[3]rotaxanes composed of two dibenzo-24-crown-8 ether wheels and an azamacrocyclic complex

Article abstract of DOI:10.1039/c8dt03225d

The azamacrocyclic complex was used as a platform for the construction of [3]rotaxanes containing two DB24C8 macrocycles per molecule. The complex unit incorporates two electron deficient π-bond systems and two N-H hydrogen bond donating groups which faci

Full text of DOI:10.1039/c8dt03225d

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[3]rotaxanes composed of two dibenzo-24-crown-
8 ether wheels and an azamacrocyclic complex†‡
Cite this: Dalton Trans., 2018, 47,
15845
Mateusz Woźny, *a Agnieszka Więckowska,b Damian Trzybiński,c Szymon Sutuła,c
c
Sławomir Domagałac and Krzysztof Woźniak
The azamacrocyclic complex was used as a platform for the construction of [3]rotaxanes containing two
DB24C8 macrocycles per molecule. The complex unit incorporates two electron deficient π-bond
systems and two N–H hydrogen bond donating groups which facilitated the formation of a 1 : 2 inter-
locked structure. Synthesis and properties of such compounds are presented. Structures of the obtained
compounds were confirmed by NMR spectroscopy, ESI mass spectrometry, elemental analysis and single
crystal X-ray diffraction. Both [3]rotaxanes containing two DB24C8 macrocycles per molecule crystallise in
P¯1 and P21/n space groups. They have different counterions (PF6 and Cl− anions, respectively) and mostly
−
Received 7th August 2018,
Accepted 9th October 2018
disordered solvent molecules such as water, methanol and acetone. Both [3]rotaxanes have a flexible axle in
which the Cl− salt takes the shape closer to the “S”-letter, while in the PF6− case the axle is more linear. The
shape results from respective packing and intra-, and intermolecular interactions among the moieties in the
rotaxane and the crystal lattice.
DOI: 10.1039/c8dt03225d
rsc.li/dalton
the crown ether cavity by the N+–H⋯O interactions, which is
manifested by short H⋯O contacts.27
Introduction
Artificial molecular devices include molecular switches based
DB24C8 is a workhorse macrocycle in our laboratory as it
on mechanically interlocked molecules (MIMs) such as cate- readily forms pseudorotaxanes with the TAM complexes by enga-
nanes and rotaxanes.1–7 These objects of the curiosity-driven ging both of its interaction modes: π-stacking and N–H⋯O hydro-
research allow us to pursue the vision of applications in gen bonding. In the DB24C8/TAM pair, the complex unit is a
materials chemistry, sensors, photonics, catalysis and mole- π-acceptor and a hydrogen bond donor. Interestingly, the TAM
cular electronics.8,9 The pioneering work of Stoddart,2 unit has two electron deficient π-bond systems and two N–H
Sauvage3 and Feringa10 in this area was honoured by the groups bearing a partial positive charge.16 Such a double-sided
Nobel Prize in Chemistry in 2016.4
structure suggests that simultaneous interaction of the TAM
Our group has constructed several [2]catenanes,11,12 mole- unit with two DB24C8 rings is, at least, in principle possible.
cular necklaces,13 and [2]rotaxanes14–16 from tetraazamacro- However, all MIMs obtained by us so far were characterized by
cyclic complexes (TAM)17 and dibenzo-24-crown-8 (DB24C8). the (TAM)2·DB24C8 composition, corresponding to one
DB24C8 is a well-known π-donor macrocycle present in many DB24C8 macrocycle enclosed between two linked TAMs.11–16
MIMs containing complementary acceptors, such as 4,4-bipyri-
The occurrence of a herein suggested, hypothetical
dinium,18,19 1,2-bis(pyridinium)ethane,20–24 or benz-imidazo- TAM·(DB24C8)2 motif, e.g. [3]rotaxane composed of a TAM
lium.25,26 DB24C8 was also widely employed in the synthesis complex and two DB24C8 rings, has never been observed,
of rotaxanes incorporating dialkylammonium ions hosted in although there are many examples of [3]rotaxanes described in
the literature.28–33 However, none of them is TAM-based and
only some incorporate DB24C8.34–39 Therefore, we have
decided to investigate whether it is possible for the TAM
aInstitute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52,
01-224 Warszawa, Poland. E-mail: mateusz.wozny@icho.edu.pl
complex to interact with two DB24C8 rings.
bFaculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warszawa, Poland
cBiological and Chemical Research Centre, Chemistry Department, University of
Warsaw, Żwirki i Wigury 101, 02-089 Warszawa, Poland
In this paper, a synthetic method deliberately aiming at [3]
rotaxanes with the TAM·(DB24C8)2 composition is proposed
and showed to be successful. The hydroxyl-terminated
TAM·(DB24C8)2 pseudorotaxanes were stoppered in a high
yielding isocyanate addition. Isocyanates were generated
during Curtius rearrangement of corresponding acyl azides. A
similar approach involving the reaction between isocyanate
†Dedicated to Professor Bohdan Korybut-Daszkiewicz on the occasion of his
75th birthday.
‡Electronic supplementary information (ESI) available: NMR spectra, X-ray crys-
tallographic information, and additional voltammetric data. CCDC 1856147 and
1856148. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c8dt03225d
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and amine or the hydroxyl groups was successfully applied to ing N–H groups. In reactions between 2 and isocyanates 3, carried
the synthesis of MIMs also in the past.40–44
out in the presence of an excess of DB24C8, we obtained a series
of mechanically interlocked molecules (Scheme 2). [2]rotaxanes
5n (28%) and 5m (24%) were the main products, but a substantial
amount of target [3]rotaxanes was also obtained – 6n (16%) and
6m (13%). This result proves that simultaneous interaction of the
TAM complex unit with two DB24C8 macrocycles is factual.
Synthesis of rotaxanes from complex 2, DB24C8 and acyl
azides, carried out under high-temperature conditions in
which the Curtius rearrangement occurs in situ, is also poss-
ible but less efficient. The reaction performed in refluxing
acetonitrile gave rotaxanes 5m and 6m in 17% and 8% yields,
respectively. The difference in yields between the high- and
room-temperature reactions can be explained by a lower equili-
brium concentration of the pseudorotaxane at higher tempera-
tures. This is in accordance with 1H NMR spectra measure-
ments of a mixture of 4n and DB24C8, suggesting that the
amount of pseudorotaxanes in dynamic equilibrium falls with
the temperature increase (Fig. 19S and 20S (ESI‡)).
