New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with mesityl and nitrobenzyl substituents

Article abstract of DOI:10.1007/s00706-016-1697-7

New indenylidene-type second generation catalysts bearing modified unsymmetrically substituted N- heterocyclic carbene ligands were synthesized. The com- plexes contain an N-mesityl and N?-nitrobenzyl substituted NHC ligand. The precursors of free carbenes—imidazolinium salts—were obtained in an easy and environment- friendly way (under aqueous or neat conditions). The new catalysts were prepared by reaction of in situ generated carbenes with a 1st generation indenylidene catalyst, containing pyridine ligands instead of tricyclohexylphosphine. The complexes were tested in RCM, CM, and ene-yne metathesis model reactions in commercial-grade solvents in air. Their activities were compared with that of commercially available indenylidene catalyst. The structures of complexes and their stability were investigated using static DFT calculations with mixed basis set.

Full text of DOI:10.1007/s00706-016-1697-7

Monatsh Chem
DOI 10.1007/s00706-016-1697-7
ORIGINAL PAPER
New indenylidene-type metathesis catalysts bearing
unsymmetrical N-heterocyclic ligands with mesityl
and nitrobenzyl substituents
Marta Malinowska1 Mariana Kozlowska1 Agnieszka Hryniewicka1
•
•
•
Stanisław Witkowski1 Jacek W. Morzycki1
•
Received: 16 December 2015 / Accepted: 7 February 2016
Ó The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract New indenylidene-type second generation cat-
alysts bearing modified unsymmetrically substituted N-
heterocyclic carbene ligands were synthesized. The com-
plexes contain an N-mesityl and N0-nitrobenzyl substituted
NHC ligand. The precursors of free carbenes—imida-
zolinium salts—were obtained in an easy and environment-
friendly way (under aqueous or neat conditions). The new
catalysts were prepared by reaction of in situ generated
carbenes with a 1st generation indenylidene catalyst, con-
taining pyridine ligands instead of tricyclohexylphosphine.
The complexes were tested in RCM, CM, and ene-yne
metathesis model reactions in commercial-grade solvents
in air. Their activities were compared with that of com-
mercially available indenylidene catalyst. The structures of
complexes and their stability were investigated using static
DFT calculations with mixed basis set.
Keywords Metathesis Á Ruthenium catalyst Á
N-Heterocyclic carbenes Á Nitro compounds Á
DFT calculations
Introduction
Olefin metathesis is a very versatile and powerful method
in organic synthesis [1]. In spite of great progress in
methodology, no universal catalyst, effective in all types of
metathetic transformations has been constructed yet [2–4].
Furthermore, also known complexes (Fig. 1) show
numerous limitations [5, 6]. Therefore chemists in many
laboratories are working on their improvement [7–9],
especially to increase their activity and stereoselectivity
[10]. Air-stable catalysts, that remain robust in commer-
cial-grade solvents, are still needed. Ruthenium
benzylidene complexes (e.g., 1 and 2, Fig. 1) were shown
to be less stable than indenylidene catalysts (e.g., 3–5,
Fig. 1) [11, 12], which are therefore attractive alternatives
to well-known and more frequently used benzylidene cat-
alysts. The indenylidene-bearing family of complexes has
exhibited a rapid growth in use in recent years and is
quickly becoming a mainstream catalyst in metathesis-type
reactions [13].
Graphical abstract
O2N
N
N
Cl
Mes
Ph
N
N
Ru
PCy3
Mes
Cl
NO2
Cl
O2
N
NO2
N
N Mes
Ph
N
Cl
Ru
PCy3
N
Mes
Cl
Cl
New indenylidene-type catalysts, bearing NHC ligands
with N-mesityl and N0-nitroaryl substituents were designed.
We believed that unsymmetrical NHCs could affect the
geometry of the metallacyclobutane intermediate produced
during the reaction with an olefin, thus increasing Z-se-
lectivity of the new catalyst. It was supposed that the olefin
preferentially approaches the Ru-methylidene center from
one side, resulting in an all-cis configuration of metalla-
cyclobutane substituents, leading to a high Z/E ratio of
olefinic products.
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1697-7) contains supplementary
material, which is available to authorized users.
& Marta Malinowska
marta.terpilowska@gmail.com
1
Institute of Chemistry, University of Białystok,
Ciołkowskiego 1K, 15-245 Białystok, Poland
123

M. Malinowska et al.
Fig. 1 Examples of known
ruthenium catalysts
O2N
NO2
N
N
N
N
N
N
NO2
Cl
Cl
Cl
6
7
8
Fig. 2 Examples of unsymmetrical imidazolinium salts
We have previously reported the synthesis of unsym-
metrically substituted imidazolinium salts 6-8 (Fig. 2) [14].
In these salts an ortho-, meta-, or para-nitro substituted
aromatic ring is present.
exchange of carbene ligands in the commercial complexes
failed probably due to poor nucleophilicity of the NHCs
bearing nitroaryl substituents [15].
The above-described observations prompted us to
design complexes with nitrobenzyl groups (type B, Fig. 3).
A methylene spacer should effectively suppress electronic
interaction with the imidazolinium ring. Separating of the
electron-deficient aromatic ring from the imidazolinium
part might enable coordination of the resulting carbene to
the ruthenium center.
