Slippage of a porphyrin macrocycle over threads of varying bulkiness: Implications for the mechanism of threading polymers through a macrocyclic ring

Article abstract of DOI:10.1002/chem.201403740

Threading of a polymer through a macrocyclic ring may occur directly, that is, by finding the end of the polymer chain, or by a process in which the polymer chain first folds and then threads through the macrocyclic ring in a hairpin-like conformation. We present kinetic and thermodynamic studies on the threading of a macrocyclic porphyrin receptor (H₂1) onto molecular threads that are blocked on one side and are open on the other side. The open side is modified by groups that vary in ease of folding and in bulkiness. Additionally, the threads contain a viologen binding site for the macrocyclic receptor, which is located close to the blocking group. The rates of threading of H₂1 were measured under various conditions, by recording as a function of time the quenching of the fluorescence of the porphyrin, which occurs when receptor H21 reaches the viologen binding site. The kinetic data suggest that threading is impossible if the receptor encounters an open side that is sterically encumbered in a similar way as a folded polymer chain. This indicates that threading of polymers through macrocyclic compounds through a folded chain mechanism is unlikely.

Full text of DOI:10.1002/chem.201403740

DOI: 10.1002/chem.201403740
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Supramolecular Chemistry |Hot Paper|
Slippage of a Porphyrin Macrocycle over Threads of Varying
Bulkiness: Implications for the Mechanism of Threading Polymers
through a Macrocyclic Ring
Alexander B. C. Deutman, Shaji Varghese, Mohamed Moalin, Johannes A. A. W. Elemans,
Alan E. Rowan,* and Roeland J. M. Nolte*[a]
Abstract: Threading of a polymer through a macrocyclic
ring may occur directly, that is, by finding the end of the
polymer chain, or by a process in which the polymer chain
first folds and then threads through the macrocyclic ring in
a hairpin-like conformation. We present kinetic and thermo-
dynamic studies on the threading of a macrocyclic porphyrin
receptor (H21) onto molecular threads that are blocked on
one side and are open on the other side. The open side is
modified by groups that vary in ease of folding and in bulki-
ness. Additionally, the threads contain a viologen binding
site for the macrocyclic receptor, which is located close to
the blocking group. The rates of threading of H21 were mea-
sured under various conditions, by recording as a function
of time the quenching of the fluorescence of the porphyrin,
which occurs when receptor H21 reaches the viologen bind-
ing site. The kinetic data suggest that threading is impossi-
ble if the receptor encounters an open side that is sterically
encumbered in a similar way as a folded polymer chain. This
indicates that threading of polymers through macrocyclic
compounds through a folded chain mechanism is unlikely.
Introduction
Previously, we have reported on a rotaxane catalyst that op-
erates in a similar way as the naturally occurring DNA poly-
merases.[5] It is composed of a toroidally shaped cage com-
pound containing a metalloporphyrin roof, which forms inclu-
sion complexes with various substrate molecules. The
manganese(III)–porphyrin complex of this macrocyclic host
(H21) was able to thread onto polymers, for example, polybuta-
The process of biopolymer translocation through pores formed
by toroidal proteins is fundamental to numerous biological
processes, including the transport of proteins across cell mem-
branes, the infection of a host cell by viral DNA, and the pack-
ing of DNA into viral capsids.[1] Understanding the way in
which biopolymers migrate through pores is very im-
portant, as it may open the possibility of developing
novel, powerful analytical methods, such as the rapid
sequencing of DNA molecules, gene therapy and the
controlled delivery of drugs.[2] In addition, the mecha-
nisms by which natural systems convert chemical
energy into directed motion is also connected to
transport phenomena through pores and studying
their mechanisms will provide in-depth information
on the underlying principles of operation of these
systems;[3] this in turn could avail researchers to
design artificial motor systems and machines that
can perform different tasks.[4]
diene, and epoxidize the double bonds of this polymer in
a “processive” manner, that is, by carrying out several rounds
of catalysis without detaching from the polymer chain. Our
previous studies on the mechanism of threading and transport
of H21 on polymers revealed that the host compound initially
binds to the outside of the polymer chain after which the poly-
mer folds back and fills the cavity of the host (entron effect).
The host subsequently moves along the polymer by a hopping
process. This looping mechanism leads to accelerated thread-
ing and also to unidirectional motion.[7] There is some similarity
[a] Dr. A. B. C. Deutman, Dr. S. Varghese, M. Moalin, Dr. J. A. A. W. Elemans,
Prof. A. E. Rowan, Prof. R. J. M. Nolte
Institute for Molecules and Materials
Radboud University Nijmegen
Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands)
Fax: (+31)24-3652929
E-mail: A.Rowan@science.ru.nl
R.Nolte@science.ru.nl
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201403740.
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with the conventional transport of proteins through pores of
membranes in biological systems, namely, the “secretion (Sec)”
pathway.[6] In this mechanism the biopolymer first binds to
a site close to the open pore in the membrane and subse-
quently threads through it. In a similar fashion the end of the
synthetic polymer may interact with the macrocyclic com-
pound by binding to it and subsequently threading through
it[7] (Figures 1 and 2a). The second type of transport of biopoly-
mers through pores in membranes in biological systems is the
twin-arginine translocation (Tat) pathway, which involves the
process of translocating a fully folded protein across the cyto-
plasmic membranes of prokaryotes and the thylakoid mem-
brane of plant chloroplasts.[6]
The intriguing question that we would like to answer is,
“can a polymer chain thread through porphyrin macrocycle
H21 in a folded conformation or not?” It is known that a flexible
polymer can adopt back-folded[8] and helical geometries,[9–14]
while it is bound inside a host compound, hence it is not un-
likely that H21 can bind to a folded polymer chain and thread
over it (Figure 2b). This mechanism might be more favourable
because the macrocycle does not have to find the open end of
the polymer chain (Figure 2a), but can start the threading pro-
cess at any position on the polymer chain.
To answer this question we decided to study the kinetics of
pseudo-rotaxane formation between porphyrin macrocycle
H21 and linear guest molecules that have a sterically crowded
blocking group at one side and
an open end at the other side.
Close to the blocked side a violo-
gen moiety is present to which
H21 strongly binds. Binding can
only occur on the open side
either by directly finding this
end or by a folded chain mecha-
nism. This approach was also
chosen in our previous studies
on the threading of H21 onto
polymers of different length.[7] To
Figure 1. Reversible formation of a complex between a polymer and macrocyclic host H21. The polymer is blocked
on one side and open on the other side. After threading the macrocycle is trapped at a viologen binding site,
which is close to the blocked side.
this end, viologen derivatives
V1–V8, containing the same
blocking group appended on
one side and a variety of termi-
nal groups appended on the other side, among which are a cy-
clododecane moiety and a variety of appended iso-alkyl moiet-
ies, were synthesized. One of the main advantages of the use
of porphyrin macrocycle H21 in threading studies is its high af-
finity for viologen derivatives (Kassoc ꢀ105–107 mꢁ1). When the
porphyrin is bound to the viologen trap its fluorescence is
quenched, hence measuring the fluorescence as a function of
time allows the study of the threading process and complex
formation at sub-micromolar concentrations. We decided to
synthesize viologen derivatives with substituents that increase
in size, with a bulkiness that is equal in size to a hairpin-folded
conformation of the polymer. By studying the kinetic process
of complex formation between H21 and viologen derivatives
V1–V8, not only the feasibility of the threading of H21 over
a folded polymer chain can be determined, but also the effect
of the bulkiness of the end group on the process of threading
can be estimated.
Results and Discussion
Synthesis of viologen derivatives
Macrocyclic host H21 was synthesized as published previous-
ly.[22,23] Viologen derivatives V1–V8 can be readily synthesized
by substitution reactions of 4,4’-bipyridine (BiPy) with primary
halides.[16] Reactions of an excess of BiPy with primary halides
can statistically provide monoalkylated bipyridinium com-
pounds. Two main approaches were chosen to synthesize viol-
Figure 2. Schematic representation of pseudo-rotaxane formation by bind-
ing and threading. a) Threading mechanism in which the macrocycle threads
onto the open end of the polymer chain and moves to the viologen trap in
a random walk along a single chain. b) Threading mechanism in which the
macrocycle binds to and moves over a folded chain eventually reaching the
viologen trap.