Results and discussion
Synthesis and spectroscopic studies
Compound 1, obtained according to the new one-pot synthetic
protocol,45 was O-methylated with methyl trifluoromethane-
sulfonate and then treated with 4-amino-1-butanol to give
complex 2 with a satisfactory yield (Scheme 1). The hydroxyl
end groups in 2 allowed us to employ fast and high yielding
isocytanate-to-hydroxyl addition at the stoppering step. In reac-
tions between 2 and 3,5-dinitro- (3n) or 3,5-methoxybenzoyl
isocyanate (3m), we obtained “bare axles” 4n and 4m
(Scheme 1). Isocyanates 3 were generated in the reaction flask
prior to the addition of the complex 2, via thermal Curtius
rearrangement of the corresponding acyl azides. The 3,5-
dinitro- and 3,5-methoxybenzoyl azides were synthesized from
benzoyl chlorides and NaN3 (yields 80% and 91%, respect-
ively). The azides are easy to purify, handle and store, and can
be treated as a protected form of the isocyanates.
Structures of the obtained compounds were confirmed by
NMR spectroscopy (1H, 13C, HSQC, ROESY; Fig. 1S–16S (ESI‡)),
mass spectrometry and elemental analysis. A comparison of NMR
spectra of an axle 4n, [2]rotaxane 5n, and [3]rotaxane 6n (Fig. 1)
In principle, the diol 2 is an appropriate substrate for
[3]pseudorotaxane synthesis, since its molecule incorporates two
electron deficient π-bond systems and two hydrogen-bond-donat-
1
showed changes in shapes and chemical shifts of H signals of
the TAM unit, occurring upon threading of DB24C8 wheels.
Scheme 1 Synthesis of the substrate for rotaxanes (complex 2) and its reaction with 3,5-dinitro (3n) or 3,5-dimethoxy isocyanate (3m), giving bare
axles 4n and 4m. Isocyanates 3 were generated in the reaction flask, through Curtius rearrangement of corresponding acyl azides, prior to the
addition of the complex 2.
Scheme 2 Threading-stoppering synthesis of [2]- and [3]rotaxanes based on DB24C8 and tetraazamacrocyclic complex. The first TAM-based [3]
rotaxanes (6n and 6m) are formed alongside [2]rotaxanes (5n and 5m). Fast and high-yielding isocyanate-to-hydroxyl addition plays a role of the
stoppering reaction.
15846 | Dalton Trans., 2018, 47, 15845–15856
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exchange. Similarly, proton b distant from DB24C8 (7.97 ppm)
does not engage in hydrogen bonding, but undergoes
exchange as evidenced by signal broadening and the presence
of chemical exchange correlations in the ROESY spectrum
(Fig. 7S (ESI‡)). A chemical shift of 7.97 ppm is characteristic
of NH groups in TAM complexes. On the other hand, the
signal of proton b located on the side threaded through
DB24C8 is pushed towards a lower field (∼8.8 ppm). This
observation can be explained by the fact that the proton in this
NH group engaged in N–H⋯O hydrogen bonding with the
crown ether. Additionally, interaction with DB24C8 freezes
chemical exchange and signal b appears as a multiplet
coupled to proton f (doublet at 8.18 ppm, J = 16.2 Hz).
In the spectra of [2]rotaxane 5n, significant changes in
nature and chemical shifts of imine protons e and e′ can also
be observed. Indeed, threading an axle through the wheel
changes electronic relationships in the complex molecule.
Protons distant from DB24C8 appear as two very broad signals
at ∼7.4 and ∼7.8 ppm. The broadening of peaks can be
explained by relatively fast rotation of the whole
ArNHCO2(CH2)4NHCH = substituent of the ligand, around the
exocyclic CvC double bond (different extent of broadening of
the signals e/e′ and b within the same substituent results from
being caused by different dynamic processes). On the DB24C8
side, however, the rotation is hindered by interaction with the
crown ether, and signals e and e′ appear as sharp singlets at
6.63 and 7.59 ppm, respectively. An exceptionally low fre-
quency of the latter signal results from the shielding by the
surrounding benzene rings of DB24C8. This characteristic
feature has been observed for all TAM/DB24C8-based rotaxanes
known so far.14,15
Fig. 1 Low field fragments of the 1H NMR spectra of axle 4n, [2]rotax-
ane 5n and [3]rotaxane 6n (600 MHz, CD3CN, 25 °C). HAr denote
protons in aromatic rings of DB24C8.
In the spectrum of 4n, both acidic NH groups of protons, a
In the 1H NMR spectrum of the [3]rotaxane 6n, protons a–d
(NHCO2) and b (NH
9.69 ppm). Protons b are coupled to protons f (7.87 ppm, NH– longer duplicated, owing to the symmetric structure of the
CHv), with a vicinal trans coupling constant: J = 15.6 Hz. molecule. Hydrogen-bonding protons in NH groups (b) are
Protons b are characterized by an unusually high value of the coupled to protons
with 16.8 Hz. Since two
̲–CHv), appear at low field (10.12 and and f (8.34, 8.63, 8.56, 8.42 and 8.08 ppm, respectively) are no
̲
f
J =
chemical shift (9.69 ppm), compared with other known TAM DB24C8 macrocycles are present in the molecule, not one but
complexes. This effect can be explained by the existence of two signals e appear in the spectrum at exceptionally low
hydrogen bonds between protons b and the carbamate group. chemical shifts: 6.72 and 6.61 ppm. This is due to the fact
The interaction causes protons b not to exchange chemically that, similarly to the complex 4n, [3]rotaxane 6n exhibits cis/
and the signal retains its subtle structure.
Signals of imine protons e appear at 7.57 and 7.58 ppm, the splitting of signals e′ and f (7.57 and 8.08 ppm).
while e′ at 8.23 and 8.29 ppm (1H nuclei closer to the N atom).
Aromatic protons of dinitroaryl stoppers in 5n and 6n are
trans isomerism in the solution, which manifests itself also in
Splitting of e and e′ signals results from the existence of two also influenced by DB24C8. In 6n, doublets c, closer to the
isomers of 4n in the solution: cis and trans, differing in the DB24C8 moiety, shift by 0.20 ppm towards higher field when
spatial relationship of the two substituents of the macrocyclic compared to c in 4n. In the case of more distant protons d, the
ligand. This observation means that the rotation of both exco- change is less significant (0.07 ppm).
cyclic CvC bonds in axle 4n is slow in the NMR time-scale.
The presence of DB24C8 influences all of the signals of [2]-
[2]rotaxane 5n is composed of an axle 4n and one and [3]rotaxane axles, including these located within the high
DB24C8 macrocycle. A large signal coming from protons field fragment of the 1H NMR spectra of 5n and 6n (Fig. 5S
attached to the catechol rings of DB24C8 appears at 6.75 ppm. and 11S (ESI‡)). Similar effects can be observed when spectra
As a whole, the spectrum of 5n is more complex than in the of methoxy-substituted compounds 4m, 5m and 6m are com-
case of 4n because of the lower symmetry of the molecule.
Signals a appear at 8.40 and 8.45 ppm. The latter one,
pared (Fig. 3S, 8S, and 14S (ESI‡)).
