Heterogenization of organometallic molybdenum complexes with siloxane functional groups and their catalytic application

Article abstract of DOI:10.1002/adsc.200404285

η⁵-CpMo(CO)₃R complexes containing siloxane functional groups [(CH₂)₃Si(OMe)₃ or (CH ₂) Si(OEt)₃] attached to either the cyclopentadiene ligand or directly to Mo were grafted on the mesoporous materials MCM-41 and MCM-48 by reaction of the OR (R = Me, Et) moieties in the silane ligand and surface silanol groups (Si-OH). For the sake of comparison mesoporous materials modified with silane groups were reacted with Na⁺[CpMo(CO)₃] ^-. The XRD, N₂ adsorption-desorption, and TEM analyses provide strong evidence that the mesoporous structure of the supporting material retains its long-range ordering throughout the grafting process, despite significant reductions in surface area, pore volume and pore size. The appearance of strong IR bands around 2016 and 1956 cm^-1 on the grafted samples also shows that the η⁵- InIi(II)3E complexes have been successfully grafted. Elemental analysis reveals that the grafted samples contain 0.3-3.5 wt % Mo. ²⁹Si CP MAS-NMR spectra give clear evidence for a reduction in the numbers of the Q₃ and Q₂ sites. The formation of new peaks around -49.8, -57.9, and -66.2 ppm (T₁, T₂, and T₃) indicates esterification of silanol groups by the alkoxy groups of the silane ligand. Both the in situ and ex situ prepared samples show good catalytic activity for the epoxidation of cyclooctene.

Full text of DOI:10.1002/adsc.200404285

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Heterogenization of Organometallic Molybdenum Complexes
with Siloxane Functional Groups and their Catalytic Application
a
a
b
c
Ayyamperumal Sakthivel, Jin Zhao, Marianne Hanzlik, Anthony S. T. Chiang,
a,
a,
Wolfgang A. Herrmann, * Fritz E. Kꢀhn *
Lehrstuhl fꢀr Anorganische Chemie, Technischen Universitꢁt Mꢀnchen, Lichtenbergstraße 4,
a
85747 Garching bei Mꢀnchen, Germany
Fax: (þ49)-89-289-13473, e-mail: fritz.kuehn@ch.tum.de
b
c
Lehrstuhl fꢀr Technische Chemie I der Technischen Universitꢁt Mꢀnchen, Lichtenbergstraße 4,
85747 Garching bei Mꢀnchen, Germany
National Central University, Chung-Li, Taiwan 320, Republic of China
Received: September 8, 2004; Accepted: November 25, 2004
th
Dedicated to Prof. Dr. Richard Schrock on the occasion of his 60 birthday
5
ꢀ1
Abstract: h -CpMo(CO) R complexes containing si- bands around 2016 and 1956 cm on the grafted sam-
3
5
loxane functional groups [(CH ) Si(OMe) or (CH ) ples also shows that the h -CpMo(CO) R complexes
2
3
3
2
3
Si(OEt) ] attached to either the cyclopentadiene li- have been successfully grafted. Elemental analysis re-
3
gand or directly to Mo were grafted on the mesopo- veals that the grafted samples contain 0.3–3.5 wt %
2
9
rous materials MCM-41 and MCM-48 by reaction of Mo. Si CP MAS-NMR spectra give clear evidence
the OR (R¼Me, Et) moieties in the silane ligand for a reduction in the numbers of the Q and Q sites.
