Highly efficient chirality transfer from diamines encapsulated within a self-assembled calixarene-salen host

Article abstract of DOI:10.1002/chem.201500333

A calix[4]arene host equipped with two bis-[Zn(salphen)] complexes self-assembles into a capsular complex in the presence of a chiral diamine guest with an unexpected 2:1 ratio between the host and the guest. Effective chirality transfer from the diamine to the calix-salen hybrid host is observed by circular dichroism (CD) spectroscopy, and a high stability constant K_2,1 of 1.59×10¹¹ M^-2 for the assembled host-guest ensemble has been determined with a substantial cooperativity factor α of 6.4. Density functional calculations are used to investigate the origin of the stability of the host-guest system and the experimental CD spectrum compared with those calculated for both possible diastereoisomers showing that the M,M isomer is the one that is preferentially formed. The current system holds promise for the chirality determination of diamines, as evidenced by the investigated substrate scope and the linear relationship between the ee of the diamine and the amplitude of the observed Cotton effects.

Full text of DOI:10.1002/chem.201500333

DOI: 10.1002/chem.201500333
Full Paper
&
Host–Guest Systems
Highly Efficient Chirality Transfer from Diamines Encapsulated
within a Self-Assembled Calixarene–Salen Host
[a]
[a]
[a, b]
[a, c]
Luis Martꢀnez-Rodrꢀguez, Nuno A. G. Bandeira, Carles Bo,
and Arjan W. Kleij*
Abstract: A calix[4]arene host equipped with two bis-[Zn(sal-
phen)] complexes self-assembles into a capsular complex in
the presence of a chiral diamine guest with an unexpected
culations are used to investigate the origin of the stability of
the host–guest system and the experimental CD spectrum
compared with those calculated for both possible diastereo-
isomers showing that the M,M isomer is the one that is pref-
erentially formed. The current system holds promise for the
chirality determination of diamines, as evidenced by the in-
vestigated substrate scope and the linear relationship be-
tween the ee of the diamine and the amplitude of the ob-
served Cotton effects.
2
:1 ratio between the host and the guest. Effective chirality
transfer from the diamine to the calix–salen hybrid host is
observed by circular dichroism (CD) spectroscopy, and
11
ꢀ2
a high stability constant K2,1 of 1.59ꢁ10 m for the assem-
bled host–guest ensemble has been determined with a sub-
stantial cooperativity factor a of 6.4. Density functional cal-
[6]
Introduction
amines, amino alcohols, and diols induced by 1:1 complex
formation between the host and the guest.
The creation and transfer of chirality, sometimes referred to as
chirogenesis, plays a key role in biological processes that in-
With most reported supramolecular host systems, the trans-
fer of chiral information by interaction with chiral diamines is
hampered by the requirement of a pretreatment of the analyte
with additives, the use of a (large) excess of diamine, the re-
quirement of air-sensitive reagents, and/or a relatively low
binding constants between the host and guest partners;
owing to such challenges, the quest for an efficient host
system remains an important undertaking.
[1]
volve proteins and other natural systems such as DNA. Chiral
transmission has also been shown to be crucial in the catalytic
asymmetric synthesis of various organic compounds, in which
a metal or organic catalyst favors the formation of one pre-
[
2]
ferred chiral product in the enantiocontrolling step. Further-
more, to date highly efficient methodologies have been de-
signed to create materials with reversible and responsive fea-
tures, and smart materials have also been developed with pre-
Herein, we present a new type of supramolecular host for
chiral diamine guests that is based on a calix[4]arene–salen
hybrid structure. Each calixarene unit is functionalized by two
distal [Zn(salphen)] complexes connected to the upper rim of
the calixarene incorporating two prochiral biphenyl units
(Scheme 1; host 1). These [Zn(salphen)] complexes are known
[
3]
designed sensing purposes. The field of chirality sensing has
rapidly advanced over the last five years with a strong focus
on newly designed systems that may facilitate fast and effi-
cient determination of the concentration, absolute configura-
tion, enantiomeric excess, and/or molecular identity of a chiral
[7]
to form stable complexes with amine donors and, as such,
we anticipated the easy formation of 1:1 complexes with chiral
[
4]
analyte. Whereas bis-porphyrins have been and still continue
[
4e,5]
to be popular hosts in chirality transfer processes,
we have
recently started to use modular and easy to assemble dinuclear
and trinuclear [Zn(salen)]-based hosts that show (strong) chiro-
[4d]
genesis effects in the presence of chiral carboxylic acids, di-
[a] L. Martꢀnez-Rodrꢀguez, Dr. N. A. G. Bandeira, Prof. Dr. C. Bo,
Prof. Dr. A. W. Kleij
Institute of Chemical Research of Catalonia (ICIQ)
Av. Pa ¨ı sos Catalans 16, 43007 Tarragona (Spain)
E-mail: akleij@iciq.es
[b] Prof. Dr. C. Bo
Departament de Quꢀmica Fꢀsica i Inorgꢁnica, Universitat Rovira i Virgili
Marcel·lꢀ Domingo s/n, 43007 Tarragona (Spain)
[c] Prof. Dr. A. W. Kleij
Catalan Institute of Research and Advanced Studies (ICREA)
Pg. Lluꢀs Companys 23, 08010 Barcelona (Spain)
Scheme 1. Structures of calix–[Zn(salphen)] hosts 1 and 2 and the expected
coordination stoichiometry (1:1) and induction of chirality in host 1 by bind-
ing to one molecule of a ditopic chiral diamine.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500333.
