Crystals and aggregates of a molecular tetrarotor with multiple trityl embraces derived from tetraphenyladamantane

Article abstract of DOI:10.1021/cg300632q

Samples of tetrakis-1,3,5,7-(4′-(3″,3″,3″- triphenylpropynyl)-phenylene)adamantane and its trityl-deuterated isotopologue were synthesized and their crystallization and packing properties were analyzed within the context of formation of 4- or 6-fold phenyl embraces. The tetrahedral shape of these molecules with four propeller-like triphenylmethyl moieties generates several edge-to-face intermolecular interactions in the solid state that result in the formation of infinite chains of molecules that are tightly interlocked. The formation of analogous edge-to-face intermolecular interactions leading to aggregation in solution was also suggested by NMR experiments carried out in different solvents as a function of concentration. The formation of interdigitated chains was also manifested in fibrils and thin needles, which were documented by scanning electron microscopy (SEM). Single crystal X-ray diffraction studies revealed the presence of multiple 4-fold phenyl embraces and edge-to-face interactions as the leading motifs behind the formation of tightly interlocked molecular chains.

Full text of DOI:10.1021/cg300632q

Article
pubs.acs.org/crystal
Crystals and Aggregates of a Molecular Tetrarotor with Multiple
Trityl Embraces Derived from Tetraphenyladamantane
Antoine Stopin and Miguel A. Garcia-Garibay*
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
S
* Supporting Information
ABSTRACT: Samples of tetrakis-1,3,5,7-(4′-(3″,3″,3″-triphenyl-
propynyl)-phenylene)adamantane and its trityl-deuterated iso-
topologue were synthesized and their crystallization and packing
properties were analyzed within the context of formation of 4- or
6-fold phenyl embraces. The tetrahedral shape of these molecules
with four propeller-like triphenylmethyl moieties generates
several edge-to-face intermolecular interactions in the solid
state that result in the formation of infinite chains of molecules
that are tightly interlocked. The formation of analogous edge-to-
face intermolecular interactions leading to aggregation in solution
was also suggested by NMR experiments carried out in different
solvents as a function of concentration. The formation of
interdigitated chains was also manifested in fibrils and thin
needles, which were documented by scanning electron microscopy (SEM). Single crystal X-ray diffraction studies revealed the
presence of multiple 4-fold phenyl embraces and edge-to-face interactions as the leading motifs behind the formation of tightly
interlocked molecular chains.
(XPh3----Ph3X). Their structures may differ by their local
symmetry, which may have a point group as high as S6, and by
the number of geometrically different nearest neighbors (I, II,
etc.). Other differences include their rotators’ centroid-to-
centroid distances (m1), the distances between molecules in
neighboring chains (d1), and the displacement distances along
the chain direction between molecules in neighboring chains
(d2). Structures analyzed in our group that conform to the
motif in Figure 1b include triphenylmethyl stators with a simple
diyne rod,12 with various diethynyl substituted phenylenes (H,
NH2, CN, NO2, F, F2, NH2/NO2),13 diphenylethynyl-
diamantane,14 diethynyl biphenylene,15 with diethynyl pyridine,
pyridazine, and pyridine N-oxide,16 as well as triphenylsilyl
stators with diethynyl phenylene, cubanediyl, bicyclo[2.2.2]-
octanediyl, para-closo-dicarba-dodecacarboranediyl.17 Having
shown that the 6PE is a robust crystal engineering synthon18
for linear structures, we were interested to see whether it would
be sufficiently strong to help direct a three-dimensional
noncovalent network. To answer this question we prepared
and analyzed molecular tetrarotor 1 with one adamantane
group at the core and four triphenylmethyl groups linked by
para-ethynylene-phenylene rods arranged in a tetrahedral
arrangement (Figure 2). In principle, the linear nature of the
6PE combined with the tetrahedral structure and extended
trityl branches of compound 1 could give rise to an
INTRODUCTION
■
Over the past few years we have been interested in low-density
molecular crystals built with molecules that pack poorly and
generate some free volume in order to facilitate internal
rotation in the solid state. The most general and successful
motif in our studies consists of a small central rotator axially
linked to bulky shielding groups that act as the stator (Figure
1). We have analyzed compounds with bridging groups across
the two ends of the structure, which are analogous to
macroscopic toy gyroscopes (Figure 1a, left), and structures
with open topologies, such as 1,4-bis(3,3,3-triphenylpropinyl)-
benzene (Figure 1, right), which have a dumbbell-shaped
structure.
