Development of Solvent-Dispersible Coordination Polymer Nanocrystals and Application as Efficient Heterogeneous Catalysts

Article abstract of DOI:10.1021/acs.cgd.6b00502

Nonporous coordination polymers (CPs) constructed from flexible bridging ligands have seldom been utilized in practical applications, owing to limited solubility and/or stability in most solvents. Here we have produced nanocrystal coordination polymers (N

Full text of DOI:10.1021/acs.cgd.6b00502

Article
pubs.acs.org/crystal
Development of Solvent-Dispersible Coordination Polymer
Nanocrystals and Application as Efficient Heterogeneous Catalysts
†
,†
,‡
,†
Kiattipoom Rodpun, Nigel T. Lucas,* Eng W. Tan,* and Carla J. Meledandri*
†Department of Chemistry and The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, P.O.
Box 56, Dunedin 9054, New Zealand
‡
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
*
S Supporting Information
ABSTRACT: Nonporous coordination polymers (CPs) con-
structed from flexible bridging ligands have seldom been
utilized in practical applications, owing to limited solubility
and/or stability in most solvents. Here we have produced
nanocrystal coordination polymers (NCPs) with identical
crystalline structure to their macroscale counterparts, high
solvent dispersibility, and large effective surface area for
catalytic application. A microemulsion system has been
II
II
developed for the mild synthesis of the Zn - and Cu -NCPs,
resulting in control over the size, morphology, and reactivity.
II
II
Both Zn - and Cu -NCPs demonstrated high catalytic activity
in a ring opening reaction of cyclohexene oxide with aniline;
furthermore, reduced Cu-NCPs were employed as efficient,
reusable catalysts for an azide−alkyne cycloaddition “click” reaction in the nonpolar solvent heptane. In contrast, all macroscale
CP equivalents, prepared by conventional methods, were catalytically inactive.
INTRODUCTION
ever, the potential applications of these CPs are restricted on
account of their insolubility in nonpolar solvents as a result of
their charged network structures and instability in coordinating
polar solvents. To overcome these disadvantages and to
develop their catalytic application, herein we describe the
preparation of Zn - and Cu -CPs nanocrystals using a mild,
specifically modified microemulsion-based process. As NCPs,
these materials have solvent dispersibility while maintaining the
benefits of bulk CPs; namely, a well-defined and tailorable
composition.
■
Metal−organic materials with nanoscale dimensions, or nano-
crystal coordination polymers (NCPs), are an exciting new
class of tailorable materials that radically expand the scope of
utility of their more traditional macroscopic counterparts. For
instance, macroscopic CPs typically exhibit limited solution-
II
II
1
based behavior, but decreasing their size to the nanoscale can
afford novel properties that differ from the bulk crystal, such as
2
colloidal dispersibility. Scientists have only recently started to
appreciate the significant range of application potential of these
3
−7
materials, particularly in the areas of catalysis,
drug
molecular (ad)sorption, and as
The versatile properties of NCPs can
significantly increase the value of macroscale CPs beyond
8
−11
12−16
17
delivery,
sensing,
Factors that control the size, surface chemistry, size
distribution, morphology, and crystallinity of this new class of
materials remain poorly understood. High-profile studies have
been published, which report the preparation of nanoscale
8
,18−21
imaging agents.
22
structural investigations in terms of crystal engineering, which
have formed the bulk of the work in the general research area.
Only two types of materials classified as NCPs have been
synthesized to date: nanoscale metal organic frameworks
27
coordination polymer nanocrystals with novel shapes, but
researchers are only in the early stages of understanding which
reaction conditions to modify in order to control the size and
shape of the resulting NCPs. Our current work also addresses
this issue; the NCPs prepared have controllable morphology
and surface area, and we have identified a key factor affecting
their formation.
2
3
24
(
NMOFs) and amorphous NCPs. These NCPs are typically
prepared through the use of rigid organic ligands or building
units, combined with metals, resulting in the formation of
metal−ligand particles, often with porosity in multiple
2
5
dimensions. Nonporous, crystalline CPs prepared from
flexible multifunctional ligands are underexploited in applica-
tions requiring high dispersibility.
