Multivalent Molecular Shuttles - Effect of Increasing the Number of Centers in Switchable Catalysts

Article abstract of DOI:10.1002/ejoc.201500942

A family of three molecular shuttles based upon ammonium/triazolinium salt motifs with one, two, and three catalytic centers were prepared along with their corresponding non-interlocked threads. The switching process for all rotaxanes was tested through an in situ procedure in solution. Furthermore, their organocatalysis of two Michale-type reactions by iminium activation was tested to check whether the increase of the number of catalytic centers in the same shuttle is a decisive factor to improve their efficiencies compared with those of single-active-site organocatalytic shuttles under the same conditions.

Full text of DOI:10.1002/ejoc.201500942

FULL PAPER
DOI: 10.1002/ejoc.201500942
Multivalent Molecular Shuttles – Effect of Increasing the Number of Centers
in Switchable Catalysts
Celedonio M. Álvarez,*[a] Héctor Barbero,[a] and Daniel Miguel[a]
Keywords: Organocatalysis / Click chemistry / Rotaxanes / Molecular shuttles
A family of three molecular shuttles based upon ammonium/
triazolinium salt motifs with one, two, and three catalytic
centers were prepared along with their corresponding non-
interlocked threads. The switching process for all rotaxanes
was tested through an in situ procedure in solution. Further-
more, their organocatalysis of two Michale-type reactions by
iminium activation was tested to check whether the increase
of the number of catalytic centers in the same shuttle is a
decisive factor to improve their efficiencies compared with
those of single-active-site organocatalytic shuttles under the
same conditions.
Introduction
Results and Discussion
Rotaxanes incorporating catalytic centers in their struc-
tures have attracted the attention of many authors in this
decade,[1] and their suitability as an effective reaction plat-
form has been demonstrated. Several switchable catalysts
have been inspired[2] by how the rates and outcomes of en-
zyme-catalyzed reactions can be controlled through trigger-
induced events.[3] Synthetic catalysts that could achieve sim-
ilar influence in natural processes would become a scientific
breakthrough.
Switchable catalysts with rotaxane-based secondary
amines in their structures are of particular interest, mainly
because of their potential activation modes (iminium,[4] en-
amine,[5] and trienamine)[6] and the ease of switching be-
tween all potential stations. They have mechanically inter-
locked architectures with internal motion that can be ex-
ploited to control both the rates and outcomes of several
reactions by shielding and exposing a catalytic center.[7]
Moreover, multivalent catalysts based on polymers or
dendrimers are generally better than their monovalent
counterparts owing to their connecting frameworks.[8]
To advance the knowledge on these elegant architectures,
we found it very interesting to synthesize a new family of
molecular shuttles with dibenzylamine stations that can
perform several kinds of reactions. The difference between
them is the number of catalytic centers in their structures,
and the objective was to compare their behavior in two typi-
cal Michael-type reactions, which are well-known bench-
marks for comparison purposes.
Synthesis and Switching Process
All of the molecular-shuttle-based organocatalysts con-
sist of one, two, or three axles containing dibenzylammo-
nium and methyltriazolinium salts as binding sites along
with anthracene stoppers (Figure 1). Additionally, they bear
one, two, or three dibenzo-24-crown-8 (DB24C8) macro-
cycles, which establish very good associations with ammo-
nium salts.[9] Non-interlocked-thread analogues were also
prepared for comparison of their spectroscopic and chemi-
cal properties (Figure 2).
The synthetic procedure for the compounds presented
begins with the preparation of the ammonium salt R5-H-
PF6 (Scheme 1). This product was obtained in six steps
from methyl 4-(aminomethyl)benzoate hydrochloride and 9-
anthracenecarbaldehyde with an overall yield of 52%. This
molecule is a common building block for all of the rotax-
anes.
The strategy to obtain the threaded compounds relies on
a well-known self-assembly method: the macrocyclic poly-
ether is captured by the ammonium salt in solution fol-
lowed by a copper(I)-catalyzed azide–alkyne cycloaddition
(CuAAC) “click” reaction[10] between the terminal alkyne
and an azide-functionalized compound. Finally, the triazole
formed was methylated to create the second binding site
(Scheme 1).[11]
The preparation of the non-interlocked-thread analogues
was very similar, but in these cases the amine was protected
until the final step (Scheme 2).[12] This synthesis starts with
the cyclization of R4 instead of R5-H-PF6 with a suitable
azide and is followed by triazole methylation and a final
deprotection step. It must be noted that these compounds
are less soluble in common organic solvents and generally
less stable than their rotaxane counterparts; therefore, the
[a] GIR MIOMeT, IU CINQUIMA/Química Inorgánica, Facultad
de Ciencias, Universidad de Valladolid,
47005 Valladolid, Spain
E-mail: celedonio.alvarez@uva.es
http://miomet.blogs.uva.es/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500942.