It is well-known that dumbbell-shaped molecules have poor
shape complementarity and tend to form solvates that are often
referred to as “wheel-and-axle” complexes.1−3 Soldatov4 noted
that low density crystals are generally formed by structures that
lack complementary contacts for all of their surfaces,5 which
encompasses, among others, bulky shapes penetrated by a
rod6−8 and bulky structures interconnected by several rods.9,10
As illustrated in Figure 1b, we have shown that the
crystallization of compounds with triphenylmethyl stators and
a diethynyl-arylene or diethynyl-cycloalkylidene rod tend to
occur in a remarkably reliable manner in the form of parallel
chains of molecular rotors interacting at both ends by
complementary edge-to-face interactions characteristic of the
well-known 6-fold phenyl embrace (6PE).11 The 6PE is
characterized by a cyclic arrangement of complementary
edge-to-face interactions between adjacent Ph3X groups
Received: May 9, 2012
Revised: June 5, 2012
Published: June 11, 2012
© 2012 American Chemical Society
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bad solvents. We set out to test whether compound 1 would
crystallize with ease, form an open structure, and display
aromatic edge-to-face interactions in the form of 6-fold (6PE)
or 4-fold phenyl embraces (4PE). We report here our
crystallization studies in multiple solvents showing the
formation of thin needles and the formation of a “gel-like”
structure. We describe the experimental conditions required to
grow diffraction-quality single crystals and the resulting X-ray
molecular and crystal structures. We analyze how the packing
structure of 1 is remarkably dense and can be described in
terms of infinite chains of molecules experiencing comple-
mentary aromatic edge-to-face interaction involving the trityl
groups at the periphery and the phenyl groups attached to the
adamantyl core.
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The adamantyl tetrar-
otor 1 was synthesized from trityl chloride 2 and tetraphenyl
adamantane 4 as illustrated in Scheme 1. The deuterated trityl
chloride 2-d15 was obtained by a Friedel−Crafts reaction of
deuterated benzene and carbon tetrachloride. Compounds 3
and 3-d15 were obtained in one step, respectively, by reaction of
2 and 2-d15 with ethynylmagnesium bromide in benzene.15
Tetra-p-iodophenyl adamantane 5 was obtained in 69% yield by
iodination of tetraphenyl adamantane 4 using [bis-
(trifluoroacetoxy)iodo]benzene.19 Molecular tetrarotors 1 and
1-d60 were obtained via Sonogashira coupling of 5 with the
corresponding trityl acetylene. The structures of compound 1
and 1-d60 were confirmed by 1H, 2H, and 13C NMR, attenuated
total reflectance (ATR) FTIR, and by mass spectrometry.
Figure 1. (a) Molecular rotors with triply bridged, closed topologies,
analogous to those of macroscopic gyroscopes (left), and structures
with open topologies (right) tend to form crystals that generate
sufficient free volume for fast rotation of the central phenylene rotator.
(b) The packing of molecular rotors with triphenylmethyl stators is
dictated by aromatic edge-to-face interactions in the form of a self-
complementary 6-fold phenyl embraces (6PEs).
1
The H NMR spectra of 1 and 1-d60 showed a broad singlet
at 2.15 ppm characteristic of the adamantane methylene
hydrogens, the four phenyl groups linked to the adamantane
present the characteristic AA′BB′ spin system of para-
disubstituted benzene as two apparent doublets between 7.40
1
and 7.55 ppm. The H NMR spectrum of 1-d60 shows weak
signals between δ 7.28 and δ 7.38 due to residual hydrogens in
the starting material, while stronger signals can be seen for
compound 1 due to the triphenylmethyl groups. As expected,
the 13C NMR spectra of 1 and 1-d60 are very similar with two
alkyne signals at ca. 85 and 95 ppm, a quaternary trityl carbon
at ca. 56 ppm, and adamantane signals at ca. 39 and 47 ppm.
