Linker-free, silica-bound olefin-metathesis catalysts: Applications in heterogeneous catalysis

Article abstract of DOI:10.1002/chem.201202248

A set of heterogenized olefin-metathesis catalysts, which consisted of Ru complexes with the H₂ITap ligand (1,3-bis(2',6'-dimethyl-4'dimethyl aminophenyl)-4,5-dihydroimidazol-2-ylidene) that had been adsorbed onto a silica support, has been prepared. These complexes showed strong binding to the solid support without the need for tethering groups on the complex or functionalized silica. The catalysts were tested in the ring-opening-ring-closing-metathesis (RO-RCM) of cyclooctene (COE) and the self-metathesis of methyl oleate under continuous-flow conditions. The best complexes showed a TON>4000, which surpasses the previously reported materials that were either based on the Grubbs-Hoveyda II complex on silica or on the classical heterogeneous Re ₂O₇/B₂O₃ catalyst. Born free: Silica adsorption of ruthenium carbenes with the H₂ITap ligand (see figure) yielded heterogeneous materials without the need for tethering groups on the complex or the support. These materials were tested as catalysts in the ring-opening-ring-closing-metathesis of cyclooctene and the cross-metathesis of methyl oleate under continuous-flow conditions. The best complexes showed a TON>4000, which surpasses the most active silica-based materials. Copyright

Full text of DOI:10.1002/chem.201202248

FULL PAPER
DOI: 10.1002/chem.201202248
Linker-Free, Silica-Bound Olefin-Metathesis Catalysts:
Applications in Heterogeneous Catalysis
Josꢀ Cabrera,[a] Robin Padilla,[a] Miriam Bru,[a] Ronald Lindner,[a]
Takeharu Kageyama,[a] Kristina Wilckens,[a] Shawna L. Balof,[b] Hans-Jçrg Schanz,[c]
Richard Dehn,[d] J. Henrique Teles,[d] Stephan Deuerlein,[d] Kevin Mꢁller,[e]
Frank Rominger,[f] and Michael Limbach*[a, d]
Dedicated to Professor Christian Bruneau on the occasion of his 60th birthday
Abstract:
A
set of heterogenized
without the need for tethering groups
on the complex or functionalized silica.
The catalysts were tested in the ring-
opening–ring-closing-metathesis (RO-
RCM) of cyclooctene (COE) and the
self-metathesis of methyl oleate under
continuous-flow conditions. The best
olefin-metathesis catalysts, which con-
sisted of Ru complexes with the
H2ITap ligand (1,3-bis(2’,6’-dimethyl-
4’dimethyl aminophenyl)-4,5-dihydro-
imidazol-2-ylidene) that had been ad-
sorbed onto a silica support, has been
prepared. These complexes showed
strong binding to the solid support
complexes showed
a
TON>4000,
which surpasses the previously report-
ed materials that were either based on
the Grubbs–Hoveyda II complex on
silica or on the classical heterogeneous
Re2O7/B2O3 catalyst.
Keywords: carbenes · macrocycles ·
metathesis · ruthenium · supported
catalysts
Introduction
hand, highly active homogeneous early-[3] or late-transition-
metal carbenes[4] lack the processability of classical hetero-
geneous catalysts,[5] which is unattractive for large-scale in-
dustrial processes.
The applicability of classical heterogeneous catalysts to the
olefin-metathesis reaction is limited because these catalysts
require either harsh reaction temperatures (e.g., WO3,
>3008C)[1] or co-activators (e.g., R4Sn compounds for
Re2O7)[2] to achieve high catalytic activity. On the other
Consequently, a plethora of immobilization concepts have
been developed to combine the advantages of homogeneous
catalysts with those of heterogeneous metathesis catalysts,
that is, to obtain materials with the activity of a homogene-
ous catalyst and the usability of a heterogeneous one. Al-
though there are materials that are based on early-transi-
tion-metal complexes,[6] those hybrids are predominantly
built up of the late-transition-metal ruthenium. To minimize
leaching from the support, covalent interactions between
the surface and the ligands, such as, phosphines,[7] N-hetero-
cyclic carbene (NHC) moieties,[8] alkylidene groups,[9] or
those that serve as surrogates for anionic ligands,[10] have
been crucial. A diverse range of solid supports have been
employed, including various polymers,[7b] silicas,[11,12c] alumi-
nas,[12] and polymer–silica hybrids.[5a,13] However, one major
drawback to all of these approaches is the often laborious
synthetic work that is required to functionalize the solid
support, the metal complex, or, in most cases, both of these
components.
[a] Dr. J. Cabrera, Dr. R. Padilla, Dr. M. Bru, Dr. R. Lindner,
Dr. T. Kageyama, Dr. K. Wilckens, Dr. M. Limbach
Catalysis Research Laboratory (CaRLa)
Im Neuenheimer Feld 584, 69120 Heidelberg (Germany)
Fax : (+49)621-60-6648957
E-mail: michael.limbach@basf.com
[b] Dr. S. L. Balof
The University of Southern Mississippi
Department of Chemistry & Biochemistry
118 College Dr., Hattiesburg, MS 39406 (USA)
[c] Dr. H.-J. Schanz
Georgia Southern University, Department of Chemistry
250 Forest Drive, P.O. Box 8064
Statesboro, GA 30460 (USA)
[d] Dr. R. Dehn, Dr. J. H. Teles, Dr. S. Deuerlein, Dr. M. Limbach
BASF SE, Process Research and Chemical Engineering
Carl-Bosch-Strasse 38, 67056 Ludwigshafen (Germany)
Only recently have Sels and co-workers[14] and, later, oth-
ers[11d,15] shown that, to obtain a truly heterogeneous hybrid
metathesis catalyst, weak physical interactions between a
neutral Grubbs–Hoveyda-II-type complex and the surface
of an inorganic material are sufficient if the reaction condi-
tions are chosen appropriately. Because the interactions be-
tween the complex and the support are not covalent but
weak ones (i.e., in the dimension of a H bond),[14] polar sub-
[e] Dr. K. Mꢀller
BASF SE, Advanced Materials and Systems Research
Carl-Bosch-Strasse 38, 67056 Ludwigshafen (Germany)
[f] Dr. F. Rominger
Organisch-Chemisches Institut
Ruprecht-Karls-Universitꢁt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202248.
