Structures of potassium calix[4]arene crown ether inclusion complexes and application in polymerization of: Rac -lactide

Article abstract of DOI:10.1039/c6dt01417h

Reaction of 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L¹H₂) with KN(SiMe₃)₂ afforded a one-dimensional (1D) chain complex [K₂L¹]_n (1). Upon reaction with 1 equivalent 18-crown-6, complex 1 can convert to complex [K₂(18-crown-6)L¹] (2) which possesses a sandwich structure. Treatment of two calix[4]arene-crown ligands of 1,3-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L²H₂) and 1,2-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L³H₂) with KN(SiMe₃)₂ gave the dinuclear complex [K₂L²] (3) and the mononuclear complex [K(THF)L³H] (4), respectively. Complexes 1-4 were all characterized by single-crystal X-ray diffraction techniques. The variable temperature ¹H NMR spectrum indicates there is a quick rotation equilibrium of the two phenoxy groups in complex 3. In addition, complexes 1-4 have been tested for the ring-opening polymerization (ROP) of rac-lactide and the results showed that complexes 2 and 3 are highly active for the ROP of rac-lactide. The obtained polymers displayed low dispersity values (D) and the molecular weights are close to the calculated ones. Furthermore, complexes 2 and 3 show moderate isoselectivities of P_m = 0.67 and P_m = 0.73, respectively.

Full text of DOI:10.1039/c6dt01417h

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Structures of Potassium Calix[4]arene Crown Ether Inclusion
Complexes and Application in Polymerization of rac-Lactide
Received 00th January 20xx,
Accepted 00th January 20xx
Yingguo Li, Hongwei Zhao, Xiaoyang Mao, Xiaobo Pan, Jincai Wu*
1
DOI: 10.1039/x0xx00000x
Reaction of 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L H
2
) with KN(SiMe
3
)
2
afforded one-dimensional (1D) chain complex
1
1
[K
2
L ]n (1). Upon reaction with 1 equivalent 18-crown-6, complex 1 can convert to complex [K
2
(18-crown-6)L ] (2) which
www.rsc.org/
possessed a sandwich structure. Treatment of two calix[4]arene-crown ligands of 1,3-dihydroxy-p-tert-butyl-calix[4]arene-
2
3
crown-5 (L H
2
) and 1,2-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L H
2
) with KN(SiMe
)
3 2
gave the dinuclear complex
2
3
[K
2
L ] (3) and the mononuclear complex [K(THF)L H] (4), respectively. Complexes 1-4 were all characterized by single-
1
crystal X-ray diffraction techniques. Variable temperature H NMR spectrum indicates there is a quick rotation equilibrium
of two phenoxy groups in complex 3. In addition, complexes 1-4 have been tested for the ring-opening polymerization
(
ROP) of rac-lactide and the results showed that complexes 2 and 3 are highly active for the ROP of rac-lactide. The
obtained polymers displayed a low dispersity values (Ð) and the molecular weights are close to calculated. Furthermore,
complexes 2 and 3 can show moderate iso-selectivities of P = 0.67 and P = 0.73, respectively.
m
m
application of the alkali metal calix[
rarely explored.
4]arene complexes was
Introduction
The catalytic chemistry of calixarene derivatives has
The chemistry of calixarene has attracted considerable interest
over the last several decades because calixarenes derivatives
can form various inclusion complexes with many guest species.
As a representative of calixarenes, calix[4]arenes have been
gained much attention in some organic catalysis and
7
polymerization reactions. Recently, several calix[
4]arene
complexes have been extended into the catalytic synthesis of
environmental-friendly polymers, such as polylactide (PLA) and
polycaprolactone (PCL), which possess biorenewability,
1
widely used in supramolecular chemistry, biological
2
3
chemistry, chemical sensors due to their rigid structure,
hydrophobic, electron-rich, distinctive tunable cavity, and
8
biodegradability, and biocompatibility. For example, Redshaw
4
and co-workers reported zinc-based, magnesium-based
binding ability towards various ions and molecules.
calix[
catalytic activities for the ROP of
r
LA) and exhibit a good heteroselectivity (P = 0.85). Vigalok
4
]arene inclusion complexes which display expectant
Calix[
constructed by the coordination of metal ions, such as cone,
partial cone, -alternate and -alternate cone; some
special strong interaction with metal ions such as cation-π
4]arene complexes can possess diverse structures that
ε
-caprolactone and lactide
9
(
1
,
2
1,3
and co-workers discussed catalytic behaviors of bimetallic
alkylzinc calixarene inclusion complexes in the ROP process
4
a, 5
bond also can be found.
A number of alkali-metal
1
0
and explored a single-site catalysis mechanism. Frediani and
co-workers investigated catalytic activities of chlorotitanium
calixarenes have been reported, most of them focus on
studying the alkali metal binding properties of calixarene and
calix[4]arene complexes in the ROP of LA under solvent-free
some calix[4]arene alkali-metal complexes have been isolated
1
1
6
conditions. As we know, the physical and chemical properties
of PLA are highly associated with its stereoregularity. The
isoselective ring-opening polymerization of rac-lactide at a
to study their structures in details. But compared to
flourishing calixarence transition metal complexes, the
1
2
mild condition is still a challenging research goal. Recently we
reported some sodium and potassium phenolate complexes
can highly stereoselectively catalyze the ring-opening
1
3
polymerization of rac-lactide, the isoselectivity even can
1
4
reach to P
m
=
0.94
,
where a confined space for the catalytic
center is important for the isoselective ROP of rac-lactide.
