Sterically-limited self-assembly of Pt4 macrocycles into discrete non-covalent nanotubes: Porous supramolecular tetramers and hexamers

Article abstract of DOI:10.1002/chem.201201536

We report a template-free strategy based on steric repulsion for the isolation of discrete columnar aggregates of macrocycles. Specifically, introduction of sterically-demanding trityl-derived substituents at the periphery of Pt₄ Schiff base macrocycles limits the otherwise infinite one-dimensional columnar aggregation to discrete tetrameric and hexameric assemblies. Single crystal X-ray diffraction studies of these compounds reveal discrete nanotubes of finite length that pack inefficiently resulting in three-dimensional networks of interconnected void space. The discrete assemblies were studied by N₂ adsorption and show enhanced surface area when stacked. In the absence of bulky substituents the macrocycles are nonporous. This strategy for engineering discrete supramolecular macrocyclic aggregates may be generalized to other columnar assembling systems. Copyright

Full text of DOI:10.1002/chem.201201536

FULL PAPER
DOI: 10.1002/chem.201201536
Sterically-Limited Self-Assembly of Pt4 Macrocycles into Discrete Non-
covalent Nanotubes: Porous Supramolecular Tetramers and Hexamers
Peter D. Frischmann, Brian J. Sahli, Samuel Guieu, Brian O. Patrick, and
Mark J. MacLachlan*[a]
Abstract: We report a template-free
strategy based on steric repulsion for
the isolation of discrete columnar ag-
gregates of macrocycles. Specifically,
introduction of sterically-demanding
trityl-derived substituents at the pe-
riphery of Pt4 Schiff base macrocycles
limits the otherwise infinite one-dimen-
sional columnar aggregation to discrete
tetrameric and hexameric assemblies.
Single crystal X-ray diffraction studies
of these compounds reveal discrete
nanotubes of finite length that pack in-
efficiently resulting in three-dimension-
al networks of interconnected void
space. The discrete assemblies were
studied by N2 adsorption and show en-
hanced surface area when stacked. In
the absence of bulky substituents the
macrocycles are nonporous. This strat-
egy for engineering discrete supramo-
lecular macrocyclic aggregates may be
generalized to other columnar assem-
bling systems.
Keywords: macrocycles · micropo-
rous materials · platinum · self-as-
sembly · stacking interactions
Introduction
Controlling the aggregation of aromatic molecules into
well-defined stacks provides opportunities to study emer-
gent properties due to aggregation and allows for enhanced
engineering of supramolecular materials.[6] Common strat-
egies to access discrete aggregates of aromatic molecules
rely on H bonding,[7] electrostatic interactions,[8] or even en-
capsulation of aromatic guest molecules inside coordination
cages or virus capsids.[9] Rivera and co-workers reported
facile switching between discrete octameric, dodecameric,
and hexadecameric G tetrad assemblies due to a subtle bal-
ance of ion activity, H bonding, CH–p interactions, dipolar
interactions, and steric crowding.[10]
Nature consistently demonstrates the elegance of self-assem-
bly to organize simple molecules into complex functioning
nanosystems. Bottom-up synthetic approaches based on self-
assembly are now widely accepted as the most efficient
routes toward highly ordered, functional nanomaterials and
are much preferred over covalent strategies that lack the re-
versibility necessary for self-error-checking.[1] The next steps
in the development of functional self-assembled nanomateri-
als will require not only optimal molecular design to guide
the assembly, but also demand precise control over the di-
mensions of the self-assembled materials.[2] In Nature, pre-
cise aggregate control is best displayed by the tobacco
mosaic virus, which organizes into nanotubular aggregates
300 nm long with an 18 nm diameter resulting from the heli-
cal organization of 2130 coat proteins around a central
RNA template and the length of the template codes for the
dimensions of the assembly.[3] Utilizing similar templating
approaches, Stupp and co-workers demonstrated the dis-
crete aggregation of peptide amphiphiles organized around
a central phenylene ethynylene dumbbell shaped template,[4]
and Stoddart, Cronin, and co-workers reported a discrete
stack of 19 crown ether macrocycles as part of a [20]rotax-
ane templated by an oligoammonium thread.[5]
Organic macrocycles are one class of molecules that often
self-assemble into one-dimensional nanotubular architec-
tures and maintain their supramolecular structure after de-
AHCTUNGTRENNUNG
solvation.[11,12] Non-covalent nanotubes with permanent one-
dimensional channels frequently exhibit high surface area,
giving rise to a wealth of applications. Selective reactivity of
adsorbed guests[13] and interesting sensing applications may
arise with materials constructed in this fashion.[14] Columnar
aggregation of metal-containing macrocycles is also known;
however, the porosity of these materials has rarely been in-
vestigated.[15] In one recent report, solid-state oxidative po-
erization of columnar aggregated PtII-bipyridyl contain-
ACHUTNGRENlNUG ymACHTUNGTRENNUGN
ing macrocycles yielded microporous semiconductors with a
band gap tuned by selective guest adsorption.[16] Although
infinite one-dimensional aggregates of macrocycles are fre-
quently studied, very little is known about the discrete ag-
gregation of shape-persistent macrocycles, especially aggre-
gates beyond dimers.[17]
We recently reported the head-to-tail self-assembly of Pt4
macrocycles that organize into non-covalent nanotubes and
further self-assemble into nematic and columnar lyotropic
mesophases.[18] Here, we describe a method for controlling
[a] Dr. P. D. Frischmann, B. J. Sahli, Dr. S. Guieu, Dr. B. O. Patrick,
Prof. M. J. MacLachlan
Department of Chemistry, University of British Columbia
2036 Main Mall, Vancouver, BC, V6T 1Z1 (Canada)
Fax : (+1)604-822-2847
E-mail: mmaclach@chem.ubc.ca
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201536.
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the stacking of shape-persistent macrocycles without the use
of a template. By introducing sterically demanding substitu-
ents on the periphery of the macrocycles, as shown in
Figure 1, we have been able to stop aggregation at discrete
hexameric and tetrameric assemblies, which have both been
characterized in the solid state. This method of aggregation
control may be applicable for controlling the extent of ag-
gregation in other macrocyclic systems. Furthermore, we
demonstrate that the self-assembly of discrete macrocycle
aggregates generates materials with enhanced porosity.
Results and Discussion
Synthesis and characterization: Scheme 1 highlights the syn-
thetic routes for constructing Pt4 macrocycles 1a–d. The syn-
thesis of macrocycle 1a began by o-nitration of 4-(triphenyl-
methyl)phenol, 2a, with “claycop” followed by reduction of
the nitro group to give aminophenol 3a with the OH para
to the triphenylmethyl group. Imine condensation between
3a and 5-(3-pyridyl)salicylaldehyde yielded N-ONO imine
proACHTUNGTRENNUNGliACHTUNGTRENNUNGgand 4a. After heating K2PtCl4, K2CO3, and imine 4a
in DMSO to 1608C for 2 h, the reaction mixture was poured
into water, and pure 1a was isolated as a yellow powder by
centrifugation (75%).
