Metal-containing ditopic receptors for molecular recognition of diammonium cations

Article abstract of DOI:10.1016/S0040-4020(02)01482-5

Two new ditopic receptors for α,ω-alkanediyldiammonium cations based on a tetraazamacrocyclic (cyclidene) nickel(II) complex bearing two crown-ether residues were synthesized. The studies of the host-guest interaction between the receptors and a series of α,ω-diammonium salts by NMR titration in acetonitrile-d₃ showed that 1:1 complexes are formed with K_assoc～10³-10⁵M^-1. Receptor 1 with benzo-15-crown-5 arms showed substantial selectivity in binding of trimethylene- and tetramethylenediammonium dications, and 1-2 orders of magnitude weaker binding of shorter (C₂) or longer (C₅ and C₆) diammonium cations. Receptor 2 with benzo-18-crown-6 arms showed higher affinity to all studied diammonium cations, but the recognition of the length of α,ω-diammonium cations was less pronounced.

Full text of DOI:10.1016/S0040-4020(02)01482-5

Tetrahedron 59 (2003) 231–239
Metal-containing ditopic receptors for molecular recognition
of diammonium cations
*
Olga P. Kryatova, Alexander G. Kolchinski and Elena V. Rybak-Akimova
Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, MA 02155, USA
Received 10 July 2002; accepted 8 November 2002
Abstract—Two new ditopic receptors for a,v-alkanediyldiammonium cations based on a tetraazamacrocyclic (cyclidene) nickel(II)
complex bearing two crown-ether residues were synthesized. The studies of the host–guest interaction between the receptors and a series of
3
5
21
a,v-diammonium salts by NMR titration in acetonitrile-d showed that 1:1 complexes are formed with Kassoc,10 –10 M . Receptor 1
3
with benzo-15-crown-5 arms showed substantial selectivity in binding of trimethylene- and tetramethylenediammonium dications, and 1–2
orders of magnitude weaker binding of shorter (C ) or longer (C and C ) diammonium cations. Receptor 2 with benzo-18-crown-6 arms
2
5
6
showed higher affinity to all studied diammonium cations, but the recognition of the length of a,v-diammonium cations was less
pronounced. q 2002 Elsevier Science Ltd. All rights reserved.
9
1
. Introduction
(planar) and ‘closed’ (saddle shaped) conformations. This
dual-shape feature is needed in order to eventually obtain
switchable receptors. Earlier we prepared a receptor for
dicarboxylic acids based on a nickel(II) cyclidene platform
with two cyclic tetramine (cyclen) binding sites, which
Multipoint recognition of organic molecules is an efficient
way of designing size- and shape-selective receptors with
high affinity for substrates.
govern selectivity in host–guest binding is also important
for better understanding of molecular recognition in
biochemical processes. Incorporation of the metal ions
into multicenter receptors offers several potential advan-
1
–4
Unraveling the factors that
2
3
displayed notable length and shape-selectivity. In the case
of carboxylate recognition, the electrostatic interaction
between the dipositive metal ion in the platform and
negatively charged guest was favorable for the inclusion
complex formation.
5
–7
tages,
such as: (1) metal ion may act as an additional
binding site; (2) metal ions are reactive sites, allowing for
selective substrate transformations; (3) reactivity and
binding properties of the metal center can be altered, e.g.
by changing the oxidation states; or (4) the shape of the
receptor molecule can be regulated via reversible reactions
at the metal center.
We set out to determine whether ditopic selective guest
binding is possible in the presence of unfavorable electro-
static interaction between the metal cation in the cyclidene
platform and cationic substrates. Protonated organic amines
were chosen as guests, because amine functionality is
commonly present in biomolecules, such as amino acids,
proteins and neurotransmitters. Crown ethers, which are
known to form reasonably strong complexes with primary
We report the preparation of two ditopic hosts for
diammonium salts based on a metal-containing macrocyclic
8
–10
24
platform (cyclidene)
sites. The distinctive features of the cyclidene scaffold
bearing two crown-ether receptor
ammonium salts, were selected as receptor groups. The
molecules containing two crown ether fragments attached to
a rigid scaffold or assembled about a metal center were
shown to bind diammonium salts and, in some cases,
1
1,12
include the relative flexibility of the cleft,
which in
principle allows for the regulation of the substrate affinity
and selectivity via conformational changes in the platform,
and the positioning of the guest right above the metal center,
thus suggesting potential involvement of the metal in the
catalytic regioselective transformations of the substrates.
Examples of regioselective reagents and catalysts based on
functionalized rigid metalloporphyrins were provided by
2
5–38
displayed substantial length selectivity.
In the present
study, either high affinity (B18C6) or low affinity (B15C5)
binding groups were attached to the cyclidene platform, and
the affinity and selectivity of the resulting ditopic receptors
toward diammonium guests were compared.
1
3–19
20–22
Breslow
1
and Woggon.
5-membered cyclidene platform can adopt both ‘open’
Unlike porphyrins, the
2. Results and discussion
2
.1. Synthesis
Keywords: diammonium cations; receptors; binding properties.
*
Corresponding author. Tel.: þ1-617-627-3413; fax: þ1-617-627-3443;
e-mail: elena.rybak-akimova@tufts.edu
The synthesis of molecular tweezers 1 and 2 is outlined
0040–4020/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01482-5

232
O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
Scheme 1.
in Scheme 1. The preparation of receptor molecules 1 and 2
is based on a general reaction of the O-alkylated J a¨ ger
macrocycle ([Ni[(MeOEthi) Me [15]tetraeneN ]](PF ) )
with primary amines developed by Busch and co-workers.
The aromatic amino group is far less reactive and can hardly
based molecular tweezers. Aminomethyl-substituted benzo-
crowns, which are better suited for attaching to the edges of
J a¨ ger macrocycles, were prepared from the corresponding
hydroxymethyl benzo crowns (Scheme 1). Initial attempts
to synthesize the 4-aminomethylbenzocrowns via reductive
amination of the corresponding formyl-benzocrowns did not
succeed and were not pursued further.