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Scheme 1. Synthesis of viologen derivatives V1–V8. i) DMF, 908C, 1–5 days. ii) NH4PF6 (aq.), iii) NaH, THF, iv) KOtBu, Ph3PCH3Br, toluene, v) 1) BH3SMe3, NaOH
(aq.), H2O2 (aq.), THF; 2) Br2Ph3P, pyridine, CH2Cl2.
ogens V1–V8 (Scheme 1). In the first approach, blocking-
group-containing monoalkylated bipyridinium 2 was synthe-
sized from BiPy and bromide 1[5b] after which the terminal
groups were appended by a second substitution reaction
using primary bromides 3, 4, 5, 6, 13 and 14, providing violo-
gen derivatives V1–V3, V5, V6 and V8 after ion exchange with
NH4PF6. In the second approach, the terminal group-containing
pyridinium salts 16 and 17 were first synthesized, after which
the blocking groups were appended by nucleophilic substitu-
tion reactions with 1 providing viologen derivatives V4 and V7
after ion exchange with NH4PF6. (3-Bromo-propoxy)cyclodode-
cane 6 was synthesized by reacting 1,3-dibromopropane with
cyclododecanol in the presence of NaH.[17] In addition to 6, the
terminal alkene elimination product of 6 was also formed in
significant amounts and this product could unfortunately not
be separated from 6. This mixture of compounds was used as
such in the synthesis of V8. Bromides 13, 14 and 15 were syn-
thesized by Wittig reactions[18a] of ketones 7, 8 and 9 followed
by anti-Markovnikov bromination[19a] of the resulting alkenes
10, 11 and 12. Bipyridinium salt 17 was synthesized according
to a literature procedure.[20]
derivatives V1, V2 and V3. The 400 MHz 1H NMR spectra re-
vealed only proton resonances of the pseudo-rotaxane com-
plexes between H21 and V1, V2 and V3, respectively, and reso-
nances of the protons of unbound guests, because the ex-
change (hence the slippage) between H21 and the different
guests (V1–V3) is slow on the NMR spectroscopic timescale
and no significant coordination between the outside of H21
1
and the viologen derivatives occurred. The H NMR spectra of
the solutions containing mixtures of H21 and V4 and V5, re-
spectively, revealed slow formation of the pseudo-rotaxane
complexes (Figure 3). Over time the proton resonances of un-
complexed H21 and viologens V4 and V5 decreased in intensi-
ty at the benefit of the intensity of proton resonances of the
respective pseudo-rotaxane complexes. The slippage over the
adamantane group of V4 is significantly faster than the slip-
page over the isononyl group of V5. Where full complexation
was reached within the hour at room temperature in the slip-
page experiment using V4, for V5 this was only achieved after
1
three days of standing at room temperature. The H NMR spec-
troscopic experiments with H21 and V6–V8 revealed no
pseudo-rotaxane formation, even after prolonged standing of
the samples at elevated temperatures (508C).
1H NMR spectroscopic investigations
Thermodynamics and kinetics of pseudo-rotaxane formation
First, pseudo-rotaxane formation of H21 with viologens V1–V8
was investigated with the help of 1H NMR spectroscopy.
Chloroform/acetonitrile solutions (1:1 (v/v)) containing H21
(6.8 mm) and a slight excess of the different viologen guests
were prepared. Immediate complex formation was observed in
the case of the least bulky terminal-group-containing viologen
The evolution of macrocycle A, guest B and pseudo-rotaxane C
in time in the threading process can be completely described
by Equations (1–3). The association constant (Kassoc) between
the macrocycle and the guest is given by Equation (4). Equa-
tion (1) is the universal formula for the threading process and
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½Cꢂeq
Kassoc
¼
ð½Aꢂ0ꢁ½CꢂeqÞð½Bꢂ0ꢁ½CꢂeqÞ
ð4Þ
In the 1H NMR spectroscopic
experiments in which the
threading equilibrium is not im-
mediately reached (i.e. in the
case of viologen derivatives V4
and V5), the ratios of H21, violo-
gen and pseudo-rotaxane in
time could be easily determined
from the relative intensities of
the 1H NMR spectroscopic sig-
nals associated with each spe-
cies. By monitoring the decrease
in the relative intensities of H21
and viologen derivatives V4 and
V5, respectively, with respect to
their concomitant appearance in
the complexes as a function of
Figure 3. 1H NMR spectral changes (400 MHz, CDCl3/CD3CN 1:1 (v/v)) during the threading experiment of H21
(0.68 mm) and V5 (1.4 mm, 2 equiv) as a function of time (from bottom to top) at 458C, revealing the total disap-
pearance of the resonances of H21 and V5 at the benefit of the formation of the non-symmetrical (pseudo-)rotax-
ane complex between H21 and V5. The signals belonging to free H21 (o) and free V5 (X), and to H21 (+) and V5
(*) in the rotaxane self-assembled structure are indicated. In the first and final spectrum, some of the proton sig-
nals of H21 are assigned (see structure H21 for numbering).
can be employed independent of the relative ratios of macro-
cycle ([A]0) and guest ([B]0) or the initial amount of pseudo-ro-
taxane complex present at t=0 ([C]0). It is therefore not neces-
sary to mix equimolar amounts of macrocycle and guest to cal-
culate accurate rate constants. Equations (1–3) can also be em-
ployed to calculate rate constants in the dethreading process-
time, the rate constants for the slippage processes, kon, could
be calculated by using Equations (1–3). At equilibrium, no free
H21 could be observed at the used concentrations of this host
and viologen guests V4 or V5, which makes it impossible to
derive accurate values for Kassoc. Only a lower limit for these as-
sociation constants could be calculated from the experiments
(Table 1).
es in which koff =kon/Kassoc
.
The process of the slippage of H21 with V4 was slightly too
fast to calculate satisfactorily accurate rate constants with the
help of 1H NMR spectroscopic techniques (over 50% of
pseudo-rotaxane had already been formed after recording the
first spectrum). Therefore, it was decided to monitor pseudo-
rotaxane formation by UV/Vis spectroscopy. Solutions contain-
ing H21 (2ꢁ10ꢁ5 m) and V4 (6ꢁ10ꢁ4 m, 40 equiv) were pre-
pared in chloroform/acetonitrile 1:1 (v/v) and after the addition
of the solution of V4 to the solution of H21 the spectral
changes of the porphyrin Soret band were monitored in time.
The concentrations of V4 were chosen such that at equilibrium
H21 would be nearly completely occupied by V4, hence the
total change in absorption at any wavelength simply repre-
kon
A þ B
C
H
G
koff
ꢀ
ꢁ
ꢂ
ꢃ
q
pꢁ½Cꢂ
mðpꢁqÞt
ek
qꢁ½Cꢂ00
1ꢁ p
ꢀ
ꢃ
½Cꢂ ¼ p
ð1Þ
pꢁ½Cꢂ0
1ꢁ qꢁ½Cꢂ ek
mðpꢁqÞt
0
p ¼ ½Cꢂeq
½Aꢂ0½Bꢂ0
ð2Þ
ð3Þ
q ¼
½Cꢂeq
¼
¼
¼
Table 1. Rate constants (kon) for the threading of H21 over V1–V8 and the activation parameters (DGon, DHon, DSon) obtained from an evolution of the ki-
netic data using Eyring plots, the association constants (Kassoc) and free energies of association (DG0) of the formed complexes, and the thermodynamic
complexation parameters (DH0, DS0) obtained from an evolution of the thermodynamic data by using Van’t Hoff plots.