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strates (i.e., methyl oleate) or solvents cause significant
leaching of the complex from the support,[14] a phenomenon
that is common to other heterogenized ruthenium car-
benes.[16]
yl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-yli-
dene]).[19]
We have previously observed that ruthenium-based meta-
thesis catalysts 5, 6, and 12, which contain the hemi-labile
pyridine–alkoxide ligand (Figure 1), show extraordinary
Results and Discussion
Preparation of pre-catalysts 3–12 and their activity in the
homogeneously catalyzed ROMP of COE: Complexes 5, 6,
and 12 were prepared from commercially available second-
generation pre-complexes and a,a-dimethyl-2-pyridylmetha-
nol according to literature procedures.[17,19] The H2ITap
ligand was introduced onto the commercially available first-
generation complexes Grubbs I and BASF I by using a pro-
cedure developed by Schanz and co-workers (Scheme 1) in
Scheme 1. Synthesis of H2ITap-based pre-catalysts 1–4 and 7–9.
n-heptane.[19a] This method gave complexes 1 and 2 in good
yield (70 and 65%, respectively). However, the heterogene-
ous nature of these reactions and, in particular, the slow dis-
sociation of phosphine that was observed for BASF I under
these synthetic conditions required reaction times of up to
6 days to obtain high conversion into complex 2. Complexes
3 and 4 were obtained from similarly slow reactions of com-
plexes 1 and 2 with a,a-dimethyl-2-pyridylmethanol[17,20] in
satisfactory yields (51 and 73%, respectively) within 3 days.
Alkylidene exchange between complex 1 and appropriately
substituted butenylpyridines[21] afforded complexes 7–9 in
good yields (44–88%) within 22 h.
Figure 1. Complexes (3–12) and their precursors (1 and 2) that were em-
ployed in this study.
stickiness to unmodified, commercially available, chroma-
tography-grade silica gel.[17] This property might be a conse-
quence of ionic interactions that result from protonation of
the basic pyridine ligand by surface-silanol groups on the
silica support. This same immobilization principle has been
used to screen for optimal catalyst–support interactions and
catalyst stability on a silica-based TLC plate.[18] This adsorp-
tive, “linker-free” approach is elegant from our point of
view because the physisorption of an unmodified homogene-
ous complex onto an unmodified, inorganic material is by
far the most economical and industrially attractive immobili-
zation procedure.
In light of these above findings, we became interested in
comparing the activity, selectivity, lifetime, and amount of
precious metal leaching of materials that are based on physi-
sorption (i.e., Grubbs–Hoveyda II complex 11) with those in
which the organometallic species is most likely immobilized
through ionic interactions (i.e., pyridine–alkoxide-bearing
pre-catalysts 5, 6, and 12 and new complexes 3, 4, and 7–
10,[19a] which contain the H2ITap ligand, [1,3-bis(2’,6’-dimeth-
Complex 3 adopts a square-pyramidal structure in which
the benzylidene ligand sits in the apical position (Figure 2).
À
À
The Ru Ccarb and Ru CNHC distances in complex 3 compare
well with previously published structural data for its ana-
logue that contained the H2IMes ligand[17] (2.033(3) and
1.840(3) ꢃ versus 2.031(3) and 1.834(3) ꢃ). Nevertheless,
À
the Ru N bond is significantly elongated for the H2ITap
ligand (2.153(2) versus 2.137(2) ꢃ), which reflects its stron-
ger trans influence compared to H2IMes. In complex 7, the
pyridine–carbene moiety is disordered with respect to a
swap between the two possible apical positions of the car-
bene unit. The relative occupation of these two different ori-
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Linker-Free, Silica-Bound Olefin-Metathesis Catalysts
FULL PAPER
Figure 3. ROMP of COE at 258C by using complexes 3–12.
Again, Fischer carbene complex 4 showed the lowest
ROMP activity of all of the complexes at room temperature.
Amongst the triad of complexes 7–9 (in which the com-
plexes only differed in the number and position of methyl
groups on the pyridine ligand), pre-catalyst 7 greatly outper-
formed complexes 8 and 9 in terms of activity and gave
complete conversion within only 14 min. As expected, com-
plexes 3, 5, and 7–12 exhibited significantly higher activity
at 608C (complete conversion of COE within 4 min), whilst
Fischer carbenes 6 and 4 gave complete conversion after 7
and 25 min, respectively.
Figure 2. Single-crystal X-ray structures of pre-catalysts 3, 8, and 9; ther-
mal ellipsoids are set at 50% probability and hydrogen atoms have been
omitted for clarity. Selected distances [ꢃ] and angles [8]: compound 3:
À
À
À
À
Ru Ccarb 1.834(3), Ru O 1.9676(19), Ru CNHC
: 2.031(3), Ru N:
À
À
À
À
À
2.153(2), Ru Cl 2.3864(8); Ccarb Ru O 101.72(11), CNHC Ru Ccarb
À
À
À
À
96.35(12), Ccarb Ru N 93.46(11); compound 9: Ru Ccarb: 1.806(9), Ru
Cl1 2.3974(15), Ru Cl2 2.3626(16), Ru CNHC: 2.037(5), Ru N 2.165(4);
À
À
À
À
À
À
À
À
À
Cl Ru Cl 167.04(6), CNHC Ru Ccarb 97.6(2), Ccarb Ru N 90.8(2).
entations is about 65:35. Therefore, the base of the coordi-
nation pyramid appears to be flatter than it presumably is
and the geometry cannot be discussed quantitatively. The
Silica adsorption and heterogeneous catalytic activity under
continuous-flow conditions: To identify pre-complexes that
had optimal activity/stability and minimal leaching for sub-
sequent applications in continuous-flow reactions, the sticki-
ness of complexes 3–12 to a silica support was determined,
both by adsorption of the pure complexes from solutions in
CH2Cl2 and under catalysis conditions by adsorption onto
untreated, chromatography-grade silica gel for 30 min. In-
ductively coupled plasma–mass spectrometry (ICP-MS)
analysis revealed that all of the complexes apart from com-
plex 12 showed very strong affinity to 60A-Acros silica
(ꢀ1% of the initial Ru content was detectable in the fil-
trate; Table 1); this result was also indicated by decoloration
of the organic phase. These results complement previous
work by us[17] and by Sels and co-workers.[14]
À
CNHC Ru bond in complex 9 is shorter, as in a similar
system that contained H2IMes and o,p-dimethyl groups on
the pyridine ring,[21b] whereas the Ru N bond is elongated
À
(2.037(5) versus 2.0459(10) ꢃ and 2.165(4) versus
2.1355(9) ꢃ). Once again, both of these results point to the
better donor properties of H2ITap compared to H2IMes.
