Pillar5arenes as Supramolecular Hosts in Aqueous Biphasic Rhodium-Catalyzed Hydroformylation of Long Alkyl-chain Alkenes

Article abstract of DOI:10.1002/cctc.201801551

Aqueous biphasic catalysis continues to attract strong interest, especially when very hydrophobic substrates are concerned. Indeed, their insolubility in water strongly limit their transformation by water-soluble organometallic catalysts. To improve contacts between the substrate-containing organic phase and the catalyst-containing phase, one of the best solutions consists in using interfacial additives capable of supramolecularly recognize the substrate and/or the catalyst. In the present study, modified pillar5arenes are considered as interfacial additives and their performance is assessed in Rh-catalyzed hydroformylation of long alkyl-chain alkenes (higher olefins). Pillar5arenes substituted by carboxylate functions and methyl groups P5 A-(Me)_10-x-(CH₂COOMe)_x are compared to pillar5arenes substituted by polyethylene glycol (PEG) chains (P5 A-(Me)₅-(PEG)₅ and P5 A-(PEG)₁₀). Utilization of P5 A-(Me)_10-x-(CH₂COOMe)_x leads to high conversion and regioselectivity (linear/branched aldehyde ratio) in Rh-catalyzed hydroformylation of 1-decene and 1-hexadecene. Compared with other interfacial additives such as modified cyclodextrins, the studied pillar5arenes show lower chemo-selectivity, similar catalytic activity and higher regioselectivity.

Full text of DOI:10.1002/cctc.201801551

Accepted Article
Title: Pillar[5]arenes as supramolecular hosts in aqueous biphasic
rhodium-catalyzed hydroformylation of long alkyl-chain alkenes
Authors: Missipssa Benatmane, Kévin Cousin, Nérimel Laggoune,
Stéphane Menuel, Eric Monflier, Patrice Woisel, Frederic
Hapiot, and Jonathan Potier
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ChemCatChem
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Pillar[5]arenes as supramolecular hosts in aqueous biphasic
rhodium-catalyzed hydroformylation of long alkyl-chain alkenes
[
a]
[b]
[a]
[b]
[b]
Missipssa Benatmane, Kévin Cousin, Nérimel Laggoune, Stéphane Menuel, Eric Monflier,
[
a]
[b]
[a]
Patrice Woisel, Frédéric Hapiot* and Jonathan Potier*
Abstract: Aqueous biphasic catalysis continues to attract strong
interest, especially when very hydrophobic substrates are concerned.
Indeed, their insolubility in water strongly limit their transformation by
water-soluble organometallic catalysts. To improve contacts between
the substrate-containing organic phase and the catalyst-containing
phase, one of the best solutions consists in using interfacial additives
capable of supramolecularly recognize the substrate and/or the
catalyst. In the present study, modified pillar[5]arenes are considered
as interfacial additives and their performance is assessed in Rh-
interface.10,11 Once the catalytic process is complete, the product
is release in the organic phase and another substrate molecule
gets into the host cavity. The concept has been widely exploited
with cyclodextrins12,13 (CDs), calixarenes14,15,16 or cucurbiturils17
as supramolecular hosts in various organometallic reactions,
such as hydroformylation, carbon-carbon coupling, and cleavage
of carbonates or urethanes (Tsuji-Trost reaction), to name only a
few. It occurred to us that pillararenes, that consist of
hydroquinone moieties linked together by methylene groups
catalyzed hydroformylation of long alkyl-chain alkenes (higher olefins). (Figure 1),18 , 19 could also be good candidates to molecularly
Pillar[5]arenes substituted by carboxylate functions and methyl
groups P5A-(Me)10-x-(CH COOMe) are compared to pillar[5]arenes
substituted by polyethylene glycol (PEG) chains (P5A-(Me) -(PEG)
and P5A-(PEG)10). Utilization of P5A-(Me)10-x-(CH COOMe) leads to
recognize organic substrates. Contrary to CDs and similarly to
calix[n]arenes, their external surface is not hydrophilic and
2
x
5
5
chemical modifications are required to increase their solubility in
water.2
0,21
Hence, how well the pillararenes will be substituted will
2
x
high conversion and regioselectivity (linear/branched aldehyde ratio)
in Rh-catalyzed hydroformylation of 1-decene and 1-hexadecene.
