Mechanistic studies of hoveyda-grubbs metathesis catalysts bearing S-, Br-, I-, and N-coordinating naphthalene ligands

Article abstract of DOI:10.1002/chem.201303826

Derivatives of the Hoveyda-Grubbs complex bearing S-, Br-, I-, and N-coordinating naphthalene ligands were synthesized and characterized with NMR and X-ray studies. Depending on the arrangement of the coordinating sites on the naphthalene core, the isomeric catalysts differ in activity in model metathesis reactions. In particular, complexes with the Rui￡CH bond adjacent to the second aromatic ring of the ligand suffer from difficulties experienced on their preparation and initiation. The behavior most probably derives from steric hindrance around the double bond and repulsive intraligand interactions, which result in abnormal chemical shifts of benzylidene protons observed with ¹HNMR. Furthermore EXSY studies revealed that the halogen-chelated ruthenium complexes display an equilibrium, in which major cis-Cl₂ structures are accompanied with small amounts of isomeric forms. In general, contents of the minor forms, measured at 80°C, correlate with the observed activity trends of the catalysts, although some exceptions complicate the mechanistic picture. We assume that for the family of halogen-chelated metathesis catalysts the initiation mechanism starts with the cis-Cl ₂a?trans-Cl₂ isomerization, although further steps may become rate-limiting for selected systems. Isomerization first: A family of halogen-chelated Hoveyda-Grubbs complexes displays a cis-Cl₂a?trans-Cl₂ equilibrium in solution. Relative contents of the minor trans forms go along with the activity of the metathesis catalysts, suggesting its participation in the initiation mechanism (see figure). A unique effect of the naphthalene ligands enables control of the activity over a broad range, from moderately achieve to dormant, and was manifested in ¹HNMR for complexes with repulsive H×××H intraligand interactions (Mes=Mesityl).

Full text of DOI:10.1002/chem.201303826

DOI: 10.1002/chem.201303826
Full Paper
&
Metathesis Reactions
Mechanistic Studies of Hoveyda–Grubbs Metathesis Catalysts
Bearing S-, Br-, I-, and N-coordinating Naphthalene Ligands
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Krzysztof Grudzien, Karolina Zukowska, Maura Malinska, Krzysztof Wozniak, and
Michał Barbasiewicz*[a]
Abstract: Derivatives of the Hoveyda–Grubbs complex bear-
ing S-, Br-, I-, and N-coordinating naphthalene ligands were
synthesized and characterized with NMR and X-ray studies.
Depending on the arrangement of the coordinating sites on
the naphthalene core, the isomeric catalysts differ in activity
in model metathesis reactions. In particular, complexes with
the Ru=CH bond adjacent to the second aromatic ring of
the ligand suffer from difficulties experienced on their prepa-
ration and initiation. The behavior most probably derives
from steric hindrance around the double bond and repulsive
intraligand interactions, which result in abnormal chemical
shifts of benzylidene protons observed with 1H NMR. Fur-
thermore EXSY studies revealed that the halogen-chelated
ruthenium complexes display an equilibrium, in which major
cis-Cl2 structures are accompanied with small amounts of
isomeric forms. In general, contents of the minor forms,
measured at 808C, correlate with the observed activity
trends of the catalysts, although some exceptions compli-
cate the mechanistic picture. We assume that for the family
of halogen-chelated metathesis catalysts the initiation mech-
anism starts with the cis-Cl2Ðtrans-Cl2 isomerization, al-
though further steps may become rate-limiting for selected
systems.
Olefin metathesis is a valuable tool for the formation of
carbon–carbon multiple bonds that developed from industrial
high temperature heterogenic processes into highly efficient
homogenous systems for synthesis of fine-chemicals, pharma-
ceuticals, natural products, and other functionalized molecules.
With the aim of development of catalysts able for efficient
transformations of the olefins under mild conditions a large
number of ruthenium and molybdenum complexes were syn-
thesized.[1–3] Among systems of ultimate practical importance
complex 1, reported by Hoveyda,[4] was demonstrated to com-
bine high stability and activity in metathesis reactions, dupli-
cated further in a palette of related structures bearing chelat-
ing benzylidene ligands (Figure 1).[5]
In numerous modifications of the parent structure, general
trends associated with electronic[6] and steric[7] activation of
the catalysts were based on weakening of the O···Ru interac-
tion that facilitates opening of the chelate ring and entering of
the released propagating species into the catalytic cycle.[8]
Apart from the early studies unique ligand effect was observed
for isomeric naphthalene complexes 2, which substantially dif-
fered in activity in model metathesis reactions. Complex 2a,
bearing angular tricyclic structure, remained inactive at RT,[9]
Figure 1. Selected ruthenium complexes with chelating benzylidene li-
gands.[4,9,10,14b,15] Mes-2,4,6-trimethylphenyl.
while peri-substituted naphthalene catalyst 2c was an excellent
initiator, outstanding from 1 and its benzoanalogue 2b.[10] The
unique behavior was attributed to electronic effects operating
in the chelate rings, and degree of p-electron delocalization
leading some of the them into inactive Fisher-type or aromatic
structures.[9] Although, nature[11] and magnitude[12] of the elec-
tronic effects was questioned, it remained undoubted that the
naphthalene ligands differ in electronic and molecular struc-
tures, and both factors actually influence the initiation process.
At the same time another concept in development of the
structure 1 concerned changes of coordinating heteroatom
present in the chelate ring. In particular analogues with nitro-
˙
´
´
´
[a] K. Grudzien, K. Zukowska, M. Malinska, Prof. K. Wozniak,
Dr. M. Barbasiewicz
Faculty of Chemistry, University of Warsaw
Pasteura 1, 02-093 Warsaw (Poland)
Fax: (+48)22-822-5996
E-mail: barbasiewicz@chem.uw.edu.pl
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303826.
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gen,[13] sulfur (e.g., 3)[14] and covalently bonded halogen atoms
(e.g., 4a–c)[15] achieved great interest concerning their practical
applications[13c,16] and mechanistic studies.[5,17] The sulfur-che-
lated complexes were observed in two isomeric forms varied
by spatial orientation of ligands on the coordination sphere of
the ruthenium. These similar to 1, with trans orientation of the
halides, were isolated as kinetic products, which slowly con-
verted into thermodynamically preferred cis-Cl2 ones (e.g.,
3).[14b] Interconversion between the two forms was considered
a key step of the initiation process, in which minor amounts of
much more active trans isomer, present in equilibrium, act as
actual precatalyst.[14c,18] In turn complexes of covalently
bonded halogen atoms (e.g., 4) displayed the cis-Cl2 geometry
accompanied with high activity in model metathesis reaction-
s.[15a] Moreover, in the investigated series introduction of elec-
tron withdrawing NO2 group in para position of the benzyli-
dene ring (4b) caused decrease of the catalytic activity, in con-
trast to the behavior of ether-chelated systems.[6] The reduced
activity clearly contrasted with thermodynamic destabilization
of the chelate demonstrated on ligand exchange experiments,
and led to the conclusion, that the Ru···IꢀAr interaction is not
broken in the rate-determining step of the initiation proc-
ess.[15b] Another interesting effect was observed for ortho-nitro-
substituted iodocomplex 4c.[15c] In this case the chelate ring
was stabilized by the presence of adjacent NO2 group, and the
through-space interaction with the coordinating iodine atom
quenched catalytic activity of the catalyst at RT.
