Design of bis-NHC Ru-complexes featuring diarylmethylene N-substituents for olefin metathesis

Article abstract of DOI:10.24820/ark.5550190.p010.894

New ruthenium indenylidene complexes containing N-heterocyclic carbene (NHC) ligands were synthesized and evaluated in olefin metathesis. The presence of two symmetrical saturated NHCs featuring N-diarylmethylene fragments (R= H, OMe or F) led to robust ruthenium precatalysts with a good latency. A kinetic study was investigated showing that a thermal stimulus (>60 °C) is required to reach an efficient catalytic initiation. Interestingly, a slight electronic effect was observed depending on the presence of an electron-donating or –withdrawing group within the diarylmethylene moiety. These complexes showed good activity at 1 mol% of catalyst loading in selected ring-closing metathesis (RCM) and cross-metathesis (CM) transformations.

Full text of DOI:10.24820/ark.5550190.p010.894

The Free Internet Journal
for Organic Chemistry
Paper
Archive for
Organic Chemistry
Arkivoc 2019, part iv, 0-0
to be inserted by editorial office
Design of bis-NHC Ru-complexes featuring diarylmethylene N-substituents for
olefin metathesis
Idriss Curbet,a Jennifer Morvan,a Sophie Colombel-Rouen,a Thierry Roisnel,b Christophe Crévisy,a
and Marc Mauduita,*
a Univ Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR - UMR 6226, F-35000 Rennes,
France. b Univ Rennes, CNRS, ISCR - UMR 6226, F-35000 Rennes, France
Email: marc.mauduit@ensc-rennes.fr
Dedicated to Professor Stephen Hanessian for his landmark contributions to chemistry
Received 01-28-2019
Accepted 03-20-2019
Published on line 04-26-2019
Abstract
New ruthenium indenylidene complexes containing N-heterocyclic carbene (NHC) ligands were synthesized
and evaluated in olefin metathesis. The presence of two symmetrical saturated NHCs featuring N-
diarylmethylene fragments (R= H, OMe or F) led to robust ruthenium precatalysts with a good latency. A
kinetic study was investigated showing that a thermal stimulus (>60 °C) is required to reach an efficient
catalytic initiation. Interestingly, a slight electronic effect was observed depending on the presence of an
electron-donating or –withdrawing group within the diarylmethylene moiety. These complexes showed good
activity at 1 mol% of catalyst loading in selected ring-closing metathesis (RCM) and cross-metathesis (CM)
transformations.
R
R
Good chemical stability
N
N
Require a thermal stimulus
(>60 °C)
R
R
H
H
H
H
R
R
Cl
Ph
Ru
Modular initiation rates
depending on R group
Cl
Active at 1 mol% in RCM
& CM
N
N
R
R
R = H, F or OMe
Keywords: Olefin metathesis, catalyst, ruthenium, NHC, diaminocarbenes, 1,3-dialkylimidazolinium salts
DOI: https://doi.org/10.24820/ark.5550190.p010.894
Page 1
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
Introduction
In the past few decades, olefin metathesis has gained widespread attractiveness and become rapidly one of
the most efficient tools in organic chemistry, thanks to the development of well-defined, air stable and easy to
handle ruthenium-arylidene complexes with high tolerance towards many organic functions.1 Since the
pioneer report of phosphine-based Grubbs first-generation catalyst in early 1990s,2 the quest for more robust
and powerful complexes has never stopped.3 The main achievement in this field was the replacement of one
phosphorus ligand by a N-Heterocyclic Carbene (NHC) which led to more stable and more active complexes,
known as Grubbs second generation catalyst.4 While a plethora of catalysts bearing one diaminocarbene unit
were developed,5 the particular class of Ru-complexes featuring two NHCs, as depicted in Figure 1, has been
less investigated.
Page 2
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
Figure 1. (A) Previously reported ruthenium-based complexes bearing two NHC ligands. (B) Newly designed
bis-NHC ruthenium precatalysts Ru-11.
