Synthesis of calix[4]arene-Cryptand hybrid systems: A new generation of hosts for metal ions and molecules

Article abstract of DOI:10.1055/s-1998-1961

A Cryptand with derivatizable secondary amino nitrogens has been successfully coupled to the lower rim of a calix[4]arene through different spacer units.

Full text of DOI:10.1055/s-1998-1961

December 1998
SYNLETT
1331
Synthesis of Calix[4]arene-Cryptand Hybrid Systems: A New Generation of Hosts for Metal
Ions and Molecules
*
Prasun Bandyopadhyay and Parimal K. Bharadwaj
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
Fax: 91 512 590007; email: pkb@iitk.ernet.in
Received 12 August 1998
Abstract: A Cryptand with derivatizable secondary amino nitrogens
has been successfully coupled to the lower rim of a calix[4]arene
through different spacer units.
Calixarenes as hosts are an important class of compounds in
1,2
supramolecular chemistry . Both the upper and the lower rim of
calixarenes have been substituted to have molecules endowed with
selective host-guest chemistry. For example, the lower rim has been
3
4
transformed to have calix-mono-crowns or calix-bis-crowns which
5
have a high selectivity towards alkali cations. Azamacrocycles and
porphyrins have also been attached to impart specific properties to
calixarenes. Besides, reports on pendant phosphino- , bipyridyl- , and
thioether- substituted calixarenes are also available. A cryptand unit
6
7
8
8
Reagents and conditions:(i) Br(CH ) COOEt, K CO , acetone, N ,
2 n
2
3
2
reflux, 15h (ii) KOH, EtOH, H O, reflux, 2h (iii) SOCl , benzene,
reflux, 2h
has been built around the lower rim of calix[4]arene to have a
calixcryptand . Surprisingly, no report is available in the literature
2
2
9
where a cryptand is attached to a calixarene through spacer units. We
became interested in the synthesis of such systems for more than one
reason. These systems can act as multi-site ligands bearing potential
binding sites for transition metals, alkali/alkaline-earth metals and
organic fragments as characteristics of both the calixarene and the
cryptand units are built into one host molecule (Figure 1). Such systems
can be useful in having not only heterometallic complexes but can also
Scheme 1
13
The hybrid systems 8 and 9 were synthesized (Scheme 2 ) by treating
the cryptand
presence of Et N as base under an argon atmosphere. The isolated pale
yellow solid was purified by recrystallization from methanol.
14
with 6 and 7 respectively in dry dichloromethane in
3
Both 8 and 9 readily react with copper(II)-as well as nickel(II)-
perchlorate salts in dichloromethane at RT forming 1:1 complexes. The
Cu(II) complex in either case was green in color and showed ligand-
field transitions at 670 nm and 805 nm. The EPR spectrum showed a
broad signal (g =2.07) in the solid state at 298 K which becomes
av
sharper at 77 K without revealing any fine structure. In MeOH (ca. 1×
-3
10 M) at 298 K, an axial spectrum was obtained which changed to a
broad signal upon cooling to 77 K. The purple nickel(II) complex in
acetonitrile exhibited two weak ligand-field bands at 955 and 570 nm.
15
The spectral characteristics were reminiscent of those obtained on the
Cu(II)- and Ni(II)-cryptates thus revealing the fact that both the
transition metal ions were bonded inside the N end of the cavity of the
4
cryptand and not bonded to the calixarene moiety. Further complexation
with alkali metal ions which are expected to be bonded to the calixarene
unit are in progress.
In summary, we have reported two new hybrid systems which can be
synthesized easily. The yields are high in both the cases. Currently our
efforts are to apply different strategies to obtain hybrid systems through
both the lower and upper rims of calix[4]arene with different types of
spacer units to modulate the behavior of the hosts thus formed. Efforts
are also on to derivatize these molecules to get a new generation of
amphiphiles.
Figure 1
be made useful in having photonic devices with complex logics which
are otherwise not possible with either unit. Moreover, novel amphiphilic
molecules can also be envisaged which can be potentially useful in a
number of areas like photoinduced charge separation, drug-delivery,
synthetic vesicles/micelles, new generation Langmuir-Blodgett film etc.
Acknowledgement
Synthesis of the molecules were achieved in several stages. p-Tert-
butylcalix[4]arene (1) was converted to either 1,3-distal diester (2) or
Financial support from the Department of Science and Technology, New
Delhi, India (No. SP/S1/F-08/96 to PKB) is gratefully acknowledged.
PB wishes to thank the UGC for a fellowship.
10
1,3-distal diester (3) following slight modification of the published
11
procedure . Compounds 2 and 3 were hydrolyzed to form the diacids 4
and 5 in ~95% yield. The diacids were converted to the corresponding
acid chlorides 6 and 7 by refluxing with SOCl in benzene for 2h
2
12
followed by usual work-up (Scheme 1).