The activity of pre-catalysts 3–12 was evaluated in the ho-
mogeneously catalyzed ring-opening metathesis polymeriza-
tion (ROMP) of cyclooctene (COE) (Scheme 2, Figure 2).
Scheme 2. ROMP of COE by using complexes 3–12; for details, see
Figure 3.
Table 1. Ru adsorption of complexes 3–10 and 12 onto silica.[a]
Complex Initial [Ru]
[ppm][b]
[Ru] after adsorption
[ppm][c]
Initial [Ru] Split
[%]
At 258C, the pyridine–alkoxide-based complexes with the
1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (SIMes) ligand,
that is, complexes 5, 6 and 12, only showed moderate activi-
ty. Fischer carbene complex 6 was unreactive at room tem-
perature. Interestingly, the Grubbs–Hoveyda II complex
(11) reached full conversion within 2 min, whereas its
H2ITap-modified analogue (10) reached complete conver-
sion after 6 min.[19a] A similar trend in reactivity, albeit less
pronounced, was observed for the SIMes- and H2ITap-ligat-
ed complexes for the two pairs of complexes 3/5 and 4/6
(Figure 3).
3
4
5
6
7
8
9
10
12
3007
3007
5390
5390
5815
2255
5370
5370
5390
7
21
7
30
23
22
5
0.2
0.7
0.1
0.6
0.4
1.0
0.09
0.16
4.3
het.
–
[d]
het.
[d]
–
het.
het.
het.
het.
het.
9
234
[a] Silica/Ru-complex mass ratio (mg) was 2:1 with an adsorption time of
30 min. [b] 60A-Acros silica. [c] Determined by ICP-MS. [d] No activity
up to 808C. het.=heterogeneous.
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M. Limbach et al.
The materials for the heterogeneously catalyzed continu-
ous-flow experiments were prepared according to a simple
transfer procedure: Complexes 3–12 were dissolved in
CH2Cl2, silica (Grace SP550-10020, calcined at 5508C prior
to use) was added, and the solvent was removed from the
slurry in vacuo to provide the desired materials (3@silica–
12@silica).
Prior to the evaluation of their potential in the RO-RCM
of cis-COE[22] (Scheme 3), which represents one of the short-
est routes to macrocyclic skeletons,[23] we ensured that mate-
rable (19% versus 17% at 95% conversion), 11@silica gives
significantly higher selectivity for smaller oligomers (i.e., 2–
5 mers, 74% versus 60%). The same trend was observed for
the SIMes/H2ITap couple 3@silica/5@silica (20 versus 26%
selectivity for the 2 mer and 57% versus 72% for 2–5 mers).
In terms of activity, the order was reversed: Despite contin-
uous deactivation within the first 7 h, material 3@silica was
more active than its SIMes counterpart (5@silica, 2900
versus 2150 TONs). Whereas materials 7@silica and 8@silica
exhibited similar activities, material 9@silica was the most
active and most selective of those that contained complexes
with tethered pyridine ligands (TON=2700, 3250, and 4250,
respectively).
The alkylidene moiety was crucial for the stability of pyri-
dine alkoxide materials 5@silica and 12@silica, as shown by
the much higher activity of the indenylidene carbine versus
the benzylidene carbene (TON=3650 versus 2150, that is,
42% versus 14% conversion after 1350 min). Nevertheless,
the selectivity for the 2 mer and for small oligomers (2–
5 mer) was virtually identical (about 25% and 70%).
Scheme 3. RO-RCM of COE catalyzed by heterogenized pre-complexes
3@silica–12@silica.
rials 3@silica, 5@silica, and 7–12@silica acted as truly heter-
ogeneous catalysts (i.e., that their catalysis was not due to
homogeneous species that had desorbed from the support
during the continuous-flow experiments; Table 1) by per-
forming a split test. Because materials 4@silica and 6@silica
showed low reactivity (<10% conversion within 1 h, even at
elevated temperatures), they were omitted from subsequent
continuous-flow studies.
For the actual continuous-flow experiments, a solution of
0.7 wt.% COE in cyclohexane was pumped at 608C through
a cylindrical steel reactor that was charged with the Ru-im-
pregnated silica materials (3@silica, 5@silica, or 7@silica–
12@silica, 0.2–0.6 wt.% Ru; Figure 3). For comparative pur-
poses, we also tested a benchmark material that was derived
from the Grubbs–Hoveyda II complex (11@silica)[14] and
Re2O7/B2O3@silica, which is a classical heterogeneous meta-
thesis catalyst.[24]
In terms of lifetime and activity, material 11@silica, which
contained the SIMes-derived Grubbs–Hoveyda II complex,
and material 10@silica, which contained an analogous com-
plex with an H2ITap ligand, showed the best performance
(94 versus 87% conversion after 1350 min, that is, 4350
versus 4250 TON; Figure 3 and Table 2). Although their se-
lectivities for the cyclic dimer (2 mer) of COE were compa-
All of the materials that were derived from an organome-
tallic pre-complex (3@silica, 5@silica, and 7@silica–
12@silica) performed substantially better than the classical,
state-of-the-art heterogeneous Re2O7 catalyst,[24a] both in
terms of activity and selectivity (TON>4200 versus 250,
with the best new materials, 9@silica–11@silica; Table 2).
The leaching of Ru from the support during the course of
the reaction was mostly <10%, as determined by ICP-MS
analysis of the fresh and used materials. Thus, leaching was
very low with respect to the absolute values, considering the
low initial catalyst loading (<0.1 wt.%). Furthermore, the
activities that were obtained with 11@silica and the new
H2ITap materials (9@silica and 10@silica) outperformed that
initially reported by Sels and co-workers[14] by a factor of>
10 and that of other systems even by a factor of>40.[23]
These results clearly demonstrate the importance of the
chemical reactor on the outcome of a metathesis reaction.[25]
For materials 10@silica and 11@silica, which turned out to
be the best heterogeneous catalysts in the RO-RCM of
COE, we also studied the self-metathesis of a solution of
methyl oleate in cyclohexane (50 wt.%; Scheme 4 and
Figure 4).[26] This substrate can be considered to be a “prov-
ing ground” for heterogenized catalyst systems owing to the
greater potential for leaching that is caused by the polar
substrate, as well as to trace impurities in the natural prod-
uct. The commercially available methyl oleate that was em-
ployed in this study contained 13 ppm of active oxygen, as
analyzed by using the Wheeler method.[27]
Table 2. Analysis of the continuous-flow reactions of COE.
