Effect of the resorcin[4]arene host on the catalytic epoxidation of a Mn(III)-based resorcin[4]arene-metalloporphyrin conjugate

Article abstract of DOI:10.1039/c5ra13767e

The single-crystal X-ray diffraction data, binding behavior, and epoxidation reactions of the cavitand resorcin[4]arene-porphyrin conjugate are presented. Polar and nonpolar organic molecules such as pyridine and styrene were included in the cavity of res

Full text of DOI:10.1039/c5ra13767e

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Effect of the resorcin[4]arene host on the catalytic
epoxidation of a Mn(III)-based resorcin[4]arene–
metalloporphyrin conjugate†
Cite this: RSC Adv., 2015, 5, 88154
*
Talal F. Al-Azemi and Mickey Vinodh
The single-crystal X-ray diffraction data, binding behavior, and epoxidation reactions of the cavitand
resorcin[4]arene–porphyrin conjugate are presented. Polar and nonpolar organic molecules such as
pyridine and styrene were included in the cavity of resorcin[4]arene to form a 1 : 1 complex in the solid
state, as demonstrated by single-crystal X-ray diffraction analysis. Binding studies revealed that the
presence of resorcin[4]arene enhanced the association constant, obtained from UV titration, by 50%
compared to the original porphyrin. The epoxidation reaction of alkenes with the Mn(III)-based resorcin
[4]arene–porphyrin conjugate showed enhanced activity and depended on the olefins and axial ligands
used.
Received 13th July 2015
Accepted 6th October 2015
DOI: 10.1039/c5ra13767e
www.rsc.org/advances
selectivity. For example, regio- and stereo-selective oxidation
has been achieved, in which cis-stilbene is oxidized with a major
preference for the production of the cis-epoxide.13d
Introduction
Metalloporphyrin-based supramolecular architectures have
gained considerable attention for their stabilities and ability to
increase catalytic activities.1,2 Functional materials comprising
metalloporphyrins and macrocyclic cavitands such as cyclo-
dextrins,3,4 calixarenes,5–7 and resorcinarenes8–10 are attractive
model systems. The combination of the well-known catalytic
efficiency of metalloporphyrins with the receptor characteristics
of these cavitands has been shown to provide synergistic
advantages in the stability, reactivity, and selectivity of the
porphyrin fragments.5–10
The success of a macrocyclic receptor depends on its guest
inclusion capabilities to ensure strong and precise molecular
recognition. On the other hand, epoxides are versatile inter-
mediates in organic synthesis. In natural systems, alkene
epoxidation occurs through the enzymatic action of cytochrome
P450.9 Synthetic models, especially Mn(III)–porphyrins have
been extensively investigated as catalysts for alkene epoxida-
tions.11–13 In the presence of an oxygen donor and an activating
axial ligand, it is reported that a Mn(V)]O species rst forms in
the Mn(III)-catalyzed epoxidation, which then transfers its
oxygen to the alkene substrate to form the epoxide. Many of
these model systems utilize Mn(III)–porphyrins that are func-
tionalized with straps or caps to establish an environment in
which the oxygen transfer from the metal to the substrate is
under steric control, resulting in enhanced reaction rates and
Appropriate structural modications of the receptor entity
are always necessary to tune the special features of guest
encapsulation and reactivity. Although, there are many exam-
ples in the literature of the synthesis of resorcinarene–
porphyrin conjugates and their use in guest complexation, the
use of Mn(III)–resorcinarene–porphyrin conjugates as a catalyst
in alkene epoxidation reactions has not been reported. We have
previously reported the synthesis of the resorcin[4]arene–
porphyrin conjugate and the effect of resorcin[4]arene (RC) on
the quenching behavior of the porphyrin fragment (Scheme 1).14
In this work, we report single-crystal X-ray diffraction studies of
the resorcin[4]arene–porphyrin conjugate (RCP) and the inclu-
sion of polar and nonpolar organic molecules in the solid state.
The effects of the shape and size of the cavity on the substrate
and the axial-ligand binding behavior of the conjugate were
studied in detail and will be discussed. The catalytic epoxida-
tion of Mn(III)-based resorcin[4]arene–metalloporphyrin and the
Department of Chemistry, Kuwait University, PO Box 5969, Safat 13060, Kuwait.