The first bis-NHC complexes Ru-1a-d were described in 1998 by Hermann and co-workers, prior the synthesis
of the Grubbs second generation catalyst.6-8 However, due to the slow dissociation of the NHC ligand, these
complexes are considered as latent catalysts that require a thermal stimulus to reach satisfactory activities in
various olefin metathesis transformations. Nevertheless, this behaviour is crucial in materials science in which
a perfect control of the catalyst initiation is required for metathesis polymerisation.9 Since these pioneering
works, other groups have reported bis-NHC Ru-complexes, by varying the NHC N-substituents (Ru-2-4),
showing interesting properties in Ring-Opening Metathesis Polymerisation (ROMP).10-12 In 2010, Plenio and
co-workers proposed an elegant strategy to improve the activity of this class of catalysts by introducing an
electron-deficient NHC ligand.13-14 The corresponding Ru-5 complex was quite efficient in challenging RCM
leading to tetrasubstituted olefins. This concept was then reinforced by Plenio and Nolan with the
introduction of small NHC units (Ru-6-7) enabling to enhance the stability of the related complexes but also to
improve their ability to promote RCM transformations at catalyst loadings as low as 0.05 mol%.15-16 In 2011,
Grubbs and Bertrand reported the synthesis of the latent complex Ru-8 containing a NHC and a mesoionic
carbene (MIC).17 Instead of the usual thermal activation as external stimulus, they proposed to involve a
BrØnsted acid promoting the protonolysis of the MIC ligand. The resulting catalyst proved to be extremely
active, surpassing current commercial Ru-catalysts. More recently, we synthesised two new latent complexes
Ru-9 and Ru-10 bearing two unsymmetrical unsaturated N-cycloalkyl-NHCs that were activated by anhydrous
HCl.18 These catalysts were quite efficient in various metathesis transformations, notably in macrocyclic RCM
of terminal dienes affording various macrocyclic odorant molecules of remarkable >99% purity.19 In front of
these results, we decided to continue the development of latent Ru-complexes by introducing novel NHC
ligands. We report herein the synthesis of new ruthenium indenylidene complexes Ru-11 containing two
symmetrical NHCs featuring diarylmethylene fragments.20-22 As expected, these complexes combine a good
chemical stability and a relatively good latency. Furthermore, we observed a slight electronic effect on the
catalyst activity depending on the presence of an electron-donating (R = OMe) or -withdrawing group (R = F)
within the diarylmethylene moiety.
Results and Discussion
We started our study by the synthesis of NHC precursors, namely imidazolinium salts 3a-c incorporating the N-
diarylmethylene substituents, that were readily accessible in a two-step procedure (Scheme 1).
Ethylenediamine 1 was reacted overnight with commercially available benzophenone derivatives 2a-c and
NaBH3CN in refluxing ethanol under acidic conditions (pH 5) to lead to the corresponding substituted
diamines. The latter were then condensed with triethylorthoformate in the presence of ammonium
tetrafluoroborate in neat conditions to afford expected imidazolinium salts 3a-c in moderate to good isolated
yields (19-46%, 2 steps). The structure of 3a was confirmed by single crystal X-ray diffraction (Scheme 1).23 The
targeted complexes Ru-11a-c were synthesized in low to good yields (25-88%) by employing an excess of
azolium salts (3 equiv) in presence of potassium hexamethyldisilazane (KHMDS) followed by the addition of
commercially available (PCy3)2Cl2Ru-indenylidene complex M1. Before studying their ability to catalyze olefin
metathesis reactions, we decided to examined their chemical stability in toluene-d8 (10 mM) at 60 °C (Figure
2). As expected, each complex showed a relatively good thermal stability as a full decomposition occurred
after four days for the less stable one (Ru-11b) and in more than three weeks for the more stable one (Ru-
Page 3
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
11a). This significant difference of stability could be connected to the presence of the electron-
withdrawing/donating groups within the aromatic fragments promoting a beneficial or detrimental electronic
effect on the NHC units. Nevertheless, we suspected also that fluorine atoms could interact directly with the
ruthenium center through intermolecular interactions, leading to a faster decomposition of complex Ru-11b.24
O
H2N
X-ray structure of 3a
+
NH2
R
R
1
2a-c
1. NaBH3CN
EtOH (pH 5), reflux, 12 h
R
R
2. NH4BF4, HC(OEt)3
120 °C, 2 h
N
N
R
R
BF4
N
R
R
H
H
H
H
PCy3
Cl
Ru
R
R
Cl
1) KHMDS
2)
Ph
Ph
Ru
N
toluene, r.t.
5 min.