We recently reported the synthesis and characterization of
Received: March 31, 2016
Revised: May 6, 2016
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Zn - and Cu -coordination polymers of flexible ditopic
26
carboxylate-containing ligands (denoted CnCOOH). How-
©
XXXX American Chemical Society
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Figure 1. Schematic representation of NCP synthesis through the use of three water-in-oil (w/o) microemulsions (M = Zn, Cu; n = 3, 5, 10, 11).
Details of the synthesis are described in the text.
II
Figure 2. Representative TEM images obtained for Cu -C5COOH NCP samples prepared through (a) a fast rate of NaHCO addition and (b) a
3
slow rate of NaHCO addition.
3
RESULTS AND DISCUSSION
microemulsions. The second microemulsion contained an
■
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aqueous solution of M(ClO ) ·6H O within the reverse micelle
4
2
II
2
Preparation of NCPs. Zn - and Cu -NCPs were prepared
II
cores, where M = Zn or Cu . The two microemulsions were
mixed (Figure 1a), during which time reverse micelle collisions
and coalescence of the droplets took place, leading to exchange
of the solubilized contents. The CnCOOH ligand remained
protonated, preventing crystal nucleation at this stage (Figure
1b). A third microemulsion (microemulsion 3) was prepared,
using tailored modifications of a conventional microemulsion-
2
8−32
based synthesis,
the process of which is depicted in Figure
1
, and briefly described here. Two microemulsions were
prepared, which separately contained synthetic precursors
within the aqueous core of the reverse micelles. In the present
case, the CnCOOH ligand (n = 3, 5, 10, or 11) was dissolved in
0
.1 M H SO to retain the protonated state of the N atoms, and
which contained a saturated solution of NaHCO within the
3
2
4
it was this acidic solution that formed the inner core of the
reverse micelles in one of the two initially prepared
reverse micelle cores. Upon addition of basic microemulsion 3
to the mixture of the first two microemulsions (Figure 1c),
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Article
collision and coalescence of the reverse micelles led to
deprotonation of the ligand, enabling subsequent growth of
micrographs are 40 ± 9 and 17 ± 4 nm, respectively. With
this in mind, the overall size of the raspberry-like structures
could potentially be controlled by intentionally preparing either
greater or fewer numbers of seed crystals within each cluster,
adjusted through variation of the total amount of reactive ligand
used in the synthesis.
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II
the Zn - or Cu -NCPs (Figure 1d). NCP extraction was
carried out through addition of excess polar solvent, which
destabilizes the microemulsion and induces phase separation
3
3,34
(Figure 1e).
In all cases, the NCPs were found to partition
into the nonpolar heptane phase, which was subsequently
separated, washed, and retained for further characterization.
NCP Crystal Structure. X-ray powder diffraction (XRPD)
was used to characterize the crystal structure of each NCP
sample by comparing the XRPD pattern to that of the
conventionally prepared, macroscopic CP counterpart (follow-
ing grinding to a fine powder), as demonstrated by Kitagawa et
The rate of microemulsion 3 (NaHCO ) addition emerged
3
as a key factor contributing to the mechanism of NCP
formation, as NaHCO causes deprotonation of the nitrogen
3
35
II
donor atoms of the CnCOOH ligand, thereby initiating
complexation and crystallization. Transmission electron mi-
croscopy (TEM) images for representative NCP samples
prepared using a faster and slower rate of microemulsion 3
addition are shown in Figure 2. No significant differences in
particle morphology were apparent across the entire series of
al. The XRPD patterns for representative samples of Cu -CPs
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and their Cu -NCP counterparts are shown in Figure 3 (a
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Zn and Cu NCPs; alkyl chain length of the ligand caused no
detectable difference in the NCP morphology (see Figures S1−
II
S4 for TEM images of some Zn -NCPs prepared in this study).
