Studies on electronic effects in O-, N- and S-chelated ruthenium olefin-metathesis catalysts

Article abstract of DOI:10.1002/chem.200903457

A short overview on the structural design of the Hoveyda-Grubbs-type ruthenium initiators chelated through oxygen, nitrogen or sulfur atoms is presented. Our aim was to compare and contrast O-, N- and S-chelated ruthenium complexes to better understand the impact of electron-withdrawing and -donating substituents on the geometry and activity of the ruthenium complexes and to gain further insight into the trans-cis isomerisation process of the S-chelated complexes. To evaluate the different effects of chelating heteroatoms and to probe electronic effects on sulfur- and nitrogen-chelated latent catalysts, we synthesised a series of novel complexes. These catalysts were compared against two well-known oxygen-chelated initiators and a sulfoxide-chelated complex. The structures of the new complexes have been determined by single-crystal X-ray diffraction and analysed to search for correlations between the structural features and activity. The replacement of the oxygen-chelating atom by a sulfur or nitrogen atom resulted in catalysts that were inert at room temperature for typical ring-closing metathesis (RCM) and cross-metathesis reactions and showed catalytic activity only at higher temperatures. Furthermore, one nitrogen-chelated initiator demonstrated thermo-switchable behaviour in RCM reactions, similar to its sulfur-chelated counterparts.

Full text of DOI:10.1002/chem.200903457

DOI: 10.1002/chem.200903457
Studies on Electronic Effects in O-, N- and S-Chelated Ruthenium
Olefin-Metathesis Catalysts
Eyal Tzur,[a] Anna Szadkowska,[d] Amos Ben-Asuly,[a, b] Anna Makal,[e]
Israel Goldberg,[c] Krzysztof Wozniak,[e] Karol Grela,*[d, e] and N. Gabriel Lemcoff*[a]
´
Abstract: A short overview on the
structural design of the Hoveyda–
Grubbs-type ruthenium initiators che-
lated through oxygen, nitrogen or
sulfur atoms is presented. Our aim was
to compare and contrast O-, N- and S-
chelated ruthenium complexes to
better understand the impact of elec-
tron-withdrawing and -donating sub-
stituents on the geometry and activity
of the ruthenium complexes and to
gain further insight into the trans–cis
isomerisation process of the S-chelated
complexes. To evaluate the different ef-
fects of chelating heteroatoms and to
probe electronic effects on sulfur- and
nitrogen-chelated latent catalysts, we
synthesised a series of novel complexes.
These catalysts were compared against
two well-known oxygen-chelated initia-
tors and a sulfoxide-chelated complex.
The structures of the new complexes
have been determined by single-crystal
X-ray diffraction and analysed to
search for correlations between the
structural features and activity. The re-
placement of the oxygen-chelating
atom by a sulfur or nitrogen atom re-
sulted in catalysts that were inert at
room temperature for typical ring-clos-
ing metathesis (RCM) and cross-meta-
thesis reactions and showed catalytic
activity only at higher temperatures.
Furthermore, one nitrogen-chelated in-
itiator demonstrated thermo-switchable
behaviour in RCM reactions, similar to
its sulfur-chelated counterparts.
Keywords: carbenes
·
chelates
·
·
ligand design
ruthenium
·
metathesis
Introduction
The great efficacy and scope of olefin metathesis reactions
have induced much effort in the study of ruthenium carbene
initiators. The successful achievements in this area have led
to impressive catalysts that assist olefin metathesis with un-
precedented efficiency.[1] Without a doubt, two of the most
significant modifications on the original first-generation
Grubbs ruthenium catalyst[2] were the substitution of one of
the tricyclohexylphosphine ligands by a more potent sigma-
electron donor, the N-heterocyclic carbene (second-genera-
tion Grubbs catalyst)[3] and the replacement of the second
phosphine ligand by an ortho-isopropoxy benzylidene
moiety capable of chelation (Hoveyda–Grubbs).[4] Predicta-
bly, alteration of the chelated benzylidene radically altered
the reactivity of the catalysts. Changes in steric strain,[5] che-
late ring size,[6] the chelated heteroatom[5–7] and electron
density on the aromatic ring of the chelated benzylidenes[8]
have been shown to afford catalysts with activities that
range from latent[9] (no activity at room temperature), such
as complex 1cis (Scheme 1), to one of the most reactive
ruthenium catalysts to date. For example, Hoveyda–Grubbs
[a] E. Tzur, Dr. A. Ben-Asuly, Dr. N. G. Lemcoff
Department of Chemistry, Ben-Gurion University of the Negev
Beer-Sheva 84105 (Israel)
Fax : (+972)86461740
E-mail: lemcoff@bgu.ac.il
[b] Dr. A. Ben-Asuly
Achva Academic College, Shikmim 79800 (Israel)
[c] Prof. I. Goldberg
Department of Chemistry, Tel-Aviv University
Tel Aviv 69978 (Israel)
[d] A. Szadkowska, Prof. K. Grela
Institute of Organic Chemistry PAS, Kasprzaka 44/52
01-224 Warszawa (Poland)
Fax : (+48)22-343-2109
E-mail: klgrela@gmail.com
´
[e] A. Makal, Prof. K. Wozniak, Prof. K. Grela
Department of Chemistry, Warsaw University, Pasteura 1
02-093 Warzsawa (Poland)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200903457.
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FULL PAPER
tivity noticeably, however, the
position of the isopropoxy
EDG greatly influenced the re-
action rate (complexes 10 and
12 in Scheme 3). Moreover, a
methyl group para to the che-
lated isopropoxy moiety, as in
11, had a significantly stronger
retardation effect than the
stronger
alkoxy group in 12 (Scheme 3).
electron-donating
Scheme 1. Selected complexes exhibit different reactivity in metathesis reactions.
Blechert et al. concluded that
catalyst 2 has been successfully fine-tuned to increase its ac-
tivity by the introduction of an electron-withdrawing group
(EWG) to diminish the donor properties of the oxygen
atom. As a result, nitro-substituted Hoveyda–Grubbs cata-
lyst 3 has found a number of applications in various studies.
When mainly steric effects were probed, two different ap-
proaches were discerned. Firstly, the introduction of a bulky
group ortho to the chelated heteroatom, such as in the Ble-
chert system 5,[10] and secondly, the direct substitution of the
heteroatom with a bulkier group (complexes 4 and 6 in
Scheme 2).[5] The most typical results demonstrated that the
use of bulkier ligands promoted faster reactions.[4a,5a,11]
Nonetheless, we find in the literature some examples that
are not in accordance with this trend. For instance, Grubbsꢁ
imine-chelated initiator 6 promoted faster reaction with an
isopropyl derivative than with
a tert-butyl derivative
(Scheme 2).[5b]
When electronic effects were probed, the results were
even more puzzling at first glance. The activation of rutheni-
um-chelated catalysts by EWGs is well established; most
prominently, as detailed above, we find that in complex 3
the introduction of a nitro group para to the chelated iso-
propoxy unit significantly enhanced reaction initiation.[8a]
On the other hand, Grela and Kim showed that the intro-
duction of two methoxy groups, prominent electron-donat-
ing groups (EDGs), had a com-
Scheme 2. Steric effects in chelated alkylidene catalysts.
to be able to predict catalyst initiation rates mainly the elec-
tronic effects on the benzylidene carbon must be taken into
account. Recently, the lack of linear relationships between
parable
(albeit
less
pro-
A
nounced) activation effect.[8b]
similar observation in chiral
Ru-based complexes was also
made, by the group of Hovey-
da.[8f] In addition, a study by
Blechert et al.[8c] shows that
when moderate EWGs such as
fluoro (7 and 8) or trifluoro-
methyl (9) are introduced para
to the benzylidene carbon atom
or the chelated oxygen atom
(Scheme 3) the rate of ring-
closing metathesis (RCM) of di-
allyl tosylamide remains rela-
tively unchanged. In other
words, the position of the EWG
did not alter the catalyst reac- Scheme 3. Electronic effects on Blechert initiators.
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K. Grela, N. G. Lemcoff et al.
electronic and steric effects for ruthenium Hoveyda–
Grubbs-type catalysts was discussed in yet another example
of modification of these catalysts by electronic effects.[8e]
The design of efficient catalytic switches necessitates a
comprehensive understanding of the chemical changes that
can be made to a catalyst to deactivate it: the off position.
