Synthesis and evaluation of molecular rotors with large and bulky tert-butyldiphenylsilyloxy-substituted trityl stators

Article abstract of DOI:10.1021/jo301078a

The search for voluminous stators that may accommodate large rotator units and speed rotational dynamics in the solid state led us to investigate a simple and efficient method for the synthesis of molecular rotors with tert-butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators. Additionally, solid state characterization of these systems with two-, four-, and six-TBDPS groups provided us with a description of their crystallinity and thermal stability. Among them, molecular rotor 7c with the largest and most symmetric stator resulting from six peripheral silyl groups showed the best tendency to crystallize, and the study of its isotopologue 7c-d₄ by solid state ²H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-d ₄ rotator in the kHz regime.

Full text of DOI:10.1021/jo301078a

Article
pubs.acs.org/joc
Synthesis and Evaluation of Molecular Rotors with Large and Bulky
tert-Butyldiphenylsilyloxy-Substituted Trityl Stators
Rafael Arcos-Ramos,† Braulio Rodríguez-Molina,‡ Margarita Romero,† J. Manuel Mendez-Stivalet,†
́
María Eugenia Ochoa,§ Pedro I. Ramírez-Montes,§ Rosa Santillan,§ Miguel A. Garcia-Garibay,*,‡
and Norberto Farfan*,†
́
†Facultad de Química, Departamento de Química Organ
́
ica, Universidad Nacional Auton
‡Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
§Departamento de Química, Centro de Investigacion
y de Estudios Avanzados del IPN, Mexico D.F. Apdo. Postal 14-740, 07000,
Mexico
́ ́ ́ ́
oma de Mexico, 04510 Mexico D.F., Mexico
́
́
́
S
* Supporting Information
ABSTRACT: The search for voluminous stators that may
accommodate large rotator units and speed rotational
dynamics in the solid state led us to investigate a simple and
efficient method for the synthesis of molecular rotors with tert-
butyldiphenylsilyl-protected (TBDPS) triphenylmethyl stators.
Additionally, solid state characterization of these systems with
two-, four-, and six-TBDPS groups provided us with a
description of their crystallinity and thermal stability. Among
them, molecular rotor 7c with the largest and most symmetric
stator resulting from six peripheral silyl groups showed the best
tendency to crystallize, and the study of its isotopologue 7c-d4
2
by solid state H NMR revealed a 2-fold motion of the 1,4-diethynylphenylene-d4 rotator in the kHz regime.
INTRODUCTION
■
The study and control of rotational motion at the molecular
scale is attractive for the development of functional materials
with functions that can be traced to mechanical processes at the
macroscopic level.1,2 In recent years, our group has focused on
the design, synthesis, and dynamic characterization of
amphidynamic crystals,3 built with components that form an
ordered rigid framework linked to structural elements that are
able to experience fast internal motion. Although the
conjunction of phase order and rapid dynamics are intuitively
regarded as mutually exclusive in condensed-phase matter, we
and others have shown that internal motion in crystalline solids
may be successfully engineered by taking advantage of several
suitable platforms and fine-tuned structures.3a,4 In our group,
we have explored a series of molecular rotors intended to
emulate the structure and function of macroscopic gyroscopes.
The blueprints for molecular rotors that can form
amphidynamic molecular crystals require three essential
elements: (1) a mobile part, or rotator, that performs the
rotary motion, (2) an ideally barrierless axle, that connects the
rotator to the stator, and (3) a bulky static group acting as the
shielding framework to take the role of a stator (Figure 1). The
characterization of their internal molecular dynamics using
several solid state NMR techniques has shown that their
rotational frequencies can reach the GHz regime. It has been
shown, experimentally3,5 and computationally,6 that the
frequency and geometry of motion of the rotator frequently
Figure 1. Diagram showing the analogy between macroscopic and
molecular gyroscopes.
depend on the close contacts with neighboring rotors or
intermolecular interactions with solvent molecules within the
crystal lattice. Current efforts to control the frequency of the
internal motion are based on the use of rotators with higher
axial symmetry to reduce rotational barriers7 and on changes in
Received: May 24, 2012
© XXXX American Chemical Society
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Scheme 1
the architecture of the static components to isolate the rotary
parts. The latter approach comprises the study of several stator
structures, including substituted triptycenes,7 substituted trityl
groups,8,9 steroids,10 and the use of porous solids, such as
metal−organic frameworks (MOFs).11
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Substituted trityl
alcohols 5a−c with the tert-butyldiphenylsilyl protecting groups
in meta-position were obtained by lithiation with n-butyllithium
of previously reported (3-bromophenoxy)-tert-butyldiphenylsi-
lane 116 and subsequent reaction with the appropriate carbonyl
compound 2−4 as outlined in Scheme 1. The reaction with
benzophenone 2 gave alcohol 5a in 88% yield. Similarly, trityl
alcohols 5b and 5c were isolated pure in 82 and 80% starting
from methyl benzoate 3 and diethyl carbonate 4, respectively.
For compounds 5a−c, the IR spectra showed O−H hydroxyl
stretching broad bands between 3567 and 3446 cm−1. They
also presented characteristic signals in 1H NMR that
correspond to the proton in the −OH group at δ = 2.60−
2.18 and those from the tert-butyl group at δ = 1.07. Solution
13C NMR experiments for compounds 5a−c revealed signals at
δ = 155.3 that confirm the phenoxy-substituted carbon atom
and two signals in the aliphatic region ca. 26.8 and 19.6 ppm
corresponding to the tert-butyl substituent from the quaternary
and methyl carbons, respectively. Additionally, 29Si NMR
spectra of these compounds showed a singlet between δ =
−5.13 and −5.29 that corroborates the presence of the silane
groups.
Considering that the relatively large dimensions of
biomolecular rotors such as the bacterial flagellum (cross-
section ca. 20−40 nm)12 and ATP synthase (cross-section ca. 8
nm)13 may be essential for their complex function, we believe
that one of the most interesting structural variables in the field
of artificial molecular rotors will be an increase in the size of the
molecular components.1,4,14 With that in mind, we begun a
search for simple strategies that produce much larger molecular
stators that may be able to shield and support the motion of
significantly larger molecular rotators. In this paper we report
the synthesis of molecular rotors with tert-butyldiphenylsilyl-
protected triphenylmethyl stators. The desired structures place
the tert-butyldiphenylsilyl functionalities (TBDPS) on the meta-
position of the phenyl rings in the trityl groups to increase the
molecular volume and steric shielding around the rotator. We
selected the bulky silyloxy groups due to their potentially
simple installation using a modular and convergent synthetic
approach. The selection of TBDPS, in particular, was based on
its large size and higher stability under acidic or basic
conditions as compared to that of other silyl-protecting
groups.15 We report here the synthesis of symmetric molecular
rotors 7a−c with one, two, or three protecting groups in each
half of the stator and a small phenylene rotator, by following a
simple four step methodology. After establishing the solid state
properties and crystallinity of all the samples, the hexasilyl-
substituted derivative 7c, with a molecular weight of 2137.2
amu, gave the most promising crystals, which were selected to
explore the internal dynamics of the rotator in the solid state by
taking advantage of quadrupolar echo 2H NMR. The 2H NMR
line shape of phenylene-labeled 7c-d4 obtained at 298 K
suggested that the 1,4-diethynylphenylene rotator undergoes a
2-fold flip motion with a frequency in the kilohertz regime.