3
2
and surface silanol groups (Si-OH). For the sake of The formation of new peaks around ꢀ49.8, ꢀ57.9,
comparison mesoporous materials modified with si- and ꢀ66.2 ppm (T , T , and T ) indicates esterifica-
1
2
3
þ
ꢀ
lane groups were reacted with Na [CpMo(CO) ] . tion of silanol groups by the alkoxy groups of the si-
3
The XRD, N adsorption-desorption, and TEM anal- lane ligand. Both the in situ and ex situ prepared sam-
2
yses provide strong evidence that the mesoporous ples show good catalytic activity for the epoxidation
structure of the supporting material retains its long- of cyclooctene.
range ordering throughout the grafting process, de-
spite significant reductions in surface area, pore vol- Keywords: catalysis; epoxidation; grafting; molybde-
ume and pore size. The appearance of strong IR num; siloxane
Introduction
the carbonyl complexes are in situ oxidized – also by
TBHP – to their oxo congeners. The carbonyl precursor
Various molybdenum(VI) complexes are known to be compounds can be stored for long time without any
versatile catalysts for the oxidation of organic sub- problems while the oxides are somewhat more sensi-
[
1]
[5]
strates. Molybdenum-based catalysts have been ap- tive. Additionally, Cp’Mo(CO) R complexes (R¼alk-
3
plied for the industrial epoxidation of propylene, utiliz- yl) and their oxidized congeners are also known and
ing tert-butyl hydroperoxide (TBHP) as oxidizing agent have already been successfully utilized as homogeneous
[
2]
[6]
since the late 1960 s. A lot of work has been dedicated catalysts or catalyst precursors. However, industrial in-
to the understanding of the involved catalytic reactions terest is still to a significant degree focused on heteroge-
in subsequent years in order to improve both yields and neous catalysts due to their advantages, e.g., easier prod-
[3]
[7]
selectivities. During the last decade several well de- uct/catalyst separation. Among the various supporting
fined homogeneous epoxidation catalysts have been de- materials studied, the mesoporous silicates known as
veloped and described. Recently cyclopentadienyl- MCM-41 and MCM-48 with regular pore size, large
[
4]
[8]
molybdenum complexes of the formula Cp’MoO Cl surface areas, large number of surface silanol groups,
2
were found to be efficient homogeneous catalysts for and high chemical and thermal stability, are potential
[
5]
the epoxidation of alkenes with TBHP as the oxidant.
Furthermore, it became clear that the direct application supports.
of their carbonyl precursor compounds of the formula Different approaches have been used in order to ob-
CpMo(CO) Cl leads to equally efficient catalysts, since tain heterogeneous molybdenum catalysts for olefin ep-
and promising candidates as both catalysts and catalyst
[9]
3
Adv. Synth. Catal. 2005, 347, 473–483
DOI: 10.1002/adsc.200404285
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Figure 1. Formulae of complexes 1 –3.
Figure 2. Formulae of the heterogenized complexes.
Scheme 1.
oxidation. A general problem is that Mo(VI) cannot remove residual SiꢀOH groups, which were considered
easily be incorporated into the tetrahedral positions of to be favourable for the catalytic reaction on the surface
[
12]
the silicate framework of molecular sieves owing to its of the mesoporous material,
reduced the catalyst
[
10]
[15]
large ionic size and charge.
Mo(VI) complexes, however, have been reported to be
active and recyclable catalysts for olefin epoxidation with silane functional groups, either attached directly
Polymer supported leaching significantly.
During the last decades organometallic complexes
[11]
with TBHP. Nevertheless, in the latter case problems to the metal centre or to a cyclopentadienyl ligand
are reported to have occurred during the catalytic reac- have been reported. These functional groups often
tions such as swelling or leaching of the active species in contributed a considerable kinetic stabilization to the
the organic solution phase. Another strategy for the con- resulting complexes. The introduction of an alkoxysi-
finement of metal centres in mesoporous silicates is the lane group in the organometallic complexes has re-
covalent attachment of organometallic or coordination ceived additional attention, owing to the ease of hetero-
[
16]
[
16]
[
12]
compounds to form a hybrid material.
modified MCM-41 and MCM-48 materials were synthe- organic or inorganic supports.
