Synthesis of crystalline molecular gyrotops and phenylene rotation inside the cage

Article abstract of DOI:10.1021/jo501539h

Phenylene-bridged macrocage molecules were synthesized as molecular gyrotops because the rotor can rotate even in a crystal. The chain-length-dependent properties of the molecular gyrotops were investigated in order to explore the potential to create new molecular materials. The formation of the cage in the synthesis of each molecular gyrotop depended on the length of the alkyl chains of the precursor. The rotation modes and energy barriers for phenylene rotation inside the crystals of the molecular gyrotops were changed by varying the chain length of the cage.

Full text of DOI:10.1021/jo501539h

Article
pubs.acs.org/joc
Synthesis of Crystalline Molecular Gyrotops and Phenylene Rotation
inside the Cage
,
†
‡
‡
‡
§
Wataru Setaka,* Kazuyuki Inoue, Sayaka Higa, Seiki Yoshigai, Hirohiko Kono,
and Kentaro Yamaguchi‡
†Division of Applied Chemistry, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Hachioji, Tokyo
92-0397, Japan
1
‡
Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, Sanuki, Kagawa 769-2193, Japan
§Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
S Supporting Information
*
ABSTRACT: Phenylene-bridged macrocage molecules were synthesized as molecular gyrotops because the rotor can rotate
even in a crystal. The chain-length-dependent properties of the molecular gyrotops were investigated in order to explore the
potential to create new molecular materials. The formation of the cage in the synthesis of each molecular gyrotop depended on
the length of the alkyl chains of the precursor. The rotation modes and energy barriers for phenylene rotation inside the crystals
of the molecular gyrotops were changed by varying the chain length of the cage.
INTRODUCTION
■
Molecular rotors, which show rotation of a part of the
molecule, have been studied widely. The physical and chemical
properties of the molecules tend to be affected by the molecular
motion; therefore, the control of molecular motion inside a
single crystal has been investigated to explore the potential for
the creation of new molecular materials. Thus, much attention
has been focused on the chemistry of molecular machines that
1
exhibit mechanical motions of parts of the molecules. Indeed, a
Figure 1. (a) Schematic representation of a gyrotop, which consists of
a cage and a rotor. (b) Structural formula of the molecular gyrotops
studied.
number of molecular rotors have been designed, synthesized,
and characterized to date, and their rotational dynamics have
been revealed.
1
−7
In particular, the chemistry of partial molecular rotations in
the crystalline state has been studied. Macrocyclic molecules
having a rotor surrounded by a three-spoke stator are expected
crystal of molecular gyrotop 1 (Figure 1) showed temperature-
dependent birefringence, which was reported as the first change
in optical properties due to the rotation of a phenylene rotor in
2
−6
to have functions of gyroscopes and gyrotops (Figure 1).
5d
The chemistry of molecular gyroscopes and gyrotops and
related molecules has been reported by Garcia-Garibay and co-
a crystal. A similar molecular gyrotop exhibited remarkable
inflation of the cage in the crystalline state due to the dynamics
of the phenylene rotor, and an unusually high thermal
expansion coefficient of the crystal was observed, suggesting a
2
,6
3
4,5
workers, Gladysz and co-workers, and our group. The
synthesis and dynamics of the rotors have also been studied,
and the rotor functions have been reported recently. Studies of
the physical properties that change as a result of thermally
induced rotation of the rotor are both interesting and important
for the development of new functions and applications of
organic molecules.
5e
novel function for the dynamic states of the molecules.
Control of the rotation, for example, its orientation and
energy barriers, may allow the creation of novel functional
materials based on the dynamic states of the rotor. We recently
reported that 1,4-naphthalenediyl-bridged molecular gyrotops
We recently reported the synthesis and properties of
crystalline molecular gyrotops having a phenylene rotor
surrounded by three long alkyl spokes. Especially, a single
Received: July 11, 2014
©
XXXX American Chemical Society
A
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Scheme 1
with various cage sizes showed a chain-length dependence of
The yields of the cage and noncage isomers obtained by
RCM of precursors 5−8 are summarized in Table 1. We
5c
the energy barrier for the rotation of the rotor in solution. In
that study, it was found that the molecular gyrotop surrounded
by three tetradecyl (C ) chain derivatives did not show
Table 1. Yields of the Cages and their Noncage Isomers in
1
4
rotation of the naphthalenediyl inside the cage in solution,
whereas the 1,4-naphthalenediyl moieties of the gyrotops with
hexadecyl (C ) and octadecyl (C ) chain derivatives showed
restricted and rapid rotation about an axis in solution,
respectively. Therefore, the rotation of the naphthalenediyl
rotor in molecular gyrotops can be controlled in solution by
changing the size of the cage steric effects.