Considering the nontoxicity of potassium ion for human body
and the good inclusion effect of calix[4]arene, herein four
calix[ ]arene potassium complexes were synthesized as
4
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1
2
3
15
16
catalysts for the ROP of rac-lactide and the special
configurations of these calix[4]arene potassium complexes
also were presented. To our knowledge, no potassium
(
(
(
L
L
L
H
2
H
2
H
2
),
1
1
,
3
2
-dihydroxy-p-tert-butyl-calix[
4
4
]arene-crown-
5
5
), and
,
-dihydroxy-p-tert-butyl-calix[
]arene-crown-
17
)
as three potential dianionic calix[
4
]arene ligands were
(Scheme ) can
be obtained in a moderate yield (50.7%) by the reaction of
and KN(SiMe . As our previous work shown, crown ethers
play an important role for the high stereoselective ROP of rac-
calix[4]arene inclusion complexes have been reported for the synthesized as previously described. Complex
1
1
1
ROP of lactide.
L H
2
3 2
)
1
3c
1
Results and discussion
lactide,
complex
ligand. Complex
34.5%) through the reaction of complex
mixed solvent of toluene and THF at room temperature.
therefore
together with 18-crown-
can also be obtained in a moderate yield
and 18-crown- in a
L
H
2
was used further to synthesize
2
6
as a second auxiliary
Synthesis and characterization of calix[4]arene complexes 1-4
2
Alkali metal ions have only one positive charge, usually
monoanionic phenol ligands are favorable for alkali metal
phenolate catalysts for the ROP of lactide to avoid several
different active centers. Given that calix[4]arene can include
one metal cation in a perfect cone cavity which possibly is not
active for the ROP of lactide as dinuclear zinc complexes
(
1
6
2
3
Calix[
ether moiety at
and were prepared through the reaction of
with one or two equivalents of KN(SiMe
4
]arene-crown type ligands of
2 2
L H and L H fuse crown
1
,
3
and positions respectively. Complexes
1, 2
2
3
3
4
2 2
L H or L H
3 2
) .
1
0
reported by Vigalok,
1
,
3
-dipropoxy-p-tert-butyl-calix[4]arene
1
2
3
Scheme 1. Synthesis of
L
H
2
,
L
H
2
,
L
H
2
and complexes 1-4
.
2
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space for the potassium center which is a potential catalytic
center and we also want to utilize the coordination effect of
crown ether to break the
to give a mononuclear and single-site catalyst. As we
expected, upon addition of 18-crown- to the solution of
complex in a mixed solvent of toluene and THF, the
potassium ion (K ) at exo position was capped by the oxygen
atoms of crown ether. K remains immersed in the cavity of
calix[ ]arene ligand as that in complex . The potential
catalytic center of K is sandwiched well by the coordination of
1 and complex 2
(methyl carbon four oxygen atoms of calix[4]arene ligand and two oxygen
1D zigzag polymeric chain of complex
1
6
1
1
2
4
1
1
Figure 1. Molecular structures of complex
atoms of the tert-butyl groups and all of the hydrogen atoms are omitted for
clarity).
.013(3), K2-O1 2.732(2), K2-O2 2.574(3), symmetry code of A: x, 0.5-y, z.
Selected bond lengths (Å): K1-O1 2.5073(12), K1-O2 3.2646(13), K1-O5 bond lengths of 2.5073
.8409(15), K2-O1 2.6313(13), symmetry code of A: 1-x, y, 0.5-z.
1
: Selected bond lengths (Å): K1-O1 2.462(3), K1-O2 2.477(3), K1-O3 atoms (O
5
and O
5
A) of 18-crown-
12) Å and 2.8409
to the corresponding bond lengths in other previously
reported complexes. The bond distance of K -O bond of
.2646 13) Å in complex is obviously longer than that of K
bond 3.013 ) Å in complex , which can be attributed to
the coordination of 18-crown- in complex . The other four
oxygen atoms of 18-crown- do not coordinate to K because
the K -O and K -O bond distances of 3.511 16) Å and
.520 18) Å are very long, bond valence sum analyses show the
bond order of K
is out of our design that only two oxygen atoms of 18-crown-
6
. The K
1-O1 and K1-O5
3
2:
(
(
15) Å are comparable
2
1
2
Crystals of complex
solution. The molecular structure of
adopts exo fashion to bond to two oxygen atoms of propyloxy
and O A) and two oxygen atoms of phenolate groups (O
and O ). A weak intermolecular cation- interaction between
two molecules in solid state can be found because the average
distance between K and an aromatic ring (C15-C18) of
another calix[ ]arene complex is 3.070 Å (Figure S ) and
similar phenomena can be found in other calix[ ]arene
interaction, complex
D zigzag polymeric chain in the solid structure (Figure
is coordinated by two phenolate anionic oxygen atoms
and O ) and has cation- interactions with two benzene
-C ) of two phenolate groups of this calix[ ]arene
ligand. The distance between K and the aromatic benzene
1
were obtained from a saturated THF
3
O
(
2
1-
1
is shown in Figure . K
1
1
3
(
3
1
6
2
(O
3
3
1
6
1
2
π
1
6
1
7
(
3
(
1
1
9
1-O6 or K1-O7 is just about 0.02. Although it
4
1
4
6
1
13
1
8
coordinate to K
demonstrate complex
Figure S14 and Figure S15). The H NMR spectrum obtained at
different temperatures also confirmed that the 18-crown-
1
, the single set H NMR and C NMR spectra
complexes. Because of this cation-
forms a
π
1
2
has a monomeric structure in solution
1
1
(
S
1). K
2
6
(O
1
2
π
cannot dissociate from complex
coordination species (Figure S
crown-
complex
Because only two oxygen atoms of 18-crown-
to one potassium ion in complex , the coordination
interaction is not strong enough to suppress the dissociation of
2
when there was no other
rings (C
1
6
4
2), which illustrates that 18-
2
6
has succeeded to convert the aggregate structure of
to a monomeric structure of complex
ring is about 2.773 Å indicating these cation-
π
interactions are
1
2.