E-mail: t.alazemi@ku.edu.kw; Fax: +965-2481-6482; Tel: +965-2498-5540
† Electronic supplementary information (ESI) available. CCDC 958843–958847.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5ra13767e
Scheme
conjugate (RCP).
1 Synthesis of the cavitand resorcin[4]arene–porphyrin
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size dependence of the encapsulation ability of the resorcin[4]
arene conjugate in the epoxidation reactions of alkene is also
reported.
Single crystal X-ray diffraction analysis
Singles crystals of RC and RCP that were suitable for single-
crystal X-ray diffraction were grown from the solvent diffusion
method using ethyl acetate and hexane. The single-crystal data
were collected on a diffractometer (R-AXIS RAPID, Rigaku, Japan)
diffractometer using Rigaku's Crystal clear soware package at
Experimental section
The synthesis and characterization of cavitand RC and their ꢀ123 ꢁC. The structure was solved and rened using the Bruker
SHELXTL Soware Package (structure solution program:
SHELXS-97; renement program: SHELXL-97). The crystallo-
graphic data for the structures reported in this paper have been
deposited at the Cambridge Crystallographic Data Centre as
supplementary publications (CCDC 958843–958847). Copies of
the data can be obtained, free of charge, upon submission of
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44(0) 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
porphyrin-appended analogue, RCP, along with the zinc-based
metal derivative, were prepared according to previously re-
ported procedures (see ESI†).14
Characterization
Ultraviolet-visible (UV-vis) spectra were recorded on a UV-vis
spectrophotometer (Varian Cary 5, Agilent, USA). Fast atom
bombardment (FAB) mass analysis was performed using a mass
spectrometer (DFS High Resolution GC/MS, Thermo Scientic,
USA). Proton nuclear magnetic resonance (1H NMR) spectros-
copy was performed using two spectrometers (Avance II,
600 MHz, Bruker, Germany; DPX 400, 400 MHz, Bruker,
Germany). All single-crystal X-ray diffraction data were collected
on a diffractometer (R-AXIS RAPID, Rigaku, Japan) using ltered
Mo Ka radiation. The data were collected at a temperature of
ꢀ123 ꢁC (Oxford Cryosystems, UK). The structure was solved by
direct methods and expanded using Fourier analysis. The non-
hydrogen atoms were rened anisotropically; the hydrogen
atoms were rened using the riding model. Gas chromatog-
raphy (GC) analysis was performed on a gas chromatograph
(GC-2010, Shimadzu GC-2010, Japan) with a ame ionization
detector (FID) detector using a chiral capillary column (length:
30 m, ID: 0.25 mm) (Supelco b-Dex 225, Sigma-Aldrich, USA).
Flash column chromatography was performed using sukuca gek
(Silica gel 60, 230–400 mesh ASTM, EMD Millipore, Merck
KGaA, Germany). All other reagents and solvents were of
reagent-grade purity and used without further purication.
UV-vis titrations
A 25 mL sample of the porphyrins solution was prepared at
a concentration of 8 mM in spectroscopic-grade solvent (chloro-
form was dried over calcium chloride and neutral alumina). A
10 mL sample of the ligand solution was prepared at a concen-
tration of 0.004–0.2 M in a spectroscopic-grade solvent. All
titration experiments were carried out with 5 mL of a receptor
solution in a quartz cell at 298 K, and UV-vis spectra were
recorded upon successive addition of aliquots of the stock
solution of the appropriate ligands with a microsyringe. The
UV-vis absorbance at three different wavelengths was tted to
a 1 : 1 binding isotherm by nonlinear least-squares treatment
using Microso Excel to determine the association constant, Ka.15
Epoxidation reaction-procedure
The epoxidation studies of the catalyst systems, cavitand
Mn-based RCP (MnRCP) and Mn–tetratolylporphyrin (MnTTP),
were carried out simultaneously for each set of substrate–ligand
combination. Under typical reaction conditions, the catalyst
(0.5 mmol) dissolved in dichloromethane (2 mL) in a 10 mL round
bottom ask. The axial pyridine ligand (200 mmol) was added to
the solution and stirred slowly for 5 min. Styrene (500 mmol) was
then added and the solution was stirred again for another 5 min.