Compared with other interfacial additives such as modified
cyclodextrins, the studied pillar[5]arenes show lower chemo-
selectivity, similar catalytic activity and higher regioselectivity.
play a huge role in determining their ability to adsorb at the
aqueous/organic interface and subsequently interact with the
substrate.
Introduction
Figure 1. Structure of a) cyclodextrins, b) calixarenes, and c) pillararenes.
The interest of chemists in Supramolecular Catalysis has recently
been illustrated by reference publications. 1 , 2 , 3 Nowadays,
countless examples support the efficacy of catalytic systems
whose cohesion is ensured by weak interactions. Among them,
Astonishingly, there are less than a handful of reports on the use
of pillararenes in organometallic catalysis. 22 , 23 , 24 To our
knowledge, nothing has been reported so far on the use of
pillararenes in aqueous biphasic catalysis. Herein is described the
synthesis of water soluble pillar[5]arenes appropriately modified
by both methyl and carboxyl groups or polyethylene glycol (PEG)
chains. Their catalytic performance was assessed in Rh-
catalyzed hydroformylation of higher olefins, a model reaction of
industrial significance 25 that has been widely studied under
biphasic conditions.26 We show below that water soluble modified
pillar[5]arenes are very efficient in this regards as they display
excellent catalytic activity and better regioselectivity than CDs.
We especially show that the number and the nature of the
substituents should be accurately controlled and that the
pillar[5]arene’s cavity remains accessible to host higher olefins
and favor their conversion into aldehydes at the aqueous/organic
interface.
4
5,6
those based on hydrogen bonding and coordination chemistry
are the most popular, but systems based on other types of
attractive interactions (ion-dipole, 7 electrostatic 8 or ionic
9
hydrogen bond ) also proved to be successful to design effective
catalysts. Of interest, catalytic systems that make use of
hydrophobic effects proved to be especially suitable for the
conversion of hydrophobic substrates under aqueous biphasic
conditions. For example, appropriate hydrophobic substrates may
enter into the cavity of supramolecular receptors, and favor
contacts with the organometallic catalyst at the aqueous/organic
[
[
a]
b]
M. Benatmane, Dr. N. Laggoune, Prof. P. Woisel, Dr. J. Potier
Univ. Lille, CNRS, INRA, ENSCL, UMR 8207 – UMET – Unité
Matériaux et Transformations, F-59000 Lille, France. E-mail:
jonathan.potier@univ-lille.fr
K. Cousin, Dr. S. Menuel, Prof. E. Monflier, Prof. F. Hapiot
Univ. Artois, CNRS, Centrale Lille, ENSCL, Univ. Lille, UMR 8181,
Unité de Catalyse et de Chimie du Solide (UCCS), F-62300 Lens,
France.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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ChemCatChem
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Results and Discussion
pillar[5]arenes being insoluble in water, substitution of their
macrocyclic structure by hydrophilic groups is required. Three
different water soluble pillar[5]arenes were synthesized and
compared in the present study.
Synthesis of modified pillar[5]arenes
Pillar[5]arenes are chosen as potentially interesting molecular
receptors because the size of their cavity can advantageously
accommodate the linear alkyl chain of higher olefins.21 However,
2 x 3 2 3 3 2 3
Scheme 1. Synthesis of water soluble pillar[5]arenes P5A-(Me)10-x-(CH COONa) . R = H or CH . R’ = CH COOCH or CH . R’’= CH COONa or CH .
1
Figure 2. MALDI-TOF (a) and H NMR spectra (D
2
O, 25 °C) (b) of P5A-(Me)6.3-(CH
2
COONa)3.7 (compound 14).