Results and discussion
Two types of ruthenium catalysts with modified NHCs
ligands were designed (Fig. 3). The first one (type A) is
based on earlier reported salts 6–8 as the source of NHC
carbene. Several attempts were undertaken to obtain new
catalysts of type A via exchange with the commercial
Hoveyda-Grubbs 1st generation complex (2) or complex 3.
However, all experiments aimed at the NHC ligand
exchange were unsuccessful. An alternative way involving
the NHC carbene generation in situ by thermal decompo-
sition of 2–(pentafluorophenyl)imidazolidine 10 in the
presence of 2 was also attempted. The method also proved
unsuccessful. The adduct 10 was synthesized by acid-cat-
alyzed condensation of 2,3,4,5,6-pentafluorobenzaldehyde
with diaryl substituted ethylenediamine 9, prepared
according to our earlier procedure [14] (Scheme 1).
Synthesis of new imidazolinium salts
New unsymmetrical imidazolinium salts, substituted with
one nitrobenzyl group (as in the type B catalyst, Fig. 3)
were synthesized in a simple and efficient way. N-Mesityl-
1,2-diaminoethane (11) was obtained according to the
modified literature procedure [16]. Condensation of 11 and
ortho– or para-nitrobenzaldehyde under neat conditions
followed by reduction of the resulting imines gave corre-
sponding ethylenediamines in high yields. The compound
12a was converted to dihydrochloride and subjected to
cyclization with trimethyl orthoformate to give the corre-
sponding imidazolinium salt 13a in 77 % yield. In a similar
way the compound 12b was converted to 13b in 80 % yield
(Scheme 2).
We assume that coordination of a carbene, containing
the nitroaryl group directly connected with an imida-
zolinium ring, to the ruthenium center is not feasible. The
123

New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with…
Fig. 3 Proposed new catalysts
O2N
O2N
N
Cl
N
N
N
Cl
Ru
Ru
X
X
Cl
Cl
L
L
A
B
X, L - isopropoxybenzylidene ligand (as in Hoveyda-Grubbs type complexes)
or
X - 3-phenylindenylidene; L - PCy3
Synthesis of new catalysts
two singlets from the aromatic protons) have been well
1
resolved in H NMR. These signals appear also as sepa-
The synthesis of new ruthenium catalysts of type B bearing
a modified NHCs by reaction of in situ generated carbenes
(from new salts 13a and 13b) with the commercially
available indenylidene 1st generation catalyst 3 was
attempted. Unfortunately, the reaction failed probably due
to poor nucleophilicity of the NHCs compared to tricy-
clohexylphosphine ligand in the complex 3. This issue will
be the subject of further detailed investigations (e.g.,
including the Nolan and Cavallo method [17]). To obviate
the problem the PCy3 ligand in 3 was first exchanged for
the more labile one—pyridine [18]. A study of the obtained
complex Cl2Ru(PCy3)-(pyridine)2(3-phenylindenylidene)
(4) revealed that pyridine ligands can be exchanged with
NHCs bearing electron-withdrawing nitro groups [15]. The
bis(pyridine) adduct 4 was obtained from the catalyst 3
with an excess of pyridine as a brownish red solid and
sensitive to air and moisture [19]. The carbenes, generated
in situ from the imidazolinium salts 13a and 13b by
deprotonation with potassium tert-butoxide, were used to
synthesize new ruthenium catalysts. The complexes 14a
and 14b were obtained in 15 and 22 % yields, respectively
(Scheme 3). The attempts to increase the yields were
unsuccessful.
rated singlets in the spectrum of catalyst 5 with
symmetrically substituted NHC [20]. In the 13C NMR
spectra signals from the carbenic carbons were weak. The
HMBC correlation of 14a confirmed the catalyst structure
and showed good correlation of the attached proton signal
from indenylidene group with the weak carbenic carbon
peak.
Testing of new catalysts
The catalytic activity of the new catalysts was investigated
in model RCM, CM, and ene-yne reactions using a reagent-
grade non-degassed solvents in air (Table 1). The reactivity
of the complexes was compared to that of 5. Several
indenylidene-type catalysts have been recently tested in air
[15, 21]. The catalysts proved to be active in RCM reac-
tions leading to di-, tri-, or tetrasubstituted olefins.
Complexes 14a and 14b initiated RCM significantly faster
than 5 (Fig. 4).
In the RCM reaction of diethyl diallylmalonate catalysts
14a and 14b revealed higher reactivity than the commercial
catalyst 5 when the reactions were carried out at 30 °C
(Table 1, entry 1b) and comparable reactivity at elevated
temperature (Table 1, entry 1a). The new complexes more
efficiently promoted the formation of a trisubstituted dou-
ble bond than 5. The conversion using complex 14a was
1
The H NMR spectrum confirmed the structure of the
obtained catalysts. The signals derived from the mesityl
group protons (three singlets from the methyl groups and
123