Alcohols 5a−c were subsequently converted into their
alkynyl derivatives by a two-step sequence that involves the
exchange of the −OH group to −Cl using HCl in a solution of
the compounds 5a−c in CH2Cl2. The resultant solid was
dissolved and reacted with ethynylmagnesium bromide, to give
the desired alkyne compounds 6a−c with moderate yields
between 59 and 77%. The infrared analysis of compounds 6a−c
showed a band in the region 3304−3296 cm−1 attributable to
the stretching of the C−H bond in free alkynes. In addition to
1
the signals from the aromatic stator, the H NMR spectra
presented a singlet in the interval δ = 2.55−2.20 ppm from the
proton in the alkyne group. The same functional group is
responsible for the signals at ca. 89 and 73 ppm in 13C NMR in
all derivatives. Additional structural information may be
gathered from the crystal structure of compound 6a, which
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Scheme 2
Scheme 3
crystallizes from hexanes/ethyl acetate in a P21/c space group
(see Table S1, Supporting Information).
9a and 9c as main products (50 and 90% yield, respectively),
with the homocoupling product 9c easily crystallizing after
The alkynes 6a−c were further reacted with 1,4-diiodoben-
zene to afford the desired molecular rotors 7a−c using the
Sonogashira cross coupling method with Pd(0) under N2
atmosphere; each reaction gave moderate yields of ca. 75%.
In addition to the desired rotors, monocoupled compounds
8a−c were also obtained as minor products. High resolution
mass spectrometry confirmed the synthesis of desired
molecular rotors 7a−c, with observed peaks at m/z
1119.4974, 1627.7207, and 2135.9479 that match with the
expected molecular ions for molecules with two, four, and six
silyl-protecting groups, respectively. Compound 7c has the
largest formula weight of all the compounds studies in our
group to date, with a bis(tri-(meta-terphenyl)methyl) derivative
that has a FW = 1523.94 as a relatively distant second. The
synthesis of molecular rotors 7a−c from alkynes 6a−c was also
corroborated by 13C NMR spectroscopy, where two additional
signals coming from the central phenylene ring appeared at ca.
131 (CH carbons) and 123 ppm (ipso carbons). Furthermore,
29Si NMR confirms the presence of the silyl protecting groups,
with chemical shifts at −4.81, −5.01, and −5.16 ppm. On the
other hand, monocoupling products 8a−c were readily
identified by the characteristic 13C NMR signal approximately
at 93 ppm that corresponds to the aryl-iodide substitution.
In order to study the internal dynamics of 7c by means of 2H
solid state NMR, we pursued the synthesis of the deuterated
analogue 7c-d4 (Scheme 2). This molecular rotor was obtained
from the reaction of compound 6c with 1,4-diiodobenzene-d4,
prepared as described in the literature.17
column with its structure solved in the space group P1 (see
Table S1, Supporting Information).
̅
Detailed inspection of the crystalline packing of homocou-
pling product 9c showed that the silyl-protecting groups fold
toward the dialkynyl axis. The puckered array may be favored
by intramolecular interactions of the C−H···π type between
phenyl rings in the TBDPS moieties lying in the opposite trityl
fragment. This conformation of the silyl groups allowed the
presence of six-phenyl embrace interactions (6PE) between
adjacent molecules as shown in Figure 2. The observation that
Figure 2. Diagram of the homocoupling compound 9c showing the
collinear intermolecular interaction between trityl groups in blue,
forming a six-phenyl embrace. The tert-butyldiphenyl fragments in
green accommodate around the butadiyne molecular axis, shown here
in red.
It is important to note that initial reactions using the same
Sonogashira coupling conditions but longer reaction times
between alkynes 6a and 6c with commercially available 1,4-
dibromobenzene-d4 (Scheme 3) afforded dialkynyl compounds
C
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the adopted conformation of a given substituent could permit
or interfere with the 6PE was previously examined by Dance et
al. in a detailed manner.18 It is interesting to note that the
CH···π interactions found in compound 9c (and also in
derivative 6c) fall into the commonly observed type III
classification introduced by Malone et al.,19 significantly
deviated from an ideal T geometry. The occurrence of this
geometry is attributed to the shallow potential, which allows
many binding arrangements of similar energy.
As mentioned above, powder X-ray diffraction analysis was
employed to explore the crystallinity of samples 7a, 7b, and 7c-
d4, and it was also used to select the samples that were later
studied by solid state NMR. The powder pattern from
compound 7a showed broad Bragg diffraction peaks in the
4−50 degrees (2θ) range indicating low crystallinity of the
sample. The X-ray diffractogram of 7b was consistent with an
amorphous solid, with a broad featureless pattern. Conversely,
freshly recrystallized samples of 7c−d4 from a saturated
dichloromethane solution presented a powder pattern with
sharp peaks between the 4−50 degrees (2θ) range that agrees
very well with the calculated20,21 diffractogram obtained from
the structural model proposed above (Figure 3b), giving us
confidence that our model is qualitatively correct.
Solid State Characterization. Calorimetric and X-ray
Diffraction Experiments. Recrystallized samples of compounds
7a−c were studied by differential scanning calorimetry and
thermogravimetric analysis to ascertain their thermal stability
upon heating in the range 25−300 °C. Compounds 7a and 7c
solidified after their respective purification steps, but compound
7b formed an oil that could be solidified only at low
temperatures. A common feature observed in all DSC
experiments is a broad, endothermic transition starting about
40 °C that was correlated to the loss of dichloromethane
according to TGA experiments. After desolvation, compound
7a melts at 178−182 °C, in agreement with the visual
observation of the melting point. A third endothermic
transition occurs between 190 and 195 °C, which was
attributed to decomposition of the sample. Solid samples of
7b showed no additional transitions after the solvent loss as the
compound gradually became an oil. Compound 7c and its
deuterated analogue were crystallized from dichloromethane.
