Four-component zinc-porphyrin/zinc-salphen nanorotor

Article abstract of DOI:10.1039/c7dt01323j

An off-axis supramolecular rotor was composed of four components: a zinc-porphyrin based stator with four phenanthroline stations and a zinc-salphen based rotator were self-assembled with DABCO and four copper(i) ions to furnish the rotor ROT-2 in quantitative yield. The DABCO serves as a connecting axle between the rotator and the stator, while the rotator is additionally connected to two copper(i)-loaded phenanthroline stations of the stator via its two pyridine terminals (N_py → [Cu(phen)]⁺). For the thermally activated rotation both N_py → [Cu(phen)]⁺ interactions have to be cleaved. Due to the high energy barrier of the rotation the slow motion was monitored by ROESY. The reduced speed (k₂₉₈ = 0.2 s^-1) was rationalised in terms of ground state stabilisation of the rotor as suggested by computational insight. Additional VT ¹H-NMR investigation was undertaken to study the motion of DABCO that is sandwiched between zinc porphyrin and zinc salphen. The diagnostic splitting of the geminal DABCO protons was rationalised on the basis of the asymmetry induced by the salphen that generates a diastereotopic environment. Computations reproduced the experimental NMR with excellent agreement.

Full text of DOI:10.1039/c7dt01323j

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Four-component zinc-porphyrin/zinc-salphen
nanorotor†
Cite this: DOI: 10.1039/c7dt01323j
Merve S. Özer, Anup Rana, Pronay K. Biswas and Michael Schmittel
*
An off-axis supramolecular rotor was composed of four components: a zinc-porphyrin based stator with
four phenanthroline stations and a zinc-salphen based rotator were self-assembled with DABCO and four
copper(I) ions to furnish the rotor ROT-2 in quantitative yield. The DABCO serves as a connecting axle
between the rotator and the stator, while the rotator is additionally connected to two copper(I)-loaded
phenanthroline stations of the stator via its two pyridine terminals (Npy → [Cu(phen)]+). For the thermally
activated rotation both Npy → [Cu(phen)]+ interactions have to be cleaved. Due to the high energy barrier
of the rotation the slow motion was monitored by ROESY. The reduced speed (k298 = 0.2 s−1) was
rationalised in terms of ground state stabilisation of the rotor as suggested by computational insight.
Additional VT 1H-NMR investigation was undertaken to study the motion of DABCO that is sandwiched
between zinc porphyrin and zinc salphen. The diagnostic splitting of the geminal DABCO protons was
rationalised on the basis of the asymmetry induced by the salphen that generates a diastereotopic
environment. Computations reproduced the experimental NMR with excellent agreement.
Received 12th April 2017,
Accepted 23rd June 2017
DOI: 10.1039/c7dt01323j
rsc.li/dalton
block in materials chemistry applications,21 suggesting its valu-
able utility in supramolecular machinery as well.
Introduction
Inspired by nature, useful and fascinating molecular
machines1–3 – mostly based on covalent frameworks – have
been constructed for highly specific tasks and practical work.4
Results and discussion
New
design
principles5
allowing
multi-component
assembly6–10 in combination with well-established thermally
activated motion, such as translation11,12 and rotation,13
should open the door for creating new multi-component
machinery with interesting dynamic behavior.14–17 Recently,
various multicomponent nanorotors were prepared by our
group.18 In the four-component nanorotors,18a two distinctly
ornamented zinc porphyrins (stator and rotator) are sand-
wiched together by means of two axial NDABCO → zinc(II)
porphyrin (ZnPor) and two Npy → [Cu(phen)]+ interactions
(= HETPYP binding: HETeroleptic PYridine and Phenanthroline
metal complexation19), a building principle that we will also
apply in the actual investigation.
