Dioxomolybdenum(VI) epoxidation catalyst supported on mesoporous silica containing phosphane oxide groups

Article abstract of DOI:10.1002/ejic.200900918

A new mesoporous hybrid material (denoted LP-TEPPPOMo) has been prepared by tethering [MoO₂Cl₂] onto mesoporous silica previously functionalised with phosphane oxide spacer ligands. The LP-TEPPPO-Mo material was tested in the liquid-phase epoxidation of olefins [cis-cyclooctene, (R)(+)-limonene, trans-2-octene and 1-octene] with tBuOOH, at 55 °C, and without a co-solvent, giving at least 90 % selectivity to the corresponding epoxide at 36-77% conversion: in the case of limonene, regioselectivity favours the epoxidation of the endocyclic double bond, giving mainly 1, 2-epoxy-p-menth-8-ene. The catalytic system based on a liquid-liquid biphasic system containing the homogeneous complex [MoCl₂(O) ₂(OP(CH₂CH₃)(Ph)₂J₂] dissolved in the ionic liquid 1butyl-4-methylpyridinium tetrafluoroborate leads to lower epoxide selectivity (91 % at 64 % conversion) in the reaction of cyclooctene in comparison to that observed for LPTEPPPO-Mo (100% at 87% conversion). The reused solidliquid and liquid-liquid biphasic catalytic systems show partial loss of catalytic activity.

Full text of DOI:10.1002/ejic.200900918

FULL PAPER
DOI: 10.1002/ejic.200900918
Dioxomolybdenum(VI) Epoxidation Catalyst Supported on Mesoporous Silica
Containing Phosphane Oxide Groups
Alichandra Castro,[a] João C. Alonso,[b] Patrícia Neves,[a] Anabela A. Valente,*[a] and
Paula Ferreira*[b]
Keywords: Molybdenum / P ligands / Mesoporous materials / Homogeneous catalysis / Epoxidation / Ionic liquids
A new mesoporous hybrid material (denoted LP-TEPPPO-
menth-8-ene. The catalytic system based on a liquid–liquid
Mo) has been prepared by tethering [MoO2Cl2] onto mesopo- biphasic system containing the homogeneous complex [Mo-
rous silica previously functionalised with phosphane oxide
spacer ligands. The LP-TEPPPO-Mo material was tested in
the liquid-phase epoxidation of olefins [cis-cyclooctene, (R)-
(+)-limonene, trans-2-octene and 1-octene] with tBuOOH, at
55 °C, and without a co-solvent, giving at least 90% selectiv-
ity to the corresponding epoxide at 36–77% conversion: in
the case of limonene, regioselectivity favours the epoxidation
of the endocyclic double bond, giving mainly 1,2-epoxy-p-
Cl2(O)2{OP(CH2CH3)(Ph)2}2] dissolved in the ionic liquid 1-
butyl-4-methylpyridinium tetrafluoroborate leads to lower
epoxide selectivity (91% at 64% conversion) in the reaction
of cyclooctene in comparison to that observed for LP-
TEPPPO-Mo (100% at 87% conversion). The reused solid–
liquid and liquid–liquid biphasic catalytic systems show par-
tial loss of catalytic activity.