From the images, it is clear that the rate of addition affects the
size and shape of the all NCPs. A faster addition resulted in the
formation of single crystals of elongated nonspherical structures
(Figure 2a). In contrast, very discrete seed crystals clustered
together to form raspberry-like structures with a slow rate of
microemulsion 3 addition (Figure 2b). These differences can be
explained in terms of the concentration of reactive solution
species during the formation and growth of the nanocrystals.
Through rapid addition of NaHCO , a high concentration of
3
reactive (deprotonated) ligand is present from the beginning of
the process, and continuous stirring of the microemulsion
mixture ensures a high rate of reactive ligand/metal mixing.
TEM images of NCPs prepared via rapid addition of NaHCO3
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Figure 3. XRPD patterns for representative samples of Cu -C5COOH
(top) CPs and Cu -C5COOH NCPs (bottom).
II
(Figure 2a) show a relatively uniform size and shape of the
NCPs; the length and width of 313 particles were measured
directly from the micrographs as 28 ± 8 and 13 ± 4 nm,
respectively. A fast nucleation process is essential for obtaining
such a monodisperse size distribution. During this process, all
nuclei are rapidly generated at the same time, then continue to
grow until all ligand is consumed, leading to a highly uniform
NCP size. If nucleation events were to occur at multiple times
throughout the process, the growth history of the NCPs would
not be equivalent, leading to a more polydisperse size
distribution.
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series of XRPD patterns of Zn - and Cu -CPs and NCP
samples can be found in the Supporting Information). The
XRPD patterns of the NCPs in all cases are well coincident
with those of their macroscopic crystal counterparts, and no
apparent broadening of the peaks of the nanoscale samples was
observed. Such broadening can occur as a result of amorphous
components within the sample; thus, the absence of broadening
reveals the NCP samples were highly crystalline with good
phase purity, despite the presence of other anions during the
synthesis (e.g., SO42 ). A review of the relevant literature
reveals that discussion related to the coordination environment
of macroscopic crystals and comparison with NCP counterparts
are relatively rare. To our knowledge, only one published report
has demonstrated the coordination environment of NCPs
−
Through slower addition of NaHCO , the reactive ligand
3
concentration is limited throughout the synthesis and is under
experimenter control. In other words, the interval between the
addition of each microemulsion 3 (NaHCO -containing)
3
droplet to the acidic microemulsion 1 and 2 mixture was
extended over a long period of time. In this way, the
deprotonated ligand concentration is initially very low; hence,
NCP size saturation occurs rapidly as crystal growth is arrested
before the next droplet addition. This leads to the ultrasmall
size of the seed crystals, estimated to be in the range of 4−6
nm. The seed crystals can then act as nucleation templates to
provide sites for the formation of additional nuclei/seed
3
6
(gadolinium NMOFs), making our study, when considered
26
together with our previously published work, quite unique.
Having established that each type of NCP synthesized in this
work has an identical crystal structure to that of its equivalent
macroscopic crystal, it was of interest to estimate the number of
monomers (and thereby metal centers) contained within each
NCP. From the X-ray crystallography of the macroscale CP
crystals, the volume of each monomer can be accurately
determined, which, when compared with seed crystal volume
from TEM, allows the total number of monomers per NCP to
be estimated. For example, the ultrasmall seed crystals of Cu -
C5COOH shown in Figure 2b have an average particle volume
estimated to be 60 nm and a monomer volume of 0.56 nm
from crystallography, suggesting that there is on the order of
26
crystals, upon further addition of NaHCO . This process
3
continues until either the addition of NaHCO is terminated or
3
the initial amount of the ligand or metal ions present within the
reverse micelles has been completely consumed, and the overall
result is the formation of raspberry-like NCP clusters composed
of a number of ∼4−6 nm seed crystals (Figure 2b). The length
and width of 203 clusters measured directly from the
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3
3
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Crystal Growth & Design
00 monomer units per particle. It is anticipated that a large
Article
1
proportion of the monomer metal centers are located on the
surface, thereby influencing both the physical properties and
chemical reactivity of these particles.