The phase-transfer regent (t-butyl ammonium iodide, 35 mmol)
was added to this system followed by the addition of sodium
hypochlorite solution (0.6 M, 2 mL). The reaction mixture was
stirred at room temperature, and at predetermined intervals,
a small aliquant (200 mL) was withdrawn from the organic phase
and passed through a small silica gel column (length: 1 cm;
diameter: 5 mm) and eluted with dichloromethane (1 mL). The
dichloromethane was dried over Na2SO4 and removed by ltra-
tion. Finally, 1 mL of the eluted CH2Cl2 was injected into the GC
column to determine the progress of the reaction.
Synthesis manganese derivatives of RCP
Manganese derivative of porphyrin resorcin[4]arene conju-
gate (Mn(III)RCP). RCP (200 mg) was dissolved in a chloroform–
methanol mixture (2 : 1 v/v, 50 mL). Mn(OAc)2 (200 Mg) added
to the solution and reuxed for 5 h. When the metal insertion
was complete (indicated by the disappearance of the 650 nm
peak in the UV-vis spectrum), the solvent was evaporated. The
residue was extracted with dichloromethane (50 mL) and
washed with water 3–4 times to remove unreacted manganese
salt. The porphyrin solution was then dried and dissolved in
chloroform (50 mL). A saturated NaCl solution (100 mL) was
added to this solution and stirred at room temperature for 8 h.
The water layer was then removed and the chloroform was
evaporated. The crude material was dissolved in dichloro-
methane (50 mL) and washed several times with water. The
solvent was nally removed under reduced temperature and the
product was dried under vacuum until a constant weight was
obtained (>90% yield). UV-vis spectrum recorded in CH2Cl2,
Results and discussion
Crystallography: crystal structure of resorcin[4]arene host
with small guest molecules
lmax (nm) (3 ꢂ 10ꢀ5 Mꢀ1 cmꢀ1): 377 (0.58), 402 (0.49), 479 (1.14), Resorcin[4]arenes are well known for their ability to encapsulate
586 (0.10) and 622 (0.13). FAB mass: 1653 [M ꢀ Cl].
small organic and cationic species.16,17 The porphyrin unit is
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attached to the cavitand resorcin[4]arene moiety through
a methyl ether linkage. Such a spacer is expected to provide
sufficient exibility to the porphyrin unit to orient at a stable low-
energy position with respect to RC. Single crystals of RCP that
were suitable for X-ray diffraction were obtained by controlled
solvent evaporation of RCP dissolved in ethyl acetate. The crystal
structure of RCP obtained from the XRD data is depicted in
Fig. 1. The crystal network was found to contain one solvent ethyl
acetate molecule per RCP molecule, occupying the void between
porphyrin and resorcinarene. The molecular structure obtained
from the crystal data demonstrates the orientation of the
porphyrin unit over the RC cavity in the solid state.
The unit cell of the RCP crystal contains two resorcin[4]arene–
porphyrin conjugates per cell. As demonstrated in Fig. 2, the RCs
in each unit cell are occupied in diagonal positions and the
porphyrins are intercalated at the center. The three-dimensional
packing of the RCP crystal is arranged in a zigzag fashion, with
alternate species inverted from each other (see ESI†).
Because of the difficulty associated with obtaining the RCP
crystal structure by single-crystal X-ray diffraction analysis, and
in order to demonstrate the ability of RC to accommodate small
organic molecules, a bowl-shaped rigid RC was co-crystallized
with styrene and pyridine. The X-ray crystal structure of the
crown-like structure of the bridged cavitand methyleneoxy
resorcin[4]arene is shown in Fig. 3. The top most diameter of
Fig. 2 Unit cell of RCP crystals (color code: red – oxygen, gray –
carbon; the hydrogen atoms are hidden for clarity).
inclusion compounds to crystallize. The inclusion complexes of
RC with pyridine (RCPY) and styrene (RCSTY), derived from
XRD data, are depicted in Fig. 4. Even if their physical shape and
size in the crystalline state are different, the crysatllographic
space group of both RCPY and RCSTY were observed to be the
same and the unit cell parameters are almost similar.
Single-crystal X-ray diffraction studies have shown that the
terminal double bond of styrene and the nitrogen atom of
pyridine are outside the cavity of the host molecule. In a host–
guest environment, the ease with which these guest molecules
t inside the host molecules as well as the availability of their
reactive functional sites to engage in chemical reactions are very
important attributes of efficient guest molecules. Such encap-
sulation characteristics could be easily demonstrated in the
solid state by the single-crystal X-ray diffraction technique.