Chem. Eur. J. 2015, 21, 1 – 8
1
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diamines; each molecule of complex 1 would thus bind one
molecule of diamine. However, the unusual formation of 2:1
host–guest assemblies, in which two molecules of calixarene–
bis-[Zn(salphen)] interact with only one diamine molecule, was
noted with concomitant, cooperative and diastereo-selective
encapsulation of the chiral diamine guest. The underlying rea-
sons for this unusual observation have been investigated in
detail by using various experimental and computational meth-
ods, and the use of these types of calix–salen host systems in
the determination of the absolute configuration and ee of the
diamine is also detailed.
calixarene–bis-[Zn(salphen)] complex in 83% yield. Likewise,
the mono-Zn host
2 (see the Supporting Information,
Scheme S2) was prepared in a similar way in 99% yield from
its calixarene—salphen precursors. Complex 2 represents a con-
trol compound in the chirality transfer experiments, as will be
discussed below.
The potential induction of chirality by chiral diamines and
thus a conformational control within host structure 1 was first
probed in the presence of (1R,2R)-(+)-1,2-diphenylethylenedi-
amine a (Scheme 2) and the UV/Vis and circular dichroism (CD)
features of 1 in the presence of this chiral diamine were stud-
ꢀ
5
ied. Titration of a solution of 1 (CH Cl ; 6ꢁ10 m) with a solu-
2
ꢀ
2
4
tion of the diamine a (CH Cl ; 6ꢁ10 m) showed typical UV/Vis
2
2
Results and Discussion
changes of a [Zn(salphen)]-derived complex (Figure 1a). A
small but detectable bathochromic shift (Dl=6 nm) was
noted together with a significant decrease of the absorption
We first designed host 1 (Scheme 2; see the Supporting Infor-
mation, Schemes S1 and S2 and Figures S1–S16, for more de-
upon
addition
of
higher
amounts of diamine a. Similar
bathochromic shifts of [Zn(sal-
phen)] species were detected in
the
presence
of
pyridine
[8]
donors.
However, in these
cases an increasing absorption
was detected at higher concen-
trations of analyte due to aggre-
gate-to-monomer transitions of
these materials. Thus, in the
present case it seems that host
molecule 1 does not seem to be
in an aggregated state, render-
ing it useful for interaction with
suitable ditopic substrates such
as diamine a. The CD spectra of
1
(Figure 1b and 1d) showed
typical Cotton effects at l=416
and 476 nm, with an unexpected
saturation point after the addi-
tion of 0.5 equivalents of di-
amine a, that is, at a 2:1 host–
[9]
guest ratio (Figure 1c).
The
species formed at this ratio
proved to be rather stable as
a large excess of 40 equivalents
of the diamine guest were re-
quired to fully disrupt the 2:1 as-
sembly (see the Supporting In-
formation, Figure S28).
Scheme 2. Synthesis of bis-[Zn(salphen)] host 1 and structures of chiral diamines a and b.
tails) incorporating two co-facially orientated [Zn(salphen)]
units that should accommodate the binding of suitable chiral
The binding constant K2,1 represents the binding of each di-
amine with two equivalents of calixarene host 1; if this binding
2
diamine guests and block CarylꢀC rotation of the biphenyl
process is cooperative (i.e., K1,1 <K
) then K2,1 =aKM where
aryl
1,1!2,1
units leading to chirality transfer effects.
a is the cooperativity factor and K represents the microscopic
M
The synthesis of host 1 started off by using known calixar-
ene–disalicylaldehyde A-1 and treatment with the ketamine re-
agent B (see the Supporting Information, Scheme S1) furnish-
ing the calixarene–bis-salphen ligand B-1 in 70% yield. The Zn-
based host 1 was then prepared from B-1 by reaction with
binding constant. The K value can be derived from the equa-
M
tion K1,1 =2 K with two possible and identical binding sites for
M
the amine. To evaluate possible cooperative effects in the for-
mation of (1) ·a, we first determined K by titration of model
2
1,1
complex 2 (Scheme 1) with benzylamine, giving a value of
5
ꢀ1
a stoichiometric amount of ZnEt in THF to give the desired
3.14ꢁ10 m . The binding constant K was hereafter deter-
2
2,1
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and S39). Furthermore, in the
2
:1 system (see Figure 1e) two
key features were observed. The
first is the presence of multiple
p–p stacking interactions (virtu-
ally absent in the 1:1 complex;
see the Supporting Information,
Figure S40) between the phenyl
groups of the guest and the
phenyl groups of the coordinat-
ed [Zn(salphen)] units of two cal-
ix[4]arene–bis-[Zn(salphen)]
hosts, which helps to stabilize
the assembled 2:1 complex. In
line with this observation is the
1
significant H NMR upfield shift
detected for the imine H of host
1
in the presence of diamine
[10]
guest a ([D ]acetone).
