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Journal of Chemical Crystallography (JOCC) PP1285-jocc-490920 July 9, 2004 3:54 Style file version Nov. 07, 2000

Journal of Chemical Crystallography, Vol. 34, No. 7, July 2004 (C© 2004)

X-ray crystal and molecular structure of upper rimmonoformylated calix[4]arene system

Vandana Arora,(1) H.M. Chawla,(1)∗ and Geeta Hundal(2)∗

Received March 28, 2004

Selective formylation under controlled conditions leads to the formation of a mono-formylated compound 11-formyl-25,27-bis(ethoxycarbonylmethoxy)-calix[4]arene (1).The spectroscopic results indicated that the calix[4]arene is present in a cone conforma-tion. The crystal and molecular structure of (1) has been determined by X-ray diffrac-tion methods. The crystal data are monoclinic, space groupP21/c, M = 624.66, a =10.341(1),b = 15.176(1),c = 20.121(1) A, β = 91.90◦(1), V = 3156.0(4) A3, Z = 4,Dc = 1.315 g cm−3. The structure confirms the cone conformation for the molecule in thesolid state as well.

KEY WORDS: Calix[4]arene; monoformylation; crystal structure; H-bonding.

Introduction

The interest in calix[4]arene chemistry israpidly increasing because its derivatives can forminclusion complexes with cations or with neutralmolecules.1 The parentp-tert-butylcalix[4]arenecontains two interesting substructures. At thelower rim four hydroxyl groups are present invery close proximity; these can be used for cationbinding2 and transport.3 The upper rim containsa hydrophobic cavity that is potentially able tocomplex neutral substrates. Surprisingly, only alimited number of complexes are described withhydrophobic organic substrates complexed in theupper rim cavity. Except for some complexes inthe solid state4 and the complexes in water based

(1) Department of Chemistry, Indian Institute of Technology, NewDelhi, India.

(2) Department of Chemistry, Guru Nanak Dev University, Amritsar143005, Punjab, India.∗ To whom correspondence should be addressed; e-mail:

geetahundal@yahoo.com.

on hydrophobic and electrostatic forces,5 only afew amines are known to complex in the upperrim cavity in solution.6 The reason is the lack ofappropriate functionalization at the upper rim. Al-though several short synthetic routes have beendeveloped to introduce functional groups into thephenyl rings7 they all lead to tetra-substitutedcalix[4]arenes, having the same substituent at allthe para positions. In principle, it would be desir-able to have individual control of the para substi-tution of the four aromatic rings. Numerous re-ports have been published to obtain selectively1,3-disubstituted calixarenes which requires firstthe easier diametrical 1,3-dialkylation of the phe-nolic oxygen atoms at the lower rim.8 How-ever, this strategy when applied to obtain mono-substituted calixarenes resulted in poor yields.9

Keeping this in view, we exploited the possi-bility of obtaining monoformylated calixareneby varying the reaction parameters. Introductionof the formyl group at the upper rim providesan important intermediate that can be employed

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466 Arora, Chawla, and Hundal

Scheme 1

for a variety of chemical transformations: diol,chloromethyl, carboxylic acid,10etc. Monoformy-lated calixarene will thus provide a potential in-termediate for the synthesis of calixarenes con-taining a single substituent at the “upper rim.”Here we report the X-ray crystal structure of onesuch monoformylated product, 11-formyl-25,27-bis(ethoxycarbonylmethoxy)-calix[4]arene (1), toconfirm its structure and justify its cone confor-mation in the solid state.

Table 1. Crystal Data

Empirical formula C37H36O9

Formula weight 624.686Temperature 293(2) KWavelength 1.5418ACrystal system MonoclinicSpace group P21/ca = 10.341(1)A α = 90.0b = 15.176(1)A β = 91.90(1)◦

c = 20.121(1)A γ = 90.0V = 3156.0(4) A3 Z = 4Density (calc.) 1.3147 m gm−3

µ 7.714 cm−1

Crystal size 0.2× 0.2× 0.1 mmRange for data collection (θ ) 3.65 to 64.73◦Reflections collected 5374Independent reflections 5208Observed reflections 3872Refinement method Full-matrix least-squares onF2

Data/restraints/parameters 3872/0/416Goodness of fit onF2 1.023Final R indices [I > 2σ (I )] R1= 0.1139,wR2= 0.2761R indices (all data) R1= 0.1462,wR2= 0.2993Largest diff. peak and hole 0.433 and−0.419 eA−3

Deposition number CCDC 203642

Experimental

The synthesis, crystallisation, and spec-troscopic characterization of the compound

Table 2. Atomic Coordinates (×104) and Equivalent IsotropicDisplacement Parameters (A2 × 103) for 1

x y z U(eq)

