Influence of Rotator Design on the Speed of Self-Assembled Four-Component Nanorotors: Coordinative Versus Dispersive Interactions

Article abstract of DOI:10.1021/acs.inorgchem.7b00740

Four-component nanorotors are prepared by the self-assembly of stator [Cu₄(4)]⁴⁺with its four copper(I)-loaded phenanthroline stations and various rotators carrying one, two, or three pyridine terminals. The fourth component, 1,4-diazabicyclo[2.2.2]octane, serves as a connecting axle between rotator and stator. Capitalizing on the heteroleptic pyridyl and phenanthroline metal complexes concept, the rotator’s pyridine terminals are connected to the copper(I)-loaded phenanthroline stations (N_py → [Cu(phen)]⁺) in the STOP state and disconnected in the transition state of rotation. As the barrier of the thermally activated rotation, measured by variable-temperature ¹H NMR, is mainly governed by attractive forces between stator stations and rotator terminals, it increases along the series E_a (monopyridine rotator) < E_a (dipyridine rotator) < E_a (tripyridine rotator). However, there are even distinct differences in rate between rotors with equal number of rotator terminals. The change from the 5,10-dipyridyl (cis) to 5,15-dipyridyl (trans) zinc porphyrin rotator enhances the rotational frequency by almost 1000-fold. Density functional theory computational results suggest that not only coordinative N_py → [Cu(phen)]⁺ interactions but also dispersive attraction influence the barrier of rotation.

Full text of DOI:10.1021/acs.inorgchem.7b00740

Article
pubs.acs.org/IC
Influence of Rotator Design on the Speed of Self-Assembled Four-
Component Nanorotors: Coordinative Versus Dispersive Interactions
Pronay Kumar Biswas,† Suchismita Saha,† Yerramsetti Nanaji, Anup Rana, and Michael Schmittel*
Center of Micro- and Nanochemistry and Engineering, University of Siegen, Adolf−Reichwein−Str. 2, D-57068 Siegen, Germany
S
* Supporting Information
ABSTRACT: Four-component nanorotors are prepared by the
self-assembly of stator [Cu4(4)]4+ with its four copper(I)-
loaded phenanthroline stations and various rotators carrying
one, two, or three pyridine terminals. The fourth component,
1,4-diazabicyclo[2.2.2]octane, serves as a connecting axle
between rotator and stator. Capitalizing on the heteroleptic
pyridyl and phenanthroline metal complexes concept, the
rotator’s pyridine terminals are connected to the copper(I)-
loaded phenanthroline stations (Npy → [Cu(phen)]+) in the
STOP state and disconnected in the transition state of rotation.
As the barrier of the thermally activated rotation, measured by
variable-temperature 1H NMR, is mainly governed by attractive
forces between stator stations and rotator terminals, it increases
along the series Ea (monopyridine rotator) < Ea (dipyridine rotator) < Ea (tripyridine rotator). However, there are even distinct
differences in rate between rotors with equal number of rotator terminals. The change from the 5,10-dipyridyl (cis) to 5,15-
dipyridyl (trans) zinc porphyrin rotator enhances the rotational frequency by almost 1000-fold. Density functional theory
computational results suggest that not only coordinative Npy → [Cu(phen)]+ interactions but also dispersive attraction influence
the barrier of rotation.
connectors, that is, (c) metal ion(s) and (d) a hinge.
Additionally, speed regulation in such multicomponent nano-
rotors was demonstrated by addition of external brake stones as
a fifth component.29,31 In the present work, we will describe the
influence of the rotator design on the speed of the nanorotor
and the unexpected finding of the importance of dispersive
interactions32−34 in the rate-determining step.
INTRODUCTION
■
The mode of operation of many biological motors1 is based on
a stepwise rotary motion, as, for instance, in adenosine 5′-
diphosphate (ATP) synthase2,3 driving the synthesis of ATP
from adenosine 5′-triphosphate (ADP). Being inspired from
the gamut of rotary motions in living cells, chemists have been
designing increasingly complex artificial molecular machines.4−7
Among them, unidirectional molecular motors,8−11 gears,12,13
pumps,14 walkers,15−17 caterpillars,18 etc. have gained ample
interest. However, most advanced machineries are assembled in
a covalent fashion until now, whereas biological machines like
the ATP synthase are typically composed of various
components. Artificial multicomponent machineries remain
extremely rare, because the tools for the spatiotemporal
heteroassembly are still limited.19 Notable exceptions have
been reported by Stoddart20 (supramolecular elevator) and by
Shionoya,21,22 Shinkei,23 Kume/Nishihara,24,25 Kobayashi,26
Crowley,27 Takeuchi,28 as well as our group29,30 (supra-
molecular nanorotors). Currently, structural variations in
artificial multicomponent machinery and their effects on the
kinetics of motion remain largely unexplored, because most
designs do not tolerate decisive spatiotemporal changes. Any
improvement of the working efficiency of molecular machinery,
however, will require the optimization of static and moving
parts, as in real-world machines.
RESULTS AND DISCUSSION
■
In the above-mentioned multicomponent supramolecular
nanorotors,29,30 two differently decorated zinc porphyrins
(stator and rotator) are sandwiched together by means of
two axial NDABCO → zinc(II) porphyrin (ZnPor)35 and two Npy
→
[Cu(phen)]+ interactions (DABCO
= 1,4-
diazabicyclo[2.2.2]octane; phen = phenanthroline; py =
pyridine), a construction principle that we will also use in the
present study (see Figure 1). The Npy → [Cu(phen)]+
interaction connects the pyridine terminals (Npy) of the rotator
with the copper(I)-loaded phenanthroline stations [Cu-
(phen)]+ of the stator via the HETeroleptic PYridine and
Phenanthroline (HETPYP) complexation strategy,36,37 which
involves complexes of type [Cu(phen)(py)]+. Because the
copper(I) ion is surrounded by only three strong donors, such
complexes are less stable and more dynamic than those of the
Our design of supramolecular nanorotors29 comprises four
distinct components: (a) stator, (b) rotator, and two
Received: March 25, 2017
© XXXX American Chemical Society
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Figure 1. (a) All four components of the self-assembled nanorotors and their cartoon representations. (b) Cartoon representations of the four-
component nanorotors.
