Cu(ii) templated formation of [: N] pseudorotaxanes (n = 2, 3, 4) using a tris-amino ether macrocyclic wheel and multidentate axles

Article abstract of DOI:10.1039/c9dt01067j

A tris-amine and oxy-ether functionalised macrocyclic wheel (NaphMC) and various phenanthroline based multidentate axles (L1, L2 and L3) are utilised for the formation of [n]pseudorotaxanes (n = 2, 3, 4) in high yields via Cu(ii) temptation and π-π stacking interactions. The systematic development of threaded supramolecular architectures i.e. [2]pseudorotaxane {[2]CuPR(ClO₄)₂}, [3]pseudorotaxane {[3]CuPR(ClO₄)₄} and [4]pseudorotaxane {[4]CuPR(ClO₄)₆} from bidentate L1, linear tetradentate L2 and tripodal hexadentate L3 respectively is described. All the [n]pseudorotaxanes are well characterized by several spectroscopy and other experimental techniques such as electrospray ionization mass spectrometry (ESI-MS), isothermal titration calorimetric (ITC) study, UV/Vis, EPR, IR and elemental analysis. Moreover, the single crystal X-ray analysis of [2]pseudorotaxane confirmed the threading of L1 in the cavity of NaphMC, resulting in the formation of a penta-coordinated Cu(ii) ternary complex. ITC studies revealed the order of binding constant values for the formation of [n]pseudorotaxanes from the NaphMC-Cu(ii) complex and multidentate axles as L3 > L2 > L1. Finally, we have also shown the ability of Ni(ii) to act as a metal template in the formation of [n]pseudorotaxanes.

Full text of DOI:10.1039/c9dt01067j

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

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Cu(II) templated formation of [n]Pseudorotaxanes (n= 2,3,4) using
a tris-amino ether macrocyclic wheel and multidentate axles
.
Somnath Bej, Mandira Nandi, Tamal Kanti Ghosh and Pradyut Ghosh*
Received 00th January 20xx,
Accepted 00th January 20xx
A tris-amine and oxy-ether functionalised macrocyclic wheel (NaphMC) and various phenanthroline based multidentate
axles (L1, L2 and L3) are utilised for the formation of [n]Pseudorotaxanes (n=2,3,4) in high yields via Cu(II) temptation and
π–π stacking interactions. Systematic development of threaded supramolecular architectures i.e. [2]pseudorotaxane
{[2]CuPR(ClO4)2}, [3]pseudorotaxane {[3]CuPR(ClO4)4} and [4]pseudorotaxane {[4]CuPR(ClO4)6} from bidentate L1, linear
tetradentate L2 and tripodal hexadentate L3 respectively are described. All the [n]Pseudorotaxanes are well characterized
by several spectroscopic and other experimental techniques such as electrospray ionization mass spectrometry (ESI-MS),
Isothermal Titration Calorimetric (ITC) study, UV/Vis, EPR, IR and elemental analysis. Moreover, the single crystal X-ray
analysis of [2]pseudorotaxane confirmed the threading of L1 in the cavity of NaphMC, resulting in the formation of penta-
coordinated Cu(II) ternary complex. ITC studies revealed the order of binding constant values for the formation of
[n]Pseudorotaxanes from NaphMC-Cu(II) complex and multidentate axles as L3  L2  L1. Finally, we have also shown the
DOI: 10.1039/x0xx00000x
www.rsc.org/
ability
of
Ni(II)
to
act
as
a
metal
template
in
the
formation
of
[n]Pseudorotaxanes.
have explored the synthesis and other properties of [2]- and
[3]pseudorotaxanes by utilising various approaches.13 In this
direction, numerous examples for the formation of
[n]Pseudorotaxanes based on various type of wheels such as
cryptand, pillar[n]arene, cucurbit[n]urils, cyclodextrin and
crown ether via non-covalent interactions are widely
reported.14 However, synthesis and other applications of
higher order metal ion templated threaded architechtures
(e.g. [4]pseudorotaxane and higher) having interesting
structural complexities are scarcely reported in literature.11c, 15
In this regard, herein we report a systematic development of
mono-, bi-, and tri-nuclear Cu(II) templated [2], [3], and
[4]pseudorotaxanes respectively from NaphMC (Chart 1) and
Introduction
In recent years, new generation of threaded molecular
architectures such as pseudorotaxanes, rotaxanes and
catenanes have shown immense interest to the scientific
community for their synthetic challenges, structural
complexities and other potential applications in various fields
such as molecular machineries,1 materials science,2 polymer
chemistry,3 molecular sensor,4 molecular recognition4-5 and
biological science.6 Several threaded macromolecular
architectures including mechanically interlocked molecules
(MIMs) are synthesized by utilising various efficient non-
covalent interactions such as cation/anion templation,5b, 7 π-π
stacking,8 hydrogen bonding9 and halogen bonding
interactions.10 Pseudorotaxanes are the essential building
blocks for the synthesis of MIMs (e.g. rotaxanes, catenanes
and knots) and prototypes for other molecular machineries
which are of current interest in the field of supramolecular
11
chemistry.2b,
Development of synthetic threaded
architectures having structural complexities is growing
continuously and has led to the search for new wheels and
axles for the construction of higher order [n]Pseudorotaxanes
and relevant advanced architectures depending upon the
binding strength of host-guest interactions.7e, 12 In this regard,
it is noteworthy to mention here that several research groups
School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A &
2B Raja S. C. Mullick Road, Kolkata 700032, India. E-mail: icpg@iacs.res.in
†Electronic Supplementary Information (ESI) available. CCDC 1892956. For ESI and
Chart 1. Chemical structure of macrocycle (NaphMC) and axles (L1-L3).
crystallographic
data
in
CIF
or
other
electronic
format
See
DOI: 10.1039/x0xx00000x
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newly synthesized tetra- and hexa-dentate axles (L2 and L3) multidentate axles for the preparation of higher order
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DOI: 10.1039/C9DT01067J
along with bi-dentate axle, L1 (Chart 1). Involvement of metal pseudorotaxanes. In this direction, we have synthesized
ion coordination and π–π stacking interactions between the bipodal-tetradentate axle, L2 and tripodal-hexadentate axle,
axles (L1-L3) and NaphMC resulted in significantly high yields L3 from L1 for the synthesis of [3]pseudorotaxane
of the [n]Pseudorotaxanes.