O1 1754(4) 7712(3) 1135(2) 76(1)O2 766(5) 11829(3) 1460(3) 99(2)O3 2778(4) 6808(2) 53(2) 64(1)O4 159(5) 6690(3) −132(2) 93(2)O5 404(5) 5886(4) −1058(2) 99(2)O6 4202(4) 6281(3) 1353(2) 72(1)O7 2690(4) 6831(2) 2409(2) 64(1)O8 2652(5) 5051(3) 2374(2) 90(1)O9 2059(5) 4992(3) 3425(2) 92(2)C1 1400(6) 9045(4) 1679(2) 61(1)C2 1209(5) 9934(4) 1655(3) 65(1)C3 1229(5) 10408(4) 1056(3) 65(1)C4 1469(5) 9932(4) 479(3) 65(2)C5 1664(5) 039(4) 472(2) 59(1)C6 1609(5) 8589(3) 1078(2) 58(1)C7 1949(6) 8568(4) −170(2) 67(2)C8 3344(5) 8285(4) −213(2) 60(1)C9 4274(6) 8891(4) −385(3) 70(2)C10 5566(6) 8638(4) −412(3) 72(2)C11 5925(6) 7799(4) −240(2) 68(2)C12 5028(5) 7162(4) −58(2) 58(1)C13 3734(5) 7435(4) −87(2) 59(1)C14 5465(6) 6271(4) 184(2) 66(2)C15 6193(6) 6356(4) 851(3) 62(1)C16 7520(7) 6434(4) 901(3) 80(2)C17 8165(6) 6570(5) 1507(4) 85(2)C18 7466(6) 6627(4) 2075(3) 76(2)C19 6137(6) 6540(3) 2057(3) 63(1)C20 5497(5) 6390(4) 1440(2) 59(1)C21 5387(6) 6593(4) 2696(2) 67(2)C22 4703(6) 7470(4) 2783(2) 63(1)C23 5376(7) 8204(4) 3026(3) 73(2)C24 4780(7) 9008(4) 3062(3) 76(2)C25 3519(7) 9104(4) 2842(2) 71(2)C26 2803(6) 8403(3) 2601(2) 61(1)C27 3403(6) 7577(3) 2606(2) 58(1)C28 1426(6) 8539(4) 2334(2) 67(2)C29 1011(6) 11336(4) 998(4) 79(2)C30 2293(6) 6351(4) −527(3) 75(2)C31 822(6) 6351(4) −543(3) 71(2)C32 −1029(8) 5845(6) −1174(4) 109(3)C33 −1473(9) 5078(6) −828(4) 113(3)C34 2173(7) 6377(4) 2963(3) 73(2)C35 2308(6) 5419(4) 2870(3) 66(2)C36 2222(11) 4044(5) 3425(4) 115(3)C37 3592(12) 3840(5) 3621(4) 136(4)

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Monoformylated calix[4]arene system 467

Fig. 1. ORTEP diagram of (1) showing ellipsoids with 30% probability. Thehydrogens have been removed for clarity.

11-formyl-25,27-bis(ethoxycarbonylmethoxy)-calix[4]arene (1) has already been reported.11

X-ray crystal data were collected on a Seifertsingle crystal diffractometer. The relevant crystaldata and refinement parameters are given inTable 1. The structure was solved by directmethods and refined by full matrix least-squarestechniques onF2 using SHELXTL.12 All thenonhydrogen atoms were refined anisotropically.The hydrogens were fixed geometrically as ridingatoms with a displacement parameter equal to 1.2(CH, CH2) or 1.5 (CH3) times that of the parentatom. No absorption correction was applied.The structure was refined toR1 = 0.1139,wR2 = 0.2761, for observed reflections and 416parameters. TheR-factors are on the higher sidebecause of poor quality of the crystals. Torsionangles and H-bonding were calculated by usingPARST.13 Crystal data have been deposited with

the Cambridge Crystallographic Data Center,under reference CCDC 203642. The fractionalcoordinates and equivalent isotropic thermalparameters are given in Table 2.

