Synthesis and catalytic activity of ruthenium indenylidene complexes bearing unsymmetrical NHC containing a heteroaromatic moiety

Article abstract of DOI:10.1039/c6ra18210k

New robust and air stable ruthenium(ii) indenylidene second generation olefin metathesis catalysts with unsymmetrical N-heterocyclic carbene (NHC) ligands were synthesized. Model metathesis reactions were performed in the presence of newly-developed complexes in commercial grade toluene under air, leading to high conversions and good selectivities.

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Synthesis and catalytic activity of ruthenium indenylidene complexes
bearing unsymmetrical NHC containing a heteroaromatic moiety
Michał Smoleńa, Wioletta Kośnika, Rafał Loskab, Roman Gajdaa, Maura Malińskaa, Krzysztof Woźniaka
and Karol Grela*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Abstract
New robust and air stable ruthenium(II) indenylidene second
generation olefin metathesis catalysts with unsymmetrical
10 Nꢀheterocyclic carbene (NHC) ligands were synthesized. Model
metathesis reactions were performed in the presence of newlyꢀ
developed complexes in commercial grade toluene under air,
leading to high conversions and good selectivities.
An example of such a modification is the application of
unsymmetrical 2,5ꢀsubstituted NHC ligands.1a,b Ruthenium
alkylidene complexes bearing NHC ligand with one aliphatic and
35 one aromatic substituent7 have been shown to be significantly
more active in some applications than their symmetrical parent
Grubbs 2nd generation catalyst (Grubbs II, Fig.1).8ꢀ10 This effect
is attributed to the smaller steric bulk of the aliphatic substituent
of these modified NHC ligands rather than changes in their σꢀ
40 electron donating ability.1(a),11
In this manuscript we focused our attention to the ruthenium
indenylidene complexes for several reasons (UmicoreTM M2 Fig.
1); in some cases they have been shown to be more stable than
their benzylidene counterparts.12,13 Modifications of the NHC
45 ligand can induce profound changes in the activity pattern of the
resulting indenylidene catalysts, making some of them more
active than parent catalyst UmicoreTM M214,15 and although
numerous ruthenium benzylidene metathesis catalysts containing
unsymmetrical NHC ligands have been reported,16,17 the NHCꢀ
50 modified indenylidene complexes were much less explored.18
Previously we demonstrated that the replacement of one mesityl
group (Mes, Fig. 1) with a less bulky CH2ꢀaromatic group results
in an increased activity of the corresponding NHCꢀligated Ru
catalysts.18a,18b We anticipated that the heteroaromatic group19 can
55 further modify the electronic and steric properties of this ligand.
Herein we report the synthesis, properties and Xꢀray analysis of
indenylidene 2nd generation catalysts13,20 bearing methyleneꢀ
heteroaryl substituted unsymmetrical NHC ligands, their stability
and performance in olefin metathesis, including selectivity in
60 crossꢀmetathesis (CM), in ethenolysis and in the diastereoꢀ
selective ringꢀrearrangement metathesis (DRRM) reactions.8
Introduction
15 The search for new stable olefin metathesis catalysts
is a permanent challenge due to growing importance of olefin
metathesis not only in academia but also in industry.1,2 A major
breakthrough in the area of the ruthenium based metathesis
catalysts was the replacement of a phosphine ligand in a Grubbs
20 1st generation complex with an Nꢀheterocyclic carbene (NHC).3
An NHCꢀcontaining 2nd generation Grubbs catalysts have been
extensively studied due to their numerous advantages: improved
stability towards air4 and moisture as well as increased reactivity
towards functionalised alkenes in industrial grade solvents.5 As
25 such variation in the steric and electronic characteristics of the
NHC has proven to be fertile ground for the development of the
new metathesis active complexes.5,6
Fig. 1 New indenylidene ruthenium catalysts 5aꢀd and Hoveydaꢀtype
30
catalyst 7 with unsymmetrical NHC ligand and selected commercially
available catalysts.
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which could be synthesised from the imidazolinium salt already
35 in hand presented a viable alternative.23 Salts 3aꢀd were reacted
with chloroform in the presence of KOH to form NHCꢀadducts
4a (65%), 4b (33%), 4c (81%) and 4d (78%). Subsequent
elimination of chloroform from these NHCꢀadducts by heating in
the presence of UmicoreTM M1 (Fig. 1) generated the
40 corresponding carbenes inꢀsitu and afforded new catalysts 5a
(55%), 5b (32%), 5c (30%) and 5d (10%) as red crystalline
solids. Additionally, we successfully prepared Hoveydaꢀtype
catalyst 7 (64 %) by the deprotonation of imidazolinium salt (3a)
and reaction of corresponding carbene with Hoveyda I (Fig. 1) in
45 presence of CuCl (Scheme 3).