Cl
Cl
R
H
H
PCy3
R
M1 (0.25 eq)
N
N
3a R = H (46%)
3b R = F (45%)
60 °C, 3 h
3c R = OMe (19%)
R
R
Ru-11a R = H (73%)
Ru-11b R = F (88%)
Ru-11c R = OMe (25%)
Scheme 1. Synthesis of NHC precursors 3a-c and related Ru-complexes Ru-11a-c.
Page 4
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
Figure 2. Chemical stability of complexes Ru-11a-c in toluene-d8 (0.01 M) at 60 °C. Pre-catalyst decomposition
was monitored by 1H NMR spectroscopy with anthracene as internal standard. Ru-11a (orange) ; Ru-11b
(blue) ; Ru-11c (green).
Having bis-NHC Ru-complexes Ru-11a-c in hand and their respective chemical stability behavior being
evaluated, we next investigated their activity profiles in Ring-Closing Metathesis (RCM) of sterically-
demanding methallyl-allyl diethylmalonate 4 (Figure 3) under homogeneous standard conditions (i.e. toluene
0.1 M, 1 mol%)25 at 60 and 80 °C. As depicted in figure 3, the initiation rate of catalyst Ru-11a at 60 °C
appeared more pronounced than that of catalyst Ru-11b and the conversion remained incomplete for both
complexes reaching respectively 75 and 70% after 24 h. As expected, at 80 °C, higher initiation rates were
observed, but with no significant difference between Ru-11a and Ru-11b. Nevertheless, in accordance with
their intrinsic thermal stability mentioned above (Figure 2), the catalytic death of Ru-11b occurred within 60
minutes, leading to only 80% conversion while the more stable Ru-11a afforded the full completion of the
metathesis transformation over 3 h. Regarding the complex Ru-11c featuring p-methoxyphenyl groups on the
NHC, the initiation rate was lower and the catalytic death operated before the completion of the reaction,
reaching a maximum of 92% conversion over 15 h.
EtO2C CO2Et
EtO2C CO2Et
catalyst (1 mol%)
toluene (0.1 M), 60 °C
4
5
Figure 3. Catalytic activity profiles of complexes Ru-11a-c for RCM of methallyl-allyl diethylmalonate 4 at 60 °C
1
(dotted line) and 80 °C (solid line). Conversions were monitored by H NMR spectroscopy with mesitylene as
internal standard. Ru-11a (orange) ; Ru-11b (blue) ; Ru-11c (green).
We next evaluated the catalytic performance of complexes Ru-11a and Ru-11b in a selection of olefin
metathesis transformations performed in toluene (0.1M) at 80 °C with 1 mol% catalyst loading (Table 1).26 To
Page 5
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
our delight, excellent conversions and isolated yields (69-97%) were achieved in all RCM after 3 to 5 h of
reaction (entries 1-8). Of note, no significant difference regarding the catalytic performance occurred between
involved precatalysts as similar level of conversions and yields were observed. Interestingly, Ru-11a and Ru-
11b showed also good reactivity toward the reluctant substrate 16 leading to the corresponding tetra-
substituted cyclic olefin 17 in 69 and 71% isolated yield respectively (entry 6). Concerning the CM
transformation (entry 9), precatalyst Ru-11a showed higher efficiency by affording the expected metathesis
product 23 in good 71% isolated yield whereas 55% were reached with Ru-11b.
Table 1. Substrate scope in olefin metathesis transformations catalyzed by Ru-11a and Ru-11b.a
Entry
substrate
EtO2C CO2Et
product
catalyst
time (h)
5
Conv.b(yield)c
92% (77%)
EtO2C CO2Et
Ru-11a
1
Ru-11b
Ru-11a
5
3
95% (83%)
97% (89%)
6
7
EtO2C CO2Et
EtO2C CO2Et
2
3
4
Ru-11b
Ru-11a
3
5
>98% (97%)
95% (82%)
8
9
Ts
N
Ts
N
10
11
Ru-11b
Ru-11a
5
5
85% (77%)
97% (86%)
Ts
N
Ts
N
Ru-11b
Ru-11a
4
5
>98% (92%)
97% (83%)
12
Ts
N
13
Ts
N
5
6
7
Ru-11b
Ru-11a
5
5
94% (86%)
74% (71%)
14
Ts
N
15
Ts
N
Ru-11b
Ru-11a
5
5
76% (69%)
95% (87%)
16
17
O
O
Ru-11b
Ru-11a
5
5
95% (88%)
>98% (nd)
18
19
21
8d
9
Ru-11b
Ru-11a
5
5
>98% (nd)
Nd (71%)e
20
Ph
Ph
Ph
22
23
Ru-11b
5
Nd (55%)e
Page 6
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
a
b
1
Reaction conditions: 1 mol% catalyst, toluene (0.1 M), 80 °C. Conversions were determined by H NMR
c
d
spectroscopy with trimethoxybenzene as internal standard. Isolated yield after purification on silica gel.