Some examples of switchable metathesis catalysts in the lit-
erature include catalysts that may be activated/deactivated
by changes in the acidity of the media,[12] by changes in tem-
perature,[7a] by the addition/removal of deactivating li-
gands[13] or by photo-activation.[14] For example, Lemcoff
et al. recently disclosed a series of sulfur-chelated latent cat-
alysts that were able to promote olefin metathesis reactions
only at elevated temperatures and showed thermo-switcha-
ble behaviour for RCM.[5a,7a,c]
To evaluate the effect of the chelated heteroatom and to
probe electronic effects in sulfur- and nitrogen-chelated
latent catalysts, we synthesised novel complexes 27–31.
These were compared with well-known initiators 2 and 3,
which are chelated through an oxygen atom, and with the
recently published sulfoxide-chelated complex 13.[11]
Scheme 4. Synthesis of ligands 19–23.
Scheme 5. Synthesis of styrene 25.
The new complexes were characterised with the aid of
single-crystal X-ray structures, and their catalytic perfor-
mance was evaluated in RCM and cross-metathesis (CM)
reactions at room temperature and above.
Results and Discussion
Scheme 6. Synthesis of sulfone styrene 26.
Synthesis of ruthenium complexes: The styrene derivatives
19–23 were synthesised as shown in Scheme 4.
with styrenes 19–22 and 25, respectively, in the presence of
CuCl in dichloromethane (Scheme 7). All our attempts to
obtain a sulfone-chelated complex with styrene 26 were un-
successful, which implied that the oxygen atoms in the sul-
fone are probably not good chelating atoms in these com-
plexes.
The commercially available aldehyde starting materials
were treated with potassium carbonate and the correspond-
ing nucleophile in dry DMF to afford the substitution prod-
ucts 14–18 (Scheme 4). Subsequent treatment with methyl-
triphenylphosphonium salt and potassium tert-butoxide gave
the desired styrenes 19–23.
ꢀ
An S(O)-chelated ligand that contained an EWG ( NO2)
Structural characterisation of the prepared complexes: Com-
plexes 27–31 were fully characterised by NMR spectroscopy
and FAB-MS (see the Supporting Information). Single crys-
tals of good quality for X-ray analysis were also obtained
for all new complexes (Figure 1). Several structures of N-
and O-chelated ruthenium have already been deposited in
Cambridge Structural Database[15] and these were included
in calculations of the average bond lengths and angles
(Figure 2). The list of reference codes for the utilised struc-
was prepared in accordance with the procedure shown in
Scheme 5. Aldehyde 17 was transformed into the sulfoxide-
substituted styrene 25 by bromine-promoted oxidation fol-
lowed by a Wittig reaction.
Sulfone styrene 26 was synthesised by straightforward per-
oxide oxidation of 23 (Scheme 6).
The final step in the synthesis of novel complexes 27–31
involved typical ligand-exchange reactions of complex 32
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Electronic Effects in Heteroatom-Chelated Ruthenium Catalysts
FULL PAPER
ces in X-chelated ruthenium
complexes (X=O, N, S(O), S)
ꢀ
were found. Firstly, the Ru X
distance increases with increas-
ing atomic number, although it
is significantly shorter in sulfox-
ide complexes than in sulfide
ꢀ
complexes. Also the X C29
bond length increases monoton-
ically from N to O to S (Fig-
ꢀ
ure 2a), whereas the C23 C28
bond length tends to decrease.
ꢀ
ꢀ
The C1 Ru and the X C28
bond lengths are shortest for
the O-chelates due to the sp2
hybridisation of the oxygen
atom and charge flows. Interest-
ingly, the N- and S-chelates
ꢀ
show similar C1 Ru lengths,
which may also reflect the fact
that in both cases the X atom is
sp3 hybridised. Additionally, the
ꢀ
Ru Cl average bond length
tends to be shorter for O- and
ꢀ
S(O)-chelates. The C22 C23
bond length is the most con-
served across all the chelates
(Figure 2a).
Scheme 7. Synthesis of N- and S-chelated complexes 27–31 by ligand exchange.
The angle variability is great-
er for the valence angles, espe-
tures is enclosed in the Supporting Information (Part III,
Table A1).
cially those which involve the X atom. In particular the
C28-X-C29 angle values for the N- and O-chelates differ sig-
nificantly from the values obtained when X=S or S(O). The
Cl-Ru-Cl angle varies within a small range of 157.5–1608.
The C1-Ru-X angle tends to be smaller for the nitrogen and
Structural comparison of the O-, S- and N-substituted Hov-
eyda-type catalysts: The following similarities and differen-
Figure 1. Crystal structure of a) 27, b) 28, c) 29, d) 1trans, e) 30cis, f) 31. Ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.
Chem. Eur. J. 2010, 16, 8726 – 8737
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K. Grela, N. G. Lemcoff et al.
three valence angles around the oxygen atom deviate from
3608 by no more than 38 (see Part III of the Supporting In-
formation, Table A1), which clearly indicates a planar con-
figuration and, therefore, sp2 hybridisation at the oxygen
atom. The valence angles around the chelated sulfur atom
tend to be much smaller and the bond angle values (Fig-
ure 2b) suggest partial sp3d hybridisation of sulfur. This can
be explained by the second-order Jahn–Teller effect, that is,
by the presence of a very low-lying excited state of the
sulfur atom, in which the 3d orbitals are occupied. Mixing
with the ground state lowers the ground-state energy and re-
sults in the geometry modifications. For instance, the Ru1-S-
C28 angle in 30cis is smaller than 1008 and the C28-S-C29
angle is 1008, rather than the 109.58 ideally expected in the
case of sp3 hybridisation. The Ru1-X-C29 angle is more than
1208. The corresponding angles for 1trans (Figure 1 in Part III
of the Supporting Information) have values of 96, 102 and
1148, respectively, and in the case of sulfoxides the angles
Ru1-S-C28 and C28-S-C29 have values around 1008.
Impact of EWG or EDG substituents on the geometry of
complexes: The overall impact of EWG or EDG substitu-
tion on the structure of the main chelate is quite small.
Most of the differences between the samples are well below
three standard deviations for a given parameter, in particu-
ꢀ
ꢀ
lar the N Ru distance appears invariable. Similarly, the N3
ꢀ
ꢀ
ꢀ
C29, N3 C30, C22 C23 and C23 C24 bond lengths may be
considered insensitive to the substitutions. There are small
changes in the bond lengths in the substituted benzene ring,
which may be described as the increased differentiation of
the bonds lengths (decreased aromaticity, measured by the
harmonic oscillator measure of aromaticity (HOMA)[19]
ꢀ
ꢀ
index). Bond C24 C25 is shortened, whereas bonds C25
ꢀ
C26 and C27 C28 get longer. Still, the changes are on the
border of statistical significance (Table 1). The only parame-
Table 1. Mean bond lengths, standard deviations and calculated HOMA
index from experimental geometries of the compounds 27, 28 and 29.
Complex Mean bond length of aromatic Bond standard de- HOMA
ꢀ
C C bonds[ꢂ]
viation [ꢂ]
27
28
29
1.391
1.391
1.380
0.008
0.010
0.016
0.99
0.98
0.93
Figure 2. Selected a) average bond lengths [ꢂ] and b) average valence
angles [8] for different Ru–X coordinated complexes (averages of the
complexes in this article and others; see Table A1 in the Supporting In-
formation). The values refer to the chelated heteroatom (X) in the fol-
lowing order: X=N, O, S(O), S.
ters that seem to change significantly upon nitro substitution
ꢀ
are the Ru Cl1 bond length (elongated by 0.02 ꢂ) and the
sulfur atoms (173.2 and 174.48, respectively) and larger for
the O- and S(O)-chelates (1778). However, only the differ-
ences observed for angles and bond lengths that involve the
X atom are significantly larger than the standard deviation
of the parameters in question.