M. Malinowska et al.
good, while with 14b it was only moderate (Table 1, entry
2). Surprisingly, in the RCM reactions of diethyl dimethyl
allylmalonate leading to tetrasubstituted olefin using
complexes 14a and 14b yields were lower than those for 5
(Table 1, entry 3). Although the results obtained for 5
(Table 1, entries 2 and 3) were worse than those reported
under inert conditions [22, 23], they are reliable. The
experiments performed simultaneously with the same batch
of reagents in air clearly showed differences in reactivity of
5, 14a, and 14b. The tested catalysts very effectively
promoted ring-closing ene-yne metathesis (Table 1, entry
4). Catalyst 14b demonstrated high efficiency in the cross
metathesis reaction of allylbenzene with cis-1,4-diace-
toxybut-2-ene. In this transformation 14b gave higher yield
than 5. It should be noted that both complexes 14a and 14b
showed approximately three times higher Z-selectivity than
123

New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with…
Table 1 Comparative
Entry
Substrates
Products
Condiꢀons
Catalyst
14a
14b
5
Conversion/%a
investigation of catalysts in
RCM, CM and ene-yne
reactions
99
97
99
53
79
31
60 °C, 0.5 h,
toluene, 0.1 M
1a
EtOOC COOEt
EtOOC COOEt
1 mol% [Ru]
30 °C, 2 h
CH2Cl2, 0.1 M
1 mol% [Ru]
14a
14b
5
16
15
1b
2
EtOOC COOEt
EtOOC COOEt
20 °C, 3 h,
CH2Cl2, 0.1 M
14a
14b
71
41
2 mol% [Ru]
17
18
28
5
EtOOC COOEt
EtOOC COOEt
80 °C, 5 h,
toluene, 0.1 M
5 mol% [Ru]
40 °C, 8 h,
14a
7
3
14b
5
19
20
19
38
99
Ph
O
14a
14b
5
Ph
Ph
O
Ph
4
CH2Cl2, 0.1 M
2 mol% [Ru]
30 °C, 20 h,
99
22
21
+
99
OAc
14a
14b
5
45 (E/Z 4:1)
86 (E/Z 3.5:1)
73 (E/Z 11:1)
OAc
5b
CH2Cl2, 0.1 M
2.5 mol% [Ru]
AcO
23
24
25
a Determined by 1H NMR
b E/Z raꢀo determined by 1H NMR, yield of isolated product
that observed for 5 (20 % Z-isomer for 14a, 22 % for 14b,
and 8 % for 5; Table 1, entry 5).
DFT calculations
The reactivity and E/Z selectivity of synthesized complexes
14a and 14b are directly connected with the geometrical
parameters and additional intramolecular interactions in a
particular isomer. In order to estimate the most probable
structure of the indenylidene-type second generation cata-
lysts the static DFT calculations were performed. We have
considered 13 different conformers of each catalysts 14a
and 14b. After geometry optimization some of the con-
formers converged to a similar local minimum or had very
Fig. 4 RCM of diethyl diallyl malonate in CH2Cl2 at 30 °C with
1 mol% catalyst 5, 14a, and 14b. Conversion was determined by H
NMR spectroscopy
1
123

M. Malinowska et al.
Fig. 5 The global minima structures of 14a (a) and 14b (b) complexes with the corresponding values of absolute (Eabs) and relative (Erel) energy
obtained using B3LYP/6-311G(d,p)-LANL2DZ for P, Cl, and Ru atoms
close absolute energies. As a result, we have chosen 6
conformers per isomer (see Supplementary Material) to
show the structural diversity of the synthesized catalysts
and influence of weak interactions on their catalytic
activity. The global minima structures of 14a and 14b are
shown in Fig. 5 and represent the most stable structures of
complexes in the gas phase. More detailed description of
these structures is available in Supplementary Material.
On the basis of computational results we have esti-
mated the structural determinants which influence the
stability and E/Z selectivity of the synthesized catalysts.
Weak intramolecular interactions such as C–HÁÁÁO,
C–HÁÁÁCl, C–HÁÁÁp hydrogen bonds and attractive p–p
stacking interactions are among them. The structural
parameters of the mentioned H-bonds, that denote their
strength, are shown in Supplementary Material. No
specific interactions between the o-nitro group of complex
14a and the ruthenium atom were identified. The average
Ru–P, Ru-Cl(1), and Ru-Cl(2) bond lengths amount 2.52,
Ru-methylidene center and therefore relatively more of a
Z-olefinic product is formed.
Conclusion
In summary, the synthesis of two new ruthenium
indenylidene-type catalysts bearing unsymmetrical NHC
ligand was described. A three-step protocol for the syn-
thesis of unsymmetrical precursors of NHC with mesityl
and nitrobenzyl substituents was elaborated. Despite initial
failures in synthesis of catalysts associated with weak
nucleophilicity of nitroaryl substituted NHCs, new com-
plexes with nitrobenzyl substituted NHC were obtained.
The complexes were tested in model RCM, leading to
formation of five-membered cyclic products bearing di-,
tri-, or tetrasubstituted double bonds, as well as ene-yne
reactions. The metathesis reactions were carried out in
commercial-grade solvents in air. The catalysts were also
tested in a model CM reaction of allylbenzene with cis-1,4-
diacetoxybut-2-ene showing increased Z-selectivity. The
reactivity and higher Z-selectivity compared to 5 of the
synthesized catalysts were explained on the basis of their
conformational preferences determined by the static DFT
calculations.
˚
˚
2.45, and 2.55 A for 14a and 2.53, 2.48, and 2.54 A for
14b, respectively.