As for
6
the free host 1, this resonance is
located at d=9.09 ppm. In the
presence of a it is shifted to
8.64 ppm (Dd=ꢀ0.45 ppm; for
completeness, calixarene–bis-sal-
phen B-1 gives rise to a reso-
nance at d=8.80 ppm). Such an
upfield shift is much larger than
has been previously reported for
pyridine coordination to [Zn(sal-
phen)], which typically results in
very small shifts for the imi-
[8b]
ne H. Therefore, it seems rea-
sonable to suggest that the
imine protons in 1 are affected
by the encapsulation process
and are located near to the
p surface of the diamine guest
ꢀ
5
Figure 1. a) Detail of the UV/Vis spectrum for 1 (6ꢁ10 m; CH
amine a (0–100 equiv); b) CD spectroscopic changes for host 1 (6ꢁ10 m; CH
.50 equivalents of diamine b; c) titration curve for 1 using the CD data at l=416 nm; d) CD response for 1 in
2 2
Cl ) in the presence of increasing amounts of di-
ꢀ
5
2
2
Cl ) in the presence of 0.06–
1
ꢀ
4
2 2 2
the presence of 0.5 equivalents of diamine a at [1]=2ꢁ10 m (CH Cl ); e) computed structure of assembly (1) ·b.
mined using fluorescence titration data of 1 in the presence of
diamine a and was found to be very high (1.59ꢁ0.14ꢁ
a (see the Supporting Information, Figures S40 and S42).
The second remarkable feature is the conformation of the
two non-coordinated [Zn(salphen)] units (one present in each
calix[4]arene–bis-[Zn(salphen)] host), which shows some
11
ꢀ2
1
0 m ) with an a value of 6.4, in line with a strong, coopera-
tive binding of a (for full details, see the Supporting Informa-
tion). Interestingly, a similar preferred 2:1 stoichiometry be-
tween host 1 and diamines b and d (Figures S29–S32) was
found as evidenced by their titration data, thus pointing to
more general and similar chirality transfer behavior for 1 in the
presence of chiral diamines.
degree of distortion of the N O2 tetradentate coordination
2
plane of the salphen ligand with the Zn ion pushed “inwards”
(see the Supporting Information, Figure S41). As a result, these
non-coordinated [Zn(salphen)] units are sterically congested
and not easily approached by incoming ligands (cf., diamines
such as b). Both features (Figures S40 and S41) support the
high stability found for the 2:1 assembly, and the coordination
of the diamine b to two molecules of 1 results in the coopera-
tive and full encapsulation of the diamine guest.
To understand in more detail the binding mode in (1) ·b,
2
a number of additional experiments were conducted. Struc-
tures for both the 1:1 and the 2:1 assemblies based on 1 and
diamine b were generated and fully optimized using a ONIOM
QM/QM strategy (see also Supporting Information for details
and Figure 1e). Interestingly, the 1:1 host–guest complex
shows a higher degree of distortion within each [Zn(salphen)]
unit as a consequence of the ditopic binding of diamine b. In
the 2:1 model, this effect is less pronounced, showing this
system to be of significantly lower energy (ꢀ36.3 versus
1
H DOSY NMR spectroscopy (CD Cl ; see the Supporting In-
2
2
formation, Figure S43) was also carried out, suggesting a molec-
ular radius of 11.0 ꢃ that is close to the estimation derived
from the computed structure for assembly (1) ·b by DFT
2
(11.4 ꢃ; see the Supporting Information, Figure S39). Since the
CD results for (1) ·b point to a clear transfer of chirality from
2
ꢀ
1
ꢀ
27.4 kcalmol ; see the Supporting Information, Figures S38
the diamine to the host, the CD traces of both possible (M,M)
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Table 1. Collected CD data for host 1 in the presence of chiral ditopic li-
[
a]
gands a–l.
Figure 2. Comparison between the computed CD spectra for diastereoiso-
meric assemblies (P,P)-(1) ·b (red) and (M,M)-(1) ·b (green) and the experi-
mental observed one (dashed).
2
2
ꢀ
1
ꢀ1 [b,c]
ꢀ1
ꢀ1 [b,c]
Diamine guest
l [nm]
416
De [m cm
]
De [m cm
]
and (P,P) configured diastereoisomers were calculated by DFT
[
11]
methods.
The calculated CD spectrum for (M,M)-(1) ·b
5.6
ꢀ6.4
ꢀ5.4
6.6
ꢀ3.2
1.2
21
ꢀ20
ꢀ23
20
2
a
b
c
476
416
476
420
showed a remarkable resemblance to the experimental one,
suggesting that this diastereoisomer should be the predomi-
nant species in solution (Figure 2). The large resemblance of
the experimental and calculated CD traces for the 2:1 assembly
ꢀ6.6
1.8
484
4
4
4
4
26
75
13
76
ꢀ4.0
0.3
ꢀ9.5
6.3
ꢀ6.4
3.0
ꢀ1.8
0
ꢀ15
4.7
ꢀ13
14
26
24
ꢀ6.1
2.0
ꢀ3.6
0.7
(
1) ·a is further support for a selective encapsulation process.