Scheme 1. Synthesis of 1,2- and 2,3-disubstituted naphthalene ligands. Re-
agents and conditions: a) nBuLi, Et2O, ꢀ308C to RT, then iPrSSiPr, ꢀ508C to
RT, 6, 84%; b) nBuLi, TMEDA, Et2O, then DMF, 7, 22%; c) Ph3PCH3Br or
Ph3PC2H5Br, t-PeOK, THF, 08C to RT, 8, 95%; 13, 96%; 14a, 92%; 14b, 92%;
15a, 97%; 15b, 88%; 18, 85%; d) N,N,N’-trimethylethylenediamine, nBuLi,
THF, ꢀ208C, then 9 (or 16), then nBuLi, ꢀ208C, 21 h, then electrophile,
ꢀ508C to RT, 10, 61%; 11, 34%; 12, 40%; 17, 7%.
In our report we present experimental studies of the S-, Br-,
I-, and N-coordinated complexes bearing naphthalene ligands.
The synthetic results, accompanied with structural and spectro-
scopic studies, shed more light on the initiation mechanism
and structure-activity relationships in the metathesis catalysts.
Scheme 2. Synthesis of 1,8-disubstituted naphthalene ligands. Metalation of
1,8-diiodonaphthalene leads to a monolithio derivative, which upon treat-
ment with DMF converts into two different products depending on the reac-
tion conditions. Reagents and conditions: a) H2SO4, H2O, NaNO2, ꢀ208C,
then KI, to 408C, 20, 53%; b) nBuLi, Et2O, ꢀ788C to ꢀ308C, then DMF,
ꢀ788C, then temperature, overnight; c) Ph3PC2H5Br, t-PeOK, THF, 08C, 22,
82%; d) Ph3PCH3Br, t-PeOK, THF, 08C to RT, 24, 62%.
Results and Discussion
Synthesis of ligands
Our studies began from the preparation of bidentate organic
ligands for further exchange reactions with the ruthenium
complexes. In most cases the syntheses consisted of metala-
tion reaction as a key step for functionalization of the naphtha-
lenic substrates (Scheme 1). Reaction of 1-bromonaphthalene
(5) with nBuLi, followed by the addition of diisopropyldisulfide
gave aryl sulfide 6 in 84% of yield. Directed ortho metalation
(DoM)[19] of the product and quenching of the resulted aryllithi-
um with DMF afforded aldehyde 7. Remaining 1,2- and 2,3-di-
substituted naphthalene ligands were synthesized from 1- and
2-formylnaphthalenes using convenient procedure described
by Comins.[20] The aldehydes 9 and 16 were subjected to the
lithium salt of N,N,N’-trimethylethylenediamine, and so-formed
adducts were in situ metalated with nBuLi followed by the ad-
dition of electrophiles (iPrSSiPr, CBr4, I2) to give functionalized
products in reasonable yields (10–12 and 17).[21]
(20) in 53% of yield. In the next step we planned to transform
one of the iodine atoms into the formyl group of aldehyde.
Thus, 20 was selectively monometalated with nBuLi,[23] and the
resulted lithioarene was treated with DMF followed by warm-
ing of the reaction mixture to RT. Although the procedure was
successfully applied for the synthesis of various aromatic alde-
hydes,[12] we failed to obtain the desired 1-formyl-8-iodonaph-
thalene (21). Instead, after the reaction we observed presence
of 1-formyl-8-(N,N-dimethylamino)naphthalene (23), which was
isolated in 74% of yield. Formation of 23 was surprising, but
became reasonable, when mechanism of the reaction with
DMF was considered (Scheme 2, bottom). Due to crowding of
two bulky substituents,[24] iodine atom and tetrahedral aminal
anion, between peri positions of the naphthalene,[25] the iodine
anion was expelled and replaced with dimethylamine anion re-
leased from the carbonyl group.[26] When the same reaction
In turn synthesis of peri-substituted naphthalene ligand 22
required a different approach (Scheme 2). 1,8-Diaminonaphtha-
lene (19) was diazotized at low temperature according to the
modified literature method[22] to give 1,8-diiodonaphthalene
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was repeated at lower temperature (ꢀ308C), course of the re-
arrangement was suppressed, and the expected iodoaldehyde
21 was isolated in good yield (74%). The serendipitous obser-
vation encouraged us to transform the both aldehydes into li-
gands for further transformations. So finally, all of the synthe-
sized aldehydes were converted into vinyl or propenyl deriva-
tives using Wittig reagents under usual conditions.
Synthesis and properties of the sulfur complexes
In the next step the ligands were reacted with commercially
available indenylidene ruthenium complexes (25 and 26,
Figure 2)[27] under the literature conditions.[14a,15a]
Figure 2. Indenylidene ruthenium complexes 25 and 26[27] used as sub-
strates for the ligand exchange reactions.
At the beginning ligands with the sulfur chelating arm were
used for the exchange reactions with 25. The experiments
were carried out in refluxing dichloromethane with CuCl as
a catalyst, following general procedure described by Lemcoff
(Figure 3, top).[14a,28] Under these conditions reactions of styr-
enes 27 and 8 led initially to trans-Cl2 isomers, which slowly
converted into more polar cis-Cl2 forms, as observed on TLC.
When the reactions were arrested before the isomerization
process was complete, we were able to isolate both of the
products with each of the ligands. However, in reaction of 13
only one polar product was observed, and the complex was
isolated by chromatography in 55% of yield. The unusual be-
havior was confirmed, when the reactions were performed in
NMR tubes under similar conditions (Figure 3, bottom). In case
of benzene ligand 27 transient product with benzylidene peak
present at 17.31 ppm slowly converted into another one ob-
served at 17.20 ppm, in accordance with the literature data.[13b]
Similar behavior was displayed by 8, where two consecutive
products were observed at 17.50 and 17.49 ppm, respective-
ly.[29] In turn, reaction of naphthalene ligand 13 clearly contrast-
ed by exclusive appearance of one peak around 18.48 ppm. It
is worth to stress, that all of the complexes were formed with
similar rates, although 28 was outstanding, when only forma-
tion of the cis-Cl2 isomers was considered. From the presented
data two scenarios seemed to be reliable: a) The cis-28 com-
plex is formed directly in a ligand exchange reaction of the
substrates, or b) transient trans-28 intermediate is not ob-
served, because of its fast isomerization under the reaction
conditions. To search for the missing isomer we attempted UV
irradiation of the complexes. As demonstrated by Lemcoff, the
stimulus causes dissociation of the coordinating Ru···S bond,
and so-formed 14e¯ species freely isomerize and re-associate
into a mixture of cis and trans-Cl2 products.[14d] Indeed, after
Figure 3. Synthesis of complexes 3, 28, and 29. In reactions of ligands 27
and 8 intermediate trans-Cl2 complexes slowly converted into thermody-
namic cis forms, while for ligand 13 only one polar product was formed
1
(top). The results were confirmed with H NMR studies, where appearance of
two (3 and 29) and one (28) benzylidene peaks were observed on the reac-
tion course (bottom). The array experiments were conducted with CuCl as
a catalyst in CD2Cl2 at 408C, and the NMR acquisitions were repeated in
1
10 min intervals. H NMR chemical shift values of benzylidene protons mea-
sured in CD2Cl2 solutions at RT are shown nearby the structures.