The co-conformational freedom in studied rotaxanes was
corresponding to the carbamate group on the side that is not not observed. NMR data suggest that DB24C8 resides solely on
threaded through the DB24C8 wheel, is broad due to chemical the TAM unit: dinitrobenzene groups in 5n and 6n rotate freely
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causing signals c to be averaged (Fig. 1); also, there is no summarized in Table 1. The full list of bond lengths, valence
ROESY correlation between the wheel and the stoppers (Fig. 7S and torsion angles can be found in Tables 1S–6S (ESI‡). The
and 13S (ESI‡)). This is consistent with the below described representation of molecular structure of both compounds is
voltammetric results, as well as with the X-ray data for the presented in Fig. 2.
rotaxanes in the solid state.
In the 6nCl, the conformation of the [3]rotaxane axle is the
closest to the “S”-shape, while in 6n the mentioned moiety is
more extended with two phenyl rings of the 3,5-dinitrophenyl
X-ray crystallographic studies
Attempts to obtain single-crystals suitable for X-ray diffraction substituents separated by a distance of 30.61(2) Å (Table 2). In
measurements of all synthesized compounds were undertaken. both compounds, the adjacent dibenzo-24-crown-8 ether
However, they were successful only in the case of 6n (hexa- wheels are located close to the Ni center of TAM2+ unit in a
fluorophosphate salt) and its counterion exchanged congener way that aromatic rings denoted by C12–C17 atoms are
(6nCl, dichloride salt).
involved in the Ni⋯π contacts (Fig. 2, Tables 9S and 12S‡). The
Single-crystal X-ray diffraction analysis confirmed the com- position of the crown ethers is also stabilized by the N–H⋯O
position of the investigated compounds and both consist of and C–H⋯O hydrogen bonds between the H-atoms of the CH–
the same [3]rotaxane axle. However, they contain different NH spacers and C–H fragments of the TAM complex and the
anions and solvent molecules in their crystal lattices. The 6n oxygen atoms of the DB24C8 unit (Fig. 3, Tables 7S and 11S‡).
ˉ
crystallizes in the triclinic P1 space group with half of the [3] In 6n, two weak intramolecular C–H⋯O hydrogen bonds were
rotaxane cation (the Ni-atom is situated at the inversion identified (Fig. 3a and Table 7S‡) whereas in 6nCl only one
centre), one PF6− anion and additional solvent molecules used interaction of this type is present (Fig. 3b and Table 11S‡).
for crystallization (water, methanol and acetone) in the asym-
In the crystal of 6n, the ionic species and solvent molecules
metric part of the unit cell (Fig. 17Sa (ESI‡)). The mentioned form specific 3D supramolecular architecture (see Fig. 4).
solvents are in a non-stoichiometric ratio to the [3]rotaxane Apparently, the positively charged [3]rotaxane moieties form
−
moiety. All nitro groups of the [3]rotaxane axle and the PF6
cavities in the crystal lattice which are filled in by disordered
counterions are disordered over two positions. In turn, the anions and solvent molecules. The arrangement of species in
latter compound (6nCl) crystallizes in the monoclinic P21/n the crystal is dominated by the formation of hydrogen bonds
space group with half of the [3]rotaxane cation (as in the pre- (Table 7S‡); however neighboring [3]rotaxane axles participate
vious case, the Ni-atom is also located at the inversion centre), also in the intermolecular π–π contacts (Table 8S‡ and Fig. 5)
one chloride anion and one molecule of acetonitrile in the involving adjacent aromatic rings of the 3,5-dinitrophenyl sub-
−
asymmetric part of the unit cell (Fig. 17Sb (ESI‡)). The details stituents. Interestingly, also the PF6 counterions are involved
of crystallographic data and the refinement parameters are in the C–F⋯π contacts with aforementioned aromatic rings
Table 1 Crystal data and structure refinement details for 6n and 6nCl
Identification code
6n
6nCl
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C87.92H118.26F12N12NiO30.89P2
2186.13
100(2)
Triclinic
ˉ
P1
C86H110Cl2N14NiO28
1917.48
100(2)
Monoclinic
P21/n
12.7551(3)
a/Å
11.7523(3)
b/Å
c/Å
13.4144(3)
16.3890(4)
22.9462(4)
16.8432 (4)
α/°
β/°
76.0271(19)
89.369(2)
90
110.074 (2)
γ/°
81.8124(19)
2480.98(11)
90
Volume/Å3
4630.20 (17)
Z
1
2
ρcalc/g cm−3
1.463
1.529
1.375
0.353
μ/mm−1
F(000)
1143.0
2020.0
Crystal size/mm3
Radiation
0.16 × 0.12 × 0.05
CuKα (λ = 1.54184 Å)
5.558 to 153.618
−14 ≤ h ≤ 14, −16 ≤ k ≤ 16, −20 ≤ l ≤ 16
51 296
10 402 [Rint = 0.0300, Rsigma = 0.0241]
10 402/227/790
0.41 × 0.20 × 0.11
MoKα (λ = 0.71073 Å)
3.49 to 50.246
−14 ≤ h ≤ 15, −27 ≤ k ≤ 24, −15 ≤ l ≤ 20
33 438
8265 [Rint = 0.0295, Rsigma = 0.0266]
8265/0/599
1.057
R1 = 0.0318, wR2 = 0.0703
R1 = 0.0410, wR2 = 0.0748
0.27/−0.33
2Θ range for data collection/°
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indexes [I ≥ 2σ(I)]
Final R indexes [all data]
Largest diff. peak/hole/e Å−3
1.026
R1 = 0.0399, wR2 = 0.1071
R1 = 0.0467, wR2 = 0.1130
0.84/−0.41
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Fig. 2 Molecular structure of 6n (a) and 6nCl (b) with atomic labelling scheme. The Ni⋯π interactions are represented by dotted lines. Hydrogen
atoms and molecules of solvents were omitted for clarity. In the case of 6n only the main parts of disordered fragments are shown. The Cg5, Cg6
and Cg7 denote the geometric centers of gravity of the aromatic rings delineated by the C12–C17, C18–C23 and C30–C35 atoms, respectively.
Symmetry code (i): −x, −y + 2, −z (a); −x + 1, −y + 1, −z + 1 (b).
(Table 10S‡ and Fig. 5). These weak intermolecular inter-
actions play the role of a “glue” which is strengthening the
Table 2 Selected distances [Å] for 6n and 6nCl. The Cg5, Cg6 and Cg7
whole crystal structure.
denote the geometric centers of gravity of the aromatic rings delineated
by the C12–C17, C18–C23 and C30–C35 atoms, respectively (Fig. 2 and
17S (ESI)). Symmetry code (i): −x, −y + 2, −z (6n); −x + 1, −y + 1, −z + 1
(6nCl)
The supramolecular architecture of 6nCl is presented in
Fig. 6. In the crystal of this compound, the neighboring
cations and anions are held together by the N–H⋯Cl and
C–H⋯Cl hydrogen bonds (Fig. 6 and Table 11S‡) involving the
fragments of the [3]rotaxane axle and the ether moiety. The
molecules of acetonitrile are participating in the weak C–H⋯N
intermolecular interactions with DB24C8 ether wheels
(Table 11S‡). The whole crystal structure is stabilized by the
network of weak C–H⋯O hydrogen bonds (Table 11S‡) and
CvO⋯π contacts (Fig. 6b and Table 13S‡) between adjacent
[3]rotaxane cations.