Catalyst[a] Selectivity Selectivity TON[c] Initial
Final
[Ru]
Ru
loss
2 mer
2–5 mer
[Ru]
[%][b]
[%][b]
[ppm][c] [ppm][d] [%]
[e]
Re2O7
6
20
26
20
19
25
7
57
72
57
51
68
250
2900
2150
2700
3250
4250
4250
4350
3650
–
700
530
910
540
390
420
670
510
–
620
510
910
490
360
390
650
450
–
11.4
3.92
0
9.26
7.69
7.14
2.99
Guard beds (i.e., pre-purification columns that were filled
with an adsorbent) were utilized to remove these trace per-
3@SiO2
5@SiO2
7@SiO2
8@SiO2
9@SiO2
10@SiO2 17[f]
11@SiO2 19[f]
12@SiO2 24
60[f]
74[f]
73
11.8
[a] On Grace SP500-10020. [b] At 70% conversion. [c] 24 h run time.
[d] Analysis by ICP-MS. [e] On D11-10 silica. [f] At 95% conversion.
Scheme 4. Self-metathesis of methyl oleate; for details, see Table 3.
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Linker-Free, Silica-Bound Olefin-Metathesis Catalysts
FULL PAPER
Figure 5. Self-metathesis of methyl oleate as a function of time in a con-
tinuous-flow setup. Conditions: Steel reactor (14 mmꢄ45 cm) with a solu-
tion of methyl oleate in cyclohexane (50 wt.%), T=608C, flow rate:
2 mLminÀ1, pressure: 2 bar Ar, support: Grace SP550-10020.
Figure 4. Conversion of COE as a function of time in a continuous-flow
setup. Conditions: Steel reactor (14 mmꢄ45 cm) with a solution of COE
in cyclohexane (0.7 wt.%), T=608C, flow rate: 8 mLminÀ1, pressure:
2 bar Ar, support: Grace SP550-10020, Re2O7/B2O3 was immobilized on
D11-10 silica.[24a]
ROMP of COE. These complexes are especially suitable for
their heterogenization on a conventional silica support and
their corresponding derivative materials have shown extra-
ordinarily high activity in the RO-RCM of COE and in the
self-metathesis of methyl oleate. In all cases, ruthenium
leaching from the support was low and the reactions were
found to be heterogeneous in nature. In continuous-flow ex-
periments, the hybrid materials turned out to be far superior
to a standard heterogeneous catalyst in the RO-RCM of
COE. In the self-metathesis of methyl oleate, the material
with the H2ITap-modified Grubbs–Hoveyda II complex was
significantly more active than the state-of-the-art system.
Studies to determine the structure of the active catalyst are
underway and the application of new “linker-free” catalysts
to other reactions remains a future goal.
oxide impurities, which could act as catalyst poisons, from
the reaction feed. In front of the heterogeneous catalyst bed
that was packed with 10@silica and 11@silica, two additional
beds that were filled with charcoal (2ꢄ20 g, Norit A Supra)
were installed to adsorb these catalyst poisons before the
methyl oleate feed reached the catalyst bed.[28]
Both materials 10@silica and 11@silica showed significant
Ru leaching (19 and 12%, respectively), as determined by a
comparison of the amount of ruthenium on the fresh and
spent catalysts by ICP-MS (Table 3). The Ru leaching from
Table 3. Self-metathesis of methyl oleate at 608C.
Catalyst[a] TON[b] Initial [Ru]
[ppm][c]
Final [Ru]
[ppm][c]
Ru loss
[%]
10@SiO2 4950
11@SiO2 3550
530
690
430
610
18.9
11.7
Experimental Section
[a] Grace SP500-10020. [b] 8 h run time. [c] Analysis by ICP-MS.
General considerations: All manipulations were carried out under an
inert atmosphere by using standard Schlenk techniques or in an argon-
filled glovebox unless otherwise noted. All glassware was oven dried
prior to use. Solvents were collected from an MBraun Solvent Purifica-
tion System and stored over 4 ꢃ molecular sieves. Deuterated solvents
were degassed by freeze–pump–thaw cycles and stored over 4 ꢃ molecu-
lar sieves. NMR spectra were collected on Bruker Avance 200 MHz,
Bruker Avance 300 MHz, Bruker Avance 500 MHz or Bruker Avance
600 MHz spectrometers and the chemical shifts were referenced to resid-
ual protons of the deuterated solvent. Melting points were measured on
a Stuart SMP30 apparatus. MS was carried out by the Mass Spectrometry
Facility at the Organic Chemistry Institute of the University of Heidel-
berg on a JEOL JMS-700 instrument. ICP-MS analysis was done at the
Analytical Division of BASF SE in Ludwigshafen, Germany. All GC
analysis was carried out on a Hewlett Packard 5890 Series II that was
equipped with an Agilent HP-5 capillary column (15 mꢄ0.32 mmꢄ
0.25 mm); program: 608C (5 min), 108CminÀ1 to 3008C (15 min),
108CminÀ1 to 3208C (18 min); retention times (RO-RCM of COE): 5.5
(COE), 20.1 (2 mer), 28.2 (3 mer), 37.2 (4 mer), 55.1 min (5 mer); reten-
tion times (self-metathesis of methyl oleate): 27.2 (octadecene), 27.3 (oc-
tadecene), 31.3 (methyl oleate), 35.2 min (dimethyl 9-actadecenedioate).
H2ITap·HCl and complex 1 were both prepared according to literature
procedures.[19a] Ligands a,a-dimethyl-2-pyridylmethanol,[17] 2-(but-3-en-1-
yl)-l-pyridine, 2-(but-3-en-1-yl)-6-methylpyridine, and 2-(but-3-en-1-yl)-
10@silica was more pronounced than that from 11@silica.
This finding is counterintuitive, because we initially deter-
mined that the binding of complex 10 to the silica gel was
stronger than of complex 11 owing to protonation of the
H2ITap ligand by the silanol supports. Nevertheless, the cat-
alytic activity of 10@silica over 24 h was significantly higher
than that of SIMes-derived 11@silica (TON=4950 versus
3550). This result was also reflected by the fact that
10@silica maintained about 60% conversion of methyl
oleate after an initial deactivation period, whereas 11@silica
became steadily deactivated to provide only about 15%
conversion at the end of the run (Figure 5).
