C). The lack of activity of this azoxy
catalyst in RCM of dienes containing terminal C-C double bonds at room temperature and high
activity in ring opening metathesis polymerization (ROMP) of bicyclo[2.2.1]hept-2-ene
(norbornene, NBE) permitted the ROMP of the challenging monomer: 5-vinyl-2-norbornene
yielding soluble polymers with cyclopentenylenevinylene chains with vinyl pendant groups.
KEYWORDS: Olefin metathesis, ring opening metathesis polymerisation (ROMP), ruthenium
Introduction
Olefin metathesis is widely used as a synthetic methodology in various fields, including
synthetic organic chemistry [1], polymer chemistry [2,3], biochemistry [4], and materials science
[5]. The application of olefin metathesis in these fields has been facilitated by the development of
various increasingly sophisticated and specialised catalysts tailored to the requirements of these
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applications. Due to the huge interest in olefin metathesis, new catalysts are continually
developed and the latest trends focus on the development of latent type of metathesis catalysts
(Figure 1).
Figure 1. Grubbs-Hoveyda catalyst 1 and selected latent catalysts for olefin metathesis.
The “latent” catalysts are of great importance in the polymer chemistry since it is possible to
effectively admix the catalyst in bulk monomer and store until a metathesis reaction is desired
[6]. The trigger for initiation can be heat [7], light [8], chemical activation [9] or ultrasound [10].
The use of chelating carbene ligands at the ruthenium centre is the most promising approach to
synthesis of a latent catalyst [5a]. Such chelating ligands are bidentate and stabilize the resting
state of the catalyst at room temperature while at elevated temperature a coordination site is
vacated. The group of Van der Schaaf described thermo-switchable ruthenium complex with 2-
pyridylethanyl-carbene ligand [11], the Lemcoff and Grela groups presented latent metathesis
initiators with a chelating quinoline, sulfoxide, sulfone and benzylidene thioether ligands [12].
Recently, Sashuk presented a thermo- and photo-switchable ruthenium initiator with N-chelating
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azo benzene moiety, which coordinates to the ruthenium through either of the two nitrogen atoms
[13].
Ring opening metathesis polymerization (ROMP) is among the polymerization techniques of
choice, affording polymers exhibiting tailored characteristics [2]. Moreover, ROMP mediated by
Ru carbene initiators is reliable, flexible and functional-group tolerant. Highly strained
norbornene and its derivatives are the most commonly used monomers for ROMP mainly due to
its commercial availability or accessibility via Diels-Alder reaction. Despite ROMP becoming a
valuable method for the synthesis of structurally precise polymers, relatively little is known about
ROMP of norbornene-type monomers containing vinyl moieties. In this case it is conceivable that
the monomers with vinyl groups can also participate in cross-metathesis reaction, which might
complicate the polymerization process leading to an insoluble cross-linked polymer. This may
especially be true in the presence of a more reactive Grubbs-Hoveyda catalysts. Up to now, the
poly(5-vinyl-norbornene) polymers with unsaturated main chain and vinyl pedant groups were
achieved almost exclusively with less active W- and V-based initiators [14-18]. According to our
best knowledge, there is only one example of ROMP of 5-vinyl-2-norbornene mediated by
Grubbs-Hoveyda type Ru alkylidene complex leading to soluble polymers unfortunately with
high polydispersity indexes (PDI = 4.6 - 8.5) [19].
In the search for new architectures of potentially thermo-switchable ruthenium-alkylidene
complexes we turned our attention to the relatively unexplored class of azoxybenzenes. Herein,
we report the synthesis of new ruthenium complex 11 with azoxybenzene ligand, its structural
characterization and thermo-switchability assessment in a model ring closing metathesis (RCM)
reaction of diethyl diallylmalonate. Finally ring opening metathesis polymerization (ROMP) of
norbornene and its vinyl derivative is described, demonstrating the potential usefulness of the
newly obtained complex.
Results and discussion
Synthesis of the catalyst
The synthesis of the desired 2-vinylnitrosobenzene precursor was planned via a two step
reaction starting from commercial 2-bromoaniline. In the first step, the 1-bromo-2-
nitrosobenzene dimer 6 was synthesized from 2-bromoaniline in 83% yield according to the
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literature [20] by an oxidation with Oxone® in a mixture of dichloromethane (DCM) and water
(Scheme 1).