For the off-axis supramolecular rotor, we chose zinc porphyrin-
based stator 1 and zinc-salphen skeleton 2 as a rotator
(Chart 1), the latter equipped with tert-butyl groups to over-
come solubility problems.22
The synthetic scheme leading to zinc salphen 2 is illus-
trated in Scheme 1. Compounds 5,23 6,24
7
25 and 8 26 were pre-
pared according to the literature procedures. Two subsequent
Suzuki couplings afforded the pyridine-terminated salicyl-
aldehyde 10 in good yield from compounds 7 and 8. Finally, the
condensation of salicylaldehyde 10 and the ortho-phenylene
diamine derivative 11 in the presence of Zn(OAc)2 afforded the
desired zinc salphen 2 in good yield (86%). A full characteri-
sation of rotator 2 was possible by NMR, ESI-MS and elemental
analysis. The NMR spectra had to be recorded in DMSO-d6 as a
coordinating solvent to prevent the de-metallation of the
salphen ligand.27 In DCM, rotator 2 experienced de-metalation
as confirmed by ESI-MS (Fig. S15†), whereas the desired peak
m/z = 937.7 was observed in THF (Fig. S16†).
Here, we present a four-component off-axis nanorotor.
Different from previous work, the porphyrin unit of the rotator
is replaced by a salphen core and the DABCO axle connects with
the rotator off the midpoint between the two pyridine term-
inals.20 The salphen moiety has found ample use as a building
Analogous to the procedure leading to the known rotor18a
[Cu2(1)(3)(DABCO)]2+, we combined compounds 1 and 2 with
DABCO and copper(I) ions (1 : 1 : 1 : 2) affording the four-
component rotor ROT-1 = [Cu2(1)(2)(DABCO)]2+ (Scheme 2).
1H NMR confirmed the formation of the rotor assembly, in
Center for Micro- and Nanochemistry and Engineering, Organische Chemie I,
Universität Siegen, D-57068 Siegen, Germany.
E-mail: schmittel@chemie.uni-siegen.de
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7dt01323j
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Chart 1 Molecular structures and cartoon representations of stator 1 and rotator 2 & 3 units.
Scheme 1 Synthetic scheme leading to rotator 2.
particular by comparison with the earlier reported NMR the stator are connected to the rotators’ pyridine terminals via
1
data.18a For instance, H NMR shows the pyridine protons c-H two Npy → [Cu(phen)]+ (= HETPYP) interactions (Fig. S7†).
and d-H to be characteristically upfield shifted at 7.01 and Furthermore, the diagnostic signals resonating at 0.47 and
6.92 ppm, respectively. It suggests that the 5,15-positions of −3.10 ppm indicate that DABCO is sandwiched between the
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Scheme 2 Preparation of ROT-1 and ROT-2 (cartoon representation).
Fig. 1 Partial 1H NMR spectra of stator 1, the copper(I)-loaded stator
[Cu4(1)]4+ (1 + 4 equiv. of Cu+), ROT-1 and ROT-2 in CD2Cl2.
stator and the rotator, which was also proven by a correlation
in the 1H–1H COSY spectrum (Fig. S8†). In contrast to the zinc stant k298 = 0.2 s−1 (Fig. S12 and S13†) from the integration
porphyrin with its strong ring current causing upfield shifts of the diagonal and cross signals. As a result, the energy
(δDABCO = −3.10 ppm),28 the salphen does not instigate drastic barrier of rotational spinning was determined as ΔG≠
=
298
changes upon axial coordination.20a Therefore, the chemical 77.0 kJ mol−1
.
shifts of the DABCO protons differ drastically. Furthermore, To rationalise the high rotational barrier for rotor ROT-2,
the proton signals of the four phenanthroline stations in we undertook computations and started with a comparison of
stator 1 appear as two sets, one for the phenanthrolines the ground state stabilisation of ROT-2 vs. ROT-3 = [Cu4(1)(3)
loaded with the rotator and Cu+, and the other for the (DABCO)]4+, the latter representing a high-speed rotor (ΔG≠
unloaded free stations.