From the DSC trace, after the initial endothermic transition
ascribed to loss of solvent, a peak corresponding to the melting
process was observed beginning at 97 °C and ending at 114 °C.
Although no high quality single crystals from molecular
rotors 7a−c have been obtained, crystallization attempts with
dichloromethane yielded weakly diffracting crystals of com-
pound 7c. The structure was solved in the space group P21/c
and confirmed the connectivity of the desired molecular rotor
(Figure 3a). The structure contained considerable degree of
Solid State NMR Experiments. The analysis and 13C NMR
characterization in solution of silyl-protected molecular rotors
7a−c revealed a highly congested aromatic region in the spectra
that would prevent a detailed line shape analysis using variable
temperature solid state NMR. 13C NMR CPMAS experiments
at room temperature of the molecular rotor 7a confirmed this
assumption. To circumvent this, crystalline samples of
molecular rotor 7c-d4 synthesized as described above were
2
studied using H NMR spin echo line shape analysis.
Deuterium solid state NMR is a technique widely used to
describe rotational dynamics in molecular crystals because the
quadrupolar moment of the deuterium nucleus gives rise to
quadrupole coupling constants in the 140−220 kHz range,
which results in linewidths that are very highly sensitive to
nuclear motion over a wide dynamic range.22 The pattern of a
single crystal with only one type of C−2H bond with a
symmetric quadrupolar tensor would give a doublet with a
quadrupolar splitting Δν that depends on the orientation angle
β that the bond makes with respect to the external field:
Δν = 3/4(e2qzzQ /h)(3 cos2 β − 1)
= 3/4(QCC)(3 cos2 β − 1)
The variable Q represents the electric quadrupole moment of
the deuterium, e and h are the electric charge and Planck
constant, and qzz is the magnitude of the principal component
of electric field gradient tensor, which lies along the C−2H
bond. The technique is based on the analysis of the changes in
the shape of the powder spectrum at different temperatures.
The line shape of the powder pattern is sensitive to the
frequency and geometry of molecular motions with correlation
times of the order of 104 to 107 Hz. Variations in line shape can
be described with angular displacements of the C−2H bonds
between specific sites in purposely enriched samples.
Spin echo experiments at room temperature of compound
7c-d4 showed a poor signal-to-noise ratio even at higher
number of transients (ca. 80 000). The central phenylene in the
molecule with 98 atom % D, represents only 0.37% of the total
mass of the sample. In spite of this dilution, the experimental
signal was used to establish a qualitative reference of the
molecular dynamics using a conic model based on a 180° jump
motion. Knowing that deuterium line shape from samples with
slow exchanging components (frequencies <10 kHz) display a
Pake pattern with peaks splitting by ca. 130−132 kHz (Figure
4b, bottom), it was observed that the central phenylene in 7c-d4
is not completely static. As shown in Figure 4b (middle), the
line shape at ambient temperature could be approximately
simulated23 using a 2-fold flip model with a rotational frequency
that is higher than 10 kHz but lower than the ca. 10.0 MHz
Figure 3. (a) Space filling model showing only one molecule of the
highly disordered compound 7c with the central 1,4-diethynylpheny-
lene fragment in red, the trityl groups in blue, and the protecting
groups in green. (b) Comparison between the calculated (top, red)
and experimental powder X-ray patterns of solid samples of 7c-d4 from
dichloromethane (bottom, blue).
disorder, particularly severe in the tert-butyldiphenylsilyl
groups, and could not be further refined to acceptable
publication standards. Nevertheless, the coordinates of the
proposed model were employed to calculate the X-ray powder
pattern and determine the identity of the bulk solids prior to
solid state spectroscopic studies.
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1401, 1328, 1112, 935, 777, 701, 614, 515; 1H NMR (300 MHz,
CDCl3) δ 7.79−7.76 (4H, m), 7.53−7.41 (6H, m), 7.09 (1H, t, J = 2.0
Hz), 7.06 (1H, ddd, J = 8.0, 2.0, 1.0 Hz), 6.94 (1H, t, J = 8.0 Hz), 6.59
(1H, ddd, J = 8.0, 2.0, 1.0 Hz), 1.17 (9H, s); 13C NMR (75.5 MHz,
CDCl3) δ 156.6, 135.7, 132.5, 130.4, 130.3, 128.1, 124.5, 123.4, 122.6,
118.6, 26.7, 19.7; 29Si NMR (59.6 MHz, CDCl3) δ −4.55; MS (DIP)
412 ([M + 1]+, 29), 411 (M+, 0.6), 356 (24), 355 (100), 354 (24), 353
(93), 277 (10) 274 (11), 273 (12). Anal. Calcd for C22H23BrOSi: C,
64.23; H, 5.63. Found: C, 64.17; H, 5.87.
[3-(tert-Butyl-diphenyl-silanyloxy)-phenyl]-diphenyl-metha-
nol (5a). A solution of 1 (3.00 g, 7.3 mmol) in freshly distilled THF
(50 mL) was cooled down to −78 °C in a dry ice bath. Subsequently,
n-butyllithium (3.2 mL, 2.5 M in hexanes, 8.0 mmol) was added
dropwise, and the reaction mixture was stirred for 30 min at −78 °C.
Then, benzophenone 2 (1.33 g, 7.3 mmol) dissolved in dry THF (50
mL) was added. After stirring for 2 h at −78 °C, the reaction was
quenched with saturated solution of NH4Cl. The aqueous phase was
extracted with CH2Cl2, and the organic phase was dried over
anhydrous Na2SO4. Purification on silica gel column chromatography,
eluting with hexane/ethyl ether (200:3) yielded compound 5a (3.50 g,
93%) as a white crystalline solid: mp 88−89 °C; IR (KBr) ν 3567,
3447, 3058, 2930, 2858, 1596, 1481, 1428, 1391, 1286, 1255, 701, 614,
Figure 4. (a) Cone model employed to describe the motion of the
phenylene ring between two sites related by 180°. (b) Calculated
deuterium lineshapes from a rotator undergoing 2-fold flips in the fast
exchange (top) and static regime (bottom). In the middle,
experimental line shape of 7c-d4 situated in the intermediate regime
(the dotted line, included as visual reference, represents a 150 kHz
frequency motion).
1
498; H NMR (270 MHz, CDCl3) δ 7.62 (4H, d, J = 7.1 Hz), 7.41−
limit of the fast exchange regime, which is shown in the top
frame of Figure 4b. This type of low frequency motion
observed in 7c-d4 has been also reported in molecular rotors
containing smaller stators and high activation barriers that
result from several intermolecular contacts,3a which could be
the case in the present system.