Br
Br
Oxone,
DCM/H2O
(1:1)
O
NH2
N
Br
N+
N
O
2
83%
Br
O-
6 (monomer)
6 (dimer)
Scheme 1. Synthesis of 2-bromonitrosobenzene dimer.
Next, we attempted to install the vinyl moiety to form a precursor for a chelating azoxy-
benzylidene ligand. Despite our efforts, we were unable to obtain the desired 2-
vinylnitrosobenzene (7). Instead we observed formation of a number of partially reduced
compounds (Scheme 2). After some experimentation, we were able to establish conditions for the
tandem vinylation-reduction yielding vinyl derivative 8 as the major product. Interestingly, only
this isomer was formed, i.e. the isomer with the vinyl group exclusively installed at the N(→O)
bearing benzene ring. In this reaction bromide 6 was reacted with 1.5 eq. tributyl(vinyl)tin in the
presence of catalytic amount of Pd(PPh3)4 (5 mol%) in a toluene (Scheme 2) leading to 8 in 28%
yield. As a byproduct (up to 6% of the yield) in this reaction compound 10 was isolated.
Surprisingly, the reaction of 2-bromonitrosobenzene with 1.1 eq. or 2.0 eq. of the vinyl donor did
not work any better and we observed only the formation of compound 9 (49% of yield). To our
knowledge this is the first example of the reduction of a nitrosobenzene to a azoxybenzene
derivative with an organic tin compound under Stille reaction conditions.
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Scheme 2. Synthesis of ligand precursor 8.
Due to the difficulty of synthesizing 7, we opted to test another design of the chelating Ru
complex, derived from compound 8. We considered two possible modes of chelation via either
N- and O-chelates. To test this ligand precursor 8 was reacted with 2nd-generation Grubbs catalyst
[RuCl2(PCy3)(SIMes)(CHPh)] in the presence of CuCl, used as a phosphine scavenger. After
‘carbene exchange’, flash chromatography yielded a brick-red colored microcrystalline solid,
later characterized as compound 11 in 48%.
Scheme 3. Synthesis of complex 11 with azoxybenzene motif.
Compound 11 was found to be perfectly stable at room temperature and can be handled under air
for a long periods of time (6-12 months).
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1
13
The complex was characterized by H and C NMR spectra. It contains a N-chelating
azoxybenzene motif which coordinates to the ruthenium center through both the nitrogen and
benzylidene carbene forming a six-membered chelate complex. The NMR spectra exhibited the
characteristic features for a Cs symmetric compound with trans dichloro geometry [12e]. The
1
benzylidene proton gave a singlet at
δ
17.9 ppm in H NMR and the corresponding carbon was
13
found at
δ
303 ppm in C NMR, almost the same as those reported for the ruthenium carbene
complex 5 bearing azobenzene functionality [13]. For the catalysts with chelating carbene ligands
13
based on imines the corresponding proton was found in the range 18.4-18.7 ppm, while the C
NMR spectra shows the alkylidene carbon shifted downfield (341-343 ppm) [7a].
X-ray Crystallographic Studies
A single crystal of compound 11 suitable for X-ray diffraction studies was grown at +5ºC from
a trichloromethane/n-hexane solution. This allowed us to confirm the molecular assignment of
the novel catalyst unambiguously (Figure 2). Important bond lengths and angles can be found in
the captions of Figure 2. Further crystallographic details are given in the Supporting Information.
X-Ray crystal structure analysis reveals that catalyst 11 is a five-coordinate monomeric
ruthenium complex chelated by a bromo substituted azoxybenzene ligand. The coordination
geometry of ruthenium center is a distorted square pyramid the apex of which is formed by the
carbene atom C(4) with Ru–C bond of 1.826(2) Å. The base of the square pyramid is formed by
the two chloro ligands Cl(1) and Cl(2) in a mutually trans arrangement while the remaining
coordination sites are occupied by the C(1) atom of the NHC ligand and azoxy nitrogen N(3).