Results and discussion
Imidazolinium salts 3aꢀd have been obtained in a linear and short
synthetic sequence (Scheme 1).
5
Scheme 3 Synthesis of Hoveydaꢀtype catalyst 7.
Scheme 1 Synthesis of indenylidene catalysts 5aꢀb.
To compare the activity of new indenylidene catalysts 5aꢀd in
50 olefin metathesis, we selected the ringꢀclosing metathesis (RCM)
of diethyl diallylmalonate 8 as a model reaction. RCM of diene 8
was performed under standard conditions, in toluene, with 0.1 M
concentration of the substrate, using 1 mol% of the catalyst. The
commercially available UmicoreTM M2 catalyst (6) was
55 employed as a reference (Scheme 4).
Commercially available thiopheneꢀ2ꢀcarbaldehyde (1a), furanꢀ2ꢀ
carbaldehyde (1b) along with 1ꢀbenzothiopheneꢀ2ꢀcarbaldehyde
10 (1c) and 1ꢀbenzofuranꢀ2ꢀcarbaldehyde (1d); were prepared
according to literature procedure21 and were converted to
corresponding 1,2ꢀdiamines 2aꢀd via condensation with N1ꢀ
mesitylethaneꢀ1,2ꢀdiamine. The crude imines were then reduced
inꢀsitu with NaBH4 to furnish the corresponding diamines in 80%
15 (2a), 78% (2b), 84% (2c) and 84% (2d) isolated yields. Reaction
of 2aꢀd with triethyl orthoformate afforded imidazolinium
chloride salts, which readily underwent metathesis with NH4BF4
yielding corresponding tetrafluoroborate salts 3a (76%), 3b
(68%), 3c (76%) and 3d (75%). This step was necessary to aid
20 purification of imidazolinium salts by either filtration through
silica gel or crystallization from methylene chlorideꢀtoluene
mixture. Having the NHC precursors in hand, we attempted to
obtain their Ru indenylidene complexes 5aꢀd. Utilising a
conventional metalation route,22 we generated the carbene in
25 solution by deprotonation before reacting with UmicoreTM M1.
Scheme 4 RCM of diethyl diallylmalonate 8.
80
70
60
50
40
30
5a
5b
20
5c
5d
10
6
0
0
1
2
3
4
Time [h]
60 Fig. 2 Reaction profile of RCM of diethyl diallylmalonate 8 (0.1 M) with
1 mol% of catalysts 5aꢀd and 6 (UmicoreTM M2) in dry and degassed
toluene at 30 °C under argon.
Scheme 2 Synthesis of indenylidene catalysts 5cꢀd.
The reaction profiles of complexes 5aꢀd obtained at 30 °C
displayed significant differences in activity (Fig. 2). The catalyst
65 5a was the most active of the series, affording comparable RCM
as UmicoreTM M2, 6 after 3 h.
However, this approach was unsuccessful. Reaction of
30 imidazolinium salt 3b with potassium tertꢀpentoxide in toluene
for 1 hour followed by the addition of commercially available
catalyst UmicoreTM M1 (Fig. 1) afforded corresponding complex
5b in very low yield (7%). Fortunately chloroformꢀNHC adducts,
2
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In contrast, the activity of benzyl derived catalysts 5c and 5d was
significantly decreased under these conditions with conversions
20 remaining below 50% over the same period. Next, we examined
the influence of temperature on the reactivity of complexes 5aꢀd
(Fig. 3 and Fig. 4). Again, the catalyst 5a was found to be most
active at 70 °C (Fig. 2) and 90 °C (Fig. 3), reaching full
conversion after 5 min and almost perfectly duplicating the
25 reaction profile of 6. The catalysts 5b and 5c also exceed 90%
conversion after this time (Fig. 4) while catalyst 5d remained the
least active across all temperature ranges.
100
80
60
40
20
0
5a
5b
5c
5d
6
0
10
20
30
40
100
80
Time [min]
Fig. 3 Reaction profile of RCM of diethyl diallylmalonate 8 (0.1 M) with
1 mol% of catalysts 5aꢀd and 6 (UmicoreTM M2) in dry and degassed
toluene at 70 °C under argon.