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first evidences of the importance of ammonium salt encap-
sulation was provided.
To date, the switching process in this kind of compound
has been attempted in many ways, and the best choice is to
wash briefly the organic solution containing the molecular
shuttle with an aqueous solution of NaOH (1 m),[7] followed
by typical workup. Nevertheless, this method cannot be
considered as a true on/off process because it does not oc-
cur in situ and involves a separation procedure. Our method
is a real on/off switching process that is performed entirely
in situ without any purification step. Thus, this method was
applied as follows: NaOH (1.1 equiv. per binding site) dis-
solved in D2O (1 m) was added to a solution of the rotaxane
in [D6]acetone under vigorous stirring, and a 1H NMR
spectrum was recorded after a few minutes. This medium is
basic enough to deprotonate the ammonium salt to yield
the amine, which is a worse binding site than the triazolin-
ium salt; therefore, the macrocycle is forced to move along
the axis to interact with the second station. The addition
of CF3CO2H (1.1 equiv. per binding site) reprotonates the
amine, and it is again preferable for the crown ether to re-
cover the initial position to establish strong intermolecular
interactions. The role of the anthracene moieties is to pre-
vent undesired dethreading through their bulk.[13]
Although this method seems to be more valuable, it is
not definitive, as the concentration of dissolved salts (so-
dium trifluoroacetate in this case) increases as the success-
ive switching cycles are performed, and the amount of
1
HDO severely complicates the H NMR spectra.
For 1-H-PF6, the set of signals corresponding to the
benzylic protons (H9 and H11, Figure 3) next to the ammo-
nium salt are broadened and shifted downfield compared
with those of the non-interlocked 4-H-PF6 (see Supporting
Information). This confirms that strong hydrogen bonding
occurs between the macrocycle and the ammonium salt in
the axle.
Moreover, their relative position is observed in the
NOESY spectrum (Figure 4, left), and the correlation
Figure 1. Molecular shuttles with one, two, and three catalytic sites
reported in this study.
Figure 2. Non-interlocked-thread analogues.
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Multivalent Molecular Shuttles
Scheme 1. Synthesis of shuttles 1-H-PF6, 2-H-PF6, and 3-H-PF6. Reagents and conditions: (a) 1. Methyl 4-(aminomethyl)benzoate hydro-
chloride, microwave (MW); 2. NaBH4, MeOH; 3. LiAlH4, THF, –78 °C; 4. Boc2O, I2, MeOH; 5. NaH, propargyl bromide, THF; 6.
CF3CO2H, NH4PF6, H2O/DCM. (b) DB24C8, 9-(azidomethyl)anthracene, 1,4-bis(azidomethyl)benzene or 1,3,5-tris(azidomethyl)benz-
ene, [Cu(NCMe)4]PF6, 2,6-lutidine, DCM. (c) 1. Me3OBF4; 2. NH4PF6, H2O/DCM.
cross-peaks between the CH2 macrocycle signals and all nu- surprising, as the change of counterion affects the chemical
clei next to the ammonium station in the axle show the environment of nearby nuclei,[15] and the triazolinium salt/
spatial proximity of both fragments.
macrocyclic ether couple is used to bind anions in solu-
When the rotaxane is switched (Figure 3, b), a set of sig- tion.[16] The switching process can be performed several
nals is modified substantially along with other minor times without appreciable signs of decomposition (Figure 3,
changes. As expected, the biggest changes are observed for d and e).