prolonged exposition of CDCl3 solutions of cis-isomers of 3, 28
and 29 to the UV light (366 nm) we observed presence of new
1
benzylidene peaks at H NMR spectra (their content in the mix-
tures was 28%, 4.5%, and 8%, respectively).[30,31] In case of 3
and 29 chemical shift values of the benzylidene protons
agreed with those observed in synthetic experiments for trans-
Cl2 isomers, while for 28 the new signal appeared at
19.32 ppm, and its content remained intact under ambient
conditions. To compare relative rates of isomerization of the
sulfur complexes we used analytical samples of trans-3 and
trans-29 dissolved in CD2Cl2, and mixture of isomers after irra-
diation of CD2Cl2 solution of cis-28, in which content of the
trans form reached 7%. The samples were individually thermo-
stated at 408C in the NMR spectrometer, and their proton
spectra were recorded in 10 min intervals, giving after 12 hꢁ
98% of the restored cis-Cl2 form in each case. Although data
of the latter isomerization was necessarily less accurate due to
the very low concentration of trans-28 in the initial mixture,
relative rates of the processes followed an order 29>3ꢁ28.
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From the results it become evident that ligand exchange reac-
tion between indenylidene complex 25 and naphthalene
ligand 13 gives directly a cis-Cl2 isomer, without formation of
transient trans product (Figure 3, top).[32] Interesting conse-
quences of the reasoning may arise from invoking of the prin-
ciple of microscopic reversibility.[33] Demand for the same
mechanism of the catalyst formation and initiation at the mi-
croscopic scale requires, that complex cis-28 directly initiates
to the 14e¯ species without preceding isomerization to trans-
28. The idea goes along with intriguing observations of differ-
ent E/Z selectivity in ring opening metathesis polimerization
(ROMP) displayed by isomers of 3, which suggested that in
some cases intermediate trans-Cl2 complexes may be not in-
volved in the initiation process.[14c]
shielded by ca. +1 ppm (18.45 ppm), as compared with cis-29
(17.46 ppm) and cis-3 (17.15 ppm), and the same applied for
transient trans-28 complex observed after UV-irradiation
(19.29 ppm vs. 17.47 for trans-29 and 17.26 ppm for trans-3, in
CD2Cl2). Although in ether-chelated naphthalene complexes
(e.g., 2a) the abnormal chemical shifts accompanied with di-
minished catalytic activity were attributed to p-electronic ef-
fects,[9] the reasoning seemed to be unlikely for the sulfur che-
lates. Considering that p-electronic structure of the naphtha-
lene is extended by the conjugated chelate ring, the both iso-
meric ligands 8 and 13 should display virtually the same prop-
erties, in contrast with experiments. Thus, more probable
explanation of the differences arose from steric effect of the
naphthalene ligand 13, which alters mechanism of formation
of the ruthenium complex 28, and manifests at the 1H NMR
spectrum, due to a chance proximity of benzylidene proton
with adjacent fragment of the structure (e.g., mesityl ring). To
verify the idea complexes trans-29, cis-28 and cis-29 were stud-
ied with X-ray analysis and their structures are presented at
Figure 5. Structure of trans-29 (top) displayed many similarities
Next, catalytic activity of the complexes 3, 28 and 29 was
tested in model metathesis reactions, separately for trans and
cis isomers as a consequence of their disparate activities (Fig-
ure 4).[14d]
Figure 4. Activity profiles of 1 mol% of complexes 3, 28 and 29 in RCM of
DEDAM in 0.2m solutions. The catalysts were tested: trans-Cl2 isomers in
non-degassed CD2Cl2 at 408C (detected by NMR, left), and cis-Cl2 isomers in
1,2-dichloroethane at 808C (preparative experiments, detected by GC, right).
Notice that different timescales were applied for the plots.
The RCM reactions of diethyl diallylmalonate (DEDAM, con-
centration 0.2m) catalyzed with 1 mol% of trans-Cl2 complexes
3 and 29 were conducted in CD2Cl2 at 408C, and followed with
1H NMR according to our standard procedure[12] (Figure 4, left).
In the experiments complex trans-3 appeared to be more
active than trans-29, probably as a consequence of faster iso-
merization of the latter to the latent cis form and smaller con-
tent of the active catalyst in the reaction mixture.[34] Due to
very low activity, cis-Cl2 complexes were tested in preparative
experiments in 1,2-dichloroethane at 808C for 2 days, and sam-
ples were analyzed with GC using internal standard (Figure 4,
right).[30] Activity of the cis-Cl2 complexes increased in the
series 29>3>28, following the same order as relative isomeri-
zation rates of the corresponding trans-Cl2 catalysts. From the
latter data we deduced that effect of the naphthalene ligands
in complexes cis-28 and cis-29 acts in opposite directions, de-
creasing activity of the first catalyst and accelerating of the
latter one, as compared with cis-3. Pronounced differences be-
Figure 5. ORTEP[36] representations of complexes trans-29 (in two projec-
tions, top), cis-28 (one arbitrarily chosen molecule, middle) and cis-29
(bottom) shown as thermal ellipsoids drawn at the 50% probability level.
The cis-Cl2 complexes show similar atom arrangements, when displayed
from the bottom: benzylidene hydrogen atoms (in gray circles) neighbor
with CꢀC bonds and methyl groups of mesityl rings.
1
tween the two systems were observed also at H NMR spectra
of CD2Cl2 solutions, where benzylidene peak of cis-28 was de-
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to the parent system trans-3, described in literature.[13b] Isopro-
pyl substituent on the coordinating sulfur atom was deformed
from the plane of the naphthalene ring by 828[35] (788 in trans-
3), and core of the ligand was twisted from the axis constitut-
ed by Ru-NHC bond by 228 (198 in trans-3). In the same way
the both cis-Cl2 naphthalene complexes (28 and 29, middle
and bottom, respectively) displayed only little variations from
cis-3.[13b] Particularly, in the structures we observed that the
benzylidene protons (marked with gray circles) were located in
essentially the same positions, when considering rotation of
the NHC ligand around the RuꢀC bond. Thus, anisotropy of
neighboring mesityl rings was unlikely to explain the observed
NMR differences. The issue is discussed further in the next sec-
tion.