Lewis base ligands possessing at least one trialkoxysilyl
pending group, which reacts with the silica surface to form
covalent Si–O–Si bonds. The T-method generally involves
the initial preparation of silica functionalised with N-donor
spacer ligands, followed by ligand exchange of the precur-
sor [MoO2Cl2S2], where S is a solvent molecule (e.g., tetra-
hydrofuran or acetonitrile), with the spacer ligands. In the
case of the T-method, steric constraints and/or diffusion
limitations during the catalyst immobilisation step may be
less important than in the case of the G-method and allow
greater metal loadings to be reached. The coordination
chemistry of MoVI with phosphane oxide and phosphonate
ligands is interesting, as these compounds can be easily syn-
thesised in good yields and are relatively stable under atmo-
spheric conditions.[22–27]
In this work, a new mesostructured hybrid material, de-
noted LP-TEPPPO-Mo, has been prepared via the T-
method, by introducing [MoO2Cl2] into a mesoporous silica
functionalised with phosphane oxide spacer ligands. Merc-
kle and Blümel have previously reported that for the phos-
phane Ph2P(CH2)3Si(OEt)3 (TEPPP) immobilised on dif-
ferent oxide supports (MgO, TiO2, Al2O3 and SiO2), SiO2
is the most favourable support with respect to stability
towards ligand leaching.[28] The LP-TEPPPO-Mo material
was tested as a catalyst in the epoxidation of cis-cyclooc-
tene, (R)-(+)-limonene, trans-2-octene and 1-octene with
tBuOOH, at 55 °C, without a co-solvent. For comparison,
the complex [MoCl2(O)2{OP(CH2CH3)(Ph)2}2] (1) was
tested without a co-solvent or under liquid–liquid biphasic
conditions using an ionic liquid.
Introduction
Heterogeneous catalytic epoxidation is a topic of great
interest in the field of catalysis due to significant industrial
interest.[1–4] In the heterogenisation of homogeneous cata-
lysts for liquid-phase reactions, covalent host–guest interac-
tions are desirable in terms of catalyst stability. The group
of Thiel reported that oxodiperoxomolybdenum(VI) species
supported on mesoporous silicon-containing hybrid materi-
als may possess high stability against leaching of the active
species into the liquid phase during the epoxidation of cy-
clooctene with tert-butyl hydroperoxide (tBuOOH).[5–9]
Molybdenum(VI) complexes possessing the [MoO2Cl2] core
are effective catalysts for the selective epoxidation of olefins
with the use of tBuOOH as the mono-oxygen source[10–18]
and have been supported on ordered mesoporous MCM-41
or MCM-48 supports via two different approaches using
organosilanes: direct grafting (denoted G-method) or teth-
ering (or indirect grafting, denoted T-method).[19–21] The G-
method involves the preparation of complexes of the type
[MoO2Cl2L], where L is one bidentate or two monodentate
[a] Department of Chemistry, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
E-mail: atav@ua.pt
[b] Department of Ceramics and Glass Engineering, CICECO,
University of Aveiro,
3810-193 Aveiro, Portugal
Fax: +351-234401470
E-mail: pcferreira@ua.pt
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900918.
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Dioxomolybdenum Epoxidation Catalyst Supported on Mesoporous Silica
LP-TEPPPO-Mo materials, mainly Qn species can be ob-
Results and Discussion
served (Figure S2, Supporting Information). The Tm 29Si
[Tm = RSi(OSi)m(OH)3–m] environments are not clearly ob-
served (usually in the range –69 to 87 ppm) most likely due
to their low quantity. The 13C CP MAS NMR spectra of
the LP-TEPPPO and LP-TEPPPO-Mo materials (Fig-
ure S3, Supporting Information) display a signal at δ =
130 ppm corresponding to the phenyl group of the phos-
phane ligand, and the resonances at δ = 61.2, 29.2 and
14.0 ppm can be assigned to the methylene groups (in the
order from left to right) in the PCH2CH2CH2Si groups. The
presence of reminiscent ethoxy groups is not clear due to
the possible overlapping of the peaks assigned to these
groups (expectedly δ ≈ 16 and 57 ppm for the CH3 and
CH2, respectively) with the peak at δ = 14.0 ppm (associ-
ated to PCH2CH2CH2Si) and the spinning side band at δ ≈
58.5 ppm. The 31P (CP) MAS spectra of the LP-TEPPPO
and LP-TEPPPO-Mo materials revealed the presence of the
phosphane oxide specie at δ = 39.0 ppm (Figure S4, Sup-
porting Information). A second peak at δ = 22 ppm may be
related to a PV species of the type (EtO)3Si(CH2)3(Ph)2P-
(-O-[SiO2])2 formed in a side reaction of the phosphane pre-
cursor with the silica surface.[30] The phosphorus atom in
these groups is expectedly not available for coordination
with molybdenum and may be located in the vicinity of sur-
face silanol groups, which is supported by the increase in
the relative intensity of the peak at δ = 22 pm relative to
that at δ = 39.0 ppm when cross polarisation is applied.