the protons close to the shuttle stations. Thus, the most
This new switching procedure for 1-H-PF6 was applied
1
remarkable changes are for the signals of the benzylic CH2 for the other shuttles. The H NMR spectra of 2-H-PF6
groups next to the ammonium salt, which undergo an up- (Figure 5, left) and 3-H-PF6 (Figure 5, right) are very sim-
field shift of ΔδH9 = –1.05 and ΔδH11 = –0.79 ppm. ilar to that of 1-H-PF6 but show less signals owing to the
Furthermore, all protons near the triazolinium moiety are high symmetry of these shuttles. The variation in chemical
shifted, and the shifts for H20 and H21 are the most signifi- shifts upon switching was analogous to that observed for
cant (Figure 3, ΔδH20 = 0.69 ppm downfield and ΔδH21
=
the previous shuttle, but some signals corresponding to the
–0.41 ppm upfield). Every signal corresponding to the macrocycle were broadened and, therefore, showed the ex-
macrocycle also changes (Figure 3). Additionally, the pected lack of freedom in Brownian motion, possibly be-
NOESY spectrum yields correlation cross-peaks between cause of the mutual proximity of the macrocycle ethers. Ad-
the CH2 macrocycle signals and all nuclei next to the triaz- ditionally, for 3-H-PF6, the immediate exchange of the pro-
olinium station, which confirms their relative situation.
ton of the triazolinium salt (H20) with a deuteron after the
After reprotonation, the ring recovers its initial position addition of the first aliquot of NaOH 1 m in D2O showed
as expected, but the spectrum is not exactly like the first the acidity of this proton. This effect was also observed if
one recorded (Figure 3, c). Several signals have been slightly the other molecular shuttles were stored in solution for a
changed relative to the original ones.[14] This effect is not long time.
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Scheme 2. Synthesis of non-interlocked threads 4-H-PF6, 5-H-PF6, and 6-H-PF6. Reagents and conditions: (a) 1. Methyl 4-(aminomethyl)-
benzoate hydrochloride, MW; 2. NaBH4, MeOH; 3. LiAlH4, THF, –78 °C; 4. Boc2O, I2, MeOH; 5. NaH, propargyl bromide, THF. (b)
9-(Azidomethyl)anthracene, 1,4-bis(azidomethyl)benzene or 1,3,5-tris(azidomethyl)benzene, [Cu(NCMe)4]PF6, 2,6-lutidine, DCM. (c) 1.
Me3OBF4; 2. NH4PF6, H2O/DCM. (d) CF3CO2H, NH4PF6, H2O/DCM.
1
Figure 3. H NMR spectra (500 MHz, [D6]acetone) of a [2]rotaxane switched twice: (a) 1-H-PF6, (b) 1-PF6, (c) 1-H-PF6-CF3CO2, (d) 1-
PF6, (e) 1-H-PF6-CF3CO2.
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Multivalent Molecular Shuttles
Figure 4. NOESY spectra (500 MHz, [D6]acetone) of 1-H-PF6 and 1-PF6. The circles depict the NOE correlations between the axle and
macrocycle mechanically bonded.
Figure 5. 1H NMR spectra (500 MHz, [D6]acetone) of [3]rotaxane switched twice (left): (a) 2-H-PF6, (b) 2-PF6, (c) 2-H-PF6-CF3CO2, (d)
1
2-PF6, and (e) 2-H-PF6-CF3CO2; H NMR spectra (500 MHz, [D6]acetone) of [4]rotaxane switched twice (right): (a) 3-H-PF6, (b) 3-PF6,
(c) 3-H-PF6-CF3CO2, (d) 3-PF6, (e) 3H-PF6-CF3CO2.
Catalytic Behavior
Once the control over the position of the macrocycles
was observed in all of the molecular shuttles, two sets of
catalytic tests were performed. Both were Michael-type re-
actions, which can be catalyzed by secondary amines
through iminium activation to yield an adduct after C–S or
C–C bond formation.
Scheme 3. Typical operation of an organocatalyst switched by pH
changes.
For regular ammonium–triazolinium switchable organo-
catalysts, the procedure works as follows: if the catalytic
center is covered by the macrocycle, no reaction should be
observed at all because that center is blocked, and the reac-
The first reaction between trans-cinnamaldehyde and
tants are not allowed to access the site (Scheme 3, left), but 1H,1H,2H,2H-perfluorodecanethiol (Table 1) has already
catalysis occurs if the catalytic center is exposed (Scheme 3, been reported by Leigh et al.[7a] It was catalyzed by a molec-
right).
ular shuttle, and the rotaxane was switched through wash-
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ing with aqueous NaOH. We performed the same pro-
cedure but switched the rotaxanes with the protocol de-
scribed above (with a near-stoichiometric amount of NaOH
in D2O) to avoid possible rate enhancement owing to de-
protonation of the thiol by an excess of sodium hydroxide
(Table 1).