Synthesis of pillar[5]arenes substituted by methyl and sodium
carboxylated methyl groups
Persubstituted pillar[5]arenes P5A-(Me)10 (compound 1) are
prepared according to a procedure from the literature (Scheme
chloroacetate in acetonitrile in the presence of potassium
carbonate at 80 °C for 48 h affords pillar[5]arenes randomly
substituted by both methyl and methyl carboxymethyl groups
2 x
(P5A-(Me)10-x-(CH COOMe) with x being the number of methyl
1
).27 1 is then subjected to partial demethylation with BBr
3
(x equiv. carboxymethyl groups distributed on both sides of the macrocycle,
with respect to 1 with x≤10) in chloroform for 12 h at room
temperature. Depending on the amount of BBr , six different
pillar[5]arenes P5A-(Me)10-x-(H) (compounds 2-7) with various
degrees of substitution in hydroxyl groups are obtained (3.7, 5.7,
.8, 8.6, 9.2 and 10). Subsequent reaction with methyl
compounds 8-13). Further saponification of the ester functions
under basic conditions (NaOH in water at 100 °C for 12 h) leads
to the corresponding pillar[5]arenes featuring methyl and sodium
carboxylmethyl groups randomly substituted onto the cyclic
3
x
7
2 x
structure P5A-(Me)10-x-(CH COONa) (compounds 14-19).
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The synthesized modified pillar[5]arenes are characterized by
NMR spectroscopy. 1 shows three signals at 6.77, 3.77 and 3.65
ppm relative to aromatic protons (10H), methylene bridge (10H)
and the presence of numerous peaks at 6.5 and 3.8 ppm relative
to aromatic protons and randomly distributed methoxy groups,
respectively (ESI). For the characterization of final water soluble
pillar[5]arenes, MALDI-TOF and NMR study in water were
coupled to determine the proportion of methoxy and carboxylate
groups (Figure 2).
and methoxy groups (30H), respectively. Reaction with BBr
offers partially demethylated compounds 2-7 as confirmed by the
decrease in intensity of the signal relative to the methoxy groups
3
Scheme 2. Syntheses of water soluble pillar[5]arenes 20 and 21.
Table 1. Synthesized compounds.
P5A-(R)10-x-(R’)
x
R
R’
x
0
1
2
3
4
5
6
7
8
9
Me
Me
Me
Me
Me
Me
-
-
Synthesis of water soluble P5A substituted by PEG chains
H
3.7
Pillar[5]arenes substituted by PEG chains featuring an average
number of 45 ethyleneoxy units have also been considered as
additives as PEG chains are well-known to help partitioning
organic substrates within aqueous biphasic systems. 28 , 29 The
synthesis of the studied PEG-substituted pillar[5]arenes is
inspired by chemical modification of pillar[5]arenes described in
the literature. 30 , 31 Para-propargyloxy anisole reacts with
paraformaldehyde to afford pillar[5]arenes substituted by an equal
number of methyl and propargyl groups (Scheme 2a).