{[3]CuPR(ClO4)2} and [4]pseudorotaxane {[4]CuPR(ClO4)2}
having two and three chelating phenanthroline units
respectively as shown in Fig. 1. Chelating phen units are
attached with a central benzene platform via aliphatic linkers
in L2 and L3 in such a way that the pendant phenanthroline
moieties are flexible enough to thread into multiple
macrocycles (NaphMC) via coordination with Cu(II) to form
higher order pseudorotaxanes. Interestingly, efficient binding
of phenanthroline based axles with NaphMC and Cu(II) along
with π–π stacking interactions between electron rich naphthyl
unit of NaphMC and electron deficient phen unit of the axles
can result in efficient synthesis of [n]Pseudorotaxanes
(n=2,3,4) with high yields.
Results and discussion
Designing Aspects:
Towards our goal of development of threaded architectures
with structural diversities, we have strategically designed the
macrocycle and multidentate axles to synthesize
[n]Pseudorotaxanes with increasing structural complexities.
Previously, our group reported tris amine based heteroditopic
macrocycle and phenanthroline axle based selective formation
of [2]pseudorotaxane with Cu(II) metal ion over other
transition metal ions and bidentate axles.13o, 14f Moreover, we
have also successfully demonstrated the efficient formation of
[2]pseudorotaxanes in high yields from electron deficient
bidentate 1,10-phenanthroline (phen) axle and electron rich
naphthalene containing tris amine based macrocycle, NaphMC
via Cu(II) temptation and π–π stacking interaction with high
association constant values.16 Inspired by the above
mentioned results, herein we have utilized Cu(II) as a
templating agent for the efficient synthesis of
pseudorotaxanes. As we have also noticed that phenanthroline
based axles showed high affinity towards the formation of
pseudorotaxanes with Cu(II) and tris-amine based
macrocycles, phenanthroline moiety has been incorporated in
all the axles (L1-L4) as the metal binding unit. Accordingly, in
order to synthesize higher homologues of [2]pseudorotaxane,
we have introduced 4-methyl-1,10-phenanthroline (L1) as an
axle (without affecting the coordination motif) to develop
[2]pseudorotaxane {[2]CuPR(ClO4)2} where the substituted
methyl group of L1 can be further functionalized to produce
Synthesis and Characterization of NaphMC, L2 and L3:
The oxy-ether and tris-amine functionalised NaphMC was
prepared by following the reported procedure16 (Scheme 1S,
t
Scheme 1. Synthetic route of L2: (i) 1,6-dibromo hexane, BuOK, DMF, RT, 12h,
reflux, another 18h, 68 %; (ii) Phen-Acid, TBAF, THF, RT, 12h, 74 %.
Fig. 1 Cartoon- representation of designing strategies for the construction of transition metal based [n]Pseudorotaxane (n=2, 3, 4), Counter anions are omitted for clarity.
2 | J. Name., 2012, 00, 1-3
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was stirred for 3-4h at RT and after that the solvent was
evaporated to obtain [2]CuPR(ClO4)2 as green solid in 83%
yield (Scheme 3). By using similar reaction procedure as
mentioned above, reaction of two equivalents of NaphMC and
Cu(II) along with of one equivalent of tetra dentate ligand L2 at
RT led to the formation of [3]pseudorotaxanes
{[3]CuPR(ClO4)4} in 79% yield (Scheme 3) and reaction of one
equivalent of hexadentate tripodal L3 along with three
equivalent of NaphMC and Cu(II) in RT yielded
[4]pseudorotaxanes {[4]CuPR(ClO4)6} in 71% yield (Scheme 3).
Thorough synthetic procedures for the formation of
[n]Pseudorotaxanes (n=2,3,4) are given in the experimental
section. All the ternary complexes were well characterized by
several spectroscopic and other experimental techniques (Fig.
13S- Fig. 41S, ESI†).
Scheme 2. Synthetic route of L3: (i) 1,6-dibromo hexane, K2CO3, DMF, RT, 24h, 83 %; (ii)
Phen-Acid, TBAF, THF, RT, 12h, 78 %.
ESI†). 1, 10-phenanthroline-4-carboxylic acid (Phen-Acid) was
also prepared from literature reported procedure17 (Scheme
2S, ESI†) and further used for the synthesis of newly designed
axles L2 and L3. The synthetic route and chemical structures of
L2 and L3 are shown in scheme 1 and 2 respectively. Both the
axles L2 and L3 were synthesized in four steps with high yields
as described in the experimental section. All of the above
mentioned compounds were well characterized by 1H, 13C-
NMR and mass spectrometric techniques as shown in ESI (Fig.
1S- Fig. 12S, ESI†).
Detailed experimental studies were performed in order to
Synthesis and Characterization of [n]Pseudorotaxanes
{[2]CuPR(ClO4)2, [3]CuPR(ClO4)4 and [4]CuPR(ClO4)6 }:
After the successful synthesis of NaphMC, L2 and L3, we have
carried out the synthesis of [n]Pseudorotaxanes (n=2,3,4) from
NaphMC, Cu(ClO4)2 and corresponding axles (L1-L3). Initially,
the macrocycle, NaphMC was reacted with Cu(ClO4)2.6H2O to
form NaphMC-Cu(II) complex (Scheme 3S, ESI†) in CHCl3-
CH3OH (2:8) binary solvent mixture as reported previously.16
After that, one equivalent of L1 was added to the solution in
situ at room temperature (RT). The resultant reaction mixture
Scheme 3. Synthetic route of formation of [2], [3], [4]pseudorotaxanes {([2]CuPR)2+
([3]CuPR)4+ and ([4]CuPR)6+}. Counter anions are omitted for clarity.
,
Fig. 2: ESI-MS (+ve) spectra of [2], [3], [4]pseudorotaxanes (A) [2]CuPR(ClO4)2, (B) [3]CuPR(ClO4)4 and (C) [4]CuPR(ClO4)6 with their isotopic distribution patterns of corresponding
ion peak (inset shows red line for experimental and black line for calculated patterns of their isotopic distribution model).