60
5
10
15
40
5a
5b
5c
5d
6
100
80
20
0
0
20
40
60
80
Time [min]
60
5a
5b
Fig. 6 Reaction profile of RCM of diethyl diallylmalonate 8 (0.1 M) with
30 1 mol% of catalysts 5aꢀd and 6 (UmicoreTM M2) in nonꢀdegassed toluene
(HPLC grade, SigmaꢀAldrich) at 50 °C under air.
5c
5d
6
40
20
0
The activity of catalysts 5aꢀd at 50 °C was visibly different in dry
distilled toluene under argon and in HPLC grade solvent exposed
35 to air (Fig. 5 and Fig. 6). In the case of RCM of diene 8 carried
out under argon in the dry distilled solvent, similar conversion of
about 80% was achieved for complexes 5a, 5b. In the case of 5c,
5d lower conversion of 65% was obtained (Fig. 5).
Reaction profiles of RCM of diene 8 promoted by catalysts 5aꢀd
40 were quite different in a HPLC grade toluene under air at 50 °C.
Under such conditions the activity of complexes 5b, 5c and 5d
dropped significantly. In the case of 5b only 74% was achieved
while for 5c and 5d it was 71% and 55%, respectively.
Surprisingly, catalyst 5a both in nonꢀdegassed HPLC grade
45 toluene under air and in degassed toluene under argon showed
similar activity and stability, allowing to achieve up to 87% of
conversion in the model reaction (Fig. 6).
0
5
10
15
Time [min]
Fig. 4 Reaction profile of RCM of diethyl diallylmalonate 8 (0.1 M) with
1 mol% of catalysts 5aꢀd and 6 (UmicoreTM M2) in dry and degassed
toluene at 90 °C under argon.
100
80
60
5a
5b
40
5c
5d
6
20
0
0
20
40
60
80
Time [min]
50 Scheme 5 Diastereoselective ring rearrangment metathesis (DRRM) of
cyclopentene (10).
Fig. 5 Reaction profile of RCM of diethyl diallylmalonate 8 (0.1 M) with
1 mol% of catalysts 5aꢀd and 6 (UmicoreTM M2) in dry and degassed
toluene at 50 °C under argon.
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improved with a complex bearing a designer NHC ligand.7b,c We
expected that unsymmetrical NHC moiety would increase the
diastereoselectivity of the catalysts.18 Therefore we decided to
15 carry out a comparative study on performance of complexes 5aꢀd
and commercially available catalyst UmicoreTM M2 in this
particular reaction.
Table 1 Result of DRRM with different catalysts.
Entry
Catalyst
Conversion (%)a
T (°C) trans : cisa
1
2
3
Gru I, Hov Ib
95
95
58
rt
rt
1:1
2:1
Gru II, Hov IIb
Blechert catalystb
rt
9:1
4
5
6
6 (M2)
6 (M2)
5a
>99
>99
95
rtc
2.0:1
3.3:1
3.6:1
5.3:1
3.0:1
4.1:1
3.4:1
4.5:1
3:1:1
3.9:1
As one would expect, catalyst UmicoreTM M2 gave almost the
same result as other SIMesꢀbearing catalysts (trans/cis d.r. =
20 2.0/1, entry 4). In addition, better distereoselectivity was obtained
at 50 °C. However, application of the new catalyst 5a resulted in
much higher diastereoselectivity: trans/cis d.r. = 3.6/1 and high
conversion (entry 6). Catalyst 5c, bearing a benzothiophene
fragment, showed the second highest diastereoselectivity
25 trans/cis d.r. = 3.4/1 (entry 10). Interestingly, furan and
benzofuran complexes 5b and 5d gave much lower
diastereoselectivity (trans/cis d.r. = 3.0/1 and 3.1/1 respectively,
entries 8, 12).
50d
rtc
7
8
5a
5b
>99
62
50d
rtc
9
5b
90
50d
rtc
10
11
12
13
5c
5c
5d
5d
57
98
56
98
50d
rtc
50d
a Determined by gas chromatography.
b Results reported by Blechert et al.6b,c
c Time reaction 17 hours
5
d Time reaction 1 hour
All of the new unsymmetrical catalysts exhibited greater
30 diastereoselectivity at higher temperature (50 °C) than at rt:
catalyst 5a (trans/cis d.r. = 5.3/1, entry 7), 5b (trans/cis d.r. =
4.1/1, entry 9), 5c (trans/cis d.r. = 4.5/1, entry 11) and 5d
(trans/cis d.r. = 3.9/1, entry 13).