7.38 (2H, m), 7.34−7.29 (4H, t, J = 7.1 Hz), 7.21−7.19 (6H, m),
7.07−7.05 (5H, m), 6.84 (1H, d, J = 7.5 Hz), 6.77 (1H, d, J = 8.0 Hz),
6.58 (1H, d, J = 1.6 Hz), 2.60 (1H, s), 1.07 (9H, s, C(CH3)3); 13C
NMR (67.9 MHz, CDCl3) δ 155.3, 148.3, 146.7, 135.7, 132.9, 130.0,
129.0, 127.9, 127.9, 127.8, 127.2, 120.7, 120.1, 118.8, 81.9, 26.8, 19.6;
29Si NMR (59.6 MHz, CDCl3) δ −5.13; HRMS (APCI-TOF) Calcd
for C35H35O2Si−H2O, 497.2295, found 497.2290, error 1.04 ppm; MS
(DIP) 515 ([M + 1]+, 4), 514 (M+, 8), 458 (38), 457 (100), 361 (24),
301 (10), 259 (19). Anal. Calcd for C35H34O2Si: C, 81.67; H, 6.66.
Found: C, 81.71; H, 6.61.
CONCLUSIONS
■
We have synthesized molecular rotors 7a−c with one, two, and
three tert-butyldiphenylsilyl groups in each of the two trityl
groups of the stator using an effective four step methodology,
which also proved the high stability of the bulky silyl groups.
Samples with the small diethynyl phenylene rotator were
characterized by the inclusion of solvent molecules, which were
able to escape under normal temperature and pressure, making
the crystals difficult to maintain and characterize. It was shown
that the sample with three silyl substituents on each end of the
molecule, 7c, gives the most promising crystals, highlighting the
importance of symmetry in the crystallization of these relatively
large compounds. After showing that a relatively low quality
crystal structure of 7c resulted in a calculated powder X-ray
diffraction pattern that is nearly identical to the one obtained
from experiment, we decided to explore the rotational
dynamics of the central phenylene of 7c using solid state
NMR. Knowing that the large number of aromatic rings would
limit the information available from solid state 13C NMR, we
tert-Butyl-[3-(1,1-diphenyl-prop-2-ynyl)-phenoxy]-diphenyl-
silane (6a). Hydrochloric acid gas (generated in situ by dropwise
addition of H2SO4 to NaCl) was slowly bubbled through a solution of
alcohol 5a (0.77 g, 1.5 mmol) in CH2Cl2 (50 mL) at room
temperature. After 5 h stirring, the solvent was completely removed at
reduced pressure, and the solid was redissolved in benzene (25 mL);
ethynylmagnesium bromide (6.0 mL, 0.5 M in THF, 3.0 mmol) was
then added, and the reaction was stirred at room temperature over 48
h. After this time, the reaction was quenched by addition of saturated
NH4Cl, the organic phase was extracted twice with CH2Cl2, and the
combined organic portions were dried over anhydrous Na2SO4.
Column chromatography purification on silica gel, with hexane/ethyl
ether (200:1) yielded compound 6a (0.60 g, 77%) as a white
crystalline solid: mp 143−145 °C; IR (KBr) ν 3303, 3071, 2932, 2859,
1
1596, 1488, 1428, 1262, 1113, 884, 742, 698; H NMR (270 MHz,
CDCl3) δ 7.59−7.56 (4H, d, J = 7.4 Hz), 7.42−7.24 (6H, m), 7.17−
7.11 (6H, m), 7.09−6.98 (5H, m), 6.88 (1H, d, J = 7.8 Hz), 6.76 (1H,
d, J = 8.1 Hz), 6.55 (1H, s), 2.55 (1H, s), 1.04 (9H, s); 13C NMR
(67.9 MHz) δ 155.3, 145.9, 144.6, 135.7, 132.8, 129.8, 129.0, 128.0,
127.8, 126.8, 122.0, 121.1, 118.5, 89.6, 73.4, 55.3, 26.7, 19.5; 29Si NMR
(53.6 MHz, CDCl3) δ −4.95; HRMS (APCI-TOF) Calcd for
C37H35OSi, 523.2442, found 523.2451, error 2.34 ppm; MS (DIP)
523 ([M + 1]+, 3), 522 (M+, 8), 466 (20), 465 (47), 388 (33), 387
(100), 309 (23), 265 (15). Anal. Calcd for C37H34OSi: C, 85.01; H,
6.56. Found: C, 85.06; H, 6.29.
1,4-Bis-{[(3-(tert-butyl-diphenyl-silanyloxy)-diphenyl)-phe-
nylmethyl]-ethynyl}-phenylene (7a). A mixture of 1,4-diiodoben-
zene (0.095 g, 0.3 mmol), alkyne 6a (0.30 g, 0.6 mmol) Pd(PPh3)2Cl2
(0.021 g, 0.03 mmol), CuI (0.011 g, 0.06 mmol) and diisopropyl
amine (0.5 mL) in THF (25 mL) previously degassed was refluxed for
2.5 h. After this time, the reaction was cooled down to room
temperature and quenched with saturated NH4Cl. The organic phase
was twice extracted with CH2Cl2, and the combined organic portions
were dried over anhydrous Na2SO4. The solvent was removed at
reduced pressure followed by purification by column chromatography
on neutral alumina, eluting with hexane/ethyl ether (199:1) to afford
0.24 g (74%) of rotor 7a as a white crystalline solid: mp 183−184 °C;
2
investigated the rotational dynamics of 7c using solid state H
NMR with the deuterated analogue 7c-d4. Although a complete
description of the internal motion by solid state H NMR was
2
not practical because of the high dilution of the deuterons
(0.37%) and the low stability of the solvent-containing crystals,
the experimental line shape showed that the rotation of the
central phenylene occurs in the intermediate regime, with the
1,4-diethynylphenylene-d4 rotator undergoing 180° jumps at ca.
150 kHz. We conclude from these studies that more symmetric
silyl derivatives in the most symmetric conformations may
provide suitable stators for a new generation of molecular
rotors that have larger rotating units.
EXPERIMENTAL SECTION
(3-Bromo-phenoxy)-tert-butyl-diphenyl-silane (1). The com-
pound 1 was obtained following the described procedure24 to afford a
transparent liquid (14.0 g, 98%): IR (KBr) ν 3417, 3136, 1642, 1472,
■
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IR (KBr) ν 3069. 2958, 2932, 2859, 1957, 1725, 1595, 1486, 1428,
1262, 1112, 975, 699, 500; H NMR (400 MHz, CDCl3) δ 7.59 (4H,
435 (10), 361 (7), 199 (8), 135 (12). Anal. Calcd for C51H52O3Si2: C,
79.64; H, 6.81. Found: C, 79.67; H, 6.88.