[g]
¼
[i]
¼[j]
¼[j]
[h]
[i]
[j]
[j]
Guest
kon [mꢁ1 sꢁ1
]
DGon [kJmolꢁ1
]
DHon [kJmolꢁ1
]
DSon [Jmolꢁ1 Kꢁ1
]
Kassoc [mꢁ1
]
DG0 [kJmolꢁ1
]
DH0 [kJmolꢁ1
]
DS0 [Jmolꢁ1 Kꢁ1
]
[e]
[e]
V1[a]
V2[a]
V3[a]
V4[b]
V5[c]
5ꢁ106
3ꢁ106
6.0ꢁ105
7.9
35
36
40
68
80
15
–
21
42
63
ꢁ67
1.3ꢁ107
6.8ꢁ106
1.1ꢁ107
>106[e]
ꢁ41
ꢁ39
ꢁ40
–
–
72
68
–
–
[d]
[d]
–
ꢁ18
ꢁ20
ꢁ64
ꢁ87
ꢁ56
[e]
[e]
[e]
–
–
–
–
[e]
[e]
[e]
7.0ꢁ10ꢁ2
>106[e]
–
–
[f]
[f]
[f]
[f]
[f]
[f]
[f]
[f]
V6–V8
–
–
–
–
–
–
1
[a] Determined by fluorescence titrations in CHCl3/CH3CN 1:1, (v/v). [b] Determined by UV/Vis titrations in CHCl3/CH3CN 1:1 (v/v). [c] Determined by H NMR
spectroscopic experiments in CDCl3/CD3CN 1:1 (v/v). [d] Threading rate was too high to be measured accurately at the used experimental conditions.
[e] Association constant was too high to be calculated accurately at the used experimental concentrations. [f] No complex formation was observed. [g] Esti-
mated error <15%. [h] Estimated error <35%. [i] Estimated error 1 kJmolꢁ1. [j] Estimated error 2 kJmolꢁ1
.
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sented the change in the amount of free H21 with respect to
the pseudo-rotaxane complex between H21 and V4. The con-
centration of pseudo-rotaxane in time, [C]t, in the experiment
is therefore given by: [C]t =[A]0{AtꢁA0}/{AeqꢁA0}, in which A0, At
and Aeq are the absorbance at t=0, t, and t=1, respectively.
A small redshift of the porphyrin Soret band and an isosbestic
point were observed upon formation of the pseudo-rotaxane
complex. The evolution of the absorbances at different wave-
lengths in time (Figure 4a) could be fitted with the help of
(see Figure 4b for complexation between H21 and V3). The
fluorescence emission curves in time could be fitted with the
use of Equations (1–4), providing the values of kon and Kassoc in
plural, thereby significantly minimizing the error both in kon
and Kassoc
.
To investigate the effect of the temperature on the kinetics
of the process, the slippage of H21 over the terminal groups of
V1–V5 was monitored at at least three different temperatures
by using either of the above described methods. The enthalpic
¼
¼
(DHon) and entropic (DSon) contri-
butions to the total free energy
¼
of activation (DGon) were deter-
mined from the straight lines of
the Eyring Plots (Figure 5a). In
addition, the enthalpic (DH0) and
entropic (DS0) contributions to
the total free binding energy
(DG0) of pseudo-rotaxane forma-
tion between H21 and V2 or V3
could be determined with the
help of Van‘t Hoff plots (Fig-
ure 5b). All the thermodynamic
and kinetic data are listed in
Table 1.
Figure 4. a) Evolution of the absorbance of the porphyrin Soret band of H21 (1.6ꢁ10ꢁ4 m) at different wavelengths
in time after the addition of 50 equivalents of V4 in CHCl3/CH3CN (1:1, v/v) at 258C. b) Fluorescence emission
(grey dots) of H21 after the addition of increasing amounts of V3 in time in CHCl3/CH3CN (1:1, v/v) at 18C. While
mixing, the cuvettes were removed from the spectrometer which results in the local drops in fluorescence. The
black lines indicate the fits that are obtained by using Equations (1–4). The constants kon and Kassoc, calculated
from the individual threading curves, are all in the same order of magnitude, which stresses the accuracy of the
data analysis.
Kinetic data
Earlier reports in the literature
have shown that very subtle
Equations (1–3). In fact, such an excess of V4 was
used that the kinetics of the threading could also be
fitted with (pseudo)first order binding isotherms, and
the calculated averaged rate constant for the thread-
s
ing of H21 with V4, kon =7.9mꢁ1 ꢁ1), was in good
agreement with the rate constant determined by
1H NMR spectroscopy (kon =8.5mꢁ1 sꢁ1).
To derive the rate constants for the threading of
H21 over the least bulky terminal groups of the violo-
gens, that is, those of V1–V3, threading experiments
were performed at low concentrations (10ꢁ6 m) of
H21 and these guests in a 1:1 (v/v) mixture of chloro-
form and acetonitrile. Since upon the binding of viol-
ogen derivatives the porphyrin fluorescence emission
is fully quenched, the kinetics and thermodynamics
of complex formation could be easily monitored by
recording this fluorescence emission in time. The
pseudo-rotaxane concentration [C] is given by [C]t =
Figure 5. a) Eyring plots for the threading of H21 over V1, V3, V4 and V5. b) Van ‘t Hoff
plots for the complexation of H21 with V2 and V3 (error bars are indicated by the hori-
zontal lines).
[A]0{E0ꢁEt}/E0, in which E0 and Et are the fluorescence emissions
at t=0 and t, respectively. To obtain as many data as possible
in a short time span, it was decided to perform titration experi-
ments in which solutions containing low concentrations (2-4ꢁ
10ꢁ7 mꢁ1) of the viologen derivatives were added to a solution
containing H21. After each addition, the fluorescence emission
slowly reached a new equilibrium position, and at that point
a following batch of viologen-containing solution was added
changes in terminal groups of a thread, such as going from an
ethyl to an isopropyl[21] or from a cyclohexane to a cyclohep-
tane substituent,[15j] resulting in an all-or-nothing effect for the
slippage of a macrocycle over these terminal groups. A small
increase in terminal group bulkiness can increase the steric
hindrance to the level that the barrier for slippage becomes in-
surmountable. A similar and perhaps even more subtle all-or-
nothing effect was observed in the present study. While a very
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low value for the rate constant was observed for the threading
of H21 over V5, which indicated that H21 can only just slip
over the isononyl group, threading over the longer substitu-
ents of V6, V7 and over the cyclododecyl moiety of V8 ap-
peared to be not possible. Obviously, the cavity of H21 is not
large enough to allow slippage of the cyclododecyl terminal
group of V8. The all-or-nothing effect observed between V5
and V6 clearly indicates that very subtle differences in steric
bulk govern whether threading is possible or not. It moreover
provides a clear hint on the mechanism by which the isononyl
of V5 group is traversed. Two plausible mechanisms for this
process can be rationalised. A first one, in which the macrocy-
cle threads onto a single n-butyl chain, after which it moves in
a second step over both the second chain and part of the viol-
ogen moiety (Figure 6a), similar to the mechanism reported for
cumferences of the Van der Waals surfaces of the different
transition-state conformations (the most bulky part of the ter-
minal groups in their least bulky conformations) were estimat-
ed with the help of Corey–Pauling–Koltun (CPK) models. Al-
though for V5 and V6 the differences in substituent bulkiness
are very marginal (within 8%, see Figure 6), the transition-state
conformations of the second mechanism were less ‘bulky’ than
those of the first. A measurement of the largest inner circum-
ference of H21 (19.8 ꢂ, see Figure 7), moreover, revealed that
only the transition-state conformation of the isononyl group in
the second mechanism (Figure 6b, 19.4 ꢂ) is within the dimen-
sions of the cavity. These results tentatively suggest that H21
threads over the isononyl group of V5 according to the
second mechanism, in which the chain ends of the terminal
group are tweezed together (Figure 6b). The slightly more
bulky terminal group of V6 just exceeds the dimensions of the
cavity, resulting in no threading.