Cl1-Ru1-Cl2 angle, which is broadened by over 78. The
plane of the benzylidene ligand is also more rotated with re-
spect to the plane that contains ruthenium, C1 and N3. The
torsion angle of C22-Ru1-N3-C28 increases by 48 upon sub-
stitution, which illustrates this rotation. p-Methoxy substitu-
tion, in the case of 29, results in a general decrease in length
of most bonds in the benzene moiety, as well as significant
Sulfur and oxygen atom hybridisation: The valence angles
around the chelated oxygen atom adopt values close to 110
and 1208 and are, on average, 108 higher than the analogous
angles around the sulfur atom (Figure 2b). The sum of the
ꢀ
reduction of the C22=Ru and Cl2 Ru bond lengths. On the
other hand, the Cl1 Ru bond length gets longer. The angles
in the benzene moiety behave in correlation with elongation
ꢀ
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Electronic Effects in Heteroatom-Chelated Ruthenium Catalysts
FULL PAPER
or reduction of the adjacent bond lengths. There is also an
interesting increase (28) in the value of the C1-Ru-N3 angle.
The Cl-Ru-Cl angle adopts a value of 1648, which is 48
larger than in the unsubstituted structure and 38 smaller
than in the nitro-substituted catalyst. The relative rotation
of the benzylidene moiety with respect to the plane contain-
ing Ru1, C1 and N3 is illustrated by the C22-Ru1-N3-C28 tor-
sion angle, which increases upon methoxy substitution.
There are some significant differences in the relative ori-
entation of the mesityl (Mes) substituents with respect to
the main complex site. In the case of 27, the plane of the
imidazole ring is bent away from the Cl2 chlorine atom with
ꢀ
respect to the C1 Ru1 bond. The Mes arms do not locate
above the benzylidene unit in the main complex and are
bent towards each other and the Cl1 chlorine atom. In the
ꢀ
case of structure 28, the C1 Ru1 bond is coplanar with imi-
dazole. One of the Mes arms locates directly above the ben-
zylidene moiety in the main complex and the main axes of
the two Mes groups are parallel. In the case of the methoxy
substitution in the structure 29, the imidazole plane and
ꢀ
Ru C1 bond are again collinear, but the Mes substituents
are bent, similar to 28. However, these effects may result
from different crystal packing of the structures as well as
from substitution effects. Comparisons of the bond lengths
and angles in the structures of 27, 28 and 29 are displayed in
Figure 3.
Relative reactivity studies: To explore the reactivity profiles
of the catalysts, various olefin substrates were reacted.
Tables 2–4 summarise the results for RCM and CM reac-
tions. Overall, and in line with many of our studies, the
trend observed for RCM of diethyl diallylmalonate
(Figure 4) was observed in the other metathesis reactions as
well.
Catalysts containing O-donor ligands: The phosphine-free
systems 2 and 5, introduced by the groups of Hoveyda[4a]
and Blechert,[4b,9] display high reactivity levels towards elec-
tron-deficient substrates, such as acrylonitrile and fluorinat-
ed olefins. Excellent air stability, easy storage and handling,
the possibility of catalyst reuse and of catalyst immobilisa-
tion make clear the advantages of this system. In spite of
the promising application profile observed in reactions of 2,
this catalyst proved to initiate more slowly than other phos-
phine systems, probably as the result of electronic factors
(iPrO!Ru electron donation).[15] More detailed studies on
catalytic activation resulted in the preparation of nitro-sub-
stituted Hoveyda catalyst 3.[8a,b] The strong EWG para to
the isopropoxy donor in 3 weakens the iPrO!Ru chelation
and facilitates initiation of the catalytic cycle. Consequently,
3 possesses dramatically enhanced catalyst performance in
model RCM and CM reactions (Table 2).
Figure 3. Selected a) bond lengths [ꢂ] and b) valence angles [8] in the
structures of 27, 28 and 29. The values are reported in the following
order: R1=H (27), R1=NO2 (28), R1=OMe (29).
Oxygen-chelated initiators 2 and 3 exhibited good activity
in model metathesis reactions (Table 2, entries 1–4). Howev-
er, nitro-substituted complex 3 serves as an effective RCM
catalyst for the formation of disubstituted double bonds
even at 08C. Furthermore, the potential of a nitro-substitut-
Figure 4. RCM conversions [%] of diethyl diallylmalonate (0.1m) with
several catalysts (1 mol%) in toluene after 24 h at 248C.
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K. Grela, N. G. Lemcoff et al.
Table 2. Formation of disubstituted double bonds promoted by catalysts
Table 3. Formation of disubstituted double bonds promoted by catalysts
2 and 3.[a]
27, 28 and 29.[a]
Entry
Substrate
Product
Catalyst
[mol%]
Yield
[%]
T
[8C]
t
Entry
Substrate
Product
Catalyst
Yield
[%]
T
[8C]
t
G
[h]
[h]
2 (1)
3 (1)
40
92
0
0
4
2
27
27
28
28
29
29
18
89
37
90
8
55
55
24
24
55
55
2
24
2
24
2
1
1
2 (1)
3 (1)
48
99
0
0
4
1
2
61
24
27
28
29
95
99
98
55
24
55
21
7
24
2 (1)
3 (1)
50
99
0
0
4
1
2
3
3
4
5
27
28
29
55[b]
25[b]
28[b]
55
24
55
92
2
48
2 (2.5)
3 (2.5)
52
78
0
0
8
8
27[c]
27
0
45
78
82
93
100
0
24
55
55
55
24
24
24
55
55
16
6
24
69
27
0.5
24
6
2 (1)
3 (1)
37
89
24
24
6
6
27
27[d]
28
4
28[e]
29
[a] Conditions: 1–2.5 mol% of catalyst, [substrate]=0.02m, dichlorome-
thane, yields determined by GC.
29
29
70
86
24
27
27
28
28
29
29
56
78
63
85
35
52
55
55
24
24
55
55
5
24
5
24
5
ed catalyst for more challenging metathesis reactions has
been proved in a CM reaction (Table 2, entry 5).
5
Catalysts containing N-donor ligands: The results of typical
RCM and CM reactions of the new N-chelated complexes
27, 28 and 29 are summarised in Table 3.
N-Chelated complex 27 was inert to typical RCM reac-
tions at room temperature and showed activity only at
higher temperatures (Table 3, entry 4). However, nitro-sub-
stituted N-chelated catalyst 28 showed an impressive accel-
24
[a] Conditions: 1 mol% catalyst, [substrate]=0.1m in toluene, yields de-
termined by GC. [b] Olefin isomerisation affords an additional seven-
membered ring product, longer reaction times promoted higher yields of
the isomerisation product. [c] [substrate]=0.2m. [d] 0.1 mol% catalyst.
[e] In dichloromethane.
ꢀ
eration effect. Thus, the introduction of an EWG ( NO2)
transformed a room-temperature latent catalyst into an
active catalyst (Figure 4 and Table 3). To determine the ef-
fects of EDGs in latent catalysts, we explored the activity of
catalyst 29. As expected, catalyst 29 showed no activity at
room temperature and was less active than 27 at higher tem-
peratures (Table 3, entries 1, 3 and 5). However, the diethyl
diallylmalonate RCM rate was higher than that observed for
catalyst 27 at these temperatures (Table 3, entry 4), similar
to the results obtained by Hoveyda et al. with the chiral O-
chelated complexes.[8f] The benchmark RCM reaction of di-
ethyl diallylmalonate with catalysts 27 and 29 was followed
by GC–MS and the results are presented in Figure 5.
~
&
Figure 5. Catalytic behaviour of 27 ( ) and 29 ( ) in the RCM of diethyl
diallylmalonate (c=0.1m, toluene, T=658C, 1 mol% catalyst). Products
analysed by GC–MS.
Thermo-switchable behaviour of catalyst 27: Additionally,
we examined the thermo-switchable behaviour of 27. Reac-
tions with intermittent periods of heating and cooling
(558C/258C) were carried out in toluene under a nitrogen
atmosphere. As shown in Figure 6, catalyst 27 demonstrated
a thermo-switchable behaviour, similar to our previous ob-
servations on sulfur-chelated ruthenium benzylidene cata-
lysts.[7a]
Catalysts containing S-donor ligands: Noting the significant
activation effect of the nitro group in catalyst 28 (as well as
in 3), we tested the effect of the addition of a nitro group to
latent S-chelated complex 1cis. Surprisingly, nitro-substituted
complex 30cis was found to be inert to RCM reactions at
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Electronic Effects in Heteroatom-Chelated Ruthenium Catalysts
FULL PAPER
eight-membered rings and CM; Table 4, entries 3 and 5). In-
itiators 1cis and 30cis required high temperatures to induce
metathesis reactions (908C). Based on the performance in
model reactions, shown in Table 4, we conclude that elec-
tronic effects seem to play a decisive role in increasing the
catalytic activity of the sulfoxide-chelated complexes, where-
as sulfide-chelated complexes remain latent.