298
= 45.0 kJ mol−1).18a For fast computations, two model systems,
In spite of DABCO being sandwiched between the rotator ROT-2′ & ROT-3′, were constructed from ROT-2 and ROT-3; a
and the stator as clearly evidenced by the characteristic signals representative of ROT-2′ is illustrated in Fig. 2. In both model
in 1H NMR, the ESI-MS was devoid of a mass peak proving the systems, the two stator arms which are not coordinated
presence of [Cu2(1)(2)(DABCO)]2+ for ROT-1 possibly due to the via copper(I) ions to the pyridines of the rotator are omitted.
lower binding constant of DABCO to ZnII(salphen).20b In fact, The model systems as well as both rotators 2 and 3 were opti-
the ESI-MS reveals a mass peak at 1777.3 representing the mised by applying the ONIOM method as implemented in
assembly [Cu2(1)(2)]2+ without DABCO (Fig. S17 and S18†). Gaussian 09.31 The low layer was treated with PM6-D3 and the
Equally, DABCO was not detected in the other mass peaks high layer with DFT-D3.32 Finally, the isodesmic reaction
appearing in the mass spectrum.
shown in Scheme 3 was evaluated computationally revealing
Due to the symmetry of the rotor, the rotation in ROT-1 that rotor ROT-2′ is more stable than ROT-3′ by 33.9 kJ mol−1
.
cannot be investigated by 1H NMR. Thus, two more equi-
A
substantial portion of the energy difference, i.e.
valents of [Cu(CH3CN)4]PF6 were added to ROT-1 to furnish 13.8 kJ mol−1, arises from dispersion. Interestingly, the experi-
rotor ROT-2 (Scheme 2). Originally, it was assumed that all mental ΔΔG≠ = 32.0 kJ mol−1 between the two rotors ROT-2
298
1
four stations of the stator would be equivalent in H NMR due and ROT-3 matches well with the computed difference in the
to the rapid rotation, but still two sets of phenanthroline ground-state energy of 33.9 kJ mol−1. Such a finding indicates
protons were detected in ROT-2. Diagnostically, the protons of that the rotators’ pyridine terminals of both rotors ROT-2 and
the previously “free” stations were shifted downfield due to the ROT-3 have almost fully dissociated from their copper(I)
complexation by Cu+ ions, as outlined in Fig. 1. The individual centres in the transition state, because only in a late transition
chemical shift differences between the two sets of phenanthro- state we expect the ground state difference to correspond to
lines amount to 0.24–0.38 ppm (Table S1†). In the case of
ROT-2, there appears an additional signal belonging to DABCO
at 0.11 ppm (for explanation, vide infra) apart from the two
signals at 0.47 and −3.10 ppm. The DOSY spectrum indicates that
there is a single diffusion coefficient at D = 3.2 × 10−10 m2 s−1
belonging to the assembly including DABCO and its hydro-
dynamic radius was calculated as 17 Å (Fig. S11†).
Clearly, finding two sets of phenanthrolines in ROT-2
suggests that the rotation is slower than the NMR time scale.
For slower exchange processes in dynamic systems 2D NMR
Fig. 2 ONIOM partition for the model system ROT-2’ (see Scheme 3).
The ball & stick model is for the high layer and the wireframe is for the
techniques, such as EXSY29 or ROESY, may be useful. For
ROT-2, the use of the ROESY method30 provided the rate con- low layer.
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Scheme 3 Isodesmic reaction to check the relative ground state stability of ROT-2’ and ROT-3’.
the transition state difference. Moreover this result suggests
that even though the local environment of the Npy → [Cu
(phen)]+ interactions is identical in both rotors, a large differ-
ence may arise due to the strain in the bent assembly and dis-
persion effects between the rotator and the stator.
In order to confirm the presence of DABCO within the
assembly, a VT 1H NMR of ROT-2 was recorded (Fig. 3a).