Higher Z-selectivity of the synthesized 14a and 14b
compared to the commercial complex 5 is mainly due to
the unsymmetrical NHC ligand, which induces the
indenylidene ligand to be located on the side of the mesityl
group, but not the nitrobenzyl one. The relative energy
differences between such conformers amount about 50 and
20 kJ/mol for 14a and 14b, respectively (see Supplemen-
tary Material). Additionally, the movements of chlorine
ligands are suppressed due to the presence of stabilizing
C–HÁÁÁCl H-bonds. Therefore, olefin molecules are
restricted to the nitrobenzyl side for binding to the
Experimental
Most manipulations of organometallic compounds were
carried out using standard Schlenk techniques under an
atmosphere of dry argon. CH2Cl2, hexane, toluene, and
123

New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with…
evaporated in vacuo to give 4.317 g of a pale yellow oil
1
chloroform were dried by distillation over CaH2, pyridine
over KOH. Melting points were determined on a Kofler
(97 %). IR, H and 13C NMR spectra were found to be
1
apparatus of the Boetius type. H and 13C NMR spectra
identical with those described in literature [25].
were recorded on a Bruker Avance II spectrometer (400
and 100 MHz, respectively). Spectra are referenced rela-
tive to the chemical shift (d) of TMS. Mass spectra were
obtained with Micromass LCT TOF and AutoSpec Premier
(Waters) spectrometers. Infrared spectra were recorded on
a FT-IR spectrometer as KBr pellets or as solid samples
using the ATR technique. Flash chromatography (FC) was
performed on silica gel 230–400 mesh. Yields refer to
chromatographically purified products unless otherwise
stated. Catalysts 3 and 5 were commercially available.
Substrates for testing catalysts in RCM reactions were
prepared by allylation of commercial diethyl malonate with
allyl bromide and/or 3-chloro-2-methylpropene according
General procedure for the preparation of diamines
12a and 12b
An appropriate aldehyde (1 equiv.), 11 (1.5 equiv.) and
˚
molecular sieves 4 A were stirred under Ar atmosphere
overnight. Then, to the resulting mixture 10-30 cm3 of
MeOH was added and the flask was placed in an ice-
cooling bath. Next NaBH4 (5 equiv.) was added portion-
wise (three portions with 10 min intervals) and the mixture
was stirred for 2 h at room temperature. The solvent was
evaporated to dryness and the crude mixture was washed
with saturated NaHCO3 (aq.) solution until pH became
slightly basic. The product was extracted with ethyl acet-
ate. Combined organic layers were washed with brine and
water and dried over anhydrous Na2SO4. The solvent was
evaporated in vacuo, and the obtained solid was purified
by flash chromatography (hexane-AcOEt) to afford the
expected product.
1
to Hensle [24]. Their purity was estimated by H NMR
spectroscopy and found to be at least 95 %. Other chemi-
cals are commercially available and used as received.
N-Mesityl-N’-(2-nitrophenyl)ethylenediamine (9) was pre-
pared according to literature [14].
N-Mesityl-N0-(3-nitrophenyl)-2–(pentafluorophenyl)imida-
zoline (10, C24H20F5N3O2)
N-(2-Nitrobenzyl)-N0-mesitylethylenediamine
To a solution of 72 mg N-mesityl-N0-(3-nitrophenyl)ethylene-
diamine (0.24 mmol) in 0.5 cm3 AcOH 80 mg 2,3,4,5,6–
pentafluorobenzaldehyde (0.41 mmol) was added and the
reaction mixture was stirred for 1 h. The resulting precipitate
was filtered off and washed with cold methanol to afford
80 mg (70 %) of compound 10 as a yellow solid. M.p.:
163–164 °C; 1H NMR (400 MHz, CDCl3): d = 7.58 (d, 1H,
J = 7.9 Hz, H-Ar), 7.41 (s, 1H, H-Ar), 7.32 (t, 1H,
J = 8.2 Hz, H-Ar), 6.91 (s, 1H, H-Ar), 6.81 (s, 1H, H-Ar),
6.78 (m, 1H, H-Ar), 6.39 (s, 1H, CHC6F5), 3.99 (q, 1H,
J = 7.9 Hz, CH2), 3.91 (t, 1H, J = 7.6 Hz, CH2), 3.83 (m,
1H, CH2), 3.65 (q, 1H, J = 8.0 Hz, CH2), 2.34 (s, 3H, CH3),
2.27 (s, 3H, CH3), 1.95 (s, 3H, CH3) ppm; 13C NMR
(100 MHz, CDCl3): d = 149.3, 144.6, 138.9, 138.0, 136.7,
136.6, 130.6, 129.9, 129.3, 117.5, 115.0, 112.0, 106.5, 70.4,
50.5, 47.1, 20.8, 18.2, 17.9 ppm; MS (ES ?): m/z = 476
([M-H]?), 430 ([M-NO2]?).