To determine the kinetic profiles of the active sulfoxide
catalysts 13 and 31 and to test a more challenging substrate
for RCM, we measured the progress of the RCM reaction
of diethyl allylmethallylmalonate (Figure 7). Both catalysts
showed high activity with this substrate and almost full con-
version was achieved in under 2 h at 408C with 1 mol% cat-
alyst in toluene.
Figure 6. Thermo-switchable behaviour of catalyst 27 in the RCM of di-
ethyl diallylmalonate (c=0.1m, toluene, 1 mol% catalyst). Dashed line:
248C; solid line: 558C.
room temperature and showed activity only at higher tem-
peratures (Table 4, entry 4, and Figure 4). Due to the negli-
gible activation obtained by this procedure, we decided to
compare the catalytic activity of S-chelated initiators 1cis and
30cis with their sulfoxide counterparts 13 and 31. Sulfoxide
initiator 31 turned out to be the most active from the group
of S-chelated catalysts. However, tests of catalytic activity
showed that catalyst 31 proceeded in typical RCM reactions
just slightly faster than initiator 13. The most significant dif-
ferences in catalyst performance between complexes 13 and
31 were observed for more demanding substrates (RCM of
~
&
Figure 7. Catalytic behaviour of catalysts 13 ( ) and 31 ( ) in the RCM
of diethyl allylmethallylmalonate (c=0.1m, toluene, T=408C, 1 mol%
catalyst). Products analysed by GC.
Table 4. Formation of disubstituted double bonds promoted by catalysts
1cis, 13, 30cis and 31.
Kinetic isomerisation of 1trans to 1cis: The relative stability of
both isomers (trans and cis) provided the opportunity to
measure the kinetics of the isomerisation process by integra-
tion of the characteristic benzylidene protons in the
1H NMR spectrum of 1. Deuterated dichloromethane,
CD2Cl2, was chosen for measuring kinetic isomerisation of
compound 1. This process is shown in Figure 8. The results
of this experiment showed that complex 1trans converts com-
pletely into 1cis after 50 h at 238C. As shown in Figure 8, the
data was fitted by an exponential relationship with correla-
tion coefficient R2 =0.9974 and a calculated rate constant
k=1.2ꢃ10ꢀ2 hꢀ1.
Entry
Substrate
Product
Catalyst
Yield
[%]
T
[8C]
t
[h]
1
75
86
70
85
94
98
86
93
31[b]
32[b]
42
90
90
24
24
90
90
24
24
90
90
24
24
28
28
24
24
18
18
24
24
48
48
24
24
30
13
31
1
30
13
31
1
1
2
3
30
13
31
87
1
1
0
84
55
0.2
91
97
98
64
57
19
53
24
90
90
24
90
24
24
90
90
24
24
24
48
48
24
41
24
24
47
42
24
24
Trans–cis isomerisation: It appears that the O-, N- and
S(O)-chelates are more stable in the trans conformation,
while S-chelates isomerise to the cis isomer.[17a] From a
structural point of view, this could be attributed to the pre-
ferred sp3d hybridisation of the sulfur atom and the steric ef-
fects that result from it. The structure of 30cis (Figure 1e) il-
lustrates that if the sulfur atom displayed sp2 hybridisation
(and therefore a planar configuration of the linked substitu-
ents) then the isopropyl ligand in the cis conformation could
have been in steric conflict with one of the Mes substituents.
Notably, there are few examples of crystallographic struc-
tures of Ru–O and Ru–N chelates that display cis-dichloro
1[c]
30
30
13
31
1
4
30
13
31
5
[a] Conditions: [substrate]=0.1m in toluene, yields determined by GC.
[b] Olefin isomerisation gives an additional seven-membered ring prod-
uct. [c] 0.1 mol% catalyst.
Chem. Eur. J. 2010, 16, 8726 – 8737
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8733

K. Grela, N. G. Lemcoff et al.
ration. The introduction of a nitro group in the sulfoxide-
chelated complex enhanced its reactivity, especially in de-
manding cases (RCM of eight-membered rings and CM).
The study of latent metathesis catalysts and the means to ac-
tivate them has important practical applications and it may
also provide vital insights into the intricate mechanism of
the metathesis reactions of strongly chelated complexes.
Experimental Section
General: All reagents were of reagent grade quality, purchased commer-
cially from Sigma, Aldrich or Fluka and used without further purifica-
tion. All solvents were dried and distilled prior to use. Purification by
column chromatography was performed on Davisil Chromatographic
silica gel (40–60 mm). TLC analyses were performed by using Merck pre-
coated silica gel (0.2 mm) aluminium-backed sheets. Gas chromatography
data was obtained under standard conditions with an Agilent 6850 GC
equipped with an Agilent 5973 MSD and an Agilent HP5-MS column.
NMR spectra were recorded on Bruker DPX200, Avance III 400 or
DPX500 instruments. Chemical shifts (d, ppm) are reported relative to
Me4Si as the internal standard or relative to the residual solvent peak.
MS data was obtained by using a Bruker Daltonics Ion-Trap MS Esquire
3000 Plus equipped with atmospheric pressure chemical ionisation
(APCI).
Figure 8. Kinetic isomerisation (1H NMR spectroscopy) of 1trans to 1cis in
CD2Cl2 at 238C.
General procedure for synthesis of aldehydes (14–18): The corresponding
benzaldehyde (16.1 mmol), potassium carbonate (17.1 mmol) and the ap-
propriate nucleophile (17.1 mmol) were dissolved in DMF (10 mL) in a
50 mL round-bottomed flask under dry nitrogen and topped with a reflux
condenser. The reaction mixture was heated at 55–808C for 24 h. After
cooling, the mixture was added to saturated aqueous potassium carbon-
ate solution (50 mL) and extracted with diethyl ether or dichloromethane
(3ꢃ50 mL). The extracts were dried over anhydrous magnesium sulfate
and evaporated under reduced pressure. The crude product was purified
by chromatography on silica gel to afford the desired aldehyde.
coordination.[7b,17] In these cases, the chelated heteroatom is
enclosed within a six-membered aromatic ring, well-ordered
in the case of an aliphatic nitrogen atom and disordered in
the case of an oxygen atom. In 1cis and 30cis, the structure of
the ligands does not entail steric clashes with the Mes
moiety in the cis coordination. It is possible that the unoccu-
pied 3d orbitals of the sulfur atom play a crucial part in the
formation of transition states in the isomerisation process.
The fact that the cis isomer was not observed for the sulfox-
ide-chelated catalysts would support such a hypothesis be-
cause, in the case of sulfoxides, the sulfur atom hybridisation
is closer to sp3. Therefore, the d orbitals have a smaller
impact on the sulfur bonding and, moreover, the presence
of the oxygen atom could shield possible interactions of the
sulfur d orbitals with the Ru or Cl orbitals.
Compound 14: The yellow-brown oil was purified by chromatography on
silica gel (95:5 petroleum ether (60–80)/dichloromethane) to afford 14 as
a yellow oil (2.20 g, 78%). 1H NMR (200 MHz, CDCl3): d=1.98 (m,
4H), 3.36 (m, 4H), 6.81 (m, 2H), 7.38 (dt, J=1.9, 7.6 Hz, 2H), 7.70 (dd,
J=1.6, 7.8 Hz, 1H), 10.08 ppm (s, 1H); 13C NMR (50 MHz, CDCl3): d=
25.9, 52.6, 114.5, 116.4, 122.9, 133.1, 135.9, 134.1 190.1 ppm; MS (EI): m/z
(%): 39 (9), 51 (17), 65 (11), 77 (41), 91 (35), 106 (86), 118 (91), 130 (18),
146 (46), 156 (13), 175 (100).
Compound 15: The yellow-brown solid was purified by recrystallisation
from hot ethanol to afford 15 as a yellow solid (2.30 g, 65%). 1H NMR
(200 MHz, CDCl3): d=2.06 (m, 4H), 3.44 (m, 4H), 6.77 (d, J=9.7 Hz,
1H), 8.16 (dd, J=2.8, 9.4 Hz, 1H), 8.58 (d, J=2.8 Hz, 1H), 9.98 ppm (s,
1H); 13C NMR (50 MHz, CDCl3): d=25.8, 52.9, 114.3, 120.8, 128.6, 131.3,
136.7, 151.8 187.8 ppm; MS (EI): m/z (%): 41 (6), 51 (8), 63 (8), 70 (18),
77 (14), 91 (12), 105 (16), 117 (26), 131 (6), 145 (12), 151 (100), 164 (45),
173 (13), 190 (8), 220 (79).