NCP Surface Characteristics. Zeta potential measure-
ments of NCPs dispersed in heptane revealed NCP surfaces
carry a significant positive charge (ζ > +60 mV), the source of
which must come from terminal surface-bound metal ions.
Assuming that the NCPs, particularly the raspberry-like NCPs,
are formed through the mechanism described above, then the
slow addition of NaHCO causes the introduction of a low
3
concentration of reactive deprotonated ligands to a system in
which metal ions are in excess, at least until the final stages of
the process. Seed crystal growth will proceed until the available
monomer units in solution are consumed, and considering the
Figure 4. Reactions investigated using the NCPs synthesized as
catalysts: (a) ring opening addition of aniline to cyclohexene oxide;
(
b) azide−alkyne cycloaddition “click” reaction between benzyl azide
26
and phenylacetylene.
1:1 metal−ligand complex stoichiometry and the excess of
metal ions in solution, the CPs likely terminate with a metal
cation at the NCP surface, resulting in the positive zeta
potential values observed.
(phenylamino)cyclohexanol (Figure S15, Supporting Informa-
tion).
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This premise was validated through attenuated total
reflectance-infrared (ATR-IR) spectroscopy measurements. IR
spectra for relevant ligand and CP and NCP samples, along
with the corresponding band assignments, are provided in the
Supporting Information (Figures S10−S14, Table S2). Analysis
of NCP IR spectra revealed a notable absence of the CO
stretching mode observed in spectra obtained for the
corresponding CPs prepared on the macroscopic scale, and
observed more prominently in the spectra for the ditopic
carboxylate ligands prior to complexation. The absence of the
CO stretching mode for NCP samples can be interpreted as
substantial or complete coordination of the carboxylate oxygen
atoms of the ligand to the metal ions, as would be the case if the
coordination terminates at a metal ion. As the CP crystals
prepared on the macroscopic scale were not formed under
conditions of a large excess of metal ions, predictions of the
surface composition becomes more difficult. In this case,
growth of the CPs would not necessarily terminate at a metal
ion, hence the presence of a weak CO stretching vibration
observed in the IR spectra of the CPs (see Supporting
Information).
Catalytic Activity of NCPs. The NCPs prepared,
particularly the raspberry-like NCPs, have enhanced surface
area due to their nanoscale structure and a high density of metal
ions at their surfaces, and were investigated for catalytic activity
in two distinct reactions. Due to the dispersibility of the NCPs
in heptane, catalytic reactions rarely performed in nonpolar
solvents due to the insolubility of homogeneous catalysts were
selected to be the focus of the investigation. In this study, the
ring opening reaction of cyclohexene oxide with aniline and the
Both Zn - and Cu -NCPs can be employed as an efficient
catalyst for the ring opening reaction and can be easily
recovered by filtration and reused three more times without a
significant loss in their activity (see Supporting Information).
No obvious signs of catalyst leaching were observed (from the
appearance and NMR analysis of the crude product).
Furthermore, it should be noted that a molar equivalent of
the insoluble, finely ground powders of the metal perchlorate
II
precursors and the macrocrystalline counterparts of the Zn -
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and Cu -NCPs were all found to be inactive in this reaction,
even with extended reaction times.
Although a large number of literature reports have involved
studies of the catalytic ring opening reaction of epoxides with
39,40
amines,
few accounts exist of the use of coordination
polymers or nanoscale materials as the corresponding catalysts
41,42
II
for these reactions.
Tanaka et al. utilized a Cu -MOF as a
catalyst for the ring opening reaction of cyclohexene oxide with
43
aniline. The catalytic mechanism of this reaction has been
proposed to involve the heterogeneous catalyst acting as a
44
Lewis acid. In this mechanism, the reaction takes place at
Lewis acidic Cu sites, which play an important role as electron
acceptors to increase the reactivity of the starting materials. As
the zeta potential values of our NCPs were characterized as
being highly positive, these results support the hypothesis that
the catalytic activity is associated with Lewis acidity of the
43
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NCPs. Compared with the work of Tanaka, our Zn - and
II
Cu -NCPs have higher catalytic activity, as demonstrated by a
relatively shorter reaction time and higher percentage yield.