Table 1. Results observed in the first reaction.[a]
Figure 6. 1H NMR spectra (500 MHz, CDCl3) for the first reaction
with 1-H-PF6 as the catalyst: (a) 1H,1H,2H,2H-perfluoro-
decanethiol, (b) trans-cinnamaldehyde, (c) pure adduct, (d) reaction
mixture with 1-H-PF6 inactive, and (e) reaction mixture with 1-PF6
active at maximum conversion.
Entry Compound
Conversion after
30 min [%][b]
Conversion after
4 h [%][b]
[c]
1
1-H-PF6[c]
2-H-PF6[c]
3-H-PF6
1-PF6
0
0
0
0
0
0
2
3
4
50
68
80
10
8
12
20
45
65
74
72
79
85
25
21
28
35
70
75
83
5
2-PF6
10). These compounds are the counterparts of inactive rot-
axanes and, therefore, have ammonium salts as catalytic
centers. Even with the catalysts in this state, the reaction
occurred, in contrast to the behavior observed for rotaxanes
in the inactive position (Table 1, Entries 1–3). This evidence
shows the importance of the encapsulation of the catalytic
center because non-interlocked threads can still catalyze the
reaction even in the protonated state; however, if this am-
monium salt is covered by the macrocycle, the shuttle can-
not perform the catalysis, and the reaction is fully stopped.
Nevertheless, all of these dumbbell-shaped molecules are
generally better catalysts than dibenzylamine under the
same conditions (Table 1, Entry 7); therefore, their structure
6
3-PF6
7
dibenzylamine
[c]
8
4-H-PF6[c]
9
5-H-PF6[c]
6-H-PF6
4-PF6
10
11
12
13
5-PF6
6-PF6
[a] Summarized conditions for all entries: trans-cinnamaldehyde
(0.14 mmol), 1H,1H,2H,2H-perfluorodecanethiol (0.168 mmol),
catalyst (5mol-%), CDCl3 (1.4 mL), and NaOH (1.2 equiv. for each
catalytic site). [b] Determined by integration of the CH2 signals in
1
the H NMR spectra. [c] These compounds were not treated with
NaOH.
As expected, with the shuttles in the inactive position enhances the catalytic behavior at their active sites.
(Figure 6, d), that is, with the ether attached to the ammo- A similar protocol was applied for the second reaction, in
nium station, no reaction was observed. On the other hand, which the nucleophile was diethyl malonate (Table 2). The
with the ether switched to the triazole position, the catalytic reaction did not proceeded well in chlorinated solvents;
site was exposed, and the signals corresponding to the ad- therefore, we had to switch to a solvent in which the reac-
duct appeared (Figure 6, e). All of the shuttles followed the tion occurred and the rotaxanes were soluble. The best
behavior described above. This experiment was performed choice was deuterated acetonitrile.
with non-interlocked threads in the protonated and depro-
tonated states for comparison.
In this case, total conversion could be achieved with 3-
PF6 in the presence of excess aldehyde, but the reaction
Thus, shuttles in the inactive position cannot catalyze the times are notably longer at room temperature. Again, if the
reaction, as shown clearly in Table 1, Entries 1–3. However, shuttles are protonated, encapsulation prevents catalysis
if the shuttle is switched (Table 1, Entries 4–6), the reaction (Figure 7, d). If the shuttles are switched, catalysis occurs
reaches a conversion of 85% for the best rotaxane, 3-PF6. (Figure 7, e).
Interestingly, the initial rate seems to be very high and then
No catalysis occurred for the shuttles with the ammo-
decreases until the maximum conversion is achieved. The nium salt covered by the macrocycle (Table 2, Entries 1–3).
double rotaxane 2-PF6 (Table 1, Entry 5) is better catalyst The initial conversions for the switched shuttles (Table 2,
than the single rotaxane 1-PF6, and the triple rotaxane 3- Entries 4–6) resemble the same pattern found for the first
PF6 is the best catalyst (Table 1, Entry 6).
reaction, and the best performance was observed for the
For the non-interlocked threads, we found the same triple [4]rotaxane 3-PF6. The corresponding non-inter-
trend as that for 4-PF6, 5-PF6, and 6-PF6 (Table 1, En- locked threads (Table 2, Entries 11–13) behave in a similar
tries 11–13), which are the switched counterparts of the way.
active rotaxanes with dibenzylamine catalytic sites. Each
Once more, the protonated threads catalyzed the reaction
conversion is similar to the initial conversion observed for (Table 2, Entries 8–10), and similar conversions were ob-
the respective rotaxane. However, the behavior of 4-H-PF6, served for the nonprotonated threads; therefore, these rot-
5-H-PF6, and 6-H-PF6 is very different (Table 1, Entries 8– axanes are very good on/off systems.