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determine the formation of [2]CuPR(ClO4)2, [3]CuPR(ClO4)4 peaks matched well with the theoretical isotopic distribution
and [4]CuPR(ClO4)6. Initially, ESI-MS studies of [2]CuPR(ClO4)2 pattern as obtained from the natural abundance of elements
showed prominent molecular ion peaks at m/z= 933.2562 (Fig. 2). So, mass spectrometric analysis of all the
(calc. 933.2566) and 417.1539 (calc. 417.1541), which can be pseudorotaxanes indicated their formation from NaphMC and
- +
-
assigned to {[2]CuPR(ClO4)2-ClO4 } and {[2]CuPR(ClO4)2-2ClO4 respective axles.
}
2+
species respectively (Fig. 2). Similarly, ESI-MS spectrum of
[3]CuPR(ClO4)4 showed the presence of characteristic Isothermal Titration Calorimetric (ITC) Experiment:
molecular ion peaks at m/z = 1128.3229 (calc. 1128.3223) and
In order to get thermodynamic insight into the formation of
719.2326 (calc. 719.2320), which correspond to the presence
[n]Pseudorotaxanes (n=2,3,4), ITC experiments were
- 2+
- 3+
of {[3]CuPR(ClO4)4-2ClO4 }
and {[3]CuPR(ClO4)4-3ClO4 }
performed with NaphMC-Cu(II) and axles (L1-L3) in CH3CN at
298K. In all the ITC studies, respective axle solution in CH3CN is
taken in the cell and titrated with NaphMC-Cu(II) solution in
CH3CN. Details of ITC experiments are provided in the
experimental section and values of all the thermodynamic
parameters (obtained from ITC titrations) are given in Table 1.
In all the cases, the titration data showed smooth and
molecular species respectively (Fig 2). Finally, in case of
[4]CuPR(ClO4)6, prominent molecular ion peaks at
m/z=1722.4463 (calc. 1722.4460) and 1115.3148 (calc.
- 2+
1115.3144) indicated the presence of {[4]CuPR(ClO4)6-2ClO4 }
- 3+
and {[4]CuPR(ClO4)6-3ClO4 } respectively (Fig.13S- Fig.15S,
ESI†). The isotopic distribution pattern of all the observed
Table 1: Thermodynamic parameter and association constants for [2]CuPR(ClO4)2, [3]CuPR(ClO4)4 and [4]CuPR(ClO4)6 complex.
Complex
Host
L1
Guest
Fitting model
One site
K (M-1)
H
(Kcal/mol)
H=-22.1
S(cal/mol/deg)
S=-46.5
[2]CuPR(ClO4)2
[3]CuPR(ClO4)4
[4]CuPR(ClO4)6
NaphMC-Cu(II)
NaphMC-Cu(II)
NaphMC-Cu(II)
K=1.06x106
L2
Sequential two
sites
Sequential three
sites
K1=1.04x105
K2=3.14x104
K1=1.34x106
K2=6.27x104
K3=1.34x105
H1=-58.4
H2=-167.1
H1=-8.2
H2=-11.4
H3=-2.9
S1=-173.0
S2=-539.0
S1=0.464
S2=-16.1
S3=13.8
L3
Fig. 3: Isothermal titration calorimetric titration plots (A) between L1 (0.02 mM) and NaphMC-Cu(II) solution (0.2 mM); (B) between L2 (0.01 mM) and NaphMC-Cu(II) solution
(0.14 mM);(C) between L3 (0.04 mM) and NaphMC-Cu(II) solution (0.84 mM) at 298 K in CH3CN. In all the graphs, upper part shows the heat flow experimentally observed in each
titration against time. The lower part signifies integrated isotherms(acquired by integrating the peaks of the above plot) vs molar ratio (A) one site binding model and (B, C)
sequential binding model (n = 2,3 respectively).
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exothermic titration profiles which were fitted to the maxima at 281 nm and 282 nm respectively (Fig. 4). Thus, the
appropriate binding models. In case of titration of NaphMC- change in absorption characteristics during the formation of
Cu(II) with L1, the titration data points were fitted to one site [3]CuPR(ClO4)4 and [4]CuPR(ClO4)6 are similar with that of
binding model which showed exothermic binding process with [2]CuPR(ClO4)2 (Fig. 4). As the metal center and the binding
binding constant value of 1.06x106 (Fig. 3, Table 1). On the units of axle and macrocycles are similar in cases of [2], [3] and
other hand, during the titration of NaphMC-Cu(II) with L2, [4]pseudorotaxanes, correlating similar changes in absorption
titration data points were fitted to a sequential two sites characteristics during the formation of all the pseudorotaxanes
binding model which yielded the binding constant values of K1 supported the threading of L2 and L3 inside the macrocycle
= 1.04x105 and K2 = 3.14x104 (Fig. 3, Table 1). Finally, titration during the formation of [3] and [4]pseudorotaxanes
of NaphMC-Cu(II) with L3 gave the binding constant values of respectively. These process got saturated after addition of
K1 = 1.34x106, K2 = 6.27x104 and K3=1.34x105 upon fitting the nearly one, two and three equivalents of NaphMC-Cu(II) into
titration data points to sequential three sites binding model the solution of L1, L2 and L3 respectively (Fig. 16S- Fig. 18S,
(Fig. 3, Table 1). It is clearly evident from table 1 that binding ESI†). Molar ratio plot analysis for the above three titrations
processes of NaphMC-Cu(II) with L1-L3 were highly enthalpy showed the existence of 1: 1, 1: 2 and 1: 3 {axle: NaphMC-
and entropy driven processes which led to high binding Cu(II)} complex in solution for L1, L2 and L3 respectively (Fig.
constant values in case of all the pseudorotaxanes with the 19S- Fig. 21S, ESI†). Furthermore, the isolated threaded
following order L3  L2  L1.
complexes showed characteristic absorption maxima (λmax) at
276 nm, 282 nm and 283 nm for [2], [3] and
[4]pseudorotaxanes respectively (Fig. 22S(A), ESI†).