RCM Reactions of Bis(silyl)benzenes 5−8
yields/%
16
18
a
precursor
cage
isomer
isomer/cage ratio
c
c
5
6
7
8
(n = 12)
(n = 14)
(n = 16)
(n = 18)
0
0
−
0
b
d
24
10
23
0
43
39
4.3
1.7
Here we report the chain-length dependence of the
formation and rotation mode of the rotor inside the cage in
the crystalline state. The properties of the molecular gyrotop 1
with C chains were compared to those of molecular gyrotops
a
b
c
d
Formation ratio. Reference 5d. Not detected. Reference 5a.
14
recently reported the optimization of the reaction conditions of
the RCM; we applied the reaction using Grubbs’ first-
generation catalyst under reflux, which are the best conditions
with C16 chains (2) and C18 chains (3).
5a
RESULTS AND DISCUSSION
for cage production. Although the desired cage was not
produced by the reaction of bis(silyl)benzene 5, the highest
cage yield was achieved by the RCM of 6. Hence, the dodecyl
■
Synthesis of the Molecular Gyrotops. Molecular gyro-
tops and gyroscopes consist of a cage and a rotor (Figure 1). In
the present molecular gyrotops, the cage was constructed of
three long alkyl spokes, and a benzene ring was applied as a
rotor. Benzene is known to have a strong anisotropy in its
physical properties in the in-plane and out-of-plane directions
because of its planar structure; therefore, its physical properties
may be switched to isotropic by rotation of the ring.
(
C ) spokes were too short to form the cage, whereas the C
1
2
1
4
spokes were suitable for the phenylene rotor. In the syntheses
of 2 and 3, noncage isomers 2i and 3i were also obtained,
probably because the side chains of the cages were too long for
the phenylene rotor. The sum of the yields of the cage and
noncage isomers was less than 65% in all cases. Thus, the major
products of these reactions were polymeric byproducts,
although highly dilute conditions were applied in order to
prevent intermolecular RCM. Remarkably, the chain length of
the precursor affected the formation ratio of the cage and
noncage isomers, that is, this ratio plausibly depends on the
stability of the reaction intermediates and the products because
The route for the synthesis of the molecular gyrotops is
5d
5a
shown in Scheme 1. The syntheses of 1 and 3 have been
reported previously, whereas the synthesis of 2 was newly
achieved by applying the same method, as described in the
following. The reaction of trichlorosilane with ω-alkenylmag-
nesium bromides gave trialkenylsilanes 13−16. After chlorina-
tion of the trialkenylsilanes, the reactions of p-dilithiobenzene
with the resulting trialkenylchlorosilanes afforded p-bis(tri-ω-
8
of the RCM equilibrium reaction. Although the statistical
formation ratio of the cage isomer to the noncage isomer is 1:3,
5a
as described in the previous report, the cage is the dominant
isomer in the syntheses of 1 and 3.
8
alkenylsilyl)benzenes 5−8. Ring-closing metathesis (RCM) of
the bis(silyl)benzenes followed by hydrogenation under 3 atm
The stereochemistry of alkene junctions formed by RCM
reactions was investigated before the hydrogenation reaction.
Although only the (E,E,E) cage was obtained before hydro-
H in the presence of Pd/C afforded a mixture of the cage and
2
byproducts. The cage compounds were isolated from the
reaction mixture by preparative gel-permeation chromatog-
5e
genation in the synthesis of 1, a complex mixture including
both E and Z junctions was formed in the syntheses of 2 and
1
raphy (GPC). These isolated compounds were identified by H
and 13C NMR spectroscopy.
3, probably because of the long chains of the cages.
5a
B
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5d
5a
Figure 2. Molecular structures of (a) 1, (b) 2, and (c) 3 as determined by X-ray crystallography: (top) ball-and-stick models of the molecules;
(
bottom) packing diagrams. Hydrogen atoms and disordered atoms on the side chains have been omitted for clarity.
2
Figure 3. Temperature-dependent solid-state H NMR spectra of (a) 1-d (ref 5d), (b) 2-d , and (c) 3-d [observed spectra, solid lines; simulated
4
4
4
spectra, dotted lines). A schematic drawing of exchange mechanism is shown above each spectrum. Estimated exchange rate constants k, angular
displacements Δ, and ratios of populations of the phenylene sites (p :p ) are shown].
1
2
X-ray Crystallographic Analyses of the Molecular
(C2/c for 1 and Cc for 2). Indeed, the shapes of cages of 1 and
Gyrotops. The structures of 1 and 3 were determined by X-
ray diffraction of single crystals obtained through recrystalliza-
tion from tetrahydrofuran/methanol solutions, as reported
2 are almost spherical. Although 1 has C symmetry (with the
2
C2 axis perpendicular to the rotation axis of the rotor), 2
possesses no symmetry inside the molecule. On the other hand,
cage 3, in which two of the three alkyl chains are separated, is
completely different from 1 and 2 because of its different crystal
system (triclinic). The results indicate that the alkyl chains of 3
are too long to form a spherical cage.