Azoxy ligand is twisted with a dihedral angle of 116.06° between the two aromatic rings and is
bound via a dative interaction through the nitrogen lone pair with Ru(1)–N(3) distance of
2.088(2) Å. The N(3)-N(4) distances of 1.297(2) Å are typical N-N bond lengths in coordinated
azoxy molecules (1.279-1.312 Å) [21]. It is noteworthy that the open side of the Ru coordination
is comparatively crowded by the presence of the bulky phenyl rings. However, in comparison to
earlier presented thermally triggered ruthenium catalysts [7, 22], the geometry of 11 is quite
unique. The molecular structure of the azoxy ligand coordinates metal center simultaneously by
carbene atom C(4) and additional nitrogen donor N(3). It seems, that the neutral nitrogen donor
could be reversible exchange in a metathesis reactions without reorganisation coordination sphere
around the metal centre. This should allow to access the ruthenium active site relatively easy and
altered its chemical activity as catalyst.
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Figure 2. The molecular structure of 11 (thermal ellipsoids at 50% probability level; hydrogen
atoms and co-crystallized CHCl3 molecule omitted for clarity); selected bond lengths (Å) and
angles (°): Ru(1)–Cl(1) 2.3632(5), Ru(1)–Cl(2) 2.3562(5), Ru(1)–N(3) 2.088(2), Ru(1)–C(1)
2.054(2), Ru(1)–C(4) 1.826(2), C(4)–C(5) 1.450(3), N(3)–N(4) 1.295(2), N(4)–O(1) 1.257(2),
Cl(1)–Ru(1)–Cl(2) 164.88(2), C(1)–Ru(1)–N(3) 169.70(7), C(4)–Ru(1)–N(3) 89.15(8),
C(5)−C(4)−Ru(1) 124.76(14).
Catalytic Performance Tests
The activity of complex 11 was evaluated by employing standard tests for metathesis catalysts.
Thus, catalytic performance of 11 was investigated in the ring closing metathesis (RCM) of
diethyl diallylmalonate (DEDAM) and the ring opening metathesis polymerization (ROMP) of
norbornene (14) (Scheme 4). These reactions were selected because they are representative of
processes of interest to the organic and polymer chemistry communities.
O
O
O
O
EtO
OEt
EtO
OEt
1 mol% [Ru]
c = 0.1M
toluene
12
13
[Ru]
c = 0.1M
toluene or DCM
14
poly(14)
Scheme 4. RCM of diethyl diallylmalonate (12) and ROMP of norbornene (14) mediated by 11.
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Firstly, the RCM of DEDAM was examined at different temperatures in toluene under air
(Figure 3). In a demonstration of the latent nature of the azoxybenzene catalyst the RCM reaction
of DEDAM was monitored by NMR at 25ºC for a one hour, during this time no metathesis
product 13 was detected. Even for longer reaction time the lack of catalyst activity was still
observed. However, its activity was dramatically increased at elevated temperatures. At a catalyst
loading of 1.0 mol % the product 13 was achieved in conversion 60% at 80ºC and 81% at 100ºC
after 60 minutes. Extension of the reaction time up to 90 minutes resulted in conversion 16% at
40 ºC and 99% at 80ºC (see the Supporting Information).
100°C(1%mol)
100
80
60
40
20
0
80°C (1%mol)
25°C (1%mol)
0
10
20
30
40
50
60
time (min)
Figure 3. Conversion-time diagram for the RCM of diethyl diallylmalonate 12 (0.1 M) in
toluene with 1 mol% catalyst.
It is noteworthy that despite of such extreme reaction conditions (toluene 100ºC) catalyst solution
remained almost unchanged orange colour, which indicates that the catalyst is still active.
Nitrogen containing ligands are strong electron donor in the ruthenium complex, which explains
high initiation temperature (80ºC-100ºC) for the catalyst. Slugovc et al. [23] have previously
shown that in the case of nitrogen donor ligands six-membered ring size are more stable than 5-
membered increasing the precatalyst stability and initiation.
Due to the importance of precatalyst latency for ROMP, we decided to investigate latent
catalyst 11 with highly strained ROMP monomer, norbornene (14), as detailed in Table 1.
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Table 1. ROMP of 14 and 15 initiated by complex 11.
monomer
(M)
11
b
solvent
time (h) Conv (%)a
Mn
PDIb
cis/transc
mol%
1
1
DCM
3
1
100
100
100
95
20 639
18 923
32 046
19 240
9 917
1.29
1.21
1.10
1.20
3.21
3.10
61/39
59/41
65/35
58/42
-
14
14
14
14
15
15
toluene
toluene
toluene
toluene
toluene
0.33
0.1
1
2
5
6
80d
81d
0.1
24
10 322
-
a)
1
Reaction conditions: [M] = 0.1 mol·dm-3, RT;
conversion determined by H NMR;
b)
c)
determined by GPC in THF relative to polystyrene standard; cis/trans double bonds of
poly(14) calculated from 1H NMR; d) yield calculated based on the weight of poly(15).