To further investigate the scope, a series of other (potential-
2
d
e
f
ly) ditopic substrates (Table 1; b–l) were then combined with
[
12]
host 1 and their CD spectra recorded. As expected, (1S,2S)-
ꢀ)-1,2-diphenylethylenediamine b showed opposite Cotton ef-
424
4
4
4
4
81
24
80
20
(
fects to those of diamine a. Other diamine substrates having
a (1S,2S) configuration (c–f) showed similar Cotton effects to b,
suggesting that host 1 could be useful to determine the abso-
lute configurations of chiral diamines. Interestingly, when chiral
diamines g and h (incorporating only one chiral center) were
used, similar CD behavior was noted to that for b–f, and there-
fore the presence of only one chiral center in the diamine sub-
strate seems to be required for effective chirality transmission.
A more rigid diamine such as i did not lead to any observable
chirality transfer; apparently, the rigidity of this diamine does
not allow for productive diamine complexation as noted for a–
h. The absence of any CD signals in the presence of ditopic sys-
g
ꢀ2.3
0
0
h
480
–
i–l
0
ꢀ
5
[a] Measured in CH Cl at [1]=6ꢁ10 m. [b] DA values are De/32982.
[c] Data refer to the CD output at [1]=2ꢁ10 m. Note that for potentially
ditopic substrates i–l, no output was observed at either concentration of
except for j (De=13.0m cm at l=464 nm). For representative CD
spectra, see Figures 1d and 2; see also the Supporting Information.
2
2
ꢀ4
ꢀ1
ꢀ1
1
Conclusion
ꢀ5
tems j–k (at [1]=6ꢁ10 m) emphasizes the requirement for
the presence of two (electron-rich) N-donor atoms in the guest
structure. The fact that O-donor-based amino alcohol j, amide-
based k, and diol l did not produce any useful CD output is in
line with previous work on the coordination behavior of
In summary, we have presented a unique self-assembled host–
guest system with an unexpected binding motif between the
host and the guest. Two molecules of host 1 bind one diamine
guest molecule to form an encapsulated system with effective
chirality transfer from the guest to the host, as indicated by
CD spectroscopy. The high stability of this new host–guest
system prospectively allows for the determination of low con-
centrations of chiral diamines, their absolute configuration,
and their enantiomeric excess.
[Zn(salphen)] species that (strongly) prefer N-donor over alco-
[
13]
hol ligands. Finally, various ratios of a and b in the presence
of host 1 were then analyzed by CD spectroscopy and the am-
plitude of the Cotton effects compared with the actual ee
values of the diamine samples (see the Supporting Informa-
tion). A linear dependence was found and the calibration
showed low absolute errors in the ee determinations (around
Experimental Section
1
%), a feature potentially useful for practical applications, as
[14]
General methods and materials: Compound A-1, mono-5-bro-
motetrapropoxycalix[4]arene,
[15]
detection by CD/fluorescence spectroscopy allows for very low
3-(tert-butyl)-2-hydroxy-5-(4,4,5,5-
ꢀ5
ꢀ6
[16]
concentrations (10 –10 m) of diamine to be determined.
tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde,
(S)-1-phenyl-
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[17]
[18]
13
ethane-1,2-diamine, and (S)-2-amino-2-phenylacetamide were
(s, 2H); C NMR (125 MHz, CDCl ): d=10.0, 11.0, 23.2, 23.7, 29.4,
3
prepared as reported previously. All others chemicals are commer-
29.8, 31.1, 31.4, 34.2, 35.2, 35.4, 76.6, 77.4, 118.4, 118.5, 119.3, 122.3,
123.6, 125.3, 126.8, 127.0, 127.7, 128.3, 128.4, 128.8, 129.3, 131.2,
133.2, 134.4, 135.6, 137.4, 138.2, 138.7, 139.5, 142.1, 155.4, 157.4,
160.0, 160.3, 162.8, 176.0 ppm; HRMS (ESI+, MeOH): m/z calcd for
C116H133O N : 1710.0118; found: 1710.0064.
1
cially available from Aldrich and were used as received. H NMR
1
3
and C NMR spectra were recorded on Bruker Avance 500 NMR
spectrometers at 297 K. Chemical shifts are reported in ppm rela-
tive to the residual solvent peaks in CDCl3 (d=7.26 ppm) and
8
4
[
D ]DMSO (d=2.50 ppm). Mass analyses were carried out by the
6
Bis-(4,6-di-tert-butylphenol-salphen)calix[4]arene zinc complex
1): Under an argon atmosphere, compound B-1 (100 mg,
.059 mmol) was dissolved in dry THF (10 mL), and then a solution
High Resolution Mass Spectrometry Unit at the ICIQ in Tarragona,
Spain. UV/Vis and CD spectra were recorded on an Applied Photo-
physics Circular Dichroism Chirascan Spectrophotometer using
host 1 at 6ꢁ10 m in DCM, using the following parameters: step-
size 2 nm, time-per-point 0.5 s, 3 repeats per sample, T=248C. Fur-
ther details are mentioned in each respective section provided
below.