ꢀ
the rigid bowl is about 8.8 A and that of the lower end is about
ꢀ
5.6 A, which is suitable for accommodating small organic
molecules or ions. The aliphatic heptyl chains extend down-
wards and are slightly disordered at the tail ends owing to the
thermal motions (Fig. 3).
Crystals of the inclusion compounds were obtained by
co-crystallizing saturated solutions of the host (resorcin[4]
arene) with the respective guests (pyridine or styrene). The
saturated solutions were prepared by dissolving the host in
a warm solvent (guest, at 70 ꢁC) under gentle stirring. The
solutions were slowly cooled and evaporated, allowing the
Binding studies
Encouraged by results of the study on the crystal structure,
which showed the ability of cavitand RC to accommodate polar
Fig. 1 Molecular structure of RCP derived from single-crystal X-ray
diffraction data: (a) thermal ellipsoid representation (50% probability); Fig. 3 Structure of resorcinarene framework from the crystal data of
(b) capped-sticks representation in which the hydrogen atoms and the resorcin[4]arene–styrene (RCSTY); the styrene and all hydrogen atoms
trapped ethyl acetate moiety are hidden for clarity. Color code: red – are hidden to show the structure more clearly: (a) side view; (b) top
oxygen, blue – nitrogen, gray – carbon, black – hydrogen.
view. Color code: red – oxygen, gray – carbon.
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isotherm and the binding constant was determined from
nonlinear least-square tting,15 using the change in the absor-
bance at 430 nm; the results are summarized in Table 1. The
calculated association constant of ZnTTP (1.06 ꢂ 103 Mꢀ1) is
similar to that calculated for Zn–tetraphenylporphyrin (ZnTPP)
by UV titration.13c,17 On the other hand, the calculated Ka of Zn(II)
RCP in chloroform is 1.54 ꢂ 103 Mꢀ1, which is approximately
50% higher than that of ZnTTP. Similarly, titration of ZnRCP
with 4-tert–butylpyridine, gave Ka ¼ 1.46 ꢂ 103 Mꢀ1, which is
slightly lower than Ka of ZnTTP. From the UV-vis titration
experiment, it is evident that the increase in Ka of ZnRCP bound
to pyridine was due to the favorable encapsulation of the axial
ligand (pyridine) stabilized by the p-wall of the resorcinarene
conjugate host. In contrast, the bulky substituent in 4-tert–
butylpyridine prevented the accommodation inside the RC
cavity, and the guest was thus bound to Zn–porphyrin from the
opposite side of RC. The results of the binding study are in
agreement with single-crystal X-ray data. In particular, the free
rotation of the ether linkage in RCP exhibited lower binding
affinity than the highly rigid cavities of cap-or-clip porphyrins
reported in the literature.5,13c
Fig. 4 Thermal ellipsoid representation of the crystal structure of (a)
resorcin[4]arene–pyridine (RCPY) and (b) resorcin[4]arene–styrene
(RCSTY). Color code: red – oxygen, blue – nitrogen, gray – carbon,
black – hydrogen.
and nonpolar neutral molecules such as pyridine and styrene,
the Zn(II)-based resorcin[4]arene–metalloporphyrin conjugate
(Zn(II)RCP) was prepared quantitatively from the reaction of free
base porphyrin with excess Zn(OAc)2 in CHCl3. Zn–porphyrin is
known to bind only one axial ligand, resulting in a ve-
coordinated zinc atom.18 In order to demonstrate the ability of
Zn(II)RCP to incorporate pyridine into the cavity in a solution,
Epoxidation reactions
It is well-known that a manganese porphyrin catalyzes epoxi-
dation of styrene in the presence of an oxygen source, and the
rate of product formation is greatly increased by the presence of
pyridine. The role of pyridine is to coordinate to the axial
binding studies were performed in CHCl3 with pyridine deriva- position of Mn–porphyrin and thereby facilitate the formation
tives using UV titration. For comparison, analogous experiments of Mn(V)–oxo species,11–13 which is essential for epoxidation
with Zn–tetratolylporphyrin (ZnTTP) were also performed.
In Fig. 5a, the absorption spectra of ZnRCP in chloroform
exhibit transitions that are characteristic of Zn(II)–porphyrins.
reactions. The Mn(III)-based resorcin[4]arene–metalloporphyrin
conjugate (Mn(III)RCP) was prepared from the reaction of the
free base porphyrin core of RCP with Mn(OAc)2 in a chloroform–
methanol mixture, followed by treatment with saturated NaCl.