2
2
4
6 2
9
3
9,40
be attached to J a¨ ger platforms.
sterically non-hindered aliphatic secondary amines react
A limited number of
3
9,41,42
smoothly with J a¨ ger macrocycles,
cases steric hindrance prevents or retards cyclidene
formation. Additionally, strong bases (such as secon-
dary amines) promote deacylation of J a¨ ger and cyclidene
macrocycles. Consequently, aza-crowns or amino-
benzocrowns were inappropriate precursors for cyclidene-
although in many
Attaching aminomethyl-benzocrowns to O-methylated
J a¨ ger platforms proceeded uneventfully and yielded target
compounds 1 and 2, which were characterized by elemental
analysis, mass-, UV–Vis and NMR spectroscopy (see
Section 4). The assignment of the NMR spectra was based
3
9,43
4
0,44
4
2,45
on previously published data for similar compounds.
1
The H NMR spectrum of compound 1 is shown in Figure 1.
The signals of the protons of the cyclidene platform are
relatively broad with varying intensity, especially signal M,
but the integration is in agreement with the assignment. The
broad peaks of the cyclidene methylene groups can be
4
6,47
explained by ‘flexing’ of the platform.
2.2. Reactions with ammonium salts
Host–guest interaction between receptors and diammonium
1
salts (Scheme 2) was studied by H NMR titration in
CH CN-d ; typical spectral changes are shown in Figure 2.
3
3
Addition of a diammonium salt to the acetonitrile solution
of a tweezer resulted in chemical shift changes for the
protons of the host and guest. For the host, both the receptor
1
Figure 1. H NMR spectrum of tweezer 1 in CD
3
CN.
Scheme 2.

O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
233
Table 1. Maximum changes in the chemical shift of the protons of CH
2
-
groups of the cyclidene platform for tweezers 1 and 2 (signals J and M;
CN, T¼298 K,
Fig. 2) due to the complexation with substrates. CD
23
3
22
C
(tweezer 1)¼1.0£10 M, C(tweezer 2)¼1.0£10
M
Cation-substrate
Dmaxd (Hz)
J
M
Tweezer 1
Tweezer 2 Tweezer1 Tweezer 2
2
2
2
2
2
2
2
2
2
2
þ
þ
þ
þ
þ
a
a
(
(
(
(
(
(
(
CH
CH
CH
CH
CH
2
2
2
2
2
)
)
)
)
)
2
3
4
5
6
(NH
(NH
(NH
(NH
(NH
3
3
3
3
3
)
)
)
)
)
73
95
102
66
62
81
,10
84
121
128
122
100
120
,10
119
181
182
144
162
150
10
.100
115
.100a
.100
180
2
2
þ
þ
a
C
C
6
H
H
4
)(CH
)(CH
2
)
2
(NH
3
)
.100
10
a
a
6
5
2
)(NH
3
)
a
It was impossible to find the exact value because of overlapping of the
signals.
1
Figure 2. H NMR spectra of acetonitrile solutions of pure tweezer 1
22
10 M); tweezer 1 and tetramethylenediammonium thiocyanate in ratio
(
2.5:1 and 1:1; pure tetramethylenediammonium salt (from top to bottom).
strongly suggests that both protonated mono- and diamines
interact with the crown ether receptor sites, but their binding
modes are different. Unlike monofunctional guests, the
diammonium cations can be encapsulated between both
receptor ‘arms’, causing a conformational change of the
cyclidene macrocycle upon complexation with ditopic
substrates. Similar conformation-dependent NMR shifts of
crown arms and the tetraazamacrocyclic platform signals
shifted, but to a different extent. The protons of the crown
residues showed only a slight upfield shift (#15 Hz), while
the protons of the tetraazamacrocyclic platform shifted by
2
0–170 Hz. This trend cannot be interpreted in terms of a
direct coordination of the guest to the cyclidene platform
rather than to the appended crown ethers, because no
interaction between the diammonium guests and a nickel(II)
macrocycle 3 lacking crown ether residues (Scheme 3) was
observed by NMR. Small changes in the NMR spectra of
crown ethers upon alkylammonim cation binding are
4
6,47
monoalkylated cyclidene complexes have been reported.
The changes in the chemical shift of the CH groups J and M
2
upon ditopic substrate binding might also be due to the
proximity of the aromatic p-systems of the benzocrown
residues in the complexes.
2
8,48,49
common.
The most pronounced changes occurred
for the signals of the methylene groups (J and M) of the
tertrazamacrocyclic platform, which are remote from the
guest binding sites (Fig. 2). The methylene signal M at d
Unfortunately, the signals of the platform could not be used
to monitor the equilibrium by NMR titration because they
overlapped with several other signals during the titration. It
was convenient to follow the reactions by measuring the
1
1
.85 ppm shifted downfield by ,0.33–0.56 ppm (100–
70 Hz). Signal J overlapped with the signal of methylene
changes in the chemical shifts of the a-CH groups of the
2
protons of crown residue in the spectrum of free tweezers
and shifted upfield by ,0.25–0.4 ppm (73–128 Hz) upon
binding with a diammonium cation (Table 1).
diammonium cations. These signals did not overlap with
other signals and were highly sensitive to complex
formation (Fig. 2, Table 2). Addition of an excess of the
parent monotopic host (benzo-15-crown-5 or benzo-18-
crown-6) to diammonium cations caused a smaller change
in the chemical shift of the aliphatic protons of cations
compared to the titration with equivalent amounts of ditopic
tweezers 1 or 2, respectively (Table 2). These results agree
with the ditopic binding of diammonium salts with both
receptor sites of the tweezers.