Not surprisingly, the monomer was polymerized leading poly(NBE)s with the molecular
weights (Mn) and polydispersities (PDI) in a range of 32 000 to 19 000 g/mol and 1.10 to 1.29,
respectively. The higher than expected Mn of poly(NBE)s and the lack of a linear relationship
between the Mn of the polymers and the [14]/[11] ratio suggests high propagation rates and slow
initiation rates as well as competing chain-transfer reactions [24]. In fact, monitoring by 1H NMR
spectroscopy the ROMP of 14 (100 equivalents) in the presence of the azoxybenzene catalyst in
deuterated benzene at room temperature shows the lack of propagating species and very low
conversion of initiator. Moreover, alkylidene protons of propagating species were not detectable
during this reaction.
The cis/trans ratio of the obtained poly(NBE) by using the investigated initiator 11 is c.a.
60/40 regardless of solvent used, which is typical for 2nd generation Grubbs initiators bearing
SIMes ligand [25-27].
The complete lack of activity of the new catalyst in RCM toward terminal C-C double bonds,
and at the same time its high activity in ROMP of NBE at room temperature inspired us to test
the complex activity in ROMP of 5-vinyl-2-norbornene (15, Scheme 5).
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[Ru]
c = 0.1M
toluene
15
poly(15)
Scheme 5. ROMP reaction 5-vinyl-2-norbornene (15) mediated by 11.
First the reaction of 15 mediated by catalyst 11 in C6D6 at room temperature was followed by
1
means of H NMR spectroscopy, in order to provide some information about the initiator’s
activity toward vinyl group of the monomer. During the reaction, the disappearance of signals
arising from the internal olefinic protons of 15 and the emergence of signals characteristic for the
vinylene protons of polymer chain at δ 5.24 ppm were observed. Simultaneously, the vinyl
protons signals at δ 5.74 and 4.81 ppm were left intact, indicating that the complex 11 reacts
selectively with the internal C-C double bond of the strained bicycle. Careful investigation of
alkylidene region (above 20 ppm) revealed that small amount of the catalyst rearranges to
propagating species, as in the case of ROMP of 14.
The catalytic polymerization reactions of 15 in the presence of different ratios of 11 were then
studied and the results are detailed in Table 1. To our satisfaction, in the presence of complex 11
the polymerization occurs smoothly at room temperature giving polymers soluble in common
organic solvents. Reducing the catalyst’s loading lead to the ROMP reaction requiring a longer
time to complete. Not surprisingly, the initiator produced poly(15) with a broad polydispersites
(3.10 – 3.21) due to chain-transfer reactions [24]. However, the obtained Mn are similar and
polydispersities are lower in comparison with polymers prepared by Balcar et al [19].
1
In order to confirm the structure of the poly(15) H NMR and IR spectra were measured (see
Supplementary Information, Figures S2 and S3). In the 1H NMR spectrum two broad signals at δ
5.68 and 4.86 ppm arising from the vinyl protons and a signal at δ 5.19 ppm due to the olefinic
protons in the polymer chain were observed indicating that the pendant vinyl group was left intact
1
(Fig. S2) [14]. From H NMR spectrum it is possible to estimate if any vinyl groups were
consumed. For this, the integration ratio of resonances due to vinyl protons at δ 4.86 ppm (2H)
and aliphatic protons (7H) in a range of 3.2 and 0.8 ppm was calculated giving a value of 2/7.2.
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Such good agreement between theoretical and calculated integration ratio supports the lack of
pendant vinyl groups metathesis in the presence of complex 11.