type [Cu(phen)2]+. It is thus no surprise that, by our rotor
design, the rotator moves with respect to the stator about
station in the stator. The reaction furnished exclusively C1 =
1
[Cu(5)]+, as seen in the H NMR from protons 9-H, 3,8-H,
DABCO as a dynamic hinge by cleaving the Npy
→
4,7-H, and 5,6-H of 5 that are all shifted downfield due to the
electron-demanding metal ion (Figure 2b). Then, 1 equiv of 4-
iodopyridine (6) was added to C1. The resulting heteroleptic
complex C2 = [Cu(5)(6)]+ was characterized unambiguously
[Cu(phen)]+ interaction(s).29
To quantitatively afford HETPYP complexes of type
[Cu(phen)(py)]+, the copper(I) phenanthroline motifs in the
stator must be sterically shielded, since thereby competitive
formation of the thermodynamically more stable homoleptic
copper phenanthroline complexes [Cu(phen)2]+ is pre-
vented.38−40 In contrast, steric shielding does not preclude
the construction of HETPYP complexes. Their formation is
driven by coordinative interactions (Npy → [Cu(phen)]+) and
by π−π stacking between the pyridine and the aryl moieties of
the shielded phenanthroline. To get some further insight into
the rotational speed and its dependency on the rotator’s nature,
structurally different rotators with a varying number of pyridine
terminals along with possible isomers (1, 2a, 2b, 3) were
investigated (Figure 1).
by H NMR, H−1H COSY, and electrospray ionization mass
spectrometry (ESI-MS). In the 1H NMR spectrum, proton 9-H
(Figure 2b) and all anthracene protons experience an upfield
shift owing to the shielding effect of the pyridine ring
(Supporting Information, Figure S39). Reciprocally, the
pyridine protons c-H and d-H are shifted upfield from 7.69
and 8.69 ppm to 7.25 and 6.54 ppm, respectively, because of
the shielding effect of both the anthracene and mesityl moieties
(Figure 2b). They appear as broad signals due to the dynamic
nature of C2. From a UV−vis titration the binding constant of
6 to C1 = [Cu(5)]+ in CH2Cl2 was determined as log K = 3.6
0.1 (Supporting Information, Figure S90). To study
experimentally the dynamics, ligands 5, 6 and [Cu(CH3CN)4]-
PF6 were mixed in 2:1:2 ratio to furnish a 1:1 mixture of C1
1
1
To evaluate the Npy → [Cu(phen)]+ interaction separately, 1
equiv of [Cu(CH3CN)4]PF6 was mixed with 1 equiv of ligand 5
(Figure 2), the latter representing the shielded phenanthroline
1
and C2. At room temperature, the H NMR of the C1/C2
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Figure 2. (a) Model complexes C1 and C2. (b) Comparison of partial 1H NMR (CD2Cl2, 400 MHz, 298 K) of 6, 5, C1, C2 and C1/C2 (1:1). (c)
1
Partial VT H NMR (CD2Cl2, 600 MHz) of C1/C2 showing the splitting of 9-H (asterisk marked).
Figure 3. (a) Cartoon representation of ROT-1 and ROT-1′. (b) Comparison of partial 1H NMR (CD2Cl2, 400 MHz, 298 K) of ROT-1 and ROT-
1′. Protons that correspond to the HETPYP-complexed phenanthroline (9c-H, 13c-H) are different from those that belong to the unloaded
1
phenanthrolines (9u-H, 13u-H) and the averaged signals (9-H and 13-H) in ROT-1′. (c) Partial VT H NMR (CD2Cl2, 600 MHz) of ROT-1′
shows the splitting of the 9-H signal (red asterisk) and upfield shift of c-H upon lowering temperature (blue asterisk).
mixture displays a single set of all phenanthroline protons at the
average positions of those in C1 and C2 (Figure 2b). Because
of the very fast dynamic exchange protons c-H and d-H
broaden and are impossible to detect in the NMR at room
temperature, while they show up at low temperature (Figure
mol−1 (log K = 3.6), the intrinsic barrier of this self-exchange is
strongly (77%) determined by the thermodynamics of the
pyridine−copper bond cleavage.
The fast dynamics of this self-exchange encouraged us to
design a four-component supramolecular nanorotor based on
the very same Npy → [Cu(5)]+ coordination motif. Therefore,
rotators 1, 2a, 2b, and 3 were synthesized by Sonogashira
coupling of the corresponding zinc(II)-(4-iodophenyl)-
mesitylporphyrins with 4-ethynylpyridine. Details are given in
the Supporting Information. To prepare ROT-1 (Figure 1),
rotator 1 was mixed with stator 4, DABCO, and [Cu-
(CH3CN)4]PF6 (1:1:1:1) in CD2Cl2. As anticipated, the
NMR displays two singlets (3:1 ratio) for mesityl protons 9-
H at 6.92 and 6.96 ppm (Figure 3b). The pyridine protons d-H
1
2c). In a variable-temperature (VT) H NMR experiment, the
signal for protons 9-H splits into two singlets (1:1 ratio: one
sharp and one broad) upon lowering the temperature to −75
°C with the coalescence point being at ca. −50 °C (Figure 2c).
The two singlets refer to protons 9-H in C1 (δ = 6.87 ppm)
and in C2 (δ = 6.64 ppm). The exchange rate of pyridine 6
between C1 and C2 was determined as ∼150 MHz at 25 °C,
which furnishes an activation barrier ΔG‡298 = 26.5 kJ mol−1. As
the cleavage of C2 → C1 + 6 is endergonic by ΔG298 ≈ 20.5 kJ
C
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1
Figure 4. (a) Cartoon representation of ROT-2a and ROT-2a′. (b) Comparison of partial H NMR (CD2Cl2, 400 MHz, 298 K) of ROT-2a and
ROT-2a′. Mesityl protons 9c-H and 9u-H denote protons at C-9 of HETPYP-complexed and unloaded phenanthrolines, respectively, in ROT-2a.
Alike, 9-H represents the averaged proton signal in ROT-2a′. (c) Partial VT 1H NMR (CD2Cl2, 600 MHz) of ROT-2a′ showing the splitting of 9-H
signal (red asterisk). The signal downfield to 9-H refers to c-H.
and c-H are dynamically broadened and exhibit a diagnostic
upfield shift to 6.02 and 7.02 ppm, respectively, due to the
shielding effects of the mesityl and anthracenyl groups of 4.