The addition of a monoammonium salt (benzylammonium
perchlorate) to the acetonitrile solution of the tweezers 1 or
1
2
did not cause such a drastic change in the H NMR spectra
of the tweezer: only chemical shifts by #10 Hz were
observed (Table 1). However, the signals of the monofunc-
tional guest were shifted, indicating that the complexation
between the monoammonim cation and the crown ethers
appended to the cyclidene platform occurred. This result
The stoichiometry of the host–guest complexes was
0
established by Job’s method of continuos variations. The
5
Table 2. Maximum changes in the chemical shift of the protons in the
difunctional guest (hexamethylenediammoium cation) upon interaction
with crown ether-containing hosts. CD
1
3
CN, T¼298 K, C(dication)
¼
22
.0£10
M
2
)
þ
(Hz)
Host
D
maxd for the protons of (NH
3
)
2
(CH
2
6
a
b
g
B15C5
42
52
70
55
54
68
113
88
66
77
109
91
Tweezer 1
Tweezer 2
B18C6
Scheme 3.

234
O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
Figure 3. Job’s plot for the system containing tweezer 1 and hexamethyl-
enediammonium salt in CD CN. The total concentration of the host (H) and
the guest (G) was kept constant at 2£10 M. The change in the proton
chemical shift of the aCH group of hexamethylenediammonum cation (G)
was followed. The value (Dd )(x ), where x denotes molar fraction of the
guest, was plotted vs molar fraction of the host (x ).
1
Figure 5. H NMR-titration curves of hexamethylenediammonium
3
2
2
22
thiocyanate with tweezer 1 (curve 1) (C
(Cdication¼10 M) (curve 2): proton chemical shift of aCH group in
dication
¼10 M) and tweezer 2
23
2
2
G
G
G
diammonium cation vs amount of equivalents of the tweezer added.
H
B15C5-containing host 1, leaving the second ammonium
group uncoordinated. In a slow exchange rate, encapsulated
binding mode (Scheme 2) could be distinguishable by NMR
from the ‘sandwiched’ binding mode of the diamine.
Job’s plot for the system tweezer 1–hexamethylendiammo-
nium thiocyanate is shown, as an example, in Figure 3,
1
where the complexation-induced shift of guest H NMR
resonance was followed as a function of the host mole
5
0
fraction, keeping their total concentration constant. In all
tweezer–diammonium cation systems, 1:1 complexes were
found by Job’s method in agreement with the bidentate
inclusion of the guest depicted in Scheme 2. Control
experiments showed a 2:1 complexation between simple
parent crowns (B15C5 or B18C6) and diammonium cations,
a 1:2 complexation between ditopic tweezer (1 or 2) and
monoammonium cations, and a 1:1 complexation between
monotopic crowns (B15C5 or B18C6) and monoammonium
cations. These observations, as well as similar behavior of
The variable temperature experiment was performed for the
solution containing tweezer 1 and hexamethylenediammo-
nium thiocyanate in a 1:1 ratio (Fig. 4). With decreasing
temperature, the signals of the CH groups of the cation
2
became slightly broader and were shifted upfield, indicating
that the yield of the host–guest complex increases at lower
temperatures as is expected for an association process.
Cooling the sample also caused the signals J and M of the
tweezer platform to broaden slightly and to move upfield,
again showing an equilibrium shift toward formation of
the host–guest complex. Although the low temperature
NMR experiment was inconclusive, the stoichiometry of
the complexes (1:1 for 1þdiammonium guest vs 1:2 for
1þmonoammonium guest) and the amine length selectivity
displayed by host 1 (see below) agree with the bindentate
inclusion of the diamines (Scheme 2).
1
5C5 and 18C6 derivatives in our experiments, suggest that
þ
under our experimental conditions, each RNH3 group
interacts with one crown ether ring. An alternative
possibility exists for the B15C5 derivatives, where two
types of complexes with monoamonium salts in either 1:1 or
2
:1 ratios could be formed, and their binding constants were
5
1
comparable. In the 2:1 complexes, one ammonium group
is sandwiched between two crown ether rings. In principle,
one terminal ammonium group of the difunctional guest
could be sandwiched between two receptor sites of the
Association constants for 1:1 host–guest complexes were
determined from the binding curves (Fig. 5) by nonlinear
regression methods that gave excellent fits to a 1:1 model
for the association between a host and guest. The results of
1
the H NMR titrations of the diammonium salts (thiocyanate
or perchlorate) with the ditopic molecular receptors are
summarized in Table 3.
A dipositive charge localized in the platform does not
negatively affect the binding as can be seen from comparing
the binding affinities of the ditopic receptors 1 and 2 with the
corresponding data for the binding of monoammonium salts
by simple benzo crowns. A moderate chelate effect was
registered for the B18C6 derivative 2, while a substantial
increase in alkyl diammonium binding affinities was
registered in several cases for the B15C5 derivative 1
(Table 3). As expected, B18C6-containing host 2 displays
higher guest binding affinities than its B15C5-containing
counterpart 1. This behavior parallels guest binding
2
affinities of monomeric crown ethers.
4,52,53
1
Figure 4. H NMR spectra of the acetonitrile solution containing tweezer 1
(
different temperatures.