The cis/trans double bond ratio in the polymer chain couldn’t be assessed due to the overlap of
their respective signals with one other [14]. However, IR spectroscopy can permit us to draw
some conclusions concerning the microstructure of the polymer (Fig. S3). The spectrum of
poly(15) exhibits three bands for the pendant vinyl groups; one at 1639 cm-1 assigned to the
stretching vibration
vibration
ν
(C=C) and the two other at 993 and 907 cm-1 arising from the deformation
1
δ
(H-C=). This is in close agreement with the results obtained from H NMR spectrum
of poly(15). Comparing the IR spectra of poly(15) and poly(14) obtained under the same
conditions, the occurrence of bands at 966 and 738 cm-1 indicating olefinic deformation
(H-C=)
δ
of trans and cis olefinic units in polymer chain was observed [28], suggesting that cis/trans ratio
of both polymers are similar.
Conclusions
In conclusion, we have developed, partially on a serendipitous way, a new latent catalyst
system derived from Grubbs 2nd catalyst bearing chelating azoxybenzene ligand. The complex
was inactive in RCM reaction at room temperature but can be subsequently activated by elevated
temperature. Under such conditions, the studied complex was efficient in RCM, had a short
initiation period, and led for the reaction under air. Complex 11 readily polymerised norbornene
at room temperature. The lack of activity of the catalyst in RCM and high activity in ROMP of
NBE at room temperature allowed us to successively carry out ROMP reactions of 5-vinyl-2-
norbornene. Metathesis occurs selectively at the internal olefin yielding soluble polymers with
cyclopentenylenevinylene main chains with vinyl pendant groups. The apparently lack of cross-
linking leaves vinyl pedant groups intact, ripe for further elaboration.
We are continuing to explore the utility of the latent catalyst 11 in the development of new
high temperature polymerization applications.
Experimental section
All reagents were purchased from Sigma-Aldrich, Strem, TCI and Alfa Aesar chemical
companies and used without further purification. Toluene was distilled over potassium under
atmosphere of argon. CH2Cl2 and 5-vinyl-2-norbornene (15) (95%, mixture of endo and exo,
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Sigma-Aldrich) were dried and distilled from CaH2 and stored under inert atmosphere. For
testing the activity of catalyst in RCM HPLC grade solvents (Aldrich), CH2Cl2 and toluene were
used as received. Analytical thin-layer chromatography (TLC) was performed using silica gel 60
F254 precoated plates (0.25 mm thickness) with a fluorescent indicator. Visualization of TLC
plates was performed by UV light either KMnO4 or I2 stains. Flash chromatography was
performed using silica gel 60 (230-400 mesh). NMR spectra were recorded on Agilent 400-MR
DD2 400 MHz, Bruker AMX-300 or Avance-500 MHz spectrometers. NMR chemical shifts are
reported in ppm, and referred to residual solvent peak at 7.26 ppm and 77.16 ppm for 1H and 13C
1
1
in CDCl3, 5.32 and 53.84 ppm for H and 13C in CD2Cl2, 2.50 ppm and 39.52 ppm for H
respectively. The following abbreviations are used in reporting NMR data: s (singlet), d
(doublet), t (triplet), q (quartet), m (multiplet), br (broad). Coupling constants (J) are in Hz.
Spectra are reported as follows: chemical shift (δ, ppm), multiplicity, integration, coupling
constants (Hz). IR spectra were recorded on a Nicolet 8700A FTIR spectrometer. Wave numbers
are in cm-1. GC analyses were performed using Clarus 580 chromatograph using durene as an
internal standard. Micro-analyses were made using CHN 2400 Perkin-Elmer apparatus. Melting
points were recorded on OptiMelt SRS with heating rate 10°C/min. High resolution electrospray
mass spectra (ESI-HRMS) were recorded on Quattro LC triple quadrupole mass spectrometer.
The mass spectrometer was calibrated with an internal standard solution of sodium formate or
sodium iodide in MeOH. IR spectra were measured with a Bruker 113V FTIR instrument in KBr
pellets. Gel Permeation Chromatography (GPC) data were obtained using a Viscotek GPC max
equipped with a refractive index detector Viscotek VE 3580 and 300 mm Phenomenex Phenogel
5 µm 500 Å column. Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1.0 mL/min
at 30°C. Polystyrene standards were used for calibration.
The reactions were carried out under nitrogen using the conventional vacuum/nitrogen line
technique.