Reaction performed at 60 °C;. e E/Z Ratio: 8/2; determined by 1H NMR spectroscopy. Nd: no determined.
Conclusions
To conclude, 3 new ruthenium indenylidene complexes containing N-heterocyclic carbene (NHC) ligands were
synthesized and evaluated in olefin metathesis. The presence of two symmetrical saturated NHC units
featuring N-(diarylmethyl) fragments [(RC6H4)2CH-; R= H, OMe or F)] led to highly robust ruthenium
precatalysts Ru-11a-c. The full decomposition of catalysts occurred after 4 days at 60 °C for the least stable
complex and in more than three weeks for the most stable one. These new latent catalysts could be activated
by a thermal stimulus (80 °C) to reach a faster catalytic initiation with a full completion in the Ru-11a catalyzed
RCM of methallyl-allyl diethylmalonate over 3 h. Interestingly, a slight electronic effect was observed
depending on the presence of an electron-donating or –withdrawing group within the diarylmethylene
moiety. Moreover, complexes Ru-11a and Ru-11b showed good activity at 1 mol% of catalyst loading in a
selection of ring-closing metathesis (RCM) and cross-metathesis (CM) transformations. Further studies to
extend the design of N-diarylmethyl fragments for asymmetric metathesis are currently underway and will be
reported soon.
Experimental Section
General. All reactions were carried out under an atmosphere of argon using standard Schlenk techniques.
Toluene, diethyl ether, dichloromethane and tetrahydrofuran were purified using MBraun Solvent Purification
Systems. All commercial chemicals were used as received unless otherwise noted. The 1 M solution of
hydrogen chloride in ethanol and 0.5 M solution of KHMDS were purchased from Acros Organics with AcroSeal
packaging. NMR spectra were recorded on a Bruker ARX400 spectrometer (1H (400 MHz), 13C (101 MHz), 19F
(376 MHz) and 11B (128 MHz)) with complete proton decoupling for 13C. Chemical shifts are reported in parts
1
per million with the solvent resonance as the internal standard (CDCl3, H: δ 7.26 ppm, 13C: δ 77.16 ppm;
DMSO, 1H: δ 2.50 ppm, 13C: δ 39.52 ppm). Coupling constants are reported in Hertz (Hz). Abbreviations are
used as follows: s = singlet, d = doublet, t = triplet, dd = double doublet, td = triple doublet, q = quartet, m =
multiplet. High Resolution Mass Spectrometry (HRMS) was recorded on a Waters QTof-I spectrometer using
electrospray ionization at the Centre Régional de Mesures Physiques de l’Ouest (CRMPO), Université de
Rennes 1. Melting points were measured on a Stuart Melting Point Apparatus SMP3 and are uncorrected.
General procedure for synthesis of imidazolinium salts. Ethylenediamine (1 equiv), diarylketone (2 or 3
equiv), sodium cyanoborohydride (3 equiv) and ethanol (3 mL/mmol) were added in a round bottom flask. The
pH of the solution was adjusted at 5-6 with a 1 M solution of HCl.EtOH and the mixture was refluxed
overnight. After cooling to room temperature, the solvent was evaporated and the crude mixture was
dissolved in DCM and washed with a saturated solution of NaHCO3. The crude product was purified by flash
chromatography (DCM/acetone as eluent) and used for the next step. Then, the diamine (1 equiv), NH4BF4 (1
equiv) and triethylorthoformate (1 mL/mmol of diamine) were heated at 120 °C during 2 h under an argon
atmosphere. The volatiles were removed under vacuum and the corresponding imidazolinium salt was
purified by precipitation with diethyl ether or by flash chromatography on silica gel (DCM/acetone).