2
10 M) and tetramethylenediammonium thiocyanate in a ratio 1:1 at
2
The recognition of the length of a,v-diamines was

O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
235
2
Table 3. Association constants (Kassoc, M ) for 1:1 host–guest complexes of tweezers 1 and 2 and benzocrowns with diammonium and monoammonium
1
cations at 298 K
Host
Guest
K
assoc
log Kassoc
Method
Solvent
þ
51
B15C5
NH
NH
4
2.16
Calorim
CH
CH
3
CN
CN
48
2
3
.30
.03
NMR
Potent
3
7
0
MeOH
CH CN
þ
2
1
NMR, H
3
(CH)
2
C
6
H
5
5.5£10
2.74
3
2
4
þ
3
3
4
5
3
3
1
NMR, H
Tweezer 1
(NH
3
3
3
3
3
3
)
)
)
)
)
)
2
2
2
2
2
2
(CH
(CH
(CH
(CH
(CH
(CH
2
)
)
)
)
)
)
2
2
2
2
3
2
4
2
5
2
6
C
6
H
3£10
3.48
3.60
4.70
5.00
3.60
3.10
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
CN
CN
CN
CN
CN
CN
þ
1
NMR, H
(
(
(
(
(
NH
NH
NH
NH
NH
2
2
2
2
2
4£10
þ
þ
þ
þ
1
NMR, H
5£10
1
NMR, H
1£10
1
NMR, H
4£10
1
NMR, H
1.25£10
þ
70
Potent
Calorim
Calorim
24
NMR
B18C6
NH
NH
NH
4
4.14
4.27
4.07
3.54
4.70
MeOH
MeOH
þ
71
4
þ
4
24
CH
CH
CH
3
3
3
CN
CN
CN
þ
3
4
t-BuNH
NH
3
3.5£10
þ
1
3
(CH)
2
C
6
H
5
5£10
NMR, H
2
2
þ
2
4
4
4
2
4
4
2
4
1
NMR, H
Tweezer 2
(CH
3
)
2
(NH
2
)
)
)
)
2
2
2
2
3
2
4
(CH
2
)
1.2£10
3£10
7£10
9£10
2.08
4.48
4.85
4.95
2.78
4.48
4.30
2.48
4.70
CH
CH
CH
CH
3
3
3
3
CN
CN
CN
CN
þ
1
NMR, H
(
(
(
NH
NH
NH
3
3
3
)
)
)
2
2
2
(CH
(CH
(CH
2
2
2
þ
þ
1
NMR, H
1
NMR, H
1
NMR, H
6
£10
MeOH
2
5
2
6
þ
þ
1
NMR, H
(
(
NH
NH
3
)
)
2
(CH
(CH
2
)
)
3£10
CH
CH
3
CN
CN
1
NMR, H
3
2
2
2£10
3
1
NMR, H
3
£10
MeOH
CH CN
2
4
þ
1
NMR, H
(
NH
3
)
2
(CH
2
)
2
C
6
H
5£10
3
investigated on a series of aliphatic difunctional guests with
two primary ammonium groups separated by 2–6 carbons.
Tweezer 1 bearing B15C5 arms showed substantial
selectivity, with the strongest complexation of trimethylene-
and tetramethylenediammonium cations, and 1–2 orders of
magnitude weaker binding of a shorter (C ) or longer (C
constants were lower than in acetonitrile, but the difference
in the values of log Kassoc remained small (Table 3).
It is likely that the relatively small energy penalty upon
reorganization of the host in order to bind a ‘non-optimal’
guest is sensed by the low-affinity receptor 1, but does not
lead to discrimination against non-optimal guests by the
high-affinity receptor 2. It is also possible that the larger
rings of 18C6 receptor sites allow for an easier accommo-
dation of diammonium substrates of different length
between the receptor arms. In ammonium complexes with
B18C6, both ‘perched’ and ‘nested’ geometries are possible,
where three symmetric hydrogen bonds are formed between
the ammonium group and three oxygen atoms of the crown
in its preferred D3d conformation. In the former case, the
2
5
and C ) diammonium salts (Table 3). The chemical shift
6
changes of the CH -groups in the cyclidene platform of the
2
tweezer 1 due to the addition of different diammonium salts
also depended on the lengh of the diammonium cation, as
shown in Table 1. The largest shifts were observed with
tetramethylenediammonium and trimethylenediammonium
cations indicating that these cations provide the best fit.
The optimal length of the diamine guests agrees well
with the cavity width of saddle-shaped cyclidenes (ca.
˚
9
˚
7
covalently bridged cyclidene systems
A). The results of molecular modeling studies on
1
ammonium atom lies 0.8–0.9 A above the mean plane of
the oxygen atoms. In the latter case, which is easily
accessible when its stability is enhanced by other inter-
1,12,54
also demon-
strated that the six-atom (C ) linker spans the cavity with the
least steric strain.
6
2
þ
actions (such as additional hydrogen bonds in H NNH
3 3
complex), it moves almost to the center of the ring and is
bound to the lower triangle of 18C6 oxygens.
55–57
The guest binding affinity of the B18C6-containing tweezer
2
In
reveals the same trend in optimal length of the
contrast, only the perching complexes are stable for the
B15C5 derivatives, with the ammonium group located ca.
diammonium substrates as were seen for the tweezer 1,
although the length selectivity is significantly less pro-
nounced (Table 3). Values of the chemical shifts of the
methylene protons from the cyclidene platforms were
virtually independent of the nature of the diammonium
cation in this case (Table 1). It appears that the higher guest
binding affinity of tweezer 2 masks its potential selectivity
in encapsulating diammonium substrates of different length.
Indeed, the equilibrium constants for supramolecular host–
guest complexes with tweezer 2 show strong binding for all
primary diammonium cations (Table 3). The NMR titration
of the diammonium salts with the strongest and weakest
binding (C and C chains, respectively) was also done in
˚
2.0 A above the mean plane of the oxygen atoms.
57
Strong binding affinity of the B18C6 derivative 2 is also
exemplified in the ability of this host to complex secondary
diamines (Table 3). There was no evidence for piperidine
binding to the complex 1 under our experimental conditions.
3. Conclusion
In the present study, two compounds based on a nickel(II)
cyclidene platform bearing two crown-ether receptors
(B18C6 or B15C5) were synthesized. Studies of host–guest
4
6
methanol. As expected, in the protic solvent binding

236
O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
interaction between the tweezers and a,v-diammonium
1
Benzo[15]crown-5 (10.5 g, 39.1 mmol) and hexamethylene
tetramine (5.72 g, 41 mmol) were mixed with trifluoroacetic
acid (29 ml) under N . The reaction mixture was heated to
1008C and kept at this temperature for 24 h. The dark red
mixture was cooled to 58C, mixed with ice (450 g), and
stirred for 1 h. The product was extracted with chloroform
(4£250 ml), the chloroform layer was dried over mag-
nesium sulfate, filtered, and rotary evaporated. The
concentrated residue was loaded on a silica chromatography
cations by H NMR titration in CD CN showed that 1:1
3
3
5
21
complexes are formed with Kassoc,10 –10 M . B15C5-
derivative (1) showed substantial selectivity in binding of
trimethylene- and tetramethylenediammonium cations.
Higher affinity of the B18C6 receptor arms of host 2 to
the diammonium substrates resulted in stronger, but less
selective binding properties.