Synthesis of ligand
1-bromo-2-nitrosobenzene (6). To a solution of 2-bromoaniline (2 g, 11.62 mmol) in DCM
(10ml) Oxone® (7.14 g, 23.24 mmol) dissolved in water (10 ml) was added. The
O
N+
mixture was stirred under argon at room temperature until TLC monitoring
Br
Br
N
O-
indicated complete consumption of the starting material (12-18h). After separation
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of the layers, the aqueous layer was extracted with DCM (3x30 ml). The combined organic layers
were washed with 3% HCl, saturated sodium bicarbonate solution, water, brine and dried over
MgSO4. Purification by silica-gel chromatography (c-Hex:EtOAc, 30:1) yielded product as a
yellow powder (yield 83%). Crystalline nitrosobenzene was a pale yellow substance due to the
formation of dimer, however in organic solvents that dimer dissociates to the corresponding
monomer, which was visualized as a change in the color of the reaction mixture from yellow to
green. 1H NMR (400 MHz, CDCl3): δ = 7.98 (dd, 1H, J = 8.0, 4.0, Ar-H), 7.53 (ddd, 1H, J = 9.6,
7.2, 1.6, Ar-H), 7.27 (ddd, 1H, J = 9.6, 7.6, 1.2, Ar-H), 6.21 (dd, 1H, J = 8.0, 7.6, Ar-H),
13C NMR (100 MHz, CDCl3): δ = 161.1, 136.6, 135.2, 133.2, 108.9. Anal. Calcd. for C6H4BrNO:
C, 38.74; H, 2.17; N, 7.53; Found: C, 38.38; H, 2.16; N, 7.45.
General procedure for the Stille reaction. The bromide (110 mg, 0.59 mmol), CH2=CHSnBu3
and 5% mol of Pd(PPh3)4 were placed in a Schlenk tube under argon. Dry toluene was added
(5ml) and a mixture was refluxed. Progress of the reaction was monitored by TLC (c-
Hex:EtOAc, 10:1). After full consumption of the substrates the reaction mixture was cooled
down to RT and was stirred with an aqueous solution of KF. The organic phase was separated
and water phase was extracted with DCM (3x20 ml). The organic phases were dried over MgSO4,
filtered and evaporated. The residue was chromatographed with c-Hex:EtOAc, 50:1. Depending
on the reaction condition, three compounds 8, 9, 10 were obtained.
1-bromo-2-[(2-vinylphenyl)-NNO-azoxy]benzene (8). The compound was isolated as a pale
1
yellow oil, it decomposed very fast. H NMR (400 MHz, CDCl3): δ = 7.90 (d,
1H, J = 8.0, Ar-H), 7.81 (d, 1H, J = 8.0, Ar-H), 7.76-7.73 (m, 2H, Ar-H), 7.53-
N
7.43 (m, 1H, Ar-H), 7.42-7.41 (m, 2H, Ar-H), 7.24-7.13 (m, 2H, Ar-H, CH),
5.81 (d, 1H, J = 16.0, CH=CH2), 5.45 (d, 1H, J = 8.0, CH=CH2), 13C NMR (100
Br
N+
O-
MHz, CDCl3): δ = 142.6, 133.4, 131.7, 130.7, 129.4, 128.3, 127.6, 127.2, 124.0,
123.4, 119.1, 117.8; IR (film from CH2Cl2): ν = 3061, 2917, 1568, 1433, 1410, 1259, 1030, 902,
735cm-1; Anal. Calcd. for C14H11BrN2O: C, 55.47; H, 3.66; N, 9.24; Found: C, 55.70; H, 3.46; N,
9.65, m/z 325.0, [M+Na]+, HRMS calcd. for C14H11N2ONaBr 324.9952, found 324.9940.