sized by grafting MoO X (X¼Cl, Br) and CpMo(CO) Cl, successfully synthesized and characterized a series of cy-
Recently, genization of these transition metal complexes by using
[5,14–16]
Recently, we have
2
2
3
the latter being quite efficient homogeneous epoxi- clopendadienyl-molybdenum complexes containing a
[13]
[17]
dation catalysts. Additionally, surface-fixed bidentate siloxane functional group. In this work such com-
Lewis bases have been used to bind catalytically Mo(VI) plexes (compounds 1–3, see Figure 1) are reported
[
14]
complexes as described by GonÅalves et al. and, inde- to be turned into ꢃsurface organometallic catalystsꢄ
[
15]
pendently, by Thiel et al. Silylation using Me SiCl to by fixing them to MCM-41 and MCM-48 (Figure 2).
3
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Mo Complexes with Siloxane Functional Groups
Additionally, the in situ synthesis of surface fixed ure 2). The in situ grafting of the CpMo complexes is car-
CpMoR(CO) by functionalization of the mesoporous ried out by silylation of MCM-41 and MCM-48 followed
3
þ
ꢀ
framework with Cl(CH ) Si(OMe) or ClCH Si(OEt)
followed by the reaction of Na [CpMo(CO) ] with which are represented as SM-41SG, SM-48SG, SM-
by treatment with Na [CpMo(CO) ] (see Scheme 1)
2
3
3
2
3
3
þ
ꢀ
3
the chloride ion of the silane functional group on 41ESG and SM-48ESG.
MCM-41 and MCM-48 is presented (Scheme 1).
The powder XRD patterns of the parent MCM-41
Figure 3 a), and the corresponding grafted Mo samples
SM-41CpSG, SM-41MoSG, SM-41MoESG, SM-41SG
(
(
Results and Discussion
and SM-41ESG) are depicted in Figure 3 b – f. In each
case all four reflections are observed in the 2 q range
2
–88, with an indexing corresponding to a hexagonal
Synthesis and Textural Characterization
cell showing the (100), (110), and (200) and (210) planes.
Figure 3A – F show the XRD patterns of the parent
The compounds 1–3 are prepared as described previ- MCM-48 and the corresponding samples with the graft-
[17]
ously. They are slightly air sensitive and very well ed Mo complexes (SM-48CpSG, SM-48MoSG, SM-
soluble both in non-polar (e.g., n-hexane) and polar 48MoESG, SM-48SG and SM-48ESG), which exhibit a
(
e.g., THF) solvents. The IR spectra (KBr) of com- main reflection corresponding to the (211) plane along
pounds 1–3 show strong absorption bands at 2016, with a shoulder peak derived from the (220) plane, typ-
ꢀ
13
1
1
956 and 1963 cm , respectively, from terminal carbon- ical for cubic cells. These peaks together with the sextet
1
29
yl groups. The H, C and Si NMR spectra as well as el- pattern observed between the 2q angles 38 – 68, are char-
[
17]
emental analysis confirm the purity of the complexes.
acteristic of a cubic mesoporous MCM-48 structure.
The treatment of the complexes 1–3 with calcined and Compared to parent MCM-41 and MCM-48, the grafted
dehydrated MCM-41 and MCM-48 leads to the modi- samples show a decrease in the relative intensities of the
fied materials which are respectively designated as XRD reflections and there is a clear shift to higher 2 q
SM-41CpSG,
SM-48CpSG,
SM-41MoSG,
SM- values. These changes originate from a contraction of
48MoSG, SM-41MoESG and SM-41MoESG (see Fig- the unit cells of the grafted samples, because of the im-
Figure 3. Powder XRD pattern of (a, A) SM-41, SM-48; (b, B) SM-41CpSG, SM-48CpSG; (c, C) SM-41MoSG, SM-48MoSG;
d, D) SM-41MoESG, SM-48MoESG; (e, E) SM-41SG, SM-48SG and (f, F) SM-41ESG, SM-48ESG.
(
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Table 1. Textural properties of MCM-41/MCM-48 and of the grafted samples.