Strong signals at ca. 121, 125, 132, and 149 ppm in both 13C
NMR spectra correspond to the phenyl groups linked to the
adamantane. The triphenylmethyl groups for both compounds
present a signal at ca. 145 ppm corresponding to the ipso-
carbon. The other carbons of the trityl groups can be seen as
three singlets between 126 and 129 ppm for compound 1, but
they appear as three multiplets in the same range for 1-d60 due
to the carbon-deuterium coupling. The IR spectrum of
compound 1-d60 displays a signal at ca. 2275 cm−1
corresponding to the stretching of the carbon−deuterium
bonds. Visual melting point observations indicated that
compounds 1 and 1-d60 decompose before melting above 400
°C. The molecular ions of the two isotopologues were observed
by mass spectrometry and conformed well with the expect-
ations based on the respective molecular masses.
Figure 2. Tetrakis-1,3,5,7-(4′-(3″,3″,3″-triphenylpropynyl)-phenylene)-
adamantane molecular tetratorors 1 and 1-d60.
interpenetrated diamond lattice. In contrast, aromatic edge-to-
face interactions with lower symmetry would give rise to lower
symmetry packing structures.
With the purpose of probing the presence of aromatic
1
2
interactions in solution using H and H NMR in a variety of
deuterated and non-deuterated solvents, we prepared com-
pound 1 in its natural abundance and trityl-deuterated forms
(1-d60, Scheme 1). We wanted to investigate whether the edge-
to-face interactions that tend to occur in the solid state, would
be present in solution, potentially resulting in anisotropic
shielding effects that could be observed in the form of
concentration-dependent chemical shifts, and/or by changing
the characteristics of the solvent using mixtures of good and
Crystallization Studies. The crystallization of compound 1
was investigated in different solvent systems. A large number of
trials showed indistinguishable behavior of compounds 1 and 1-
d60. The solvents used for these tests were determined by the
relatively low solubility of 1, which is high in tetrahydrofuran
(THF), dichloromethane (DCM), and chloroform but low in
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Scheme 1
most other solvents. Slow evaporation of a DCM solution of
compound 1 yielded very thin needles that were too small to
obtain a crystal structure. Similar results were obtained upon
addition of other poor solvents such as benzene, methanol,
ethyl acetate, or toluene. Similar results were also obtained by
slow evaporation of a solution of 1 in chloroform or THF in the
presence of toluene. Tests were also carried out by slow
diffusion of various solvents into a solution of 1 in DCM,
chloroform, or THF. Once again, the needles formed were too
small for single crystal X-ray diffraction analysis.
similar results. However, support for a rather weak aggregate in
solution was obtained from a series of 1H NMR spectra of 1-d60
acquired at 500 MHz in THF-d8 as a function of concentration
with samples that varied from 2.5 mM up to 26 mM, which is
close to the solubility limit. Taking the signal of the adamantyl
methylene hydrogens as an internal standard, we were able to
determine the displacement of the sharp residual hydrogens of
the deuterated trityl groups with accuracy to look for
concentration-dependent field effects on their chemical shifts.
We detected small but characteristic upfield chemical shift
changes in these signals of up to 2.00 0.05 Hz and 3.00
0.05 Hz for the ortho- and para-phenyl trityl hydrogens,
respectively, and a downfield shift of 2.00 0.05 Hz for the
meta-hydrogens. Signals corresponding to the para-phenylene
rotators attached to the adamantyl group also displayed upfield
Crystallizations were also tested by slow diffusion of
methanol toward a concentrated solution of 1 in THF.