Distance
A⋯B
6n
6nCl
Ni1⋯Cg6
Ni1⋯Cg7
Cg5⋯Cg5
Cg6⋯Cg7i
N3⋯N3i
3.64(2)
6.34(2)
30.61(2)
5.37(2)
11.07(2)
25.95(2)
3.86(2)
5.75(2)
25.06(2)
8.22(2)
11.03(2)
21.93(2)
N4⋯N4i
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Fig. 3 Illustration of the hydrogen bonds involving fragments of the TAM complex and DB24C8 unit in the independent part of the crystal lattices
of 6n (a) and 6nCl (b). The N–H⋯O and C–H⋯O intermolecular interactions are represented by dashed lines. The H-atoms not involved in these
interactions and molecules of solvents were omitted for clarity. Only the main parts of disordered nitro groups are shown. (*) indicates intra-
molecular interaction.
Fig. 4 General view on the packing of moieties in the crystal of 6n, where (a) projection along the b-direction, (b) view from the side. The cavities
filled by disordered anions and solvent molecules are highlighted in orange. The H-atoms were omitted for clarity.
Electrochemical studies
In the axle molecule 4n, the nickel(II) ion coordinated by the
TAM ligand is electroactive and undergoes one-electron, revers-
ible oxidation to the +3 oxidation state at Ep = 1.11 V (vs. non-
aqueous Ag/AgCl, Fig. 7). This value of Ep is surprising, since
similar nickel(II) TAM complexes have been consistently
reported to oxidize at about 1.3 V.11,12,14–16 This significant
difference can be explained by the unprecedented presence of
partially negatively charged nitro groups within the 4n mole-
cule. Nitro groups apparently interact with the positively
charged TAM3+/2+ unit, stabilizing the higher oxidation state of
4n and thus lowering the value of its oxidation potential.
Dinitroaryl stoppers are also electroactive and their reduction
Fig. 5 Illustration of the network of weak intermolecular C–F⋯π and
π–π interactions in the crystal of 6n. The H-atoms and molecules of sol-
vents were omitted for clarity. Only the main parts of the disordered
fragment are shown. The contacts are represented by dotted lines. The
signals are observed at ca. −0.7 V.
Upon threading of DB24C8 wheels which encircle the
complex moiety, this stabilizing intramolecular interaction
becomes impeded. Moreover, excessive steric hindrance,
especially in the case of 6n where the TAM unit is encircled by
C–F⋯π contacts are highlighted in green, and π–π in blue. Symmetry
codes: (iii) −x, −y, −z + 1, (v) −x + 1, −y, −z + 1.
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Fig. 8 Square wave voltammograms recorded on the GCE in 0.1 M
TBAHFP/DMF solution of 6n – solid line, 6nCl – dotted line, frequency =
5 Hz, reference electrode: Ag/AgCl in methanol.
(Fig. 7). In our previous studies [2]rotaxanes always oxidized
easier than the corresponding axles due to the stabilization
coming from π–π interaction between DB24C8 and TAM3+/2+
units.11,12,14–16 Here, the order of Ep values is reversed, simply
because the stabilizing effect of nitro groups is stronger than
that of DB24C8. Irreversible oxidation of DB24C8 is placed at
about 1.60 V as reported earlier.16,17
In the case of 5n, the second peak was observed during vol-
tammetric measurements at 1.01 V (Fig. 7). This signal corres-
ponds to the redox process of the +1 charged product of
proton dissociation from 5n (both exocyclic NH proton and
protons in carbamate groups are acidic). Indeed, an additional
experiment in which triethylamine was added to the solution
resulted in the expected enhancement of the 1.01 V signal and
disappearance of the 1.14 V one (Fig. 18S (ESI‡)). Similar dis-
sociation-related effects on the electrochemical behavior of the
TAM complex were observed in the previous paper.16
Moreover, this observation is in accordance with 1H NMR data,
where acidic protons in 5n (and only in 5n) were shown to be
labile and participating in chemical exchange.
Fig. 6 General view on the packing of ions and solvent molecules in
the crystal of 6nCl, where (a) projection along the a-direction and (b)
detailed view on the intermolecular interactions in the crystal network.
The H-atoms not participating in the interactions between cations and
anions were omitted for clarity. The N–H⋯Cl and C–H⋯Cl hydrogen
bonds are represented by dotted lines and the CvO⋯π by dotted lines.
Symmetry codes: (ii) x + 1/2, −y + 1/2, z − 1/2; (vii) −x + 2, −y, −z + 1.
Upon replacing the hexafluorophosphate counterions in 6n
by chloride ions in 6nCl, the nickel(II) oxidation potential in [3]
rotaxane shifts even more toward less positive values: 1.03 V
(Fig. 8). This can be explained similarly to the influence of nitro
groups. The coordinating chloride ions, which are additionally
−
smaller than PF6 in 6n, diffuse to the center of the molecule
and stabilize the higher oxidation state more easily.
Fig. 7 Differential pulse voltammograms recorded on the GCE in 0.1 M
TBAHFP/DMF solution of 4n – solid line, 5n – dashed line, 6n – short-
dashed line, amplitude = 50 mV, tp = 10 ms, reference electrode: Ag/
AgCl in methanol.
Experimental
Materials and methods
four catechol rings, results in difficult access of counterions Acetonitrile and dichloromethane were dried over P2O5, dis-
compensating the charge after the oxidation process. tilled and stored under Ar. Toluene was dried with sodium,
Therefore, [2]rotaxane 5n and [3]rotaxane 6n oxidize at slightly distilled and stored with Na and under Ar. All other solvents
higher potentials than the axle: 1.14 and 1.18 V, respectively and reagents were used without additional purification: 3,5-
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dimethoxybenzoyl chloride (>98%, TCI Chemicals,); 3,5-di- CON3), 7.17 (d, J = 2.4 Hz, 2 H, HAr ortho to CON3). 13C NMR
nitrobenzoyl chloride for fluorescence (>98.0%, Aldrich); (100 MHz, CDCl3): 55.8 (CH3), 107.1 (Csp2–H “ortho” to CON3),
sodium azide (POCh); methyl trifluoromethanesulfonate 107.3 (Csp2–H “para” to CON3), 132.6 (Csp2–CON3), 161.0 (Csp2
–
(>98%, Aldrich); 4-amino-1-butanol (>98%, TCI Chemicals); O), 172.4 (CON3).
ammonium hexafluorophosphate (99.8%, Apollo Scientific);
3,5-Dinitrobenzoyl azide (3n) was synthesized from 3,5-di-
dibenzo-24-crown-8 (>98%, TCI Chemicals); silica gel 60 H for nitrobenzoyl chloride according to the above described pro-
thin-layer chromatography (Merck); aluminium oxide 60 cedure. Caution should be exercised as the compound may
GF254 neutral (type E) for thin-layer chromatography (Merck); explode at elevated temperature. Yield: 91%. 1H NMR
silica gel 60 silanized for column chromatography (400 MHz, CDCl3): 9.15 (d, J = 2.1 Hz, 2 H, HAr ortho to CON3),
(0.063–0.200 mm, Merck). 3,5-Dimethoxybenzoyl and 3,5-di- 9.25 (t, J = 2.1 Hz, 1 H, HAr para to CON3). 13C NMR (100 MHz,
nitrobenzoyl azides were stored in a dry and sealed container CDCl3): 123.4 (Csp2–H “para” to CON3), 129.2 (Csp2–H “ortho” to
within a freezer.