1
3,3-Bis-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-3-phenyl-
propyne (6b). Hydrochloric acid gas (generated in situ by dropwise
addition of H2SO4 to NaCl) was bubbled slowly through a solution of
alcohol 5b (1.00 g, 1.3 mmol) in CH2Cl2 (50 mL) at room
temperature. After 5 h of bubbling, the solvent was completely
removed at reduced pressure, and the solid was redissolved in benzene
(25 mL). Then, ethynylmagnesium bromide (5.21 mL, 0.5 M, 2.6
mmol) was added, and the reaction was stirred 48 h at room
temperature. After this time, the reaction was quenched with saturated
solution of NH4Cl, and the organic phase extracted twice with CH2Cl2.
The combined organic portions were dried over anhydrous Na2SO4.
Removal of the solvent followed by purification by column
chromatography on silica gel, using hexanes/ethyl ether (200:1)
yielded compound 6b (0.60 g, 59%) as a colorless oil: IR (KBr) ν
3304, 3071, 2934, 2860, 1594, 1482, 1429, 1258, 1112, 1002, 889, 870,
761, 701, 615, 500; 1H NMR (400 MHz, CDCl3) δ 7.67−7.56 (8H, dt,
J = 8.0, 1.6 Hz), 7.43−7.26 (12H, m), 7.15−7.04 (3H, m), 6.96−6.87
(4H, m), 6.70−6.63 (4H, m), 6.59−6.50 (2H, d, J = 8.0 Hz), 2.41
(1H, s), 1.07 (18H, s); 13C NMR (100.5 MHz, CDCl3) δ 155.4, 145.9,
144.5, 135.8, 133.1, 129.9, 128.9, 128.7, 127.9, 126.7, 122.1, 121.2,
118.5, 89.4, 73.3, 55.2, 26.9, 19.6; 29Si NMR (53.6 MHz, CDCl3) δ
−5.07; HRMS (APCI-TOF) Calcd for C53H54O2Si2, 777.3578, found
777.3579, error 0.045 ppm MS (DIP) 777 ([M + 1]+, 15), 776 ([M+],
22), 641 (24), 585 (18), 466 (42), 465 (100), 403 (27), 387 (18), 367
(21), 331 (18), 259 (44).
d, J = 7.1 Hz), 7.38 (2H, t, J = 7.8 Hz), 7.22−7.16 (6H, m), 7.12−7.06
(5H, m), 6.92 (1H, dt, J = 7.9, 0.9 Hz), 6.79 (1H, dd, J = 8.1, 2.4 Hz),
6.60, (1H, t, J = 1.8 Hz), 1.06 (9H, s); 13C NMR (67.9 MHz, CDCl3)
δ 155.3, 146.3, 145.0, 135.6, 132.7, 131.4, 129.8, 129.0, 128.9, 127.9,
127.7, 126.7, 123.2, 122.1, 121.1, 118.5, 97.1, 84.8, 55.9, 26.6, 19.4; 29Si
NMR (79.5 MHz, CDCl3) δ −4.81; MS (FAB) 1120 (3) [(M + H)+],
1042 (5), 787 (9), 497 (70), 197 (78), 135 (100), 105 (47); HRMS
(APCI-TOF) Calcd for C80H71O2Si2, 1119.4987, found 1119.4974,
error 1.17. Anal. Calcd for C80H70O2Si2: C, 85.82; H, 6.30. Found: C,
85.65; H, 6.75.
([3-(tert-Butyl-diphenyl-silanyloxy)-diphenyl]-phenylmeth-
yl)-4-iodophenylethyne (8a). Colorless oil (0.05 g, 24%): IR (KBr)
1
ν 3067, 2933, 2859, 1595, 1484, 1428, 1264, 756, 700, 614, 500; H
NMR (270 MHz, CDCl3) δ 7.66−7.51 (8H, m), 7.41−7.31 (2H, m),
7.30−7.22 (4H, m), 7.15 (6H, t, J = 3.2 Hz), 7.10−7.01 (5H, m),
6.89−6.84 (1H, m), 6.76 (1H, dd, J = 8.0, 2.3 Hz), 6.57 (1H, t, J = 2.3
Hz), 1.03 (9H, s); 13C NMR (67.9 MHz, CDCl3) δ 155.4, 146.2,
144.9, 137.4, 135.6, 133.3, 132.8, 129.9, 129.0, 129.0, 128.0, 127.0,
126.8, 123.2, 122.1, 121.1, 118.6, 97.0, 93.8, 84.1, 55.9, 26.7, 19.5; 29Si
NMR (53.6 MHz, CDCl3) δ −4.89; MS (DIP) 725 ([M + 1]+, 6), 724
(M+, 13), 668 (50), 667 (100), 589 (26), 513 (11), 463 (29), 385
(46), 361 (36), 259 (14), 239 (17), 167 (14), 135 (15); HRMS
(APCI-TOF) Calcd for C43H38IOSi H, 725.1731, found 725.1735,
error 0.52. Anal. Calcd for C43H37IOSi: C, 71.26; H, 5.15. Found: C,
71.05; H, 5.12.