Under these conditions, the formation of needles occurred at
the interface of the two solvents. Further experiments involving
the fast addition of methanol into a solution of compound 1 in
tetrahydrofuran resulted in the formation of a suspension that
settles with time and takes the appearance of a weak gel after
removal of the excess solvent. This behavior suggested the
formation of nanofibers as a result of nonbonding interactions
between molecules of 1.
and downfield shifts of 1.80
0.05 and 0.50
0.05 Hz,
respectively. Considering that the edge-to-face-interactions
characteristic of a 6-fold trityl embraces should result in
shielding effects for all the edge-on aromatic hydrogens, we
tentatively suggest that analogous aggregates with multiple
types aromatic interactions are formed also in solution (see
Supporting Information).
Scanning Electron Microscopy (SEM). The results
observed upon crystallization of 1 under two representative
conditions were analyzed by scanning electron microscopy
(SEM). These included the formation of thin single needles
and a suspension at the interface of slowly diffusing methanol
into a concentrated solution of 1 in THF and the formation of a
weak “gel-like” system upon fast addition of a solution of 1 in
THF to methanol followed by removal of the excess solvent.
Samples were deposited from their respective solutions onto a
silicon wafer (1.0.0) previously treated with a piranha solution
consisting of mixture of water, hydrochloric acid, and hydrogen
peroxide under reflux, in order to obtain a smooth surface. The
silicon wafers were dried under a slow flow of argon and placed
in a desiccator overnight before SEM analysis.
1
2
Aggregation in Solution Studied by H and H NMR.
We speculated that 6-fold (6PE) and 4-fold (4PE) trityl
embraces involving aromatic edge-to-face interacions, if present
in solution, should result in chemical shift displacements of the
aromatic trityl protons due to the anisotropic field effects of the
interacting π-systems.20 To explore this, compound 1 was
dissolved in deuterated THF (5 mg in 0.5 mL) and deuterated
methanol was then added in small portions (50 μL). A shift of
the aromatic protons observed upon addition of methanol was
correlated with a change in the chemical shift of the adamantyl
aliphatic hydrogens and was interpreted as an indication of the
change in solvent properties rather than to aggregation effects.
After addition of 300 μL of methanol, the sample began to
cloud and precipitate with the concomitant broadening of the
aromatic proton signals. Analogous experiments using
deuterium NMR with samples of 1-d60 in natural abundance
THF with the subsequent slow addition of methanol gave
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Figure 3. SEM pictures of compound 1 obtained (left) by slow diffusion of methanol into a concentrated solution of 1 in THF and (right) by
addition of methanol into a concentrated solution of 1 in THF.
Figure 4. Views from the molecular and crystal structure of 1 at 100 K. (a) Molecular structure with thermal ellipsoids at 50% probability, (b) unit
cell along the c-axis with solvent included, and, (c) space-filling representation of the packing structure illustrating the formation of linear chains of
interlocking molecules along the c-axis (left to right). Hydrogen atoms are omitted and molecules in the chain are illustrated in alternating dark and
light colors.
The needles obtained by slow nucleation were between ca.
10 to 30 μm wide and several hundreds of micrometers long
(Figure 3 left). These needles presented rectangular cross
sections with sharp edges and were found to be very brittle
when exposed to external forces. The suspension that appeared
at the interface of THF and methanol consisted of very thin
needles, between 1 to 15 μm wide (Figure 3 right) with excess
of the compound precipitated in the form of fibrils. The
presence of thin needles or aggregates over three different
scales suggested to us the formation of a dominant one-
dimensional close packing array. In agreement with this
suggestion, the rapidly precipitated “gel-like” samples were
shown to consist of similar fibrils and thin needles.
Single Crystal X-ray Diffraction Analysis. X-ray quality
single crystalline needles slightly larger than those obtained
from THF-MeOH were obtained by slow evaporation of a
solution of compound 1 in pure toluene. The X-ray
crystallographic data were collected at 100 K with a crystal of
1,21 and the structure was solved in the chiral orthorhombic
space group P21212 with one-half molecule of 1 and one
molecule of toluene per asymmetric unit. The unit cell contains
two molecules of compound 1 and four molecules of toluene. A
depiction of the unit cell is shown in Figure 4 with four
molecules each of 1 and toluene. Notably, compound 1
crystallizes with a structure in the point group S4 with
triphenylmethyl groups having different propeller chiralities, P
and M. The two crystallographically different alkynyl axles
present in the molecule are slightly bent, with angles C10−
C13−C14 of 174.6° and C37−C40−C41 of 173.3°. The
phenylene groups directly linked to the adamantane unit are
eclipsed with one of the three adamantyl Cquat−CH2 bonds, and
the C−Ph bonds of the trityl groups are in a staggered
conformation with respect to the three Cquat−CH2 bonds
coming out of the adamantane core.