The larger overall surface area, due to the nanoscale size effect,
is presumably the major contributing factor to the catalytic
performance of our NCPs.
3
7,38
azide−alkyne cycloaddition “click” reaction
were selected as
The copper-catalyzed azide−alkyne cycloaddition “click”
37,38
representative reactions (Figure 4).
reaction
between benzyl azide and phenylacetate, carried
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Heptane suspensions of Zn - and Cu -C5COOH NCPs
were investigated to evaluate their catalytic activity for the ring
opening reaction of cyclohexene oxide with aniline. The
amount of NCP used was varied to establish the conditions
for complete conversion to product. It was determined that for
a 10 mmol scale reaction at room temperature, the use of 0.80
out in heptane, was optimized by using a reduced form of Cu-
C5COOH NCPs (Figure 4b). The desired “click” product was
obtained in high yield (98%) after 7 h at room temperature.
II
Prior to the reaction, the Cu -NCPs required conversion to a
I
reduced Cu-NCP form, presumed to contain Cu on account of
the color change, for use as a “click” catalyst. Hydrazine
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mmol of Zn or Cu -C5COOH NCPs provided the desired
product in quantitative yield in 9 h (Table S3, Supporting
Information). The percentage conversion to product was
monohydrate was added to heptane suspensions of Cu -NCPs
II
to reduce the Cu ions. The blue color of the suspension
changed rapidly to a light brown color (Figure 5), indicative of
the successful reduction of copper. Dynamic light scattering
measurements confirmed that the addition of hydrazine to the
1
determined by H NMR integration of methylene signals of
the starting material, cyclohexene oxide, and the product, 2-
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Figure 5. Photographs showing the color of the heptane suspension containing copper-based NCPs before (a) and after (b) the addition of
hydrazine monohydrate. The corresponding DLS results obtained for each suspension are also shown in the form of size distribution by intensity
plots.
II
NCP suspensions and subsequent reduction of the Cu -NCPs
did not affect the colloidal nature of the systems and that the
average size of the particles remained unchanged. As shown in
Figure 5, the mean hydrodynamic (Z-Avg) diameter of the
small amount of catalyst required, these results show that the
reduced Cu-NCPs can be employed as an efficient catalyst for
the azide−alkyne cycloaddition “click” reaction. It is also
noteworthy that the reaction was conducted in a nonpolar
organic solvent (heptane), usually not amenable for use in
cycloaddition “click” reactions due to the low solubility of the
II
Cu -C5COOH NCPs prior to hydrazine addition was 18.3 nm
with a polydispersity index (PDI) of 0.252. Following hydrazine
treatment, the reduced Cu-NCPs were found to have a Z-Avg
value of 18.5 nm (PDI = 0.257).
To investigate the catalytic performance of reduced Cu-
NCPs, H NMR spectra were recorded following the optimized
h reaction time for experiments utilizing 0−0.10 mmol of
reduced Cu-C5COOH NCPs (Figure 6). The percentage of
copper catalyst (typically CuSO ). In addition, a molar
4
equivalent of the finely ground powders of the macroscale
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Cu -CP crystals, the precursor Cu(ClO ) ·6H O, and the
4
2
2
1
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unreduced Cu -NCPs were all tested as catalysts for the “click”
reaction; no reaction took place for any of these three systems
indicating that the catalytic activity observed with the reduced
Cu-NCPs is unique to this material.
7
CONCLUSIONS
■
We have successfully developed a preparation method to
synthesize NCPs inside reverse micelles within a heptane-based
microemulsion system. The Zn - and Cu -NCPs prepared in
this work have controllable morphology and surface area;
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NaHCO addition rate is a key factor here in NCP formation.