Assuming a similar threading mechanism, the circumferenc-
es of the Van der Waals surfaces of all the different terminal
groups in their proposed transition-state geometries were de-
termined and the slippage rate constants were plotted versus
these circumferences (Figure 7b). The plot clearly shows that
when the circumferences of the terminal groups approach the
inner circumference of the macrocycle, the rate constant for
threading tends to zero. This is another good indication that
indeed the steric interactions between terminal group and the
macrocycle determine the relative rates and feasibility of the
threading process. The enthalpic contributions to the activa-
Figure 6. Space-filling molecular models of proposed slippage transition-
state conformations of the terminal groups of V5 (left) and V6 (right) for the
back-folding mechanism (a and c) and the tweezed double chain mecha-
nism (b and d). The maximum circumferences of the Van der Waals surfaces
in the transition-state geometries are indicated to stress that conforma-
tion (b) is the least bulky.
¼
tion energy (DHon), obtained by evaluation of the threading at
different temperatures, point in the same direction: a clear in-
crease in enthalpy of activation is observed upon increasing
the terminal group bulkiness (Table 1), which is in line with the
idea that the steric repulsion is enthalpic in origin.
Although in all cases the slippage is entropically unfavoura-
ble, no trend could be observed in the values of the entropy
the slippage of bis-p-phenylene[34]crown-10 over 4-R-phenyl-
bis(4-tert-butyl-phenyl)methane-based stoppers.[15i] Assuming
this mechanism, the bottle-neck of the slippage lies for V5 in
traversing the part at which H21 needs to overcome
the steric bulk of the second part of the chain and
the viologen group. A second possible mechanism is
that the two isononyl chain ends are ‘tweezed’ to-
gether in close proximity and the threading occurs
over a double chain, as presented in Figure 6b. The
first mechanism can be considered unlikely due to
the need for a presumably highly unfavourable back-
folding of the alkyl chain onto the viologen moiety,
in which this chain gets in close proximity to the re-
pelling positive charge on the viologen. 1H NMR
spectroscopic studies do not suggest such a back-
folding of the alkyl chain. Also the second mecha-
nism is at first sight not very likely, since it needs an
organization of the highly flexible alkyl chains in
a very specifically tweezed geometry, which would, in
¼
of activation (DSon). The differences in the obtained activation
parameters observed for the threading over the adamantane
Figure 7. a) Circumferences of the terminal groups of V1–V8 that H21 has to surmount
before complex formation can occur and the inner circumference of the cavity of H21, all
based on Van der Waals surfaces. b) Rate constants for the slippage of H21 over the dif-
ferent terminal groups plotted against the circumference of these groups and the inner
principle, be entropically highly unfavourable, al-
though the same entropic argument can also be ap-
plied to the first mechanism. To determine which of
the two mechanisms is the most likely one, the cir- circumference of the cavity of H21.
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group of V4 and the isononyl group of V5 are intriguing. The
rate constant for slippage over the adamantane is more than
two orders of magnitude higher than the rate constant for the
slippage over the isononyl group. While the adamantane
group has a fixed and nearly spherical geometry and is there-
fore readily organized for the threading of H21, the isononyl
group can be expected to be very flexible and needs to preor-
ganize in its least bulky conformation to allow threading of
H21. Based on these differences in flexibility one would there-
fore expect a more negative value for the entropy of activation
V2. The results suggest, on the other hand, that it is entropical-
ly more favourable to form the complex between H21 and V2
than the complex between H21 and V3. This might be the
result of a relatively better solvation of V3 compared to V2 in
the used solvent system, because of the larger nonpolar cyclo-
hexyl substituents compared to the isopropyl substituents,
which reduces the relative ‘need’ for V3 to form a complex
with H21 compared to V2. It is also possible that the extra sta-
bilization of the complex between H21 and V3 by the cyclo-
hexyl group is entropically more demanding.
¼
(DSon) for slippage over the isononyl terminal group than over
the adamantane group. However, the contrary was derived
from the variable temperature experiments, which suggests
that other factors than the flexibility of the terminal groups,
like for instance differences in terminal group solvation, enthal-
py–entropy compensation or the flexibility of the receptor also
play a crucial role in the threading process. It can also be
argued that the isononyl group already is preferentially organ-
ised in the ‘tweezed’ conformation in the rather polar solvent
mixture. Irrespective of what exactly causes the experimentally
obtained activation parameters, the main difference between
the threading over the terminal groups of V4 and V5 is reflect-
Conclusion
The present study indicates that the ease of threading porphy-
rin macrocycle H21 over viologen-containing guests with differ-
ent terminal groups strongly depends on the size complemen-
tarities and subsequent steric interactions between the Van
der Waals surfaces of the macrocycle and the terminal group.
The rate constants of threading decrease upon increasing the
bulkiness of the terminal group, and when the dimensions of
its Van der Waals surface exceeds that of the inner Van der
Waals surface of the macrocycle, the barrier for the threading
becomes insurmountable, resulting in an all-or-nothing effect.
The results strongly suggest that movement of H21 over
a looped polymeric chain, as proposed previously, is highly un-
favourable, if not impossible. The experiments revealed that
no threading occurred over the terminal groups of V6, V7 and
V8, and a very low rate constant for the threading over the ter-
minal group of V5. The observed rate constant for the thread-
ing over the isononyl terminal group of V5 is more than five
orders of magnitude lower than the previously reported rate
constant for the movement of H21 over a poly-THF terminal
group of 54 nm length.[7b] It can thus be concluded that in the
threading of polymeric substrates, H21 first binds onto the
open end of the polymer chain after which it traverses the
complete polymer chain before it reaches the viologen binding
site, and that threading over a folded polymer chain is unlikely.
¼
ed in the enthalpy of activation (DHon). This difference is most
probably caused by a less favourable fit of the isononyl group
of V5 inside the cavity of H21 compared to the adamantane
group of V4, which stresses once more that steric hindrance is
the main rate-determining factor in the threading process.
Thermodynamic data
The binding free energy of the pseudo-rotaxane complexes of
H21 with V2 and V3 are a result of both favourable enthalpic
(DH0) and entropic contributions (DS0), as can be concluded
from the data in Table 1. In addition to stabilizing non-covalent
binding interactions (such as p–p interactions, Van der Waals
interactions and dipole–dipole interactions) between H21 and
the viologen derivatives, which are most likely enthalpic of
origin, there is also a strong entropic driving force for complex
formation. This is most probably the result of desolvation of
the viologen moieties and the cavity of H21 upon formation of
the pseudo-rotaxane complexes. The association constant of
H21 with V3 is larger than that of H21 with V2 (Table 1). This
observation is in line with our previous findings that an in-
crease in the size of the viologen substituents results in stron-
ger complex formation with H21.[5b] Although the electronic
properties of the viologen derivatives with different substitu-
ents are expected to be slightly different, and hence also the
viologen–macrocycle interactions, this effect is proposed to be
mainly the result of extra stabilizing (Van der Waals interactions
between the macrocyle and the substituents in the formed
host–guest complexes. For this reason, the cyclohexyl group of
V3 can provide more of these stabilizing interactions in the
complex with H21 than the isopropyl group of V2. The validity
of this hypothesis is emphasized by the different enthalpic
contributions (DH0) to the binding free energy (DG0), which
reveal a more favourable enthalpy of binding in the complex
between H21 and V3 than in the complex between H21 and
Experimental Section
Materials and methods
Chloroform and acetonitrile used in the titration experiments were
distilled from CaCl2. THF was distilled under nitrogen from sodium
and benzophenone. Dichloromethane was distilled under nitrogen
from CaCl2. Toluene was distilled under nitrogen from sodium. All
other solvents and chemicals were commercial products and used
as received. Fluorescence experiments were performed on
a Perkin–Elmer LS50B luminescence spectrometer equipped with
a thermostatted cuvette holder. UV/Vis spectra were recorded on
a Cary 100 Conc (Varian, Middelburg) UV/Vis spectrometer. MALDI-
TOF mass spectroscopy was performed on a Bruker Biflex III spec-
trometer. HRMS were measured on a JEOL JMS-T100CS AccuTOF.