Two sets of broad singlets at −4.57 and −4.85 ppm
corresponding to the DABCO protons confirm that DABCO
acts as hinge between the two different zinc porphyrins 1 and 4
(Supporting Information, Figure S40).29,31
the two singlets appear at 6.85 and 6.92 ppm (1:3). These two
singlets are assigned to Cu+-loaded phenanthroline stations that
are either connected to the pyridine terminal or not. The
characteristic upfield shift of the pyridine protons c-H upon
lowering the temperature may be explained owing to the
increasing π−π stacking from the aryl groups of the
phenanthroline stations (Figure 3c). These findings suggest
that at 25 °C all four phenanthroline stations behave chemically
All phenanthroline protons (3-H, 4-H, 5-H, 6-H, 7-H, and 8-
H) show as two sets of signals at a 3:1 ratio as well. One of the
signal sets is shifted more downfield than the other: the former
refers to the HETPYP-complexed phenanthroline protons,
while the upfield-shifted set of signals belongs to the
1
equivalent due to rotation in ROT-1′. While the VT H NMR
provides the rate constant k = 22 000 s−1 at 25 °C, the rotation
is almost frozen (k = 0.5 s−1) at −75 °C. The free energy
activation barrier for exchange in ROT-1′ is 48.3 kJ mol−1 at 25
°C, which is much higher than that in the model system (cf.
1
uncoordinated phenanthroline stations. The H NMR shifts
thus clearly confirm formation of ROT-1 as a heterosandwich
structure, which was additionally characterized by 1H−1H
COSY, ESI-MS, and elemental analysis. The finding of separate
sets of protons (3:1) seems to advocate that ROT-1 is a static
assembly. However, fact is that there is no observable present
for detecting the motion (= cleavage and reassociation of the
rotator arm at the single copper phenanthroline station). After
addition of 3 equiv more of [Cu(CH3CN)4]PF6 to ROT-1, the
resulting ROT-1′ (Figure 3a) shows fully averaged signals for
protons 9-H and 13-H (Figure 3b) as well as for all other
phenanthroline station protons (Supporting Information,
ΔG‡
= 26.5 kJ mol−1). As a consequence, the Npy
→
298
[Cu(5)]+ bond cleavage is much more difficult in ROT-1′ than
in the model system (krel = 1:6800). Several effects may
contribute to this difference: (i) in the rotor cooperative
stabilization is possible, (ii) in case of the model complex C2
there are several departure pathways possible to cleave the Npy
→ [Cu(5)]+ bond that are prevented in ROT-1′, and (iii)
significant dispersive attractions present in ROT-1′ arising from
surface contact between stator and rotator additionally
contribute to the reduced speed of ROT-1′ (vide infra).
In the following, the rotors were varied by implementing the
dipyridine rotators 2a (trans) and 2b (cis) and the tripyridine
rotator 3. In all rotors (ROT-2a′, ROT-2b′, ROT-3′, prepared
in the same manner as ROT-1′) the DABCO protons and
1
Figure S42). H-DOSY corroborates that ROT-1′ is a single
species in solution (Supporting Information, Figure S70). In
ROT-1′ 16 equiv of CH3CN (arising from four [Cu-
(CH3CN)4]PF6) stabilize the copper(I) phenanthroline com-
plex units that are not coordinated to the rotator arm. Without
CH3CN, the rotor assembly is unstable, most likely because the
[Cu(phen)]+ station is not stable as such without contact to the
pyridine arm but may be stabilized as [Cu(phen) (CH3CN)n]+
(n = 1 or 2).
1
protons c-H and d-H show at comparable H NMR positions
confirming the formation of a bis-porphyrin heterosandwich
assembly of stator and rotator (see Supporting Information).
For both dipyridine rotators 2a and 2b, one would expect
that the pyridine terminals need to depart from phenanthroline
stations either simultaneously or stepwise. In both scenarios,
the overall transition-state barrier of rotation should be higher
than that in ROT-1′.
The dynamic spinning in the nanorotor was monitored by
1
VT H NMR in the range from 25 to −75 °C in CD2Cl2
1
(Figure 3c). At 25 °C, protons 9-H appear as a sharp singlet at
6.95 ppm, while upon lowering the temperature the singlet
starts to broaden at ca. −45 °C. Below this temperature, a
splitting of the singlet peak into two sets of singlets was
observed. Upon lowering the temperature further, the
separation between the two singlets increases, and at −75 °C
In the H NMR spectrum of ROT-2a′ (trans) at 25 °C,
mesityl protons 9-H of all four phenanthroline stations appear
as a singlet at 6.95 ppm suggesting rapid rotation (Figure 4b).
The VT 1H NMR study was performed from 25 to −5 °C at an
interval of 5 °C (Figure 4c) showing a splitting of proton 9-H
into two singlets (ratio 1:1) with coalescence broadening
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around 20 °C. The singlets at 6.93 and 6.94 ppm are well-
resolved at −5 °C and are assigned to protons 9c-H (for
HETPYP complexed) and 9Cu-H (for the Cu+-loaded
phenanthroline stations), respectively. From a simulation of
Table 1. Experimental Rotational Frequency and Activation
Barriers at 25 °C, Calculated from VT H NMR
1
model/
nanorotor
ΔH‡
ΔS‡
ΔG‡
25
(kJ mol−1
)
(J mol−1 K−1
)
(kJ mol−1
)
k25 (s−1
)
1
the VT H NMR signals, the rate constants were determined
C1/C2 (1:1)
ROT-1′
ROT-2a′
ROT-2b′
ROT-3′
26.5
48.3
1.5 × 108
2.2 × 104
3.8 × 102
0.4
between −5 and 25 °C. The rate constant is k = 380 s−1 at 25
°C, and the corresponding free energy activation barrier is 58.4
kJ mol−1.
49.7
66.5
6.3
28.1
58.4
75.6
1
In the H NMR of ROT-2b′, received after addition of 2
>79.0
<0.1
equiv of [Cu(CH3CN)4]PF6 to ROT-2b, protons 9c-H and
9Cu-H do not form an averaged signal. Since they remain
separated, there is either no or very slow rotation on the NMR
time scale. In such scenarios, the 1H−1H ROESY experiment is
a very valuable tool to detect any slow exchange between two
separated signals (kex = 0.2−100 Hz).18,41 If the rotor is
spinning in this frequency range, HETPYP-complexed
phenanthroline moieties should exhibit exchange correlation
signals with the Cu+-loaded phenanthroline moieties. Indeed,
all proton signals of the HETPYP-complexed phenanthroline
stations show exchange correlation in the 1H−1H ROESY with
Cu+-loaded phenanthroline stations. The well-separated pro-
tons 12-H signals were chosen to calculate the rate of rotation
(Figure 5c). The signals indicate slow exchange at a rate
constant k = 0.4 s−1 (25 °C).