3
Moreover, it was confirmed that these NCPs have the same
crystal structure as their macroscale counterparts. However, in
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contrast to their macroscale counterparts, the Zn - and Cu -
NCPs provide efficient catalytic activity in the absence of
intrinsic porosity, demonstrated in the ring opening reaction of
cyclohexene oxide with aniline, and when reduced, the Cu-
NCPs can be employed as a catalyst for the azide−alkyne
cycloaddition “click” reaction. This is the first time that the
“
click” reaction has been carried out in heptane, for many
organic substrates, a more appropriate solvent than the
conventional “click” conditions. The work presented has
provided new insight into the mechanism of NCP formation
and opens up new pathways to develop improved size-
controlled NCPs of various compositions. Our method is a
versatile strategy, distinctly different from other microemulsion
methods reported, and is applicable to a plethora of other
metal/ligand combinations as a means to tune structural and
functional aspects of NCPs for applications requiring solvent
dispersibility.
1
Figure 6. H NMR spectra (CDCl ) depicting conversions in the
3
azide−alkyne cycloaddition “click” reaction between benzyl azide (1.5
mmol) and phenylacetylene (1.0 mmol) after 7 h with varying the
amount of reduced Cu-C5COOH NCPs. The ratios refer to the
relative integration of the #-to-* resonances, belonging to a proton of
the product (1-benzyl-4-phenyl-1,2,3-triazole), and starting material
(
phenylacetylene), respectively.
1
conversion to product was determined from the H NMR
spectra by comparing the integral ratio of the upfield acetylenic
proton singlet of the limiting reagent phenylacetylene (3.10
ppm) with the downfield triazole ring proton singlet (7.66
ppm) of the “click” product. The percentage conversion, which
increased from 12−100%, can be attributed to the reduced Cu-
NCP catalyst, which was used in increasing amounts from
EXPERIMENTAL SECTION
■
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Preparation of Zn - and Cu -NCPs. In the interest of space, only
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the details for the preparation of Zn -C5COOH NCPs and Cu -
C5COOH NCPs are provided here. The preparation of the remaining
NCPs in the CnCOOH ligand series (C3, C5, C10, and C11) is
described in the Supporting Information.
0
.02−0.10 mmol. With a relatively short reaction time and
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Three microemulsions were prepared: microemulsion 1 was
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.cgd.6b00502.
■
prepared by dissolving AOT (3.0 g, 6.7 mmol) in 20 mL of n-
26
*
S
heptane. C5COOH ligand (0.250 mmol) was dissolved in 1.25 mL
of 0.1 M H SO , and this solution was added dropwise with stirring to
2
4
the AOT/heptane solution; microemulsion 2 was prepared by first
dissolving AOT (1.5 g, 3.4 mmol) in 10 mL of n-heptane. M(ClO ) ·
4
2
Full details of synthetic and characterization methods
including time/loading optimization experiments and
NMR spectra for the ring opening catalysis experiment;
6
H O (M = Zn or Cu 0.250 mmol) was dissolved in 0.63 mL of
2
deionized H O, and this solution was added dropwise with stirring to
2
the AOT/heptane solution; microemulsion 3 was prepared by first
dissolving AOT (3.0 g, 6.7 mmol) in 20 mL of n-heptane. A saturated
solution of NaHCO in deionized H O (1.25 mL) was added dropwise
II
TEM images of Zn -NCPs with different CnCOOH
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II
ligands; XRPD data for a series of Zn - and Cu -CP and
the corresponding NCP samples; ATR-IR spectra
obtained for relevant CnCOOH ligand and CP and
NCP samples with corresponding band assignments
(PDF)
3
2
with stirring to the AOT/heptane solution.
Microemulsion 2 was added dropwise with rapid stirring to
microemulsion 1. After the mixture was allowed to stir for 15 min,
microemulsion 3 was added at the desired rate (dropwise; “slow”, ∼1
drop/10 min, or “fast”, entire volume as a single addition) with rapid
stirring. The resultant microemulsion was stirred for 1 h, after which
stirring was discontinued. To recover the NCPs, 50 mL of a mixture of
AUTHOR INFORMATION
Corresponding Authors
*E-mail: nlucas@chemistry.otago.ac.nz.