Page 7
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
1H-1,3-Dibenzhydryl-4,5-dihydroimidazolinium tetrafluoroborate (3a). Following the general procedure for
the synthesis of symmetric imidazolinium salts with benzophenone (3.681 g, 20.2 mmol) and ethylenediamine
(680 µL, 10.2 mmol), the desired product was isolated as a white solid (2.2983 g, 46% yield) after purification
by chromatography on silica gel (DCM/acetone 98/2). mp 205 °C; 1H NMR (400 MHz, DMSO-d6) : δ (ppm) 8.22
(s, 1H), 7.45-7.34 (m, 20H), 6.25 (s, 2H), 3.85 (s, 4H); 13C NMR (101 MHz, DMSO-d6) : δ (ppm) 158.1, 136.7,
129.0, 128.6, 128.2, 64.8, 48.0; 19F NMR (376 MHz, DMSO-d6) : δ (ppm) -148.3, -148.2; 11B NMR (128 MHz,
DMSO-d6) : δ ppm) 1.2; HRMS (ESI) : m/z : M+ (C29H27N2) calc. : 403.21742 ; found : 403.2173 (1 ppm).
1H-1,3-Bis[di-(4-fluorophenyl)methyl]-4,5-dihydroimidazolinium tetrafluoroborate (3b). Following the
general procedure for the synthesis of symmetric imidazolinium salts with 4,4' difluorobenzophenone (3.298
g, 15.1 mmol), ethylenediamine (350 µL, 5.2 mmol) the desired product was isolated as a white solid (1.259 g,
1
45% yield) after precipitation. mp 194 °C; H NMR (400 MHz, DMSO-d6) : δ (ppm) 8.17 (s, 1H), 7.40-7.36 (m,
8H), 7.29-7.24 (m, 8H), 6.22 (s, 2H), 3.80 (s, 4H); 13C NMR (101 MHz, DMSO-d6) : δ ppm) 162.1 (d, J 246.6 Hz),
158.2, 132.8 (d, J 3.1 Hz), 130.5 (d, J 8.5 Hz), 115.9 (d, J 21.7 Hz), 63.4, 47.8; 19F NMR (376 MHz, DMSO-d6) : δ
(ppm) -148.3, -148.2, -113.3; 11B NMR (128 MHz, DMSO-d6) : δ (ppm) -1.3; HRMS (ESI) : m/z : M+ (C29H23N2F4)
calc. : 475.17974 ; found : 475.1794 (1 ppm).
1H-1,3-Bis[di(4-methoxyphenyl)methyl]-4,5-dihydroimidazolinium tetrafluoroborate (3c). Following the
general procedure for the synthesis of symmetric imidazolinium salts with 4,4'-dimethoxybenzophenone
(3.677 g, 15.2 mmol), ethylenediamine (330 µL, 4.9 mmol) the desired product was isolated as a white solid
(0.570 g, 19% yield) after purification by chromatography on silica gel (DCM/acetone 100/0 to 95/5). mp 57 °C;
1H NMR (400 MHz, DMSO-d6) : δ (ppm) 8.04 (s, 1H), 7.23-7.20 (m, 8H), 6.97-6.94 (m, 8H), 6.07 (s, 2H), 3.77 (s,
4H), 3.73 (s, 12H); 13C NMR (101 MHz, DMSO-d6) : δ (ppm) 159.2, 157.5, 129.5, 128.8, 114.4, 63.9, 55.2, 47.7;
19F NMR (376 MHz, DMSO-d6) : δ ppm) -148.3, -148.2; 11B NMR (128 MHz, DMSO-d6) : δ (ppm) –1.3; HRMS
(ESI) : m/z : M+ (C33H35N2O4) calc. : 523.25913 ; found : 523.2595 (1 ppm).
General procedure for synthesis of bis-carbene complexes. In the glovebox, to a suspension of imidazolinium
salt (4 equiv) in toluene (1 mL/mmol of Ru) was added a 0.5 M solution of potassium bis(trimethylsilyl)amide
in
toluene
(4
equiv).
After
5
minutes
of
stirring,
dichloro-(3-phenyl-1H-inden-1-
ylidene)bis(tricyclohexylphosphine)ruthenium(II) or M1 (1 eq.) was added and the mixture was stirred at 60 °C
outside of the glovebox during 3 h. The crude mixture was purified by flash chromatography using a mixture of
Pentane/Et2O solvent (9/1 to 7/3).