1,4-Bis-(3,3-bis-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-
3-phenyl-propynyl)-phenylene (7b). A solution of 1,4-diiodoben-
zene (0.053 g, 0.2 mmol), alkyne 6b (0.25 g, 0.3 mmol), Pd(PPh3)2Cl2
(0.011 g, 0.02 mmol), CuI (0.006 g, 0.03 mmol) and diisopropyl
amine (0.5 mL) in THF (25 mL) previously degassed was refluxed for
2.5 h. After this time, the reaction was cooled down to room
temperature and quenched with saturated NH4Cl. The organic phase
was twice extracted with CH2Cl2, and the combined organic portions
were dried over anhydrous Na2SO4. The solvent was removed
followed by column chromatography purification on neutral alumina
using hexanes/ethyl ether (200:1) yielded 0.19 g (73%) of the rotor
7b, as colorless oil that slowly solidifies at low temperature: IR (KBr) ν
3069, 2931, 2857, 2346, 1594, 1483, 1427, 1258, 1111, 1001, 868, 699,
1,6-Bis(3-((tert-butyldiphenylsilyl)oxy)phenyl)-1,1,6,6-tetra-
phenylhexa-2,4-diyne (9a). A solution of 1,4-dibromobenzene-d4
(0.046 g, 0.2 mmol) and alkyne 5 (0.20 g, 0.4 mmol) in THF (25 mL)
containing Pd(PPh3)2Cl2 (0.014 g, 0.02 mmol), CuI (0.007 g, 0.04
mmol) and diisopropyl amine (0.5 mL) previously degassed was
refluxed for 2.5 h. At this time, the reaction was cooled to room
temperature and quenched with saturated NH4Cl. The aqueous phase
was twice extracted with CH2Cl2, and the combined organic portions
were dried over anhydrous Na2SO4. The solvent was removed at
reduced pressure, followed by purification by column chromatography
on neutral alumina, eluting with hexane/ethyl ether (99:1) to afford
0.20 g (50%) of the dialkyne compound as the main product, a white
crystalline solid: mp 223−224 °C; IR (KBr) ν 3055, 2934, 2859, 1595,
1487, 1427, 1265, 1111, 971, 881, 742, 698, 503; 1H NMR (270 MHz,
CDCl3) δ 7.55−7.51 (8H, dt, J = 6.0, 1.5 Hz), 7.36−7.20 (12H, m),
7.17−7.09 (12H, m), 7.05 (2H, t, J= 8.0 Hz), 6.98−6.93 (8H, m),
6.88−6.82 (2H, m), 6.73 (2H, ddd, J = 8.0, 2.5, 1.0 Hz), 1.00 (18H, s);
13C NMR (67.9 MHz, CDCl3) δ 155.3, 145.5, 144.2, 135.6, 132.7,
1
500; H NMR (270 MHz, CDCl3) δ 7.66−7.57 (8H, dd, J = 6.6, 1.2
Hz), 7.41−7.22 (12H, m), 7.17−7.05 (5H, m), 7.00−6.94 (4H, m),
6.74 (2H, t, J = 2.0 Hz), 6.69 (2H, dd, J = 7.9, 1.6 Hz), 6.60 (2H, d, J =
7.6 Hz), 1.08 (18H, s); 13C NMR (67.9 MHz, CDCl3) δ 155.4, 146.3,
144.9, 135.7, 133.0, 131.4, 129.9, 129.0, 128.7, 127.8, 126.7, 123.2,
122.1, 121.1, 118.4, 96.9, 84.9, 55.8, 26.8, 19.6; 29Si NMR (53.6 MHz,
CDCl3) δ −5.01; MS (FAB) 1627 (2) [(M+ + H)+], 1626 (1) [(M +
)], 1550 (1), 1315 (1), 1295 (3), 751 (6), 259 (10), 197 (70), 135
(100), 121 (10), 105 (12); HRMS (APCI-TOF) Calcd for
C112H107O4Si4, 1627.7241, found 1627.7207, error 1.77 ppm. Anal.
Calcd for C112H106O4Si4: C, 82.61; H, 6.56. Found: C, 82.42; H, 6.39.
(Bis-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-phenylmeth-
yl)-4-iodophenylethyne (8b). Colorless oil (0.05 g, 24%): IR (KBr)
129.8, 129.0, 128.0, 127.7, 126.8, 122.1, 121.0, 118.6, 83.8, 69.8, 56.0,
26.6, 19.4; 29Si NMR (53.7 MHz, CDCl3) δ −4.77 (2 Si); HRMS
(APCI-TOF) Calcd for C74H67O2Si2, 1043.4674, found 1043.4677,
error 0.27 ppm.
Bis-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-phenyl-
methanol (5b). A solution of 1 (1.00 g, 2.4 mmol) in THF (50 mL)
was cooled down to −78 °C in a dry ice bath. Subsequently, n-
butyllithium (1.1 mL, 2.5 M in THF, 2.7 mmol) was added to the
mixture and stirred for 0.5 h at −78 °C. Then, methyl benzoate 3
(0.17 g, 1.2 mmol) was added. After stirring for 2 h at −78 °C, the
reaction was quenched with saturated solution of NH4Cl. The organic
phase was extracted with CH2Cl2 and dried over anhydrous Na2SO4.
Column chromatography on silica gel, using hexanes yielded 5b (0.77
g, 83%) as a yellow oil: IR (KBr) ν 3472, 3071, 2933, 2859, 1596,
1
ν 3067, 2933, 2859, 1595, 1484, 1428, 1264, 756, 700, 614, 500; H
NMR (270 MHz, CDCl3) δ 7.66−7.51 (8H, m), 7.41−7.31 (2H, m),
7.30−7.22 (4H, m), 7.15 (6H, t, J = 3.2 Hz), 7.10−7.01 (5H, m),
6.89−6.84 (1H, m), 6.76 (1H, dd, J = 8.0, 2.3 Hz), 6.57 (1H, t, J = 2.3
Hz), 1.03 (9H, s); 13C NMR (67.9 MHz, CDCl3) δ 155.4, 146.2,
144.9, 137.4, 135.6, 133.3, 132.8, 129.9, 129.0, 129.0, 128.0, 127.0,
126.8, 123.2, 122.1, 121.1, 118.6, 97.0, 93.8, 84.1, 55.9, 26.7, 19.5; 29Si
NMR (53.6 MHz, CDCl3) δ −4.89; HRMS (APCI-TOF) Calcd for
C43H38IOSi, 725.1731, found 725.1735, error 0.52 ppm; MS (DIP)
725 ([M + 1]+, 6), 724 (M + , 13), 668 (50), 667 (100), 589 (26),
513 (11), 463 (29), 385 (46), 361 (36), 259 (14), 239 (17), 167 (14),
135 (15). Anal. Calcd for C59H55IO2Si2: C, 72.37; H, 5.66. Found: C,
72.26; H, 5.50.