Conclusion
We have put forward a series of new ruthenium bidentate
benzylidene catalysts based on sulfur and nitrogen chelation.
These novel catalysts were thoroughly characterised and
studied by spectroscopic and crystallographic techniques,
which showed that EWG and EDG substituents have a
minor effect on the structures of the catalysts. Our study
also shows that latent nitrogen-chelated ruthenium benzyli-
denes may be strongly activated by reducing the electron
density on the chelating aromatic group. In contrast, the in-
troduction of EWGs on the sulfur-chelated benzylidene
complexes could not awaken the latent catalysts. In this
case, only direct oxidation of the sulfide ligand to a chiral
(racemic) sulfoxide activated the dormant catalyst. This oxi-
dation also transformed the geometry from a relatively inert
cis-dichloro form to a more common trans-dichloro configu-
Compound 16: The crude product was purified by chromatography on
silica gel (5:1 petroleum ether (60–80)/ethyl acetate) to afford 16 as a
yellow oil (0.80 g, 30%). 1H NMR (200 MHz, CDCl3): d=1.98 (m, 4H),
3.34 (m, 4H), 3.79 (s, 3H), 6.86 (d, J=3.1 Hz, 1H), 7.05 (dd, J=3.1,
9.0 Hz, 1H), 7.27 (s, 1H), 10.21 ppm (s, 1H); 13C NMR (50 MHz,
CDCl3): d=25.7, 53.6, 55.7, 112.2, 116.9, 123.3, 123.9, 146.7, 151.9,
190.3 ppm; MS (EI): m/z (%): 134 (37), 136 (50), 148 (17), 149 (27), 162
(21), 176 (11), 190 (54), 204 (27), 205 (100), 206 (13).
Compound 17: The yellow-brown solid was filtered, washed with water
and purified by chromatography on silica gel (10:1 petroleum ether (60–
80)/diethyl ether) to give 17 as a yellow solid (1.81 g, 50%). 1H NMR
(200 MHz, CDCl3): d=1.46 (d, J=6.9 Hz, 6H), 3.67 (septet, J=6.9 Hz,
1H), 7.55 (d, J=8.7 Hz, 1H), 8.32 (dd, J=2.5, 8.7 Hz, 1H), 8.66 (d, J=
2.5 Hz, 1H), 10.3 ppm (s, 1H); 13C NMR (50 MHz, CDCl3): d=22.5, 36.6,
127.2, 127.4, 127.9, 133.4, 144.7, 150.8, 189.1 ppm; MS (EI): m/z (%): 43
8734
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 8726 – 8737

Electronic Effects in Heteroatom-Chelated Ruthenium Catalysts
FULL PAPER
(67), 69 (28), 108 (30), 125 (13), 136 (53), 149 (45), 166 (33), 182 (100),
183 (92), 192 (11), 210 (22), 225 (69).
135.3, 142.0, 154.5 ppm; MS : m/z (%): 39 (3), 51 (3), 65 (4), 77 (7), 91
(8), 117 (16), 132 (11), 160 (71), 174 (14), 188 (100), 203 (79).
Compound 18:[5a] The crude product was purified by chromatography on
silica gel (1:1 n-hexane/ dichloromethane) to give 18 as a yellow oil
(2.08 g, 85%). 1H NMR (200 MHz, CDCl3): d=2.49 (s, 3H), 7.24–7.58
(m, 3H), 7.80 (dd, J=1.4, 7.6 Hz, 1H), 10.25 ppm (s, 1H).
Compound 22: The crude product was purified by chromatography on
silica gel (4:1 petroleum ether (60–80)/diethyl ether) to give 22 as a
yellow oil (0.50 g, 81%). 1H NMR (200 MHz, CDCl3): d=1.37 (d, J=
6.6 Hz, 6H), 3.56 (septet, J=6.6 Hz, 1H), 5.50 (dd, J=0.9, 10.9 Hz, 1H),
5.80 (dd, J=0.9, 17.2 Hz, 1H), 7.09 (dd, J=10.9, 17.2 Hz, 1H), 7.40 (d,
J=8.7 Hz, 1H), 8.04 (dd, J=2.5, 8.7 Hz, 1H), 8.30 ppm (d, J=2.5 Hz,
1H); 13C NMR (50 MHz, CDCl3): d=22.8, 37.1, 118.4, 120.9, 122.3, 128.2,
132.8, 138.4, 144.5, 145.5 ppm; GC–MS (EI): m/z (%): 39 (3), 63 (3), 69
(3), 89 (8), 133, (11), 134 (100), 135 (11), 163 (10), 180 (35), 223 (15).
Compound 23:[5a] The crude product was purified by chromatography on
silica gel (petroleum ether (60–80)) to give 23 as a colourless oil (0.33 g,
79%). 1H NMR (200 MHz, CDCl3): d=2.43 (s, 3H), 5.32 (dd, J=1.2,
10.9 Hz, 1H), 5.67 (dd, J=1.2, 17.4 Hz, 1H), 7.05–7.26 (m, 4H), 7.46 ppm
(dd, J=10.9, 17.4 Hz, 1H).
Compound 24: A solution of 17 (0.338 g, 1.5 mmol) in dichloromethane
(10 mL) and a solution of KHCO3 (1.18 g) in H2O (10 mL) were mixed
vigorously. A solution of bromine (0.264 g, 1.93 mmol) in dichlorome-
thane (1.5 mL) was added dropwise (each drop was added after partial
decolourisation of the mixture). After 20 min a flat spatula of solid
Na2SO3 and dichloromethane (40 mL) were added. The organic phase
was separated, washed with brine and dried over anhydrous MgSO4. The
solvent was evaporated under reduced pressure and the residue was puri-
fied by column chromatography (3:1–1:1 c-hexane/ethyl acetate) to give
24 as yellow crystals (0.250 g, 1.04 mmol, 70%). M.p. 118--1208C;
1H NMR (400 MHz, CDCl3): d=0.93–0.98 (d, J=7.1 Hz, 3H), 1.58–1.63
(d, J=7.1 Hz, 3H), 3.12 (septet, J=7.1 Hz, 1H), 8.40–8.46 (m, 1H), 8.62–
8.68 (m, 1H), 8.78–8.84 (m, 1H), 10.16 ppm (s, 1H); 13C NMR (100 MHz,
CDCl3): d=12.0, 18.6, 53.4, 128.1, 128.2, 133.6, 149.3, 154.2, 189.9 ppm;
IR (KBr): n˜ =3372, 3080, 3061, 3018, 2977, 2930, 2867, 1956, 1854, 1736,
1693, 1603, 1574, 1528, 1464, 1413, 1382, 1367, 1351, 1314, 1231, 1199,
1170, 1142, 1129, 1107, 1057, 1037, 1023, 1013, 952, 926, 914, 875, 852,
821, 743, 722, 704, 670, 577, 562, 538, 517, 502, 451, 433 cmꢀ1; MS (EI):
m/z (%): 39 (18), 41 (22), 43 (41), 75 (10), 136 (20), 152 (14), 181 (34), 82
(100), 183 (14), 199 (68), 200 (14); HRMS (EI): m/z: calcd for
C10H11O4SN: 241.04088 [M]+; found: 241.04034; elemental analysis calcd
(%) for C10H11O4SN: C 49.78, H 4.60, S 13.29, N 5.81; found: C 49.63, H
4.58, S 13.14, N 5.78.