Synthesis and properties of the halogen complexes
In the next step we focused on family of the Hoveyda-type
complexes chelated with covalently-bonded halogen atoms,
represented in literature by bromo- and iodocoordinated struc-
tures with cis-Cl2 geometry (Figure 6).[15,16]
Scheme 3. Synthesis of halogen-coordinated complexes 30 and 33-36. Re-
agents and conditions: a) Naphthalene ligand (15b, 18, 31, 22; 1.2 equiv),
complex 26 (1.0 equiv), toluene, 808C, 30 min, then filtration; 36, not ob-
served; 33, 68%; 30, 87%;[15a] 34, 36% (48% with 1.5 equiv of 22); b) Naph-
thalene ligand (14a, 15a; 1.2 equiv), complex 26 (1.0 equiv), toluene, 1118C,
15 min, then filtration; 35, 8%; 36, 8%.[37] 1H NMR chemical shift values of
benzylidene protons measured in CD2Cl2 solutions at RT are shown nearby
the structures.
best of our knowledge for the Hoveyda-type complexes effect
of substituents present on the benzylidene ring in ortho posi-
tion to the Ru=CH group was not explored in literature. The
only data concerning properties of similar systems are limited
to ether-chelated naphthalene complex 2a,[9,10] and derivative
of complex 2b, in which two isopropoxyl groups, present in
positions 1 and 3 of the ligand, surround the Ru=CH fragment
(see Figure 1).[12] Interestingly, the both catalysts required more
harsh conditions during its preparation and initiation, for ex-
ample, improved procedure of synthesis of 2a utilized vinyl
ligand precursor and reaction temperature increased to
858C.[39] Following the idea we applied vinyl[40] ligands 14a
and 15a, and repeated the reactions in boiling toluene
(1118C). Indeed, the expected complexes 35 and 36 were
formed in diminished yields (8%, in both cases).[37] Anyway, it
is worth to stress that the complexes remained stable under
the harsh reaction conditions, and the behavior clearly con-
trasts with the common knowledge about the systems coordi-
nated with covalently-bonded halogen atoms and the metal–
carbene complexes in general.
Figure 6. Selected ruthenium complexes chelated with covalently bonded
halogen atoms. H NMR chemical shift values of benzylidene protons mea-
sured in CD2Cl2 solutions at RT are shown nearby the structures.[15a,b]
1
The two classes, derived from different coordinating halogen
atoms, displayed disparate properties. In general, iodocomplex-
es were formed in high yields and their activity varied over
a broad range from moderately active (e.g., 4a) to dormant at
RT (4c). In turn bromocomplexes displayed almost identical ac-
tivity in the series, but their preparation was affected by donor
abilities of the substituents that resulted in decreasing yields
isolated under usual reaction conditions (31a>31b>
31c).[15a,b,37]
In the present studies we attempted to synthesize of all iso-
meric iodocomplexes derived from 1,2-, 2,3-, and 1,8-substitut-
ed naphthalene ligands. Thus, series of styrenes 18, 31 and 22
was subjected to the reactions with indenylidene ruthenium
complex 26 according to the general procedure,[15a] and corre-
sponding products 33, 30 and 34 were isolated in good to
moderate yields (68%, 87%,[15a] and 36%, respectively;
Scheme 3). Surprisingly, under the same conditions ligand 15b
with olefinic substituent crowded between iodine atom and
adjacent aromatic ring failed to give the expected product,
and the same applied for the bromoligand 14b.[38] We con-
nected the fact, that sulfur complex 28 with similar ligand
structure was formed directly as a cis-Cl2 isomer, and reckoned
that the disparate reactivity of the ligands may derive from the
presence of distal aromatic ring of the naphthalene. To the
Next, the synthesized complexes were characterized with
multiple techniques. Structures of 33, 34, and 35 were con-
firmed with X-ray studies, and all of them displayed cis-Cl2 ge-
ometry, with only minor differences from the previously report-
1
ed structures of 4a–c, 30, 31a, and 32.[15] In turn, at H NMR
spectra benzylidene protons of complexes 35 and 36 displayed
exceptional chemical shift values (19.18 and 19.59 ppm, re-
spectively), unprecedented for the chelated pentacoordinated
Hoveyda-type systems. Again, as in case of the sulfur chelates,
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the deshielding effect emerged only for ligands, in which Ru=C
bond neighbored with distant aromatic ring of the naphtha-
lene. Finally, the synthesized halogen-chelated catalysts were
tested in model RCM reactions with DEDAM and diethyl allyl-
methallylmalonate under ambient conditions (Figure 7).[41]
plex 3 only the cis-Cl2 form was detected by 1H NMR, even
when the sample was heated to 1458C.[14c] The behavior was
consistent with the latent character of the catalyst, which re-
quired much higher temperatures and prolonged reaction
times to initiate (see Figure 4, right). From this perspective,
complexes coordinated with covalently bonded halogen
atoms, which displayed pronounced activity under ambient
conditions, seemed to be interesting target for further NMR
studies. Indeed, careful examination of the benzylidene region
of analytical 1H NMR spectrum of iodocomplex 4a revealed
presence of additional resonance peak of very low intensity
(approximately half of the intensity of 13C satellites, that is,
0.2%), accompanying the major one. Interestingly, in bromo-
complex 32 content of similar peak was as high as 5% at RT,
and increased to 15% after heating of the sample to 808C. The
facts agreed well with the equilibrium process, for which con-
tent of the minor form should increase with temperature.[43] To
prove our hypothesis we performed spin-exchange spectrosco-
py (EXSY)[44] of CDCl3 solution of 32 at 808C, and crosspeaks
with the same phase as diagonal signals confirmed the actual
dynamic process operating in the system (Figure 8).
Figure 7. Activity profiles of 1 mol% of complexes 4a, 30, 31c, and 32–36
in RCM of DEDAM (left) and diethyl allylmethallylmalonate (right) in 0.2m
1
non-degassed CD2Cl2 solutions of the substrates detected by H NMR.[42]
Interestingly, the iodonaphthalene complexes followed quite
similar activity trends to that displayed by ether-chelated cata-
lysts (2a–c, see Figure 1).[10] Namely, peri-substituted naphtha-
lene complex 34 appeared to be more active than 4a and 33,
while catalyst 36 with angular tricyclic structure remained inac-
tive under ambient conditions. The latent character was ob-
served also for bromocomplex 35, suggesting presence of the
same structural barrier for the naphthalene ligand 14a. How-
ever, the both latent catalysts (35 and 36) efficiently catalyzed
DEDAM metathesis cyclization, when the temperature was in-
creased to 558C.[30]
NMR studies of the halogen-chelated complexes and conse-
quences for the initiation mechanism
Figure 8. EXSY[44] spectrum of benzylidene region of complex 32 (NOESY se-
quence, mixing time 500 ms, measured at 808C in a CDCl3 solution in sealed
tube).
Summarizing the current findings, complexes of naphthalene
ligands with distant aromatic ring adjacent to the Ru=CH bond
display difficulties on the initiation process accompanied with
strong deshielding of benzylidene protons, observed by NMR.