2
column (3 cm£25 cm) and eluted with CHCl /MeOH (2%
3
4
. Experimental
MeOH). The target product was contained in the first
fraction (which has a small yellow tail). Evaporation of the
solvent yielded pale-yellow oil, which solidefied upon
recrystallization from heptane. Yield 2.5 g (8.4 mmol,
22%). This material was also obtained by the reaction of
benzo-15-crown-5 with N-methylformanilide according to
4
.1. General
Chemicals (reagent grade) and solvents were purchased
from Aldrich or Acros and used as received.
6
5
the procedure described by Hyde et al. in 26% yield, and
from dichlorotetraethylene glycol and catechol by method
The starting dimethoxy cyclidene [Ni[(MeOEthi) Me [15]-
2
tetraeneN ]](PF ) and [Ni[(MeNMe ) Me [15]tetra-
4
2
6
0
1
described by Wu and co-workers in 16% yield. H NMR
(CHCl
6 2
2 2
2
eneN ]](PF ) were synthesized according to the
4
3
-d): d 9.83 (s, 1H), 7.43 (dd, J¼6, 1.3 Hz, 1H), 7.37
6 2
5
8
published procedure. Dichloropentaethyleneglycol was
prepared from pentaethylene glycol and SOCl as described
(d, J¼1.3 Hz), 6.93 (d, J¼6 Hz, 1H), 4.22–4.15 (m, 4H),
3.96–3.89 (m, 4H), 3.77–3.74 (m, 8H).
2
5
9
by Pedersen. Benzo-[15-crown-5] and benzo-[18-crown-
] were obtained from catechol and dichlorotetraethylene or
dichloropentaethylene glycol, respectively, according to the
0
obtained form benzo-18-crown-6 according to a modified
6
4.2.2. 4 -Formylbenzo-[18-crown-6]. The compound was
6
0
65
method described by Izatt group.
procedure described by Hyde et al. with a work up adapted
6
6
from Shuying. After extraction of the crude product into
chloroform and removing the solvent under reduced
pressure, the residual brown oil was dissolved in small
amount of dichloromethane and mixed with a suitable
The diammonium guests were prepared as thiocyanate or
perchlorate salts (that have sufficient solubility in organic
solvents) after treatment of the corresponding commercial
diamines with hydrogen thiocyanate or perchloric acid in
ethanol.
amount of Al O (neutral) to get a caramel-like oil. The
2 3
extraction of the material was done by treatment of the
mixture with hot Et O. After cooling the ether solution in
2
NMR spectra were recorded on a Bruker AM-300
spectrometer, IR spectra on a Mattison 1000 FTIR
spectrometer, and UV-Vis spectra on a Hitachi U-2000
spectrophotometer. Mass-spectra were measured at Mass
Consortium (San Diego, CA) (electrospray ionization) and
Mass Spectrometry Service Laboratory at University of
Minnesota Department of Chemistry (HRMS). Elemental
analyses were performed by Desert Analytics, Tucson, AZ.
the freezer, the product crystallized as white needles (55%
1
yield). H NMR (CHCl
1.8 Hz, 1H), 7.40 (d, J¼1.8 Hz, 1H), 6.94 (d, J¼8 Hz, 1H),
-d): d 9.86 (s, 1H), 7.44 (dd, J¼8,
3
4.26–4.20 (m, 4H), 3.96–3.90 (m, 4H), 3.80–3.71 (m, 8H),
1
3
3.69 (s, 4H); C NMR (CHCl -d): d 191.4, 154.8, 130.5,
3
127.3, 112.3, 111.5, 71.4, 71.3, 71.2, 71.1, 71.0, 69.7, 69.6,
69.4, 69.3.
0
pound was obtained by reduction of the formyl-derivative
4.2.3. 4 -Hydroxymethylbenzo-[15-crown-5]. The com-
NMR titration experiments were carried out according to the
2
3
65
procedure described earlier. Kassoc values were determined
following the proton signals of a-CH2 group of the
diammonium cations and calculated by nonlinear least-
squares fit of the titration curve for reversible 1:1
using a modified procedure described by Hyde et al.
0
4 -Formylbenzo[15-crown-5] (2.5 g, 8.5 mmol) was sus-
pended in 26 ml of absolute ethanol, and the mixture was
cooled to 08C. Sodium borohydride (0.32 g, 8.5 mmol) was
added to this suspension in small portions, maintaining the
temperature below 78C. After the addition of sodium
borohydride, the mixture was stirred at 08C for 1 h 40 min,
and then the solvent was rotary evaporated. The residue was
washed with brine and extracted with methylene chloride
(3£30 ml). The combined extracts were dried over mag-
6
1,62
complexation.
the estimated error was ,10%. The concentration of the
On the basis of repetitive measurements,
diammonium salts (thyocyanates or perchlorates) used for
2
2
titration with tweezer 1 was 1.0£10 M, except for
trimethylene- and tetramethylenediamonium thiocyanate
where 1.0£10 M solutions were used because of the
2
3
low solubility of these salts in acetonitrile. All measure-
2
nesium sulfate, filtered, and rotary evaporated, yielding
3
1
ments for tweezer 2 were done at 1.0£10 M concentration
2.4 g (8.1 mmol, 95%) of an oily product. H NMR (CHCl
3
-
of the diammonium salts.
d): d 6.89 (d, J¼1.4 Hz, 1H), 6.85 (dd, J¼6, 1.4 Hz, 1H),
6
.80 (d, J¼6 Hz, 1H), 4.57 (m, 2H), 4.10 (m, 4H), 3.90(m,
4
4
.2. Synthetic procedures
4H), 3.75 (m, 8H), 2.50 (br.s, 1H).