Sample
Mo [wt %]
Interplane
distance [nm]
Unit cell
parameter [nm]
BET surface
Pore
diameter [nm]
[a]
[b]
2
ꢀ1
area [m g
]
MCM-41
–
3.80
3.62
3.60
3.31
3.69
3.37
3.97
3.90
3.92
3.81
3.90
3.65
4.39
4.18
4.16
3.82
4.26
3.89
9.72
9.55
9.60
9.33
9.55
8.94
839
620
640
–
726
–
1043
790
680
–
840
–
2.74
2.5–3.1
2.3–3.1
–
1.9–2.1
–
2.41
2.24–3.5
2.27–3.5
–
2.1
–
SM-41CpSG
SM-41MoSG
SM-41MoESG
SM-41SG
SM-41ESG
MCM-48
SM-48CpSG
SM-48MoSG
SM-48MoESG
SM-48SG
2.3
1.7
0.3
1.03
0.94
–
3.41
1.83
0.4
1.18
1.27
SM-48ESG
[
[
a]
b]
d100 for MCM-41 and d for MCM-48.
211
p
2
2
2 1/2
a¯ ¼2d100
/
3 for MCM-41; a¯ ¼dhkl (h þk þl ) for MCM-48.
mobilization of the bulky organosilane groups on the mesoporous solids. Awell-defined sharp inflection is ob-
channels of MCM-41 and MCM-48 by reaction with sur- served between the relative pressure (p/p ) of 0.3–0.4
0
[
14]
face silanol (Si-OH) groups. The intensity reduction is due to capillary condensation of nitrogen inside the pri-
mainly due to contrast matching between the silicate mary mesoporous channels. Compared to parent meso-
framework and organic moieties located inside the porous samples, the modified samples (Figure 4) exhibit
[
14]
channels of the mesoporous molecular sieves. The re- a decrease in N uptake due to the presence of bulky or-
2
sults clearly indicate that the structure of the mesopo- ganometallic complexes grafted on the mesoporous
rous materials remains intact through the grafting pro- channels. The calculated textural parameters using
cedure.
XRD and adsorption/desorption isotherms are summar-
The low temperature N adsorption/desorptions iso- ized in Table 1. The parent MCM-41 and MCM-48 sam-
2
therm of parent MCM-41 and MCM-48 are of type ples exhibit narrow pore size distributions with average
[
18]
(
IV) according to the IUPAC and characteristic for pore diameters of 2.7and2.4 nm, respectively. The graft-
ed materials exhibit a broader pore size distribution and
display also a decrease in surface area and unit cell vol-
ume. The decrease of the unit cell value and the broad
distribution of pore size evidences that the organometal-
lic complexes in the grafted mesoporous samples are
mainly located on internal surfaces of the mesoporous
[
14]
materials.
The TEM images (Figure 5) of the grafted samples
provide strong evidence that the mesoporous structure
[
8,9]
of the support retains long-range ordering
through-
out the grafting process and that the channels remain ac-
cessible. The ED pattern of grafted samples shows the
reflection of the (100) and the (110) planes, which fur-
ther support the presence of long-range ordering in
the samples. Elemental analyses (EAs) of the grafted
samples of compounds 1–3 reveal (Table 1) an Mo load-
ing of 0.3–3.5 wt %. The complexes containing methoxy-
silane units enable somewhat higher Mo complex load-
ing on the surfaces than the complex containing ethoxy
ligands. This may be due to the higher reactivity of the
methoxy groups with silanol moieties in the mesoporous
channels in comparison to the ethoxy groups. Further-
more, it is evident that direct grafting is more efficient
and leads to higher Mo complex loading on the surface
Figure 4. N adsorption/desorption isotherms of complexes 1 than in situ grafting. EA further confirms clearly the de-
2
and 2 grafted on MCM-41 and MCM-48.