Surprisingly, the synthetic crux in constructing Pt4 macro-
cycles 1b–d lies in the new chemistry developed for synthe-
sizing bulky aminophenols 3b–d (Scheme 1). Initially, we at-
tempted to synthesize 2-amino-4-[tris(4-tert-butylphenyl)-
ACHTUNGTRENNUNGmethyl]phenol (the OH-para isomer of 3c) by the same
route as 3a. However, 4-[tris(4-tert-butylphenyl)methyl]phe-
nol could not be nitrated in appreciable yield by a variety of
nitration strategies. Compound 3a has also been synthesized
with an electrophilic aromatic
Figure 1. Molecular structure of Pt4 macrocycles 1a–e.
substitution route.[19] This ap-
proach involves acid catalyzed
in situ dehydration of triphen-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
goes electrophilic aromatic
substitution of o-aminophenol
at the position para to the hy-
droxyl group. Attempts to iso-
late the OH-para isomer of 3c
from tris(4-tert-butylphenyl)-
methanol with the same reac-
tion conditions (refluxing HCl/
AcOH) were unsuccessful.
Literature procedures for in-
stalling tris(4-tert-butylphenyl)-
methyl groups on aromatic
rings use the desired activated
aromatic ring (e.g., phenol or
aniline) as the solvent during
triarylcarbenium cation gener-
ation (conducted at 1008C).[20]
In these cases the hydroxyl or
Scheme 1. Synthetic route to Pt4 macrocycles 1a–d. a) Compound 2a was mixed with a suspension of “clay-
cop” in ether/acetic anhydride. The nitrated product was reduced in THF with hydrazine and Pd/C. b) Amino-
phenol 3a–d and 5-(3-pyridyl)salicylaldehyde were heated at reflux in EtOH, cooled to room temperature,
and then filtered. c) Triarylmethanol 2b–d was heated at reflux in CH3COCl for 16 h, the solvent was re-
moved, and intermediate 2-Cl was mixed with solid tert-butyl-N-(2-hydroxyphenyl)carbamate and heated to
160–1658C for 15–30 min. d) Imine 4a–d, K2PtCl4, and K2CO3 were heated to 130–1558C in DMSO for 2–3 h
and 1a–d was isolated by centrifugation.
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Sterically-Limited Self-Assembly of Pt4 Macrocycles
FULL PAPER
amine functional group directs tritylation at the para posi-
tion. Attempts to isolate the OH-para isomer of 3c by the
same route with o-aminophenol as solvent (conducted at
1808C) were unsuccessful and yielded only unidentifiable
black tar-like residues. The observed decomposition was
likely due to the elevated reaction temperature required to
melt o-aminophenol (1728C) compared to phenol (418C) or
aniline (À68C). To reduce the reaction temperature, o-ami-
nophenol was replaced by tert-butyl-N-(2-hydroxyphenyl)-
carbamate (m.p. 1428C), and tris(4-tert-butylphenyl)metha-
nol was replaced by tris(4-tert-butylphenyl)methyl chloride
to avoid the otherwise necessary addition of an acid catalyst.
These two reagents were intimately mixed in the solid state
and heated to 1658C under inert atmosphere (Scheme 1,
step c). This procedure yielded 3c in 83% yield after work-
up. Despite literature precedent demonstrating OH to be a
stronger para directing group than NH2 and Boc-NH, our
conditions yield the NH2-para regioisomer, later confirmed
by single-crystal X-ray diffraction (SCXRD). Aminophenols
3b and 3d with NH2-para regiochemistry were prepared by
the same general procedure in 43 and 32% yield, respective-
ly.
tion yields intermediate i-2 and adventitious water reacts
with i-2 to evolve CO2 and product 3b–d. Imines 4b–d were
isolated from 3b–d and 5-(3-pyridyl)salicylaldehyde by the
same procedure as 4a (Scheme 1). The eight-component
self-assembly from imines 4a–d and PtII yielded Pt4 macro-
cycles 1a–d in 65–88% yield.
Even with bulky substituents, significant aggregation of
Pt4 macrocycles 1a–d is observed by matrix-assisted laser-
desorption time-of-flight (MALDI-TOF) mass spectrometry.
Aggregates as large as hexamers are observed for the bulki-
est macrocycle 1d at m/z 26883. Only Pt4 macrocycles 1c–d
are soluble enough in common organic solvents to permit
1H NMR spectroscopic analysis. Variable concentration
1H NMR experiments revealed that 1c dimerizes in CDCl3
with Kdim =3200CAHTUNGTRENNUNG
ic process was observed for 1d in CDCl3; however, spectral
overlap and intense monomer resonances in the 1H NMR
spectra prohibited quantitative analysis of the data. Extend-
ed solution aggregation is likely hindered by rotation of the
bulky triarylmethyl substituents.
Solid-state organization: Single crystals of 1c suitable for
SCXRD analysis were grown by slow evaporation of a
CHCl3/EtOH solution containing 1c. The crystals quickly
cracked upon removal from the mother liquor, and similar
behavior was observed when crystals were chilled on the dif-
fractometer below À508C due to co-crystallized solvent
evanescing. Because of the immense number of reflections
and disordered solvent mole-
The observed regiochemistry is rationalized by the pro-
posed mechanism shown in Scheme 2. Heating promotes in-
tramolecular transesterification and tBuOH leaves, generat-
ing 2(3H)-benzoxazolone, i-1.[21] Intermediate i-1 is a known
N-para directing agent in Friedel–Crafts acylation and reacts
with a triarylcarbenium cation formed in situ.[22] Deprotona-
cules in the structure of 1c,
synchrotron radiation was re-
quired to collect an adequate
data set. Pt4 macrocycle 1c
crystallizes in the monoclinic
space group P21/c with unit
cell dimensions, a=41.4112(8),
b=59.5868(12),
and
c=
64.3617(12) ꢁ,
a calculated
unit cell volume of 156483 ꢁ3,
and the unreduced formula
C
4704H4800N192O192Pt96 (exclud-
ing solvent). Without modeling
any disordered solvent, the
data set refined to R1=0.1334
and wR2=0.4435; however,
after applying the SQUEEZE
function of PLATON[23] to ac-
count for disordered solvent
occupying lattice voids, the
final refinement converged
with R1=0.0888 and wR2=
0.2804.[24] A total solvent acces-
sible void space of 102982 ꢁ3
was located in the SQUEEZE
analysis indicating that 66% of
the crystal volume is occupied
by disordered solvent.
Scheme 2. Proposed mechanism to explain the observed NH2-para regiochemistry of triarylmethyl-substituted
aminophenols 3b–d.
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M. J. MacLachlan et al.
A single unit cell of 1c contains 24 macrocycles arranged
into four discrete hexameric nanotubes. Figure 2 depicts the
asymmetric unit, a stacked hexamer with an external diame-
ter of approximately 40 ꢁ, a height of 35 ꢁ, and a central
nels are visible not only in the central nanotube but also
through the periphery. Winding channels created in the
space between the macrocycles and the bulky substituents
are also accessible to guest molecules and run perpendicular
to the axis of hexamer aggregation.