1332
LETTERS
SYNLETT
8.
9.
Beer, P. D.; Chen, Z.; Goulden, A.; Grieve, A.; Hesek, D.;
Szemes, F.; Wear, T. J. Chem. Soc. Chem. Commun. 1994, 1269.
Beer, P. D.; Martin, J. P.; Drew, M. G. B. Tetrahedron. 1992, 48,
9917.
10. Gutsche, C. D.; Iqbal, M. Org. Synth. 1990, 68, 234.
11. Collins, E. M.; McKervey, M. A.; Madigan, E.; Moran, M. B.;
Owens, M.; Ferguson, G.; Harris, S. J. J. Chem. Soc. Perkin Trans.
I. 1991, 3177.
12. The spectroscopic data collected on 2, 4 and 6 were found to be
o
same as reported. Analytical data of compound 3: m.p. 157 C.
1
H-NMR (80 MHz, CDCl , ppm) δ 0.99(s,18H), 1.12(s,18H),
3
1.30(t,6H), 3.20(d,4H), 4.70(m,12H), 6.91(s,4H), 7.11(s,4H),
o
1
7.12(s,2H); Analytical data of 5: m.p. 205 C (decomposed). H-
NMR (80 MHz, CDCl , ppm) 1.00(s,18H), 1.30(s,18H),
3
3.40(d,4H), 4.50(m,16H), 6.90(s,4H), 7.10(s,4H), 7.20(s,4H). All
new products gave satisfactory analytical elemental analysis data.
Compound 7 was unstable at room temperature, so it was used for
further reaction immediately without characterization.
13. Experimental Procedure: In a typical synthesis, the cryptand (0.25
mmol, 0.140g) was dissolved in 25 ml dry dichloromethane and to
it was added triethylamine (0.49 mmol, 0.070 ml) with constant
o
stirring at room temperature. The mixture was cooled to 0 C in an
ice-salt bath. To this mixture, a solution of 6 and 7 (0.25 ml) in 25
ml dry dichloromethane was added dropwise over a period of 1h
under argon atmosphere with constant stirring while maintaining
o
the temperature at 0 C. After the addition was complete, the
solution was allowed to warm up to room temperature and kept on
stirring for another 21h. It was then filtered and the solvent was
evaporated to almost dryness. The residue was shaken with 40 ml
of cold water. The desired compound was extracted from the
Scheme 2
aqueous medium with CHCl . The CHCl layer after drying over
3
3
anhydrous Na SO was evaporated completely to obtain a light
2
4
References and Notes
yellow solid which was recrystallized from methanol to get pure 8
1.
(a) Vicens, J.; Bohmer, V. Calixarene a Versatile Class of
o
1
and 9 in over 55% yield. Analytical data for 8: m.p. 130 C; H-
Macrocyclic Compounds; Kluwer Academic Publishers;
Drodrecht, 1991. (b) Gutsche, C. D. Calixarenes, Monograms in
Supramolecular Chemistry; Stodart, J.F., Ed.; The Royal Society
of Chemistry: London, 1989; Vol. 1. (c) Bohmer. V. Angew.
Chem., Int. Ed. Engl. 1995, 34, 713 and references there in.
NMR (300 MHz, CDCl , ppm) δ 0.97 (s,18H); 1.11 (s,18H); 2.49
3
(s,6H); 3.30 (t,14H); 3.73 (s,6H); 4.19 (m,10H); 7.09 (m,20H);
13
C-NMR (21 MHz, CDCl , ppm) δ 31.78, 32.79, 48.60, 54.97,
3
55.20, 67.74, 75.64, 78.79, 111.59, 120.98, 127.16, 128.94,
+
-
131.63, 157.33; FAB-mass: m/z=1289 (8 ); IR (KBr): 1600 cm
2.
3.
(a) Haino, T.; Yamada, K.; Fukuzawa, Y. Synlett 1997, 673. (b)
Dubberley, S. R.; Blake, A. J.; Mountford, P. Chem. Commun.
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Lett. 1996, 37, 6315.
1
(s,br, C=O stretching); Found: C, 75.42; H, 7.12; N, 5.41.
N O requires C, 75.49; H, 7.90; N, 5.43. Analytical data
for 9: m.p. 80 C; H-NMR (300 MHz, CDCl , ppm) δ 0.99
C
H
81 101
5 9
o
1
3
(s,18H); 1.31 (s,18H); 2.68 (m,12H); 3.30 (t,14H); 3.73 (s,6H);
13
Reinhoudt, D. N.; Dijkstra, P. J; in ‘t Veld, P. J. A.; Bugge, K. E.;
Harkema, S.; Ungaro, R.; Ghidini, E. J. Am. Chem. Soc. 1987,
109, 4761.
4.18 (m,18H); 7.18 (m,20H); C-NMR (21 MHz, CDCl , ppm) δ
3
31.67, 32.81, 44.15, 47.35, 48.84, 54.68, 55.14, 67.74, 75.58,
78.79, 111.59, 120.99, 127.68, 128.99, 131.64, 157.28; FAB-
+
-1
mass: m/z = 1344 (9 ); IR (KBr): 1600 cm (s,br, C=O
4.
5.
Ghidini, E.; Ugozzoli, F.; Ungaro, R.; Harkema, S.; Al-Fald, A.;
Reinhoudt, D. N. J. Am. Chem. Soc. 1990, 112, 6979.
stretching); Found: C, 75.86; H, 8.19; N, 5.19. C
H
N O
85 109 5 9
requires C, 75.90; H, 8.17; N, 5.21.
Beer, P. D.; Drew, M. G. B.; Leeson, P. B.; Lyssenko, K.; Ogden,
M. I. J. Chem. Soc. Chem. Commun. 1995, 929.
14. Ragunathanan, K. G.; Bharadwaj, P. K. Tetrahedron Lett., 1992,
33, 7582.
6.
7.
Millbradt, R.; Weiss, J. Tetrahedron Lett. 1995, 36, 2999.
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935.