1
1483, 1429, 1277, 1112, 1003, 871, 701, 613, 501; H NMR (400
MHz, CDCl3) δ 7.66 (8H, dt, J = 8.0, 1.2 Hz), 7.47−7.39 (4H, m),
7.38−7.31 (8H, m), 7.21−7.11 (3H, m), 7.00−6.94 (4H, m), 6.73−
6.65 (4H, m), 6.63−6.58 (2H, dq, J = 17.7, 0.9 Hz), 2.44 (1H, s), 1.12
(18H, s); 13C NMR (100 MHz, CDCl3) δ 155.2, 148.1, 146.4, 135.7,
135.7, 133.0, 129.9, 128.7, 127.8, 127.7, 127.7, 127.0, 120.9, 119.7,
118.6, 81.5, 26.8, 19.6; 29Si NMR (59.6 MHz, CDCl3) δ −5.29; HRMS
(APCI-TOF) Calcd for C51H53O3Si2−H2O, 751.3422, found
751.3431, error 1.17 ppm; MS (DIP) 769 ([M + 1]+, 3), 768
([M+], 5), 712 (61), 711 (100), 693 (19), 514 (29), 513 (66), 495 (5),
Tris-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-methanol
(5c). A solution of 1 (3.00 g, 7.3 mmol) in THF (50 mL) was cooled
down to −78 °C in a dry ice bath. Subsequently, n-butyllithium (3.2
mL, 2.5 M in THF, 8.0 mmol) was added, and the mixture was stirred
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Article
for 30 min at −78 °C. Then, diethyl carbonate 4 (0.29 g, 2.4 mmol) in
THF (20 mL) was added. After stirring for 2 h at −78 °C, the reaction
was quenched with a saturated solution of NH4Cl. The organic phase
was extracted twice with CH2Cl2, and the organic phases were dried
over anhydrous Na2SO4. Column chromatography on silica gel, eluting
with hexanes/ethyl ether (199:1) yielded compound 5c (2.00 g, 80%)
as a white crystalline solid: mp 100−101 °C; IR (KBr) ν 3446, 3052,
2932, 2858, 1583, 1480, 1429, 1283, 1245, 1111, 1001, 954, 864, 788,
m), 7.38−7.20 (22H, m), 6.84−6.68 (6H, m) 6.63−6.53 (3H, m), 6.31
(3H, t, J = 7.8 Hz), 1.05 (27H, s); 13C NMR (100.5 MHz, CDCl3) δ
155.2, 145.9, 137.2, 135.6, 133.3, 133.0, 129.9, 128.5, 127.7, 123.2,
121.9, 120.9, 118.3, 96.5, 93.4, 84.0, 55.5, 26.8, 19.6; 29Si NMR (53.7
MHz, CDCl3) δ −5.3; HRMS (APCI-TOF) Calcd for C75H74IO3Si3,
1233.3985, found 1233.3985, error 0.009 ppm. Anal. Calcd for
C75H73IO3Si3: C, 73.03; H, 5.96. Found: C, 72.93; H, 5.85.
1,4-Bis-((tris-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-
methanyl)-ethynyl)-phenylene-d4 (7c-d4). A solution of 1,4-
diiodobenzene-d4 (0.053 g, 0.2 mmol) and alkyne 6c (0.328 g, 0.3
mmol) in THF (50 mL) containing Pd(PPh3)3Cl2 (0.011 g, 0.02
mmol), CuI (0.006 g, 0.03 mmol) and diisopropyl amine (1 mL)
previously degassed was refluxed (6 h). After this time, the reaction
was cooled down to room temperature and quenched with saturated
solution of NH4Cl. The organic phase was extracted with CH2Cl2, and
the combined organic portions were dried over anhydrous Na2SO4.
The solvent was removed at reduced pressure followed by
chromatography purifications on neutral alumina, using hexanes/
ethyl ether (199:1) to afford 0.17 g, (50%) of compound 7c-d4 as a
white crystalline solid: mp 118−119 °C; FTIR (ATR) ν 3072, 2955,
2931, 2857, 1959, 1594, 1582, 1481, 1428, 1277, 1254, 1113, 1005,
998, 959, 898, 861, 695, 610, 499, 491; 1H NMR (270 MHz, CDCl3) δ
7.64−7.56 (24H, m), 7.34−7.24 (36H, m), 6.84 (6H, t, J = 8.1 Hz),
6.80 (6H, m), 6.60 (6H, dd, J = 7.8, 2.7 Hz), 6.40 (6H, d, J = 7.8 Hz),
1.07 (54H, s); 13C NMR (75.5 MHz, CDCl3) δ 155.2, 146.1, 135.6,
133.0, 129.9, 128.5, 127.8, 122.8, 122.0, 121.0, 118.2, 96.5, 84.8, 55.6,
26.8, 19.6; 29Si NMR (53.7 MHz, CDCl3) δ −5.16; HRMS (APCI-
TOF) Calcd for C144H147O6Si6, 2139.9807, found 2139.9838, error
1.40 ppm. Anal. Calcd for C144H138D4O6Si6: C, 80.77, H, 6.87 Found
for C, 80.71, H, 6.70.
1
701, 616, 503; H NMR (270 MHz, CDCl3) δ 7.67−7.58 (12H, m),
7.44−7.23 (20H, m), 6.82 (3H, t, J = 8.0 Hz), 6.66 (3H, t, J = 2.2 Hz),
6.57 (3H, ddd, J = 8.0, 2.4, 0.9 Hz), 6.38 (3H, dq, J = 7.8 Hz, 1.7 Hz),
2.18 (1H, br, −OH), 1.08 (27H, s); 13C NMR: (67.9 MHz, CDCl3) δ
155.2, 148.0, 135.8, 133.2, 130.0, 128.5, 127.9, 121.0, 119.6, 118.6,
81.4, 26.9, 19.7; 29Si NMR (53.6 MHz, CDCl3) δ −5.20; HRMS
(APCI-TOF) Calcd for C67H71O4Si3−H2O, 1005.4549, Found
1005.4545; MS (FAB) 1007 (14) [(M−CH3)+], 965 (9), 767 (7),
691 (4), 359 (10), 197 (60), 135 (100), 121 (18); 0.40 ppm Anal.
Calcd for C67H70O4Si3: C, 78.62; H, 6.89. Found: C, 78.66; H, 6.84.
Tris-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-methane-
ethyne (6c). Hydrochloric acid gas (generated in situ by dropwise
addition of H2SO4 to NaCl) was slowly bubbled through a solution of
alcohol 5c (1.0 g, 1.0 mmol) in CH2Cl2 (50 mL) at room temperature.
After 5 h of reaction, the solvent was completely removed at reduced
pressure, and the solid was redissolved in benzene (25 mL); then,
ethynylmagnesium bromide (3.91 mL, 0.5 M, 2.0 mmol) was added,
and the reaction was stirred at room temperature over the weekend.
After this time, the reaction was quenched with saturated solution of
NH4Cl, and the organic phase was extracted twice with CH2Cl2. The
combined organic portions were dried over anhydrous Na2SO4.