By comparing the rotator’s structure in different rotors, one
would expect ΔG‡ values for ROT-2a′ and ROT-2b′ to be
qualitatively double than that of ROT-1′ due to presence of
doubled binding sites. Surprisingly, ΔG‡ values for both ROT-
2a′ and ROT-2b′ are much less than double than that of ROT-
1′. A classic interpretation would be that the binding in both
ROT-2a′ and ROT-2b′ is accompanied by significant strain
that is fully released in the transition state (in Figure 6,
Figure 6. Experimentally determined free energies of activation for the
nanorotors in this study, setting the transition states to the same
energy level.
transition states are set to the same energy level). Among both
rotors, ΔG‡ for ROT-2a′ deviates even more from the expected
value (2 × 48.3 = 96.6 kJ mol−1). To comprehend the reasons
behind it, we took a closer view at both rotors, expecting that
the ΔΔG‡ may primarily be the consequence of two factors:
either (a) ground-state or (b) transition-state differences.
Clearly, the rotary motion is faster in case of ROT-2a′ (k =
380 s−1) than in ROT-2b′ (k = 0.4 s−1), albeit both rotators
have similar binding sites that differ only in spatial orientation.
For further clarification we decided to investigate the energy
profile of the rotation computationally. To speed the
computations while using a relatively large basis set, the simple
model system (ROT-4, Figure 7) was constructed. In ROT-4,
both the rotator and stator are monoarm compounds with
hydrogens at the meso-positions of the porphyrins. First, we
optimized ROT-4 at B3LYP-D3(BJ)-gCP/def2-SVP level. To
obtain computational transition state (TS) energies close to the
experimental data, one acetonitrile (CH3CN) had to be
coordinated to the copper(I) ion of ROT-4, while another
one had to be added for nucleophilic displacement of the
rotator arm. In our search for the TS we increased the distance
between the copper and pyridine nitrogen (Cu1−N2). When
the Cu1−N2 bond distance increased in ROT-4 (Figure 7), the
Cu1−N3 bond distance (between copper and the attacking
acetonitrile) started to decrease automatically. The results
suggest a TS with a barrier height of 33.9 kJ mol−1 for the
Figure 5. (a) Cartoon representation of ROT-2b and ROT-2b′. (b)
Comparison of partial 1H NMR (CD2Cl2, 400 MHz, 298 K) of ROT-
2b and ROT-2b′. Protons 12c-H, 12u-H, and 12Cu-H correspond to
12-H of HETPYP-complexed phenanthroline, unloaded phenanthro-
1
line, and Cu+-loaded phenanthroline, respectively. (c) Partial H−1H
ROESY NMR (CD2Cl2, 600 MHz, 298 K) of ROT-2b′.
From earlier discussions regarding rotary motion it is
expected that in the case of ROT-3′ due to presence of three
arms, the kinetic stabilization will be even higher than that of
ROT-2a′ or ROT-2b′. As a consequence, rotation of ROT-3′
1
should be very slow. Indeed, the H NMR of ROT-3′ shows
that phenanthroline protons 9-H (9c-H and 9Cu-H) remain
separated as in case of ROT-2b′. In the 1H−1H ROESY study,
none of the protons for HETPYP-complexed and the Cu+-
loaded phenanthroline stations show any kind of exchange
correlation (Supporting Information, Figure S68), which clearly
suggests that ROT-3′ just behaves as a nondynamic hetero bis-
porphyrin sandwich assembly (k < 0.1 Hz at 25 °C).
From the discussion of all the rotors it is clear that the
rotational speed follows the trend ROT-1′ > ROT-2a′ > ROT-
2b′ > ROT-3′, while the corresponding free energy barriers
follow the reverse (Table 1).
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binding sites of stator and rotator. Because the barrier height of
66.9 kJ mol−1 (gas phase) is much too high compared to the
experimental number (48.3 kJ mol−1), a solvent correction42
was implemented, which indeed brought down the computed
barrier to 31.3 kJ mol−1 (at B3LYP-D3(BJ)-gCP/def2-SVP/
COSMO(CH2Cl2)//B3LYP-D3(BJ)-gCP/def2-SVP level).
Three different “conformational” states can be realized in
ROT-2a′ and ROT-2b′. In State-1 (Figure 8), none of the
rotator arms is coordinated to copper(I) centers. At the same
time, there is no surface contact between rotator and stator
arms. In contrast, in State-2, both rotator arms are coordinated
to copper(I) centers as illustrated in Figure 8. State-3 can be
realized as a mixture of State-1 and State-2; that is, one rotator
arm is coordinated to the copper(I) phenanthroline station, and
the other one is lying on top of the adjacent stator arm without
contact to the copper(I) center. Because computations on
ROT-4 support State-1 as the TS for rotation, the States-2 and
3 are possible starting minima.
Computations at B3LYP-D3(BJ)/3-21G level predict that
both rotators 2a and 2b are of similar energy (ΔE = 0.2 kJ
mol−1) as free compounds.43 Because attractive/repulsive
forces between stator and rotator arms are not present in
State-1, rotors ROT-2a′ and ROT-2b′ should exhibit identical
absolute energies (Figure 9). Thus, the different rotational rates
of ROT-2a′ and ROT-2b′ should arise from energetic
differences in the ground states, that is, either from State-2
or State-3. Surprisingly, computational results at B3LYP-
D3(BJ)/3-21G predict that State-3 is energetically preferred
over State-2 for both rotors. In case of ROT-2a′, the former
one is preferred by 14.0 kJ mol−1, and for ROT-2b′ the same
preference is 31.3 kJ mol−1. A detailed investigation suggests
that these differences arise mainly due to dispersive stabilization
of State-3 for both rotors (see Supporting Information).
After identification of State-3 as the ground state of the
nanorotors, the isodesmic reaction ROT-2a′(State-3) + 2b →
Figure 7. Energy profile of rotary motion of ROT-4. The black
numbers are relative electronic energies (B3LYP-D3(BJ)-gCP/def2-
SVP), while the corresponding italics give relative energies after
inclusion of solvation (B3LYP-D3(BJ)-gCP/def2-SVP/COSMO-
(CH2Cl2)//B3LYP-D3(BJ)-gCP/def2-SVP). The colored numbers
provide the bond distances.
breaking of HETPYP binding. Surprisingly though, when the
rotator and stator arm were constrained opposite to each other
(at a dihedral angle of 180°, no binding possible), the energy of
the system is much higher (66.9 kJ mol−1) than that of the TS
(33.9 kJ mol−1). Thus, the Cu1−N2 bond breaking only
contributes roughly half to the full barrier. The other portion of
the barrier arises from the loss of attractive interactions
between stator and rotator arms. The corresponding dispersive
attractions develop all the way from the zinc porphyrin until the
Figure 8. (top) Views of three states for ROT-2b′ are shown. Similar states for ROT-2a′ were also considered but not shown in this figure. The red
colored portion is for stator, the blue one is for rotator, and the black one is for acetonitrile. (bottom) The figure represents State-3 of ROT-2b′.