Hence, the effective P/Mo molar ratio involved in the com-
plexation reaction may be less than 1.8.
Preparation and Characterisation of the Catalysts
Mesostructured LP-TEPPPO-Mo
The supported catalyst LP-TEPPPO-Mo was prepared
from a large pore mesoporous silica (LP) by using the T-
method (Scheme 1). In a first step, phosphane pendant
groups were introduced to the LP by treating the latter with
an excess amount of the (diphenylphosphanyl)propyltrie-
thoxysilane precursor (TEPPP). An oxidising treatment was
applied to transform the surface phosphane groups into
phosphane oxide groups, and finally, the metal precursor
[MoO2Cl2] was introduced. The resultant material, denoted
LP-TEPPPO-Mo, possesses 0.17 mmol/g of Mo and a P/
Mo mol ratio of 1.8.
The powder XRD patterns of the pristine LP, LP-
TEPPPO and LP-TEPPPO-Mo materials (not shown) dis-
play broad diffractions in the range 2θ = 0.5–4°, indicating
poor long-range order. The three materials exhibit irrevers-
ible type IV nitrogen adsorption–desorption isotherms
(characteristic of mesoporous solids) with capillary conden-
sation steps in the relative pressure range of 0.65–0.84 (Fig-
ure S1, Supporting Information). The grafting of organosil-
ane onto LP leads to a significant decrease in SBET and
Vp. On the basis of the estimated van der Waals molecular
volume for TEPPPO (ca. 400 Å3)[29] one could expect a Vp
value of ca. 1.59 cm3 g–1 for LP-TEPPPO, which is slightly
higher than the value calculated from the nitrogen isotherm
(1.33 cm3 g–1; Table S1, Supporting Information). Possibly a
fraction of the organic ligands is located at the pore en-
trances, leading to partial pore blockage. Upon treatment
of LP-TEPPPO with [MoO2Cl2], the values of SBET and Vp
further decrease, albeit to a smaller extent than that ob-
served for the organosilane grafting step. The pore-size dis-
Catalytic Epoxidation of Olefins
The catalytic performance of LP-TEPPPO-Mo was in-
tribution curves are rather broad with a maximum (dp) at vestigated in the epoxidation of cis-cyclooctene with
ca. 11.5 nm, which is consistent with the XRD data.
tBuOOH, at 55 °C, without a co-solvent. Control experi-
The 29Si CP MAS and MAS NMR spectra of the pristine ments were performed by using LP or LP-TEPPPO (with-
LP material (not shown) display the typical Qn resonances out Mo): LP gives 5% conversion after 24 h and cyclo-
[Qn = Si(OSi)n(OH)4–n] of a pure silica material. In the 29Si octene oxide is the only product, whereas LP-TEPPPO
CP MAS and MAS NMR spectra of the LP-TEPPPO and gives 29% conversion at 24 h with 61% epoxide selectivity
Scheme 1. Preparation of LP-TEPPPO-Mo by using the T-method.