Removal of the solvent followed by column chromatography
purification on silica gel, using hexanes/ethyl ether (199.5:0.5) yielded
compound 6c (0.66 g, 66%) as a colorless oil: IR (KBr) ν 3296, 3052,
2932, 2857, 1596, 1476, 1429, 1282, 1244, 1112, 947, 863, 787, 700,
1,1,1,6,6,6-Hexakis(3-((tert-butyldiphenylsilyl)oxy)phenyl)-
hexa-2,4-diyne (9c). A solution of 1,4-dibromobenzene-d4 (0.015 g,
0.1 mmol) and alkyne 6c (0.13 g, 0.1 mmol) in THF (50 mL)
containing Pd(PPh3)3Cl2 (0.004 g, 0.01 mmol), CuI (0.002 g, 0.01
mmol) and diisopropyl amine (1 mL) previously degassed was
refluxed (6 h). After this time, the reaction was cooled down to room
temperature and quenched with saturated solution of NH4Cl. The
organic phase was extracted with CH2Cl2, and the combined organic
portions were dried over anhydrous Na2SO4. The solvent was removed
at reduced pressure followed by chromatography purifications on
neutral alumina, using hexanes/ethyl ether (199:1) to afford 0.08 g,
(65%) of compound 9c as a white crystalline solid: mp 171−172 °C;
IR (KBr) ν 3053, 2931, 2856, 1596, 1474, 1428, 1281, 1110, 946, 862,
1
619, 503; H NMR (270 MHz, CDCl3) δ 7.60 (12H, d, J = 6.6 Hz),
7.38−7.22 (18H, m), 6.78 (3H, dt, J = 8.0, 1.5 Hz), 6.69 (3H, d, J =
1.8 Hz), 6.54 (3H, dd, J = 8.0, 0.7 Hz), 6.31 (3H, d, J = 8.0 Hz), 2.20
(1H, s), 1.04 (27H, s); 13C NMR (67.9 MHz, CDCl3) δ 155.3, 145.8,
135.8, 133.2, 129.9, 128.5, 127.8, 122.0, 121.0, 118.3, 89.0, 73.3, 55.0,
26.9, 19.7; 29Si NMR (79.4 MHz, CDCl3) δ −5.23; MS (FAB) 1031
(2) [(M + H)+], 895 (2), 699 (10), 641 (5), 621 (4), 259 (20), 197
(90), 135 (100). Anal. Calcd for C69H70O3Si3: C, 80.34; H, 6.84.
Found: C, 80.38; H, 6.80.
1,4-Bis-((tris-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-
methanyl)-ethynyl)-phenylene (7c). A solution of 1,4-diiodoben-
zene (0.3 g, 0.1 mmol) and alkyne 6c (0.20 g, 0.2 mmol) in THF (25
mL) containing Pd(PPh3)2Cl2 (0.007 g, 0.01 mmol), CuI (0.004 g,
0.02 mmol) and diisopropyl amine (0.5 mL) previously degassed was
refluxed for 2.5 h. After this time, the reaction was cooled down to
room temperature and quenched with saturated solution of NH4Cl.
The organic phase was extracted twice with CH2Cl2, and the combined
organic portions were dried over anhydrous Na2SO4. The solvent was
removed at reduced pressure followed by column chromatography
purification on neutral alumina, using hexanes/ethyl ether (199:1) to
afford compound 7c (0.16 g, 75%) as a white crystalline solid: mp
125−127 °C; IR (KBr) ν 3070, 2933, 2858, 2221, 1593, 1481, 1428,
1256, 1111, 1004, 901, 865, 700, 612, 501; 1H NMR (300 MHz,
CDCl3) δ 7.66 (24H, dd, J = 8.0, 1.4 Hz), 7.40−7.24 (36H, m), 7.04
(4H, s), 6.90−6.82 (12H, m), 6.68−6.63 (6H, m), 6.39 (6H, d, J = 8.4
Hz), 1.09 (54H, s); 13C NMR (75.5 MHz, CDCl3) δ 155.2, 146.1,
135.6, 133.1, 131.3, 129.9, 128.5, 127.8, 123.0, 122.0, 121.0, 118.3,
96.5, 84.9, 55.6, 26.8, 19.6; 29Si NMR (79.4 MHz, CDCl3) δ −5.16;
HRMS (APCI-TOF) Calcd for C144H143O6Si6, 2135.9494, found
2135.9479, error 0.74 ppm; MS (FAB) 2136 (4) [(M + H)+], 1924
(2), 1806 (4), 1590 (3), 1323 (2), 1207 (3), 1037 (3), 899 (3), 622
(25), 391 (21), 219 (100). Anal. Calcd for C144H142O6Si6: C, 80.93, H,
6.70. Found C, 80.44, H, 6.58.
1
786, 697, 618; H NMR (270 MHz, CDCl3) δ 7.55 (12H, d, J = 6.6
Hz), 7.28−7.16 (18H, m), 6.76 (3H, t, J = 8.0 Hz), 6.55 (3H, t, J = 1.8
Hz), 6.50 (3H, dd, J = 8.0, 0.7 Hz), 6.41 (3H, d, J = 8.0 Hz), 1.00
(27H, s); 13C NMR (67.9 MHz, CDCl3) δ 155.1, 145.4, 135.6, 133.0,
129.9, 128.6, 127.8, 122.2, 121.0, 118.4, 83.4, 67.9, 55.87, 26.8, 19.6;
29Si NMR (79.4 MHz, CDCl3) δ −5.02; MS (FAB) 2062 (1) [M +
H+], 1984 (1), 1743 (1), 1029 (1), 675 (1), 259 (10), 197 (60), 135
(100).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C NMR spectral data, CIF files for compounds 6a, 9a, 9c
and X-ray diffraction analysis. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: norberto.farfan@gmail.com; mgg@chem.ucla.edu.
■
Notes
The authors declare no competing financial interest.
Tris-[3-(tert-butyl-diphenyl-silanyloxy)-phenyl]-methyl)-4-
iodophenylethyne (8c). Colorless oil (0.025 g, 20%): IR (KBr) ν
3438, 3070, 2930, 2857, 1594, 1482, 1427, 1252, 1111, 1005, 863, 785,
737, 698, 610, 500; H NMR (270 MHz, CDCl3) δ 7.70−7.50 (12H,
ACKNOWLEDGMENTS
■
The authors thank UNAM (PAPIIT IN-214010) and
CONACYT for financial support and granting scholarships to
1
G
dx.doi.org/10.1021/jo301078a | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
with a fwhm (full width at half-maximum) of 0.1° 2θ (medium
resolution), also assuming laboratory X-ray source type and fixed slit
widths, Cu Kα1 (λ = 1.5406 Å).
(21) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl.
Crystallogr. 2006, 39, 453−457.
(22) Ratcliffe, C. I. Rotational & Translational Dynamics. In NMR
Crystallography; Harris, R. K., Wasylishen, R. E., Duer, M. J., Eds.;
Wiley: Hoboken, NJ, 2009.
́
́
R. Arcos-Ramos and P. Ramırez Montes; M.A. Leyva-Ramırez
for X-ray data collection; and G. Cuellar for HRMS. Work at
UCLA has been supported by Grant NSF DMR1101934 and a
́
́
postdoctoral fellowship to B. Rodrıguez-Molina from
CONACYT (Mexico).
́
REFERENCES
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considered. All reflections have a symmetric pseudo-Voigt peak shape
H
dx.doi.org/10.1021/jo301078a | J. Org. Chem. XXXX, XXX, XXX−XXX