Moreover, for sulfur complex 28 the effect changes mechanism
of the ligand exchange reaction with the ruthenium complex
25, while for bromo- and iodosubstituted ligands 14a and 15a
it causes a barrier, which results in decreased yields of forma-
tion of complexes 35 and 36. The obtained results provoke an
obvious question about actual initiation mechanism of halo-
gen-coordinated complexes. Does it consist of cis-to-trans-Cl2
isomerization, followed by the chelate dissociation, or the pre-
catalysts directly recombine with olefins in their cis-Cl2
forms?[15b] Although initiation mechanism was studied on the
sulfur-chelated catalysts, experimental evidence of the isomeri-
zation process utilized complexes with sterically demanding li-
gands, which destabilized structures of the thermodynamically
preferred cis-Cl2 forms. In turn, in solution of the parent com-
Although the minor form present in the mixture was not
fully characterized, we suppose that the structure corresponds
to the missing trans-Cl2 isomer. In particular, examination of
3.7–4.3 ppm region, with the multiplet characteristic for
NCH2CH2N fragment of the cis-Cl2 isomer, revealed presence of
additional sharp singlet, expected for symmetric structure of
the trans-Cl2 form, in which the four protons become equiva-
lent due to symmetry and exchange processes.[30,45] The peak
integration agreed with intensity of the minor form observed
in benzylidene region, and content of the both species in-
creased with temperature in parallel manner. Considering that
the initiation mechanism consists of the isomerization process,
higher contents of the active trans-Cl2 forms should translate
into more active catalysts. Thus, to correlate the observed
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in the iodochelates further destabilize the minor iso-
mers, and the destabilization reaches limit of detec-
tion of the equilibrium form for 4c, in which the
Ru···I interaction is strengthened by the presence of
adjacent NO2 group, as demonstrated in ligand ex-
change experiments.[15c] Moreover, in some cases
steric effect of demanding naphthalene ligands su-
perimposes with the electronic effects, as in com-
plexes 35 and 36, where additional strain in the trans
isomers may arise from repulsion with mesityl ring of
the NHC ligand (see Scheme 3, bottom). From this
perspective plausible scenario of the initiation mech-
anism of the catalysts consists of the cis-to-trans-Cl2
isomerization as a first step of complex multistage
process. For most of the investigated catalysts the re-
action is observed under ambient conditions, and
Table 1. Contents of the minor equilibrium forms of the halogen-chelated complexes
in CDCl3 solutions measured with H NMR at 808C (sealed tubes).
1
31c
Me
31b
MeO NMe2
31a
32
35
bromocomplexes
content of the minor form 15% 14% 14%
15% 5%
34
4b
NO2
4d[b]
Br
4a
H
1%
4e[b]
NMe2
1%
30
36
4c
iodocomplexes[a]
content of the minor form 5%[c] 4%
2%
1% n.d. n.d.
[a] Accidental overlap of the minor benzylidene peak with 13C satellite and impurity
peak prevented us from definite determination of the content for complex 33.
[b] Complexes 4d and 4e continued series of iodocomplexes substituted in para posi-
tion to the coordinating iodine atom, as depicted on Figure 1 (4d, R=Br;[15b] 4e, R=
NMe2[15a]).[c] For the peri-substituted naphthalene complex 34 presence of two minor
equilibrium forms was observed (minor1ÐmajorÐminor2 ca. 5:100:2).[30]
equilibrium process with the catalytic activity of the halogen-
chelated metathesis catalysts, spectra of series of the com-
plexes were recorded at 808C in CDCl3 solutions (sealed tubes),
and relative contents of the minor forms are presented at
Table 1. Indeed, the results roughly correlated with the activi-
ties, but some peculiarities required further analysis. In accord-
ance with the activity trends[15a,b] (see Figure 7, left) bromocom-
plexes 31a–c, and 32 displayed higher contents of the equilib-
rium forms of 14–15%, and only latent complex 35, bearing
crowded naphthalene ligand, diverged from the series (5%). In
turn less active iodocomplexes were more differentiated, and
displayed a gradual decrease of the content from 5% for peri-
substituted naphthalene complex 34, to ca. 1% for 4a, 4e and
30, and right down to the complex 4c, stabilized with
a through-space NO2!I interaction,[15c] for which the equilibri-
um form was not detected. However, the broad correlation
clearly failed to reproduce other effects, for example, related to
substituents, reported for iodocomplexes 4a–b,d–e.[15b] In our
studies the trans-Cl2 form present in equilibrium was mostly
preferred for acceptor substituted complex 4b (4%), and its
content gradually decreased to 2% for bromocomplex 4d, and
to 1% for other structures (4a,e). In turn catalytic performance
displayed a maximum in the investigated series for unsubsti-
tuted catalyst 4a, with relatively deprived initiation of both ac-
ceptor- and donor-substituted systems.[15b] Analysis of the iso-
merization process, and structural factors, which may influence
relative stabilities of the isomeric forms present in equilibrium,
pointed our attention to the trans influence of the NHC ligand.
The effect was claimed to destabilize trans-Cl2 structures by
weakening of the ruthenium-heteroatom bond in heavier ana-
logs of the Hoveyda complex.[17] Thus, more strongly s-donat-
ing sites of sulfur, selenium, and phosphorus atoms present in
the chelating ligands escape from the disfavored axial position
on the opposite site to the NHC donor, and at the same time
bind more tightly to the metal center in the isomeric cis-Cl2
forms, stabilizing them. The picture agrees well with the elec-
tronic effect of substituents on the equilibrium of the isomeri-
zation process in the family of halogen-chelated ruthenium
complexes. In general more electronegative bromine atoms
are weaker s-donors than iodine atoms that manifests in
higher contents of their trans-Cl2 structures. Donor substituents
likely it controls their activity by changes related to the equilib-
rium processes displayed at the beginning of the catalytic
cycle. However, for selected systems, as 4b, following steps of
the initiation mechanism, for example, association of the sub-
strate,[8b] formation[8e] and fission of metallacyclobutane, and
decoordination of the ligand,[8d] may become rate-limiting, and
thus control the observed catalytic activity. The situation is ex-
emplified by catalyst 35, for which content of the trans-Cl2
form is significant (5%), and clearly contrasts with latent be-
havior of the system displayed at RT. We believe that in this
case one of the further steps is limiting, and corresponds to
the highest barrier on the energy landscape of the mechanism.
Interestingly, it is worth to stress that despite numerous struc-
tural variants tested, we did not observe opposite situation,
when catalyst with small content of the equilibrium form was
exceptionally active in the series. The fact confirms the hypoth-
esis that fast initiation of the catalysts requires higher concen-
trations of their transient trans-Cl2 forms.