Dichloro-bis(1,3-dibenzhydryl-4,5-dihydroimidazol-2-ylidene)-(3-phenyl-1H-inden-1-ylidene) ruthenium(II)
(Ru-11a). Following the general procedure for the synthesis of bis-carbene complexes with 3a (301.7 mg, 0.61
mmol), KHMDS solution (1.23 mL, 0.61 mmol) and M1 (141.3 mg, 0.15 mmol) the desired product was
obtained as a red solid (132 mg, 73% yield). 1H NMR (400 MHz, CDCl3) : δ ppm) 8.66 (dd, J 7.5, 1.2 Hz, 1H), 7.77
(s, 2H), 7.41-7.32 (m, 3H), 7.31-7.18 (m, 22H), 7.17-7.12 (m, 2H), 7.09-6.93 (m, 16H), 6.91-6.83 (m, 1H), 6.84-
6.77 (m, 4H), 6.77-6.72 (m, 1H), 5.85 (s, 2H), 3.51-3.34 (m, 4H), 3.28-3.17 (m, 4H); 13C NMR (101 MHz, CDCl3) :
δ ppm) 296.5, 214.4, 142.3, 140.8, 140.2, 140.0, 139.4, 138.6,138.5, 138.2, 135.9, 130.3, 130.2, 129.3, 129.2,
128.8, 128.2, 127.9, 127.8, 127.6 127.5, 127.3, 126.9, 126.7, 117.2, 65.5, 64.4, 46.3, 45.6; HRMS (ESI) : m/z :
M+ (C73H62N435Cl2102Ru) calc. : 1166.33895; found : 1166.3400 (1 ppm).
Dichloro-bis(1,3-[di-(4-fluorophenyl)methyl]-4,5-dihydroimidazol-2-ylidene)-(3-phenyl-1H-inden-1-ylidene)
ruthenium(II) (Ru-11b). Following the general procedure for the synthesis of bis-carbene complexes with 3b
(104.3 mg, 0.18 mmol), KHMDS solution (0.36 mL, 1.18 mmol) and M1 (39.1 mg, 0.04 mmol) the desired
product was obtained as a red solid (48.5 mg, 88% yield). 1H NMR (400 MHz, CDCl3) : δ ppm) 8.54 (dd, J 7.5, 1.1
Hz, 1H), 7.58 (s, 2H), 7.46-7.41 (m, 1H), 7.32-7.28 (m, 2H), 7.25-7.12 (m, 12H), 7.07 (td, J 7.4, 1.2 Hz, 1H), 6.98-
Page 8
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
6.90 (m, 12H), 6.80 (dd, J 7.4, 1 Hz, 1H), 6.73-6.63 (m, 12H), 5.72 (s, 2H), 3.40-3.35 (m, 4H), 3.20-3.15 (m, 4H);
13C NMR (101 MHz, CDCl3) : δ ppm) 297.1, 214.6, 163.1, 163.0, 161.4 (d, J 248.3 Hz), 160.7, 160.6, 142.3, 141.3,
140.0, 138.1, 135.2, 135.1, 135.1, 134.5 (d, J 3.0 Hz), 133.7 (d, J 3.4 Hz), 133.6 (d, J 3.2 Hz), 131.8 (d, J 7.1 Hz),
131.7 (d, J 7.2 Hz), 130.7 (d, J 2.8 Hz), 130.6 (d, J 2.6 Hz), 129.5, 129.2, 129.0, 128.7, 128.4, 126.9, 117.6, 115.1,
115.0, 114.9, 114.8, 114.7, 114.6, 64.4, 63.3, 46.0, 45.3; 19F NMR (376 MHz, CDCl3) : δ ppm) -114.3, -114.3, -
115.1, -115.7; HRMS (ESI) : m/z : M+ (C73H54N4F8 35Cl2 102Ru) calc. : 1310.26358 ; found : 1310.2648 (1 ppm).