The crystal structure of 1 has a packing coefficient of 0.733,
which falls in the range of 0.65−0.77 typically observed for
molecular crystals. The unit cell dimensions are 20.994 Å,
32.153 Å, and 6.953 Å, with the smaller c-axis being the
direction of the interdigitated triphenyl propynyl chains that
experience two types of phenyl embraces.22 As shown in Figure
4c, the packing structure may be described in terms of infinite
chains of interlocking molecules that translate along the
direction of the c-axis. The crystal structure of 1 shows
multiple edge-to-face interactions involving the phenyl groups
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a
Table 1. Geometric Parameters Involved in the Four-Fold Phenyl Embrace (4PE) Illustrated in Figure 6
πedge → πface
contact
π···π (Å)
H···π (Å)
C−H···π (°)
ϕ (°)
a
IID → IA /I IB → IC
IA → IIB / IC → IID
C12−H12···π5
C39−H39···π1
5.255
4.975
3.156
2.851
146.7
148.3
75.9
78.6
b
a
Symmetry codes: (a) −x, −y + 1, z − 1; (b) x, y, z + 1.
attached to the adamantane at the core and the phenyl groups
of the peripheral trityl moieties. Aromatic edge-to-face
interactions were identified by searching for close distances
among the aromatic C−H bonds and the π-ring centroids of
the phenyl and phenylene rings in the structure.23 Notably, two
sets of such interactions were identified. One involves only the
phenyl groups attached to the adamantane core, and the second
involves one of the adamantyl phenyls with three more phenyl
groups from the outer trityls. The first set is reported in Table 1
and shown schematically in Figure 5 with edge-to-face
and the face of C, the edge of C and the face of D, closing the
cycle with the edge of D and the face of A. Rings A and C are
related by a 2-fold symmetric axis and are crystallographically
nonequivalent to rings B and D, which are symmetrically
related to each other.
Shown in Figure 6 with a sketch that defines the notation
used below is the second set of “distorted” 4-fold phenyl
Figure 6. Distorted 4-fold phenyl embrace (4PE) including phenyl
rings attached to the adamantyl and trityl groups of two neighbors
along the chain shown in a schematic manner and in a space-filling
model (parts of the molecules were omitted for clarity).
Figure 5. Four-fold phenyl embrace involving four phenyl groups
linked to two different adamantyl moieties shown in a schematic
manner and in a space-filling model (parts of the molecules not
involved in the phenyl embraces were omitted for clarity).
embraces that can be identified. These involve one phenyl
group linked to the adamantyl moieties (labeled α and shown
in red), one phenyl ring from a trityl group within the same
molecule (labeled γ, in blue), and two from an adjacent
molecule along the chain (labeled β and γ, also in blue). As
indicated by the green arrows in the figure, the cyclic array in
this case follows a connectivity that goes from the edge of ring
α the face of ring β, from the edge of β to the face of γ, from the
edge of γ to the face of δ, with the cycle closing from the edge
of δ to the face of α. The geometric features of these
interactions, which are all distinct, are documented numerically
in Table 2.