1
NMR spectra were taken on a Varian Inova 400 (400 MHz, H and
2D spectra) instrument or on a Bruker DMX 300 (75 MHz, 13C spec-
tra) machine and were calibrated to an internal standard of tetra-
methylsilane (d=0.00 ppm). Porphyrin macrocycle H21 was synthe-
sized according to a literature procedure.[22,23]
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(3-Bromo-propoxy)cyclododecane (6)
Synthesis of the primary bromides 13, 14 and 15[19a]
A solution of cyclododecanol (0.26 g, 1.1 mmol) in dry THF (4 mL)
was added dropwise over a period of 10 min to a 08C suspension
of NaH (0.11 g of 60% NaH in mineral oil, 2.8 mmol) in dry THF
(3 mL) under an argon atmosphere. The reaction mixture was al-
lowed to warm to room temperature, stirred for 1 h and then
cooled to 08C after which 1,3-dibromopropane (2.2 mL, 24 mmol)
was added slowly. The reaction mixture was allowed to warm to
room temperature again, stirred for 1 h, cooled to 08C and then
mixed with diethyl ether (14 mL), neutralized with aqueous 1.0m
HCl (14 mL) and stirred for 1 h at room temperature. The ether
layer was washed with aqueous 1.0m HCl (1ꢁ), brine (2ꢁ) and
dried over MgSO4. The drying agent was filtered off, the solvents
were evaporated and the remaining 1,3-dibromopropane was dis-
tilled off to give 70 mg of a mixture of 6 and its alkene derivative
as a white solid in a molar ratio of circa 1 to 2. This mixture was di-
rectly used for the synthesis of V8. 1H NMR (400 MHz, CDCl3)
alkene characteristics: d=5.92 (m, 1H, H2C=CH), 5.27 (m, 1H,
CH2CH=CHtrans), 5.15 (m, 1H, CH2CH=CHcis), 3.98 (dt, 2H, C=CHCH2,
J=5.6, 1.2 Hz), 3.47 (m, 1H, cyclododecane CH), 1.28–1.36 (m, 22H,
cyclododecane (CH2)11); bromide characteristics: 3.55 (t, 2H, OCH2,
J=6 Hz), 3.53 (t, 2H, BrCH2, J=6.8 Hz), 2.07 (q, 2H, BrCH2CH2, J=
5.2 Hz), 3.42 (m, 1H, cyclododecane CH), 1.28–1.36 (m, 22H, cyclo-
dodecane (CH2)11).
Alcohol synthesis
A 08C solution of the corresponding methylene compound (10, 11
or 12 respectively) in dry THF was treated dropwise with a 2.0m
solution of borane methyl sulfide in toluene. After 2 h of stirring at
08C, the reaction mixture was warmed to room temperature,
stirred for an additional 2.5 h, cooled to 08C and neutralized with
ethanol, aqueous 3.0m NaOH and 35% aqueous H2O2. After 30 min
of stirring, the reaction mixture was allowed to warm to room tem-
perature and stirred overnight. The basic mixture was treated with
aqueous 1m HCl, the organic layer was separated and the aqueous
layer was extracted with diethyl ether (3ꢁ). The combined organic
phases were washed with brine (2ꢁ) and then dried over MgSO4.
The drying agent was filtered off and the filtrate was evaporated.
The crude mixture was subjected to a flash silica column to obtain
the corresponding primary alcohol.
2-Butylhexan-1-ol:[19b] Methylene solution: 10 (0.40 g, 2.9 mmol) in
THF (30 mL); borane solution: 0.90 mL, 1.8 mmol; neutralization
solutions: ethanol (6 mL), aqueous 3.0m NaOH (35 mL) and aque-
ous 35% H2O2 (35 mL); eluent: n-pentane/diethyl ether, 9:1 (v/v);
yield=0.32 g as a colourless liquid (2.0 mmol, 69%); 1H NMR
(400 MHz, CDCl3): d=3.54 (t, 2H, HOCH2, J=5.6 Hz), 1.45 (m, 1H,
HOCH2CH), 1.38–1.22 (m, 12H, HOCH2-CHCH2CH2CH2), 1.18 (t, 1H,
OH, J=5.6 Hz), 0.90 ppm (t, 6H, CH3, J=7.2 Hz); 13C NMR (75 MHz,
CDCl3): d=65.14, 40.00, 30.14, 28.62, 22.61, 13.57 ppm.
General synthesis of the methylene compounds 10, 11,
12[18a]
2-Heptylnonan-1-ol:[19c] Methylene solution: 11 (1.5 g, 6.7 mmol) in
THF (50 mL); borane solution: 2.3 mL, 4.6 mmol; neutralization sol-
utions: ethanol (12 mL), aqueous 3.0m NaOH (75 mL) and aqueous
35% H2O2 (75 mL); eluent: n-heptane/diethyl ether, 1:1 (v/v);
yield=1.5 g as a white solid (6.2 mmol, 93%); 1H NMR (400 MHz,
CDCl3): d=3.54 (m, 2H, HOCH2), 1.45 (m, 1H, HOCH2CH), 1.36–1.20
(m, 24H, HOCH2-CH(CH2)6), 1.20 (s, 1H, OH), 0.88 ppm (t, 6H, CH3,
J=7.2 Hz).
At room temperature, KOtBu (1.2 g, 11 mmol) was added in four
portions to a solution of methyltriphenylphosphonium bromide
(3.3 g, 9.3 mmol) in dry toluene (70 mL). The mixture was refluxed
for 1 h under an argon atmosphere and then cooled to room tem-
perature. A mixture of the corresponding ketone in dry toluene
was added dropwise and then stirred for 30 min. A saturated aque-
ous NH4Cl solution (30 mL) was added to the reaction mixture,
which was then extracted with diethyl ether (3ꢁ). The combined
organic phases were washed with brine (2ꢁ) and then dried over
MgSO4. The drying agent was filtered off and the filtrate was
evaporated in the presence of an excess of silica to avoid stopping
of the column by the remaining organic salts. The silica mixture
was put on a flash silica column and the product eluted to obtain
the corresponding methylene product.
2-Heptadecylnonadecan-1-ol: Methylene solution: 12 (1.3 g,
2.7 mmol) in THF (30 mL); borane solution: 0.9 mL, 1.8 mmol; neu-
tralization solutions: ethanol (5 mL), aqueous 3.0m NaOH (30 mL)
and aqueous 35% H2O2 (30 mL); eluent: n-heptane/diethyl ether,
1:1 (v/v); yield=1.0 g as a white solid (1.9 mmol, 72%); 1H NMR
(400 MHz, CD3CN:CDCl3, 1:1 (v/v)): d=3.43 (t, 2H, HOCH2, J=
5.6 Hz), 2.18 (m, 1H, HOCH2CH), 2.13–2.04 (m, HOCH2-CHCH2
chain), 1.35–1.10 (m, CH3CH2 chain), 1.25 (t„ 1H, OH), 0.88 ppm (t,
6H, CH3, J=7.2 Hz).
5-Methylene-nonane (10):[18b] Ketone mixture: 7 (1.0 g, 7.0 mmol)
in toluene (5 mL); eluent: n-pentane; yield=0.63 g as a colourless
1
Bromination reaction
liquid (4.5 mmol, 64%); H NMR (400 MHz, CDCl3): d=4.69 (q, 2H,
C=CH2, J=0.8 Hz), 2.00 (t, 4H, CH2=CCH2, J=8.0 Hz), 1.40 (m, 8H,
CH2=CCH2CH2CH2), 0.91 ppm (t, 6H, CH3, J=7.2 Hz).
A solution of the corresponding alcohol and pyridine in dry di-
chloromethane was added to a 08C suspension of triphenylphos-
phine dibromide in dry dichloromethane. The reaction mixture was
stirred at 08C for 15 min and for 1 h at room temperature, and was
subsequently neutralized with 10% of aqueous sodium bisulfite.
The organic layer was separated and the aqueous layer extracted
with dichloromethane (2ꢁ) and diethyl ether (1ꢁ). The combined
organic phases were dried over MgSO4, filtered and then evaporat-
ed in the presence of an excess of silica to avoid stopping of the
column by the remaining organic salts. The product was purified
on a flash silica column and the eluent was evaporated to obtain
the corresponding primary bromide.