1H NMR spectroscopy data indicates that macrocycle 1c
has C4h symmetry in solution. When two macrocycles come
together in a face-to-face aggregate, there are two ways they
may associate: syn and anti. In the syn configuration, the
head-to-tail aggregation is arranged in the same direction
[both clockwise (CW) or counter-clockwise (CCW)] and in
the anti configuration the two macrocycles rotate in opposite
directions (CW/CCW). In the hexameric assembly of 1c ob-
served in the solid state, the macrocycles are arranged as
follows, when viewed from one end of the stack: CW, CCW,
CCW, CW, CW, CCW.[27] In other words, the face-to-face ar-
rangement of macrocycles alternate anti-syn-anti-syn-anti
through the stack.
Hexamers of 1c aggregate in a pseudolamellar fashion
and create significant porosity between layers. Convergence
of the channels running along the a- and c-axes, shown in
Figure 3a and c, respectively, makes an interconnected two-
Figure 2. Solid-state packing of Pt4 macrocycle 1c depicted as space fill-
ing. Each distinct macrocycle is represented as a different color and one
macrocycle is colored with the elemental composition (C=green, N=
blue, O=red, H=white, Pt=yellow). a) Side view of the hexamer omit-
ting peripheral substituents. b) Top-down view of a single macrocycle
with molecular dimensions. c) Side view of the hexamer showing the in-
terdigitated peripheral substituents. d) Top view of the hexamer.
channel 6 ꢁ in diameter (accounting for van der Waals
radii). There is one intermolecular Pt–Pt contact less than
the sum of the van der Waals radii (3.33 ꢁ, between the cen-
tral orange and yellow macrocycles);[25] however, the steri-
cally demanding periphery dominates the vertical alignment
of the macrocycles and does not rule out the potential for
extended axial Pt–Pt interactions in the absence of bulky
substituents. Within a single macrocycle the adjacent and di-
agonal Pt–Pt distances are 11 and 16 ꢁ, respectively.
Figure 2a visually captures the countering forces of favor-
able columnar aggregation and sterically-limited self-assem-
bly. Instead of aggregating as infinite columns, 1c must in-
creasingly deviate from planarity to accommodate the steric
requirements of the tris(4-tert-butylphenyl)methyl substitu-
ents. At the core of the hexamer, the two macrocycles (rep-
resented with yellow and orange in Figure 2a) are nearly co-
planar with sufficient space for the bulky periphery. As ad-
ditional macrocycles stack, the substituent “jigsaw puzzle”
(Figure 2c) becomes tighter until eventually the steric bulk
around the terminal macrocycles prevents further columnar
assembly.[26] The macrocycles capping the hexamer (green
and blue in Figure 2a) are puckered by as much as 538, al-
lowed by twisting of the pyridyl-salicylidine connection (di-
hedral angles from 20–368). Inefficient packing of the pe-
ripheral substituents is evident from Figure 2d where chan-
Figure 3. Extended packing of one unit cell containing 24 1c macrocycles.
View down the: a) a-axis, b) b-axis, and c) c-axis. Protons are omitted and
the tris(4-tert-butylphenyl)methyl substituents are represented as sticks to
help visualize the porous channels.
dimensional network of void space. The porous network is
extended in three dimensions through the channels in the
central nanotube and substituents, visible in Figure 2d. Off-
setting of the hexamer stacks down the b-axis is evident in
Figure 3b, preventing optimal viewing of these pores.
Bulkier substituents should limit aggregation to discrete
stacks smaller than hexamers and that is exactly what we
observe in the solid-state structure of 1d. SCXRD analysis
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Sterically-Limited Self-Assembly of Pt4 Macrocycles
FULL PAPER
was conducted on yellow prismatic crystals of 1d grown
from a CHCl3/DMSO solution. Macrocycle 1d crystallized
in the monoclinic space group C2/c where the unit cell con-
sists of four discrete tetrameric stacks of 1d with the dimen-
sions a=63.534(3), b=40.473(3), and c=51.828(2) ꢁ, calcu-
lated unit cell volume of 132928(12) ꢁ3, and unreduced for-
mula C4288H3968N128O128Pt64 (excluding solvent). Although
some co-crystallized CHCl3 molecules were located and
modeled in the final refinement, including one in the central
channel of the tetramer, many could not be found in the dif-
ference map. In the absence of solvent molecules,
SQUEEZE analysis revealed 59236 ꢁ3 of solvent-accessible
void space (45% of the unit cell volume). The final refine-
ment converged with R1=0.1190 and wR2=0.3859.
yl-4-yl)methyl groups are interwoven with the peripheral
groups of the other macrocycles. This back-folded conforma-
tion prevents further aggregation as the face of the bottom
macrocycle is effectively blocked by the peripheral groups
of the central macrocycles (Figure 4d).
When viewed from the end of the tetrameric stack, the
macrocycles in 1d are arranged in CW, CW, CCW, CCW
order. As with the hexameric assembly of 1c, this means
that the face-to-face arrangement of the macrocycles in 1d
alternate: syn-anti-syn.
The long-range packing of 1d tetramers is depicted in
Figure 5. If each tetramer is interpreted as a lattice point,
Four half macrocycles are found in the asymmetric unit of
1d making up half of the tetrameric stack depicted in
Figure 4. Each discrete tetramer has an external diameter of
approximately 45 ꢁ, a height of 31 ꢁ, and a central channel
6 ꢁ in diameter (accounting for van der Waals radii). Unlike
the hexamer, the two macrocycles at the core of the tetra-
ACHTUNGTRENNUNGmer (red and orange) are significantly distorted from planar-
ity, puckered by 438 and 498, respectively, and nesting one
inside the other. Interestingly, the macrocycle on top of the
stack (green) is nearly planar with the peripheral tris(4’-tert-
butylbiphenyl-4-yl)methyl groups opened like a flower (Fig-
ure 4b). Because of the phenyl extension at the periphery of
1d there is significantly more space near the core of the
stack compared to the hexamer of 1c. To fill this space, the
bottom macrocycle (yellow) folds back towards the center
of the tetramer where the peripheral tris(4’-tert-butylbiphen-
Figure 5. Extended packing of one unit cell of 1d where the second half
of four of the tetramers has been included for clarity. View down the:
a) a-axis, b) b-axis, and c) c-axis. Protons and co-crystallized CHCl3 mole-
cules are omitted and the tris(4’-tert-butylbiphenyl-4-yl)methyl substitu-
ents are represented as sticks to help visualize the porous channels.
the tetramers organize in a slightly distorted face-centered
cubic lattice with large solvent-accessible cavities, where
each cavity is surrounded by six tetramers. These larger void
spaces are connected due to inefficient packing between tet-
ramers and the central nanotubular channels resulting in a
three-dimensional network of guest-accessible void space.
Although we cannot conclude that Pt4 macrocycles 1a
and 1b organize the same as 1c or 1d in the solid state,
powder X-ray diffraction (PXRD) experiments show similar
reflections (see the Supporting Information) suggesting simi-
lar columnar aggregation. We hypothesize that 1a and 1b
Figure 4. Solid-state packing of a tetramer of 1d depicted as space filling.
Each distinct macrocycle is represented as a different color and one mac-
rocycle is colored with the elemental composition (C=green, N=blue,
O=red, H=white, Pt=yellow). a) Side view of the tetramer omitting pe-
ripheral substituents. b) Side view of the tetramer showing the interdigi-
tated peripheral substituents. c) Top-down view of the tetramer.
d) Bottom-up view of the tetramer. Co-crystallized CHCl3 has been omit-
ted for clarity.