Packing diagrams of the crystals of 1−3 are also shown in
Figure 2. In all of the crystals, the molecules are arranged
according to their rotation axes. In the crystal structures of 1
with 2, the phenylenes are arranged perpendicularly about a
slightly titled rotation axis.
5
a,d
previously.
Similarly, recrystallization of the purified
molecular gyrotop 2 afforded single crystals suitable for X-ray
diffraction. Figure 2 shows the molecular structures of the
molecular gyrotops 1−3 in the corresponding single crystals as
determined by X-ray crystallography. The single crystal of 2 was
formed as an overly thin plate and cracked when the
temperature was lowered; thus, the X-ray diffraction study of
the single crystal of 2 had to be carried out at a relatively high
temperature (270 K). In all of the cage compounds, the three
alkyl chains effectively surround the phenylene moiety. The
crystal structures of 1 and 2 are almost identical, having the
same crystal system (monoclinic) and similar space groups
Phenylene Dynamics of the Molecular Gyrotops in
the Crystals. The rates and angular ranges of the phenylene
2
flips inside the crystals were estimated by solid-state H NMR
C
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9
spectroscopy. In a previous report, the temperature-dependent
2
solid-state H NMR spectra of 1-d (in which the phenylene
4
moiety was labeled with four deuterium atoms) were
5
d
investigated. The phenylene ring of 1-d slowly undergoes a
4
1
80° flip between the two equilibrium sites that were confirmed
5d
by X-ray structural analysis. The flipping rate was accelerated
with increasing temperature between 230 and 260 K. The
activation energy (E ) for the phenylene flip of 1-d was
a
4
estimated to be 10.3 kcal/mol from the Arrhenius plot of the
5
d
flipping rates. The line widths of the observed spectra
narrowed above 270 K, indicating continuous rotation of the
phenylene moiety in 1-d at a rate exceeding the fast-exchange
4
limit (>4 MHz). The spectra were theoretically reproduced by
assuming a 180° flip in the fast-exchange limit (4 MHz) with an
angular displacement (Δ) that is comparable to the 2σ range of
the oscillation angle of the phenylene around the equilibrium
position with a Gaussian distribution (cf. Figure 3a).
2
Figure 4. Temperature-dependent H spin−lattice relaxation times
(T ) in molecular gyrotops 1 (red circles; ref 5d), 2 (green triangles),
1
and 3 (blue squares) in crystal form. The lines are fits to the relaxation
model shown in eq 1, for which the parameters are listed in Table 2.
In contrast to the phenylene flipping with angular displace-
ment observed for 1-d in the crystal, the phenylene of 2-d4
4
showed different dynamic behavior inside the crystal. Figure 3b
displays the temperature-dependent solid-state H NMR
2
typical nuclear quadrupolar relaxation with a sharp minimum.
The relaxation model shown in eq 1 was used to analyze the
temperature dependence of T1:
spectra of 2-d . The line shape of the spectrum at 230 K is
4
different from that of 1-d . The observed spectra were
4
simulated by assuming a 90° jump with unequal populations
⎛
⎞
1
τ
4τ
1
0
(
p ≠ p ). With increasing temperature, the rate of jumping
= K⎜
+
2
⎟
1
2
2
2
2
T
⎝1 + ω τ
1 + 4ω τ ⎠
1
0
0
(1)
increased, and the populations were averaged in the range 230−
290 K.
where K is an effective coupling constant that depends on the
quadruple coupling constant, τ is a single correlation time that
obeys the Arrhenius rule [i.e., τ = τ exp(E /RT)], and ω /2π
is the Larmor frequency of deuterium. According to this model,
the observed T values were consistent with the calculated ones.
The best fit parameters for these calculations using the
relaxation model shown in eq 1 are given in Table 2. These
On the other hand, the phenylene of 3-d showed another
4
dynamic behavior inside the crystal. Figure 3c displays the
2
∞
a
0
temperature-dependent solid-state H NMR spectra of 3-d .
4
With increasing temperature, the line widths of the observed
spectra narrowed and the shapes of the spectra altered. The
observed spectra were theoretically reproduced by assuming a
six-site exchange mechanism and applying different populations
of benzene rings that can exist at three positions every 120°
1
a
Table 2. Fit Parameters for the Theoretical Curves of T as
a Function of Temperature for Gyrotops 1−3
10
1
around the axis of rotation. The simulated spectra reproduced
the observed spectra accurately. It is difficult to distinguish
precisely between the “six-site exchange applying different
/kcal mol−
1
gyrotop
K
τ
/s
E
∞
a
b
10
−16
−15
−14
b
b
populations” mechanism for 3-d and the “180° flip with
1 (n = 14)
2 (n = 16)
3 (n = 18)
5.8 × 10
6.6 × 10
4.65 × 10
3.0 × 10
3.0 × 10
9.0
4
1
0
angular displacements” mechanism for 1-d4 because these
mechanisms are intrinsically identical. In this work, if the
angular displacements around the equilibrium positions were
observed on the NMR time scale, the exchange mechanism is
assigned as the “six-site exchange applying different popula-
tions” mechanism.