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Multivalent Molecular Shuttles
Table 2. Results observed in the second reaction.[a]
modated in a very crowded situation. Regarding the cata-
lytic behavior of the shuttles, the importance of covering the
catalytic site is evident because catalysis is very effectively
prevented if the macrocycle is situated at the ammonium
station. Additionally, all of the rotaxanes perform better
than dibenzylamine under the same conditions. Finally, we
found that increasing the number of catalytic centers on the
rotaxane is a decisive factor for the improvement of their
performance.
Entry
Compound
Conversion after Conversion after
30 min [%] [b]
24 h[b]
Nevertheless, the number of sites is not the only factor
to be considered, and other factors must be taken into ac-
count, for instance, the flexibility of the rotaxanes and their
solubility are the most important.
These results may open a new route for the synthesis of
better-designed multivalent molecular shuttles to enhance
further their performance as on/off catalysts.
[c]
1
2
3
4
5
6
7
8
1-H-PF6[c]
0
0
0
0
0
0
2-H-PF6[c]
3-H-PF6
1-PF6
5
68
80
100
65
32
45
80
65
75
100
2-PF6
3-PF6
13
20
12
5
14
19
6
dibenzylamine
[c]
4-H-PF6[c]
9
5-H-PF6[c]
6-H-PF6
4-PF6
10
11
12
13
Experimental Section
5-PF6
6-PF6
15
22
Methyl 4-{[(Anthracen-9-ylmethyl)amino]methyl}benzoate (R1):
Methyl-4-(aminomethyl)benzoate (0.41 g, 2.5 mmol) was mixed
with 9-anthracenecarbaldehyde (0.52 g, 2.5 mmol) in a 10 mL vial
specially adapted for the microwave reactor. The mixture was
heated at 140 °C for 15 min with vigorous stirring. After the mix-
ture cooled to room temperature, all of the water drops that formed
during the reaction were removed manually to furnish a bright red
crude product at the bottom of the vial (the imine). This protocol
was repeated six times, and all of the crude products were combined
(6.5 g, 18.4 mmol) and immediately dissolved in hot MeOH
(250 mL). NaBH4 (2.09 g, 55 mmol) was added carefully portion-
wise, and the mixture was heated under reflux for 20 h. Then, the
methanol was removed under vacuum, water (300 mL) was added,
and the solution was extracted with dichloromethane (DCM;
4ϫ200 mL). All organic phases were combined, dried with anhy-
drous MgSO4, filtered, and concentrated in vacuo to afford a crude
product, which was purified by column chromatography (SiO2 gel,
hexane/AcOEt 3:1) to finally afford a yellow solid with spectro-
scopic data that agreed with those reported previously (5.55 g, 85%
yield after two steps).[17]
[a] Summarized conditions for all entries: trans-cinnamaldehyde
(0.28 mmol), diethyl malonate (0.14 mmol), catalyst (10mol-%),
CD3CN (1.4 mL), and NaOH (1.2 equiv. for each catalytic site). [b]
Determined by integration of the aldehyde signals in the H NMR
spectra. [c] These compounds were not treated with NaOH.