(12a, C18H23N3O2)
General procedure was followed using 624 mg 2-nitroben-
zaldehyde (4.13 mmol), 1.094 g N-mesityl-1,2-diaminoethane
(6.2 mmol), and 785 mg NaBH4 (20.65 mmol). After
purification (FC, hexane-AcOEt, v/v 1:1) 1.181 g (91 %)
12a was obtained as a yellow powder. M.p.: 40.1–43 °C;
IR (KBr): v = 3341, 3278, 1616, 1555, 1426, 1117 cm-1
;
1H NMR (400 MHz, CDCl3): d = 7.98 (dd, 1H, J = 8.2,
1.0 Hz, H-Ar), 7.65-7.59 (m, 2H, H-Ar), 7.44 (m, 1H,
H-Ar), 6.84 (s, 2H, H-Ar), 4.12 (s, 2H, CH2), 3.09-3.07 (m,
2H, CH2), 2.88-2.86 (m, 2H, CH2), 2.65 (brs, 2H, NH),
2.29 (s, 6H, 2 9 o-CH3), 2.26 (s, 3H, p-CH3) ppm; 13C
NMR (100 MHz, CDCl3): d = 149.2, 143.6, 135.6, 133.1,
131.2, 129.6, 129.4, 128.0, 124.8, 50.7, 49.6, 48.3, 20.6,
18.4 ppm; MS (ESI?): m/z = 336 ([M?Na]?), 314
([M?H]?).
N-(4-Nitrobenzyl)-N’-mesitylethylenediamine
(12b, C18H23N3O2)
N-Mesitylethylenediamine (11)
Mesitylamine (7 cm3, 50 mmol) and 5.13 g bromoethy-
lamine hydrobromide (25 mmol) were vigorously stirred in
12.5 cm3 of water at 95 °C overnight. After cooling to
room temperature, 15 cm3 of water was added and the
solution was extracted with ethyl acetate. The aqueous
phase was evaporated to dryness, the resulting solid was
recrystallized from MeOH/AcOEt to give a white powder.
To the resulting product 50 cm3 of 20 % KOH (aq.) and
CH2Cl2 were added. The residue was vigorously stirred,
then separated organic layers were washed with brine,
water and dried over anhydrous Na2SO4. The solvent was
General procedure was followed using 971 mg 4-nitroben-
zaldehyde (6.43 mmol), 1.679 g N-mesityl-1,2-diaminoethane
(9.65 mmol), and 1.222 g NaBH4 (32.17 mmol). After
purification (FC, hexane-AcOEt, v/v 1:1) 1.913 g (95 %)
12b was obtained as a yellow powder. M.p.: 56.1-58.6 °C;
IR: v = 3350, 2914, 1604, 1515, 1340 cm-1 1H NMR
;
(400 MHz, CDCl3): d = 8.39 (d, 2H, J = 8.7 Hz, H-Ar),
7.54 (d, 2H, J = 8.6 Hz, H-Ar), 6.85 (s, 2H, H-Ar), 3.97 (s,
2H, CH2), 3.08–3.10 (m, 2H, CH2), 2.86-2.89 (m, 2H,
CH2), 2.30 (s, 6H, 2x o-CH3), 2.26 (s, 3H, p-CH3) ppm;
13C NMR (100 MHz, CDCl3): d = 148.0, 147.0, 143.4,
123

M. Malinowska et al.
131.2, 129.5, 129.4, 128.5, 123.5, 53.0, 49.5, 48.1, 20.4,
18.3 ppm; MS (EI ?): m/z = 148 (MesNHCH?2 •), 313
(M?).
resulting red solid, the imidazolinium salt (2 equiv.) and
t-BuOK (2 equiv.) were placed in a flame dried Schlenk
tube and dry toluene was added. The mixture was stirred
for 30 min at 80 °C in a preheated oil bath. The progress of
the reaction was monitored by TLC (hexane-AcOEt, v/v
7:3). After complete consumption of substrate the reaction
mixture was cooled down to room temperature and the
solvent was evaporated. The crude product was purified by
a silica gel chromatography to afford the expected product.
1-Mesityl-3-(2-nitrobenzyl)imidazolinium chloride
(13a, C19H22ClN3O2)
To a suspension of 1.548 g 12a (4.95 mmol) in methanol,
1 cm3 of conc. HCl (9.89 mmol) was added. The solvent
was evaporated, and the dihydrochloride was treated with
7.5 cm3 of trimethyl orthoformate. The reaction mixture
was refluxed under Ar atmosphere for 2 h, and the solvent
was evaporated in vacuo. The residue was dissolved in a
small volume of methylene chloride, and the product was
precipitated with diethyl ether to yield 13a (1.373 g; 77 %)
as a white solid. M.p.: 195–199 °C; IR: v = 3372, 2918,
[[1-Mesityl-3-(2-nitrobenzyl)-2-imidazolidinylidene]-
dichloro-(3-phenyl-1H-inden-1-ylidene)(tricyclo-
hexylphosphine)]ruthenium(II)
(14a, C52H64Cl2N3O2PRu)
General procedure was followed using 26 mg
3
1635, 1518, 1341 cm-1 1H NMR (400 MHz, CDCl3):
;
(0.028 mmol), 20 mg salt 13a (0.056 mmol), and 6 mg
t-BuOK (0.056 mmol). FC (hexane-AcOEt, v/v 8:1) yielded
4 mg of a carmine solid (15 %). IR: v = 3726, 2924, 2850,
d = 9.46 (s, 1H, CH), 8.33 (d, 1H, J = 7.7 Hz, H-Ar), 8.10
(d, 1H, J = 8.2 Hz, H-Ar), 7.78 (t, 1H, J = 7.5 Hz, H-Ar),
7.62 (t, 1H, J = 7.3 Hz, H-Ar), 6.94 (s, 2H, H-Ar), 5.57 (s,
2H, CH2), 4.33-4.27 (m, 2H, CH2), 4.16-4.10 (m, 2H,
CH2), 2.32 (s, 6H, 2x o–CH3), 2.29 (s, 3H, p-CH3) ppm;
13C NMR (100 MHz, CDCl3): d = 159.7, 148.5, 140.0,
135.0, 134.6, 133.4, 130.3, 129.7, 127.8, 125.2, 51.0, 48.7,
48.6, 20.8, 17.7 ppm; MS (ES?): m/z = 324 ([M–Cl]?).