strong. Due to the two kinds of interaction, K
2
is situated endo
6
can coordinate
into the cavity of the calix[
conformation of this calix[ ]arene ligand is an elliptical cone. In
the H NMR spectrum, two pairs of doublets at 3.56 ppm ( H)
and 3.68 ppm ( H) for methylene groups, two singlet tert-butyl
peaks, and two aromatic peaks indicate the C2v symmetry of
4]arene ligand. And the
2
4
1
4
1
4
8
-crown-
, this is not possible because crown ether moiety fuse
]arene ligand. The molecular structure of
was depicted in Figure A and B). Because some
6 in the catalytic progress. While in complexes 3 and
4
+
together with calix[
complex
4
this complex despite of the presence of an intermolecular K -
1
π
3
3
2
(
3
3
interaction (Figure S12). While carbon peaks in C NMR
spectrum are more complicated than H NMR in alkane carbon
1
moisture enters the solution in the crystallization progress,
there are two different molecular structures in one
region, for example, there are three set peaks for tert-butyl
asymmetric unit. As shown in Figure
by one oxygen atom (O ) of phenoxy, five oxygen atoms (O
, O , O , O ) from the chain of crown ether. It is interesting
K1 is stabilized additionally by a cation-π interaction to one
phenoxy benzene ring (C -C ) with an average K∙∙∙C distance of
.130 Å. This cation-π interaction leads the orientation of this
2 (3A), K1 is coordinated
groups which indicate polymer complex
1 may dissociate to
2
3,
some aggregates or monomer in solution (Figure S13). This
solid structure is different to the dimeric sodium O-methylate
O
4
5
6
7
calix[
workers.
Crystals of complex
were obtained from a saturated THF solution, the structure of
complex is shown in Figure . The second auxiliary ligand of
4]arene complex reported by Mountford and co-
3
5
6
a
3
2
suitable for X-ray structural analysis
phenoxy moiety to be inversed, consequently the structure of
calixarene backbone changes to a partial-cone conformation.
2
1
K2 is coordinated by two oxygen atoms of O1 and O2 and two
the crown ether is deliberately used to construct a confined
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+
intramolecular K -
crown- phenol groups. Compared to complexes
not embedded well in the cavity of calix[ ]arene because of
the twisted partial-cone conformation. In order to get more
π
interactions with the benzene rings of
5
1
and , K is
2
2
4
insight into the structure of complex
1
temperature H NMR spectrum of complex
3, the variable
3 was performed.
When the temperature decreases, the singlet tert-butyl peak
at 1.36 ppm (18H) splits into two singlet peaks which have the
same amounts of protons; the aromatic peaks at 7.07 ppm (
split into four peaks gradually and each peak also has a same
integral value (some peaks were included in CDCl and the
8H)
Figure 3. A quick transformation equilibrium reaction for complex
3 in solution.
3
residue toluene); and a doublet proton peak appears at 2.98
ppm belonging to equatorial protons of methylene groups
2
0
(
Heq) (Figure
results suggest that there is a transformation equilibrium
reaction for complex in solution possibly because of the
rotation of two benzene rings 1ꢀ 6, 15ꢀ 20) as shown in
Figure . Line shape analysis of these VT- H NMR spectra
revealed a coalesce temperature (T ) and small exchange
4 and Figure S3). These VT-NMR experimental
3
(
C
C
C
C
1
3
c
−
1
1
reaction barriers ΔG≠ of 12.6 kcal mol (T = 253 K, H NMR
c
(
400Hz)), which suggests this transformation equilibrium
reaction is very quick. The structure of another molecule in the
asymmetric unit in Figure B) is similar except that there is
one water molecule coordinated to K . This water linked the
two molecules together with a hydrogen bond between the
oxygen atom (O15) of water and the oxygen atom of O
Figure S ). The coordination of water suggests K may be a
potential active catalytic center, K and K may be not active
2 (3
4
1
Figure 4. H NMR spectra (CDCl
3
1) taken at different temperatures of complex
3
1
ϧ
-1
c
(T = 253 K, Δ́ = 12.6 kcalmol , H NMR (400Hz)).
(
4
4
1
3
Initially we also wanted to synthesize a bimetallic
3
due to the crowded surroundings of crown ether chain and the
coordinated benzene ring.
complex using
2
L H in an attempt to explore the influence of
the crown ether chain in different substituted positions to the
structure of potassium complexes, but it was not successful
even after excess KN(SiMe
mixture. This suggests the monometallic complex
As shown in Figure ), the structure of complex
definitely different to the above bimetallic complexes. The sole
potassium ion K is coordinated by two oxygen atoms (O and
) of phenol moieties, five oxygen atoms (O , O , O , O
and O ) from the chain of crown ether, and one oxygen atom
) from THF solvent. There is a strong intramolecular
3
)
2
was added in the reaction
is stable.
is
4
2
(
4
4
1
1
O2
3
4
5
6,
7
(O8
hydrogen bond of
O1-H1∙∙∙O2, because of which the
conformation of calix[
1
4]arene ligand is a perfect cone, and the
H NMR also has confirmed this (Figure S18). The hydrogen
bond is strong enough to suppress the coordination of another
potassium ion into the cavity of calix[4
hydrogen bond, the catalytic activity of complex
]arene. Because of this
is
4
remarkably different to above three complexes which will be
illustrated in the following catalytic part.
ROP of rac-Lactide catalyzed by complexes 1-4.