(
0
of ZnEt (1m, 0.12 mL, 0.118 mmol) was added dropwise and the
2
ꢀ
5
reaction mixture was stirred for 4 h. The solvent was then removed
by evaporation to afford 1 as a bright orange solid (yield: 83%).
1
H NMR (500 MHz, DMSO): d=0.91 (t, J=7.5 Hz, 6H), 1.02 (s, 18H),
1
4
4
2
2
9
2
.09–1.15 (m, 24H), 1.45 (s, 18H), 1.83–1.90 (m, 4H), 1.95–2.03 (m,
H), 3.22–3.26 (m, 4H), 3.62–3.68 (m, 4H), 4.01–4.07 (m, 4H), 4.38–
.45 (m, 4H), 4.94 (s, 4H), 6.21–6.28 (m, 8H), 6.33 (d, J=6.7 Hz,
H), 6.48 (d, J=7.9 Hz, 2H), 6.57–6.81 (m, 4H), 7.07 (t, J=8.0 Hz,
H), 7.23–7.28 (m, 4H), 7.37–7.45 (m, 10H), 7.56–7.69 (m, 4H),
Syntheses
Precursor (3,5-di-tert-butyl-2-hydroxyphenyl)(phenyl)methanone
(
13
.04 ppm (s, 2H); C NMR (125 MHz, DMSO): d=10.0, 11.0, 22.8,
3.3, 29.6, 29.8, 30.3, 31.3, 33.6, 35.0, 35.3, 35.6, 76.1, 77.0, 114.7,
A): Under an argon atmosphere, 3,5-di-tert-butylsalicylic acid
(
1.0 g, 4 mmol) was dissolved in dry THF (30 mL). A phenyllithium
115.9, 119.1, 119.7, 121.9, 125.5, 126.0, 126.4, 127.3, 127.6, 128.0,
solution (1.8m in dibutyl ether, 13 mL, 25 mmol) was added drop-
wise at 08C. The solution was then stirred at 108C for 18 h. Then,
freshly distilled Me SiCl (7 mL, 56 mmol) was added, and the reac-
tion mixture was stirred for 1 h. Dilute aqueous HCl (3m, 30 mL)
was then added, and the organic phase was extracted with diethyl
ether (3ꢁ30 mL) and the combined extracts were dried over
Na SO . The product was purified by column chromatography
1
1
1
28.2, 128.5, 129.0, 132.0, 132.9, 134.9, 136.5, 136.8, 140.2, 140.3,
40.7, 141.2, 141.7, 155.0, 156.0, 159.6, 162.9, 170.1, 171.4, 174.2,
75.8 ppm; HRMS (MALDI+, dctb): m/z calcd for C116H O N Zn
2
3
130
8
4
+
(M+2H) : 1836.8628; found: 1836.8772.
5-Mono-[1-(3-tert-butyl-2-hydroxy-1-formylphenyl)]-25,26,27,26-
2
4
tetra-propoxy-calix[4]arene (B-2): Under an argon atmosphere,
Pd(OAc)2 (10 mg, 0.045 mmol) and P(o-tol)3 (27 mg, 0.089 mmol)
were dissolved in previously deoxygenated toluene (25 mL). After
(
5:95 up to 10:90 v/v ethyl acetate/hexane) to give A as a yellow
1
solid (yield: 92%). H NMR (500 MHz, CDCl ): d=1.25 (s, 9H), 1.49
3
(
s, 9H), 7.44 (d, J=2.4 Hz, 2H), 7.71–7.48 (m, 5H), 12.71 ppm (s,
stirring the mixture for 30 min, mono-5-bromotetrapropoxycalix[4]-
1
3
[15]
1
1
2
3
H); C NMR (125 MHz, CDCl ): d=29.6, 31.4, 34.4, 35.4, 118.2,
arene (500 mg, 0.74 mmol)
and 3-(tert-butyl)-2-hydroxy-5-
3
28.0, 128.3, 129.4, 131.4, 131.7, 138.0, 138.9, 140.0, 160.1,
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde (268 mg,
[16]
02.7 ppm; HRMS (ESI+, MeOH): m/z calcd for C H O Na:
0.89 mmol) were dissolved in deoxygenated MeOH (5 mL) and
2
1
26
2
33.1825; found: 333.1828.