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A. Castro, J. C. Alonso, P. Neves, A. A. Valente, P. Ferreira
To assess the homo/heterogeneous nature of the catalytic
FULL PAPER
(cyclooctane-1,2-diol was the only byproduct; Table 1). The
LP-TEPPPO-Mo catalyst leads to significant improvements reaction in the presence of LP-TEPPPO-Mo, a leaching test
in the reaction rate and epoxide selectivity in relation to was performed by filtering off the reaction solution after
those of LP-TEPPPO: the initial TOF calculated for a 30 min through a 0.2 µm PVDF w/GMF Whatman mem-
–1
10 min reaction is 648 molmol
h
and after 24 h conver- brane, at 55 °C, and leaving it to react for 150 min. No in-
Mo
sion reaches 87% with 100% epoxide selectivity. In the case crease in olefin conversion was observed after the filtration
of complex 1, the initial TOF is 519 molmolMo h–1, which step, in contrast to that observed in the presence of LP-
is comparable to that observed for LP-TEPPPO-Mo, and TEPPPO-Mo, suggesting that the catalytic reaction is
quantitative epoxide yield is reached at 24 h. For complex heterogeneous in nature. The FTIR spectra of fresh and
1 and LP-TEPPPO-Mo, iodometric titrations indicated that recovered solids were identical (not shown). The LP-
tBuOOH is essentially consumed in the olefin epoxidation TEPPPO-Mo was reused twice at 55 °C (Figure 1). Epoxide
process. The epoxide yields at 24 h are comparable with selectivity is always 100%, although the catalytic activity
those reported in the literature for several micelle-templated decreases in consecutive runs: conversion at 24 h is 87, 77
mesoporous silica-supported complexes of the type and 73% for runs 1, 2 and 3, respectively. After the recycl-
[MoO2Cl2L] or [CpMo(CO)3(X)] (Cp = cyclopentadienyl li- ing runs, the solid was separated from the reaction mixture
gand; X = methyl, siloxane) possessing a –Si(OEt)3 moiety by centrifugation, thoroughly washed with n-hexane and
on the L, Cp or X ligand.[7] The kinetic curve for LP- dried at room temperature overnight. ICP-AES analyses
TEPPPO-Mo is comparable to that of MCM-41-supported (experimental error of 5%) of the recovered solid indicated
[MoO(O)2L] complexes, used as a catalyst in the same reac- reductions in the initial P and Mo contents (mmolg–1) of
tion.[8,9]
16 and 17%, respectively. These results together with those
The LP-TEPPPO-Mo catalyst was further tested in the obtained for the leaching test, suggest that the leached spe-
reactions of (R)-(+)-limonene, 1-octene and trans-2-octene cies are inactive and/or leaching of active species does not
with tBuOOH, at 55 °C, without a co-solvent (Table 1). A occur to a measurable extent in the initial stage (at least
comparative study for 1-octene and trans-2-octene indicates 30 min) of the catalytic reaction. On the basis of the charac-
that the latter substrate is more reactive than the former terisation studies, the LP-TEPPPO-Mo material may pos-
(epoxide yield at 4 h is 9 and 45% for 1-octene and 2- sess a diversity of surface species because (i) grafting of the
octene, respectively). These results suggest that more-substi- organosilane precursor onto the mesoporous silica may give
tuted (electron richer) olefins tend to be more reactive than mono-, di- and tripodal surface species; (ii) molybdenum
less-substituted ones, which is congruent with the mechan- species with different Mo/P mol ratios may be formed;
istic considerations reported in the literature for the epoxid- (iii) the molybdenum precursor may react with surface or-
ation of olefins with tBuOOH in the presence of pseudo- ganosilane groups or with silanols to give species that are
octahedral complexes possessing the [MoO2]2+ moiety and susceptible to metal leaching.[36] Leaching of Mo and P may
organic Lewis base N,O,S ligands,[31–34] and for Mimoun- be attributed to certain populations of the respective sur-
type peroxo complexes of the type [MoO(O2)2{OP(CH3)3}] face species.
(R = H, alkyl).[35] The reaction of (R)-(+)-limonene gives
Merckle and Blümel have previously reported that
mainly 1,2-epoxy-p-menth-8-ene (denoted P1) formed in TEPPP immobilised on silica surfaces may be partially de-
72% yield at 4 h: byproducts include mainly 1,2–8,9-diep- tached in polar/protic medium.[28] The group of Thiel re-
oxy-p-menthane (P2), p-menta-1,8-dien-7-ol and 4-isopro- ported for molybdenum(VI) complexes supported on sili-
pyl-1-methylcyclohexane-1,2-diol. The molar ratio P1/P2 at con-containing materials that catalyst stability towards
90% conversion (at 24 h reaction) is 5.7, indicating that re- leaching phenomena may be improved by (i) decreasing the
gioselectivity favours the epoxidation of the endocyclic C1– concentration of surface silanol groups (with concomitant
C2 double bond.
increase in the surface hydrophobicity) by silanisation[8,9] or
Table 1. Reaction of olefins with tBuOOH in the presence of complex 1 or LP-TEPPPO-Mo at 55 °C.