Subsequent copper-catalyzed alkyne-azide cycloaddition
H
H
5.7
7.8
H
8.6
H
9.2
H
10
Me
Me
Me
Me
Me
-
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
2
2
2
2
2
2
COOMe 3.7
COOMe 5.7
COOMe 7.8
COOMe 8.6
COOMe 9.2
COOMe 10
COONa 3.7
COONa 5.7
COONa 7.8
COONa 8.6
COONa 9.2
COONa 10
10
11
12
13
14
(
CuAAC) with PEG chains end-functionalized by azide in
acetonitrile at 60 °C for 24 h produces pillar[5]arenes 20 which is
substituted by five methyl groups and five PEG-triazolylmethyl
moieties. Similarly, para-dipropargyloxy benzene condenses with
paraformaldehyde to yield pillar[5]arenes persubstitued by
propargyl groups (Scheme 2b). Subsequent CuAAC gives the
expected pillar[5]arene 21 persubstituted by ten PEG-
triazolylmethyl moieties.32
Me
Me
Me
Me
Me
-
15
16
17
18
19
2
0
1
Me
-
PEG
PEG
5
2
10
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Surface tension
leads to lower surface tension. For example, adsorption of the
very hydrophilic pillar[5]arenes (x = 10) at the interface is very
weak as the surface tension is only reduced from 72 mN.m-1 for
pure water to 59 mN.m-1 at 0.032 mol.L . Surface tension assays
of 20 and 21 were performed in lower concentration ranges
(Figure 3.b) because their molar weight is 5 to 10 times higher
than 14-19. The concentrations applied in catalysis were still
considered in this study. The two pillar[5]arenes do not show any
significant change in surface tension with the concentration, 21
being slightly more adsorbed than 20in the catalytic concentration
Surface tension measurements were carried out at the air/water
interface to establish correlation between the catalytic results and
the surface adsorption of modified pillar[5]arenes (Figure 3). In
all cases, no clear CMC is identified. A slight decrease in the
surface tension with the concentration is observed showing the
capability of the modified pillar[5]arenes to adsorb at the interface
layer without forming micelles. Concerning compounds 14-19, the
decrease in the surface tension is more marked with the addition
of carboxylate functions (Figure 3.a). Indeed, the surface tension
evolves from 63 to 37 mN.m-1 at the catalytic concentration (red
dotted line) for pillar[5]arenes featuring 3.7 and 8.6 carboxylate
functions, respectively. Higher carboxylate substitution degree
-1
-1
range (47 and 49 mN.m , respectively).
Figure 3. Surface tension measurements at 20 °C of a) compounds 14-19, and b) compounds 20 and 21.
results are obtained for pillar[5]arenes displaying good adsorption
capability at the aqueous/organic interface (Figure 3). However,
the surface tension at the aqueous/organic interface is not fully
responsible for the observed results as the highest conversion is
obtained with 16 whose adsorption is slightly lower than the most
surface active pillar[5]arene (17). This results tend to prove that
the availability of the cavity is as important as the adsorption
capability of the macrocycle. Indeed, when the pillar[5]arene has
too many carboxylate functions, the hydrophobic substrate has
more difficulties to be recognized and its conversion decreases.
This assertion is confirmed with 19. While it shows the same
adsorption ability than 14, its effectiveness in catalysis is more
than twice as low (Table 2, entries 1 and 6). Accordingly, while 19
adsorbs properly at the interface, it proves inappropriate to
recognize hydrophilic substrates. Additionally, its strong anionic
character probably repels the anionic TPPTS-based catalyst,
resulting in lower probability of contacts between the small
proportion of 19-included substrate and the catalyst. A similar
Rh-catalyzed hydroformylation of higher olefins
Hydroformylation of 1-decene
While the Rh-catalyzed hydroformylation of lower alkenes has
been well described in the literature, 33 , 34 hydroformylation of
higher olefins remains
a challenge (because of obvious
insolubility issues), not only in terms of catalytic activity but also
in terms of chemo- and regioselectivities. In the following
paragraph are summarized results obtained in rhodium-catalyzed
hydroformylation of 1-decene and 1-hexadecene with compounds
14-21 as interfacial additives. The results are also compared to
the randomly methylated -CD (RAME--CD), one of the best
molecular receptors in aqueous biphasic catalysis so far.
In an initial exploratory study to assess the potential of modified
pillar[5]arenes in aqueous biphasic catalysis, the performance of
1
4-19 is evaluated in Rh-catalyzed hydroformylation of 1-decene.