added to the mixture with an aqueous solution of K CO (2m,
2
3
5
mL). After 40 h stirring at 658C, the reaction mixture was allowed
Precursor (E)-2-{[(2-aminophenyl)imino]-(phenyl)methyl}-4,6-di-
tert-butylphenol (B): Compound A (300 mg, 0.88 mmol) was dis-
solved in toluene (20 mL) and o-phenylenediamine (191 mg,
to cool and water (10 mL) and aqueous HCl (1m, 5 mL) were
added. The crude product was filtered through Celite and extract-
ed with ethyl acetate (3ꢁ30 mL). The organic phases were com-
1
.76 mmol) and p-toluenesulfonic acid (8 mg, 0.09 mmol) were
bined and dried over Na SO . The solvent was removed by evapo-
added to the mixture. The reaction was performed using a Dean–
Stark apparatus (120–1308C) for 30 h. The reaction mixture was al-
lowed to cool and the resultant precipitate was filtered off and
2
4
ration and the white solid obtained was further triturated with
1
MeOH to give B-2 (yield: 71%). H NMR (500 MHz, CDCl ): d=0.95
3
(
t, J=7.4 Hz, 6H), 1.04 (t, J=7.4 Hz, 3H), 1.07 (t, J=7.4 Hz, 3H),
washed with MeOH (3ꢁ10 mL) to give B as a yellow solid (yield:
1
1
1
3
(
7
.40 (s, 9H), 1.86–2.01 (m, 8H), 3.15 (d, J=13.4 Hz, 2H), 3.20 (d, J=
3.4 Hz, 2H), 3.76 (t, J=7.1 Hz, 2H), 3.81 (t, J=7.1 Hz, 2H), 3.91–
.98 (m, 4H), 4.46 (d, J=13.4 Hz, 2H), 4.50 (d, J=13.4 Hz, 2H), 6.06
7
4%). H NMR (500 MHz, CDCl ): d=1.15 (s, 9H), 1.51 (s, 9H), 3.84
3
(
s, 2H), 6.27 (dd, J=1.5 Hz; 8.0 Hz, 1H), 6.40 (td, J=1.4 Hz; 7.6 Hz,
1
1
7
H), 6.67 (dd, J=1.4 Hz; 8.0 Hz, 1H), 6.81 (td, J=1.5 Hz; 7.6 Hz,
H), 6.96 (d, J=2.5 Hz, 1H), 7.17–7.23 (m, 2H), 7.30–7.34 (m, 3H),
.46 (d, J=2.5 Hz, 1H), 14.90 ppm (s, 1H); C NMR (125 MHz,
t, J=7.5 Hz, 1H), 6.31 (d, J=7.5 Hz, 2H), 6.51 (s, 2H), 6.74 (t, J=
13
.5 Hz, 2H), 6.85 (d, J=7.5 Hz, 2H), 6.89 (d, J=7.5 Hz, 2H), 7.22 (d,
13
J=7.5 Hz, 2H), 9.86 (s, 1H), 11.65 ppm (s. 1H); C NMR (125 MHz,
CDCl ): d=10.3, 10.7, 23.3, 23.5, 23.6, 29.4, 29.8, 31.1, 31.3, 35.0,
7
1
1
CDCl ): d=29.7, 31.4, 34.3, 35.4, 115.2, 118.1, 119.0, 122.2, 125.6,
3
1
1
27.0, 128.1, 128.3, 128.5, 129.1, 134.2, 135.1, 136.7, 137.4, 139.1,
39.4, 159.9, 176.2 ppm; HRMS (ESI+, MeOH): m/z calcd for
3
7.0, 77.1, 77.4, 120.6, 121.8, 122.0, 126.2, 127.7, 128.7, 128.8, 129.7,
32.9, 133.4, 133.7, 134.4, 134.9, 136.0, 136.3, 138.0, 155.8, 156.1,
57.4, 160.0, 197.5 ppm; HRMS (ESI+, MeOH): m/z calcd for
C H ON : 401.2587; found: 401.2584.
2
7
33
2
Bis-(4,6-di-tert-butylphenol-salphen)calix[4]arene ligand (B-1):
Compounds A-1 (150 mg, 0.16 mmol) and B (134 mg, 0.33 mmol)
C H O Na: 791.4282; found: 791.4281.
51
60
6
were dissolved in a 50:50 v/v MeOH/CHCl solvent mixture (10 mL).
5-Mono-(4,6-di-tert-butylphenol-salphen)calix[4]arene ligand (C-
2): Compounds B-2 (100 mg, 0.13 mmol) and B (78 mg, 0.20 mmol)
were dissolved in a 1:1 v/v MeOH/CHCl3 solvent mixture (5 mL).
The reaction mixture was stirred and heated at reflux for 30 h, after
which TLC showed full consumption of the aldehyde reagent. The
solvent was then removed by evaporation to afford a yellow solid,
3
The reaction mixture was heated at reflux for 48 h (until all alde-
hyde had been consumed, as monitored by TLC). The solvent was
then removed by evaporation to afford a yellow solid, which was
washed and triturated with MeOH to give B-1 (yield: 70%).