7.4
6.6
5.0 × 1010
a
b
ω /2π = 76.7 MHz. Reference 5d.
0
results indicate that the phenylene flip was enhanced with
increasing temperature and that the rates completely exhibited
the Arrhenius behavior over the temperature range 230−370 K
(at least). The activation energies were estimated to be 9.0, 7.4,
and 6.6 kcal mol− for 1-d , 2-d , and 3-d , respectively. These
values decrease with increasing cage size, indicating that the
steric interactions between the phenylene and the cage affect
the energy barrier.
DFT Calculations on Molecular Gyrotops. DFT
calculations were performed to estimate the energy barriers
for phenylene rotation in molecular gyrotops 1−3. First, the
molecular structures were optimized at the B3LYP/6-31G*
level using the Gaussian 09 program package, and the initial
coordinates of the atoms were taken from the single-crystal X-
ray analysis data. The optimized structures and X-ray structures
were comparable, as shown in Figure 5. For the confirmation of
a qualitative agreement between these structures, root-mean-
square distances (RMSd) between all silicon and carbon pairs
were estimated; these values were 0.451, 1.009, and 0.369 Å for
The temperature-dependent 2H NMR spectra of the
molecular gyrotops 1-d , 2-d , and 3-d were completely
4
4
4
reversible over the temperature range 220−350 K. The
dynamic behaviors of the phenylene rotors in the molecular
gyrotops are basically similar, as they show thermally
accelerated rotation with angular displacements. However,
slightly different mechanisms are needed for the precise analysis
of the spectra. These differences in the rotation mechanism
may be ascribed to subtle differences in the cage structure that
determine the rotational potentials, as described later.
1
4
4
4
For the estimation of the energy barrier for the rotation of
11
the phenylene, the temperature-dependent spin−lattice relax-
9
ation time (T ) was investigated. The inversion−recovery
1
quadrupole echo pulse sequence was used to measure the T1
values for the molecular gyrotops. Figure 4 compares the
2
experimentally determined H NMR T values for molecular
1
gyrotops 1-d , 2-d , and 3-d with the calculated T values. The
4
4
4
1
T1 values are remarkably dependent on temperature and exhibit
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Figure 5. Comparison between the X-ray structures (green) and optimized structures from DFT calculations (B3LYP/6-31G*) (sky blue). RMS
distances (RMSd) between all silicon and carbon pairs and C1−Si1−C2−C3 dihedral angles θ determined by X-ray crystallography and DFT
calculations: (a) 1 [RMSd = 0.451 Å for 50 pairs; θ = 101.0° (X-ray), 104.90 (calcd)]; (b) 2 [RMSd = 1.009 Å for 56 pairs; θ = 54.9° (X-ray), 40.58°
(
calcd)]; (c) 3 [RMSd = 0.369 Å for 62 pairs; θ = −69.3° (X-ray), −88.90° (calcd)].
1
, 2, and 3, respectively. The small RMSd values indicate that
CONCLUSION
■
the optimized molecular structures adequately reflect the
structures of the molecules in the crystalline state.
The chain-length dependence of the properties of molecular
gyrotops was investigated. The formation of the cage in the
synthesis of the molecular gyrotops depended on the length of
the alkyl chains of the precursor. The rotation modes and
energy barriers for phenylene rotation inside the crystals of the
molecular gyrotops were varied by changing the chain length of
the cage. Theoretical calculations of the phenylene rotational
potential curves were in good qualitative agreement with the
observed dynamics. It is therefore concluded that the potential
curves for phenylene rotation in the crystalline state are
determined by the structure of the cage in the molecular
gyrotop.
The rotational potentials of the phenylene rings in molecular
gyrotops 1, 2, and 3 were calculated at the B3LYP/6-31G*
level. In these calculations, the coordinates of the cages and the
two ipso carbons were fixed to those in the optimized structure
as shown in Figure 5, and the coordinates of the residual four
phenylene CH atoms were optimized at various C1−Si1−C2−
C3 dihedral angles θ (see Figure 5). Figure 6 shows the plots of
EXPERIMENTAL SECTION
■
General. The reactions were performed under anhydrous
conditions using argon, unless otherwise noted. The chemical shifts
1
13
of H (400 MHz) and C (100 MHz) NMR spectra are based on the
residual solvent resonances. 29Si (79 MHz) NMR chemical shifts are
referenced to external tetramethylsilane. The assignment of the NMR
1
13
signals was carried out by using 1D and 2D NMR techniques ( H, C,
DEPT, COSY, and HSQC).
