7,11,15,28-Tetra­methyl-1,21,23,25-tetra­kis(2-phenyl­ethyl)resorcin[4]arene ethyl acetate clathrate

Michael G Mc Kay; Holger B Friedrich; Glenn E M Maguire

doi:10.1107/S160053680705711X

. 2007 Dec 6;64(Pt 1):o98. doi: 10.1107/S160053680705711X

7,11,15,28-Tetramethyl-1,21,23,25-tetrakis(2-phenylethyl)resorcin[4]arene ethyl acetate clathrate

Michael G Mc Kay ^a, Holger B Friedrich ^a, Glenn E M Maguire ^a,^*

PMCID: PMC2915052 PMID: 21200974

Abstract

The title compound, C₆₈H₆₄O₈·C₄H₈O₂, is a new resorcin[4]arene cavitand synthetic precursor, obtained by alkylation of a previously reported resorcin[4]arene. The additional alkyl bridges significantly rigidify the structure and enforce a ‘bowl’ shape on the molecular cavity. In the crystal structure, the molecule lies on a crystallographic mirror plane, and a single ethyl acetate molecule (also lying on the mirror plane) is present within the compound cavity, illustrating the host capabilities of the molecule.

Related literature

For related literature, see: Cram et al. (1988 ▶); Eisler et al. (2002 ▶); Friedrich et al. (2007 ▶); Piepers & Kellog (1978 ▶); Roman et al. (1999 ▶); Sebo et al. (2000 ▶).

Experimental

Crystal data

C₆₈H₆₄O₈·C₄H₈O₂
M _r = 1097.30
Orthorhombic,
a = 24.3288 (4) Å
b = 20.6279 (4) Å
c = 11.7828 (2) Å
V = 5913.22 (18) Å³
Z = 4
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 173 (2) K
0.39 × 0.27 × 0.19 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: none
49448 measured reflections
5981 independent reflections
3934 reflections with I > 2σ(I)
R _int = 0.062

Refinement

R[F ² > 2σ(F ²)] = 0.063
wR(F ²) = 0.209
S = 1.04
5981 reflections
455 parameters
131 restraints
H-atom parameters constrained
Δρ_max = 1.16 e Å⁻³
Δρ_min = −0.55 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: SAINT-NT (Bruker, 2005 ▶); data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL (Bruker, 1997 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680705711X/bi2251sup1.cif

e-64-00o98-sup1.cif^{(33.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053680705711X/bi2251Isup2.hkl

e-64-00o98-Isup2.hkl^{(287KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The financial support of the DST–NRF Centre of Excellence in Catalysis, c*change, is duly acknowledged. Our thanks go to Dr Manuel Fernandes at the University of the Witwatersrand for performing the data acquisition and structure solution.

supplementary crystallographic information

Comment

The title compound is obtained by alkylation of the hydroxyl groups of a resorcin[4]arene octol material whose structure has been previously reported (Friedrich et al., 2007). The alkylating agent, CH₂BrCl, results in the formation of four OCH₂O ether bridges between the four aromatic units of the resorcin[4]arene starting material (Fig. 1). The bridges rigidify the molecular structure, fixing the compound in a "bowl" shape (Fig. 2) with an enforced cavity that can accommodate guest molecules.

The 2-phenylethyl "feet" of the compound are orientated such that the aromatic rings are arranged in an edge-to-face manner. Such C—H···π interactions have also been observed in the resorcin[4]arene octol precursor (Friedrich et al., 2007). Interestingly, only two of the feet orientate in such a manner (Fig. 3). The presence of the ethyl acetate molecule within the molecular cavity forces the remaining two aromatic units apart, disrupting complete C—H···π interaction comparable to that as seen for the precursor. Similar disruption has also been reported previously for related structures.

Experimental

The synthesis of the resorcin[4]arene octol precursor can proceed via two different synthetic approaches. The older protocol as set out by Cram et al. (1988) involves heating a solution of the resorcin[4]arene starting material and the CH₂BrCl in the presence of K₂CO₃ at atmospheric pressure. Reaction proceeds over a number of days, often accompanied by addition of further equivalents of the alkylating reagent. However, since CH₂BrCl is volatile and boils at 341 K, the reaction temperature is limited to a range between 333 and 343 K. This results in yields of 40–60%. More recently, Roman et al. (1999) reported a procedure which made use of a sealed tube as a reaction vessel, heated to 361 K. The reagents are heated in the presence of Cs₂CO₃, which is used instead of K₂CO₃ due to the templating ability of the caesium cation, which aids in the formation of macrocyclic assemblies such as cavitands (Piepers & Kellog, 1978). Under these conditions, yields are in excess of 80%; indeed, the use of the protocol of Kaifer et al. in the synthesis of the resorcin[4]arene octol precursor gave a yield of 92%.

To prepare the title compound (Scheme 2): dry resorcin[4]arene octol (1.00 g, 1.66 mmol) and Cs₂CO₃ (3.00 g, 9.21 mmol) were added with stirring to dry DMSO (10 ml) in a pressure tube (ACE pressure tube, Aldrich). To the resulting pink solution, CH₂BrCl (3.00 ml, 46.0 mmol) was added followed by further DMSO (10 ml). The tube was sealed and heated at 360 K for 16 h. After cooling to room temperature, the tube contents were poured into 2% HCl (200 ml) and the voluminous solid formed was filtered and washed with water. The cream coloured solid was chromatographed on silica gel using a mobile phase of 70:30 hexane-ethyl acetate (R_f = 0.59). The fractions collected were concentrated on a rotary evaporator to yield a cream coloured solid. The solid was stirred in methanol overnight, and filtered to yield the product as a white powder (0.97 g, 92%, m.p. 418–420 K). Crystals suitable for X-ray diffraction analysis were grown by slow liquid diffusion of methanol into a solution of the title compound in 1:1 ethyl acetate:hexane.