The ROP of rac-lactide catalyzed by potassium complexes
was systematically conducted in the presence of BnOH as a co-
(methyl carbon initiator. The polymerization of rac-lactide almost completed
1-4
Figure 2. Molecular structures of complex
atoms of the tert-butyl groups and all of the hydrogen atoms are omitted for
clarity (except H1 of complex
3 and complex 4
4
)). 3A: Selected bond lengths (Å): K1-O2 2.520(3), within
3
] :[BnOH] was used (Table
min for complex
2
when a 200:1:2 ratio of [rac-
, entry ) with a complex
K1-O3 2.788(3), K1-O4 3.018(4), K1-O5 2.884(4), K1-O6 3.028(4), K1-O7 2.786(4),
K2-O1 2.546(3), K2-O2 2.607(4). 3B: Selected bond lengths (Å): K3-O9 2.530(3), LA]0:[
K3-O10 2.782(4), K3-O11 3.044(4), K3-O12 2.916(4), K3-O13 3.019(4), K3-O14
2
0
0
1
1
2
.780(4), K4-O8 2.556(3), K4-O9 2.649(4), K4-O15 2.935(3).
lengths (Å): K1-O1 2.6666(18), K1-O2 2.6680(18), K1-O3 2.7406(18), K1-O4
.875(2), K1-O5 2.895(2), K1-O6 2.7867(19), K1-O7 2.8443(17), K1-O8 2.828(2), temperature, while the same reaction consumed 5.5 h in
O1-H1 1.24(3), O2-H1 1.20(3).
4
: Selected bond concentration of 2.0 mM in 5.0 mL toluene at room
2
2 2
CH Cl to reach a 97% yield (Table 1, entry 2), and only 95%
4
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lactide can be converted to polymer in THF within 10 h (Table Molecular weights of final polymers are smaller than we
1
3a,
1
, entry
3
). The phenomenon is similar to our previous work.
When 1.0 equiv. amount of BnOH was used, we found the
molecular weights of the final polymers (Table , entry 4 and 6
expected (Table
1, entry 16). As the aforementioned structure
1
3b
1
)
are smaller than expected, which may result from a cyclization
side reaction. In fact a cyclization reaction can happen for the
ROP of lactide catalyzed by phenolate potassium complexes
directly in the absence of alcohol via a coordination insertion
mechanism, which has been reported by Tabernero and us
1
4, 21
recently.
phenoxy in complex
Table , entry ). Therefore, this is a serious side-reaction for
In this system the polymerization initated by
2
is also uncontrollable, but it is very quick
(
1
5
the ploymerization in the presence of BnOH which is initiated
by BnOH. To overcome this problem, the amount of BnOH was
increased to two equivalents of the catalyst to suppress the
phenoxy to initiate the ROP reaction directly; as expected, this
side reaction decreases to an acceptable level. The molecular
weights of polymers are close to calculated and increased
linearly with the ratio of [rac-LA] :[BnOH] (Table
1
, entries
), and the second feed experiment (Table
entry 12) in which another portion of rac-lactide monomer was
1
1,
0
0
and
7
-9
, Figure S
7
1
Figure 5. Homonuclear decoupled H NMR spectrum (CDCl
3
, 400 MHz) of the
as
values determined for all tetrads on the
had gone to completion also controllable. To address the basic of Bernoulli statistics, and all peaks have been deconvoluted completely
the slight epimerization and transestierfication reactions are not considered in
added after the polymerization of the first addition of rac-LA methine region of the poly(rac-lactide) produced from rac-LA with complex
3
a catalyst (Table 1, entry 25). The P
m
(
possibility of achieving immortal polymerization with complex this calculation).
by introducing several equivalents of chain-transfer agent,
polymerizations were conducted in the presence of 5.0
10.0 of complex
equiv. of BnOH toward complex (Table
, entries 10 and 11). ring of calix[
The molecular weights of polymers also agree with the of K is not crowded, thus the active center may change from
calculated Mn based on one chain growing per BnOH. When
to K2. However, the open catalytic center of K -O (phenoxy)
2
,
3
4
, K
1
is embedded by crown ether and a benzene
, the surrounding
2
1
]arene ligand. Compared to K1
2
+
-
K
1
BnOH reached 10 equivalents, the dispersity values of the cannot avoid some side reactions, like transesterification,
polymers become broad which may result from the partial cyclization. When the amounts of BnOH were increased to 10
dissociation of the crown group for the competitive equivalents to complex
coordination and hydrogen bond actions of BnOH to complex
reactions can partially suppress some side reactions that
As a result, it can produce many complicated components and initiated by phenoxide
the process of ROP becomes uncontrollable (Figures S and S
). becomes controllable to an acceptable level. The molecular
Compared to complex , complex
also displays high catalytic weights of polymers agree well with the calculated Mn now
activities when a 200:1:2 ratio of [rac-LA]0:[
] :[BnOH] was (Table , entries 17 and 20 23, Figure S ); the dispersity values
, entry 15). However, the PDIs are broad which of the polymers are also low. The iso-selectivity can reach to
3, more fast polymer chain exchange
2
.