Conclusion
We have prepared a series of new, H2ITap-based complexes
and explored their potential in the homogeneously catalyzed
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4,6-dimethylpyridine were prepared and purified according to literature
procedures.[29] Solutions of potassium tert-amylate, Grubbs I, BASF I, and
Grubbs–Hoveyda I were purchased from either Sigma Aldrich or Strem
and used as received. Silica for the split tests was obtained from Acros
(60A-Acros); silica for the continuous-flow experiments was obtained
from W.R. Grace (Grace SP550-10020). Activated charcoal (Norit A
Supra) was obtained from Acros. X-ray intensities were corrected for
Lorentz and polarization effects. An empirical absorption correction was
applied by using SADABS,[30] based on the Laue symmetry of the recip-
rocal space. The structure was solved by using direct methods and refined
108.7880(10)8; V=1797.99(16) ꢃ3; 1=1.343 gcmÀ3; T=200(2) K; qmax
=
25.448; Mo Ka radiation; l=0.71073 ꢃ; 0.58 w-scans with a CCD area
detector, which covers the asymmetric unit in reciprocal space with a
mean redundancy of 4.0 and a completeness of 97.7% to a resolution of
0.83 ꢃ; total reflns: 26613; unique reflns: 6497 (RACTHNUGRTENUNG(int)=0.0659); ob-
served reflns 5473 (I>2s(I)); m=0.55 mmÀ1; Tmin =0.92, Tmax =0.95, re-
fined parameters: 423; hydrogen atoms were treated by using appropriate
riding models; GOF=1.05 for the observed reflections; final residual
values R1(F)=0.038, wR(F2)=0.074 for observed reflections; residual
electron density: À0.65–0.34 eꢃÀ3
.
against F2 with
a full-matrix least-squares algorithm by using the
Complex 4: Complex 2 (346 mg, 368 mmol), tBuLi (220 mL, 1.7m in n-
pentane), and 2-(pyridin-2-yl)propan-2-ol (50 mg, 364 mmol) were reacted
together according the procedure for complex 3 in THF (10 mL). The re-
action mixture was stirred vigorously at RT for 3 days. After removal of
the solvent, the crude residue was dissolved in benzene (15 mL), filtered
through a pad of Celite, and the solvent was removed. To the resulting
solid was added n-hexane (5 mL). The suspension was stirred overnight
and filtered through a pad of Celite; the filtrate was then discarded. At
this point, benzene was added to the Celite pad and, after evaporation of
this filtrate, pure compound 4 was obtained. After drying on a high-
vacuum line, compound 4 was obtained as a brown solid (203 mg, 74%).
SHELXTL (Version 2008/4) software package.[31]
Complex 2: H2ITap·HCl (374 mg, 0.93 mmol) and KOtBu (120 mg,
1.07 mmol) were heated at 808C in n-heptane (60 mL) for 30 min. After
the slurry was cooled to RT, BASF I (606 mg, 0.77 mmol) was added and
the mixture was stirred at 608C for 6 days, during which time a light-pink
precipitate was formed. The reaction mixture was cooled to RT and fil-
tered on air. The residue was washed with n-heptane (2ꢄ10 mL) and
dried in a vacuum oven at 608C for 4 h. A mixture of 2-propanol and an
aqueous solution of ammonium chloride (0.5m, 3:1 v/v, 50 mL) was
added to the residue under non-inert conditions and the mixture was so-
nicated at 308C for 60 min. The slurry was filtered on air and the residue
was washed with MeOH (2ꢄ10 mL) and dried in a vacuum oven at 608C
for 2 h to give compound 2 (474 mg, 65%); M.p. 221–2238C; 1H NMR
(600 MHz, C6D6): d=17.98 (s; Ru=CH), 7.21 (d, J=7.9 Hz, 2H), 6.97 (t,
1
M.p. 165–1688C (dec.); H NMR (C6D6, 600 MHz): d=15.85 (s, 1H; Ru=
CH), 9.76 (d, J=5.60 Hz, 1H; o-Py), 6.99 (br d, J=6.40 Hz, 2H; o-SPh),
6.85 (m, 2H; m-SPh), 6.59 (br t, J=7.10 Hz, 1H; p-SPh), 6.48 (br d, J=
7.80 Hz, 2H; m,p-Py), 6.32 (s, 2H; C6H2), 6.31 (s, 2H; C6H2), 6.25 (t, J=
À
À
À
J=7.6 Hz, 2H), 6.88 (t, J=7.3 Hz, 1H, =CH C6H5), 6.50 (s, 2H), 6.13 (s,
6.50 Hz, 1H; m-Py), 3.47 (br s, 4H; N CH2), 2.76 (s, 6H; C6H2 CH3),
À
À
2H; 2ꢄC6H2), 3.35 (m, 4H; CH2 CH2), 2.89 (s, 6H), 2.75 (s, 6H; 2ꢄN-
2.72 (s, 6H; C6H2 CH3), 2.41 (s, 12H; N
G
13
(CH3)2), 2.60 (s, 6H), 2.28 (s, 6H; 2ꢄC6H
(CH3)2), 1.88 (br m, 6H), 1.65
(CH3)2), 1.17 ppm (s, 3H; OC
(CH3)2); C NMR (C6D6): d=264.0, (Ru
(br m, 6H), 1.54 (br m, 3H), 1.36–1.40 (br m, 7H), 1.21–1.26 (br m, 7H),
C), 215.7 (Ru=C), 174.8, 151.2, 149.8, 142.0, 139.4, 138.7, 135.1, 129.2,
128.7, 125.8, 120.9, 118.5, 112.1, 112.0 (aryl-C), 84.8 ((OCACHTUNGTERNU(NG CH3)2), 51.7
1.11–1.19 ppm (br m, 4H; PCy3); 13C{1H} NMR (150 MHz, C6D6): d=
31 13
272.0 (Ru=CH), 219.4 (d, 2J
( P, C)=80.9 Hz, N C N), 150.3, 149.3,
(N CH2), 39.8 (N
(CH2)2), 31.1, 30.7 (OC
(CH3)2, 20.0, 19.9 ppm (aryl-
À À
À
141.6, 140.2, 138.5, 129.2, 128.5, 128.1, 126.3, 125.4, 125.2, 112.5, 111.8 (s,
CH3); MS (FAB): m/z (%): 759.3 (12) [M]+, 724.4 (14) [MÀCl]+, 365.3
(91) H2ITap; HRMS (FAB): m/z calcd for C38H48Cl2OSN5Ru: 759.2312
[M]+; found: 759.2379.