The reaction is performed under 50 bar of CO/H (1:1) at 80 °C in
water, Rh(CO) (acac) as metal precursor (acac
2
2
a
=
behavior was reported for cyclodextrins highly substituted by
acetylacetonate) and the sodium salt of the trisulfonated
triphenylphosphine (TPPTS) as a ligand. Table 2 summarizes the
catalytic results. The conversion in carbon-carbon double bonds
is increased up to 85% with increasing the number of sodium
carboxylate methyl groups (x) up to ca. 8, then goes down for
higher carboxylate substitution degrees (Figure 4). Thus, as
observed for randomly modified CDs,35 the substrate conversion
is highly related to the pillar[5]arene substitution degree. This may
be partly related to surface tension properties. Indeed, the best
sulfobutyl groups.36
Interestingly, conversion and chemoselectivity follows an
opposite trend. The aldehyde selectivity slightly decreases for x
from 3.7 to 5.7, then increases with increasing x. The highest
aldehyde selectivity is observed with 19. This is consistent with
the suggestion that contacts between the Rh-catalyst and the
substrate included into the cavity of 19 are more constrained than
with other P5A derivatives substituted both with methyl and
carboxymethyl groups. In other words, 19 orient the included
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ChemCatChem
10.1002/cctc.201801551
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substrate to react through a more selective pathway when
approaching the Rh-catalyst. However, it should be noted that the
using 19 as molecular receptor (l/b of 4.1 vs 1.8 for RAME--CD).
The point one learns from this information is that the studied
pillar[5]arenes do not interact with the TPPTS ligand, as
confirmed by 2D T-ROESY analysis (Figure 5). Indeed, inclusion
of TPPTS into the receptor’s cavity usually results in the shift of
the equilibriums between the catalytic species towards low
phosphane-coordinated rhodium species responsible for the
formation of branched aldehydes. 37 This is typically what is
observed with RAME--CD. In the present case, as TPPTS does
not interact with the cavity of compounds 14-19, equilibriums are
not altered and linear aldehydes are mainly formed.
“
protecting” effect of the cavity towards side-reactions is lower
than what is observed with RAME--CD (98% aldehyde selectivity
under the same experimental conditions, entry 12), suggesting a
not-so-deep inclusion of 1-decene into the pillar[5]arene’s cavity.
Table 2. Aqueous biphasic hydroformylation of 1-decene using modified
pillar[5]arenes and RAME--CD[
a]
Entry
Additive
Eq./Rh
Conv.
%)
Sel. Ald
(%)[
Sel. Iso
(%)
l/b[d]
b]
[c]
(
1
2
3
4
5
6
7
8
9
14
10
74
76
85
76
51
33
96
100
13
83
16
97
71
65
66
67
69
78
81
92
57
77
59
98
29
35
34
33
31
22
19
8
2.6
2.4
2.4
2.5
2.5
4.1
2.4
2.4
2.5
2.6
2.5
1.7
15
10
16
10
17
10
18
10
19
10
20
0.5
0.75
3.75
0.75
7.50
10
20
2
Figure 5. 2D T-ROESY NMR spectrum (D 0, 25 °C) of TPPTS/15 mixture (1:1).
PEG45
21
43
23
41
2
10
11
12
The l/b ratios measured with 14-19 are rather high and agree well
with those obtained in former studies on homogeneous and
biphasic hydroformylation.25 This constitutes a major advantage
over modified -CDs. Basically, 14-19 better compare with
modified -CDs (smaller cavity than -CDs).38
PEG45
RAME-

-CD
To get deeper insight into the performance of modified
pillar[5]arenes under aqueous biphasic conditions, a series of
experiments is performed using 20 or 21 as both molecular
receptors and interfacial additives (Table 2). The recognition
capability of the pillar[5]arene’s cavity and the amphiphilic nature
of the PEG chains are combined to speed up the hydroformylation
of 1-decene into the corresponding linear and branched
aldehydes. As expected, the use of PEG-derived pillar[5]arenes
leads to higher conversions under the same experimental
conditions because of the ability of PEG to better partition 1-
decene between the two phases within the interfacial layer. 96%
of 1-decene are converted within 3 h using 0. 5 equiv. of 20 with
respect to Rh (Table 2, Entry 7), a conversion surpassing any of
the conversions obtained with 14-19 (85% at best). Complete
conversion of the carbon-carbon double bonds is achieved using
1
3
-
10
5
59
41
2.8
[
a] Conditions: 1-decene (307 µL, 1.63 mmol), Rh(CO)
mmol), TPPTS (33 mg, 0.058 mmol), water (6 mL), 3 h, 80 °C, 50 bar CO/H
1/1), 1500 rpm. [b]aldehyde selectivity. [c] selectivity in isomerized products.
d] linear to branched aldehydes ratio.
