A bis-calixarene from olefin metathesis

A ring-closing olefin metathesis reaction of tetrakis(allyloxy)calix[4]arene gave the bis calixarene, (15E,40E,60E)-65,74-bis(prop-2-en-1-yloxy)-13,18,38,43,58,63-hexaoxadodecacyclo[28.26.8.720,36.111,45.151,55.05,57.07,12.019,24.026,64.032,37.044,49.168,72]tetraheptaconta-1,3,5(57),7,9,11,15,19(24),20,22,26,28,30(64),32,34,36,40,44(49),45,47,51,53,55(65),60,68,70,72(74)-heptacosaene, C74H68O8. It is a cage formed from two calix[4]arene units joined by butenyl groups at three of the O atoms on the narrow rim. The fourth O atom on each calixarene unit is joined with an allyl group. Each of the calix[4]arene units has a flattened cone conformation in which the allyloxy-substituted aryl group and the opposite aryl group are close together and almost parallel [dihedral angle between planes = 1.09 (11)°], and the other two aryl groups are splayed outward [dihedral angle between planes = 79.53 (11)°]. No guest molecule (e.g. solvent) was observed within the cage. The alkene C atoms of one of the links between the calixarene moieties are disordered over two orientations with occupancies of 0.533 (9) and 0.467 (9).


Experimental
In an attempt to prepare calixarenes with small bridges using ring-closing olefin metathesis, a novel bis--calix[4]arene was isolated. The crystal structure shows that the calixarene units in the cage are in a flattened or pinched conformation.
For example, the distance across the ring between para carbons C4A and C4C is 9.696 (7) Å, while the distance between C4B and C4D is 5.298 (6) Å. The degree of flattening of a cone calix[4]arene is frequently described (Arduini et al. 1995;Arduini et al. 1996b;Drew et al. 1997)

Experimental
A 22-mg (0.027 mmol) sample of first generation Grubbs catalyst was weighed into a 100 ml 3-necked flask in a glove bag under nitrogen. The flask was then connected to a nitrogen line, and 50 ml of dichloromethane (distilled from CaH 2 ) followed by 62 mg (0.106 mmol) of tetrakis(allyloxy)calix[4]arene (Ho et al., 1996) in 5 ml of dichloromethane were each added by syringe. The resulting mixture was stirred under reflux (oil bath temperature 45 °C) for 3.5 h. Solvent was removed on a rotary evaporator, and the residue was suspended in 3 ml of dichloromethane and chromatographed (35 g of silica gel, 2.5 x 22.5 cm, gradient elution with hexane/dichloromethane). White crystals (2 mg) suitable for X-ray diffraction were obtained from a fraction using hexane/dichloromethane 2:3.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distances of 0.93 -0.97Å U iso (H) = 1.2U eq (C). The alkene carbon atoms of one of the links between the calixarene moities were disordered over two orientations with occupancies of 0.543 (9) and 0.457 (9). Since this was on a symmetry element the usual idealizing parameters of SHELXTL could not be used and its position was generated and then fixed.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.