crease of Cl on the SM-41SG and SM-48 SG samples in
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Figure 5. TEM images of (a) SM-48CpSG, (b) SM-48MoSG (c) SM-41MoESG.
comparison to the SM-41S and SM-48S samples. There- tion of the isolated silanol groups (single and geminal)
fore, it is clear that a considerable amount of Cl is utiliz- by nucleophilic substitution at the silicon atom in the or-
þ
ꢀ
[14]
ed for the reaction with the Na [CpMo(CO) ] salt.
ganic ligand. However, Figure 8 also shows consider-
3
Figure 6 depicts the FT-IR spectra of parent calcined able unreacted silanol groups remaining after the graft-
2
9
mesoporous MCM-41, MCM-48 and grafted samples. ing. The Si CP MAS NMR spectra also exhibit two ad-
ꢀ
1
The bands at 1206, 1060, and 794 cm are attributed ditional signals at d¼ ꢀ49.8 and ꢀ57.9 ppm assigned
to stretching vibrations of the mesoporous framework to T and T organosilica species, respectively,
1
2
(
2
SiꢀOꢀSi). New, comparatively small bands around [T ¼RSi(OSi) (OR) ]. A weak, broad signal at d¼
m
m
3–m
ꢀ
1
016 and 1956 cm can be assigned to terminal carbon-
ꢀ66.2 ppm can be assigned to a T environment. The
3
yl (CO) group vibrations of the grafted compounds. Ad- amounts of T and T are much higher in the case of
1
2
ꢀ
1
ditional bonds appear in the range of 2949 and 2853 cm
SM-41MoSG than in the case of SM-41CpSG, which
due to CꢀH stretching vibrations, originating from the suggests that the Mo loading is much higher in the for-
CH groups present in the silane ligand. In order to mer case than in the later. This observation is in good
2
transfer the Mo precursor in the formal oxidation state
þII to the catalytically active species in the formal oxi-
dation stateþVI, the SM-41CpSG and SM-41MoSG
agreement with the EAs (Table 1).
samples are treated with TBHP. The FT-IR spectra re- Catalytic Applications
corded prior to and after oxidation are shown in Fig-
ure 7. After the treatment with TBHP the bands around The grafted samples are tested as heterogeneous cata-
ꢀ
1
2
9
016 and 1956 cm disappear and new bands around lysts in olefin epoxidation, with cyclooctene being the
ꢀ
1
14 and 964 cm are formed, indicating the oxidative substrate and TBHP as the oxidizing agent. The results
conversion of the MoꢀCO groups into Mo¼O spe- are summarized in Table 2. The SM-41SG and SM-
[5,13,19]
cies . The oxidative decarbonylation method has al- 48SG materials show about 65–68% cyclooctene con-
ready been successfully applied for the oxidation of version with nearly 100% epoxide selectivity after 24 h
Cp’Mo(CO) X and Cp’Mo(CO) R complexes, both in reaction time. In the cases of SM-41CpSG, SM-
3
3
[5,6]
[13]
homogeneous and heterogeneous phase.
41MoSG, SM-48CpSG, and SM-48MoSG 95–100%
The parent MCM-41 and the grafted samples were ex- conversion and about 100% selectivity are obtained.