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M. J. MacLachlan et al.
Table 1. BET and Langmuir surface area of 1a–e and 3a–d determined
from N2 adsorption at 77 K.
organize into much longer aggregates or even infinite col-
umnar arrays due to the smaller peripheral trityl substitu-
ents.
Compound
BET [m2 gÀ1
]
Langmuir [m2 gÀ1
]
1a
1b
1c
1d
1e
3a
3b
3c
3d
54
27
309
391
3
8
6
12
47
83
39
448
577
5
15
9
21
76
Nitrogen adsorption: Discrete molecules, once thought to be
nonporous due to efficient solid-state packing, are emerging
as alternative microporous materials with surprisingly high
surface area, low density, and adsorbate selectivity.[28,29] Mo-
lecular porosity may arise when individual molecules have
permanent covalent cavities (intrinsic porosity) or pack inef-
ficiently in the solid state (extrinsic porosity).[30] In the case
of macrocyclic assemblies, the parallel arrays of non-cova-
lent nanotubes with permanent one-dimensional porosity
may be considered intrinsically porous as the central cavity
is permanent. Sterically-limited aggregation of macrocycles
disrupts columnar packing and provides opportunities to en-
gineer extrinsic porosity into the solid-state organization.
Further insight into the porosity of Pt4 macrocycles was
obtained by N2 adsorption experiments. To clarify the influ-
ence on porosity of rigid aromatic/bulky substituents from
nanotube formation we tested the adsorption properties of
Pt4 macrocycles 1a–e and bulky aminophenols 3a–d. Dry
samples were heated to 1008C under vacuum for 2 h prior
to analysis, and PXRD analyses were acquired before and
after gas adsorption to confirm structural integrity was
maintained after analysis. Gas adsorption isotherms for Pt4
macrocycles 1a–d are depicted in Figure 6. BET and Lang-
muir surface area values are shown in Table 1. Isotherms for
macrocycles 1a–e and aminophenols 3a–d are best de-
space. In the absence of substituents, Pt4 macrocycle 1e is
nonporous and likely packs in a staggered fashion making
the central cavity inaccessible to adsorbates (see PXRD in
the Supporting Information). The combination of both pe-
ripheral steric bulk and sterically-limited non-covalent nano-
tube assembly dramatically enhances the surface area of
these molecules. Pt4 macrocycle assemblies exhibit molecu-
lar porosity as much as 25-times greater than the component
aminophenols (3c to 1c) due to the sterically-limited self-as-
sembled packing motif. Interestingly, macrocycles 1a and 1b
are regioisomers, where the trityl substituent is either para
to O or N, respectively; however, 1a has twice the surface
area of 1b. Trityl substituents of isomer 1a are located
closer to the core of the macrocycle and may further inhibit
nanotube aggregation resulting in smaller aggregates (e.g.,
tetramers) with greater net porosity. This observation sug-
gests that O-para isomers of 1c and 1d may also exhibit sig-
nificantly enhanced porosity over the N-para isomers report-
ed here. Even though the calculated void space of 1c is
larger than that of 1d, N2 adsorption experiments show that
1d has a higher surface area indicating that comparing the
calculated void space from SCXRD experiments is not
always a reliable method to quantitatively predict overall
surface area between similar structures.
ACHTUNGTRENNUNGscribed as Type I isotherms, classifying these materials as mi-
croporous.[31] The Pt4 macrocycle with the most sterically de-
manding periphery, 1d, exhibits the largest surface area,
391 m2 gÀ1 (BET), and an adsorption isotherm with mostly
Type I and some Type II characteristics.
Most notable from the surface area data presented in
Table 1 is the direct correlation between increased steric
bulk and increased surface area for both the aminophenols
and the Pt4 macrocycles. Bulkier substituents on the macro-
cycle periphery may enhance the extrinsic porosity[32] and/or
alter the extent of nanotube aggregation, creating more void
Conclusion
To accelerate the application of supramolecular materials,
new concepts for controlling the dimensions of self-assem-
bled materials are needed. This report highlights a new tem-
plate-free strategy for constructing discrete, porous, nano-
tubular aggregates of macrocycles that may be easily applied
to other macrocyclic systems. The remarkable solid-state
structures of shape-persistent Pt4 macrocycles equipped with
bulky substituents reveal stacked hexamers and tetramers.
By tuning the bulkiness of the substituents on the macrocy-
cle, it may be possible to accurately control the extent of ag-
gregation. We demonstrate through gas adsorption that ster-
ically-limited stacking of macrocycles is a way to obtain mo-
lecular materials with substantial porosity. Molecular engi-
neering of discrete Pt4 macrocycle aggregates with latent
functionality and enhanced surface area are ongoing efforts
in our laboratory.
Figure 6. N2 adsorption/desorption isotherms for Pt4 macrocycles 1a–d
(solid=adsorption, hollow=desorption).
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with N2 and transferred to the Schlenk flask containing the imine via sy-
ringe. The mixture was heated to 1308C for 3 h. The solution became
opaque as the product precipitated. After cooling to room temperature,
H2O (50 mL) was added and the suspension was centrifuged. The super-
natant was decanted and a wash, centrifuge, decant cycle was repeated
four more times, once with 30 mL of H2O and three times with 20 mL of
methanol. After drying, 290 mg (0.0999 mmol, 74%) of 1b was isolated
as a yellow-orange solid. The low solubility of the compound did not
allow for study by NMR spectroscopy.
Experimental Section
Materials: Compounds 1a, 1e, 3a, and 4a were prepared by our previ-
ously published procedures.[18] Compounds 1c, 3c, and 4c were prepared
by our previously published procedures; however, crystallographic evi-
dence presented here shows that they are N-para isomers and not the O-
para isomers originally reported.[18] For this reason the syntheses of cor-
rectly assigned N-para 1c, 3c, and 4c are reported here. Compounds
2a,[19] 2c,[20] 2d,[XXX] 5-(3-pyridyl)-salicylaldehyde,[33] and tert-butyl N-(2-
hydroxyphenyl)carbamate[34] were prepared by literature methods. Com-
pound 2b is commercially available. All reactions were carried out under
air unless otherwise noted.
Data for N-para-trityl Pt4 macrocycle (1b): MALDI-TOF MS: m/z (%):
2905 [M]+, 5812 [M2]+, 8714 [M3]+, 11619 [M4]+, 14524 [M5]+, 17429
[M6]+; FT-IR (neat): v˜ =3083, 3054, 3027, 2921, 2852, 1597, 1574, 1527,
1485, 1466, 1443, 1420, 1402, 1378, 1313, 1277, 1173, 1076, 1034, 1002,
977, 942, 915, 893, 869, 847, 795, 742, 699, 685, 664, 650, 634, 620, 605,
572, 553, 528, 491, 458, 436 cmÀ1; UV/Vis (CHCl3): lmax (e)=451 (5.7ꢂ
105), 427 (7.1ꢂ105), 306 nm (9.5ꢂ105 LmolÀ1 cmÀ1); elemental analysis
calcd (%) for C148H104N8O8Pt4·2CH3OH: C 60.72, H 3.80, N 3.78; found:
C 60.73, H 3.78, N 3.74; m.p.>3008C.