Compound 25: In a Schlenk flask, solid methyltriphenylphosphonium
bromide (0.41 g, 1.15 mmol) and toluene (6 mL) were placed under
argon. Potassium tert-pentylate (1.7m in toluene, 0.67 mL, 1.15 mmol)
was added dropwise at 58C. The reaction mixture was warmed to RT and
stirred for 2 h. The mixture was cooled to 58C and a solution of 24
(0.23 g, 0.96 mmol) in toluene (4 mL) was added, the mixture was al-
lowed to warm to RT and was stirred overnight. A saturated aqueous so-
lution NH4Cl (15 mL) was added, the aqueous layer was extracted with
tert-butyl methyl ether (3ꢃ20 mL) and the organic layer was dried over
anhydrous MgSO4. The solvent was evaporated under reduced pressure
and the product was purified by short-column chromatography (2:3 c-
hexane/ethyl acetate) to give 25 as a yellow solid (0.168 g, 0.7 mmol,
73%). M.p. 69–718C; 1H NMR (500 MHz, CDCl3): d=0.99–1.02 (d, J=
7.0 Hz, 3H), 1.35–1.38 (d, J=7.0 Hz, 3H), 2.91 (septet, J=6.9 Hz, 1H),
5.59 (d, J=11 Hz, 1H), 5.94 (d, J=17.2 Hz, 1H), 6.89 (dd, J=11.0,
17.2 Hz, 1H), 8.04–8.06 (m, 1H) 8.26–8.28 (m, 1H), 8.36–8.37 ppm (m,
1H); 13C NMR (125 MHz, CDCl3): d=12.6, 17.4, 53.4, 120.8, 120.8, 126.6,
129.9, 137.0, 147.2 149.7 ppm; IR (KBr): n˜ =3134, 3093, 3082, 3064, 2969,
2930, 2871, 2090, 2062, 1941, 1879, 1865, 1813, 1736, 1690, 1628, 1598,
1568, 1523, 1454, 1415, 1384, 1366, 1346, 1313, 1294, 1242, 1179, 1168,
1129, 1094, 1068, 1031, 989, 982, 939, 931, 902, 914, 878, 846, 798, 750,
General procedure for synthesis of styrenes (19–23): Methyl triphenyl-
phosphonium iodide (0.78 g, 1.94 mmol) was dissolved in diethyl ether
(15 mL) in a 50 mL round-bottomed flask at 08C under dry nitrogen. Po-
tassium tert-butoxide (0.24 g, 2.08 mmol) was added in one portion and
the mixture was stirred for 10 min at RT. Aldehyde (14–18) (1.39 mmol)
was added in one portion at 08C and the reaction mixture was stirred for
24 h at RT. The mixture was added to saturated aqueous sodium bicar-
bonate solution (100 mL) and was extracted with dichloromethane (3ꢃ
50 mL). The combined organic extracts were dried over anhydrous mag-
nesium sulfate and evaporated under reduced pressure. The crude prod-
uct was purified by chromatography on silica gel to afford the desired
styrene.
740, 694, 668, 653, 591, 567, 560, 534, 514, 501, 481, 471, 438, 408 cmꢀ1
;
MS (EI): m/z (%): 43 (18), 121 (7), 133 (7), 134 (82), 135(6), 163 (9), 180
(100), 181 (13), 197 (53), 239 (7); HRMS (EI): m/z: calcd for
C11H13O3SN: 239.06162 [M]+; found: 239.06217; elemental analysis calcd
(%) for C10H11O4SN: C 55.21, H 5.48, S 13.40, N 5.85; found: C 55.33, H
5.48, S 13.33, N 5.74.
Compound 26:[18] Styrene 23 (69 mg, 0.46 mmol) was added to a solution
of 30% aqueous H2O2 (0.8 mL), sodium dodecyl sulfate (6.4 mg,
0.022 mmol) and 37% aqueous HCl (4.5 mL) and the reaction mixture
was stirred overnight at RT. The reaction mixture was added to a saturat-
ed aqueous solution of sodium sulfate (20 mL) and extracted with ethyl
acetate (3ꢃ10 mL). The crude product was purified by chromatography
on silica gel (2:1 petroleum ether/ethyl acetate), followed by a second
column chromatography (9:1 petroleum ether/ethyl acetate) to give the
pure sulfone 26 (5.9 mg, 0.032 mmol, 7%).
Compound 19: The crude product was purified by chromatography on
silica gel (95:5 petroleum ether (60–80)/dichloromethane) to give 19 as a
1
bright yellow oil (0.15 g, 62%). H NMR (200 MHz, CDCl3): d=1.95 (m,
4H), 3.23 (m, 4H), 5.22 (dd, J=1.8, 10.9 Hz, 1H), 5.59 (dd, J=1.8,
17.3 Hz, 1H), 6.92 (m, 2H), 7.01 (dd, J=10.9, 17.3 Hz, 1H), 7.21 (dt, J=
1.8, 7.6 Hz, 1H), 7.42 ppm (dd, J=1.8, 7.6 Hz, 1H); 13C NMR (50 MHz,
CDCl3): d=24.9, 51.8, 112.3, 115.5, 120.0, 127.9, 128.1, 129.4 136.6,
148.4 ppm; MS (EI): m/z (%): 39 (5), 51 (7), 65 (4), 77 (21), 103 (11), 117
(32), 130 (100), 144 (60), 173 (67).
Compound 20: The crude product was purified by chromatography on
silica gel (2:1 petroleum ether (60–80)/diethyl ether) to give 20 as an
orange-brown solid (0.16 g, 89%). 1H NMR (200 MHz, CDCl3): d=1.97
(m, 4H), 3.50 (m, 4H), 5.28 (dd, J=1.2, 10.9 Hz, 1H), 5.54 (dd, J=1.2,
17.2 Hz, 1H), 6.61 (d, J=9.0 Hz, 1H), 7.98 (dd, J=10.9, 17.4 Hz, 1H),
7.99 (dd, J=2.8, 9.3 Hz, 1H), 8.14 ppm (d, J=2.8 Hz, 1H); 13C NMR
(50 MHz, CDCl3): d=25.8, 51.8, 112.3, 115.0, 124.5, 125.3 126.1, 136.5
138.0, 152.3 ppm; GC–MS (EI): m/z (%): 39 (5), 51 (6), 63 (7), 77 (13),
89 (10), 103 (15), 116 (18), 129 (24), 143 (27), 157 (13), 171 (51), 175 (86),
189 (50), 218 (100).
General procedure for catalyst preparation (27–30): Styrene (14–18)
(0.14 mmol), cuprous chloride (0.17 mmol) and second-generation
Grubbs catalyst (0.14 mmol) were dissolved in dichloromethane (6 mL)
in a 10 mL round-bottomed flask topped with a reflux condenser under
dry nitrogen. The reaction mixture was heated at reflux temperature for
3–5 h. The resulting mixture was concentrated to 2–3 mL CH2Cl2. The
crude product was purified by chromatography on silica gel to afford the
desired catalyst.
Compound 27: The crude product was purified by chromatography on
silica gel (7:3 n-hexane/acetone) to give 27 as a green solid (75.0 mg,
84%). Crystals suitable for X-ray analysis were obtained by slow diffu-
sion between hexanes and a solution of 22 in dichloromethane at ꢀ188C.
1H NMR (500 MHz, CD2Cl2, 260 K): d=1.18 (m, 2H), 1.54 (m, 3H), 1.56
(s, 2H), 2.32 (s, 3H), 2.36 (s, 6H), 2.43 (s, 3H), 2.49 (m, 2H), 2.52 (s,
6H), 3.81 (m, 2H), 4.11 (s, 4H), 6.85 (d, J=7.3 Hz, 1H), 7.00 (s, 2H),
7.07 (s, 2H), 7.19 (t, J=7.3 Hz, 1H), 7.20 (d, J=8.1 Hz, 1H), 7.58 (t, J=
Compound 21: The yellow-brown oil was purified by chromatography on
silica gel (1:0–4:1 petroleum ether (60–80)/diethyl ether) to give 21 as a
yellow oil (0.57 g, 82%). 1H NMR (200 MHz, CDCl3): d=1.91 (m, 4H),
3.07 (m, 4H), 3.80 (s, 3H), 5.23 (dd, J=1.6, 10.8 Hz, 1H), 5.62 (dd, J=
1.6, 17.4 Hz, 1H), 6.77 (dd, J=3.0, 8.7 Hz, 1H), 6.94 (d, J=8.7 Hz, 1H),
7.02 (d, J=3.0 Hz, 1H), 7.04 ppm (dd, J=10.8, 17.4 Hz, 1H); 13C NMR
(50 MHz, CDCl3): d=24.4, 52.5, 55.5, 112.3, 113.1, 113.5, 117.7, 131.9,
Chem. Eur. J. 2010, 16, 8726 – 8737
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8735

K. Grela, N. G. Lemcoff et al.
7.3 Hz, 1H), 16.89 ppm (s, 1H); 13C NMR (125 MHz, CD2Cl2, 240 K): d=
17.8, 20.2, 20.5, 20.7, 22.1, 50.6, 51.5, 58.1, 119.9, 122.2, 127.9, 128.3, 129.0,
133.5, 137.1, 137.6, 138.3, 138.5, 139.6, 147.1, 155.3, 169.9, 209.7,
302.0 ppm; HRMS (FAB): m/z: calcd for C32H39Cl2N3Ru: 637.16 [M]+;
found: 637.13.