The interaction in Figure 6 can be viewed as analogous to the
one present in tetraphenylmethane, with one of the rings
containing an acetylene group that acts as an extender and
distorts the symmetry of the molecule. It is notable that no
specific interactions appear to exist between trityl groups in
adjacent chains, indicating that the intermolecular 6-fold phenyl
embrace may not be sufficiently strong to dictate the formation
of extended tetrahedral networks.
interactions highlighted with green arrows. Included in the
table are the centroid-to-centroid distances below 5.3 Å, the
associated C−H···π distances, the C−H···π angles between the
C−H bond vector and a vector drawn from the aromatic
hydrogen to the centroid of the ring, and the angle Φ, formed
between the plane of the aromatic ring and the projection of
the C−H vector to the plane of aromatic ring. It should be
noted that idealized edge-to-face, or T-interactions would have
a π-centroid-to-π-centroid distance of ca. 5 Å, a C−H···π angle
of 90°, and an angle Φ = 180°. It is well-known however that
the corresponding potential is relatively soft and large variations
on these parameters are frequently observed. Analyzed closely,
the interaction in Figure 5 constitutes an asymmetric 4-fold
phenyl embrace similar to the one described by Boldog and co-
workers for the 1,3,5,7-tetraphenyladamantane, with two
phenyl groups from each side of the embracing molecules
involved in interactions along the two directions of the chain.24
The interaction is not symmetric as it pertains to the roles of
the phenyl groups involved in the edge-to-face interactions, as
illustrated schematically in the top of Figure 5 with aromatic
rings labeled A−D and the arrows indicating the direction of
the C−H···π vector. Interactions occur in a cyclic manner
between the edge of ring A and the face of ring B, the edge of B
CONCLUSIONS
■
We have prepared samples of tetrakis-1,3,5,7-(4′-(3″,3″,3″-
triphenylpropynyl)-phenylene)adamantane 1 and its deuterated
analogue 1-d60 and characterized their crystallization behavior
in order to evaluate the formation of 6-fold and 4-fold phenyl
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2852, 1596, 1504, 1490, 1446, 1031, 1026, 842, 834, 758, 740, 726,
695; HRMS C118H89 [M + H+] calcd 1505.6959; found 1505.6900
Tetrakis-1,3,5,7-(4′-(3″,3″,3″-triphenylpropynyl)-
phenylene)adamantane (1-d60). In a 100-mL three-neck round-
bottom flask were added 25 mL of distilled THF and 25 mL of
diisopropylamine and the solvents were degassed for 1 h with argon.
Compound 3-d15 (540 mg, 1.9 mmol), compound 5 (300 mg, 0.32
mmol), bis(triphenylphosphine)palladium(II) dichloride (22 mg,
0.031 mmol), and copper(I) iodide (6 mg, 0.032 mmol) were added
and the mixture was refluxed for 2 days under argon. The reaction
mixture was then washed with 25 mL of saturated ammonium chloride
solution and then extracted with DCM (50 mL then 2 × 25 mL). The
organic phases were then combined, washed successively with water
(25 mL) and brine (25 mL), dried over magnesium sulfate, and the
solvent was evaporated. The crude product was purified by silica gel
column chromatography (DCM/hexanes: 5:95 to 25:75) to afford 358
mg of compound 1-d60 as a white powder (72% yield). mp dec > 400
°C. 1H NMR (500 MHz, CDCl3): δ 7.55 (app d, 8H, J = 8.4 Hz), 7.46
(app d, 8H, J = 8.4 Hz), 2.16 (br s, 12H); 13C NMR (125 MHz,
CDCl3): δ 149.12, 145.37, 131.88, 129.07 (m), 127.63 (m), 126.45
(m), 125.09, 121.72, 95.68, 85.00, 56.08, 47.01, 39.42; FTIR (solid
HATR, cm−1): 3032, 2923, 2849, 2275, 1560, 1507, 1361, 1329, 1020,
904, 865, 838, 827; HRMS C118H29D60 [M + H+] calcd 1566.0725;
found 1566.0725.