Olefin
Catalyst
Conversion[a] (%)
Epoxide selectivity[b] (%)
cis-Cyclooctene
LP-TEPPPO-Mo
57/87
(39/77)[c]
20/29
–/5
100/100
(100/100)[c]
61/61
LP-TEPPPO
LP
–/100
Complex 1
96/100
52/64
(36/67)[c]
77/90
9/36
100/100
91/91
Complex 1/[BMPy][BF4]
(100/100)[c]
90/80[d]
100/100
100/100
(R)-(+)-Limonene
1-Octene
trans-2-Octene
LP-TEPPPO-Mo
LP-TEPPPO-Mo
LP-TEPPPO-Mo
45/65
[a] Olefin conversion at 4 h/24 h without a co-solvent unless specified in the “Catalyst” column. [b] Selectivity to the corresponding
epoxide at 4 h/24 h (1,2-epoxy-p-menth-8-ene in the case of limonene). [c] Catalytic results for the second reaction run. [d] Byproducts
include 1,2–8,9-diepoxy-p-menthane formed in 2%/14% selectivity at 4 h/24 h, respectively.
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Dioxomolybdenum Epoxidation Catalyst Supported on Mesoporous Silica
amount of active species are different in the two runs and/
or a fraction of active metal species is extracted with the
products in the workup procedures.
Conclusions
A
mesostructured hybrid material (denoted LP-
TEPPPO-Mo) has been prepared by introducing [MoO2Cl2]
into a mesoporous silica functionalised with phosphane ox-
ide spacer ligands. The hybrid support (LP-TEPPPO) pos-
sesses mainly two types of P species: phosphane oxide pen-
dant groups of the type Si(CH2)3(Ph)2P=O and possibly
(EtO)3Si(CH2)3(Ph)2P(-O-[SiO2])2. The latter are expectedly
not available for complexation with the molybdenum(VI)
precursor. The LP-TEPPPO-Mo material was tested as a
catalyst in the liquid-phase epoxidation of olefins [cis-cyclo-
octene, (R)-(+)-limonene, trans-2-octene and 1-octene] with
tBuOOH at 55 °C and without a co-solvent: the respective
epoxides were obtained in relatively high yields (e.g., 72%
1,2-epoxy-p-menth-8-ene in the limonene reaction at 24 h
with regioselectivity favouring the epoxidation of the endo-
cyclic double bond). A disadvantage of this catalyst is the
occurrence of Mo and P leaching during catalysis and a
concomitant decrease in catalytic activity in recycling runs.
These results may be related to the presence of a diversity
of surface groups in LP-TEPPPO-Mo. Improvements in
catalyst stability may be accomplished by preparing a uni-
form, single-site mesostructured catalyst using alternative
synthesis methodologies, such as organosilane templated-
co-condensation of TEPPP with another organic precursor
in an attempt to improve the dispersion and stability of the
P surface groups towards leaching and minimise the
amount of silanol groups (reactive with the metal precursor
to give different metal species that are susceptible to leach-
ing[36]).
Figure 1. Reaction of cis-cyclooctene with tBuOOH at 55 °C with-
out co-solvent in the presence of complex 1 (᭺), LP-TEPPPO (ᮀ),
LP-TEPPPO-Mo [run 1 (+); run 2 (–)] or using the complex 1/
[BMPy][BF4] liquid–liquid biphasic system [run 1 (∆); run 2 (ϫ)].