1
4, 21
and polymerization reaction
5
6
2
1
1
1
-
8
0
0
used (Table
may be attributed to the existence of several active centers 0.73 (P
because complex
has aggregate structures in solution as the decoupled H NMR spectra of the methine region of a
mentioned above. It is notable that complexes and
have typical sample (Table , entry 25, P 0.73, Figures and S ).
isoselectivity for the ROP of rac-lactide, Pm values range from No improvements can be achieved by alternating the solvent
.60 to 0.67 (Table , entries 13
15). The isoselectivity to CH Cl or THF (Table , entries 18 and 19). It is to note a
cannot increase remarkably even at ꢀ60 C (Table
, entry 13). slight epimerization can happen in this system which can be
Compared to potassium phenolate complexes reported verified by the analysis of poly-L-lactide (Table , entry 26
recently by us, the isoselectivies are not very high which hints Figure S ), which also can decrease the isoselectivity of
for the ROP of rac-lactide. Compared to complex
center is important for a high stereoselectivity of ROP of rac- the catalytic activity of complex is very low under the same
lactide.
conditions when complex was used as a catalyst for the ROP
In order to further explore the effect of the catalytic of rac-LA (Table , entry 27). The phenomena can be
subtle environment of the catalytic K -O (phenoxy) center in rationalized because the negative charge of the oxygen atom
the ROP of rac-LA processes, complexes and
with fused of phenoxy is low due to the intramolecular hydrogen bond
crown moiety in calix[
]arene ligands were also applied in the interaction, consequently the basicity of phenoxy group is not
ROP of rac-lactide. Complex , which contains
- substituent very strong to form the intermolecular hydrogen bond (a
1
o
) at ꢀ60 C (Table 1, entry 25), which can be verified by
m
1
1
1
2
1
m
=
5
9
0
1
7
-9
,
,
2
2
1
o
1
1
,
9
3
+
-
at a suitably confined space of the catalytic K -O (phenoxy) complex
3,
4
4
1
+
-
3
4
4
3
1, 3
crown moiety, is also a highly active catalyst for the ROP of second hydrogen bond) with benzyl alcohol; thus it is not
rac-lactide with two amounts of BnOH as a co-initiator. easily activate benzyl alcohol to initiate the ROP of lactide.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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DOI: 10.1039/C6DT01417H
ARTICLE
Journal Name
In order to get more insight into the ROP mechanism, the not very serious because the molecular weights are close to
1
H NMR spectroscopy of a final polymer was analyzed which the calculated values (Figure S11).
revealed that the polymer chain is end-capped by one benzyl
ester and a hydroxyl (Table , entry 17, Figure S10). The ESI
mass spectrum of a final polymer (Table , entry 17, Figure
and Figure S11) confirmed it further by a series of main peaks
at 144m + 108 23 with a charge of + , which can be assigned
to m(C ) + BnOH + Na . It is to be noted that there is
another series of peaks at 0.5 × (144m + 108 23 19) with a
charge of + , which can be attributed to m(C ) + BnOH +
) / 3 with a
1
Conclusion
1
6
Four calix[
been synthesized and their crystal structures, which represent
rare examples of alkali metal calix[ ]arene crown complexes,
were analyzed in details. Calix[ ]arene crown complex
exhibits a sandwich structure. In dinuclear complex
4]arene crown derivative potassium complexes have
+
1
+
6 8 4
H O
4
+
+
4
2
2
6
H
8
O
4
3
, there is
+
+
Na + H
3
O ; and peaks at (144m + 108
can be attributed to m(C
O (Figure was enlarged in Figure S11). This information
+
23
+
19
×
2
a quick transformation equilibrium reaction in solution
because of the rotation of two phenoxy groups. Due to the
+
charge of +
3
6 8 4
H O ) + BnOH + Na +
+
2H
3
6
presence of intramolecular hydrogen bond, complex
stable mononuclear complex. Complexes and show high
activities and moderate iso-selectivities for the ROP of rac-LA.
Complex also exhibited high activity, but the molecular
weights of the final polymers are not consistent with the
expected values, while complex showed a very low activity
due to the presence of intramolecular hydrogen bond.
Furthermore, complex also can be used to obtain an isotactic
4 is a
indicates that BnOH is a real initiator for the ROP of lactide,
therefore, as the monomer activated mechanism supposed for
most alkali metal phenoxides, the lactide can be activated
2
3
1
+
after coordinating to K , and consequently the activated BnOH
2
2
can attack the carbonyl group to initiate the ROP reaction.
Some weak series of peaks (at about 1479.46 with a charge of
and at about 2364.71 with a charge of + ) with a difference
in molecular mass of 72 Da hint some trans-esterification
4
+2
1
3
~
m
PLA with a P = 0.73.
reactions happen during this polymerization process, but it is
Table 1. rac-Lactide Polymerization Catalyzed by 1-4.
b
c
d
e
entry
1
cat.
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
3
3
3
3
3
3
3
3
3
3
3
4
[LA]
0
/[Cat]
0
/[BnOH]
0
t
conv(%)
Mncal.(g/mol)
13500
14100
13800
27400
12100
13600
21200
28300
34300
14000
6900
Mnobs.(g/mol)
13400
11700
8500
Ð
P
m
200:1:2
200:1:2
200:1:2
200:1:1
100:1:0
100:1:1
300:1:2
400:1:2
500:1:2
500:1:5
500:1:10
3 min
5.5 h
93
97
95
95
84
94
98
98
95
96
95
96
90
93
95
89
98
90
99
98
97
99
96
98
98
98
89
1.21
1.32
1.58
1.26
1.21
1.23
1.23
1.23
1.19
1.32
1.48
1.22
1.19
1.68
1.42
1.17
1.08
1.03
1.23
1.07
1.07
1.07
1.07
1.20
1.06
1.06
1.06
0.63
0.60
0.57
0.65
0.65
0.60
0.64
0.65
0.65
0.65
0.60
0.65
0.67
0.61
0.60
0.52
0.60
0.59
0.59
0.60
0.62
0.62
0.62
0.59
0.73
0.94
0.60
f
2
g
3
10 h
4
5
6
7
8
9
5 min
4 min
3 min
3.5 min
4 min
4 min
3 min
2 min
3(3) min
1 h
16200
16100
10800
21200
26200
30100
12600
5700
1
1
1
0
1
2
200(200) :1:2
200:1:2
27800
13100
13500
13800
12900
2900
25400
17600
8300
i
13
1
1
1
1
4
5
6
7
100:1:1
5 min
4 min
5.5 h
200:1:2
13400
6200
200:1:2
200:1:10
200:1:10
200:1:10
250:1:10
300:1:10
350:1:10
400:1:10
1000:1:10
200:1:10
200:1:10
200:1:10
10 min
12.5 h
6 h
2700
f
1
8
2700
2300
g
1
9
3000
3800
2
0
1
2
3
12 min
16 min
17 min
24 min
4 h
3600
3300
2
2
2
4300
3900
5100
4700
5600
5400
h
2
4
14200
2900
14300
2500
i
j
2
5
6
7.2 h
2
6.5 h
2900
2800
2
7
4.5 h
2700
2800
a
b
1
c
Reactions were performed in 5 mL of toluene, [cat.]
