1
88
J. Pastva et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 184–192
Table 3
in Table 4. For substrate/Ru molar ratio = 100, RCM of 1,7-octadiene
proceeded smoothly giving high conversions even at low reac-
a
XPS binding energies (± 0.2 eV) for complexes and catalysts used.
◦
◦
Sample
Ru 3d5/2
C 1s
Cl 2p
P 2s
tion temperatures (84% at 0 C and 98% at 30 C). On the other
◦
hand, RCM of DEDAM required reaction temperature 80 C to
II
281.2
–
280.4
284.8
284.8
284.8
198.2
–
198.3
188.5
189.7
189.5
SBA-15 modified
II/SBA-15
obtain 90% conversion. Selectivity in all RCM reactions was very
high (95–100%, see Table 4). The products of cycloisomerization
a
(diethyl
3-methyl-4-methylenecyclopentane-1,1-dicarboxylate
The line C 1s (284.8 eV) was used as a reference for spectra calibration.
for DEDAM, 1-(trifluoroacetyl)-3-methyl-4-methylenepyrrolidine
for DAF) were observed as the only side products. The side product
of RCM of DAC was not identified.
the majority of P is in the phosphine state being able to react with
Ru alkylidene by phosphine ligand exchange.
In metathesis of 1-decene, 5-hexenyl acetate, and methyl 10-
undecenoate lower conversions were reached (57%, 77%, and 64%,
respectively). As ethylene was removed from the reaction mix-
ture, higher conversions were expected. It should be noticed that
approximately the same incomplete conversions were achieved
for these three substrates using II as a homogeneous catalyst
under same reaction conditions (see conversion curves in Sup-
porting Information, Figs. S6–S8). The shape of conversion curves
for II shows a strong retardation of the reactions at prolonged
reaction times suggesting a gradual catalyst deactivation. The
inherent deactivation of Hoveyda–Grubbs catalyst was described
and reaction mechanisms were outlined [3,49,50]. As concerns
selectivity, double bond shift isomerization followed by cross-
metathesis is responsible for the formation of small amounts of
side products (heptadecene, 1,9-diacetoxynonene, dimethyl 1,19-
nonadecenedioate for metathesis of 1-decene, 5-hexenyl acetate
and 10-undecenoate, respectively). In cross-metathesis of DAB
with AllB a 1.5-fold excess of DAB was used to reduce the homo-
metathesis of AllB to 1,4-diphenyl-2-butene (Scheme 3). With
II/SBA-15, AllB and DAB conversions achieved (33% and 23%,
respectively) are lower in comparison with the homogeneous
experiment (53% for AllB and 33% for DAB; see Supporting Informa-
tion, Fig. S9). However, the selectivity for cross-metathesis product
was approximately the same (79% for II/SBA-15 and 81% for II).
The main by-product was formed by homometathesis of allyl-
benzene (1,4-diphenyl-2-butene). In ROMP of COE (COE/Ru molar
ratio = 500), catalyst II/SBA-15 provided high molecular weight
The results of the immobilization of Ru complex II on the
modified sieves (see Scheme 2) are described in Table 1. The cata-
lysts labeled according the support used as II/SBA-15, II/MCM-48,
II/SBA-16, and II/MCM-41 were prepared. The immobilization was
not quantitative under the conditions applied and the fractions
of Ru captured on the sieves (f) differed according to the sieve
architecture – the highest being for hexagonal SBA-15 and MCM-
4
1 (0.83, 0.82, respectively) and the lowest for cubic cage-like
SBA-16 (0.48). As a result, different amounts of II had to be used
for obtaining the catalyst of the approximately same Ru loadings
(
1 wt.%). XRD as well as nitrogen adsorption measurements con-
firmed that the support structure was preserved in all catalysts (see
Supporting Information, Figs. S4 and S5). The textural parameters
of catalysts are compared with those of parent and/or P modified
supports in Table 2. As expected, the introduction of organic linkers
into the pores of supports resulted in decreased nitrogen adsorp-
tion capacity. It is reflected by significantly lower SBET values and
reduced pore volumes as compared with the parent supports (see
Table 2). Subsequent immobilization of complex II led only to small
changes in textural parameters, because of a low amount of com-
plex introduced (Table 2). For catalyst function it is important that
the changes of average pore diameter are rather small (for SBA-15
and MCM-41 nearly negligible).