Despite the fast rotation of DABCO at room temperature,33 the
six protons next to the salphen unit are not equivalent and
they resonate as two broad signals with the ratio 1 : 1. Upon
cooling down to −75 °C, the chemical shift difference between
the magnetically non-equivalent protons increased, yet at the
same time the six DABCO protons next to the porphyrin
equally started splitting (ratio 1 : 1).
Fig. 4 ONIOM partition of ROT-2’ for NMR computations. The ball &
stick model is for the high layer and the wireframe is for the low layer.
This phenomenon was further investigated by compu-
tational studies. To obtain a reasonably good geometry
mimicking the real porphyrin–DABCO–salphen sandwich
complex, a different partition scheme (Fig. 4) was applied for
the ONIOM computations. Now, the porphyrin–DABCO–
salphen sandwich was treated in the high layer by applying the
DFT34 method while the rest of ROT-2′ was evaluated on the
PM6-D3 level. Then, for a conformational analysis the sand-
wiched DABCO was rotated about the Zn–NDABCO–NDABCO–Zn
axis. Two minima were located, denoted as conf-1 and conf-2
in Fig. 5. Their relative populations change from 1.00 over 0.25
(25 °C) to 0.29 (0 °C), 0.34 (−25 °C), 0.42 (−50 °C) and 0.54
(−75 °C).
Fig. 5 Schematic representation of the two minima Conf-1 and Conf-2.
Red atoms represent those from zinc salphen.
Finally to compute the NMR35 spectra, two simplified
model systems, Conf-1M and Conf-2M (Fig. 6), were constructed
to mimic Conf-1 and Conf-2 (for justification, see the ESI†).
Because the rotation of DABCO is too fast to be frozen in our
VT experiments (the overall rotational barrier is computed as
8.4 kJ mol−1 at 25 °C), the computed chemical shifts for H1,
Fig. 6 Conf-1M and Conf-2M for NMR computation.
Fig. 3 Partial VT 1H NMR (600 MHz) of ROT-2 in CD2Cl2 at various temperatures. (a) Experimental and (b) computed spectra.
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H2 and H3 will appear as average values; the same is true for used without further purification. Et3N was distilled over
Ha, Hb and Hc. The averaging was applied for both Conf-1M calcium hydride. A general outline for the preparation of
and Conf-2M separately. Finally, Boltzmann weightage was rotator 2 is provided in Scheme 1. 2-Hydroxy-3-tert-butyl-benz-
applied at various temperatures and the computed NMR aldehyde (5),23 5-bromo-3-tert-butyl-2-hydroxybenzaldehyde
spectra are represented in Fig. 3b. Computed NMRs deviate (6),24 3-(tert-butyl)-2-hydroxy-5-(4,4,5,5-tetramethyl-1,3,2-dioxa-
only a little with respect to the experiment. The shifts of the borolan-2-yl)benzaldehyde (7),25 1,4-dibromo-2,3,5,6-tetra-
downfield signals near −0.2 ppm are less pronounced in the methylbenzene (8)26 and stator 1 18a were synthesised accord-
computations but they are in line with the experiment. ing to the literature methods. The numbering of the carbon
Computed upfield signals near −4.7 ppm clearly separate on skeleton in the molecular formulae as shown in the manu-
lowering the temperature. By considering the size of the script does not comply with the IUPAC nomenclature rules; it
system and the approximation made to compute the NMR, the is only used for assignments of NMR signals. The ROESY spec-
match of the computed NMR with the experimental one is trum was obtained with a 1.5 s relaxation delay, using 2 K data
qualitatively excellent. From the variable temperature experi- points in the t2 dimension and 400 in t1. Scans were taken for
ment and computational analysis, it is evident that the DABCO each measurement (32 scans) and the spectrum was recorded
residue in ROT-2 rotates rapidly while being sandwiched in with 300 ms mixing time.
between salphen and porphyrin. Further splitting of the
4′-Bromo-5-tert-butyl-4-hydroxy-2′,3′,5′,6′-tetramethylbiphenyl-
DABCO signals on lowering the temperature is a result of chan- 3-carbaldehyde (9). A modified literature procedure was fol-
ging populations of different conformers, namely Conf-1 and lowed.26 A Schlenk tube charged with 3-tert-butyl-2-hydroxy-5-
Conf-2.