Interestingly, the absorption maxima of all the isolated
complexes of {[2]CuPR(ClO4)2}, {[3]CuPR(ClO4)4} and
{[4]CuPR(ClO4)6} obtained by reacting NaphMC-Cu(II) with L1,
L2, and L3 respectively, matched perfectly with the final
spectra of respective UV/Vis titration experiments (Fig. 4)
which indicated the formation of the corresponding
pseudorotaxanes. Absorption titration data points for the
titration of NaphMC-Cu(II) with L1 were fitted to a one site
binding model via non-linear fitting model which yielded
binding constant value of 3.08x106 M-1 (Fig. 23S, ESI†).
Similarly, fitting of titration data points of NaphMC-Cu(II) with
L2 yielded binding constant values of 1.48x106 M-1 and
3.77x105 M-1 for K1 and K2 respectively (Fig. 24S, ESI†). As
appropriate binding model for fitting the data points of 1:3 (H:
Photophysical Studies:
In order to revalidate the experimental results obtained from
ITC studies for the binding of L1-L3 with NaphMC-Cu(II),
UV/Vis titration experiments were carried out between axles
(L1-L3) and NaphMC-Cu(II) in CH3CN at 298K. UV/Vis titration
between NaphMC-Cu(II) and L1 suggested that the absorption
maxima of L1 at 263 nm (n-* transition) decreases with
concomitant increase of new absorption maxima at 277 nm
(Fig. 4), which matched well with the general pattern of
change in absorption maxima with similar kind of threaded
[2]pseudorotaxanes having analogous tris-amine macrocycle,
phenanthroline based axle and Cu(II) salt.13m,
titration of L2 and L3 with NaphMC-Cu(II), absorption maxima
of L2 and L3 at 274 nm and 275 nm respectively decreases
gradually with concomitant generation of new absorption
16
In case of
Fig. 4. UV/Vis titration profile:(A) between L1 (1x10-5 M) with NaphMC-Cu(II) (1x10-4 M) in CH3CN at 298 K, (B) between L2 (1x10-5 M) with NaphMC-Cu(II) (2.8x10-4 M) in CH3CN at
298 K, (C) between L3 (1x10-5 M) with NaphMC-Cu(II) (4.4x10-4 M) in CH3CN at 298 K.
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G) stoichiometric binding was not available, we could not Å between the electron rich naphthyl unit of NaphMC and
determine the binding constant values for the formation of electron deficient phenanthroline unit of L1 in the complex
[4]CuPR(ClO4)6 from NaphMC-Cu(II) and L3. As we moved from suggested the existence of π–π stacking interactions in solid
[2]pseudorotaxane to [3] and [4]pseudorotaxanes, we did not state. Ellipsoid and space-filling model in Fig. 5 revealed
observe any significant alteration in the properties of the complete threading of L1 inside the cavity of NaphMC in
threaded
complexes.
However,
on-going
from [2]pseudorotaxane. However, even after several attempts, we
[2]pseudorotaxane to [3] and [4]pseudorotaxanes, minor shift could not isolate single crystals of [3]- and
of the absorption maxima corresponding to n-* transition [4]pseudorotaxanes. As a result, the exact coordination
from 276 nm to 282 nm and 283 nm were observed environment around Cu(II) centres in these two complexes
respectively. All the pseudorotaxanes were found to be non- could not be determined.
emissive in nature when they were excited at their respective EPR Characterization:
absorption maxima (Fig. 22S(B), ESI†).
Single Crystal X-Ray Diffraction Analysis:
In order to determine the coordination geometry of Cu(II) in all
the synthesized mono-, bi- and tri-nuclear Cu(II) templated
In order to determine the coordination environment around pseudorotaxanes, all of them were subjected to X-band EPR
Cu(II) in the pseudorotaxanes by single crystal X-ray spectroscopy at 80K in CH3CN. The values of g parameters and
spectroscopy, considerable amount of efforts were given to EPR spectra of [2]CuPR(ClO4)2, [3]CuPR(ClO4)4 and
crystallize all the pseudorotaxanes. Single crystals of [4]CuPR(ClO4)6 in CH3CN are provided in Table 2 and ESI† (Fig.
[2]pseudorotaxane, [2]CuPR(OTf)2 were obtained by 28S- Fig. 30S, ESI†). In all the cases, EPR spectra showed the
-
exchanging ClO4 counter anion of [2]CuPR(ClO4)2 with OTf- pattern of g|| > g⊥ (Table 2) which indicated the presence of
2
2
anion. Green colored single crystals of [2]CuPR(OTf)2 were the unpaired electron in dx –y orbital of Cu(II) in all the
obtained upon slow evaporation of solution of complexes. This result clearly indicated that Cu(II) centre is
[2]CuPR(ClO4)2 and excess NaOTf in CH3CN (Fig. 5). All the present in distorted square pyramidal geometrical
a
a
crystallographic details are provided in ESI† (Table 1S and Fig. arrangement upon coordination of axle with the NaphMC-
25S- Fig. 27S). Detailed crystal structure analysis showed that, Cu(II) in all the ternary complexes as reported previously.14f, 14g
OTf- based [2]Pseuorotaxane adopts
penta-coordinated
Now, it should be mentioned here that the flexibility of the
phenanthroline binding unit in bi and tripodal axles (L2 and L3)
through the attachment of aliphatic spacer between central
benzene ring and pendant phenanthroline units are critical
criteria for the formation of higher order [3] and
[4]pseudorotaxanes. In this regard, we have synthesized a new
ester functionalised tripodal hexadentate axle, L4 which
contains less flexible C2-alkyl chain spacer unit instead of more
flexible C6-alkyl chain spacer (L3) attached with benzene
platform. L4 was synthesized in four steps via tribromo ester, C
in 68.8% yield (Scheme 4S and Fig. 31S- Fig. 35S, ESI†). After
successful synthesis of L4, we have examined it’s ability
towards the formation of Cu(II) templated [4]pseudorotaxanes
arrangement around the central Cu(II) centre, in which three
coordination sites are provided by tris amine of NaphMC and
remaining two coordination sites are occupied by the
bidentate phenanthroline unit of L1. Structural parameter (τ)
value of 0.638 which is in between the geometrical spectrum
of square pyramidal and trigonal bipyramidal geometries,
suggested the presence of distorted TBP geometry in
[2]CuPR(OTf)2. Significantly short distance of 3.372 and 3.405
Table 2. g|| , g⊥ values for the [n]Pseudorotaxanes (n=2,3,4)
Complex
g||
g⊥
[2]CuPR(ClO4)2
2.22806
2.02293
[3]CuPR(ClO4)4
[4]CuPR(ClO4)6
2.22132
2.24085
2.01676
2.02176
Fig. 5: Ellipsoid model (40% probability level) and space-filling model of
([2]CuPR)2+. Counter anions and hydrogens are omitted for clarity.