*E-mail: ewtan@chemistry.otago.ac.nz.
E-mail: cmeledandri@chemistry.otago.ac.nz.
■
1
:1 acetone-methanol was added to the resultant microemulsion. Two
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II
phases formed and the Zn - and Cu -NCPs were found to partition
into the upper heptane phase. The heptane phase was separated, to
which another aliquot of acetone-methanol was subsequently added,
again resulting in the formation of two phases. The heptane phase
containing the NCPs was separated and collected. This acetone-
methanol washing procedure was repeated two additional times to
ensure complete removal of AOT. The resulting heptane suspension
of NCPs was centrifuged for 30 min at 10,000 rpm. After
centrifugation, the supernatant was collected and retained for
characterization.
*
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors acknowledge Lisa Bucke for graphics support,
Richard Easingwood, Otago Centre for Electron Microscopy,
for TEM assistance, and Damian Walls for XRPD assistance.
K.R. acknowledges the Mahidol Wittayanusorn School
MWITS) and the Royal Thai government for financial
support, and the University of Otago for a doctoral scholarship.
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Zn - and Cu -NCPs as Heterogeneous Catalysts. All reagents
were commercially available and used without further purification.
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Herein, Zn -C5COOH NCPs and Cu -C5COOH NCPs were
selected as representative catalysts as C5COOH is the ligand in the
middle range of the alkyl linkers. Reaction conditions were optimized
(
accordingly. All reactions were monitored by TLC on silica gel 60 F2
54
1
(0.25 mm), visualization being effected with UV irradiation. H NMR
ABBREVIATIONS
CP, coordination polymer; NCP, nanocrystal coordination
polymer
■
spectra were obtained at 25 °C on a 400 MHz Varian 400-MR
spectrometer. Solutions were made up in CDCl . Chemical shifts are
3
1
reported relative to residual solvent signals ( H NMR: CDCl 7.26
3
ppm).
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Ring Opening Reaction of Cyclohexene Oxide with Aniline.
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■
(
́
, M.; Suska, A.; Bergman, P.;
II
II
Uvdal, K. J. Am. Chem. Soc. 2010, 132, 10391−10397.
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(
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(
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crude product was washed with brine and evaporated to dryness to
give 2-(phenylamino)cyclohexanol (94−96%). H NMR (CDCl ): δ
1
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3
7
1
2
1
.19 (t, 2H, Ar-H), 6.73 (t, 1H, Ar-H), 6.69 (dd, 2H, Ar-H), 3.35 (ddd,
H, -CH-OH), 3.11 (ddd, 1H, -CH-NH), 2.88 (bs, 2H, -OH, -NH),
.16−2.07 (m, 2H, CH -CH-OH), 1.80−1.69 (m, 2H, CH -CH-NH),
2
2
.45−1.25 (m, 3H), 1.12−0.99 (m, 1H).
Azide−Alkyne Cycloaddition “Click” Reaction. The amount of
II
Cu -NCP powder used in the reaction was varied (0.02, 0.04, 0.06,
.08, and 0.10 mmol) to compare the relative conversions. Hydrazine
0
II
monohydrate (2 mol equiv) was added to a suspension of Cu -
C5COOH NCPs (1 mol equiv) in heptane (1 mL). The blue
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was filtered through a Celite pad, which retained the reduced Cu-NCP
II
́
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1
triazole (98%). H NMR (CDCl ): δ 7.81−7.79 (m, 2H, Ar-H), 7.66
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3
(
s, 1H, triazole-H), 7.38−7.26 (m, 8H, Ar-H), 5.58 (s, 2H, Ph-CH ).
2
F
DOI: 10.1021/acs.cgd.6b00502
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DOI: 10.1021/acs.cgd.6b00502
Cryst. Growth Des. XXXX, XXX, XXX−XXX