Cite this: RSC Advances, 2013, 3, 5785

Received 10th January 2013,Accepted 19th February 2013

Ferrocenyl substituted calixarenes: synthesis, structureand properties3

DOI: 10.1039/c3ra00146f

www.rsc.org/advances

Rekha Sharma, Ramesh Margani, Shaikh M. Mobin and Rajneesh Misra*

A set of ferrocenyl substituted calix[4]arenes were designed and

synthesized by the Pd-catalyzed Sonogashira cross coupling

reaction. The photophysical and electrochemical data show a

substantial electronic interaction between the ferrocene unit and

the calixarene core. Calixarenes 5a–5c are non-emissive in nature

and the absorption maxima of 5a–5c exhibit a red shifted

absorption. The calixarene core exhibits a cone conformation,

which was confirmed by 1H NMR and X-ray crystallography. The

crystal packing of 5a exhibits a C–H–p bonded 2-D network.

The calixarene molecular system has been widely explored in ion-pair recognition and in non-linear optics (NLO).1–7, The calixarenescaffold can be selectively functionalized at the phenolic OHgroups (lower rim) as well as at the para positions of the phenolrings (upper rim). Therefore substituting the donor group at theupper rim will result in a donor–acceptor (D–A) system.7,8,17-23 Theliterature reveals that calixarenes with an extended p-conjugationexhibit a superior NLO performance.9–11 We were interested inincorporating the donor group at the upper rim of the calixarenescaffold and exploring its properties. Ferrocene is a redox activestrong donor.12–16 In this report, we have incorporated theferrocenyl groups at the para position of the calixarene scaffoldand explored the effect of the ferrocene unit on the photophysical,structural, and electrochemical behavior of calixarenes.

Ferrocenyl substituted calixarenes, 5a–5c, were synthesized bythe Pd-catalyzed Sonogashira cross coupling reaction of tetraiodocalixarene, 4, with the corresponding ethynyl ferrocene.7,5

Tetraiodo calixarene, 4, was synthesized by a three step reactionsequence (Scheme 1). The reaction sequence involves: (a)debutylation of tert-butylcalix[4]arene, 1, in the presence of AlCl3and phenol;24 (b) alkylation of debutylated calix[4]arene, 2, withpropyl bromide in the presence of NaH and DMF;25 (c) iodination

of tetrapropoxy-calix[4]arene in the presence of iodine and silvertrifluoroacetate.26

Tetraiodo-calixarene, 4, was reacted with ethynylferrocene,4-ferrocenylphenylacetylene and 3-ferrocenylphenylacetylene,which resulted in calixarenes 5a–5c in 79%, 70% and 72% yields,respectively. Ferrocenyl calixarenes, 5a–5c, were well characterizedby 1H NMR, 13C NMR, and HRMS techniques. Compound 5a wasalso characterized by single crystal X-ray diffraction.

The literature reveals that calix[4]arene exists in four differentconformations, namely cone, partial-cone, 1,2-alternate and 1,3-alternate.7 Ferrocenyl substituted calixarenes, 5a–5c, were found tobe in the cone conformation. The cone conformation of thecalix[4]arene core was confirmed by 1H NMR and the conforma-tion of calixarene 5a was also confirmed by single crystal X-rayanalysis. The methylene bridge protons in the cone conformationappear as two sets of doublets at 4.42 and 3.16 ppm for 5a, at 4.38and 3.12 ppm for 5b and at 4.47 and 3.22 ppm for 5c. In addition,the 13C NMR spectra of compounds 5a–5c show the characteristicpeaks of methylene bridge carbons at ca. 31 ppm for the coneconformation.

Thermal stability is the significant requisite for practicalapplications of organic chromophores. The thermal properties offerrocenyl substituted calixarenes, 5a–5c, were evaluated usingthermogravimetric analysis (TGA) at a heating rate of 10 uC min21

under a nitrogen atmosphere (Fig. S13, see the ESI3). TGA resultsfor compounds 5a–5c show that a 10 wt.% loss in nitrogenatmosphere occurs from 330–430 uC. The trend in thermalstability follows the order 5b > 5c > 5a.

The UV-visible absorption spectra of all the compounds wererecorded in dichloromethane on a Cary-100 Bio UV-visiblespectrophotometer with a concentration of 1.0 6 1025 M atroom temperature. The cyclic voltammetric (CV) studies forcalixarenes 5a–5c were carried out with an electrochemical systemutilizing a three-electrode configuration consisting of a platinum(working) electrode, a platinum wire (auxiliary) electrode and anAg/Ag+ (reference) electrode. The experiments were performed indry dichloromethane with 0.1 M tetrabutylammoniumhexafluor-ophosphate (Bu4NPF6) as the supporting electrolyte at a concen-tration of 1.0 6 1024 M. The crystal structure was solved by direct

Department of Chemistry, Indian Institute of Technology Indore, 452017, India.