2
(acac) (3 mg, 0.012
2
(
[
0.75 equiv. of 20 with respect to Rh (Table 2, entry 8). To our
delight, the aldehyde selectivity is also increased to 92% while the
l/b ratio remained constant at 2.4. Conversely, persubstitution of
the pillar[5]arene macrocycle by PEG-triazolylmethyl moieties has
a detrimental effect on both the conversion and the aldehyde
selectivity (Table 2, entry 10), probably because the recognition
of the substrate within the cavity is hampered by the bulky PEG-
triazolylmethyl substituents. Comparison with PEG45 (blank runs
realized with PEG45 mol% equivalent to PEG-based pillararenes)
highlights the pillararene/PEG combination in hydroformylation of
Figure 4. Variation of the conversion in hydroformylation of 1-decene and 1-
hexadecene with the average number of carboxymethyl groups onto
compounds 14-19.
The regioselectivity, for its part, is higher than that measured with
RAME--CD. The linear to branched (l/b) ratio is especially high
1-decene as conversions are multiplied by a factor up to 8 (Table
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FULL PAPER
2
, compare entries 8 et 9 and entries 10 et 11). The result also
advantages of P5A derivatives over PEG45 (Table 3, entries 8
and 10) and RAME--CD (Table 3, entry 11) are also significant
for 1-hexadecene both in terms of conversion and selectivity. As
described above, the linear to branched ratio is especially high
compared to RAME--CD because of the absence of interaction
between P5A derivatives and TPPTS.
favorably compares with RAME-β-CD (97% conv., Table 2, entry
2). However, as observed above with compounds 14-19, the
1
chemoselectivity measured with 20 is lower than with RAME--
CD (81% vs 98% aldehyde selectivity), indicative of the lowest
ability of 20 to protect the substrate against isomerization. The
regioselectivity (l/b of 2.4), for its part, is in the range of what is
classically observed under aqueous biphasic conditions without
receptor/ligand interaction (l/b~2.5).
Reusability of the catalytic system
To assess the viability of the studied system over several catalytic
runs, we performed additional experiments as follows. Rh-
catalyzed hydroformylation of 1-decene is carried out using
compounds 14-19 as interfacial additive and molecular receptor
under the catalytic conditions described in Table 2. Once the
product resulting from Run 1 has been recovered, the catalyst-
containing solution is reused over four additional consecutives
runs. Satisfyingly, both conversions and selectivities remain
constant, indicative of the robustness of the studied catalytic
system under aqueous biphasic conditions (Figure 6).
Hydroformylation of 1-hexadecene
The use of modified pillararenes and cyclodextrins is then
extended to Rh-catalyzed hydroformylation of 1-hexadecene, a
much more hydrophobic olefin (Table 3).
Table 3. Aqueous biphasic Rh-catalyzed hydroformylation of 1-hexadecene
with modified pillar[5]arenes and cyclodextrins.[
a]
Entry
Additive
Eq./Rh
Conv (%)
Sel. Ald
(
Sel.
Iso.
(
l/b[d]
%)[
b]
%)[c]
1
2
3
4
5
6
7
8
9
14
10
61
66
72
67
56
22
58
12
50
15
56
56
56
55
56
55
55
53
45
49
47
65
44
44
45
44
45
45
47
55
51
53
35
2.3
2.5
2.4
2.4
2.5
2.5
2.6
2.5
2.6
2.5
1.5
15
10
16
10
17
10
18
10
19
10
20
0.75
3.75
0.75
7.5
10
Figure 6. Reusability of the aqueous 16-containing solution in Rh-catalyzed
hydroformylation of 1-decene. Conditions: see Table 2.