Equipment: 1H and 13C NMR spectra were recorded on a Bruker AV-
300, AV-400, or AV-600 spectrometer. 13C NMR spectra were recorded
by using a proton decoupled pulse sequence. 1H and 13C NMR spectra
were calibrated to the residual protonated solvent at d=7.27 and
77.00 ppm, respectively, in CDCl3, or at d=2.50 and 39.51 ppm, respec-
tively, in [D6]DMSO. UV/Vis spectra were obtained in CHCl3 or CH2Cl2
(ca. 1ꢂ10À6 m) on a Varian Cary 5000 UV/Vis/near-IR spectrophotometer
by using a 1 cm quartz cuvette. IR spectra were collected neat in the
solid state on a Thermo Nicolet 6700 FT-IR spectrometer. MALDI-TOF
mass spectra were obtained in a trans-2-[3-(4-tert-butylphenyl)-2-methyl-
2-propenylidene]-malonitrile (DCTB) matrix (1:10 analyte/matrix, sol-
vent free) at the UBC Microanalytical Services Laboratory on a Bruker
Biflex IV instrument. The best mass accuracy was achieved at low laser
power, and some accuracy was sacrificed when collecting with the high
laser power required to observe high mass aggregates. Electrospray ioni-
zation mass spectra (ESI-MS) were recorded on a Bruker Esquire LC in-
strument. Elemental analyses (C, H, N) were performed at the UBC Mi-
croanalytical Services Laboratory. Melting points were obtained on a
Fisher–Johnꢃs melting point apparatus. Intensity data for SCXRD were
collected for 1c on a D8 goniostat equipped with a Bruker APEXII
CCD detector at Beamline 11.3.1 at the Advanced Light Source (Law-
rence Berkeley National Laboratory) and for 1d on a Bruker APEX
DUO diffractometer with cross-coupled multilayer optics CuKa radiation
at the UBC X-ray diffraction facility. See the SCXRD section in the Sup-
porting Information for more details about the experiments. A Bruker
D8 Advance with Cu radiation and a NaI scintillation detector was used
for powder X-ray diffraction analysis. Nitrogen adsorption studies were
performed by using a Micromeritics ASAP 2000.
Synthesis of N-para-tris(4-tert-butylphenyl)methyl substituted Pt4 macro-
cycle (1c): A suspension of K2PtCl4 (83.5 mg, 0.201 mmol) in DMSO
(15 mL) was sparged with N2 and then heated to 1008C until all of the
salt dissolved. A separate Schlenk flask was charged with imine 4c
(141 mg, 0.201 mmol) and K2CO3 (42 mg, 0.30 mmol) and two cycles of
evacuation/N2 purging were conducted. The K2PtCl4 solution was trans-
ferred via syringe to the flask containing imine and K2CO3 and the mix-
ture was heated at 1558C for 3 h. The yellow suspension was cooled to
room temperature and H2O (50 mL) was added followed by centrifuga-
tion. After decanting the supernatant solution, four cycles of washing,
centrifuging, and decanting were performed, once with water and three
times with MeOH. Upon drying the precipitate, 117 mg of 1c was isolat-
ed as a yellow powder (0.0327 mmol, 65%).
Data for N-para-tris(4-tert-butylphenyl)methyl substituted Pt4 macrocy-
cle (1c): Dimerization and chemical shift equivalence prohibited full as-
signment of the 13C NMR data. Dimer 1H NMR (400 MHz, CDCl3): d=
8.89 (d, J=6.0 Hz, 1H), 8.52 (s, 1H), 8.22 (s, 1H), 7.80 (s, 1H), 7.63 (m,
1H), 7.58 (m, 1H), 7.38 (d, J=9.2 Hz, 1H), 7.30–7.25 (m, 13H), 7.21 (d,
J=8.4 Hz, 1H), 6.63 (m, 1H), 6.54 (m, 1H), 1.32 ppm (s, 27H); 13C NMR
(151 MHz, CDCl3): d=166.9, 162.3, 149.2, 148.6, 148.5, 148.4, 148.2,
147.7, 144.3, 144.3, 144.1, 143.2, 137.6, 137.3, 135.6, 134.0, 131.1, 131.0,
129.6, 124.9, 124.5, 124.4, 124.2, 123.6, 123.1, 122.8, 122.3, 120.5, 120.5,
114.3, 114.1, 64.1, 34.6, 34.5, 31.7 ppm; MALDI-TOF MS: m/z (%): 849
[4cPtÀ2H]+, 1789 [(4cPt)2À3H]+, 3576 [M]+, 7152 [M2]+, 10725 [M3]+,
14297 [M4]+, 17869 [M5]+; FT-IR (neat): v˜ =3084, 3029, 2958, 2903, 2866,
1604, 1575, 1506, 1482, 1463, 1362, 1317, 1269, 1174, 1018, 812, 800, 690,
576, 550 cmÀ1; UV/Vis (CH2Cl2): lmax (e)=452 (9.0ꢂ104), 426 (9.8ꢂ104),
312 nm (2.1ꢂ105 LmolÀ1 cmÀ1); elemental analysis calcd (%) for
C196H200O8N8Pt4: C 65.83, H 5.64, N 3.13; found: C 66.16, H 5.98, N 2.99;
m.p.>3008C.
Single-crystal X-ray diffraction study of 1c: CCDC-851250 (1c) contains
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. C1176H1200N48O48Pt24,
Mw =21456.42 gmolÀ1 yellow rod (0.20ꢂ0.15ꢂ0.06 mm3), monoclinic,
,
space group P21/c, a=41.4112(8), b=59.5868(12), c=64.3617(12) ꢁ, a=
g=90.00, b=99.8340(10), V=156483(5) ꢁ3, Z=4, 1calcd =0.804 gcmÀ3
000 =35976, radiation l=0.7749 ꢁ, T=225.0(1) K, 2qmax =34.548, 649278
,
F
reflections collected, 95287 unique (Rint =0.1278). Final GOF=1.539,
R1=0.1334, wR2=0.4435, R indices based on 51532 reflections with I>
2s(I). Further details can be found in the Supporting Information.
Synthesis of N-para tris(4’-tert-butylbiphenyl-4-yl)methyl substituted Pt4
macrocycle (1d): In a round-bottom flask, K2PtCl4 (223 mg, 0.537 mmol)
was dissolved in DMSO (50 mL) at 1008C and sparged with N2. A sepa-
rate Schlenk flask was charged with imine 4d (500 mg, 0.546 mmol) and
1.5 equiv K2CO3 (112 mg, 0.810 mmol) and then put through three evacu-
ation/N2 purging cycles. Under N2 the K2PtCl4 solution was transferred to
the Schlenk flask containing imine and K2CO3 with a cannula and the
suspension was submerged in an oil bath preheated to 708C. The reaction
mixture was then heated at 1558C for 3 h. Upon cooling to room temper-
ature, H2O (50 mL) was added yielding a yellow/brown precipitate that
was left at À108C for 1 h. The reaction mixture was then put through
five centrifuge, wash, and decant cycles (reaction mixture, H2O, and 3ꢂ
MeOH) and then dried under vacuum yielding 1d as a fine yellow
powder (532 mg, 0.119 mmol, 88%).