(ii) preparing hybrid mesoporous materials by the co-con-
densation of an organosilane (ligand) precursor with silica
reagents (e.g., tetraalkoxysilanes).[5,6]
An alternative approach for facilitating the recycling of
the homogeneous catalysts is to dissolve the complex in an
appropriate ionic liquid (IL) to give a biphasic liquid–liquid
(L-L) system where the catalyst is dissolved in the IL phase.
The catalytic performance of complex 1 was further investi-
gated in the reaction of cis-cyclooctene with tBuOOH by
using the IL 1-butyl-4-methylpyridinium tetrafluoroborate
([BMPy][BF4]) at 55 °C. The choice of this IL resides in
the fact that it is (i) readily available and relatively cheap,
(ii) dissolves the metal complex and (iii) although it solu-
bilises tBuOOH, it is immiscible with the olefin. Under
these reaction conditions, the main product is cyclooctene
oxide and cyclooctane-1,2-diol is the only byproduct, which
is most likely formed through ring opening of the epoxide:
although epoxide selectivity decreases from 100% at 29%
conversion to 91% at 44–64% conversion, selectivity to the
diol increases proportionally. The reaction is slower (initial
TOF = 120 molmolMo h–1; conversion at 24 h = 64%) and
less selective to the epoxide than that observed for complex
1 without a co-solvent (initial TOF = 519 molmolMo h–1;
100% epoxide yield at 24 h), under similar reaction condi-
tions (Table 1, Figure 1). Possibly mass transfer limitations
exist in the case of the biphasic L-L system and/or the na-
ture of the active metal species present in the ionic and neu-
tral reaction media are different.
The catalytic system based on a liquid–liquid biphasic
system containing the homogeneous complex [MoCl2(O)2-
{OP(CH2CH3)(Ph)2}2] dissolved in the ionic liquid 1-butyl-
4-methylpyridinium tetrafluoroborate and used in the reac-
tion of cyclooctene does not lead to major improvements
in terms of catalyst recyclability and epoxide selectivity is
lower in comparison to that observed for LP-TEPPPO-Mo.
Experimental Section
Materials and Characterisation Techniques: Starting reagents were
acquired from Aldrich and commercially dried solvents from Acros
Organics and used as received. The catalysts were prepared by
using standard Schlenk techniques under a nitrogen atmosphere.
The products of the cyclooctene reaction were extracted
after a 24 h-run by using n-hexane (immiscible with the IL),
and the resulting catalyst/[BMPy][BF4] mixture was reused
in a second run. The olefin and oxidant were added to the
catalyst/[BMPy][BF4] mixture in the same amounts as those
used for the first run, and the reaction was monitored for
24 h at 55 °C. In contrast to that observed for the first run,
in the second run the epoxide is the only product until 68%
conversion (reached at 24 h; Table 1, Figure 1). The reac-
tion is slower in the second run, although the conversion
Powder X-ray diffraction (PXRD) data were collected with a Phil-
ips XЈPert MPD diffractometer (Cu-Kα X-radiation,
λ =
1.54060 Å) fitted with a graphite monochromator and a flat plate
sample holder, in a Bragg–Brentano para-focusing optics configu-
ration. Samples were step-scanned in 0.02° 2θ steps with a counting
time of 2 s per step. Nitrogen adsorption isotherms at –196 °C were
measured by using a Gemini 2375 Micromeritics Instrument (Eng.