1-bromo-2-[(2-bromophenyl)-NNO-azoxy]benzene (9). The compound was isolated as a white
powder, mp: 111-112 °C. 1H NMR (400 MHz, CDCl3): δ = 7.96 (d, 1H, J = 8.0,
Ar-H), 7.76-7.69 (m, 3H, Ar-H), 7.49-7.35 (m, 3H, Ar-H), 7.25-7.20 (m, 1H,
N
Br
Br
N+
O-
13

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Ar-H); 13C NMR (100 MHz, CDCl3): δ = 142.6, 134.1, 133.4, 131.3, 129.7, 128.3, 127.7, 125.2,
123.4, 119.3, 115.0 ; IR (film from CH2Cl2): ν = 3061, 2917, 1606, 1471, 1439, 1410, 1327,
1259, 1030, 902, 735cm-1; m/z 376.9, [M+Na]+, HRMS calcd. for C12H8NaBr2 376.8901, found
376.8887. The analytical data corresponded to the literature.[29]
1-vinyl-2-[(2-vinylphenyl)-NNO-azoxy]benzene (10). The compound was isolated as mixture
with compound 9 (5-10%) as a pale yellow oil, it decomposed very fast. 1H
NMR (400 MHz, CDCl3): δ = 8.26-8.24 (m, 2H, Ar-H), 7.70-7.65 (m, 2H, Ar-
N
H), 7.49-7.32 (m, 4H, Ar-H), 7.21-7.14 (m, 1H, CH=CH2), 7.06-7.00 (m, 1H,
N+
O-
CH=CH2), 5.79 (d, 1H, J = 16.0, CH=CH2), 5.74 (d, 1H, J = 20.0, CH=CH2),
13
5.40 (d, 1H, J = 12.0, CH=CH2), 5.30 (d, 1H, J = 12.0, CH=CH2); C NMR
(100 MHz, CDCl3): δ = 141.0, 135.5, 134.3, 133.8, 132.7, 131.7, 130.2, 129.1, 128.3, 128.2,
127.1, 127.8, 125.9, 123.7, 121.7, 117.7, 116.1; IR (film from CH2Cl2): ν = 1465, 1346, 1045,
1025, 927, 750, 590, 440cm-1.
Synthesis of ruthenium complex (11)
In a flame dry Schlenk tube 2nd generation Grubbs catalyst (98 mg, 0.11
N
N
Mes
Mes
mmol), CuCl (12.0 mg, 0.12 mmol) and ligand precursor 7 (35.0 mg, 0.11
mmol) were placed. Then, dry DCM was added under atmosphere of argon
and a mixture was heated to 30ºC. The progress of the reaction was
monitored by TLC (c-Hex:EtOAc, 2:1). After 20 min the reaction mixture
Cl
Cl
Ru
N
N+
Br
O-
was cooled down to RT and the solvent was evaporated. Purification by silica-gel
chromatography (c-Hex:EtOAc, 10:1, followed by c-Hex:EtOAc, 3:2) yielded brick-red solid
(48%). A single crystal of compound 11 suitable for X-ray diffraction studies was grown at a
temperature of +5ºC from a trichloromethane/n-hexane solution. 1H NMR (400 MHz, CD2Cl2): δ
= 17.9 (s, 1H, Ru=CHAr), 8.50 (d, 1H, J = 12.0, Ar-H), 7.87 (dd, 1H, J = 16.0, 8.0, Ar-H), 7.45-
6.88 (m, 10H, Ar-H), 4.28-4.04 (m, 4H, CH2× 2), 2.67-2.34 (br, 15H, CH3 × 5), 2.01 (s, 3H,
CH3); 13C NMR (125 MHz, CD2Cl2): δ = 303.9, 210.9, 142.8, 140.3, 136.8, 134.5, 132.7, 130.5,
129.5, 128.7, 128.0, 125.7, 125.0, 123.0, 116.6, 77.5, 52.2, 51.1, 20.9, 19.9, 19.8, 18.4, 17.6; IR
(film from CH2Cl2): ν = 2913, 1607, 1481, 1414, 1258, 1013, 924, 849, 806, 763, 645, 576, 552
cm-1; Anal. Calcd. for C34H36BrCl2N4ORu: C, 53.13; H, 4.72; N, 7.29; Found: C, 53.81; H, 4.76;
N, 7.27, m/z 791.0, [M+Na]+.
14

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Crystallography
.
Selected single crystals of 11 were mounted in inert oil and transferred to the cold gas stream of
the diffractometer. Diffraction data was measured at 120.0(2) K with mirror monochromated
Mo−Kα radiation on the Oxford Diffraction Gemini A Ultra diffractometer. Cell refinement and
data collection as well as data reduction and analysis were performed with the crysalispro [30].
Absorption effects were corrected analytically from the crystal shape. The structures were solved
by direct methods and subsequent Fourier-difference synthesis with shelxs−97 [31]. Full-matrix
least-squares refinement method against F2 values were carried out by using the shelxl−2013 [31]
and olex2 [30] programs. All non hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were added to the structure model at geometrically idealized
coordinates and refined as riding atoms. The unit cell of 11 contains molecules of solvents:
CHCl3. Crystal data and structure refinement parameters are given in Table S4 (Supplementary
data). Crystallographic data were deposited in Cambridge Crystallographic Database Centre
(CCDC 1537635).