Single-crystal X-ray diffraction study of 1d: CCDC-877945 (1d) contains
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. X-ray crystal data for
1d: C268H248N8O8Pt4·4.5(CHCl3), Mw =9515.36 gmolÀ1
, yellow prism
(0.27ꢂ0.19ꢂ0.17 mm3), monoclinic, space group C2/c, a=63.534(3), b=
40.473(3), c=51.828(2) ꢁ, a=g=90.00, b=94.103(3), V=132928(12) ꢁ3,
Z=8, 1calcd =0.951 gcmÀ3, F000 =38696, radiation l=39.00 cmÀ1, T=90.0-
ACHTUNGTRENNUNG(0.1) K, 2qmax =101.328, 637374 reflections collected, 69889 unique (Rint =
0.146). Final GOF=1.34, R1=0.1190, wR2=0.3859, R indices based on
69889 reflections with I>2s(I). Further details can be found in the Sup-
porting Information.
Data for N-para tris(4’-tert-butylbiphenyl-4-yl)methyl substituted Pt4
macrocycle (1d): Dynamic behavior and the intensity of biphenyl reso-
nances prevented exact interpretation of the 1H and 13C NMR spectra.
1H NMR (600 MHz, CDCl3): d=9.02, 8.80, 8.76, 8.64, 8.53, 8.50, 8.48,
8.40, 8.36, 8.25, 8.16, 8.09, 7.94, 7.81, 7.79, 7.73, 7.67, 7.56–7.19, 7.07, 7.01,
6.96, 6.95, 6.84, 6.77, 6.76, 6.65, 6.60, 6.58, 6.52, 6.46, 6.38, 6.32, 6.22, 5.97,
Synthesis of N-para-trityl Pt4 macrocycle (1b): A Schlenk flask charged
with 4b (287 mg, 0.539 mmol) and K2CO3 (223 mg, 1.62 mmol) was sub-
jected to three cycles of evacuation/N2 purging. A second Schlenk flask
was charged with K2PtCl4 (235 mg, 0.566 mmol) and DMSO (50 mL) and
heated until complete dissolution of the salt. This solution was sparged
Chem. Eur. J. 2012, 00, 0 – 0
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M. J. MacLachlan et al.
5.89, 5.71, 1.37, 1.34, 1.33, 1.26, 1.23, 1.18 ppm; 13C NMR (150.9 MHz,
CDCl3): d=150.1, 149.9, 145.8, 145.7, 145.5, 139.0, 138.8, 138.6, 138.3,
138.2, 138.0, 137.8, 137.7, 137.6, 137.3, 131.4, 131.3, 130.8, 126.8, 126.7,
126.6, 126.4, 126.1, 125.9, 125.8, 125.7, 125.6, 125.4, 34.5, 34.4, 31.4, 31.3,
29.7, 29.6 ppm; MALDI-TOF MS: m/z (%): 4490 [M]+, 8973 [M2]+,
13451 [M3]+, 17930 [M4]+, 22406 [M5]+, 26883 [M6]+; FT-IR (neat): v˜ =
3027, 2961, 2903, 2867, 1605, 1575, 1526, 1496, 1463, 1423, 1393, 1379,
1363, 1314, 1269, 1197, 1173, 1146, 1113, 1004, 917, 810, 771, 764, 744,
693, 660, 637, 577, 563, 532, 463 cmÀ1; UV/Vis (CHCl3): lmax (e)=454
(7.7ꢂ104), 428 (8.2ꢂ104), 267 nm (3.4ꢂ105 LmolÀ1 cmÀ1); elemental anal-
ysis calcd (%) for C268H248N8O8Pt4·5H2O: C 70.29, H 5.68, N 2.45; found:
C 70.32, H 5.60, N 2.44; m.p.>3008C.
Synthesis of 5-[tris(4’-tert-butylbiphenyl-4-yl)methyl]-2-aminophenol
(3d): Compound 2d (2.40 g, 3.65 mmol) was suspended in acetyl chloride
(60 mL) under N2 and heated to reflux. After 16 h at reflux, the reaction
was cooled to room temperature and the solvent was removed under
vacuum yielding tris(4’-tert-butylbiphenyl-4-yl)methyl chloride as a white
solid. Without further purification, the solid was finely ground with
2.1 equiv tert-butyl N-(2-hydroxyphenyl)carbamate (1.64 g, 7.84 mmol) by
using a mortar and pestle to ensure intimate mixing of the solids. A
Schlenk tube was then charged with the finely ground mixture and two
evacuation/N2 purging cycles were performed. Under N2 the Schlenk
tube was then submerged in an oil bath that was preheated to 1608C.
The solids began to melt, turned blue/red, gas evolved, and finally the re-
action solidified. After 30 min at 1608C the reaction was removed from
the oil bath and cooled to room temperature. At room temperature the
crude solid was sonicated in a mixture of DCM and MeOH until every-
thing dissolved and then the solution was transferred to a round-bottom
flask. Silica gel (5–10 mL) was added to the solution followed by removal
of solvent under vacuum. A column was dry loaded with the crude prod-
uct on silica gel and eluted with DCM. Pure 3d eluted with an Rf of ap-
proximately 0.4 and was isolated as a light pink solid (880 mg, 1.18 mmol,
32%).
Synthesis of 2-amino-5-tritylphenol (3b): Trityl chloride (1.11 g,
3.98 mmol) and tert-butyl N-(2-hydroxyphenyl)carbamate (1.00 g,
4.78 mmol) were thoroughly mixed in a Schlenk tube and subjected to
three cycles of evacuation/N2 purging. The Schlenk tube was then im-
mersed in an oil bath preheated to 1208C and heated to 1608C over the
course of 15 min. Stirring was applied throughout the reaction. The solids
quickly melted and turned deep purple while gas evolved. The mixture
solidified after several minutes and was maintained at 1608C for an addi-
tional 15 min. After cooling to room temperature MeOH (15 mL) was
added and the mixture was stirred for 20 min, followed by filtration. The
dark purple solid (782 mg) thus obtained was dry-loaded onto a silica gel
column and eluted with 20:1 DCM/CH3CN. The product eluted with an
Rf of approximately 0.4. The desired fractions were concentrated yielding
604 mg (1.72 mmol, 43%) of pink solid that was pure by 1H NMR spec-
troscopy. The solid was used as is; however, an off-white solid could be
obtained after several recrystallizations from xylenes with significant re-
duction in yield.
Data for 2-amino-5-tritylphenol (3b): 1H NMR (400 MHz, [D6]DMSO):
d=8.81 (bs, 1H), 7.29–7.12 (m, 15H), 6.47–6.45 (m, 2H), 6.29 (dd, J=
8.4, 2.2 Hz, 1H), 4.45 ppm (bs, 2H); 13C NMR (100.6 MHz, [D6]DMSO):
d=147.1, 143.0, 134.5, 134.4, 130.5, 127.4, 125.6, 121.6, 117.4, 113.1,
63.8 ppm; ESI-MS (MeOH): m/z (%): 352.2 [M+H]+; HRMS (ESI)
calcd for C25H22NO: 352.1701; found: 352.1696 (À1.5 ppm); FT-IR (neat):
v˜ =3524, 3401, 3326, 3205, 1593, 1519, 1490, 1439, 1286, 1262, 1224, 1180,
1151, 1126, 1082, 1034, 1001, 977, 860, 823, 759, 745, 700, 659, 637, 613,
576, 535, 511, 493, 456, 411 cmÀ1; UV/Vis (CHCl3): lmax (e)=297 nm
(4.1ꢂ103 LmolÀ1 cmÀ1); m.p. 2388C (decomp.).