Based on the single-crystal XRD analysis of RCP and the ability
of cavitand RC to encapsulate guest substrates such as pyridine
Specically,
a symmetry-permitted transition centered at
424 nm corresponding to the Soret band, as well as a transition
at 550 nm (Q band) are clearly visible. The addition of pyridine
or 4-tert-butylpyridine resulted in hyperchromic shis in the and styrene inside the cavity and the favorable orientation of
absorption spectra: a new Soret band appears at 430 nm and two functional groups over the resorcinarene moiety in the crystal
Q bands appear at 563 and 603 nm. A typical example of UV
titration is shown in Fig. 5b.
To characterize the effect of the RC conjugate on the binding
affinity of Zn(II)RCP, UV-vis titration experiments of Zn(II)RCP
and ZnTTP with pyridine and 4-tert-butylpyridine as guests were
performed in chloroform. The data tted well to a 1 : 1 binding
network, in addition, the result obtained from the binding
studies. Different olen and axial ligand combinations—styr-
ene:t-butylpyridine, t-butylstyrene:pyridine, and t-butylstyr-
ene:t-butylpyridine—were used to study the effect of the RC
cavity in the epoxidation reaction of Mn(III)RCP. Similarly, in the
investigation of epoxidation reactions, Mn(III)–tetratolylpor-
phyrin (MnTTP) was prepared and epoxidation experiments
Table 1 Association constants, Ka (Mꢀ1), for the formation of 1 : 1
complexes measured by UV-vis titration in CHCl3 at 298 K (with
percentage error)a
Entry
Porphyrin
ZnTTP
Ligand
Ka (Mꢀ1
)
1
2
3
4
Pyridine
4-tert-Butylpyridine
Pyridine
1.06 ꢂ 103 (5%)
1.67 ꢂ 103 (3%)
1.54 ꢂ 103 (6%)
1.41 ꢂ 103 (5%)
ZnRCP
Fig. 5 (a) Absorption spectral changes observed in a dry chloroform
solution of ZnRCP (8 mM) by addition of pyridine (0–10ꢀ3 M) at 25 ꢁC.
(b) The binding isotherm of the ZnRCP–pyridine system at 424 nm (C)
and 430 nm (B).
4-tert-Butylpyridine
a
The titration data was tted to the 1 : 1 binding model, error <8%. Ka
was measured from the change in absorbance at 430 nm.
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Fig. 8 Plot of conversion (%) as a function of reaction time of the
epoxidation reaction of styrene catalyzed by MnTTP (C)and MnRCP
(B) in the presence of t-butylpyridine as an axial ligand.
Fig. 6 Representation of the combinations of substrate and axial
ligand utilized in the MnRCP-catalyzed epoxidation reactions: (a)
pyridine–4-tert-butylstyrene; (b) 4-tert-butylpyridine–styrene.
Using the bulky t-butylpyridine as axial ligand is expected to
enable the substrate (styrene) to be encapsulated inside the RC
cavity (Fig. 6b). Fig. 8 shows the results of the epoxidation of
styrene and 4-tert-butylpyridine as the axial ligand catalyzed by
MnRCP and MnTTP. In the initial stages, MnRCP showed
higher conversion rate than MnTTP, which is an indication of
the role of the RC host in the epoxidation reaction. However, the
increased activity of MnTTP can be explained in terms of the
favorable electronic effects induced by the tert-butyl functional
groups at the gamma position of pyridine, which increased the
coordinating ability of pyridine by increasing the basicity. In the
absence of an axial ligand, epoxidation of both styrene and
t-butylstyrene was observed to be negligible for these catalyst
systems (data not shown).
were conducted for comparison. The combinations of substrate
and axial ligand utilized in the MnRCP-catalyzed epoxidation
reactions are depicted in Fig. 6.
The results of the epoxidation reaction of 4-tert-buylstyrene
catalyzed by MnRCP and MnTTP in the presence of pyridine as
an axial ligand are shown in Fig. 7. At the initial epoxidation
rate, the MnRCP-catalyzed conversion of styrene was approxi-
mately 10 times higher than that of the MnTTP-catalyzed
conversion, which is generally related to the higher binding
constant of the axial ligand. The signicant variations in epox-
idation performance exhibited by MnRCP compared to the
unconjugated porphyrin at the initial stages clearly show the
role of the cavity in enhancing the catalytic epoxidation (see
Fig. 5a). The obtained data are in agreement with the results of
single-crystal XRD studies and the binding studies of the ZnRCP
analogue, in which the rate enhancing effect was the result of
the inclusion of pyridine inside the RC cavity.