Results and discussion

The final structure of the compound isshown in Fig. 1. All the bond distances andbond angles are normal. The torsion anglesχ and ϕ around ArCH2 bonds about C7,C14, C21, and C28 as defined in literature14

are 106.4(6)◦, −79.7(6)◦, 66.7(7)◦, −93.6(6)◦,103.1(6)◦,−80.8(7)◦, 70.1(7)◦, and−96.4(6)◦, re-spectively. This alternate± sequence is charac-teristic for the cone conformation and a deviationfrom ±90◦ indicates its deformation from a per-fect open cone conformation as found inp-tert-butylcalix[4]arene: toluene4a complex (LBC). All

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468 Arora, Chawla, and Hundal

four aromatic rings are planar with a maximumdeviation of 0.03A from a least square plane.The connecting methylene C atoms C7, C14, C21,and C28 form an approximate plane where al-ternate C atoms lie±0.17 and±0.18 A aboveand below the plane. The interplanar angles foundbetween this plane and the rings A (C1–C6),B (C8–C13), C (C15–C20), and D (C22–C27) are137.7(1)◦, 106.2(1)◦, 134.2(2)◦, and 109.1(1)◦, re-spectively, as compared to 120◦ found in LBCwhere there is no substitution at the lower rim.The interplanar angles between the pairs AC andBD are 91.9(2)◦ and 35.3(2)◦, respectively. ThusB and D are almost parallel whereas A and Care perpendicular to each other. Similarly A isperpendicular to B (91.9◦(2)) and D(101.9◦(2))but C is perpendicular to B (97.5◦(2)) and

Fig. 2.Showing packing of the molecule and intramolecular O· · ·O H-bonding.

parallel to D (134.2◦(2)). Both the ethoxycar-bonylmethoxy groups are having similar ex-tended conformations. Both O3C30 C31 O4and O7 C34 C35 O8 arecis thus making boththe carbonyl groupsendowith respect to the calixcavity.

The H-bonding calculations show seven in-tramoleculal and five intermolecular H-bondinginteractions some of which have been shown inthe packing diagram (Fig. 2). There is a strong in-tramolecular H-bond between the hydroxyl oxy-gens O1 and O6 and ether oxygens O3 andO7 (Table 3). The O1 atom is acting as a H-bond donor towards O3 and O6 is donating H-bond to O7. This intramolecular H-bonding is thereason of forming a cone conformation for thecalix[4]arene. In the absence of this interaction

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Monoformylated calix[4]arene system 469

Table 3. Showing H-Bonding Interactions

S. no. X H· · ·Y X · · ·Y A H· · ·Y A 6 X H· · ·Y (◦)

1. O1 H1A· · ·O3 2.810(5) 2.0 1582. O6 H6A· · ·O7 2.806(4) 2.0 1573. C7 H1B· · ·O3 2.838(8) 2.4 1064. C14 H14B· · ·O3 2.9000(7) 2.5 1075. C7 H7B· · ·O4 3.400(8) 2.4 1706. C21 H21A· · ·O7 2.853(7) 2.4 1057. C21 H21A· · ·O8 3.711(8) 2.8 1638. C16 H16A· · ·O4a 3.506(8) 2.6 1519. C18 H18A· · ·O2b 3.430(8) 2.5 173

10. C28 H28B· · ·O5c 3.546(7) 2.7 14811. C32 H32B· · ·O8d 3.197(9) 2.4 13912. C34 H34A· · ·O2e 3.359(9) 2.4 158

ax + 1,+y,+z.b−x + 1,+y− 0.5,−z+ 0.5.cx,−y+ 0.5+ 1,+z+ 0.5.d−x,−y+ 2,−z.ex,−y+ 1,−z.

other conformations become more probable as hasbeen seen in the calix[4]arenes systems where allfour hydroxyl groups at the lower rim have beensubstituted by methoxy groups.15 In those threecalix[4]arenes systems there were various sub-stituents at the upper rim like NO2 groups, Br,and COCH3 but all of them had methoxy groups atthe lower rim. The absence of hydroxyl hydrogensto form intramolecular H-bonding resulted in aninward flattened partial cone conformation16 forall of these molecules. The O3 atom is also in-tramolecularly H-bonded17 to methylene C7 andC14 whereas O7 is accepting a H-bond frommethylene C21. The carbonyl oxygens O4 andO8 are accepting intramolecular H-bonds frombridgehead methylene carbons C7 and C21, re-spectively, which are facilitated by the endo natureof these carbonyl groups. At the same time theseare involved in the formation of two intermolecu-lar H-bonds, phenylene C16 and methylene C32,respectively. Thus both of these carbonyl groupsare acting as double H-bond acceptors and hencealso contributing to the formation of a cone con-formation of the molecules. The oxygen O2 ofthe aldehyde group is forming two intermolecu-

lar H-bonds with methylene C34 and phenyleneC18 coming from two different symmetry relatedmolecules. Noπ − π interactions were found inthe packing of the molecule.

Acknowledgments

G.H. is thankful to Prof. Martin Martinez-Ripoll from CSIC, Rocasolano, Serrano, Madrid(Spain), for kindly collecting the data on this crys-tal. V.A. is thankful to CSIR, New Delhi for theresearch fellowship and Department of Scienceand Technology for financial assistance.

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