E-mail: rajneeshmisra@iiti.ac.in; Fax: +91 731 2361 482; Tel: +91 731 2438 710

3 Electronic supplementary information (ESI) available: General experimentalmethods, copies of 1H NMR and HRMS spectra of all the new compounds andcrystallographic information file (CIF) for compound 5a. CCDC 903776. For the ESIand crystallographic data in CIF or other electronic format see DOI: 10.1039/c3ra00146f

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methods using SHELXS-97 and were refined by full matrix least-squares with SHELXL-97 refining on F2.

The single crystal of ferrocenyl calixarene 5a was obtained by aslow diffusion of methanol into a chloroform solution at roomtemperature. The single crystal X-ray structural analysis confirmedthe conical shape of ferrocenyl calixarene 5a, which crystallizes inthe orthorhombic Pcab space group. The crystal structure of 5a isshown in Fig. 1 and the important crystallographic parameters arelisted in Table S1 (see the ESI3).

The dihedral angle between the plane of phenyl rings of thecalixarene core and the plane of cyclopentadienyl rings of differentferrocenyl subunits is 23.71u, 41.20u, 13.03u and 70.39u, respec-tively. The cyclopentadienyl rings of ferrocene Fe1 show eclipsedconformations, ferrocene Fe4 shows a staggered conformationand ferrocenes Fe2 and Fe3 show eclipsed skew conformations(Fig. 1).

The crystal packing diagram of the ferrocenyl calixarene 5areveals intermolecular C–H–p interactions between the twoadjacent molecules (Fig. 2). These C–H–p interactions are listed

in Table S2 (see the ESI3 for details). The crystal structure showsthat the two molecules are interconnected via C–H–p interactionsinvolving hydrogen H83 with the phenyl ring (C18, C13, C14, C16,C17, C15, 2.675 Å) of the calixarene core and hydrogen H26 withthe cyclopentadienyl ring (C80, C81, C82, C83, C79, 3.19 Å) of theferrocene ring. Another C–H–p interaction involves hydrogen H51with the cyclopentadienyl ring (C86, C87, C88, C84, C85, 3.597 Å)of the ferrocene ring, which leads to the formation of a 2-Dnetwork where all the alkyl groups are outwards and the ferrocenerings are arranged inwards (Fig. 2).

The electrochemical properties of ferrocenyl substitutedcalixarenes, 5a–5c, were explored by cyclic voltammetric analysis.The electrochemical data of 5a–5c are listed in Table 1 and arepresentative cyclic voltammogram is presented in Fig. 3. Thecyclic voltammograms of ferrocenyl substituted calixarenes, 5a–5c,exhibit one reversible oxidation wave of ferrocene–ferrocenium atE1/2 = 0.57 V, 0.51 V and 0.47 V, respectively.

From the CV it is very clear that the peak is a statistical averageof multiple ferrocene peaks which is responsible for the broadnessof the peak.31–33 The oxidation potential data of calixarenes 5a–5creveal that the oxidation of the ferrocene unit in calixarenes 5a–5cbecomes difficult compared to free ferrocene, which reflects thestrong electronic communication between the ferrocenyl unit andthe calixarene core in 5a–5c. Calixarene 5a shows the hardestoxidation compared to 5b and 5c, which indicates a maximumelectronic communication in calixarene 5a. The trend in theoxidation potential of the ferrocenyl moiety in the ferrocenylsubstituted calixarenes, 5a–5c, follows the order 5a > 5b > 5c.

The UV-visible absorption spectra of ferrocenyl substitutedcalixarenes, 5a–5c, were recorded in dichloromethane. Theabsorption spectrum is shown in Fig. 4 and the data are listedin Table 1. Ferrocenyl substituted calixarenes, 5a–5c, exhibit astrong absorption band between 263–311 nm, corresponding tothe pAp* transition,27 and a weak band at 435 nm correspondingto the d–d transition27 for the iron of ferrocene.

Scheme 1 Synthesis of ferrocenyl calixarenes, 5a–5c.

Fig. 1 Single crystal X-ray structure of compound 5a, (a) front view and (b) side view(the hydrogen atoms have been omitted for clarity).

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The absorption maxima of ferrocenyl substituted calixarenes,5a–5c, exhibit a red shifted absorption with a high molarextinction coefficient (e) as the conjugation length is enhanced.This reflects the effective electronic communication between theferrocenyl unit and the calixarene core in compounds 5a–5c. Incalixarene 5c the meta substituted ferrocene disrupts the extendedp-conjugation compared to 5b, therefore, a lower red shift isobserved for compound 5c.28 Ferrocenyl calixarenes, 5a–5c, arenon emissive in nature due to the fast non-radiative deactivationof the excited state with intramolecular charge transfers.29,30

Fig. 2 The supramolecular structure of compound 5a along the c axis. The secondary interactions are shown by dashed lines (the hydrogen atoms have been omitted forclarity).