Materials. Commercially available reagents were used as received
without further purification. Anhydrous THF, hexane, and dichloro-
methane were purchased from a chemical supplier. Grubbs’ catalysts
(first and second generation), which are commercially available, were
5a
Figure 6. Potential energy for phenylene rotation as a function of the
C1−Si−C2−C3 dihedral angle θ (atom labeling shown in Figure 5)
calculated at the B3LYP/6-31G* level for 1 (red circles), 2 (green
triangles), and 3 (blue squares).
5d
used for the RCM reactions. The syntheses of silanes 14 and 16,
5
d
5a
5d 5a
bis(silyl)benzenes 6 and 8, and molecular gyrotops 1, 3, and
5
a
3i have been reported previously.
Synthesis of Tri-6-heptenylsilane (13). A 1.0 M THF solution
of 6-heptenylmagnesium bromide (200 mL, 200 mmol) prepared from
the corresponding alkenyl bromide and magnesium was placed into a
two-neck flame-dried round-bottom flask (200 mL) equipped with a
magnetic stirrer, a condenser, and a dropping funnel. Trichlorosilane
the calculated energy for each dihedral angle, and the dihedral
angle of the calculated most stable structure was set equal to 0°.
Only one minimum of the potential curve in the θ range
between −90° and +90° was observed for 1 and 3, indicating
that a 180° flip between the two equilibrium sites is a plausible
mechanism for the phenylene motion. These almost flat
potential curves suggest the occurrence of angular displace-
ments of the phenylene at higher temperatures. On the other
hand, the potential curve for 2 shows two minima in the range,
indicating that a 90° jump mechanism is suitable to describe the
phenylene dynamics. These calculated features are in good
qualitative agreement with the observed dynamics of the
phenylene in these molecules. However, the calculated energy
barriers for the phenylene dynamics are higher than the
experimentally determined values because relaxation of the cage
was not allowed in these calculations. Hence, further
investigation is necessary for quantitative analysis of the
(8.13 g, 60 mmol) was introduced dropwise into the reaction flask
cooled by a water bath. The reaction mixture was stirred at ambient
temperature for 15 h. The mixture was hydrolyzed with dilute
HCl(aq) and extracted with hexane. The organic layer was washed
with saturated NaHCO (aq) and dried over anhydrous Na SO .
3
2
4
Concentration and column chromatography [Merck silica gel 60,
particle size 63−200 μm, hexane as eluent (R
= 0.9)] of the residue
f
1
afforded 13 as a colorless oil (18.35 g, 57.3 mmol, 95% yield). H
NMR (CDCl , 400 MHz): δ 0.55−0.62 (m, 6H, SiCH ), 1.27−1.45
3
2
(
m, 24H), 2.039 (tddd, J = 7.0, 7.0, 1.7, 1.4 Hz, 6H, H CCH−
2
CH −), 3.689 (septet, J = 3.2 Hz, 1H, SiH), 4.926 (ddt, J = 6.8, 2.4,
2
1
.4 Hz, 6H, terminal H C), 4.989 (ddt, J = 16.8, 2.4, 1.5 Hz, 6H,
2
terminal H C), 5.804 (ddt, J = 16.8, 10.4, 6.8 Hz, 6H, H CCH−).
2
2
13
C NMR (CDCl , 100 MHz): δ 11.26, 24.53, 28.61, 32.82, 33.72,
3
29
1
14.12 (−CHCH ), 139.08 (−CHCH ). Si NMR (CDCl , 79.5
2
2
3
MHz): δ −6.49. Anal. Calcd for C H Si: C, 78.67; H, 12.57. Found:
C, 78.63; H, 12.42.
21 40
4
b
potential curves.
E
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Synthesis of Tri-8-nonenylsilane (15). Compound 15 was
synthesized from 8-nonenylmagnesium bromide using the same
procedure as for 13 and was obtained as colorless oil in 98% yield.
unsaturated cyclized mixtures with (E/Z)-alkenyl junctions (0.8 g).
Then hydrogen gas (3 atm) was introduced into a toluene (5 mL)
solution of the reaction mixture in the presence of 10% Pd/C (0.03 g)
in an autoclave, and the mixture was allowed to stand for 72 h at 60
1
H NMR (CDCl , 400 MHz): δ 0.53−0.62 (m, 6H, SiCH ), 1.24−
3
2
1
.42 (m, 30H), 2.034 (tddd, J = 7.0, 7.0, 1.7, 1.4 Hz, 6H, H CCH−
°C. After the excess H gas was released, the mixture was filtered to
2
2
CH −), 3.668 (septet, J = 3.2 Hz, 1H, SiH), 4.918 (ddt, J = 6.8, 2.4,
remove Pd/C. The volatile materials were removed in vacuo. Fractions
containing 2 and 2i were collected using GPC with chloroform as the
solvent. Pure compounds 2 (0.080 g, 0.09 mmol, 10% yield) and 2i
(0.351 g, 0.40 mmol, 43% yield) were obtained after removal of the
solvent in vacuo. Compound 2: colorless crystals, mp 143.3−143.9 °C.