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde (7)
(500 mg, 1.64 mmol), 1,4-dibromo-2,3,5,6-tetramethylbenzene
(8) (572 mg, 1.97 mmol), Pd(PPh3)4 (95 mg, 0.082 mmol) and
K2CO3 (340 mg, 2.46 mmol) was placed under N2 by successive
vacuum–N2 cycles. Thoroughly degassed DME (6 mL) and
Conclusion
In conclusion, we prepared and characterised the new salphen degassed water (1.2 mL) were introduced via a cannula into
ligand 2 and incorporated it into the four-component nano- the Schlenk vessel. The mixture was heated at 90 °C for 24 h.
rotor ROT-2. The rotational rate in ROT-2 was found to be Water (20 mL) was added and the aqueous layer was extracted
much lower than that of ROT-3, a previously described with CH2Cl2 (3 × 50 mL). The organic layer was dried over
system.18a Computations demonstrated that ROT-2′ has a MgSO4 and the solvents were removed under reduced pressure.
much higher ground-state stabilisation than ROT-3′; the differ- The residue was purified by a column on silica gel (hexane/
ence amounts to 33.9 kJ mol−1. Interestingly, the experimental ethyl acetate = 99 : 1, Rf = 0.26) to afford the expected product
rotational barrier of ROT-2 is higher than that of ROT-3 by the (353 mg, 55%) as a white solid; mp: 126 °C; 1H NMR
same token, i.e. 32.0 kJ mol−1. Such a finding suggests that the (400 MHz, CDCl3) δ 11.81 (s, 1H, OH), 9.87 (d, J = 4.6 Hz, 1H,
high ground-state stabilisation of ROT-2 leads to a very slow CHO), 7.26 (d, J = 2.1 Hz, 1H, Har), 7.12 (d, J = 2.1 Hz, 1H, Har),
rotation. In addition, the geminal hydrogens in DABCO are 2.47 (s, 6H, CH3), 2.00 (s, 6H, CH3), 1.43 (s, 9H, tBu); 13C NMR
diastereotopic in ROT-2. As the experimental and computed (101 MHz, CDCl3) δ 197.3, 160.1, 140.0, 138.8, 135.6, 134.2,
proton shifts, both at low and high temperatures, agree rather 133.9, 133.0, 132.1, 128.8, 120.6, 35.1, 29.5, 21.4, 19.4; IR (KBr)
well, it is clear that the DABCO is sandwiched between the ν 2998, 2959, 2865, 1639, 1411, 1382, 1360, 1267, 1225, 1172,
zinc porphyrin and zinc salphen moieties, despite some con- 778, 699 cm−1; Anal. Calcd for C21H25BrO2: C, 64.78; H, 6.47;
tradictory evidence from the ESI mass spectral analysis.
found: C, 64.63; H, 6.37.
5-tert-Butyl-4-hydroxy-2′,3′,5′,6′-tetramethyl-4′-(pyridin-4-yl)
biphenyl-3-carbaldehyde (10).
A mixture of aldehyde 9
(250 mg, 642 µmol), 4-pyridinyl boronic acid (87 mg,
0.71 mmol), sodium carbonate (102 mg, 962 µmol) and
Pd(dppf)Cl2 (26.0 mg, 35.5 µmol) was stirred in DME : H2O
Experimental part
General remarks
1H and 13C NMR spectra were recorded on Bruker Avance (v/v 3 : 1, 8 mL, degassed with N2) and stirred at 100 °C for 3 h.