1
H NMR (500 MHz, CDCl ): d=0.88–1.00 (m, 12H), 1.11 (s, 18H),
3
1
1.36 (s, 18H), 1.53 (s, 18H), 1.84–2.03 (m, 8H), 3.23 (d, J=13.5 Hz,
4H), 3.66–3.80 (m, 4H), 3.99–4.12 (m, 4H), 4.52 (d, J=13.0 Hz, 4H),
6.16–6.35 (m, 8H), 6.86–6.92 (m, 2H), 7.03–7.33 (m, 18H), 7.46 (d,
which was triturated with MeOH to give C-2 (yield: 62%). H NMR
(500 MHz, CDCl ): d=0.96 (t, J=7.4 Hz, 6H), 1.01–1.06 (m, 6H),
3
1.09 (s, 9H), 1.27 (s, 9H), 1.51 (s, 9H), 1.86–1.98 (m, 8H), 3.17 (dd,
J=9.5 Hz, 4H), 7.63 (s, 2H), 8.53 (s, 2H), 13.88 (s, 2H), 14.70 ppm
J=6.7 Hz; 13.5 Hz, 4H), 3.78 (t, J=7.3 Hz, 2H), 3.83 (t, J=7.3 Hz,
Chem. Eur. J. 2015, 21, 1 – 8
www.chemeurj.org
5
ꢂ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
2
7
2
7
1
2
1
1
1
1
H), 3.92 (t, J=7.5 Hz, 4H), 4.47 (t, J=13.5 Hz, 4H), 6.15 (t, J=
.5 Hz, 1H), 6.38 (d, J=7.5 Hz, 2H), 6.58 (s, 2H), 6.69 (t, J=7.5 Hz,
H), 6.76–6.91 (m, 6H), 7.00–7.13 (m, 8H), 7.20 (t, J=7.3 Hz, 2H),
.42 (d, J=2.3 Hz, 1H), 8.31 (s, 1H), 13.72 (s, 1H), 16.64 ppm (s,
tronic circular dichroism (ECD) rotatory strength values of the dinu-
clear complexes were computed with time dependent density
[27,28]
functional theory (TDDFT)
as implemented in Gaussian 09 se-
lecting thirty singlet to singlet transitions in an all electron single
point calculation. The computed intensities were broadened by
a Gaussian function to be comparable to the experimentally deter-
mined spectrum. For the tetranuclear complexes, the calculation of
ECD spectra in Gaussian 09 was exceedingly demanding, as it in-
volves a very large number of excitations, so it was opted to com-
1
3
H); C NMR (125 MHz, CDCl ): d=10.3, 10.6, 10.7, 23.3, 23.5, 23.6,
3
9.3, 29.8, 31.1, 31.3, 31.4, 34.1, 35.0, 35.4, 118.2, 118.5, 119.1, 122.0,
23.6, 125.2, 126.3, 126.7, 127.6, 128.8, 128.2, 128.6, 128.7, 128.8,
28.9, 129.6, 131.5, 134.5, 134.6, 134.9, 135.6, 135.8, 136.0, 137.4,
37.6, 138.7, 139.6, 142.1, 155.6, 156.2, 157.3, 159.7, 160.2, 162.8,
75.9 ppm; HRMS (ESI+, MeOH): m/z calcd for C H N O :
[29]
pute these ECD transitions with the ADF
program, in which
78
91
2
6
1
151.6872; found: 1151.6850.
a single-point calculation was performed on the previously opti-
mized ONIOM geometry. A double-zeta basis set was employed on
all the light atoms while employing a triple-zeta basis set on zinc.
One advantage in favor of expediting this demanding calculation
was the inclusion of [He] and [Ne] frozen cores on the light ele-
ments (apart from hydrogen) and zinc, respectively. The basis sets
were further augmented with one polarization d function for C, N,
and O and a p function for Zn. A total of three hundred singlet-to-
singlet excitations were calculated to reproduce the excitation
spectra of the tetranuclear zinc complexes. The GGA class BLYP
functional was employed rather than the aforementioned B3LYP
used in Gaussian to eschew the computation of exact exchange in-
tegrals.
5
-Mono-(4,6-di-tert-butylphenolsalphen)calix[4]arene zinc com-
plex (2): Under an argon atmosphere, precursor compound C-2
100 mg, 0.086 mmol) was dissolved in dry THF (10 mL). A solution
(
of ZnEt (1m, 0.09 mL, 0.09 mmol) was then added dropwise and
the mixture was further stirred for 4 h. The solvent was removed
2
by evaporation to afford 2 as a bright orange solid (yield: 99%).
1
H NMR (500 MHz, DMSO): d=0.96 (t, J=7.5 Hz, 6H), 0.99–1.05 (m,
1
3
7
2
5H), 1.39 (s, 9H), 1.52 (s, 9H), 1.87 (dt, J=7.3 Hz; 14.3 Hz, 8H),
.14–3.24 (m, 4H), 3.70–3.88 (m, 4H), 4.30–4.42 (m, 4H), 6.04 (t, J=
.7 Hz, 1H), 6.33 (d, J=7.5 Hz, 2H), 6.57 (s, 2H), 6.68 (t, J=7.3 Hz,
H), 6.76–6.88 (m, 6H), 6.96 (s, 1H), 7.03–7.42 (m, 14H), 8.88 ppm
1
3
(
s, 1H); C NMR (125 MHz, DMSO): d=10.2, 10.4, 10.5, 22.8, 22.9,
2
3
1
1
1
1
1
3.0, 29.4, 29.5, 29.7, 30.2, 30.4, 30.7, 31.0, 31.1, 33.5, 34.6, 34.9,
5.0, 35.4, 76.3, 116.4, 118.9, 119.1, 121.5, 121.6, 121.8, 124.6, 124.7,
25.2, 125.3, 125.7, 126.5, 127.5, 128.0, 128.2, 128.3, 128.9, 129.7,
31.3, 131.8, 134.2, 134.4, 134.6, 135.1, 136.2, 137.8, 139.9, 140.0,
41.0, 154.3, 155.8, 155.9, 156.3, 156.6, 162.6, 170.9, 171.0,
74.0 ppm; HRMS (MALDI+, dctb): m/z calcd for C H N O Zn:
Acknowledgements
We thank ICIQ, ICREA, and the Spanish Ministerio de Economꢀa
y Competitividad (MINECO) through projects CTQ-2014–60419-
R and CTQ2014–52824-R, and the Severo Ochoa Excellence Ac-
creditation 2014–2018 through project SEV-2013–0319. We
also thank AGAUR for support through 2014-SGR-409. Dr.