29
amined by solid-state Si CP MAS NMR spectroscopy. The initial activities (based on the TOFs) are highest
The parent MCM-41 exhibits two broad elaborate reso- for SM-41CpSG, SM-41MoSG, SM-48CpSG and SM-
29
nances in the Si CP MAS NMR spectrum at d¼ ꢀ 48MoSG. These materials have longer hydrocarbon
1
13.0 and ꢀ103.8 ppm, assigned to Q and Q species bridges between the Mo atoms and the surface SiꢀO
4
5
of the silica framework, respectively, [Q ¼Si(OSi)
groups than the ESG-materials, thus reducing the influ-
n
n
[
14]
(
OH)4 ] (Figure 8). Aweak shoulder is also observed ence of the electron donor abilities of the surface on the
–n
at d¼ ꢀ94.5 ppm for the Q species. The grafting of Lewis acidity of the catalytic centres (see Figure 1 and
2
5
complexes 1–3 and the in situ grafting of h -CpMo com- Scheme 1). The slightly more pronounced steric bulk
plexes on mesoporous materials result in the reduction of the remaining ethoxy groups (after the heterogeniza-
of the Q and Q resonances, and a concurrent increase tion reaction) in the case of the ESG materials may also
2
3
of the Q resonance. This is consistent with an esterifica- contribute to the generally somewhat lower initial activ-
4
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Figure 6. FT-IR spectrum of (a, A) SM-41, SM-48; (b, B) SM-41MoSG, SM-48MoSG; (c, C) SM -41CpSG, SM-48CpSG; (d, D)
SM-41MoESG, SM-48MoESG; (e, E) SM-41SG, SM-48SG and (f, F) SM-41ESG, SM-48ESG.
Figure 7. FT-IR spectrum of (a) SM-41MoSG, (b) SM -41CpSG, (c) SM-41MoSG-TBHP treated and (d) SM-41CpSG-TBHP
treated samples.
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Mo Complexes with Siloxane Functional Groups
29
Figure 8. Si CP MAS NMR spectrum of (a) SM-41; (b) SM-41CpSG; (c) SM -41MoSG and (d) SM-41SG.
ity of these catalysts. The prehistory (heterogenization due to the chemisorptions of organic molecules on the
method) of the complexes, however, seems also to surface, as such preventing the access of substrate and
have a certain impact on the catalytic activities (the oxidant molecules to the active Mo species. This was
MoSG and MoESG materials are more active than the confirmed by TG-MS analysis of SM-48MoSG before
SG and ESG materials). The reasons for this observa- and after reactions (Figure 9). The TG-mass spectrum
tion, however, are not yet completely understood and of SM-48MoSG before reaction shows about 10%
are still under investigation. All the catalysts, however, weight loss up to 10008C, due to decomposition of com-
show TOFs in the same order of magnitude as the re- plex 2 present in the channels of the mesoporous mo-
spective homogeneous catalysts 1–3, thus indicating lecular sieves. However, SM-48MoSG after reaction dis-
that the reaction is not diffusion limited. This is in plays a weight loss of about 23%, being 13% higher than
good agreement with the results obtained by TEM and that of the original sample. This increase in weight is at-
BET analyses where the pore channels are found to re- tributed to a considerable amount of chemisorbed coke
main accessible after grafting with the complexes 1 to present on the grafted samples after reaction. In order to
3
. After the first catalytic run the catalyst was washed avoid the thermal destruction of the active Mo complex,
several times with dichloromethane to remove physisor- the (chemisorbed organic) cokes are not removed by
bed molecules and the reaction was repeated several calcination. In order to examine the extent of leaching,
times. The catalysts are found to be active even after sev- which could also account for the activity loss, control ex-
eral catalytic runs, however, the catalytic activity de- periments were performed. The catalytic reaction is in-
creases. The observed decrease in activity is very likely terrupted after a 50% conversion of the substrate, the
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Figure 9. TG-mass spectrum of SM-48MoSG (a) before reaction and (b) after reaction.
solution is filtered off at reaction temperature and the Conclusions
filtrate is examined for its catalytic activity. This activity,
however, is negligible (<5% epoxide yield (i.e., within Successful grafting of the complexes 1–3 by the utiliza-
the measurement error) in the 24 h after filtration), tion of a metal- or ligand-attached siloxane group on the
thus demonstrating that catalyst leaching does not play mesoporous molecular sieves MCM-41 and MCM-48 is
a significant role.
achieved without significant loss of ordering. The in situ
Table 2. Oxidation of cyclooctene with various CpMo complexes grafted on MCM-41/MCM-48.
st
rd
[a]
Catalysts
1 run
3
run
TOF
4
h
24 h
4 h
24 h
Con.