1
(4-{[(Anthracen-9-ylmethyl)amino]methyl}phenyl)methanol (R2): R1
(5.33 g, 15 mmol) was dissolved in dry tetrahydrofuran (THF;
160 mL) under a N2 atmosphere. The solution was degassed and
cooled to –78 °C. Lithium aluminium hydride (15 mL of a 1m solu-
tion in THF, 15 mmol) was added dropwise. The mixture was al-
lowed to reach room temperature and then stirred for 3 h. Water
(250 mL) was added, and the solution was extracted with DCM
(3ϫ400 mL). All of organic phases were combined, dried with an-
hydrous MgSO4, filtered, and concentrated under vacuum to afford
an orange oil (4.67 g, 95% yield) that eventually solidified. 1H
NMR (400 MHz, CDCl3): δ = 8.40 (s, 1 H, H1), 8.22 (d, J = 8.6 Hz,
2 H, H6), 8.00 (d, J = 7.9 Hz, 2 H, H3), 7.54–7.43 (m, 4 H, H4,
H5), 7.41 and 7.35 (AB system, 4 H, H12, H13), 4.69 (s, 2 H, H15),
4.68 (s, 2 H, H9), 4.02 (s, 2 H, H10) ppm. 13C NMR (100 MHz,
CDCl3): δ = 139.95 (C14), 139.81 (C11), 131.68 (C2), 131.59 (C8),
130.46 (C7), 129.27 (C3), 128.70 (C12), 127.41 (C1), 127.30 (C13),
126.21 (C4), 125.06 (C5), 124.26 (C6), 65.30 (C15), 54.08 (C10), 45.02
(C9) ppm. MS (ESI+): m/z = 328 [M + H]+ (calcd. 328.17 for
C23H22NO).
1
Figure 7. H NMR spectra (500 MHz, CD3CN) for the second re-
action: (a) diethyl malonate, (b) trans-cinnamaldehyde, (c) pure ad-
duct, (d) reaction mixture with 1-H-PF6 inactive, and (e) reaction
mixture with 1-PF6 active at maximum conversion.
Conclusions
A set of three pH-based molecular shuttles bearing am-
monium and triazolinium groups as stations for threaded
macrocycles have been prepared along with their non-inter-
locked analogues, and their abilities to perform switchable
organocatalysis have been tested with two different
Michael-type reactions.
The results provide very interesting insights: firstly, the
switching process can be performed in situ to avoid separa-
tion procedures. Secondly, phenylene moieties or triply sub-
stituted benzene rings are sufficient links between axles in
tert-Butyl
(Anthracen-9-ylmethyl)[4-(hydroxymethyl)benzyl]carb-
big shuttles, as all of the macrocyclic rings can be accom- amate (R3): R2 (4.56 g, 14 mmol), di-tert-butyl dicarbonate
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C. M. Álvarez, H. Barbero, D. Miguel
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(Boc2O; 3.04 g, 14 mmol), and I2 (0.35 g, 1.4 mmol) were mixed
under a nitrogen atmosphere and dissolved in MeOH (20 mL). The
mixture was stirred for 6 h at room temperature. Then, the solvent
was evaporated, and the residue was redissolved in DCM (200 mL)
and washed with an aqueous solution of Na2S2O3 (5%, 150 mL).
The organic phase was washed again with 20 mL of satd. aqueous
NaHCO3, dried with anhydrous MgSO4, filtered, and concentrated
under reduced pressure to afford a brown oil, which was subjected
to column chromatography (SiO2 gel, hexane/AcOEt 2:1) to afford
R3 as a pale yellow solid (5.39 g, 90% yield). 1H NMR (400 MHz,
CDCl3): δ = 8.41 (s, 1 H, H1), 8.20 (br, 2 H, H6), 7.98 (d, J =
7.8 Hz, 2 H, H3), 7.52–7.35 (m, 4 H, H4, H5), 7.19 (br, 2 H, H16),
6.88 (br, 2 H, H15), 5.56 (s, 2 H, H9), 4.65 (s, 2 H, H18), 4.04 (s, 2
H, H13), 1.73 (br, 3 H, H12Ј), 1.53 (br, 6 H, H12) ppm. 13C NMR
(100 MHz, CDCl3): δ = 155.93 (C10), 139.42 (C17), 137.79 (C14),
131.39 (C8), 131.35 (C2, C7), 129.07 (C3), 128.25 (C1), 126.95 (C15),
126.87 (C16), 126.12 (C4), 124.96 (C5), 124.43 (C6), 80.33 (C11),
65.05 (C18), 47.55 (C13), 40.92 (C9), 28.48 (C12) ppm. MS (ESI+):
m/z = 428 [M + H]+ (calcd. 428.22 for C28H30NO3).
131.47 (C12), 131.10 (C11), 130.36 (C3), 129.24 (C13), 128.43 (C5),
126.45 (C4), 124.14 (C6), 122.42 (C8), 80.56 (C17), 76.30 (C18), 71.41
(C15), 58.02 (C16), 53.06 (C10), 44.23 (C9) ppm. MS (ESI+): m/z =
366 [M – PF6]+ (calcd. 366.19 for C26H24NO).