Dichloro-bis(1,3-[di-(4-methoxyphenyl)methyl]-4,5-dihydroimidazol-2-ylidene)-(3-phenyl-1H-inden-1-
ylidene) ruthenium(II) (Ru-11c). Following the general procedure for the synthesis of bis-carbene complexes
with 3c (349.3 mg, 0.57 mmol), KHMDS solution (1.15 mL, 0.57 mmol) and M1 (132 mg, 0.14 mmol) the
1
desired product was obtained as a red solid (50.4 mg, 25% yield). H NMR (400 MHz, CDCl3) : δ ppm) 8.66 (d, J
7.6 Hz, 1H), 7.50 (s, 2H), 7.38-7.27 (m, 4H), 7.19-7.07 (m, 10H), 6.99-6.93 (m, 1H), 6.92-6.81 (m, 6H), 6.79-6.69
(m, 12H), 6.55-6.48 (m, 8H), 5.70 (s, 2H), 3.79-3.77 (m, 12H), 3.71 (s, 6H), 3.57 (s, 6H), 3.43-3.37 (m, 4H), 3.23-
3.10 (m, 4H); 13C NMR (101 MHz, CDCl3) : δ ppm) 294.9, 214.1, 158.8, 158.3, 158.2, 142.8, 140.3, 139.6, 138.3,
136.1, 132.1, 131.8, 131.5, 130.8, 130.3, 129.1, 128.3, 128.2, 127.4, 127.1, 117.0, 113.2, 113.1, 113.0, 64.5,
63.4, 55.3, 55.2, 55.1, 55.0, 45.9, 45.2; HRMS (ESI) : m/z : M+ (C81H78N4O8 35Cl2 102Ru) calc. : 1406.42347 ;
found : 1406.4244 (1 ppm).
General procedure for stability studies. In a glovebox a NMR tube was charged with Ru complex (0.005
mmol), anthracene (0.005 mmol) as the internal standard, and toluene-d8 (0.5 mL). The tube was sealed and
shaken vigorously. A 1H NMR spectrum was recorded for reference at time = 0. The tube was then placed in an
oil bath set at 60 °C. Degradation was monitored by observing the disappearance of the most downfield signal
( = 8.66 ppm for Ru-11a,  = 8.54 ppm for Ru-11b,  = 8.66 ppm for Ru-11c) by 1H NMR.
General procedure for kinetic studies. Diethyl allyl(methallyl)malonate (51 mg, 0.2 mmol), mesitylene (9.2µL,
0.066 mmol) as the internal standard and toluene (1.8 mL) were added in a schlenk tube under argon. The
solution was equilibrated at desired temperature before the catalyst addition (0.2 mL of a 0.01 M solution of
1
catalyst, 1 mol%). Aliquots were taken and the conversion was calculated from H NMR spectra by comparing
the characteristic signal for allylic proton to the internal standard.
General procedure for metathesis reactions. To a Schlenk apparatus was filled the substrate (0.3 mmol) and
toluene (3 mL, c = 0.1M) under argon, the precatalyst (0.003 mmol) was added. The media was heated at 80 °C
and the progress of the reaction was monitored by TLC until complete conversion or until the catalyst death
was observed. The solvent was removed under vacuum and trimethoxybenzene (0.1 mmol) was added in the
1
mixture as internal standard to determine the conversion by H NMR. Then the crude residue was purified by
column chromatography to yield the pure product. All products description and spectra are available in the
supporting information.
Acknowledgements
This work was supported by the FASO (grant to IC; Z-SELECT) and the Région Bretagne (ARED 2018 N° 601 –
BIOMETA; grant to JM). SR, CC and MM acknowledge the Ecole Nationale Supérieure de Chimie de Rennes
(ENSCR) and the Centre National de la Recherche Scientifique (CNRS) for financial supports. Special thanks to
Umicore AG & Co for a generous gift of M1 ruthenium complex.
Page 9
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
Supplementary Material
1
Characterization data (for all new products), copies of H and 13C NMR, HRMS and melting point associated
with this paper.
References
1. Grubbs, R. H.; Wenzel, A. G.; O’Leary, D. J.; Khosravi, E. Eds., Handbook of Metathesis, 2nd Edition; Wiley-
VCH: Weinheim, Germany, 2015.
https://doi.org/10.1002/9783527674107
2. Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1992, 114, 3974.
https://doi.org/10.1021/ja00036a053
3. Grela, K. Ed., Olefin Metathesis: Theory and Practice, Wiley-VCH: Weinheim, Germany, 2014.
https://doi.org/10.1002/9781118711613
4. Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953.
https://doi.org/10.1021/ol990909q
5. Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746.
https://doi.org/10.1021/cr9002424
6. Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann, W. A. Angew. Chem. Int. Ed. 1998, 38, 2490.