0
0
.2.1. 4 -Formylbenzo-[15-crown-5]. The compound was
4.2.4. (4 )-Hydroxymethylbenzo-[18-crown-6]. The com-
synthesized from benzo-15-crown-5 and hexamethylene
tetramine as described below using published procedures for
obtaining the formyl-derivatives of similar compounds.
pound was synthesized using the same method as described
above for the B15C5-derivative, starting with 3.2 g
(9.4 mmol) of 4 -formylbenzo-[18-crown-6], 0.34 g of
0
6
3,64

O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
237
NaBH , and 30 ml of EtOH. After solvent evaporation,
4
residue was not treated with brine, but was washed with
4.2.8. Phthalimidomethylbenzo-[18-crown-6]. The com-
pound was obtained by the procedure described above,
starting with chloromethylbenzo-[18-crown-6] (2.55 g,
7.07 mmol), potassium phthalimide (1.39 g, 7.50 mmol) in
water instead, and extracted with CH Cl (3£30 ml). Yield:
2
2
1
2
1
8
.7 g (7.9 mmol, 84%). H NMR (CHCl -d): d 6.95 (d, J¼
3
1
.7 Hz, 1H), 6.89 (dd, J¼8.1, 1.7 Hz, 1H), 6.82 (d, J¼
24 ml of DMF. Yield: 2.2 g (4.67 mmol, 66%). H NMR
(CHCl -d): d 7.86–7.83 (m, 2H), 7.73–7.70 (m, 2H), 7.00–
.1 Hz, 1H), 4.62 (s, 2H), 4.20–4.13 (m, 4H), 4.00–3.95
3
(
2
1
m, 4H), 3.8–3.76 (m, 4H), 3.72–3.70 (m, 4H), 3.68 (s, 4H),
.66 (br.s. 1H). C NMR (CHCl -d): d 149.4, 148.6, 135.0,
3
6.97 (m, 2H), 6.80 (d, J¼8.7 Hz, 1H), 4.74 (s, 2H), 4.13–
1
3
4.10 (m, 2H), 4.09–4.06 (m, 2H), 3.89–3.84 (m, 4H), 3.72
(s, 8H). C NMR (CHCl -d): d 168.5, 149.4, 134.4, 132.6,
1
3
20.2, 114.4, 113.4, 71.2, 71.1, 70.0, 69.6, 69.5, 69.3, 65.3.
2
3
þ
m/z (ESMS): 341 ([M2H] ), 343 ([MH] ). Anal. calcd for
C H O : C, 59.64; H, 7.65; found: C, 58.69; H, 7.77.
130.0, 123.7, 122.3, 115.3, 114.6, 71.3, 71.2, 70.0, 69.6,
41.8.). FT-IR (KBr): n 3450, 2922, 2876, 1773, 1717, 1616,
1
7
26
7
1
520, 1469, 1436, 1396, 1352, 1262, 1127, 991, 961, 746,
0
pound was prepared by modification of known pro-
þ
Anal. calcd for C H NO : C, 63.68, H, 6.20, N 2.97;
þ
4
.2.5. 4 -Chloromethylbenzo-[15-crown-5]. The com-
723, 658, 531. m/z (ESMS): 472 ([MH] ), 494 ([MþNa] ).
2
5
29
6
6
7,68
cedures. Hydroxymethylbenzo-[15-crown-5] (2.5 g,
.4 mmol) was dissolved in 150 ml of methylene chloride,
found: C, 63.70, H, 6.07, N 2.66.
8
and fine powder of potassium carbonate (3.39 g, 24.5 mmol)
0
69
4.2.9. 4 -Aminomethylbenzo-[15-crown-5]. The phthali-
mide derivative of 4-methylbenzo-[15-crown-5] (1.5 g,
3.5 mmol) was dissolved in 45 ml of hot ethanol. To this
solution, 0.45 g (14 mmol) of anhydrous hydrazine in 15 ml
of ethanol was added, and the reaction mixture was refluxed
for 2 h. The reaction mixture was cooled on an ice bath and
filtered, the precipitate of phtalhydrazide was washed with
ice-cold ethanol. The combined filtrates were rotary
evaporated, producing 1.2 g of crude off-white semi-
crystalline solid. The residue was washed with chloroform;
and undissolved solid residue was discarded. The chloro-
form filtrate was rotary evaporated to a final volume of
about 20 ml, and refrigerated for several hours. An
additional amount of solid phthalhydrazide formed was
separated by filtration, and the solvent was removed by
rotary evaporation. The residue was treated with 20 ml of
hot acetonitrile and filtered. Evaporation of the solvent
was added. The mixture was cooled to 08C under N , and
2
thionyl chloride (1.13 ml, 16 mmol) was added. The
reaction was stirred for 45 min, then filtered, and the
solvent was removed on a rotary evaporator, yielding 2.91 g
of the semi-solid product, which was used without further
þ
þ
purification. m/z (ESMS): 318 ([MH] ), 356 ([MþK] ).
0
pound was obtained using the same procedure as above
4
.2.6. 4 -Chloromethylbenzo-[18-crown-6]. The com-
0
benzo-[18-crown-6] (2.7 g, 7.9 mmol), CH Cl (170 ml),
for the B15C5-derivative, starting with 4 -hydroxymethyl-
2
2
K CO
2
(3.60 g, 26.1 mmol), and SOCl2 (2.07 g,
1
7.4 mmol). Yield: 2.55 g (7.07 mmol, 90%). H NMR
3
1
(
CHCl -d): d 6.91 (m, 2H), 6.80 (d, J¼8.0 Hz, 1H), 4.61 (s,
3
2
4
1
6
1
7
H), 4.23–4.15 (m, 4H), 4.00–3.92 (m, 4H), 3.79–3.75 (m,
H), 3.73–3.68 (m, 12H). C NMR (CHCl -d): d 148.8,
1
3
3
44.5, 130.7, 121.8, 115.1, 113.3, 70.9, 70.8, 69.5, 68.9,
3.5, 46.7. FT-IR (KBr): n 3377, 2903, 1650, 1597, 1520,
455, 1425, 1271, 1182, 1129, 1099, 993, 957, 844, 812,
resulted in transparent yellow oil of the product. Yield:
1
0.98 g (3.4 mmol, 50%). H NMR (CHCl -d), d: 6.85–6.81
3
(m, 3H), 4.15–4.10 (m, 4H), 3.90–3.88 (m, 4H), 3.78 (s,
13
þ
þ
18, 692, 609. m/z (ESMS): 361 ([MH] ), 399 ([MþK] ).