The XPS results are in agreement with II immobilized accord-
ing to Scheme 2. The stoichiometry for SBA-15 modified with
P linkers and for catalyst II/SBA-15 calculated from XPS were
Si1.0O1.97P0.042C0.92 and Si1.0O1.95Ru0.008Cl0.015P0.046C0.99, respec-
tively. The Ru/P ratio shows the excess of P indicating that only
about 20% of P linkers participated in the Ru immobilization. Si/P
ratios for modified support and catalyst should be the same accord-
ing to Scheme 2. A slight increase in P concentration in catalyst
might be connected with a partial trapping of liberated PCy3 in the
sieves as it was recently described [47]. The XPS binding energies
for complexes II, SBA-15 modified support and catalyst II/SBA-15
are provided in Table 3. Binding energies for complex II are in agree-
ment with the values of Jarzembska et al. [48] (taking into account
the difference in values of C1s binding energy used for spectra cal-
ibration). The increase in the binding energy of P 2s and P 2p for
II/SBA-15 in comparison with II can be ascribed to the dominating
contribution of free P linkers in II/SBA-15. A lower value of binding
energy of Ru 3d5/2 electrons in II/SBA-15 in comparison with that in
the free complex II may be connected with the changes in geometry
of Ru coordination sphere as a result of the immobilization. Similar
changes have already been observed for the immobilization of I on
mesoporous molecular sieves via phosphine ligand exchange [38].
polymer (Mw = 160,000, M = 84,000) in 74% yield.
n
Fig. 4a and b shows conversion curves of RCM of 1,7-octadiene
with homogeneous catalyst II and heterogeneous catalysts II/SBA-
◦
1
(
5, II/MCM-48, II/SBA-16, and II/MCM-41 in toluene at 0 C
◦ ◦
Fig. 4a) and 30 C (Fig. 4b). At 0 C a strong increase in
initial reaction rates (expressed by TOF30 and TOF5 values,
−1
respectively) in the order II/MCM-41 (TOF30 = 0.002 s ) ≤ II/SBA-
−1
−1
1
6 (TOF30 = 0.004 s ) < II/MCM-48 (TOF = 0.010 s ) ≤ II/SBA-15
30
−1 −1
(
TOF30 = 0.012 s ) < II (TOF5 = 0.143 s ) was observed. Conversion
values achieved after 5 h reaction increased in the same way. This
may reflect the influence of diffusion rate in catalyst pores on the
initiation and/or propagation step of the catalytic process. Raising
◦
the temperature to 30 C reaction rates of all catalysts increased
considerably and the differences between individual heteroge-
neous catalysts was suppressed. Although the initial reaction rates
−1
of heterogeneous catalysts (TOF30 = 0.030 s ) remained lower than
−1
that of II (TOF5 = 0.290 s ), the conversion after 5 h is the same for
all catalyst (98%).
The effect of support pore size on catalyst activity has already
been observed [17,19]. As concerns immobilized Ru alkylidenes, the
increasing activity with increasing pore size was found for RCM of
citronellene [24] and for metathesis of methyl oleate [38]. In addi-
tion, three-dimensional pore systems (MCM-48, SBA-16) can be
more advantageous for molecular diffusion than one-dimensional
channel-like pore systems (MCM-41 and SBA-15) [51]. Locating
Hoveyda–Grubbs alkylidene into confined space of cage-like sys-
tem contributed to catalyst stability and prolonged its life time
[25]. In our case, the pore size seems to be decisive. For SBA-16 the
entrance diameter (4.7 nm) is more important for catalyst activity
3.2. Catalytic activity
The catalytic activity was tested in (i) RCM of 1,7-octadiene,
diethyl
trifluoroacetamide (DAF), and tert-butyl N,N-diallylcarbamate
DAC), (ii) metathesis of 1-decene, 5-hexenyl acetate, and methyl
diallylmalonate
(DEDAM),
N,N-diallyl-2,2,2-
(
1
2
0-undecenoate, (iii) cross-metathesis of cis-1,4-diacetoxy-
-butene (DAB) with allylbenzene (AllB), and (iv) ROMP of
cyclooctene. The results achieved with II/SBA-15 are summarized