1
1525, 1488, 1444, 1344, 1269 cm-1; H NMR (400 MHz,
CDCl3): d = 8.60 (d, 1H, J = 6.9 Hz, H-Ar), 8.43 (d, 1H,
J = 7.2 Hz, H-Ar), 8.01 (dd, 1H, J = 8.7, 1.2 Hz, H-Ar),
7.77 (m, 1H, H-Ar), 7.72 (m, 2H, H-Ar), 7.53 (m, 3H, H-Ar),
7.42 (t, 3H, J = 7.6 Hz, H-Ar), 7.21 (s, 1H, H-Ar), 7.17-
7.24 (m, 1H, H-Ar), 7.05 (m, 1H, H-Ar), 6.43 (s, 1H, H-Ar),
6.04 (s, 2H, CH2), 3.74 (m, 4H, 2x CH2), 2.25-3.25 (m, 3H,
Cy), 2.18 (s, 3H, -CH3), 2.06 (s, 3H, -CH3), 1.90 (s, 3H,
-CH3), 1.21–1.40 (m, 13H, Cy), 1.12-1.01 (m, 7H, Cy),
0.87–0.97 (m, 10H, Cy) ppm; 13C NMR (100 MHz, CDCl3):
d = 291.8, 188.1, 149.8, 140.5, 137.3, 137.1, 136.8, 134.1,
133.7, 133.5, 132.1, 130.9, 129.6, 128.9, 128.6, 128.5,
128.1, 128.0, 127.7, 127.4, 127.3, 126.4, 124.2, 116.1, 52.1,
50.7, 48.8, 35.6, 35.0, 32.8, 32.7, 29.6, 29.4, 27.8, 27.7, 27.6,
27.5, 27.0, 26.9, 26.3, 26.1, 21.0, 18.5, 18.4 ppm; MS
1-Mesityl-3-(4-nitrobenzyl)imidazolinium chloride
(13b, C19H22ClN3O2)
Trimethyl orthoformate (9.5 cm3, 82 mmol) was added to
1.280 g 12b (4.08 mmol) and 765 mg ammonium chloride
(14.3 mmol). The reaction mixture was refluxed, and the
progress of reaction was monitored by TLC. After 2 h the
solvent was evaporated, and the crude product was
dissolved in a small volume of methylene chloride. The
product 13b (1.177 g; 80 %) was precipitated as a white
solid with diethyl ether. M.p.: 267 °C; IR: v = 3383, 3038,
(ESI?): m/z = 988 ([M ? Na]?), 930 ([M-Cl]?); HR-MS
35
64
(ESI?): m/z calcd for C52H ClN3O2P102Ru [M-Cl]?
1632, 1518, 1337 cm-1 1H NMR (400 MHz, CDCl3):
;
930.3509, found 930.3468 (4.4 ppm).
d = 10.37 (s, 1H, CH), 8.25 (d, 2H, J = 8.3 Hz, H-Ar),
7.80 (d, 2H, J = 8.4 Hz, H-Ar), 6.92 (s, 2H, H-Ar), 5.47 (s,
2H, CH2), 4.11 (s, 4H, CH2), 2.30 (s, 6H, 2x CH3), 2.28 (s,
3H, CH3) ppm; 13C NMR (100 MHz, CDCl3): d = 160.1,
148.1, 140.4, 140.3, 134.9, 130.4, 130.3, 129.9, 124.2,
51.0, 48.3, 20.9, 18.0 ppm; MS (ES ?): m/z = 324
([M–Cl]?).