aryl-C), 52.2, 51.9 (s, N CH2 CH2 N), 39.8, 39.5 (N CH3), 32.2 (d, 1J-
(31P, 13C)=15.4 Hz), 29.5 (s), 28.1 (d, 2J(31P, 13C)=9.8 Hz), 26.6 (s; PCy3),
20.9, 19.8 ppm (C6H2A
(CH3)2); 31P{1H} NMR (121.4 MHz, C6D6): d=
À
À
À
À
N
ACHTUNGTRENNUNG
CHTUNGTRENNUNG
Complex 7: Complex 1 (100 mg, 110 mmol) and 2-(3’-butenyl)pyridine
(22 mg, 170 mmol) were stirred in tBuOMe (20 mL) at RT for 16 h. After
this time, the resulting greenish slurry was filtered on air and the residue
was washed with tBuOMe (2ꢄ10 mL) and dried in a vacuum oven
(608C, 4 h) to give compound 7 (64 mg, 88%) as an olive/brownish-green
powder. M.p. 233–2358C (dec.); 1H NMR (300.1 MHz, C6D6): d=18.99
(t, J=2.5 Hz, 1H; Ru=CH), 8.26 (m, 1H), 6.56 (m, 1H), 6.59 (s, 4H;
23.4 ppm (s); MS (FAB): m/z (%): 938.4 (4) [M]+, 365.3 (100) H2ITap;
HRMS (FAB): m/z calcd for C48H71Cl2N4PSRu: 938.3558 [M]+; found:
938.3565.
Complex 3: Inside
a glove box, 2-(pyridin-2-yl)propan-2-ol (188 mg,
1.37 mmol) was dissolved in THF (50 mL). tBuLi (810 mL, 1.7m in n-pen-
tane) was slowly added to the mixture with vigorous stirring and the
color turned to light-yellow/reddish. Complex 1 (1.25 g, 1.37 mmol) was
added to this mixture in one portion and the resulting dark-purple-col-
ored solution was sealed, removed from the glove box, and heated at
508C on an oil bath for 3 days. After this time, the mixture was cooled to
RT and the solvent was removed on a high-vacuum line. The resulting
dark residue was dissolved in benzene (25 mL) and filtered through a
pad of Celite (3.5ꢄ2.5 cm). The solvent was again removed on the high-
vacuum line and n-hexane (10 mL) was added to the remaining dark resi-
due. The suspension was sonicated (10 min) and filtered through a pad of
Celite; the filtrate was then discarded. At this point, benzene was added
to the Celite pad and, after evaporation of this filtrate, pure compound 3
was obtained as a dark-green solid (503 mg, 50%). M.p. 208–2118C
À
À
À
C6H2), 6.27 (m, 1H), 6.16 (m, 1H; C5H4N), 3.53 (s, 4H; N CH2 CH2
À
N), 3.41 (t, J=6.0 Hz, 2H), 2.84 (m, 2H; CH2 CH2), 2.77 (br s, 12H;
C6H
G
N
(CH3)2); 13C{1H} NMR (75.9 MHz,
À
C6D6): d=334.5 (Ru C), 217.9 (Ru=C), 162.3, 150.5, 150.3, 140.0 (br),
139.1 (br), 135.6, 123.4, 120.9, 112.5 (aryl-C), 54.0, 34.1 (CH2 CH2), 51.5
À
À
À
À
(br, N CH2 CH2 N), 40.3 (N
(CH3)2), 20.8 (br), 19.7 ppm (br, aryl-CH3);
MS (FAB): m/z (%): 655.2 (100) [M]+, 365.3 (65) H2ITap; HRMS (FAB):
m/z calcd for C31H41Cl2N5Ru: 655.1782 [M]+; found: 655.1785.
Complex 8: Inside
a glove box, 2-(but-3-en-1-yl)-6-methylpyridine
(90 mg, 611 mmol) was added to a suspension of complex 1 (400 mg,
440 mmol) in tBuOMe (50 mL). The flask was then sealed, removed from
the glove box, and stirred vigorously at RT for 22 h. The reaction mixture
was filtered on air and the resulting solid was washed with tBuOMe (2ꢄ
30 mL). The solid was then resuspended in benzene and filtered through
a pad of Celite. After the evaporation of benzene and drying on a high-
vacuum line, complex 8 was isolated as an olive-brown solid (222 mg,
75%). M.p. 238–2418C (dec.); 1H NMR (600 MHz, C6D6,): d=18.98 (t,
J=4.8 Hz, 1H; Ru=CH), 6.29 (s, C6H2, 2H), 6.53 (s, 2H; C6H2), 6.51 (m,
1H; C5H4N), 6.19 (d, J=7.6 Hz, 1H; Py), 6.15 (d, J=7.6 Hz, 1H;
C5H4N), 3.53 (br m, 2H), 3.46(br m, 2H; N CH2 CH2 N), 3.04 (m, 2H;
2ACTHNUGTREN(NUNG CH3)2), 2.72 (br m, 2H; CH2 CH2), 2.62 (s,
12H; N(CH3)2), 2.60 (s, 6H; C6H2ACHTNGUTERN(NUG CH3)2), 2.48 ppm (s, 3H; C5H4N
CH3); C{ H} NMR (150 MHz, C6D6): d=340.1 (Ru C), 219.2 (Ru=C),
160.7, 160.4, 150.8, 150.3, 141.1, 138.4, 135.3, 130.4, 128.4, 122.1, 121.0,
1
(dec.); H NMR (C6D6, 600 MHz): d=18.30 (s, 1H; Ru=CH), 9.71 (d, J=
5.00 Hz, 1H; o-Py), 7.87 (d, J=7.38 Hz, 2H; o-Ph), 6.98 (t, J=7.35 Hz,
1H; p-Ph), 6.91 (t, J=7.58 Hz, 2H; m-Ph), 6.52 (d, J=3.00 Hz, 2H;
C6H2), 6.38 (d, J=3.00 Hz, 2H; C6H2), 6.28 (m, 1H; m-Py), 6.09 (m, 2H;
À
À
p,m-Py), 3.54 (br s, 4H; N CH2), 2.83 (s, 6H; C6H2 CH3), 2.71 (s, 6H;
À
C6H2 CH3), 2.46 (s, 12H; N
N
ACHTUGNTREN(UNNG CH3)2), 0.74 ppm
13
À
(s, 3H; OC
U
(Ru=C), 174.7, 154.8, 150.3, 139.8, 138.7, 134.2, 129.7, 128.4, 126.2, 125.9,
À
À
À
À
120.0, 117.4, 112.5, 112.3 (aryl-C), 83.8 (OC
N
À
À
CH2 CH2), 2.93 (s, 6H; C6H
(N
(CH2)2), 31.0, 27.2 (OC
(CH3)2, 20.00 ppm (aryl-CH3); MS (FAB): m/z
À
A
(%): 727.3 (5) [M]+, 691.3 (14) [MÀCl]+, 365.3 (100) H2ITap; HRMS
13
1
À
(FAB): m/z calcd for C38H48Cl2ON5Ru: 727.2598 [M]+; found: 727.2259.