2
1
.4 Hz, 6H, terminal H C), 4.982 (ddt, J = 16.8, 2.4, 1.5 Hz, 6H,
2
terminal H C), 5.802 (ddt, J = 16.8, 10.4, 6.8 Hz, 6H, H CCH−).
2
2
1
3
C NMR (CDCl , 100 MHz): δ 11.31, 24.67, 28.97, 29.06, 29.17,
3
29
3
3.30, 33.81, 114.08 (−CHCH ), 139.16 (−CHCH ). Si NMR
2
2
1
(
CDCl , 79.5 MHz): δ −6.44. Anal. Calcd for C H Si: C, 80.11; H,
H NMR (CDCl , 400 MHz): δ 0.71−0.78 (m, 12H, SiCH ), 1.18−
3
27 52
3
2
13
1
2.95. Found: C, 80.00; H, 13.32.
1.40 (m, 84H), 7.47 (s, 4H, aromatic CH). C NMR (CDCl , 100
3
Synthesis of 1,4-Bis(tri-6-heptenylsilyl)benzene (5). a. Prep-
MHz): δ 12.42, 23.23, 27.69, 28.12, 28.22, 28.79, 28.89, 32.89, 133.43
aration of the Chlorosilane. CuCl (11.02 g, 82 mmol) and CuI (0.06
29
2
(aromatic CH), 138.02 (SiC). Si NMR (CDCl , 79.5 MHz): δ
3
g, 0.3 mmol) were placed into a two-neck round-bottom flask (300
mL) equipped with a magnetic stirrer, a condenser, and a dropping
funnel. Dry THF (150 mL) was added into the flask. After dropwise
addition of 13 (12.8 g, 40 mmol) into the reaction flask, the mixture
was stirred at rt for 12 h. The volatile materials were removed under
reduced pressure. Anhydrous hexane (∼50 mL) was added to the
residual mixture, and cuprous halide was filtered off using Celite.
Evaporation of the filtrate afforded 9 (13.36 g, 94% yield) in 80%
−
2.14. Anal. Calcd for C H Si : C, 80.51; H, 12.51. Found: C,
0.40; H, 12.51. Compound 2i: colorless oil, bp >300 °C. H NMR
54 100 2
1
8
(
CDCl , 400 MHz): δ 0.65−0.72 (m, 4H, SiCH ), 0.73−0.90 (m, 8H,
3
2
SiCH ), 1.15−1.25 (m, 28H), 1.25−1.42 (m, 56H), 7.43 (s, 4H,
aromatic CH). C NMR (CDCl , 100 MHz): δ 11.89 (4C), 13.19
2
13
3
(2C), 23.05 (4C), 23.63 (2C), 27.10 (4C), 27.61 (4C), 27.64 (2 ×
4
2
C), 27.72 (2C), 27.98 (4C), 28.26 (2C), 28.31 (2C), 28.37 (2C),
8.57 (2C), 32.59 (4C), 33.40 (2C), 133.22 (aromatic CH), 138.40
1
purity as determined by H NMR spectroscopy, and the corresponding
29
(
SiC). Si NMR (CDCl , 79.5 MHz): δ −1.93. Anal. Calcd for
5
3
siloxane was obtained as a hydrolyzed product. Further purification
was not carried out because of the compound’s high boiling point and
hydrolyzability.
b. Synthesis of the Bis(silyl)benzene. p-Dibromobenzene (2.1 g, 9.0
mmol) and dry THF (20 mL) were placed in a Schlenk flask (100
mL). A tert-BuLi solution (1.6 M in pentane, 22 mL, 4.0 equiv) was
added dropwise to the solution at −78 °C. The reaction mixture
turned yellow and was stirred for an additional 1 h at −78 °C. The
reaction mixture was warmed to 0 °C, and then chlorosilane 9 (6.5 g,
C H Si : C, 80.51; H, 12.51. Found: C, 80.56; H, 12.85.
4
100
2
RCM of Compound 5 for Synthesis of Molecular Gyrotop 4.
The RCM reaction of bis(silyl)benzene 5 and subsequent hydro-
genation was investigated using the same procedure as for the
synthesis of 2. However, only polymeric products were obtained, and
the desired molecular gyrotop 4 and its isomer 4i were not formed at
all.