5-(Bromomethyl)nonane (13):[19b] The triphenylphosphine dibro-
mide suspension was prepared from triphenylphosphine (0.55 g,
2.1 mmol) and bromine (0.11 mL, 2.1 mmol) in dichloromethane
(9 mL). Alcohol solution: 2-butylhexan-1-ol (0.25 g, 1.6 mmol) and
pyridine (0.40 mL, 5.0 mmol) in dichloromethane (2 mL); eluent: n-
8-Methylene-pentadecane (11):[18c] Ketone mixture:
8 (2.1 g,
9.2 mmol) in toluene (5 mL); eluent: n-heptane; yield=1.5 g as
1
a white solid (6.7 mmol, 72%); H NMR (400 MHz, CDCl3): d=4.68
(q, 2H, C=CH2, J=1.2 Hz), 1.99 (t, 4H,CH2=CCH2, J=8.0 Hz), 1.41 (q,
4H,
CH2=CCH2CH2,
J=6.8 Hz),
1.28
(m,
16H,
CH2=
CCH2CH2CH2CH2CH2CH2), 0.88 ppm (t, 6H, CH3, J=7.2 Hz).
18-Methylene-pentatriacontane (12):[18d] Ketone mixture: 9 (4.6 g,
9.2 mmol) in toluene (10 mL); eluent: n-heptane; yield=1.34 g as
1
a white solid (2.66 mmol, 30%); H NMR (400 MHz, CDCl3): d=4.68
(m, 2H, C=CH2), 1.99 (t, 4H,CH2=CCH2, J=7.2 Hz), 1.40 (dd, 4H,
CH2=CCH2CH2, J=6.8 Hz), 1.26 (m, 56H, CH2=CCH2CH2 (CH2)14), 0.88
(t, 6H, CH3, J=7.2 Hz).
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pentane; yield=0.22 g as a colourless liquid (0.99 mmol, 62%);
1H NMR (400 MHz, CDCl3): d=3.45 (d, 2H, BrCH2, J=4.8 Hz), 1.60
(m, 1H, BrCH2CH), 1.44–1.17 (m, 12H, CH2), 0.91 ppm (t, 6H, CH3,
J=7.2 Hz).
CD3CN/CDCl3, 1:1 (v/v)): d=8.93 (d, 2H, BipyH, J=6.8 Hz), 8.91 (d,
2H, BipyH, J=6.8 Hz), 8.40 (m, 4H, BipyH), 7.02 (s, 1H, ArH), 6.73
(d, 2H, ortho-ArH, J=0.8 Hz), 4.67 (t, 2H, NCH2, J=7.6 Hz), 4.62 (t,
2H, NCH2, J=7.2 Hz), 4.00 (t, 2H, OCH2, J=6.4 Hz), 2.14 (dd, 2H,
CH2, J=8 Hz), 2.04 (dd, 2H, CH2, J=7 Hz), 1.86 (dd, 2H, Ar-OCH2-
CH2, J=7.6 Hz), 1.61 (dd, 2H, CH2, J=7.2 Hz), 1.40 (m, 4H, CH2)
1.30 (s, 18H, CH3), 0.93 ppm (t, 3H, CH3, J=6.8 Hz); 13C NMR
(75 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=158.17, 151.71, 149.44, 149.38,
145.10, 126.82, 114.34, 108.35, 66.60, 61.84, 61.73, 34.33, 30.62,
30.43, 30.34, 28.11, 27.29, 22.10, 21.38, 12.94 ppm; MALDI-TOF MS
(m/z): 502.43 [Mꢁ2PF6]+.
8-(Bromomethyl)pentadecane (14): The triphenylphosphine dibro-
mide suspension was prepared from triphenylphosphine (1.4 g,
5.4 mmol) and bromine (0.28 mL, 5.5 mmol) in dichloromethane
(20 mL). Alcohol solution: 2-heptylnonan-1-ol (1.0 g, 4.1 mmol) and
pyridine (0.90 mL, 11 mmol) in dichloromethane (4 mL); eluent: n-
heptane; yield=1.0 g as a white solid (3.3 mmol, 80%); 1H NMR
(400 MHz, CDCl3): d=3.45 (d, 2H, BrCH2, J=4.8 Hz), 1.59 (m, 1H,
BrCH2CH), 1.43–1.19 (m, 24H, CH2), 0.89 ppm (t, 6H, CH3, J=
7.2 Hz).
1-[5-(3,5-Di-tert-butylphenoxy)pentyl]-1’-isobutyl-4,4’-bipyridine-
1,1’-diium dihexafluorophosphate (V2): Bromide solution:
(91 mg, 0.18 mmol) and 4 (26 mg, 0.19 mmol) in DMF (1 mL).
Yield=20 mg as
white solid (0.026 mmol, 14%); 1H NMR
2
18-(Bromomethyl)pentatriacontane (15): The triphenylphosphine
dibromide suspension was prepared from triphenylphosphine
(0.66 g, 2.5 mmol) and bromine (0.13 mL, 2.5 mmol) in dichlorome-
thane (10 mL). Alcohol solution: 2-Heptadecylnonadecan-1-ol
(1.0 g, 1.9 mmol) and pyridine (0.40 mL, 5.0 mmol) in dichlorome-
thane (2 mL); eluent: n-heptane; yield=0.90 g as a white solid
a
(400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=8.93 (d, 2H, BipyH, J=
6.4 Hz), 8.87 (d, 2H, BipyH, J=6.4 Hz), 8.40 (m, 4H, BipyH), 7.02 (s,
1H, para-ArH), 6.73 (d, 2H, ortho-ArH, J=1.2 Hz), 4.67 (t, 2H, NCH2,
J=7.2 Hz), 4.47 (d, 2H, NCH2, J=7.2 Hz), 4.00 (t, 2H, OCH2, J=
6.4 Hz), 2.32 (m, 1H, CH), 2.15 (m, under water peak, 2H, CH2), 1.86
(dd, 2H, CH2, J=7.6 Hz), 1.61 (dd, 2H, CH2, J=7.2 Hz), 1.30 (s, 18H,
CH3), 1.02 ppm (d, 6H, CH3, J=6.4 Hz); 13C NMR (75 MHz, CD3CN/
CDCl3, 1:1 (v/v)): d=158.18, 151.74, 145.19, 145.13, 126.82, 126.79,
114.37, 108.32, 67.94, 66.59, 61.68, 34.29, 30.51, 28.08, 22.09,
18.04 ppm; MALDI-TOF MS (m/z): 488.18 (Mꢁ2PF6)+; HRMS (ESI):
m/z: calcd for C33H48F6N2O1P1: 633.3408 [MꢁPF6]+; found: 633.3396.
1
(1.5 mmol, 79%); H NMR (400 MHz, CDCl3): d=3.45 (d, 2H, BrCH2,
J=4.8 Hz), 1.58 (m, 1H, BrCH2CH), 1.43–1.19 (m, 24H, CH2),
0.88 ppm (t, 6H, CH3, J=7.2 Hz).
1-Adamantyl-4-(pyridin-4-yl)pyridinium
hexafluorophosphate
(17): This compound was synthesized according to a literature pro-
cedure.[20] 1H NMR (400 MHz, CD3CN/CDCl3, 1:1 v/v): d=9.04 (d, 2H,
BipyH, J=6.8 Hz), 8.85 (d, 2H, BipyH, J=6.4 Hz), 8.33 (d, 2H, BipyH,
J=6.4 Hz), 7.82 (d, 2H, BipyH, J=6.4 Hz), 2.39 (m, 3H, adamanta-
neCH), 2.32 (m, 6H, amantane CH2), 1.84 ppm (m, 6H, adamantane
CH2).