Data for 5-[tris(4’-tert-butylbiphenyl-4-yl)methyl]-2-aminophenol (3d):
1H NMR (300 MHz, [D6]DMSO): d=8.97 (bs, 1H), 7.62–7.58 (m, 12H),
7.47 (d, J=8.7 Hz, 6H), 7.30 (d, J=8.7 Hz, 6H), 6.58 (d, J=1.8 Hz, 1H),
6.52 (d, J=8.4 Hz, 1H), 6.43 (dd, J=8.4, 1.8 Hz, 1H), 4.49 (bs, 2H),
1.31 ppm (s, 27H); 13C NMR (100.6 MHz, [D6]DMSO): d=149.8, 146.1,
143.1, 137.3, 136.8, 134.6, 134.3, 131.0, 126.2, 125.7, 125.6, 121.5, 117.3,
113.3, 63.2, 38.9, 31.1 ppm; ESI-MS (MeOH): m/z (%): 748.5 [M+H]+;
FT-IR (neat): v˜ =3028, 2961, 2903, 2867, 1604, 1521, 1494, 1460, 1439,
1393, 1363, 1285, 1268, 1258, 1220, 1150, 1113, 1004, 875, 846, 817, 771,
764, 747, 733, 681, 619, 563, 547, 533, 455 cmÀ1; UV/Vis (CHCl3): lmax
(e)=269 nm (7.4ꢂ104 LmolÀ1 cmÀ1); elemental analysis calcd (%) for
C55H57NO: C 88.31, H 7.68, N 1.87; found: C 87.61, H 7.60, N 1.90; m.p.
2508C (decomp.).
Synthesis of N-para-trityl N-ONO imine (4b): A suspension of 3b:
(228 mg, 0.649 mmol) and 5-(3-pyridyl)salicylaldehyde (136 mg,
0.681 mmol) in tetrahydrofuran (20 mL) and ethanol (10 mL) was heated
at reflux for 10 h. The solvent was removed by rotary evaporation to pro-
duce a peach-colored solid. The product was purified by trituration with
hot methanol (30 mL) to yield 0.258 g of 4b (0.484 mmol, 71%).
Data for N-para-trityl N-ONO imine (4b): 1H NMR (400 MHz,
[D6]DMSO): d=13.94 (s, 1H), 9.72 (s, 1H), 9.06 (s, 1H), 8.90 (bs, 1H),
8.53 (bm, 1H), 8.06 (d, J=8.2 Hz, 1H), 8.00 (d, J=2.0 Hz, 1H), 7.77 (dd,
J=8.6, 2.4 Hz, 1H), 7.47 (dd, J=7.6, 4.9 Hz, 1H), 7.15–7.38 (m, 16H),
7.05 (d, J=8.6 Hz, 1H), 6.88 (d, J=1.6 Hz, 1H), 6.66 ppm (dd, J=8.6,
1.6 Hz, 1H); 13C NMR (100.6 MHz, [D6]DMSO): d=161.2, 160.9, 150.3,
147.9, 147.1, 146.8, 146.3, 133.3, 132.3, 131.2, 130.5, 130.4, 127.7, 127.5,
126.0, 122.2, 119.9, 119.0, 118.7, 117.6, 64.3 ppm; ESI-MS (DCM/MeOH):
m/z (%): 533.2 [M+H]+; HRMS (ESI) calcd for C37H29N2O2: 533.2229;
found: 533.2232 (+0.6 ppm); FT-IR (neat): v˜ =3059, 3019, 2973, 1618,
1596, 1490, 1474, 1408, 1300, 1278, 1256, 1246, 1172, 1128, 1118, 1083,
1064, 1033, 970, 953, 881, 853, 832, 823, 798, 748, 700, 662, 637, 614, 587,
491, 423 cmÀ1; UV/Vis (CHCl3): lmax (e)=374 (1.4ꢂ105), 261 nm (3.0ꢂ
105 LmolÀ1 cmÀ1); m.p. 273–2758C (decomp.).
Synthesis of 5-[tris(4-tert-butylphenyl)methyl]-2-aminophenol (3c): Inti-
mate mixing of the white powders tris(4-tert-butylphenyl)methyl chloride
(300 mg, 0.671 mmol) and tert-butyl-N-(2-hydroxyphenyl)carbamate
(480 mg, 2.29 mmol) in a Schlenk tube was followed by two cycles of
evacuation/N2 purging. The Schlenk tube was then submerged in an oil
bath preheated to 1508C while being stirred under inert atmosphere.
Over 15 min, the reaction was heated to 1658C and during that time tert-
butyl N-(2-hydroxyphenyl)carbamate melted, the solution turned deep
red, gas evolved, and then the mixture rapidly solidified. When gas evolu-
tion ceased, the heat was turned off and upon cooling to room tempera-
ture a pink solid was isolated. The crude mixture was dissolved in DCM
with a little MeOH, dry loaded onto silica gel, and subjected to column
chromatography in 40:1 DCM/CH3CN (product eluted with an Rf of
~0.5). The desired fractions were combined and dried under reduced
pressure to give 3c as a pink solid (289 mg, 83%). Recrystallization from
toluene/hexanes gave 3c as a white solid in high purity for satisfactory el-
emental analysis.
Synthesis of N-para-tris(4-tert-butylphenyl)methyl substituted N-ONO
imine (4c): A round-bottom flask was charged with 5-(3-pyridyl)-salic
ACHTUNGTRENNUNGyl-
AHCTUNGTRENNUNG
1
(20 mL) then heated at reflux for 15 h. The reaction was cooled to room
temperature and imine 4c was isolated by filtration as an orange solid
(151 mg, 67%).
Data for 5-[tris(4-tert-butylphenyl)methyl]-2-aminophenol (3c): H NMR
(400 MHz, [D6]DMSO): d=8.76 (bs, 1H), 7.27 (d, J=8.5 Hz, 6H), 7.09
(d, J=8.5 Hz, 6H), 6.50 (d, J=1.7 Hz, 1H), 6.44 (d, J=7.9 Hz, 1H), 6.33
(dd, J=7.9, 1.7 Hz, 1H), 4.40 (bs, 2H), 1.26 ppm (s, 27H); 13C NMR
(100.6 MHz, CDCl3): d=148.3, 144.2, 142.7, 132.0, 130.8, 124.4, 124.0,
118.5, 115.7, 63.1, 34.3, 31.4 ppm; ESI-MS (MeOH): m/z (%): 520.6 [M+
H]+, 411.5 [MÀC6H6NO]+; FT-IR (neat): v˜ =3085, 2057, 2958, 2901,
2866, 1506, 1475, 1441, 1285, 1269, 1202, 1018, 823, 705, 578 cmÀ1; UV/Vis
(CH2Cl2): lmax (e)=303 nm (3.8ꢂ103 LmolÀ1 cmÀ1); elemental analysis
calcd (%) for C37H45NO: C 85.50, H 8.73, N 2.69; found: C 85.22, H 8.73,
N 2.68; m.p. 3008C (decomp.).