CON3), 134.2 (Csp2–CON3), 149.0 (Csp2–NO2), 168.9 (CON3).
4m: 3,5-Dimethoxybenzoyl azide (114.4 mg, 0.55 mmol, 3
eq.) was closed under an argon atmosphere in a dry, two-neck
Synthetic procedures
Equipment: Elemental analyzer PERKIN-ELMER type 240; flask equipped with a balloon. The flask was immersed in an
mass spectrometer MALDI Synapt G2-S; nuclear magnetic reso- oil bath preheated to 100 °C. After 3 h of heating and stirring,
nance spectrometers Varian VNMRS 600 MHz and Varian the product was allowed to cool to RT and 1 ml of a solution of
Mercury 400 MHz (chemical shifts reported in reference to 2 (135.3 mg, 0.183 mmol, 1 eq.) in anhyd. CH3CN was added
acetonitrile residual peak (1.94 ppm (1H) and 118.26 ppm through a silicone stopper. The solution was allowed to stand
(13C)). The assignment of the 13C signals was supported by at RT for 12 h, followed by evaporation to dryness. The result-
1H–13C HSQC spectra.
Complex 1: This compound was synthesized according to column, with an eluent composed of NH4PF6, CH3CN and H2O
the new, one-pot synthesis.45
(10 mg : 1 ml : 1 ml). The last/major fraction was partially con-
ing orange-coloured solid was purified on a silanized silica gel
Complex 2: Methyl trifluoromethanesulfonate (721.1 µl, centrated yielding an orange-coloured precipitate. The title
6.372 mmol, 2.1 eq.) was added to the refluxing suspension of compound was filtered, rinsed with H2O, dried and stored
1 (924.6 mg, 3.032 mmol, 1.0 eq.) in CH2Cl2 (100 ml, anhyd.). in vacuo over P2O5. Yield 144.1 mg (71%). Anal. calc. for
After 4 h of stirring at reflux, 4-aminobutan-1-ol (587.4 µl, C38H52N8NiO8·2PF6·H2O (1115.51): C 40.92, H 4.88, N 10.04%;
6.372 mmol, 2.1 eq.) was added and the heat source was found C 40.93, H 4.87, N 10.01%. TOF MS ES+ (CH3CN, m/z):
1
removed. 15 min later, the suspension was evaporated to 403.2 [M]2+. H NMR (600 MHz, CD3CN) δ 1.69–1.80 (comp, 8
dryness. Purification was performed on a silanized silica gel H, CH2(CH2 2
column, with an eluent composed of NH4PF6, CH3CN and H2O 6.4 Hz, 4 H, NHCH
̲
) CH2); 3.38–3.58 (br m, 8 H, N(CH2)2N); 3.54 (t, J =
2); 3.73 (s, 12 H, CH3); 4.15 (t, J = 6.1 Hz, 4
̲
(10 mg : 1.0 ml : 1.5 ml). The first fraction was partially concen- H, CH2OCO); 6.19 (t, J = 2.2 Hz, 2 H, HAr para to NHCO2); 6.65
trated yielding an orange-coloured precipitate. The title com- (d, J = 2.0 Hz, 4 H, HAr ortho to NHCO2); 7.66 (br s, 2 H,
pound was filtered, rinsed with H2O, dried and stored in vacuo vCHN); 7.3–8.4 (set of broad signals, 8 H, CHvN, NH). 13C
over P2O5. Yield 1.669
C20H34N6NiO2·2PF6 (739.15): C 32.50, H 4.64, N 11.37%; found (NHC
C 32.24, H 4.87, N 11.27%. TOF MS ES+ (CH3CN, m/z): 224.1 95.6 (Csp2–H “para” to NHCO2), 97.8 (Csp2–H “ortho” to
[M]2+. 1H NMR (400 MHz, CD3CN) δ 1.51–1.59 (m, 4 H, NHCO2), 104.3 (C
vCHN), 141.6 (Csp2–NHCO2), 154.5 (CvO),
CH2CH2OH); 1.68–1.76 (m, 4 H, CH2CH2NH); 2.73 (br s, 2 H, 155.0 br and 160.6 br (CHvN), 162.2 (Csp2–OMe), 164.0
OH); 3.47–3.62 (m, 16 H, N(CH2)2N, CH2NH, CH2OH); 7.49, (vCHN).