0
= 2.0 mM, at room temperature in addition to the annotated. Determined by H NMR spectroscopy. Calculated
d
from the molecular weight of rac-LA × [LA] /[BnOH]
0
0
× conversion yield + MBnOH. Measured by GPC in THF calibrated with standard polystyrene samples and corrected
2
3 e
1
f
using the Mark−Houwink factor of 0.58. Determined by analysis of all of the tetrad signals in the methine region of the homonuclear-decoupled H NMR spectrum.
g
h
i
o
j
2 2
In 5 mL of CH Cl . In5 mL of THF. In 10 mL of Toluene. -60 C. L-LA was used.
6
| J. Name., 2012, 00, 1-3
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Journal Name
Ple Da sae l tdo onn To rt aa nd sj ua sct t mi o an r sg ins
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DOI: 10.1039/C6DT01417H
ARTICLE
1
299.40
z=2
100
1371.42
z=2
9
5
1227.38
z=2
1443.45
z=2
90
8
5
1154.86
z=2
80
1064.67
z=3
1515.47
z=2
75
1016.32
z=3
7
0
1587.49
z=2
9
68.31
65
920.29
z=3
z=3
60
1659.51
z=2
55
5
0
1732.03
z=2
45
2003.60
z=1
1
859.56
z=1
4
0
2147.64
z=1
2
292.69
z=1
8
73.93
z=3
35
1804.05
z=2
1
998.64
z=1
876.08
30
1
2287.73
z=1
25
2142.69
z=1
z=2
8
24.27
z=3
20
2436.73
z=1
2
164.62
z=?
219.66
z=1
2020.12
z=2
2580.77
z=1
15
2294.69
z=1
2
10
2452.71
z=1
2582.78 2724.81
z=1
z=?
5
0
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
m/z
1900
2000
2100
2200
2300
2400
2500
2600
2700
2800
Figure 6. ESI-MS spectrum of poly(rac-LA) prepared by the ROP of rac-LA (Table 1, entry 17).
from toluene and ethyl acetate. CDCl , C D and toluene-d
8
3
6
6
were purchased from J&K Scientific, Ltd., in Beijing and were
dried over activated molecular sieves. KN(SiMe3)2 was
Experimental section
General considerations
purchased from J&K Scientific Ltd. and used as received. 18
-
crown-6 was purchased from local companies and dried under
vacuum.
Synthesis of complex 1 A solution of L H2 (0.73 g, 1.0 mmol) and
All syntheses and manipulations of air- and moisture-sensitive
materials were performed under a dry nitrogen atmosphere or
1
1
in a glovebox using standard Schlenk techniques. The H NMR
1
3
3 2
KN(SiMe ) (2.2 mL, 2.2 mmol, 1.0 M in THF) was stirred in
and C NMR spectra were recorded on a JEOL ECS-400 MHz
1
toluene (20 mL) at room temperature under a N atmosphere
and Varian Mercury Plus 300 MHz spectrometer. H NMR
chemical shifts are reported in ppm with the residual protons
2
for 12 h. The mixture changed into a turbid liquid and a white
in deuterated solvents as follows: δ 7.26 ppm for chloroform- precipitate was separated by filtration. The solid residue was
1
3
d, δ 7.16 ppm for benzene-d
6
,
δ 2.08 ppm for toluene-d
NMR chemical shifts are reported in ppm with the residual
8
.
C
C
washed with a mixed solvent of toluene and n-hexane and
1
3
1
dried in vacuo. Yield: 0.41 g (50.7%). H NMR (300 MHz, CDCl
7.20 (s, Ar-H, 4H), 7.01 (s, Ar-H, 4H), 3.75 (t, J = Hz, -CH2-,
H each), 1.81 (m, -
3
):
in the solvents: δ 77.0 ppm for chloroform-d, δ 128.0 ppm for
benzene-d δ 137.48 ppm for toluene-d . The elemental
δ
6
6
,
8
4
H), 3.68
,
3.56 (d each, J = 12 Hz, Ar-CH -Ar,
2
4
compositions of the complexes were measured using an
Elemental Vario EL series CHN analyzer with the samples under
a nitrogen atmosphere. The molecular weights (Mn and Mw)
and the molecular mass distributions (Mw/Mn) of the polymer
CH
2
CH
3
,
4
H), 1.28 (s, -C(CH
3
3
)
3
,
18H), 1.19 (s, -C(CH
H). C NMR (100 MHz, CDCl
129.0 128.2 127.6
33.7 33.4 ((CH C-), 32.2
23.1 (-CH -), 10.5 10.2 (-CH ). Anal. Calcd for
: C 74.21, H 8.22. Found: C 73.98, H 7.88
3
)
3
,
18H), 1.02
): δ 152.6
75.0 (-
31.5 31.4
1
(
t, J = 6.0 Hz, -CH
45.2 138.0 130.4
OCH -), 34.0 33.8
(CH C-), 23.7
3
,
6
3
,
1
,
,
,
,
,
,
125.9 (Ar-C), 76.0
31.8
,
2
,
,
,
3
)
3
,
,
,
samples were measured by gel permeation chromatography
o
(
3
)
3
,
2
,
3
(GPC) at 25 C using THF as a solvent, an eluent flow rate of
1
C
50
H
66
K
2
O
4
.