In the next step we focused on abnormal chemical shift
values of benzylidene protons in complexes cis-28
(18.45 ppm), 35 (19.18 ppm), and 36 (19.59 ppm). The unique
effect was observed exclusively for one isomer of the naphtha-
lene ligands in sulfur- and bromine-coordinated structures,
while in series of iodocomplexes also peri-substituted system
34 displayed a relatively high value of 18.69 ppm, as compared
with the parent benzene complex 4a (18.08 ppm), and two
other naphthalene complexes: linear 33 (18.08 ppm) and angu-
lar 30 (18.26 ppm). To reveal the riddle we focused on structur-
al similarities between the complexes and tricyclic aromatic hy-
drocarbons (PAHs).[10] In particular, angular structures of com-
plexes 28, 35 and 36 resembled molecule of phenanthrene,
1
which displays interesting H NMR properties concerning pro-
tons located in a so-called “bay region”.[46] Exceedingly small
H···H distances in the area result in deshielding effect (van der
Waals shift) of their resonances, which amounts to ca.
+1 ppm, when compared with other protons in the molecule
(Figure 9, left).
By analysis of the ruthenium complexes, similar distances
between benzylidene protons and adjacent protons of organic
ligands should decrease in series from benzene complex 4a, to
peri-substituted system 34, and to structure 36 with the steri-
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issues it resembled its ether-chelated analogue 2c, with slant-
ing core of the ligand and high chemical shift value of benzyli-
dene proton (18.32 ppm vs. 18.66 ppm for 2c).[10] However, the
catalyst appeared to be inactive in model DEDAM cyclization
at 258C and 558C, and only at 808C in [D8]toluene it initiated
slowly giving 24% of conversion of the substrate after 1 h.[30]
The activity clearly contrasted with properties of 2c, which was
very fast initiator at RT.
Figure 9. 1H NMR chemical shift values of phenanthrene:[46c] protons located
in the ‘bay-region’ of the system are deshielded as compared with the rest
of the molecule (left). Preliminary analysis reveals that intraligand H···H dis-
tances in the isomeric iodocomplexes should decrease in a series
4a>34>36 (right).
Conclusion
In conclusions, we presented synthesis and properties of deriv-
atives of the Hoveyda–Grubbs metathesis catalyst, bearing
chelating naphthalene ligands with coordinating sites of sulfur,
bromine, iodine, and nitrogen atoms. Synthesis of sulfur-che-
lated systems revealed pronounced differences between prop-
erties of complexes derived from 1,2-disubstituted naphtha-
lene. Complex 28, with sterically demanding naphthalene
ligand, was formed directly as a cis-Cl2 isomer, while isomeric
system 29 gave intermediate trans-Cl2 structure, which isomer-
ized to the thermodynamic cis form, in accord with the behav-
ior of similar complexes described in literature. Moreover, the
cally demanding naphthalene ligand (Figure 9, right). Similar
situation appears also in angular tricyclic complexes chelated
with sulfur and bromine atoms cis-28 and 35, for which the
intraligand H···H contacts should be relatively short. The rea-
soning easily explains the exceptional values of chemical shifts
of the benzylidene protons, but also demands for similar de-
shielding effect acting in opposite direction on adjacent pro-
tons of aromatic ligands crowded by proximate benzylidene
groups. Indeed, when peak resonances of ligand protons adja-
cent to the Ru=CH groups were assigned with NOE experi-
ments, we observed the values considerably larger for cis-28,
35 and 36 (8.00, 8.10 and 8.05 ppm, respectively), as compared
with other structures (6.75–7.33 ppm). Quantitative correlations
1
unique ligand effect in 28 was manifested at H NMR spectra
with strong deshielding of benzylidene proton (ca.+1 ppm),
and decreased initiation rate of the catalyst. Similar peculiari-
ties were observed for halogen-chelated ruthenium complexes
35 and 36, bearing naphthalene ligands with Ru=CH bond
crowded with the distant aromatic ring. Synthesis of the com-
plexes required harsh reaction conditions and resulted in cata-
lysts with pronounced latency in model metathesis reactions.
The two systems diverged also with exceptional chemical
shifts of benzylidene protons, which were attributed to the
H···H intraligand interactions present in a ‘bay-like’ region of
the angular tricyclic structures. Spin-exchange spectroscopy
(EXSY) studies of the halogen-chelated complexes revealed
also presence of an equilibrium process, attributed to cis–
trans-Cl2 isomerization in solution. By correlation of relative
contents of the minor trans-Cl2 forms with activity of the meta-
thesis catalysts we reckoned that their initiation process plausi-
bly begins with the isomerization, although further steps of
the mechanism may become rate-limiting and control the cata-
lytic activity in selected systems.
1
between the H NMR chemical shifts and the intraligand H···H
distances extracted from the X-ray data and Nuclear Overhaus-
er Effect (NOE) NMR measurements[47] are discussed further in
the Supporting Information.
Synthesis and properties of the nitrogen coordinated com-
plex
In the last step we synthesized nitrogen-chelated complex 37
in exchange reaction between 25 and ligand 24, obtained
after rearrangement of peri-substituted naphthalene system
(see Scheme 2). The complex was isolated in 76% of yield, and
characterized with NMR and X-ray analysis (Figure 10). In many
Experimental Section
CCDC-951666 (33), CCDC-951667 (34), CCDC-951668 (35), CCDC-
951669 (37), CCDC-951670 (cis-28), CCDC-951671 (cis-29), and
CCDC-951672 (trans-29) contain the supplementary crystallograph-
ic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
Figure 10. Synthesis (top) and ORTEP[36] representation (in two projections,
bottom) of nitrogen-chelated complex 37 shown as thermal ellipsoids
drawn at the 50% probability level. Reagents and conditions: a) 25, CuCl,
CH2Cl2, 408C, 3 h; 37, 76%.
This work was financed from the Polish Ministry of Science and
Higher Education grant number No. N N204 152436. NMR stud-
ies presented in the report were carried out at the Biological
Chem. Eur. J. 2014, 20, 2819 – 2828
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´
Trans. 2013, 42, 355–358; c) M. Barbasiewicz, M. Malinska, K. Błocki, J.
Organomet. Chem. 2013, 745–746, 8–11.
[16] International patent application, Umicore AG
and Chemical Research Centre, University of Warsaw, estab-
lished within the project co-financed by European Union from
the European Regional Development Fund under the Opera-
tional Programme Innovative Economy, 2007–2013. The au-
thors thank: the Umicore AG & Co. KG for donation of the M2
and M31 complexes, Prof. Karol Grela for support and opportu-
nity to perform independent research program in the field, Dr.
Michał Chmielewski for sharing of photochemical reactor, and
& Co. KG, WO2012/
168183A1, 2012.
[17] Ch. E. Diesendruck, E. Tzur, A. Ben-Asuly, I. Goldberg, B. F. Straub, N. G.
Lemcoff, Inorg. Chem. 2009, 48, 10819–10825.
[18] For a similar reasoning concerning the N-coordinated complexes, see:
A. Poater, F. Ragone, A. Correa, A. Szadkowska, M. Barbasiewicz, K.
Grela, L. Cavallo, Chem. Eur. J. 2010, 16, 14354–14364.