[[1-Mesityl-3-(2-nitrobenzyl)-2-imidazolidinylidene]-
dichloro-(3-phenyl-1H-inden-1-ylidene)(tricyclohexylphos-
phine)]ruthenium(II)
(14b, C52H64Cl2N3O2PRu)
General procedure was followed using 26 mg
3
(0.028 mmol), 20 mg salt 13b (0.056 mmol), and 6 mg
t-BuOK (0.056 mmol). FC (hexane-AcOEt, v/v 8:1)
yielded 6 mg of a carmine solid (22 %). IR: v = 3734,
3625, 2920, 2850, 1526, 1488, 1445, 1269 cm-1; 1H NMR
(400 MHz, CDCl3): d = 8.60 (d, 1H, J = 7.4 Hz, H-Ar),
8.42 (d, 1H, J = 7.1 Hz, H-Ar), 8.01 (dd, 1H, J = 8.2,
1.1 Hz, H-Ar), 7.77 (m, 1H, H-Ar), 7.71 (m, 2H, H-Ar),
7.53 (m, 2H, H-Ar), 7.42 (m, 2H, H-Ar), 7.25-7.15 (m, 3H,
H-Ar), 7.20 (s, 1H, H-Ar), 7.05 (m, 1H, H-Ar), 6.43 (s, 1H,
H-Ar), 6.04 (s, 2H, CH2), 3.76-3.72 (m, 4H, 2x CH2), 2.37-
2.32 (m, 3H, Cy), 2.18 (s, 3H, -CH3), 2.06 (s, 3H, -CH3),
1.89 (s, 3H, -CH3), 1.82-0.86 (m, 30H, Cy) ppm; 13C NMR
General procedure for the preparation of catalysts
14a and 14b
The catalyst 3 (1 equiv.) was placed in a flame dried
Schlenk tube and dry hexane was added under Ar atmo-
sphere. To this suspension dry pyridine (10 equiv.) was
added. The mixture was stirred 1 h at room temperature
before adding dry hexane. The suspension was stored at
-20 °C overnight. The resulting precipitate was filtered and
washed with hexane and dried under vacuum. Next the
123

New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with…
(100 MHz, CDCl3): d = 196.7, 149.8, 140.5, 137.1, 136.7,
133.5, 132.1, 130.9, 128.9, 128.8, 128.7, 128.5, 128.1,
127.7, 127.3, 126.4, 124.2, 116.1, 68.0, 65.7, 52.1, 50.7,
50.7, 50.1, 48.8, 48.5, 35.1, 32.8, 32.7, 30.9, 29.6, 29.5,
27.7, 27.6, 27.5, 27.0, 26.9, 26.4, 25.6, 21.0, 19.5,
18.5 ppm (Ru = C not observed); MS (ESI?): m/z =
988 ([M?Na]?).
General CM procedure for alkenes 23 and 24
To a mixture of alkene 23 (0.1 mmol, 1 equiv.) and alkene
24 (2 equiv.) in CH2Cl2 a solution of a catalyst (5, 14a, or
14b; 2.5 mol%) in CH2Cl2 was added. The resulting mix-
ture was stirred at 30 °C for 20 h and monitored by TLC.
The FC (hexane–ethyl acetate v/v 9:1) purification of the
crude product yielded 25 as a colorless oil. The E/Z ratio
1
General RCM procedure for 15 in CH2Cl2
was determined by H NMR. Spectroscopic characteriza-
tion of product 25 agreed with literature data [28].
To a solution of alkene 15 in CH2Cl2 (0.1 M) a solution of
catalyst 5, 14a, or 14b (1 mol%) in CH2Cl2 was added. The
resulting mixture was stirred at 30 °C for 15, 30, 60, and
120 min and controlled by TLC. The crude product was
Computational details
The classical density functional B3LYP [29] with a mixed
basis set of the Los Alamos angular momentum projected
effective core potential (ECP) using double-f contraction
of valence functions (LANL2DZ) for ruthenium, phos-
phorus, chlorine [30] and 6-311G(d,p) basis set for other
atoms [31] was used for geometry optimization and energy
calculation in the gas phase. The geometry optimization
was performed using the Broyden–Fletcher–Goldfarb–
Shanno (BFGS) algorithm. The high energy and wave-
function convergence criteria of 5 9 10-6 and 1 9 10-8
Hartree, respectively, were used. The level of theory used
for calculations has been recently implemented for geom-
etry optimization in transition-metal-catalyzed reactions
including olefin metathesis with Ru catalysts [32–34]. To
treat dispersion interactions in catalysts the empirical dis-
persion correction of Grimme (D3) with the Becke–
Johnson damping scheme was additionally used [35, 36].
All calculations were performed with ORCA program
package (version 3.0.1) [37]. Avogadro program [38] was
used to visualize structures of the examined complexes.
1
analyzed by H NMR. Spectroscopic characterization of
product 16 agreed with literature data [26].
General RCM procedure for 15 in toluene
To a solution of alkene 15 in toluene (0.1 M) a solution of
catalyst 5, 14a, or 14b (1 mol%) in toluene was added. The
resulting mixture was stirred at 60 °C for 30 min and
controlled by TLC. The crude product was analyzed by 1H
NMR. Spectroscopic characterization of product 16 agreed
with literature data [26].
General RCM procedure for 17
To a solution of alkene 17 in CH2Cl2 (0.1 M) a solution of
catalyst 5, 14a, or 14b (2 mol%) in CH2Cl2 was added. The
resulting mixture was stirred at 20 °C for 3 h and con-
1
trolled by TLC. The crude product was analyzed by H
NMR. Spectroscopic characterization of product 18 agreed
with literature data [26].
Acknowledgments Financial support from the Polish National
Science Center (UMO-2011/02/A/ST5/00459) is gratefully acknowl-
edged. The calculations were partially performed at the
Interdisciplinary Center for Mathematical and Computational
Modeling of the University of Warsaw under Grant No. G63-0.
General RCM procedure for 19
To a solution of alkene 19 in toluene (0.1 M) a solution of
catalyst 5, 14a, or 14b (5 mol%) in toluene was added. The
resulting mixture was stirred at 80 °C for 5 h and moni-
tored by TLC. The crude product was analyzed by 1H
NMR. Spectroscopic characterization of product 20 agreed
with literature data [26].