Blechert et al. performed diastereoselective ring rearrangement
metathesis of cyclopentene 10 (Scheme 5) with first and second
generation Grubbs and HoveydaꢀGrubbs catalysts. The reaction
10 does not proceed in a truly diastereoselective manner (Table 1,
entries 1ꢀ2), but selectivity (trans/cis d.r. = 9/1, entry 3) can be
35
Table 2 Application of catalysts 5aꢀd and 6 in RCM, CM and EneꢀYne reactions.a
Time
(min)
Conversion
(%)b
Entry
Substrate
Product
Catalyst (mol%)
5a (1)
5b (1)
5c (1)
5d (1)
6 (M2) (1)
7 (1)
30
30
120
120
180
60
>99
99
93
95
96
93
94
1
Hoveyda II (1)
60
5a (1)
5b (1)
5c (1)
5d (1)
6 (M2) (1)
7 (1)
30
30
30
30
60
60
10
>99
>99
99
2
99
>99
>99
>99
Hoveyda II (1)
5a (2)
5b (2)
5c (2)
30
30
60
44
>99
99
3
4
5d(2)
6 (M2) (2)
7 (2)
180
30
240
5
64
>99
42
Hoveyda II (2)
99
5a (2)
5b (2)
5c (2)
5d (2)
6 (M2) (2)
7 (2)
180
180
180
180
180
300
300
70c E/Z 4.0/1d
55c E/Z 3.2/1d
62c E/Z 3.4/1d
54c E/Z 3.2/1d
75c E/Z 9.4/1d
68 c E/Z 3.7/1d
76 c E/Z 9.3/1d
Hoveyda II (2)
a All reactions were performed in nonꢀdegassed toluene (HPLC grade, SigmaꢀAldrich) at 50 ºC under air.
40 b Conversion was determined by gas chromatography using durene as internal standard.
c Isolated yield.
d E/Z ratio was determined by gas chromatography.
4
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45 We tested catalysts 5a, 7 and compared their activity to
commercially available catalysts UmicoreTM M2 and Hoveyda
II (Table 3). All catalytic tests were performed at 50 °C using
low catalysts loading (500 ppm). The commercially available
catalysts UmicoreTM M2 and Hoveyda II achieved conversions
50 of 77% and 71%, respectively. The new catalysts 5a and 7 gave
14% and 39% of conversion. As we expected the catalysts 5a and
7 showed higher selectivity in favour of the major ethenolysis
products (23 and 24) compared to catalysts UmicoreTM M2 and
Hoveyda II.
Encouraged by the results from the initial catalytic tests (Fig. 2ꢀ6)
relative to UmicoreTM M2, we decided to investigate the
performance of the new catalysts with a small selection of
substrates in nonꢀdegassed HPLC grade toluene (Table 2). Under
these conditions all catalysts tested, including the commercial
UmicoreTM M2 showed very high activity in ring closing
metathesis (RCM) of standard test substrates (entries 1ꢀ2).
However, the new unsymmetrical catalysts required shorter
reaction times to reach full conversion (Table 2, entry 1ꢀ2). In the
10 case of eneꢀyne metathesis (RCEYM), catalysts 5b, 5c as well as
Hoveyda II and UmicoreTM M2, showed very high activity, in
contrast to complexes 5a, 5d and 7 which gave lower conversion
in reaction of enyne 17, although no clear link to heterocyclic
substituent can be drawn. In the crossꢀmetathesis (CM) of
15 allylbenzene (19) and 1,4ꢀdiacetoxybutꢀ2ꢀene (20) all of the new
catalysts afforded more Z isomer than UmicoreTM M2. The
results presented in Table 2 demonstrate the efficiency of new
catalysts 5aꢀd bearing unsymmetrical NHC ligands for
performing metathesis reaction in commercial grade solvent
20 under air.
5
55
X-ray analysis
Red crystals of 5a, 5b, 5c and 5d suitable for singleꢀcrystal Xꢀray
diffraction studies were obtained by slow evaporation of
60 concentrated solutions of these compounds in methylene chloride
and nꢀpentane. All the relevant experimental details are presented
in the Electronic Supporting Information (ESI) (see Tables S3a
and S3b). All of these catalysts crystallized in the monoclinic
crystal system.