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= singlet, d = doublet, t = triplet, dd = doublet of doublets, ddd =
doublet of doublets of doublets, bs = broad singlet, m = multiplet. The
coupling constant values are given in hertz (Hz). Full proton
assignments are given in Supporting Information. Electrospray
ionization (ESI-MS) spectra were recorded on a Thermo-Quest
̈
LCQ deca. Melting points of compounds were measured on a BUCHI
510 instrument and are not corrected. Infrared spectra were recorded
on a Varian 1000 FT-IR instrument. Elemental analysis was performed
using the EA-3000 CHNS analyzer. UV−vis spectra were recorded on
a Cary Win 50 (298 K) spectrometer.
Pre-Rotor Complex ROT-1. In an NMR tube, stator 4 (1.65 mg,
0.619 μmol) was mixed with 1 equiv of [Cu(CH3CN)4]PF6 (0.234
mg, 0.619 μmol) salt and dissolved in a small amount of CD2Cl2,
followed by addition of rotator 1 (0.560 mg, 0.619 μmol) and DABCO
(69.0 μg, 0.619 μmol). After subsequent sonication for 10 min the
complex was obtained in quantitative yield. mp: decomp > 60 °C. IR
(KBr): ν = 3442, 3435, 3066, 3037, 2952, 2924, 2851, 2336, 2218,
1620, 1601, 1487, 1444, 1380, 1203, 1097, 995, 848, 796, 767, 641,
Figure 9. Rotational energy profile for ROT-2a′ and ROT-2b′
(computed).
1
629, 558 cm−1. H NMR (CD2Cl2, 400 MHz): δ = −4.85 (bs, 6H),
−4.57 (bs, 6H), 1.26 (s, 9H), 1.54 (s, 9H, f′-H), 1.97 (s, CH3, CH3CN
from [Cu(CH3CN)4]PF6), 2.05 (s, 18H), 2.06 (s, 6H), 2.29 (s, 9H),
2.34 (s, 3H), 2.60 (s, 9H), 6.02 (bs, 2H), 6.92 (s, 6H), 6.96 (s, 2H),
ROT-2b′(State-3) + 2a, should provide insight in the relative
ground-state energies. Accordingly, rotor ROT-2b′ has a lower
ground-state energy than ROT-2a′, by 16.5 kJ mol−1! This
energy difference matches very well with the experimentally
observed barrier difference of 17.2 kJ mol−1 at 25 °C suggesting
that the different kinetics of ROT-2a′ and ROT-2b′ arises
exclusively from different ground-state energies. The origin of
the differential ground-state stabilization can be best rational-
ized by differences in dispersive attraction. ROT-2b′ receives
28.0 kJ mol−1 more stabilization from dispersion than ROT-
2a′.
3
7.02 (bs, 2H), 7.26 (bs, 6H), 7.47−7.57 (m, 10H), 7.63 (d, J = 8.2
3
Hz, 3H), 7.66 (d, J = 8.2 Hz, 2H), 7.73−7.81 (m, 18H), 7.89 (bs,
2H), 7.94 (d, 3J = 8.2 Hz, 3H), 8.02 (d, 3J = 8.2 Hz, 1H), 8.06 (d, 3J =
8.8 Hz, 3H), 8.08 (d, 3J = 8.8 Hz, 3H), 8.16−8.22 (m, 8H), 8.31−8.37
(m, 11H), 8.41 (d, 3J = 4.2 Hz, 2H), 8.43 (d, 3J = 8.2 Hz, 3H), 8.53 (d,
3J = 4.2 Hz, 2H), 8.59 (d, 3J = 8.2 Hz, 3H), 8.73 (s, 4H), 8.76 (d, 3J =
4.6 Hz, 2H), 8.78 (d, 3J = 4.6 Hz, 2H), 8.82 (d, 3J = 8.2 Hz, 1H), 8.96
3
3
3
(d, J = 8.8 Hz, 2H), 9.02 (d, J = 8.2 Hz, 1H), 9.04 (d, J = 8.8 Hz,
6H) ppm. Anal. Calcd for C258H185CuF6N19PZn2·9CH2Cl2: C, 69.19;
H, 4.50; N, 6.01. Found: C, 68.89; H, 4.40; N, 5.72%. ESI-MS: m/z
(%) 1816.8 (100) [Cu(1)(4)·H]2+.
On the one hand, in ROT-1′ with its single-arm rotator 1 the
single HETPYP linkage and the rather small dispersive
stabilization between rotator and stator lead to maximum
speed. On the other hand, in ROT-3′ with its three-arm rotator
(3), three HETPYP linkages and strong dispersive stabilization
prevent any rotation at room temperature.
Nanorotor ROT-1′. [Cu(CH3CN)4]PF6 (3 equiv, 0.692 mg, 1.86
μmol) was added to ROT-1. After sonication for 10 min ROT-1′
formed quantitatively. mp: decomp > 60 °C. IR (KBr): ν = 3445,
2952, 2923, 2853, 2221, 1654, 1616, 1491, 1442, 1382, 1202, 995, 855,
1
850, 767, 560 cm−1. H NMR (CD2Cl2, 400 MHz): δ = −4.80 (bs,
6H), −4.60 (bs, 6H), 1.26 (s, 9H), 1.36 (s, 6H), 1.65 (s, 3H), 1.97 (s,
CH3, CH3CN from [Cu(CH3CN)4]PF6), 2.01 (s, 24H), 2.31 (s,
CONCLUSION
3
■
12H), 2.60 (s, 3H), 2.61 (s, 6H), 6.05 (d, J = 5.6 Hz, 2H), 6.95 (s,
3
In conclusion, we demonstrate that our approach to supra-
molecular four-component nanomachinery allows variation of
rotator without compromising on the basis function of a
thermally activated nanorotor.10 As predicted, strong binding
between the departing pyridine terminals and the copper
phenanthroline stations controls the rotational speed of the
machinery. Importantly, this binding involves both coordinative
(Npy → [Cu(phen)]+) and attractive dispersive interactions.