2H), 3.74 (s, 8H). C NMR (CHCl -d), d: 149.3; 148.0;
3
þ
HRMS: calcd for C H O Cl [M ]: 360.1340, found:
1
136.6 119.8; 114.3; 113.3; 71.1; 70.5; 69.7; 69.3, 69.1; 46.1.
7 25 6
3
60.1361.
0
4
.2.10. 4 -Aminomethylbenzo-[18-crown-6]. The com-
4
.2.7. Phthalimidomethylbenzo-[15-crown-5]. Chloro-
pound was synthesized according to the procedure
above, using phtalimidomethylbenzo-[18-crown-6] (1.9 g,
4.0 mmol), 50 ml of hot EtOH, and 0.513 g (16.0 mmol) of
methylbenzo-[15-crown-5] (2.8 g, 8.8 mmol) and potassium
phthalimide (1.8 g, 9.7 mmol) were mixed with 30 ml of
dimethylformamide and heated at 908C for 1 h. The reaction
mixture was cooled, 60 ml of chloroform were added, and
the mixture was poured into 250 ml of water. The chloro-
form layer was separated, and the aqueous layer was
extracted with an additional amount of chloroform
1
anhydrous hydrazine. Yield: 1.19 g (3.49 mmol, 87%). H
NMR (CH Cl-d ): d 6.88–6.82 (m, 3H), 4.18–4.11 (m,
3
3
4H), 3.94–3.86 (m, 4H), 3.80 (s, 2H), 3.78–3.72 (m, 8H),
1
3
3.69 (s, 4H), 1.98 (br.s, 2H). C NMR (CHCl -d): d 149.1;
3
148.0; 135.3 120.5; 114.4; 113.7; 71.15; 71.11; 71.05;
2
71.01; 70.0; 69.4, 69.3; 46.1. m/z (ESMS): 340 ([M2H] ),
(
2£200 ml). The combined chloroform extracts were
washed with 0.15 M NaOH (2£400 ml), and with water
4£500 ml). The chloroform extract was dried over
magnesium sulfate, filtered, and rotary evaporated, yielding
g of an oily product, which was recrystallized from 30 ml
þ
þ
342 ([MH] ). HRMS: calcd for C H NO Na [MþNa] :
1
7
27
6
(
364.1736, found: 364.1731.
0
3
4.2.11. [Ni[(4 -aminonomethylbenzo-[15-crown-5])
Me [15]tetraeneN ]](PF ) (tweezer 1/host 1). Bis-meth-
2 4 6 2
2
-
1
of ethanol. Yield: 1.85 g (4.32 mmol, 91%). H NMR
CHCl -d): d 7.84–7.80 (m, 2H), 7.70–7.66 (m, 2H), 7.0–
(
oxy Ni[15]J a¨ ger (PF ) (0.4 g, 0.6 mmol) was dissolved
6 2
3
6
.96 (m, 2H), 6.77 (d, J¼6.3, 1H), 4.74 (s, 2H), 4.13–4.10
in 10 ml of acetonitrile and mixed with a solution of
0
(
m, 2H), 4.09–4.06 (m, 2H), 3.89–3.84 (m, 4H), 3.72 (s,
4 -aminomethylbenzo-[15-crown-5] (0.5 g, 1.7 mmol) in
1
3
8
1
6
1
9
H). C NMR (CHCl -d): d 168.5, 149.5, 149.2, 134.4,
3
10 ml of acetonitrile. The reaction mixture gradually turned
red. After 10 min, the acetonitrile was removed on a rotary
evaporator at room temperature, leaving a red film. The film
was dissolved in 50 ml of boiling methanol. Upon cooling to
ambient temperature, some oil was deposited. The mixture
was decanted from the oil and cooled on ice, yielding orange
32.5, 130.0, 123.7, 122.3, 115.1, 114.3, 71.5, 70.9, 70.0,
9.5, 69.4, 41.8. FT-IR (KBr): n 3432, 2948, 2874, 1769,
715, 1611, 1514, 1469, 1436, 1394, 1337, 1266, 1141, 991,
41, 756, 725, 665, 528. HRMS: calcd for C H NO
7
2
3
25
þ
M ]: 427.1631, found: 427.1624.
[

238
O. P. Kryatova et al. / Tetrahedron 59 (2003) 231–239
crystalline precipitate. The precipitate was filtered, immedi-
ately washed with diethyl ether and dried. The yield of this
fraction was 0.15 g. Additional amount of the product was
isolated from the oily material deposited from methanol.
The material was dissolved upon heating in the filtrate
obtained in the above workup, and the mixture was cooled
on ice. A semi-crystalline solid was filtered and immedi-
ately washed with ether, yielding 0.28 g of the product. Both
molecular Chemistry. Fabbrizzi, L., Poggi, A., Eds.; Kluwer
Academic: Dordrecht, 1994.
7. Canary, J. W.; Gibb, B. C. Progr. Inorg. Chem. 1997, 45,
1–82.
8. Busch, D. H. Pure Appl. Chem. 1980, 52, 2477–2484.
9. Busch, D. H.; Alcock, N. W. Chem. Rev. 1994, 94, 585–623.
10. Kolchinski, A. G.; Korybut-Daszkiewicz, B.; Rybak-
Akimova, E. V.; Busch, D. H.; Alcock, N. W.; Clase, H. J.
J. Am. Chem. Soc. 1997, 119, 4160–4171.
fractions (0.43 g, (0.35 mmol, 62%) gave identical spectra.
1
H NMR (CHCl -d): d 7.65 (s, 2H), 6.96–6.92 (m, 6H),
3
11. Rybak-Akimova, E. V.; Kuczera, K.; Jas, G. S.; Deng, Y.;
Busch, D. H. Inorg. Chem. 1999, 38, 3423.