M. C. Costa, University of Aveiro). The mesostructured materials
after 24 h is similar for both runs. Possibly, the nature and were pretreated at 150 °C prior to analysis. Microanalyses for C
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A. Castro, J. C. Alonso, P. Neves, A. A. Valente, P. Ferreira
FULL PAPER
and H were carried out at the Department of Chemistry, University
of Aveiro (M. M. Marques). The P and Mo contents were deter-
mined by ICP-AES at the Central Laboratory for Analysis, Univer-
sity of Aveiro (L. Carvalho). Infrared spectra (KBr pellets) were
measured by using a Mattson 7000 FT spectrometer. 13C, 29Si and
31P solid-state NMR spectra were recorded at 100.62, 79.49 and
161.98 MHz, respectively, with a (9.4-T) Bruker Avance 400P spec-
trometer. 29Si MAS NMR spectra were recorded with 40° pulses,
spinning rates 5.0–5.5 kHz and 60-s recycle delays. 29Si CP MAS
NMR spectra were recorded with 4-µs 1H 90° pulses, 8 ms contact
time, a spinning rate of 5 kHz and 4-s recycle delays. For 31P MAS
NMR spectra were recorded with 45° pulses, spinning rate of
15 kHz, 1H decoupling and a 60 s recycle delay. Chemical shifts are
quoted in parts per million from phosphoric acid (85%). 13C CP
MAS NMR spectra were recorded with 4.5-µs 1H 90° pulses, 2 ms
contact time, a spinning rate of 7 kHz and 4-s recycle delays. Chem-
ical shifts are quoted in ppm from TMS. 13C spectra were also
recorded in the solid state at 125.76 MHz with a Bruker Avance
500 spectrometer.
from TMS): δ = 130 (Ph), 61.2 (P-CH2-), 29.2 (-CH2CH2CH2-),
14.0 (-CH2Si) ppm. 31P (CP) MAS NMR (ppm from H3PO4, 85%):
δ = 39 [(Ph)2P(O)(CH2)3SiϵO-(SiO2)], 22 {(EtO)3Si(CH2)3(Ph)2P-
[-O-(SiO2)]2} ppm.
For anchoring the [MoO2Cl2] complex, a solution of [MoO2Cl2]
(0.0601 g, 3.022ϫ10–4 mol) dissolved in dichloromethane (5 mL)
was added to LP-TEPPPO (0.186 g), and the mixture was stirred
overnight at room temperature. The light-green solid in suspension
was separated by filtration, washed with dichloromethane and
dried in vacuo, giving LP-TEPPPO-Mo (0.17 mmol/g of Mo and a
P/Mo mol ratio of 1.8). 29Si (CP) MAS NMR (ppm from TMS): δ
= –91.2, –102.6 (br., Q3), –111.2 (br., Q4) ppm. 13C CP MAS NMR
(ppm from TMS): δ = 130 (Ph), 61.2 (P-CH2-), 29.2 (-CH2CH2-
CH2-), 14.0 (-CH2Si) ppm. 31P (CP) MAS NMR (ppm from
H3PO4, 85%): δ = 39 {(Ph)2P(O)(CH2)3SiϵO-[SiO2]}, 22 {(EtO)3-
Si(CH2)3(Ph)2P[-O-(SiO2)]2}.
Catalytic Reactions: The liquid-phase olefin epoxidation reactions
were carried out in air and autogenous pressure, in batch microre-
actors equipped with a magnetic stirrer and a sampling valve, and
immersed in an oil bath heated at 55 °C. Typically, the reaction
vessels were loaded with the olefin (1.8 mmol), tBuOOH (5.5  in
decane; 2.75 mmol) and complex 1 (18 µmol) or LP-TEPPPO-Mo
(4.8 mg, 4.3 µmol Mo). The reactions were carried out without a
co-solvent in the case of LP-TEPPPO-Mo and complex 1 or by
using the ionic liquid 1-butyl-4-methylpyridinium tetrafluoroborate
([BMPy][BF4], 0.1 mL) in the case of complex 1.
Preparation of the Catalysts
[MoCl2(O)2{OP(CH2CH3)(Ph)2}2] (1): Complex 1 was synthesised
by following a procedure similar to that described in the literature
by Hursthouse et al.:[37] Ethyldiphenylphosphane oxide (0.500 g,
2.17 mmol) was added to [MoO2Cl2] (0.200 g, 1.00 mmol) in
dichloromethane (5 mL), under a nitrogen atmosphere. The solu-
tion was stirred for 2 h and then left at 5 °C for 8 d, giving a solid
containing colourless transparent crystals (yield: 99%). The solid
was separated by filtration, washed with n-hexane and dried at
room temperature. C28H30Cl2MoO4P2 (659.33): calcd. C 51.01, H
4.59; found C 50.28, H 4.66. 1H NMR (300 MHz, CDCl3, room
temperature): δ = 7.30–7.76 (m, 10 H, Ph), 2.45 (9, 3JH,H = 6.00 Hz,
The course of the reactions was monitored by using a Varian 3900
GC equipped with a capillary column (SPB-5, 20 mϫ0.25 mm)
and a flame ionisation detector. For quantification of the products,
nonane or undecane were used as internal standards added after
the reaction. The reaction products were identified by GC–MS
[Trace GC 2000 Series (Thermo Quest CE Instruments) – DSQ II
(Thermo Scientific)], using He as the carrier gas.