Activity data
1
RCM reaction of diethyl diallylmalonate (DEDAM) monitored by HNMR. In a NMR tube
DEDAM (34.4 mg, 0.143 mmol) was weighed. Then, the tube was filled with non-distilled and
non-degassed toluene (0.5 ml). Pre-catalyst (11) (7.1 µmol) was weighed in the 2 ml flask and the
toluene was added (1.0 ml). The aliquot of the pre-catalyst (0.2 ml, 1.4 µmol) was injected into a
solution of substrate in NMR tube. Data points were collected over an appropriate period of time
using Varian array function at 25°C, 80°C, and 100°C.
RCM reaction of diethyl diallylmalonate (DEDAM) monitored by GC. In a Schelnk tube
DEDAM (34.4 mg, 0.143 mmol) was weighed. Then, the tube was filled with non-distilled and
non-degassed toluene (0.7 ml). Pre-catalyst (11) (1 mol % or 5 mol %) was weighed and added
into a solution of the substrate. Reaction was carried out at 25°C, 40°C, and 80°C. Small amounts
of the reaction mixture were removed from the flask time to time, diluted with CH2Cl2, and
quenched with ethyl vinyl ether before GC analysis.
Procedure for ROMP of 14 and 15. In a typical experiment, monomer (0.1 mol·dm-3) dissolved
in toluene or DCM was added to the initiator 11 dissolved in 0.5 cm3 of the same solvent. The
reaction was allowed to run for an appropriate time at room temperature under nitrogen. The
course of the reaction was monitored by sampling (0.1 cm3) and analysis by 1H NMR. Next, the
15

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reaction was quenched with ethyl vinyl ether (c.a. 0.5 cm3). The polymer was precipitated into an
excess of methanol, isolated and dried under vacuum.
Procedure for ROMP of 14 and 15 in NMR tube. Under a nitrogen atmosphere, complex 11
(0.7 mg, 0.0009 mmol) was weighted into a NMR tube. The benzene-d6 was then added to the
NMR tube via a syringe. Next the relevant monomer (100 equiv.) was added to the NMR tube.
The reactions were monitored by 1H NMR spectroscopy at room temperature.
1
Poly(norbornene) (poly(14)). H NMR (500 MHz, CDCl3): δ = 5.23 (2H, trans HC2,3), 5.18
(2H, cis HC2,3), 2.76 (2H, cis HC1,4), 2.41 (2H, trans HC1,4), 1.74 (3H,
HC5,6,7), 1.33 (2H, H2C5,6), 1.02 (1H, HC7). IR (KBr pellets, cm-1): 966
7
2
3
1
4
trans vinylene δ(H-C=), 738 cis vinylene δ(H-C=).
6
5
1
Poly(5-vinyl-2-norbornene) (poly(15)). H NMR (500 MHz, CDCl3): δ = 5.71 (1H, HC8), 5.27
(2H, HC2,3), 4.90 (2H, H2C9), 5.27 (2H, HC2,3), 2.92, 2.81, 2.62, 2.49, 2.22
7
2
3
1
4
(3H, HC1,4,5), 1.95, 1.71, 1,61, 1.29, 1.19 (4H, H2C6,7). IR (KBr pellets,
cm1): 1639 ν(C=C), 993 and 907 δ(H-C=), 966 trans vinylene δ(H-C=),
749 cis vinylene δ(H-C=).
6
5
9
8
Acknowledgments
The financial support from the Polish National Science Centre, grant number UMO-
2012/04/S/ST5/00062 is gratefully acknowledged.
Supplementary data
The supporting information associated with this article can be found at
Corresponding author
*Karol Grela
Phone: +48-22-8220211 ext. 420, Fax: +48-22-8220211
e-mail address: klgrela@gmail.com
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



Thermo-switchable ruthenium alkylidene complex were isolated and characterized.
The complex was inactive in RCM and active in ROMP at room temperature.
ROMP of 5-vinyl-2-norbornene yielding soluble polymers with vinyl pendant groups.
It provides one-step synthesis of polymers carrying C=C bonds in side chains.