1525, 1482, 1428, 1380, 1346, 1317, 1267, 1212, 1188, 1109, 1085, 1039,
904, 856, 832, 817, 741, 717, 702, 627, 605, 591, 581, 539, 476 cmꢀ1; HRMS
(ESI): m/z: calcd for C31H37Cl2N2O3SRu: 703.70; found: 703.60; elemen-
tal analysis calcd (%) for C31H37Cl2N3O3SRu: C 52.91, H 5.30, S 4.56, N
5.97; found: C 52.69, H 5.53, S 4.60, N 5.77.
General procedure for metathesis reactions: Olefin (0.2 mmol) and cata-
lyst (0.002 mmol) were dissolved in toluene (2 mL) in a 5 mL round-bot-
tomed flask topped with a reflux condenser under dry nitrogen. The reac-
tion mixture was heated at reflux temperature and monitored by GC–
MS.
Compound 28: The crude product was purified by chromatography on
silica gel (7:3 n-hexane/acetone) to give 28 as
a dark-green solid
(54.0 mg, 52%). Crystals suitable for X-ray analysis were obtained by
slow diffusion between hexanes and a solution of 23 in dichloromethane
at 48C. 1H NMR (500 MHz, CD2Cl2, 216 K): d=1.11 (m, 2H), 1.57 (m,
2H), 2.29 (s, 3H), 2.33 (s, 6H), 2.47 (s, 11H), 3.78 (m, 2H), 4.13 (s, 4H),
6.99 (s, 2H), 7.10 (s, 2H), 7.33 (d, J=8.8 Hz, 1H), 7.61 (d, J=2.2 Hz,
1H), 8.42 (dd, J=2.6, 8.8 Hz, 1H), 16.71 ppm (s, 1H); 13C NMR
(125 MHz, CDCl3): d=19.0, 20.6, 21.3, 23.4, 52.0, 59.5, 114.5, 122.3, 123.6,
129.7, 139.5, 148.6, 154.2, 209.2, 295.2 ppm; HRMS (FAB): m/z: calcd for
C32H38Cl2N4O2Ru: 682.14 [M]+; found: 682.12.
General procedure for metathesis reactions with catalysts 2 and 3: Olefin
(0.350 mmol) and catalyst (0.004 mmol) were dissolved in dichlorome-
thane (17.5 mL) in a 25 mL round-bottomed flask under dry argon. The
same conditions were applied for providing metathesis reactions at 08C,
as well as, at 248C.
Compound 29: The crude product was purified by chromatography on
silica gel (7:3 n-hexane/acetone) to give 29 as
a dark-green solid
(37.4 mg, 40%). Crystals suitable for X-ray analysis were obtained by
slow diffusion between hexanes and a solution of 24 in dichloromethane
at 48C. 1H NMR (500 MHz, CD2Cl2, 250 K): d=1.14 (m, 2H), 1.52 (m,
2H), 2.31 (s, 3H), 2.37 (s, 6H), 2.39 (m, 2H), 2.42 (s, 3H), 2.51 (s, 6H),
3.74 (s, 3H), 3.77 (m, 2H), 4.12 (s, 4H), 6.30 (s, 1H), 6.99 (s, 2H), 7.08 (s,
2H), 7.10 (s, 1H), 7.10 (s, 1H), 16.75 ppm (s, 1H); 13C NMR (125 MHz,
CD2Cl2): d=18.9, 20.8, 21.3, 23.1, 52.1, 56.0, 59.0, 104.4, 114.4, 123.2,
129.6, 139.1, 141.1, 157.1, 160.0, 211.6, 300.9 ppm; HRMS (FAB): m/z:
calcd for C33H41Cl2N3ORu: 667.17 [M]+; found: 667.27.
Acknowledgements
The Israel Science Foundation and the Edmond J. Safra Foundation are
gratefully acknowledged for financial support (N.G.L., A.B., E.T.). K.G.
and K.W. thank the Foundation for Polish Science for the “Mistrz” pro-
fessorships. A.S. and K.G. are grateful for the grant number
N
N204157636, which was provided by the Polish Ministry of Science and
Higher Education. A.S. thanks the Foundation for Polish Science for the
START fellowship.
Compound 30: The crude product was purified by chromatography on
silica gel (7:3 n-hexane/acetone) to give 30 as
a dark-green solid
(50.0 mg, 52%). Crystals suitable for X-ray analysis were obtained by
[1] For selected reviews on olefin metathesis, see: a) T. M. Trnka, R. H.
Grubbs, Acc. Chem. Res. 2001, 34, 18–29; b) R. H. Grubbs, Hand-
book of Metathesis, Wiley, Weinheim, 2003; c) S. J. Connon, S. Ble-
chert, Angew. Chem. 2003, 115, 1944–1968; Angew. Chem. Int. Ed.
2003, 42, 1900–1923; d) D. Astruc, New J. Chem. 2005, 29, 42–56;
e) H. Clavier, K. Grela, A. Kirschning, M. Mauduit, S. P. Nolan,
Angew. Chem. 2007, 119, 6906–6922; Angew. Chem. Int. Ed. 2007,
46, 6786–6801; f) E. Colacino, J. Martinez, F. Lamaty, Coord. Chem.
Rev. 2007, 251, 726–764; g) M. Bieniek, A. Michrowska, D. L.
Usanov, K. Grela, Chem. Eur. J. 2008, 14, 806–818; h) V. Dragutan,
I. Dragutan, F. Verpoort, Platinum Met. Rev. 2005, 49,33–40; i) C. E.
Diesendruck, E. Tzur, N. G. Lemcoff, Eur. J. Inorg. Chem. 2009,
4185–4203.
slow diffusion between pentane and a solution of 25 in dichloromethane
1
at 48C. H NMR (500 MHz, CD2Cl2): d=0.83 (d, J=6.5 Hz, 3H), 1.50 (d,
J=7.3 Hz, 3H), 1.60 (s, 3H), 2.09 (s, 3H), 2.13 (s, 3H), 2.39 (s, 3H), 2.46
(s, 3H), 2.58 (s, 3H), 2.63 (s, 3H), 3.78 (m, 1H), 3.84 (m, 1H), 3.91 (m,
1H), 4.04 (m, 1H), 4.14 (m, 1H), 6.02 (s, 1H), 6.98 (s, 1H), 7.06 (s, 1H),
7.14 (s, 1H), 7.63 (m, 2H), 8.34 (dd, J=2.2, 8.7 Hz, 1H), 17.18 ppm (s,
1H); 13C NMR (125 MHz, CD2Cl2): d=18.0, 18.9, 19.9, 20.5, 20.9, 21.3,
21.5, 24.4, 40.5, 51.7, 51.9, 117.3, 122.2, 128.7, 129.1, 130.1, 130.2, 130.7,
131.1, 131.3, 135.8, 137.3, 138.4, 139.8, 140.6, 141.0, 142.7, 149.7, 156.6,
212.4, 280.5 ppm; HRMS (FAB): m/z: calcd for C31H43Cl2N3O2RuS:
693.15 [M]+; found: 693.10.
Compound 31: Compound 25 (0.05 g, 0.21 mmol), CuCl (0.021 g,
0.21 mmol) and anhydrous CH2Cl2 (14 mL) were placed in a Schlenk
flask. Grubbs second-generation carbene complex (0.161 g, 0.19 mmol)
was added and the solution was stirred under argon at 408C for 30 min.