3
4 H, PCH2-), 1.13 (t, JH,H = 6.00 Hz, 6 H, -CH2CH3) ppm. 31P
NMR (300 MHz, CDCl3, room temperature): δ = 49 ppm. IR (KBr
pellets): ν = 901, 944 (νMo=O); 1173, 1146 (νP=O); 321 (νMo–Cl); 3057
˜
Supporting Information (see footnote on the first page of this arti-
cle): Parameters for the LP related materials; nitrogen adsorption–
desorption isotherms and pore-size distribution curves for LP, LP-
TEPPPO and LP-TEPPPO-Mo; 29Si CP MAS and MAS NMR
spectra of LP-TEPPPO and LP-TEPPPO-Mo; 13C CP MAS NMR
spectra of LP-TEPPPO and LP-TEPPPO-Mo; 31P CP MAS and
MAS NMR spectra of LP-TEPPPO HM and LP-TEPPPO-Mo.
[ν(C–H)Ph]; 1232–1482 [ν(C–C)Ph]; 1238 [δp(CH)]; 1030 [νs(CC)]; 719
[δop(CH)] cm–1.
Mesoporous Silica-Supported Molybdenum(VI) Complex (LP-
TEPPPO-Mo): The (diphenylphosphanyl)propyltriethoxysilane
precursor (TEPPP) was prepared by a modified literature pro-
cedure:[38,39] Potassium diphenylphosphide (0.5  in THF, 20 mL)
was added dropwise to a solution of 1-chloro-3-(triethoxysilyl)pro-
pane (2.40 mL, 0.01 mol) in THF (20 mL). The mixture was stirred
for 3 h at 15 °C and left at room temperature overnight. The Acknowledgments
workup of the reactions consisted of the evaporation of THF, ad-
dition of pentane to precipitate the salt and dissolution of the prod-
ucts. After filtration and evaporation of pentane, the resulting yel-
low oil was distilled under reduced pressure (1 Torr) at 240 °C. H
The authors are grateful to Programa Operacional Ciência e In-
ovação – 2010, Fundo Europeu de Desenvolvimento Regional and
Fundação para a Ciência e a Tecnologia for financial support
(POCI/CTM/ 55648/2004 and PPCDT/CTM/55648/2004). The au-
thors wish to express their gratitude to Doctors Ana S. Dias and
Martyn Pillinger (Centre for research in ceramics and composite
materials – CICECO) for supplying the LP silica.
1
NMR (300 MHz, CDCl3, room temperature): δ = 7.20–7.33 (m, 10
3
3
H, Ph), 3.79 (q, JH,H = 7.06 Hz, 6 H, OCH2CH3), 2.06 (t, JH,H
= 7.70 Hz, 2 H, PCH2-), 1.44–1.57 (m, 2 H, CH2CH2CH2), 1.10 (t,
3JH,H = 7.06 Hz, 9 H, OCH2CH3), 0.74 (t, JH,H = 7.93 Hz, 2 H,
3
-CH2Si) ppm. 31P NMR (300 MHz, CDCl3, room temperature): δ
= –16.8 ppm. IR (KBr pellets): ν = 3051 [ν(C–H)Ph], 1363–1481
˜
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Received: September 15, 2009
Published Online: December 14, 2009
Eur. J. Inorg. Chem. 2010, 602–607
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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