On increasing the number of binding interactions, the
activation barrier for the rotation increases. In case of the
triarm rotator, the rotation stops completely. On moving from
the trans to cis diarm rotor, that is, changing only the spatial
orientation of the binding sites, the rotational speed of the
nanorotor is reduced by a factor of ca. 1000. Computational
results suggest that this drastic change is due to dispersive
attractions31−33 stabilizing the ground state of the cis rotor. The
variation of rotational speed by structural change of the rotator
suggests further investigations on the role of other rotor’s
components on the overall function and speed.
8H), 7.00 (d, J = 5.6 Hz, 2H), 7.05 (bs, 2H), 7.17 (s, 3H), 7.40 (s,
3H), 7.57−7.65 (m, 16H), 7.78−7.83 (m, 12H), 7.96 (d, 3J = 8.2 Hz,
3
6H), 8.22 (bs, 10H), 8.28−8.36 (m, 18H), 8.41 (d, J = 4.6 Hz, 2H),
3
3
8.55 (d, J = 4.6 Hz, 2H), 8.75 (bs, 12H), 8.95 (d, J = 8.2 Hz, 4H),
9.05 (d, 3J = 8.8 Hz, 8H) ppm. Elemental analysis: Upon removal of
CH3CN (which arises from the Cu(I) salt), the assembly is not stable.
ESI-MS: m/z (%) 955.8 (100) [Cu4(1)(4)]4+, 730.4 (20) [Cu4(4)]4+.
Pre-Rotor Complex ROT-2a. In an NMR tube, stator 4 (1.48 mg,
0.554 μmol) and 2 equiv of [Cu(CH3CN)4]PF6 (0.413 mg, 1.11
μmol) were dissolved in a small amount of CD2Cl2, followed by
addition of rotator 2a (0.534 mg, 0.554 μmol) and DABCO (62.1 μg,
0.554 μmol). Subsequent sonication for 10 min furnished the complex
in quantitative yield. mp: decomp > 60 °C. IR (KBr): ν = 3439, 2957,
2923, 2852, 2331, 2221, 1604, 1488, 1450, 1202, 995, 845, 795, 767,
1
758, 641, 558 cm−1. H NMR (CD2Cl2, 400 MHz): δ = −4.85 (bs,
6H), −4.76 (bs, 6H), 1.31 (s, 6H), 1.72 (s, 6H), 1.97 (s, CH3, CH3CN
from [Cu(CH3CN)4]PF6), 2.05 (s, 12H), 2.06 (s, 12H), 2.30 (s, 6H),
3
2.35 (s, 6H), 2.61 (s, 6H), 6.02 (d, J = 5.6 Hz, 4H), 6.87 (bs, 2H),
6.92 (s, 4H), 6.96 (s, 4H), 6.98 (d, 3J = 5.6 Hz, 4H), 7.15 (s, 2H), 7.43
(s, 2H), 7.48−7.51 (m, 4H), 7.53−7.57 (m, 6H), 7.63−7.68 (m, 12H),
3
3
7.73−7.82 (m, 14H), 7.96 (d, J = 8.0 Hz, 2H), 8.03 (d, J = 8.0 Hz,
3
3
2H), 8.06 (d, J = 8.8 Hz, 2H), 8.09 (d, J = 8.8 Hz, 2H), 8.15−8.23
(m, 10H), 8.33−8.39 (m, 8H), 8.43 (bs, 4H), 8.44 (d, J = 8.0 Hz,
3
EXPERIMENTAL SECTION
■
3
3
2H), 8.57 (bs, 4H), 8.60 (d, J = 8.0 Hz, 2H), 8.75 (d, J = 4.4 Hz,
4H), 8.78 (d, 3J = 4.4 Hz, 4H), 8.84 (d, 3J = 8.0 Hz, 2H), 8.95 (d, 3J =
8.8 Hz, 4H), 8.98 (d, 3J = 8.0 Hz, 2H), 9.04 (d, 3J = 8.8 Hz, 4H) ppm.
Anal. Calcd for C262H182Cu2F12N20P2Zn2·7CH2Cl2: C, 67.98; H, 4.16;
N, 5.89. Found: C, 68.40; H, 4.26; N, 5.61%. ESI-MS: m/z (%) 1877.4
(100) [Cu2(2a)(4)]2+, 1678.9 (45) [Cu4(4) (DABCO) (CH3CN)]-
Bruker Avance (400 MHz) and Varian (600 MHz) spectrometers were
1
used to measure H and 13C NMR spectra using a deuterated solvent
as the lock and residual protiated solvent as internal reference (CDCl3:
δH 7.26 ppm, δC 77.0 ppm; CD2Cl2: δH 5.32 ppm, δC 53.8 ppm,
tetrahydrofuran-d8: δH 1.72 ppm, 3.58 ppm, δC 25.3 ppm, 67.2 ppm).
The following abbreviations were used to define NMR peak patterns: s
G
DOI: 10.1021/acs.inorgchem.7b00740
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(PF6)22+, 1629.3 (25) [Cu4(4) (CH3CN)](PF6)22+, 1252.0 (20)
[Cu2(2a)(4)]3+, 930.4 (5) [Cu2(4)]3+.
(0.502 mg, 0.491 μmol) and DABCO (55.0 μg, 0.491 μmol).