[19] V. Snieckus, Chem. Rev. 1990, 90, 879–933.
[20] D. L. Comins, J. D. Brown, J. Org. Chem. 1984, 49, 1078–1083.
[21] For a similar synthesis of thioaldehydes, see: T. Yamamoto, S. Shina-
mura, E. Miyazaki, K. Takimiya, Bull. Chem. Soc. Jpn. 2010, 83, 120–130.
[22] Low temperature (ꢀ208C) and vigorous mechanical stirring is crucial to
perform the reaction. We applied a modified procedure described in:
H. O. House, D. G. Koepsell, W. J. Campbell, J. Org. Chem. 1972, 37,
1003–1011.
´
´
Prof. Wiktor Kozminski for valuable discussions concerning the
NMR studies.
Keywords: homogeneous
metathesis · naphthalene ligands · NMR spectroscopy
catalysis
·
isomerization
·
[23] H. E. Katz, Organometallics 1986, 5, 2308–2311.
[24] H. Bock, M. Sievert, Z. Havlas, Chem. Eur. J. 1998, 4, 677–685.
[25] a) P. Kilian, F. R. Knight, J. D. Woollins, Chem. Eur. J. 2011, 17, 2302–
2328; b) P. Kilian, F. R. Knight, J. D. Woollins, Coord. Chem. Rev. 2011,
255, 1387–1413.
[26] Except of the SN2 pathway, also SNAr mechanism can be considered for
the transformation, see: R. K. Norris, J. A. McMahon, ARKIVOC 2003, x,
139–155.
[27] Indenylidene ruthenium complexes 25 and 26 are commercially avail-
able from Umicore AG & Co. KG as catalysts “M2” and “M31”, respective-
ly (trade names). For their preparation, see: S. Monsaert, R. Drozdzak, V.
Dragutan, I. Dragutan, F. Verpoort, Eur. J. Inorg. Chem. 2008, 432–440;
and references cited therein.
[28] For a procedure of ligand exchange reaction with Amberlyst resin as
a scavenger, see: P. Kos, R. Savka, H. Plenio, Adv. Synth. Catal. 2013, 355,
439–447.
[29] The chemical shift values of benzylidene protons at the spectra stacks
presented on Figure 3 were measured at 408C in the reaction mixtures.
Therefore they differ slightly from the values of recorded at RT for pure
analytical solutions of the complexes, presented above the structures.
[30] For details see the Supporting Information.
[31] The 28:72 mixture of isomers after irradiation of the complex 3 agrees
well with the results of photochemical experiments reported by Lemc-
off (27:73). See the Supporting Information in Ref. [14d].
[32] The fact that the complex trans-28 isomerizes at comparable rate to
trans-3 and trans-29 demands, that it should be observed in the syn-
thetic experiments that was not actually the case (Figure 3, bottom).
Moreover formation of disfavored intermediate along the reaction path
should inhibit formation of cis-28.
[1] G. C. Vougioukalakis, R. H. Grubbs, Chem. Rev. 2010, 110, 1746–1787.
[2] C. Samojłowicz, M. Bieniek, K. Grela, Chem. Rev. 2009, 109, 3708–3742.
[3] For recent developments of the molybdenum-based metathesis cata-
lysts, see: a) J. Heppekausen, A. Fꢁrstner, Angew. Chem. 2011, 123,
7975–7978; Angew. Chem. Int. Ed. 2011, 50, 7829–7832; b) S. J. Mal-
colmson, S. J. Meek, E. S. Sattely, R. R. Schrock, A. H. Hoveyda, Nature
2008, 456, 933–937.
[4] a) S. B. Garber, J. S. Kingsbury, B. L. Gray, A. H. Hoveyda, J. Am. Chem.
Soc. 2000, 122, 8168–8179; b) J. S. Kingsbury, J. P. A. Harrity, P. J. Bonita-
tebus, Jr., A. H. Hoveyda, J. Am. Chem. Soc. 1999, 121, 791–799.
[5] Y. Vidavsky, A. Anaby, N. G. Lemcoff, Dalton Trans. 2012, 41, 32–43.
[6] A. Michrowska, R. Bujok, S. Harutyunyan, V. Sashuk, G. Dolgonos, K.
Grela, J. Am. Chem. Soc. 2004, 126, 9318–9325.
[7] H. Wakamatsu, S. Blechert, Angew. Chem. 2002, 114, 2509–2511; Angew.
Chem. Int. Ed. 2002, 41, 2403–2405.
[8] a) I. W. Ashworth, I. H. Hillier, D. J. Nelson, J. M. Percy, M. A. Vincent,
Chem. Commun. 2011, 47, 5428–5430; b) V. Thiel, M. Hendann, K.-J.
Wannowius, H. Plenio, J. Am. Chem. Soc. 2012, 134, 1104–1114; c) T. Vor-
falt, K.-J. Wannowius, H. Plenio, Angew. Chem. 2010, 122, 5665–5668;
Angew. Chem. Int. Ed. 2010, 49, 5533–5536; d) F. NuÇez-Zarur, X. Solans-
Monfort, L. Rodrꢂguez-Santiago, M. Sodupe, Organometallics 2012, 31,
4203–4215; e) I. W. Ashworth, I. H. Hillier, D. J. Nelson, J. M. Percy, M. A.
Vincent, ACS Catal. 2013, 3, 1929–1939.
[9] M. Barbasiewicz, A. Szadkowska, A. Makal, K. Jarzembska, K. Woz´niak, K.
Grela, Chem. Eur. J. 2008, 14, 9330–9337.
´
[10] M. Barbasiewicz, K. Grudzien, M. Malinska, Organometallics 2012, 31,
3171–3177.
[33] M. B. Smith, J. March, March’s Advanced Organic Chemistry: Reactions,
Mechanisms, 6th ed., John Wiley & Sons, New Jersey, 2007, pp. 309–
309.
[11] F. NuÇez-Zarur, J. Poater, L. Rodrꢂguez-Santiago, X. Solans-Monfort, M.
Solꢃ, M. Sodupe, Comput. Theor. Chem. 2012, 996, 57–67.
´
[12] K. Grudzien, M. Malinska, M. Barbasiewicz, Organometallics 2012, 31,
[34] Interestingly, in the NMR experiments conducted with 1 mol% of the
catalysts at 0.2m concentration of the substrate we were able to detect
not only progress of the main metathesis reaction, but also, a back-
ground isomerization process of resting amounts of the trans-Cl2 com-
plexes (qualitatively). The observed isomerization rates agreed with
those determined on pure samples, supporting that trans-29 isomerizes
faster, and thus its smaller activity arises from lower concentration in
the reaction mixture.[30]
[35] The orientation of the iPr group, common for the sulfur chelates, clearly
contrasts with structures of the ether systems (1–2), for which out-of-
plane distortion of the coordinating OiPr arm results in destabilization
of the Ru···O bond.[7] In consequence, the orientation in complexes 3,
28 and 29 may effectively suppress resonance between heteroatom
and aromatic ring, making the p-electronic effects virtually impossible.