Brown crystal (polyhedron); crystal dimensions: 0.15ꢄ0.14ꢄ0.10 mm3;
crystal system: triclinic; space group P1; Z=2; a=10.0712(5), b=
10.2020(5), c=18.4951(10) ꢃ; a=90.5830(10), b=91.5880(10), g=
112.5, 112.4 (aryl-C), 53.9 (N CH2 CH2 N), 51.7 (CH2 CH2), 50.6, 40.2
À
À
À
À
ꢀ
À
À
(NACHTGNUETRN(UNG CH3)2), 31.9 (CH2 CH2), 22.1, 21.2 (aryl-CH3), 19.1 ppm (C5H4N
CH3); MS (FAB): m/z (%): 669.2 (49) [M]+, 634.2 (15) [MÀCl]+, 365.4
&
6
&
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Linker-Free, Silica-Bound Olefin-Metathesis Catalysts
FULL PAPER
(100) H2ITap; HRMS (FAB): m/z calcd for C32H43Cl2N5Ru: 669.1942
[M]+; found: 669.1951.
the COE solution was recorded. Next, the solution of the catalyst was
added to the COE mixture by injection through a septum. The reactions
Brown crystal (polyhedron); crystal dimensions: 0.16ꢄ0.12ꢄ0.12 mm3;
crystal system: monoclinic; space group P21/c; Z=4; a=12.0613(6), b=
16.0056(8), c=18.5848(10) ꢃ; a=90, b=108.5260(10), g=908; V=
3401.8(3) ꢃ3; 1=1.384 gcmÀ3; T=200(2) K; qmax =25.688; Mo Ka radia-
tion; l=0.71073 ꢃ; 0.58 w-scans with a CCD area detector, which cover-
ing the asymmetric unit in reciprocal space with a mean redundancy of
7.73 and a completeness of 99.8% to a resolution of 0.82 ꢃ; total reflns:
À
were monitored by integration of the signals at d=5.51 (COE, =CH )
and 5.46 ppm (polyCOE, CH) against the mesitylene signal at d=
6.8 ppm.
Preparation of the heterogenized complexes: Inside a glove box, a solu-
tion of the respective Ru complex in CH2Cl2 (40 mL) was prepared.
Grace SP550-10020 silica was calcinated at 5508C for 4 h under a nitro-
gen atmosphere prior to use. Next, the silica was added to the solution
and the mixture was shaken thoroughly and allowed to stand for 2 h. The
solvent was removed and the resulting solid was dried under vacuum at
408C. The amounts of Ru complex and silica (in parenthesis) that were
used in the COE experiments are as follows: Re2O7: 461 mg (15.4 g), 3:
97 mg (18.9 g), 7: 115 mg (18.7 g), 8: 79 mg (18.3 g), 9: 52 mg (19.2 g), 10:
88 mg (19.2 g), 11: 81 mg (20.4 g). The amounts of Ru complex and silica
(in parenthesis) that were used in the self-metathesis of methyl oleate ex-
periments are as follows: 10: 88 mg (18.4 g), 11: 81 mg (18.2 g).
50528; unique reflns: 6452 (RACTHUNRTGNEUNG(int)=0.0503); observed reflns 5220 (I>
2s(I)); m=0.65 mmÀ1; Tmin =0.90, Tmax =0.93, refined parameters: 483;
hydrogen atoms were treated by using appropriate riding models; GOF=
1.12 for the observed reflections; final residual values R1(F)=0.045,
wR(F2)=0.079 for observed reflections; residual electron density: À0.86–
0.73 eꢃÀ3
.
Complex 9: By using the above-described procedure, complex 9 was pre-
pared from 2-(but-3-en-1-yl)-4,6-dimethylpyridine (124 mg, 769 mmol)
and complex 1 (500 mg, 551 mmol) in tBuOMe (50 mL). After stirring for
24 h, the reaction mixture was filtered and the solid was washed with n-
pentane (3ꢄ5 mL) and tBuOMe (20 mL). The residue was dried in vacuo
to afford complex 9 as olive-brown solid (165 mg, 44%). M.p. 235–2388C
(dec.); 1H NMR (600 MHz, C6D6): d=19.00 (t, 1H; J=4.8 Hz, Ru=CH),
6.61 (s, C6H2, 2H), 6.54 (s, 2H; C6H2), 6.00 (s, 1H; C5H2N), 5.97 (s, 1H;
Continuous-flow experiments: All reactions were carried out under an
argon atmosphere with deoxygenated reagents and solvents. COE was
stored for 24 h over Selexorb CD to remove any trace amounts of stabil-
izer. No further purification of COE was carried out prior to use. A steel
reactor (diameter: 14 mm, length: 45 cm) was charged with the catalyst.
A solution of COE in cyclohexane (0.7 wt.%) was pumped through the
reactor at 608C with a flow rate of 8 mLminÀ1 and a pressure of 2 bar.
The reactions were monitored by sampling the resulting solution with a
GCMS probe. Split tests were conducted by removing two aliquots of the
reaction mixture, one of which was quenched with excess ethylvinylether.
The samples were allowed to stand overnight and then analyzed by GC.
For the self-metathesis reactions, a solution of methyl oleate in cyclohex-
ane (50 wt.%) was used with a flow rate of 2 mLminÀ1. Temperatures
and pressures were the same as in the COE reactions.
À
À
À
C5H2N), 3.54 (br m, 2H), 3.47 (m, 2H; N CH2 CH2 N), 3.09 (m, 2H;
À
À
CH2 CH2), 2.94 (s, 6H; C6H CHTUNGTRENNNUG
2A
6H), 2.63 (s, 6H; N
A
C5H4N o-CH3), 1.55 ppm (s, 3H; C5H4N p-CH3); 13C{1H} NMR
(100 MHz, C6D6): d=340.2 (Ru=C), 219.9 (Ru=C), 160.3, 159.8, 151.1,
150.5, 146.7, 141.3, 138.7, 130.7, 123.5, 122.4, 112.8, 112.7, 112.6, 54.2, 51.9
À
À
À
À
À
À
À
(N CH2 CH2 N), 50.8 (CH2 CH2), 40.5 (NACHTUNGTRNE(GNU CH3)2), 31.9 (CH2 CH2),
À
22.1, 21.5 (aryl-CH3), 20.1, 19.4 ppm (C5H4N CH3); MS (FAB): m/z (%):
683.2 (31) [M]+, 649.2 (10) [MÀCl]+, 611.0 (19) [MÀ2Cl]+, 365.3 (100)
H2ITap; HRMS (FAB): m/z calcd for C33H45Cl2N5Ru: 683.2099 [M]+;
found: 683.2104.