Noemꢀ Cabello, Sofꢀa Arnal, and Vanessa Martꢀnez are acknowl-
edged for the mass analyses, and Dr. Gemma Aragay for help
with the binding studies and data interpretation. N.A.G.B.
gratefully acknowledges the COFUND grant 291787-ICIQ-IPMP
for financial support.
78
88
2
6
212.5934; found: 1212.5929.
Titration studies: To determinate K , a UV/Vis spectroscopy was
m
carried out on mono-[Zn(salphen)]–calix[4]arene complex
Scheme 1) as a reference and benzylamine as the titrant (see the
Supporting Information for more details). The titration data was
2
(
[19]
imported to SPECFIT/32
thus determined. Fluorescence spectra were also recorded (to de-
termine K ) by using a Fluorolog Horiba Jobin Yvon Spectropho-
tometer. To record the fluorescence spectra of compound 1, an ex-
citation wavelength of l=416 nm was used. This titration data
was imported to SPECFIT/32 and the constant K , using the previ-
ously determined K , was calculated. The constant K was deter-
mined at 1.585ꢁ10 m .
and the association constant Km was
2
,1
2,1
Keywords: calixarenes · chirality transfer · encapsulation ·
host–guest systems · salens
m
11
2,1
ꢀ2
[
[
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[
21]
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(
Figure S42). The high layer was described with the density func-
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as:
E(ONIOM2)=Ehigh layer (subsystem)+Elow layer (full system)ꢀE
low layer
(
subsystem)- The geometries were optimized without any con-
straints until the default convergence criteria were met. The elec-
&
&
Chem. Eur. J. 2015, 21, 1 – 8
www.chemeurj.org
6
ꢂ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
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V. P. Osinga, S. Patchkovskii, P. H. T. Philipsen, D. Post, C. C. Pye, W. Rave-
nek, P. Ros, P. R. T. Schipper, G. Schreckenbach, J. G. Snijders, M. Sola, M.
Swart, D. Swerhone, G. te Velde, P. Vernooijs, L. Versluis, O. Visser, F.
Wang, E. van Wezenbeek, G. Wiesenekker, S. K. Wolff, T. K. Woo, A. L. Ya-
kovlev, T. Ziegler, ADF, revision ADF-2013.01, http://www.scm.com, Sci-
entific Computing and Modelling NV: Amsterdam, the Netherlands,
Therefore H NMR studies were conducted in [D
6
]acetone, despite the
limited solubility of 1 in this solvent. See also: S. J. Wezenberg, E. C. Es-
cudero-Adꢄn, J. Benet-Buchholz, A. W. Kleij, Org. Lett. 2008, 10, 3311–
3314.
[
[
[
11] The (M,M) and (P,P) designations stand for the chiral conformations of
both biphenyl units in 1 upon binding to chiral diamine a. Both (M,P)
and (P,M) isomers of 1 are meso and should not give any signal in the
CD experiments.
12] The fact that no Cotton effects were observed for any of the substrates
a–l in the presence of mononuclear complex 2 suggests that ditopic
binding/coordination of the diamine substrate is requisite for efficient
chirality transfer.
2
013.
13] a) A. W. Kleij, D. M. Tooke, M. Kuil, M. Lutz, A. L. Spek, J. N. H. Reek,
Chem. Eur. J. 2005, 11, 4743–4750; b) S. J. Wezenberg, E. C. Escudero-
Adꢄn, J. Benet-Buchholz, A. W. Kleij, Inorg. Chem. 2008, 47, 2925–2927;
Received: January 26, 2015
Published online on && &&, 0000
Chem. Eur. J. 2015, 21, 1 – 8
www.chemeurj.org
7
ꢂ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
The host with the most: A calix[4]arene
functionalized with two [Zn(salphen)]
complexes shows highly effective chiral-
ity transfer effects in the presence of
chiral diamines. The operating modus of
the system involves a unique encapsula-
tion of the diamine guest. This calixar-
ene–salphen hybrid host holds promise
for the determination of the absolute
configuration and ee of diamines.
&
Host–Guest Systems
L. Martꢀnez-Rodrꢀguez, N. A. G. Bandeira,
C. Bo, A. W. Kleij*
&
& – &&
Highly Efficient Chirality Transfer from
Diamines Encapsulated within a Self-
Assembled Calixarene–Salen Host
&
&
Chem. Eur. J. 2015, 21, 1 – 8
www.chemeurj.org
8
ꢂ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!