mL/min, and narrow polystyrene standards as reference
samples. The measurements were performed using a Waters
1
Synthesis of complex
KN(SiMe 2.2 mL, 2.2 mmol, 1.0 M in THF), and 18-crown-
0.29 g, 1.1 mmol) in toluene (10 mL) and THF (10 mL) was
stirred at room temperature under a N atmosphere for 12 h.
2
2 A solution of L H (0.73 g, 1.0 mmol),
3
)
2
(
6
1
525 binary system that was equipped with a Waters 2414 RI
2
6
(
detector using two Styragel columns (10 -10 kg/mol). Each
2
reported value was corrected using a factor of 0.58 for
2
3
The volatiles were removed in vacuo. The residue was
separated and recrystallized with a mixed solvent of THF and
polylactide according to the literature. The ESI mass
spectroscopic data was obtained by using a Thermo Scientific
Orbitrap Elite MS (LTQ Orbitrap Elit).
n-hexane. The solid was dried under vacuum. Yield: 0.37
g
1
(
34.5%). H NMR (400 MHz, C
Ar-H, 4H), 4.58 (br, Ar-CH -Ar, 4H), 3.81 (br, -CH
crown ether-H, 24H), 3.42 (br, Ar-CH -Ar, H), 1.64 (m, -CH CH ,
6
D
6
): δ 7.42 (s, Ar-H, 4H), 7.22 (s,
Materials
2
2
-, 4H), 3.54(s,
Toluene, THF, and n-hexane were dried by refluxing with
4
2
2
3
sodium and benzophenoneketyl under a N
2
atmosphere.
4
H), 1.53 (s, -C(CH
3
)
3
,
18H), 1.05 (s, -C(CH
3
)
3
,
18H), 0.75 (t, J = 8.0
137.4 131.7
25.8 (Ar-C), 77.0 (-OCH -), 71.1 (crown ether-C), 34.1, 33.9
2
2
2
3
2 5
CH Cl and CH CN were dried over P O . Rac-LA was purchased
1
3
Hz, -CH
3
,
6
H). C NMR (100 MHz, C ): δ 145.3
6
D
6
,
,
,
from Daigang BIO Engineer Ltd. of China and recrystallized
1
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J. Name., 2013, 00, 1-3 | 7
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ARTICLE
(CH ) C-), 32.7, 31.4 ((CH ) C-), 22.8 (-CH -), 10.2 (-CH ). Anal. factor calculations. The crystal data and refinement results
3 3 2 3
Journal Name
(
3
3
Calcd for C62
Synthesis of complex
2.2 mL, 2.2mmol, 1.0 M in THF) were dissolved in toluene (20
mL) and stirred at room temperature under a N atmosphere
H
90
K
2
O
10: C 69.36, H 8.45. Found: C 69.02, H 8.28
.
were summarized in Table S1.
2
3
2 3 2
L H (0.80 g, 1.0 mmol) and KN(SiMe )
(
Acknowledgements
2
for 12 h. After standing still for a while, a white solid was Financial support from the National Natural Science
settled at the base of the flask; then the white solid was Foundation of China (No. 21271092, 21401161, 21171078),
separated and recrystallized with a mixed solvent of toluene the Science Foundation of Gansu Province of China
and n-hexane. The solid was dried under vacuum. Yield: 0.52
g
(1308RJ2A121), the project for the National Basic Science
Personnel Training Fund (J1103307), and the ScGrid of the
Supercomputing Center of the Chinese Academy of Sciences
are gratefully acknowledged.
1
(
58.8%). H NMR (400MHz, CDCl
3
): δ 7.07 (m, Ar-H,
O-, 16H), 3.75 3.25 (m, Ar-CH
18H), 1.09 (s, -C(CH
): δ 154.3 144.8 136.3 130.1
70.6 70.2 70.1 (-OCH CH O-), 33.9
1.2 ((CH C-). Anal. Calcd for C52
Found: C 70.30, H 7.59
Synthesis of complex
toluene (10 mL) and THF (10 mL), then KN(SiMe
8
H), 3.99
,
3
.82
-
3.54 (m, -OCH
2
CH
2
-
2
-Ar,
8
H),
1
3
1
.36 (s, -C(CH
3
)
3
,
3 3
) , 18H). C NMR (100
MHz, CDCl
C), 70.9
3
,
,
,
,
129.0
,
128.2
,
124.9 (Ar-
,
,
,
2
2
,
33.5 ((CH
3
)
3
C-), 32.4
,
.
References
3
3
)
3
68 2 7
H K O : C 70.71, H 7.76
1
(a)P. Molenveld, J. F. J. Engbersen and D. N. Reinhoudt,
Chem. Soc. Rev., 2000, 29, 75-86; (b)A. Casnati, F. Sansone
and R. Ungaro, Acc. Chem. Res., 2003, 36, 246-254; (c)E.
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Zorzi, N. Guidolin, L. Randaccio, R. Purrello and S. Geremia, J.
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Y. Chen, Y. Su, D. Yan, X. Zhu and G. Zhou, Chem. Commun.,
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.