General Procedure for Rotaxane Synthesis (Click Reaction) to Give
R6-H-PF6, R7-H-PF6, or R8-H-PF6: R5-H-PF6, S4, S5, or S6 and
DB24C8 were mixed in suitable proportions under an inert
atmosphere and dissolved in dry and degassed DCM. The dark
solution was stirred for enough time at room temperature. Then,
[Cu(NCMe)4]PF6 and 2,6-lutidine were added, and the mixture was
stirred at room temperature for 5 or 6 d. After such time, the sol-
vent was removed under vacuum, and the crude product was puri-
fied by column chromatography.
General Procedure for Rotaxane Methylation to Give Molecular
Shuttles 1-H-PF6, 2-H-PF6, or 3-H-PF6: R6-H-PF6, R7-H-PF6, or
R8-H-PF6 and trimethyloxonium tetrafluoroborate were mixed in
dry DCM under a N2 atmosphere. The mixture was degassed and
stirred at room temperature until the complete dissolution of the
tetrafluoroborate salt was observed. The solution was diluted with
DCM, and ammonium hexafluorophosphate dissolved in MiliQ
water was added. The biphasic mixture was stirred vigorously, and
the organic phase was extracted, dried with anhydrous MgSO4, fil-
tered, and concentrated to yield the expected molecular shuttle.
tert-Butyl
(Anthracen-9-ylmethyl){4-[(prop-2-yn-1-yloxy)methyl]-
benzyl}carbamate (R4): R3 (1.07 g, 2.5 mmol) and NaH (0.42 g,
14 mmol) were placed in a Schlenk flask under a nitrogen atmo-
sphere. Dry and degassed THF (50 mL) was added, and the mix-
ture was heated under reflux for 90 min. Then, the mixture was
allowed to reach room temperature, and a solution of propargyl
bromide in toluene (80wt.-%, 1.88 mL) was added. This mixture
was heated under reflux overnight. The reaction was then allowed
to reach room temperature and concentrated under reduced pres-
sure. DCM (100 mL) and water (100 mL) were added carefully, and
the crude product was extracted with DCM (3ϫ 100 mL). The
combined organic phases were dried with anhydrous MgSO4, fil-
tered, and concentrated to yield a brown oil, which eventually so-
lidified and was used in the next step without further purification
(1.07 g, 92% yield). 1H NMR (400 MHz, CDCl3): δ = 8.43 (s, 1 H,
H1), 8.20 (s, 2 H, H6), 8.00 (d, J = 7.4 Hz, 2 H, H3), 7.51–7.37 (m,
4 H, H4, H5), 7.19 (br, 2 H, H16), 6.89 (br, 2 H, H15), 5.57 (s, 2 H,
H9), 4.58 (s, 2 H, H18), 4.17 (s, 2 H, H19), 4.05 (s, 2 H, H13), 2.51
(t, J = 2.3 Hz, 1 H, H21), 1.73 (br, 3 H, H12Ј), 1.52 (br, 6 H, H12)
ppm. 13C NMR (100 MHz, CDCl3): δ = 155.93 (C10), 138.19 (C14),
135.67 (C17), 131.39 (C8), 131.33 (C2, C7), 129.07 (C3), 128.22 (C1),
128.04 (C16), 126.85 (C15), 126.13 (C4), 124.96 (C5), 124.44 (C6),
79.70 (C20), 77.24 (C11), 74.63 (C21), 71.29 (C18), 56.97 (C19), 47.54
(C13), 40.90 (C9), 29.70 (C12) ppm. MS (ESI+): m/z = 466 [M +
H]+ (calcd. 466.23 for C31H32NO3).
General Procedure for Non-Interlocked-Thread Precursors by Click
Reaction to Give T1, T2 or T3: R4, S3, S4, or S5 and [Cu(NCMe)4]-
PF6 were placed in a Schlenk flask under a nitrogen atmosphere.
Dried and degassed DCM and 2,6-lutidine were added. The mix-
ture was stirred at room temperature for 5 d and then concentrated
to afford
a crude product, which was purified by column
chromatography.
General Procedure for the Methylation of Non-Interlocked-Thread
Precursors to Give T4-PF6, T5-PF6, or T6-PF6: Trimethyloxonium
tetrafluoroborate was added to a solution of T1, T2, or T3 in dry
and degassed DCM. The mixture was stirred at room temperature
until the complete dissolution of the tetrafluoroborate salt was ob-
served. The solution was then diluted with DCM, and an aqueous
solution of NH4PF6 in MiliQ water was added. The mixture was
stirred vigorously, and the organic phase was extracted, dried with
anhydrous MgSO4, filtered, and concentrated under reduced pres-
sure to afford T4-PF6, T5-PF6, or T6-PF6 which was used in the
next step without further purification.