X-ray Crystallographic Analysis of Molecular Gyrotop 2. The
diffraction data of molecular gyrotop 2 were collected using graphite-
monochromatized Mo Kα radiation (λ = 0.71069 Å). Crystallographic
1
8.3 mmol) was added. After 12 h of stirring at rt, the mixture was
hydrolyzed with dilute HCl(aq) and extracted with hexane. The
data for 2 (270 K): monoclinic, Cc, a = 28.51(6) Å, b = 12.34(2) Å, c =
organic layer was washed with saturated NaHCO (aq) and dried over
3
3
1
7.98(4) Å, β = 121.13(2)°, V = 5414(18) Å , R = 0.12.16 [I >
1
anhydrous Na SO . Concentration and column chromatography
2
4
2
σ(I)], wR2 = 0.4879 (all data). The crystallographic data were
[
=
Merck silica gel 60, particle size 63−200 μm, hexane as eluent (R
f
deposited at the Cambridge Crystallographic Data Centre (CCDC-
1003587). The X-ray crystallographic analyses of 1, 3 and 3i were
reported previously, and the data were deposited in the CCDC as
follows: CCDC-830990 for 1, CCDC-988815 for 3, and CCDC-
0.5)] of the residue afforded 5 as a colorless oil (4.4 g, 6.2 mmol,
1
6
9% yield). H NMR (CDCl , 400 MHz): δ 0.74−0.81 (m, 12H,
3
5a,d
SiCH ), 1.28−1.42 (m, 36H), 2.016 (tddd, J = 7.0, 6.8, 1.7, 1.4 Hz,
1
2
2H, H CCH−CH −), 4.926 (ddt, J = 10.4, 2.4, 1.4 Hz, 6H,
2
2
9
88816 for 3i. 2
terminal H C), 4.989 (ddt, J = 16.8, 2.4, 1.7 Hz, 6H, terminal
2
Solid-State H NMR Analysis of Molecular Gyrotops 2-d and
4
H C), 5.804 (ddt, J = 16.8, 10.4, 6.8 Hz, 6H, H CCH−), 7.431
2
2
2
1
3
3-d
4
. The temperature-dependent solid-state H NMR spectra of 2-d
4
(
s, 4H, C H ). C NMR (CDCl , 100 MHz): δ 12.39, 23.65, 28.51,
6 4 3
and 3-d were investigated using the same procedure as reported
previously for 1-d
4
3
3.25, 33.74, 114.11 (−CHCH ), 133.23 (aromatic CH), 138.31
2
5d
29
4
.
The details are as follows. The data were
(
SiC), 139.16 (−CHCH ). Si NMR (CDCl , 79.5 MHz): δ −2.33.
2
3
recorded using a quadrupolar echo pulse sequence (d −90° pulse−τ −
1
1
Anal. Calcd for C H Si : C, 80.59; H, 11.55. Found: C, 80.36; H,
48 82 2
9
0° pulse−τ −FID; 90° pulse = 4.2 μs, τ = 30 μs, τ = 20 μs, d = 20
2
1
2
1
1
1.30.
Synthesis of 1,4-Bis(tri-8-nonenylsilyl)benzene (7). Com-
pound 7 was synthesized from 15 using the same procedure as for
. Pure compound 7 (4.4 g, 0.5 mmol, 55% yield) was obtained as a
2
s). Simulations of the H NMR spectra were performed using NMR-
1
0a
WEBLAB. The following parameters were used for the simulations:
quadrupolar coupling constant (q ) = 130 kHz, asymmetry parameter
(η) = 0, line broadening = 3 kHz. The temperature dependence of the
spin−lattice relaxation time (T ) in the H NMR spectra was recorded
using an inversion−recovery quadrupolar echo pulse sequence (d −
5
cc
1
colorless oil. H NMR (CDCl , 500 MHz): δ 0.750 (t, J = 7.5 Hz,
3
2
1
2H, SiCH ), 1.20−1.40 (m, 48H), 2.019 (tddd, J = 7.0, 6.8, 1.7, 1.4
1
2
Hz, 12H, H CCH−CH −), 4.914 (ddt, J = 10.4, 2.4, 1.4 Hz, 6H,
1
2
2
1
80° pulse−d −90° pulse−τ −90° pulse−τ −FID; 90° pulse = 4.2 μs,
terminal H C), 4.976 (ddt, J = 16.8, 2.4, 1.7 Hz, 6H, terminal
2
1
2
2
τ = 30 μs, τ = 20 μs, d = 5−3 s, d varied) and standard T analysis
H C), 5.794 (ddt, J = 16.8, 10.4, 6.8 Hz, 6H, H CCH−), 7.412
1
2
1
2
1
2
2
1
3
software. The spin−lattice relaxation rate is known to depend on the
(
s, 4H, C H ). C NMR (CDCl , 125.8 MHz): δ 12.48, 23.82, 28.98,
6 4 3
motional model for the exchange process. Several special types of
2
9.09 (overlapped), 33.76, 33.83, 114.10 (−CHCH ), 133.23
2
1
2
2
9
motions have been discussed to date. Further detailed investigations
are required for the determination of parameters for the appropriate
special model.