(400 MHz) and Varian (600 MHz) spectrometers using a deute- After cooling to rt, the reaction contents were poured into
rated solvent as the lock and a residual protiated solvent as the H2O (10 mL). The aqueous mixture was extracted with CH2Cl2
internal reference. The following abbreviations were utilised to (3 × 15 mL) and the combined extracts were dried over MgSO4
describe the signal patterns: s = singlet, d = doublet, t = triplet, before being concentrated under reduced pressure. The crude
dd = doublet of doublets, td = triplet of doublets, dt = doublet aldehyde was purified by flash chromatography on silica gel
of triplets, br = broad and m = multiplet. Electrospray ionis- (DCM/EtOAc = 4 : 1, Rf = 0.33) to afford a white solid (238 mg,
1
ation (ESI) mass spectra were recorded on a Thermo-Quest 96%); mp: 155 °C; H NMR (400 MHz, CDCl3) δ 11.81 (s, 1H,
LCQ deca. The melting points were measured on a Büchi OH), 9.88 (s, 1H, CHO), 8.70 (br d, J = 4.7 Hz, 2H, [α and α′]-H),
SMP-20 and are uncorrected. Infrared spectra were recorded 7.35 (d, J = 2.1 Hz, 1H, Har), 7.20 (d, J = 2.1 Hz, 1H, Har),
on a Varian 1000 FT-IR instrument. Elemental analysis was 7.16 (br d, J = 4.7 Hz, 1H, [β or β′]-H), 7.15 (br d, J = 4.7 Hz, 1H,
done using the EA 3000 CHNS. Commercial reagents were [β′or β]-H), 1.98 (s, 6H, CH3), 1.95 (s, 6H, CH3), 1.45 (s, 9H,
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tBu); 13C NMR (101 MHz, CDCl3) δ 197.3, 160.1, 151.2, 150.1,
Preparation of ROT-2. [Cu(CH3CN)4]PF6 (602 μg, 1.62 μmol)
140.8, 139.0, 138.7, 135.7, 133.2, 132.8, 132.2, 131.3, 125.0, in CD2Cl2 was added to ROT-1 (in an NMR tube) and the
120.7, 35.2, 29.5, 18.3, 18.2; IR (KBr) ν 2923, 2853, 1651, 1594, mixture was sonicated for 15 min to furnish ROT-2; mp:
1448, 1407, 1265, 1265, 1201, 1162, 812, 738, 770 cm−1; Anal. 151 °C; 1H NMR (400 MHz, CD2Cl2): δ 9.05 (br s, 2H, β-H), 8.99
Calcd for C26H29NO2: C, 80.59; H, 7.54; N, 3.61; found: (d, J = 4.6 Hz, 2H, β-H), 8.95 (d, J = 4.6 Hz, 1H, β-H), 8.94 (d, J =
C, 80.66; H, 7.60; N, 3.47.