In order to provide better understanding of the role of the RC
conjugate in the catalytic performance of MnRCP, a bulky
substrate (4-tert-butylstyrene) and an axial ligand (4-tert-butyl-
pyridine) were used (Fig. 9). MnRCP exhibited lower catalytic
Fig. 7 Plot of conversion (%) as a function of reaction time of the Fig. 9 Plot of percent conversion (%) as a function of reaction time of
epoxidation reaction of t-butylstyrene catalyzed by MnTTP (C)and the epoxidation reaction of t-butylstyrene catalyzed by MnTTP (C)and
MnRCP (B)in the presence of pyridine as an axial ligand.
MnRCP (B)in the presence of t-butylpyridine as an axial ligand.
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activity than the MnTTP, indicating that RC played no role in
the epoxidation reaction, and clearly showing the dependence
of the conjugate on the size and shape of pyridines or styrenes
present in the reaction medium.
Even though the analysis of these systems was complicated
by the possible competition between the occurrence of the
epoxidation reactions inside and outside the RC cavity, the
results clearly show that the variations in epoxidation efficiency
exhibited by Mn(III)-based resorcinarene–metalloporphyrin
conjugates can be correlated with the recognition characteris-
tics of the corresponding RC conjugates towards olens and
pyridines under study.
3 Y. Kuroda, T. Sera and H. Ogoshi, J. Am. Chem. Soc., 1991,
113, 2793; R. Breslow, X. Zhang and Y. Huang, J. Am.
Chem. Soc., 1997, 119, 4535; L. Weber, R. Hommel,
S. J. Behling, G. Haufe and H. Hennig, J. Am. Chem. Soc.,
1994, 116, 2400.
4 A. Puglisi, R. Purrello, E. Rizzarelli, S. Sortino and G. Vecchio,
New J. Chem., 2007, 31, 1499; K. Hosokawa, Y. Miura, T. Kiba,
T. Kakuchi and S. F. Sato, Chem. Lett., 2008, 37, 60; Y. Guo,
P. Zhang, J. Chao, S. Shuang and C. Dong, Spectrochim.
Acta, Part A, 2008, 71A, 946; X.-X. Li, J.-W. Wang, Y.-J. Guo,
L.-H. Kong and J.-H. Pan, J. Inclusion Phenom. Macrocyclic
Chem., 2007, 58, 307.
5 H. Iwamoto, Y. Yukimasa and Y. Fukazawa, Tetrahedron Lett.,
2002, 43, 8191.
6 N. Zh. Mamardashvili and O. I. Koifman, Russ. J. Gen. Chem.,
2005, 6, 787.
Conclusions
The results of our research clearly demonstrate the impact of
the size and shape of the cavitand resorcin[4]arene on the
stability and reactivity of the porphyrin fragment. Single-crystal
X-ray diffraction technique studies revealed the formation of an
inclusion complex of resorcinarene with pyridine and styrene in
the solid state. The binding studies showed that the presence of
resorcin[4]arene led to a 50% increase in the association
constant of Zn–porphyrin with pyridine as the axial ligand.
Because the rigid bowl-shaped cavitand resorcin[4]arene was
a batter host for pyridine and styrene, the Mn(III)-based metal-
loporphyrin system showed higher catalytic efficiency in epox-
idation reaction when coordinated with the pyridine axial
ligand or encapsulation of styrene inside the cavity of the
resorcin[4]arene conjugate. Further studies and modications
of resorcinarene–porphyrin conjugates in terms of the increases
in rigidly, stability, and catalytic activity are underway in our
laboratories.
7 D. M. Rudkevich, W. Verboom and D. N. Reinhoudt, J. Org.
Chem., 1995, 60, 6585.
8 S. D. Starnes, D. M. Rudkevich and J. Rebek, Org. Lett., 2000,
14, 1995; J. Nakazawa, M. Mizuki, Y. Shimazaki, F. Tani and
Y. Naruta, Org. Lett., 2006, 19, 4275; J. Nakazawa, Y. Sakae,
M. Mizuk and Y. Naruta, J. Org. Chem., 2007, 72, 9448;
J. Nakazawa, J. Hagiwara, M. Mizuki, Y. Shimazaki, F. Tani
and Y. Naruta, Angew. Chem., 2005, 117, 2810.