1-(Cyclohexylmethyl)-1’-[5-(3,5-di-tert-butylphenoxy)pentyl]-4,4’-
bipyridine-1,1’-diium dihexafluorophosphate (V3): Bromide solu-
tion: 2 (91 mg, 0.18 mmol) and 5 (33 mg, 0.19 mmol) in DMF
1
(1 mL). Yield=50 mg as a white solid (0.061 mmol, 34%); H NMR
1-(Pentatriacontan-18-yl)-4-(pyridin-4-yl)pyridinium
bromide
(400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=8.94 (d, 2H, BipyH, J=
7.2 Hz), 8.85 (d, 2H, BipyH, J=7.2 Hz), 8.42 (d, 2H, BipyH, J=
3.6 Hz), 8.41 (d, 2H, BipyH, J=3.2 Hz), 7.02 (t, 1H, para-ArH, J=
1.6 Hz), 6.73 (d, 2H, ortho-ArH, J=1.6 Hz), 4.67 (t, 2H, NCH2, J=
7.6 Hz), 4.48 (d, 2H, NCH2, J=7.6 Hz), 4.00 (t, 2H, OCH2, J=6.4 Hz),
2.12 (dd, 2H, CH2, J=7.6 Hz), 2.00 (m, 1H, CH), 1.86 (dd, 2H, CH2,
J=7.6 Hz), 1.78 (m, 2H), 1.71 (m, 1H), 1.64 (m, 2H), 1.61 (m, 2H,
CH2), 1.30 (s, 18H, CH3), 1.26 (m, 3H), 1.13 ppm (m, 2H); 13C NMR
(75 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=158.15, 151.72, 149.42, 145.13,
126.83, 126.72, 114.35, 108.32, 67.11, 66.57, 61.72, 39.04, 34.33,
30.61, 30.45, 28.94, 28.11, 25.19, 24.72, 22.12 ppm; MALDI-TOF MS
(m/z): 528.21 [Mꢁ2PF6]+; HRMS (ESI): m/z: calcd for C36H52F6N2O1P1:
673.3721 [MꢁPF6]+; found: 673.3715.
(16): Bromide 15 (450 mg, 0.77 mmol) and 4,4’-bipyridine (1.4 g,
9.4 mmol) were dissolved in dry MeCN (20 mL) and the mixture
was gently refluxed for 7 days under an argon atmosphere. After
cooling to room temperature, the mixture was precipitated from
diethyl ether (2ꢁ), toluene (2ꢁ) and then dried in vacuo to obtain
16 as a white solid in a yield of 300 mg (0.41 mmol, 53%). In addi-
tion to 16, also iso-C33 and iso-C31 derivatives, which must be the
result of impurities in the commercially available ketone, were
1
found to be present in the product. H NMR (400 MHz, CDCl3): d=
9.39 (d, 2H, BipyH, J=6.8 Hz), 8.88 (d, 2H, BipyH, J=6.0 Hz), 8.36
(d, 2H, BipyH, J=7.2 Hz), 7.71 (d, 2H, BipyH, J=6.0 Hz), 4.87 (d,
2H, NCH2, J=7.6 Hz), 2.06 (m, 1H, CH), 1.44–1.16 (m, 64H, CH2),
0.88 ppm (t, 6H, CH3, J=6.8 Hz); 13C NMR (75 MHz, CDCl3): d=
153.24, 151.02, 145.47, 140.27, 125.08, 120.95, 65.23, 40.01, 31.44,
29.97, 29.22, 25.58, 22.20, 13.63 ppm; MALDI-TOF MS (m/z): 661.50
[MꢁBr]+, 633.46 [MꢁBr iso-C33]+, 605.43 [MꢁBr iso-C31]+.
1-(2-Butylhexyl)-1’-[5-(3,5-di-tert-butylphenoxy)pentyl]-4,4’-bi-
pyridine-1,1’-diium dihexafluorophosphate (V5): Bromide solu-
tion: 2 (91 mg, 0.18 mmol) and 13 (220 mg, 1.0 mmol) in DMF
1
(1 mL). Yield=17 mg as a white solid (0.020 mmol, 11%); H NMR
(400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=8.95 (d, 2H, BipyH, J=6 Hz),
8.88 (d, 2H, BipyH, J=6.4 Hz), 8.45 (m, 4H, BipyH), 7.01 (s, 1H,
para-ArH), 6.73 (d, 2H, ortho-ArH, J=1.2 Hz), 4.68 (t, 2H, NCH2, J=
7.6 Hz), 4.53 (d, 2H, NCH2, J=7.2 Hz), 4.00 (t, 2H, OCH2, J=6.4 Hz),
2.15 (m, under water peak, 2H, CH2), 2.08 (m, 1H, CH), 1.86 (dd,
2H, CH2, J=7.6 Hz), 1.62 (dd, 2H, CH2, J=7.2 Hz), 1.40–1.20 (m,
12H, CH2), 1.30 (s, 18H, CH3), 0.90 ppm (t, 6H, CH3, J=6.8 Hz);
13C NMR (75 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=158.15, 151.70,
149.51, 149.35, 145.33, 145.11, 126.86, 126.76, 114.34, 108.34, 66.59,
65.45, 61.77, 39.51, 34.35, 30.67, 30.45, 29.33, 28.13, 27.38, 22.16,
13.18 ppm; MALDI-TOF MS (m/z): 572.10 [Mꢁ2PF6]+; HRMS (ESI):
m/z: calcd for C39H60F6N2O1P1: 717.4347 [MꢁPF6]+; found: 717.4344.
General synthesis of viologen derivatives V1, V2, V3, V5 and
V6
A 25 mL flask, closed with a septum, containing a solution of 2
and primary bromide (3, 4, 5, 6, 13 or 14) in DMF was stirred for
3 days at 958C. After cooling, Et2O was added and the precipitate
was filtered off and washed with 20 mL of Et2O. The resulting solid
was mixed with acetone (2 mL) followed by the addition of an
excess of NH4PF6 (s) and the product was precipitated by the addi-
tion of water (10 mL). The precipitate was filtered off, washed with
water (40 mL) followed by Et2O (10 mL) and then dried to obtain
the corresponding viologen.
1-[5-(3,5-Di-tert-butylphenoxy)pentyl]-1’-pentyl-4,4’-bipyridine-
1,1’-diium dihexafluorophosphate (V1):[7a] Bromide solution: 3
(182 mg, 0.36 mmol) and 2 (540 mg, 3.6 mmol) in DMF (2 mL);
yield=1.9 g as a white solid (2.4 mmol, 67%); 1H NMR (400 MHz,
1-[5-(3,5-Di-tert-butylphenoxy)pentyl]-1’-(2-heptylnonyl)-4,4’-bi-
pyridine-1,1’-diium dihexafluorophosphate (V6): Bromide solu-
tion: 2 (91 mg, 0.18 mmol) and 14 (520 mg, 1.7 mmol) in 1 mL
DMF. Yield=33 mg as a white solid (0.035 mmol, 19%); 1H NMR
Chem. Eur. J. 2014, 20, 1 – 12
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(400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=8.95 (d, 2H, BipyH, J=
5.6 Hz), 8.86 (d, 2H, BipyH, J=6 Hz), 8.45 (bs, 4H, BipyH), 7.02 (s,
1H, para-ArH), 6.73 (s, 2H, ortho-ArH), 4.68 (t, 2H, NCH2, J=7.6 Hz),
4.51 (d, 2H, NCH2, J=7.6 Hz), 4.00 (t, 2H, OCH2, J=6 Hz), 2.14 (m,
2H, CH2), 2.08 (m, under water peak, 1H, CH), 1.86 (dd, 2H, CH2,
J=6.8 Hz), 1.63 (dd, 2H, CH2, J=7.2 Hz), 1.45–1.15 (m, 24H, CH2),
1.30 (s, 18H, CH3), 0.88 ppm (t, 6H, CH3, J=6.8 Hz); 13C NMR
(75 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=151.73, 145.33, 145.12, 126.89,
126.77, 114.39, 108.29, 66.53, 65.54, 61.90, 61.82, 39.64, 34.37,
31.19, 30.72, 30.50, 29.66, 29.07, 28.56, 28.14, 25.28, 22.04,
13.40 ppm; MALDI-TOF MS (m/z): 656.18 [Mꢁ2PF6]+; HRMS (ESI):
m/z: calcd for C45H72F6N2O1P1: 801.5286 [MꢁPF6]+; found: 801.5291.