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://
creativecommons.org/licenses/by/4.0/), which permits unrestricted
use, distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
General ene-yne procedure for 21
To a solution of alkene in CH2Cl2 (0.1 M) a solution of
catalyst 5, 14a, or 14b (2 mol%) in CH2Cl2 was added. The
resulting mixture was stirred at 40 °C for 8 h and moni-
tored by TLC. The crude product was analyzed by 1H
NMR. Spectroscopic characterization of product 20 agreed
with literature data [27].
References
1. Grubbs RH, Wenzel AG, O’Leary DJ, Khosravi E (2015)
Handbook of Metathesis, 2nd edn. Wiley, Weinheim
2. Samojłowicz C, Bieniek M, Grela K (2009) Chem Rev 109:3708
3. Vougioukalakis GC, Grubbs RH (2009) Chem Rev 110:1746
123

M. Malinowska et al.
´
´
4. Ablialimov O, Ke˛dziorek M, Malinska M, Wozniak K, Grela K
21. Guidone S, Songis O, Nahra F, Cazin CSJ (2015) ACS Catal
5:2697
(2014) Organometallics 33:2160
5. Grela K (2014) Olefin Metathesis: Theory and Practice. Wiley,
Weinheim
6. Gade LH, Hofmann P (2014) Molecular catalysts: structure and
functional design. Wiley, Weinheim
22. Broggi J, Urbina-Blanco CA, Clavier H, Leitgeb A, Slugovc C,
Slawin AMZ, Nolan SP (2010) Chem Eur J 16:9215
23. Urbina-Blanco CA, Leitgeb A, Slugovc C, Bantreil X, Clavier H,
Slawin AMZ, Nolan SP (2011) Chem Eur J 17:5045
24. Hensle EM, Tobis J, Tiller JC, Bannwarth W (2008) J Fluorine
Chem 129:968
7. Meek SJ, O’Brien RV, Llaveria J, Schrock RR, Hoveyda AH
(2011) Nature 471:461
8. Zhang W, Moore JS (2007) Adv Synth Catal 349:93
9. Coperet C, Basset JM (2007) Adv Synth Catal 349:78
10. Shahane S, Bruneau C, Fischmeister C (2013) ChemCatChem
5:3436
11. Boeda F, Clavier H, Nolan SP (2008) Chem Commun 2726
´
´
12. Ablialimov O, Ke˛dziorek M, Torborg C, Malinska M, Wozniak
25. Marshall C, Ward MF, Skakle JMS (2006) Synthesis 1040
26. Taber DF, Frankowski KJ (2003) J Org Chem 68:6047
27. Fu¨rstner A, Ackermann L, Gabor B, Goddard R, Lehmann CW,
Mynott R, Stelzer F, Thiel OR (2001) Chem Eur J 7:3236
28. Chatterjee AK, Choi T-L, Sanders DP, Grubbs RH (2003) J Am
Chem Soc 125:11360
K, Grela K (2012) Organometallics 31:7316
29. Lee C, Yang W, Parr RG (1988) Phys Rev B 37:785
30. Hay PJ, Wadt WR (1985) J Chem Phys 82:284
31. Krishnan R, Binkley JS, Seeger R, Pople JA (1980) J Chem Phys
72:650
13. Piola L, Nahra F, Nolan SP (2015) Beilstein J Org Chem 11:2038
14. Malinowska M, Hryniewicka A, Witkowski S, Morzycki JW
(2014) Monatsh Chem 145:1653
¨
15. Vorfalt T, Leuthaußer S, Plenio H (2009) Angew Chem Int Ed
48:5191
32. Herbert MB, Suslick BA, Liu P, Zou L, Dornan PK, Houk KN,
Grubbs RH (2015) J Am Chem Soc 137:5782
´
16. Roche SP, Teyssot M-L, Gautier A (2010) Tetrahedron Lett
51:1265
33. Pazio A, Wozniak K, Grela K, Trzaskowski B (2015) Organo-
metallics 34:563
17. Poater A, Falivene L, Urbina-Blanco CA, Manzini S, Nolan SP,
Cavallo L (2013) Proc Comp Sci 18:845
18. Sanford MS, Love JA, Grubbs RH (2001) Organometallics
20:5314
19. Clavier H, Petersen JL, Nolan SP (2006) J Organomet Chem
691:5444
34. Engle KM, Lu G, Luo S-X, Henling LM, Takase MK, Liu P,
Houk KN, Grubbs RH (2015) J Am Chem Soc 137:5782
35. Grimme S, Ehrlich S, Goerigk L (2011) J Comput Chem 32:1456
36. Grimme S, Antony J, Ehrlich S, Krieg H (2010) J Chem Phys
132:154104
37. Neese F (2012) Wiley Interdiscip Rev Comput Mol Sci 2:73
38. Hanwell M, Curtis D, Lonie D, Vandermeersch T, Zurek E,
Hutchison G (2012) J Cheminform 4:17
20. Monsaert S, Drozdzak R, Dragutan V, Dragutan I, Verpoort F
(2008) Eur J Inorg Chem 432
123