From this point forth all manipulations were carried out in air with re-
agent-grade solvents. The reaction mixture was concentrated under
vacuum and the residue was dissolved in ethyl acetate (5 mL). The white
precipitate was filtered off and the filtrate was concentrated under
vacuum. The product was purified by column chromatography (c-hexane,
then 1:1 c-hexane/ethyl acetate); compound 31 was separated as a light-
green band. The solvent was evaporated under reduced pressure, the
product was dissolved in a small amount of ethyl acetate and n-heptane
was added until green crystals precipitated. The precipitate was filtered
off, washed with n-heptane and dried in vacuo to afford complex 31 as a
light-green solid (0.12 mmol, 0.084 g, 65%). Crystals suitable for X-ray
analysis were obtained by slow diffusion between n-hexane and a solu-
tion of 31 in dichloromethane at 48C. The additional oxygen atom in the
coordination sphere of ruthenium in the crystal structure of complex 31
belongs to a water molecule, which is present in the crystal structure of
the complex (Figure 1 f), but we see no evidence for it in the NMR spec-
tra or elemental analysis. 1H NMR (500 MHz, CDCl3): d=0.88–0.91 (m,
3H), 1.06–1.68 (m, 6H), 2.30–2.50 (m, 12H), 2.55–2.60 (m, 6H), 3.41
(septet, J=6.8 Hz, 1H) 4.14 (s, 4H), 7.04–7.06 (m, 2H), 7.08–7.11 (m,
2H), 7.50–7.54 (m, 1H), 7.85–7.87 (m, 1H) 8.50–8.52 (m, 1H), 16.64 ppm
(s, 1H); 13C NMR (125 MHz, CDCl3): d=15.7, 15.8, 19.1, 21.0, 51.8, 52.7,
114.6, 121.9, 128.0, 129.7, 129.9, 138.1, 138.4, 145.0, 151.8, 156.4, 204.8,
297.3 ppm; IR (KBr): n˜ =3590, 3414, 3082, 2958, 2923, 2867, 1636, 1600,
[2] a) P. Schwab, M. B. France, J. W. Ziller, R. H. Grubbs, Angew.
Chem. 1995, 107, 2179–2181; Angew. Chem. Int. Ed. Engl. 1995, 34,
2039–2041; b) P. Schwab, R. H. Grubbs, J. W. Ziller, J. Am. Chem.
Soc. 1996, 118, 100–110.
[3] a) M. Scholl, S. Ding, C. W. Lee, R. H. Grubbs, Org. Lett. 1999, 1,
953–956; b) T. M. Trnka, J. P. Morgan, M. S. Sanford, T. E. Wilhelm,
M. Scholl, T.-L. Choi, S. Ding, M. W. Day, R. H. Grubbs, J. Am.
Chem. Soc. 2003, 125, 2546–2558.
[4] a) S. B. Garber, J. S. Kingsbury, B. L. Gray, A. H. Hoveyda, J. Am.
Chem. Soc. 2000, 122, 8168–8179; b) S. Gessler, S. Randl, S. Ble-
chert, Tetrahedron Lett. 2000, 41, 9973–9976.
[5] a) T. Kost, M. Sigalov, I. Goldberg, A. Ben-Asuly, N. G. Lemcoff, J.
Organomet. Chem. 2008, 693, 2200–2203; b) A. Hejl, M. W. Day,
R. H. Grubbs, Organometallics 2006, 25, 6149–6154.
[6] C. Slugovc, D. Burtscher, F. Stelzer, K. Mereiter, Organometallics
2005, 24, 2255–2258.
[7] a) A. Ben-Asuly, E. Tzur, C. E. Diesendruck, M. Sigalov, I. Gold-
berg, N. G. Lemcoff, Organometallics 2008, 27, 811–813; b) X.
Gstrein, D. Burtscher, A. Szadkowska, M. Barbasiewicz, F. Stelzer,
K. Grela, C. Slugovc, J. Polym. Sci. Polym. Chem. Ed. 2007, 45,
3494–3500; c) C. E. Diesendruck, Y. Vidavsky, A. Ben-Asuly, N. G.
Lemcoff, J. Polym. Sci. Polym. Chem. Ed. 2009, 47, 4209–4213.
[8] a) K. Grela, S. Harutyunyan, A. Michrowska, Angew. Chem. 2002,
114, 4210–4212; Angew. Chem. Int. Ed. 2002, 41, 4038–4040; b) K.
Grela, M. Kim, Eur. J. Org. Chem. 2003, 963–966; c) M. Zaja, S. J.
Connon, A. M. Dunne, M. Rivard, N. Buschmann, J. Jiricek, S. Ble-
8736
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Chem. Eur. J. 2010, 16, 8726 – 8737

Electronic Effects in Heteroatom-Chelated Ruthenium Catalysts
FULL PAPER
chert, Tetrahedron 2003, 59, 6545–6558; d) M. Barbasiewicz, M. Bi-
eniek, A. Michrowska, A. Szadkowska, A. Makal, K. Wozniak, K.
Grela, Adv. Synth. Catal. 2007, 349, 193–203; e) R. Ettari, N.
Micale, J. Organomet. Chem. 2007, 692, 3574–3576; f) J. J. Van Veld-
huizen, D. G. Gillingham, S. B. Garber, O. Kataoka, A. H. Hoveyda,
J. Am. Chem. Soc. 2003, 125, 12502–12508.
P’Pool, N. J. Berger, E. J. Valente, A. M. Shiller, H. J. Schanz, Dalton
Trans. 2008, 42, 5791–5799.
[13] S. J. P’Pool, H. J. Schanz, J. Am. Chem. Soc. 2007, 129, 14200–
14212.
[14] A. Ben-Asuly, A. Aharoni, C. E. Diesendruck, Y. Vidavsky, I. Gold-
berg, B. F. Straub, N. G. Lemcoff, Organometallics 2009, 28, 4652–
4655.
[15] F. H. Allen, Acta Crystallogr. Sect. B 2002, 58, 380–388.
[16] T. Ritter, A. Hejl, A. G. Wenzel, T. W. Funk, R. H. Grubbs, Organo-
metallics 2006, 25, 5740–5745.
[17] a) C. E. Diesendruck, E. Tzur, A. Ben-Asuly, I. Goldberg, B. F.
Straub, N. G. Lemcoff, Inorg. Chem. 2009, 48, 10819–10825; b) M.
Barbasiewicz, A. Szadkowska, R. Bujok, K. Grela, Organometallics
2006, 25, 3599–3604; c) C. Slugovc, B. Perner, F. Stelzer, K. Mereit-
er, Organometallics 2004, 23, 3622–3626; d) T. Ung, A. Hejl, R. H.
Grubbs, Y. Schrodi, Organometallics 2004, 23, 5399–5401.
[18] For an alternative synthesis, see: J. Mihailo, Z. Anorg. Allg. Chem.
1956, 288, 324–328.
[9] For papers on latent catalysts, see: a) S. Monsaert, A. Lozano Vila,
R. Drozdzak, P. Van Der Voort, F. Verpoort, Chem. Soc. Rev. 2009,
38, 3360–3372; b) S. Monsaert, R. Drozdzak, F. Verpoort, Chim.
Oggi 2008, 26, 93—96; c) F. Ding, Y. Sun, S. Monsaert, R. Drozdzak,
I. Dragutan, V. Dragutan, F. Verpoort, Curr. Org. Synth. 2008, 5,
291–304; d) C. E. Diesendruck, O. Iliashevsky, A. Ben-Asuly, I.
Goldberg, N. G. Lemcoff, Macromol. Symp. 2010.
[10] H. Wakamatsu, S. Blechert, Angew. Chem. 2002, 114, 2509–2511;
Angew. Chem. Int. Ed. 2002, 41, 2403–2405.
[11] A. Szadkowska, A. Makal, K. Wozniak, R. Kadyrov, K. Grela, Or-
ganometallics 2009, 28, 2693–2700.
[12] a) R. Gawin, A. Makal, K. Wozniak, M. Mauduit, K. Grela, Angew.
Chem. 2007, 119, 7344–7347; Angew. Chem. Int. Ed. 2007, 46, 7206–
7209; b) S. L. Balof, B. Yu, A. B. Lowe, Ya. Ling, Y. Zhang, H. J.
Schanz, Eur. J. Inorg. Chem. 2009, 13, 1717–1722; c) S. L. Balof, S. J.
[19] J. Kruszewski, T. M. Krygowski, Tetrahedron Lett. 1972, 13, 3842–
3842.
Received: December 17, 2009
Published online: June 16, 2010
Chem. Eur. J. 2010, 16, 8726 – 8737
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8737