Synthesis of salphen ligand 2. Following a general proce- 8.5 Hz, 2H, [4 or 7]-H, complexed), 8.78 (d, J = 8.5 Hz, 2H, [4 or 7]-
dure,20a solution of 4,5-dimethyl-1,2-phenylenediamine H, complexed), 8.74 (d, J = 8.5 Hz, 1H, [4 or 7]-H, Cu+ loaded),
4.6 Hz, 1H, β-H), 8.90 (d, J = 4.6 Hz, 2H, β-H), 8.81 (d, J =
a
(16.7 mg, 0.120 mmol), aldehyde 10 (100 mg, 0.260 mmol), 8.73 (d, J = 8.5 Hz, 1H, [4 or 7]-H, Cu+ loaded), 8.70 (d, J =
Zn(OAc)2·2H2O (81.0 mg, 0.370 mmol) and neat NEt3 (100 μL) 8.5 Hz, 1H, [4 or 7]-H, Cu+ loaded), 8.69 (d, J = 8.5 Hz, 1H,
in MeOH (6 mL) was stirred for 18 h at room temperature. The [4 or 7]-H, Cu+ loaded), 8.47 (br s, 2H, [10 or 11]-H), 8.46 (br d,
desired compound was isolated by filtration and dried in vacuo J = 7.7 Hz, 1H, [10 or 11]-H), 8.39 (br d, J = 7.7 Hz, 1H, [10 or
to yield an orange solid (99 mg, 86%); mp: 117 °C; 1H NMR 11]-H), 8.32 (br d, J = 7.7 Hz, 1H, [10 or 11]-H), 8.25 (s, 6H,
(400 MHz, DMSO) δ 9.01 (s, 2H, e-H), 8.67 (d, J = 5.2 Hz, 4H, [5 and 6]-H, complexed and [10 or 11]-H), 8.18 (s, 6H, [5 and 6]-
d-H), 7.70 (s, 2H, f-H), 7.23 (d, J = 5.2 Hz, 4H, c-H), 7.06 (d, J = H, Cu+ loaded and [10 or 11]-H), 8.09–8.00 (m, 7H, [3 and 8]-H,
2.1 Hz, 2H, Har), 6.96 (d, J = 2.1 Hz, 2H, Har), 2.32 (s, 6H, CH3), complexed and [10 or 11]-H), 8.00–7.91 (m, 6H, [3 and 8]-H,
2.02 (s, 12H, CH3), 1.88 (s, 12H, CH3), 1.52 (s, 18H, tBu); Cu+ loaded and [10 or 11]-H), 7.89 (br d, J = 7.7 Hz, 1H, [10 or
13C NMR (101 MHz, DMSO) δ 170.5, 161.5, 150.5, 149.8, 142.0, 11]-H), 7.83 (br d, J = 7.7 Hz, 1H, [10 or 11]-H), 7.19 (br s, 2H,
141.4, 137.7, 137.1, 135.5, 133.9, 132.2, 131.6, 130.1, 124.9, e-H), 7.07 (br s, 4H, 9-H, complexed), 7.05 (s, 4H, 9-H, Cu+
119.1, 116.7, 35.2, 29.7, 19.6, 18.1, 17.9; IR (KBr) ν 2923, 2853, loaded), 7.01 (br d, J = 5.4 Hz, 4H, c-H), 6.94 (d, J = 5.4 Hz, 4H,
1612, 1589, 1519, 1463, 1382, 1219, 1158, 1021, 815, 793, d-H), 6.91 (br s, 2H, f-H), 6.81 (br d, J = 1.6 Hz, 2H, [b or a]-H),
488 cm−1; ESI-MS: m/z (%) 937 (100) [M + H]+ Anal. Calcd for 6.56 (br d, J = 1.6 Hz, 2H, [a or b]-H), 2.72 (s, 12H, CH3), 2.71
C60H64N4O2Zn·2H2O: C, 73.94; H, 7.03; N, 5.75; found: C, (s, 6H, CH3), 2.70 (s, 6H, CH3), 2.51 (s, 6H, CH3), 2.38 (s, 12H,
74.16; H, 6.93; N, 5.42.
CH3), 2.33 (s, 12H, CH3), 2.23 (s, 6H, CH3), 2.17 (s, 6H, CH3),
Preparation of ROT-1. In an NMR tube stator 1 (2.01 mg, 2.15 (s, 12H, CH3), 2.06 (s, 12H, CH3), 2.05 (s, 12H, CH3), 2.02
0.808 μmol), rotator 2 (0.758 mg, 0.808 μmol) and DABCO (s, 12H, CH3), 1.21 (s, 18H, t-Bu), 0.47 (br t, J = 7.6 Hz, 3H,
(91.0 μg, 0.808 μmol) were mixed in CD2Cl2. Then, after the CH2-DABCO), 0.11 (br s, 3H, CH2-DABCO) −3.10 (br t, J = 7.6
addition of [Cu(CH3CN)4]PF6 (602 μg, 1.62 μmol) the solution Hz, 6H, CH2-DABCO); IR (KBr) ν 2922, 2853, 1612, 1586, 1494,
was sonicated for 1 h to afford ROT-1; mp: 150 °C; 1H NMR 1459, 1383, 1356, 1166, 996, 841, 557 cm−1; Anal. Calcd for
(400 MHz, CD2Cl2): δ 8.99 (d, J = 4.6 Hz, 2H, β-H), 8.97 (d, J =
C242H216Cu4F24N18O2P4Zn2·3CH2Cl2: C, 63.58; H, 4.83; N, 5.45;