(
(
1
aromatic CH), 138.44 (SiC), 139.23 (−CHCH ). Si NMR
2
CDCl , 99 MHz): δ −2.39. Anal. Calcd for C H Si : C, 81.55; H,
3
60 106
2
2.09. Found: C, 81.75; H, 12.22.
Synthesis of Molecular Gyrotop 2. A dichloromethane solution
200 mL) of 7 (0.800 g, 0.9 mmol) was added dropwise with stirring
DFT Calculations for Molecular Gyrotops. The molecular
structures were optimized using Gaussian 09, revision D.01, and the
initial coordinates of atoms were taken from the single-crystal X-ray
analysis data. The structural parameters of the optimized structures are
shown in the Supporting Information. In the calculations of the
rotational potentials of the phenylene ring in molecular gyrotops 1−3,
the coordinates of the cages and two ipso carbons were fixed to those
in the optimized structure, and the coordinates of the residual four
phenylene CH atoms were optimized at various dihedral angles θ.
(
over 12 h at 40 °C to a solution of dichloromethane (600 mL) in the
presence of Grubbs’ first-generation catalyst (0.02 g, 0.02 mmol).
During the reaction, the catalyst (0.02 g, 0.06 mmol) was added to the
flask twice (every 2 h). The mixture was stirred for a further 8 h. The
volatile materials were removed in vacuo, and the benzene-soluble
fraction was treated by flash column chromatography (silica gel,
benzene) to remove the metal catalysts. The fraction contained
F
dx.doi.org/10.1021/jo501539h | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
J. Am. Chem. Soc. 2002, 124, 7719. (d) Dominguez, Z.; Khuong, T. A.
V.; Sanrame, C. N.; Dang, H.; Nunez, J. E.; Garcia-Garibay, M. A. J.
̃
ASSOCIATED CONTENT
Supporting Information
Copies of NMR spectra for all new compounds (2, 2i, 5, 7, 13,
and 15), details of the solid-state H NMR study of 2-d and 3-
d , atomic coordinates from DFT calculations on 1−3, and a
CIF file for compound 2. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
*
S
Am. Chem. Soc. 2003, 125, 8827. (e) Horansky, R. D.; Clarke, L. I.;
Winston, E. B.; Price, J. C.; Karlen, S. D.; Jarowski, P. D.; Santillan, R.;
Garcia-Garibay, M. A. Phys. Rev. B 2006, 74, No. 054306. (f) Horansky,
R. D.; Clarke, L. I.; Price, J. C.; Khuong, T.-A. V.; Jarowski, P. D.;
Garcia-Garibay, M. A. Phys. Rev. B 2005, 72, No. 014302.
(g) Vogelsberg, C. S.; Bracco, S.; Beretta, M.; Comotti, A.; Sozzani,
P.; Garcia-Garibay, M. A. J. Phys. Chem. B 2012, 116, 1623.
2
4
4
(
h) Czajkowska-Szczykowska, D.; Rodríguez-Molina, B.; Magan
Vergara, N. E.; Santillan, R.; Morzycki, J. W.; Garcia-Garibay, M. A. J.
Org. Chem. 2012, 77, 9970. (i) Rodríguez-Molina, B.; Perez-Estrada,
̃
a-
AUTHOR INFORMATION
Corresponding Author
E-mail: wsetaka@tmu.ac.jp.
■
́
*
S.; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2013, 135, 10388.
Notes
(j) Rodríguez-Molina, B.; Ochoa, M. E.; Romero, M.; Khan, S. I.;
Farfan
́
, N.; Santillan, R.; Garcia-Garibay, M. A. Cryst. Growth Des.
pfl,
The authors declare no competing financial interest.
2
013, 13, 5107. (k) Torres-Huerta, A.; Rodríguez-Molina, B.; Ho
̈
H.; Garcia-Garibay, M. A. Organometallics 2014, 33, 354. (l) Jiang, X.;
Rodríguez-Molina, B.; Nazarian, N.; Garcia-Garibay, M. A. J. Am.
Chem. Soc. 2014, 136, 8871−8874.
ACKNOWLEDGMENTS
■
This work was supported by a JSPS Grant-in-Aid for Scientific
Research (B) (25288042) and the Kurata Memorial Hitachi
Science and Technology Foundation.
(7) (a) Bastien, G.; Lemouchi, C.; Wzietek, P.; Simonov, S.; Zorina,
L.; Rodríguez-Fortea, A.; Canadell, E.; Batail, P. Z. Anorg. Allg. Chem.
014, 640, 1127. (b) Lemouchi, C.; Yamamoto, H.; Kato, R.;
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dx.doi.org/10.1021/jo501539h | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
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dx.doi.org/10.1021/jo501539h | J. Org. Chem. XXXX, XXX, XXX−XXX