PEG45
21
Conclusions
1
0
1
PEG45
RAME-
In this study, we developed the synthesis of pillar[5]arenes
substituted by both methyl and carboxylate groups or PEG chains.
The modified pillar[5]arenes adsorb differently at the air/aqueous
interface depending on the substitution degree. Their ability to
favor the conversion of hydrophobic substrate under biphasic
conditions was assessed in Rh-catalyzed hydroformylation of
terminal alkenes. The main advantage of modified pillar[5]arenes
over cyclodextrins lies in their ability to reduce the surface tension,
recognize the substrate, and above all prevent interaction with
ligands stabilizing the organometallic species in water. While a
decrease of the linear to branched aldehyde ratio is usually
observed with cyclodextrins as interfacial additive, the proportion
of linear and branched aldehydes is high (l/b up to 4.1) using
modified pillar[5]arenes substituted by both methyl and
carboxylate groups or PEG chains in comparison with reactions
carried out under homogeneous conditions. However, the
chemoselectivity is modest (aldehyde selectivity up to 92%),
possibly because of the lower ability of modified pillararenes to
protect the substrate against isomerization. Additionally, the
pillar[5]arene-based catalytic system is robust as it is reusable
over five consecutives catalytic runs. Experiments are currently
1

-CD
12
-
10
4
30
70
2.5
[
a] Conditions: 1-hexadecene (468 µL, 1.63 mmol), Rh(CO)
mmol), TPPTS (33 mg, 0.058 mmol), water (6 mL), 3 h, 80 °C, 50 bar CO/H
1/1), 1500 rpm. [b] aldehyde selectivity. [c] selectivity in isomerized alkenes. [d]
linear to branched aldehydes ratio.
2
(acac) (3 mg, 0.012
2
(
Here again, the number of carboxylate and methyl groups
determines the ability of compounds 14-19 to convert the
substrate into aldehyde. As previously observed for 1-decene
(
Figure 4), the maximum in conversion of 1-hexadecene is
observed for 16 (Table 3, entry 3). The latter displays a fine
balance of carboxylate and methyl groups to ensure both
adsorption at the aqueous/organic interface and molecular
recognition of 1-hexadecene. The chemo- and regioselectivities
remain constant irrespective of the substitution degree, indicative
of the absence of interaction between host and ligands throughout
the catalytic process. 20 proves slightly more effective to convert
1
-hexadecene than 21. Indeed, 20 is more prone to include the
substrate because it is less encumbered than 21 and permits
highest accessibility to the cavity (entries 6 and 7). The
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10.1002/cctc.201801551
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on-going to widen their utilization to other organometallic catalytic
reactions.
the crude product was washed with ethanol/water (6:4) mixture and pure
acetone. Yellow pale powders were obtained in all cases (Yields: 70-75%).
P5A-(Me)
In a two-necked round flask were dissolved P5A-(Me)
mg, 0.016 mol, 1 eq.) and 182 mg of PEG45-N (0.09 mol, 5.5 eq., prepared
following a literature procedure ) in anhydrous acetonitrile (5 mL) under
nitrogen. Then, Cu(MeCN) PF (35 mg, 0.09 mol, 5.5 eq.) was added and
5 5
-(PEG) and P5A-(PEG)10 (20 and 21)
5
5
-(propargyl) (13.4
3
39
Experimental Details
4
6
the mixture was stirred under nitrogen at 60 °C for 48 h. The solvent was
evaporated under vacuum and the resulting compound 20 was purified by
dialysis in water. The same procedure was applied for the synthesis of 21
Synthesis of P5A-(Me)10 (1)
In a 250 mL round flask were dissolved 1,4-dimethoxybenzene (5.52g, 40
mmol) and paraformaldehyde (3.72g, 120 mmol) in 1,2-dichloroethane (40
3 6
using 11 eq. of PEG2000-N (364 mg) and CuPF (70 mg). The products
mL). Then, boron trifluoride diethyl etherate [BF
3 2 5
.O(C H )
2
] (6.25 mL, 40
were obtained as white powders in ca. 70% yield.