3
4
L
H2 (0.80 g, 1.0 mmol) was dissolved in
1.1 mL, 1.1
3 2
) (
mmol, 1.0 M in THF) was added. The solution was stirred at
room temperature under a N2 atmosphere for 12 h. The
volatiles were removed in vacuum and the residue
recrystallized with a mixed solvent of toluene and n-hexane.
1
The solid was dried under vacuum. Yield: 0.29 g (34.3%). H
NMR (400MHz, C
.29 (s, Ar-H, H), 4.94 (m, Ar-CH
CH -Ar, H), 3.46(d, J = 12Hz, Ar-CH -Ar,
6
D
6
): δ 7.44 (s, Ar-H,
2
H), 7.36 (s, Ar-H,
H),4.58 (d, J = 12 Hz, Ar-
H), 2.83 (d, J = 12 Hz,
H), 3.62 3.51 (m, -
O-, H), 3.12 (m, -
Hz, -OCH CH O-, H), 1.36 (s, -
18H). C NMR (100 MHz, C ):
126.1
2H),
7
2
2
-Ar,
3
1
2
2
(a)L. Baldini, A. Casnati, F. Sansone and R. Ungaro, Chem.
Soc. Rev., 2007, 36, 254-266; (b)A. Dondoni and A. Marra,
Chem. Rev., 2010, 110, 4949-4977; (c)A. Pandya, P. G.
2
2
Ar-CH
2
-Ar,
2
H), 3.68 (m, -OCH
2
CH
2
O-,
CH
2
-
OCH
OCH
2
CH
CH
2
O-,
O-,
4H), 3.24 (m, -OCH
2
2
4
Sutariya, A. Lodha and S. K. Menon, Nanoscale, 2013,
5,
2
2
4
H), 2.95 (t, J =
8
2
2
2
2364-2371; (d)T. Sawada, H. Hisada and M. Fujita, J. Am.
Chem. Soc., 2014, 136, 4449-4451; (e)M. Song, Z. Sun, C.
Han, D. Tian, H. Li and L. Jiang, Chem.-Eur. J., 2014, 20, 7987-
1
3
C(CH
3
)
3
,
18H), 1.19 (s, -C(CH
152.5 146.1 136.0
124.5 (Ar-C), 75.8 69.3
C-), 32.3 31.4 ((CH
3
)
3
,
6 6
D
δ
157.9
,
,
,
,
134.9
,
133.8
,
129.5
,
127.1
,
,
7
993; (f)V. Bagnacani, V. Franceschi, L. Fantuzzi, A. Casnati,
124.9
,
,
,
68.9 67.8 (-OCH
,
2
CH
2
O-), 34.2
,
33.8
: C
G. Donofrio, F. Sansone and R. Ungaro, Bioconjug. Chem.,
2012, 23, 993-1002.
(a)D. Diamond and M. A. McKervey, Chem. Soc. Rev., 1996,
(
(CH
3
)
3
,
3
)
3
C-). Anal. Calcd for C52
H69KO
7
3
73.90, H 8.23. Found: C 73.63, H 7.98.
2
1
1
5, 15-24; (b)A. Ikeda and S. Shinkai, Chem. Rev., 1997, 97,
713-1734; (c)J. S. Kim and D. T. Quang, Chem. Rev., 2007,
07, 3780-3799; (d)R. Rathore, S. H. Abdelwahed and I. A.
General procedure for polymerization of rac-Lactide.
typical polymerization procedure is shown in
[LA] /[cat.] /[BnOH] 200 ; Table , entry ). A solution of
complex 0.0107 g, 0.010 mmol) , BnOH (100.00 uL, 0.1 M in
toluene) and rac-Lactide (0.2880 g, 2.0 mmol) in toluene ( mL)
was stirred at room temperature for min and quenched by a
few drops of water. Then the solvent was removed under
vacuum, white crystalline solid was obtained by
A
Guzei, J. Am. Chem. Soc., 2004, 126, 13582-13583; (e)B.
Schazmann, N. Alhashimy and D. Diamond, J. Am. Chem.
Soc., 2006, 128, 8607-8614; (f)M. Echabaane, A. Rouis, I.
Bonnamour and H. Ben Ouada, Mater. Chem. Phys., 2013,
141, 781-789; (g)Y. H. Lee, H. Liu, J. Y. Lee, S. H. Kim, S. K.
(
0
0
0
=
:1
:
1
1
4
2
(
5
5
Kim, J. L. Sessler, Y. Kim and J. S. Kim, Chem.-Eur. J., 2010, 16
5
,
895-5901; (h)R. K. Pathak, J. Dessingou and C. P. Rao, Anal.
a
Chem., 2012, 84, 8294-8300; (i)A. K. Jain, V. K. Gupta, L. P.
Singh and J. R. Raisoni, Electrochim. Acta, 2006, 51, 2547-
2553; (j)C. D. Gutsche and K. C. Nam, J. Am. Chem. Soc.,
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recrystallization from a CH
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SYNOPSIS TOC (Word Style “SN_Synopsis_TOC”)
A series of potassium calix[4]arene crown ether inclusion complexes have been synthesized. Calix[4]arene complex
sandwich structure with 18-crown-6 as a second auxiliary ligand. When crown ether chain is fused into calix[4]arene, dinuclear
complex and mononuclear complex can be obtained. There is a quick transformation equilibrium reaction in solution because
of the rotation of two phenoxy groups in complex . Due to the presence of intramolecular hydrogen bond, complex is a stable
mononuclear complex. Complexes and show high activities and iso-selectivities for the ROP of rac-LA, while complex
showed a very low activity due to the presence of an intramolecular hydrogen bond. Furthermore, complex also can be used to
obtain an isotactic PLA with a P = 0.73.
2 exhibits a
3
4
3
4
2
3
4
3
m