CCDC-889082 (3), CCDC-889083 (8), and CCDC-889084 (9) contain the
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Colorless crystal (plate); crystal dimensions: 0.42ꢄ0.29ꢄ0.05 mm3; crys-
ꢀ
tal system: triclinic; space group P1; Z=2; a=9.0231(12), b=15.596(2),
c=16.665(2) ꢃ; a=113.141(3), b=92.240(3), g=94.452(3)8; V=
2143.8(5) ꢃ3; 1=1.294 gcmÀ3; T=200(2) K; qmax =25.078; Mo Ka radia-
tion; l=0.71073 ꢃ; 0.58 w-scans with a CCD area detector, which covers
the asymmetric unit in reciprocal space with a mean redundancy of 2.84
and a completeness of 98.3% to a resolution of 0.84 ꢃ; total reflns
Acknowledgements
J.C., R.P., M.B., R.L., T.K., K.W., and M.L. work at the CaRLa of Hei-
delberg University, which is co-financed by the University of Heidelberg,
the state of Baden-Wꢀrttemberg, and by BASF SE. Support of these in-
stitutions is gratefully acknowledged. S.L.B. thanks the Trent Lott Na-
tional Center for an Innovation Award. H.J.S. would like to acknowledge
BASF SE for financial support.
21449; unique reflns: 7499 (RACTHNUGRTENUNG(int)=0.0503); observed reflns: 5830 (I>
2s(I)); m=0.53 mmÀ1; Tmin =0.81, Tmax =0.97; refined parameters: 473;
hydrogen atoms were treated by using appropriate riding models; GOF=
1.10 for the observed reflections; final residual values R1(F)=0.064,
wR(F2)=0.154 for the observed reflections; residual electron density:
À1.10–1.05 eꢃÀ3
.
Complex 10: Inside a glove box, potassium tert-amylate (460 mL, 1.7m in
toluene, 782 mmol) was added to a suspension of H2ITap·HCl (300 mg,
775 mmol) in n-hexane (20 mL). The mixture was stirred vigorously for
1 h, during which time it turned to an opaque yellow color. Next,
Grubbs–Hoveyda I (452 mg, 753 mmol) was added to the mixture and the
flask was sealed, removed from the glove box, connected to a high-
vacuum line, and heated in an oil bath at 608C for 4 h. During this time,
the color of the mixture changed to dark brown and a green precipitate
was formed. After cooling the mixture to RT, the green precipitate was
filtered off and washed with Et2O (2ꢄ20 mL). The green solid was then
extracted with CH2Cl2 (3ꢄ10 mL). The mixture was concentrated in
vacuo and, after drying under high vacuum, complex 10 was obtained as
a dark-green solid (425 mg, 82%). The spectroscopic data of the product
matched those previously reported.[19a]
[1] R. L. Banks, S. G. Kukes, J. Mol. Catal. 1985, 28, 117–131.
[2] E. F. G. Woerlee, R. H. A. Bosma, J. M. M. Van Eijl, J. C. Mol, Appl.
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[3] a) J. H. Wengrovius, R. R. Schrock, M. R. Churchill, J. R. Missert,
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[4] a) G. C. Fu, S. T. Nguyen, R. H. Grubbs, J. Am. Chem. Soc. 1993,
115, 9856–9857; b) B. J. Keitz, K. Endo, P. R. Patel, M. B. Herbert,
R. H. Grubbs, J. Am. Chem. Soc. 2012, 134, 693–699; c) M. A. O.
Volland, S. M. Hansen, F. Rominger, P. Hofmann, Organometallics
2004, 23, 800–816.
[5] For recent reviews in the context of olefin metathesis, see: a) M. R.
Buchmeiser, Chem. Rev. 2009, 109, 303–321; b) 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; c) C.
Copꢅret, J.-M. Basset, Adv. Synth. Catal. 2007, 349, 78–92; d) M. R.
Maurya, J. C. Pessoa, J. Organomet. Chem. 2011, 696, 244–254;
e) A. C. Marr, P. C. Marr, Dalton Trans. 2011, 40, 20–26; f) A.
Corma, H. Garcia, Top. Catal. 2008, 48, 8–31; g) R. Duque, E. Ochs-
Homogeneous ROMP reactions: COE was purchased from Sigma Al-
drich, degassed, and used without further purification. Mesitylene
(1 equiv in the monomer) was used as an internal standard. Inside a
glove box, an NMR tube was charged with COE (0.5 mL, 0.12m in
C6D6). The appropriate amount of catalyst (0.5 mol%) was dissolved in
C6D6 (0.1 mL) and stored in a capped vial. Both the catalyst solution and
the COE sample were removed from the glove box and a spectrum of
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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ÞÞ
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M. Limbach et al.
ˇ
ˇ
ˇ
ner, H. Clavier, F. Caijo, S. P. Nolan, M. Mauduit, D. J. Cole-Hamil-
ton, Green Chem. 2011, 13, 1187–1195.
cek, J. Dꢅdecek, Z. Bastl, M. Lamac, J. Mol. Catal. A Chem. 2010,
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Published online: && &&, 0000
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8
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www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Linker-Free, Silica-Bound Olefin-Metathesis Catalysts
FULL PAPER
Born free: Silica adsorption of ruthe-
nium carbenes with the H2ITap ligand
(see figure) yielded heterogeneous
materials without the need for tether-
ing groups on the complex or the sup-
port. These materials were tested as
catalysts in the ring-opening–ring-clos-
ing-metathesis of cyclooctene and the
cross-metathesis of methyl oleate
under continuous-flow conditions. The
best complexes showed a TON>4000,
which surpasses the most active silica-
based materials.
Metathesis
J. Cabrera, R. Padilla, M. Bru,
R. Lindner, T. Kageyama, K. Wilckens,
S. L. Balof, H.-J. Schanz, R. Dehn,
J. H. Teles, S. Deuerlein, K. Mꢀller,
F. Rominger, M. Limbach* . &&&& — &&&&
Linker-Free, Silica-Bound Olefin-
Metathesis Catalysts: Applications in
Heterogeneous Catalysis
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!