7.51, 7.95 and 7.97 (4 × s, 4 × 1 H, CHvN); 7.66 (d, J = 14.8 Hz, 4n: Neat 3,5-dinitrobenzoyl azide explodes at elevated temp-
2 H, vCHN); 8.28 (very br s, 2 H, NH). 13C NMR (100 MHz, eratures and needs to be rearranged in the presence of a
CD3CN) 27.3, 30.0 (NHCH2(CH2)2CH2OH); 51.6, 61.9 solvent. A solution of 3,5-dinitrobenzoyl azide (105.0 mg,
(NHCH2(CH2)2CH2OH); 59.3, 59.5, 60.2 and 60.4 (N(CH2)2N); 0.443 mmol, 2.5 eq.) in anhyd. toluene (1.1 ml) was closed
104.1 (CvCHN); 155.0 and 160.6 (CHvN); 163.9 (vCHN). under an argon atmosphere in a dry, two-neck flask equipped
3,5-Dimethoxybenzoyl azide (3m): solution of 3,5- with a condenser and balloon. The flask was immersed in an
g
(74%). Anal. calc. for NMR (150 MHz, CD3CN) δ 26.4 and 26.8 (CH2(C
̲
̲
̲
̲
̲
̲
̲
̲
̲
̲
δ
̲
̲
̲
̲
̲
A
dimethoxybenzoyl chloride (4.022 g, 0.020 mol, 1 eq.) in oil bath preheated to 120 °C. After 3 h of heating and stirring,
acetone (10 ml) was added dropwise over 30 min to the ice- the solution was allowed to cool to RT. 2 ml of a solution of 2
cold solution of NaN3 (2.610 g, 0.040 mmol, 2 eq.) in H2O (130.8 mg, 0.177 mmol, 1 eq.) in anhyd. CH3CN was then
(10 ml). After 1 h of stirring, acetone was evaporated on a added through a silicone stopper. The mixture was stirred over-
rotovap without heating. The precipitate was filtered, rinsed night at RT and then evaporated to dryness. CH3CN was added
with H2O, and purified on silicagel with CH2Cl2/n-hexane to the yellow solid thus obtained, and the suspension was
(1 : 1vol) as an eluent. The first major fraction was evaporated sonicated in an ultrasonic bath for 15 min, followed by stirring
to dryness (without heating) to give the title compound as a at reflux for 15 min. Filtration yielded an orange filtrate (dis-
colourless solid. Yield: 3.314 g (80%). 1H NMR (400 MHz, carded) and some insoluble material which was washed with
CDCl3): 3.84 (s, 6 H, CH3), 6.69 (t, J = 2.4 Hz, 1 H, HAr para to CH3CN and n-hexane. After drying in vacuo over P2O5 the
15852 | Dalton Trans., 2018, 47, 15845–15856
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poorly soluble solid was confirmed to be the title compound 7.59 ppm); 6.77–6.83 (m, 8 H, HAr of the crown ether); 7.31,
in its pure form. Yield 88.2 mg (43%). Anal. calc. for 7.37, 7.85 and 7.91 (4 × s, 4 × 0.5 H, CHvN); 7.59 and 8.18 (2 ×
C34H40N12NiO12·2PF6 (1157.38): C 35.28, H 3.48, N 14.52%; d, J = 15.1 and 16.0 Hz, 2 × 1 H, vCHN); 7.66 and 7.73 (2 × br
found C 35.30, H 3.54, N 14.54%. TOF MS ES+ (CH3CN, m/z): s, 2 × 1 H, NHCO2); 8.10 (very br, 1 H, NH
̲
433.3 [C34H40N12NiO12]2+. 1H NMR (600 MHz, CD3CN) δ 8.72–8.81 (m, 1 H, NH
1.72–1.80 (comp, 8 H, CH2(CH2 2
N(CH2)2N and NHCH2
̲
̲
̲
̲
̲
Hz, 2 H, vCHN); 8.50 (t, J = 2.1 Hz, 2 H, HAr para to NHCO2); (C
8.68 (d, J = 1.8 Hz, 4 H, HAr ortho to NHCO2); 9.92–10.0 (m, 2 (C
̲
̲H2); 71.3 (CH2O
̲
H, NH
CD3CN) δ 26.4 and 26.9 (CH2(C
59.2, 59.4, 60.1, 60.4 (N(CH2)2N), 65.7 (C
(CvCHN), 112.5 (Csp2–H “para” to NHCO2), 118.6 (Csp2–H 154.6 (CvO); 154.65, 154.77, 158.77, 158.80, 160.03 and
“ortho” to NHCO2), 143.0 (Csp2–NHCO2), 149.8 (Csp2–NO2), 160.19 (CHvN); 162.1 and 162.2 (Csp2–OMe); 163.5 (vCHN
154.7 (CvO), 155.7 and 160.7 (CHvN), 164.6 (vCHN). (bare side)); 166.9 (vCHN (crown side)). For [3]rotaxane 6m:
̲
CH2); 10.13 (br s, 2 H, NHCO2). 13C NMR (150 MHz, and 97.78 br (Csp2–H “ortho” to NHCO2); 104.2 and 104.4
̲
̲H2CH2), (C̲
̲
̲
̲
̲
̲
Rotaxanes 5m and 6m: 3,5-Dimethoxyphenyl isocyanate was anal. calc. for C86H116N8NiO24·2PF6 (1994.51): C 51.79, H 5.86,
prepared from 3,5-dimethoxybenzoyl azide (350.3 mg, N 5.62%; found C 51.60, H 5.69, N 5.67%. TOF MS ES+
1
1.691 mmol, 2.5 eq.) as in the procedure for 4m. After cooling (CH3CN, m/z): 851.6 [M]2+. H NMR (600 MHz, CD3CN) δ 1.71
to RT, CH2Cl2 (5 ml) was added through a silicone stopper and (br comp, 8 H, CH2(CH2 2
the syringe was filled with the resulting solution. The emptied N(CH2)2N); 2.82 and 2.95 (2 × br t, J = 6.4 and 6.3 Hz, 2 × 2 H,
flask was loaded with a solution of DB24C8 (3.031 g, N(CH2)2N); 3.52–3.60 (br m, 4 H, NHCH2); 3.65–3.77 (br m, 16
6.758 mmol, 10 eq.) in CH2Cl2 (9 ml). Isocyanate/CH2Cl2 and a H, CH2O(CH2)2O); 3.71 (s, 12 H, CH3); 3.70–3.76 and 3.88–3.94
solution of 2 (499.7 mg, 0.676 mmol, 1 eq.) in CH3CN (5 ml, (2 × br m, 2 × 8 H, ArOCH2CH2); 3.95–4.01 and 4.04–4.10 (2 ×
̲ ) CH2); 2.67 and 3.03 (2 × br s, 2 × 2 H,
̲
̲
̲
second syringe) were simultaneously added dropwise to br m, 2 × 8 H, ArOCH2); 4.09–4.15 (br m, 4 H, CH2OCO); 6.17
DB24C8/CH2Cl2 over 3 h. The mixture was stirred overnight, (t, J = 2.2 Hz, 2 H, Csp2–H para to NHCO2); 6.64 (d, J = 2.1 Hz, 4
evaporated to dryness, redissolved in CH2Cl2, and poured onto H, Csp2–H ortho to NHCO2); 6.69 and 6.78 (2 × br s, 2 × 1 H,
an alumina DCVC column (40 g). An excess of DB24C8 was CHvN); 6.81–6.88 (m, 16 H, HAr in the crown ether); 7.61–7.65
separated during elution with CH2Cl2. Then, an orange- (comp, 4 H, CHvN and NHCO2); 8.10 (d, J = 15.9 Hz, 2 H,
colored band of cationic complexes was forced to leave the vCHN); 8.56–8.65 (m, 2 H, NH
column with a NH4PF6/CH3CN (10 g l−1) solution. The result- CD3CN) δ 27.0 and 27.1 (CH2(C
H2)2CH2); 51.0 (NHC
ing mixture was evaporated to dryness and applied to a sila- (CH3); 58.7, 59.6, 59.7 (N(CH2)2N); 65.1 (CH2OCO); 68.6
nized silica gel column. RP chromatographic separation was (ArOCH2); 71.0 (ArOCH2CH2); 71.5 (CH2O(CH2)2O); 95.7 (Csp2
performed by means of gradient elution with 40–70%vol. of H “para” to NHCO2); 97.7 (Csp2–H “ortho” to NHCO2); 104.06
NH4PF6/CH3CN (10 g l−1) in H2O. Minor bands were discarded, and 104.11 (C
vCHN); 113.0 (Csp2–H “ortho” to OCH2); 121.9
whereas two major orange-coloured fractions were partially (Csp2–H “meta” to OCH2); 141.6 (Csp2–NHCO2); 148.9 (Csp2
̲
̲
̲
̲
̲
̲
–
̲
̲
–
concentrated yielding oily precipitates. Samples were filtered, OCH2); 154.5 (CvO); 154.8, 154.9, 158.9 and 159.2 (CHvN);
rinsed with H2O, dissolved in CH2Cl2, separated from an 162.1 (Csp2–OMe); 166.5 (vCHN).