mmol) was added to the solution and the mixture was stirred at room
temperature for 30 min. Addition of methanol (200 mL) resulted in the
precipitation of solids. After filtration, the latter were purified by silica gel
Catalytic experiment
In a typical experiment, Rh(CO)
three times by vacuum–N cycles and dissolved in a degassed solution of
2
(acac) (3 mg, 0.012 mmol) was degassed
column chromatography using a CH
2
Cl
2
/petroleum spirit mixture (60/40).
2
1
was obtained in 80% yield (4.86 g) as a pale yellow powder.
P5A derivative (0.058 mmol) in water (6 mL). The resulting solution was
stirred at 1500 rpm at room temperature until all of the rhodium complexes
were dissolved (2 h). The substrate (1.63 mmol) was poured into an
Synthesis of P5A-(Me)10-x-(H)
In a 250 mL round flask was dissolved P5A-(Me)10 (3 g, 3.95 mmol) in 200
mL of anhydrous CHCl . The solution was degassed by bubbling with
nitrogen. Then, BBr was added in well-defined quantity to obtain the
x
(2-7)
autoclave and N
under nitrogen into the autoclave. Once the desired temperature was
reached, the autoclave was pressurized under CO/H (1:1) pressure
2
-purged. The catalytic solution was then cannulated
3
3
2
desired degree of substitution in hydroxyl groups (see Table S1). The
solution was then stirred at room temperature for 15 h under nitrogen. The
reaction was stopped by addition of pure water (200 mL). After
(typically 50 bar) and the solution was vigorously stirred (1500 rpm). When
the reaction was complete, the apparatus was cooled down to room
1
temperature and depressurized. The products were analyzed by H and
13
decantation, the organic layer was washed with 0.5
hydrochloric acid, dried with Na SO and evaporated to yield compounds
-7 as pale yellow powders (Yields: 85-90%).
M
aqueous
C NMR experiments. All runs were performed at least twice in order to
2
4
ensure reproducibility.
2
P5A-(Me)10-x-(CH
In a 250 mL two-necked round flask were introduced compounds 2-7 (2.50
g, 1 eq.), K CO (20 eq.), and anhydrous acetonitrile (180 mL). After
degassing, methyl chloroacetate (10 eq.) was injected and the mixture was
stirred under reflux for 48 h. After filtration of excess K CO , the solvent
2 x
COOMe) (8-13)
Acknowledgements
2
3
Chevreul Institute (FR 2638), Ministère de l’Enseignement
Supérieur et de la Recherche, Région Nord – Pas de Calais and
FEDER are acknowledged for supporting and funding partially
this work. We thank Dr. Nicolas Kania and D. Prevost for technical
assistance.
2
3
was evaporated and the product was recrystallized in chloroform/diethyl
ether. 8-13 were obtained in 55-60% yield as pale yellow powders.
2 x
P5A-(Me)10-x-(CH COONa) (14-19)
In a 100 mL round flask was prepared a saturated solution of NaOH (12
mL) in ethanol (40 mL). Compounds 8-13 (1.5 g) was then introduced and
the mixture was heated to reflux and stirred for 15 h. The product was
precipitated with aqueous hydrochloric acid (50 mL) and filtered to obtain
Keywords: Pillararenes • aqueous biphasic catalysis •
P5A-(Me)10-x-(CH
derivatives 14-19 were obtained by stirring P5A-(Me)10-x-(CH
aqueous NaOH (1 eq.) at room temperature for 5 h. After lyophilisation,
2
COOH)x. The expected methyl carboxymethylated
hydroformylation • molecular recognition • inclusion complexes
2
COOH) in
x
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Entry for the Table of Contents
FULL PAPER
Modified pillar[5]arenes are interesting
interfacial additives in Rh-catalyzed
hydroformylation of long alkyl-chain
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