65 Considering crystal structures of 5a and 5b, one can see that they
crystallized in the C2/c space group with one molecule in the
asymmetric unit. The molecules are placed at general positions
and both arrangements are isostructural (see the projection of
molecular arrangement in the unit cell presented in Fig. S1 in
70 ESI). This is not surprising, as the corresponding unit cell
parameters for crystals of both compounds are very much alike.
Moreover, the geometrical parameters such as bond lengths and
valence angles are almost identical with the only significant
difference being that of geometry of heteroaromatic rings (all
75 geometric parameters are presented in the Tables 4 and 5 in the
ESI). In both structures, the cavities between the main molecules
are filled in by disordered solvent molecules of dichloromethane.
However, also the molecules of catalysts are significantly
affected by disorder. Fiveꢀmembered heterocyclic rings
80 (containing sulphur atom in the case of 5a or oxygen atom in the
case of 5b) adopt one of two positions. The difference between
both positions is that the heteroatom is on the opposite side of the
ring. Additionally, the phenylindene groups due to rotation along
Ru1ꢀC17 adopt one of two positions too. The ratio of two
85 possible occupancies of disordered group in the case of 5a and 5b
is similar, ca. 86:14, so it is clear that one of them is significantly
preferred. Surprisingly, the preferred orientation of the
phenylindene group in the case of 5a is different than in the case
of 5b. This is clearly visible when one overlaps both molecules
90 (see Fig. 7). Both positions of the disordered heterocyclic ring are
in both cases (catalysts 5a and 5b) on the same side as phenyl
ring of phenylindene group. When molecules are superimposed it
is noticeable that the phenyl rings occupy opposite sides of the
molecular backbone (C1ꢀRu1ꢀP1). This means that the preferred
95 position of the phenylindene group in 5a is rotated about 180° in
regard to the preferred position of the phenylindene group in 5b.
Then we focused on research of ethenolysis (Scheme 6) which
allows to obtain terminal olefins from renewable biomass
feedstocks.24 In recent reports there are some examples of olefin
metathesis catalysts which demonstrate good activity and
25 selectivity in ethenolysis reactions.25 These results led us to
believe that our new catalysts bearing a heteroaromatic moiety
would show promising ethenolysis selectivity.
O
O
O
O
O
O
O
O
30
500 ppm cat.
ethylene
22
23
24
25
26
35
Scheme 6 Ethenolysis of ethyl oleate (22).
Table 3 Ethenolysis of ethyl oleate (22) with different catalysts.a
Entry
Catalyst
Conversion Yield (%) Yield (%) Selectivityd
(%)b
23c
24 c
1
2
3
5a
UmicoreTM M2
7
14
77
39
71
10
34
23
20
12
35
28
25
79
63
78
43
4
Hoveyda II
a
Reaction conditions: etlyl oleate (22) = 15 mmol, catalyst = 0.0075
mmol, (500 ppm), 10 bar of ethylene, 3 hours, 50 °C. b Conversion was
40 determined by gas chromatography using tetradecane as internal standard.
Conversion = 100 – 100 × (final moles of 22/initial moles of 22). c Yield
d
= 100 × (moles of 23 or 24 / initial moles of 22). Selectivity = 100 ×
(moles of 23 + moles of 24)/[(moles of 23 + moles of 24) + 2 × (moles of
25 + moles of 26)].
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The crystal structure of 5c is quite similar to structures 5a and 5b.
Catalyst 5c crystallized in the C2/c space group with one
molecule in the asymmetric unit as well. However, the problem
of disorder affects the main molecule differently. The
benzothiophene group adopts two positions, the angle between
planes on which lie atoms in both positions is 4.3°(4). In a similar
way the phenyl ring of phenylindene group is disordered, it
adopts two positions, the angle between planes on which lie
atoms in both positions is 15°(1). All geometric parameters
5
10 describing 5c are presented in the Table 6 in ESI.
Fig.
8
ORTEP drawing showing 50% thermal ellipsoids of the
45 investigated compounds. From left to right: upper row 5a and 5b; lower
row 5c and 5d. Hydrogen atoms are shown as open circles. For structure
5d one of two molecules from asymmetric unit is presented.