Subsequent sonication for 10 min furnished the complex in
quantitative yield. mp: decomp > 60 °C. IR (KBr): ν = 2947, 2923,
2852, 2220, 1664, 1608, 1482, 1458, 1379, 1202, 995, 841, 794, 768,
640, 557, 405 cm−1. 1H NMR (CD2Cl2, 400 MHz): δ = −[5.01−4.97]
(m, 6H), −[4.94−4.90] (m, 6H), 1.44 (s, 3H), 1.59 (s, 3H, f′-H), 1.97
(s, CH3, CH3CN from [Cu(CH3CN)4]PF6), 2.06 (s, 6H), 2.07 (s,
9H), 2.08 (s, 9H), 2.30 (s, 3H), 2.35 (s, 9H), 2.61 (s, 3H), 6.01−6.04
(m, 6H), 6.87 (d, 3J = 8.0 Hz, 2H), 6.92−7.01 (m, 14H), 7.06 (d, 3J =
8.0 Hz, 2H), 7.18 (s, 1H), 7.39 (s, 1H), 7.49−7.58 (m, 8H), 7.64 (d, 3J
Nanorotor ROT-2a′. [Cu(CH3CN)4]PF6 (2 equiv, 0.413 mg, 1.11
μmol) was added to ROT-2a. Sonication for 10 min afforded ROT-
2a′ quantitatively. mp: decomp > 60 °C. IR (KBr): ν = 3444, 2967,
2922, 2851, 2218, 1616, 1489, 1482, 1482, 1439, 1200, 995, 852, 848,
768, 559 cm−1. 1H NMR (CD2Cl2, 400 MHz): δ = −[4.85−4.82] (m,
6H), −[4.77−4.73] (m, 6H), 1.32 (s, 6H), 1.73 (s, 6H), 1.93 (s, CH3,
CH3CN from [Cu(CH3CN)4]PF6), 1.98 (s, 12H), 2.06 (s, 12H), 2.31
(s, 6H), 2.34 (s, 6H), 2.61 (s, 6H), 6.06 (d, 3J = 5.6 Hz, 4H), 6.87 (bs,
3
3
= 8.0 Hz, 1H), 7.65−7.69 (m, 10H), 7.73−7.81 (m, 12H), 7.88 (d, J
2H), 6.95 (s, 8H), 6.98 (d, J = 5.6 Hz, 4H), 7.14 (s, 2H), 7.42 (s,
= 8.0 Hz, 2H), 7.95 (d, 3J = 8.0 Hz, 1H), 7.99−8.01 (m, 2H), 8.03 (d,
2H), 7.53−7.57 (m, 6H), 7.59−7.66 (m, 14H), 7.73−7.80 (m, 6H),
3J = 8.0 Hz, 3H), 8.08−8.09 (m, 2H), 8.13−8.17 (m, 4H), 8.20−8.24
3
3
7.84−7.88 (m, 4H), 7.93 (d, J = 8.0 Hz, 2H), 8.02 (d, J = 8.0 Hz,
3
3
3
2H), 8.16 (d, J = 8.0 Hz, 6H), 8.24 (d, J = 8.0 Hz, 6H), 8.27−8.39
(m, 16H), 8.42 (d, 3J = 4.8, 4H), 8.58 (d, 3J = 4.8, 4H), 8.72−8.75 (m,
6H), 8.78 (d, 3J = 4.4, 4H), 8.82 (d, 3J = 8.0, 2H), 8.93−8,96 (m, 6H),
8.98 (d, J = 8.0, 2H), 9.09 (d, J = 8.8 Hz, 4H) ppm. Elemental
analysis: Upon removal of CH3CN (which arises from the Cu(I) salt),
the assembly is not stable. ESI-MS: m/z (%) 970.3 (100)
[Cu4(2a)(4)]4+.
(m, 4H), 8.33−8.39 (m, 11H), 8.40−8.44, (m, 3H), 8.47 (d, J = 4.4
3
3
Hz, 2H), 8.48 (d, J = 8.0 Hz, 2H), 8.57−8.62 (m, 5H), 8.63 (d, J =
4.4 Hz, 2H), 8.73 (d, 3J = 4.4 Hz, 2H), 8.76 (d, 3J = 4.4 Hz, 2H), 8.81
3
3
3
(s, 4H), 8.83 (d, J = 8.0 Hz, 3H), 8.93−9.03 (m, 11H) ppm. Anal.
Calcd for C266H179Cu3F18N21P3Zn2·7 CH2Cl2: C, 65.15; H, 3.75; N,
6.08. Found: C, 65.31; H, 3.87; N, 5.86%. ESI-MS: m/z (%) 1329.0
(100) [Cu3(3)(4) (DABCO)]3+.
Pre-Rotor Complex ROT-2b. In an NMR tube, stator 4 (1.16 mg,
0.435 μmol) and 2 equiv of [Cu(CH3CN)4]PF6 (0.325 mg, 0.871
μmol) were dissolved in CD2Cl2, followed by addition of rotator 2b
(0.420 mg, 0.435 μmol) and DABCO (49.0 μg, 0.435 μmol).
Subsequent sonication for 10 min furnished the complex in
quantitative yield. mp: decomp > 60 °C. IR (KBr): ν = 3853, 3441,
2957, 2922, 2852, 2213, 1601, 1487, 1443, 1202, 995, 844, 795, 767,
Nanorotor ROT-3′. [Cu(CH3CN)4]PF6 (1 equiv, 0.184 mg, 0.491
μmol) was added to ROT-3. Subsequent sonication for 10 min
afforded ROT-3′ quantitatively. mp: decomp > 60 °C. IR (KBr): ν =
2957, 2924, 2853, 2218, 1614, 1384, 1093, 1203, 996, 869, 846, 796,
559 cm−1. 1H NMR (CD2Cl2, 400 MHz): δ = −[5.00−4.96] (m, 6H),
−[4.93−4.88] (m, 6H),1.44 (s, 3H), 1.59 (s, 3H), 1.95 (s, CH3,
CH3CN from [Cu(CH3CN)4]PF6), 1.98 (s, 6H), 2.06 (s, 6H), 2.07 (s,
12H), 2.30 (s, 3H), 2.35(s, 9H), 2.60 (s, 3H), 6.02−6.04 (m, 6H),
1
757, 628, 615, 607, 557 cm−1. H NMR (CD2Cl2, 400 MHz): δ =
3
3
6.88 (d, J = 8.0 Hz, 2H), 6.95−7.01 (m, 14H), 7.08 (d, J = 8.0 Hz,
2H), 7.18 (s, 1H), 7.37 (s, 1H), 7.53−7.61 (m, 8H), 7.64−7.70 (m,
−[4.88−4.85] (m, 6H), −[4.81−4.77] (m, 6H), 1.50 (s, 6H), 1.51 (s,
6H), 1.97 (s, CH3, CH3CN from [Cu(CH3CN)4]PF6), 2.05 (s, 12H),
2.06 (s, 6H), 2.08 (s, 6H), 2.29 (s, 6H), 2.35 (s, 6H), 2.60 (s, 6H),
6.03 (d, 3J = 6.4 Hz, 4H), 6.91 (s, 4H), 6.95 (s, 2H), 6.98 (s, 2H), 7.00
3
10H), 7.73−7.79 (m, 10H), 7.84−7.91 (m, 4H), 7.94 (d, J = 8.0 Hz,
1H), 7.99−8.04 (m, 5H), 8.14−8.16 (m, 4H), 8.20−8.26 (m, 4H),
8.26−8.28 (m, 2H), 8.33−8.39 (m, 14H), 8.46−8.48 (m, 4H), 8.57−
3
3
(d, J = 6.4 Hz, 4H), 7.04 (d, J = 8.0 Hz, 2H), 7.18 (s, 2H), 7.37 (s,
3
3
8.60 (bs, 4H), 8.63 (d, J = 4.4 Hz, 2H) 8.72−8.75 (m, 3H), 8.76 (d,
2H), 7.48−7.52 (m, 4H), 7.54−7.58 (m, 6H), 7.63 (d, J = 8.0 Hz,
2H, 3J = 4.4 Hz), 8.81−8.84 (m, 7H), 8.93−8.99 (m, 10H), 9.07 (d, 3J
= 8.8 Hz, 2H) ppm. Elemental analysis: Upon removal of CH3CN
(which arises from the Cu(I) salt), the assembly is not stable. ESI-MS:
m/z (%) 985.4 (100) [Cu4(3)(4)]4+.