(108 mg of the mixture containing 6 and the elimination product
of 6) was stirred for 3 days at 958C. After cooling, Et2O was added
and a gel was formed; the gel was sonicated and the solvents
were evaporated. The crude product was dissolved in MeCN, pre-
cipitated with diethylether, and the precipitate was filtered off and
subsequently washed with 20 mL of diethyl ether. The resulting
solid was mixed with acetone (2 mL) followed by the addition of
an excess of NH4PF6 (s) and the product was precipitated by the
addition of water (10 mL). The white precipitate was filtered off,
washed with 40 mL of water followed by 10 mL of Et2O and then
dried to obtain a yield of 8 mg (0.0085 mmol, 9.8%). It was not
possible to purify this compound to obtain an analytically pure
sample. 1H NMR (400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=8.94 (bd,
4H, BipyH), 8.40 (bd, 4H, BipyH), 7.02 (s, 1H, para-ArH), 6.73 (d, 2H,
ortho-ArH, J=1.6 Hz), 4.75 (t, 2H, NCH2, J=6.8 Hz), 4.68 (t, 2H,
NCH2, J=7.2 Hz), 4.00 (t, 2H, OCH2, J=5.6 Hz), 3.53 (t, 2H, cyclodo-
decane OCH2, J=5.6 Hz), 3.37 (m, 1H, CH), 2.27 (dd, 2H, CH2, J=
5.6 Hz), 2.12 (m, under water peak, 2H, CH2), 1.87 (dd, 2H, CH2, J=
7.6 Hz), 1.63 (m, 2H, CH2), 1.30 (s, 18H, CH3), 1.28–1.36 ppm (m,
22H, cyclododecane (CH2)11).
1-[5-(3,5-Di-tert-butylphenoxy)pentyl]-1’-adamantyl-4,4’-bipyri-
dine-1,1’-diium dihexafluorophosphate (V4):
A
25 mL flask,
(53 mg,
closed with septum, containing solution of 1
a
a
0.15 mmol) and 17 (50 mg, 0.11 mmol) in DMF (1 mL) was stirred
for 4 days at 908C. After cooling, Et2O was added and the precipi-
tate was filtered off and washed with Et2O (20 mL). The resulting
solid was mixed with acetone (2 mL) followed by the addition of
an excess of NH4PF6 (s) and the product was precipitated by the
addition of 10 mL of water. The precipitate was filtered off, washed
with water (40 mL) followed by Et2O (10 mL) and then dried to
obtain V4 in a yield of 11 mg as a white solid (0.013 mmol, 12%).
1H NMR (400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=9.18 (d, 2H, BipyH,
J=6.8 Hz), 8.93 (d, 2H, BipyH, J=6.4 Hz), 8.43 (m, 4H, BipyH), 7.02
(s, 1H, para-ArH), 6.73 (s, 2H, ortho-ArH), 4.67 (t, 2H, NCH2, J=
7.6 Hz), 4.00 (t, 2H, OCH2, J=6.4 Hz), 2.43 (m, 3H, CH), 2.34 (m, 6H,
CH2), 2.15 (m, under water peak, 2H, CH2), 1.86 (m, under adaman-
tane proton peaks, 2H, CH2), 1.85 (m, 6H, CH2), 1.61 (dd, 2H, CH2,
J=7.2 Hz), 1.30 ppm (s, 18H, CH3); 13C NMR (75 MHz, CD3CN/CDCl3,
1:1 (v/v)): d=151.73, 148.90, 145.09, 142.07, 126.85, 126.48, 114.39,
108.30, 66.58, 61.72, 41.51, 34.21, 30.60, 29.68, 28.11, 22.15 ppm;
MALDI-TOF MS (m/z): 566.30 [Mꢁ2PF6]+; HRMS (ESI): m/z: calcd for
C39H54F6N2O1P1: 711.3877 [MꢁPF6]+; found: 711.3859.
Acknowledgements
This research was supported by the European Research Council
in the form of an ERC Advanced grant to R.J.M.N. and S.V.
(ALPROS-290886) and an ERC Starting grant to J.A.A.W.E
(NANOCAT-259064). Further financial support was obtained
from the Council for the Chemical Sciences of the Netherlands
Organization for Scientific Research (CW-NWO) (Vidi grant for
J.A.A.W.E and Vici grant for A.E.R) and from the Ministry of Edu-
cation, Culture and Science (Gravity program 024.001.035).
1-[5-(3,5-Di-tert-butylphenoxy)pentyl]-1’-(2-heptadecylnonadec-
Keywords: dynamic covalent chemistry
·
porphyrins
·
yl)-4,4’-bipyridine-1,1’-diium dihexafluorophosphate (V7):
A
rotaxanes · slippage · supramolecular chemistry
25 mL flask, closed with a septum, containing a solution of
1 (1.4 g, 4.0 mmol) and 16 (250 mg, 0.34 mmol) in DMF (4 mL) was
stirred for 6 days at 908C. After cooling, Et2O was added and the
precipitate was filtered off and washed with Et2O (20 mL) and tolu-
ene. The resulting solid was mixed with 2 mL of acetone followed
by the addition of an excess of NH4PF6 (s) and the product was
precipitated by the addition of water (10 mL). The precipitate was
filtered, washed with water (40 mL) followed by Et2O (10 mL) and
then dried to obtain V7 as a white solid in a yield of 306 mg
(0.25 mmol, 73%); 1H NMR (400 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=
8.95 (d, 2H, BipyH, J=6.8 Hz), 8.86 (d, 2H, BipyH, J=6.8 Hz), 8.42
(t, 4H, BipyH, J=6.4 Hz), 7.02 (t, 1H, para-ArH, J=1.6 Hz), 6.73 (d,
2H, ortho-ArH, J=1.6 Hz), 4.68 (t, 2H, NCH2, J=7.6 Hz), 4.51 (d, 2H,
NCH2, J=7.6 Hz), 4.00 (t, 2H, OCH2, J=6 Hz), 2.11 (m, under water
peak, 2H, CH2), 2.04 (m, under water peak, 1H, CH), 1.86 (dd, 2H,
CH2, J=7.2 Hz), 1.62 (dd, 2H, CH2, J=7.2 Hz), 1.45–1.15 (m, 64H,
CH2), 1.30 (s, 18H, CH3), 0.88 ppm (t, 6H, CH3, J=6.8 Hz); 13C NMR
(75 MHz, CD3CN/CDCl3, 1:1 (v/v)): d=158.14, 151.73, 149.44, 149.29,
145.34, 145.13, 126.84, 126.74, 114.37, 108.31, 66.57, 65.45, 61.74,
39.54, 34.33, 31.31, 30.61, 29.54, 29.07, 28.11, 25.19, 22.08,
13.34 ppm; MALDI-TOF MS (m/z): 936.65 [Mꢁ2PF6]+, iso-C33:
908.60 [Mꢁ2PF6]+, iso-C33: 880.54 [Mꢁ2PF6]+; HRMS (ESI): m/z:
calcd for C65H112F6N2O1P1: 1081.8416 [MꢁPF6]+; found: 1081.8406.
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Received: June 6, 2014
Published online on && &&, 0000
Chem. Eur. J. 2014, 20, 1 – 12
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FULL PAPER
Kinetic and thermodynamic studies on
the threading of a macrocyclic porphy-
rin receptor (H21) onto molecular
threads that are blocked on one side
and are open on the other side were
performed. The results suggest that
threading is impossible if the receptor
encounters an open side that is sterical-
ly encumbered in a similar way as
a folded polymer chain (see figure).
&
Supramolecular Chemistry
A. B. C. Deutman, S. Varghese, M. Moalin,
J. A. A. W. Elemans, A. E. Rowan,*
R. J. M. Nolte*
&& – &&
Slippage of a Porphyrin Macrocycle
over Threads of Varying Bulkiness:
Implications for the Mechanism of
Threading Polymers through
a Macrocyclic Ring
&
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Chem. Eur. J. 2014, 20, 1 – 12
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!