9 J. T. Groves and Y. Z. Han, in Cytochrome P 450: Structure,
mechanism and Biochemistry, ed. P. R. Ortiz de Montellano,
Plenum Press, New York, 2nd edn, 1995, pp. 3–48.
10 D. Fankhauser, D. Kolarski, W. R. Gruning and F. Diederich,
Eur. J. Org. Chem., 2014, 17, 3575; B. Botta, P. Ricciardi,
C. Galeffi, M. Botta, A. Ta, R. Pogni, R. Iacovino,
I. Garella, I. B. Blasio and G. D. Monache, Org. Biomol.
Chem., 2003, 1, 3131.
11 D. Monti, A. Pastorini, G. Mancini, S. Borocci and
P. Tagliatesta, J. Mol. Catal. A: Chem., 2002, 179, 125.
12 V. Pardines and G. Pratvil, Angew. Chem., Int. Ed., 2013, 52,
2185.
13 (a) J. A. Elemans, M. B. Claase, P. P. Aarts, A. E. Rowan,
A. P. Schenning and R. J. Nolte, J. Org. Chem., 1999, 64,
7009; (b) J. A. Elemans, E. J. Bijsterveld, A. E. Rowan and
R. J. Nolte, Eur. J. Org. Chem., 2007, 5,751; (c)
J. A. Elemans, E. J. Bijsterveld, A. E. Rowan and R. J. Nolte,
Chem. Commun., 2000, 2443; (d) J. A. Elemans,
E. J. Bijsterveld, A. E. Rowan and R. J. Nolte, Nature, 2003,
424, 915.
Acknowledgements
The support of the University of Kuwait, received through
research grant no. SC01/12, and the facilities of ANALAB and
SAF (grant no. GS01/01, GS03/01, GS01/03, GS01/05, and GS03/
08) are gratefully acknowledged.
Notes and references
1 Y. Ninomiya, M. Kozaki, S. Suzuki and K. Okada, Bull. Chem.
Soc. Jpn., 2014, 87, 1195; N. T. Nguyen, G. M. Mamardashvili, 14 T. F. Al-Azemi and M. Vinodh, Tetrahedron, 2011, 67, 2585.
O. M. Kulikova, I. G. Scheblykin, N. Z. Mamardashvili and 15 M. Hong, Y. Zhang and Y. Liu, J. Org. Chem., 2015, 80, 1849;
W. Dehaen, RSC Adv., 2014, 4, 19703; C. Li, X. Zhao,
X. Gao, Q. Wang and Z. Li, Chin. J. Chem., 2013, 31, 582;
S. Busi, H. Saxell, R. Frohlich and K. Rissanen,
CrystEngComm, 2008, 10, 1803.
C. B. KC, G. N. Lim, P. A. Karr and F. D'Souza, Chem.–Eur. 16 Y. Kikuchi, Y. Kato, Y. Tanaka, H. Toi and Y. Aoyama, J. Am.
J., 2014, 20, 7725; N. T. Nguyen, G. M. Mamardashvili,
M. Gruzdev, N. Z. Mamardashvili and W. Dehaen,
Supramol. Chem., 2013, 3, 180.
2 M. Vinodh, F. H. Alipour, A. A. Mohamod and T. F. Al-Azemi,
Molecules, 2012, 17, 11763; R. Beletskaya, V. S. Tyurin,
A. S. Tsivadze, R. Guilard and C. Stern, Chem. Rev., 2009,
109, 1659; A. K. Burrell, D. L. Officer, P. G. Plieger and
D. C. Reid, Chem. Rev., 2001, 101, 2751.
Chem. Soc., 1991, 113, 1349; S. Zheng and P. Coppens,
Chem.–Eur. J., 2005, 11, 3583.
17 G. M. Mamardashvili, Russ. J. Coord. Chem., 2006, 10, 756;
A. Mulholland, P. Thordason, E. J. Mensforth and
S. Langford, Org. Biomol. Chem., 2012, 10, 6045; O. Middel,
W. Verboom and D. N. Reinhoudt, J. Org. Chem., 2001, 66,
3998.
18 P. Thordarson, Chem. Soc. Rev., 2011, 40, 1305.
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