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titration experiments (Fig. 46S- Fig. 48S, ESI†) which indicated
by ESI-MS and UV/Vis spectroscopic studies. ESI-MS analysis
showed molecular ion peak at m/z=1699.4115 (calc.
1699.4113), corresponding to [NaphMC.Cu(II).L4.ClO4 ] , which
View Article Online
the formation of respective pseudorotaxanes.
DOI: 10.1039/C9DT01067J
- +
Conclusions
indicated the formation of [2]pseudorotaxane only without the
presence of any peaks corresponding to other higher order
pseudorotaxanes (Fig. 36S, ESI†). On the other hand, the
UV/Vis titration experiment between NaphMC-Cu(II) and L4
showed gradual decrease in intensity of the parent absorption
band at max= 276 nm with simultaneous generation of a new
peak at max= 280 nm upon addition of NaphMC-Cu(II) in the
axle (L4) solution in CH3CN (Fig. 37S, ESI†). Analysis of titration
data showed the formation of 1:1 {NaphMC-Cu(II): L4}
complex in solution (Fig. 38S, ESI†) which indicated the
formation of only [2]pseudorotaxane among other higher
order pseudorotaxanes. Thus, less flexible C2-alkyl spacer
based axle, L4 failed to produce higher order [3] and
[4]pseudorotaxanes as opposed to more flexible C6-alkyl
spacer based axle, L3.
In summary, we have demonstrated the systematic
development of [2]-, [3]-, and [4]pseudorotaxanes from
bidentate, bipodal-tetradentate and tripodal- hexadentate
axles respectively via Cu(II) temptation and π–π stacking
interactions using an amino ether macrocyclic wheel. Further,
efficiency of Ni(II) as a metal template for the formation of [2]-
, [3]-, and [4]pseudorotaxanes has also been demonstrated.
We are currently focusing on the construction of higher
generation pseudorotaxanes and rotaxanes consist of various
functional groups towards the development of new materials.
Experimental Section
General details
All reactions were carried out under the atmosphere of argon
gas. Commercially available reagents were purchased and used
as received. Solvents were dried following the literature
procedures. Copper perchlorate was stored in a vacuum
desiccator and used for experiments. The electronic spray
ionization (ESI) mass spectra were carried out by using solvent
(CH3CN/ CH3OH) on a QToF–Micro YA 263 Mass spectrometer
in positive ion mode. 1H NMR and 13C NMR spectra were
recorded on an FT-NMR Bruker DPX 400/500 MHz NMR
spectrometer. The absorption studies were carried out using
Perkin-Elmer Lambda 900 UV–Vis–NIR spectrometer with
quartz cuvette of 1 cm path length. The isothermal titration
calorimetric (ITC) studies were carried out with a Micro-Cal VP-
ITC instrument using HPLC grade CH3CN at 298K. Elemental
analysis was performed by using Perkin-Elmer 2500 series II
elemental analyzer, Perkin-Elmer, USA. EPR spectra were
recorded by using a JEOL JES-FA200 spectrometer with an X
band micro web unit. Fourier transform infrared (FT-IR) studies
Furthermore, in order to investigate the efficiency of other
transition metal {except Cu(II)} in the synthesis of
[n]Pseudorotaxanes (n=2,3,4), Ni(ClO4)2 6H2O was employed as
another transition metal templating agent for the synthesis of
[n]Pseudorotaxanes (n=2,3,4). In this direction, we have
synthesized NaphMC-Ni(II) complex (Scheme 5S, ESI†) and
pseudorotaxanes (Scheme 6S, ESI†) by following the similar
.
procedure
of
formation
of
Cu(II)
templated
[n]Pseudorotaxanes (n=2,3,4) as mentioned in the
experimental section. Formation of NaphMC-Ni(II) complex
was supported by ESI-MS analysis which showed the presence
of a prominent molecular ion peak at m/z=734.1778 (calc.
-
734.1779), that revealed the presence of {NaphMC.Ni(II).ClO4
+
}
species (Fig. 42S, ESI†). Afterwards, Ni(II) templated
(n=2,3,4) were prepared and
[n]pseudorotaxanes
characterized by ESI-MS, UV/Vis and elemental analysis
studies. ESI-MS of [2]NiPR(ClO4)2, [3]NiPR(ClO4)4 and
[4]NiPR(ClO4)6 complexes showed the presence of the
molecular ion peaks at m/z = 928.2621 (calc. 928.2623),
2345.6048 (calc. 2345.6046) and 1714.9547 (calc. 1714.9546)
were performed on
a
SHIMADZU FTIR-8400S IR
-
which correspond to {[2]NiPR(ClO4)2-ClO4 }+, {[3]NiPR(ClO4)4-
spectrophotometer with KBr pellets.
-
-
ClO4 }+ and {[4]NiPR(ClO4)6-2ClO4 }2+ species respectively (Fig.
43S- Fig. 45S, ESI†). The experimentally observed isotopic
distribution patterns of all the complexes matched well with
the simulated patterns which are obtained from natural
abundance of the elements. Additionally, UV/Vis titration
studies were performed towards the formation of Ni(II)
templated pseudorotaxanes with NaphMC-Ni(II) complex and
all the axles (L1-L3). The absorption maxima of the L1, L2 and
L3 at 263 nm, 274 nm and 275 nm gradually decreases with
concomitant increase in absorption maxima at 274 nm, 283
nm and 284 nm respectively upon addition of NaphMC-Ni(II)
complex in the axle solutions (Fig. 46S- Fig. 48S, ESI†). Molar
ratio plot analysis from all the above mentioned titrations
indicated the formation of 1: 1, 1: 2 and 1: 3 {axle: NaphMC-
Ni(II)} complexes in cases of [2]NiPR(ClO4)2, [3]NiPR(ClO4)4 and
[4]NiPR(ClO4)6 respectively (Fig. 49S- Fig. 51S, ESI†).
