Calixarene-based molecular capsule from olefin metathesis

The reaction of tetrakis(allyloxy)calix[4]arene with the first-generation Grubbs catalyst, followed by catalytic hydrogenation, gave the novel bis-calixarene 15,20,46,51,64,69,74,79-octaoxatridecacyclo[32.28.8.83,28.113,53.122,44.09,14.021,26.038,70.040,45.052,57.059,63.07,80.032,73]octaconta-1(63),3,5,7(80),9(14),10,12,21,23,25,28(73),29,31,34,36,38(70),40,42,44,52,54,56,59,61-tetracosaene benzene monosolvate, C72H72O8·C6H6. The structure consists of two calix[4]arene units connected by four-carbon chains at each of the four O atoms on their narrow rims, to form a cage. Each of the calix[4]arene units has a flattened cone conformation in which two of the opposite aryl groups are closer together and nearly parallel [dihedral angle between planes = 7.35 (16)°], and the other two aryl groups are splayed outward [dihedral angle between planes = 72.20 (8)°]. While the cavity contains no solvent or other guest molecule, there is benzene solvent molecule in the lattice. Two of the alkyl linking arms were disordered over two conformations with occupancies of 0.582 (3)/0.418 (3) and 0.33 (4)/0.467 (4). They were constrained to have similar metrical and thermal parameters.


Related literature
For literature related to the use of calixarenes as easily isolable reaction products, see: Asfari et al. (2001); Gutsche (2008). For literature related to the preparation of bridged calixarenes, see: Yang & Swager (2007); Hailu et al. (2012). For literature related to the conformation of calixarenes, see: Arduini et al. (1995Arduini et al. ( , 1996; Drew et al. (1997). For literature related to starting material and catalyst used, see: Ho et al. (1996); Vougioukalakis & Grubbs (2010 et al., 1995;Arduini et al., 1996;Drew et al., 1997)  s by slightly opening the glass stopper on one of the necks. The reaction mixture was stirred at room temperature for 6 h.
The mixture was then filtered on Celite and solvent removed by rotary evaporator to give 68 mg of white solid product.
The product was then chromatographed (8.56 g of silica gel, 1.2 x 18 cm, gradient elution with hexane/dichloromethane).
Attempted recrystallization of an 8-mg fraction (which showed only one spot on TLC) using CH 2 Cl 2 and MeOH, and finally benzene gave white crystals suitable for X-ray diffraction analysis.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distance of 0.95 and 0.99 Å U iso (H) = 1.2U eq (C).

Computing details
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.03 e Å −3 Δρ min = −0.24 e Å −3 Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.