excess of water, precipitated with n-hexane, and dried and
Rotaxanes 5n and 6n: 3,5-Dinitrophenyl isocyanate was pre-
stored in vacuo over P2O5. Yields: 253.9 mg (24%) of 5m and pared from 3,5-dinitrobenzoyl azide (417.8 mg, 1.762 mmol,
170.5 mg (13%) of 6m. For [2]rotaxane 5m: anal. calc. for 2.5 eq.) as in the procedure for 4n. Rotaxanes were synthesized
C62H84N8NiO16·2PF6 (1546.00): C 48.17, H 5.48, N 7.25%; and purified following the above described procedure for their
found C 48.20, H 5.58, N 7.10%. TOF MS ES+ (CH3CN, m/z): methoxy-congeners. Two major orange-coloured fractions col-
627.5 [M]2+. 1H NMR (600 MHz, CD3CN) δ 1.69–1.79 and lected from the column yielded crystalline precipitates which
1.80–89 (2 × m, 2 × 4 H, CH2(CH2̲ )2CH2); 2.85–2.96 (2 H), were filtered, rinsed with H2O, n-hexane and dried and stored
3.11–3.17 (1 H), 3.18–3.28 (3 H), 3.29–3.34 (1 H), and 3.37–3.41 in vacuo over P2O5. Yields: 320.1 mg (28%) of 5n and 232.6 mg
(1 H) (5 × m, Σ 8 H, N(CH2)2N); 3.52 (t, J = 6.4 Hz, 2 H, (16%) of 6n. For [2]rotaxane 5n: anal. calc. for
NHCH
CH2O(CH2 2
̲
2); 3.64–3.69 (m, 2 H, NHCH2
̲
); 3.69–3.77 (comp, all 8 of C58H72N12NiO20·2PF6 (1605.88): C 43.38, H 4.52, N 10.47%;
̲
) O and 4 of ArOCH2CH2
̲
); 3.70 (s, 6 H, CH3 (crown found C 43.17, H 4.57, N 10.47%. TOF MS ES+ (CH3CN, m/z):
side)); 3.74 (s, 6 H, CH3 (bare side)); 3.79–3.83 (m, 4 of 657.4 [M]2+. H NMR (600 MHz, CD3CN) δ 1.75–1.79 (br comp,
1
ArOCH2); 3.95–4.01 (m, 4 of ArOCH2CH2
ArOCH2); 4.16 (t, J = 6.2 Hz, 2 H, CH2OCvO); 4.21–4.25 (br t, 2 CH2(CH2 2
H, CH2OCvO); 6.16 and 6.20 (2 × t, J = 2.2 Hz, 2 × 1 H, HAr 2 × 2 H, N(CH2)2N); 3.16 and 3.34 (2 × br s, 2 × 2 H, N(CH2)2N);
para to NHCO2); 6.63 and 6.68 (2 × d, J = 2.0 Hz, 2 × 2 H, HAr 3.50–3.56 and 3.64–3.69 (2 × br m, 2 × 2 H, NHCH2); 3.69–3.74
ortho to NHCO2); 6.63 and 7.59 (2 × s, 2 × 1 H, CHvN, over- (m, 4 H, ArOCH2CH2); 3.77 (s, 8 H, CH2O(CH2)2O); 3.78–3.82
layed with a doublet at 6.63 ppm, and respectively, doublet at (m, 4 H, ArOCH2); 3.98–4.08 (comp, 8 H, 4 of ArOCH2 and 4 of
̲
); 4.05–4.10 (m, 4 of 4 H, CH2(CH2 2
̲ ) CH2 (bare side)); 1.82–1.92 (br comp, 4 H,
̲
) CH2 (crown side)); 2.89 and 3.22 (2 × br t, J = 6.6 Hz,
̲
̲
̲
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ArOCH2CH2
̲
); 4.24–4.28 (m, 2 H, CH2OCO (bare side)); 4.35 (t, were collected at 100(2) K on the Agilent Technologies
J = 6.0 Hz, 2 H, CH2OCO (crown side)); 6.63 and 7.59 (2 × s, 2 × SuperNova Dual (6n) or Single Source (6nCl) diffractometers
1 H, CHvN (crown side)); 6.72–6.78 (br m, 8 H, HAr in the with CuKα (λ = 1.54184 Å) (6n) and MoKα (λ = 0.71073 Å)
crown ether); 7.36 and 7.82 (2 × br s, 2 × 1 H, CHvN (bare (6nCl) using CrysAlis RED software.46 The crystals were posi-
side)); 7.58 (s, 1 H, vCHN (bare side)); 7.97 (br s, 1 H, NH
(bare side)); 8.18 (d, J = 16.2 Hz, 1 H, vCHN (crown side)); ∼50 mm from the EOS CCD detector, respectively. A complete
8.40 (s, 1 H, NHCO2 (crown side)); 8.41 (t, J = 2.0 Hz, 1 H, Csp2 data set was collected at 1° intervals with counting time ranges
̲CH2 tioned at ∼70 mm from the ATLAS CCD detector and at
–
H para to NHCO2 (crown side)); 8.45 (br s, 1 H, NHCO2 (bare 2.5–15 and 10–70 s for 6n and 6nCl, respectively. In total, 5294
side)); 8.55 (t, J = 2.0 Hz, 2 H, Csp2–H ortho to NHCO2 (crown and 669 frames were collected for 6n and 6nCl, respectively.