Additionally, absorption maxima of all the isolated complexes
of [2]NiPR(ClO4)2, [3]NiPR(ClO4)4 and [4]NiPR(ClO4)6 obtained
by reacting NaphMC-Ni(II) with L1, L2, and L3 respectively (Fig.
52S, ESI†), matched perfectly with the final spectra of UV/Vis
Synthesis of NaphMC and Phen-Acid:
Naphthalene
containing
oxy-ether
and
tris-amine
functionalized macrocycle (NaphMC) was prepared via three
step process by following the reported procedure.16 1,10-
phenanthroline-4-carboxylic acid (Phen-Acid) was also
synthesized by using literature procedure.17 The characteristic
data of NaphMC and Phen-Acid were perfectly matched with
the reported data.
Synthesis of compound A:
Terephthalic acid (332 mg, 2 mmol) and excess 1,6-di
bromohexane (1216 µL, 8 mmol) were reacted in DMF medium
in presence of potassium tert-butoxide (561 mg, 5 mmol) at
room temperature (RT) under argon atmosphere for 12h then
the reaction mixture was refluxed for another 18h. The
reaction was cooled to RT and evaporated to dryness under
vacuum. The crude was dissolved in excess of CHCl3 and
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Journal Name
filtered by using sintered crucible. After complete evaporation Synthesis of axle L3:
of the filtrate, the crude residue was purified via silica gel
View Article Online
DOI: 10.1039/C9DT01067J
TBAF (142 mg, 0.45 mmol) was added to dissolve the Phen-
Acid (100 mg, 0.45 mmol) in dry THF and Compound B (70 mg,
0.1 mmol) was added dropwise to the reaction mixture at 0°C
at stirring condition. The reaction mixture was allowed to stir
at RT for 12h maintaining the inert atmosphere. Then, the
solvent was evaporated under vacuum and was extracted with
CHCl3 and water by washing the organic layer with NaHCO3
and brine solution (three times). The organic layer were
collected and dried over anhydrous sodium sulfate. After the
evaporation desired compound was isolated and characterized
as solid axle L3. Yield 12.6 mg (78%). HRMS (ESI-MS): m/z
column chromatography using 3% ethylacetate-hexane as
eluent and the oily liquid product was obtained as compound
A, which was characterized as pure form. Yield 403 mg (68%).
HRMS (ESI-MS): m/z calculated for C20H28Br2NaO4 [Comp A
+Na]+ = 513.0252, found = 513.0278. 1H NMR (400 MHz,
CDCl3): δ (ppm) 1.48-1.53 (m, 8H, -CH2), 1.79-1.91 (m, 8H, -
CH2), 3.42 (t, 4H, J = 6.4 Hz ,- CH2), 4.35 (t, 4H, J = 6.8 Hz ,-
OCH2), 8.10 (s, 4H, Ar-H). 13C NMR (100 MHz, CDCl3): δ (ppm)
25.4, 28.0, 28.7,32.8, 33.8, 65.4, 129.7, 134.3, 166.0.
Synthesis of axle L2:
calculated for C66H61N6O12 [L3 +H]+ = 1129.4347, found =
1
Phen-Acid (67 mg, 0.3 mmol) was dissolved in dry THF in 1129.4349. H NMR (400 MHz, CDCl3): δ (ppm) 1.73-1.89 (m,
presence of tetra-n-butyl ammonium fluoride (TBAF) (95 mg, 24H, -CH2), 4.37-4.50 (m, 12H, -CH2), 7.65-7.68 (m, 3H, Ar-H),
0.3 mmol). Compound A (49 mg, 0.1 mmol) was added 7.89 (d, 3H, J = 9.2 Hz, Ar-H), 8.09 (d, 3H, J = 4.4 Hz, Ar-H), 8.26
dropwise at 0°C to the reaction mixture. The reaction mixture (d, 3H, J = 7.6 Hz, Ar-H), 8.76-8.82 (m, 6H, Ar-H), 9.20-9.29 (m,
was stirred at RT for 12h under argon atmosphere. After that 6H, Ar-H). 13C NMR (100 MHz, CDCl3): δ (ppm) 25.9, 25.9, 28.7,
the solvent was removed under vacuum and the product was 65.8, 66.1, 123.6, 123.7, 123.8, 126.2, 128.2, 128.5, 131.6,
extracted with CHCl3 and water, by washing the organic layer 134.6, 135.5, 136.0, 146.1, 147.4, 149.9, 150.8, 165.2, 166.4.
repeatedly with NaHCO3 and brine solution. Then, the organic
layer was evaporated and dried completely in vacuo after Synthesis of compound C:
dried over anhydrous sodium sulfate. The solid was isolated Compound
and characterized as pure form. Yield 11.7 mg (74%). HRMS synthetic procedure as compound B. Compound C was isolated
(ESI-MS): m/z calculated for C46H42N4NaO8 [L2 +Na]+ as solid form and was characterized thoroughly. Yield: 86%. 1H
C was synthesized by following the similar
=
801.2900, found = 801.2907. 1H NMR (500 MHz, CDCl3): δ NMR (400 MHz, CDCl3): δ (ppm) 3.68 (t, 6H, J = 6.0 Hz, -CH2),
(ppm) 1.58 (br, 8H, -CH2), 1.83-1.92 (m, 8H, -CH2), 4.37 (t, 4H, 4.70 (t, 6H, J = 6.0 Hz, -CH2), 8.91 (s, 3H, Ar-H). 13C NMR (100
J = 6.5 Hz, - OCH2), 4.50 (t, 4H, J = 7.0 Hz, - OCH2), 7.68 (q, 2H, J MHz, CDCl3): δ (ppm) 28.4, 65.0, 131.1, 135.3, 164.4.
= 4.0 Hz, Ar-H), 7.91 (d, 2H, J = 9.0 Hz, Ar-H), 8.09 (m, 6H, Ar-
H), 8.28 (d, 2H, Ar-H), 8.79 (d, 2H, J = 9.0 Hz, Ar-H), 9.22 (d, 2H, Synthesis of axle L4:
J = 3.0 Hz, Ar-H), 9.29 (d, 2H, J = 4.5 Hz, Ar-H). 13C NMR (100 Axle L4 was prepared by following a similar procedure as axle
MHz, CDCl3): δ (ppm) 25.9, 25.9, 28.8, 65.4, 66.1, 123.6, 123.7, L3. The product was isolated and characterized. Yield: 80%.