Table 2. Geometric Parameters Involved in the Four-Fold
Phenyl Embrace Illustrated in Figure 6
a
πedge
π
→
face
π···π
(Å)
H···π
(Å)
C−H···π
(°)
contact
ϕ (°)
b
Iα → IIβ
IIβ → Iγ
Iγ → IIδ
IIδ → Iα
Iα′ → IIβ′
IIβ′ → Iγ′
Iγ′ → IIδ′
IIδ′ → Iα′
C9−H9···π2
4.674
4.882
5.131
4.955
4.602
5.201
5.522
4.421
2.655
2.979
3.462
3.037
2.799
3.299
3.744
2.996
139.6
133.8
123.9
134.9
127.9
134.3
129.9
112.5
79.6
82.3
71.9
77.8
80.1
75.7
65.8
79.5
c
b
c
c
b
c
b
C20−H20···π3
C27−H27···π4
C33−H33···π1
C36−H36···π6
C47−H47···π8
C60−H60···π7
C50−H50···π5
a
Symmetry codes: (b) x, y, z + 1; (c) x, y, z − 1.
embraces. Crystallization studies revealed the formation of
ultrathin fibrils that form a “gel-like” network, and long brittle
needles with well-developed edges and rectangular cross
sections. Both were analyzed by scanning electron microscopy.
Single crystal X-ray diffraction analysis of compound 1
confirmed the presence of two distinct 4-fold phenyl embraces
with a range of edge-to-face interactions that lead to the
formation of infinite molecular chains in a relatively close-
packed crystal structure. Weak intermolecular interactions
ASSOCIATED CONTENT
■
S
* Supporting Information
1
FTIR, H and 13C NMR spectra of compounds 1 and 1-d60.
1
detected in solution as a function of concentration by H
This material is available free of charge via the Internet at
http://pubs.acs.org.
NMR and a packing structure with multiple phenyl embraces
confirm that these interactions are ubiquitous and important
but perhaps not sufficiently strong to direct the packing motif
by themselves.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mgg@chem.ucla.edu.
■
EXPERIMENTAL SECTION
Compounds 2-d15, 3, 3-d15, and 5 were synthesized following reported
procedures. All commercial chemicals were used without further
■
Notes
The authors declare no competing financial interest.
1
purification. THF was distilled over sodium and benzophenone. H
and 13C NMR spectra were acquired in CDCl3 respectively at 500 and
ACKNOWLEDGMENTS
We thank the National Science Foundation for support through
Grant DMR1101934.
125 MHz on a Bruker spectrometer. NMR chemical shifts are reported
̈
■
in parts per million (ppm) relative to the residual peak of the solvent
(CDCl3: 1H δ = 7.26 ppm; 13C δ = 77.16 ppm). Multiplicity is
abbreviated to s (singlet), d (doublet), m (multiplet), br (broad), and
app (apparent). 2H NMR were acquired in natural abundance solvents
at 77 MHz. IR spectra were recorded on a Perkin-Elmer ATR-FTIR
instrument. Decomposition temperatures were determined using a
standard melting point apparatus. Mass spectra were acquired on an
Agilent 6210 LCMS system. The X-ray crystal structure was acquired
at 100 K on a Bruker Smart 1000K diffractometer. SEM pictures were
obtained using a JEOL JSM-6700F FE-SEM microscope.
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phenylene)adamantane (1). In a 50-mL three-neck round-bottom
flask were added 5 mL of distilled THF and 5 mL of diisopropylamine
and the solvents were degassed for 30 min with argon. Compound 3
(100 mg, 0.36 mmol), compound 5 (58 mg, 0.06 mmol),
bis(triphenylphosphine)palladium(II) dichloride (4 mg, 0.006
mmol), and copper(I) iodide (1.2 mg, 0.006 mmol) were added and
the mixture was refluxed for 2 days under argon. The reaction mixture
was then washed with 5 mL of saturated ammonium chloride solution
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phases were then combined, washed successively with water (5 mL)
and brine (5 mL), dried over magnesium sulfate and the solvent was
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1
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(60% yield). mp dec >400 °C. H NMR (500 MHz, CDCl3): δ 7.50
(app d, 8H, J = 8.3 Hz), 7.41 (app d, 8H, J = 8.3 Hz), 7.34−7.24 (m,
60H), 2.12 (br s, 12H); 13C NMR (125 MHz, CDCl3): δ 149.13,
145.52, 131.88, 129.34, 128.15, 126.96, 125.10, 121.71, 95.68, 85.07,
56.26, 47.02, 39.43; FTIR (solid HATR, cm−1): 3058, 3024, 2922,
3797
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