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 supramolecular chemistry 1,2 . 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 transformed to have calix-mono-crowns 3 or calix-bis-crowns 4 which have a high selectivity towards alkali cations. Azamacrocycles 5 and porphyrins 6 have also been attached to impart specific properties to calixarenes. Besides, reports on pendant phosphino- 7 , bipyridyl- 8 , and thioether- substituted 8 calixarenes are also available. A cryptand unit has been built around the lower rim of calix[4]arene to have a calixcryptand 9 . Surprisingly, no report is available in the literature 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 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. Synthesis of the molecules were achieved in several stages. p-Tert- butylcalix[4]arene 10 (1) was converted to either 1,3-distal diester (2) or 1,3-distal diester (3) following slight modification of the published procedure 11 . 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 2 in benzene for 2h followed by usual work-up 12 (Scheme 1). The hybrid systems 8 and 9 were synthesized 13 (Scheme 2 ) by treating the cryptand 14 with 6 and 7 respectively in dry dichloromethane in presence of Et 3 N as base under an argon atmosphere. The isolated pale yellow solid was purified by recrystallization from methanol. 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 av =2.07) in the solid state at 298 K which becomes sharper at 77 K without revealing any fine structure. In MeOH (ca. 1× 10 -3 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. The spectral characteristics were reminiscent of those obtained 15 on the Cu(II)- and Ni(II)-cryptates thus revealing the fact that both the transition metal ions were bonded inside the N 4 end of the cavity of the 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. Acknowledgement 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. Figure 1 Reagents and conditions:(i) Br(CH 2 ) n COOEt, K 2 CO 3 , acetone, N 2 , reflux, 15h (ii) KOH, EtOH, H 2 O, reflux, 2h (iii) SOCl 2 , benzene, reflux, 2h Scheme 1 Downloaded by: University of Queensland. Copyrighted material.