123.8, 126.2, 128.2, 128.5, 129.7, 134.3, 135.5, 136.0, 149.8, HRMS (ESI-MS): m/z calculated for C54H37N6O12 [L4 +H]+
150.8, 165.9, 166.4.
=
961.2469, found = 961.2468. 1H NMR (500 MHz, CDCl3): δ
(ppm) 4.67-4.83 (m, 12H, -CH2), 7.64-7.69 (m, 3H, Ar-H), 7.80-
7.85 (m, 3H, Ar-H), 8.07-8.11 (m, 3H, Ar-H), 8.23-8.29 (m, 3H,
Ar-H), 8.67-8.72 (m, 3H, Ar-H), 8.90-8.99 (m, 3H, Ar-H), 9.20-
9.30 (m, 6H, Ar-H). 13C NMR (125 MHz, CDCl3): δ (ppm) 63.4,
63.5, 123.7, 123.8, 123.9, 126.1, 128.3, 128.4, 131.3, 134.6,
135.2, 135.6, 136.3, 147.0, 149.9, 150.6, 164.6, 165.9.
Synthesis of compound B:
Excess of 1,6-di bromohexane (912 µL, 6 mmol) was added to
the mixture of benzene-1,3,5-tricarboxylic acid (210 mg, 1
mmol), and anhydrous K2CO3 (828 mg, 6 mmol) in DMF at RT
under argon gas for 24h. The DMF was evaporated under
vacuum and the reaction mixture was extracted with CHCl3
and water. The organic layer was washed repeatedly by brine
Synthesis of [2]pseudorotaxanes {[2]CuPR(ClO4)2}:
solution and dried over anhydrous sodium sulfate. The organic NaphMC (58 mg, 0.1 mmol) was dissolved in CHCl3 and
solvent was evaporated in vacuo and to removed excess 1,6- Cu(ClO4)2 .6H2O (37 mg, 0.1 mmol) in CH3OH was added to it.
dibromohexane from the crude, filtering column The reaction mixture was stirred for 2h at RT. In situ,
chromatography was performed by using 60-120 mesh silica equivalent amount of bidentate chelating ligand (L1) (19.4 mg,
gel with 4% ethylacetate-hexane as eluent. The product 0.1 mmol) was added to the above reaction mixture. The
compound B was isolated as liquid form of and characterized. resultant mixture was stirred at RT for another 3-4h. As a
Yield 276.4 mg (83%). HRMS (ESI-MS): m/z calculated for result, Cu(II) templated heteroleptic ternary complex i.e.
1
C27H40Br3O6 [Comp B +H]+ = 697.0375, found = 697.0371. H [2]pseudorotaxane {[2]CuPR(ClO4)2} was formed. Then, the
NMR (400 MHz, CDCl3): δ (ppm) 1.49-1.54 (m, 12H, -CH2), solvent was evaporated and dried. By washing the solid
1.79-1.94 (m, 12H, -CH2), 3.42 (t, 6H, J = 6.8 Hz, -CH2), 4.39 (t, residue with CHCl3 and diethylether, the greenish colored solid
6H, J = 6.8 Hz, -OCH2), 8.83 (s, 3H, Ar-H). 13C NMR (100 MHz, was isolated as {[2]CuPR(ClO4)2} in yield 83%. Anal. calcd. For
CDCl3): δ (ppm) 25.4, 28.0, 28.7, 32.8, 33.7, 65.7, 131.6, 134.6, [2]CuPR(ClO4)2, C49H49Cl2CuN5O12 (MW = 1034.39) C, 56.90; H,
165.2.
4.77; N, 6.77; found: C, 56.23; H, 4.71; N, 6.48. HRMS (ESI-MS)
-
{[2]CuPR(ClO4)2-ClO4 =C49H49ClCuN5O8}+: calcd, m/z
=
8 | J. Name., 2012, 00, 1-3
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-
933.2566; found, m/z = 933.2562; {[2]CuPR(ClO4)2-2ClO4 Characterization of {[2]NiPR(ClO4)2}: yield 71%.VieAwnAartli.clecOalnclidne.
=C49H49CuN5O4}2+: calcd, m/z = 417.1541; found, m/z = For [2]NiPR(ClO4)2, C49H49Cl2NiN5O12 (MW = 1029.53) C, 57.16;
DOI: 10.1039/C9DT01067J
417.1537; IR (KBr, ν cm−1): 437, 462, 518, 671, 765, 821, 848, H, 4.80; N, 6.80; found: C, 56.98; H, 4.71; N, 6.55. HRMS (ESI-
-
933, 1089, 1120, 1143, 1232, 1251, 1278, 1396,1431, 1456, MS) {[2]NiPR(ClO4)2-ClO4 =C49H49ClNiN5O8}+: calcd, m/z =
-
1506, 1581, 1649, 2921, 3421. Absorption spectra studies: 928.2623; found, m/z = 928.2621; {[2]NiPR(ClO4)2-2ClO4
λmax= 276 nm in CH3CN solvent and molar extinction coefficient =C49H49NiN5O4}2+: calcd, m/z = 414.6569; found, m/z =
value in CH3CN (ε) = 3.14x104 M-1 cm-1.
414.6562; Absorption maxima (λmax) = 274 nm in CH3CN.
Synthesis of [3]pseudorotaxane {[3]CuPR(ClO4)4}:
Characterization of {[3]NiPR(ClO4)4}: yield 64%. Anal. calcd.
For {[3]NiPR(ClO4)4}, C118H120Cl4Ni2N10O32 (MW = 2449.46) C,
57.86; H, 4.94; N, 5.72; found: C, 57.42; H, 4.82; N, 5.52. HRMS
Cu(ClO4)2.6H2O (37 mg, 0.1 mmol) was dissolved in CH3OH and
added to a solution of NaphMC (58 mg, 0.1 mmol) in CHCl3.