4
3
.61 (s, 4H), 4.07–4.05 (m, 8H), 3.81–3.77 (m, 8H), 3.65–
.61 (m, 20H), 3.24 (m, 4H), 2.34 (s, 6H), 2.16 (s, 6H), 1.86
1
1
1
2. Rybak-Akimova, E. V.; Kuczera, K. Inorg. Chem. 2000, 39,
2462–2472.
(
m, 2H). UV–Vis (CH CN) lmax (log 1) 480 (3.15), 382
3
(
4.62), 284 (4.45) nm. FT-IR (KBr): n 3430, 3262, 2932,
3. Breslow, R.; Yang, J.; Yan, J. M. Tetrahedron 2002, 58,
6
2
8
875, 1571, 1519, 1450, 1390, 1350, 1268, 1134, 1052, 941,
2
53–659.
44, 560, 521. m/z (ESMS): 1223 ([M2H] ), 1369
þ
4. Belvedere, S.; Breslow, R. Bioorg. Chem. 2001, 29, 321–331.
2
þ
([MþPF ] ), 1079 ([M2PF ] ), 933 ([M2PF –HPF ] ).
Anal. calcd for NiC H N O P F : C, 46.06; H, 5.59; N,
6
6
6
6
15. Yang, J.; Breslow, R. Tetrahedron Lett. 2000, 41, 8063–8067.
16. Yang, J.; Weinberg, R.; Breslow, R. Chem. Commun. 2000,
47 66 6 10 2 12
6
.86; found: C, 46.10; H, 5.81; N, 6.50.
5
31–532.
1
7. Breslow, R.; Dong, S. D. Chem. Rev. 1998, 98, 1997–2011.
8. Breslow, R.; Gabriele, B.; Yang, J. Tetrahedron Lett. 1998, 39,
0
tetraeneN ]](PF ) (tweezer 2/host 2). The compound was
4
.2.12. [Ni[(4 -aminomethylbenzo-[18-crown-6]) Me [15]-
2
2
1
4
6 2
2
887–2890.
obtained using the procedure for synthesis of B15C5
derivative as described above, starting with bis-methoxy
Ni[15]J a¨ ger (PF6)2 (0.83 g, 1.19 mmol) in CH CN
1
9. Breslow, R. Acc. Chem. Res. 1995, 28, 146–153.
0. French, R. R.; Holzer, P.; Leuenberger, M.; Nold, M. C.;
Woggon, W.-D. J. Inorg. Biochem. 2002, 88, 295–304.
1. Woggon, W.-D.; Wagenknecht, H.-A.; Claude, C. J. Inorg.
Biochem. 2001, 83, 289–300.
2
3
(
20 ml), and 4-aminomethylbenzo-[18-crown-6] (1.18 g,
2
2
2
2
2
2
2
3
6
2
.46 mmol) in CH CN (10 ml). Yield 0.95 g (0.72 mmol,
3
1
1%). H NMR (CH CN-d ): 7.60 (s, 2H), d 2.17 (s, 8H),
3
3
2. French, R. R.; Holzer, P.; Leuenberger, M. G.; Woggon, W.-D.
Angew. Chem., Int. Ed. 2000, 39, 1267–1269.
.32 (s, 6H), 3.23 (m, 4H), 3.35 (s, 8H), 3.58 (m, 20H), 3.73
(
m, 8H), 4.14 (m, 8H), 4.60 (s, 4H), 6.91 (m, 4H), 7.05 (s,
H). C NMR (CH CN-d ): d 172.2, 167.3, 158.3, 149.6,
3 3
3. Kryatova, O. P.; Kolchinskii, A. G.; Rybak-Akimova, E. V.
J. Inclusion Phenom. Macrocycl. Chem. 2002, 42, 251–260.
4. Izatt, R. M.; Pawlak, K.; Bradshaw, J. S.; Bruening, R. L.
Chem. Rev. 1991, 91, 1721–2085.
1
3
2
1
7
3
1
49.3, 129.3, 122.1, 113.8, 113.3, 111.3, 71.5, 71.4, 71.3,
0.0, 69.0, 60.0, 50.6, 48.0, 26.5, 20.3, 18.1. FT-IR (KBr): n
440, 3244, 2913, 1570, 1521, 1457, 1387, 1351, 1266,
125, 1097, 1061, 955, 849, 561, 522. m/z (ESMS): 1312
5. Tsubaki, K.; Nuruzzaman, M.; Kusumoto, T.; Hayashi, N.;
Wang, B.-G.; Fuji, K. Org. Lett. 2001, 3, 4071–4073.
6. Tsubaki, K.; Tanaka, H.; Furuta, T.; Kinoshita, T.; Fuji, K.
Tetrahedron Lett. 2000, 41, 6089–6093.
2
2
þ
([M2H] ), 1459 ([MþPF ] ), 1022 ([M2H–2PF ] ).
Anal. calcd for NiC H N O P F ·0.5Et O: C, 47.12;
6
6
51 76 6 12 2 12 2
H, 6.04; N, 6.22; found: C, 47.57; H, 5.98; N, 6.46.
7. Fuji, K.; Tsubaki, K.; Tanaka, K.; Hayashi, N.; Otsubo, T.;
Kinoshita, T. J. Am. Chem. Soc. 1999, 121, 3807–3808.
8. Prevot-Halter, I.; Weiss, J. New J. Chem. 1998, 869–874.
9. Jeong, K.; Park, J. W.; Cho, Y. L. Tetrahedron Lett. 1996, 37,
2
2
Acknowledgements
2
795–2798.
3
3
3
0. Goodman, M. S.; Jubian, V.; Linton, B.; Hamilton, A. D. J. Am.
This work was supported by Tufts University (startup funds
and Faculty Research Award to E. R. A.). We thank Paul
Filson for exploring alternative ways of the preparation of
functionalized benzocrowns.
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1
771–1774.
2. Fages, F.; Desvergne, J. P.; Kampke, K.; Bouas-Laurent, H.;
Lehn, J. M.; Meyer, M.; Albrecht-Gary, A. M. J. Am. Chem.
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3
3. Smeets, J. W. H.; Sijbesma, R. P.; Van Dalen, L.; Spek, A. L.;
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