Preliminary theoretical treatments of anisole and thioanisole molecules
at DFT B3LYP/6–31G(d,p) level of theory revealed that the both mole-
cules prefer a planar conformation, which enable conjugation between
heteroatom and the aromatic ring.[30]
3636–3646.
[13] a) M. Barbasiewicz, A. Szadkowska, R. Bujok, K. Grela, Organometallics
2006, 25, 3599–3604; b) E. Tzur, A. Szadkowska, A. Ben-Asuly, A. Makal,
´
I. Goldberg, K. Wozniak, K. Grela, N. G. Lemcoff, Chem. Eur. J. 2010, 16,
8726–8737; c) L. H. Peeck, R. D. Savka, H. Plenio, Chem. Eur. J. 2012, 18,
12845–12853.
[14] a) T. Kost, M. Sigalov, I. Goldberg, A. Ben-Asuly, N. G. Lemcoff, J. Organo-
met. Chem. 2008, 693, 2200–2203; b) A. Ben-Asuly, E. Tzur, C. E. Diesen-
druck, M. Sigalov, I. Goldberg, N. G. Lemcoff, Organometallics 2008, 27,
811–813; c) A. Aharoni, Y. Vidavsky, Ch. E. Diesendruck, A. Ben-Asuly, I.
Goldberg, N. G. Lemcoff, Organometallics 2011, 30, 1607–1615; d) A.
Ben-Asuly, A. Aharoni, Ch. E. Diesendruck, Y. Vidavsky, I. Goldberg, B. F.
Straub, N. G. Lemcoff, Organometallics 2009, 28, 4652–4655; e) Y. Ginz-
burg, A. Anaby, Y. Vidavsky, Ch. E. Diesendruck, A. Ben-Asuly, I. Gold-
berg, N. G. Lemcoff, Organometallics 2011, 30, 3430–3437; f) A. Szad-
´
kowska, A. Makal, K. Wozniak, R. Kadyrov, K. Grela, Organometallics
2009, 28, 2693–2700; g) A. Szadkowska, K. Zukowska, A. E. Pazio, K.
Woz´niak, R. Kadyrov, K. Grela, Organometallics 2011, 30, 1130–1138;
˙
˙
h) K. Zukowska, A. Szadkowska, B. Trzaskowski, A. Pazio, Ł. Pa˛czek, K.
[36] We wish to acknowledge the use of a free version of Ortep-3 for Win-
dows program: L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565–565.
[37] The reported yields correspond to the amounts of products isolated
under routine conditions, and were not optimized. Observations made
´
Wozniak, K. Grela, Organometallics 2013, 32, 2192–2198.
[15] a) M. Barbasiewicz, M. Michalak, K. Grela, Chem. Eur. J. 2012, 18, 14237–
´
14241; b) M. Barbasiewicz, K. Błocki, M. Malinska, R. Pawłowski, Dalton
Chem. Eur. J. 2014, 20, 2819 – 2828 www.chemeurj.org
2827
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
on synthesis of complex 34 suggest that they can be improved with
larger excess of the applied ligand.[30]
However, the halogen-coordinated ruthenium complexes were sparing-
ly soluble in C6D6 or [D8]toluene, and thus regular studies we performed
in CDCl3 solutions. The samples were sealed in screw-cap NMR tubes to
extend range of temperatures for the measurements (b.p. of CDCl3 =
618C).
[38] Ligand exchange reactions between complex 26, and ligands: 2-iodo-
propenylbenzene and 31 were investigated with 1H NMR in CD2Cl2 and
[D8]toluene solutions at 408C. In dichloromethane we observed exclu-
sive formation of single benzylidene peaks, corresponding to the cis-Cl2
structures of complexes 4a and 30, while in toluene solutions the reso-
nances were accompanied with other peaks at range 19–20 ppm.[30]
[39] A. Leitgeb, A. Szadkowska, M. Michalak, M. Barbasiewicz, K. Grela, C. Slu-
govc, J. Polym. Sci. Part A 2011, 49, 3448–3454.
[40] The different reactivity of vinyl (CH=CH2) and propenyl (CH=CH-CH3)
ligand precursors may arise from their alternate mode of approach to
the ruthenium center, compare: Z. J. Wang, W. R. Jackson, A. J. Robin-
son, Org. Lett. 2013, 15, 3006–3009.
[41] Reaction of complex 32 with propyl vinyl ether in a CD2Cl2 solution at
258C led to at least three different products observed at 1H NMR spec-
trum at 16.72, 13.78, and 13.21 ppm.[30]
[42] The NMR activity profile measurements were performed according to
the procedure described in Ref. [12]. Time “0” (zero) at the plots
(Figure 4, left, and Figure 7) corresponds to the beginning of the NMR
acquisition under equilibrated conditions. However, manipulation, shim-
ming and preheating of the samples caused some inevitable delay
before beginning of the experiment.
[44] C. L. Perrin, T. J. Dwyer, Chem. Rev. 1990, 90, 935–967.
[45] For a discussion, see: a) M. W. Kotyk, S. I. Gorelsky, J. C. Conrad, C. Carra,
D. E. Fogg, Organometallics 2009, 28, 5424–5431; b) S. Leuthꢄußer, V.
Schmidts, C. M. Thiele, H. Plenio, Chem. Eur. J. 2008, 14, 5465–5481.
[46] a) E. Kleinpeter, S. Klod, J. Am. Chem. Soc. 2004, 126, 2231–2236; b) H.
Gunther, NMR Spectroscopy: Basic Principles, Concepts, and Applications
in Chemistry, 2nd Ed., John Wiley
& Sons, Chichester, 1995; c) S.
Grimme, C. Mꢁck-Lichtenfeld, G. Erker, G. Kehr, H. Wang, H. Beckers, H.
Willner, Angew. Chem. 2009, 121, 2629–2633; Angew. Chem. Int. Ed.
2009, 48, 2592–2595; d) C. Reid, J. Mol. Spectrosc. 1957, 1, 18–23; e) M.
ˇ
ˇ
Dracꢂnsky, P. Jansa, P. Bour, Chem. Eur. J. 2012, 18, 981–986.
[47] a) D. Neuhaus, M. P. Williamson, The Nuclear Overhauser Effect in Struc-
tural and Conformational Analysis, 2nd Ed., Wiley-VCH, Weinheim, 2000;
b) J. K. M. Sanders, B. K. Hunter, Modern NMR Spectroscopy, 2nd Ed.,
Oxford Univesity Press, Oxford, 1993, chapter 6.
Received: September 30, 2013
Revised: November 29, 2013
[43] Equilibrium constant of the isomerization process should depend on
polarity of the solvent, and less polar trans-Cl2 forms should be pre-
ferred in less polar solvents, see Ref. [14c] and references cited therein.
Published online on February 12, 2014
Chem. Eur. J. 2014, 20, 2819 – 2828
www.chemeurj.org
2828
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