The reaction mixture was stirred at RT for 2h. Then, the
tetradentate chelating ligand (L2) (38 mg, 0.05 mmol) was
added to the above reaction mixture. The resultant mixture
was stirred for another 3-4h at RT. Afterward, solvent was
removed by vacuum and the crude product was washed with
CHCl3 and diethylether. [3]pseudorotaxane {[3]CuPR(ClO4)4}
was isolated as greenish solid in yield 79%. Anal. calcd. For
{[3]CuPR(ClO4)4}, C118H120Cl4Cu2N10O32 (MW = 2459.16) C,
57.63; H, 4.92; N, 5.70; found: C, 57.39; H, 4.81; N, 5.49. HRMS
-
(ESI-MS) {[3]NiPR(ClO4)4-ClO4 = C118H120Cl3Ni2N10O28}+: calcd,
m/z = 2345.6046; found, m/z = 2345.6048; {[3]NiPR(ClO4)4-
-
2ClO4 =C118H120Cl2Ni2N10O24}2+: calcd, m/z = 1123.3280; found,
m/z = 1123.3282. Absorption maxima (λmax) = 283 nm in
CH3CN.
Characterization of {[4]NiPR(ClO4)6}: yield 49%. Anal. calcd.
For {[4]NiPR(ClO4)6}, C174H177Cl6Ni3N15O48 (MW= 3635.13) C,
57.49; H, 4.91; N, 5.78; found: C, 57.23; H, 4.79; N, 5.58. HRMS
-
(ESI-MS) {[4]NiPR(ClO4)6-2ClO4 =C174H177Cl4Ni3N15O40}2+: calcd,
-
(ESI-MS) {[3]CuPR(ClO4)4-2ClO4 =C118H120Cl2Cu2N10O24}2+: calcd,
m/z = 1714.9546; found, m/z = 1714.9547. Absorption maxima
(λmax) = 284 nm in CH3CN.
m/z = 1128.3223; found, m/z = 1128.3229; {[3]CuPR(ClO4)4-
-
3ClO4 =C118H120ClCu2N10O20}3+: calcd, m/z = 719.2320; found,
m/z = 719.2326. IR (KBr, ν cm−1): 378, 391, 673, 721, 1053,
1074, 1118, 1251, 1390, 1454, 1512, 1539, 1577, 1649, 1716,
Conflicts of interest
2854, 2923, 3423, 3442. Absorption spectra studies: λmax
=
There are no conflicts to declare.
282 nm in CH3CN solvent and molar extinction coefficient
value in CH3CN (ε) = 6.81x104 M-1 cm-1.
Acknowledgements
Synthesis of [4]pseudorotaxane{[4]CuPR(ClO4)6}:
P.G. gratefully thanks the Science and Engineering Research
Board (SERB), New Delhi (Project SR/S1/IC-39/2012) for
financial support. S. Bej acknowledges the Council of Scientific
& Industrial Research (CSIR), New Delhi for SRF. M. Nandi and
T. K. Ghosh acknowledge DST-Inspire and IACS, Kolkata for SRF
and post-doctoral fellowship respectively. The authors are
thankful to Dr. S. Santra for his valuable suggestion during the
work. The single crystal X-ray analysis was performed at the
DST-funded National Single Crystal X-ray facility at the School
of Chemical Science, IACS.
NaphMC (86.5 mg, 0.15 mmol) in CHCl3 and Cu(ClO4)2.6H2O
(55 mg, 0.15 mmol) in CH3OH were stirred for 2h at RT. After
that, the hexadentate chelating ligand (L3)(56 mg, 0.05 mmol)
was added in situ in the reaction container, resulting
[4]pseudorotaxanes i.e. penta coordinated Cu(II) templated
heteroleptic ternary complex {[4]CuPR(ClO4)6}. The reaction
was stirred at RT for another 3-4h. Solvent was evaporated
and the resultant solid was washed with CHCl3 and
diethylether. The green colored solid was isolated as
{[4]CuPR(ClO4)6} in 71% yield. Anal. calcd. For [4]CuPR(ClO4)6,
C174H177Cl6Cu3N15O48 (MW= 3649.69) C, 57.26; H, 4.89; N, 5.76;
found: C, 57.01; H, 4.76; N, 5.62.
HRMS (ESI-MS)
References
-
{[4]CuPR(ClO4)6-2ClO4 =C174H177Cl4Cu3N15O40}2+: calcd, m/z =
-
1. (a)K. Zhu, G. Baggi and S. J. Loeb, Nat. Chem., 2018, 10, 625-
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Jacquot de Rouville, Y. Y. Botros and J. F. Stoddart, Org.
1722.4460; found, m/z = 1722.4463, {[4]CuPR(ClO4)6-3ClO4
=C174H177Cl3Cu3N15O36}3+: calcd, m/z= 1115.3144; found, m/z =
1115.3148. IR (KBr, ν cm−1): 379,624, 673, 725, 746, 763, 817,
935, 1093, 1118, 1251, 1278, 1396, 1452, 1504, 1583, 1625,
1724, 2925, 3249, 3423. Absorption spectra studies: λmax
=
283 nm in CH3CN solvent and molar extinction coefficient
value in CH3CN (ε) = 7.95x104 M-1 cm-1.
Synthesis of Ni(II) templated [n]Pseudorotaxanes (n=2,3,4)
:
Ni(II) templated [n]Pseudorotaxanes(n=2,3,4) were prepared
by following the similar synthetic procedures as in cases of
Cu(II) templated [n]Pseudorotaxanes (n=2,3,4).
This journal is © The Royal Society of Chemistry 20xx
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Journal Name
Biomol. Chem., 2011, 9, 7126-7133; (j)S. Goldup, Nature, 13. (a)B. H. Northrop, S. J. Khan and J. F. StoddaVrtie,wOArrtgic.leLOentlitn.e,
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ARTICLE
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DOI: 10.1039/C9DT01067J
Table of Contents
Cu(II) templated formation of [n]Pseudorotaxanes (n= 2,3,4) using a tris-amino ether
macrocyclic wheel and multidentate axles
Somnath Bej, Mandira Nandi, Tamal Kanti Ghosh and Pradyut Ghosh*
Systematic development of mono-, bi- and tri-nuclear [n]Pseudorotaxanes (n=2,3,4) via Cu(II) templation and π–π stacking
interactions.
This journal is © The Royal Society of Chemistry 20xx
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