Sel.
Con.
Sel.
Con.
Sel.
Con.
Sel.
SM-41SG
SM-48SG
36
32
13
13
66
88
50
97
11
21
98
88
100
97
58
82
39
100
53
68
66
35
63
95
100
95
100
33
100
99
82
92
79
100
87
100
73
13
8
50
100
71
31
33
28
47
46
73
57
80
27
29
44
80
64
64
98
90
91
70
89
95
2800
4850
2900
3150
10100
8100
8400
10200
4900
6300
SM-41ESG
SM-48ESG
SM-41CpSG
SM-48CpSG
SM-41MoSG
SM-48MoSG
SM-41MoESG
SM-48MoESG
14
17
17
21
24
25
7
64
100
100
85
61
100
100
45
46
78
10
[
a]
TOFs are calculated after 5 min reaction time of the first catalytic run.
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and ex situ grafted samples are active and highly selec- Grafting and Characterization Methods
tive catalysts for the cyclooctene epoxidation with the
Grafting experiments were carried out using standard Schlenk
oxidizing agent TBHP. The samples 1 and 2, containing
methoxysilane display both higher complex loadings on
the surfaces and higher catalytic activity in the epoxida-
techniques under an argon atmosphere with the following pro-
cedure: First the mesoporous molecular sieves MCM-41/48
ꢀ
3
were pre-activated at 473 K under vacuum (10 mbar) for
tion reaction owing to the higher reactivity of the me- 4 h to remove physisorbed water. The activated sample was
thoxy functional groups with the siloxane groups of treated with 0.2 mmol of complexes 1–3 in 30 mL dry THF un-
the surface. Catalyst leaching seems not to be a pro- der an argon atmosphere. The mixture was stirred at 339 K for
2
4 h. The resulting solution was filtered off and the pale orange
nounced problem, but significant activity losses occur
after several runs, very likely due to coke formation
and chemisorption of organic molecules on the surface.
solid was washed repeatedly with CH Cl until all physisorbed
2
2
Cp complex was removed from the surface. The washed sam-
ples were dried under vacuum at room temperature. The mate-
rials prepared from the complexes 1–3 on MCM-41 and MCM-
4
8 are designated as SM-41CpSG, SM-48CpSG, SM-41MoSG,
SM-48MoSG, SM-41MoESG and SM-48MoESG, respectively.
The in situ grafting (Scheme 1) was carried out according to
the following procedure: first the mesoporous molecular sieve
Experimental Section
(
MCM-41 or MCM-48, respectively) was silylated with chloro-
propyltrimethoxy- and chloromethyltriethoxysilane using dry
toluene (30 mL) as solvent under an argon atmosphere at 383
K for 24 h. Then excess silane was removed by filtration fol-
lowed by washing several times with dichloromethane. The re-
sulting solid was driedunder vacuum at room temperature. The
samples silylated with chloropropyltrimethoxysilane and
chloromethyltriethoxysilane are designated as SM-41S, SM-
48S, SM-41ES and SM-48ES, respectively. After drying, the si-
Synthetic Procedures
Mesoporous molecular sieves are synthesized following the
[
9]
procedures described earlier with molar gel compositions
of SiO : 0.2 NaOH : 0.27 TMAOH : 0.27 CTABr : 60 H O
2
2
for MCM-41, and 5.0 SiO : 2.5 NaOH : 0.87 CTABr : 0.13
2
Brij30 : 400 H O for MCM-48 respectively. Solvents were dried
2
by standard procedures (THF, with Na/benzophenone ketyl;
þ
lylated samples were treated with 2 mmol of Na
CH Cl with CaH ), distilled under argon and kept over 4 ꢅ
ꢀ
2
2
2
[CpMo(CO)3] salt in 30 mL dry THF under an argon atmos-
molecular sieves. The homogeneous catalysts 1–3 were synthe-
sized as published previously.
phere. The mixture was again stirred for 24 h at 339 K. The in
situ grafted sample was filtered off and the resulting orange sol-
id was washed repeatedly with CH Cl to remove all physisor-
[17]
2
2
bed CpMo salt. The washed samples were dried under vacuum
at room temperature. The samples prepared by the in situ
method are named SM-41SG, SM-48SG, SM-41ESG, and
SM-48ESG.