Table 1 Photophysical and electrochemical data of ferrocenyl calixarenes, 5a–5c

Compound Photophysical dataa Electrochemical datab

lmax (nm)/e (M21 cm21) Eox (V)

Ferrocene — 0.465a 263 (130 000) 0.575b 311 (72 000) 0.515c 284 (226 000) 0.47

a Measured in dichloromethane at a 1.0 6 1025 M concentration.b Recorded by cyclic voltammetry using 1.0 6 1024 M solutions of5a–5c, containing a 0.1 M solution of Bu4NPF6 in DCM, at a 100 mVs21 scan rate vs. an Ag/Ag+ electrode.

Fig. 3 Cyclic voltammogram of 1.0 6 1024 M solutions of compound 5a in CH2Cl2containing 0.1 M Bu4NPF6 as the supporting electrolyte, recorded at a scan speed of100 mV s21.

Fig. 4 Electronic absorption spectra of compounds 5a–5c (1.0 6 1025 Mconcentration) recorded in dichloromethane.

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In summary, we have synthesized a series of ferrocenylsubstituted calixarenes by the Pd-catatalyzed Sonogashira cross-coupling reaction. The UV-visible absorption and electrochemicalstudies of these molecules show a strong electronic interaction.The study of the NLO properties of these molecules is currentlyongoing in our group.

Acknowledgements

The work was supported by DST and CSIR, Govt. of India, New Delhi.We gratefully acknowledge Sophisticated Instrumentation Centre(SIC), IIT Indore.

Notes and references

1 (a) C. D. Gutsche, Calixarenes, The Royal Society of Chemistry,Cambridge, UK, 1989; (b) A. Ikoda, T. Tsudera and S. Shinkai, J.Org. Chem., 2000, 112, 818.

2 W. Abraham, J. Inclusion Phenom. Macrocyclic Chem., 2002, 43,159–174.

3 L. Grubert, H. Hennig and W. Abraham, Tetrahedron, 2009, 65,5936–5944.

4 (a) D. M. Homden and C. Redshaw, Chem. Rev., 2008, 108,5086–5130; (b) S. E. Matthews, P. Schmitt, V. Felix, M. G.B. Drew and P. D. Beer, J. Am. Chem. Soc., 2000, 124, 1341.

5 (a) E. Kelderman, L. Derhaeg, G. J. T. Heesik, W. Verboom, J. F.J. Engbersen, N. F. Van Hulst, A. Persoons and D. N. Reinhoudt,Angew. Chem., Int. Ed. Engl., 1992, 31, 1075; (b) F. Vocanson,P. Seigle-Ferrand, R. Lamartine, A. Fort, A. W. Coleman,P. Shahgaldian, J. Mugnier and A. Zerroukhi, J. Mater. Chem.,2003, 1596.

6 (a) H. Lu, B. Yan and J. Liu, Inorg. Chem., 2009, 48, 3966–3975;(b) O. Sahin and M. Yilmaz, Tetrahedron, 2011, 67, 3501–3508.

7 (a) P. K. Lo and M. S. Wong, Sensors, 2008, 8, 5313–5335; (b) K.L. Chan, J. P. F. Lim, X. Yang, A. Dodabalapur, G. E. Jabbourand A. Sellinger, Chem. Commun., 2012, 48, 5106–5108.

8 B. Tomapatanaget and T. Tuntulani, Tetrahedron Lett., 2001, 42,8105–8109.

9 G. Hennrich, M. T. Murillo, P. Prados, K. Song, I. Asselberghs,K. Clays, A. persons, J. B. Buchholz and J. Mendoza, Chem.Commun., 2005, 2747–2749.

10 E. Kelderman, L. Derhaeg, W. Verboom, J. F. J. Engbersen,S. Harkema, A. Persoons and D. N. Reinhoudt, Supramol. Chem.,1993, 183.

11 P. J. A. Kenis, E. G. Kerver, B. H. M. Snellik-Rue, G. J.V. Hummel, S. Harkema, M. C. Flipse, R. H. Woundenberg, J. F.J. Engbersen and D. A. Reinhoudt, Eur. J. Org. Chem., 1998,1089.