4.6 Hz, 2H, β-H), 8.94 (d, J = 4.6 Hz, 2H, β-H), 8.90 (d, J = 4.6 found: C, 63.31; H, 4.61; N, 5.49.
Hz, 2H, β-H), 8.81 (d, J = 8.1 Hz, 2H, [4 or 7]-H, complexed),
8.79 (d, J = 8.1 Hz, 2H, [4 or 7]-H, complexed), 8.46 (br s, 4H,
[10 or 11]-H), 8.40 (d, J = 8.1 Hz, 2H, [4 or 7]-H, uncomplexed),
8.37 (d, J = 8.1 Hz, 2H, [4 or 7]-H, uncomplexed), 8.36 (br s,
2H, [10 or 11]-H), 8.26 (s, 4H, [5 and 6]-H, complexed), 8.24
Acknowledgements
We thank the DFG (Schm 647/20-1) and the University of
(br d, J = 8.2 Hz, 1H, [10 or 11]-H), 8.10 (br d, J = 8.2 Hz, 1H,
[10 or 11]-H), 8.07 (d, J = 8.1 Hz, 2H, [3 or 8]-H, complexed),
8.04 (s, 4H, [10 or 11]-H), 8.02 (d, J = 8.1 Hz, 2H, [3 or 8]-H,
complexed), 7.97 (br d, J = 8.2 Hz, 1H, [10 or 11]-H), 7.95 (br d,
J = 8.2 Hz, 1H, [10 or 11]-H), 7.94 (s, 4H, [5 and 6]-H, uncom-
plexed), 7.89 (br d, J = 8.2 Hz, 1H, [10 or 11]-H), 7.81 (br d, J =
8.2 Hz, 1H, [10 or 11]-H), 7.60 (d, J = 8.1 Hz, 2H, [3 or 8]-H,
uncomplexed), 7.59 (d, J = 8.1 Hz, 2H, [3 or 8]-H, uncom-
plexed), 7.19 (br s, 2H, e-H), 7.07 (br s, 4H, 9-H, complexed),
7.01 (br d, J = 5.0 Hz, 4H, c-H), 6.99 (s, 4H, 9-H, uncomplexed),
6.92 (br d, J = 5.0 Hz, 4H, d-H), 6.91 (s, 2H, f-H), 6.81 (br s, 2H,
[b or a]-H), 6.55 (br d, J = 1.8 Hz, 2H, [a or b]-H), 2.71 (s, 12H,
CH3), 2.69 (s, 12H, CH3), 2.51 (s, 6H, CH3), 2.36 (s, 12H, CH3),
2.34 (s, 12H, CH3), 2.23 (s, 6H, CH3), 2.17 (s, 6H, CH3), 2.15 (s,
12H, CH3), 2.07 (s, 12H, CH3), 2.05 (s, 12H, CH3), 2.02 (s, 12H,
CH3), 1.21 (s, 18H, t-Bu), 0.47 (br t, J = 7.4 Hz, 6H, DABCO),
−3.10 (br t, J = 7.7 Hz, 6H, DABCO); IR (KBr) ν 2922, 2852,
Siegen for their continued support in particular for providing
the Linux Cluster HorUS for computations.
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35 Computed at the GIAO-B3LYP/6-31+G**/PCM(CH2Cl2) level.
This journal is © The Royal Society of Chemistry 2017
Dalton Trans.