Synthesis of Complex 1
Microanalyses were performed at the Mikroanalytisches
Laboratorium of the Technische Universitꢁt Mꢀnchen (M.
Barth and co-workers). IR spectra were measured with a Uni-
can Mattson Model 7000 FTIR spectrometer using KBr pellets.
Powder XRD data were collected with a Phillips Xꢄpert diffrac-
tometer using Cu-Ka radiation filtered by Ni. Nitrogen adsorp-
tion-desorption measurements were carried out at 77 K, using a
gravimetric adsorption apparatus equipped with a CI electron-
ic MK2-M5 microbalance and an Edwards Barocel pressure
sensor. Before analysis, calcined MCM-41/48 was degassed at
723 K overnight to a residual pressure of ca. 10–24 mbar. A
lower degassing temperature of 413 K was used for the modi-
fied materials (to minimize destruction of the grafted com-
plex). The specific surface areas (SBET) were determined by
the BET method. The total pore volume (VP) was estimated
from the N uptake at p/p ¼0.95, using the liquid nitrogen den-
Mo(CO) was added to a deep orange solution of sodium (tri-
methoxysilylpropyl)cyclopentadienyl in 30 mLTHF. After re-
fluxing for 18 h, the obtained deep orange solution of the so-
6
dium salt, NaMo(CO) C (CH ) Si(OCH ) H was cooled to
3
5
2
3
3
3
4
room temperature and methyl iodide was then added drop-
wise. After stirring at room temperature for 12 h, the solvent
was removed from the reaction mixture in oil pump vacuum
at room temperature until a sticky, deep brown residue re-
mained. This residue was extracted with n-hexane three times
and the obtained orange red solution chromatographed on Flo-
risil (60–100 mesh) with n-hexane as solvent. The yellow frac-
tion was eluted with n-hexane and diethyl ether (1:1) and col-
lected. After removal of all solvents, compound 1 was obtained
as a brown yellow oil.
The complexes 2 and 3 were synthesized using a solution of
NaMo(CO) C H in 30 mL THF, which was treated with 3-io-
2
0
ꢀ
3
3
5
5
sity of 0.8081 g cm . The pore size distribution curves (PSD,
the differential volume adsorbed with respect to the differen-
tial pore size per unit mass as a function of pore width) were
computed from the desorption branch of the experimental iso-
therms, using a method based on the area of the pore walls.
Transmission electron micrographs (TEM) were recorded on
a JEOL JEM 2010 microscope operated at 120 kV. Thermogra-
vimetric mass spectra analysis (TG-MS) measurements were
conducted with a Netzsch TG209 system; typically about
10 mg of sample were heated from 300 to 1473 K at 10 K
dopropyltrimethoxysilane or iodomethyltriethoxysilane. Af-
ter stirring the reaction mixture at room temperature for
12 h, the solvent was removed in oil pump vacuum at room
temperature until a sticky deep brown residue remained, the
residue was extracted with n-hexane three times and the ob-
tained orange red solution chromatographed on Florisil (60–
100 mesh) with n-hexane as solvent. The yellow fraction was
eluted with n-hexane and diethyl ether (1:1) and collected. Af-
ter removal of all solvents, compounds 2 and 3 were obtained as
brown yellow oils.
ꢀ
1
29
min under argon. Si CP MAS NMR spectra were recorded
Adv. Synth. Catal. 2005, 347, 473–483
asc.wiley-vch.de
ꢂ 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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