https://doi.org/10.1002/(SICI)1521-3773(19981002)37:18<2490::AID-ANIE2490>3.0.CO;2-X
7. Weskamp, T.; Kohl, F. J.; Herrmann, W. A. J. Organomet. Chem. 1999, 582, 362.
https://doi.org/10.1016/S0022-328X(99)00163-1
8. Ackermann, L.; Fürstner, A.; Weskamp, T.; Kolh, F. J.; Herrmann, W. A. Tetrahedron Lett. 1999, 40, 4787.
https://doi.org/10.1016/S0040-4039(99)00919-3
9. Ung, T.; Helj, A.; Grubbs, R. H.; Schrodi, Y. Organometallics 2004, 23, 5399.
https://doi.org/10.1021/om0493210
10. Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T.-L.; Ding, S.; Day, M. D.;
Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546.
https://doi.org/10.1021/ja021146w
11. Conrad, J. C.; Yap, G. P. A.; Fogg, D. E. Organometallics 2003, 22, 1986.
https://doi.org/10.1021/om0302084
12. Ledoux, N.; Allaert, B.; Linden, A.; Van Der Voort, P.; Verpoort, F. Organometallics 2007, 26, 1052.
13. https://doi.org/10.1021/om060937u
Vorfalt, T.; Leuthäusser, S.; Plenio, H. Angew. Chem. Int. Ed. 2009, 48, 5191.
https://doi.org/10.1002/anie.200900935
14. Sashuk, V.; Peeck, L. H.; Plenio, H. Chem. Eur. J. 2010, 16, 3983.
https://doi.org/10.1002/chem.200903275
15. Bantreil, X.; Randall, R. A. M.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2010, 29, 3007.
https://doi.org/10.1021/om100310f
Page 10
©ARKAT USA, Inc

Arkivoc 2019, iv, 0-0
Curbet, I. et al.
16. Peeck, L. H.; Plenio, H. Organometallics 2010, 29, 2761.
https://doi.org/10.1021/om1002717
17. Keitz, B. K.; Bouffard, J.; Bertrand, G.; Grubbs, B. J. Am. Chem. Soc. 2011, 133, 8498.
https://doi.org/10.1021/ja203070r
18. Rouen, M.; Queval, P.; Falivene, L.; Allard, J.; Toupet, L.; Crévisy, C.; Caijo, F.; Baslé, O.; Cavallo, L.; Mauduit,
M. Chem. Eur. J. 2014, 20, 13716.
https://doi.org/10.1002/chem.201403934
19. Dumas, A.; Colombel-Rouen, S.; Curbet, I.; Forcher, G.; Tripoteau, F.; Caijo, F.; Queval, P.; Rouen, M.; Baslé,
O.; Mauduit, M. Cat. Sci. Techn. 2019, 9, 436-443.
https://doi.org/10.1039/c8cy02115e
20. Selim, K. B.; Matsumoto, Y.; Yamada, K.-I.; Tamioka, K. Angew. Chem. Int. Ed. 2009, 48, 8733. For a
pioneering study dealing with NHC ligands featuring a diarylmethylene fragment in transition metal-
catalyzed reaction
https://doi.org/10.1002/ange.200904676
21. Yigit, B. Transition Met. Chem. 2012, 37, 183. For previously reported Pd(II)complexes bearing a
diphenylmethylene-NHC ligand.
https://doi.org/10.1007/s11243-011-9573-0
22. Yigit, B.; Yigit, M. Özdemir, Inorga Chimica Acta 2017, 467, 75. For previously reported Rh(I)complexes
bearing a diphenylmethylene-NHC ligand
https://doi.org/10.1016/j.ica.2017.07.055
23. CCDC- 1891522 contains the supplementary crystallographic data for this paper. This data can be obtained
free
of
charge
from
The
Cambridge
Crystallographic
Data
Centre
via:
https://www.ccdc.cam.ac.uk/structures/.
24. Ritter, T.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 11768. For a previous report of Ru-
complexes containing a N-fluoro-aryl NHC unit
https://doi.org/10.1021/ja064091x
25. Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006, 25, 5740.
https://doi.org/10.1021/om060520o
26. Due to the low yield reached in the synthesis of Ru-11c, its catalytic performance towards substrates 6-22
was not examined.
Page 11
©ARKAT USA, Inc