The ruthenium atom is five coordinated in the studied molecules
50 (see plots on Fig. 8 and 9). In the group of 5aꢀd catalysts the bond
lengths between the ruthenium atom and ligands do not differ by
more than 3 estimated standard deviations. The only exceptions
are the Ru(1)ꢀCl(1) and Ru(1)ꢀCl(2) bonds for 5c and 5d in
respect to the 5a and 5b structures. The substitution of the
55 heteroaromatic ring results in a small change in geometry of the
NHC ligand.
Fig. 7 Overlapping of 5a (green) and 5b (red) molecules. Hydrogen atoms
have been omitted and heterocyclic ring is shown as ordered for clarity. In
the case of disordered phenylindene group, the preferred orientation for
15 each catalyst is chosen.
The structure of 5d differs from previously described structures.
Catalyst 5d crystallized in C2 space group with two molecules in
the asymmetric unit, placed at general positions. The lack of the
20 centre of symmetry (in regard to structures 5a, 5b and 5c) is
caused by disorder. One of the molecules contains a significantly
disordered phenylindene group (in the same way as in the cases
of 5a and 5c described above) while the other one does not. As a
result these molecules are not equivalent and cannot be simply
25 transformed one into another by the centre of symmetry. All
geometric parameters describing 5d are presented in the Table 7
in ESI. Catalyst 7 crystallized in the triclinic crystal system, space
group Pꢀ1. Green crystals of 7 do not contain any solvent
molecules. There are eight molecules of 7 in the unit cell (four in
30 the asymmetric unit), which are placed at general positions. The
fiveꢀmembered heterocyclic rings (containing sulphur atoms) are
disordered. Despite the fact that all four molecules in the
asymmetric unit are disordered, only in one molecule disorder is
distinct enough to be modelled. In this molecule, heterocyclic
35 ring has two positions (see Fig. 9). The ratio between both
positions is ca. 3 to 1, which means that the ring adopts one of the
position three times more frequent than the other one. The
tendency of such heterocyclic rings to be disordered is also
observed in the case of 5a and 5b, where fiveꢀmembered rings
40 containing sulphur (or oxygen) are also disordered in a similar
way.
Fig. 9 ORTEP drawing showing 50% thermal ellipsoids of the catalyst 7.
60 Hydrogen atoms are shown as open circles. One of four molecules from
asymmetric unit is presented.
The Ru(1)C(1)N(2) valence angle is equal to 119.4(4)º,
118.7(3)º, 118.4(4)°, 118.3(9)º and 118.3(8)º for 5a, 5b, 5c
65 and the two asymmetric molecules of 5d, respectively.
CCDC 1453866ꢀ1453870 entries contain the supplementary
crystallographic data (CIF files) for this paper. They can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif or
70 from the authors.
Conclusions
In summary, we have disclosed the synthesis and characterization
of four new rutheniumꢀindenylidene complexes and one new
Hoveydaꢀtype complex bearing unsymmetrical NHC ligands. The
75 investigation of their catalytic performance in benchmark
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metathesis reactions performed under air in commercial grade
12 F. Boeda, H. Clavier and S. P. Nolan, Chem. Commun., 2008,
2726–2740.
solvent has shown that complexes 5aꢀd are potent catalysts for
olefin metathesis reactions in commercial grade solvent under air.
In DRRM reaction, catalysts 5a, 5b, 5c and 5d exhibited better
diastereoselectivity than standard SIMesꢀbearing catalysts,
Grubbs II, Hoveyda II and UmicoreTM M2. In ethenolysis
reaction, catalysts 5a and 7 showed much better selectivity in
favour of the main ethenolysis products than commercially
available catalysts UmicoreTM M2 and Hoveyda II.
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Biological and Chemical Research Centre, Faculty of Chemistry,
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b Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka
15 44/52, 01ꢀ224 Warsaw, Poland
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† Electronic Supplementary Information (ESI) available: experimental
procedures, characterization data for all previously unreported
compounds. See DOI: 10.1039/b000000x/
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‡The Authors thank the Foundation for Polish Science for the `TEAM'
Programme coꢀfinanced by the European Regional Development Fund,
Operational Program Innovative Economy 2007ꢀ2013.
The study was carried out at the Biological and Chemical Research
25 Centre, University of Warsaw, established within the project coꢀfinanced
by European Union from the European Regional Development Fund
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New ruthenium(II) indenylidene catalysts were
synthesized and used in olefin metathesis reactions in
toluene under air, leading to high conversions and
good selectivities.