12 (a) P. Gautam, B. Dhokale, V. Shukla, P. C. Singh, K. S. Bindraand R. Misra, J. Photochem. Photobiol., A, 2012, 239, 24–27; (b)R. Maragani, T. Jadhav, S. M. Mobin and R. Misra, Tetrahedron,2012, 68, 7302–7308; (c) B. Dhokale, P. Gautam, S. M. Mobinand R. Misra, Dalton Trans., 2013, 42, 1512–1518.

13 (a) P. Gautam, B. Dhokale, S. M. Mobin and R. Misra, RSC Adv.,2012, 2, 12105–12107; (b) R. Misra, P. Gautam, R. Sharma andM. S. Mobin, Tetrahedron Lett., 2013, 54, 381–383; (c)R. Margani, T. Jadhav, S. M. Mobin and R. Misra, RSC Adv.,2013, 3, 2889–2892; (d) T. Jadhav, R. Margani, S. M. Mobin andR. Misra, Dalton Trans., 2013, DOI: 10.1039/c3dt33065f.

14 P. V. Solntsev, K. L. Spurgin, J. R. Sabin, A. A. Heikal and V.N. Nemykin, Inorg. Chem., 2012, 51, 6537–6547.

15 V. N. Nemykin, E. A. Makarova, J. O. Grosland, G. R. Hadt andY. A. Koposov, Inorg. Chem., 2007, 46, 9591–9601.

16 M. L. H. Green, S. R. Marder, M. E. Thompson, J. A. Bandy,D. Bloor, P. V. Kolinsky and R. J. Jones, Nature, 1987, 330,360–362.

17 P. Webber, P. D. Beer, G. Z. Chen, V. Felix and M. G. Drew, J.Am. Chem. Soc., 2003, 125, 5774–5785.

18 I. Szymanska, H. Radecka, J. Radecki, P. A. Gale and C.N. Warriner, J. Electroanal. Chem., 2006, 591, 223–228.

19 N. L. Poul, B. Douziech, J. Zeitouny, G. Thiabaud, F. Conan,N. Cosquer, I. Jabin, O. Reinaud and Y. L. Mest, J. Am. Chem.Soc., 2009, 113, 17800–17807.

20 T. Shoji, J. Higashi, S. Ito, K. Toyota, T. Iwamoto and N. Morita,Eur. J. Org. Chem., 2009, 34, 5948–5952.

21 E. Metay, M. C. Duclos, S. Pellet-Rostaing, M. Lemaire, J. Schulz,R. Kannappan, C. Bucher, E. Saint-Aman and C. Chaix, Eur. J.Org. Chem., 2008, 25, 4304–4312.

22 A. J. Evans, S. E. Matthews, A. R. Cowley and P. D. Beer, DaltonTrans., 2003(24), 4644–4650.

23 P. D. Beer and E. Hayes, Coord. Chem. Rev., 2003, 240, 167–189.24 (a) D. C. Gutsche and K. C. Nam, J. Am. Chem. Soc., 1988, 110,

6153–6162; (b) M. A. Qazi, I. Qureshi and S. Memon, New J.Chem., 2010, 34, 2579–2586.

25 D. Alessandro, M. Alberto, S. Marie-Christine, C. Alessandro,S. Francesco and U. Rocco, Chem.–Eur. J., 1997, 3, 1774–1782.

26 A. Arturo, G. Giovanna, P. Andrea, S. Andrea and U. Franco, J.Org. Chem., 2001, 66, 8302–8308.

27 B. Shaabani and Z. Shaghaghi, Tetrahedron, 2010, 66, 3259–3264.28 R. Misra, R. Kumar, T. K. Chandrashekar and C. H. Suresh, J.

Am. Chem. Soc., 2006, 128, 16083–16091.29 (a) B. Dhokale, P. Gautam and R. Misra, Tetrahedron Lett., 2012,

53, 2352–2354; (b) J. Rochford and M. T. P. Rooney, Inorg.Chem., 2007, 46, 7247; (c) M. R. Rao, K. V. Pavan Kumar andM. Ravikanth, J. Organomet. Chem., 2010, 695, 863–869.

30 (a) S. Fery-Forgues and J. Delavaux-Nicot, J. Photochem. Photobiol.,A, 2000, 132, 137–159; (b) V. A. Nadtochenko, N. N. Denisov, V.Y. Gak, N. V. Abramova and N. M. Loim, Russ. Chem. Bull., 1999,148, 1900; (c) S. Barlow and S. R. Marder, Chem. Commun., 2000,1555–1562.

31 B. Tomapatanaget, T. Tuntulani and O. Chailapakul, Org. Lett.,2003, 5, 1539–1542.

32 F. Yang, Z. Liu, B. Hong and H. Guo, J. Inclusion Phenom.Macrocyclic Chem., 2012, 72, 183–188.

33 K. Dhanalakshmi and G. Sundararajan, J. Organomet. Chem.,2002, 645, 27–32.

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