Data for N-para-tris(4-tert-butylphenyl)methyl substituted N-ONO
imine (4c): 1H NMR (400 MHz, [D6]DMSO): d=13.96 (s, 1H), 9.70 (s,
1H), 9.04 (s, 1H), 8.90 (bs, 1H), 8.53 (bs, 1H), 8.06 (m, 1H), 7.99 (d, J=
2.8 Hz, 1H), 7.76 (dd, J=8.8, 2.8 Hz, 1H), 7.47 (m, 1H), 7.33 (d, J=
8.8 Hz, 6H), 7.28 (d, J=8.8 Hz, 1H), 7.15 (d, J=8.8 Hz, 6H), 7.05 (d, J=
8.4 Hz, 1H), 6.92 (d, J=2.0 Hz, 1H), 6.69 (dd, J=8.4, 2.0 Hz, 1H),
1.27 ppm (s, 27H); 13C NMR (100.6 MHz, CDCl3): d=162.6, 160.8, 149.2,
148.9, 148.2, 147.8, 143.5, 133.8, 132.7, 132.0, 130.8, 130.7, 130.6, 129.3,
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Sterically-Limited Self-Assembly of Pt4 Macrocycles
FULL PAPER
124.6, 124.2, 124.0, 119.8, 119.1, 118.2, 117.2, 63.7, 34.3, 31.4 ppm; ESI-
MS (MeOH): m/z (%): 701.7 [M+H]+, 699.7 [MÀH]À; FT-IR (neat): v˜ =
3084, 3057, 2959, 2902, 2866, 1623, 1587, 1532, 1505, 1476, 1418, 1269,
1244, 1171, 1109, 1017, 833, 822, 801, 750, 705, 680, 635, 586 cmÀ1; UV/
Vis (CH2Cl2): lmax (e)=378 (2.9ꢂ104), 263 nm (5.7ꢂ104 LmolÀ1 cmÀ1); el-
Lehn, Angew. Chem. 2004, 116, 3781; Angew. Chem. Int. Ed. 2004,
43, 3695.
[8] a) M. Martꢅn-Hidalgo, J. M. Rivera, Chem. Commun. 2011, 47,
12485; b) L. Di Costanzo, S. Geremia, L. Randaccio, R. Purrello, R.
Lauceri, D. Sciotto, F. G. Gulino, V. Pavone, Angew. Chem. 2001,
113, 4375; Angew. Chem. Int. Ed. 2001, 40, 4245.
emental analysis calcd (%) for C49H52O2N2·1= H2O: C 82.90, H 7.52, N
2
3.95; found: C 82.69, H 7.38, N 3.91; m.p. 3008C (decomp.).
[9] a) M. Brasch, A. de La Escosura, Y. Ma, C. Uetrecht, A. J. R. Heck,
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Synthesis of N-para tris(4’-tert-butylbiphenyl-4-yl)methyl substituted N-
ONO imine (4d): A round-bottom flask was charged with 3d (617 mg,
0.825 mmol) and 5-(3-pyridyl)-salicylaldehyde (164 mg, 0.823 mmol) in
EtOH (50 mL) and heated at reflux for 2 h. The orange suspension was
cooled to room temperature, filtered on a Buchner funnel, and the pre-
cipitate was washed with MeOH until the filtrate was nearly colorless.
Upon drying the solvent-swollen product under vacuum, imine 4d was
isolated as a deep red solid (660 mg, 0.721 mmol, 88%).
Data for N-para tris(4’-tert-butylbiphenyl-4-yl)methyl substituted N-
ONO imine (4d): 1H NMR (300 MHz, [D6]DMSO): d=13.97 (s, 1H),
9.81 (s, 1H), 9.09 (s, 1H), 8.90 (bs, 1H), 8.53 (bs, 1H), 8.06 (d, J=8.1 Hz,
1H), 8.02 (s, 1H), 7.77 (dd, J=8.7, 1.8 Hz, 1H), 7.67–7.59 (m, 13H), 7.47
(d, J=8.4 Hz, 7H), 7.36 (d, J=8.4 Hz, 6H), 7.06 (d, J=8.7 Hz, 1H), 7.01
(d, J=1.8 Hz, 1H), 6.81 (dd, J=8.7, 1.8 Hz, 1H), 1.30 ppm (s, 27H);
13C NMR (100.6 MHz, [D6]DMSO): d=161.2, 161.0, 150.5, 149.9, 147.9,
147.1, 146.7, 145.2, 137.6, 136.6, 133.3, 132.4, 131.2, 130.9, 130.4, 127.6,
126.2, 125.9, 125.7, 123.8, 122.1, 119.9, 118.9, 117.6, 63.7, 34.2, 31.1 ppm;
MALDI-TOF MS: m/z (%): 929.7 [M+H]+; FT-IR (neat): v˜ =3027,
2959, 2902, 2866, 1621, 1572, 1493, 1421, 1392, 1362, 1294, 1268, 1173,
1112, 1003, 878, 804, 764, 744, 708, 673, 627, 563, 533, 491 cmÀ1; UV/Vis
(CHCl3): lmax (e)=376 (1.3ꢂ104), 269 nm (9.3ꢂ104 LmolÀ1 cmÀ1); ele-
mental analysis calcd (%) for C67H64N2O2: C 86.60, H 6.94, N 3.01;
found: C 85.84, H 6.95, N 2.98; m.p. 266–2678C.
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Acknowledgements
We are grateful to NSERC (Discovery Grant) for funding. P.D.F. thanks
UBC for a Pacific Century Graduate Fellowship. Crystallographic data
for 1c were collected through the SCrALS (Service Crystallography at
Advanced Light Source) program at the Small-Crystal Crystallography
Beamline 11.3.1 (developed by the Experimental Systems Group) at the
Advanced Light Source (ALS). The ALS is supported by the US Depart-
ment of Energy, Office of Energy Sciences Materials Sciences Division,
under contract DE-AC03-76SF00098 at Lawrence Berkeley National
Laboratory.
´
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M. J. MacLachlan et al.
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Received: May 2, 2012
Published online: && &&, 0000
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Chem. Eur. J. 0000, 00, 0 – 0
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Sterically-Limited Self-Assembly of Pt4 Macrocycles
FULL PAPER
Stacked to the max: Sterically
Self-Assembly
demanding substituents limit the col-
umnar organization of metallomacro-
cycles into discrete hexamers and tet-
ramers (see figure). By limiting one-
dimensional macrocycle aggregation to
finite non-covalent nanotubes, signifi-
cant molecular porosity is engineered
into the materials. The concepts pre-
sented here for isolating discrete
aggregates may be generalized to
other one-dimensional assembling sys-
tems.
P. D. Frischmann, B. J. Sahli, S. Guieu,
B. O. Patrick,
M. J. MacLachlan* .......... &&&& — &&&&
Sterically-Limited Self-Assembly of
Pt4 Macrocycles into Discrete Non-
covalent Nanotubes: Porous Supramo-
lecular Tetramers and Hexamers
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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