3
2H), 7.64 (d, J = 8.0 Hz, 2H), 7.66−7.70 (m, 4H), 7.74−7.80 (m,
14H), 7.88 (d, 3J = 8.0 Hz, 2H), 7.95 (d, 3J = 8.0 Hz, 2H), 8.00 (d, 3J =
8.0 Hz, 2H), 8.03 (d, 3J = 8.0 Hz, 2H), 8.06 (d, 3J = 8.8 Hz, 2H), 8.09
3
(d, J = 8.8 Hz, 2H), 8.17−8.23 (m, 8H), 8.33−8.39 (m, 10H), 8.44
3
3
3
(d, J = 8.0 Hz, 2H), 8.45 (d, J = 4.4 Hz, 2H), 8.49 (d, J = 8.0 Hz,
2H), 8.54 (d, 3J = 4.4 Hz, 2H), 8.58−8.60 (m, 4H), 8.71 (s, 2H), 8.75
(d, 3J = 4.4 Hz, 2H), 8.78 (d, 3J = 4.4 Hz, 2H), 8.81 (s, 2H), 8.83 (d, 3J
ASSOCIATED CONTENT
■
3
3
S
* Supporting Information
= 8.0 Hz, 2H), 8.95 (d, J = 8.8 Hz, 4H), 8.98 (d, J = 8.0 Hz, 2H),
9.02 (d, 3 J
=
8.8 Hz, 4H) ppm. Anal. Calcd for
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00740.
C262H182Cu2F12N20P2Zn2·6CH2Cl2: C, 68.96; H, 4.19; N, 6.00.
Found: C, 68.94; H, 4.35; N, 5.65%. ESI-MS: m/z (%) 1877.4
(100) [Cu2(2b)(4)]2+, 1679.8 (20) [Cu4(4) (DABCO) (CH3CN)]-
2+
(PF6)22+, 1628.8 (15) [Cu4(4) (CH3CN)](PF6)2
.
Synthesis and characterization of ligands and model
complexes, proton assignment of all rotors, rate constant
determination, binding constant measurement, and
computational coordinates (PDF)
Nanorotor ROT-2b′. [Cu(CH3CN)4]PF6 (2 equiv, 0.325 mg,
0.871 μmol) was added to ROT-2b. Sonication for 10 min afforded
ROT-2b′ quantitatively. mp: decomp > 60 °C. IR (KBr): ν = 3444,
2964, 2923, 2851, 2218, 1614, 1493, 1442, 1386, 1203, 995, 868, 864,
768, 559 cm−1. 1H NMR (CD2Cl2, 400 MHz): δ = −[4.86−4.82] (m,
6H), −[4.80−4.76] (m, 6H), 1.51 (s, 6H), 1.53 (s, 6H), 1.92 (s, CH3,
CH3CN from [Cu(CH3CN)4]PF6), 1.99 (s, 12H), 2.06 (s, 6H), 2.08
(s, 6H), 2.30 (s, 6H), 2.34 (s, 6H), 2.60 (s, 6H), 6.05 (d, 3J = 6.4 Hz,
4H), 6.95 (s, 6H), 6.97 (s, 2H), 7.00 (d, 3J = 6.4 Hz, 4H), 7.05 (d, 3J =
8.0 Hz, 2H), 7.19 (s, 2H), 7.35 (s, 2H), 7.54−7.63 (m, 12H), 7.66−
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: schmittel@chemie.uni-siegen.de.
ORCID
3
7.72 (m, 6H), 7.74−7.81 (m, 8H), 7.84−7.90 (m, 6H), 7.94 (d, J =
Michael Schmittel: 0000-0001-8622-2883
3
3
8.0 Hz, 2H), 8.00 (d, J = 8.0 Hz, 2H), 8.03 (d, J = 8.0 Hz, 2H),
3
8.14−8.22 (m, 4H), 8.25 (d, J = 8.0 Hz, 4H), 8.28−8.31 (m, 4H),
Author Contributions
3
3
†Both authors contributed equally to the paper.
8.33−8.39 (m, 12H), 8.45 (d, J = 4.4 Hz, 2H), 8.49 (d, J = 8.0 Hz,
2H), 8.55 (d, 3J = 4.4 Hz, 2H), 8.60 (s, 2H), 8.70 (s, 2H), 8.74 (d, 3J =
8.0 Hz, 2H), 8.76 (d, 3J = 4.4 Hz, 2H), 8.80 (d, 3J = 4.4 Hz, 2H), 8.83
(d, 3J = 8.0 Hz, 2H), 8.84 (s, 2H), 8.95 (d, 3J = 8.0 Hz, 2H), 8.96−9.00
Notes
The authors declare no competing financial interest.
3
(m, 6H), 9.07 (d, J = 8.8 Hz, 4H) ppm. Elemental analysis: Upon
removal of CH3CN (which arises from the Cu(I) salt), the assembly is
ACKNOWLEDGMENTS
not stable. ESI-MS: m/z (%) 971.5 (100) [Cu4(2b)(4)]4+.
■
We thank the DFG (Schm 647/20-1) and the Univ. of Siegen
for continued support, in particular, for providing the Linux
Cluster HorUS for computations.
Pre-Rotor Complex ROT-3. In an NMR tube stator 4 (1.31 mg,
0.491 μmol) and 3 equiv of [Cu(CH3CN)4]PF6 (0.549 mg, 1.47
μmol) were dissolved in CD2Cl2 followed by addition of rotator 3
H
DOI: 10.1021/acs.inorgchem.7b00740
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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DOI: 10.1021/acs.inorgchem.7b00740
Inorg. Chem. XXXX, XXX, XXX−XXX