side)); 8.57 (d, J = 2.0 Hz, 1 H, Csp2–H para to NHCO2 (bare The analytical numerical absorption correction using a multi-
side)); 8.68 (d, J = 1.9 Hz, 2 H, Csp2–H ortho to NHCO2 (bare faceted crystal model based on expressions derived by
side)); 8.75–8.83 (m, 1 H, NH
(150 MHz, CD3CN) δ 26.3, 26.9, 27.3 and 27.4 (CH2(C
51.0 and 51.1 (NHCH2); 58.6 br and 59.5 br (N(CH2)2N); 66.0 crystal model (6n) implemented in SCALE3 ABSPACK scaling
and 66.3 (CH2OCO); 68.3 (ArOCH2); 71.0 (ArOCH2C
H2); 71.3 algorithm, were applied.46 The data were corrected for
(CH2O(CH2)2O); 104.2 and 104.4 (CvCHN); 112.7 (Csp2–H Lorentzian and polarization effects. Data reduction and ana-
̲
̲
̲
̲
̲
̲
̲
“ortho” to OCH2); 112.8 and 113.0 (Csp2–H “para” to NHCO2); lysis were carried out with the CrysAlis program.46 The struc-
118.8 (Csp2–H “ortho” to NHCO2, the second one overlayed with ture determination procedure was carried out using the SHELX
a solvent residual signal); 121.7 (Csp2–H “meta” to OCH2); package.48 The structure was solved by direct methods and
142.3 and 142.4 (Csp2–NHCO2); 148.9 (C̲sp2–OCH2); 149.6 and then successive least-squares refinement was carried out based
149.8 (Csp2–NO2); 154.4 and 154.5 (CvO); 154.8 and 158.9 on the full-matrix least-squares method on F2 using the
(CHvN); 163.5 and 167.0 (vCHN). For [3]rotaxane 6n: anal. SHELXL program. The hydrogen atoms, except those linked to
calc. for C82H104N12NiO28·2PF6 (2054.39): C 47.94, H 5.10, N the O-atom of the water molecule in 6n, and imine N-atoms in
8.18%; found C 47.90, H 5.24, N 7.97%. TOF MS ES+ (CH3CN, 6nCl, were positioned geometrically, with X–H equal to 0.84,
1
m/z): 881.5 [M]2+. H NMR (600 MHz, CD3CN) δ 1.77 (br comp, 0.88, 0.95 and 0.99 Å for hydroxyl, imine, aromatic, methyl and
8 H, CH2(CH2 2
N(CH2)2N); 2.72 and 2.86 (2 × br t, J = 6.4 and 6.4 Hz, 2 × 2 H, and 0.97 for imine, aromatic, methylene and methyl H-atoms,
N(CH2)2N); 3.54–3.62 (br m, 4 H, NHCH2); 3.66–3.78 (comp, 24 respectively in 6nCl, and constrained to ride on their parent
H, 8 of ArOCH2CH2 and 16 of CH2O(CH2)2O); 3.91–3.98 (comp, atoms with Uiso(H) = xUeq(C,N,O), where x = 1.2 for the aro-
16 H, 8 of ArOCH2 and 8 of ArOCH2CH2); 4.01–4.08 (br m, 8 H, matic, methylene and imine H-atoms, and x = 1.5 for the
̲ ) CH2); 2.56 and 2.95 (2 × br s, 2 × 2 H, methylene H-atoms, respectively in 6n, and 0.85, 0.93, 0.96
̲
̲
̲
̲
ArOCH2); 4.23–4.29 (br m, 4 H, CH2OCO); 6.61 and 6.72 (2 × br s, methyl and hydroxyl H-atoms. The H-atoms of the water mole-
2 × 1 H, CHvN); 6.75–6.80 (br m, 16 H, HAr of the crown ether); cule in 6n and those linked to the imine N-atoms in 6nCl were
7.56 and 7.57 (2 × s, 2 × 1 H, CHvN); 8.08 (d, J = 15.8 Hz, 2 H, located on a Fourier difference map and constrained to ride on
vCHN); 8.37 (s, 2 H, NHCO2); 8.42 (br s, 2 H, Csp2–H para to their parent atom with Uiso(H) = xUeq(O,N), where x = 1.2 or 1.5
NHCO2); 8.56 (br s, 4 H, Csp2–H ortho to NHCO2); 8.60–8.67 (m, 2 for N or O-atom, respectively. All nitro groups of the [3]rotaxa-
−
H, NHC
and 27.32 (CH2(CH2 2
(N(CH2)2N); 66.2 (CH2
(ArOCH2CH2); 71.5 (CH2O(CH2 2
̲
H2). 13C NMR (150 MHz, CD3CN) δ 27.12, 27.17, 27.27 neaxle, and the PF6 anions in 6n are disordered in two posi-
̲
) CH2); 50.9 (NHCH2
OCO); 68.52 and 68.55 (ArOCH2); 71.0 0.89 : 0.11 for the nitro groups and the PF6 counterions,
) O); 104.0 and 104.1 (CvCHN); respectively. Occupancy parameters of solvent moieties in 6nCl
̲
); 58.60, 59.59 and 59.62 tions with the site occupancy factors of 0.59 : 0.41 and
−
̲
̲
̲
̲
112.8 (Csp2–H “para” to NHCO2); 112.9 (Csp2–H “ortho” to OCH2); were less than 100% and they were refined freely; thus solvent
∼118 (Csp2–H “ortho” to NHCO2, overlayed with a solvent residual molecules were in a non-stoichiometric ratio to the main [3]
signal); 121.8 (Csp2–H “meta” to OCH2); 142.3 (Csp2–NHCO2); 148.8 rotaxane moiety. The atoms of disordered parts of the struc-
(Cs̲ p2–OCH2); 149.6 (Csp2–NO2); 154.4 (CvO); 154.7, 154.8, 158.8 tures were subject to numerous SADI, DELU and RIGU
and 159.1 (CHvN); 166.6 (vCHN).
restraints.
The figures for this publication were prepared using Olex2
6nCl: Bis(hexafluorophosphate) [3]rotaxane 6n (78.5 mg,
0.038 mmol) was dissolved in CH3CN (1.5 ml) and a solution and Mercury programs.49 All molecular interactions in the
of tetrabutylammonium chloride (21.2 mg, 2 eq.) in CH3CN crystal were identified using the PLATON program.50
(1 ml) was added. 6nCl precipitated instantaneously, was fil-
CCDC 1856147 and 1856148‡ contain the supplementary
tered, rinsed with CH3CN and recrystallized from acetone/ crystallographic data.
methanol. These crystals were subjected to X-ray crystallo-
Electrochemical studies
graphic studies. Anal. calc. for C82H104N12NiO28·2Cl (1835.37):
C 53.66, H 5.71, N 9.16%; found C 53.59, H 5.80, N 9.11%.
Electrochemical experiments were carried out using a CH
Instrument 650D potentiostat (CH Instruments, Inc., Austin,
TX) in a three electrode arrangement, with a silver/silver chlor-
X-ray crystallographic studies
Good quality single-crystal specimens of 6n and 6nCl were ide (Ag/AgCl) electrode filled with saturated TBACl in methanol
selected for X-ray diffraction data collection. Diffraction data as the reference, platinum foil as the counter and a glassy
15854 | Dalton Trans., 2018, 47, 15845–15856
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carbon electrode (GCE, BAS, 3 mm diameter) as the working 100 grant (DT – structural analysis) and the data collection was
electrode. The reference electrode was separated from the accomplished at the Core Facility for crystallographic and bio-
working solution by an electrolytic bridge filled with 0.1 M physical research to support the development of medicinal pro-
tetrabutylammonium hexafluorophosphate/DMF (TBAHFP/ ducts sponsored by the Foundation for Polish Science (FNP).
DMF) solution. The reference potential electrode was cali-
brated by using the ferrocene oxidation process in the same
TBAHFP/DMF solution. 0.1 M TBAHFP/DMF was used as the
supporting electrolyte solution. Argon was used to deaerate the
Notes and references
solution and an argon blanket was maintained over the solu-
tion during all experiments. All experiments were carried out
at 25 °C. The GC electrode was polished mechanically with 1.0,
0.3 and 0.05 µm alumina powder on a Buehler polishing cloth
to a mirror-like surface. Finally, it was rinsed with methanol
and sonicated in pure methanol.
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ˉ
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