General Procedure for Boc Deprotection to Obtain Final Non-inter-
locked Threads 4-H-PF6, 5-H-PF6, and 6-H-PF6: Trifluoroacetic
acid was added to a solution of T4-PF6, T5-PF6, or T6-PF6 in
chloroform (10 mL). The dark mixture was stirred at room tem-
perature for 30 min. The solvents were removed, and the resulting
black oil was diluted with DCM (20 mL). Ammonium hexafluoro-
phosphate in MiliQ water (15 mL) was added, and the biphasic
mixture was stirred vigorously for 30 min. Then, both layers were
separated, and the organic phase was dried with anhydrous
MgSO4, filtered, and concentrated to afford a thick black oil, which
was subjected to purification by column chromatography.
1-(Anthracen-9-yl)-N-{4-[(prop-2-yn-1-yloxy)methyl]benzyl}meth-
anaminium Hexafluorophosphate (R5-H-PF6): Trifluoroacetic acid
(10 mL) was added to a solution of R4 (0.93 g, 2 mmol) in chloro-
form (100 mL), and the mixture was stirred overnight at room tem-
perature. The solvent was then removed under vacuum, and the
resulting crude product was redissolved in DCM (20 mL) and an
aqueous solution (10 mL) of ammonium hexafluorophosphate
(1.63 g, 10 mmol) in MiliQ water. The biphasic mixture was stirred
vigorously for 10 min and extracted in a separating funnel. Hexane
(20 mL) was added to the organic phase, and the mixture was
stored at –20 °C for 12 h. The brown crystals were collected by
filtration and dried under vacuum to afford R5 as a dark brownish
General Procedure for Catalytic Reaction 1: trans-Cinnamaldehyde
(17.6 μL,
0.14 mmol),
1H,1H,2H,2H-perfluorodecanethiol
solid (0.57 g, 78% yield). 1H NMR (400 MHz, [D6]acetone): δ = (48.0 μL, 0.168 mmol), and the catalyst (5mol-%) were mixed in a
8.79 (s, 1 H, H1), 8.31 (d, J = 8.7 Hz, 2 H, H6), 8.19 (d, J = 8.2 Hz,
2 H, H3), 7.74 (d, J = 8.1 Hz, 2 H, H12), 7.68–7.56 (AB System, 4
round-bottom flask. CDCl3 (1400 μL) was added as well as the
appropriate amount (1.2 equiv. for each catalytic site) of a 1m solu-
H, H4, H5), 7.52 (d, J = 8.2 Hz, 2 H, H13), 5.69 (s, 2 H, H9), 5.02 tion of NaOH in D2O if necessary. The mixture was stirred vigor-
(s, 2 H, H10), 4.66 (s, 2 H, H15), 4.25 (d, J = 2.4 Hz, 2 H, H16),
3.02 (t, J = 2.4 Hz, 1 H, H18) ppm. 13C NMR (100 MHz, [D6]- spectra were recorded to check the reaction progress. Once the reac-
acetone): δ = 140.94 (C14), 132.31 (C2), 131.90 (C7), 131.63 (C1),
tion was finished, the crude product was subjected immediately to
ously at room temperature. Aliquots were taken, and 1H NMR
6638
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 6631–6640

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General Procedure for Catalytic Reaction 2: trans-Cinnamaldehyde
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1
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check the reaction progress. Once the reaction was finished, the
crude product was subjected immediately to purification by column
chromatography (SiO2 gel, hexane/AcOEt,2:1) to yield the expected
addition product if the reaction was successful.
Supporting Information (see footnote on the first page of this arti-
cle): A detailed overview of the complete synthesis, atom number-
ing, NMR spectra, and other details.
Acknowledgments
This work was funded by the Spanish Ministerio de Economía y
Competitividad (MINECO) (CTQ 2013-41067-P). H. B. acknowl-
edges with thanks the Spanish Ministerio de Educación y Ciencia
(MEC) for a grant.
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Received: July 17, 2015
Published Online: September 23, 2015
6640
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Eur. J. Org. Chem. 2015, 6631–6640